Direct and indirect effects of human interferon alpha on renal cell carcinoma: a new in vitro assay system for evaluating cytokine-mediated antitumor effects.

A highly purified natural alpha-interferon (nIFN alpha) was tested in vitro for direct and indirect antiproliferative activity against renal cell carcinoma (RCC), using a modified human tumor clonogenic assay and clinically achievable concentrations. In preclinical experiments, the indirect (cytokine-mediated) antiproliferative activity of nIFN alpha was investigated using ACHN cells (established human RCC cell line). Continuous exposure to nIFN alpha at concentrations of more than 5 IU/ml in the presence of feeder cells (a mixture of 5 x 10(4) monocytes/dish and 5 x 10(5) lymphocytes/dish, obtained from healthy donors) significantly inhibited colony formation of ACHN cells in comparison with growth inhibition in the absence of feeder cells (P < 0.05). Various cytokines were measured in the supernatants lying over the medium on the feeder-layer agarose containing the same conditioned feeder cells. With IFN alpha at 500 IU/ml, tumor necrosis factor alpha (TNF alpha) and IFN gamma were detected at markedly high levels for 2-24 h. Neutralizing anti-TNF alpha monoclonal antibody significantly reduced the indirect antiproliferative activity. Using our modified human tumor clonogenic assay technique, sufficient numbers of colonies for drug testing were observed in 19 of 31 surgical specimens (61.3%). In these clinical materials, nIFN alpha at a clinically achievable concentration (50 IU/ml) significantly inhibited colony growth in the presence of feeder cells consisting of 5 x 10(4) monocytes/dish and 5 x 10(5) lymphocytes/dish, obtained from the patient whose tumor was examined (P < 0.05). In colony-forming cases, a significant correlation between the percentage colony survival and TNF alpha concentration in the supernatant was observed (r = -0.95, P < 0.01). These results suggest that this assay system may be an appropriate technique for evaluating the antiproliferative activities of nIFN alpha involving cytokine-mediated action, and that TNF alpha may play an important role in this cytokine-mediated activity.