ANTISENSE ENZYME INHIBITORS FOR METABOLIC REDIRECTION

Abstract: A method is described for improving the pharmacokinetics of a drug in a subject, by co-administering oligomers, preferably PMO's (phosphorodiamidate morpholino oligonucleotides), antisense to RNAs encoding drug-metabolizing enzymes, particularly p450 enzymes. The oligomers reduce production of the drug-metabolizing enzymes, which extends drug half-life and effectiveness and/or decreases drug toxicity.

Description: Antisense Enzyme Inhibitors for Metabolic Redirection Field of the Invention The present invention relates to methods of improving the performance of drugs which are metabolized by p450 enzymes, by antisense inhibition of the particular enzyme. Typically, the p450 enzyme is induced by an exogenous substance or by the drug itself. Background of the Invention When a drug is introduced to a biological system, multiple pharmacokinetic processes begin to affect the ultimate efficiency of the drug, determining how rapidly, in what concentration, and for how long the drug will be available to the target organ. In general, lipophilic xenobiotics are metabolized to more polar and hence more readily excretable products. The role metabolism plays in the inactivation of lipid soluble drugs can be quite dramatic. For example, lipophilic barbiturates such as thiopental and phenobarbital would have extremely long half-lives were it not for their metabolic conversion to more water soluble compounds. Many potential anticancer drugs are deemed unbeneficial because their half-life is too brief to achieve any useful therapeutic effect. The metabolic conversion of an ingested compound (such as a drug or a food additive) into a form which is readily cleared from the body is termed biotransformation or detoxification. Compounds ingested by organisms are generally biotransformed in two phases. In Phase 1, termed functionalization, a reactive site, such as an amine, thiol, or hydroxyl group, is introduced, generally via an oxidation reaction. In Phase 2, termed conjugation, a water-soluble group is added to the reactive site. Phase 2 typically involves addition of a glucuronic acid, sulfuric acid, acetic acid or amino acid to the compound. Phase 1 reactions are frequently catalyzed by the cytochrome p450 superfamily of enzymes. In a typical Phase 1 reaction, a cytochrome p450 enzyme uses oxygen and NADH to add a reactive group, such as a hydroxyl radical, to a drug. The reactive intermediates produced may be much more toxic than the parent molecule, and may cause damage to proteins, RNA, and DNA within the cell (Vermeulen, N.P.E., "Role of metabolism in chemical toxicity," in: Ioannides, C, ed., CYTOCHROME P450: METABOLIC AND TOXICOLOGICAL ASPECTS. Boca Raton, FL: CRC Press, Inc; 1996, pp 29-53). Phase 2 conjugation reactions, which generally follow Phase 1 activation reactions, often reduce the toxicity of reactive intermediates formed by Phase 1 reactions. Phase 2 conjugation transforms the drug into a water-soluble compound that can be excreted, e.g. through urine or bile. Several types of conjugation reactions occur in the body, including glucuronidation, sulfation, and glutathione and amino acid conjugation. In some instances, the parent drug may already possess a functional group that forms a conjugate directly. For example, the hydrazide moiety of isoniazide is known to form an acetyl conjugate in a Phase 2 reaction. This conjugate is then a substrate for a Phase 1 type reaction, namely, hydrolysis to isonicotinic acid. Thus, Phase 2 reactions may in some instances actually precede Phase 1 reactions. Correlations have been noted between altered Phase 1 and/or Phase 2 metabolic activities and increased risk of diseases such as cancers and liver disease, and in adverse drug responses. For example, some drugs (such as acetaminophen) are metabolically converted to reactive intermediates that are toxic to various organs. These toxic reactions may not be apparent at low drug dosages, when subsequent steps or alternative pathways are not overwhelmed or compromised and the availability of endogenous co-substrates (glutathione, glucuronic acid, sulfate) is not limited. When these resources are exhausted, however, the toxic pathway may prevail, resulting in overt organ toxicity or carcinogenesis. Many drugs and other xenobiotic agents are capable of inducing genes which encode drug-metabolic enzymes, enhancing the levels of these enzymes and, consequently, accelerating the metabolic reactions catalyzed by these enzymes. Such accelerated metabolism may cause a decrease in the half-life and pharmacologic efficacy of the substrate drug. Induction genes encoding drug-metabolizing compounds could exacerbate drug-mediated tissue toxicity by increasing steady-state levels of reactive or toxic intermediates. A need exists in the art for modulating the pharmacokinetics of various drugs in patients. The present invention achieves this by decreasing the production of one or more specific drug- metabolizing enzymes which are induced either by the drug itself or by another xenobiotic agent to which the patients have been exposed. Decreased drug metabolism results in an increased drug half-life. The dosage of the drug can then be reduced, since the lower dose has equivalent bioavailability to that of a higher dose in the absence of such modulation, and toxicities associated with high drug dosage can be circumvented. Reducing the availability of metabolically toxic pathways thus increases the safety of the drug. Summary of the Invention In one aspect, the invention provides a method of improving the pharmacokinetics of a drug administered to a subject, where the drug is known to be metabolized in vivo by a cytochrome p450 enzyme that reduces the effectiveness of the drug. In accordance with the method, one co-administers with the drug a morpholino antisense oligomer effective to reduce synthesis of the drug-metabolizing cytochrome p450 enzyme, by hybridizing to a target RNA molecule which encodes the enzyme. In an advantageous feature of the invention, the antisense oligomer can be administered orally or transdermally. For oral administration, a typical dose is at least 1 mg/kg body weight. In one embodiment, the drug is paclitaxel, and the targeted enzyme is CYP3A4. In preferred embodiments of the method, the drug itself induces the drug-metabolizing p450 enzyme, or the subject has been exposed to a xenobiotic agent which induces such an enzyme. In selected embodiments, the enzyme is CYP2E1, and the drug is acetaminophen; or the enzyme is from the CYP2B or CYP3A subfamily, preferably CYP2B1, and the drag is phenobarbital or hexobarbital. In further embodiments, the enzyme is CYP3A4, and the drug is an antibiotic selected from the group consisting of clarithromycin, erythromycin, rifampicin, rifampin, rifabutin, and rapamycin; or the enzyme is CYP3A4 or CYP1A2, and the drug contains an estrogen or estradiol. In still further embodiments, the enzyme is CYP3A4, the drug is a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor, and the inducing xenobiotic is a CYP3A4-inducing non-nucleoside reverse transcriptase inhibitor. The antisense oligomer preferably hybridizes to the target region of RNA with a T m greater than 37°C. In one embodiment, the antisense oligomer hybridizes to a region of the target RNA molecule which includes the AUG translation start site. In another embodiment, the target RNA molecule is pre-mRNA, and the antisense oligomer hybridizes to a region of the pre-mRNA which includes an intron-exon boundary or an exon-intron boundary. Preferably, the antisense oligomer is at least 15 nucleotides in length. Preferred oligomers are morpholino oligomers having an uncharged backbone comprising intersubunit linkages selected from the group consisting of the structures presented in Figs. 6AA-6EE. Preferably, the linkages are phosphoramidate or, more preferably, phosphorodiamidate linkages, as represented at Figure 6B-B, where X=NH 2 , NHR, or NRR', Y=0, and Z=0, or where X=OR, Y=NH or NR', and Z=0, and R and R' are groups which do not interfere with target binding. Preferably, R and R' are moieties independently selected from alkyl, polyalkyleneoxy, and a combination thereof, which may be substituted with one or more groups selected from hydroxy, alkoxy, amino, alkylamino, thiol, alkanethiol, halogen, oxo, carboxylic acid, carboxylic ester, and inorganic ester. In selected embodiments, each said moiety R and R', independent of substitution, is from 1 to 6 chain atoms (carbon and/or oxygen) in length. NRR' may also represents a nitrogen heterocycle having 5-7 ring atoms selected from nitrogen, carbon, oxygen, and sulfur, and having at least as many carbon ring atoms as non-carbon ring atoms. The sequence of the oligonucleotide can be one selected from the group consisting of SEQ ID NOs: 16-35 and 46-47, preferably from SEQ ID NOs: 26-35 and 46-47 (targeted to human RNA sequences), and more preferably from SEQ ID NOs: 27, 30, 34, 35, and 46-47. The targeted cytochrome p450 enzyme is preferably selected from the group consisting of CYP1A1, CYP1A2, CYP2A6, CYP2B1, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A2, CYP3A4, and CYP6A1 enzymes. In a preferred embodiment, where the subject is a human subject, the cytochrome p450 is preferably selected from the group consisting of CYP1A1, CYP1A2, CYP2A6, CYP2B1, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 enzymes, and more preferably from the group consisting of CYP1A2, CYP2B1, CYP2E1, and CYP3A4 enzymes. These and other objects and features of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings. Brief Description of the Drawings Fig. 1 shows the steps in oxidation of a drug by a cytochrome p450; Fig. 2 shows alternative pathways for acetaminophen metabolism, leading to a toxic product or to a non-toxic mercapturate conjugate, where GSH = glutathione and AC* = reactive intermediate; Fig. 3 depicts the results of ELISA for Cytochrome p450 2B1 (CYP2B1) from liver microsomes treated with various antisense oligonucleotides (see Example 1), in the presence or absence of the CYP2B1 inducing agent phenobarbital (PB); Fig. 4 depicts the levels of CYP2E1 isozyme from cultures treated with increasing amounts of the antisense oligonucleotide 2E1-1560 (SEQ ID NO: 19), assayed by ELISA for comparative amounts of the CYP2E1 isozyme present (see Example 2); Fig. 5 shows several preferred subunits having 5-atom (A), six-atom (B) and seven-atom (C-E) linking groups suitable for forming polymers; Figs. 6A-A to 6E-E show the repeating subunit segment of exemplary moφholino oligonucleotides, designated A-A through E-E, constructed using subunits A-E, respectively, of Figure 5; and Fig. 7 shows a Western blot of liver microsome samples comparing relative levels of CYP3A2 isozyme in rats injected i.p. with saline (lane 1), or with 15 nmoles of CYP3A2 antisense PMO, SEQ ID NO: 25 (lanes 2 and 3), or orally administered 60 nmoles of CYP3A2 antisense PMO (lanes 4 and 5), 24 hours prior to organ harvesting, where the lanes labeled "NADPH Reductase" are a control for total protein on the blot. Detailed Description of the Invention I. Definitions The terms below, as used herein, have the following meanings, unless indicated otherwise: A "xenobiotic" is a chemical substance which is foreign to a biological system. Xenobiotics include: naturally occurring compounds which are foreign, i.e., non-native, to the biological system in question, drugs, environmental agents, carcinogens, and insecticides. A "drug" refers to a chemical substance administered to an animal for a therapeutic purpose. Such agents may take the form of ions, small organic molecules, peptides, proteins or polypeptides, oligonucleotides, and oligosaccharides, for example. The agent is typically administered to cause an observable and desirable change in the structure, function, or composition of a cell upon uptake by the cell. Such changes include, for example, increased or decreased expression of one or more mRNAs, increased or decreased expression of one or more proteins, phosphorylation of a protein or other cell component, inhibition or activation of an enzyme, inhibition or activation of binding between members of a binding pair, an increased or decreased rate of synthesis of a