Assessment of brain delivery of a model ABCB1/ABCG2 substrate in patients with non-contrast-enhancing brain tumors with positron emission tomography.

Abstract

BACKGROUND:

P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) are two efflux transporters expressed at the blood-brain barrier which effectively restrict the brain distribution of the majority of currently known anticancer drugs. High-grade brain tumors often possess a disrupted blood-brain tumor barrier (BBTB) leading to enhanced accumulation of magnetic resonance imaging contrast agents, and possibly anticancer drugs, as compared to normal brain. In contrast to high-grade brain tumors, considerably less information is available with respect to BBTB integrity in lower grade brain tumors.

MATERIALS AND METHODS:

We performed positron emission tomography imaging with the radiolabeled ABCB1 inhibitor [11C]tariquidar, a prototypical ABCB1/ABCG2 substrate, in seven patients with non-contrast -enhancing brain tumors (WHO grades I-III). In addition, ABCB1 and ABCG2 levels were determined in surgically resected tumor tissue of four patients using quantitative targeted absolute proteomics.

RESULTS:

Brain distribution of [11C]tariquidar was found to be very low across the whole brain and not significantly different between tumor and tumor-free brain tissue. Only one patient showed a small area of enhanced [11C]tariquidar uptake within the brain tumor. ABCG2/ABCB1 ratios in surgically resected tumor tissue (1.4 ± 0.2) were comparable to previously reported ABCG2/ABCB1 ratios in isolated human micro-vessels (1.3), which suggested that no overexpression of ABCB1 or ABCG2 occurred in the investigated tumors.

CONCLUSIONS:

Our data suggest that the investigated brain tumors had an intact BBTB, which is impermeable to anticancer drugs, which are dual ABCB1/ABCG2 substrates. Therefore, effective drugs for antitumor treatment should have high passive permeability and lack ABCB1/ABCG2 substrate affinity.

TRIAL REGISTRATION:

European Union Drug Regulating Authorities Clinical Trials Database (EUDRACT), 2011-004189-13. Registered on 23 February 2012, https://www.clinicaltrialsregister.eu/ctr-search/search?query=2011-004189-13.

• Authors: Beatrix Wulkersdorfer, Martin Bauer, Rudolf Karch, Harald Stefanits, Cécile Philippe, Maria Weber, Thomas Czech, Marie-Claude Menet, Xavier Declèves, Johannes A Hainfellner, Matthias Preusser, Marcus Hacker, Markus Zeitlinger, Markus Müller, Oliver Langer
• Journal: EJNMMI research (EJNMMI Res) Vol. 9 Issue 1 Pg. 110 (Dec 12 2019) ISSN: 2191-219X [Print] Germany
• PMID: 31832814 (Publication Type: Journal Article)