Differentiation of the mechanism of micronuclei induced by cysteine and glutathione conjugates of methylenedi-p-phenyl diisocyanate from that of 4,4'-methylenedianiline

Comparative evaluation of three methylene dianiline isomers in the bacterial reverse mutation assay, the in vitro gene mutation test, and the in vitro chromosomal aberration test

4,4'-MDA is classified as a genotoxic carcinogen based on numerous in vitro and animal data. The consequential assumption that a safe threshold does not exist is not only applied to 4,4'-MDA but also to its structural isomers and impurities 2,2'- and 2,4'-MDA in the absence of substance-specific data. This constitutes a problem in human risk assessments for all three substances as the inherent risks of 2,2'- and 2,4'-MDA and their contribution as impurities to that of 4,4'-MDA are essentially unknown. A comparative in vitro genotoxicity dataset consisting of the bacterial reverse mutation (Ames) test and the chromosomal aberration test in human lymphocytes (both performed according to the current OECD Guidelines) was generated for all three isomers. Furthermore, an in vitro gene mutation test in Chinese hamster ovary (CHO) cells (HPRT locus assay) was conducted with 2,4'-MDA. The results indicate differences regarding the genotoxic mechanism and potential, respectively, between the three structures and suggest that the no-threshold assumption for 4,4'-MDA may not be appropriate for 2,2'- and 2,4'-MDA.

Synthesis of minoxidil conjugates and their evaluation as HL-60 differentiation agents

Activation of minoxidil (MNX) with N,N'-carbonyldiimidazole and coupling with natural polyamines (PAs) and commercially available aliphatic or aromatic amines provided a series of new conjugates which were evaluated for their ability to induce differentiation to HL-60 acute myeloid leukemia cancer cells, using a modified NBTZ reduction test. Although neither MNX nor 4,4'-methylenedianiline (MDA) or 2,7-diaminofluorene (DAF), alone or in combination, had any effect, the MNX-spermine (SPM) conjugate (11) and the conjugates 7 and 8 of MNX with MDA and DAF exhibited a differentiation-inducing effect at a concentration of 10 μM without being toxic on proliferating human peripheral blood mononuclear cells.