DELIVERY OF EXOGENOUS COMPOUNDS

Abstract: The invention discloses methods and materials for the receptor-mediated transport of targeted exogenous compounds across biological membranes of pathogenic agents. The invention also discloses methods and materials for treating infection by pathogenic agents, including Microbacterium tuberculosis.

Description: DELTVERY OF EXOGENOUS COMPOUNDS Field of the Invention The present invention discloses delivery of various exogenous compounds across membranes of pathogens. It permits the study of pathogens and the detection and treatment of pathogenic infections. The invention can be used, inter alia, in the treatment of infections caused by bacteria such as Mycobacterium tuberculosis having resistance to one or more conventional chemotherapeutic agents. Background of the Invention The acquisition of multidrug resistance by pathogenic agents is rendering existing medications and diagnostic reagents useless for treatment of pathogenic infections. Similarly, newly discovered or synthesized therapeutics may be excluded from entry into a pathogen or metabolized to a harmless product by virtue of the therapeutics' similarity to molecular structures recognized by multidrug resistance enzymes. Pathogenic organisms can acquire resistance to multiple drugs by a number of mechanisms, including mutation of an existing gene or by introduction of a new gene from another organism. The acquisition of drug resistance frequently occurs upon prolonged exposure to a cytostatic or cytocidal compound. The acquisition of new genes may occur, for example, by transfer of a plasmid during bacterial conjugation by transfer of exogenous DNA by bacteriophage infection. The emergence of drug-resistant bacteria in general and drug-resistant tuberculosis in particular is rapidly becoming a major public health problem in the U.S. and around the world (Editorial. Reviving the antibiotic miracle? Science 264: 360-365, 1994). The urgency in finding new treatment modalities for drug-resistant tuberculosis is emphasized by two recently published molecular and conventional epidemiological studies (Alland, D., et al. Transmission of tuberculosis in New York City. An analysis by DNA fingerprinting and conventional epidemiologic methods. New Engl. J. Med. 330: 1710-1716, 1994; Small, P.M., et al. The epidemiology of tuberculosis in San Francisco. A population-based study using conventional and molecular methods. New Engl. J. Med., 330: 1703-1709, 1994). Not only was it demonstrated by utilization of DNA fingerprinting that more than a third of the newly diagnosed TB cases in New York and San Francisco are the result of recent person to person transmission, rather than activation of latent infections, but also that nearly half of the isolates from patients with recently transmitted infections in New York were drug-resistant M. tuberculosis. Of these drug-resistant isolates, half were resistant to multiple drugs. Drug-resistant M. tuberculosis strains, because of their ability to lead to a long infectious state, are especially active in the rece person to person transmissions. Tuberculosis is the most widespread of human pathogenic diseases, having an annual number of new cases of active infection of 7.5 million cases and an annual number of deaths attributable to tuberculosis of 2.5 million worldwide according to the World Health Organizatio (Editorial, The Global Challenge of tuberculosis. The Lancet 344: 277-279, 1994). Modern chemotherapy of tuberculosis began in 1952 with the development of isoniazi (isonicotinic acid hydrazide) which along with rifampin (or rifampicin) is still the mainstay of the treatment of tuberculosis. Streptomycin, which was shown to be effective in the treatment o tuberculosis before 1952. frequently resulted in treatment failure due to the rapidly developing resistance to streptomycin. Combinations of streptomycin with aminosalicylic acid and isoniazi were then utilized resulting in a high degree of cures in tuberculosis patients. The antituberculosis drugs that currently are being clinically utilized are isoniazid, rifampin, pyrazinamide and ethambutol as first line oral drugs; streptomycin, amikacin, kanamycin and capreomycin as injectable drugs; ofloxacin, ciprofloxacin, ethionamide, aminosalicylic acid and D-cycloserine as second-line oral drugs (Iseman, M.D. Treatment of multidrug-resistant tuberculosis. New England Journal of Medicine 329: 784-791, 1993; Mandell, G.L. and Sande. M.A. Antimicrobial agents, drugs used in the chemotherapy of tuberculosis and leprosy in The Pharmacological Basis of Therapeutics, Gilman A.G. et al. Editors, Pergamon Press, 1990, pp. 1 146-1164). Drug resistance and multidrug resistance in tuberculosis originates in spontaneous mutations which occur at predictable rates in the tubercle bacilli. The mutations are not linked and the rise of drug-resistant organisms is the result of these pre-existing mutations rather than a result of drug treatment or another novel mechanism not yet established or understood (Heym, et al. Implications of multidrug resistance for the future of short-course chemotherapy of tuberculosis: a molecular study. The Lancet 344: 293-298, 1994). Thus, the emergence of drug resistance is the direct result of the survival of random pre-existing mutations and the selection the mutation-carrying organisms due to the killing of drug-sensitive organisms by effective drugs. Drug resistance in tubercle bacilli does not involve mechanisms related to the existence of increased efflux of drugs through multidrug resistant (MDR) channels as is the case with other drug-resistant bacteria and parasites such as Plasmodiumfalciparum. Oligonucleotides containing a base sequence complementary to selected sequences present on mRNAs were shown during the last several years to inhibit the synthesis of the specific proteins coded for by the targeted mRNAs. These oligonucleotides, known as antisense, comprise a new class of therapeutic agents and have been demonstrated to inhibit the replication and expression of human immunodeficiency virus (HIV), as well as other viruses or cellular proteins in in vitro or in vivo screening systems. The internucleoside phosphate group of oligodeoxynucleotides can be chemically modified, for example, to methylphosphonates, phosphorothioates, or phosphoroamidates in order to increase nuclease resistance of the modified oligonucleotide, without serious effects on its base sequence-specific hybridization to target mRNAs. Such modifications can afford reductions in the 50% inhibitory concentrations (IC 50 ) to the 10" 7 M range. U.S. Patent Number 4,806,463 entitled "Inhibition of HTLV-III by exogenous oligonucleotides" to Goodchild and Zamecnik disclosed for the first time the use of modified oligonucleotides including oligodeoxynucleotide phosphorothioates which are oligonucleotides modified on the internal phosphate groups, for inhibiting the replication and gene expression of HTLV-III virus now called Human Immunodeficiency Virus (HIV). U.S. Patent Number 5,276,019 entitled "Inhibitors for replication of retroviruses and for the expression of oncogene products" to Cohen et al. also discloses the use of modified oligodeoxynucleotide phosphorothioates for inhibiting viral replication in a host as well as inhibiting the replication of a human immunodeficiency virus replication in particular. The disclosures of these two patents are incorporated herein by reference. Oligonucleotide drugs inhibit the expression of specific genes by three potential mechanisms. For RNA targets, at least two mechanisms of inhibition can be envisioned. Oligodeoxynucleotide hybridization to the complementary RNA sequences may inhibit the processing, nuclear export, or translation of mRNA by blocking the access of functional machinery to requisite mRNA sequences. Alternatively, oligodeoxynucleotide hybridization may lead to RNA cleavage by means of RNase H activities, which are DNA-RNA hybrid-dependent ribonucleases present in all cells examined. Evidence for both RNase H-dependent and independent modes of action has been presented for mRNA translational inhibition by complementary oligodeoxynucleotides in cell-free systems. Oligonucleotides can also be targeted to specific sequences of the DNA double helix where they inhibit transcription of specific genes (antigene or triplex strategy). The development of oligonucleotides and their modifications as therapeutic agents has been accelerated by recent advances in synthetic oligonucleotide chemistry. Summary of the Invention The invention involves the discovery that exogenous compounds may be coupled to particular types of targeting molecules, for example either D-cycloserine or D-glucosamine, an transported across a membrane of a pathogenic agent. The targeting molecule binds to its receptor on a pathogenic agent and acts as a carrier for the exogenous compound as the targetin molecule is transported across the cell membrane. The invention is effective for delivery of exogenous compounds to any pathogenic agent having a receptor for the targeting molecule. Targeting molecules such as D-cycloserine and D-glucosamine are particularly suited for treati mammals because mammalian cells do not carry receptors for these targeting molecules. Thus, the invention involves treating a mammal with compositions comprising targeting molecules f which pathogenic agents have a receptor and for which mammalian cells do not have a receptor According to one aspect of the invention, a method for enhancing transport of an exogenous compound across a molecule of a pathogenic agent is provided. The pathogenic age is contacted, in vitro or in vivo, with a conjugate of a targeting