Effect of simvastatin on castration-resistant prostate cancer cells

In castration-resistant prostate cancer (CRPC), recent evidence has demonstrated the persistence of intratumoral androgens through de novo steroidogenesis despite androgen deprivation therapy. The multi-step androgen synthesis pathway originates from common precursor cholesterol molecule, which can be obtained by cells from several major sources including intracellular synthesis through 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) enzyme. The inhibition of this enzyme by the use of statins has been investigated in various prostate cancer models with inconclusive results. In addition, the role of statins as a possible therapeutic agent for blocking de novo androgen synthesis in established CRPC models has not been thoroughly investigated. Castration-resistant C4-2 and androgen-sensitive LNCaP cells were treated with simvastatin (SV) for 48 hours. Cellular responses to SV were analyzed using cell proliferation and cytotoxicity assays. Cellular growth curve was generated by measuring the total cell count using haemocytometer over the course of 8 days. HMGCR activity was assessed by the incorporation of ¹⁴C-acetic acid into cholesterol that was detected by thin layer chromatography. Western blotting technique was used to determine the HMGCR protein expression in the cell lines. Intracellular cholesterol, prostate specific antigen (PSA) secretion, and intracellular testosterone levels were quantified using enzyme-linked immunosorbent assays (ELISA). % cytotoxicity of castration-resistant C4-2 cells following 48-hour SV treatment significantly increased at SV concentration greater than 60 μM compared to vehicle control. Corresponding results were observed in cell viability data where a significant decrease in cell viability occurred in C4-2 cells treated with SV concentration greater than 75 μM compared to vehicle control. A significant difference in the total cell count compared to vehicle control occurred in C4-2 cells treated with 75 μM SV on Day 8, 72 hours after the removal of SV. HMGCR activity was significantly decreased up to 50% and 70% at 50 μM and 75 μM SV, respectively, compared to vehicle control in C4-2 cells; on Day 8 continuous inhibition of HMGCR activity was observed in cells treated with 75 μM SV. SV did not affect HMGCR protein expression in C4-2 cells, while 80% decrease in total intracellular cholesterol concentration was observed in the cells treated with 75 μM SV compared to vehicle control. Prostate specific antigen concentration in media of C4-2 cells treated with 50 μM and 75 μM SV was significantly different compared to PSA level in vehicle control, whereas intracellular testosterone concentration was not statistically different in C4-2 cells following 48-hour SV treatment compared to vehicle control. In conclusion, inhibition of the HMGCR using SV lowered the viability of castration-resistant C4-2 cells. The ability of SV to limit the intracellular cholesterol synthesis and concentration may contribute to the effect seen in cell viability. Clinically, SV may be considered as primary therapy in patients with established CRPC; however further tests must be conducted to support the findings in this study.Pharmaceutical Sciences, Faculty ofGraduat