Enhanced antiproliferative activity of interferon with maitake mushroom extract (PDF) on prostate cancer cells. Free

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Introduction: Although interferons (IFNs) have been used as immunotherapy for patients with prostate cancer, the outcomes have not yet been satisfactory with a poor prognosis. A bioactive extract (PDF) from maitake mushroom (Grifola frondosa) has been shown to have immunomodulatory and anticancer activities, implying its utility in cancer treatment. Accordingly, we investigated if such a mushroom extract might be able to enhance/improve a poor efficacy of IFN in prostate cancer cells in vitro.
 Methods: Recombinant IFN-α and the commercially available maitake mushroom extract, PDF, were tested on the growth of human prostate cancer PC-3 cells. Dose-dependent effects of IFN-α (0-50,000 IU/ml), PDF (0-1,000 μg/ml), or their combinations were examined on cell proliferation. To explore the antiproliferative mechanism, cell cycle and Western blot analyses were performed and the activity of DNA-PK, a cell cycle regulatory protein kinase, was also assessed.
 Results: Little effects of IFN-α alone were seen up to 50,000 (50K) IU/ml where an ≈60% growth reduction was eventually attained. Similarly, PDF had no significant effects up to 700 μg/ml with an ≈50% growth reduction. When the various concentrations of IFN-α and PDF were combined, the combination of a relatively low concentration (10K IU/ml) of IFN-α and 200 μg/ml of PDF resulted in an ≈70% growth reduction. This was accompanied by a 62% increase in the G₁ phase cell population due to a blockage of G₁-S phase progression, revealed by cell cycle analysis. Western blots further confirmed such a G₁ growth arrest by exhibiting an ≈80% down-regulation of G₁-specific cell cycle regulators (CDK2, CDK4, and cyclin D₁). In addition, DNA-PK activity in IFN-α/PDF-treated cells was almost 3-fold higher than that in controls, indicating its active role in the cell cycle regulation.Conclusions: This study shows that IFN-α at the low, ineffective concentration (10K IU/ml) can be synergistically potentiated with PDF (200 μg/ml), inducing a significant (70%) growth reduction in PC-3 cells. Such an enhanced antiproliferative effect is attributed to a G₁ cell cycle arrest, concomitant with DNA-PK activation, leading to the cascade events that act on the cell cycle to ultimately cease cell proliferation. Thus, the IFN-α/PDF combination could be considered a potential modality for a more effective treatment of prostate cancer.