HDAC Inhibition Upregulates PD-1 Ligands in Melanoma and Augments Immunotherapy with PD-1 Blockade

Abstract

Expression of PD-1 ligands by tumors and interaction with PD-1 expressing T cells in the tumor microenvironment can result in tolerance. Therapies targeting this co-inhibitory axis have proven clinically successful in the treatment of metastatic melanoma, non-small cell lung cancer and other malignancies. Therapeutic agents targeting the epigenetic regulatory family of histone deacetylases (HDACs) have shown clinical success in the treatment of some hematologic malignancies. Beyond direct tumor cell cytotoxicity, HDAC inhibitors have also been shown to alter the immunogenicity and enhance anti-tumor immune responses. Here we show that class I histone deacetylase inhibitors upregulated the expression of PD-L1 and, to a lesser degree, PD-L2 in melanomas. Evaluation of human and murine cell lines and patient tumors treated with a variety of HDAC inhibitors in vitro displayed upregulation of these ligands. This upregulation was robust and durable, with enhanced expression lasting past 96 hours. These results were validated in vivo in a B16F10 syngeneic murine model. Mechanistically, HDAC inhibitor treatment resulted in rapid upregulation of histone acetylation of the PD-L1 gene leading to enhanced and durable gene expression. The efficacy of combining HDAC inhibition with PD-1 blockade for treatment of melanoma was also explored in a murine B16F10 model. Mice receiving combination therapy had a slower tumor progression and increased survival compared to control and single agent treatments. These results highlight the ability of epigenetic modifiers to augment immunotherapies, providing a rationale for combining HDAC inhibitors with PD-1 blockade.

Epigenetic priming of both tumor and NK cells augments antibody-dependent cellular cytotoxicity elicited by the anti-PD-L1 antibody avelumab against multiple carcinoma cell types

“…A previous study demonstrated PD-L1 elevation in melanoma cell lines and patient melanoma biopsies after entinostat treatment. 24 Here we demonstrate that HDAC inhibition elevates PD-L1 levels across diverse carcinoma cell types in vitro and in human prostate and NSCL cancer xenografts (Table 1, Figure 1). Normally, this would be considered a disadvantageous effect of HDAC inhibition because PD-L1 is involved in promoting tolerance and decreasing immune surveillance.…”

Epigenetic Modifiers in Immunotherapy: a Focus on Checkpoint Inhibitors

“…In particular, class I HDAC inhibition causes upregulation of PD-L1, and PD-L2 to a less extent, in human and murine cell lines in vitro. This was confirmed in vivo in a murine cell melanoma model where mice, receiving a combination treatment with HDACi panobinostat and an anti-PD-1, showed slower tumor progression and increased survival [105]. However, as seen with other signaling pathways, HDAC i nhibition may be tissue and HDAC specific.…”

“…Preclinical studies suggest that the upregulation of immune checkpoints is epigenetically regulated through the action of HDACi that modulate PD-L1 expression in melanoma [104,105]. In particular, class I HDAC inhibition causes upregulation of PD-L1, and PD-L2 to a less extent, in human and murine cell lines in vitro.…”

Epigenetics in Melanoma Development and Drug Resistance

“…Further evidence of epigenetically regulated PD-L1 expression is provided by studies using HDAC inhibitors in melanoma cell lines. Specifically, treatment with class I HDAC inhibitors resulted in increased acetylation of histone 3 in PD-L1 and PD-L2 promoter regions, which resulted in increased PD-L1 expression in vitro and in vivo [104].…”