Properties of cell lots suitable for focus assay in the chemical transformation of Syrian hamster cells in culture.

Various lots of cells obtained from Syrian hamster tissues were examined to determine their suitability for focus assay in chemical transformation in culture. Only a few lots of cells showed growth with sparse cell density during cultivation for 3 weeks without subcultivation, and not all lots of cells produced morphologically transformed foci after treatment with a carcinogen. Further, responsiveness to a tumor promotor, 12-O-tetradecanoly phorbol-13-acetate (TPA), differed among different cell lots; cell lots which induced abundant growth consisting of small spindle-shaped multilayered cells upon treatment with TPA corresponded to those in which carcinogen treatment induced transformed colonies. When TPA was applied in transformation experiments, the morphologically transformed foci grew larger in cultures maintained in the TPA medium than in cultures kept in the TPA-free medium. We suggest that cell lots which show relatively sparse cell density at confluent culture and which show abundant growth consisting of small multilayered cells upon induction with TPA are suitable for transformation assay.