Zhang, Liang

Abstract Pontine H3 K27-altered diffuse midline gliomas (DMGs) are rare, fatal pediatric brain tumors resistant to systemic therapies due to the blood-brain barrier (BBB) and efflux transporters (ETs), which actively clear drugs from the brain. Convection-enhanced delivery (CED) bypasses the BBB by directly infusing therapeutics into the tumor, but maintaining adequate drug concentrations remains a challenge. This study explores strategies to enhance drug-tumor residence time and improve treatment efficacy. Using chemical modeling, FDA-approved drugs identified in prior high-throughput screening efforts were classified based on physiochemical properties impacting CED pharmacokinetics, including BBB penetration and ET substrate status. Drug behavior was validated in patient-derived in vitro and in vivo DMG models. The impact of systemic drug co-administration on drug retention and therapeutic efficacy was evaluated using multiple patient-derived orthotopic xenograft (PDOX) models. ET substrate drugs exhibited rapid elimination from the brain post-CED, limiting their therapeutic potential. However, systemic everolimus administration prolonged drug retention and potentiated the effects of efflux substrate drugs delivered via CED (e.g., topotecan, ponatinib). This combinatorial approach significantly enhanced anticancer effects in multiple PDOX models, demonstrating improved tumor control compared to monotherapy. Overall, these findings suggest that pharmacological inhibition of ETs via systemic everolimus administration can enhance drug retention in DMG when combined with CED. The observed synergistic effects highlight a promising strategy to overcome drug clearance limitations and improve treatment outcomes. Further clinical investigation is warranted to validate this approach in patients.

Abstract Background Atypical teratoid rhabdoid tumor (ATRT) is a deadly central nervous system embryonal tumor caused by loss of SMARCB1, a core subunit of SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complexes. SMARCB1-deficient cancers are defined by loss of cell differentiation-associated enhancers, but how SWI/SNF interacts with other arbiters of cell differentiation (specifically lineage-specific transcription factors [TFs]) remains poorly understood. Methods We leveraged a multi-omics approach, patient-derived ATRT cells, and patient-derived orthotopic xenografts to investigate the interplay of SWI/SNF with lineage-specific TFs in a clinically relevant setting. Results We observe that an activating protein 1 (AP-1)-dependent transcriptional regulatory network is lost in ATRT, and AP-1 and lineage-specific TFs TEAD1 and ZIC2 require SMARCB1 for enhancer binding. SMARCB1-dependent SWI/SNF integrates transcriptional functions of lineage-specific TFs into a core regulatory circuit that depends on the AP-1 subunit c-JUN, whose expression is determined by a SMARCB1-dependent super-enhancer that is lost in ATRT-MYC. In the absence of SMARCB1, lineage-specific TFs are sequestered to promoters, where they maintain core transcriptional programs necessary for cell survival. Targeting residual, promoter-proximal TF activity by a protein degrader of the SWI/SNF ATPase SMARCA4 or small-molecule inhibitors that indirectly inhibit AP-1 and TEAD activity abrogates expression of these networks, reducing cell viability in vitro and prolonging survival in an orthotopic patient-derived xenograft model. Conclusions These results demonstrate SWI/SNF complexes are critical for lineage-specific TF binding and activity at both promoters and enhancers. In the context of ATRT, these findings reveal a previously underappreciated therapeutic vulnerability in targeting residual promoter-proximal TF function in ATRT.

Abstract H3 K27-altered diffuse midline gliomas (DMG) are uniformly lethal tumors for which no therapy has been found to be effective. The blood-brain barrier (BBB) restricts uptake and accumulation of systemically administered drugs in the brain. Convection-enhanced delivery (CED) circumvents the BBB by directly infusing therapeutics into the tumor, facilitating homogenous distribution of drugs at high local concentrations with minimal systemic toxicity. However, most drugs given by CED are rapidly cleared from the brain, severely limiting its therapeutic potential. Here, we determine the impact of drug characteristics rather than mechanism of action on compatibility with CED. Various medicinal chemistry prediction models were interrogated to define drug categories predicated on inherent physicochemical properties of the drugs. A panel of FDA-approved drugs with biologically validated activity in DMG were selected for each group: panobinostat/ponatinib, everolimus/topotecan, tolnaftate/tretinoin, and carmofur/eltrombopag. In vivo pharmacokinetic studies of these drugs delivered by CED into the pons of tumor-naïve mice showed that drugs expected to be less likely to undergo active efflux persisted at the site of infusion over prolonged periods of time. Conversely, efflux transporter (ET) substrate drugs were quickly excreted from the brain and readily detectable in the plasma following CED. Based on the observed brain and plasma concentration-time profiles, the brain exit rate constant and clearance out of the brain were much higher for ET substrate drugs compared with ET non-substrates, resulting in a significant increase in the residence time (the time spent by drugs in the brain) in the absence of ET-mediated clearance. These properties were further validated in efficacy studies in DMG animal models. The proclivity of many drugs to be rapidly effluxed from the brain after CED generates a vulnerability that can be exploited for the development of novel therapeutic regimens, such as with pharmacokinetics-informed drug selection or concomitant dosing of ET-inhibiting drugs.

