Abstract 3113: Effects of an up-regulated ATR-CHEK1 pathway in head and neck squamous cell carcinomas

Abstract

Abstract Background: The ATR-CHEK1 pathway is upregulated in a subset of head and neck squamous cell carcinoma (HNSCC) cell lines with loss of the G1 cell cycle checkpoint. We hypothesized that the upregulated ATR-CHEK1 pathway protects HNSCC from mitotic catastrophe (cell death) by enhancing the G2M phase checkpoint and that inhibition of this pathway may sensitize HNSCC to DNA damaging agents. Methods and Results: In HNSCC, we observed gain, amplification or translocation of the ATR gene in 8 of 20 cell lines studied; whereas the CHEK1 gene is partially lost in 12 of 20 cell lines. ATR and CHEK1 FISH in paraffin sections of primary head and neck squamous cell carcinomas confirmed our findings in HNSCC cell lines. We observed that both ATR and CHEK1 are overexpressed by quantitative PCR in five of eight HNSCC cell lines with loss of the G1 cell cycle checkpoint. Inhibition of ATR and CHEK1 with caffeine or specific inhibition with the respective siRNAs results in increased susceptibility of HNSCC to ionizing radiation by clonogenic cell survival assay. siRNA-mediated ATR or CHEK1 knockdown leads to loss of G2M checkpoint accumulation and increased sub-G0 apoptotic population by flow cytometric analysis. The mechanism of cell death after ATR and CHEK1 knockdown is by mitotic catastrophe, as evidenced by increased premature chromatin condensation. Conclusions: The ATR-CHEK1 pathway is up-regulated in a subset of HNSCC with loss of G1 phase cell cycle checkpoint. The up-regulated ATR-CHEK1 pathway protects these HNSCC from mitotic catastrophe by enhancing the G2M phase cell cycle checkpoints and inhibition of ATR and/or CHEK1 increase the sensitivity of the HNSCC to ionizing radiation. We conclude that inhibition of the up-regulated ATR-CHEK1 pathway in HNSCC may potentiate or increase the efficacy of the current therapeutic modalities for HNSCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3113. doi:1538-7445.AM2012-3113