Investigations of the novel checkpoint kinase 1 inhibitor SRA737 in non-small cell lung cancer and colorectal cancer cells of differing gene status.

Aim: In response to DNA damage the serine/threonine-specific protein kinase checkpoint kinase 1 (CHK1) is activated allowing cells to enter S phase (S) and G2 phase (G2) cell-cycle arrest. CHK1 inhibitors are expected to prevent cells from entering such arrest, thereby enhancing DNA damage-induced cytotoxicity. In contrast, normal cells with intact ataxia-telangiectasia mutated (ATM), CHK2 and tumour suppressor protein 53 (P53) signalling are still able to enter cell-cycle arrest using the functioning G1/S checkpoint, thereby being rescued from enhanced cytotoxicity. The main objective of this work is to investigate the effects of the novel CHK1 inhibitor SRA737 on pairs of non-small cell lung cancer (NSCLC) and colorectal cancer (CRC) cell lines, all with genetic aberrations rendering them susceptible to replication stress but of differing tumour protein 53 () gene status, focusing on DNA damage induction and the subsequent effects on cell proliferation and viability.

Methods: NSCLC cell lines H23 [ mutant (MUT)] and A549 [ wild-type (WT)] and CRC cell lines HT29 ( MUT) and HCT116 ( WT) were incubated with differing micromolar concentrations of SRA737 for 24 h and then analysed using alkaline comet and phosphorylated H2A.X variant histone (γH2AX)-foci assays to assess mostly DNA single strand break and double strand break damage, respectively. Cell-counting/trypan blue staining was also performed to assess cell proliferation/viability.

Results: Clear concentration-dependent increases in comet formation and γH2AX-foci/cell were noted for the MUT cells with no or lower increases being noted in the corresponding WT cells. Also, greater anti-proliferative and cell killing effects were noted in the MUT cells than in the WT cells.

Conclusions: This study's data suggests that P53 status/functioning is a key factor in determining the sensitivity of NSCLC and CRC cancer cells towards CHK1 inhibition, even in circumstances conducive to high replicative stress.