Purpose: Glioblastoma brain tumor and brain metastases from primary breast or lung cancer have limited treatment options, primarily due to the extremely invasive and aggressive nature of tumors; the largely impermeable blood-brain barrier (BBB); and presence of efflux transporters at BBB. We aimed to improve brain delivery of drugs by intravenous injection of a mixture of brain penetrating peptide K16ApoE and drug encapsulated long circulating nanoemulsions. We also explored the potential mechanisms that account for its brain delivery.
Methods: Oil-in-water nanoemulsions (NE) containing medium-chain triglycerides oil and co-surfactants were prepared by a spontaneous self-emulsification method (SNNE) and conventional high speed homogenization and sonication method (CNE). The nanoemulsions were mixed and injected with 20 nmol of K16ApoE peptide that comprising 16 lysine residues and 20 amino acids corresponding to the low-density lipoprotein receptor binding sequence from apolipoprotein E in healthy and tumor bearing mice.
Results: Nanoemulsions had mean particle size less than 200 nm (CNE: 190 nm,+35 mV; SNNE: 120 nm, -10 mV). In vitro, both NE was taken up by brain capillary endothelial cells bEnd.3 and glioblastoma cell U87-luc in a serum- dependent manner (10% FBS> 5%FBS> 2.5%FBS> serum free). Both the bEnd3 and U87-luc cells express high levels of an endocytic low density lipoprotein receptor-related protein 1 (LRP1) receptor. Using LRP1 antagonist receptor-associated protein (RAP) to block a ligand binding to LRP1 led to significant decrease of cellular uptake of NE. The addition of one of LRP1 ligand apolipoprotein E (12.5-25 μg/mL) in the serum free medium resulted in significantly higher cellular uptake of NE in bEnd3 cells and U87-luc cells, suggesting the NE can be imported into the brain and brain tumor cells by binding to apolipoprotein E via LRP1 receptor mediated transcytosis. In vivo, intravenous injection of near-infrared labeled NE significantly improved its brain accumulation in comparison to that of free dye. When 20 nmol of K16ApoE peptide and NE mixture was inject intravenously, the peptide transiently opened the BBB and allowed even higher amount of NE accumulation at brain tumor.
Conclusions: Our study demonstrates that nanoemulsion is a promising nanocarrier to deliver imaging or therapeutic agents for the diagnosis or systemic treatment of brain tumor or brain metastasis. K16ApoE peptide is a brain penetrating peptide and can help transport nanoparticles to the brain tissue without the need for chemical modification of surface of nanoparticles. Binding of nanoemulsion to apolipoprotein E and involvement of LRP1 receptor-mediated transcytosis could be important steps in mediating the uptake of nanoemulsion in the brain endothelial cells and brain tumor cells.
Citation Format: Xinli Liu, Tanvirul Hye. Targeting brain tumor and brain metastases using brain penetrating peptide and long circulating nanoemulsions. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2163.