Objective: To examine whether the combination of interferon (IFN)-alpha and maitake mushroom D-fraction (PDF), a bioactive mushroom extract, might potentiate the anticancer activity of IFN-alpha in bladder cancer T24 cells in vitro.
Materials and methods: Effects of recombinant IFN-alpha(2b) (0-50 000 IU/mL), PDF (0-700 microg/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-alpha(2b) was able to induce a significant ( approximately 50%) growth reduction at 20 000 IU/mL, which further declined to approximately 66% at 50 000 IU/mL. PDF had no effects up to 200 microg/mL, but there was an approximately 20% and approximately 53% growth reduction at 400 and 700 microg/mL, respectively. When the varying concentrations of IFN-alpha(2b) and PDF were combined, 10 000 IU/mL of IFN-alpha(2b) combined with 200 microg/mL of PDF resulted in an approximately 75% growth reduction. This was accompanied by a G(1) cell cycle arrest, shown by cell cycle analysis. Concurrently, DNA-PK activity in IFN-alpha(2b)/PDF-treated cells was almost three-fold higher than controls.
Conclusions: The combination of IFN-alpha(2b) (10 000 IU/mL) and PDF (200 microg/mL) reduced growth by approximately 75% in T24 cells. This appears to be due to a synergistic potentiation of these two agents, inducing a G(1) arrest with DNA-PK activation. Therefore, the IFN-alpha(2b)/PDF combination could trigger DNA-PK activation that may act on the cell cycle to cease cancer cell growth.