Advances in Molecular Imaging of Locally Delivered Targeted Therapeutics for Central Nervous System Tumors

Current status and advances to improving drug delivery in diffuse intrinsic pontine glioma

Diffuse midline glioma (DMG), including tumors diagnosed in the brainstem (diffuse intrinsic pontine glioma - DIPG), is the primary cause of brain tumor-related death in pediatric patients. DIPG is characterized by a median survival of <12 months from diagnosis, harboring the worst 5-year survival rate of any cancer. Corticosteroids and radiation are the mainstay of therapy; however, they only provide transient relief from the devastating neurological symptoms. Numerous therapies have been investigated for DIPG, but the majority have been unsuccessful in demonstrating a survival benefit beyond radiation alone. Although many barriers hinder brain drug delivery in DIPG, one of the most significant challenges is the blood-brain barrier (BBB). Therapeutic compounds must possess specific properties to enable efficient passage across the BBB. In brain cancer, the BBB is referred to as the blood-brain tumor barrier (BBTB), where tumors disrupt the structure and function of the BBB, which may provide opportunities for drug delivery. However, the biological characteristics of the brainstem's BBB/BBTB, both under normal physiological conditions and in response to DIPG, are poorly understood, which further complicates treatment. Better characterization of the changes that occur in the BBB/BBTB of DIPG patients is essential, as this informs future treatment strategies. Many novel drug delivery technologies have been investigated to bypass or disrupt the BBB/BBTB, including convection enhanced delivery, focused ultrasound, nanoparticle-mediated delivery, and intranasal delivery, all of which are yet to be clinically established for the treatment of DIPG. Herein, we review what is known about the BBB/BBTB and discuss the current status, limitations, and advances of conventional and novel treatments to improving brain drug delivery in DIPG.

Convection Enhanced Delivery for Diffuse Intrinsic Pontine Glioma: Review of a Single Institution Experience

Diffuse intrinsic pontine gliomas (DIPGs) are a pontine subtype of diffuse midline gliomas (DMGs), primary central nervous system (CNS) tumors of childhood that carry a terrible prognosis. Because of the highly infiltrative growth pattern and the anatomical position, cytoreductive surgery is not an option. An initial response to radiation therapy is invariably followed by recurrence; mortality occurs approximately 11 months after diagnosis. The development of novel therapeutics with great preclinical promise has been hindered by the tightly regulated blood-brain barrier (BBB), which segregates the tumor comportment from the systemic circulation. One possible solution to this obstacle is the use of convection enhanced delivery (CED), a local delivery strategy that bypasses the BBB by direct infusion into the tumor through a small caliber cannula. We have recently shown CED to be safe in children with DIPG (NCT01502917). In this review, we discuss our experience with CED, its advantages, and technical advancements that are occurring in the field. We also highlight hurdles that will likely need to be overcome in demonstrating clinical benefit with this therapeutic strategy.

PET, image-guided HDAC inhibition of pediatric diffuse midline glioma improves survival in murine models

Efforts at altering the dismal prognosis of pediatric midline gliomas focus on direct delivery strategies like convection-enhanced delivery (CED), where a cannula is implanted into tumor. Successful CED treatments require confirmation of tumor coverage, dosimetry, and longitudinal in vivo pharmacokinetic monitoring. These properties would be best determined clinically with image-guided dosimetry using theranostic agents. In this study, we combine CED with novel, molecular-grade positron emission tomography (PET) imaging and show how PETobinostat, a novel PET-imageable HDAC inhibitor, is effective against DIPG models. PET data reveal that CED has significant mouse-to-mouse variability; imaging is used to modulate CED infusions to maximize tumor saturation. The use of PET-guided CED results in survival prolongation in mouse models; imaging shows the need of CED to achieve high brain concentrations. This work demonstrates how personalized image-guided drug delivery may be useful in potentiating CED-based treatment algorithms and supports a foundation for clinical translation of PETobinostat.

