Abstract:
A process is provided for oxidatively modifying nucleic acids containing a target nucleotide. The nucleic acid is contacted with a polyaza metal comlex in the presence of an oxidizing agent so that the nucleic acid is modified at or near the target nucleotide. Also provided are a kit for carrying out the process and a method for treating neoplastic growth by administering to a subject having neoplastic growth, an effective amount of a polyaza metal complex which is capable of modifying DNA.

Description:
,15 N? 14? 
     A kit is also provided for a nucleic acid assay for locating guanine groups in nucleic acids, oligonucleotides, polynucleotides, RNA and single-stranded DNA, and non-base paired guanine groups in double-stranded DNA. The kit comprises a polyaza metal complex selected from Structures I-III and their derivatives, an oxidant selected from the group consisting of peracid, hypochlorite, O 2 , peroxide in combination with ascorbate, O 2  in combination with ascorbate, and a base of piperidine, N-butylamine or sodium hydroxide. The detection, for example, of labelled 5&#39;-ends in base-cleaved oligonucleotide indicates the position of guanine groups in the oligonucleotide. 
     A method is also provided for treating neoplastic growth comprising administering to a subject having a neoplastic growth, an effective amount of a polyaza metal complex of Structures I-III and their derivatives. 
     Advantageously, the process provides a new method for guanine-specific modification of DNA in sequencing technology and in therapeutics. In addition, the currently used chemical sequencing methods use volatile and toxic chemicals such as dimethylsulfate. The invention employs less toxic materials which are more easily handled. 
     For a better understanding of the present invention, together with other and further objects, reference is made to the following description, taken together with the accompanying drawings and its scope will be pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an autoradiogram of an electrophoresis of a polyacrylamide gel showing oligonucleotide cleavage products obtained using structure 1 with an oxidant and base treatment compared with control studies; 
     FIG. 2 is an autoradiogram of an electrophoresis of a polyacrylamide gel comparing efficacy of various metal complexes in the cleavage of the oligonucleotide. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Polyaza Compounds 
     The compounds useful in the invention are characterized in one regard by their ability to form stable complexes with transition metals. Stable complexes are those having measurable lifetimes at room temperature in water or common organic solvents. 
     The compounds comprise at least one ligand and a transition metal. A ligand is defined herein as a molecule that is attached to the central metal atom of a coordination compound. Preferred ligands are tetradentate or pentadentate and may comprise either macrocyclic or non-macrocyclic molecules. Other ligands, however, can also be used. It is to be understood that a tetradentate ligand has four donor atoms while a pentadentate ligand has five donor atoms. 
     The donor atoms may be nitrogen, oxygen, and/or sulfur. Preferably at least two donor atoms are nitrogens, which are separated by from two to four carbon atoms. 
     Suitable nitrogen donor groups are the amino group of peptides, or amines, imines, pyridines, imidazoles, pyrroles, and pyrazoles, with imine and pyridine groups preferred. The configuration may be square planar or pyramidal, with square planar preferred, but is not limited to these. Suitable oxygen donor groups are phenol, alcohol, carboxylic acid, and carbonyl. Examples of molecules containing oxygen donor groups are salens, salophens and crown thio ethers. Generally, crown ethers containing only oxygen donor groups are not suitable herein. Sulfur donor groups may be, e.g. thiols, thiolates and thiophenols. Complexing molecules containing sulfur groups may contain only sulfur donor groups such as in the crown thio ethers, or the sulfur groups may be combined with oxygen and/or nitrogen donor groups in a suitable ligand. 
     The ability of the ligands to form stable complexes results from the relative positions of the donor groups. Much of the rest of the ligand consists of carbon atoms that may be thought of as collectively forming a scaffold for maintaining the proper position of the donor groups. 
     Substituents on the atoms of the ligand affect the properties of the compounds, such as their ability to bind the nucleotides and DNA, their effectiveness in participating in the modification of nucleotides and DNA, their solubility in various solvents, and the stability of the complex they form with transition metals. The atoms of the ligands are normally substituted with sufficient hydrogen atoms to form a stable compound. It should be appreciated, however, that any positions in the ligands, whether or not so indicated herein, may be substituted with any other group and still do substantially the same thing in substantially the same way to accomplish the same result and are, therefore, to be considered equivalent to positions bearing hydrogen atoms as substituents for the purpose of determining the scope of the present invention. 
