Effects of <italic>Lycium ruthenicum</italic> Murray anthocyanin Pt3G on the proliferation and apoptosis of prostate cancer LNCaP andPC-3 cells

Lycium ruthenicum Murray ( L. ruthenicum), known as “black Goji”, has been widely distributed in northwest of China. The fruit of L. ruthenicum has been used as a traditional Chinese medicine for a long time. Many modern studies indicated that the fruit of L. ruthenicum has a variety of biological activities such as antioxidant, anti-inflammatory, anti-cancer, neuroprotective, and potential prevention of cardiovascular disease. The fruit of L. ruthenicumis black in color and rich in anthocyanins. It has been reported that petunidin 3- O-[6- O-(4- O-( trans-p-coumaroyl)-α-l-rhamnopyranosyl)-β-D-glucopyranoside]-5- O-[β-D-glucopyranoside] (Pt3G) is the main constituent of anthocyanins in fully ripe fruits of L. ruthenicum. In our previous study, we found that the Pt3G from the fruit of L. ruthenicum could inhibit the proliferation of prostate cancer DU145 cells through ROS/PTEN/PI3K/Akt pathway. To further explore the mechanisms underlying the inhibitory effect of Pt3G on proliferation of prostate cancer cells, the prostate cancer LNCaP and PC-3 cells were used in this study. MTT assay was used to determine the proliferation rate of cells treated with different concentrations of Pt3G solution. To verify whether the inhibitory effect of Pt3G on the proliferation of prostate cancer cell is due to apoptosis, flow cytometric analysis and TUNEL assay were used to detect cell apoptosis, and the Western Blot analysis was used to detect the expression of apoptosis related proteins. The mitochondrial membrane potential in LNCaP and PC-3 cells was analyzed with JC-1 fluorescent dye. Our results showed that Pt3G inhibited the proliferation of LNCaP and PC-3 cells in a concentration dependent manner. The half inhibitory concentrations (IC50) of Pt3G against LNCaP and PC-3 cells were 601.97 and 445.79 μg/mL at 24 h after treatment, respectively. Flow cytometry and TUNEL results showed that the mean percentages of apoptotic cells were significantly increased in the Pt3G treated LNCaP and PC-3 cells as compared to the control group. Furthermore, Pt3G could lead to excess reactive oxygen species (ROS) generation, decreased the mitochondrial membrane permeability and was able to induce prostate cancer cells arrest in S phase after 24 h treatment. Western Blot analysis showed that the expression levels of tumor suppressor PTEN in prostate cancer cells were significantly increased after Pt3G treatment. Moreover, Pt3G treatment significantly up-regulated the expression levels antiapoptotic factors PI3K, p-PI3K, Akt and p-Akt and down-regulated the expression levels proapoptotic factors Bax, cytochrome c, caspase 3 and cleaved caspase 3 in prostate cancer cells treated with Pt3G for 24 h. Taken together, these findings suggest that the Pt3G could inhibit cell proliferation and induce apoptosis of prostate cancer cells line, and its anti-tumor mechanisms may be through ROS/PTEN/PI3K/Akt signal pathway. Although the anthocyanin Pt3G from the fruit of L. ruthenicum has a chemopreventive activity against prostate cancer cells lines, its anti-tumor mechanisms needs to be further clarified in the future.