metabolite, or increased or decreased cell proliferation. "Induction" of a gene refers to the switching on or enhancement of expression of the gene by a stimulus such as an inducer molecule, e.g. a hormone or exogenous substance, or by another stimulus such as heat. In the context of the present invention, induction by an exogenous substance (xenobiotic) is typically intended. Induction of an enzyme typically results from induction of the gene encoding the enzyme. A "nuclease-resistant" oligomeric molecule (oligomer) is one whose backbone is not susceptible to nuclease cleavage. Exemplary nuclease-resistant antisense oligomers are oligonucleotide analogs, such as phosphorothioate and phosphate-amine DNA (pnDNA), both of which have a charged backbone, and methyl phosphonate, morpholino, and peptide nucleic acid (PNA) analogs, all of which have uncharged backbones. The terms "antisense oligonucleotide" and "antisense oligomer" are used interchangeably and refer to an oligomer having a sequence of nucleotide bases and a subunit-to-subunit backbone that allows the antisense oligomer to hybridize to a target sequence in an RNA by Watson-Crick base pairing, to form an RNA:oligomer heteroduplex within the target sequence. The oligomer may have exact sequence complementarity to the target sequence or near complementarity. These antisense oligomers may block or inhibit translation of the mRNA containing the target sequence, and/or modify the processing of the mRNA to produce a splice variant of the mRNA. Antisense oligonucleotides which are double-stranded DNA binding agents may inhibit gene transcription. An oligonucleotide or antisense oligomer "specifically hybridizes" to a target polynucleotide if the oligomer hybridizes to the target under physiological conditions, with a T m greater than 37°C, preferably at least 50°C, and more preferably at least 60°C, 80°C, or higher. Such hybridization preferably corresponds to stringent hybridization conditions, selected to be about 10°C lower, and preferably about 5oC lower than the thermal melting point (Tm) for the specific sequence at a defined ionic strength and pH. At a given ionic strength and pH, the Tm is the temperature at which 50% of a target sequence hybridizes to a complementary polynucleotide. Polynucleotides are described as "complementary" to one another when hybridization occurs in an antiparallel configuration between two single-stranded polynucleotides. A double- stranded polynucleotide can be "complementary" to another polynucleotide, if hybridization can occur between one of the strands of the first polynucleotide and the second. Complementarity (the degree that one polynucleotide is complementary with another) is quantifiable in terms of the proportion of bases in opposing strands that are expected to form hydrogen bonds with each other, according to generally accepted base-pairing rules. Although the antisense oligomer is not necessarily 100% complementary to the target sequence, it is effective to stably and specifically bind to the target sequence such that expression of the target sequence is modulated. The appropriate length of the oligomer to allow stable, effective binding combined with good specificity is about 8 to 40 nucleotide base units, and preferably about 12-25 base units. Mismatches, if present, are less destabilizing toward the end regions of the hybrid duplex than in the center. Oligomer bases that allow degenerate base pairing with target bases are also contemplated, assuming base-pair specificity with the target is maintained. A first sequence is an "antisense sequence" with respect to a second sequence if a polynucleotide whose sequence is the first sequence specifically hybridizes to a polynucleotide whose sequence is the second sequence. A "base-specific intracellular binding event involving a target RNA" refers to the specific binding of an oligomer with a target RNA sequence inside a cell even in the presence of many other diverse molecules. The base specificity of such binding is sequence specific. For example, a single-stranded polynucleotide can specifically bind to a single-stranded polynucleotide that is complementary in sequence. As used herein, a "morpholino oligomer" or "morpholino oligonucleotide" refers to a polymeric molecule having a backbone which supports bases capable of hydrogen bonding to typical polynucleotides, wherein the polymer lacks the ribose backbone linked by phosphodiester bonds which is typical of nucleotides and nucleosides, and instead contains a subunit with a ring nitrogen with coupling through the ring nitrogen. A preferred "moφholino" oligonucleotide is composed of moφholino subunit structures of the form shown in Figs. 5A-E, where (i) the structures are linked together by phosphorous-containing linkages, one to three atoms long, joining the moφholino nitrogen of one subunit to the 5' exocyclic carbon of an adjacent subunit, and (ii) Pi and Pj are purine or pyrimidine base-pairing moieties effective to bind, by base-specific hydrogen bonding, to a base in a polynucleotide. Exemplary structures for antisense oligonucleotides for use in the invention include the moφholino subunit types shown in Figures 5A-E, with the linkages shown in Figures 6A-A to 6E-E. The synthesis, structures, and binding characteristics of moφholino oligomers, including antisense oligomers, are described in detail in co-owned U.S. Patent Nos. 5,185,444, 5,698,685, 5,217,866, 5,142,047, 5,034,506, 5,166,315, 5,521,063, and 5,506,337, all of which are incoφorated herein by reference. In preferred embodiments, the moφholino oligomer is a phosphorodiamidate moφholino oligonucleotide (PMO), having linkages selected from a phosphorodiamidate linkage as represented at Figure 6B-B, where X=NH 2 , NHR, or NRR', Y=0, and Z=0, and an alternate phosphorodiamidate linkage as represented at Figure 6B-B, where X=OR, Y=NH or NR, and Z=0. Such structures are described, for example, in Hudziak et al., Antisense Nucleic Acid Drug Dev. 6, 267-272 (1996) and Summerton and Weller, Antisense Nucleic Acid Drug Dev. 7, 187-195 (1997). R and R' are groups which do not interfere with target binding. Preferably, R and R' are independently selected from alkyl and polyalkyleneoxy (e.g. PEG; (CH 2 CH 2 0) n ), or a combination thereof. (An example of such a combination would be -(CH 2 ) 3 (CH 2 CH 2 0) 3 -). The alkyl/polyalkyleneoxy chain may be substituted, preferably at the distal terminus, by a group selected from hydroxy, lower alkoxy, amino, lower alkylamino, thiol, lower alkanethiol, halogen, oxo, carboxylic acid, carboxylic ester, and inorganic ester (e.g. phosphate or sulfonate). Preferably, the chain (independent of substituents) is from 1 to 12 chain atoms (carbon and/or oxygen) in length, and more preferably is from 1 to 6 chain atoms in length. In selected embodiments, R and R' are independently methyl or ethyl. In one embodiment, X=N(CH 3 ) 2 , Y=0, and Z=0. NRR' may also represent a nitrogen heterocycle having 5-7 ring atoms selected from nitrogen, carbon, oxygen, and sulfur, and having at least as many carbon ring atoms as non- carbon ring atoms. Examples include moφholine, pyrrolidine, piperidine, pyridine, pyrimidine, pyrazine, triazine, triazole, pyrazole, pyrrole, isopyrrole, imidazole, oxazole, imidazole, isoxazole, and the like. "Alkyl" refers to a fully saturated acyclic monovalent radical containing carbon and hydrogen, which may be branched or a straight chain. Examples of alkyl groups are methyl, ethyl, n-butyl, t-butyl, n-heptyl, and isopropyl. "Lower alkyl" refers to an alkyl radical of one to six carbon atoms, as exemplified by methyl, ethyl, n-butyl, i-butyl, t-butyl, isoamyl, n-pentyl, and isopentyl, preferably of one to four carbon atoms. A "C-5-methyl modified" oligonucleotide is one in which the C-5 hydrogen of cytidine bases has been replaced with a methyl group. A "C-5-propyne modified "or "C-5-propyne pyrimidine-modified" oligonucleotide is one in which the C-5 methyl group of thymidine bases and/or the C-5 hydrogen of cytidine bases has been replaced with a propynyl group (-C≡C- CH 3 ). The term "modulating expression" relative to oligonucleotides refers to the ability of an antisense oligomer to either enhance or reduce the expression of a given protein by interfering with the expression or translation of RNA. In the case of enhanced protein expression, the antisense oligomer may block expression of a suppressor gene, e.g., a tumor suppressor gene. In the case of reduced protein expression, the antisense oligomer may directly block expression of a given gene, or contribute to the accelerated breakdown of the RNA transcribed from that gene. An "effective amount" relative to an antisense oligomer refers to the amount of antisense oligomer administered to a mammalian subject, either as a single dose or as part of a series of doses, that is effective to specifically hybridize to all or part of a selected target sequence, thereby reducing expression of the protein encoded by the target sequence. "Treatment" of an individual or a cell is any type of intervention in an attempt to alter the natural course of the individual or cell. Treatment includes, but is not limited to, administration of a pharmaceutical composition, and may be performed either prophylactically or subsequent to the initiation of a pathologic event or contact with an etiologic agent. The term "relative amount" is used where a comparison is made between a test measurement and a control measurement. The relative amount of a reagent forming a complex in a reaction is the amount reacting with a test specimen, compared with the amount reacting with a control specimen. The control specimen may be run separately in the same assay, or it may be part of the same sample (for example, normal tissue surrounding a malignant area in a tissue section). "Coadministration" of an antisense oligomer with a drug may be concurrent with, δ following, or, preferably, preceding administration of the drug, as long as the antisense oligomer is effective to modulate the metabolism and enhance the efficacy of the drug. The drug and oligomer may be administered by different routes; that is, the drug need not be administered orally or transdermally. Abbreviations: ON = oligonucleotide; ODN = oligodeoxyribonucleotide; PS or PS- ODN = phosphorothioate oligonucleotide; PMO = phosphoramidate or (preferably) phosphorodiamidate moφholino oligonucleotide. II. Antisense Oligomers Antisense oligomers effect changes in gene expression (transcription) and protein production (translation) by the complementary hybridization of relatively short oligonucleotides to single-stranded RNA or double-stranded DNA, such that the normal, essential functions of these intracellular nucleic acids are disrupted. (See, e.g., U.S. Pat No. 5,843,684). Two mechanisms of action of antisense oligomers on target nucleic acid molecules have been proposed. In one mechanism, antisense agents are thought to disrupt nucleic acid function via enzymatic cleavage of the targeted RNA by intracellular RNase H. The oligonucleotide or oligonucleotide analog, which must be of the deoxyribo type, hybridizes with the targeted RNA, and the duplex activates RNase H to cleave the RNA strand, thus destroying the normal function of the RNA. Phosphorothioate oligonucleotides are a prominent example of antisense oligomers that operate by this mechanism. Another mechanism, termed "hybridization arrest", involves a terminating event in which the antisense oligomer binds to the target nucleic acid and thus prevents, by steric hindrance, the binding of essential proteins, most often ribosomes, to the nucleic acid. Exemplary antisense oligomers which act by this mechanism include methylphosphonate oligonucleotides and alpha anomer oligonucleotides. (See, e.g., Cohen, OLIGONUCLEOTIDES: ANTISENSE INHIBITORS OF GENE EXPRESSION, CRC Press, Inc., Boca Raton Fla., 1989.) The utility of antisense oligomers to modulate the pharmacokinetics of drugs or other xenobiotic agents, by decreasing production of specific metabolic enzymes which are induced by and/or metabolize these agents, requires that the oligomers be amenable to synthesis in large quantities, be taken up by cells and/or transported across cell membranes, hybridize appropriately to the targeted RNA (i.e., mRNA