Abstract 4090: Inhibition of class I histone deacetylases promotes robust and durable enhancement of PDL1 expression in melanoma: Rationale for combination therapy
Authors: Woods David M. , Sodre Andressa L. , Sahakian Eva , Powers John , Lienlaf-Moreno Maritza , Perez-Villarroel Patricio , Villagra Alejandro , Pinilla-Ibarz Javier , Sotomayor Eduardo 
Published: May 2015

Abstract
Histone deacetylase inhibitors (HDACi) have shown remarkable anti-tumor activity, leading to FDA approval of two HDACi for the treatment of CTCL and several others currently at various stages of clinical development for the treatment of both solid and hematological malignancies. Previous work from our lab has shown that treatment with HDACi results in increased expression of pro-inflammatory promoting surface markers on melanoma cells, promoting enhanced T-cell activation. Recent clinical trial data has shown that blockade of the PD1/PDL1 interaction is effective in the treatment of melanoma, renal cell and non-small cell lung cancer. Importantly, responses to PD1 blocking antibodies were preferentially seen in patients with tumors expressing PDL1. Here we report that HDACi targeting class I HDACs, but not class II, augments expression of PDL1 in melanoma cells. Two murine and five human melanoma cell lines were treated for up to 72 hours with DMSO, LBH589 (pan-HDACi), MS275 (class I inhibitor), MGCD0103 (class I inhibitor), an HDAC6 specific inhibitor, or a class IIa inhibitor. Using flow cytometry, dose dependent, increases in PDL1 expression were found in the LBH589, MS275 and MGCD0103 treated groups, but not in those receiving HDAC6i or class IIa inhibitor, relative to DMSO. Increased expression was noted as early as 24 hours after treatment and peaked at 72 to 96 hours post-treatment. As IFN-γ is known to upregulate the expression of PDL1 in both normal and transformed cells, we evaluated whether these results were associated with induction of IFN-γ expression by the melanoma cells. However, no detectable levels of IFN-γ were seen in either non-treated, class I HDACi, or class II HDACi-treated cells. Melanoma cells treated with HDACi in addition to IFN-γ have enhanced expression of PDL1 relative to either treatment alone. To further gain insight into the specific HDAC regulating the expression of PDL1, preliminary experiments utilizing knockdowns (KD) of individual class I HDACs were performed. In all KD melanoma cells no increase in PDL1 expression was seen, suggesting that the increased expression of PDL1 is dependent on inhibition of multiple class I HDACs. Supporting this conclusion, treatment of class I HDAC-KDs with HDACi recapitulates the increased PDL1 expression seen with WT melanoma. Finally, in preliminary in vivo experiments combining treatment of melanoma bearing mice with anti-PDL1 antibodies, mice receiving the combination treatment had a survival advantage over those receiving PDL1 blocking antibodies or HDACi alone. These results provide a strong rationale for the evaluation of combination therapies utilizing PDL1 or PD1 blocking antibodies in combination with HDACi. Furthermore, these results support the need for further development and investigation of iso-specific HDACi in order to obtain more directed therapeutic efficacy.
Citation Format: David M. Woods, Andressa L. Sodre, Eva Sahakian, John Powers, Maritza Lienlaf-Moreno, Patricio Perez-Villarroel, Alejandro Villagra, Javier Pinilla-Ibarz, Eduardo Sotomayor. Inhibition of class I histone deacetylases promotes robust and durable enhancement of PDL1 expression in melanoma: Rationale for combination therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4090. doi:10.1158/1538-7445.AM2014-4090