Abstract PS18-24: Impact of protein corona formation on Fn14-targeted DART nanoparticle selectivity, uptake, and cytotoxicity on TNBC cells

Despite dramatic improvements in the treatment of primary breast cancers, there currently are no effective targeted therapeutics for women diagnosed with metastatic triple negative breast cancer (mTNBC), resulting in an overall survival of just ~13 months in these patients. Drug-loaded nanoparticles (NPs) offer the potential to improve the therapeutic efficacy and pharmacokinetic profile of drugs through use of passive and active targeting to metastatic tumors. However, effective and active targeting of nanodrug formulations to tumor cells is complicated by the adsorption of proteins to NP surfaces upon exposure to the systemic circulation. Termed ‘protein coronas’, this protein coat can drastically reduce the blood circulation time and targeting capability of NPs in vivo. We have developed paclitaxel (PTX)-loaded NPs that are engineered for decreased non-specific adhesivity and receptor-targeting (‘DART’) characteristics, which balance minimal recognition by circulating immune cells and low non-specific binding to tumor extracellular matrix proteins with maximal targeting to tumor tissues. These DARTs selectively bind the fibroblast growth factor-inducible 14 (Fn14) cell surface receptor, which is overexpressed in over a dozen solid cancers and their metastases, including mTNBC tumors. We recently demonstrated the enhanced therapeutic efficacy of Fn14-targeted DARTs in comparison to a non-targeted nanoformulation and Abraxane, an FDA-approved nanoformulation for mTNBC, in xenograft models of primary and intracranial TNBC. In addition, we found that these DARTs retain targeting capability and traffic to Fn14+ tumors in the presence of an endogenous protein corona in vitro and in vivo. This encouraged further investigation into the specific mechanisms of DART NP uptake in tumor cells in both the presence and absence of protein coronas using surface plasmon resonance, flow cytometry, total internal reflection fluorescence and confocal microscopy, and cytotoxicity assays. Understanding the role of protein coronas on this drug delivery platform is crucial for its clinical development and these results provide valuable new information pertaining to the optimization of NP surface properties for minimizing the impact of protein coronas and improving mTNBC tumor targeting in vivo.

Citation Format: Christine P Carney, Anshika Kapur, Nikhil Pandey, Jimena G Dancy, Aniket S Wadajkar, Graeme F Woodworth, Jeffrey A Winkles, Anthony J Kim. Impact of protein corona formation on Fn14-targeted DART nanoparticle selectivity, uptake, and cytotoxicity on TNBC cells [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-24.

A multi-center analysis of single-fraction versus hypofractionated stereotactic radiosurgery for the treatment of brain metastasis

Background

Hypofractionated-SRS (HF-SRS) may allow for improved local control and a reduced risk of radiation necrosis compared to single-fraction-SRS (SF-SRS). However, data comparing these two treatment approaches are limited. The purpose of this study was to compare clinical outcomes between SF-SRS versus HF-SRS across our multi-center academic network.

Methods

Patients treated with SF-SRS or HF-SRS for brain metastasis from 2013 to 2018 across 5 radiation oncology centers were retrospectively reviewed. SF-SRS dosing was standardized, whereas HF-SRS dosing regimens were variable. The co-primary endpoints of local control and radiation necrosis were estimated using the Kaplan Meier method. Multivariate analysis using Cox proportional hazards modeling was performed to evaluate the impact of select independent variables on the outcomes of interest. Propensity score adjustments were used to reduce the effects confounding variables. To assess dose response for HF-SRS, Biologic Effective Dose (BED) assuming an α/β of 10 (BED₁₀) was used as a surrogate for total dose.

Results

One-hundred and fifty six patients with 335 brain metastasis treated with SF-SRS (n = 222 lesions) or HF-SRS (n = 113 lesions) were included. Prior whole brain radiation was given in 33% (n = 74) and 34% (n = 38) of lesions treated with SF-SRS and HF-SRS, respectively (p = 0.30). After a median follow up time of 12 months in each cohort, the adjusted 1-year rate of local control and incidence of radiation necrosis was 91% (95% CI 86–96%) and 85% (95% CI 75–95%) (p = 0.26) and 10% (95% CI 5–15%) and 7% (95% CI 0.1–14%) (p = 0.73) for SF-SRS and HF-SRS, respectively. For lesions > 2 cm, the adjusted 1 year local control was 97% (95% CI 84–100%) for SF-SRS and 64% (95% CI 43–85%) for HF-SRS (p = 0.06). On multivariate analysis, SRS fractionation was not associated with local control and only size ≤2 cm was associated with a decreased risk of developing radiation necrosis (HR 0.21; 95% CI 0.07–0.58, p < 0.01). For HF-SRS, 1 year local control was 100% for lesions treated with a BED₁₀ ≥ 50 compared to 77% (95% CI 65–88%) for lesions that received a BED₁₀ < 50 (p = 0.09).

