Window of opportunity evaluation of blood-brain barrier permeability heterogeneity within and across high-grade glioma patients.

Background: Disruption of the blood-brain barrier (BBB) in high-grade brain tumors is characterized by contrast accumulation on diagnostic imaging. This window of opportunity study correlates contrast imaging features with the tumor distribution of BBB-permeable (levetiracetam) and -impermeable (cefazolin) drugs.

Methods: Patients with a clinical diagnosis of a high-grade brain tumor underwent MRI for surgical planning. Cefazolin and levetiracetam were administered prior to skin incision, and serial plasma and image-registered tumor samples were collected during the operation. Drug levels were measured by LC-MS/MS, tissue drug levels were corrected for residual blood, and tumor-to-plasma concentration ratios were calculated. Intraoperative microdialysis was performed in a subset of patients to measure the same two drugs.

Results: Tumor (n=125) and plasma (n=261) samples were available for analysis from 42 operative cases. Across all samples, the tumor-to-plasma ratio was significantly lower for cefazolin (marginal mean (MM): 0.15, 95% CI: 0.11-0.19) as compared to levetiracetam (MM: 0.70, 95% CI: 0.64-0.75; p<0.001). When compared between contrast-enhancing and non-enhancing regions, tumor-to-plasma ratios for cefazolin varied by 4.4-fold (0.27, 95% CI: 0.20-0.35 vs. 0.06, 95% CI: 0.04-0.08, respectively; p<0.001), and varied for levetiracetam by 1.4-fold (0.88, 95% CI: 0.78-0.97 vs. 0.61, 95% CI: 0.55-0.66, respectively; p<0.001). These results were confirmed with the intra-operative microdialysis and a population pharmacokinetic analysis.

Conclusions: This study demonstrates significant inter- and intra-tumoral heterogeneity in drug delivery for both levetiracetam and cefazolin within high-grade brain tumors that is not necessarily predicted by clinical MR-imaging and may reflect tumor-induced changes in both perfusion and BBB integrity.