Human Osteoblast Growth and Maturation in Response to Metformin and the Thienopyridone, A769662

Metformin (Met) is a biguanide drug widely used in the treatment and management of non insulin-dependent diabetes mellitus. In recent years it has emerged that Met, by stimulating adenosine monophosphate-activated protein kinase (AMPK), can promote the maturation of osteoblasts, albeit cells sourced from rodent and murine calvaria. Finding novel uses for existing drugs is especially appealing, primarily from the fiscal and time constraints posed in developing new products. Identifying agents capable of supporting human osteoblast growth and differentiation are attractive in a bone regenerative context. Since studies using Met are invariably restricted to rodent and murine osteoblasts we sought to investigate whether this biguanide might have a positive influence upon human osteoblast growth and maturation. To this end we examined the effect of Met on two osteoblast-like cell lines, MG63 and Saos-2, and compared the responses to primary human osteoblasts and their bone marrow-derived stem cell progeny. Furthermore we examined the effect of a cell permeable Met surrogate, A769662, which is a potent and far more selective activator of AMPK. Herein we report that Met is without influence on cell growth. Furthermore the application of Met, albeit in the millimolar range, actually inhibited osteoblast maturation. Conversely A769662 was toxic to the osteosarcoma-derived cell lines, MG63 and Saos-2, but without effect on the growth of primary cells or their stem cell progenitors. Since the cell lines are known to be p53 deficient we propose that activation of AMPK by A769662 could form part of the arsenal in the fight against osteosarcoma.