Abstract 4812: Vorinostat and fenretinide synergize in preclinical models of T-cell lymphoid malignancies via reactive oxygen species

Abstract

Abstract Introduction: T-cell lymphoid malignancies (TCLMs) are in need of novel and more effective therapies. Pan-histone deacetylase (HDAC) inhibitors vorinostat and belinostat, and class I specific HDAC inhibitor romidepsin have achieved FDA registration as 2nd line therapies for peripheral and/or cutaneous T-cell lymphomas. The cytotoxic retinoid fenretinide achieved durable complete responses against T-cell lymphomas in early-phase clinical trials and T-cell lymphoma patients who failed prior HDAC inhibitor treatment responded to fenretinide (Clinical Cancer Res 23:4550-4555, 2017). Fenretinide is currently being evaluated in a Phase IIa clinical trial for relapsed/refractory PTCL patients (NCT02495415). We have previously shown romidepsin and fenretinide synergize in preclinical models of T-cell lymphoid malignancies (Molecular Cancer Therapeutics 16:649-661, 2017). There exist some key differences in the activity of various classes of HDAC's, which have significantly different chemical structures and metabolic profiles. Therefore we determined if the pan-HDAC inhibitor vorinostat synergizes with fenretinide. Methods and Results: Using the DIMSCAN cytotoxicity assay, we demonstrated cytotoxic synergy between vorinostat and fenretinide in nine TCLM cell lines at clinically-achievable concentrations that lacked cytotoxicity for non-malignant cells (fibroblasts and blood mononuclear cells). In vivo, vorinostat + fenretinide + ketoconazole (enhances fenretinide exposures by inhibiting fenretinide metabolism) showed greater activity in subcutaneous (COG-LL-317m and TX-LY-183x PDX) TCLM xenograft models than single agent vorinostat or fenretinide + ketoconazole. Fenretinide + vorinostat caused a reactive oxygen species (ROS, measured by DCFDA dye)-dependent increase in apoptosis (via TUNEL assay), and histone acetylation (measured by immunoblotting). The synergistic cytotoxicity, apoptosis, and histone acetylation of fenretinide + vorinostat was abrogated by antioxidant vitamin C. Vorinostat + fenretinide activated p38 and JNK via ROS, and shRNA knockdown of p38 and JNK1 significantly decreased the synergistic cytotoxicity and apoptosis. Vorinostat + fenretinide also showed synergistic cytotoxicity for six B-lymphoid malignancy cell lines. Conclusion: Like romidepsin, vorinostat combined with fenretinide achieved synergistic activity in preclinical models of TCLMs, but not in non-malignant cells, via a novel molecular mechanism. As vorinostat is an oral agent and not a PGP substrate it may have advantages in such combination therapy. These data support conducting a clinical trial of vorinostat combined with fenretinide in relapsed and refractory TCLMs. Citation Format: Monish Ram Makena, Thinh H. Nguyen, Balakrishna Koneru, Ashly Hindle, Wan-Hsi Chen, Dattesh U. Verlekar, Min H. Kang, C. Patrick Reynolds. Vorinostat and fenretinide synergize in preclinical models of T-cell lymphoid malignancies via reactive oxygen species [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4812.