Androgen deprivation
therapy has constituted the main treatment for
prostate cancer; however,
tumors ultimately progress to
hormone-independent
prostate cancer (HIPC), and suitable therapeutic strategies for HIPC are not available.
Maspin, which is also known as mammary
serine protease inhibitor, has been suggested to be a valuable focus for targeted
cancer therapy. Specifically,
maspin has been shown to be upregulated after
androgen ablation
therapy.
Gemcitabine is used as a first-line
therapy for metastatic
castration-resistant
prostate cancer, but its disease control rate is low. Furthermore, the role of
maspin in the therapeutic efficacy of
gemcitabine for HIPC remains unclear. The expression levels of
maspin in PC-3 and DU145 cells were determined by real-time PCR and Western blotting. Furthermore, the expression of
maspin was silenced using
shRNA technology to generate
maspin-KD cells. The cytotoxicity of
gemcitabine to
prostate cancer cells was assessed using 3-[4,5-dimethylthiazol-2-yl]-3,5-
diphenyl tetrazolium
bromide (MTT) assays, whereas flow cytometry analyses and
annexin V-
propidium iodide (PI) apoptosis assays were used to assess the ability of
gemcitabine to induce apoptosis in
maspin-KD and control cells. Additionally, the expression patterns of anti-apoptosis
proteins (myeloid cell
leukemia 1 (Mcl-1) and
B cell lymphoma 2 (Bcl-2)) and pro-apoptosis
proteins (Bcl-2-associated death promoter (Bad) and
Bcl-2-associated X protein (Bax)) were determined by Western blotting. In this study, PC-3 cells were more resistant to
gemcitabine administration than DU145 cells, which correlated with the higher expression levels of
maspin observed in PC-3 cells. Furthermore,
maspin knockdown enhanced
gemcitabine-induced cell death, as evidenced by the increased number of apoptotic cells.
Gemcitabine treatment upregulated the levels of anti-apoptosis
proteins (Mcl-2 and Bcl-2) in both scrambled control and
maspin-KD cells; however, the fold changes in Mcl-1 and Bcl-2 expression were larger in
gemcitabine-treated scrambled control cells than in
maspin-KD cells. Finally, our findings indicate for the first time that
maspin may mediate the therapeutic efficacy of
gemcitabine in HIPC. Our results demonstrate that
maspin knockdown enhanced the sensitivity of
androgen-independent
prostate cancer cells to
gemcitabine. Therefore, combining
gemcitabine with a drug that targets
maspin might constitute a valuable strategy for
prostate cancer treatment.