A microplate assay for selective measurement of growth of epithelial tumor cells in direct coculture with stromal cells.

Stromal cells play an important role in regulating epithelial malignancies through diffusible factors and adhesion. Modulation of the tumor-stromal cell interaction is an attractive target for new antitumor strategies. To screen for a modulator of the interaction, we have now developed a quantitative colorimetric assay for measurement of tumor cell growth in coculture with stromal cells using rhodanile blue dye. Rhodanile blue specifically stained cytokeratin-positive tumor cells in the coculture. When human prostate carcinoma cells LNCaP, PC-3 and DU-145 were cocultured with normal prostate stromal cells (PrSC) in a microplate, growth of the prostate cancer cells in the coculture was selectively measured by the rhodanile blue staining method. Using this system, we searched for a modulator of the tumor-stromal cell interaction among clinically used drugs and natural products. As a result, we found that 5-fluorouracil, bleomycin and phthoxazolin A inhibit prostate cancer cell growth more strongly in coculture with PrSC than that in monoculture. Without need to pre-label cells and transfect a marker gene, our new method is simple, rapid and thus useful for screening for modulators of the tumor-stromal cell interaction. Furthermore, our results suggest that low molecular weight compounds modulate the tumor-stromal cell interaction.