ATR-CHEK1 signalling is critical for
genomic stability. ATR-CHEK1 signalling may be deregulated in
breast cancer and have prognostic, predictive and therapeutic significance. We investigated ATR, CHEK1 and phosphorylated CHEK1 (Ser345)
protein (pCHEK1) levels in 1712 breast
cancers. ATR and CHEK1
mRNA expression was evaluated in 1950 breast
cancers. Pre-clinically,
biological consequences of ATR gene knock down or ATR inhibition by the small molecule inhibitor (VE-821) were investigated in MCF7 and MDA-MB-231
breast cancer cell lines and in non-tumorigenic breast epithelial cells (MCF10A). High ATR and high cytoplasmic pCHEK1 levels were significantly associated with higher tumour stage, higher mitotic index, pleomorphism and lymphovascular invasion. In univariate analyses, high ATR and high cytoplasmic pCHEK1 levels were associated with poor
breast cancer specific survival (BCSS). In multivariate analysis, high ATR level remains an independent predictor of adverse outcome. At the
mRNA level, high CHEK1 remains associated with aggressive phenotypes including lymph node positivity, high grade, Her-2 overexpression, triple negative, aggressive molecular phenotypes and adverse BCSS. Pre-clinically, CHEK1 phosphorylation at
serine(345) following replication stress was impaired in ATR knock down and in
VE-821 treated
breast cancer cells.
Doxycycline inducible knockdown of ATR suppressed growth, which was restored when ATR was re-expressed. Similarly,
VE-821 treatment resulted in a dose dependent suppression of
cancer cell growth and survival (MCF7 and MDA-MB-231) but was less toxic in non-tumorigenic breast epithelial cells (MCF10A). We provide evidence that ATR and CHEK1 are promising
biomarkers and rational
drug targets for personalized
therapy in
breast cancer.