Possible immunotherapeutic potentiation with D-Fraction in prostate cancer cells

BACKGROUND Prostate cancer remains the most common malignancy among elderly men and the second leading cause of cancer death in the United States. Although several conventional therapies are currently available, they have a low efficacy and the more effective treatment modalities need to be established. Interferons (IFNs) are one of such options known as immunotherapy and demonstrated their antitumor effects on certain cancer types. Yet such antitumor activity should be improved or potentiated to have the satisfactory outcomes. In fact, combination therapy has been proposed as an alternative approach and is being underway in human and animal studies. Accordingly, we studied whether the combination of IFN-alpha and D-fraction (PDF), a bioactive mushroom extract, might potentiate anticancer activity of IFN-alpha in prostate cancer PC-3 cells in vitro. RESULTS Potential effects of recombinant IFN-alpha(2b) (0-100,000 IU/ml), PDF (0-1,000 microg/ml), or their combinations were assessed on the growth of PC-3 cells at 72 h. Cell cycle analysis using a flow cytometer and Western blot analysis were performed to explore antiproliferative mechanism of these agents. The dose-dependent study showed that IFN-alpha(2b) up to 20,000 (20 K) IU/ml had no significant effects, but >60% growth reduction was attained 60%) down-regulated in IFN/PDF-treated cells. CONCLUSION The combination of IFN-alpha(2b) (10 K IU/ml) and PDF (250 microg/ml) is capable of inducing a approximately 65% reduction in PC-3 cell growth. This appears to be due to a synergistic potentiation of two agents, leading to a G1 cell cycle arrest. Thus, it is conceivable that PDF may potentiate IFN-alpha(2b) activity, improving immunotherapy for prostate cancer.