Oxaliplatin-induced DNA Damage Research Articles

Polyvinylpyrrolidone-Polydatin nanoparticles protect against oxaliplatin induced intestinal toxicity in vitro and in vivo

Oxaliplatin (OXL) is a first-line drug for the treatment of colon cancer, with excellent efficacy. Intestinal toxicity is a common side effect of OXL, with unclear pathogenesis and a lack of effective treatment strategies. Polydatin (PD) has anti-inflammatory and antioxidant activities and is a potential drug for treating intestinal diseases, but its poor water solubility limits its application. In this study, polyvinylpyrrolidone (PVP) was used as a carrier to prepare nanoparticles loaded with PD (PVP-PD), with a particle size of 92.42 nm and exhibiting sustained release properties. In vitro results showed that PVP-PD protected NCM460 cells from OXL induced injury, mitochondrial membrane potential (MMP) disruption, and accumulation of reactive oxygen species (ROS). The in vivo results demonstrated the protective effect of PVP-PD on intestinal toxicity induced by OXL, such as alleviating weight loss and colon length reduction induced by OXL. Both in vivo and in vitro mechanisms indicated that OXL induced DNA damage and activated the cGAS-STING pathway, further inducing the expression of inflammatory factors such as IL-1β and TNF-α. PVP-PD alleviated the aforementioned changes induced by OXL by inhibiting the DNA damage-cGAS-STING pathway. In summary, our study demonstrated that the DNA damage-cGAS-STING pathway was involved in OXL induced intestinal toxicity, and PVP-PD provided a potential strategy for treating OXL induced intestinal toxicity.

PARP Inhibitor Sensitizes BRCA-mutant Pancreatic Cancer to Oxaliplatin by Suppressing the CDK1/BRCA1 Axis.

Currently, olaparib, a poly(ADP-ribose) polymerase (PARP) inhibitor, has been approved as maintenance therapy for patients with germline BRCA mutations and metastatic pancreatic cancer. However, platinum-based chemotherapy, which induces synthetic lethality with PARP inhibitor treatment, is still controversial. Hence, we aimed to examine a platinum-based drug in combination with a PARP inhibitor and generate data regarding the use of a PARP inhibitor in the overall treatment of pancreatic cancer. Using the Capan-1 cell line (BRCA2-mutant pancreatic cancer cell line), we evaluated the combinatorial effects of olaparib, a PARP inhibitor, and oxaliplatin by cell viability, combination index, western blotting, immunocytochemistry, flow cytometry, apoptosis assays and in vivo experiments. Capan-1 cells showed high sensitivity to olaparib due to the alteration in PARP activity, which led to cell death through the accumulation of oxaliplatin-induced DNA damage. Beyond DNA damage, oxaliplatin also suppressed the CDK1/BRCA1 signaling axis, which induced defects in homologous recombination repair. Additionally, inhibition of CDK1, a biomarker for oxaliplatin efficacy, induced cell death regardless of the BRCA mutation profile. Oxaliplatin may be used in combination with olaparib in PDAC patients with DNA damage repair mutations. Our findings highlight CDK1 as a potential therapeutic target for pancreatic cancer.

DYRK2 promotes chemosensitivity via p53-mediated apoptosis after DNA damage in colorectal cancer.

Dual-specificity tyrosine-regulated kinase 2 (DYRK2) is a protein kinase that phosphorylates p53-Ser46 and induces apoptosis in response to DNA damage. However, the relationship between DYRK2 expression and chemosensitivity after DNA damage in colorectal cancer has not been well investigated. The aim of the present study was to examine whether DYRK2 could be a novel marker for predicting chemosensitivity after 5-fluorouracil- and oxaliplatin-induced DNA damage in colorectal cancer. Here we showed that DYRK2 knockout decreased the chemosensitivity to 5-fluorouracil and oxaliplatin in p53 wild-type colorectal cancer cells, whereas the chemosensitivity remained unchanged in p53-deficient/mutated colorectal cancer cells. In addition, no significant differences in chemosensitivity to 5-fluorouracil and oxaliplatin between scramble and siDYRK2 p53(-/-) colorectal cancer cells were observed. Conversely, the combination of adenovirus-mediated overexpression of DYRK2 with 5-fluorouracil or oxaliplatin enhanced apoptosis and chemosensitivity through p53-Ser46 phosphorylation in p53 wild-type colorectal cancer cells. Furthermore, DYRK2 knockout decreased chemosensitivity to 5-fluorouracil and oxaliplatin in p53 wild-type xenograft mouse models. Taken together, these findings demonstrated that DYRK2 expression was associated with chemosensitivity to 5-fluorouracil and oxaliplatin in p53 wild-type colorectal cancer, suggesting the importance of evaluating the p53 status and DYRK2 expression as a novel marker in therapeutic strategies for colorectal cancer.

