Influence of C6 and CNS1 brain tumors on methotrexate pharmacokinetics in plasma and brain tissue

Purpose: Comparison of the influence of two different brain tumors (C6 and CNS1 glioma) on methotrexate (MTX) disposition in plasma, brain, and tumor tissue extracellular fluid (ECF). Methods: Serial collection of plasma samples and brain ECF dialysates after i.v. bolus administration of MTX (50 mg kg(-1)) for 4 h. Quantitation of MTX concentrations by HPLC-UV. Results: Histological studies revealed a 3-fold higher number of blood vessels in CNS1 than in C6 tumor tissue. In vivo recoveries (reverse dialysis) were significantly different in tumor tissue (C6: 8.0 +/- 3.8%; CNS1: 4.9 +/- 2.5%), and in the contralateral hemisphere (C6: 6.0 +/- 4.0%; CNS1: 3.9 +/- 2.5%) between the two tumors. Area under the concentration-time curve (AUC) in plasma was 30% higher in CNS1 than in C6 due to a lower systemic clearance. Maximum MTX levels in brain tumor ECF were significantly higher in CNS1 than in C6, and decreased faster in CNS1 than in C6 tumor-bearing rats. Penetration in tumor ECF (AUC(ECF)/AUC(Plasma) ratio) was similar in CNS1 and C6. MTX concentrations in contralateral hemisphere were significantly lower than in tumor tissue and dependent on tumor model. Conclusion: C6 and CNS1 brain tumors have a distinct yet highly variable impact on MTX penetration in brain and brain tumor ECF.