On the shuttling across the blood-brain barrier via tubule formation: Mechanism and cargo avidity bias.

The blood-brain barrier is made of polarized brain endothelial cells (BECs) phenotypically conditioned by the central nervous system (CNS). Although transport across BECs is of paramount importance for nutrient uptake as well as ridding the brain of waste products, the intracellular sorting mechanisms that regulate successful receptor-mediated transcytosis in BECs remain to be elucidated. Here, we used a synthetic multivalent system with tunable avidity to the low-density lipoprotein receptor-related protein 1 (LRP1) to investigate the mechanisms of transport across BECs. We used a combination of conventional and super-resolution microscopy, both in vivo and in vitro, accompanied with biophysical modeling of transport kinetics and membrane-bound interactions to elucidate the role of membrane-sculpting protein syndapin-2 on fast transport via tubule formation. We show that high-avidity cargo biases the LRP1 toward internalization associated with fast degradation, while mid-avidity augments the formation of syndapin-2 tubular carriers promoting a fast shuttling across.

A human co-culture cell model incorporating microglia supports glioblastoma growth and migration, and confers resistance to cytotoxics.

Despite the importance of the tumor microenvironment in regulating tumor progression, few in vitro models have been developed to understand the effects of non-neoplastic cells and extracellular matrix (ECM) on drug resistance in glioblastoma (GBM) cells. Using CellTrace-labeled human GBM and microglial (MG) cells, we established a 2D co-culture including various ratios of the two cell types. Viability, proliferation, migration, and drug response assays were carried out to assess the role of MG. A 3D model was then established using a hyaluronic acid-gelatin hydrogel to culture a mixture of GBM and MG and evaluate drug resistance. A contact co-culture of fluorescently labeled GBM and MG demonstrated that MG cells modestly promoted tumor cell proliferation (17%-30% increase) and greater migration of GBM cells (>1.5-fold increase). Notably, the presence of MG elicited drug resistance even when in a low ratio (10%-20%) relative to co-cultured tumor cells. The protective effect of MG on GBM was greater in the 3D model (>100% survival of GBM when challenged with cytotoxics). This new 3D human model demonstrated the influence of non-neoplastic cells and matrix on chemoresistance of GBM cells to three agents with different mechanisms of action suggesting that such sophisticated in vitro approaches may facilitate improved preclinical testing.

Exploring Poly(Ethylene Glycol)-Poly(Trimethylene Carbonate) Nanoparticles as Carriers of Hydrophobic Drugs to Modulate Osteoblastic Activity.

Current treatment options for bone-related disorders rely on a systemic administration of therapeutic agents that possess low solubility and intracellular bioavailability, as well as a high pharmacokinetic variability, which in turn lead to major off-target side effects. Hence, there is an unmet need of developing drug delivery systems that can improve the clinical efficacy of such therapeutic agents. Nanoparticle delivery systems might serve as promising carriers of hydrophobic molecules. Here, we propose 2 nanoparticle-based delivery systems based on monomethoxy poly(ethylene glycol)-poly(trimethyl carbonate) (mPEG-PTMC) and poly(lactide-co-glycolide) for the intracellular controlled release of a small hydrophobic drug (dexamethasone) to osteoblast cells in vitro. mPEG-PTMC self-assembles into stable nanoparticles in the absence of surfactant and shows a greater entrapment capacity of dexamethasone, while assuring bioactivity in MC3T3-E1 and bone marrow stromal cells cultured under apoptotic and osteogenic conditions, respectively. The mPEG-PTMC nanoparticles represent a potential vector for the intracellular delivery of hydrophobic drugs in the framework of bone-related diseases.

PAMAM dendrimers: blood-brain barrier transport and neuronal uptake after focal brain ischemia.

Drug delivery to the central nervous system is restricted by the blood-brain barrier (BBB). However, with the onset of stroke, the BBB becomes leaky, providing a window of opportunity to passively target the brain. Here, cationic poly(amido amine) (PAMAM) dendrimers of different generations were functionalized with poly(ethylene glycol) (PEG) to reduce cytotoxicity and prolong blood circulation half-life, aiming for a safe in vivo drug delivery system in a stroke scenario. Rhodamine B isothiocyanate (RITC) was covalently tethered to the dendrimer backbone and used as a small surrogate drug as well as for tracking purposes. The biocompatibility of PAMAM was markedly increased by PEGylation as a function of dendrimer generation and degree of functionalization. The PEGylated RITC-modified dendrimers did not affect the integrity of an in vitro BBB model. Additionally, the functionalized dendrimers remained safe when in contact with the bEnd.3 cells and rat primary astrocytes composing the in vitro BBB model after hypoxia induced by oxygen-glucose deprivation. Modification with PEG also decreased the interaction and uptake by endothelial cells of PAMAM, indicating that the transport across a leaky BBB due to focal brain ischemia would be facilitated. Next, the functionalized dendrimers were tested in contact with red blood cells showing no haemolysis for the PEGylated PAMAM, in contrast to the unmodified dendrimer. Interestingly, the PEG-modified dendrimers reduced blood clotting, which may be an added beneficial function in the context of stroke. The optimized PAMAM formulation was intravenously administered in mice after inducing permanent focal brain ischemia. Twenty-four hours after administration, dendrimers could be detected in the brain, including in neurons of the ischemic cortex. Our results suggest that the proposed formulation has the potential for becoming a successful delivery vector for therapeutic application to the injured brain after stroke reaching the ischemic neurons.

Peptide Self-Assemblies for Drug Delivery.

Peptide amphiphiles (PAs) are novel engineered biomaterials able to self-assemble into supramolecular systems that have shown significant promise in drug delivery across the cell membane and across challenging biological barriers showing promise in the field of brain diseases, regenerative medicine and cancer. PAs are amino-acid block co-polymers, with a peptide backbone composed usually of 8-30 amino acids, a hydrophilic block formed by polar amino acids, a hydrophobic block which usually entails either non-polar or aromatic amino acids and alkyl, acyl or aryl lipidic tails and in some cases a spacer or a conjugated targeting moiety. Finely tuning the balance between the hydrophilic and hydrophobic blocks results in a range of supramolecular structures that are usually stabilised by hydrophobic, electrostatic, ß-sheet hydrogen bonds and π-π stacking interactions. In an aqueous environment, the final size, shape and interfacial curvature of the PA is a result of the complex interplay of all these interactions. Lanreotide is the first PA to be licensed for the treatment of acromegaly and neuroendocrine tumours as a hydrogel administered subcutaneously, while a number of other PAs are undergoing preclinical development. This review discusses PAs architecture fundamentals that govern their self-assembly into supramolecular systems for applications in drug delivery.