Conclusions

In this comparison study of dose fractionation for the treatment of brain metastases, there was no difference in local control or radiation necrosis between HF-SRS and SF-SRS. For HF-SRS, a BED₁₀ ≥ 50 may improve local control.

Predictors and Limitations of the Penetration Depth of Photodynamic Effects in the Rodent Brain

Fluorescence-guided surgery (FGS) is routinely utilized in clinical centers around the world, whereas the combination of FGS and photodynamic therapy (PDT) has yet to reach clinical implementation and remains an active area of translational investigations. Two significant challenges to the clinical translation of PDT for brain cancer are as follows: (1) Limited light penetration depth in brain tissues and (2) Poor selectivity and delivery of the appropriate photosensitizers. To address these shortcomings, we developed nanoliposomal protoporphyrin IX (Nal-PpIX) and nanoliposomal benzoporphyrin derivative (Nal-BPD) and then evaluated their photodynamic effects as a function of depth in tissue and light fluence using rat brains. Although red light penetration depth (defined as the depth at which the incident optical energy drops to 1/e, ~37%) is typically a few millimeters in tissues, we demonstrated that the remaining optical energy could induce PDT effects up to 2 cm within brain tissues. Photobleaching and singlet oxygen yield studies between Nal-BPD and Nal-PpIX suggest that deep-tissue PDT (>1 cm) is more effective when using Nal-BPD. These findings indicate that Nal-BPD-PDT is more likely to generate cytotoxic effects deep within the brain and allow for the treatment of brain invading tumor cells centimeters away from the main, resectable tumor mass.

MCT4 regulates de novo pyrimidine biosynthesis in GBM in a lactate-independent manner

Background

Necrotic foci with surrounding hypoxic cellular pseudopalisades and microvascular hyperplasia are histological features found in glioblastoma (GBM). We have previously shown that monocarboxylate transporter 4 (MCT4) is highly expressed in necrotic/hypoxic regions in GBM and that increased levels of MCT4 are associated with worse clinical outcomes.

Methods

A combined transcriptomics and metabolomics analysis was performed to study the effects of MCT4 depletion in hypoxic GBM neurospheres. Stable and inducible MCT4-depletion systems were used to evaluate the effects of and underlining mechanisms associated with MCT4 depletion in vitro and in vivo, alone and in combination with radiation.

Results

This study establishes that conditional depletion of MCT4 profoundly impairs self-renewal and reduces the frequency and tumorigenicity of aggressive, therapy-resistant, glioblastoma stem cells. Mechanistically, we observed that MCT4 depletion induces anaplerotic glutaminolysis and abrogates de novo pyrimidine biosynthesis. The latter results in a dramatic increase in DNA damage and apoptotic cell death, phenotypes that were readily rescued by pyrimidine nucleosides supplementation. Consequently, we found that MCT4 depletion promoted a significant prolongation of survival of animals bearing established orthotopic xenografts, an effect that was extended by adjuvant treatment with focused radiation.

Conclusions

Our findings establish a novel role for MCT4 as a critical regulator of cellular deoxyribonucleotide levels and provide a new therapeutic direction related to MCT4 depletion in GBM.

