Abstract 1338: Novel implications of histone deacetylase 6 selective inhibition in melanoma T-cell immunotherapy
Authors: Laino Andressa Sodre , Woods David M. , Sarnaik Amod , Celis Esteban , Weber Jeffrey , Sotomayor Eduardo M. 
Published: August 2015

Adoptive T-cell therapy is an effective treatment for metastatic melanoma, achieving objective clinical responses in half of patients undergoing tumor infiltration lymphocyte (TIL) therapy. Epigenetic modifications are key players in regulating gene expression. Modulation of histone deacetylases (HDACs) has received attention for its implications in altering gene regulation. While HDAC pan-inhibition directly affects tumor growth, the immune system may be negatively impacted. Novel HDAC-selective inhibitors can ameliorate these undesirable effects. HDAC6 is unique in containing two catalytic domains, allowing for the development of isotype-selective inhibitors. Here a novel role of HDAC6 in T-cell immunity with important implications for adoptive cell therapy was explored. Initially a delay in B16 melanoma growth was observed in HDAC6KO mice (p&lt;0.001 at day 19). Furthermore, tumor-free HDAC6KO mice vaccinated with melanoma antigen peptides displayed a mean of 30% antigen-specific circulating CD8+ T-cells versus 12% in WT mice. Moreover, HDAC6 expression was reduced over three fold in T-cells activated in vitro. To further investigate the role(s) of HDAC6 in anti-tumor T-cell responses, the HDAC6 selective inhibitor rocilinostat was utilized. Adoptive transfer of rocilinostat-treated T-cells conferred an increased anti-melanoma response in a B16 model (day 25 mean tumor volume 800 vs. 2200 cubic mm), characterized by accumulation of central memory T-cells in the lymph nodes. To directly address the clinical potential of targeting HDAC6, T-cells from healthy human donors and melanoma patient-derived TILs were treated with rocilinostat. A modest but consistent 5% increase in central memory phenotype in healthy CD4+ and CD8+ T-cells was observed. While a decrease in the naïve, effector and effector memory subsets occurred, no differences in cell viability were seen. Rocilinostat treatment of TILs derived from different cell preparations (e.g. tumor digest, pre- and post-rapid expansion in vitro) displayed up to a three-fold increase in central memory in three patients analyzed. Impressively, repeated in vitro treatment with rocilinostat further increased the proportion of central memory CD4+ and CD8+ T-cells. Intriguingly, initial results show that the transcription factor T-BET, involved in T-cell function, was upregulated in TILs after rocilinostat treatment and in vitro expansion. Functionally, activation of rocilinosat-treated TILs resulted in increased IFNg+CD107a+ T-cells. Ultimately, rocilinostat pre-treatment of TILs or concomitantly with tumor resulted in 70% killing of HLA matched melanoma cells, compared to 50% killing by control-treated TILs, both relative to melanoma only control. These preliminary data provide a rationale for targeting HDAC6 in T-cells to improve cancer immunotherapy.

Citation Format: Andressa Sodre Laino, David M. Woods, Amod Sarnaik, Esteban Celis, Jeffrey Weber, Eduardo M. Sotomayor. Novel implications of histone deacetylase 6 selective inhibition in melanoma T-cell immunotherapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1338. doi:10.1158/1538-7445.AM2015-1338