oxaliplatin-DNA Adduct Research Articles

Genome-wide single-nucleotide resolution of oxaliplatin–DNA adduct repair in drug-sensitive and -resistant colorectal cancer cell lines

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.

Oxaliplatin-DNA Adducts as Predictive Biomarkers of FOLFOX Response in Colorectal Cancer: A Potential Treatment Optimization Strategy.

FOLFOX is one of the most effective treatments for advanced colorectal cancer. However, cumulative oxaliplatin neurotoxicity often results in halting the therapy. Oxaliplatin functions predominantly via the formation of toxic covalent drug-DNA adducts. We hypothesize that oxaliplatin-DNA adduct levels formed in vivo in peripheral blood mononuclear cells (PBMC) are proportional to tumor shrinkage caused by FOLFOX therapy. We further hypothesize that adducts induced by subtherapeutic "diagnostic microdoses" are proportional to those induced by therapeutic doses and are also predictive of response to FOLFOX therapy. These hypotheses were tested in colorectal cancer cell lines and a pilot clinical study. Four colorectal cancer cell lines were cultured with therapeutically relevant (100 μmol/L) or diagnostic microdose (1 μmol/L) concentrations of [14C]oxaliplatin. The C-14 label enabled quantification of oxaliplatin-DNA adduct level with accelerator mass spectrometry (AMS). Oxaliplatin-DNA adduct formation was correlated with oxaliplatin cytotoxicity for each cell line as measured by the MTT viability assay. Six colorectal cancer patients received by intravenous route a diagnostic microdose containing [14C]oxaliplatin prior to treatment, as well as a second [14C]oxaliplatin dose during FOLFOX chemotherapy, termed a "therapeutic dose." Oxaliplatin-DNA adduct levels from PBMC correlated significantly to mean tumor volume change of evaluable target lesions (5 of the 6 patients had measurable disease). Oxaliplatin-DNA adduct levels were linearly proportional between microdose and therapeutically relevant concentrations in cell culture experiments and patient samples, as was plasma pharmacokinetics, indicating potential utility of diagnostic microdosing.

Abstract CT055: Microdose induced oxaliplatin-DNA adducts as a predictive biomarker of response in colorectal cancer

Abstract Background Combination 5-FU and oxaliplatin (FOLFOX) is standard therapy for colorectal cancer (CRC) in neoadjuvant, adjuvant, and metastatic settings. However, oxaliplatin neuropathy is the main dose-limiting toxicity that often necessitates dose reduction or discontinuation before progression. Prediction of oxaliplatin sensitivity in tumor cells would be valuable for dose optimization to maximize anti-tumorigenic effect and limit sensory neuropathy. Oxaliplatin functions via the formation of covalent drug-DNA adducts which ultimately inhibit cell replication and promote apoptosis. Detection of these drug-DNA adducts could serve as a biomarker of oxaliplatin efficacy. We therefore hypothesized that drug-DNA adduct levels induced by sub-therapeutic "diagnostic microdoses" are proportional to those induced by therapeutic doses and are predictive of tumor responses. Methods The feasibility of this predictive diagnostic microdosing approach was assessed in CRC cell culture and a pilot clinical trial of six CRC patients. Four CRC cell lines were cultured with therapeutically relevant (100 µM) or diagnostic microdose (1 µM) concentrations of [14C]oxaliplatin. The C-14 label enabled quantification of oxaliplatin-DNA adduct levels with accelerator mass spectrometry, an ultrasensitive isotope analysis technique. Adduct formation was correlated with oxaliplatin cytotoxicity as measured by the MTT viability assay. In a pilot clinical trial (NCT02569723), six CRC patients received an intravenous diagnostic microdose containing [14C]oxaliplatin prior to treatment and a second [14C]oxaliplatin dose during FOLFOX chemotherapy. Adduct levels from peripheral blood mononuclear cells (PBMC), used as surrogates for tumor cells, were correlated to mean tumor volume change of evaluable target lesions. Results Drug-DNA adduct levels were linearly proportional between microdoses and therapeutically relevant concentrations in cell culture (R2 = 0.91, p < 0.0001) and patient samples (R2 = 0.63, p < 0.0001). Plasma pharmacokinetics of microdoses were consistent with those of therapeutic dosing. No microdose-associated toxicity was observed in this patient population. PBMC adduct levels significantly correlated with tumor shrinkage (microdose: R2 = 0.82, p = 0.033; therapeutic dose: R2=0.65, p = 0.099). Conclusion Diagnostic microdosing with oxaliplatin is feasible and is predictive of oxaliplatin sensitivity in CRC patients. Citation Format: Justin Chen, May Cho, Maike Zimmermann, Thomas Semrad, Chun-Yi Wu, Aiming Yu, Chong-Xian Pan, Paul T. Henderson, Edward J. Kim. Microdose induced oxaliplatin-DNA adducts as a predictive biomarker of response in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT055.