or pre-mRNA) and subsequently terminate or disrupt translation from the RNA. Non-ionic oligonucleotide analogs, i.e., oligomers with uncharged backbones, generally cross cell membranes more readily than their charged counteφarts. Non-ionic oligonucleotide analogs include phosphotriester- and methylphosphonate-linked DNA (Miller et al, Biochemistry 18:5134 (1979); Miller et al, J. Biol. Chem. 255:6959 (1980)), carbamate-linked nucleosides (Stirchak, E.P. et al, J. Org. Chem. 52:4202 (1987)), phosphoroamidate-linked DNA (Froehler et al, Nucleic Acids Res. 16:4831 (1988)), and peptide nucleic acids (PNAs). A preferred nonionic antisense oligomer for use in the method of the invention is an uncharged-backbone moφholino oligomer as defined above. Moφholino oligomers, such as illustrated in Figs. 5 and 6, are composed of moφholino subunit structures linked together by uncharged, phosphorous-containing linkages, one to three atoms long, joining the moφholino nitrogen of one subunit to the 5' exocyclic carbon of an adjacent subunit. Linked to each subunit is a purine or pyrimidine base-pairing moiety effective to bind, by base-specific hydrogen bonding, to a base in a polynucleotide. The pyrimidine base-pairing moieties may also include a C-5-propyne modification of thymidine and/or cytidine moieties, and/or a C-5- methyl modification of cytidine bases. Figs. 6AA-EE illustrate preferred backbone structures, showing two moφholino subunits of a multisubunit oligomer. Each ring structure includes a purine or pyrimidine or related hydrogen-bonding moiety, represented by Pj and P j , attached to the backbone moφholine moiety through a linkage in the β-orientation. The purine or pyrimidine base-pairing moieties in the oligomer are typically adenine, cytosine, guanine, uracil or thymine. Preferred structures are phosphoramidate-linked moφholino oligonucleotides as shown at Fig. 6B-B and described above. The solubility of the antisense compound, and the ability of the compound to resist precipitation on storage in solution, can be further enhanced by derivatizing the oligomer with a solubilizing moiety, such as a hydrophilic oligomer, or a charged moiety, such as a charged amino acid or organic acid. The moiety may be any biocompatible hydrophilic or charged moiety that can be coupled to the antisense compound and that does not interfere with compound binding to the target sequence. The moiety can be chemically attached to the antisense compound, e.g., at its 5' end, by well-known derivatization methods. One preferred moiety is a defined length oligo ethylene glycol moiety, such as triethylene glycol, coupled covalently to the 5' end of the antisense compound through a carbonate linkage, via a piperazine linking group forming a carbamate linkage with triethylene glycol, where the second piperazine nitrogen is coupled to the 5 '-end phosphorodiamidate linkage of the antisense. Alternatively, or in addition, the compound may be designed to include one a small number of charged backbone linkages, such as a phosphodiester linkage, preferably near one of the ends of the compound. The added moiety is preferably effective to enhance solubility of the compound to at least about 30 mgs/ml, preferably at least 50 mgs/ml in aqueous medium. Antisense oligomers of the present invention can also include modifications including, but not limited to, conjugated moieties such as cholesterol; diamine compounds with varying numbers of carbon residues between the amino groups; and terminal ribose, deoxyribose and phosphate modifications which cleave or crosslink to hybridized target nucleic acids or to associated enzymes or other proteins which bind to the target nucleic acids. Moφholino oligomers afford high target binding affinity, especially for RNA targets, and are resistant to degradation by nucleases. Binding of a moφholino oligomer to a target has been shown to give strong inactivation, due to the greater binding affinity noted above, and because the oligomer/target duplex is not susceptible to duplex unwinding mechanisms in the cell. Further, in therapeutic applications involving cellular uptake of the compound, the uncharged moφholino polymer is more efficiently transported into cells than are oligomers with charged backbones. Although targeting of a messenger RNA sequence or an unspliced pre-mRNA sequence is preferred, a double-stranded DNA, i.e. , a genomic DNA, may be targeted by using a non- ionic probe designed for sequence-specific binding to major-groove sites in duplex DNA. Oligomers suitable for forming base-specific triplex structures with a target duplex DNA are described, for example, in co-owned U.S. Patent No. 5,405,938. in vivo Effectiveness of Moφholino Oligomers. Moφholino oligonucleotides have been shown to provide significantly improved selectivity in inhibiting translation of targeted sequences in comparison to phosphorothioate oligonucleotides, which are widely used in the field. The moφholino oligomers have also been shown to inhibit translation at much lower concentrations than the corresponding phosphorothioates, and with little or no evidence of the substantial non-antisense activity exhibited by the phosphorothioates. See, for example, Summerton et al, Antisense & Nucleic Acid Drug Dev 7 (2) p63-70 (1997). The moφholino oligomers have very high nuclease resistance and good water solubility, making them good candidates for in vivo use. Because the moφholino oligomers are uncharged, they are more effective at penetrating cell membranes. They are effective when administered i.v. or i.p., or by more convenient methods such as oral or transdermal administration; see Examples 5 and 6 below. The efficacy of moφholino antisense oligonucleotides in vivo has been demonstrated, for example, in procedures described in co-owned and copending U.S. provisional application serial no. 60/117,846, filed January 29, 1999. In the procedures described therein, a phosphoramidate moφholino oligonucleotide (PMO) administered to a subject forms a heteroduplex with target RNA, which is protected in this duplex state from nuclease degradation. The duplex is expelled from the cell, and the target RNA can later be detected in a body fluid sample, e.g. a urine sample, from the subject. These results demonstrate that the moφholino oligomers (i) migrate to and enter cells in the body and (ii) bind with high affinity, via Watson-Crick base-pairing, to target nucleic acid regions, (iii) be expelled from the cells into the bloodstream in the form of a nuclease-resistant heteroduplex, and (iv) survive in the bloodstream in sufficient amount for detection in a body fluid. III. Selection of Target Genes The present invention relates to a method of improving the pharmacokinetics of a drug administered to a subject, by reducing the production of a drug-metabolizing enzyme which is up-regulated either by the drug itself or by a xenobiotic agent to which the subject has been exposed. The drug-metabolizing enzyme may convert the drug into a toxic metabolite, reduce the half-life of the drag in the subject, or both. Transcription of target RNA from the enzyme gene (i.e., the "target gene") is induced by the drug, or by a different xenobiotic agent. According to the invention, a nuclease-resistant antisense oligomer, preferably a moφholino oligomer, is targeted to a gene encoding a drag-metabolizing enzyme which reduces the half- life of the drag, or converts the drag into a toxic metabolite, or both. The antisense oligomer, preferably co-administered with the drug, is effective to reduce production of the enzyme in the subject by hybridizing to the target RNA. The production of any drug-metabolizing enzyme encoded by an endogenous xenobiotic- inducible gene may be decreased by the method of this invention. For example, important Phase 2 drug-metabolizing enzymes include epoxide hydrolases, whose substrates include carbamazepine-10,ll-epoxide; glucuronyl transferases, whose substrates include oxazepam, and which are induced by anticonvulsant drugs such as phenytoin and carbamazepine; and glutathione transferases. Selection of the enzyme will be determined by the metabolic scheme of the drug in question. A. The Cytochrome p450 Family In accordance with a preferred embodiment, the present invention provides antisense oligomers which are antisense to cytochrome p450 (CYp450) genes. The cytochrome p450s are a collection of enzymes involved in the oxidative metabolism of both endogenous and exogenous compounds. Over 200 genes encoding cytochrome p450, divided among over 30 gene families, have been identified. The p450 gene families are organized into subfamilies, which vary in regulation of gene expression and in amino acid sequence homology, substrate specificity, catalytic activity, and physiological role of the encoded enzymes. The following discussion of representative p450 genes, inducers of those genes, and substrates of the encoded enzymes, is provided for illustrative puφoses and is not intended to limit the invention. Sequences for numerous p450 genes of various species are known and available to those of skill in the art through public databases such as GenBank and review articles such as F.J. Gonzales, "The Molecular Biology of Cytochrome p450's", Pharmacological Reviews 40(4), 243-288 (1989); S.D. Black et al, "P-450 Cytochromes: Structure and Function," Adv. Enzymol. Relat. Areas Mol. Biol. 60, 35-87 (1987); D.R. Nelson et al, "The p450 Superfamily: Update on New Sequences, Gene Mapping, Accession Numbers, Early Trivial Names of Enzymes, and Nomenclature," DNA Cell Biol. 12(1), 1-51 (Jan-Feb 1993), and articles cited therein. B. Sequence Homology of p450 Enzymes and Genes High levels of sequence homology have been found among p450 enzymes and their genes in different mammalian species. For example, the rat, human and rabbit 2E1 cDNAs have been isolated and sequenced, and their amino acid sequences exhibit about 80% similarity. The human 2B subfamily cDNAs were isolated by screening liver libraries with rat 2B cDNA probes, and the isolated cDNAs demonstrated >75% amino acid similarity. The rat CYP3A enzymes, CYP3A1 and CYP3A2, are approximately 90% identical and functionally equivalent to human CYPs 3A3 and 3A4, respectively (Desjardins and Iversen, /. Pharmacol. Exp. Ther. 275(3): 1608-13, 1995). The following table shows sequence similarities among the ATG regions of mRNA from CYP3A genes of these and other species. Table 1. The following degrees of homology were found in three conserved domains of the p4503A proteins: 1. Heme-binding cysteine-containing peptide; the fifth ligand to heme iron (23 amino acid segment starting at position 435 in human protein) Dog 21/23 91.3% similarity to human protein Rat 23/23 100% Mouse 22/23 95.7% Monkey 21/23 91.3% Pig 22/23 95.7% Rabbit 20/23 87.0% 2. Membrane transition binding domain (8 amino acid segment starting at position 39 in human protein) Dog 8/8 100% similarity to human protein Rat 7/8 87.5% Mouse 7/8 87.5% Monkey 7/8 87.5% Pig 7/8 87.5% Rabbit 8/8 100% 3. Signal sequence and half-transfer sequence for membrane insertion (20 amino acid segment starting at position 167 in human protein) Dog 17/20 85% similarity to human protein Rat 18/20 90% Mouse 18/20 90% Monkey 20/20 100% Pig 19/20 95% Rabbit 16/20 80% Goat 16/20 80% Guinea pig 13/20 65% The average degree of homology over these three known functional domains (51 amino acids of 500 total) was 92.9% human to monkey, 92.5% human to rat, and 92.1 % human to dog. C. Substrates and Inducers of p450 Enzymes Genes in the CYP2B subfamily are known to be strongly induced by phenobarbital. The 2B1 and 2B2 proteins exhibit 97% amino acid similarity. These enzymes have similar substrate specificities; however, purified 2B1 (rat) has about a 5-fold higher catalytic activity than 2B2 for certain substrates, including benzphetamine and testosterone, and a two-fold to three-fold higher activity for the substrates benzo[a]pyrene and 7,12-dimethylbenzanthracene. A distinct ethanol-inducible form of p450, CYP2E1, was first identified in rabbits and later in rats and humans. The enzymes of this subfamily metabolize a large number of substrates, as shown below, including, for example, ethanol, acetone, acetoacetate, acetol, diethyl ether, p-nitrophenol, halothane, benzene, pyridine, and