Genotoxicity of the histone deacetylase inhibitor trichostatin A: Evidence for both aneugenic and clastogenic effects

806 Histone deacetylase inhibitors (HDACi) are a class of putative chemotherapeutic agents for which the mechanism of toxicity remains largely unknown. The possibility that HDACis may be genotoxic has not been thoroughly investigated. To explore this possibility we exposed human lymphoblastoid TK6 cells to the HDACi trichostatin A (TSA) and analyzed various measures of genetic damage. Numerical and structural chromosomal aberrations were analyzed using the kinetochore-antibody micronucleus assay and non-banding metaphase chromosome analysis while DNA strand breaks were investigated with the alkaline comet assay. Significant increases in structural chromosomal aberrations and kinetochore-negative micronuclei were detected at the 100 and 200nM TSA doses, whereas significant levels of aneuploidy were only observed at the 200nM dose using metaphase analysis. Therefore TSA is a clastogenic agent that also induces aneuploidy via non-dysjunction in the TK6 cell line. Increased olive tail moments of TK6 cells exposed to TSA add supportive data that TSA is a DNA damaging agent. Patterns obtained from flow cytometric analysis of annexin V staining TK6 cells indicated that genotoxicity occurs in the absence of apoptosis at all but the highest concentration of TSA suggesting that the observed genotoxicity is not a byproduct of apoptosis, but rather may be the cause of it. Flow cytometric analysis of asynchronous TK6 cells stained with propidium iodide demonstrated that TSA causes a G1 arrest prior to the occurrence of apoptosis, further evidence to indicate that TSA is a genotoxic agent. Current studies are focusing on the temporal relationship between the TSA-induced genotoxicity, cell cycle arrest, and apoptotic signals to identify if the apoptosis is due to a genotoxic-dependent or -independent mechanism. We conclude that TSA causes both chromosomal breakage and non-dysjunction in TK6 cells and postulate that the TSA-induced apoptosis observed at high doses may partially be due to this genotoxicity.