Comparison of thioguanine phenotypes in primary astrocyte cultures of each <i>Tpmt</i> genotype.

<p>(a) Primary astrocytes of each <i>Tpmt</i> genotype were exposed to thioguanine (TG) and cell viability was determined using the MTT assay. <i>Tpmt^+/−</i> and <i>Tpmt^−/−</i> astrocytes were significantly more sensitive to TG (12.5–100 µM) than <i>Tpmt^+/+</i> (p<0.04). (b) IC₅₀ values were significantly different between the three genotypes (p = 0.027) and <i>Tpmt^+/−</i> astrocytes were the most sensitive. (c) The alkaline comet assay was used to compare TG-induced DNA damage between genotypes. <i>Tpmt^+/−</i> and <i>Tpmt^−/−</i> astrocytes had significantly higher mean comet tail moments than <i>Tpmt^+/+</i> astrocytes (p = 0.033). (d) Immunoflourescence staining for γH2AX confirms IC₅₀ and comet data. <i>Tpmt^+/−</i> astrocytes had greater damage than <i>Tpmt^+/+</i>(p = 0.03). Below are representative images of γH2AX staining for control treated (left) and TG treated (right) astrocytes. γH2AX foci stained in green; nuclei stained in red (Zeiss LSM 710 Laser Scanning Microscopes, 400× magnification). Bars represent the means; whiskers represent the standard deviation (±); * p<0.05.