Harmine and Exendin-4 Combination Therapy Safely Expands Human Beta Cell Mass In Vivo

537 million people globally suffer from diabetes. Insulin-producing beta cells are reduced in number in most people with diabetes, but the majority still have some residual beta cells. Disappointingly, none of the many diabetes drugs in common use can increase human beta cell numbers. Recently, small molecules that inhibit the kinase, Dual Tyrosine-Regulated Kinase 1A (DYRK1A), have been shown to induce immunohistochemical markers of human beta cell replication, and this is enhanced by drugs that stimulate the GLP1 receptor (GLP1R) on beta cells. However, it remains to be demonstrated whether these immunohistochemical findings translate into an actual increase in human beta cell numbers in vivo. It is also unknown whether DYRK1A inhibitors together with GLP1R agonists (GLP1RAs) affect human beta cell survival. Here, we demonstrate for the first time that combination of a DYRK1A inhibitor with exendin-4 increases actual human beta cell mass in vivo by 400-700% in diabetic and non-diabetic mice over three months, reverses diabetes in vivo, without significant alteration in human alpha cell mass. The augmentation in human beta cell mass occurs through mechanisms that include enhanced human beta cell proliferation, function, and survival. The increase in human beta cell survival is mediated in part by the islet prohormone, VGF. Taken together, these findings demonstrate the remarkable therapeutic potential and safety profile of the DYRK1A inhibitor-GLP1RA combination for diabetes treatment. To address the mechanism involved in the human beta cell protective action of the harmine-exendin-4 combination, we performed RNAseq analysis on human islet grafts following one week of treatment.