Myeloid cell leukemia (Mcl-1) is a multidomain, anti-apoptotic protein, member of the Bcl-2 family proteins, an important survival factor for many cancers. Mcl-1 has a critical and distinct role(s) in maintaining cell survival and emerging as an independent and promising therapeutic target.

Through high throughout screening (HTS) of 53,300 structurally diverse synthetic organic compounds, we have discovered a number of novel inhibitors of Mcl-1. The hits identified by HTS were evaluated in a series of complementary biochemical, biophysical, functional and cellular assays to eliminate false positives and to determine the specificity and mechanism of action of these new compounds and 23 compounds were found to be inhibitors of Mcl-1. The most promising compounds, 59 and 62, have diverse chemical scaffolds. We have shown that these small molecule inhibitors bind to the BH3 binding site in Mcl-1 with IC50 values of 1,200 nM and 200 nM, respectively, and compete with BH3 peptides derived from Bid, Bim, or Noxa proteins. They bind to the Mcl-1 protein showing selectivity over two other Bcl-2 family members, Bcl-2 and Bcl-xL. NMR spectroscopy shows that 59 and 62 bind to the same BH3 domain of Mcl-1 as the Bim BH3 peptide. These initial lead compounds antagonize Mcl-1 on the functional level and they induce release of cytochrome c, inhibit cell growth and induce apoptosis in pancreatic and melanoma cancer cells with high levels of Mcl-1. We have tested several analogues of 59 and 62, both synthetic and commercially available, and established initial structure-activity relationships. One of the compounds tested (77), an analogue of 59, has improved binding affinity to Mcl-1 protein, as well as potent activity in inhibition of cell growth in cancer cells. Furthermore, by using murine embryonic fibroblasts (MEFs), wild type and deficient in both Bax and Bak (double knock out), it was demonstrated that the cytotoxic activity and induction of apoptosis by several analogues of the lead compound 59, depend on Bax and/or Bak, suggesting that they function as BH3 mimetics.

Collectively, these findings provide good promise for chemical modifications of the new identified lead compounds, 59 and 62, and their further optimization toward developing a new class of anticancer drugs, Mcl-1 inhibitors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4521.