Caffeic acid phenethyl ester as an adjuvant therapy for advanced prostate cancer.

Prostate cancer is the second most frequently diagnosed cancer of men. Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, the majority of prostate cancer patients receiving the androgen ablation therapy will ultimately develop recurrent castration-resistant tumors within 3 years. Chemotherapy shows little effect on prolonging survival for patients with metastatic hormone-refractory prostate cancer. More than 80% of prostate tumors acquire mutation or deletion of tumor suppressor phosphatase and tensin homolog (PTEN), a negative regulator of PI3K/Akt signaling. Caffeic acid phenethyl ester (CAPE) is a strong antioxidant extracted from honeybee hive propolis. Recent studies indicate that CAPE treatment suppresses tumor growth and Akt signaling in human prostate cancer cells. Combined treatments of CAPE with chemotherapeutic drugs exhibit synergistic suppression effects. Pharmacokinetic studies suggest that intraperitoneal injection of CAPE at concentration of 10mg/kg is not toxic. CAPE treatment sensitizes cancer cells to chemotherapy and radiation treatments. In addition, CAPE treatment protects therapy-associated toxicities in animal models. We therefore propose that administration of CAPE is a potential adjuvant therapy for patients with castration-resistant prostate cancer.