A simplified tritiated thymidine incorporation assay for chemosensitivity testing of human tumors

Chemosensitivity testing was performed using a simplified rapid assay based on tritiated thymidine incorporation. In this assay, 1.5 X 10(5) tumor cells were cultured for 72 h in double-layer agarose in 25 mm plastic dishes, which had a Millipore membrane sealed to the underside. After 24 h labeling of the cells with tritiated thymidine, cells were collected on the membrane by evacuating the solubilized medium through the filter sealed to the underside of the dish, which was placed in a boiling water bath. The radioactivity of the collected cells was counted by liquid scintillation. We found that 65% of 68 malignant tumors gave evaluable chemosensitivity results. Overall, chemotherapeutic drugs caused a 38% response rate in vitro. Twenty instances were evaluable for in vitro-in vivo correlations. The predictive accuracies were 93% for resistance and 67% for sensitivity. The results indicate that, with technical simplicity and shorter time course (4 days), this assay may be useful for chemosensitivity testing in human tumors.