Platinum Metal Complexes as DNA-Protein Cross-Linking Agents

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Dr. Nicolas P. Farrell, Chemistry Department, Virginia Commonwealth University, is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry Program of the Chemistry Division for research into the fundamental chemistry of DNA-protein crosslinking through ternary adduct formation by platinum and other metal compounds. The interactions of structurally distinct proteins based on topoisomerases and zinc-finger containing proteins with the bifunctional transplatinum compounds trans-[PtCl2(L)(L')] (L = NH3 and L' = pyridine, thiazole, quinoline, etc. or L = L' = pyridine, thiazole) will be examined. The platinum compounds have previously been shown to produce cellular protein-associated strand breaks in DNA and have now been shown to specifically stabilize the DNA-topoisomerase complex in leukemia cells. The hypothesis that ternary adduct formation arises from binding a DNA guanine N7 site and a protein (most likely methionine or cysteine) site to the mononuclear platinum center will be tested. Next, the chemical factors controlling preferential DNA-protein binding rather than the 'classical' DNA-DNA binding will be examined. The interactions of a model compound such as trans-[PtCl(9-Ethylguanine or 5'-Guanosinemonophosphate)(L)(L')]+ with the model protein ubiquitin will be studied. Ubiquitin is a useful model as it presents only two potential platinum binding sites (a methionine and a histidine). A functional chemical model for tyrosinephosphoester formation using a trans-platinum scaffold will be attempted. The properties of site-specific monofunctional DNA adducts will be assessed and the sites of DNA and topoisomerase binding in the ternary complexes will be delineated. A further sub-set of proteins containing the zinc- finger motif will be examined. Platinum compounds are capable of ejecting zinc from the zinc-finger sites. The fundamental chemistry underlying this novel metal exchange on bioligands will be examined by model compounds. This project will lead to a better understanding of the role of DNA conformation in protein recognition, how the nature of DNA damage affects downstream protein processing and DNA repair, and perhaps the eventual isolation of DNA-protein adducts in vivo. Additionally, the results may suggest new mechanisms of action for anticancer-active metal compounds. This work will also give a molecular explanation to the observations of significant cytotoxicity of the transplatinum geometry - an observation violating a fundamental structure-activity relationship on which the vast majority of platinum-based drug development has been based. Further, the new paradigms of genomics and proteomics emphasize target (protein)-oriented drug design. The basic chemical studies undertaken in this project will contribute to that understanding. The broader impacts will be to include undergraduate as well as graduate researchers in the activities. International collaborations with, for example, the Czech Republic and Israel will be fostered. Underrepresented groups may participate broadly in this research program.