Identification of a small molecule that stimulates human beta-cell proliferation and insulin secretion, and protects against cytotoxic stress in rat insulinoma cells
A key event in the development of both major forms of diabetes is the loss of functional pancreatic islet {beta}-cell mass. Strategies aimed at enhancing {beta}-cell regeneration have long been pursued, but methods for reliably inducing human {beta}-cell proliferation with full retention of key functions such as glucose-stimulated insulin secretion (GSIS) are still very limited. We have previously reported that overexpression of the homeobox transcription factor Nkx6.1 stimulates {beta}-cell proliferation, while also enhancing GSIS and providing protection against {beta}-cell cytotoxicity through induction of the VGF prohormone. We developed an Nkx6.1 pathway screen by stably transfecting 832/13 rat insulinoma cells with a VGF promoter-luciferase reporter construct, using the resultant cell line to screen a 630,000 compound chemical library. We isolated three compounds with consistent effects to stimulate human islet cell proliferation. Further studies of the most potent of these compounds, GNF-9228, revealed that it selectively activates human {beta}-cell relative to -cell proliferation and has no effect on {delta}-cell replication. In addition, pre-treatment, but not short term exposure of human islets to GNF-9228 enhances GSIS. GNF-9228 also protects 832/13 insulinoma cells against ER stress- and inflammatory cytokine-induced cytotoxicity. In contrast to recently emergent Dyrk1a inhibitors that stimulate human islet cell proliferation, GNF-9228 does not activate NFAT translocation. These studies have led to identification of a small molecule with pleiotropic positive effects on islet biology, including stimulation of human {beta}-cell proliferation and insulin secretion, and protection against multiple agents of cytotoxic stress.