molecule and the exogenous compound for a time sufficient to permit transport of the conjugate across the membrane. The targeting molecule is either D-cycloserine or D-glucosamine. In preferred embodiments, the exogenous compound is a cell function modifier which reduces the growth, replication or survival of the pathogenic agent. In particularly preferred embodiments, the cell function modifier is selected from the group consisting of an antisense nucleic acid, an antibiotic, an inhibitor of a pathogenic agent protease, a nucleic acid binding peptide or protein, and an enhancer of host immune system recognition of the pathogenic agent. In other embodiments th exogenous compound is linked to the targeting molecule by a bond resistant to hydrolysis in th pathogenic agent. In addition, agents which enhance the uptake of the conjugate described abo or which labelize the membrane of the pathogenic agent may be administered to enhance transport of the exogenous compound. In a particularly preferred embodiment, the targeting molecule is D-glucosamine and the conjugate is administered along with the membrane labelizing agent ethambutol. The method described herein is particularly effective for enhancin transport of exogenous molecules across the membrane of a bacterium, especially when the bacterium is multidrug resistant. According to another aspect of the invention, a composition is provided. The composition includes a conjugate of the targeting molecule, selected from the group consisting of D-cycloserine and D-glucosamine and an exogenous compound linked to the targeting molecule. The preferred exogenous compounds and targeting molecules are as described above. In preferred embodiments, the exogenous compound is a polypeptide, or an oligonucleotide. The targeting molecule can be linked to the exogenous compound by a bond resistant to hydrolysis in pathogenic agents. The composition also may include a pharmaceutically acceptable carrier. According to yet another aspect of the invention, a method for treating an infection of a pathogenic agent is provided. The method involves administering to a subject in need of such treatment the compositions described above. Preferred aspects of the composition are noted above. The invention also involves the discovery that bacterial infections, including those caused by Mycobacterium tuberculosis, are treatable using antisense technology. Experimental evidence to establish that antisense technology can be extended to treating bacterial infections has not before existed to the knowledge of the inventors. It further has been unknown whether the mechanism of drug resistance in Mycobacterium tuberculosis would act to exclude oligonucleotides introduced exogenously. Finally, it was unknown whether antisense oligonucleotides would gain access through the bacterial cell wall if introduced exogenously, even for nonresistant strains. The present invention discloses the use of antisense oligonucleotides for inhibiting bacteria] growth and thus for the treatment of bacterial infections. Since bacterial infection previously was treated by a cheap, effective and readily available assortment of antibacterial agents, a significant aspect of the present invention is the disclosure that growth of bacteria resistant to one or more of the conventional therapeutic agents nonetheless can be readily inhibited by antisense oligonucleotides. The present invention demonstrates that conventional mechanisms which yield drug-resistant bacteria do not operate to exclude oligonucleotides, that conventional antisense oligonucleotides do not gain entry through bacterial membranes, and that antisense oligonucleotides can circumvent drug-resistance in bacteria. According to one aspect of the invention, a method for treating an infection caused by a bacterium is provided. The method involves administering to a subject, preferably a human, in need of such treatment an effective amount of an antisense oligonucleotide that inhibits the growth of the bacterium. Useful oligonucleotides include oligoribonucleotides, oligodeoxyribonucleotides and modified versions of the same. Modified versions include thos with modified internucleoside linkages such as phosphorothioate linkages, methylphosphonate linkages and phosphoroamidate linkages. Phosphorothioates are preferred. The oligonucleotid also may be chemically modified at either or both ends to prevent nucleolytic degradation. The oligonucleotides are constructed and arranged such that they hybridize under physiological conditions to a bacterial gene, the expression of which is essential for bacterial metabolism and growth. The invention is not limited to metabolism and growth. The invention is not limited t treatment of any particular bacterial infection, although preferred is treatment of infection by drug resistant strains of bacteria. Various methods are provided for delivering the oligonucleotides of the invention in effective amounts. In one aspect of the invention, the subject is simultaneously treated with a compound such as ethambutol, which labilizes the bacterial wall and facilitates the delivery of the oligonucleotide into the bacterium. In another aspect of the invention, the oligonucleotides may be linked to a molecule that enhances bacterial wall transport. For example, the oligonucleotides may be covalently linked to a ligand for a receptor on a bacterium. Examples ligands include D-cycloserine and D-glucosamine. According to other aspects of the invention, articles of manufacture are contemplated. For example, antibacterial cocktails may be prepared which include a labilizing agent and the oligonucleotides of the invention. As another example, the invention provides an antibacterial agent that is an oligonucleotide of the invention covalently coupled to a molecule that enhances transport of the oligonucleotide across the bacterial cell wall. Such a molecule can be a ligand for a receptor on a bacterium. Specific examples include antisense oligonucleotides covalently coupled to D-cycloserine and D-glucosamine. These and other aspects of the invention are described in greater detail below. Detailed Description of the Invention The invention involves the discovery that exogenous molecules may be delivered to a cell by receptor-mediated endocytosis by linkage with either D-cycloserine or D-glucosamine. In this manner, molecules which are excluded or poorly taken up by a pathogenic agent may be delivered effectively to that agent. The invention is useful, for example, whenever it is desirable to enhance transport of exogenous molecules across the membrane of a pathogenic agent having a receptor for D- cycloserine or D-glucosamine. The invention thus may be used to deliver therapeutics or diagnostics across such membranes, especially to pathogenic agents which lack efficient uptake mechanisms for a particular exogenous molecule, or in which uptake mechanisms are altered by multidrug resistance. The invention in one aspect involves conjugation of an exogenous molecule and a targeting molecule, either D-cycloserine or D-glucosamine. The exogenous molecule is believed to be actively transported by a receptor-mediated endocytosis mechanism. It also involves compositions including a targeting molecule linked to one or more such molecules, including to therapeutic and/or diagnostic agents. The "conjugates" of the present invention are associated with one another in a variety of ways. If the molecules are linked together, then the targeting molecule is covalently or noncovalently bound to the exogenous compound in a manner that preserves the targeting specificity of the targeting molecule. As used herein, "linked" or "linkage" means two entities are bound to one another by any physiochemical means. It is important that the linkage be of such a nature that it does not impair substantially the effectiveness of the exogenous compound or the binding specificity of the targeting molecule. Keeping these parameters in mind, any linkage known to those of ordinary skill in the art may be employed, covalent or noncovalent. Such means and methods of linkage are well known to those skilled in the art. Linkage according to the invention need not be direct linkage. The components of the compositions of the invention may be provided with functionalized groups to facilitate their linkage and/or linker groups may be interposed between the components of these compositions to facilitate their linkage. In addition, the components of the compositions of the present invention may be synthesized in a single process, whereby the components could be regarded as one and the same entity. For example, a targeting molecule specific for an extracellular receptor could be synthesized together with the exogenous compound. These and other modifications are intended to be embraced by the present invention. Specific examples of covalent bonds include those wherein bifunctional cross-linker molecules are used. The cross-linker molecules may be homobifunctional or heterobifunctional, depending upon the nature of the molecules to be conjugated. Homobifunctional cross-linkers have two identical reactive groups. Heterobifunctional cross-linkers have two different reacti groups that allow for sequential conjugation reaction. Various types of commercially availabl cross-linkers are reactive with one or more of the following groups; primary amines, secondar amines, sulfhydryls, carboxyls, carbonyls and carbohydrates. Examples of amine-specific cross-linkers are bis(sulfosuccinimidyl) suberate, bis[2-(succinimidooxycarbonyloxy)ethyl]sulfone, disuccinimidyl suberate, disuccinimidyl tartarate, dimethyl adipimate-2 HCI, dimethyl pimelimidate-2 HC1, dimethyl suberimidate-2 