Abstract 2524: Targeting microtubule-associated protein 4 with novel small molecule CH4938056 confers antitumor activity under quasi in vivo conditions and in xenograft models

Tumor microenvironment is a major factor influencing treatment resistance to conventional anticancer therapies. Indeed, under “quasi in vivo” conditions, with low oxygen (1%), low pH (6.5) and low glucose concentration (0.01%) to mimic the environments in grafted tumors in mice or in clinical tumors, anti-proliferative activities of some conventional anticancer agents were diminished. Here, we describe the small molecule CH4938056, which has a novel chemical structure and was identified through cell-based screening under the “quasi in vivo” conditions followed by chemical modification. Our initial phenotypic profiling revealed that CH4938056 specifically arrests cells at the M phase and that it overcomes multiple resistance mechanisms to conventional anticancer agents including over-expression of MDR1 and BCRP. Then, after designing and identifying a water-soluble phosphate prodrug which successfully converts to CH4938056 after injection, we demonstrated antitumor efficacy of CH4938056 in a HCT116 xenograft model and a MDR1-overexpressing cancer model. Chemo-proteomic studies and consequent biochemical analysis revealed that CH4938056 binds to microtubule-associated protein 4 (MAP4). Moreover, CH4938056 inhibited MAP4-dependent microtubule assembly in a cell free system. siRNA-mediated knockdown of MAP4 induced chromosomal misalignment in metaphase cells, which closely resembles the primary phenotype of the CH4938056-treated cells. Under the “quasi in vivo” conditions, MAP4 expression turned out to be down-regulated (since MAP4 transcription is known to be negatively regulated by p53 which is up-regulated under these conditions) and when we knocked down MAP4 with siRNA, cancer cells became sensitive to CH4938056, which altogether is consistent with the fact that CH4935056 has antitumor activity even under the “quasi in vivo” conditions. From these observations, we conclude that CH4938056 inhibits proliferation of cancer cells by targeting MAP4. Targeting MAP4 with CH4938056 offers a novel approach for the treatment of cancer, especially for patients resistant to conventional anticancer therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2524. doi:10.1158/1538-7445.AM2011-2524