N-nitrosodimethylamine. The CYP3A subfamily is involved in the 6β-hydroxylation of testosterone and in the metabolism of numerous clinically important drugs, such as those listed below. Listed below are further examples of known inducers and substrates of members of various p450 subfamilies. See also the discussion in Klassen, ed., Casarett andDoull's Toxicology: The Basis Science of Poisons, McGraw-Hill, 1996, pp. 150 ff. Further information about cytochrome p450 substrates, inducers, and metabolites can be found in Gonzales and other review articles cited above. Current information sources available via the Internet include the "Cytochrome p450 Homepage" maintained by David Nelson at http://drnelson.utmem.edu/Cytochromep450.html, the "Cytochrome p450 Database", provided by the Institute of Biomedical Chemistry & Center for Molecular Design, at http://cpd.ibmh.msk.su/, and the "Directory of p450-containing Systems" provided by Kirill N. Degtyarenko and Peter Fabian at http://www.icgeb.trieste.it/p450/. The exemplary p450 genes discussed herein are given for illustrative puφoses only and are not intended to limit the invention. P450 family 1 (CYP1) CYP1A1: • inducers include: dioxin, PAH (polycyclic aromatic hydrocarbons) in tobacco smoke or charcoal-broiled beef, β-naphthoflavone in food • substrates include: diethylstilbestrol, 2- and 4-hydroxy estradiol CYP1A2: • inducers include: dioxin, PAH, β-naphthoflavone, cruciferous vegetables, omeprazole • substrates include: acetaminophen, phenacetin, acetanilide (analgesics), caffeine, clozapine (sedative), cyclobenzaprine (muscle relaxant), estradiol, imipramine (antidepressant), mexillitene (antiarrhythmic), naproxen (analgesic), riluzole, tacrine, theophylline (cardiac stimulant, bronchodilator, smooth muscle relaxant), warfarin. • probe reaction: caffeine 3-demethylation p450 family 2 (CYP2) CYP2A6: • inducers include: barbiturates • substrates include: coumarin, butadiene, nicotine CYP2B1: • inducers include: phenobarbital • substrates include: phenobarbital, hexobarbital CYP2C9: • inducers include: rifampin, secobarbital • substrates include: NSAIDs such as diclofenac, ibuprofen, and piroxicam; oral hypoglycemic agents such as tolbutamide and glipizide; angiotensin-2 blockers such as irbesartan, losartan, and valsartan; naproxen (analgesic); phenytoin (anticonvulsant, antiepileptic); sulfamethoxazole, tamoxifen (antineoplastic); torsemide; warfarin CYP2C19: • inducers include: rifampin, secobarbital • substrates include: hexobarbital, mephobarbital, imipramine, clomipramine, citalopram, cycloguanil, the anti-epileptics phenytoin and diazepam, S-mephenytoin, diphenylhydantoin, lansoprazole, pantoprazole, omeprazole, pentamidine, propranolol, cyclophosphamide, progesterone CYP2D6: • inducers include: dexamefhasone. rifampin • substrates include: antidepressants (imipramine, clomipramine, desimpramine), antipsychotics (haloperidol, peφhenazine, risperidone, thioridazine), beta blockers (carvedilol, S-metoprolol, propafenone, timolol), amphetamine, codeine, dextromethoφhan, fluoxetine, S- mexilletine, phenacetin, propranolol CYP2E1: • inducers include: ethanol, acetone, isoniazid, dimethyl sulfoxide, pyrazoles. • substrates include: acetaminophen; chlorzoxazone (muscle relaxant), ethanol; caffiene, theophylline; dapsone, general anesthetics such as enflurane, halothane, and methoxyflurane; nitrosamines p450 family 3 (CYP3) CYP3A1. CYP3A2: rat CYP3A subfamily; approximately 90% identical and functionally equivalent to human CYP3A3 and CYP3A4, respectively (below) CYP3A4: • inducers include: carbamazepine, phenobarbital, phenytoin, dexamethasone and other glucocorticoids; barbiturates, various steroids, antibiotics such as rifampin, rifabutin, erythromycin; phenylbutazone, sulfadimidine, sulfinpyrazone, troleandomycin • substrates include: HIN Protease Inhibitors such as indinavir, ritonavir, and saquinavir; benzodiazepines such as alprazolam, diazepam, midazolam, and triazolam; immune modulators such as cyclosporine; antihistamines such as astemizole and chloφheniramine; HMG CoA Reductase inhibitors such as atorvastatin, cerivastatin, lovastatin, and simvastatin; channel blockers such as diltiazem, felodipine, nifedipine, nisoldipine, nitrendipine, and verapamil; antibiotics such as clarithromycin, erythromycin, and rapamycin; various steroids including cortisol, testosterone, progesterone, estradiol, ethinylestradiol, hydrocortisone, prednisone, and prednisolone; acetominophen, aldrin, alfentanil, amiodarone, astemizole, benzphetamine, budesonide, carbemazepine, cyclophosphamide, ifosphamide, dapsone, digitoxin, quinidine (anti-arrhythmic), etoposide, flutamide, imipramine, lansoprazole, lidocaine, losartan, omeprazole, retinoic acid, FK506 (tacrolimus), tamoxifen, taxol (paclitaxel), teniposide, terfenadine, buspirone, haloperidol (antipsychotic), methadone, sildenafil, trazodone, theophylline, toremifine, troleandomycin, warfarin, zatosetron, zonisamide. The CYP3A family of enzymes are the most abundant CYP enzymes in the human liver. CYP3A4 is a 502 amino acid protein with molecular weight of 57kDa and has also been referred to as nifedipine oxidase, ΝF-25, P450-PCN1 or polypeptide 4. It is among the most important enzymes because it contributes to the metabolism, at least in part, of over half of all known of all drugs. The reactions catalyzed by CYP3A4 that make it such a versatile enzyme include 0-demethylation, oxidative deamination, N-hydroxylation, aliphatic oxidation and N- dealkylation. p450 family 6 (CYP6) CYP6A1: • inducers include: chlofibrate • substrates include: fatty acids D. Exemplary Drugs Metabolized by p450 Enzymes Acetaminophen: Ethanol up-regulates CYP2E1 , which metabolizes acetaminophen to a reactive quinone (Fig. 2). This reactive quinone intermediate, when produced in sufficient amounts, causes liver damage and necrosis. An oligomer antisense to the CYP2E1 gene reduces synthesis of the enzyme and decreases production of the toxic intermediate. Reducing the flux through the toxic pathway enables alternative, more desirable metabolic pathways to compensate. Sedatives: The sedative phenobarbital (PB) up-regulates several p450 genes, including those of the CYP2B and CYP3A subfamilies. Upregulation of these enzymes increases the metabolism and reduces the sedative effects of PB and the related sedative hexobarbital. Example 1 demonstrates that an antisense oligonucleotide to the CYP2B1 gene reduces synthesis of the enzyme and decreases HB metabolism, enabling lower amounts of HB be administered for the equivalent sedative effect. Such oligomers also increased the effectiveness of HB in the presence of the inducing agent phenobarbital. Example 3 demonstrates a similar effect of antisense to CYP3A2 on efficacy of midazolam (MZ). Antibiotics: The antibiotics rifampicin, rifampin, rifabutin, erythromycin, and related compounds are inducers of the CYP3A4 gene and are substrates of the enzyme product. An oligomer antisense to the CYP3A4 gene increases the serum half-life and hence the effectiveness of the antibiotic. Oral contraceptive/estrogen replacement therapy: Estrogens and estradiols are the active ingredients in oral contraceptives and in hormonal replacement therapies for post-menopausal women. Women who are also taking antibiotics such as rifampicin or erythromycin, or glucocorticoids such as dexamethasone, or who smoke, risk decreased efficacy of the estrogen/estradiol treatments due to increased metabolism of these compounds by up-regulated CYP3A4 and/or CYP1A2 enzymes. Administration of oligomers antisense to the CYP3A4 and/or CYP1A2 genes in such situations block up-regulation of these enzymes and reduces risk of pregnancy in women taking oral contraceptives, or of osteoporosis in women receiving estrogen replacement therapy. Protease Inhibitors: All protease inhibitors and non-nucleoside reverse transcriptase inhibitors currently indicated for use in treatment of HIN are substrates of p450 enzymes; in particular, they are metabolized by CYP3A4 enzymes (see e.g. Sahai, AIDS 10 Suppl S21-5, 1996) with possible participation by CYP2D6 enzymes (Kumar et al. , J. Pharmacol. Exp. Ther. 277(1) :423-31, 1996). Although protease inhibitors are reported to be inhibitors of CYP3A4, some non-nucleoside reverse transcriptase inhibitors, such as nevirapine and efavirenz, are inducers of CYP3A4 (see e.g. Muφhy et al, Expert Opin Invest Drugs 5/9: 1183-99, 1996). Given the increasing use of multidrug therapy for treatment of HIN infection, the potential for interference is high. Supplemental administration of oligomers antisense to CYP3A4 and/or CYP2D6 genes can block up-regulation of these enzymes, thus reducing the metabolism of the protease inhibitors, allowing for lower doses and reduction of sometimes serious side effects. Taxol™ (paclitaxel) exhibits cytotoxic activity in vitro against a wide variety of both human and rodent tumor cell lines including leukemia, non-small-cell lung carcinoma, small- cell lung carcinoma, colon carcinoma, CΝS carcinoma, melanoma, renal carcinoma, ovarian carcinoma and breast carcinoma. It is one of the few known effective treatments for metastatic carcinoma of the ovary or breast. Taxanes and taxoids are believed to manifest their anticancer effects by promoting polymerization of microtubules (and inhibiting depolymerization) to an extent that is deleterious to cell function, inhibiting cell replication and ultimately leading to cell death. Paclitaxel is metabolized in humans by CYP3A4. As shown below in Example 7, coadministration of an antisense PMO targeted to this enzyme increased the cytotoxic effects of the drag. E. Interindividual Nariation Enormous inter-individual variations have been reported in both enzyme content and activity in the liver and small intestines. For example, the specific content of CYP3A4 in the liver has been reported to vary by a factor of 20-fold, while the enzyme activity, as determined by the erythromycin breath test, has been reported to vary by a factor of 10-fold (Shimada et al, 1994). Small intestine CYP3A4 content has been reported to vary by a factor of 10 to 49- fold (Lown et al, 1994; Paine et al, 1997; Zhang et al, 1999). These variations in the CYP3A4 activity, in turn, are likely responsible for inter-individual variations in therapeutic efficacy and disposition of a variety of drugs. Factors that influence CYP3A4 activity include genetic polymoφhisms, physiological states, environmental (exogenous) factors and pathological conditions. These factors cause an enormous inter-individual variation in CYP3A4 activity, which can influence the therapeutic efficacy of a wide variety of drags. Current medical practice predominantly involves treating patients with a standard dose of drug, leaving no adjustment for inter-individual differences in metabolism. These differences can lead to suboptimal drag response, complete treatment failure or adverse drag reactions. An antisense approach to inhibition of P450 enzymes, particularly CYP3A4, in combination with established drags can be used to produce a narrower range of inter-individual variation and thus a more predictable response to therapy. IN. Design and Preparation of Antisense Oligomers A. Selection of Target Sequences Target sequences, including genomic sequences, pre-mRΝA, mRΝA, and/or cDΝA sequences, from genes selected according to the considerations outlined in the previous sections, may be obtained from the GenBank sequence database or from other published sources readily available to those of skill in the art. As noted above, sequences for numerous rat and human p450 genes are known and available to those of skill in the art through sources such as GenBank and review articles such as Gonzales 1989, Black et al. 1987, and Nelson et al. 1993, cited above. For example, Nelson et al. lists all database accession numbers for p450 genes that were available in the GenBank/EMBL, SwissProt, and NBRF-PIR databases as of December 1992. Accession numbers for human p450 sequences are included from the following families: CYP-1A1, 1A2, 2A6, 2A7, 2B6, 2B7P, 2C8, 2C9, 2C10, 2C17, 2C18, 2C19, 2D6, 2D7P, 2D8P, 2E1, 2F1, 3A3, 3A4, 3A5, 3A7, 4A9, 4A11, 4B1, 4F2, 4F3, 5, 7, 11A1, 11B1, 17, 19, 21A1P, 21A2, and 27. Since the publication of the 