     Suitable complexes are derivatives of the ligands shown above as Structures I-III. Illustrative of these are Structures 1-14. Structure 1 is a tetraazabicyclo designated 2,12-dimethyl-2,7,11,17-tetraazobicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentane metal complex. Synthesis of complexes of this type has been described by Karn, J. L. and Busch, D. H., &#34;Nickel(II) Complexes of the Tetradentate Macrocycle 2,12-Dimethyl-3,7,11,17-Tetraazabicyclo (11.3.1) Heptadeca-1 (17),2,11,13,15-Pentaene&#34;, Nature (London) 211, 160-163 (1966). 
     Structures 2a and 2b are examples of peptide complexes. Any peptide which satisfies the requirement for donor groups can be used. The best peptides for the current work are those including amino acids with positively charged side chains such as lysine, ornithine or arginine so that in Structures 2a and 2b, for R, for example, (CH 3 )NH 2  may be derived from ornithine, (CH 2 ) 4  NH 2  may be derived from lysine, and ##STR4## may be derived from arginine. The peptide complexes can be derived from alpha amino acids which are naturally occurring or synthetic. A DNA-cleaving metalloprotein consisting of an alpha amino acid-containing peptide and Ni(II) with the DNA-binding domain of Hin recombinase attached has been described by Mack, D. P. and Dervan, P. B., &#34;Nickel-Mediated Sequence-Specific Oxidative Cleavage of DNA by a Designed Metalloprotein&#34;, J. Am. Chem. Soc. 112, 4604, 4606 (1990). In contrast, the peptide metal complexes useful herein have a positive charge and do not require the attachment of Hin recombinase although Hin recombinase can be used. 
     Other suitable ligands are polyazamacrocycles. A typical polyazamacrocycle capable of complexing transition metal ions is 1,4,8,11-tetraazacyclotetradecane (cyclam). The ability of cyclam and its derivatives to form stable complexes with cobalt, nickel, copper and other metals and to stabilize high oxidation states of these metals has been studied by Busch, &#34;Distinctive Coordination Chemistry and Biological Significance of Complexes with Macrocyclic Ligands&#34;, Acc. Chem. Res. 11, 392-400 (1978). A suitable metal complex of this type is shown as structure 3. 
     Also useful are other polyazamacrocycles such as 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene metal complexes shown as structure 4. The synthesis of structure 4 has been described by Tait, A. M. and Busch, D. H., &#34;2,3-Dimethyl-1,4,8-Tetraazacyclotetradeca-1,3-Diene (2,3-Me 2  [14]-1,3-diene-1,4,8,11-N 4 ) Complexes&#34;, Inorg. Synth. 18, 27-29 (1978). 
     Structure 5 is a (11,13-dimethyl-1,4,7,10-tetraazacyclotrideca-10,12,-dienatonickel(II) compound. Its synthesis in the iodide form is described by Cummings, S. C., and Sievers, R. E., &#34;A New Synthetic Route to Macrocyclic Nickel(ii) Complexes with Uninegative, Schiff-Base Ligands&#34;, Inorg. Chem. 9, 1131-1136 (1970). Structure 6 is a Ni(cyclen). Cyclen is commercially available from Parish Chemical Co. The nickel nitrate complex may be prepared according to the procedure of R. Smierciak, et al., &#34;A Comparative Study of Steric Effects of Nickel(II) Complexes Containing 12-Membered Macrocyclic Ligands&#34;, Inorg. Chem. 16, 4646 (1977). 
     Structure 7 is Ni(tren)(X 2 ). The ligand, tren, is commercially available from Aldrich Chemical Co. and the nickel complex may be prepared according to Jorgensen, K., &#34;Comparative Crystal Field Studies II. Nickel(II) and Copper(II) Complexes with Polydentate Ligands and the Behavior of the Residual Places for Co-Ordination&#34;, Acta Chemica Scand. 10, 887-910 (1956). X in structures 6 and 7 is preferably any common anion, such as Cl 1   - , Br 1   -  I - , NO 3   - , ClO 4   - , CH 3  CO 2   - , PF 6   - , BF 9   -  and is most likely replaced by H 2  O when the complex is dissolved in water. 
