Macrodiolide Diversification Reveals Broad Immunosuppressive Activity That Impairs the cGAS-STING Pathway.

The development of new immunomodulatory agents can impact various areas of medicine. In particular, compounds with the ability to modulate innate immunological pathways hold significant unexplored potential. Herein, we report a modular synthetic approach to the macrodiolide natural product (-)-vermiculine, an agent previously shown to possess diverse biological effects, including cytotoxic and immunosuppressive activity. The synthesis allows for a high degree of flexibility in modifying the macrocyclic framework, including the formation of all possible stereoisomers. In total, 18 analogues were prepared. Two analogues with minor structural modifications showed clearly enhanced cancer cell line selectivity and reduced toxicity. Moreover, these compounds possessed broad inhibitory activity against innate immunological pathways in human PBMCs, including the DNA-sensing cGAS-STING pathway. Initial mechanistic characterization suggests a surprising impairment of the STING-TBK1 interaction.

CD46 activation induces distinct CXCL-10 response in monocytes and monocyte-derived dendritic cells.

CD46 is an important immune regulatory receptor with dual functions, however, the CD46 isoform distribution and the effect of CD46 activation on the cytokine production in monocytes and monocyte-derived dendritic cells (moDCs) is unclear. Here, we show that CD46 activation of moDCs downregulates LPS-induced CXCL-10 expression, while the expression of CXCL-10 in monocytes is unaffected. Furthermore, the differentiation of moDCs induces a switch towards dominance of CYT-2 isoforms of CD46. These data indicate that CD46 activation exerts different functions in monocytes and moDCs and this correlates with a switch in CD46 isoform expression upon differentiation of moDCs.

CD46 is a potent co-stimulatory receptor for expansion of human IFN-γ-producing CD8+ T cells.

Similar to CD4+ T cells, precursor CD8+ T cells are thought to depend on a co-stimulatory signal through CD28 for proliferation and differentiation into effector cells. CD46 is another co-stimulatory receptor that promotes differentiation of CD4+ T-helper cells type 1 (Th1 cells) into a regulatory phenotype with a switch from IFN-γ towards IL-10-secretion over time. Whether CD46 exerts a similar function on CD8+ T cells remains to be fully elucidated. Here, we demonstrate that CD46 co-stimulation induced secretion of IFN-γ as well as expansion of IFN-γ-secreting CD8+ T cells. In contrast to CD46 co-stimulation of CD4+ T cells, CD8+ T cells did not differentiate into a regulatory IL-10-secreting phenotype. This demonstrates that CD46 is a co-stimulatory receptor on CD8+ T cells, and that it exerts separate functions during CD4+ and CD8+ T-cell differentiation.

Divergent tropism of HHV-6AGS and HHV-6BPL1 in T cells expressing different CD46 isoform patterns.

CD46 is a receptor for HHV-6A, but its role as a receptor for HHV-6B is controversial. The significance of CD46 isoforms for HHV-6A and HHV-6B tropism is unknown. HHV-6AGS was able to initiate transcription of the viral genes U7 and U23 in the CD46+CD134- T-cell lines Peer, Jurkat, Molt3, and SupT1, whereas HHV-6BPL1 was only able to do so in Molt3 and SupT1, which expressed a CD46 isoform pattern different from Peer and Jurkat. The HHV-6BPL1-susceptible T-cell lines were characterized by low expression of the CD46 isoform BC2 and domination of isoforms containing the cytoplasmic tail, CYT-1. A HHV-6BPL1 susceptible cell line, Be13, changed over time its CD46 isoform pattern to resemble Peer and Jurkat and concomitantly lost its susceptibility to HHV-6BPL1 but not HHV-6AGS infection. We propose that isoforms of CD46 impact on HHV-6B infection and thereby in part explain the distinct tropism of HHV-6AGS and HHV-6BPL1.