Comparison of an antimetabolic assay and an antiproliferative assay, both using ³ h‐thymidine incorporation, to test drug sensitivity of human tumors

Abstract

Two assays based on the inhibition of 3H-thymidine incorporation into DNA were used to measure either the antimetabolic or the antiproliferative effects of anticancer drugs. A direct comparison of the two assays was made with cell suspensions obtained from 11 ovarian cancers and 22 malignant melanomas. Drugs with different effects on cell cycle phases were tested by both assays, for a total of 53 drug comparisons. When the sensitivity indices specific for each system was used, a significant association (p less than 0.01) was noted between the two assays. The agreement of both assays in defining in vitro sensitivity or resistance was 100% for ovarian cancer. For melanoma, 97% of samples resistant to the antimetabolic assay were also resistant to the antiproliferative assay; whereas, only 45% of samples sensitive to the antimetabolic assay were sensitive to the antiproliferative assay.

Combination chemotherapy tested in a short‐term thymidine incorporation assay in primary cultures of ovarian adenocarcinomas

“…Also it is possible that further interactive or additive effects among the drugs tested may occur at later times which could not be seen by this assay which measures effects on thymidine incorporation into DNA after three hours incubation with drug. In other studies, we have observed greater effects on DNA synthesis after 24-hour drug incubation, and increased inhibition is also seen in three-day antiproliferative assays [32]. Nevertheless, time-dependent drug effects [36] d o not seem to have led to false negative clinical correlations in the three-hour assay [32].…”

“…In other studies, we have observed greater effects on DNA synthesis after 24-hour drug incubation, and increased inhibition is also seen in three-day antiproliferative assays [32]. Nevertheless, time-dependent drug effects [36] d o not seem to have led to false negative clinical correlations in the three-hour assay [32].…”

“…The 80% cut-off level used in this study was chosen for its previous clinical correlation [5, 61 and also has been used by the Milan group [9, 321. based on a similar short-term assay. Dose response curves in the short-term "antimetabolic" assay do not reach the levels of inhibition of thymidine incorporation seen in antiproliferative assays over three days, as shown recently by direct comparison on the same samples [32]. However, this seems not to affect the assessment of tumor sensitivity due to the different cut-off level used as judged by comparison of the two assays [8, 321 or by correlation with clinical results [5-81.…”