Differentiated and exponentially growing HL60 cells exhibit different sensitivity to some genotoxic agents in the comet assay

Abstract

The aim of this study was to investigate the effect of the cell differentiation status on the sensitivity to genotoxic insults. For this, we utilized the comet assay to test the DNA damage after treatment with 5 different substances with different mechanism of action in human promyelocytic HL60 cells with or without cell differentiation. A 4-hour MMS treatment induced a significant and concentration-dependent increase in DNA damage for both differentiated and undifferentiated cells, but the difference in sensitivity was only significant at the highest concentration. A 4-hour doxorubicin treatment did not induce DNA damage in differentiated HL60 cells, while it did in undifferentiated cells with its highest tested concentration. A one-hour etoposide treatment caused significant increase in DNA damage concentration dependently in both cell variants. This DNA damage was significantly higher in undifferentiated HL60 cells with several tested concentrations of etoposide. The treatment with the oxidizing substances hydrogen peroxide and potassium bromate yielded significant DNA damage induction in both undifferentiated and differentiated cells with no difference according to the differentiation status. Doxorubicin and etoposide are known to inhibit topoisomerase II. The activity of this enzyme has been shown to be higher in undifferentiated actively proliferating cells than in differentiated cells. This may be of relevance when exposures to topoisomerase-inhibiting compounds or the genotoxicity of compounds with unknown mechanism of action are assessed in routine testing.