H and ethylene glycolbis-[succinimidyl-[succinate]]. Cross-linkers reactive with sulfhydryl gro include bismaleimidohexane, 1 ,4-di-[3'-(2'-pyridyldithio)-propionamido)]butane, l-[p-azidosalicylamido] -4-[iodoacetamido]butane, and N-[4-(p-azidosalicylamido) butyl]-3'- [2'-pyridyldithio]propionamide. Cross-linkers preferentially reactive with carbohydrates inclu azidobenzoyl hydrazide. Cross-linkers preferentially reactive with carboxyl groups include 4-[p-azidosalicylamido]butylamine. Heterobifunctional cross-linkers that react with amines a sulfhydryls include N-succinimidyl-3-[2-pyridyldithio]propionate, succinimidyl[4- iodoacetyljaminobenzoate, succinimidyl 4-[N-maleimidomethyl] cyclohexane-1-carboxylate, m-maleimidobenzoyl-N-hydroxysuccinimide ester, sulfosuccinimidyl 6-[3-[2-pyridyldithio]propionamido]hexanoate, and sulfosuccinimidyl 4-[N-maleimidomethyl cyclohexane-1-carboxylate. Heterobifunctional cross-linkers that react with carboxyl and ami groups include 1 -ethyl 3-[3-dimethylaminopropyl]-carbodiimide hydrochloride. Heterobifunctional cross-linkers that react with carbohydrates and sulfhydryls include 4-[N-maleimidomethyl]-cyclohexane 1 -carboxylhydrazide-HCl, 4-(4-N-maleimidophenyl)-butyric acid hydrazide-HCl, and 3-[2-pyridyldithio]propionyl hydrazide. The cross-linkers may also be nonselective. Examples of nonselective cross-linker are bis-[β-(4-azidosalicylamido)ethyl]disulfide and glutaraldehyde. If the exogenous molecule a synthetic nucleic acid, then amine or thiol groups may be added at any nucleotide of a synthe nucleic acid so as to provide a point of linkage for a bifunctional cross-linker molecule. The nucleic acid may be synthesized incorporating conjugation-competent reagents such as Uni-Li AminoModifier, 3'-DMT-C6-Amine-ON CPG, AminoModifier II, N-TFA-C6-AminoModifιer C6-ThiolModifier, C6-Disulfide Phosphoramidite and C6-Disulfide CPG (Clontech, Palo Alto CA). Noncovalent methods of conjugation may also be used to join the targeting molecule and the exogenous molecule. Noncovalent conjugation may be accomplished by direct or indirect means including hydrophobic interactions, ionic interactions, intercalation, binding to major or minor grooves of the nucleic acid, ionic interactions of positively and negatively charged molecules, and other affinity interactions. Covalent linkages may be noncleavable in physiologic environments or cleavable in physiologic environments, such as linkers containing disulfide bonds. In some instances the preferred bond will be subject to hydrolysis only after the composition is transported across the membrane of a pathogenic agent. For example, the composition may be joined by a bond which may be hydro lyzed by a penicillinase enzyme. Such a composition would be stable in the host but would dissociate upon transport into a pathogenic agent. Other bonds which are not hydrolyzed by the pathogenic agent may be used, so that the targeting molecule remains bound to the exogenous molecule in the pathogenic agent. Such molecules may resist degredation and/or may be subject to different intracellular transport mechanisms. One of ordinary skill in the art will be able to ascertain without undue experimentation the preferred bond for linking the targeting molecule and exogenous compound, based on the chemical properties of the molecules being linked and the preferred characteristics of the bond. Other covalent linkages are well known to those skilled in the art and will not be further described. One method of the invention is effective in cells that have either D-glucosamine or D- cycloserine receptors expressed on their cellular membranes. Such membranes may form the boundary of the cell, or may form the boundary of an intracellular space such as an organelle. Bacteria have such receptors. The present methods and compositions may be used to modify cellular function of cells in vitro, i.e., in cell culture, or in vivo, where the cells may exist as individual cells or as part of a pathogenic multicellular organism. Pathogenic organisms may be cultured from an infected host, or grown from deposited cultures, and subjected to the methods of the invention. Likewise, mammalian hosts may be treated with the compositions of the invention; because mammalian cells do not carry receptors for D-glucosamine or D-cycloserine, the compositions will be selectively targeted to pathogenic agents in the host that have the appropriate receptor. Cells comprising the pathogenic agent may exist in the extracellular spaces of a host, i.e., suspended in blood or lymph, or may be intracellular pathogens. As used herein, "receptor-mediated endocytosis" means the selective uptake of molecules into a cell, mediated by the binding of a ligand by its cognate receptor. This encompasses energy-dependent and energy-independent transport events, such as transport of a molecule with or against a concentration gradient of such a molecule, so long as the transport is dependent on binding of the ligand to a membrane-associated receptor. As used herein, "uptake enhancing agent" is intended to mean a compound that increases the amount or rate of uptake of the exogenous compound used to treat a pathogenic agent. The uptake enhancing agent may be an antimicrobial agent in its own right. An uptake enhancing agent may specifically increase uptake of a single antimicrobial compound, a class o compounds which share structural or functional equivalents, or compounds which are dissimila The uptake enhancing agent may stimulate a specific uptake pathway or may generally increase transport of molecules into a pathogenic agent. The uptake enhancing agent may, but need not, be specific for a particular pathogenic agent. The degree of specificity of an uptake enhancing agent derives from the membrane components of a pathogenic agents with which it interacts. For example, an agent which prevents synthesis or formation of a pathogen's outer membrane or cell wall components can increase transport of exogenous compounds according to the methods of the invention. Specific examples of such agents are molecules belonging to the class of β-lactam antibiotics: penicillin cephalosporins and the like. Such an agent could increase uptake of many compounds by facilitating dissolution of a concentration gradient. Another example is an agent, such as ethambutol. which increases uptake by increasing the expression of specific receptors useful in the methods of the invention for receptor-mediated transport of exogenous compounds. Other molecules which induce receptor expression will be known to those skilled in the art. Omission of molecules, for example specific nutrients, from growth medium is contemplated to be an effective method of inducing receptors for those molecules omitted in in vitro applications of th invention. A similar effect may be accomplished in vivo by changes in diet or coadministration of agents which sequester or inactivate molecules bound by the receptors of interest. The result of treatment with such agents, of which ethambutol is an example, is an increase in the expression of the receptor of interest. In the case of ethambutol, receptors for cell wall monosaccharide precursors are regulated. As used herein, "membrane labilizing agent" means an agent which creates instability in a biological membrane with respect to the exclusion of exogenous compounds. In this respec a membrane labilizing agent may be physical, chemical or biological in nature. For example, membrane labilizing agents can be agents used for nonspecifically introducing DNA into cells, such as electric current pulses, calcium phosphate, DEAE-dextran, hypoosmotic shock, high- velocity microprojectiles, and the like. Labilizing agents may also be interposed between membrane components such that openings or pores are created in the membrane. Examples of this type of labilizing agent include amphotericin B and bacterial porin proteins. Other membrane labilizing agents, will be known to those skilled in the art. The membrane labilizing agent for increasing transport of specific exogenous molecules can be chosen with no more than routine experimentation. Compounds deliverable by the targeting molecule of the invention include agents which interrupt or modify a cellular function required for growth or survival of the targeted microbe, such as antibiotics standard in the art and other agents known or thought to be effective in eliminating infection of a host. One class of compounds which can be delivered by the foregoing targeting compounds is antisense oligonucleotides, which by hybridizing in a sequence-specific manner to a target nucleic acid inhibit the synthesis of specific proteins which are essential for survival or growth of the bacterial cell. As used herein, "cell function modifier" means a compound which alters a function necessary for the growth, replication or survival of a pathogenic agent. For example, all drugs which are cytotoxic or cytostatic are cell function modifiers. More specifically, compounds which interfere with protein synthesis, nucleic acid synthesis, nucleic acid replication, cellular metabolic processes such as synthesis of energetic metabolites, lipid synthesis, glycosylation, phosphorylation, and other cellular processes are cell function modifiers. Other cell function modifiers may be specific to pathogenic organisms, such as molecules which interfere with virulence factors or molecules which block expression of pathogen-specific genes, e.g. antisense oligonucleotides. A virulence factor is defined to mean a factor produced by a pathogenic agent which is essential for manifestation of the pathogenic effects of the agent, such as invasiveness or toxicity. Invasiveness factors