CHK2 is a checkpoint kinase involved in ATM-mediated responses to DNA double-strand break (DSB). In relation to killing cancer cells, inhibition or activation of CHK2 depends on many variables such as type of DNA damaging anticancer chemicals, the genetic background of cancer cells and the specificity and efficacy of CHK2 inhibitors. CHK1 inhibitors have been found to increase the efficacy of various DNA-damaged anticancer drugs, and there are inhibitors that have been clinically tested, but there is still no agreement on selective inhibition of CHK2. We are currently evaluating potent and selective low molecular weight CHK2 inhibiting Hit chemicals as a chemosesitizer or radiosensitizer. It aims to develop strategies to enhance the effects of anticancer chemotherapy and radiation of non-small cell lung cancer (NSCLC).