Abstract
Platinum-based chemotherapies, including oxaliplatin, are a mainstay in the management of solid tumors and induce cell death by forming intrastrand dinucleotide DNA adducts. Despite their common use, they are highly toxic, and approximately half of cancer patients have tumors that are either intrinsically resistant or develop resistance. Previous studies suggest that this resistance is mediated by variations in DNA repair levels or net drug influx. Here, we aimed to better define the roles of nucleotide excision repair and DNA damage in platinum chemotherapy resistance by profiling DNA damage and repair efficiency in seven oxaliplatin-sensitive and three oxaliplatin-resistant colorectal cancer cell lines. We assayed DNA repair indirectly as toxicity and directly measured bulky adduct formation and removal from the genome by slot blot and repair capacity in an excision assay, and used excision repair sequencing (XR-seq) to map repair events genome-wide at single-nucleotide resolution. Using this combinatorial approach and proxies for oxaliplatin-DNA damage, we observed no significant differences in repair efficiency that could explain the relative sensitivities and chemotherapy resistances of these cell lines. In contrast, the levels of oxaliplatin-induced DNA damage were significantly lower in the resistant cells, indicating that decreased damage formation, rather than increased damage repair, is a major determinant of oxaliplatin resistance in these cell lines. XR-seq-based analysis of gene expression revealed up-regulation of membrane transport pathways in the resistant cells, and these pathways may contribute to resistance. In conclusion, additional research is needed to characterize the factors mitigating cellular DNA damage formation by platinum compounds.
Highlights
Platinum-based chemotherapies, including oxaliplatin, are a mainstay in the management of solid tumors and induce cell death by forming intrastrand dinucleotide DNA adducts
To study whether nucleotide excision repair efficiency is a determinant of oxaliplatin sensitivity, we used a panel of 10 colorectal cancer cell lines
Enhanced excision repair capacity has been proposed as a contributing factor in cellular resistance to platinating anticancer drugs; the current data to support this notion are inconsistent and fail to address confounding factors [11,12,13,14,15,16,17,18,19,20]
Summary
Platinum-based chemotherapies, including oxaliplatin, are a mainstay in the management of solid tumors and induce cell death by forming intrastrand dinucleotide DNA adducts Despite their common use, they are highly toxic, and approximately half of cancer patients have tumors that are either intrinsically resistant or develop resistance. We assayed DNA repair indirectly as toxicity and directly measured bulky adduct formation and removal from the genome by slot blot and repair capacity in an excision assay, and used excision repair sequencing (XR-seq) to map repair events genome-wide at single-nucleotide resolution Using this combinatorial approach and proxies for oxaliplatin–DNA damage, we observed no significant differences in repair efficiency that could explain the relative sensitivities and chemotherapy resistances of these cell lines. Platinum-based chemotherapies work by creating intrastrand dinucleotide adducts in DNA with the platinum atom covalently bound to the N7 nitrogen in adjacent guanines [4, 5] This damage is solely repaired by nucleotide excision repair (6 –8).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
