KDR and neoplasm: Further studies showed that 221a presented high antiproliferative activity against tumor cell lines MCF-7, DU-145, and HCT-116 (in the low nanomolar ranges: 4.39, 1.06, and 0.34 nM, respectively), and its mechanism of action appeared to be multifactorial, as it could inhibit multiple kinases, including VEGFR-2 (73% inhibition at 10 μM).