Electrochemical detection of Oxaliplatin induced DNA damage in G-quadruplex structures

Oxaliplatin (OXP) is a platinum-based chemotherapeutic agent that induces DNA damage by forming intra- and interstrand crosslinks, mainly at the N7s of adenine (A) and guanine (G) bases. In addition to double-stranded DNA, G-rich G-quadruplex (G4)-forming sequences can also be targeted by OXP. However, high doses of OXP can lead to drug resistance and cause serious adverse effects during treatment. To better understand the targeting of G4 structures by OXP, their interactions as well as the molecular mechanisms underlying OXP resistance and adverse effects, there is a need for a rapid, quantitative, and cost-effective method to detect OXP and the damage it causes. In this study, we successfully fabricated a graphite electrode biosensor modified with gold nanoparticles (AuNPs) to investigate the interactions between OXP and the G4-forming promoter region (Pu22) of Vascular endothelial growth factor (VEGF). The overexpression of VEGF is known to be associated with tumor progression and the stabilization of VEGF G4 by small molecules is shown to suppresses VEGF transcription in different cancer cell lines. Differential pulse voltammetry (DPV) was used to investigate the interactions between OXP and Pu22-G4 DNA by monitoring the decrease in the oxidation signal of guanine with increasing OXP concentration. Under the optimized conditions (37 °C, 1:2 v/v AuNPs/water as electrode surface modifier, and 180 min incubation time) the developed probe showed a linear dynamic range of 1.0–10.0 μM with a detection limit of 0.88 μM and limit of quantification of 2.92 μM. Fluorescence spectroscopy was also used to support the electrochemical studies. We observed a decrease in the fluorescence emission of Thioflavin T in the presence of Pu22 upon addition of OXP. To our knowledge, this is the first electrochemical sensor developed to study OXP-induced damage to G4 DNA structures. Our findings provide new insights into the interactions between VEGF G4 and OXP, which could aid in targeting VEGF G4 structures and the development of new strategies to overcome OXP resistance.

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.

The Protective Effect of Naringenin on Oxaliplatin-Induced Genotoxicity in Mice.

Oxaliplatin is a third generation platinum based anti-cancer drug used against various human malignancies but displays genotoxic properties against normal cells. Naringenin is a naturally occurring bioflavonoid that possesses anti-oxidant properties and has protective effects against DNA damage. The aim of this study is to examine the protective effects of naringenin on oxaliplatin-induced DNA damage in mice. A total of 50, male BALB/c mice were randomly divided equally into five groups. Oxaliplatin toxicity was induced by a single dose (7 mg/kg body weight (b.w.)) injection (intraperitoneally (i.p.)) of oxaliplatin. Naringenin was given orally for ten consecutive days at two doses, 20 mg/kg b.w. (dose I) and 40 mg/kg b.w. (dose II), to group I and group II, respectively. On the tenth day of the experiment, animals in groups III, IV, and V were given a single i.p. injection of oxaliplatin (7 mg/kg b.w.). All the animals were sacrificed 24 h after oxaliplatin treatment. The extent of genotoxicity was assessed by multiple genotoxicity assays (8-hydroxydeoxy-guanosine marker, comet, micronucleus and chromosomal aberration assays, oxidative stress-marker Glutathione evaluation) in order to determine diverse kinds of DNA damage. The results indicated that naringenin administration significantly reduced the DNA damage induced by oxaliplatin possibly due to its strong anti-oxidant properties. The results suggest that naringenin is a potential candidate for future development as a chemoprotective agent against chemotherapy associated complications.

HSP110 translocates to the nucleus upon genotoxic chemotherapy and promotes DNA repair in colorectal cancer cells.

