| Abstract |
Epidemiological studies of 1,3-butadiene (BD) exposures have reported a possible association with chronic myelogenous leukemia (CML), which is defined by the presence of the t(9;22) translocation (Philadelphia chromosome) creating an oncogenic BCR-ABL fusion gene. Butadiene diepoxide (DEB), the most mutagenic of three epoxides resulting from BD, forms DNA-DNA crosslink adducts that can lead to DNA double-strand breaks (DSBs). Thus, a study was designed to determine if (±)-DEB exposure of HL60 cells, a promyelocytic leukemia cell line lacking the Philadelphia chromosome, can produce t(9;22) translocations. In HL60 cells exposed for 3 h to 0-10 μM DEB, overlapping dose-response curves suggested a direct relationship between 1,4-bis-(guan-7-yl)-2,3-butanediol crosslink adduct formation (R = 0.977, P = 0.03) and cytotoxicity (R = 0.961, P = 0.002). Experiments to define the relationships between cytotoxicity and the induction of micronuclei (MN), a dosimeter of DNA DSBs, showed that 24 h exposures of HL60 cells to 0-5.0 μM DEB caused significant positive correlations between the concentration and (i) the degree of cytotoxicity (R = 0.998, p = 0.002) and (ii) the frequency of MN (R = 0.984, p = 0.016) at 48 h post exposure. To determine the relative induction of MN and t(9;22) translocations following exposures to DEB, or x-rays as a positive control for formation of t(9;22) translocations, HL60 cells were exposed for 24 h to 0, 1, 2.5, or 5 μM DEB or to 0, 2.0, 3.5, or 5.0 Gy x-rays, or treatments demonstrated to yield 0, 20%, 50%, or 80% cytotoxicity. Treatments between 0 and 3.5 Gy x-rays caused significant dose-related increases in both MN (p < 0.001) and t(9;22) translocations (p = 0.01), whereas DEB exposures causing similar cytotoxicity levels did not increase translocations over background. These data indicate that, while DEB induces DNA DSBs required for formation of MN and translocations, acute DEB exposures of HL60 cells did not produce the Philadelphia chromosome obligatory for CML.
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