Cloning ovarian carcinoma cells in an agar double layer versus a methylcellulose monolayer system. A comparison of two methods.

Human ovarian cancer cells from ten patients were cultured in the agar double layer assay as described by Hamburger and Salmon and in a methylcellulose monolayer system. The assays were compared under the same experimental conditions. The rate of positives (defined as greater than 30 colonies/dish) was 75% in the methylcellulose assay and 69% in the agar double layer. Plating efficiency ranged in the methylcellulose assay between 0.021% and 0.089% and in the agar double layer from 0.015% to 0.094%. Cytological and cytochemical staining of cells obtained from colonies in both test systems and of the tumour cells prior to plating revealed the same morphology. The methylcellulose monolayer system requires less additives than necessary in the agar double layer system. Furthermore, it is easier to handle with respect to the plating procedure and less time consuming. In addition, the effect of the anti-oestrogen tamoxifen on colony formation was tested. The dose response curves for colony formation with tamoxifen proved to be identical in both systems. At a concentration of 10(-6) M an inhibition of colony formation of more than 70% of controls was observed in the agar and in the methylcellulose system.