Title Involvement of multidrug resistance-associated protein 1 in intestinaltoxicity of methotrexate

Purpose: Methotrexate (MTX) causes dose-limiting gastrointestinal toxicity due to exposure of intestinal tissues, and is a substrate of the multidrug resistance-associated protein (MRP) 1. Here we examine the involvement of MRP1, which is reported to be highly expressed in the proliferative crypt compartment of the small intestine, in the gastrointestinal toxicity of MTX. Methods: MTX was intraperitonealy administered to mrp1 gene knockout (mrp1) and wild-type (mrp1) mice. Body weight, food and water intake were monitored, intestinal histological studies and pharmacokinetics of MTX were examined. Results: mrp1 mice more severely decreased body weight, food and water intake than mrp1 mice. Almost complete loss of villi throughout the small intestine in mrp1 mice was observed, whereas the damage was only partial in mrp1 mice. Plasma concentration and biliary excretion profiles of MTX were similar in mrp1 and mrp1 mice, though accumulation of MTX in immature proliferative cells isolated from mrp1 mice was much higher compared to mrp1 mice. Immunostaining revealed localization of Mrp1 in plasma membrane of the intestinal crypt compartment in mrp1 mice, but not in mrp1 mice. Conclusion: Mrp1 determines the exposure of proliferative cells in the small intestine to MTX, followed by gastrointestinal toxicity.