Phosphodiesterase-4 inhibitors increase pigment cells proliferation and melanization in cultured melanocytes and within a 3D skin equivalent model

Vitiligo is a common chronic autoimmune disease characterized by white macules and patches of the skin, having a negative impact on patients' life, and without any definitive cure at present. Identification of new compounds to reverse depigmentation is therefore a pressing need for this disease. The pharmacologic compounds phosphodiesterase-4 inhibitors (PDE4i) are small molecules with immunomodulatory properties, used for treatment of inflammatory dermatoses. PDE4i have shown repigmentation effects in vitiligo patients, in some case reports. We characterized the proliferative and melanogenic potential of two known PDE4i, crisaborole and roflumilast, and of a more recently designed compound, PF-07038124. We used two in vitro model systems, the primary human melanocyte culture and a 3D co-cultured skin model (MelanoDermTM), with an exploratory testing platform composed of complementary assays (spectrophotometry, melanin and proliferation assays, immunostaining, Fontana-Masson staining, qRT-PCR, western blot and whole transcriptome RNA-Sequencing). We identified that the treatment with PDE4i was associated with increased melanocyte proliferation and melanization in both in vitro models, and with increase in the melanogenic genes and proteins expression in cultured melanocytes. These effects were found to be enhanced by addition of a-MSH. In the MelanodermTM tissue, numerous genes and canonical pathways modulated by PDE4i appear to control melanocytic cell function. Our findings support the use of PDE4i with or without a-MSH agonists in vitiligo trials. Overall design: The MelanoDermTM 3D in vitro co-culture model (MatTek Corp., Ashland, MA) incorporates normal human epidermal MCs into well differentiated epidermis with normal human epidermal keratinocytes (Passeron et al., 2009). Tissues containing MCs from a Black donor (MEL-300-B) were cultured in high and low Growth Factor media, and tissues were treated with crisaborole at 10 µM, PF-07038124 at 100 nM and DMSO vehicle control at the same v/v concentration as crisaborole. Tissues were collected 72hs after drug treatments for RNA extraction.