Effective treatment of glioblastoma multiforme remains a major clinical challenge, due in part to the difficulty of delivering chemotherapeutics across the blood-brain barrier. Systemically administered drugs are often poorly bioavailable in the brain, and drug efficacy within the central nervous system can be limited by peripheral toxicity. Here, we investigate the ability of systemically administered poly (lactic-co-glycolic acid) nanoparticles (PLGA NPs) to deliver hydrophobic payloads to intracranial glioma. Hydrophobic payload encapsulated within PLGA NPs accumulated at ∼10× higher levels in tumor compared to healthy brain. Tolerability of the chemotherapeutic camptothecin (CPT) was improved by encapsulation, enabling safe administration of up to 20mg/kg drug when encapsulated within NPs. Immunohistochemistry staining for γ-H2AFX, a marker for double-strand breaks, demonstrated higher levels of drug activity in tumors treated with CPT-loaded NPs compared to free drug. CPT-loaded NPs were effective in slowing the growth of intracranial GL261 tumors in immune competent C57 albino mice, providing a significant survival benefit compared to mice receiving saline, free CPT or low dose CPT NPs (median survival of 36.5 days compared to 28, 32, 33.5 days respectively). In sum, these data demonstrate the feasibility of treating intracranial glioma with systemically administered nanoparticles loaded with the otherwise ineffective chemotherapeutic CPT.

In this work, we sought to test how surface modification of poly(lactic-co-glycolic acid) (PLGA) nanoparticles with peptide ligand alters the brain specific delivery of encapsulated molecules. For biodistribution studies, nanoparticles modified with rabies virus glycoprotein (RVG29) were loaded with small molecule drug surrogates and administered to healthy mice by lateral tail vein injection. Mice were perfused two hours after injection and major anatomical regions of the CNS were dissected (striatum, midbrain, cerebellum, hippocampus, cortex, olfactory bulb, brainstem, and cervical, thoracic, lumbar and sacral spinal cord). For functional studies, surface modified nanoparticles were loaded with the chemotherapeutic camptothecin (CPT) and administered to mice bearing intracranial GL261-Luc2 gliomas. Outcome measures included tumor growth, as measured by bioluminescent imaging, and median survival time. We observed that small molecule delivery from PLGA nanoparticles varied by as much as 150% for different tissue regions within the CNS. These differences were directly correlated to regional differences in cerebral blood volume. Although the presence of RVG29 enhanced apparent brain delivery for multiple small molecule payloads, we observed minimal evidence for targeting to muscle or spinal cord, which are the known sites for rabies virus entry into the CNS, and enhancements in brain delivery were not prolonged due to an apparent aqueous instability of the RVG29 ligand. Furthermore, we have identified concerning differences in apparent delivery kinetics as measured by different payloads: nanoparticle encapsulated DiR was observed to accumulate in the brain, whereas encapsulated Nile red was rapidly cleared. Although systemically administered CPT loaded nanoparticles slowed the growth of orthotopic brain tumors to prolong survival, the presence of RVG29 did not enhance therapeutic efficacy compared to control nanoparticles. These data are consistent with a model of delivery of hydrophobic small molecules to the brain that does not rely on internalization of polymer nanoparticles in target tissue. We discuss an important risk for discordance between biodistribution, as typically measured by drug surrogate, and therapeutic outcome, as determined by clinically relevant measurement of drug function in a disease model. These results pose critical considerations for the methods used to design and evaluate targeted drug delivery systems in vivo.

Alternative routes of administration are one approach that could be used to bypass the blood–brain barrier (BBB) for effective drug delivery to the central nervous system (CNS). Here, we focused on intranasal delivery of polymer nanoparticles. We hypothesized that surface modification of poly(lactic-co-glycolic acid) (PLGA) nanoparticles with rabies virus glycoprotein (RVG29) would increase residence time and exposure of encapsulated payload to the CNS compared to non-targeted nanoparticles. Delivery kinetics and biodistribution were analyzed by administering nanoparticles loaded with the carbocyanine dye 1,1′-Dioctadecyl-3,3,3′,3′-Tetramethylindotricarbocyanine Iodide (DiR) to healthy mice. Intranasal administration yielded minimal exposure of nanoparticle payload to most peripheral organs and rapid, effective delivery to whole brain. Regional analysis of payload delivery within the CNS revealed higher delivery to tissues closest to the trigeminal nerve, including the olfactory bulb, striatum, midbrain, brainstem, and cervical spinal cord. RVG29 surface modifications presented modest targeting benefits to the striatum, midbrain, and brainstem 2 h after administration, although targeting was not observed 30 min or 6 h after administration. Payload delivery to the trigeminal nerve was 3.5× higher for targeted nanoparticles compared to control nanoparticles 2 h after nanoparticle administration. These data support a nose-to-brain mechanism of drug delivery that closely implicates the trigeminal nerve for payload delivery from nanoparticles via transport of intact nanoparticles and eventual diffusion of payload. Olfactory and CSF routes are also observed to play a role. These data advance the utility of targeted nanoparticles for nose-to-brain drug delivery of lipophilic payloads and provide mechanistic insight to engineer effective delivery vectors to treat disease in the CNS.