     More recently, 1,4,8,11-tetraazacyclotetradecane-5,7-dione (dioxocyclam) has been developed and its ability to form complexes with certain metal ions studied (Wagler, T. R., et al., &#34;Optically Active Difunctionalized Dioxocyclam Macrocycles: Ligands for Nickel-Catalyzed Oxidation of Alkenes&#34;, J. Organ. Chem 54, 1584-1589 (1989). These complexes involve the coordination of the metal ions to a deprotonated ligand. The structure of the metal complex of dioxocyclam is shown as structure 8. Complexes of the structure 8 type are described in U.S. patent application Ser. No. 484,102, filed Feb. 23, 1990 now U.S. Pat. No. 4,987,227, issued Jan. 22, 1991 to Burrows, C. J., et al. and entitled &#34;Polyazamacrocycles and Their Metal Complexes and Oxidations Using Same&#34; which is herein incorporated by reference in its entirety. 
     Other ligands used in the complexes for these reactions include cyclam, N,N&#39;-ethylene-bis(salicylideneamine), also known as salen and 1,2-diaminobenzene-NlN-bis(salicylaldimine), also known as salophen. The structure of Ni(salen) is shown as structure 9 and structure of Ni(salophen) is shown as structure 10. Salen and salophen complexes may be prepared using the method of Poddar, S. N., et al., &#34;Metallic Complexes of Schiff&#39;s Base Derived from o-Hydroxyacetophenone and Ethylenediamine&#34;, J. Indian Chem. Soc. 40, 489-490 (1963). 
     Also suitable are dioxopentaaza macrocyclic ligands such as structure 11. Structures of this type have been synthesized by Kimura, E. et al., &#34;Novel Nickel(II) Complexes with Doubly Deprotonated Dioxopentaamine Macrocyclic Ligands for Uptake and Activation of Molecular Oxygen&#34;, J. Am. Chem. Soc. 104 4255-4257 (1982) and Kimura, et al., &#34;Macrocyclic Dioxo Pentaamines: Novel Ligands for 1:1 Ni(II)-O 2  Adduct Formation&#34;, J. Am. Chem. Soc. 106, 5497-5505 (1984). Oxygen insertion into metal complexes of structure 11 have been recently described by Chen. D. and Martell, A. E., &#34;Oxygen Insertion in the Ni(II) Complexes of Dioxopentaaza Macrocyclic Ligands&#34;, J. Am. Chem. Soc. 112, 9411-9412 (1990). Preferred groups for R&#34; in structure 11 in the process herein are fluoride, alkyl or aryl groups, especially those containing amine groups as part of the aryl or alkyl chain. 
     Other suitable ligands are porphyrins such as structure 12. The use of [meso-tetrakis (N-methyl-4-pyridyl)porphinato]manganese(III) (MnTMPP) with KHSO 5  to degrade DNA, RNA and polynucleotides has been described by Van Atta, R. B. et al., &#34;On the Chemical Nature of DNA and RNA Modification by a Hemin Model System&#34;, Biochem. 29, 4783-4789 (1990). However, the use of nickel is not suggested. 
     Other suitable complexes are thiol compounds as shown in structure 13 which may be synthesized according to Kruger, H. J. and Holm, R. H., &#34;Stabilization of Nickel(III) in a Classical N 2  S 2  Coordination Environment Containing Anionic Sulfur&#34;, Inorg. Chem. 26, 3645-3647 (1987), and oxime compounds as shown in structure 14 which may be synthesized according to Dyrssen, D., et al., &#34;On the Complex Formation of Nickel with Dimethylglyoxime&#34;, Acta Chem. Scand. 13, 51-59 (1959). 
     Some of the positions shown in Structures I-III and Structures 1-14 do not appear to be substitutents other than hydrogen. Nevertheless, these positions may be substituted by any organic or inorganic group without significantly affecting the ability of the compound to form a complex with transition metals. 
