Abstract
Methotrexate [MTX] is the cornerstone of chemotherapy for primary CNS lymphoma [PCNSL] yet how blood-brain barrier [BBB] efflux transporters ABCG2 and ABCC4 influence required high-dose therapy is unknown. To evaluate their role we used four mouse strains, C57/B6 [WT], Abcg2-/-, Abcc4-/-, and Abcg2-/-;Abcc4-/-(double knockout, DKO) and conducted brain microdialysis studies following single IV MTX doses of 50 mg/kg. Based on the AUCplasma to assess systemic exposure to MTX the rank order was Abcc4-/- < WT < Abcg2-/- < Abcg2-/-Abcc4-/-, with only the DKO exposure being significantly higher than the WT group (p<0.01), and a reflection of role of Abcg2 -in biliary excretion and Abcc4 in renal excretion. MTX brain interstitial fluid concentrations obtained by microdialysis were used to calculate the AUCbrain that found the rank order of exposure to be WT < Abcc4-/- < Abcg2-/- < Abcg2-/-Abcc4-/- with the largest difference being 4-fold; 286.13 ± 130 ug*min/ml (DKO) vs. 66.85 ± 26 (WT). Since the transporters affected the systemic disposition of MTX, particularly in the DKO group, the ratio of the AUCbrain/AUCplasma or the brain/plasma partition coefficient Kp was calculated and revealed that the double knockout strain had a significantly higher value [0.23 ± 0.09] than the WT strain [0.11 ± 0.05]. Both Abcg2 and Abcc4 limited BBB penetration of MTX, yet only when both drug efflux pumps were negated did the brain accumulation of MTX significantly increase. These findings indicate a contributory role of both ABCG2 and ABCC4 to limit MTX distribution in patients.
- The American Society for Pharmacology and Experimental Therapeutics