Engineering blood-brain barrier-permeable and tumor cell-ingestible pro-proteins for glioblastoma treatment

Intracellular protein therapeutics holds great potentials for the treatment of glioblastoma, which however, is greatly challenged by the unmet demands to concomitantly penetrate the blood-brain barrier (BBB) and glioblastoma cell membrane barrier with high efficiency and selectivity. Herein, a unique pro-protein platform was developed via facile green synthesis, which allowed efficient and selective delivery into glioblastoma cells in a carrier-free manner. Pro-proteins were engineered via reversible modification of native proteins in the aqueous buffer with 3,4-dihydroxy-phenylalanine, the substrate of L-type amino acid transporter (LAT1), bridged with a phenylboronic acid-containing linker. By harnessing the LAT1-mediated direct transport mechanism, the optimized pro-protein, named protein-M2-D, can efficiently penetrate BBB after i.v. injection, and subsequently enable selective and endocytosis-free delivery of various proteins including enzymes, toxins, and antibodies into glioblastoma cells, wherein intracellular H2O2 triggered traceless restoration of the native protein structure. Systemic administration of saporin-M2-D provoked potent anti-tumor efficacy against orthotopic U87 glioblastoma in mice, without inducing systemic toxicity. Such a facile, versatile, and robust platform renders a promising paradigm for cytosolic protein delivery and glioblastoma treatment.