STK39 and skin cancer: Compounds that inhibit OSR1 and SPAK activity have already shown promise as potential anti-cancer drugs [63–66]: Closantel, a SPAK inhibitor, inhibits cancer growth and angiogenesis when tested in a zebrafish model [65, 66], and Rafoxanide, another OSR1/SPAK inhibitor, inhibits CDK4/6 and is proposed as a potential therapeutic for skin cancer [63, 64].