Power, Erica A.

Abstract Diffuse midline gliomas (DMGs) harboring the H3K27M mutation are highly aggressive, uniformly fatal brain tumors that primarily occur in children. The blood-brain barrier (BBB), including drug efflux pumps, prevent numerous drugs from reaching CNS tumors at cytotoxic concentrations. Alisertib is an aurora kinase inhibitor that was previously identified in a drug screen as a compound of interest. However, its ability to penetrate the BBB is not well established. The goals of this study were two-fold: 1) determine the CNS distribution and clearance rates of alisertib following systemic delivery and if the BBB efflux pumps, Pgp and BCRP, alter distribution and clearance. 2) Compare alisertib distribution and clearance following convection-enhanced delivery to systemic results. WT and Pgp/BCRP knockout mice and Sprague-dawley rats underwent tail vein injection (mice and rats) or convection-enhanced delivery to the brainstem (rats only) of alisertib and sacrificed at 0, 2, 4, 8, 12, 16 and 24hours. The plasma and brain were collected and analyzed for alisertib concentration by HPLC-MS/MS. We found that in both mice and rats, alisertib concentration in the plasma and brain decreased biexponentially. Overall, Alisertib was found to be 3.14% brain penetrant. In Pgp/BCRP knockout mice, alisertib concentration in the plasma and brain decreased biexponentially, but was detected at higher concentration at all time points in the brain compared to WT mice. This resulted in a higher brain penetrance (17.26%). Differences based on anatomical brain region were significant in those rats which received convection-enhanced delivery. Alisertib was found in higher concentration in the pons and cerebellum compared to systemic delivery, but lower concentrations in the cortex and plasma. These results suggest that drug clearance may be a general mechanism limiting efficacy of drugs of interest and should be carefully considered during preclinical evaluation.

Abstract BACKGROUND Diffuse midline gliomas harboring the H3K27M mutation are aggressive and universally fatal brain tumors that primarily occur in children. The blood-brain barrier (BBB) prevents many drugs from reaching the tumor at cytotoxic concentrations and efflux pumps found on the epithelial cells of the BBB rapidly pump drugs out of the brain. Convection enhanced delivery (CED) is a drug delivery technique that bypasses the BBB by directly injecting the drug into the tumor site under a pressure gradient. Further clinical implementation of CED requires understanding drug distribution, as optimal drug physico-chemical properties have never been evaluated. METHODS Sprague Dawley rats underwent a single injection of drug by CED to the brainstem with and without an efflux pump inhibitor. Animals were euthanized at 0, 2, 4, 8, 12 and 24 hours. Their brain drug concentration/distribution was analyzed by MALDI-MSI and plasma drug concentration was measured by LC-MS/MS. RESULTS Drug distribution and brainstem concentration were increased following BBB efflux pump inhibition compared to no pump inhibition controls. Additionally, efflux pump inhibition resulted in slower drug clearance for those drugs that are known pump substrates. CONCLUSIONS BBB efflux pump inhibition resulted in a larger volume of distribution, increased drug concentration and slower drug clearance following CED to the brainstem of known efflux substrates.

OBJECTIVE Convection-enhanced delivery (CED) and osmotic pump delivery both have been promoted as promising techniques to deliver drugs to pediatric diffuse intrinsic pontine gliomas (DIPGs). Correspondingly, the aim of this study was to understand how infusate molecular weight (MW), duration of delivery, and mechanism of delivery (CED or osmotic pump) affect volume of distribution (V d ) in the brainstem, to better inform drug selection and delivery in future DIPG investigations. METHODS A series of in vivo experiments were conducted using rat models. CED and osmotic pump delivery systems were surgically implanted in the brainstem, and different MW fluorescent dextran beads were infused either once (acute) or daily for 5 days (chronic) in a volume infused (V i ). Brainstems were harvested after the last infusion, and V d was quantified using serial sectioning and fluorescence imaging. RESULTS Fluorescence imaging showed infusate uptake within the brainstem for both systems without complication. A significant inverse relationship was observed between infusate MW and V d in all settings, which was distinctly exponential in nature in the setting of acute delivery across the 570-Da to 150-kDa range. Chronic duration and CED technique resulted in significantly greater V d compared to acute duration or osmotic pump delivery, respectively. When accounting for V i , acute infusion yielded significantly greater V d /V i than chronic infusion. The distribution in CED versus osmotic pump delivery was significantly affected by infusate MW at higher weights. CONCLUSIONS Here the authors demonstrate that infusate MW, duration of infusion, and infusion mechanism all impact the V d of an infused agent and should be considered when selecting drugs and infusion parameters for novel investigations to treat DIPGs.

