Delta opiod receptor signaling modulates myeloid suppression in Myelodysplastic Syndromes Free

Myelodysplastic syndromes (MDS) are diseases for which innate immunity has been clearly established to be critical in its pathogenesis. Our group has demonstrated that accumulation of myeloid-derived suppressor cells (MDSC) in the bone marrow microenvironment, driven by the alarmin S100A9, leads to the pyroptotic death of hematopoietic stem and progenitor cells (HSPC). Recently, neurological signaling pathways have been implicated in the modulation of MDSC function, particularly the delta opioid receptor (DOR) in myeloid cells, which was uncovered through collaborative work between Moffitt and Tuhura. This was based on observations that opioids can have anti-inflammatory properties that have a negative effect on infection and wound healing through modulation of M1/M2 macrophage ratios and increases in other suppressive populations initiating the link between the mechanisms by which opioids induce their anti-inflammatory effects. Herein we aimed to understand the potential contribution of DOR in the regulation of MDSC and HSPC in primary MDS bone marrow mononuclear cells (BM-MNC) ex vivo. Bone marrow plasma concentration of the primary activation marker of DOR, cAMP, was increased in tandem with the level of S100A9. Plasma levels of the endogenous DOR ligand enkephalin were negatively correlated, consistent with the known activation of inhibitory G-protein coupled pathways by DOR that inhibit adenyl cyclase. Analysis of DOR expression on MDSC subsets in primary MDS BM-MNC showcased the more immature early (e)MDSC subset with the highest DOR expression in low/intermediate risk MDS specimens. Targeting MDS BM-MNC with a highly specific DOR antagonist WH-TX-31 (N,N-(Me)₂-Dmt-Tic-NH₂) reduced these populations in culture accompanied by increased hematopoietic potential as measured by colony-forming assays and flow cytometry. In comparison, treatment of high-risk acute myeloid leukemia (AML) specimens revealed DOR expression on CD33+ clones, which were reduced with treatment. We found similar findings in S100A9 transgenic mice, that phenocopy human MDS, with high DOR expression in immature myeloid cells and M2-like macrophages but no DOR expression in lymphocyte populations compared to aged-matched wild-type mice. Functional studies on sorted populations of CD33+DOR+ MDSC from MDS BM-MNC demonstrated abundant secretion of suppressive cytokines with corresponding modulation of T cell killing activity. These studies demonstrate the pathogenic role of DOR expression by MDSC in MDS, its potential as a driver of myeloid-immunosuppression and establish DOR antagonism as a potential effective therapeutic strategy meriting clinical investigation.