1993 article, other human sequences, such as those for CYP-lBl and CYP-2B1, have also been made available in GenBank. B. Length and Complementarity of the Antisense Oligomer The appropriate length of the antisense oligomer to allow stable, effective binding combined with good specificity is about generally 10 to 40 nucleotide base units, and preferably about 15 to 25 base units. The antisense oligomer may be 100% complementary to a desired region of the target sequence, or it may include mismatches, e.g., to accommodate coding sequence variants, such as polymoφhisms, as long as the duplex formed between the oligomer and target RNA is sufficiently stable in the cell to block or inhibit translation. Mismatches, if present, are less destabilizing toward the end regions of the hybrid duplex than in the middle. The number of mismatches allowed will depend on the length of the oligomer, the percentage of G:C basepair in the duplex and the position of the mismatch(es) in the duplex, according to well understood principles of duplex stability. Preferably, the T m of the oligomer /target sequence will be at least 37°C, more preferably at least 50°C, and most preferably at least 60°C, 80°C, or higher. Oligomer bases that allow degenerate base pairing with target bases are also contemplated, assuming base-pair specificity with the target is maintained. C. Exemplary antisense oligomers targeting p450 Exemplary oligomer sequences can be designed according to the following guidelines: 1. Each oligomer either (a) spans the AUG start codon of the indicated gene, with the CAU complement of the start codon (expressed in a 5' to 3' direction) being positioned near the center or near the 3' end of the oligomer, or (b) spans an intron-exon (splice donor) boundary or, more preferably, an exon-intron (splice acceptor) boundary of an unspliced pre- mRNA sequence; 2. has a length of about 17-25 bases; and 3. preferably terminates, at the 5' end, at a G (guanine) base, which confers stability to the duplex. Exemplary antisense oligomers having the base sequences shown in Table 2 are designed for p450 RNA-specific inhibition of translation and/or splicing. The location of the bases in the target sequence which hybridize with the oligomer, numbered according to the GenBank sequence numbering, is indicated at the right in the table. By convention, the orientation of the antisense sequences is shown in a 5' to 3' direction. In a hybrid duplex in which the target gene sequence is shown a 5' to 3' direction (by convention), the orientation of the hybridized antisense oligomer sequence would be reversed; that is in a 3' to 5' direction. The table also identifies the sequence identifier number (SEQ ID NO:) of each exemplary oligomer sequence. Preferred antisense oligomers for use in practicing the method of the invention are those identified by SEQ ID NOs: 16-17, 19, 25, 27, 30, 34-35 and 46-47, for inhibiting translation and/or splicing of target RNAs derived from the rat CYP2B1, CYP2E1, and CYP3A2 and human CYP1A2, CYP2B1, CYP2E1, and CYP3A4 genes, respectively. Table 2. E. Testing the effectiveness of the antisense oligomers The effectiveness of a given antisense oligomer molecule in inhibiting expression of the target gene may be determined by screening methods known in the art. El . In vitro screening methods: Candidate antisense oligomers can be tested in vitro in, for example, hepatocyte cell culture, to quantify the effect of the oligomer on protein produced by the target RNA in the presence and absence of drugs or other inducers. See, for example, Examples 2 and 4 below. RNA quantitation methods are known in the art, and include Northern blot and RT-PCR assays. Protein production can be evaluated by Western blot or ELISA using antibodies specific for the target enzyme. Alternatively or in addition, protein expression can be evaluated enzymatically using probe substrates specific for the target enzyme. For example, substrates are known which differentially react with various p450 isozymes (M. Burke et al, Biochem. Pharmacol. 34(18):3337-45 (1985); Gonzalez, 1989 (cited above)). Candidate oligomers are also evaluated, according to well known methods, for acute and chronic cellular toxicity, such as the effect on overall protein and DNA synthesis as measured via incoφoration of 3 H-leucine and 3 H-thymidine, respectively. It is desirable that non-specific binding of the oligomeric molecule to non-target sequences is limited. To test for non-specific binding effects, control sequences such as sense or nonsense sequences, or sequences containing mismatched bases, may be included in screening tests. Excess targeted protein or mRNA may also be added to the cell culture to determine if the effect of the antisense oligomer is reversed. E2. In vivo screening methods: Antisense compositions may be tested in vivo in animal models as described, for example, in Examples 1, 3, and 5 below. Effects of a drug can be observed directly, as in sleep time induced by hexobarbital, and/or enzyme levels can be determined by assays known in the art. As described above and in copending and co-owned US application serial no. 60/117,846, duplexes of PMO antisense oligomers with target RNA sequences have been detected in body fluid samples following in vivo administration of the PMO oligomers. Such methods could be employed for in vivo screening of target RNA binding of a given oligonucleotide. V. Pharmacokinetics and Administration The pharmacokinetics of nuclease-resistant oligonucleotides has been shown to be favorable for in vivo therapeutic treatment of various endogenous genes. To date, studies in the rat, mouse and monkey reveal an elimination half-life in plasma longer than twenty hours. It has also been shown that the liver, where most drug metabolism occurs, is an organ of accumulation for oligonucleotides. See, for example, P. Iversen et al. , Antisense Res & Dev 4: 43-52 (1994) and E. Bayever et al. , Antisense Res and Dev 3:383-390 (1993), for discussions of the pharmacokinetics of phosphorothioate oligonucleotides administered to animal subjects and to human patients. Bayever et al. conclude that safety and favorable pharmacokinetics support further investigations of phosphorothioate oligonucleotides as potential gene specific therapeutic agents in humans. Moφholino oligonucleotides have been shown to provide significantly improved selectivity in inhibiting translation of targeted sequences in comparison to the widely used phosphorothioates. The moφholino oligomers were also shown to inhibit translation at much lower concentrations than the corresponding phosphorothioates, and with little or no evidence of the non-antisense activity often exhibited by phosphorothioates. See, for example, Summerton et al, Antisense & Nucleic Acid Drug Dev 7(2):63-70 (Apr 1997). Because the moφholino oligomers are uncharged, they are more effective at penetrating cell membranes. The moφholino oligomers also have high nuclease resistance and good water solubility, making them good candidates for in vivo use. Table 3 compares pharmacokinetic and renal excretion properties of phosphorothioate (PS) and PMO oligonucleotides, such as those shown in Table 8 below, after IP injection of a single 0.1 mg dose. Table 3. Single Dose (0.1 mg) Plasma Pharmacokinetics Routes of administration of antisense oligomers include, but are not limited to, various systemic routes, including oral and parenteral routes, e.g., intravenous, subcutaneous, intraperitoneal, intramuscular, and intraarterial injection, as well as inhalation and transdermal delivery. In some cases, targeted delivery by direct administration to a particular tissue or site is preferred. The present invention particularly contemplantes oral and transdermal delivery. Examples of standard pharmaceutically accepted carriers include saline, phosphate buffered saline (PBS), water, aqueous ethanol, emulsions such as oil/water emulsions, triglyceride emulsions, wetting agents, tablets and capsules. It will be understood that the choice of suitable physiologically acceptable carrier will vary dependent upon the chosen mode of administration. Molecular conjugates useful for delivering antisense moφholino oligomers are described in U.S. Patent No. US 6,030,941 (Summerton and Weller, 2000), which is incoφorated herein by reference. The oligomers of the invention may also be administered encapsulated in liposomes. (See, e.g., Williams, S.A., Leukemia 10(12): 1980-1989, 1996; Lappalainen etal, Antiviral Res. 23:119, 1994; Uhlmann et al, "Antisense Oligonucleotides: A New Therapeutic Principle", in Chemical Reviews , Volume 90, No. 4, pp 544-584, 1990; Gregoriadis, G., Chapter 14, "Liposomes", m Drug Carriers in Biology and Medicine, pp 287-341, Academic Press, 1979.) The active ingredient, depending upon its solubility, may be present both in the aqueous phase and in the lipidic layer(s), or in what is generally termed a liposomic suspension. The lipidic layer generally comprises phospholipids, such as lecithin or sphingomyelin, steroids such as cholesterol, ionic surfactants such as diacetylphosphate, stearylamine, or phosphatidic acid, and/or other hydrophobic materials. The diameters of the liposomes generally range from about 15 nm to about 5 microns. In practicing the method of the invention, the antisense oligomer is co-administered with the drag at a desired dose and dosing schedule. Preferably, the oligonucleotide is first administered several hours to several days before first administering the drug, to allow reduction of the target enzyme level. Preferred doses for oral administration are between about 1-2 mg oligomer/kg patient body weight, assuming an oligonucleotide MW of about 7000. A typical therapeutic dose for a patient weight 70 kg would thus be about 70 mg administered once a day, although higher doses may be administered if needed. The dose may be administered once several times daily, once daily, or less often, e.g., for prophylactic puφoses. The efficacy of treatment may be followed by established tests, according to the drag whose metabolism is being modulated. Typically, the oligonucleotide will be administered at least once daily for a period of time concurrent with the administration of the drag, and may be discontinued, for example, when the drug therapy is discontinued. A. Oral Administration The oral bioavailability of antisense PMOs was demonstrated in rats, using a PMO antisense to rat CYP3A2 (SEQ ID NO: 25), as described in Example 5 below. The antisense PMO (2 mg/kg body weight) was administered to rats by oral gavage, and organs were harvested 24 hours later. A Western blot of liver microsome samples (Fig. 7, Lanes 4 and 5) showed a reduction in CYP3A2 protein greater than that obtained using 25 % of this dose administered intraperitoneally. B. Transdermal Administration Transdermal delivery of antisense oligomers may be accomplished by use of a pharmaceutically acceptable carrier adapted for topical administration, or by use of a transdermal patch. Such carriers typically include an aqueous or alcoholic solvent and one or more transdermal penetration enhancers, many of which are known in the art. See, for example, Pharmaceutical Skin Penetration Enhancement, K.A. Walters and J. Hadgraft, Eds. (Dekker, New York, 1993); Drug Permeation Enhancement: Theory and Applications, D.S. Hseih, Ed. (Dekker, New York, 1994). Examples include diols (e.g. glycerol, propylene glycol), polyethylene glycol, polypropylene glycol and sorbitan esters thereof, fatty alcohols, fatty acids, fatty acid amides, fatty acid esters (e.g. glycerol monooleate, glycerol monolinoleate, isopropyl isostearate, isopropyl linoleate, isopropyl myristate, isopropyl palmitate, sorbitan laurates and oleates), trimethylene glycol, fatty alcohol ethers, Tween® 20, 40, 60, 80, and 85, cyclodextrins, nicotinic esters, amino acids, lecithins, teφenes such as limonene or menthol, ionic compounds such as ascorbate, fatty alkyl ammonium halides, monoalkyl phosphates, sodium hyaluronate, sodium 5-methoxysalicylate, and sodium deoxycholate, dimethyl sulfoxide and related compounds, N-methyl pyrrolidone and related compounds, and azone and related compounds (see e.g. Minaskanian et al, U.S. Patent 4,879,275). Transdermal administration of an antisense PMO in