Effects of Quercetin and Docetaxel Co-treatment on Apoptosis-Related Proteins and Cell Cycle in PC-3 Cells

Since prostate cancer is the second most frequent cancer in males, innovative and supportive treatment strategies are required due to the substantial side effects of chemotherapy, particularly in advanced stages, and the emergence of drug resistance. The aim of this study is to reveal the potential of quercetin, a natural flavonoid, to modulate and support the anticancer activity of the widely used chemotherapeutic agent docetaxel in the prostate cancer PC-3 cell line. PC-3 cells were treated with different doses of docetaxel and quercetin; cell viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and IC₅₀ values were calculated. The immunoreactivity intensity of apoptosis-related markers Bax, Bcl-2, and Caspase-3 was analyzed using immunocytochemistry; The cell cycle distribution was examined using flow cytometry. In combination therapy, Bax immunoreactivity increased significantly (p<0.01), while Bcl-2 immunoreactivity decreased significantly (p<0.001). In contrast, a significant increase in Caspase-3 immunoreactivity was observed only in the docetaxel monotherapy group (p<0.01). Both docetaxel and combination groups showed an increased tendency in the G2 phase in cell cycle analysis, but these differences were not statistically significant. Based on these results, docetaxel and quercetin together can alter the Bax/Bcl-2 balance associated with the mitochondrial apoptotic pathway in PC-3 prostate cancer cells, but they do not have a better or more synergistic effect on executive caspase activation compared to docetaxel alone. It is thought that quercetin may simultaneously affect apoptotic signaling through different molecular pathways; therefore, further mechanistic investigations are needed to confirm the potential effects of the combination.