Pigment epithelium-derived factor expression prolongs survival and enhances the cytotoxicity of low-dose chemotherapy in castration-refractory prostate cancer

There is currently no cure for advanced castration-refractory prostate cancer (CRPC) despite the recent approval of several new therapeutic agents. We report here the anti-tumor effect of the angio-inhibitory pigment epithelium-derived factor (PEDF) in the metastatic LNCaP-derivative CRPC CL1 model and explore PEDF anti-neoplasic efficacy in combination with low-dose chemotherapy. Androgen-sensitive LNCaP and CRPC PC3 cell lines were examined as comparison. Using a retroviral expression system, we showed that PEDF limited the proliferation of all prostatic cell lines tested; an effect attributed to interleukin 8 (IL8)-CXCR1/IL8RA inhibition. PEDF also reduced the number and size of 3D tumor spheroids in vitro , but only induced cell differentiation in CRPC spheroids. Similarly, PEDF inhibited the migration of CRPC cells suggesting both anti-proliferative and anti-migratory functions. In vivo , PEDF decreased by 85% and 65% the growth of subcutaneous (s.c.) PC3 and CL1 tumors, respectively. In the CL1 orthotopic model, tumor intake with lethal metastases was found in all animals; nevertheless, PEDF prolonged the median survival of tumor-bearing mice (95% confidence interval: 53±0.001 to 57±1 days). Accordingly, PEDF delayed the emergence of skeletal-related event in intra-tibial xenografts. Next, we evaluated low-dose docetaxel (DTX; 5, 1, 0.5 mg/kg) or cyclophosphamide (CTX; 10–20 mg/kg) on established s.c. PC3 tumors that conditionally express PEDF anti-tumoral epitope/NT3. Although NT3–DTX-5 mg/kg combination was inefficient, NT3–DTX-1 mg/kg and -0.5 mg/kg inhibited by 95% and 87.8%, respectively, tumor growth compared with control and induced tumor stasis. Both NT3–CTX combinations were advantageous. Inversely, PEDF–DTX-5 mg/kg and PEDF–CTX-10 mg/kg delayed the most CL1 tumor growth (15, 11 and 5 days for PEDF–DTX-5 mg/kg, PEDF–CTX-10 mg/kg and single treatments, respectively) with elevated apoptosis and serum thrombospondin-1 as possible mechanism and marker, respectively. As well, both PEDF–CTX-10 mg/kg and PEDF–DTX-5 mg/kg prolonged significantly the survival of tumor-bearing mice compared with single treatments. Metastases were reduced in PEDF–DTX-5 mg/kg compared with other treatments, suggesting that PEDF–DTX delayed metastases formation. Our results advocate that PEDF/low-dose chemotherapy may represent a new therapeutic alternative for CRPC.