Abstract
Thymol is a phenolic compound that affects physiology in different cell models. However, whether
thymol affects Ca²⁺ homeostasis in prostate cancer cells is unknown. The action of this compound on
cytosolic Ca²⁺ concentrations ([Ca²⁺]i) and viability in PC3 human prostate cancer cells was explored.
The results show that thymol at concentrations of 100-1500 μM caused [Ca²⁺]i rises in a concentration-dependent
manner. Removal of extracellular Ca²⁺ reduced thymol’s effect by approximately 80%.
Thymol-induced Ca²⁺ entry was confirmed by Mn²⁺ entry-induced quench of fura-2 fluorescence, and was
inhibited by approximately 30% by Ca²⁺ entry modulators (nifedipine, econazole, SKF96365), and the
protein kinase C (PKC) inhibitor GF109203X. In Ca²⁺-free medium, treatment with the endoplasmic
reticulum Ca²⁺ pump inhibitor thapsigargin abolished thymol-induced [Ca²⁺]i rises. Treatment with thymol
also abolished thapsigargin-induced [Ca²⁺]i rises. Thymol-induced Ca²⁺ release from the endoplasmic
reticulum was abolished by the phospholipase C (PLC) inhibitor U73122. Thymol at 100-900 μM decreased
cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)
ethane-N,N,N’,N’-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Together, in PC3 cells, thymol
induced [Ca²⁺]i rises by inducing PLC-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺
entry via PKC-sensitive store-operated Ca²⁺ channels and other unknown channels. Thymol also induced
Ca²⁺-dissociated cell death.