Abstract 836: Potent antitubulin and antitumor activities influenced by the 3-D conformational shape of bicyclic fused pyrimidines

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Compounds that bind to the tubulin colchicine site cause microtubule depolymerization, inhibit the polymerization of purified tubulin and cause cancer cells to accumulate in mitosis. Some colchicine-site agents additionally have the ability to overcome multiple drug resistance mechanisms, including those mediated by the expression of P-glycoprotein (Pgp) or expression of the β-III isotype of tubulin. We have reported a series of aniline substituted pyrimidines and fused bicyclic and tricyclic pyrimidine compounds that bind to the colchicine site. These compounds are single to triple digit nanomolar inhibitors of cancer cell proliferation. We hypothesized that the conformational orientation of the 4-aniline and the fused pyrimidine scaffold plays an important role in the biological activity of these compounds. In this study, we utilized NMR (NOESY) and molecular modeling to compare the lowest energy conformation of different 4-substituted 2-methyl cyclopenta[d]pyrimidines and their microtubule depolymerizing, colchicine site binding and antiproliferative activities. Among the 4-position substituents were N-methyl-4’-methoxynaphthyl-1’-amino (1), N-methyl-6’-methoxynaphthyl-1’-amino (2) and N-methyl-5’-methoxy-2’-amino (3). The IC50 values towards the MDA-MB-435 tumor cell line were 250 nM for 1 and 10 nM for 3. NMR (NOESY) demonstrated that compound 2 lost the free rotation of the naphthyl ring attached to the cyclopenta[d]pyrimidine ring due to 5-H steric hindrance and did not cause microtubule depolymerization. Compounds 1 and 3 retain the ability to rotate the naphthyl ring even though they adopt slightly different stable conformers. The stable conformational differences of these three compounds afford different binding poses in docking to the colchicine site on tubulin (PDB: 1SA0, MOE 2012), which explains the significant differences in antiproliferative activity, microtubule depolymerizing and inhibition of colchicine binding. This study affords a lead compound that defines a 104o (orthogonal) orientation of the naphthyl ring to the cyclopenta[d]pyrimidine scaffold for the best biological activities. Citation Format: Aleem Gangjee, Weiguo Xiang, Susan L. Mooberry, Ernest Hamel. Potent antitubulin and antitumor activities influenced by the 3-D conformational shape of bicyclic fused pyrimidines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 836. doi:10.1158/1538-7445.AM2014-836