Toward optimization of blood brain barrier opening induced by laser-activated perfluorocarbon nanodroplets

The blood brain barrier (BBB), a component of the brain's natural defense system, is often a roadblock for the monitoring and treatment of neurological disorders. Recently, we introduced a technique to open the blood brain barrier through the use of laser-activated perfluorohexane nanodroplets (PFHnDs), a phase-change nanoagent that undergoes repeated vaporization and recondensation when excited by a pulsed laser. Laser-activated PFHnDs were shown to enable noninvasive and localized opening of the BBB, allowing extravasation of various sized agents into the brain tissue. In this current work, the laser-activated PFHnD-induced BBB opening is further explored. In particular, laser fluence and the number of laser pulses used for the PFHnD-induced BBB opening are examined and evaluated both qualitatively and quantitatively to determine the effect of these parameters on BBB opening. The results of these studies show trends between increased laser fluence and an increased BBB opening as well as between an increased number of laser pulses and an increased BBB opening, however, with limitations on the extent of the BBB opening after a certain number of pulses. Overall, the results of these studies serve as a guideline to choosing suitable laser parameters for safe and effective BBB opening.

Combined targeting of PI3K and MEK effector pathways via CED for DIPG therapy

Background

Midline gliomas like diffuse intrinsic pontine glioma (DIPG) carry poor prognosis and lack effective treatment options. Studies have implicated amplifications in the phosphatidylinositol 3-kinase (PI3K) signaling pathway in tumorigenesis; compensatory activation of parallel pathways (eg, mitogen-activated protein kinase [MEK]) may underlie the resistance to PI3K inhibition observed in the clinic.

Methods

Three patient-derived cell lines (SU-DIPG-IV, SU-DIPG-XIII, and SF8628) and a mouse-derived brainstem glioma cell line were treated with PI3K (ZSTK474) and MEK (trametinib) inhibitors, alone or in combination. Synergy was analyzed using Chou-Talalay combination index (CI). These agents were also used alone or in combination in a subcutaneous SU-DIPG-XIII tumor model and in an intracranial genetic mouse model of DIPG, given via convection-enhanced delivery (CED).

Results

We found that these agents abrogate cell proliferation in a dose-dependent manner. Combination treatments were found to be synergistic (CI < 1) across cell lines tested. They also showed significant tumor suppression when given systemically against a subcutaneous DIPG model (alone or in combination) or when given via direct intracranial injection (CED) in a intracranial DIPG mouse model (combination only, median survival 47 vs 35 days post-induction, P = .038). No significant short- or long-term neurotoxicity of ZSTK474 and trametinib delivered via CED was observed.

Conclusions

Our data indicate that ZSTK474 and trametinib combinatorial treatment inhibits malignant growth of DIPG cells in vitro and in vivo, prolonging survival. These results suggest a promising new combinatorial approach using CED for DIPG therapy, which warrants further investigation.

Real-Time, in Vivo Correlation of Molecular Structure with Drug Distribution in the Brain Striatum Following Convection Enhanced Delivery

The blood-brain barrier (BBB) represents a major obstacle in delivering therapeutics to brain lesions. Convection-enhanced delivery (CED), a method that bypasses the BBB through direct, cannula-mediated drug delivery, is one solution to maintaining increased, effective drug concentration at these lesions. CED was recently proven safe in a phase I clinical trial against diffuse intrinsic pontine glioma (DIPG), a childhood cancer. Unfortunately, the exact relationship between drug size, charge, and pharmacokinetic behavior in the brain parenchyma are difficult to observe in vivo. PET imaging of CED-delivered agents allows us to determine these relationships. In this study, we label different modifications of the PDGFRA inhibitor dasatinib with fluorine-18 or via a nanofiber-zirconium-89 system so that the effect of drug structure on post-CED behavior can accurately be tracked in vivo, via PET. Relatively unchanged bioactivity is confirmed in patient- and animal-model-derived cell lines of DIPG. In naïve mice, significant individual variability in CED drug clearance is observed, highlighting a need to accurately understand drug behavior during clinical translation. Generally, the half-life for a drug to clear from a CED site is short for low molecular weight dasatinib analogs that bare different charge; 1-3 (1, 32.2 min (95% CI: 27.7-37.8), 2, 44.8 min (27.3-80.8), and 3, 71.7 min (48.6-127.6) minutes) and is much longer for a dasatinib-nanofiber conjugate, 5, (42.8-57.0 days). Positron emission tomography allows us to accurately measure the effect of drug size and charge in monitoring real-time drug behavior in the brain parenchyma of live specimens.