     Accordingly, any one or more of these positions may be substituted by an inorganic substituent, such as a doubly bonded oxygen, i.e., carbonyl, or a singly bonded oxygen i.e., hydroxy. Some additional inorganic groups include, for example, amino, thio, halo, i.e., F, Cl, Br, and I, etc. 
     Organic substituents include, for example, alkyl, aryl, alkylaryl and arylalkyl. The alkyl groups may be branched or unbranched and contain 20 carbon atoms or less, preferably 8 carbon atoms or less, and more preferably 4 carbon atoms or less. Some typical examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, isobutyl, and octyl. The alkyl groups may, in whole or in part, be in the form of rings such as cyclopentyl, cyclohexyl, cycloheptyl and cyclohexylmethyl. The cyclic groups described above may be further substituted with inorganic, alkyl, or aryl groups. Any of the alkyl groups described above may have one or more double or triple bond. Moreover, any of the carbon atoms of the alkyl groups may be separated from each other or from the ring nucleus with groups such as carbonyl, oxycarbonyl, oxy, amino, thio, etc. Alkyl groups may also terminate with groups such as halo, hydroxy, amino, carboxy, etc. 
     Aryl substituents are typically phenyl, but may also be any other aryl groups such as, for example, pyrrolyl, furanyl, thiophenyl, pyridyl, thiazolyl, etc. The aryl group may, further, be substituted by an inorganic, alkyl, or other aryl group. The alkylaryl and arylalkyl groups may be any combination of alkyl and aryl groups. These groups may be further substituted. 
     Particularly important substituent groups which may be present on the ligands are appended groups which are capable of binding to DNA or nucleotides. These will be called delivery agents. Suitable delivery agents may be of different types including intercalators, groove-binding agents, oligonucleotides, proteins or protein fragments, and polyamines. The intercalators include ethidium, methidium, acridine, proflavin, phenanthroline, etc. The groove-binding agents include distamycin and netropsin. A distamycin derivative was used to direct nucleotide scission by Schultz, P. G., et al., &#34;Design and Synthesis of a Sequence-Specific DNA Cleaving Molecule. (Distamycin-EDTA)iron(II)&#34;, J. Am. Chem. Soc. 104, 6861-6863 (1982). Oligonucleotides may bind producing double helical or triple helical areas. Proteins or protein fragments which bind DNA include Hin recombinase (Mack, D. P. and Dervan, P. B., &#34;Nickel-Mediated Sequence-Specific Oxidative Cleavage of DNA by a Designed Metalloprotein&#34;, J. Am. Chem. Soc. 112, 4604-4606 (1990)). The useful polyamines include spermine and spermidine described by K. D. Stewart, &#34;The Effect of Structural Changes in a Polyamine Backbone on its DNA-Binding Properties&#34;, Biochem, Biophys. Res. Comm. 152, 1441-1446 (1988). 
     The Complexes 
     Ligands to be used in the invention form stable complexes with transition metal ions. For the purpose of this specification, transition metals are to be understood as including metals having partly filled d or f shells in any of their commonly occurring oxidation states. The useful transition metals include ions of Ni, Co, Cu, Rh, Pd, Ir, Pt, Cr, Mn, Fe, Ru, and Os. Preferred are ions of Ni, Co and Pd. Most preferred is Ni. 
     The complexes are formed by contacting a salt of the metal ion with the ligand in a suitable solvent, for example, water and methanol. Progress of the complexation is easily followed visually or spectrophotometrically. Depending upon reaction conditions such as the ligand, the metal, the pH, and the solvent, the complexation reaction may occur rapidly at room temperature, or may require heating. 
     The complexes may be four, five or six coordinate with four preferred and square planar most preferred. 
     The complexes may be deprotonated, but an overall positive charge is preferred, and a highly positive charge is most preferred. Balancing anions, counterions, or salts may be as known to those skilled in the art, such as derivatives of salts e.g. perchlorate, acetate, nitrate, chlorides, bromides, iodides, and tetrachlorozincate (ZnCl 4   -2 ). 
