Effects of combination therapy with dipeptidyl peptidase-IV and histone deacetylase inhibitors in the non-obese diabetic mouse model of type 1 diabetes.

Type 1 diabetes (T1D) results from T helper type 1 (Th1)-mediated autoimmune destruction of insulin-producing β cells. Novel experimental therapies for T1D target immunomodulation, β cell survival and inflammation. We examined combination therapy with the dipeptidyl peptidase-IV inhibitor MK-626 and the histone deacetylase inhibitor vorinostat in the non-obese diabetic (NOD) mouse model of T1D. We hypothesized that combination therapy would ameliorate T1D by providing protection from β cell inflammatory destruction while simultaneously shifting the immune response towards immune-tolerizing regulatory T cells (T(regs)). Although neither mono- nor combination therapies with MK-626 and vorinostat caused disease remission in diabetic NOD mice, the combination of MK-626 and vorinostat increased β cell area and reduced the mean insulitis score compared to diabetic control mice. In prediabetic NOD mice, MK-626 monotherapy resulted in improved glucose tolerance, a reduction in mean insulitis score and an increase in pancreatic lymph node T(reg) percentage, and combination therapy with MK-626 and vorinostat increased pancreatic lymph node T(reg) percentage. We conclude that neither single nor combination therapies using MK-626 and vorinostat induce diabetes remission in NOD mice, but combination therapy appears to have beneficial effects on β cell area, insulitis and T(reg) populations. Combinations of vorinostat and MK-626 may serve as beneficial adjunctive therapy in clinical trials for T1D prevention or remission.