Differences in the distribution of methotrexate into high grade gliomas following intravenous administration, as monitored by microdialysis, are associated with blood brain barrier integrity

Abstract

1548 Background: Microdialysis (MD) is an accepted technique to monitor neurochemicals in pts with traumatic brain injury. This study was conducted to evaluate the use of MD to define the time course of intratumoral drug concentrations in pts with high grade gliomas (HGG) receiving systemic chemotherapy. Methods: MD catheters were placed in residual HGG following tumor debulking and infused with Ringer’s solution at 1 μL/min. MD probe location and integrity of the blood brain barrier (BBB) in adjacent tissue were determined by fused MRI/CT. Highdose (12g/m2) methotrexate (MTX), was given as a 4 h iv infusion the next day. MTX was measured in plasma and dialysate samples, collected at 30 min intervals from 1 h before to 24 h after dosing, with an LC/MS assay. Results: Six pts have been enrolled without any adverse events attributed to the MD catheter. Adequate pharmacokinetics (PK) were obtained in 4/6pts. MTX plasma pharmacokinetics (PK) were very consistent between the 4 evaluable pts and similar to published data. Time courses of the uncorrected MTX concentration in extracellular fluid (CECF) exhibited two distinctly different kinetic profiles. For 2pts in whom the MD probe resided within contrast enhancing tumor, CECF increased and decreased in parallel with drug levels in plasma, with a peak CECF of 189 ± 6 μM, an apparent elimination half-life in ECF of 4.44 ± 0.07 h, and an ECF/plasma AUCratio of 0.13 ± 0.01. The other 2pts had a much lower peak CECF (10.4 ± 0.4 μM) and AUC ratio (0.028 ± 0.020), with a more prolonged ECF half-life (11.4 ± 4.5 h). Fused images from 2 of these pts showed that the MD probe was located in nonenhancing tissue. Conclusions: MD is a clinically practical technique to monitor the distribution of systemically administered drugs to brain tumors in pts. It has the capability to elucidate variations in kinetic behavior that are consistent with regional differences in BBB integrity. Appropriate interpretation of data from MD studies to evaluate the distribution of investigational new drugs into brain tumors necessarily requires radiographic determination of the region of the tumor into which the probe has been placed. No significant financial relationships to disclose.