A multicenter clinical study demonstrated the presence of a loss-of-function HSP110 mutation in about 15% of colorectal cancers, which resulted from an alternative splicing and was produced at the detriment of wild-type HSP110. Patients expressing low levels of wild-type HSP110 had excellent outcomes (i.e. response to an oxaliplatin-based chemotherapy). Here, we show in vitro, in vivo, and in patients' biopsies that HSP110 co-localizes with DNA damage (γ-H2AX). In colorectal cancer cells, HSP110 translocates into the nucleus upon treatment with genotoxic chemotherapy such as oxaliplatin. Furthermore, we show that HSP110 interacts with the Ku70/Ku80 heterodimer, an essential element of the non-homologous end joining (NHEJ) repair machinery. We also demonstrate by evaluating the resolved 53BP1 foci that depletion in HSP110 impairs repair steps of the NHEJ pathway, which is associated with an increase in DNA double-strand breaks and in the cells' sensitivity to oxaliplatin. HSP110-depleted cells sensitization to oxaliplatin-induced DNA damage is abolished upon re-expression of HSP110. Confirming a role for HSP110 in DNA non-homologous repair, SCR7 and NU7026, two inhibitors of the NHEJ pathway, circumvents HSP110-induced resistance to chemotherapy. In conclusion, HSP110 through its interaction with the Ku70/80 heterodimer may participate in DNA repair, thereby inducing a protection against genotoxic therapy.

ATM Is Required for the Repair of Oxaliplatin-Induced DNA Damage in Colorectal Cancer

ATM Is Required for the Repair of Oxaliplatin-Induced DNA Damage in Colorectal Cancer

Abstract 4802: Combination therapy in PDAC involving blockade of the APE1/Ref-1 signaling pathway: An investigation into drug synthetic lethality and anti-neuropathy therapeutic approach

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer-related mortality in the US. Most patients present with advanced disease and ~93% die within five years, with most surviving less than six months. Combination therapies including Gemcitabine (GemzarTM) and sustained release, nab-paclitaxel (AbraxaneTM) and FOLFIRINOX (5-FU/leucovorin/irinotecan/oxaliplatin) offer modest improvement in survival, albeit at an increase in side effects including chemotherapy-induced peripheral neuropathy. Data is presented on Apurinic/apyrimidinic endonuclease/redox factor-1 (APE1/Ref-1 or APE1) and redox-specific APE1 inhibitor, APX3330 and its effects on tumor cell growth and sensory neuron function. APE1 is a multifunctional protein involved in repairing DNA damage via endonuclease activity and in redox regulation of transcription factors such as HIF-1α, NFkB and STAT3. High expression levels of APE1 indicate decreased survival in PDAC as well as other cancers. Because APE1 is essential for cell viability, generation of APE1 knockout cell lines and determining a comprehensive list of genes regulated by APE1 has been difficult. To circumvent this, we performed single cell RNA-Sequencing on PDAC cells following APE1 knockdown under normoxia and hypoxia to identify differentially expressed genes and further explore APE1's effects on HIF-1α and STAT3 signaling under both conditions. Proteomic analysis on PDAC cells following APE1 knockdown in normoxia and hypoxia revealed changes in signaling downstream of APE1, complementing the transcriptomic data and providing a more complete understanding of pathways affected by APE1. We used the newly identified APE1 targets and pathways along with drug sensitivity data of cancer cell lines from the Cancer Cell Line Encyclopedia (CCLE) to generate potential combination therapies of FDA approved drugs and the APE1 redox inhibitor, APX3330 and next generation analogs. These combinations were tested using an ex vivo 3D tumor-stroma model system using patient derived cells from the tumor as well as cancer-associated fibroblasts. We identified synergy with agents such as Napabucasin and Entinostat. We also tested APX3330 in combination with drugs that are part of PDAC standard of care. In vivo studies combining APX3330 with Gemcitabine showed significantly decreased tumor volume. Combining oxaliplatin (part of FOLFIRINOX) with APX3330 caused a significant reduction in oxaliplatin-induced DNA damage in sensory neurons from a KPC orthotopic graft model, without hindering its anti-cancer activity. With the phase I clinical trial for APX3330 underway (IND 125360), the potential for APE1 targeted therapy enhancing tumor efficacy while providing neuroprotective effects in the sensory neurons provides a win-win scenario. Citation Format: Fenil L. Shah, Nadia Atallah, Michelle Grimard, Chunlu Guo, Chi Zhang, Jill Fehrenbacher, Mark R. Kelley, Melissa Fishel. Combination therapy in PDAC involving blockade of the APE1/Ref-1 signaling pathway: An investigation into drug synthetic lethality and anti-neuropathy therapeutic approach [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4802.