     The ligand-metal complexes are used in the process of the invention to modify oligonuoleotides, single-stranded DNA, non-classical duplex structures and double-stranded DNA having particular conformations, that is, extra-helical areas, cruciform DNA, abasic (non base paired G&#39;s) areas, unpaired ends, and telomeres (ends of chromosomes). In double stranded DNA, the modification is specific to these conformational areas. The oligonucleotides may be naturally occurring or synthetic. The single-stranded DNA may also be derived from separation of duplex DNA. All forms of RNA are targets for reaction also. 
     A non-diffusible species is important for site-specificity in the target nucleotide. In contrast, certain complexes, e.g. Fe(II)-EDTA, generate hydroxyl radicals which react with DNA non-specifically. In this type of non-preferred complex, the complex attaches to a binding site and generates a reactive species which diffuses with a loss of specificity. In the system described herein, the metal complex binds to a particular DNA site and the reactive agent is produced at that site when oxidant is present. A non-diffusible species is one which reacts with DNA before it is released from the specific binding site. 
     The complexes are used to modify or nick DNA or nucleotides when used with an oxidant. Some examples of oxidizing agents include peracids such as peroxymonosulfate salts, e.g. potassium peroxymonosulfate (KHSO 5 ) which is commercially available under the trademark OXONE, magnesium monoperoxyphthalate (MMPP), peroxide, alkylhydroperoxide, O 2 , hypochlorite, and peroxide or oxygen in combination with ascorbate. Particularly preferred are peroxymonosulfate, MMPP and O 2 . In physiological systems, oxygen is preferred. 
     After oxidation, excess oxidant may be quenched with a reductant such as sodium sulfite, and base treatment may be used for cleavage. Suitable bases are piperidine, N-butylamine and sodium hydroxide with a pH of about 9-13. 
     Reaction conditions include a temperature from about zero to about 100° C., from about 20° C. to about 40° C. preferred and 25°-37° C. most preferred. Reaction time is at least about 30 seconds, from about 10 minutes to an hour preferred and from about 15 minutes to about 30 minutes most preferred. The reaction may be left for an extended period of time, e.g. up to 48 hours without adverse effects. The pH may be about 3-10, with 6.5-7.5 preferred. 
     For a reaction involving, for example, a nucleotide concentration of about 0.1 to about 50 picomoles of labelled 5&#39;-ends, the metal complex may be used in an amount of from about 0.1 μM to about 10 mM, with from about 0.5 μM to about 100 μM preferred and from about 1μM to about 10 μM most preferred. The oxidant may be used in an amount of from about 0.1 μM to about 10 mM with about 50 μM to about 100 μM preferred. The ratio of metal complex to oxidant may range from about 99:1 to about 1:99. The oxidant is preferably in excess of the metal complex with a ratio of metal complex:oxidant ranging up to about 1:10,000, with from about 1:1 to about 1:50 preferred and 1:1 to 1:2 most preferred. 
     In vitro, the nucleotide or DNA is labelled in any suitable manner such as with radiolabel, and standard electrophoresis and autoradiography may be used to determine the level of modification. 
     The process of the invention for modifying DNA or sequencing is suitable for being attained using a kit. The kit may comprise a polyaza metal complex to be used with an oxidant and a base. The kit can supply a polyaza metal complex in an amount of from about 1 to about 3000 nanomolar metal complex, preferably from about 10 to about 300 nanomolar metal complex and most preferably about 25 to about 75 nanomolar of the metal complex. An oxidant is selected from the group consisting of peracid, hypochlorite, O 2 , peroxide in combination with ascorbate and O 2  in combination with ascorbate. The preferred oxidants are oxone, magnesium monoperoxyphthalate, peroxide and alkylhydroperoxide. The most preferred oxidant is oxone. If the kit is to be used in an in vivo system, e.g., in tissue culture or in an animal, the oxidant is preferably provided by dissolved oxygen already present in the system. A base may also be provided, and may be piperidine, N-butylamine or sodium hydroxide having a pH of about 9-13. 
