Targeting the delta opioid receptor (DOR) on myeloid immunosuppressive cells: Novel therapeutic approach to hematological malignancies.

Abstract

e14566 Background: Despite recent progress in the treatment options for hematological malignancies, there remains significant unmet need in some forms of blood cancer such as relapsed/refractory acute myeloid leukemia. Tumor immunosuppression, which remains a major obstacle to cancer immunotherapy, is mainly driven in the tumor microenvironment by myeloid cells including tumor-associated macrophages and myeloid-derived suppressive cells (MDSCs) who play pivotal roles in dampening anti-tumor immune response and promoting tumor progression. Thus, targeting these myeloid cells represents a promising approach to improve cancer immunotherapy. Endogenous and exogenous opioids who interact with specific G-protein coupled surface receptors (MOR, DOR and KOR), have been studied extensively in the context of pain signaling and gastrointestinal functions. However, their role in modulating immunity is still poorly understood. We recently reported that DORs are highly expressed in MDSCs and macrophages and play functional roles in modulating the activity of these myeloid cells. Based on these findings, we initiated a discovery program to identify novel DOR antagonists for use as immunomodulatory agents in hematological cancers. Methods: From our medicinal chemistry campaign, several potent and selective DOR antagonists were identified, including the lead molecule HURA-101. The DOR antagonist potency and DOR/MOR selectivity of the library compounds were assessed in the cyclic AMP functional assays in human DOR or MOR-expressing CHO cells. Results: In the in vitro opioid functional assays, HURA-101 displayed sub-nanomolar potency as DOR antagonist and excellent DOR/MOR selectivity [DOR IC 50 = 0.61 nM; MOR IC 50 > 100,000 nM]. As part of the immunological models supporting the DOR program, we established a human-derived M2a macrophage assay (M2a derived from THP-1 cells using known differentiation/polarization protocol). Importantly, the polarization of THP-1-derived M0 macrophages to the M2a phenotype resulted in a significant increase in DOR surface expression. This result is in line with previous experiments conducted using mouse-derived macrophages and demonstrating that DOR expression is higher in M2 versus M0 phenotypes. Using the THP-1 macrophage assay, the novel DOR antagonists were tested for their ability to modulate expression of macrophage markers and secretion of signaling molecules. Conclusions: To further investigate the role of DOR in modulating immune functions, we initiated a drug discovery program to identify novel DOR antagonists targeting hematological malignancies. The medicinal chemistry campaign led to the discovery of novel potent and selective DOR antagonists. The characterization of selected compounds including the lead molecule HURA-101 across pharmacological and immunological assays will be presented.