Tubeimoside-1 Induces Oxidative Stress-mediated Apoptosis And G0/G1 Phase Arrest In Human Prostate Carcinoma Cells In Vitro

Prostate cancer is one of the most commonly diagnosed cancers in men worldwide and is the second leading cause of cancer-related deaths in men.Treatment options of prostate cancer mainly include surgery,radiation therapy,hormone therapy and chemotherapy,depending upon the stage of disease and situation of patients.Androgen deprivation therapy still represents the primary treatment for prostate cancer patients.Although initially successful,this form of therapy frequently fails in advanced stage of disease and patients develop castration-resistant prostate cancer,which is almost untreatable.Surgery and radiation therapies are limited to localized prostate cancer.Thus chemotherapy remains the only option for advanced stage prostate cancer patients.Studies in recent years have shown that chemotherapeutic drugs such as docetaxel and cabazitaxel have improved the health status of prostate cancer patients,however;the prognosis of this disease remains still very poor.Apoptosis is a highly synchronized gene-controlled process which plays a key role in tissue homoeostasis by selectively killing unwanted or cancerous cells.Inhibition of apoptosis results in tumorigenesis and chemo-resistance.Cancer cells achieve higher proliferation rate by inhibiting apoptosis through various mechanisms.Mitochondria being the main component of apoptosis execution machinery,has been extensively studied in the last decade.Reactive oxygen species(ROS)are produced in cells during normal oxidative metabolism and cells’ antioxidant system neutralized them to maintain redox balance.Over-production of ROS has been shown to induce mitochondrial apoptosis.It has become an established fact now that cancer cells possess higher oxidative stress as compared to normal cells to fulfill the demand of uncontrolled growth.Recent research has shown that natural bioactive compounds targeting ROS metabolism can selectively kill cancer cells by increasing the ROS level above a toxic threshold.As cancer cells contain higher level of endogenous ROS,the toxic threshold can be easily achieved in cancer cells by targeting them with exogenous ROS generating photochemicals.Prostate cancer cells have been reported to contain higher level of ROS,therefore targeting ROS metabolism in prostate cancer cells may provide effective treatment.Traditional Chinese herbal medicine is a great source of cancer chemotherapeutic agents that has good disease coverage including cancer treatment.Tubeimoside-1(TBMS1)is a naturally occurring triterpenoid saponin,isolated from Bolbostemma paniculatum(Maxim)Franquet(Cucurbitaceae).It has been well documented that TBMS1 has potent cytotoxicity against several cancer cell lines including human glioma U87,Hep G2,esophageal squamous cell carcinoma EC109,ovarian cancer SKOV-3,CDDP-resistant A2780,choriocarcinoma JEG-3,lung cancer A549,cervical carcinoma He La and BGC823 gastric cancer cells.However,its effect on human prostate cancer remains unexplored.In the present study,we investigated cytotoxic effect of TBMS1 on human prostate carcinoma cells.We found that TBMS1 inhibited the growth and induced apoptosis and G0/G1 arrest in DU145 cells in a dose-and time-dependent manner.The TBMS1-induced apoptosis was found to be associated with ROS generation,mitochondrial dysfunction,endoplasmic reticulum stress,Bcl-2 family proteins modulation,activation of ASK-1,p38,and JNK,and increased expression of CHOP and cleaved caspases-3.The G0/G1 phase arrest was linked with increased expression of p53,p21 and decreased expression of cyclin E and cdk2.Z-VAD-FMK,a pan-caspase inhibitor partially reversed the apoptotic effect while did not prevent G0/G1 arrest indicating apoptosis and cell cycle arrest in response to TBMS1 are two independent events.Moreover,pretreatment of cells with NAC(ROS inhibitor),SB203580(p38 inhibitor),SP600125(JNK inhibitor),and Solubrinal(ER stress inhibitor)significantly reversed TBMS1-mediated apoptosis effects.In conclusion,TBMS1 induces oxidative stress-mediated apoptosis in DU145 human prostate cancer cells in vitro via the mitochondrial pathway.