     The process of the invention can also be used therapeutically to treat neoplasia in the same manner as bleomycin and cis-platin. Neoplasia may occur, for example, in animals such as mammals including humans. Neoplasia is progressive, uncontrolled cell division which, if the progeny cells remain localized at least initially, results in the formation of an abnormal growth which may be called a tumor or neoplasm. A neoplasm may be malignant or benign. A malignant neoplasm invades adjacent tissues and may metastasize. A neoplastic growth is generally considered to be a non-inflammatory mass formed by the growth of new cells and having no physiological function. The polyaza metal complexes of the invention can be formulated per se in pharmaceutical preparation or formulated in the form of pharmaceutically acceptable salts. These preparations can be prepared according to conventional chemical methods. Antibiotics such as bleomycin have used therapeutically in humans and have been administered intravenously, intramuscularly or subcutaneously. They are believed to interfere with a rapid cell division which occurs in neoplasia. When the invention is used in a physiological system, e.g. in vivo, it is contemplated that the physiological system provides the O 2  necessary to act as the oxidant so that the polyaza metal complex modifies DNA and interferes with replication, thereby affecting cell growth. The DNA modification necessary to interfere with replication may comprise oxidative damage in the DNA caused by the process of the invention. The metal complexes of the invention have the advantage of being less toxic. 
     EXAMPLES 
     As the experimental approach, a series of square planar nickel(II) and copper(II) complexes were investigated for their ability to react with DNA. Some of these complexes had been shown previously to catalyze olefin epoxidation using iodosylbenzene, NaOCl or oxone as the terminal oxidant (Yoon, H. et al., &#34;High Turnover Rates in pH-Dependent Alkene Epoxidation Using NaOCl and Square-Planar Nickel(II) Catalysts&#34;, J. Am. Chem. Soc. 112, 4568-4570 (1990). In the case of olefin epoxidation, the ability of Ni II  complexes to catalyze oxygen atom transfer chemistry was found to be highly ligand dependent. 
     Oligonucleotides were chosen for study since they are small enough to permit a detailed study yet large enough to display the base specificity for nucleotide oxidation. 
     Reactions were carried out using a purified oligonucleotide with the 15-base sequence d(CATGCGCTACCCGTG). The 5&#39;-terminus was labelled with  32  P-phosphate for analysis by gel electrophoresis and autoradiography. Samples of the oligonucleotide were incubated with various metal complexes and an excess of oxidant, either oxone, MMPP, or a 1:1 mixture of H 2  O 2  /ascorbate. 
     EXAMPLE 1 
     The pyridine-containing Schiff base complex 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene nickel(II) 2  +, i.e., (NiL 1   2+ ) (structure 1) was prepared according to the method described by Karn, J. L. and Busch, D. H., Nature (London) 211, 160-163 (1966). The complex was tested for its ability to cleave the oligonucleotide described above. 
     Samples of aqueous solutions containing 3 μM oligonucleotide (10nCi)DNA, 3 μM metal complex and 100 μM MMPP were prepared in a volume of 100 μL, buffered to pH 7.0 (10 mM potassium phosphate, 100 mM NaCl), maintained under ambient conditions and quenched after 30 minutes with 20 mM Na 2  SO 3 . 
     The samples were individually dialyzed against 1 mM EDTA at pH 8 (2×3h.) and water (1×12h.), lyophilized, treated with 0.2M piperidine for 30 min. at 90° C., lyophilized again, and resuspended in 80% formamide for electrophoresis. 
     Similar solutions were prepared with NiL 1   2+  (no oxidant); oxidants 1:1 H 2  O 2  /ascorbate, MMPP and oxone; NiL 1   2+  with 1:1 H 2  O 2  /ascorbate; and NiL 1   2+  with oxone. The solutions were prepared in the same manner as the NiL 1   2+  and MMPP solutions described above. 
     Autoradiograms of 20% polyacrylamide gels (denaturing 7M urea) were prepared showing the cleavage products obtained using NiL 1   2+ , MMPP and piperidine. The results are shown in FIG. 1. 
     Lane 1 shows NiL 1   2+  only with no oxidant. Lanes 2-4 show the control studies with oxidants alone: H 2  O 2  /ascorbate, MMPP and oxone, respectively. Lane 5 shows NiL 1   2+  with 1:1 H 2  O 2  /ascorbate. Lane 6 shows NiL 1   2+  with MMPP. Lane 7 shows NiL 1   2+  with oxone. Lane 8 is the reference G-lane. Lane 9 shows NiL 1   2+  with oxone with omission of piperidine treatment. 
