Synergistic potentiation of interferon activity with maitake mushroom d-fraction on bladder cancer cells

OBJECTIVE

To examine whether the combination of interferon (IFN)-α and maitake mushroom D-fraction (PDF), a bioactive mushroom extract, might potentiate the anticancer activity of IFN-α in bladder cancer T24 cells in vitro.

MATERIALS AND METHODS

Effects of recombinant IFN-α_2b (0–50 000 IU/mL), PDF (0–700 µg/mL), or their combinations were assessed on T24 cell growth at 72 h. Cell cycle analysis and assays for double-stranded DNA-dependent protein kinase (DNA-PK) were performed to explore possible antiproliferative mechanism of these agents.

RESULTS

IFN-α_2b was able to induce a significant (≈50%) growth reduction at 20 000 IU/mL, which further declined to ≈66% at 50 000 IU/mL. PDF had no effects up to 200 µg/mL, but there was an ≈20% and ≈53% growth reduction at 400 and 700 µg/mL, respectively. When the varying concentrations of IFN-α_2b and PDF were combined, 10 000 IU/mL of IFN-α_2b combined with 200 µg/mL of PDF resulted in an ≈75% growth reduction. This was accompanied by a G₁ cell cycle arrest, shown by cell cycle analysis. Concurrently, DNA-PK activity in IFN-α_2b/PDF-treated cells was almost three-fold higher than controls.

CONCLUSIONS

The combination of IFN-α_2b (10 000 IU/mL) and PDF (200 µg/mL) reduced growth by ≈75% in T24 cells. This appears to be due to a synergistic potentiation of these two agents, inducing a G₁ arrest with DNA-PK activation. Therefore, the IFN-α_2b/PDF combination could trigger DNA-PK activation that may act on the cell cycle to cease cancer cell growth.