Strategies for brain-targeting liposomal delivery of small hydrophobic molecules in the treatment of neurodegenerative diseases

Neurodegenerative diseases (NDs), including Alzheimer's disease (AD) and Parkinson's disease (PD), threaten the health of an ever-growing number of older people worldwide; so far, there are no effective cures. Significant efforts have been devoted to developing new drugs for NDs in recent years, and some small molecules have been shown to be promising in preclinical studies. However, the major challenge for brain-targeting drugs is how to efficiently deliver the drugs across the blood-brain barrier (BBB) to desired targets. To address this issue, liposomal delivery systems have proved to be ideal carriers for neuroprotective small molecules. Here, we summarize recent advances in the brain-targeting liposomal delivery of small hydrophobic molecules (SHMs) and propose strategies for developing liposomal SHMs as disease-modifying neurotherapeutics for NDs.

Fe3O4@Au composite magnetic nanoparticles modified with cetuximab for targeted magneto-photothermal therapy of glioma cells

Background

Thermoresponsive nanoparticles have become an attractive candidate for designing combined multimodal therapy strategies because of the onset of hyperthermia and their advantages in synergistic cancer treatment. In this paper, novel cetuximab (C225)-encapsulated core-shell Fe₃O₄@Au magnetic nanoparticles (Fe₃O₄@Au-C225 composite-targeted MNPs) were created and applied as a therapeutic nanocarrier to conduct targeted magneto-photothermal therapy against glioma cells.

Methods

The core-shell Fe₃O₄@Au magnetic nanoparticles (MNPs) were prepared, and then C225 was further absorbed to synthesize Fe₃O₄@Au-C225 composite-targeted MNPs. Their morphology, mean particle size, zeta potential, optical property, magnetic property and thermal dynamic profiles were characterized. After that, the glioma-destructive effect of magnetic fluid hyperthermia (MFH) combined with near-infrared (NIR) hyperthermia mediated by Fe₃O₄@Au-C225 composite-targeted MNPs was evaluated through in vitro and in vivo experiments.

Results

The inhibitory and apoptotic rates of Fe₃O₄@Au-C225 composite-targeted MNPs-mediated combined hyperthermia (MFH+NIR) group were significantly higher than other groups in vitro and the marked upregulation of caspase-3, caspase-8, and caspase-9 expression indicated excellent antitumor effect by inducing intrinsic apoptosis. Furthermore, Fe₃O₄@Au-C225 composite-targeted MNPs-mediated combined hyperthermia (MFH+NIR) group exhibited significant tumor growth suppression compared with other groups in vivo.

Conclusion

Our studies illustrated that Fe₃O₄@Au-C225 composite-targeted MNPs have great potential as a promising nanoplatform for human glioma therapy and could be of great value in medical use in the future.

18F-Radiolabeled Panobinostat Allows for Positron Emission Tomography Guided Delivery of a Histone Deacetylase Inhibitor

Histone deacetylase (HDAC) inhibition is becoming an increasingly popular approach to treat cancer, as HDAC overexpression is common in many malignancies. The blood-brain barrier (BBB) prevents systemically delivered drugs from reaching brain at effective concentration, making small-molecule-HDAC inhibition in brain tumors particularly challenging. To circumvent the BBB, novel routes for administering therapeutics are being considered in the clinic, and a need exists for drugs whose deliveries can be directly imaged, so that effective delivery across the BBB can be monitored. We report chemistry for radiolabeling the HDAC inhibitor, panobinostat, with fluoride-18 (compound-1). Like panobinostat, compound 1 retains nanomolar efficacy in diffuse intrinsic pontine glioma (DIPG IV and XIII) cells (IC₅₀ = 122 and 108 nM, respectively), with lesser activity against U87 glioma. With a favorable therapeutic ratio, 1 is highly selective to glioma and demonstrates considerably less toxicity toward healthy astrocyte controls (IC₅₀ = 5265 nM). Compound 1 is stable in aqueous solution at physiological pH (>7 days, fetal bovine serum), and its delivery can be imaged by positron emission tomography (PET). Compound 1 is synthesized in two steps, and employs rapid, late-stage aqueous isotopic exchange ¹⁸F-radiochemistry. PET is used to image the in vivo delivery of [¹⁸F]-1 to the murine central nervous system via convection enhanced delivery.

