Journal of Medicinal Chemistry Table 1. Antiproliferative Activity (IC50) and Eﬀect of PUB-SOs, PUB-SAs, and cDDP on Cell Cycle Progression Article aIC50 is expressed as the concentration of drug inhibiting cell proliferation by 50%. bFor ﬂow cytometry experiments, Jurkat cells were incubated for 24 h in the presence of the selected PUB-SOs and PUB-SAs at a concentration inducing an optimal arrest of cell cycle progression in S-phase. cDDP was used as positive control; n.e., not evaluated. Finally, PIB-SOs inhibit angiogenesis and tumor growth in the chick chorioallantoic membrane (CAM) assay at levels comparable to combretastatin A-4 (CA-4, 3) and exhibit low to very low toxicity toward chick embryos.16 The assessment of the antiproliferative activity and the eﬀect on cell cycle progression of the subset (compounds 4−10) of novel substituted N-phenyl-N′-(2-chloroethyl)ureas either rationally designed as antimicrotubule agents or produced as 6195 dx.doi.org/10.1021/jm3006492 | J. Med. Chem. 2012, 55, 6194−6208