Impact of global ultrasound-induced blood-brain barrier opening on the distribution of full monoclonal antibody cetuximab

Abstract

Aim/Introduction Epidermal growth factor receptor (EGFR), involved in cell proliferation and migration, is overexpressed in 50% of glioblastomas that amplify wild type EGFR. This suggests a relevance for molecularly-targeted therapy using anti-EGFR based strategies using monoclonal antibodies (mAb), such as cetuximab, for therapy. Clinical trials have shown the beneficial effects of cetuximab in various EGFR-expressing peripheral tumors, but failed in patients with recurrent glioblastoma. One of the main issues is the poor penetration of mAb into the central nervous system (CNS) due to the presence of the blood-brain barrier (BBB). Recently, ultrasound (US) in combination with microbubbles has been used to transiently open the BBB and promote the delivery of therapeutic agent to CNS. Non-invasive, dynamic and quantitative methods such as PET imaging using radiolabeled mAb may provide a translational imaging method to address the efficacy of US for the delivery of mAb into brain. Materials and Methods Cetuximab was conjugated to DFO and labeled with 89Zr at 0.5 MBq/μg. Affinity comparison between human and murine EGFR with cetuximab has been done to accurately measure kinetic constants. In vivo PET imaging and biodistribution were conducted in healthy nude male mice (no US vs US groups, n = 8) in order to follow the kinetics of the 89Zr-Cetuximab overtime. Brain uptake of 89Zr-Cetuximab was initially monitored by whole body dynamic PET, followed by static PET-CT imaging at different time points post-injection. The TACs allowed the determination of the transfer rate constants between the blood and the brain. Results Cetuximab exhibits an approximate 10-fold greater affinity with human EGFR compared to mouse counterpart. In control mice, the brain distribution of 89Zr-Cetuximab was negligible (transfer rate = 0 ± 0.006 min-1). The transfer rate increased up to 1.3 ± 0.23 min-1 when US were applied. The brain uptake without US remained constant at 0.7 ± 0.09%ID/cc overtime whereas it reached 1.34 ± 0.15%ID/cc at 1 h and stay stable during 48 hours with US (1.36% ± 0.16%ID/cc). After 72 h post-US, no significant difference between the US and the control cohorts was observed. Conclusion Here, PET imaging was successfully combined with therapeutic US to demonstrate the efficiency of this strategy for mAb delivery into brain which raises potential application for tumor treatment.