Abstract LB-342: HDAC inhibition promotes tubulin-independent cancer cell migration

Abstract

Abstract Breast cancer remains the most common cancer and second-leading cause of cancer-related death in women, with metastatic disease carrying a particularly poor prognosis. Despite advances with chemotherapeutic drugs aimed at tumor growth, we do not fully understand the effects of these drugs on the metastatic process. Histone deacetylase inhibitors (HDACi) are novel epigenetic therapies that induce cancer cell death through various mechanisms, including apoptosis, cell-cycle arrest and antiangiogenesis. Clinical trials investigating HDACi use in solid tumors are ongoing but have yielded mixed results. To date, very few studies have examined how HDACi influence the metastatic potential of breast tumor cells. Since HDAC enzymes act on both histone and non-histone targets, HDACi drugs cause dramatic increases in non-histone protein acetylation, including acetylation of alpha-tubulin. A well-known marker of stable microtubules, tubulin acetylation increases in metastatic breast tumors and predicts poor patient survival. However, the effects of HDACi on tubulin-related cytoskeletal dynamics of tumor cells have not been previously examined. The current study investigates whether the use of HDACi in breast cancer cells could promote metastatic phenotypes. Clinically-relevant HDAC pan-inhibitors that target multiple Class I HDAC enzymes (Entinostat) or both Class I and Class II (FDA-approved Vorinostat) yielded strong and rapid increases in the migration of both MCF-7 and Bt-549 breast cancer cells. In addition, Vorinostat and Entinostat were each able to strongly induce histone acetylation, while only Vorinostat induced tubulin acetylation. To determine if the increased tubulin acetylation induced by HDACi drugs was sufficient to induce tumor cell migration, we used an isotype-specific HDACi (Tubastatin) that selectively targets the Class II HDAC6 and therefore can increase tubulin acetylation. At doses which strongly induce tubulin acetylation, Tubastatin did not increase tumor cell migration or other tubulin-dependent cancer cell processes, including reattachment and microtentacle formation. Vorinostat and Entinostat therefore induce tumor cell migration through a tubulin-independent mechanism, indicating that more precise targeting of HDAC enzymes could help avoid therapeutic approaches that induce metastatic phenotypes. Citation Format: Lindsay K. Hessler, Amanda E. Boggs, Rebecca A. Whipple, Michele I. Vitolo, Kristi R. Chakrabarti, Lekhana Bhandary, Keyata N. Thompson, Stuart S. Martin. HDAC inhibition promotes tubulin-independent cancer cell migration. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-342.