BACKGROUND: The development of prostate cancer from a clinically localized, hormone-naive state to a hormone-refractory phenotype involves a complex interplay of protein kinase C (PKC) and activator protein-1 (AP-1). Therefore, the present study aimed to uncover the roles of PKC and AP-1 through midostaurin-mediated regulation—a multi-target protein kinase inhibitor.

METHODS: Androgen Receptor-negative, hormone-refractory prostate cancer cells (PC-3) were used as an in-vitro model system. The effect of midostaurin on cell viability was assessed by an MTT assay. Expression studies on PKC-α, PKC- d, different AP-1 transcription factors, and AP-1 regulating genes were analyzed by semiquantitative RT-PCR, and protein levels of Bcl-2 were evaluated by western blotting.

RESULTS: Midostaurin decreased the viability of hormone-refractory PC-3 cells. Furthermore, midostaurin significantly induced the transcripts of apoptotic-mediated PKC- d, tumor suppressor p53, cell cycle inhibitor p21^cip1/waf1, death receptor TNF-α, pro-apoptotic Bax, and Caspase-8, and eventually inhibited the expression of pro-survival PKC-ε, pro-oncogene c-Jun, c-Fos, Fra-1, positive growth regulator cyclin D1, and anti-apoptotic Bcl-2. In addition, midostaurin also decreased the protein expression of anti-apoptotic Bcl-2.

CONCLUSION: The present study provided evidence that midostaurin suppresses tumor growth and induces apoptosis in hormone-refractory PC-3 cells via modulation of PKC- d and PKC-ε expression, and regulation of PMA-altered c-Jun, c-Fos, and Fra-1 AP-1 transcription factors and their target genes involved in cell cycle regulation (cyclin D1, p53, p21, Bcl-2, and TNF-α). Thus, pharmacological targeting of PKC and AP-1 factors may have therapeutic potential against hormone-refractory prostate cancer.