Abstract 2469: Identification of novel Mcl-1 inhibitors using integrated screening approach: combining high throughput and virtual screening.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Myeloid cell leukemia-1 (Mcl-1) is a potent anti-apoptotic protein, a member of the prosurvival Bcl-2 family, and its role is emerging as a critical survival factor in a broad range of human cancers. Mcl-1 represents a very attractive molecular target for development of a new class of cancer therapy and there is still need for developing BH3 mimetics that can efficiently and selectively target Mcl-1 protein. We employed integrated screening approach through combining high throughput and virtual screening, to identify novel chemical classes as Mcl-1 inhibitors. For this purpose we developed a dual-readout HTS assay that combines two assay technologies, FP and FRET, into one system using the Mcl-1 and labeled Noxa BH3 derived peptide and optimized in a 1,536-well ultra-HTS format. This assay was used for screening a library of 102,255 compounds. As two assay platforms were utilized for the same target simultaneously, hit information was enriched identifying 1214 compounds. To further improve the output and the quality of the identified inhibitors, as well as to incorporate the structure-based knowledge of the interactions between Mcl-1 and number of BH3 peptides, we have integrated in silico target-based screening for selection of the most promising hits for further validation. The complex structure between Mcl-1 and Noxa BH3 peptide (PDB ID: [2NLA][1]) was used for the induced fit docking of 1214 hits. Followed by the scoring and ranking of the identified hits, 62 compounds were selected for further evaluation in a series of complementary biochemical, biophysical and functional assays. Several in vitro binding assays with different platform, FP, SPR, and (HSQC) NMR spectroscopy, were used to determine the binding affinity of the compounds. The binding data revealed that we have identified inhibitors with different selectivity profiles against five members of the Bcl-2 family: Mcl-1, Bcl-2, Bcl-xL, Bcl-w and A1. 15N HSQC spectra conclusively showed that newly identified compounds interact with the BH3 domain in Mcl-1 protein and affect many residues in the BH3 binding groove. Using pull down assay it was demonstrated that the identified compounds were able in a dose dependent manner to disrupt interactions between endogenous Mcl-1 protein and biotin labeled Noxa BH3 peptide. Functional studies showed that compounds can antagonize Mcl-1 function and induce cytochrome c and Smac release from the isolated mitochondria. By using murine embryonic fibroblasts (MEFs), wild type and deficient in both Bax and Bak (double knock out), it was further demonstrated that the cytotoxic activity and induction of apoptosis, depend on Bax and/or Bak, suggesting that the compounds function as BH3 mimetics. Collectively, these findings provide several different chemical classes for further chemical modifications and optimization toward developing a new class of anticancer drugs as Mcl-1 inhibitors. Citation Format: Ahmed Mady, Chenzhong Liao, Fardokht Abulwerdi, Chenxi Shen, Yuhong Du, Jeanne Stuckey, Haian Fu, Zaneta Nikolovska-Coleska. Identification of novel Mcl-1 inhibitors using integrated screening approach: combining high throughput and virtual screening. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2469. doi:10.1158/1538-7445.AM2013-2469 [1]: /lookup/external-ref?link_type=PDB&access_num=2NLA&atom=%2Fcanres%2F73%2F8_Supplement%2F2469.atom