Potentiation of Temozolomide Cytotoxicity by Poly(ADP)Ribose Polymerase Inhibitor ABT-888 Requires a Conversion of Single-Stranded DNA Damages to Double-Stranded DNA Breaks

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167

Purpose: PARP inhibitors are being developed as therapeutic agents for cancer. More than six compounds have entered clinical trials. The majority of these compounds are b-nicotinamide adenine dinucleotide (NAD þ )-competitive inhibitors. One exception is iniparib, which has been proposed to be a noncompetitive PARP inhibitor. In this study, we compare the biologic activities of two different structural classes of NAD þ -competitive compounds with iniparib and its C-nitroso metabolite.Experimental Design: Two chemical series of NAD þ -competitive PARP inhibitors, iniparib and its C-nitroso metabolite, were analyzed in enzymatic and cellular assays. Viability assays were carried out in MDA-MB-436 (BRCA1-deficient) and DLD1À/À (BRCA2-deficient) cells together with BRCA-proficient MDA-MB-231 and DLD1 þ/þ cells. Capan-1 and B16F10 xenograft models were used to compare iniparib and veliparib in vivo. Mass spectrometry and the 3 H-labeling method were used to monitor the covalent modification of proteins.Results: All NAD þ -competitive inhibitors show robust activity in a PARP cellular assay, strongly potentiate the activity of temozolomide, and elicit robust cell killing in BRCA-deficient tumor cells in vitro and in vivo. Cell killing was associated with an induction of DNA damage. In contrast, neither iniparib nor its C-nitroso metabolite inhibited PARP enzymatic or cellular activity, potentiated temozolomide, or showed activity in a BRCA-deficient setting. We find that the nitroso metabolite of iniparib forms adducts with many cysteine-containing proteins. Furthermore, both iniparib and its nitroso metabolite form protein adducts nonspecifically in tumor cells. Conclusions: Iniparib nonselectively modifies cysteine-containing proteins in tumor cells, and the primary mechanism of action for iniparib is likely not via inhibition of PARP activity. Clin Cancer Res; 18(2); 510-23. Ó2011 AACR.

Section: Introductionmentioning

confidence: 84%

Section: Combination Activity With Temozolomidementioning

confidence: 99%

Section: Combination Activity With Temozolomidementioning

confidence: 99%

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Iniparib Nonselectively Modifies Cysteine-Containing Proteins in Tumor Cells and Is Not a Bona Fide PARP Inhibitor

Liu

Shi

Maag

et al. 2012

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167

“…PARP targets proteins that facilitate DNA repair of single-stranded or double-stranded DNA breaks (27). If PARP-1 is inhibited, single-strand breaks become double-strand breaks and cell apoptosis occurs during DNA replication (28,29). Therefore, we plan to study temozolomide in combination with the PARP inhibitor ABT-888.…”

Section: Discussionmentioning

confidence: 99%

Phase II Trial of Temozolomide in Patients with Relapsed Sensitive or Refractory Small Cell Lung Cancer, with Assessment of Methylguanine-DNA Methyltransferase as a Potential Biomarker

Pietanza

Kadota

Huberman

et al. 2012

151

109

Purpose: This phase II study was conducted to assess the efficacy of temozolomide in patients with relapsed small cell lung cancer (SCLC).Experimental Design: Patients with disease progression after one or two prior chemotherapy regimens received temozolomide at 75 mg/m 2 /d for 21 days of a 28-day cycle. The primary endpoint was the overall response rate [ORR; complete response (CR) plus partial response (PR)], which was evaluated separately in sensitive and refractory cohorts. In the available tissue, we assessed O 6 -methylguanine-DNA methyltransferase (MGMT) promoter methylation status by PCR and MGMT expression by immunohistochemistry. Results: Sixty-four patients were accrued: 48 patients in the sensitive cohort and 16 in the refractory group. One CR and 10 PRs were noted in sensitive patients [ORR, 23%; 95% confidence interval (CI), 12%-37%]. Two PRs were seen in the refractory cohort (ORR, 13%; 95% CI, 2%-38%). As second-and third-line treatment, the ORR was 22% (95% CI, 9%-40%) and 19% (95% CI, 7%-36%), respectively. Among patients with target brain lesions, 38% had a CR or PR (95% CI, 14%-68%). Grade !3 thrombocytopenia and neutropenia were observed in nine patients (14%). A greater number of cases with methylated MGMT had a response compared to those with unmethylated MGMT (38% vs. 7%; P ¼ 0.08).Conclusion: Temozolomide has activity in relapsed SCLC, particularly for brain metastases. Response to temozolomide may correlate with MGMT methylation in SCLC.

