The investigation of minoxidil-induced [Ca²⁺]_irises and non-Ca²⁺-triggered cell death in PC3 human prostate cancer cells

Abstract

Minoxidil is clinically used to prevent hair loss. However, its effect on Ca homeostasis in prostate cancer cells is unclear. This study explored the effect of minoxidil on cytosolic-free Ca levels ([Ca]) and cell viability in PC3 human prostate cancer cells. Minoxidil at concentrations between 200 and 800 μM evoked [Ca] rises in a concentration-dependent manner. This Ca signal was inhibited by 60% by removal of extracellular Ca. Minoxidil-induced Ca influx was confirmed by Mn-induced quench of fura-2 fluorescence. Pre-treatment with the protein kinase C (PKC) inhibitor GF109203X, PKC activator phorbol 12-myristate 13 acetate (PMA), nifedipine and SKF96365 inhibited minoxidil-induced Ca signal in Ca containing medium by 60%. Treatment with the endoplasmic reticulum Ca pump inhibitor 2,5-ditert-butylhydroquinone (BHQ) in Ca-free medium abolished minoxidil-induced [Ca] rises. Conversely, treatment with minoxidil abolished BHQ-induced [Ca] rises. Inhibition of phospholipase C (PLC) with U73122 abolished minoxidil-evoked [Ca] rises. Overnight treatment with minoxidil killed cells at concentrations of 200-600 μM in a concentration-dependent fashion. Chelation of cytosolic Ca with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid/AM (BAPTA/AM) did not prevent minoxidil's cytotoxicity. Together, in PC3 cells, minoxidil induced [Ca] rises that involved Ca entry through PKC-regulated store-operated Ca channels and PLC-dependent Ca release from the endoplasmic reticulum. Minoxidil-induced cytotoxicity in a Ca-independent manner.