Due to emergence of resistance to available anticancer agents, there is a need to search for new cytotoxic agents. Pyrido[2,3-]pyrimidines (-) and their tricyclic derivatives () were prepared and screened for their cytotoxicity against breast MCF-7, prostate PC-3 and lung A-549 cancer cell lines as well as normal fibroblasts WI-38. The most active compounds were and compared with doxorubicin. Moreover, compounds and induced apoptosis in PC-3 and MCF-7, respectively via activation of CASP3 (in PC-3 only), Bax, p53 and down regulation of Bcl2 in addition to CDK4/6 inhibition. Pyrido[2,3-]pyrimidine represents an important core for discovery of new potent cytotoxic agents acting on the cell cycle via apoptosis induction through either intrinsic or extrinsic pathways.