Translational study identifies XPF and MUS81 as predictive biomarkers for oxaliplatin-based peri-operative chemotherapy in patients with esophageal adenocarcinoma

Oxaliplatin-based chemotherapy is used to treat patients with esophageal adenocarcinoma (EAC), but no biomarkers are currently available for patient selection. We performed a prospective, clinical trial to identify potential biomarkers associated with clinical outcomes. Tumor tissue was obtained from 38 patients with resectable EAC before and after 2 cycles of oxaliplatin-fluorouracil chemotherapy. Pre-treatment mRNA expression of 280 DNA repair (DNAR) genes was tested for association with histopathological regression at surgery, disease-free survival (DFS) and overall survival (OS). High expression of 13 DNA damage repair genes was associated with DFS less than one year (P < 0.05); expression of 11 DNAR genes were associated with worse OS (P < 0.05). From clinical associations with outcomes, two genes, ERCC1 and EME1, were identified as candidate biomarkers. In cell lines in vitro, we showed the mechanism of action related to repair of oxaliplatin-induced DNA damage by depletion and knockout of protein binding partners of the candidate biomarkers, XPF and MUS81 respectively. In clinical samples from the clinical trial, pre-treatment XPF protein levels were associated with pathological response, and MUS81 protein was associated with 1-year DFS. XPF and MUS81 merit further validation in prospective clinical trials as biomarkers that may predict clinical response of EAC to oxaliplatin-based chemotherapy.

Inhibition of B7-H3 reverses oxaliplatin resistance in human colorectal cancer cells

B7-H3, an immunoregulatory protein, has been found highly expressed in several cancer types, and involved in cancer cell migration and invasion. Here, we investigated the role of B7-H3 in oxaliplatin resistance in colorectal cancer (CRC) cells. Transient silencing of B7-H3 enhanced oxaliplatin sensitivity by increasing oxaliplatin-induced DNA damage. The overexpression of B7-H3 increased oxaliplatin resistance reducing the formation of phosphorylated histone H2AX (γH2AX) loci. The silencing of X-ray repair cross complementing group 1 (XRCC1), upregulated in B7-H3 overexpressing cells, induced an increase in cell death following oxaliplatin treatment. Finally, the upregulation of XRCC1 expression induced by B7-H3 involved PI3K-AKT pathway. In conclusion, B7-H3 promotes the oxaliplatin resistance in CRC cells upregulating the expression of XRCC1 via PI3K-AKT pathway.

Acquired resistance to oxaliplatin is not directly associated with increased resistance to DNA damage in SK-N-ASrOXALI4000, a newly established oxaliplatin-resistant sub-line of the neuroblastoma cell line SK-N-AS.

The formation of acquired drug resistance is a major reason for the failure of anti-cancer therapies after initial response. Here, we introduce a novel model of acquired oxaliplatin resistance, a sub-line of the non-MYCN-amplified neuroblastoma cell line SK-N-AS that was adapted to growth in the presence of 4000 ng/mL oxaliplatin (SK-N-ASrOXALI4000). SK-N-ASrOXALI4000 cells displayed enhanced chromosomal aberrations compared to SK-N-AS, as indicated by 24-chromosome fluorescence in situ hybridisation. Moreover, SK-N-ASrOXALI4000 cells were resistant not only to oxaliplatin but also to the two other commonly used anti-cancer platinum agents cisplatin and carboplatin. SK-N-ASrOXALI4000 cells exhibited a stable resistance phenotype that was not affected by culturing the cells for 10 weeks in the absence of oxaliplatin. Interestingly, SK-N-ASrOXALI4000 cells showed no cross resistance to gemcitabine and increased sensitivity to doxorubicin and UVC radiation, alternative treatments that like platinum drugs target DNA integrity. Notably, UVC-induced DNA damage is thought to be predominantly repaired by nucleotide excision repair and nucleotide excision repair has been described as the main oxaliplatin-induced DNA damage repair system. SK-N-ASrOXALI4000 cells were also more sensitive to lysis by influenza A virus, a candidate for oncolytic therapy, than SK-N-AS cells. In conclusion, we introduce a novel oxaliplatin resistance model. The oxaliplatin resistance mechanisms in SK-N-ASrOXALI4000 cells appear to be complex and not to directly depend on enhanced DNA repair capacity. Models of oxaliplatin resistance are of particular relevance since research on platinum drugs has so far predominantly focused on cisplatin and carboplatin.

