The benzene metabolite para-benzoquinone is genotoxic in human, phorbol-12-acetate-13-myristate induced, peripheral blood mononuclear cells at low concentrations

Benzene is one of the most prominent occupational and environmental pollutants. The substance is a proven human carcinogen that induces hematologic malignancies in humans, probably at even low doses. Yet knowledge of the mechanisms leading to benzene-induced carcinogenesis is still incomplete. Benzene itself is not genotoxic. The generation of carcinogenic metabolites involves the production of oxidized intermediates such as catechol, hydroquinone and para-benzoquinone (p-BQ) in the liver. Further activation to the ultimate carcinogenic intermediates is most probably catalyzed by myeloperoxidase (MPO). Yet the products of the MPO pathway have not been identified. If an oxidized benzene metabolite such as p-BQ was actually the precursor for the ultimate carcinogenic benzene metabolite and further activation proceeds via MPO mediated reactions, it should be possible to activate p-BQ to a genotoxic compound in vitro. We tested this hypothesis with phorbol-12-acetate-13-myristate (PMA) activated peripheral blood cells exposed to p-BQ, using the cytokinesis-block micronucleus test. Addition of 20–28 ng/ml PMA caused a significant increase of micronuclei at low and non-cytotoxic p-BQ concentrations between 0.04 and 0.2 μg/ml (0.37–1.85 μM). Thus with PMA or p-BQ alone no reproducible elevation of micronuclei was seen up to toxic concentrations. PMA and p-BQ induce micronuclei when administered jointly. Our results add further support to the hypothesis that MPO is a key enzyme in the activation of benzene

Inheritance of immunogenicity and metastatic potential in murine cell hybrids from the T-lymphoma ESb08 and normal spleen lymphocytes

T-lymphoma cells were fused with normal lymphoid cells to examine the segregation of tumorigenicity and metastatic capacity in the hybrids. In independent fusions the immunogenic ESb08 T-lymphoma line fused successfully with normal syngeneic spleen cells (from DBA/2 and CD1 mice) enriched either with T-cells or B-cells. Ten times fewer hybrids were obtained with B-cells compared to the number obtained with T-cells, and marker assays showed that both types of fusions preferentially generated T-T hybridomas. Some of the hybrids resembled their tumor parent in their ability to form primary and secondary tumors only in irradiated DBA/2 mice, whereas other hybrids lost the high ESb08 immunogenicity, were equally tumorigenic, and in some cases metastatic, in nonirradiated mice. DNA distributions of the original hybrid lines ranged from a hexaploid DNA content (expected for complete hybrids derived from a tetraploid line and normal diploid cells) to a tetraploid DNA content, confirming the reported chromosome instability of T-T hybrids. No correlation was noted between the initial DNA content and tumorigenicity, but in the case of complete hybrids, reduction in the ploidy levels always was observed in the cells of primary and metastatic lesions. One chromosomally stable and highly malignant hybrid (C2), which was analyzed for segregation of chromosomes and for drug-resistance markers, showed preferential loss of chromosomes from the normal T-cell fusion partner. The decreased immunogenicity of this hybrid could not be related to any detectable loss of chromosomes from the ESb08 tumor parent