Leinamycin is a DNA-damaging natural product with potent anticancer activity. This antibiotic is structurally unique and represents a new class of DNA-damaging antibiotics. Because of its potent anticancer activity and the novel chemical mechanisms by which leinamycin damages DNA, studies of this antibiotic are of both practical and fundamental interest. DNA damage by leinamycin is triggered by reaction of the antibiotic with thiols and recent work has shown that the compound causes both oxidative and alkylative DNA damage. The DNA-alkylation chemistry that is the focus of this proposal occurs via a surprising thiol-mediated rearrangement of leinamycin that yields an electrophilic episulfonium ion which alkylates double-stranded DNA at N7 of guanine residues. Although we have a preliminary grasp on the mechanisms by which leinamycin damages DNA, our understanding of the chemical reactions and molecular-recognition processes involved in the interaction of this antibiotic with DNA is far from complete. The work described in this proposal investigates several novel aspects of leinamycin-DNA interactions and will provide a deeper understanding of how this unusual antibiotic efficiently alkylates DNA.
The Specific Aims of the proposed work are as follows: (1) Characterize Leinamycin-DNA adducts. The includes investigation of the sequence-specificity of DNA alkylation by leinamycin, analysis of the stability of leinamycin-guanosine adducts, and searches for new leinamycin-DNA adducts (other than N7-guanosine). (2) Investigate """"""""Alternate"""""""" (Non Thiol-Activated) Modes of Leinamycin Activation. Leinamycin has thus far been characterized as a thiol-dependent DNA damaging agent. We plan to investigate several alternate, non thiol-activated modes for the activation of DNA alkylation by leinamycin that we have discovered during the course of our recent work. (3) Examine Non-Covalent DNA Association by Leinamycin. We have obtained preliminary evidence that leinamycin non-covalently associates with DNA. The structural features of the antibiotic that are important for DNA binding, the mode of DNA association and the affinity of leinamycin for duplex DNA will be examined.
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