Minnelide Overcomes Oxaliplatin Resistance by Downregulating the DNA Repair Pathway in Pancreatic Cancer

IntroductionOxaliplatin is part of pancreatic cancer therapy in the FOLFIRINOX or GEMOX/XELOX regimen. DNA damage repair is one of the factors responsible for oxaliplatin resistance that eventually develops in this cancer. Triptolide/Minnelide has been shown to be effective against pancreatic cancer in preclinical trials. In this study, we evaluated the efficacy of combination of triptolide and oxaliplatin against pancreatic cancer. MethodsHighly aggressive pancreatic cancer cells (MIA PaCa-2 and PANC-1) were treated with oxaliplatin (0–10 μM), low-dose triptolide (50 nM), or a combination of both for 24–48 h. Cell viability, apoptosis, and DNA damage were evaluated by appropriate methods. Nucleotide excision repair pathway components were quantitated using qPCR and Western blot. Combination of low doses of Minnelide and oxaliplatin was tested in an orthotopic murine model of pancreatic cancer. ResultsProliferation of pancreatic cancer cells was markedly inhibited by combination treatment. Triptolide potentiated apoptotic cell death induced by oxaliplatin and sensitized cancer cells towards oxaliplatin-induced DNA damage by suppressing the oxaliplatin-induced DNA damage repair pathway. Combination of low doses of Minnelide and oxaliplatin inhibited tumor progression by inducing significant apoptotic cell death in these tumors. ConclusionsCombination of low doses of Minnelide and oxaliplatin has immense potential to emerge as a novel therapeutic strategy against pancreatic cancer.

477 Jab1/Csn5: a new player driving the resistance to HER2-targeted therapies for breast cancer

JNK1 and JNK2, respectively) to assess the role of JNK and its iso-forms in hypoxic resistance of colon cancer cell lines to oxaliplatin. Combination indices for oxaliplatin and CC-401 were calculated based on MTT assays. Induction of cell death and DNA damage were studied using flow cytometry. Studies involving stable introduction of dominant negative JNK1 or JNK2 were conducted both on monoclonal cell lines (HT29-derived) and pooled cells (SW620, HCT116). Results: Our data demonstrate that stress signaling through JNK is induced by hypoxia in the majority of colon cancer cell lines assessed. Hypoxic resistance to oxaliplatin varies significantly, implying cell-specific effects of JNK on sensitivity. Pharmacological inhibition of JNK augments the cytotoxicity of oxaliplatin in multiple colon cancer cell lines. We also show that colon cancer cell lines differ in their responses to oxaliplatin when JNK1 or JNK2 are down-regulated, from no effect (HCT116) to increased sensitivity (HT29, SW620). Neither pharmacological, nor molecular inhibition of JNK affects significantly hypoxiaor oxaliplatininduced DNA damage. In hypoxic HT29 cells, CC-401 shows synergism with oxaliplatin, SN-38 and 5-FU with CI50 of 0.42, 0.6 and 0.63, respectively. Finally, we confirm enhancement of oxaliplatin efficacy by CC401 in vivo, in HT29-derived mouse xenografts. Conclusions: These findings in vitro and in vivo support the involvement of JNK1 in resistance to cytotoxic therapy in colorectal cancer models. Inhibition of this pathway may be a rational therapeutic approach.