Decreased nonspecific adhesivity, receptor-targeted therapeutic nanoparticles for primary and metastatic breast cancer

Development of effective tumor cell-targeted nanodrug formulations has been quite challenging, as many nanocarriers and targeting moieties exhibit nonspecific binding to cellular, extracellular, and intravascular components. We have developed a therapeutic nanoparticle formulation approach that balances cell surface receptor-specific binding affinity while maintaining minimal interactions with blood and tumor tissue components (termed "DART" nanoparticles), thereby improving blood circulation time, biodistribution, and tumor cell-specific uptake. Here, we report that paclitaxel (PTX)-DART nanoparticles directed to the cell surface receptor fibroblast growth factor-inducible 14 (Fn14) outperformed both the corresponding PTX-loaded, nontargeted nanoparticles and Abraxane, an FDA-approved PTX nanoformulation, in both a primary triple-negative breast cancer (TNBC) model and an intracranial model reflecting TNBC growth following metastatic dissemination to the brain. These results provide new insights into methods for effective development of therapeutic nanoparticles as well as support the continued development of the DART platform for primary and metastatic tumors.

The TNF receptor family member Fn14 is highly expressed in recurrent glioblastoma and in GBM patient-derived xenografts with acquired temozolomide resistance

Background

Glioblastoma (GBM) is a difficult to treat brain cancer that nearly uniformly recurs, and recurrent tumors are largely therapy resistant. Our prior work has demonstrated an important role for the tumor necrosis factor-like weak inducer of apoptosis (TWEAK) receptor fibroblast growth factor-inducible 14 (Fn14) in GBM pathobiology. In this study, we investigated Fn14 expression in recurrent GBM and in the setting of temozolomide (TMZ) resistance.

Methods

Fn14 mRNA expression levels in nonneoplastic brain, primary (newly diagnosed) GBM, and recurrent GBM (post-chemotherapy and radiation) specimens were obtained from The Cancer Genome Atlas data portal. Immunohistochemistry was performed using nonneoplastic brain, patient-matched primary and recurrent GBM, and gliosarcoma (GSM) specimens to examine Fn14 protein levels. Western blot analysis was used to compare Fn14 expression in parental TMZ-sensitive or matched TMZ-resistant patient-derived xenografts (PDXs) established from primary or recurrent tumor samples. The migratory capacity of control and Fn14-depleted TMZ-resistant GBM cells was assessed using the transwell migration assay.

Results

We found that Fn14 is more highly expressed in recurrent GBM tumors than their matched primary GBM counterparts. Fn14 expression is also significantly elevated in GSM tumors. GBM PDX cells with acquired TMZ resistance have higher Fn14 levels and greater migratory capacity than their corresponding parental TMZ-sensitive cells, and the migratory difference is due, at least in part, to Fn14 expression in the TMZ-resistant cells.

Conclusions

This study demonstrates that the Fn14 gene is highly expressed in recurrent GBM, GSM, and TMZ-resistant GBM PDX tumors. These findings suggest that Fn14 may be a valuable therapeutic target or drug delivery portal for treatment of recurrent GBM and GSM patients.

Systematic Evaluation of Light-Activatable Biohybrids for Anti-Glioma Photodynamic Therapy

Photosensitizing biomolecules (PSBM) represent a new generation of light-absorbing compounds with improved optical and physicochemical properties for biomedical applications. Despite numerous advances in lipid-, polymer-, and protein-based PSBMs, their effective use requires a fundamental understanding of how macromolecular structure influences the physicochemical and biological properties of the photosensitizer. Here, we prepared and characterized three well-defined PSBMs based on a clinically used photosensitizer, benzoporphyrin derivative (BPD). The PSBMs include 16:0 lysophosphocholine-BPD (16:0 Lyso PC-BPD), distearoyl-phosphoethanolamine-polyethylene-glycol-BPD (DSPE-PEG-BPD), and anti-EGFR cetuximab-BPD (Cet-BPD). In two glioma cell lines, DSPE-PEG-BPD exhibited the highest singlet oxygen yield but was the least phototoxic due to low cellular uptake. The 16:0 Lyso PC-BPD was most efficient in promoting cellular uptake but redirected BPD's subcellular localization from mitochondria to lysosomes. At 24 h after incubation, proteolyzed Cet-BPD was localized to mitochondria and effectively disrupted the mitochondrial membrane potential upon light activation. Our results revealed the variable trafficking and end effects of PSBMs, providing valuable insights into methods of PSBM evaluation, as well as strategies to select PSBMs based on subcellular targets and cytotoxic mechanisms. We demonstrated that biologically informed combinations of PSBMs to target lysosomes and mitochondria, concurrently, may lead to enhanced therapeutic effects against gliomas.