Molecular Dissection of Induced Platinum Resistance through Functional and Gene Expression Analysis in a Cell Culture Model of Bladder Cancer.

We report herein the development, functional and molecular characterization of an isogenic, paired bladder cancer cell culture model system for studying platinum drug resistance. The 5637 human bladder cancer cell line was cultured over ten months with stepwise increases in oxaliplatin concentration to generate a drug resistant 5637R sub cell line. The MTT assay was used to measure the cytotoxicity of several bladder cancer drugs. Liquid scintillation counting allowed quantification of cellular drug uptake and efflux of radiolabeled oxaliplatin and carboplatin. The impact of intracellular drug inactivation was assessed by chemical modulation of glutathione levels. Oxaliplatin- and carboplatin-DNA adduct formation and repair was measured using accelerator mass spectrometry. Resistance factors including apoptosis, growth factor signaling and others were assessed with RNAseq of both cell lines and included confirmation of selected transcripts by RT-PCR. Oxaliplatin, carboplatin, cisplatin and gemcitabine were significantly less cytotoxic to 5637R cells compared to the 5637 cells. In contrast, doxorubicin, methotrexate and vinblastine had no cell line dependent difference in cytotoxicity. Upon exposure to therapeutically relevant doses of oxaliplatin, 5637R cells had lower drug-DNA adduct levels than 5637 cells. This difference was partially accounted for by pre-DNA damage mechanisms such as drug uptake and intracellular inactivation by glutathione, as well as faster oxaliplatin-DNA adduct repair. In contrast, both cell lines had no significant differences in carboplatin cell uptake, efflux and drug-DNA adduct formation and repair, suggesting distinct resistance mechanisms for these two closely related drugs. The functional studies were augmented by RNAseq analysis, which demonstrated a significant change in expression of 83 transcripts, including 50 known genes and 22 novel transcripts. Most of the transcripts were not previously associated with bladder cancer chemoresistance. This model system and the associated phenotypic and genotypic data has the potential to identify some novel details of resistance mechanisms of clinical importance to bladder cancer.

Abstract 905: Molecular dissection of platinum resistance through functional analysis

Abstract BACKGROUND: Platinum (Pt) agents (cisplatin, carboplatin and oxaliplatin) are active in many cancers including bladder cancer. Chemoresistance is the most common cause of treatment failure. This study is to determine the feasibility of using ultrasensitive accelerator mass spectrometry (AMS) to identify chemoresistance after cancer cells or patients are treated with one non-toxic microdose (1/100th of therapeutic dose) of Pt agents. The long-term goal is to identify chemoresistance before cancer patients receive toxic chemotherapy, and to determine the underlying resistance mechanisms to design personalized chemotherapy. METHODS: Cellular sensitivity to chemotherapeutic agents was determined by the MTT assay. Platinum-induced DNA adduct formation and repair of adducts was measured with AMS after cells were exposed 14C-labeled carboplatin and oxaliplatin. AMS quantifies the 14C label that is attached to genomic DNA when the 14C-labled drug forms adducts with DNA. Cell uptake and efflux was measured by liquid scintillation counting. Intracellular glutathione levels were measured by colorimetric analysis. RESULTS: Compared to the parental bladder cancer 5637 cells, chemoresistant 5637R cells are resistant to oxaliplatin (IC50: 2.45 µM versus 27.27 µM, p<0.0001), and cisplatin (0.59 µM versus 2.99 µM, p=0.049), carboplatin (24.34 µM versus 72.18 µM, p<0.0001), and gemcitabine (0.12 µM versus 1.44 µM, p=0.0015). Both 5637 and 5637R cells are still sensitive to other chemotherapeutic agents commonly used in treating bladder cancer, such as doxorubicin, methotrexate and vinblastine. Consistent with our hypothesis, chemoresistant 5637R cells have low oxaliplatin-induced DNA adduct levels than the parental 5637 cells (AUC of 943 versus 2,772 adducts per 109 nucleotide-hour for 5637, p=0.001). This low level of oxaliplatin-DNA adduct formation might be secondary to the pre-DNA damage mechanisms, such as decreased uptake (AUC of 4.42 versus 5.12 X 109 oxaliplatin molecules per cell for 5637, p=0.037) and increased intracellular inactivation of oxaliplatin by glutathione (53.91 versus 46.93 nmol/mg protein for 5637, p=0.003), plus increased repair of oxaliplatin-DNA adducts (3.48 versus 1.34 adducts per 108 nucleotides per hour for 5637, p=0.0004). We found the same correlation of low Pt-DNA adduct levels and chemoresistance in non-small cell lung (NSCLC) and breast cancer cell lines, and determined the same resistant mechanisms, such as cell uptake/efflux, intracellular inactivation and DNA repair. Carboplatin had partially different resistant mechanisms. CONCLUSION: Functional analysis of major resistant steps can identify some chemoresistance mechanisms that can potentially help design personalized chemotherapy to overcome resistance. This approach can be applied to several different cancer types. A Phase 0 microdosing clinical trial is currently going on in patients with NSCLC and bladder cancer. Citation Format: Amy W. Pan, Sisi Wang, Hongyong Zhang, Ruth Vinall, Tzu-yin Lin, Michael Malfatti, Maike Zimmermann, Tiffany Scharadin, Kenneth Turteltaub, Ralph de Vere White, Chong-xian Pan, Paul Henderson. Molecular dissection of platinum resistance through functional analysis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 905. doi:10.1158/1538-7445.AM2014-905

