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Platinum-based drugs are a mainstay of solid tumor treatment and act by inducing bulky DNA adducts which should ultimately result in cell death. Unfortunately, these drugs have serious side effects and rates of resistance are high; for example about half of colorectal tumors are platinum-resistant. Understanding the molecular mechanisms of resistance could help maximize efficacy by providing targets to counter drug resistance. The overall purpose of this project is to comprehensively characterize the role of DNA intrastrand adduct formation, nucleotide excision repair, circadian rhythm, and the interplay of these processes in tumor and normal tissue response to platinum-based chemotherapy. To achieve this, we used novel methods to measure repair rates, amounts, and genome-wide patterns at single-nucleotide resolution of multiple tumor models. In a panel of 10 colorectal cancer cell lines, we demonstrate that nucleotide excision repair is not an essential component of platinum resistance as all cell lines have similar nucleotide excision repair efficiencies despite the varying responses. Damage formation, however, may partially dictate oxaliplatin response as lower damage levels correlate with oxaliplatin resistance. While all oxaliplatin-resistant cell lines in this study showed low levels of platinum induced adducts, oxaliplatin sensitive cell lines showed more variation. We next sought to address factors that may lead to this variable damage formation and response in sensitive cell lines. Notably, we identify a large DNA amplification, containing many cancer related transcripts, specific to the sensitive cell lines with low initial damage. Additionally, damage repair in normal and xenograft tissues appear to oscillate throughout a 24 hour period indicating that treatment timing impacts the platinum-DNA adduct formation. The studies described in this dissertation improve our understanding of the role of DNA damage formation and nucleotide excision repair in response to platinum-based chemotherapy and provide a foundation for understanding how circadian rhythms may impact these factors. |
