CDK6 and cancer: Compound 18a emerged as the most potent CDK6 inhibitor (IC50 = 726.25 nM) and cytotoxic against MCF-7 (IC50 = 0.01 μM), prostate PC-3 (IC50 = 1.37 μM), lung A-549 (IC50 = 1.69 μM) cancer cell lines.