     Lane 7, representing the reaction of structure 1 with 3 μM NiL 1   2+  and 100 μM oxone, exhibits a fragmentation pattern equivalent to that of the Maxam-Gilbert G-lane (lane 8). Cleavage products were observed only after treatment with piperidine (compare lanes 7 and 9). Control studies verified that neither the nickel complex alone nor the oxidants alone generated base-labile products (lanes 1-4) and a comparison of oxidants (lanes 5-7) showed that oxone produced the most reaction with DNA. This example leads to the conclusion that certain Ni-ligand complexes are excellent promoters of oxidative DNA modification at G residues giving rise to base-specific cleavage upon alkaline work-up. 
     EXAMPLE 2 
     Various metal complexes were tested for their efficacy for cleavage of the oligonucleotide using KHSO 5  as oxidant. Reaction conditions were as described in Example 1 and included 3 μM of metal complex, 3 μM of nucleotide, 100 μM of KHSO 5  and piperidine treatment. Autoradiograms of 20% polyacrylamide gels (denaturing 7M urea) were prepared. 
     The metal complexes were 1) Ni(OAc) 2 , 2) NiL 1   2+ , 3) CuL 1   2+ , 4) Ni-GGH (NiL 2 ), 5) Cu-GGH (CuL 2 ), 6) [Ni(cyclam)] 2+  (NiL 1   2+ ), 7) [Cu(cyclam)] 2+  (CuL 3   2+ ), 8) NiL 4   2+ , 9) NiL 5   + , 10) Ni(cyclen) (NO 3 ) 2  (NiL 6  X 2 ), 11) Ni(tren) (OAc) 2  (NiL 7  X 2 ), and 12) Cisplatin (cis-Pt(NH 3 ) 2  Cl 2 ). The complexes were as follows: ##STR5## 
     The results are shown in FIG. 2. Lane 1 shows Ni(OAc) 2 . Lane 2 shows NiL 1   2+ . Lane 3 shows CuL 1   2+ . Lane 4 shows NiL 2 . Lane 5 shows CuL 2 . Lane 6 shows NiL 3   2+ . Lane 7 shows CuL 3   2+ . Lane 8 shows NiL 4   2+ . Lane 9 shows NiL 5   + . Lane 10 shows Ni(cyclen)(NO 3 ) 2 . Lane 11 shows Ni(tren)(OAc) 2 . Lane 12 shows cisplatin. 
     A qualitative comparison of Ni II  complexes showed that the pyridine-containing Schiff base complex NiL 1   2+  was the most active followed by NiL 4   2+ , another Schiff base complex (compare lanes 2 and 8) and NiL 3   2+  was less active than these (lane 6). The Ni II  and Cu II  complexes of the tripeptide GGH, NiL 2  and CuL 2  have been demonstrated by Mack, D. P., et al., &#34;Design and Chemical Synthesis of a Sequence-Specific DNA-Cleaving Protein&#34;, J. Am. Chem. Soc. 110, 7572 (1988) and Mack D. P. and Dervan, P. B., &#34;Nickel-Mediated Sequence-Specific Oxidative Cleavage of DNA by a Designed Metalloprotein&#34;, J. Am. Chem. Soc. 112, 4604-4606 (1990) to give highly site-specific DNA cleavage when the tripeptide is appended to a DNA-binding protein fragment. In the present example, however, neither NiL 2   -   or CuL 2   -   led to significant amounts (lanes 4 and 5). Apparently these anionic square planar metal complexes do not interact sufficiently with DNA and the oxidant in the absence of a DNA-binding agent to yield substantial DNA reactivity. Accordingly, the three reactive Ni II  complexes are those which carry a 2+ charge and are square planar complexes of neutral tetradentate ligands. For comparison, the monocationic complex NiL 5+   was tested and slight evidence of reaction was observed in comparison to background (lane 9). The octahedral complexes [NiL 6  (H 2  O 2 )] 2+   and [NiL 7  (H 2  O 2  ] 2+   (lanes 10 and 11) were detectably active under the same conditions. Finally, comparison was made with the DNA-binding drug cis-platin which has been shown to bind to N-7 of guanines. No evidence of G-specific oxidative reactivity was obtained (lane 12). 