Towards biomarker-dependent individualized chemotherapy: Exploring cell-specific differences in oxaliplatin–DNA adduct distribution using accelerator mass spectrometry

Oxaliplatin is a third-generation platinum-based anticancer drug that is currently used in the treatment of metastatic colorectal cancer. Oxaliplatin, like other platinum-based anticancer drugs such as cisplatin and carboplatin, is known to induce apoptosis in tumor cells by binding to nuclear DNA, forming monoadducts, and intra- and interstrand diadducts. Previously, we reported an accelerator mass spectrometry (AMS) assay to measure the kinetics of oxaliplatin-induced DNA damage and repair [Hah, S. S.; Sumbad, R. A.; de Vere White, R. W.; Turteltaub, K. W.; Henderson, P. T. Chem. Res. Toxicol. 2007, 20, 1745]. Here, we describe another application of AMS to the measurement of oxaliplatin–DNA adduct distribution in cultured platinum-sensitive testicular (833 K) and platinum-resistant breast (MDA-MB-231) cancer cells, which resulted in elucidation of cell-dependent differentiation of oxaliplatin–DNA adduct formation, implying that differential adduction and/or accumulation of the drug in cellular DNA may be responsible for the sensitivity of cancer cells to platinum treatment. Ultimately, we hope to use this method to measure the intrinsic platinated DNA adduct repair capacity in cancer patients for use as a biomarker for diagnostics or a predictor of patient outcome.

Cetuximab potentiates oxaliplatin cytotoxic effect through a defect in NER and DNA replication initiation.

Preclinical studies have demonstrated that the chemotherapeutic action of oxaliplatin, a third generation platinum derivative, is improved when combined with cetuximab, a monoclonal antibody inhibitor of epidermal growth factor receptors. To explore the mechanism of this synergistic benefit, we used HCT-8 and HCT-116, two human colon cancer cell lines, respectively, responsive and non-responsive to the oxaliplatin/cetuximab combination. We examined the effect of drug exposure on glutathione-S-transferase-mediated oxaliplatin detoxification, DNA–platinum adducts formation, cell cycle distribution, apoptosis, and the expression of multiple targets involved in DNA replication, recombination, and repair. The major changes we found in HCT-8 were a stimulation of oxaliplatin–DNA adduct formation associated with reduced expression of the key enzyme (excision repair cross complementation group1: ERCC1) in the key repair process of oxaliplatin–DNA platinum adduct, the nucleotide excision repair (NER), both at the mRNA and protein levels. We also observed a reduced expression of factors involved in DNA replication initiation, which correlates with an enrichment of cells in the G1 phase of the cell cycle as well as an acceleration of apoptosis. None of these changes occurred in the non-responsive HCT-116 cell that we used as a negative control. These findings support the fact that cetuximab potentiates the oxaliplatin-mediated cytotoxic effect as the result of inhibition of NER and also DNA replication initiation.

Characterization of Oxaliplatin−DNA Adduct Formation in DNA and Differentiation of Cancer Cell Drug Sensitivity at Microdose Concentrations

(trans-R, R)-1,2-diaminocyclohexaneoxalatoplatinum(II) (oxaliplatin) is a recently approved platinum analogue for use in the chemotherapy of metastatic colorectal cancer. Like many cytotoxic drugs, oxaliplatin exerts its antitumor effects by covalent modification of DNA. We report an accelerator mass spectrometry (AMS) assay to measure the kinetics of oxaliplatin-induced DNA damage and repair. We determined the apparent rate of oxaliplatin adduction to salmon sperm DNA. The oxaliplatin-DNA adduct distribution was further investigated at the nucleoside level by HPLC-AMS. Cultured platinum-sensitive testicular (833K) and platinum-resistant breast and bladder (MDA-MB-231 and T24, respectively) cancer cells were incubated with a subpharmacological concentration of oxaliplatin (0.2 microM). Both cellular and DNA radiocarbon contents in the drug-sensitive testicular cells had approximately twice the area under the curve as compared to the more platinum-resistant cell lines, implying that differential accumulation of the drug may be responsible for the sensitivity of cancer cells to platinum treatment. The lowest concentration of radiocarbon measured was approximately 1+/-0.1 amol/microg of DNA, when assaying 1 microg of DNA. This sensitivity for measuring oxaliplatin-DNA adducts is the highest reported to date. The sensitivity offered by this method may be applicable to other DNA-damaging drugs, metabolisms studies, and diagnostics development.