Phenformin Promotes Keratinocyte Differentiation via the Calcineurin/NFAT Pathway

Abstract

Phenformin is a drug in the biguanide class that was previously used to treat type 2 diabetes. We have reported the antitumor activities of phenformin to enhance the efficacy of BRAFeMAPK kinaseeextracellular signaleregulated kinase pathway inhibition and to inhibit myeloid-derived suppressor cells in various melanoma models. Here we demonstrate that phenformin suppresses tumor growth and promotes keratinocyte differentiation in the 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate two-stage skin carcinogenesis mouse model. Moreover, phenformin enhances the suspension-induced differentiation of mouse and human keratinocytes. Mechanistically, phenformin induces the nuclear translocation of NFATc1 in keratinocytes in an AMPK-dependent manner. Pharmacologic or genetic inhibition of calcineurin and NFAT signaling reverses the effects of phenformin on keratinocyte differentiation. Taken together, our study reveals an antitumor activity of phenformin to promote keratinocyte differentiation that warrants future translational efforts to repurpose phenformin for the treatment of cutaneous squamous cell carcinomas.

Phenformin: AMP(K)ed for Potential Repurposing

“…Knockdown of AMPK or calcineurin B1 prevents the differentiating effect of phenformin, as do inhibitors targeting NFAT (VIVIT) or calcineurin (cyclosporin A). Phenformin also induces KC differentiation marker protein expression in cyst formation assays with human KCs grafted onto nude mice (Zhou et al, 2020). These data support the development of phenformin for the treatment of skin diseases characterized by hyperproliferation and abnormal differentiation.…”

“…differentiation of human keratinocytes (KCs) through AMP-activated protein kinase (AMPK)-mediated and calcineurin-mediated activation of the transcription factor nuclear factor of activated T cell (NFAT)-c1 (NFATc1) pathway (Zhou et al, 2020). Knockdown of AMPK or calcineurin B1 prevents the differentiating effect of phenformin, as do inhibitors targeting NFAT (VIVIT) or calcineurin (cyclosporin A).…”

“…These data support the development of phenformin for the treatment of skin diseases characterized by hyperproliferation and abnormal differentiation. Zhou et al (2020) have suggested that phenformin, by triggering KC differentiation through the AMPK-NFATc1 pathway, might be used to treat NMSC. However, whether or not this is the only mechanism by which phenformin functions to induce KC differentiation and inhibit skin tumor growth is as yet unknown.…”

“…A study of 16,237 patients with type II diabetes characterized as metformin ever-users or never-users showed that metformin users had a lower skin cancer risk (Tseng, 2018). The fact that phenformin is an analog of metformin and also inhibits KC proliferation and induces differentiation through AMPK (Zhou et al, 2020) suggests that phenformin and metformin may act through similar pathways to protect against NMSCs. However, phenformin may be more effective in improving treatment and prognosis in patients with cancer than metformin because it produces a greater decrease in the tumorinfiltrating MDSCs that are correlated with a worse prognosis (Qin et al, 2018).…”

“…The article by Zhou et al (2020) proposes the use of phenformin, a biguanide drug originally developed to lower blood glucose levels in patients with diabetes, for the treatment of NMSCs. These authors show that oral administration of phenformin abrogates the growth of developed tumors in the 7,12-dimethylbezanthracene (DMBA)-12-O-tetradecanoylphorbol-13-acetate (TPA) initiation-promotion two-stage mouse model of tumorigenesis.…”