     The results of the examples showed that square planar Ni II  complexes of tetraazamacrocycles such as the Schiff base complex NiL 1   2+  and nickel cyclam NiL 3   2+   were highly active agents for DNA modification under oxidative conditions compared to related copper complexes or octahedral Ni II  complexes. Both KHSO 5  (oxone) and magnesium monoperoxyphthalate (MMPP) were effective as oxidants, and peracetic acid had a lesser activity while H 2  O 2   with ascorbate was not effective under these conditions. Furthermore, oxidative DNA modification leading to strand scission after alkaline treatment occurred with high base-specificity for guanine. 
     The most successful ligands, L 1 , L 3  and L 4  are those which provide an intermediate ligand field strength stabilizing square planar or octahedral coordination geometries and rendering Ni II  highly Lewis acidic. The stronger ligand field of GGH might inhibit coordination of additional ligands in the axial positions, and the overall anionic complex, NiL 2   -   would have less electrostatic attraction to the polyanionic oligonucleotide. 
     EXAMPLE 3 
     The procedure of Example 2 is repeated except that the oxidants of Example 2 are omitted and O 2  is naturally present in the sample solutions at a concentration of about 300 μM. 
     The results are expected to be comparable to the results of Example 2. This is intended to show that oxygen can act as the terminal oxidant in the process of the invention. 
     The use of O 2  as a source of dioxygen in Ni(II) complexes was shown by Chen, D. and Martell, A. E., &#34;Oxygen Insertion in the Ni(II) Complexes of Dioxopentaaza Macrocyclic Ligands&#34;, J. Am. Chem. Soc. 112, 9411, 9412 (1990), but modification of DNA was not suggested therein. 
     EXAMPLE 4 
     The procedure of Example 2 was repeated except that double-stranded DNA was used, at the same concentration of 5&#39;-labelled ends as before. Reaction with metal complex and oxidant and final alkaline treatment and analysis were the same. The results indicate that G sites at the end of an oligonucleotide or in non-base paired regions are more reactive than normal base paired G sites. 
     EXAMPLE 5 
     The procedure for Example 4 was repeated except that the double-stranded DNA was heat denatured prior to reaction and analysis. This was done by heating the sample to 90° C. for 5 min, rapid cooling to 4° C. in an ice bath, and immediate reaction with metal complex and oxidant as described above. Analysis showed strand scission at all G-sites analogous to that obtained for single-stranded oligonucleotides. This method would be of use in DNA sequencing techniques for the location of G&#39;s. 
     EXAMPLE 6 
     In vivo Studies 
     A procedure analogous to that described in Antholine, et al., &#34;Studies on the Chemical Reactivity of Copper Bleomycin&#34;, J. Inorg. Biochem. 17, 75, (1982) for copper bleomycin is used. Erlich cells removed from mice are centrifuged, washed, and resuspended in MEM (minimal essential medium, available from GIBCO). The metal complex such as 11 is added at time zero at a concentration of 0.1-100 nmol complex per mg cell protein (10 nmol preferred). The reaction mixture is incubated at 37° C. in a Gyrotory water bath shaker. Uptake is halted by immersion of aliquots of suspension in ice-water slush, and the supernatant is separated from cells by centrifugation. Cells are washed once in 0.15M NaCl and separated again for analysis. Analysis can be carried out in two ways. 
     (1) Cells are monitored for a period of up to 72 hours to look for cell proliferation. Diminished cell proliferation compared with controls indicates effectiveness of the metal complex as a drug. 
     (2) Inhibition of DNA synthesis can be monitored by incubating with tritiated thymine, followed by washing, isolation of the DNA and analysis for amount of incorporated radiolabel. Diminished incorporation compared with control studies indicates effectivenss of the metal complex for DNA damage. 
     While there have been described what are presently believed to be the preferred embodiments of the invention, those skilled in the art will realize that changes and modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the true scope of the invention.