Syrian Hamster Embryo (SHE) cell transformation assay with and without X-ray irradiation of feeder cells using Di(2-ethylhexyl)phthalate (DEHP) and N-nitroso-N-methylnitroguanidine (MNNG)

With freshly prepared conditioned medium (used within 2 weeks of preparation), there was essentially no difference in the number of target cell colonies in the conditioned medium and in the plates with the X-ray irradiated feeder cell layer. The plating efficiencies of the vehicle controls were within the historical range for the standard SHE cell transformation assay. In more than ten experiments the positive control benzo(a)pyrene [B(a)P] elicited a significant increase in morphological transformation frequency (MTF), with or without X-ray irradiated feeder cells. Compounds, DEHP and MNNG, were tested in the SHE cell transformation assay with and without an X-ray irradiated feeder layer and using a 7-day exposure regimen. The results were comparable between experiments performed using either method. These results demonstrate the feasibility of conducting the SHE cell transformation assay without the use of an X-ray irradiated feeder layer, thereby simplifying the test procedure and assisting the scoring of morphologically transformed colonies.