Leveraging Surface Plasmon Resonance to Dissect the Interfacial Properties of Nanoparticles: Implications for Tissue Binding and Tumor Penetration

Therapeutic efficacy of nanoparticle-drug formulations for cancer applications is significantly impacted by the extent of intra-tumoral accumulation and tumor tissue penetration. We advanced the application of surface plasmon resonance to examine interfacial properties of various clinical and emerging nanoparticles related to tumor tissue penetration. We observed that amine-terminated or positively-charged dendrimers and liposomes bound strongly to tumor extracellular matrix (ECM) proteins, whereas hydroxyl/carboxyl-terminated dendrimers and PEGylated/neutrally-charged liposomes did not bind. In addition, poly(lactic-co-glycolic acid) (PLGA) nanoparticles formulated with cholic acid or F127 surfactants bound strongly to tumor ECM proteins, whereas nanoparticles formulated with poly(vinyl alcohol) did not bind. Unexpectedly, following blood serum incubation, this binding increased and particle transport in ex vivo tumor tissues reduced markedly. Finally, we characterized the protein corona on PLGA nanoparticles using quantitative proteomics. Through these studies, we identified valuable criteria for particle surface characteristics that are likely to mediate their tissue binding and tumor penetration.

Developments in Blood-Brain Barrier Penetrance and Drug Repurposing for Improved Treatment of Glioblastoma

Glioblastoma (GBM) is one of the most common, deadly, and difficult-to-treat adult brain tumors. Surgical removal of the tumor, followed by radiotherapy (RT) and temozolomide (TMZ) administration, is the current treatment modality, but this regimen only modestly improves overall patient survival. Invasion of cells into the surrounding healthy brain tissue prevents complete surgical resection and complicates treatment strategies with the goal of preserving neurological function. Despite significant efforts to increase our understanding of GBM, there have been relatively few therapeutic advances since 2005 and even fewer treatments designed to effectively treat recurrent tumors that are resistant to therapy. Thus, while there is a pressing need to move new treatments into the clinic, emerging evidence suggests that key features unique to GBM location and biology, the blood-brain barrier (BBB) and intratumoral molecular heterogeneity, respectively, stand as critical unresolved hurdles to effective therapy. Notably, genomic analyses of GBM tissues has led to the identification of numerous gene alterations that govern cell growth, invasion and survival signaling pathways; however, the drugs that show pre-clinical potential against signaling pathways mediated by these gene alterations cannot achieve effective concentrations at the tumor site. As a result, identifying BBB-penetrating drugs and utilizing new and safer methods to enhance drug delivery past the BBB has become an area of intensive research. Repurposing and combining FDA-approved drugs with evidence of penetration into the central nervous system (CNS) has also seen new interest for the treatment of both primary and recurrent GBM. In this review, we discuss emerging methods to strategically enhance drug delivery to GBM and repurpose currently-approved and previously-studied drugs using rational combination strategies.

Oxaliplatin disrupts pathological features of glioma cells and associated macrophages independent of apoptosis induction

INTRODUCTION

Emerging evidence suggests that effective treatment of glioblastoma (GBM), the most common and deadly form of adult primary brain cancer, will likely require concurrent treatment of multiple aspects of tumor pathobiology to overcome tumor heterogeneity and the complex tumor-supporting microenvironment. Recent studies in non-central nervous system (CNS) tumor cells have demonstrated that oxaliplatin (OXA) can induce multi-faceted anti-tumor effects, in particular at drug concentrations below those required to induce apoptosis. These findings motivated re-investigation of OXA for the treatment of GBM.

METHODS

The effects of OXA on murine KR158 and GL261 glioma cells including cell growth, cell death, inhibition of signal transducer and activator of transcription (STAT) activity, O-6-methylguanine-DNA methyltransferase (MGMT) expression, and immunogenic cell death (ICD) initiation, were evaluated by cytotoxicity assays, Western blot analysis, STAT3-luciferase reporter assays, qRT-PCR assays, and flow cytometry. Chemical inhibitors of endoplasmic reticulum (ER) stress were used to investigate the contribution of this cell damage response to the observed OXA effects. The effect of OXA on bone marrow-derived macrophages (BMDM) exposed to glioma conditioned media (GCM) was also analyzed by Western blot analysis.

