Effects of TNF-alpha and retinoic acid on the proliferation of the clear cell and chromophilic types of human renal cell carcinoma in vitro.

Since no effective therapeutic approach is known so far for metastatic renal cell carcinoma (RCC), we analyzed the anti-proliferative effects of TNF-alpha and retinoic acid (RA), applied either alone or in combination on 7 different RCC cell lines in vitro. In 5 out of 7 cell lines, a significant (p < 0.05) dose-dependent inhibition of tumor cell proliferation became evident after exposure to TNF-alpha, the response being of modest magnitude in 5 cell lines. In 2 cell lines the effects were more pronounced with a reduction of cell viability to 55 +/- 11% of the control. Northern blot analysis revealed no expression of TNF-alpha and p75 TNF-receptor in any cell line. All the cell lines showed p55 TNF-receptor mRNA. Scatchard analysis revealed no correlation between TNF-alpha receptor status and growth inhibitory response to TNF-alpha, the number of TNF-receptors per cell ranging from 0 to 3,976, and the affinity values from Kd = 0.621 nmol/l to Kd = 4.28 nmol/l. Exposure to RA alone resulted in significant (p < 0.05), but modest growth inhibition in 2 out of 7 cell lines with a reduction of cell viability to 83 +/- 1% of the control. In 2 out of 7 cell lines, combination of RA and TNF-alpha was significantly (p < 0.05) more effective than the single application of each compound. Northern blot analysis revealed no transcripts of CRABP I and retinoic acid receptor (RAR)-beta. All the cell lines expressed RAR-alpha mRNA and one cell line additionally expressed RAR-gamma mRNA. A correlation between RAR status and RA response was not seen.