Aaron Havas Abstracts
Aaron Havas
Ph.D. Candidate
Cancer Biology GIDP
Annual American Association of Cancer Research Conference
New Orleans, LA
April 16-20, 2016
Patients diagnosed with Diffuse Large B-cell lymphoma have an overall 60% five-year survival rate. New therapeutic approaches are needed to effectively treat aggressive forms of DLBCL that are refractory to the standard treatment or that relapse within two years of treatment. Histone deacetylase inhibitors (HDACi) are novel therapeutics that are well tolerated in humans and are being extensively evaluated in combination with other therapeutics against hematologic malignancies. Rational selection of companion therapeutics has been difficult due to the cell type- specific mechanisms of HDACi action. In order to address this, we have developed a pre-clinical model system of sensitivity and resistance to HDACi-induced cytotoxicity in DLBCL cell lines that share characteristics with aggressive DLBCL tumors. We previously reported that HDACi resistance is associated with reversible arrest in G1 that involves sustained up-regulation of cyclin-dependent kinase inhibitors. In the current study we demonstrate that HDACi-sensitive cell lines undergo mitotic arrest prior to anaphase in response to treatment with the approved HDACi, belinostat, consistent with activation of the spindle assembly checkpoint (SAC). In contrast, HDACi-resistant cell lines are capable of completing mitosis in the presence of belinostat. To force SAC activation in HDACi resistant cell lines, we used low dose microtubule targeting agents (MTA) vincristine and paclitaxel to induce maximal mitotic arrest with minimal cytotoxicity. The combination of these low dose MTAs and belinostat efficiently caused SAC failure, mitotic slippage, and apoptosis in a synergistic manner. A key mechanism associated with resistance to MTAs is their ability to induce aneuploid cell populations that survive and undergo endoreduplication. The addition of belinostat eliminated the accumulation of a vincristine-induced aneuploid population. Pan-caspase inhibition in conjunction with belinostat and vincristine co-treatment resulted in a sustained survival of the aneuploid population. Thus belinostat triggers apoptosis in the aneuploid cells to enhance the cytotoxic effects of vincristine. Our study identifies the use of low dose MTA/HDACi combinatoi n as a potential therapeutic strategy for treatment of relapsed or refractory DLBCL.
Abstract for Lay Audience
Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin’s lymphoma, which accounts for over 65,000 newly diagnosed cases within the United State each year. DLBCL is an aggressive blood cancer with a 5-year survival rate of 60% when treated with the standard of care combination chemotherapy called R-CHOP. Many patients either do not respond to R-CHOP treatment or relapse within the first two years. This disparity in response highlights a need to develop new therapeutic combinations, which will be more effective at treating these patients. A new class of drugs referred to as histone deacetylase inhibitors (HDACi) show promise in treatment of a number of different blood cancers like DLBCL and are being extensively evaluated in clinical trials. We have developed a cell-based model of DLBCL for the purpose of better understanding how these drugs work in DLBCL and to identify other therapeutics which, when combined with the HDACi, belinostat, will work synergistically to induce cell death. We have identified two responses to belinostat: 1) sensitivity characterized by cell death after failure to duplicate within mitosis, and 2) resistance characterized by growth arrest without cell death until the drug is removed and growth resumes.
Within this study we have identified a class of drugs that target mitotic progression called microtubule-targeting agents (MTA) that work synergistically in combination with belinostat to target and kill HDACi resistant cell lines. Furthermore, the combined treatment with these two drugs eliminates a form of resistance observed commonly with MTA treatment in which cells with abnormal numbers of chromosomes arise and fail to die. The results of this study advance the field by providing a rationale for combining HDACi with MTA as a potent treatment for patients who suffer from aggressive forms of DLBCL in an effort to prolong their survival.