RESULTS

We identified the OXA concentration threshold for induction of apoptosis and from this determined the drug dose and treatment period for sub-cytotoxic treatments of glioma cells. Under these experimental conditions, OXA reduced STAT3 activity, reduced MGMT levels and increased temozolomide sensitivity. In addition, there was evidence of immunogenic cell death (elevated EIF2α phosphorylation and calreticulin exposure) following prolonged OXA treatment. Notably, inhibition of ER stress reversed the OXA-mediated inhibition of STAT3 activity and MGMT expression in the tumor cells. In BMDMs exposed to GCM, OXA also reduced levels of phosphorylated STAT3 and decreased expression of Arginase 1, an enzyme known to contribute to pro-tumor functions in the tumor-immune environment.

CONCLUSIONS

OXA can induce notable multi-faceted biological effects in glioma cells and BMDMs at relatively low drug concentrations. These findings may have significant therapeutic relevance against GBM and warrant further investigation.

Differential expression of the TWEAK receptor Fn14 in IDH1 wild-type and mutant gliomas

The TNF receptor superfamily member Fn14 is overexpressed by many solid tumor types, including glioblastoma (GBM), the most common and lethal form of adult brain cancer. GBM is notable for a highly infiltrative growth pattern and several groups have reported that high Fn14 expression levels can increase tumor cell invasiveness. We reported previously that the mesenchymal and proneural GBM transcriptomic subtypes expressed the highest and lowest levels of Fn14 mRNA, respectively. Given the recent histopathological re-classification of human gliomas by the World Health Organization based on isocitrate dehydrogenase 1 (IDH1) gene mutation status, we extended this work by comparing Fn14 gene expression in IDH1 wild-type (WT) and mutant (R132H) gliomas and in cell lines engineered to overexpress the IDH1 R132H enzyme. We found that both low-grade and high-grade (i.e., GBM) IDH1 R132H gliomas exhibit low Fn14 mRNA and protein levels compared to IDH1 WT gliomas. Forced overexpression of the IDH1 R132H protein in glioma cells reduced Fn14 expression, while treatment of IDH1 R132H-overexpressing cells with the IDH1 R132H inhibitor AGI-5198 or the DNA demethylating agent 5-aza-2'-deoxycytidine increased Fn14 expression. These results support a role for Fn14 in the more aggressive and invasive phenotype associated with IDH1 WT tumors and indicate that the low levels of Fn14 gene expression noted in IDH1 R132H mutant gliomas may be due to epigenetic regulation via changes in DNA methylation.

Cross-species transcriptional analysis reveals conserved and host-specific neoplastic processes in mammalian glioma

Glioma is a unique neoplastic disease that develops exclusively in the central nervous system (CNS) and rarely metastasizes to other tissues. This feature strongly implicates the tumor-host CNS microenvironment in gliomagenesis and tumor progression. We investigated the differences and similarities in glioma biology as conveyed by transcriptomic patterns across four mammalian hosts: rats, mice, dogs, and humans. Given the inherent intra-tumoral molecular heterogeneity of human glioma, we focused this study on tumors with upregulation of the platelet-derived growth factor signaling axis, a common and early alteration in human gliomagenesis. The results reveal core neoplastic alterations in mammalian glioma, as well as unique contributions of the tumor host to neoplastic processes. Notable differences were observed in gene expression patterns as well as related biological pathways and cell populations known to mediate key elements of glioma biology, including angiogenesis, immune evasion, and brain invasion. These data provide new insights regarding mammalian models of human glioma, and how these insights and models relate to our current understanding of the human disease.

Emerging Applications of Therapeutic Ultrasound in Neuro-oncology: Moving Beyond Tumor Ablation

: Transcranial focused ultrasound (FUS) can noninvasively transmit acoustic energy with a high degree of accuracy and safety to targets and regions within the brain. Technological advances, including phased-array transducers and real-time temperature monitoring with magnetic resonance thermometry, have created new opportunities for FUS research and clinical translation. Neuro-oncology, in particular, has become a major area of interest because FUS offers a multifaceted approach to the treatment of brain tumors. FUS has the potential to generate cytotoxicity within tumor tissue, both directly via thermal ablation and indirectly through radiosensitization and sonodynamic therapy; to enhance the delivery of therapeutic agents to brain tumors by transiently opening the blood-brain barrier or improving distribution through the brain extracellular space; and to modulate the tumor microenvironment to generate an immune response. In this review, we describe each of these applications for FUS, the proposed mechanisms of action, and the preclinical and clinical studies that have set the foundation for using FUS in neuro-oncology.

