SLCO1B1 and acute lymphoblastic leukemia: SLCO1B1 encodes one of the main influx transporters expressed on the basolateral membrane of hepatocytes involved in uptake and clearance of many endogenous compounds and drugs, such as methotrexate.39SLCO1B1 rs4149056 and rs2306283 were associated with decreased membrane expression and activity of the transporter.39,40 Rs11045879 was identified in a genome-wide association study as the most important genetic factor associated with lower methotrexate clearance in patients with ALL.