Methods for determining chemosensitivity of MCF-7 cells in double-layer agar culture: labeling index depression and colony count inhibition.

An autoradiographic technique has been developed to determine the percentage of MCF-7 human breast adenocarcinoma cells in double-layer agar (DLA) culture that exhibit nuclear incorporation of 3H-thymidine (3H-TdR) after in vitro drug exposure. Depression of this percentage, termed the labeling index, correlated closely with colony count inhibition--relative to the respective control values--for cultures exposed to each of several agents including varying concentrations of 5-fluorouracil and adriamycin. If a similar autoradiographic technique can be applied to cultures from human tumor biopsy specimens, this may then lead to a clinically useful chemosensitivity assay especially applicable when DLA-cultured cell quantities are small.