ABBREVIATIONS

BBB, blood-brain barrierCED, convection-enhanced delivery5-Ala, 5-aminolevulinic acidFUS, focused ultrasoundGBM, glioblastoma multiformeHSP, heat shock proteinMRgFUS, magnetic resonance-guided focused ultrasoundpFUS, pulsed focused ultrasound.

Decreased non-specific adhesivity, receptor targeted (DART) nanoparticles exhibit improved dispersion, cellular uptake, and tumor retention in invasive gliomas

The most common and deadly form of primary brain cancer, glioblastoma (GBM), is characterized by significant intratumoral heterogeneity, microvascular proliferation, immune system suppression, and brain tissue invasion. Delivering effective and sustained treatments to the invasive GBM cells intermixed with functioning neural elements is a major goal of advanced therapeutic systems for brain cancer. Previously, we investigated the nanoparticle characteristics that enable targeting of invasive GBM cells. This revealed the importance of minimizing non-specific binding within the relatively adhesive, 'sticky' microenvironment of the brain and brain tumors in particular. We refer to such nanoformulations with decreased non-specific adhesivity and receptor targeting as 'DART' therapeutics. In this work, we applied this information toward the design and characterization of biodegradable nanocarriers, and in vivo testing in orthotopic experimental gliomas. We formulated particulate nanocarriers using poly(lactic-co-glycolic acid) (PLGA) and PLGA-polyethylene glycol (PLGA-PEG) polymers to generate sub-100nm nanoparticles with minimal binding to extracellular brain components and strong binding to the Fn14 receptor - an upregulated, conserved component in invasive GBM. Multiple particle tracking in brain tissue slices and in vivo testing in orthotopic murine malignant glioma revealed preserved nanoparticle diffusivity and increased uptake in brain tumor cells. These combined characteristics also resulted in longer retention of the DART nanoparticles within the orthotopic tumors compared to non-targeted versions. Taken together, these results and nanoparticle design considerations offer promising new methods to optimize therapeutic nanocarriers for improving drug delivery and treatment for invasive brain tumors.

Abstract 808: PDGF-A overexpression and p53 depletion in rat neural precursor cells induces large brain tumors that resemble human glioblastoma

One of the major obstacles in developing new therapeutics for glioblastoma is testing these agents in reliable models that recapitulate the tumor biology of human disease. The RCAS/tv-a system enables spatial, temporal, and cell-type specific control of oncogenic transformations in the brain. In this study, we sought to develop a rat RCAS-TVA model of glioblastoma to eventually facilitate translational studies using magnetic resonance imaging (MRI), targeted radiation, focused ultrasound, and local drug delivery strategies. We developed a high copy number nestin-promoter driven tv-a (Ntv-a) transgenic Sprague-Dawley rat line. To initiate tumors, RCAS PDGF-A and p53 shRNA constructs were injected intracranially. The tumors were followed over time using MRI and MR proton spectroscopy. Animal survival was monitored and histopathology and gene expression analyses were performed. All animals (n=8) developed tumors that could be visualized with MRI throughout the tumor formation process. Early stage tumors showed relatively homogenous characteristics with minimal mass effect. Later stage tumors demonstrated large heterogeneous lesions with evidence of necrosis, increased vascularity, and significant mass effect. MR proton spectroscopy revealed increases in choline to creatinine ratio (Cho/Cr) and decreases in NAA, consistent with aggressive tumor progression. Immunohistochemistry revealed pseudopallisading necrosis, brain invasion, and vascular proliferation, all key features of human GBM. Immunohistochemistry confirmed a high proliferative index within the tumor core as well as neovascularization as evidenced by positive Ki67 and Smooth Muscle Actin (SMA) respectively. Gene expression analysis revealed approximately 1000 differentially expressed transcripts between the normal and tumor tissue. In addition to typical markers such as Ki67 and PDGFR-A overexpression, SPP1 and POSTN both of which are linked to glioma and tumor-associated macrophages, were found to be differentially expressed in the tumor. Comparisons between the rat gene expression profile and published human TCGA data indicated that the RCAS/tv-a tumors appear to align with the proneural GBM subtype. In summary, transgenic Ntv-a rats generate reproducible brain tumors following combined PDGF-A and p53 genetic alterations. The tumor progression process from low-grade tumor to high grade malignancy can be visualized with MRI. Histopathological features strongly resemble human GBM, and gene expression analysis suggests these tumors correspond to the proneural subtype.