Excision Repair Cross-Complementation group 1 (ERCC1) C118T SNP does not affect cellular response to oxaliplatin

AimsERCC1 is involved in the repair of oxaliplatin-induced DNA damage. Studies for the association of the C118T SNP with clinical response to treatment with platinum drugs have rendered inconsistent results. We investigated the ERCC1 C118T SNP with respect to overall and progression-free survival in patients with advanced colorectal cancer (ACC) treated with oxaliplatin and in vitro DNA repair capacity after oxaliplatin exposure. In addition we discuss discrepancies from other studies concerning ERCC1 C118T. Materials and methodsProgression-free survival was determined in 145 ACC patients treated with oxaliplatin-based chemotherapy in a phase 3 trial. For the in vitro studies regarding ERCC1 functionality, we transfected an ERCC1 negative cell line with 118C or 118T ERCC1. Cellular sensitivity and DNA repair capacity after exposure to oxaliplatin was examined by Sulphorodamine B growth inhibition assay, COMET assay and Rad51 foci staining. ResultsWe found no association between ERCC1 C118T and progression-free or overall survival. In addition, transfection of either 118C or 118T restores DNA-repair capacity of UV20 cells to the same level and chemosensitivity to oxaliplatin was similar in ERCC1 118C and 118T transfected cells. ConclusionThis study shows that the ERCC1 C118T variants are not associated with survival in ACC patients treated with oxaliplatin or the in vitro sensitivity and DNA-repair capacity in 118C and 118T transfected cell lines. Therefore, ERCC1 C118T genotyping seems of no value in individualizing oxaliplatin based chemotherapy in ACC.

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.

Cells deficient in the base excision repair protein, DNA polymerase beta, are hypersensitive to oxaliplatin chemotherapy

A significant proportion of human cancers overexpress DNA polymerase beta (Pol beta), the major DNA polymerase involved in base excision repair. The underlying mechanism and biological consequences of overexpression of this protein are unknown. We examined whether Pol beta, expressed at levels found in tumor cells, is involved in the repair of DNA damage induced by oxaliplatin treatment and whether the expression status of this protein alters the sensitivity of cells to oxaliplatin. DNA damage induced by oxaliplatin treatment of HCT116 and HT29 colon cancer cells was observed to be associated with the stabilization of Pol beta protein on chromatin. In comparison with HCT116 colon cancer cells, isogenic oxaliplatin-resistant (HCT-OR) cells were found to have higher constitutive levels of Pol beta protein, faster in vitro repair of a DNA substrate containing a single nucleotide gap and faster repair of 1,2-GG oxaliplatin adduct levels in cells. In HCT-OR cells, small interfering RNA knockdown of Pol beta delayed the repair of oxaliplatin-induced DNA damage. In a different model system, Pol beta-deficient fibroblasts were less able to repair 1,2-GG oxaliplatin adducts and were hypersensitive to oxaliplatin treatment compared with isogenic Pol beta-expressing cells. Consistent with previous studies, Pol beta-deficient mouse fibroblasts were not hypersensitive to cisplatin treatment. These data provide the first link between oxaliplatin sensitivity and DNA repair involving Pol beta. They demonstrate that Pol beta modulates the sensitivity of cells to oxaliplatin treatment.

Regulation of human dUTPase gene expression and p53-mediated transcriptional repression in response to oxaliplatin-induced DNA damage

Deoxyuridine triphosphate nucleotidohydrolase (dUTPase) catalyzes the hydrolysis of dUTP to dUMP and PPi. Although dUTP is a normal intermediate in DNA synthesis, its accumulation and misincorporation into DNA is lethal. Importantly, uracil misincorporation is a mechanism of cytotoxicity induced by fluoropyrimidine chemotherapeutic agents including 5-fluorouracil (5-FU) and elevated expression of dUTPase is negatively correlated with clinical response to 5-FU-therapy. In this study we performed the first functional characterization of the dUTPase promoter and demonstrate a role for E2F-1 and Sp1 in driving dUTPase expression. We establish a direct role for both mutant and wild-type forms of p53 in modulating dUTPase promoter activity. Treatment of HCT116 p53+/+ cells with the DNA-damaging agent oxaliplatin induced a p53-dependent transcriptional downregulation of dUTPase not observed in the isogenic null cell line. Oxaliplatin treatment induced enrichment of p53 at the dUTPase promoter with a concomitant reduction in Sp1. The suppression of dUTPase by oxaliplatin promoted increased levels of dUTP that was enhanced by subsequent addition of fluoropyrimidines. The novel observation that oxaliplatin downregulates dUTPase expression may provide a mechanistic basis contributing to the synergy observed between 5-FU and oxaliplatin in the clinic. Furthermore, these studies provide the first evidence of a direct transcriptional link between the essential enzyme dUTPase and the tumor suppressor p53.

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.