accordance with the invention is described in Example 6, below, using a PMO targeted to the -3/+ 19 region of rat CYP3A2 (SEQ ID NO: 25). The vehicle employed was 95:5 propylene glycol/linoleic acid. Liver S-9 fractions were analyzed for analyzed for levels of PMO and for CYP3A enzyme activity, the latter by conversion of 7-benzyloxy-4-(trifluoromethyl)-coumarin (BFC) to 7-hydroxy-4- (trifluoromethyl)-coumarin (HFC). Results confirmed transdermal delivery of the oligomers and a substantial reduction in enzyme activity in animals treated with antisense to CYP3A (see Table 11, below). EXAMPLES The following examples are intended to illustrate but not to limit the invention. Assay reagents were purchased from GenTest Coφoration (Woburn, Massachusetts), which produces cytochrome p450 reagents and antibodies. Example 1: Coadministration of Antisense to Rat CYP2B1 with Hexobarbital 1A. Coadministration of Antisense Oligomers, Hexobarbital and/or Inducing Agent Phenobarbital Antisense oligonucleotides were designed to be complementary to target sequences within the cytochrome p450 2B1 (rat CYP2B1) gene sequence, with the objective of improving the metabolism of hexobarbital in rats. Five phosphorothioate oligomers were synthesized according to the known rat CYP2B1 sequence (GenBank Accession No. J00719). The antisense oligomers are shown in Table 4. The oligo 2B1-ATG (SEQ ID NO: 16) is a 22-mer having 100% complementarity to a region containing the AUG start codon on the rat CYP2B1 mRNA (SEQ ID NO:39, shown below Table). The oligo 2B1-NRM (SEQ ID NO: 17) has 100% complementarity to the CYP2B1 mRNA starting at base 855. The oligo 2B1- BPB (SEQ ID NO: 36) has the sequence of 2B1-NRM with a two base deletion (indicated in bold in the 2B1-NRM sequence). Each of the oligos 2B1-3MM (SEQ ID NO: 37) and 2B1- CMM (SEQ ID NO: 38) has 2 bases reversed (indicated in bold) compared to the BPB sequence. These last three oligos were compared to all sequences in GenBank and did not show homology to any sequence listed in the database. The table gives the melting temperature (T,-,), molecular weight, and % homology to CYP2B1 mRNA of each sequence. Table 4: Characteristics of ODNs Used in Example 1 Sequence targeted by 2B1-ATG: 3'-CCTCCTCGTTCTATGACCCGAGGTACCA-5' (SEQ ID NO: 39) Sequence targeted by 2B1-NRM: 3'-TCGTTTCTTCTCTCTCTCGTCCCTCTAG-5' (SEQ ID NO: 40) Male Sprague-Dawley rats (Sasco, Omaha) weighing between 210 to 290 grams were used for all studies. They were housed in animal quarters at the University of Nebraska Medical Center AAALAC-approved Animal Resource Facility. The animals were exposed to 12 hour light/dark cycle and fed Purina rat chow and tap water ad libitum. Rats were injected intraperitoneally (i.p.) with the indicated ODNs (see Table 3) once per day for 2 days, in an amount of lmg/kg body weight per injection. Control rats were injected with saline only. Rats in the "PB" groups were injected i.p. with phenobarbital (Mallinckrodt, St. Louis) at 80 g/kg body weight per injection, once per day for 2 days. In the groups in which PB was co-administered with ODN, injections were administered simultaneously. Total volume of injections for all groups was 0.1 ml/mg body weight. Animals in the "2B1-NRM + PB + PRETREATMENT" group also received a dose of 1 mg/kg of 2B1-NRM oligomer (SEQ ID NO: 17) 24 hours prior to the first administration of 2B1-NRM plus PB. Forty-eight hours following the first (non-pretreatment) injection of ODN and/or PB, the rats were injected i.p. with 100 mg/kg body weight hexobarbital (Sigma, St. Louis), in a total volume of 1 ml/kg body weight, prepared fresh daily. Sleep time, defined as the time period from when the rat is placed on its back to when it regains its righting reflex, was measured. Sleep times are given in Table 5 as the mean of each animal in the group ± standard deviation. Treatment of the various groups is summarized as follows: 1. injected with saline only. 2. injected with 80 mg/kg PB per day for 2 days. 3. injected with 1 mg 2B1-NRM per day for 2 days. 4. injected simultaneously with 1 mg ODN 2B1-NRM and 80 mg/kg PB per day for 2 days. 5. same as 4. except injected with 1 mg 2B1-NRM one day before start of 2B1-NRM + PB injections. 6. injected with 1 mg ODN 2B1-ATG per day for 2 days. 7. injected simultaneously with 1 mg ODN 2B1-ATG and 80 mg/kg PB per day for 2 days. 8. injected with 1 mg ODN 2B1-BPD per day for 2 days. 9. injected with 1 mg ODN 2B1-3MM per day for 2 days. 10. injected with 1 mg ODN 2B1-CMM per day for 2 days. Table 5: Hexobarbital Sleep Times a Significantly different from control (p < .05). b Significantly different from phenobarbital treated group (p < .03). c Significantly different from control (p < .001), 2B1-3MM (p < .001) and 2B1-CMM (p< .001). Control rats (injected only with saline during the 2-day treatment regimen) had a sleep time of about 23 minutes. PB-treated rats showed a sleep time of about 11.4 minutes, a significant reduction in sleep time over control rats, as expected. As PB stimulates CYP2B1 gene expression, hexobarbital (which is hydroxylated by CYP2B1) was more quickly metabolized in the PB-treated rat and its sedative effect was reduced. When administered alone, oligomer 2B1-NRM, SEQ ID NO: 17 (Group 3) had no effect on sleep time compared to control, which could be attributed to a low constitutive (i.e. non- induced) level of expression of CYP2B1 in the rat. Oligomer 2B1-NRM & PB administered together (Group 4) had no observable antisense effect. Since PB induction of gene expression is rapid (30-60 minutes) (Waxman and Azaroff, Biochem J. 281(3):577-92,1992), and ODN accumulation in the liver is slow (ca. 12 hours, as shown in related studies by the inventor), rats in one group were pretreated with 2B1-NRM one day before simultaneous injection of PB + 2B1-NRM (Group 5). However, the resulting sleep time was essentially the same as without pretreatment. Oligomer 2B1-ATG (SEQ ID NO: 16) alone (Group 6) did not significantly alter sleep time over control, again possibly due to low constitutive expression of CYP2B1. When 2B1- ATG and PB were injected simultaneously, however (Group 7), sleep time increased significantly over that of the PB group. Oligomer 2B1-ATG thus showed a potent in vivo antisense effect toward PB-induced CYP2B1 expression. Oligomer 2B1-3MM alone (SEQ ID NO: 37) slightly lengthened sleep time over the control. Oligomer 2B1-BPD (SEQ ID NO: 36) significantly reduced sleep time from control, suggesting an anomalous increase in HB metabolism. Oligomer 2B1-CMM (SEQ ID NO: 38) did not significantly alter HB sleep time from the control. IB. Preparation of Microsomes Microsomes were prepared, as described by Franklin and Estabrook (Arch. Biochem. Biophys. 143:318-29, 1971), for determination of enzyme level and activity. The rats were sacrificed using ethyl ether, and livers were perfused with 12 ml of 4% saline via the portal vein and then removed from the animal. The livers were minced, homogenized in 0.25 M sucrose (Sigma) and centrifuged at 8000xG for 20 minutes at 4 °C in a Sorvall RC2-B centrifuge (Dupont). The supernatant was saved, resuspended in 0.25 M sucrose, and centrifuged at 100,000xG for 45 minutes at 4°C in a Sorvall OTD55B ultracentrifuge (Dupont). The pellet was resuspended in 1.15% KC1 (Sigma) and centrifuged at 100,OOOxG for 1 hour at 4°C. The final pellet was resuspended in an equal volume buffer (10 mM Tris- acetate, 1 mM EDTA, 20% glycerol; Sigma) and frozen at -80°C. 1C. Determination of Protein Concentrations Protein concentrations were determined by Bradford assay (M.M. Bradford, Anal Biochem 72:248-54, 1976). Eighty μl aliquots of homogenate, prepared as described above, were added to a 96 well plate (Becton Dickinson Labware, Lincoln Park, NJ). Twenty μl of Bradford reagent (Bio-Rad Richmond, CA) was then added and the plates read at 595 nm on the microplate reader (Molecular Devices, Newport MN). The data was compared to standard curve generated with known concentrations of bovine serum albumin (Sigma). ID. Determination of Enzyme Activity: PROD Assay CYP2B1 enzyme activity was determined by pentoxyresorafin 0-dealkylation (PROD) activity (Burke et al, 1985). For each microsomal sample, 1 mg protein in 1 ml 0.1 M potassium phosphate buffer, 1 ml 2 μM 5-pentoxyresorufin (Pierce, Rockford, IL), and 17 μl 60 mM NADPH were mixed and incubated for 10 minutes at 37°C. The mixture was then added to a 2 ml cuvette and read on a RF5000U spectrofluorophotometer (Shimadzu, Columbia, MD), using an excitation wavelength of 530 nm and emission wavelength of 585 nm. Concentrations were calculated from a calibration curve of resorafin standards (Pierce, Rockford, IL). Results were recorded in nmol resorafin/mg protein/min. Activity of microsomes from control rats was 13.8 ± 10.1 nmol resorufin/mg prot/min. Microsomes isolated from PB groups all had significantly increased PROD activities, ranging from about 50 to 115 nmol resorufin/mg prot/min. Microsomes from 2B1-NRM, 2B1-ATG, 2B1-3MM, and 2B1-CMM treated rats (SEQ ID NOs: 17, 16, 37 and 38, respectively) showed no change from control. Although not significantly different from control, 2B1-BPD (SEQ ID NO: 36) showed a small increase in activity. (In inteφreting these results, it should be noted that the pentoxyresorafϊn 0-deaIkylation (PROD) assay measures both CYP2B1 and CYP2B2.) IE. ELISA Assay Direct measurement of CYP2B1 protein was performed by an ELISA assay, using an antibody directed to the CYP2B1 protein (Schuurs and Van Weeman, Clin Chim Acta 81(1): 1- 40, 1977). Fifty μg of microsomal proteins per well were plated in 100 μl 0.35% sodium bicarbonate buffer overnight on a 96 well nunc-immuno plate (InterMed, Skokie, IL). The microsomes were washed 3x with 1 % bovine serum albumin in PBS (PBS/BSA) and incubated for 1 hr at 37°C with 200 μl PBS/BSA. The PBS/BSA was removed, and 50 μl of CYP2B1 antibody (Oxygene, Dallas) was added and incubated for 1 hour at 37°C. The microsomes were washed 5x with saline/Tween 20™ (Sigma), and 50 μl horseradish peroxidase (HRP)- conjugated secondary antibody (Bio-Rad) was added. The microsomes were incubated for 1 hour at 37°C, then washed 5x with saline/Tween 20™ and twice with 85 % saline. HRP substrate (Kirkegaard & Perry Labs, Gaithersburg, MD) (100 μl) was added, and the absorbance at 405 nm was read continuously in a microplate reader (Molecular Devices) for 1 hour. Results were recorded as HRP activity in mOD/min. The results are shown graphically in Figure 3. The average HRP activities and n values for the various groups are given in Table 6. Table 6. As expected, HRP activity of microsomes treated with PB alone was significantly greater than the activity of microsomes from control rats, due to induction of expression of the CYP2B1 gene by PB. Microsomes of rats treated with oligomers 2B1-NRM, 2B1-ATG, 2B1- 3MM, and 2B1-CMM (SEQ ID NOs: 17, 16, 37 and 38, respectively) showed no change in HRP activity over control microsomes. Microsomes from rats in the 2B1-NRM + PB group and the 2B1-NRM + PB + PRETREATMENT group showed a decrease in HRP activity over that of the PB-alone treatment group, indicating an inhibitory effect of the 2B1-NRM oligomer on the amount of PB-induced CYP2B1 present in the microsomal fractions. Microsomes from rats in the 2B1-ATG + PB treatment group showed a significant decrease in HRP activity over the PB-alone group, indicating that the 2B1-ATG oligomer had a significant inhibitory effect on PB-induced production of CYP2B1, in agreement with the significant sleep time increases observed in that rat treatment group. Microsomes from 2B1- BPD treated rats showed an increase in CYP2B1 over control in the ELISA assay, which concurs with the anomalous sleep time reduction observed in 2B1-BPD treated rats. IF. Determination of CYP2E1 Induction Microsomal PNP (p-nitrophenol hydroxylase) activity was used as a measure of induction of CYP2E1 , as PB is known to induce many different CYPs, including CYP2E1. CYP2E1 activity was determined by PNP activity as described in Reinke and Moyer, Drug Metab. Dispos. 13:548-52, 1985; Koop, Mol. Pharmacol. 