may help the pathogenic agent elude capture or digestion by host defense mechanisms. For example, capsular polysaccharides of, inter alia, S. pneumoniae, K. pneumoniae, B. anthracis and Y. pestis inhibit adherence of host phagocytes and thereby enhance invasiveness. Cell wall components may enhance invasiveness by preventing digestion of the cell wall, and therefore prevent destruction of the pathogenic agent. Components such as the M- protein of S. pyogenes and mycolic acids of Mycobacterium species inhibit digestion by phagocytes. This type of pathogenicity factor permits intracellular invasion of host cells. In connection with pathogenic organisms, a cell function modifier may also be an inhibitor of a pathogenic toxin molecule. The methods and compositions of the invention are useful for delivery to pathogens o exogenous molecules such as antimicrobials, antimicrobial compound potentiating agents, immune system recognition enhancers, diagnostic molecules and the like. In general, the molecules to be delivered can include, but are not limited to: peptides, oligopeptides, proteins and glycoproteins, all of which may contain amino acids and linkages of natural or non-natural types; amino acids and modified amino acids; lipids, phospholipids and liposomes; antibodies; toxins; ribonucleotides and deoxyribonucleotides of natural or non-natural structure and composition; oligonucleotides and polynucleotides comprising natural and non-natural analogs or derivatives which retain biological activity; plasmids and other nucleic acid vectors which direct expression of polynucleotides or proteins; bacteriophage-derived nucleic acids or protein antisense nucleic acids; and the like. Any compound that is useful for treatment of a specific condition and which may be conjugated to D-cycloserine or D-glucosamine by art-standard methods comprising covalent or non-covalent ligands may be utilized in the methods and compositions described below. Molecules useful as antimicrobials can be delivered by the methods and compositions of the invention, such that pathogenic infection is reduced or eliminated. Antibacterial agents can be bactericidal or bacteriostatic by inhibiting replication of bacteria or inhibiting synthesis o bacterial components required for survival of the infecting organism. Antibiotics can be produced synthetically or by microorganisms. Examples of antibiotics include: penicillins, including amoxicillin, ampicillin, carbenicillin disodium, cloxacillin Na, nafcillin Na, penicillin G Na, pipericillin, and cyclacillin; cephalosporins, including cefaclor, cefotaxime Na, ceftazidime, and ceftriaxone; carbapenims and monobactams, including aztreonam, and imipenim; β-lactamase inhibitors, including clavulanate potassium, and sulbactam Na; aminoglycosides, including amikacin sulfate, gentamycin sulfate, neomycin sulfate, streptomyci sulfate, and tobramycin; macrolides, including erythromycin and derivatives; polypeptides, including bacitracin, polymyxin B sulfate, capreomycin sulfate, colostimethane Na, and daptomycin; tetracyclins; chloramphenicol and derivatives; cycloserine; spectinomycin HC1; vancomycin HC1; fluoroquinolones; and the like. Antimicrobial agents can be nucleic acids that effect a reduction or an increase of synthesis of specific gene products. For example, an antimicrobial agent may be a plasmid which directs the synthesis of a protein which is toxic to bacterial cells. Such a toxin preferably will not affect the host infected with the bacterial cells targeted by the toxin. As another example, antimicrobials may be antisense oligonucleotides or catalytic nucleic acids, including ribozymes. An effective quantity of such nucleic acid antimicrobial compounds may be sufficient to reduce expression of gene products critical to the growth or survival of bacterial cells, such as components of the cell wall, cell membrane, nutrient transport or synthesis systems, protein synthesis apparatus, nucleic acid synthesis apparatus, and the like. As a specific example, antisense oligonucleotides which hybridize to a nucleic acid encoding the glucosyltransferase enzyme of Streptococcus mutans may be delivered to such bacteria by the methods and compositions of the invention. Reduction of the glucosyltransferase enzyme, which converts sucrose to dextran and so enables the S. mutans to adhere to the surface of teeth, would reduce the amount of bacterial infection present in a host. Other compounds deliverable by the composition of the invention may be effective as antimicrobial agents by potentiating the effects of antibiotics standard in the medical arts. Such potentiating compounds may be effective as antimicrobial agents when delivered alone. Examples of potentiating agents include inducers of receptors for antibiotics, agents which increase transport of antibiotics into bacterial cells or decrease transport of antibiotics out of bacterial cells, inhibitors of bacterial enzymes which metabolize antibiotics, and the like. Compounds to be delivered also include those compounds which increase recognition of a pathogenic agent infecting a host by the immune system of the host. Such immune recognition enhancing compounds include any which impede or defeat pathogen defenses against immune recognition. Antisense oligonucleotides, ribozymes or plasmids which cause a reduction in synthesis of the capsule of an encapsulated bacterial cell to be reduced or which cause enhanced degradation of the capsule may be considered antimicrobial agents in this regard. For example, delivery of a plasmid that directs synthesis of hyaluronidase would increase degradation of a bacterial capsule, thus enhancing adherence of phagocytic cells to the treated bacterial cells. Similarly, inhibitors of peptidoglycan synthesis in Gram-positive bacteria would enhance the ability of the lytic complement proteins of the host to insert into the cell membrane of treated bacteria. Other examples are diethyl carbamozine, which alters the microfilarial surface membranes of helminths, thereby rendering them more susceptible to host defense destruction, and praziquantel which causes vacuolization and visiculation of helminthic parasites to the extent that host defense mechanisms are activated. Another example of a compound deliverable by the composition of the invention is an antisense oligonucleotide or ribozyme which would inhibit a specific protease or peptidase. Such compounds can reduce the amount an enzyme which degrades complement peptides or another effecter of immune recognition and lysis. An example of such a protease is the elastase of Psuedomonas aeruginosa which inactivates complement proteins C3a and C5a. Compounds effective in reducing protease activity present in infecting bacteria are also effective in enhancing immune surveillance which reduces infection. Regarding reduction of bacterial infection, inhibition by the methods discussed above of a class of bacterial proteases present in N. gonorrhea, meningococci of the nasopharynx, H. influenzae and S. pneumoniae, which proteases digest IgA, dimers, would increase IgA, dimer binding, and thus reduce the ability of the bacterial cells to attach to mucos surfaces of the host. Reduction of protease expression, secretion or function is an effective remedy for halting invasion of a pathogen. The delivery of antimicrobial and other compounds noted above by the methods and compositions of the invention is more specific and selective than prior art methods. The targete delivery of the invention allows a practitioner to use antimicrobial compounds of greater toxicit than previously possible, due to the lesser exposure that host tissues will endure than with prior art delivery of antimicrobials. Since the microbial compounds will be delivered specifically to infecting bacteria and other pathogens, administration of an equivalent dose of an antimicrobial compound conjugated to D-cycloserine or D-glucosamine will require less of the compound relative to treatment with the antimicrobial compound alone. Delivery of antimicrobials to infecting pathogens is also more efficient than prior art methods because the antimicrobials delivered by the compositions of the invention will be taken up by a receptor-mediated endocytosis mechanism. These improvements over other methods enable the use of lesser quantities of antimicrobial agents to effect a reduction of pathogen infection in the host. The us of the compositions of the invention results in fewer side effects of lesser severity and duration as a result of treatment of an infection than do prior art methods. Antisense oligonucleotides of the invention are short oligonucleotides (about 12-36 nucleotides long) which are comprised of a base sequence complementary to a bacterial nucleic acid sequence. Chemical modifications of oligonucleotides can be produced at their 5' or 3' end at the inter-nucleoside phosphate or any other synthetic inter-nucleoside moiety, at the sugar moiety or on the bases themselves. When applied exogenously, these oligomers may inhibit the synthesis of targeted proteins by virtue of their sequence-specific hybridization to target mRNA sequences after entering the target cell. In order to demonstrate the invention, we have utilized the bacterium Mycobacterium smegmatis which is very closely related to M. tuberculosis and which is predictive as to the clinical outcome after a drug is shown to be effective in an in vitro screening system. Justification for the use of M. smegmatis as a common and acceptable model for the development of a therapeutic modality against drug-resistant tuberculosis is due to the following well-acknowledged factors: I. M. smegmatis shares significant genetic sequences with