Abstract Diffuse midline gliomas harboring the H3K27M mutation, previously known as diffuse intrinsic pontine gliomas (DIPG), are rare and aggressive pediatric brain tumors without cure. One of the major challenge sin DIPG treatment is the effective delivery of therapeutic agents across the blood-brain barrier (BBB) to the tumor and surrounding infiltrating cells. Therefore, strategies that enhance drug delivery to the brain are of great interest. Convection-enhanced delivery (CED) is a technique that bypasses the BBB and increases drug distribution by applying hydraulic pressure to deliver compounds directly and evenly into a target region. However, knowledge in CED pharmacology and convective kinetics is still lacking. In an effort to characterize the feasibility, safety, and distribution in the brain based on molecular size of the delivered agent, we performed infusions of FITC-dextran (range 3,000 Da–150,000 Da) comparing CED and osmotic pump-based delivery into the brainstem of rodents. We calculated the area and volume of distribution (Vd) of the FITC-dextran throughout the brain. Our data showed that the Vd decreased exponentially with increased molecular weight of the FITC-dextran. Interestingly, the Vdcan maintain linearity at lower molecular weights. Maximal cross-sectional area and craniocaudal extension of fluorescence also decreased when lowering the infusate size. In addition, we developed a patient-derived DIPG orthotopic xenograft model and performed an image-guided CED cannula installation in the tumor bed. Using 3D bioluminescence imaging and computed tomography, we determined the tumor volume and the positioning of the cannula in the bulk tumor. The summation of these results supports CED as a promising technique for treating DIPG tumors. A better understanding of how drugs distribute by convection will allow us to optimize treatment regimens and, ultimately, offers hope to patients and families with this devastating disease.

Abstract BACKGROUND Diffuse midline gliomas harboring the H3K27M mutation, previously known as diffuse intrinsic pontine gliomas (DIPG), are rare and aggressive pediatric brain tumors. Over 100 clinical trials with different chemotherapeutics have failed to show any therapeutic benefit. One reason for failure is likely due to poor delivery of these agents to the brainstem. Convection-enhanced delivery (CED) is an emerging delivery technique used to directly inject the agent of interest into the brainstem under pressure. While there is evidence that this may be an effective delivery method, little work has been done to understand the optimal physical properties of these drugs. We sought characterize volume of distribution in the brain based on molecular size of the agent delivered via CED. METHODS Sprague- Dawley rats underwent a single injection of FITC-dextran (3,000 Da, 10,000 Da, 20,000 Da, 70,000 Da, 150,000 Da) via CED into the pons. Post-injection, animals were sacrificed and their brains harvested. Fluorescent microscopy imaging was used to calculate the volume of distribution of the FITC-dextran throughout the brain. RESULTS The volume of distribution (Vd) decreased exponentially according to a two-phase delay (r2= 0.94) as the molecular size of the FITC-dextran increased. The highest mean Vd (107.87mm3) was at a molecular weight of 3,000 Da, and lowest mean Vd (26.48 mm3) was at a molecular weight of 150,000 Da. ANOVA analysis was statistically significant (p= 0.0017). CONCLUSIONS As the molecular size of the FITC-dextran increased, the volume of distribution within the brain following a single injection via CED into the pons decreased. A better understanding of how drugs distribute by convection will allow us to optimize treatment regimens for DIPG tumors.

Abstract BACKGROUND Diffuse intrinsic pontine gliomas (DIPG), known today as diffuse midline gliomas with the H3K27M mutation, are inoperable and aggressive brain tumors found predominantly in children. Despite extensive research no treatment or cure has been elucidated. Studies in 2012 showed that the majority of DIPG tumors have the H3K27M mutation, but the development of novel therapeutics has been hindered by lack of good laboratory models. Although patient derived cell lines with the H3K27M mutation have increased, the development of good murine xenografts are lagging, requiring extensive time and money. Previous studies have shown that the chicken embryo Chorioallantoic Membrane (CAM) model is an affordable and time-efficient method of studying tumor biology and response to treatment. We sought to develop this in H3K27M tumors to bridge the gap between in vitro—in vivo studies. METHODS Three patient-derived H3K27M cell lines were cultured and implanted on the chick embryo CAM on day 9 post-fertilization. Tumors underwent multiple drug treatment with 0.5uM or 2.0uM Alisertib (days 11, 13, 15) or a single targeted radiation treatment at 2 Grey (day 13). Tumor volume was assessed via ultrasound on day 16. The tumor specimens were harvested and analyzed by immunohistochemistry. RESULTS Patient-derived DIPG cells implanted on the CAM maintain their molecular characteristics and form tumors on the surface of the CAM as evidenced by H&E and H3K27M status. Statistically significant differences in volume were found in three H3K27M DIPG lines in Alisertib treated tumors compared to the control (p< 0.001, p< 0.001, p= 0.005). Statistically significant differences in tumor volume were found when treating two DIPG lines with targeted radiation therapy compared to controls (p= 0.01, p= 0.02). CONCLUSIONS These results validated the CAM assay as a reliable xenograft model for studying DIPG tumor biology and determining efficacy of drug and radiation treatment.

Diffuse intrinsic pontine glioma (DIPG), otherwise known as diffuse midline glioma with H3K27M mutation, is a devastating brainstem glioma without a cure. Efforts are currently underway to better optimize molecular diagnoses through biological sampling, which today remains largely limited to surgical biopsy sampling. Surgical intervention is not without its risks, and therefore a preference remains for a less invasive modality that can provide biological information about the tumor. There is emerging evidence to suggest that a liquid biopsy, targeting biofluids such as CSF and blood plasma, presents an attractive alternative for brain tumors in general. In this update, the authors provide a summary of the progress made to date regarding the use of liquid biopsy to diagnose and monitor DIPG, and they also propose future development and applications of this technique moving forward, given its unique histone biology.