Interferon-alpha response and signal transduction pathway in transitional carcinoma cell lines

Additively enhanced antiproliferative effect of interferon combined with proanthocyanidin on bladder cancer cells

Although interferon (IFN) has been often used as immunotherapy for bladder cancer, its efficacy is rather unsatisfactory, demanding further improvement. Combination therapy is one of viable options, and grape seed proanthocyanidin (GSP) could be such an agent to be used with IFN because it has been shown to have anticancer activity. We thus investigated whether combination of IFN and GSP might enhance the overall antiproliferative effect on bladder cancer cells in vitro. Human bladder cancer T24 cells were employed and treated with the varying concentrations of recombinant IFN-α_2b (0-100,000 IU/ml), GSP (0-100 μg/ml), or their combinations. IFN-α_2b alone led to a ~50% growth reduction at 20,000 (20K) IU/ml, which further declined to ~67% at ≥50K IU/ml. Similarly, GSP alone induced a ~35% and ~100% growth reduction at 25 and ≥50 μg/ml, respectively. When IFN-α_2b and GSP were then combined, combination of 50K IU/ml IFN-α_2b and 25 μg/ml GSP resulted in a drastic >95% growth reduction. Cell cycle analysis indicated that such an enhanced growth inhibition was accompanied by a G₁ cell cycle arrest. This was further confirmed by Western blot analysis revealing that expressions of G₁-specific cell cycle regulators (CDK2, CDK4, cyclin E and p27/Kip1) were distinctly modulated with such IFN-α_2b/GSP treatment. Therefore, these findings support the notion that combination of IFN-α_2b and GSP is capable of additively enhancing antiproliferative effect on T24 cells with a G₁ cell cycle arrest, implying an adjuvant therapeutic modality for superficial bladder cancer.