CDK4 and colonic neoplasm: In another study, geldanamycin was found to inhibit cyclin E/CDK2 and CDK4 in human prostate (DU145) and human colorectal (HT29) cancer cell lines [32], and it showed synergistic activity with the CDK 4/6 inhibitor (palbociclib) in HCT116 colon cancer cells [33].