We identified six SMIs that radiosensitize K-RAS mutant rectal cancer cells: BEZ235 (PI3K/mTOR inhibitor), AZD7762 (Chk1/2 inhibitor), AZD8931 (pan-ErbB receptor inhibitor), AT-406 (inhibitor of apoptosis protein (IAP) family inhibitor), AZD6244 (MEK inhibitor), and Abt888 (PARP inhibitor). This evidence concerns the gene CHEK1 and rectal cancer.