The use of clonogenic assays in assessing the response of human lung cancer cell lines to alpha and gamma interferons alone or in combination with adriamycin

The antiproliferative and cytotoxic effects of purified IFN-alpha and recombinant IFN-gamma were investigated using both direct cell counting and a clonogenic assay on a panel of 5 established human lung cancer cell lines and for 2 of them also on their multidrug-resistant counterparts. There was considerable heterogeneity in the response of the cell lines to the IFNs in terms of growth inhibition. Clonogenic assay of IFN-treated cells indicated that, where a cell line had responded markedly to an IFN, only a small fraction of the cells remaining after IFN treatment were clonogenically viable. When cells were placed into the clonogenic assay in the presence of IFNs, the time course of colony formation was different from that seen in the control cultures for most of the cell lines. The measured "surviving fraction" was greatly dependent upon the time of colony counting. When the effects of IFNs in combination with ADM were studied, conclusions regarding the interaction of the effects of the agents also depended upon the time at which colonies were counted.