Citation Format: Nina P. Connolly, Craig S. Schneider, Amol Shetty, Su Xu, Tatsuya Ozawa, Anthony J. Kim, Jeffrey A. Winkles, Eric Holland, Graeme F. Woodworth. PDGF-A overexpression and p53 depletion in rat neural precursor cells induces large brain tumors that resemble human glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 808. doi:10.1158/1538-7445.AM2017-808

Abstract 3107: Targeting nanotherapeutics to the invasive glioblastoma margin via the cell surface receptor Fn14

The most common and deadly form of primary brain cancer, glioblastoma (GBM), is characterized by significant intratumoral heterogeneity, high vascularity, and infiltrative growth. Delivering effective and sustained treatments to the invading GBM cells without worsening damage to the adjacent brain is a major challenge. We aim to develop an innovative, local delivery approach that couples chemotherapy-loaded brain penetrating biodegradable nanoparticles with tumor cell-targeting capabilities and convection enhanced delivery (CED). We formulated sub-100 nm sized, close to neutrally charged, poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) nanoparticles with ~5% w/w carmustine (BCNU) payload coated with a fibroblast growth factor-inducible 14 (Fn14) antibody to specifically target Fn14-positive brain-invading tumor cells. We observed that PLGA surface modification using non-adhesive PEG allowed nanoparticles to rapidly move through brain tissue in ex vivo rat brain slices, potentially increasing the distribution of delivered therapeutics. We showed that Fn14-targeted nanoparticles were able to selectively bind to recombinant Fn14 but not to brain extracellular matrix proteins in surface plasmon resonance assays, as well as diffuse within brain tissue in multiple particle tracking assays. In addition, when administered intracranially, Fn14-targeted nanoparticles showed improved brain tumor retention in C57BL/6 mice bearing orthotopic KR158B tumors compared to non-targeted nanoparticles. We propose that targeting treatments to invading cancer cells using non-adhesive nanoparticles will limit non-specific interactions within brain and tumor tissue and thereby allow specific interactions at target structures and increase the BCNU therapeutic index. To test this hypothesis, we plan to determine the therapeutic efficacy of Fn14-targeted and non-targeted, non-adhesive nanoparticles, capable of releasing BCNU over a 3 week period, by intracranial CED injections in C57BL/6 mice bearing orthotopic KR158B invasive tumors.

Citation Format: Aniket S. Wadajkar, Jimena G. Dancy, Nina P. Connolly, Jeffrey A. Winkles, Graeme F. Woodworth, Anthony J. Kim. Targeting nanotherapeutics to the invasive glioblastoma margin via the cell surface receptor Fn14 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3107. doi:10.1158/1538-7445.AM2017-3107

Tumor-targeted nanotherapeutics: overcoming treatment barriers for glioblastoma

Glioblastoma (GBM) is a highly aggressive and lethal form of primary brain cancer. Numerous barriers exist to the effective treatment of GBM including the tightly controlled interface between the bloodstream and central nervous system termed the 'neurovascular unit,' a narrow and tortuous tumor extracellular space containing a dense meshwork of proteins and glycosaminoglycans, and genomic heterogeneity and instability. A major goal of GBM therapy is achieving sustained drug delivery to glioma cells while minimizing toxicity to adjacent neurons and glia. Targeted nanotherapeutics have emerged as promising drug delivery systems with the potential to improve pharmacokinetic profiles and therapeutic efficacy. Some of the key cell surface molecules that have been identified as GBM targets include the transferrin receptor, low-density lipoprotein receptor-related protein, α_v β₃ integrin, glucose transporter(s), glial fibrillary acidic protein, connexin 43, epidermal growth factor receptor (EGFR), EGFR variant III, interleukin-13 receptor α chain variant 2, and fibroblast growth factor-inducible factor 14. However, most targeted therapeutic formulations have yet to demonstrate improved efficacy related to disease progression or survival. Potential limitations to current targeted nanotherapeutics include: (1) adhesive interactions with nontarget structures, (2) low density or prevalence of the target, (3) lack of target specificity, and (4) genetic instability resulting in alterations of either the target itself or its expression level in response to treatment. In this review, we address these potential limitations in the context of the key GBM targets with the goal of advancing the understanding and development of targeted nanotherapeutics for GBM. WIREs Nanomed Nanobiotechnol 2017, 9:e1439. doi: 10.1002/wnan.1439 For further resources related to this article, please visit the WIREs website.