29:399-404, 1986). Activity was recorded as optical density (OD) per milligram of protein per minute. Microsomes from control rats had a PNP activity of 0.49 ± 0.05 OD/mg prot/min. Microsomes isolated from rat groups treated with PB (PB; 2B1-NRM + PB; 2B1-NRM + PB + pretreatment; 2B1-ATG & PB) all showed significant increases in PNP activities over that of control, demonstrating induction of CYP2E1 by PB. Since each PB group showed approximately equivalent PNP activities, the ODNs did not appear to interfere with the PB induction mechanism of CYP2E1. Microsomes isolated from rats treated with oligomers 2B1- NRM, 2B1-ATG, 2B1-BPD, 2B1-3MM and 2B1-CMM (SEQ ID NOs: 17, 16, 36, 37 and 38, respectively) alone (no PB) showed no significant differences in PNP activities from control values. All data was reported as mean ± standard deviation. The mean and standard deviation were determined by the computer program InStat2 (GraphPad, San Diego). The p values were also calculated by InStat2 using the Tukey-Kramer Multiple Comparisons Test. Example 2: Antisense Inhibition of Rat CYP2E1 Substrates to cytochrome p450 isozymes frequently control the rate of their own metabolism by modulating isozyme gene expression (Eliasson et al., J Biol Chem. 267(22): 15765-9, 1992). Cytochrome p450 IIE1 (CYP2E1) up-regulation has been attributed to increased transcription, mRNA stabilization and enhanced stability of the protein. CYP2E1 gene expression is induced by low molecular weight compounds such as ethanol, acetone, and pyrazole. The exemplary rat CYP2E1 antisense sequences given in Table 2 were used to evaluate the effectiveness of antisense targeting of specific sequences important to the processes of pre- mRNA splicing and mRNA translation. Oligonucleotides: Phosphorothioate oligonucleotides were synthesized on a 1 μmole scale by use of an Applied Biosystem Model 380A DNA Synthesizer (Foster City, CA and University of Nebraska DNA synthesis core facility), according to standard methodology (e.g. G. Zon and W.J. Stec, in Eckstein, F. (ed.), OLIGONUCLEOTIDES AND ANALOGUES: A PRACTICAL APPROACH (IRL Press at Oxford University Press), pp. 87-108 (1991). The oligonucleotides had sequences antisense to rat cytochrome CYP2E1 mRNA and pre-mRNA sequences (Umeno et al, Biochemistry 27(25): 9006-13, 1988); GenBank Locus RATCYP45I, Accession M20131). The anti-2El 30-mer, 5'-(GGT TTA TTA TTA GCT GCA GTT GGC TAT CAT)-3' (SEQ ID NO: 18), is antisense to a region in the rat CYP2E1 sequence beginning at position 1406 and containing a sequence upstream of the ATG translation start site. The sequences of the anti-2El 20-mers are as follows: 5'-(CCA AGA ACC GCC ATG GTG CC)-3' (SEQ ID NO: 19), antisense to a region beginning at position 1560 and targeting the ATG translation start site; 5'-(ACC TTG GTG AAA GAC TTG GG)-3' (SEQ ID NO: 20) antisense to a region beginning at position 1725 and targeting the splice donor of exon 1; 5'-(CCT TGT TCT TGT ACT CCT GG)-3' (SEQ ID NO: 21) antisense to a region beginning at position 2645 and targeting the splice donor of exon 2; 5'-(GAG AAG CAT GGT CAC CTG GA)-3' (SEQ ID NO: 22) antisense to a region beginning at position 6681 and targeting the splice donor of exon 4; and 5 '-(CCA ACA CAC ACA CGC TT TCQ-3' (SEQ ID NO: 23), antisense to a region beginning at position 11591 and targeting the splice acceptor of exon 9. Two nonsense oligonucleotides prepared for control puφoses include the 27-mer 5'-(TCG TCG GTC TCT CCG CTT CTT CCT GCC)-3' (SEQ ID NO: 41), antisense to rev of HIV-1 (Matsukura et al, Proc NatlAcad Sci USA 86(ll):4244-8, 1989) and the 20-mer 5'-(TCG TGA TGA ATT CTG TCG AG)-3' (SEQ ID NO: 42), with no homologous complementary sequence in the rat genome. Cell Transfection: The rat hepatoma cell line, H42E, was purchased from American Type Culture Collection (Bethesda, MD). The cells were maintained in RPMI-1640 media (Sigma, St. Louis, MO.), supplemented with 10% heat inactivated fetal bovine serum (Gibco, Grand Island, NY), penicillin G (10,000 units/ml) and streptomycin (10% mg/ml)(Sigma). The cells were subcultured at 3-4 day intervals at a density of 2 x 10 5 cells per 25 cm 2 flask in 5 ml of medium, and incubated at 37°C in a humidified atmosphere of 95 % air, 5 % C0 2 . The H42E cells were plated (2 x 10 6 to 1.25 x 10 5 for the 1 to 5 day timepoints) in 10 ml RPMI + 10% FBS in 100 mm tissue culture dishes (Becton Dickenson, Oxnard, CA) and allowed to adhere overnight. Antisense oligonucleotide (3.0 μM) and pyrazole (16 μM; Sigma) were added, and dishes were incubated at 37°C for 1 to 5 days. Cells were harvested in 2 ml 0.1 M K 2 HP0 4 pH 7.2 and homogenized into microsomes. Eight antisense oligonucleotides, as described above, were employed to test the ability of the various mRNA target regions to inhibit pyrazole-induced synthesis of the CYP2E1 enzyme. Six antisense oligonucleotides, as described above (SEQ ID NOs: 18-23), were specific to different regions along CYP2E1 mRNA. The last two sequences, MM3 and BUD (SEQ ID NOs: 41 and 42, respectively), were nonsense oligonucleotides with no targets within the CYP2E1 gene. The relative concentrations of CYP2E1 enzyme in prepared microsomes were measured by use of ELISA. Microsome dilutions of 50 to 6.25 μg/ml of each sample were plated in coupling buffer (0.06% sodium carbonate, 0.29% sodium bicarbonate, pH 9.6) in 96 well immunoassay NUNC plates (VWR Scientific, Chicago, IL). Plates were incubated overnight at 4°C to allow protein to adhere to wells. Wells were washed lOx with 0.05% Tween 20™ (Aldrich, Milwaukee, WI)/PBS, the last wash with PBS only, then blocked for 2 hours with 3% BSA (Sigma)/PBS. Wells were washed as before. The primary antibody, anti- Cytochrome p450 2E1 (Oxygene, Dallas, TX), diluted 1:200 in 1 % BSA/PBS, was added and plates were incubated for 1.5 hours. Wells were washed, and a 1:2000 dilution of the secondary antibody, horseradish peroxidase (HRP) conjugate (Bio-Rad, Richmond, CA), was added. Plates were incubated 2 hours and washed. A 1:1 dilution of ABTS Peroxidase Substrate and Peroxidase Solution B (Kirkegaard and Perry, Gaithersburg, MD) were added to the wells. Plates were read kinetically at 405 nm every 30 seconds for 1 hour with an OD max of 0.500 (Praslin, J Immunol Methods 137(l):27-35, 1991). Results are given in Table 7. Table 7: Characteristics of antisense CYP2E1 oligomers and effect on CYP2E1 enzyme levels a p<0.05. Several of the oligonucleotides produced significant reduction in levels of CYP2E1 enzyme. The antisense oligomers 2E1-1560, 2E1-11591, 2E1-1725 and 2E1-1406 (SEQ ID NOs: 19, 23, 20, and 18, respectively) reduced enzyme levels to 52%, 63%, 66% and 76% of control, respectively. Treatment with the other CYP2E1 specific oligonucleotides, as well as the nonsense oligonucleotides, resulted in CYP2E1 levels that were not significantly different from the control level. Varying doses of the antisense oligonucleotide 2E1-1560 (SEQ ID NO: 19) were investigated for inhibition of the CYP2E1 enzyme in H42E cultures. The cultures showed an increase in inhibition on an increase in oligo concentration from 0.3 μM to 3μM, at which the enzyme level was approximately 41 % of control. Above this level, the CYP2E1 protein inhibition leveled off, showing little additional inhibition at lOμM of oligonucleotide (Fig. 4). Example 3: Antisense Inhibition of Rat CYP3A2 hv PS (Phosphorothioate) and PMO Oligonucleotides and Effect on Midazolam Efficacy Antisense oligonucleotides complementary to target sequences within the cytochrome p450 3A2 (rat CYP3A2) gene sequence were prepared, with the objective of increasing the effectiveness of midazolam (MZ) in rats. Two phosphorothioate (PS) and two PMO oligomers were synthesized according to the known rat CYP3A2 sequence (GenBank Accession No. U09742; see Table 2). Table 8. Antisense Rat CYP3A2 Oligonucleotide Sequences and Controls Rat CYP3A2 mRNA (Accession #U09742): -8 -1 10 20 5'-AAGCAGGG AUG GACCUGC UUUCAGCUCU CACACUGG-3' (SEQ ID NO: 45) M: 5 '-methyl cytidine The antisense oligomers are shown in Table 8. The oligos designated AUG3A2/PMO and ATG3A2/PS have the sequence designated SEQ ID NO: 24, which targets the ATG start codon. In (-3)ATG3A2/PMO-C5M (SEQ ID NO: 25, a three-base shift from SEQ ID NO: 24), several cytidine bases are 5 '-methylated, as shown in the Table. Reverse-sequence oligos (SEQ ID NO: 43) and a c-myc sequence (SEQ ID NO: 44) were used as controls. Male Sprague-Dawley rats (Sasco, Omaha) weighing between 210 to 290 grams were used for all studies. The animals were exposed to 12 hour light/dark cycle and fed Purina rat chow and tap water ad libitum. A dose-response curve for MZ was determined by injecting rats i.p. with 20, 50 or 70 mg/kg of MZ and recording sleep times (data not shown). Sleep time was defined as the time period from when the rat was placed on its back to when it regained its righting reflex. Sleep time was measured after i.p. injection of 50 mg/kg MZ (Hoffman-La Roche, Nutley, NJ) at 0 (day 1), 24 (day 2) and 48 h (day 4). The volume of the injection was from 2.0 to 2.4 ml/rat. All animals demonstrated loss of righting reflex within 2 min after i.p. injection of MZ. The rats were treated with 0.25, 0.50 or 1.00 mg antisense ODN i.p. immediately after the animal had regained its righting reflex determined at 0 and 24 h. Control rats received saline only. Total volume injection was 0.1 ml in saline. Preparation of Microsomes Microsomes were prepared, as described by Franklin and Estabrook (cited above) for determination of enzyme level and activity. The rats were sacrificed using ethyl ether, and livers were perfused with 12 ml of 4% saline via the portal vein and then removed from the animal. The livers were minced, homogenized in 0.25 M sucrose (Sigma) and centrifuged at 8000xG for 20 minutes at 4°C in a Sorvall RC2-B centrifuge (Dupont). The supernatant was saved, resuspended in 0.25 M sucrose, and centrifuged at 100,000xG for 45 minutes at 4°C in a Sorvall OTD55B ultracentrifuge (Dupont). The pellet was resuspended in 1.15% KC1 (Sigma) and centrifuged at 100,000xG for 1 hour at 4°C. The final pellet was resuspended in an equal volume buffer (10 mM Tris-acetate, 1 mM EDTA, 20% glycerol; Sigma) and frozen at -80°C. Determination of Protein Concentrations Protein concentrations were determined by Bradford assay (M.M. Bradford, Anal Biochem 72:248-54, 1976). Eighty μl aliquots of homogenate, prepared as described above, were added to a 96 well plate (Becton Dickinson Lab ware, Lincoln Park, N ). Twenty μl of Bradford reagent (Bio-Rad Richmond, CA) was then added and the plates read at 595 nm on the microplate reader (Molecular Devices, Newport MN). The data was compared to standard curve generated with known concentrations of bovine serum albumin (Sigma). Liver Microsomal Assays for CYP3A2 Erythromycin demethylation (ED) was used a measure of CYP3A2 enzymatic activity (Gonzalez, Pharmacol. Rev. 40:243-87, 1989). Activity was recorded as micromoles of formaldehyde per milligram of protein per minute. Western blot of CYP3A2 Western blot analysis of CYP3A2 was carried out using the method described by Tracewell et al, Toxicol Appl Pharmacol. 135(2): 179-84, 1995. Band intensities were determined by a Molecular Dynamics Personal Densitometer (Sunnyvale, CA) with ImageQuant version 3.3 software (Molecular Dynamics). Statistical analysis All microsomal data were reported as mean standard error of the mean (S.E.) as determined by the computer program InStat2 (GraphPad, San Diego). The P values were also calculated by InStat2 with the Tukey multiple comparison test. Standard curve and graphs were generated using Prism (GraphPad). Results: Sleep Time: Table 9 shows the change in sleep time (MZ ST) and ED activity (a marker for CYP3A2) for animals receiving the various treatments. Both the PMO and PS oligos targeting the start codon (SEQ ID NOs: 24 and 25) showed an increase in sleep time, as would result from inhibition of CYP3A2 and consequent inhibition of metabolism of the MZ. The PMO oligo, however, was effective at one-tenth the concentration of the PS oligo. Control oligos (SEQ ID NOs: 43 and 44) showed little or no change from the saline-only control. ED Activity: All of the anti-3A2 oligos (SEQ ID NOs: 24 and 25) reduced ED activity to some extent, with the 5'-C-methyl modified PMO (SEQ ID NO: 25) showing greater activity than the unmodified oligo. Activity in animals administered control oligos was not significantly different from the saline control. Table 9. Effect of Anti-CYP3A2 Oligonucleotides on MZ Sleep Time and ED Activity in Rats All values represent the mean + standard error of the mean. MZ ST - midazolam sleep time, min; ED - erythromycin demethylase activity (in vitro marker for CYP3A2), μmol HCOH/mg/min. (a) Significantly different from saline, myc, and rev groups, p<0.0 1. (b) Significantly different from myc and saline groups, p<0.05. Example 4: Antisense Inhibition of Human CYP3A4 in Transfected Cells V79 cells were stably transfected with the human CYP3A4 gene. The cells were scrape loaded with lOuM PMO having the sequences shown below, targeting the ATG start codon of human CYP3A4 mRNA (SEQ ID NOs: 46, 46, and 35; see Table 2). A sequence targeting the ATG rat CYP3A2 (SEQ ID NO: 25, with C-mefhyl substitution) was also employed. Activity was assayed in S-9 fractions via 7-benzyloxy-4-(trifluoromethyl)-coumarin conversion to fluorescent product 7-hydroxy-4-(trifluoromethyl)-coumarin, a CYP3A4 specific reaction. Results are given in Table 10. 