Treatment with the Chk1 inhibitor G�6976 enhances cisplatin cytotoxicity in SCLC cells

Abstract

Abstract. Acquired chemoresistance is a major obstacle in successful treatment of small cell lung cancer (SCLC). DNA damage responses can potentially contribute to resistance by halting the cell cycle following exposure to therapeutic agents, thereby facilitating repair of drug-induced lesions and protecting tumour cells from death. The Chk1 protein kinase is a key regulator in this response. We analysed the status of cell cycle checkpoint proteins and the effects of the Chk1 inhibitor Gö6976 on cisplatin toxicity in SCLC cell lines. IC 50 s for cisplatin were determined using the MTT assay in six SCLC cell lines. Effects on cell cycle distribution and apoptosis were determined by flow cytometry and caspase 3 activation in the presence or absence of the Chk1 inhibitor Gö6976. The activation of checkpoint proteins was determined by Western blotting. Cell lines were divided into chemosensitive and chemoresistant groups on the basis of our results. While checkpoint responses were detected in these cell lines through Western blotting, some of these responses were delayed or weaker than those seen in other cell types in response to DNA damage and replication stress. Gö6976 significantly (p<0.05) enhanced the levels of apoptosis seen in response to a clinically relevant dose of cisplatin (<6 µM) and decreased drug-induced G2 arrest in chemosensitive cells. Our data suggest a role for Chk1 in chemoresistance of SCLC cells and a potential approach to improve initial response of SCLC to cisplatin therapy.

CHK1 Inhibition in Small-Cell Lung Cancer Produces Single-Agent Activity in Biomarker-Defined Disease Subsets and Combination Activity with Cisplatin or Olaparib

“…Although a prior study showed that CHK1 targeting could enhance the cytotoxicity of cisplatin in a small number of SCLC cell lines (40), the current study significantly expands upon this work and reports additional novel findings. First, by leveraging a large panel of molecularly profiled cell lines, we identify for the first time biomarker-defined SCLC subsets with enhanced vulnerability to CHK1 inhibition.…”

Cancer cells that survive checkpoint adaptation contain micronuclei that harbor damaged DNA

“…With this information we could then test the prediction that the inhibition of Chk1 would cause more cells to enter mitosis with damaged DNA and therefore generate additional micronuclei. 31 We observed that the percentage of micronuclei in cells co-treated with a checkpoint inhibitor and cisplatin was higher than the percentage of cells with micronuclei after treatment with cisplatin alone. This finding suggested that inhibiting Chk1 permits entry into mitosis, 32 which generates additional micronuclei.…”

Checkpoint kinase 1 protein expression indicates sensitization to therapy by checkpoint kinase 1 inhibition in non–small cell lung cancer

“…It has also been shown that CHK1 inhibitors sensitize pancreatic cancer cells to gemcitabine or radiation [32] and that the sensitization mechanism is attributable to G2 checkpoint abrogation and inhibition of homologous recombination repair DNA damage response [14,16]. CHK1 inhibitors have been combined with numerous chemotherapeutics, including cisplatin [33,34] and paclitaxel [35]. Although we did not observe any sensitization when we combined AZD7762 with cisplatin (data not shown), we did see a reduction in both proliferation and clonogenic survival with both gemcitabine and pemetrexed, with a greater reduction in high versus low CHK1 expressing NSCLC cells.…”