Harmine hydrochloride

Harmine inhibits substrate phosphorylation by DYRK1A more potently than it inhibits substrate phosphorylation by the closely related kinase DYRK1B [half maximal inhibitory concentrations (IC50) of 33 nM versus 166 nM, respectively] and by the more distant members of the family, DYRK2 and DYRK4 (1.9 μM and 80 μM, respectively). Much higher concentrations of harmine are required to suppress tyrosine autophosphorylation of the translational intermediate of DYRK1A in a bacterial in vitro translation system (IC50 = 1.9 μM). Harmine inhibits the phosphorylation of a specific substrate by DYRK1A in cultured cells with a potency similar to that observed in vitro (IC50=48 nM), without negative effects on the viability of the cells. Harmine does not inhibit tyrosine autophosphorylation of DYRK1A in HEK293 cells^[1]. Harmine is able to induce beta cell proliferation, increase islet mass and improve glycemic control. It is a CNS stimulant^[2].

The effects of inhibitors on cell proliferation and viability are determined using a tetrazolium salt-based assay (WST-1). HeLa or HEK293 cells are seeded at a density of 5000 cells per well on 96-well plates. After overnight culture, serial dilutions of harmine in culture medium are applied to the wells (as triplicate samples) and the cells are cultured for 56 h without changing the medium, before the WST-1 assay is performed.

In a partial pancreatectomy (PPX) model, harmine treatment induces Ki-67 labeling in beta cells in both sham-operated mice and in mice subjected to PPX, with the most robust proliferation in the beta cells of harmine-treated PPX mice. In the PPX model, regeneration of beta cell mass is substantially more rapid in the harmine-treated mice than in the controls, reaching near-normal values in only 14 d. In a euglycemic nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mouse model, BrdU and Ki-67 labeling is two- to threefold higher in human beta cells transplanted into the renal capsule of harmine-treated compared to control euglycemic mice, without evidence of beta cell death. In a marginal mass human islet transplant model in streptozotocin-diabetic NOD-SCID mice, harmine treatment also results in near normal glycemic control. Harmine induces production of the important beta cell transcription factors NKX6.1, PDX1 and MAFA.