M. tuberculosis. The antisense drug developed relies on hybridization with the mycobacterial genetic machinery for the inhibition of expression of proteins essential for growth; II. M. smegmatis has been utilized in the past as an initial mycobacterial model for the development of antituberculosis drugs because of its faster rate of proliferation as compared to M. tuberculosis; III. M. smegmatis, which is a non-pathogen in man, is the preferred choice for studies of targeted drug development in drug-resistant M. tuberculosis. Utilization of multidrug-resistant (MDR) M. tuberculosis for these studies would be impossible because of the requirements for extensive microbiological and biochemical manipulations, which would produce an unacceptable risk and require a much longer period of initial studies. Mycobacterium smegmatis has been commonly used as a model for the biochemical studies and efficacy screening related to the development of antimycobacterial drugs in general and antituberculosis drugs in particular. It has been discovered that under many conditions, oligodeoxynucleo-tide phosphorothioates do not enter bacteria. Two strategies were successfully utilized to enable entry of oligonucleotides into bacterial cells. One employed the presence of very low levels of ethambutol and the other involved utilization of oligomers covalently attached to a D-cycloserine or D-glucosamine molecule whereby entry into the bacterial cell is achieved by a receptor-mediated process. Significant sequence-specific growth inhibition of M. smegmatis was obtained by modified oligonucleotides complementary in sequence to a specific region of the mycobacterium aspartokinase (ask) gene when utilized in combinations with ethambutol (as compared to ethambutol alone) or as a D-cycloserine covalent adduct without the presence of any other cytotoxic or cytostatic agent. Sequence-specific oligodeoxynucleotide phosphorothioate which a molecule of D-glucosamine was covalently attached is taken up by M. smegmatis in th presence of ethambutol at a much higher rate than the unmodified oligomer under the same conditions resulting in substantially increased growth inhibition and indicating an upregulation of hexose uptake due to the inhibition by ethambutol of the synthesis of carbohydrate precursor of cell wall. We thus demonstrate here that modified oligonucleotides can be utilized for the inhibition of bacterial growth and that the growth of isoniazid-resistant, rifampicin-resistant an streptomycin-resistant strains of M. smegmatis can be inhibited to the same degree as drug-sensitive strains of the same organism. The present invention therefore demonstrates that modified oligonucleotides can circumvent drug-resistance in bacteria, particularly when conjugated to a targeting molecule such as D-cycloserine or D-glucosamine. Other exogenous molecules may also be delivered by the methods and compositions of the invention in order to circumvent drug resistance in pathogenic agents. Individual components of the compositions may be chosen to overcome the mechanisms by which a particular pathogenic agent exhibits drug resistance. For example, the targeting molecules described above are effective for overcoming drug resistance in pathogenic agents which have reduced uptake of a particular dru by inducing receptor-mediated transport of such drug into the pathogenic agent. Other drug resistance strategies of pathogenic agents, i.e., expression of multiple drug resistance transport proteins or increased degradation of antimicrobial drugs, may be circumvented by other characteristics of the compositions of the invention. For example, covalent attachment of a targeting molecule to an exogenous compound may alter the steric properties of the drug chosen such that it is not transportable by multiple drug resistance proteins. Conjugation of a targeting molecule to a drug may also be effective in shielding a particular site of the drug from degradative enzymes of the microbe. We have conducted experiments utilizing Mycobacterium smegmatis grown in liquid medium (Jacobs, Jr., W.R., Kalpana, G.V., Cirillo, J.D., Pascopella, L., Snapper, S.B., Udani, R.A., Jones, W., Barletta, R.G. and Bloom, B.R. Genetic systems for mycobacteria. Methods i Enzymology. 204: 537-555, 1991), which show that these bacterial cells do not allow entry of oligodeoxynucleotide phosphorothioates across the bacterial cell membrane and into the intracellular compartments. Under normal condition no significant growth inhibitory activity was observed with a wide range of oligodeoxynucleotide phosphorothioates up to concentration of 25 μM. The mycobacterial cell envelope architecture and especially the outer wall layer (OL) have been long known to prevent entry of hydrophilic drugs into the mycobacterial cell and to favor entry of lipophilic drugs which are easily solubilized within the lipid portion of the outer wall layer (Rastogi, N., Goh, K.S. and David, H.L. Enhancement of drug susceptibility of Mycobacterium avium by inhibitors of cell envelope synthesis. Antimicrob. Agents Chemother. 34: 759-764, 1990). Ethambutol, a drug which has been in clinical practice for the treatment of tuberculosis and infections caused by other mycobacteria since 1966 (Heifets, L.B., Iseman, M.D. and Lindholm-Levy, P.J. Ethambutol MICs and MBCs for Mycobacterium avium complex and Mycobacterium tuberculosis. Antimicrob. Agents Chemother. 30: 927-932, 1986 and references cited therein) was reported to be effective in increasing drug susceptibility of mycobacteria by inhibiting cell envelope synthesis (Hoffner, S.E., Kallenius, G., Beezer, A.E. and Sevenson, S.B. Studies on the mechanisms of synergistic effects of ethambutol and other antibacterial drugs on Mycobacterium avium complex. Acta Leprologica (Geneva) 7 (Suppl 1): 195-199, 1989). The mechanisms of ethambutol activities in disrupting cell wall synthesis in mycobacteria have been identified. They include the inhibition of mycolic acid transfer into the cell wall (Takayama, K., Armstrong, E.L., Kunugi, K.A., and Kilburn, J.O. Inhibition by ethambutol of mycolic acid transfer into the cell wall of Mycobacterium smegmatis. Antimicrob. Agents Chemother. 16: 240-242, 1979) and the inhibition of biosynthesis from glucose of monosaccharides utilized for the synthesis of cell wall oligo and polysaccharides (Takayama, K. and Kilburn, J.O. Inhibition of synthesis of arabinogalactan by ethambutol in Mycobacterium smegmatis. Antimicrob. Agents Chemother.33: 1493-1499, 1989). These initial effects of ethambutol are followed by the decrease of mycolic acid transfer into mycobacterial cell wall as being the final result of the ethambutol promoted inhibition of cell wall arabinogalactan accumulation (Silve, G., Valero-Guillen, P., Quemard, A., Dupont, M.-A., Daffe, M. and Laneelle, G. Ethambutol inhibition of glucose metabolism in mycobacteria: a possible target of the drug. Antimicrob. Agents Chemother. 37: 1536-1538, 1993). It was discovered in the present invention that ethambutol can promote the uptake by bacteria of antisense oligonucleotides. EXAMPLE 1 Determination of growth of M. smegmatis was performed in liquid cultures (Jacobs, Jr., W.R. et al. Genetic systems for mycobacteria, supra) with cell counting that was done by an electronic Coulter Counter Model Z with an appropriate probe for counting bacterial particles. This method of cell counting is highly accurate as we have shown by its equivalency with plati on agar and colony counts after serial dilutions. The assessment of growth by colony growth in Middlebrook 7H 10 agar was being utilized as well. Growth of M. smegmatis was determined b actual cell counts as well as determinations of MIC (minimum inhibitory concentration) and MBC (minimum bacteriocidal concentration) which are the minimal concentrations of inhibitor required to inhibit growth of at least 99% of the bacterial cells (MIC) or to kill at least 99% of the bacterial population (MBC). Wild type strains of M. smegmatis were either mc 2 155 (kindly supplied by W.R. Jacobs, Jr.) (Jacobs Jr. W.R. et al. Genetic systems for mycobacteria, supra and other single colony isolates from ATCC (Amer.Tissue Culture Collection) strain 607 isolated by ourselves. Strains resistant to isoniazid, rifampin or streptomycin were isolated in our laboratory according to published procedures that are based on the existence of spontaneous M. smegmatis mutations which yield resistance to a single drug at mutational frequencies of 10" 6 to 10" 7 . (Heym, B. and Cole, S.T. Isolation and characterization of isoniazid-resistant mutants o Mycobacterium smegmatis and aurum. Res. Microbiol. 143: 721-730, 1992). All the methodologies for the synthesis and modifications of oligodeoxynucleotides and their modifications follow published procedures (Cardullo, R.A., Agrawal, S. Flores, C, Zamecnik, P.C. and Wolf, D.E. Detection of nucleic acid hybridization by nonradiative fluorescence resonance energy transfer. Proc. Natl. Acad. Sci. USA 85: 8790-8794, 1988; Agrawal, S. and Tang, J.Y. Efficient synthesis of oligoribonucleotide and its phosphorothioate analogue using H-phosphonate approach. Tetrahedron Letters 31 : 7541-7544, 1990; Metelev, V. and Agrawal, S. Ion exchange high-performance liquid chromatography analysis of oligonucleotide phosphorothioates. Anal. Biochem. 