Abstract 257: Class I HDAC inhibition upregulates PD-1 ligands in melanoma and increases the efficacy of PD-1 blockade (2015)

Abstract Ligation of co-inhibitory molecules such as PD-L1/PD-1 are known mechanisms of tumor escape. Blockade of this specific pathway with antibodies against PD-1 has proven effective in the treatment of metastatic melanoma, with response rates of 30-40% (Topalian, SL et al. 2012). However, since the majority of patients fail to respond, approaches to augment the efficacy of this approach are needed. We report herein that histone deacetylase (HDAC) inhibitors against class I HDACs generate robust and durable upregulation of PD-L1 and PD-L2 in melanoma cell lines as well as patient tumor samples. Combining the HDAC inhibitor LBH589 with PD-1 blockade in a murine melanoma model results in delayed tumor growth and increased survival, superior to either single agent. Initially, we evaluated the expression of PD-L1 by flow cytometry on several melanoma cell lines treated with the HDAC inhibitors LBH589, MS275 and MGCD0103. At 72 hours, all treatments resulted in increased PD-L1 surface expression. As a follow-up, additional inhibitors and time points were assessed. Upregulation was seen at 24 hours after treatment and continued past 96 hours. However, these effects were not observed with HDAC6 or class IIa specific inhibitors. We then evaluated a larger panel of HDACi on several patient derived melanomas. We observed dose dependent upregulation with all inhibitors with inhibition of HDAC1, HDAC2 and/or HDAC3, but no impact of HDAC6, HDAC8 or class IIa specific inhibitors. Additionally, we observed low level, but consistent upregulation of PD-L2 in conjunction with PD-L1. These in vitro results were validated in vivo using a B16 murine melanoma model and patient xenografts in SCID mice. Chromatin immunoprecipitation analysis shows that treatment of melanoma with an HDAC inhibitor results in increased histone acetylation at the PD-L1 promoter. Previous studies have demonstrated PD-L1 regulation by STAT3 (Wolfle SJ et al. 2011), in addition to HDAC inhibitor alteration of STAT3 activation (Gupta M. et al 2012). We are currently evaluating alterations in STAT3 signaling in HDAC inhibitor treated melanoma. Given the anti-melanoma properties of LBH589 and its augmentation of immunogenicity previously reported by our group, combination therapy using PD-1 blocking antibodies with LBH589 was explored. Treatment of B16 melanoma-bearing C57BL/6 mice with the combination resulted in tumor progression delay (p = 0.01) compared to control and single agent treatments. Accompanying this tumor delay was an increase in overall survival (p = 0.03). These results highlight the ability of epigenetic modifying agents to augment immunogenicity and increase the efficacy of current immunotherapies. These results provide a strong rationale for combining LBH589 with PD-1 blockade for the treatment of metastatic melanoma. Citation Format: David M. Woods, Andressa L. Sodre, Amod Sarnaik, Eduardo M. Sotomayor, Jeffrey Weber. Class I HDAC inhibition upregulates PD-1 ligands in melanoma and increases the efficacy of PD-1 blockade. [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 257. doi:10.1158/1538-7445.AM2015-257