Induction of mosaic sex-linked recessive lethals in the different germ cell stages of Drosophila melanogaster by bleomycin

Bleomycin, unlike other male-mouse mutagens, is most effective in spermatogonia, inducing primarily deletions

Dominant-lethal tests [P.D. Sudman, J.C. Rutledge, J.B. Bishop, W.M. Generoso, Bleomycin: female-specific dominant lethal effects in mice, Mutat. Res. 296 (1992) 205-217] had suggested that Bleomycin sulfate (Blenoxane), BLM, might be a female-specific mutagen. While confirming that BLM is indeed a powerful inducer of dominant-lethal mutations in females that fails to induce such mutations in postspermatogonial stages of males, we have shown in a specific-locus test that BLM is, in fact, mutagenic in males. This mutagenicity, however, is restricted to spermatogonia (stem-cell and differentiating stages), for which the specific-locus mutation rate differed significantly (P<0.008) from the historical control rate. In treated groups, dominant mutations, also, originated only in spermatogonia. With regard to mutation frequencies, this germ-cell-stage pattern is different from that for radiation and for any other chemical studied to date, except ethylnitrosourea (ENU). However, the nature of the spermatogonial specific-locus mutations differentiates BLM from ENU as well, because BLM induced primarily (or, perhaps, exclusively) multilocus deletions. Heretofore, no chemical that induced specific-locus mutations in spermatogonia did not also induce specific-locus as well as dominant-lethal mutations in postspermatogonial stages, making the dominant lethal test, up till now, predictive of male mutagenicity in general. The BLM results now demonstrate that there are chemicals that can induce specific-locus mutations in spermatogonia without testing positive in postspermatogonial stages. Thus, BLM, while not female-specific, is unique, (a) in its germ-cell-stage specificity in males, and (b) in inducing a type of mutation (deletions) that is atypical for the responding germ-cell stages (spermatogonia).

The effect of trifluoperazine on the genotoxicity of bleomycin in cultured human lymphocytes

The effects of trifluoperazine on the toxicity and mutagenicity of bleomycin were examined in cultured human lymphocytes. Lymphocyte cultures were initiated from three adult healthy non-smoking male volunteers. Cultures were exposed to the drugs for either three or twenty hours prior to cell collection. The toxic and clastogenic effects of the different treatments were represented by the reduction in the mitotic indices and the induction of chromosomal aberrations (CA) respectively. Both TFP and BLM significantly increased CA frequencies and reduced the mitotic indices (MI) following all treatments. The reduction in the mitotic indices and the increase in CA frequencies induced by the combined administration of both BLM and TFP were highly significant (p < or = 0.001), but they were not significantly different from the sum of those induced by the separate treatments with the two drugs. These combined treatments, however, potentiated the odds ratios compared to those of the separate drug treatments. Therefore, though the effect of TFP on the clastogenic and cytotoxic effects of BLM was additive, the observed potentiation of the odds ratios of the combined treatments compared to those of the separate treatments suggested a significant enhancement in the expected chemotherapeutic effects of BLM when administered with TFP.

The mutagenic and toxic effects of bleomycin and trifluoperazine in Drosophila melanogaster

The mutagenic and toxic effects of trifluoperazine and bleomycin on Drosophila were investigated in the progenies of males injected with 0.2 microliter of bleomycin and/or trifluoperazine. The Muller-5 method was used to study the induction of complete- and mosaic-sex-linked recessive lethals induced by 0.1 microgram/ml bleomycin and/or 0.1 mM trifluoperazine in the five successive broods, mainly representing the different stages of spermatogenesis. Trifluoperazine increased the induction rate of sex-linked recessive mutations above the spontaneous rates of the control, but these increases were not statistically significant at the 5% level27 in any of the five different broods. Contrary to trifluoperazine, bleomycin significantly (5% level)27 increased the induction rate of the complete sex-linked recessive lethals over those of the control in the meiotic and premeiotic broods C and D, and the meiotic brood E. As with the separate treatment with bleomycin, the frequencies of the complete sex-linked recessive lethals induced by the simultaneous combination treatment of 0.1 microgram/ml bleomycin and 0.1 mM trifluoperazine were significantly higher than those of the control at the 5%27 level, only in the meiotic and premeiotic broods, but they were not significantly higher than those induced by bleomycin treatment alone19. Treatments with 0.1 mM trifluoperazine enhanced the toxicity, sterility and the number of mutated clusters induced by 0.1 mM bleomycin but did not significantly increase the rates of induced lethals over the additive effects of both drugs in the meiotic and premeiotic stages, suggesting no potentiation effects for trifluoperazine over those of bleomycin in Drosophila. Higher concentrations of the two drugs could not be used due to their high toxicity and sterility effects.