200: 342-346, 1992). Utilizing ethambutol in liquid medium at levels of 0.5-1.0 g/ml, which are 5- 10-fold lower than the plasma levels that are achieved in man (Mandell, G.L. and Sande, M.A. Antimicrobial agents, in The Pharmacological Basis of Therapeutics. Gilman, A.G., Rail, T.W., Nies, A.S. and Taylor P., Editors, pp. 1152-1153, Pergamon Press, 1990), M. smegmatis became susceptible to the entry and inhibition of growth, as compared to ethambutol treatment alone, by oligodeoxynucleotide phosphorothioates directed at specific genetic targets. Several different oligodeoxynucleotide phosphorothioates complementary to several sense sequences of the coding and non-coding regions of published mycobacterial gene nucleotide sequences were synthesized. Antisense oligomers complementary to a conserved region of mycobacterial aspartokinase gene (ask) were proven highly effective in inhibiting growth of M. smegmatis in the liquid medium screening system (Table I). The aspartokinase (ask) gene, which was identified upstream of and in an operon with the aspartate semialdehyde dehydrogenase (asd) gene, codes for a protein that catalyzes key biosynthetic pathways (Cirillo, J.D., Weisbrod, T.R., Pascopella, L., Bloom, B.R. and Jacobs, Jr., W.R. Isolation and characterization of the aspartokinase and aspartate semialdehyde dehydrogenase operon from mycobacteria. Mol. Microbiol. 11: 629-639, 1994). Table I. Inhibition of M. smegmatis Growth in Broth Cultures by Oligodeoxynucleotide Phosphorothioates (ODS) in the Presence of Ethambutol 3 Ethambutol ODS at 2.5 μM Cell Numbers per Strain 1 * g/ml Initial Concentration ml x10 6 24 hrs 48 hrs 72 ftrs ATCC 607 None None 620 c 605 582 None ODS8 d 610 602 593 None ODS33 e 612 603 590 None ODS55 f 615 600 585 0.5 None 71 240 41 1 0.5 ODS8 32 49 60 0.5 ODS33 33 48 57 0.5 ODS55 30 45 52 1 None 39 109 172 1 ODS8 18 37 40 1 ODS33 15 20 33 1 ODS55 15 21 34 5 None 25 68 1 1 1 5 ODS8 14 27 44 5 ODS33 14 21 37 5 ODS55 13 13 20 Data represent the averages of two independent experiments. b All inoculations were performed with 10 x 10 6 cells per ml of culture. Results for another wild type strain of M. smegmatis as well as for isoniazid-resistant, streptomycin-resistant and rifampicin-resistant strains of M. smegmatis were quantitatively similar. c 620 x 10 6 cells per ml represent the saturation density of M. smegmatis cells in liquid culture under these conditions. d A 21 -mer {21 nucleotides in length) oligodeoxynucleotide phosphorothioate complementary to nucleotide sequence 1533-1553 of the M. smegmatis ask-asd operon. e A 27-mer oligodeoxynucleotide phosphorothioate complementary to nucleotide sequence 1527-1553 of the M. smegmatis ask-asd operon. f A 36-mer oligodeoxynucleotide phosphorothioate complementary to nucleotide sequence 1518-1553 of the M. smegmatis ask-asd operon. EXAMPLE ? The region of nucleotide sequence 1499-1553 inside the reading frame of M. smegmatis ask-asd operon which contains a single transcriptional start at the 5'-end of the ask gene was proven the best genetic target (Table I). This region codes for a highly conserved sequence among mycobacterial and other bacterial species and is indicated to code for the active site of the aspartokinase protein (Cirillo, J.D. et al. Isolation and characterization of the aspartokinase and aspartate semialdehyde dehydrogenase operon from mycobacteria. supra). The bacterial growth inhibition efficacy of antisense oligonucleotides with complementary sequences directed against this particular region of the ask gene is further understood in light of its expected additional inhibition of the asd gene expression. Both the Ask and Asd proteins catalyze biosynthetic reactions which affect the mycobacterial cell wall integrity. Several 21-mer and 27-mer oligonucleotides complementary to various segments of this region demonstrated efficacy in combinations with ethambutol. Assays of the sensitivity of oligodeoxynucleotide phosphorothioates in inhibiting growth of M. smegmatis were conducted in liquid medium in the presence of low levels of ethambutol (0.5-5.0 g/ml) and effective oligomers yielded up to 90% inhibition of growth at 2.5 μM concentration as compared to growth in the presence of the same levels of ethambutol alone (Table II). Parent and M. smegmatis strains resistant to isoniazid, rifampicin and streptomycin selected in our lab from an ATCC 607 colony as a parent strain followed by isolation of the drug-resistant mutants according to published general procedures (Heym, B. and Cole, S.T. Isolation and characterization of isoniazid-resistant mutants of Mycobacterium smegmatis and Mycobacterium aurum. supra) yielded the same sensitivity to the antisense oligonucleotide-mediated growth inhibition thus indicating the circumvention of individual drug resistance. Table II. MIC of Ethambutol in the presence of Oligodeoxynucleotide Phosphorotioates in Broth Cultures Strain b ODS Initial ODS Concentration μM MIC C g/ml ATCC 607 None None 25 ODS33 d 1 20 ODS33 2.5 10 ODS33 10 7.5 mc 2 155 None None 30 ODS33 1 20 ODS33 2.5 12.5 ODS33 10 7.5 a Data represent the average of two independent experiments. All inoculations were performed with 100 x 10 6 cells per ml of culture. Results were similar for the isoniazid-resistant, streptomycin-resistant and rifampicin-resistant strains. The MICs were determined as the minimum concentration of ethambutol that inhibited at least 99% of cell growth during two weeks in a broth culture. Described in the footnote to Table I. EXAMPLE 3 Since ethambutol leads to intracellular depletion of cell wall monosaccharide precursors and the inhibition of growth of M. smegmatis by ethambutol can be reversed by additions of D-glucosamine, D-galactose, D-mannose or D-arabinose but not by the addition of D-glucose or D-fructose (Silve, G. et al. Ethambutol inhibition of glucose metabolism in mycobacteria: a possible target of the drug, supra), we capitalized on a potential upregulation of cell wall monosaccharide precursor uptake by M. smegmatis in the presence of ethambutol. Oligonucleotides that were effective in inhibiting M. smegmatis growth in the presence of ethambutol were covalently attached to D-glucosamine via a phosphate linker at the oligonucleotide 3'-end utilizing established chemical procedures involving H-phosphorate chemistry with purification and analysis as referred to earlier. The covalent adduct of D-glucosamine to oligodeoxynucleotide phosphorothioates yields marked increases in the growth inhibitory activities of the oligonucleotides in the presence of ethambutol (Table III). Table III. Inhibition of M. smegmatis Growth in Broth Cultures by Covalently-Modified Oligodeoxynucleotide Phosphorothioates 3 Cell Numbers per Ethambutol ODS at 5 uM ml xl O 6 Strain 0 g/ml Initial Concentration 24 hrs 48 firs 72 hrs ATCC 607 None None 650 609 582 None ODS8-DA c 581 477 41 7 None ODS8-DS 0 268 21 3 1 28 None ODS8-LS e 604 541 446 None ODS8-DG' 576 492 407 0.5 None 77 189 388 0.5 ODS-DA 45 67 120 0.5 ODS8-DS 52 63 1 05 0.5 ODS8-LS 46 65 98 0.5 ODS8-DG 31 26 44 a Data represent the average of two independent experiments. b All inoculations were performed with 10 x 10 6 cells per ml of culture Results for another wild type strains of M. smegmatis as well as for isoniazid-resistant, streptomycin-resistant and nfampicin-resistant strains of M. smegmatis were quantitatively similar. 650 x 10 6 cells per ml represent the saturation density of M. smegmatis in broth culture under these conditions. Oligonucleotide ODS8-DA is identical in its nucleotide sequence to ODS8 except for a covalent modification of its 3'-end with a molecule of D-alanine. Oligonucleotide ODS8-DS is identical in its nucleotide sequence to ODS8 except for a covalent modification at its 3'-end with a molecule of D-cyclosenne. Oligonucleotide 0DS8-LS is identical in its nucleotide sequence to 0DS8 except for a covalent modification at its 3'-end with a molecule of L-cycloseπne. f Oligonucleotide ODS8-DG is identical in its nucleotide sequence to ODS8 except for a covalent modification at its 3'-end with a molecule of D-glucosamine EXAMPLE 4 After this initial success in utilizing a covalently attached ligand for the enhancement of uptake of an antisense oligonucleotide into M. smegmatis, we embarked on a search for a ligand that would enable the uptake and subsequent inhibition of growth of M. smegmatis by oligodeoxynucleotide phosphorothioates without the presence of ethambutol. The only ligand among the several that were synthesized and tested which yielded positive results was D-cycloserine. D-cycloserine is a broad spectrum antibiotic which has been utilized as part of an antituberculosis regimen (Mandell, G.L. and Sande, M.A. Antimicrobial agents, in The Pharmacological Basis of Therapeutics. Gilman, A.G., Rail, T.W., Nies, A.S. and Taylor, P. Editors, pp. 1156, Pergamon Press, 1990). It is generally thought to be taken up by the uptake system that is utilized for D-alanine since its inhibitory activities in bacteria are related to reactions in which D-alanine is involved in bacterial cell wall synthesis. Oligodeoxynucleotide phosphorothioates which inhibit M. smegmatis growth in the presence of ethambutol were covalently attached to D-cycloserine utilizing a 3'-end phosphate linker in a manner similar to the synthesis of D-glucosamine-modified oligomers. A 21-mer oligodeoxynucleotide phosphorothioate covalently attached to D-cycloserine and having a base sequence complementary to the previously discussed region of the ask gene typically yielded a 60-70% inhibition of M. smegmatis in liquid medium at a concentration of 5 μM (Table III). The same oligonucleotide without the D-cycloserine ligand or when covalently bound to L-cycloserine, D-or L-alanine, L-azaserine and a variety of other ligands, was without any effect on M. smegmatis growth under identical conditions (Table III). Free D-cycloserine itself, in liquid medium at levels equivalent to the levels present as a covalent part of the antisense oligonucleotide (1.0 μg/ml) yielded minimal inhibition of growth (Table IV). A 10-30 fold excess of this level of D-cycloserine, when present in the liquid medium (10-30 μg/ml), produced a significant inhibition of M. smegmatis growth. More importantly, these levels of free D-cycloserine, when present along with a 5 μM concentration of D-cycloserine-modified antisense oligonucleotides, did not add to the inhibitory activities of the modified oligonucleotide but actually reduced the level of inhibition to about the level achieved by free D-cycloserine (Table IV). These data indicate that free D-cycloserine is competing for the same receptor that is involved in the cellular uptake of the D-cycloserine-modified oligonucleotide and thus successfully blocks uptake and subsequent growth inhibitory activities of the D-cycloserine- modified oligonucleotide. Table IV. Inhibition of M. smegmatis Growth in Broth Cultures by Covalently-Modified Oligodeoxynucleotide Phosphorothioates 2 Cell Numbers per ODS at 5μM Free D-cycloserine ml x 10 6 Strain" Initial Concentration μg/ml 24 hrs 48 hrs 72 hrs ATCC 607 None None 632 560 513 ODS8 None 610 557 495 ODS8-DS c None 291 233 168 ODS8-DS 30 381 287 225 None 1 617 549 504 None 5 551 482 420 None 30 363 291 236 Data represent the average of two independent experiments. All inoculations were performed with 10 x 10 6 cells per ml of culture. Results obtained with other wild type strains of M. smegmatis as well as with isoniazid-resistant, streptomycin-resistant and πfampicin-resistaπt strains of M. smegmatis were quantitatively similar. 632 x 10 6 cells per ml represent the saturation density of M. smegmatis in broth culture under these conditions. As described in the footnote to Table III. In conclusion, the present invention demonstrates through the use of drug-resistant Mycobacterium smegmatis as a scientifically acceptable model of drug-resistant tuberculosis in particular and drug-resistant bacteria in general that: Oligodeoxynucleotides and their phosphorothioate derivatives (oligodeoxynucleotide phosphorothioates) with a nucleotide sequence complementary ("antisense") to sequences of genes that code for proteins that affect bacterial cell growth or metabolism, can be used for inhibiting pathogenic cell growth in a fashion that circumvents resistance to a variety of drugs. The oligonucleotides. however, in many cases have to be afforded with facilitated entry across the pathogenic cell membrane and into the cell, a process which is achieved by one of the following two methods: I. The use of membrane labilizing agents, such as ethambutol in Mycobacteria, which enables the entry of oligonucleotides into the mycobacterial cell with the resulting significant inhibition of growth. II. The use of oligonucleotides covalently attached to D-cyclosamine or D- glucosamine which is a ligand of a cell receptor and thus enables the facilitated entry of the modified oligonucleotide into the pathogenic cell without the presence of membrane labilizing agents. The rapid entry of these compounds into the bacterial cell is due to the interaction of the covalently bound ligand with its receptor. The covalently attached ligands do not affect the growth-inhibitory activities of the oligonucleotide inside the cell. Chemical modifications of oligonucleotides protect these oligonucleotides from biological degradation by nuclease action and enable the covalent modification of the oligonucleotides with a small ligand molecule such as D-cycloserine or D-glucosamine as disclosed in this invention, utilizing established chemical procedures involving H-phosphorate chemistry (Cardullo, R.A.. Agrawal. S., Flores, C, Zamecnik, P.C. and Wolf, D.E. Detection of nucleic acid hybridization by nonradiative fluorescence resonance energy transfer. Proc. Natl. Acad. Sci.USA 85:8790-8794. 1988; Agrawal. S. and Tang, J.Y. Efficient synthesis of oligoribonucleotide and its phosphorothioate analogue using H-phosphorate approach. Tetrahedron Letters 31 :7541 -7544, 1990) with purification and analysis as described (Metelev, V. and Agrawal. S. Ion exchange high-performance liquid chromatography analysis of oligonucleotide phosphorothioates. Anal. Biochem. 200:342-346. 1992). Although the examples above describe methods and products relating to Mycobacterium smegmatis and, by implication, Mycobacterium tuberculosis, the invention is not so limited. The invention is applicable to both resistant and nonresistant strains of bacteria, and pathogenic agents in general. Drug-resistance, as noted, is an emerging major public health problem and resistance to conventional effective, cheap antibiotics is evident in strains of a wide variety of microorganisms in addition to Mycobacterium tuberculosis. The invention thus has particular importance for treating such strains. Examples of bacterial strains which developed resistance to mainstay antibiotics include Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, Neisseria gonorrhoeae, Shigella fiexneri, Haemophilus influenzae and Neisseria meningitidis among disease causing bacteria (Sande, M.A., Kapusnik-Uner, J.E. and Mandell, G.L. "Chemotherapy of Microbial Diseases' * , in The Pharmacological Basis of Therapeutics. Gilman, A.G., Rail, T.W., Nies, A.S. and Taylor, P., Editors, pp. 1018-1046, Pergamon Press, 1990). The methodology disclosed in the present invention can be utilized to inhibit the growth of a broad spectrum of bacterial species. As another specific example, in E. coli which actively takes up D-cycloserine (Mandell, G.L. and Sande, M.A. "Antimicrobial agents' " , in The Pharmacological Basis of Therapeutics. Gilman, A.G, Rail, T.W., Nies, A.S. and Taylor, P., Editors, pp. 1 156, Pergamon Press, 1990), the gene encoding aspartokinase III (Ask protein) has been sequenced (Cassan, M., Parsot, C, Cohen, G.N. and Patte, J.-C. Nucleotide sequence of lysC gene encoding the lysine-sensitive aspartokinase III of Escherichia coli K12. J. Biol. Chem. 261 :1052-1057, 1986) and therefore D-cycloserine-modified oligodeoxynucleotide phosphorothioate with a base sequence complementary to the comparable region of E. coli ask gene is expected to inhibit the growth of the bacteria by mechanisms disclosed here. The invention may also be used for the treatment of parasitic infections, such as protozoan and metazoan infections, where resistance to antimicrobial drugs has developed (Webster, L.T., Jr., "Chemotherapy of Parasitic Infections" in The Pharmacological Basis of Therapeutics. Gilman, A.G., Rail. T.W.. Nies, A.S. and Taylor, P. editors, pp. 954, Proga mon Press, 1990). The Examples demonstrate the feasibility of enhancing transport of large, hydrophilic molecules by attaching such molecules to a ligand for a bacterial cell receptor. It will be obvious to one of ordinary skill in the art that the invention is not limited to the receptor-mediated transport of oligonucleotides across bacterial cell membranes. Rather, the invention encompasses compositions and methods for delivery of exogenous molecules across biological membranes by a receptor-mediated process involving the receptors for D-glucosame or D-cycloserine. It is intended that the exogenous molecules so delivered not be limited to oligonucleotides. Molecules which may be delivered according to the invention may be large or small, charged or neutral, polar or non-polar. Advances in the art of molecular conjugation enable one of ordinary skill in the art to link many types of molecules, disclosed above, to the ligands useful in the invention. The chemistries of such molecular linkages, described above, are well known to one of ordinary skill in the art. Similarly, the skilled artisan will recognize that the methods and compositions of the invention are useful for delivery of molecules to virtually any biological membrane which includes a receptor for D-cycloserine, D- glucosamine or biologically functional equivalents thereof. The membranes targeted by the invention include naturally occurring membranes which envelop pathogenic organisms, synthetic membranes and membranes into which an appropriate receptor has been introduced by e.g. membrane fusion, viral transduction or transection of a receptor- encoding nucleic acid by biological, chemical or physical means. Those skilled in the art will be able to determine, with no more than routine experimentation, genes that are essential for pathogenic agent metabolism and growth and the regions of such genes that will be effective as antisense targets. Typically such regions are those that are highly conserved. When administered, the formulations of the present invention are applied in pharmaceutically acceptable formulations. Such preparations may routinely contain pharmaceutically acceptable concentrations of salt, buffering agents, preservatives, compatible carriers, and optionally other therapeutic ingredients. The conjugate of the invention may be administered rjgr ≤e (neat) or in the form of a pharmaceutically acceptable salt. When used in medicine the salts should be pharmaceutically acceptable, but non-pharmaceutically acceptable salts may conveniently be used to prepare pharmaceutically acceptable salts thereof and are not excluded from the scope of the invention. Such pharmacologically and pharmaceutically acceptable salts include, but are not limited to, those prepared from the following acids: hydrochloric, hydrobromic, sulphuric, nitric, phosphoric, maleic, acetic, salicyclic, p-toluene sulphonic, tartaric, citric, methane sulphonic, formic, malonic, succinic, naphthalene-2-sulphonic, and benzene sulphonic. Also, pharmaceutically acceptable salts can be prepared as alkyline metal or alkyline earth salts, such as sodium, potassium or calcium salts of the carboxylic acid group. Suitable buffering