Usefulness of abrin as a positive control for the human tumor clonogenic assay

Abstract

A series of approaches were tested in order to develop a simple technique for introducing a routine positive control into the Human Tumor Clonogenic Assay. Of the various techniques tested, the best proved to be the addition of the toxic plant lectin abrin to the culture system. When added to the agar underlayer of the culture system so that the final abrin concentration in culture was 10 μg/ml, survival of human tumor colonyforming units (TCFU) was reduced to <1% of control in 16/34 (47%) of human tumors, to < 10% in 33/34 (97%) and to <30% in all tumors tested (100%). A clear dose-response relationship to fractional survival was observed for individual tumors tested at multiple dose levels of abrin. When the dosage of abrin was reduced to 1 μg/ml, survival of TCFU was reduced to <30% in 25/28 (89.2%) of experiments. Inclusion of abrin controls in clonogenic assays thus provides an excellent and reproducible positive control to which cytotoxic effects of a variety of therapeutic agents can be compared.