Rakesh K. Singh

Mechanism of Inhibition of the MeTC7 Ligand That Covalently Binds to VDR To Reduce PD-L1 Expression

Cancer-associated overexpression of the Vitamin D Receptor (VDR) is associated with good or poor prognosis, depending on the cancer type and stage. Here, we show that VDR is overexpressed in ovarian malignant tissues and upregulates PD-L1 surface expression in tumor cells, enabling immune evasion by the tumors. MeTC7, a VDR antagonist, has demonstrated strong inhibition of PD-L1 expression in vitro and in vivo. Using structural mass spectrometry and biophysical methods, we showed that MeTC7 binds covalently to VDR in the canonical ligand-binding pocket. Using ligand excess, additional covalently bound molecules were observed. Hydrogen-deuterium exchange mass spectrometry revealed that MeTC7 binding prevents optimal folding of the C-terminal region of VDR and impacts H10, which is part of the dimerization interface. Overall, our findings highlight a new mechanism of action for a VDR antagonist ligand and provide support for the use of the MeTC7 antagonist to inhibit PD-L1 and block tumorigenesis.

HE4 Overexpression by Ovarian Cancer Promotes a Suppressive Tumor Immune Microenvironment and Enhanced Tumor and Macrophage PD-L1 Expression

Abstract Ovarian cancer is a highly fatal malignancy characterized by early chemotherapy responsiveness but the eventual development of resistance. Immune targeting therapies are changing treatment paradigms for numerous cancer types but have had minimal success in ovarian cancer. Through retrospective patient sample analysis, we have determined that high human epididymis protein 4 (HE4) production correlates with multiple markers of immune suppression in ovarian cancer, including lower CD8+ T cell infiltration, higher PD-L1 expression, and an increase in the peripheral monocyte to lymphocyte ratio. To further understand the impact that HE4 has on the immune microenvironment in ovarian cancer, we injected rats with syngeneic HE4 high– and low–expressing cancer cells and analyzed the differences in their tumor and ascites immune milieu. We found that high tumoral HE4 expression promotes an ascites cytokine profile that is rich in myeloid-recruiting and differentiation factors, with an influx of M2 macrophages and increased arginase 1 production. Additionally, CTL activation is significantly reduced in the ascites fluid, and there is a trend toward lower CTL infiltration of the tumor, whereas NK cell recruitment to the ascites and tumor is also reduced. PD-L1 expression by tumor cells and macrophages is increased by HE4 through a novel posttranscriptional mechanism. Our data have identified HE4 as a mediator of tumor-immune suppression in ovarian cancer, highlighting this molecule as a potential therapeutic target for the treatment of this devastating disease.