A NOVEL CELL-BASED ASSAY FOR THE EVALUATION OF ANTI-RAS COMPOUNDS

In order to identify drugs active against mutated ras oncogenes we hav e developed an in vitro assay employing two clones of the human fibros arcoma cell-line, HT1080 which carries an N-ras gene mutated at codon 61. Clone, HT1080scc2, retains the transformed phenotype of the parent al line, whilst the other, HT1081c, is a morphologically flat, non-tum ourigenic, revertant with under-representation of the chromosome carry ing the transforming N-ras allele. The clear implication of mutant ras in maintaining the transformed nature of HT1080scc2 was confirmed whe n these cells were microinjected with the pan ras neutralising antibod y Y13-259, which resulted in the morphological detransformation of the se cells to a phenotype resembling that of the HT10801c clone. A numbe r of known anti-cancer drugs with modes of action unrelated to ras fun ction were found to be equipotent against both clones. However, when c ompounds chosen on the grounds of their potential selective cytotoxic or differentiating activity were tested some interesting results were obtained. Thus 8-bromo cAMP affected some morphological detransformati on of HT1080scc2 cells and reduced their colony forming potential. The IMP-dehydrogenase inhibitors, tiazafurin and mycophenolic acid also f lattened the morphology of the transformed clone. Fumagillin, an antib iotic reported to exhibit selective activity against ras transformed c ells showed very marked and selective cytostatic effects against HT108 0scc2 cells with IC50 values as low as 1 x 10(-11) M.