Effects of nitrosocarbaryl on BALB/3T3 cells

Carbaryl(N-methyl-1-naphthylcarbamate) and its nitrosated product, N-nitrosocarbaryl, were tested for their effects of BALB/3T3 (clone A31) cells in culture. Nitrosocarbaryl, but not carbaryl, caused transformation of the BALB/3T3 fibroblasts, but neither chemical induced the complete expression of endogenous murine leukemia virus. Transformed cells differed from the parental control cells by loss of contact inhibition, change in morphology, growth in soft agar, growth to higher saturation densities, and tumorigenicity in normal newborn and irradiated weanling mice and athymic (nude) mice. Transformed clones were found to be negative for expression of RNA tumor virus antigens, viral reverse transcriptase, and infectious virus. Thus, it appears that nitrosocarbaryl can transform BALB/3T3 cells to tumorigenic cells with altered biological properties but without complete activation of RNA tumor viruses in the transformed cells. Expression of viral antigen in the transformed cells was inducible by iododeoxyuridine, indicating that the endogenous viral genome was retained in an unexpressed state.