5' -CTG GGA TGA GAG CCA TCA C-3' SEQ ID NO: 46 human CYP3A4 5' -CTG GGA TGA GAG CCA TCA CT-3 ' SEQ ID NO: 47 5'-GT CTG GGA TGA GAG CCA TCA C-3' SEQ ID NO: 35 5 '-GAG TG AAA GMA GGT MMA TMM M-3' SEQ ID NO: 25 rat CYP3A2 Table 10. Antisense Inhibition of Human CYP3A4 As shown in the table, the human antisense sequences significantly reduced enzyme activity. The anti-rat oligo, which in this case has only about 55% homology with the human sequence targeted, showed no reduction in enzyme activity. Example 5: Oral Administration of PMO Antisense Oligomers Figure 7 shows a Western blot of liver microsome samples obtained from rats which were administered a phosphorodiamidate moφholino oligonucleotide (PMO) antisense to the rat CYP3A2 gene (SEQ ID NO: 25, with no C-methyl modifications), either i.p. or orally. The blot was first probed with anti-rat CYP3A2 antibodies. After stripping off antibodies, the blot was re-probed with antibodies to NADPH Reductase as a control for total protein loading in the various lanes. Each rat weighed approximately 200 gm, and was treated 24 hours prior to organ harvesting with the following: saline, injected intraperitoneally (lane 1); 15 nmoles of PMO 1- 0-328, injected intraperitoneally (lanes 2 and 3); 60 nmoles of PMO 1-0-328, administered orally (lanes 4 and 5). Each lane corresponds to a different test animal. No significant reduction in CYP3A2 protein compared to the saline-injected control was observed 24 hours after i.p. injection of 15 nmoles (approx. 0.5 mg/kg body weight) PMO (lanes 2-3); however, in other experiments, a modest decrease in CYP3A2 enzyme activity was observed under these conditions. Furthermore, a significant reduction in CYP3A2 protein level was observed by Western blot when a second injection of 15 nmoles PMO was administered 24 hours following the first, and organs were harvested 24 hours thereafter (data not shown). In a test of the oral bioavailability of antisense PMOs, 60 nmoles of the antisense PMO (2 mg/kg body weight, four times the i.p dose used above) were administered to rats by oral gavage, and organs were harvested 24 hours later. Lanes 4 and 5 show a significant reduction in CYP3A2 protein compared to lanes 2 and 3, showing that the relative oral bioavailability of the antisense PMO is substantially greater than 25% of the i.p. administered PMO. Example 6: Transdermal Administration of PMO Antisense Oligomers A PMO targeted to the -3/+ 19 region of rat CYP3A2, having SEQ ID NO: 25 (5 '-GAG CTG AAA GCA GGT CCA TCC C-3'), was used. Three groups of 4 animals each were treated as follows: Antisense Group: 3 mg/rat AVI-4472 (SEQ ID NO: 25) Control Group: 3 mg/rat AVI-4126 (antisense to c-myc; SEQ ID NO: 44) Vehicle Group: Vehicle only For the Antisense and Control groups, a formulation of 3 mg PMO in 100 μL of 95:5 propylene glycol/linoleic acid (vehicle) was applied over the right rear flank of 280-300 gm rats. The area was shaved immediately prior to PMO administration and was determined to be free of any visible cuts or bruises. The PMO formulation was applied over an area of 200 mm 2 using a plastic ring as guide. It was observed that the formulation disappeared visually from the skin in 3 to 5 minutes. All rats were euthanized 24 hrs following the transdermal application. Liver S-9 fractions were analyzed for CYP3A enzyme activity by conversion of 7-benzyloxy-4-(trifluoromethyl)- coumarin (BFC) to 7-hydroxy-4-(trifluoromethyl)-coumarin (HFC). The reaction is specific for CYP3A, and the fluorescent product formation can be monitored at an excitation wavelength of 409 nm and emission wavelength of 530nm. Liver samples from the Control PMO group were analyzed for levels of PMO, and revealed 9.9 + 0.7 μg PMO/ rat liver 24 hrs following transdermal application, establishing transdermal delivery of the oligomers. As the data in Table 11 shows, a substantial reduction in enzyme activity was observed in the animals treated with antisense to CYP3A, while the results for the control antisense were essentially similar to the vehicle-only control. Table 11. Reduction of CYP3A2 Activity by Transdermallv Delivered Antisense PMO Example 7: Enhanced Cvtotoxicitv of Paclitaxel Co-administered with Antisense to CYP3A4 Cell viability of primary human hepatocytes and caco-2/h3A4 cells (human colon carcinoma cell line caco-2 transfected with CYP3A4 cDNA on an extrachromosomal vector p220CMV3A4; Gentest, Woburn, MA) was assessed following co-treatment with SEQ ID NO: 47 or control PMO in combination with three cytotoxic drugs: paclitaxel, cyclophosphamide and cisplatin. Of these, the first is metabolized to less cytotoxic metabolites by CYP3A4, the second is a prodrag that requires metabolic activation by CYP3A4 to become cytotoxic, and the third is not metabolized by CYP3A4. Cells were treated with PMO 24 hours prior to addition of cytotoxic drugs. Cell viability was determined by MTT assay after an additional 24 hours incubation with 5 μM paclitaxel, 600 μM cyclophosphamide or 7 μM cisplatin. Addition of the antisense PMO having sequence SEQ ID NO: 47 in combination with paclitaxel reduced cell viability in both model systems, as expected from greater exposure of the cells to unmetabolized paclitaxel. Co-treatment of cells with the antisense PMO and cyclophosphamide significantly increased the cell viability in both model systems compared to treatment with cyclophosphamide alone. Co-treatment of cells with cisplatin and the antisense PMO did not significantly alter cell viability from this moderately cytotoxic toxic dose of cisplatin. Additional studies were carried out to investigate the mechanism of alteration of paclitaxel toxicity by antisense PMO in caco-2/h3A4 cells. Cells were treated with control or antisense PMO (SEQ ID NO: 47) 24 hours prior to addition of 5 μM paclitaxel. After an additional 24 hours paclitaxel incubation, flow cytometry was employed to determine the cell cycle distribution of the caco-2/h3A4 cells. The addition of paclitaxel alone to the cells increased the percent of viable cells in GJG 0 phase, a cell cycle checkpoint indicative of DNA damage. It is likely that the DNA damage was produced predominantly by the 3'-(p-hydroxyphenyl)taxol metabolite produced by CYP3A4. Conversely, viable caco-2/h3A4 cells treated with antisense PMO (SEQ ID NO: 47) and paclitaxel accumulated largely in the S phase of the cell cycle, indicating a release of the G S DNA damage checkpoint and a return to paclitaxel's mechanism of action at the microtubule level.

Claims: It is claimed: 1. A method of improving in a subject the pharmacokinetics of a drug, comprising co-administering with said drug a moφholino antisense oligomer effective to reduce synthesis of a drag-metabolizing cytochrome p450 enzyme that reduces the effectiveness of the drug, by hybridizing to a target RNA molecule which encodes said enzyme, wherein the antisense oligomer is administered to the subject orally or transdermally. 2. The method of claim 1, wherein the moφholino oligomer has intersubunit linkages selected from the group consisting of the structures presented in Figs. 6AA-6EE. 3. The method of claim 2, wherein said linkages are phosphorodiamidate linkages as represented at Figure 6B-B, where X=NH 2 , NHR, or NRR', Y=0, and Z=0, or where X=OR, Y=NH or NR', and Z=0, and R and R' are groups which do not interfere with target binding. 4. The method of claim 3, wherein R and R' are moieties independently selected from alkyl, polyalkyleneoxy, and a combination thereof, which may be substituted with one or more groups selected from hydroxy, alkoxy, amino, alkylamino, thiol, alkanethiol, halogen, oxo, carboxylic acid, carboxylic ester, and inorganic ester. 5. The method of claim 4, wherein each said moiety R and R', independent of substitution, is from 1 to 6 atoms in length. 6. The method of claim 3, wherein NRR' represents a nitrogen heterocycle having 5-7 ring atoms selected from nitrogen, carbon, oxygen, and sulfur, and having at least as many carbon ring atoms as non-carbon ring atoms. 7. The method of claim 1, wherein the antisense oligomer is at least 15 nucleotides in length. 8. The method of claim 1, wherein the antisense oligomer hybridizes to a region of the target RNA with a T m greater than 37°C. 9. The method of claim 1 , wherein the antisense oligomer hybridizes to a region of the target RNA molecule which includes the AUG translation start site. 10. The method of claim 1, wherein the target RNA molecule is pre-mRNA, and the antisense oligomer hybridizes to a region of the pre-mRNA which includes an intron-exon boundary or an exon-intron boundary. 11. The method of claim 1, wherein the drag either induces said drug-metabolizing cytochrome p450 enzyme, or is administered to a subject who has been exposed to a xenobiotic agent which induces such an enzyme. 12. The method of claim 11, wherein the drag induces the cytochrome p450 enzyme. 13. The method of claim 1, wherein said cytochrome p450 is selected from the group consisting of CYPIAI, CYP1A2, CYP2A6, CYP2B1, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A2, CYP3A4, and CYP6A1. 14. The method of claim 1, wherein the subject is a human subject, and the cytochrome p450 is selected from the group consisting of CYPIAI, CYP1A2, CYP2A6, CYP2B1, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4. 15. The method of claim 14, wherein the cytochrome p450 is selected from the group consisting of CYP1A2, CYP2B1, CYP2E1, and CYP3A4. 16. The method of claim 1, wherein the cytochrome p450 is CYP2E1, and the drug is acetaminophen. 17. The method of claim 1 , wherein the cytochrome p450 is from the CYP2B or CYP3A subfamily, and the drug is phenobarbital or hexobarbital. 18. The method of claim 17, wherein the cytochrome p450 is CYP2B1. 19. The method of claim 1, wherein the cytochrome p450 is CYP3A4, and the drug is an antibiotic selected from the group consisting of clarithromycin, erythromycin, rifampicin, rifampin, rifabutin, and rapamycin. 20. The method of claim 1, wherein the cytochrome p450 is CYP3A4 or CYP1A2, and the drag contains an estrogen or estradiol. 21. The method of claim 11, wherein the cytochrome p450 is CYP3A4, the drag is a protease inhibitor or non-nucleoside reverse transcriptase inhibitor, and the xenobiotic agent is a CYP3A4-inducing non-nucleoside reverse transcriptase inhibitor. 22. The method of claim 1, wherein the drag is paclitaxel, and the cytochrome p450 is human CYP3A4. 23. The method of claim 22, wherein the antisense oligomer is selected from the group consisting of SEQ ID NOs: 35, 46, and 47. 24. The method of claim 1, wherein the antisense oligomer is selected from the group consisting of SEQ ID NOs: 16-35 and SEQ ID NO: 46-47. 25. The method of claim 24, wherein the oligomer is selected from the group consisting of SEQ ID NOs: 26-35 and SEQ ID NOs: 46-47. 26. The method of claim 25, wherein the oligomer is selected from the group consisting of SEQ ID NOs: 27, 30, 34, 35, and 46-47.

Inventors: IVERSEN PATRICK L, IVERSEN, PATRICK, L.
Applicants: AVI BIOPHARMA INC, IVERSEN PATRICK L, AVI BIOPHARMA, INC., IVERSEN, PATRICK, L.
Application year: 2001
Main classification: A61K31
IPC codes: A61K31, A61K38, A61K45, A61K48, A61P3, A61P5, A61P25, A61P29, A61P31, A61P43, C07H21, C12N15