The blood-brain barrier (BBB) poses a unique challenge for drug delivery to the central nervous system (CNS). The BBB consists of a continuous layer of specialized endothelial cells linked together by tight junctions, pericytes, nonfenestrated basal lamina, and astrocytic foot processes. This complex barrier controls and limits the systemic delivery of therapeutics to the CNS. Several innovative strategies have been explored to enhance the transport of therapeutics across the BBB, each with individual advantages and disadvantages. Ongoing advances in delivery approaches that overcome the BBB are enabling more effective therapies for CNS diseases. In this review, we discuss: (1) the physiological properties of the BBB, (2) conventional strategies to enhance paracellular and transcellular transport through the BBB, (3) emerging concepts to overcome the BBB, and (4) alternative CNS drug delivery strategies that bypass the BBB entirely. Based on these exciting advances, we anticipate that in the near future, drug delivery research efforts will lead to more effective therapeutic interventions for diseases of the CNS.

A major limitation in the treatment of glioblastoma (GBM), the most common and deadly primary brain cancer, is delivery of therapeutics to invading tumor cells outside of the area that is safe for surgical removal. A promising way to target invading GBM cells is via drug-loaded nanoparticles that bind to fibroblast growth factor-inducible 14 (Fn14), thereby potentially improving efficacy and reducing toxicity. However, achieving broad particle distribution and nanoparticle targeting within the brain remains a significant challenge due to the adhesive extracellular matrix (ECM) and clearance mechanisms in the brain. In this work, we developed Fn14 monoclonal antibody-decorated nanoparticles that can efficiently penetrate brain tissue. We show these Fn14-targeted brain tissue penetrating nanoparticles are able to (i) selectively bind to recombinant Fn14 but not brain ECM proteins, (ii) associate with and be internalized by Fn14-positive GBM cells, and (iii) diffuse within brain tissue in a manner similar to non-targeted brain penetrating nanoparticles. In addition, when administered intracranially, Fn14-targeted nanoparticles showed improved tumor cell co-localization in mice bearing human GBM xenografts compared to non-targeted nanoparticles. Minimizing non-specific binding of targeted nanoparticles in the brain may greatly improve the access of particulate delivery systems to remote brain tumor cells and other brain targets.

Fibroblast growth factor-inducible 14 (Fn14; TNFRSF12A) is the cell surface receptor for the tumor necrosis factor (TNF) family member TNF-like weak inducer of apoptosis (TWEAK). The Fn14 gene is normally expressed at low levels in healthy tissues but expression is significantly increased after tissue injury and in many solid tumor types, including glioblastoma (GB; formerly referred to as ‘glioblastoma multiforme’ or GBM). GB is the most common and aggressive primary malignant brain tumor, and the current standard-of-care therapeutic regimen has a relatively small impact on patient survival, primarily because glioma cells have an inherent propensity to invade into normal brain parenchyma, which invariably leads to tumor recurrence and patient death. Despite major, concerted efforts to find new treatments, a new GB therapeutic that improves survival has not been introduced since 2005. In this review article, we summarize studies indicating that (i) Fn14 gene expression is low in normal brain tissue but up-regulated in advanced brain cancers and, in particular, in GB tumors exhibiting the mesenchymal molecular subtype, (ii) Fn14 expression can be detected in glioma cells residing in both the tumor core and invasive rim regions, with the maximal levels found in the invading glioma cells located within normal brain tissue, and (iii) TWEAK:Fn14 engagement as well as Fn14 overexpression can stimulate glioma cell migration, invasion, and resistance to chemotherapeutic agents in vitro. We also discuss two new therapeutic platforms that are currently in development that leverage Fn14 overexpression in GB tumors as a way to deliver cytotoxic agents to the glioma cells remaining after surgical resection while sparing normal healthy brain cells.