agents include: acetic acid and a salt (1-2% W V); citric acid and a salt (1-3% W V); boric acid and a salt (0.5-2.5% W/V); and phosphoric acid and a salt (0.8-2% W/V). Suitable preservatives include benzalkonium chloride (0.003-0.03% W/V); chlorobutanol (0.3-0.9% W/V); parabens (0.01-0.25% W/V) and thimerosal (0.004-0.02% W/V). The preparations of the present invention may be a pharmaceutical composition having an effective amount of the conjugate of the invention optionally included in a pharmaceutically-acceptable carrier. The term "pharmaceutically-acceptable carrier" as used herein means one or more compatible solid or liquid filler, dilutants or encapsulating substances which are suitable for administration to a human or other animal. The components of oral drug formulations include diluents, binders, lubricants, glidants, disintegrants, coloring agents and flavoring agents. The components of aerosol formulations include solubilized active ingredients, antioxidants, solvent blends and propellants for solution formulations, and micronized and suspended active ingredients, dispersing agents and propellants for suspension formulations. Encapsulating substances for the preparation of enteric-coated oral formulations include cellulose acetate phthalate. polyvinyl acetate phthalate, hydroxypropyl methylcellulose phthalate and methacrylic acid ester copolymers. A variety of administration routes are available. The particular mode selected will depend, of course, upon the particular conjugate selected, the particular condition being treated and the dosage required for therapeutic efficacy. The methods of this invention, generally speaking, involve delivering the conjugates of the invention to the bloodstream. The preferred mode of administration is via parenteral injection, including intraveneous and locoregional administration, i.e., intraperitoneal, intraarterial. intratumoral. intravessicle, and intrathecal. Compositions suitable for parenteral administration conveniently comprise a sterile aqueous preparation of the polysaccharide, which can be isotonic with the blood of the recipient. Among the acceptable vehicles and solvents that may be employed are water, Ringer's solution, and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solvent or suspending medium. For this purpose any bland fixed oil may be employed including synthetic mono or di-glycerides. In addition, fatty acids such as oleic acid find use in the preparation of injectables. Carrier formulations suitable for subcutaneous, intramuscular, intraperitoneal, intraveneous, etc. administrations may be found in Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, PA. Compositions may be conveniently presented in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. All methods include the step of bringing the conjugate into association with a carrier which constitutes one or more accessory ingredients. In general, the compositions are prepared by uniformly and intimately bringing the conjugate into association with a liquid carrier, a finely divided solid carrier, or both, and then, if necessary, shaping the product. The invention in another aspect involves a slow release drug delivery system. This aspect of the invention would permit the targeting of drugs to certain localized regions of the body for subsequent release to surrounding tissue. This aspect of the invention also would permit inclusion of conjugates of a targeting molecule and an exogenous molecule as a component of otherwise conventional sustained release deliver}' systems. The conjugates, for example, can be included in diffusion and diffusion/erosion systems. Such systems include polymer based systems formed from natural and synthetic polymers such as polymers of lactic acid, polymers of glycolic acid, polymers of lactic acid and glycolic acid, polyesters, cellulose, collagen, and polymer hydrogel systems such as those formed from polyhyaluronic acid, gelatin, polymethacrylates and the like. Numerous sustained release systems are well known to those skilled in the art. Such systems can avoid repeated administrations of the conjugates of the invention, increasing convenience to the subject and the physician. The conjugates of the invention are administered in therapeutically effective amounts. A therapeutically effective amount will be determined by the parameters discussed below; but, in any event, is that amount which beneficially treats the condition for which it is administered. It is believed that doses ranging from 1 nanogram/kilogram to 100 milligrams/kilogram, depending upon the mode of administration, will be effective. The preferred range is believed to be between about 500 nanograms and 500 micrograms/kilogram, and most preferably between 1 microgram and 100 micrograms/kilogram. The absolute amount will depend upon a variety of factors, including whether the administration is in a single or multiple doses, the extent of pathogenic infection, and individual patient parameters including age, physical condition. size and weight. These factors are well known to those of ordinary skill in the art and can be addressed with no more than routine experimentation. It is preferred generally that a maximum dose be used, that it, the highest safe dose according to sound medical judgment. Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

Claims: CLAIMS 1. A method for enhancing transport of an exogenous compound across a membrane of a pathogenic agent, comprising: contacting the pathogenic agent with the exogenous compound linked to a targeting molecule selected from the group consisting of D-cycloserine and D- glucosamine, for a period of time sufficient to permit transport of the composition across the membrane of the pathogenic agent. 2. The method of claim 1, wherein the exogenous compound is a cell function modifier which reduces the growth, replication, or survival of the pathogenic agent. 3. The method of claim 2, wherein the cell function modifier is selected from the group consisting of an antisense nucleic acid, an antibiotic, an inhibitor of a pathogenic agent protease, and an enhancer of host immune system recognition of the pathogenic agent. 4. The method of claims 1 -3, wherein the targeting molecule is linked to the exogenous compound by a bond resistant to hydrolysis in the pathogenic agent. 5. The method of claims 1-3, further comprising contacting the pathogenic agent with an uptake enhancing agent which upregulates the expression of a receptor for the targeting molecule. 6. The method of claims 1 -3, further comprising contacting the pathogenic agent with a membrane labilizing agent. 7. The method of claim 6, wherein the membrane labilizing agent is ethambutol. 8. The methods of claims 1 -7 wherein the targeting molecule is D-glucosamine. 9. The methods of claims 1-7 wherein the targeting molecule is D-cycloserine. 10. The method of claims 1 -9, wherein the pathogenic agent is a bacterium. 1 1. The method of claim 10, wherein the bacterium is multidrug resistant. 5 12. The method of claims 10-11, wherein the bacterium is Mycobacterium tuberculosis. 13. The method of claims 1-12, wherein the exogenous compound is an antisense oligonucleotide that hybridizes under physiological conditions to a gene the expression of 10 which is essential for metabolism or growth of the pathogenic agent. 14. A composition for delivery of an exogenous compound to a pathogenic agent by receptor-mediated endocytosis, comprising: a targeting molecule selected from the group consisting of D-cycloserine and D- ] 5 glucosamine, and the exogenous compound linked to the targeting molecule. 15. The composition of claim 14, wherein the exogenous compound is a cell function modifier which reduces the growth, replication, or survival of the pathogenic agent. 0 16. The composition of claim 15, wherein the cell function modifier is selected from the group consisting of an antisense nucleic acid, an antibiotic, an inhibitor of a pathogenic agent protease, a nucleic acid binding peptide or protein, and an enhancer of host immune system recognition of the pathogenic agent. 5 17. The composition of claims 14-16, wherein the targeting molecule is linked to the exogenous compound by a bond resistant to hydrolysis in the pathogenic agent. 18. The composition of claims 14-17 further comprising a pharmaceutically acceptable 0 carrier. 19. The composition of claims 14-18. wherein the targeting molecule is D-cycloserine. 20. The composition of claims 14-18, wherein the targeting molecule is D- glucosamine. 21. The composition of claims 14-20, wherein the exogenous compound is an antisense oligonucleotide. 22. The composition of claim 21 , wherein the antisense oligonucleotide hybridizes under physiological conditions to a gene the expression of which is essential for metabolism or growth of the pathogenic agent. 23. The composition of claims 14-22, wherein the pathogenic agent is multidrug resistant. 24. The composition of claims 14-23, wherein the pathogenic agent is a bacterium. 25. The composition of claims 14-23, wherein the pathogenic agent is Mycobacterium tuberculosis. 26. A method for treating an infection of a pathogenic agent comprising: administering to a subject in need of such treatment the composition of claims 14-21.

Inventors: METELEV VALERI, RAPAPORT ELIEZER, ZAMECNIK PAUL C, METELEV, VALERI, RAPAPORT, ELIEZER, ZAMECNIK, PAUL, C.
Applicants: METELEV VALERI, RAPAPORT ELIEZER, WORCESTER FOUND EX BIOLOGY, ZAMECNIK PAUL C, METELEV, VALERI, RAPAPORT, ELIEZER, WORCESTER FOUNDATION FOR BIOMEDICAL RESEARCH, INC., ZAMECNIK, PAUL, C.
Application year: 1996
Main classification: A61K47
IPC codes: A61K31, A61K38, A61K45, A61K47, A61K48, A61P31, A61P43, C12N1