Novel hybrids of brefeldin A and nitrogen mustards with improved antiproliferative selectivity: Design, synthesis and antitumor biological evaluation.

A series of novel conjugates of brefeldin A (11a-c, 12a-c and 13a-c) were obtained by introducing a variety of nitrogen mustards at 4-OH or 7-OH position to explore more efficacious and less toxic antitumor agents. The antiproliferative activities were tested against three cancer cell lines (HL-60, PC-3 and Bel-7402) and one multidrug resistant cell line Bel-7402/5-FU. Among them, compound 11a was the strongest derivative with IC values of 4.48, 9.37, 0.2 and 0.84 μM, respectively, and more potent than nitrogen mustards. Though the antiproliferative potency was weaker than the lead compound brefeldin A, 11a displayed lower toxicity than brefeldin A (IC < 0.001 μM) with an IC of 9.74 μM against normal human liver L-O2 cells, showing good selectivity between normal and malignant liver cells. The mechanism studies confirmed that 11a could induce apoptosis, arrest cell cycle at the G1 phase and lead to mitochondrial dysfunction in Bel-7402 cells at submicromolar concentrations. Furthermore, 11a induced the intrinsic apoptotic mitochondrial pathway in Bel-7402 cells, evidenced by the enhanced expression of the pro-apoptotic protein Bax, cyto-c and p53, and the reduced expression of the anti-apoptotic protein Bcl-2. The caspase-9 and -3 levels were also up-regulated.