Drug Resistance in HER2-Positive Breast Cancer Brain Metastases: Blame the Barrier or the Brain?

The brain is the most common site of first metastasis for patients with HER2-positive breast cancer treated with HER2-targeting drugs. However, the development of effective therapies for breast cancer brain metastases (BCBM) is limited by an incomplete understanding of the mechanisms governing drug sensitivity in the central nervous system. Pharmacodynamic data from patients and in vivo models suggest that inadequate drug penetration across the "blood-tumor" barrier is not the whole story. Using HER2-positive BCBMs as a case study, we highlight recent data from orthotopic brain metastasis models that implicate brain-specific drug resistance mechanisms in BCBMs and suggest a translational research paradigm to guide drug development for treatment of BCBMs. Clin Cancer Res; 24(8); 1795-804. ©2018 AACR.

Effects of major parameters of nanoparticles on their physical and chemical properties and recent application of nanodrug delivery system in targeted chemotherapy

Chemotherapy is still one of the main cancer therapy treatments, but the curative effect of chemotherapy is relatively low, as such the development of a new cancer treatment is highly desirable. The gradual maturation of nanotechnology provides an innovative perspective not only for cancer therapy but also for many other applications. There are a diverse variety of nanoparticles available, and choosing the appropriate carriers according to the demand is the key issue. The performance of nanoparticles is affected by many parameters, mainly size, shape, surface charge, and toxicity. Using nanoparticles as the carriers to realize passive targeting and active targeting can improve the efficacy of chemotherapy drugs significantly, reduce the mortality rate of cancer patients, and improve the quality of life of patients. In recent years, there has been extensive research on nanocarriers. In this review, the effects of several major parameters of nanoparticles on their physical and chemical properties are reviewed, and then the recent progress in the application of several commonly used nanoparticles is presented.

A Murine Model for Quantitative, Real-Time Evaluation of Convection-Enhanced Delivery (RT-CED) Using an 18[F]-Positron Emitting, Fluorescent Derivative of Dasatinib

The blood brain barrier can limit the efficacy of systemically delivered drugs in treating neurological malignancies; therefore, alternate routes of drug administration must be considered. The Abl-kinase inhibitor, dasatinib, is modified to give compound 1 ([¹⁸F]-1) so that ¹⁸F-positron emission tomography (PET) and fluorescent imaging can both be used to observe drug delivery to murine orthotopic glioma. In vitro Western blotting, binding studies (IC₅₀ = 22 ± 5 nmol/L), and cell viability assays (IC₅₀ = 46 ± 30 nmol/L) confirm nanomolar, in vitro effectiveness of [¹⁸F]-1, a dasatinib derivative that is visible by ¹⁸F-PET and fluorescence. [¹⁸F]-1 is used to image dynamic direct drug delivery via two different drug delivery techniques to orthotopic murine brainstem glioma (mBSG) bearing mice. Convection enhanced delivery (CED) delivers higher concentrations of drug to glioma-containing volumes versus systemic, tail-vein delivery. Accurate delivery and clearance data pertaining to dasatinib are observed, providing personalized information that is important in dosimetry and redosing. Cases of missed drug delivery are immediately recognized by PET/CT, allowing for prompt intervention in the case of missed delivery. Mol Cancer Ther; 16(12); 2902-12. ©2017 AACR.

Nanomaterials for convection-enhanced delivery of agents to treat brain tumors

Nanomaterials represent a promising and versatile platform for the delivery of therapeutics to the brain. Treatment of brain tumors has been a long-standing challenge in the field of neuro-oncology. The current standard of care - a multimodal approach of surgery, radiation and chemotherapy - yields only a modest therapeutic benefit for patients with malignant gliomas. A major obstacle for treatment is the failure to achieve sufficient delivery of therapeutics at the tumor site. Recent advances in local drug delivery techniques, along with the development of highly effective brain-penetrating nanocarriers, have significantly improved treatment and imaging of brain tumors in preclinical studies. The major advantage of this combined strategy is the ability to optimize local therapy, by maintaining an effective and sustained concentration of therapeutics in the brain with minimal systemic toxicity. This review highlights some of the latest developments, significant advancements and current challenges in local delivery of nanomaterials for the treatment of brain tumors.