Bifunctionality and Antitumor Efficacy of ZG-126, a Vitamin D Receptor Agonist/Histone Deacetylase Inhibitor Hybrid Molecule.

Analogues of hormonal vitamin D, 1,25-dihydroxyvitamin D (1,25D), signal through the nuclear vitamin D receptor (VDR). They have potential in combination therapies with other anticancer agents such as histone deacetylase inhibitors (HDACi's). Here, we characterize the ZG series of hybrid compounds that combine HDACi within the backbone of a VDR agonist. All display improved solubility, with ZG-126 being the most robustly bifunctional molecule in multiple cell lines. ZG-126 is well tolerated and strongly induces VDR target gene expression in vivo at therapeutic doses. Its antitumor efficacy is superior to 1,25D and the HDACi SAHA, separately or together, in mouse models of melanoma and triple-negative breast cancer (TNBC). Notably, ZG-126 treatment reduces metastases almost 4-fold in an aggressive TNBC model. ZG-126 also reduces total macrophage infiltration and the proportion of immunosuppressive M2-polarized macrophages in TNBC tumors by 2-fold. ZG-126 thus represents a bifunctional and efficacious anticancer agent with improved physicochemical properties.

Cutting Edge: Aire Is a Coactivator of the Vitamin D Receptor.

Vitamin D deficiency is associated with the development of autoimmunity, which arises from defects in T cell tolerance to self-antigens. Interactions of developing T cells with medullary thymic epithelial cells, which express tissue-restricted Ags, are essential for the establishment of central tolerance. However, vitamin D signaling in the thymus is poorly characterized. We find that stromal and hematopoietic cells in the mouse thymus express the vitamin D receptor (Vdr) and Cyp27b1, the enzyme that produces hormonal 1,25-dihydroxyvitamin D (1,25D). Treatment of cultured thymic slices with 1,25D enhances expression of the critical medullary thymic epithelial cell transcription factor autoimmune regulator (Aire), its colocalization with the Vdr, and enhances tissue-restricted Ag gene expression. Moreover, the Vdr interacts with Aire in a 1,25D-dependent manner and recruits Aire to DNA at vitamin D response elements, where it acts as a Vdr coactivator. These data link vitamin D signaling directly to critical transcriptional events necessary for central tolerance.

Migration-induced cell shattering due to DOCK8 deficiency causes a type 2-biased helper T cell response.

Mutations that impact immune cell migration and result in immune deficiency illustrate the importance of cell movement in host defense. In humans, loss-of-function mutations in DOCK8, a guanine exchange factor involved in hematopoietic cell migration, lead to immunodeficiency and, paradoxically, allergic disease. Here, we demonstrate that, like humans, Dock8-/- mice have a profound type 2 CD4+ helper T (TH2) cell bias upon pulmonary infection with Cryptococcus neoformans and other non-TH2 stimuli. We found that recruited Dock8-/-CX3CR1+ mononuclear phagocytes are exquisitely sensitive to migration-induced cell shattering, releasing interleukin (IL)-1ß that drives granulocyte-macrophage colony-stimulating factor (GM-CSF) production by CD4+ T cells. Blocking IL-1ß, GM-CSF or caspase activation eliminated the type-2 skew in mice lacking Dock8. Notably, treatment of infected wild-type mice with apoptotic cells significantly increased GM-CSF production and TH2 cell differentiation. This reveals an important role for cell death in driving type 2 signals during infection, which may have implications for understanding the etiology of type 2 CD4+ T cell responses in allergic disease.