Repurposing platinum-based chemotherapies for multi-modal treatment of glioblastoma

Glioblastoma (GBM) is a fatal brain cancer for which new treatment options are sorely needed. Platinum-based drugs have been investigated extensively for GBM treatment but few have shown significant efficacy without major central nervous system (CNS) and systemic toxicities. The relative success of platinum drugs for treatment of non-CNS cancers indicates great therapeutic potential when effectively delivered to the tumor region(s). New insights into the broad anticancer effects of platinum drugs, particularly immunomodulatory effects, and innovative delivery strategies that can maximize these multi-modal effects and minimize toxicities may promote the re-purposing of this chemotherapeutic drug class for GBM treatment.

Non-specific binding and steric hindrance thresholds for penetration of particulate drug carriers within tumor tissue

Therapeutic nanoparticles (NPs) approved for clinical use in solid tumor therapy provide only modest improvements in patient survival, in part due to physiological barriers that limit delivery of the particles throughout the entire tumor. Here, we explore the thresholds for NP size and surface poly(ethylene glycol) (PEG) density for penetration within tumor tissue extracellular matrix (ECM). We found that NPs as large as 62nm, but less than 110nm in diameter, diffused rapidly within a tumor ECM preparation (Matrigel) and breast tumor xenograft slices ex vivo. Studies of PEG-density revealed that increasing PEG density enhanced NP diffusion and that PEG density below a critical value led to adhesion of NP to ECM. Non-specific binding of NPs to tumor ECM components was assessed by surface plasmon resonance (SPR), which revealed excellent correlation with the particle diffusion results. Intravital microscopy of NP spread in breast tumor tissue confirmed a significant difference in tumor tissue penetration between the 62 and 110nm PEG-coated NPs, as well as between PEG-coated and uncoated NPs. SPR assays also revealed that Abraxane, an FDA-approved non-PEGylated NP formulation used for cancer therapy, binds to tumor ECM. Our results establish limitations on the size and surface PEG density parameters required to achieve uniform and broad dispersion within tumor tissue and highlight the utility of SPR as a high throughput method to screen NPs for tumor penetration.

Pulsed ultrasound expands the extracellular and perivascular spaces of the brain

Diffusion within the extracellular and perivascular spaces of the brain plays an important role in biological processes, therapeutic delivery, and clearance mechanisms within the central nervous system. Recently, ultrasound has been used to enhance the dispersion of locally administered molecules and particles within the brain, but ultrasound-mediated effects on the brain parenchyma remain poorly understood. We combined an electron microscopy-based ultrastructural analysis with high-resolution tracking of non-adhesive nanoparticles in order to probe changes in the extracellular and perivascular spaces of the brain following a non-destructive pulsed ultrasound regimen known to alter diffusivity in other tissues. Freshly obtained rat brain neocortical slices underwent sham treatment or pulsed, low intensity ultrasound for 5min at 1MHz. Transmission electron microscopy revealed intact cells and blood vessels and evidence of enlarged spaces, particularly adjacent to blood vessels, in ultrasound-treated brain slices. Additionally, ultrasound significantly increased the diffusion rate of 100nm, 200nm, and 500nm nanoparticles that were injected into the brain slices, while 2000nm particles were unaffected. In ultrasound-treated slices, 91.6% of the 100nm particles, 20.7% of the 200nm particles, 13.8% of the 500nm particles, and 0% of the 2000nm particles exhibited diffusive motion. Thus, pulsed ultrasound can have meaningful structural effects on the brain extracellular and perivascular spaces without evidence of tissue disruption.

Evolving Drug Delivery Strategies to Overcome the Blood Brain Barrier

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.

Abstract B46: Development of biodegradable Fn14-targeted nanoparticles for controlled drug delivery for invasive brain tumors

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.

Surface plasmon resonance as a high throughput method to evaluate specific and non-specific binding of nanotherapeutics

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. 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.