Surface plasmon resonance (SPR) is a powerful analytical technique used to quantitatively examine the interactions between various biomolecules, such as proteins and nucleic acids. The technique has been particularly useful in screening and evaluating binding affinity of novel small molecule and biomolecule-derived therapeutics for various diseases and applications including lupus medications, thrombin inhibitors, HIV protease inhibitors, DNA gyrase inhibitors and many others. Recently, there has been increasing interest in nanotherapeutics (nanoRx), due to their unique properties and potential for controlled release of encapsulated drugs and structure-specific targeting to diseased tissues. Targeted nanoRx offer the potential to solve many drug delivery challenges by enabling, specific interactions between molecules on the surface of the nanoparticle and molecules in the diseased tissue, while minimizing off-target interactions toward non-diseased tissues. These properties are largely dependent upon careful control and balance of nanoRx interactions and binding properties with tissues in vivo. Given the great promise of nanoRx with regard to engineering specific molecular interactions, SPR can rapidly quantify small aliquots of nanoRx formulations for desired and undesired molecular interactions. Moving forward, we believe that utilization of SPR in the screening and design of nanoRx has the potential to greatly improve the development of targeted nanoRx formulations and eventually lead to improved therapeutic efficacy. In this review, we discuss (1) the fundamental principles of SPR and basic quantitative analysis of SPR data, (2) previous applications of SPR in the study of non-particulate therapeutics and nanoRx, and (3) future opportunities for the use of SPR in the evaluation of nanoRx.

Introduction: A major limitation associated with treatment of glioblastoma (GBM), the most common and deadly primary brain cancer, is delivery of therapeutics to invading tumor cells outside of the area that is safe for surgical removal. Recent advances in nanotechnology have allowed the incorporation of different therapeutic and targeting agents into nanoparticles offering the potential for improved detection, prevention, and treatment of various cancers. A promising way to target brain-invading GBM cells is via targeted therapeutics that bind to the cell surface receptor fibroblast growth-factor-inducible 14 (Fn14), which is specifically upregulated on the surface of invading GBM cells. Objective: In this study, we aim to develop a biodegradable nanoparticle platform that employs a dense, low-molecular weight PEG coating coupled with a Fn14-specific monoclonal antibody (mAb) in order to maximize brain tissue penetration and GBM cell targeting Materials and Methods: We previously showed that PEG-coated model polystyrene (PS) nanoparticles conjugated to the Fn14 mAb named ITEM4 bind strongly and selectively to the Fn14 extracellular domain. We synthesized a variety of PS-based brain tissue penetrating PEG-coated nanoparticles and characterized the (i) specificity of nanoparticle binding to Fn14 and (ii) nonspecific binding to brain ECM components, using surface plasmon resonance (SPR) and multiple particle tracking (MPT) assays. In parallel, we are transferring these findings and methodology towards formulation of biodegradable drug-loaded nanoparticles with matched size, surface chemistries, and Fn14 binding affinities for controlled drug delivery into brain tumors. We are loading biodegradable nanoparticles, including poly(lactic-co-glycolic acid) (PLGA), polyglutamic acid (PGA), and polysebacic acid (PSA) polymer platforms, with chemotherapeutics (i.e. cisplatin and bis-chloroethylnitrosurea (BCNU)) to study the optimization of drug-loading with particle penetration and targeting. Results: The equilibrium binding affinity (KD) of nanoparticles scaled nearly linear with the surface density of the ITEM4 molecules, indicating that the adhesiveness of nanoparticle formulations depends on the ITEM4 molecular presentation on the nanoparticle surface. PEG-coated Fn14-targeted nanoparticles of ~100 nm in diameter were able to rapidly penetrate brain tissue by MPT experiment in rat brain slices. In contrast, uncoated nanoparticles were immobilized in brain tissue. We have preliminary data that suggests we can develop biodegradable nanoparticles that provide sustained release of a wide range of rugs over several days. We have successfully encapsulated cisplatin and BCNU to the polymer backbone of PGA and PLGA containing a low-molecular weight PEG coating. Additional surface modifications have been made to enable Fn14 targeting by conjugating ITEM4 on the particle surface. Particles will undergo complete physicochemical characterization to optimize Fn14 targeting, nanoparticle movement, drug release kinetics, and in vivo efficacy. Conclusion: We have developed a nanoparticle platform that can diffuse and penetrate within brain tissue and selectively target remote experimental GBM tumors. Using this approach we can optimize therapeutics versions to improve drug efficacy while limiting many of the side effects and risks of free drug and non-targeted therapies. Citation Format: Jimena G. Perez, Craig S. Schneider, Nina Connolly, Jeffrey A. Winkles, Graeme F. Woodworth, Anthony J. Kim. Development of biodegradable Fn14-targeted nanoparticles for controlled drug delivery for invasive brain tumors. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr B46.