Objective: Doxorubicin-induced acute cardiotoxicity is associated with the Gly671Val (G671V; rs45511401) variant of multidrug resistance-associated protein 1 (MRP1). Doxorubicin redox cycling causes lipid peroxidation and generation of the reactive electrophile, 4-hydroxy-2-trans-nonenal (HNE). Glutathione forms conjugates with HNE, yielding an MRP1 substrate, GS-HNE, whose intracellular accumulation can cause toxicity.
Methods: We established stable HEK293 cell lines overexpressing wild-type MRP1 (HEKMRP1), G671V (HEKG671V), and R433S (HEKR433S), a variant not associated with doxorubicin-induced cardiotoxicity and investigated the sensitivity of HEKG671V cells to doxorubicin and transport capacity of G671V toward GS-HNE.
Results: In ATP-dependent transport studies using plasma membrane-derived vesicles, the Vmax (pmol/min/mg) for GS-HNE transport was the lowest for G671V (69±4) and the highest for R433S (972±213) compared with wild-type MRP1 (416±22), whereas the Km values were 2.8±0.4, 6.0 or more, and 1.7±0.2 µmol/l, respectively. In cells, the doxorubicin IC50 (48 h) was not different in HEKMRP1 (463 nmol/l) versus HEKR433S (645 nmol/l), but this parameter was significantly lower in HEKG671V (181 nmol/l). HEKG671V retained significantly (approximately 20%) more, whereas HEKR433S retained significantly less intracellular doxorubicin than HEKMRP1. Similarly, HEKG671V cells treated with 1.5 µmol/l of doxorubicin for 24 h retained significantly more GS-HNE. In cells treated with 0.5 µmol/l of doxorubicin for 48 , glutathione and glutathione disulfide levels and the glutathione/glutathione disulfide ratio were significantly decreased in HEKG671V versus HEKMRP1; these values were similar in HEKR433S versus HEKMRP1.
Conclusion: These data suggest that decreased MRP1-dependent GS-HNE efflux contributes to increased doxorubicin toxicity in HEKG671V and potentially in individuals carrying the G671V variant.