“…5, 6). Single-strand breaks induced by endogenous DNA damage, radiation, or alkylation can become lethal double-strand breaks (DSB) during replication if PARP is inhibited (7,8) and the accumulation of DSBs acts as triggers of cell death. Thus, the use of PARP inhibitors to enhance DNA-damaging agents, such as TMZ, is being evaluated in the clinic and shows promise as a therapeutic…”

mentioning

confidence: 99%

ABT-888 Confers BroadIn vivoActivity in Combination with Temozolomide in Diverse Tumors

Palma

Wang

Rodrı́guez

et al. 2009

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128

Purpose: ABT-888, currently in phase 2 trials, is a potent oral poly(ADP-ribose) polymerase inhibitor that enhances the activity of multiple DNA-damaging agents, including temozolomide (TMZ). We investigated ABT-888+TMZ combination therapy in multiple xenograft models representing various human tumors having different responses to TMZ. Experimental Design: ABT-888+TMZ efficacy in xenograft tumors implanted in subcutaneous, orthotopic, and metastatic sites was assessed by tumor burden, expression of poly(ADP-ribose) polymer, and O 6 -methylguanine methyltransferase (MGMT). Results: Varying levels of ABT-888+TMZ sensitivity were evident across a broad histologic spectrum of models (55-100% tumor growth inhibition) in B-cell lymphoma, small cell lung carcinoma, non-small cell lung carcinoma, pancreatic, ovarian, breast, and prostate xenografts, including numerous regressions. Combination efficacy in otherwise TMZ nonresponsive tumors suggests that TMZ resistance may be overcome by poly(ADP-ribose) polymerase inhibition. Profound ABT-888+TMZ efficacy was seen in experimental metastases models that acquired resistance to TMZ. Moreover, TMZ resistance was overcome in crossover treatments, indicating that combination therapy may overcome acquired TMZ resistance. Neither tumor MGMT, mismatch repair, nor poly(ADP-ribose) polymer correlated with the degree of sensitivity to ABT-888+TMZ. Conclusions: Robust ABT-888+TMZ efficacy is observed across a spectrum of tumor types, including orthotopic and metastatic implantation. As many TMZ nonresponsive tumors proved sensitive to ABT-888+TMZ, this novel combination may broaden the clinical use of TMZ beyond melanoma and glioma. Although TMZ resistance may be influenced by MGMT, neither MGMT nor other mechanisms of TMZ resistance (mismatch repair) precluded sensitivity to ABT-888+TMZ. Underlying mechanisms of TMZ resistance in these models are not completely understood but likely involve mechanisms independent of MGMT. (Clin Cancer Res 2009;15(23):7277-90) ABT-888 is a new poly(ADP-ribose) polymerase (PARP) inhibitor with excellent potency (K I , 5.2 and 2.9 nmol/L, PARP-1/ PARP-2) and oral bioavailability (1). As shown previously, ABT-888 enhanced the activity of multiple DNA-damaging agents, including cisplatin, carboplatin, cyclophosphamide, irinotecan, radiation, and temozolomide (TMZ), in various xenograft and syngeneic preclinical models (2). In this study, we evaluated in detail the activity of TMZ and the ability of ABT-888 to enhance TMZ antitumor activity in multiple xenograft tumors implanted in subcutaneous, orthotopic, and metastatic sites.The PARP family of enzymes is characterized by the ability to ADP ribosylate protein substrates, implicated in many cellular processes (differentiation, gene regulation, protein degradation, replication, transcription, cell cycle progression, and methylation), and overall maintenance of genomic stability (3, 4). PARP is also critical for single-strand break repair by base excision repair (BER) that can lead to radioresi...