title: Comet assay measures of DNA damage as biomarkers of irinotecan response in colorectal cancer in vitro and in vivo.
abstract: The use of irinotecan to treat metastatic colorectal cancer (CRC) is limited by unpredictable response and variable toxicity; however, no reliable clinical biomarkers are available. Here, we report a study to ascertain whether irinotecan-induced DNA damage measures are suitable/superior biomarkers of irinotecan effect. CRC-cell lines (HCT-116 and HT-29) were treated in vitro with irinotecan and peripheral blood lymphocytes (PBL) were isolated from patients before and after receiving irinotecan-based chemotherapy. Levels of in vitro-, in vivo-, and ex vivo-induced DNA damage were measured using the Comet assay; correlations between damage levels with in vitro cell survival and follow-up clinical data were investigated. Irinotecan-induced DNA damage was detectable in both CRC cell-lines in vitro, with higher levels of immediate and residual damage noted for the more sensitive HT-29 cells. DNA damage was not detected in vivo, but was measurable in PBLs upon mitogenic stimulation prior to ex vivo SN-38 treatment. Results showed that, following corrections for experimental error, those patients whose PBLs demonstrated higher levels of DNA damage following 10 h of SN-38 exposure ex vivo had significantly longer times to progression than those with lower damage levels (median 291 vs. 173 days, P = 0.014). To conclude, higher levels of irinotecan-induced initial and residual damage correlated with greater cell kill in vitro and a better clinical response. Consequently, DNA damage measures may represent superior biomarkers of irinotecan effect compared to the more often-studied genetic assays for differential drug metabolism.
authors.affiliation: Department of Cancer Studies & Molecular Medicine, University of Leicester, Leicester, United Kingdom.
authors.forename: Joanna P
authors.initials: JP
authors.lastname: Wood
authors.affiliation: Department of Cancer Studies & Molecular Medicine, University of Leicester, Leicester, United Kingdom.
authors.forename: Andrew J O
authors.initials: AJ
authors.lastname: Smith
authors.affiliation: Department of Cancer Studies & Molecular Medicine, University of Leicester, Leicester, United Kingdom.
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Bowman
authors.affiliation: Department of Cancer Studies & Molecular Medicine, University of Leicester, Leicester, United Kingdom.
authors.forename: Anne L
authors.initials: AL
authors.lastname: Thomas
authors.affiliation: Department of Cancer Studies & Molecular Medicine, University of Leicester, Leicester, United Kingdom.
authors.forename: George D D
authors.initials: GD
authors.lastname: Jones
mesh_terms: D000328:Adult; D000368:Aged; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology* / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D015415:Biomarkers; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000401:mortality; D020552:Comet Assay; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects; D018450:Disease Progression; D005260:Female; D005838:Genotype; D014453:Glucuronosyltransferase / Q000235:genetics; D006801:Humans; D000077146:Irinotecan; D008297:Male; D008875:Middle Aged; D011110:Polymorphism, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D016896:Treatment Outcome; D000099148:UGT1A1 Enzyme
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D015415:Biomarkers; D002166:Camptothecin; D014453:Glucuronosyltransferase; D000077146:Irinotecan; D059004:Topoisomerase I Inhibitors; D000099148:UGT1A1 Enzyme
keywords: Biomarker; DNA damage and repair; colorectal cancer; comet assay; topoisomerase-I inhibitor