H3 K27–altered diffuse midline gliomas (DMGs) are frequently biopsied to obtain tissue diagnosis, inform clinical decision-making, and determine clinical trial eligibility. Tissue yield from biopsies is typically low, leaving little material available for research. To advance understanding of disease biology and promote preclinical testing of novel therapeutics, collecting viable cellular material from treatment-naive tumors is of paramount importance. Here, the authors report the feasibility of a practicable technique for creating DMG cell lines and patient-derived xenografts (PDXs) without the need for additional biopsy specimens. Tumor cells are obtained by probe washing immediately after completion of biopsy. Wash fluid is collected, and viable cells are expanded in vitro. Cultured cells are used to establish PDX rodent models. A total of 5 patient samples were collected by this technique. Viable tumor cells were obtained from 3 of the 5 samples, and cell lines suitable for experiments were obtained within 6–8 months. Orthotopic implantation and flank engraftment was successful in 1 of the 3 established cell lines. Animals harboring intracranial tumors were euthanized due to disease burden 6–7 months after stereotactic injection. Flank tumors formed within 4–5 months and were serially passaged. Molecular and tissue analyses confirmed retention of H3 K27M expression and loss of H3 K27me3 in all cell lines and PDXs.

Abstract Background H3K27-altered diffuse midline glioma (DMG) is the deadliest pediatric brain tumor; despite intensive research efforts, every clinical trial to date has failed. Is this because we are choosing the wrong drugs? Or are drug delivery and other pharmacokinetic variables at play? We hypothesize that the answer is likely a combination, where optimization may result in a much needed novel therapeutic approach. Methods We used in vitro drug screening, patient samples, and shRNA knockdown models to identify an upregulated target in DMG. A single small molecule protein kinase inhibitor with translational potential was selected for systemic and direct, loco-regional delivery to patient-derived xenografts (PDX) and genetically engineered mouse models (GEMM). Pharmacokinetic studies were conducted in non-tumor bearing rats. Results Aurora kinase (AK) inhibitors demonstrated strong antitumor effects in DMG drug screens. Additional in vitro studies corroborated the importance of AK to DMG survival. Systemic delivery of alisertib showed promise in subcutaneous PDX but not intracranial GEMM and PDX models. Repeated loco-regional drug administration into the tumor through convection-enhanced delivery (CED) was equally inefficacious, and pharmacokinetic studies revealed rapid clearance of alisertib from the brain. In an effort to increase the drug to tumor residence time, continuous CED over 7 days improved drug retention in the rodent brainstem and significantly extended survival in both orthotopic PDXs and GEMMs. Conclusions These studies provide evidence for increasing drug-tumor residence time of promising targeted therapies via extended CED as a valuable treatment strategy for DMG.

Abstract H3K27-altered diffuse midline glioma (DMG) is a uniformly lethal CNS cancer that predominately occurs in children. In the last decade, while studies revealing the molecular underpinnings of the disease have paved the way for novel therapeutic strategies, this tumor remains a death sentence. Our lab and others have identified numerous drugs of high interest for treating this devasting disease, however, every trial has failed to show benefit. Is our failure to translate these laboratory findings due to the fact we have not found the right drugs or treatment regimens yet? Or is this a failure to get the drugs to the tumor? Or is this simply a very bad disease to treat? The answer is likely multifactorial. Our lab, in collaboration with others, have strong data to show that simply getting drugs to the tumor will not result in a positive benefit. Most drugs are rapidly cleared from their target space. Utilizing techniques that increase the drug-tumor resonance time is necessary to translate our basic science findings to our patients. Picking the right drug and the delivery mechanism is not enough for a positive effect. Here, we assessed the efficacy of a previously identified inhibitor, alisertib, delivered by short-term convection-enhanced delivery or a continuous osmotic pump and found that continuous, direct delivery results in a significant increase in survival (p = 0.0002). Furthermore, long-term survivors showed a decreased tumor burden and on-target drug effects. These data support that translation into patients must consider three factors: 1) selection of a potent therapy, 2) selection of the proper delivery method for that therapy, 3) modulation to ensure that the therapy remains in the targeted tissue long enough for desired effect. Keeping these basic tenets at the forefront of development may finally lead to a more effective treatment strategy for this devastating disease

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 Diffuse midline glioma (DMG) is a lethal brain tumor that typically occurs in children. Numerous studies have demonstrated the central role of the H3K27M mutation and secondary loss of H3K27 trimethylation (H3K27me3) in DMG tumorigenesis. Understanding how the H3K27M mutation alters the epigenetic landscape of the cell is necessary for revealing molecular targets that are critical to tumorigenesis. To investigate the epigenetic effects of H3K27M mutation in DMG, we developed revertant DMG cell lines with the mutant methionine residue reverted to wildtype (i.e., M27K). Revertant cells were analyzed for epigenetic changes and phenotypic differences in vitro and in vivo. H3M27K DMG cells grew in culture but displayed diminished proliferative capacity. H3M27K cells demonstrated total loss of H3K27M expression and restored trimethylation of H3K27 and H3K4. Furthermore, consistent with the hypothesis that the H3K27M mutation impacts H3 phosphorylation via expression of Aurora Kinase during mitosis, H3M27K cells demonstrated reduced expression of both Aurora Kinase A and phosphorylation of H3 serine residues 10 and 28. In line with the critical role of H3S10 phosphorylation in chromatin segregation, H3M27K cells also demonstrated restored chromosome segregation compared to H3K27M cells. In vivo data will be discussed. Revertance of the H3K27M mutation reduces tumorigenesis in DMG tumors. Isogenic H3M27K cells display reversal of key epigenetic changes associated with oncogenesis in DMG. The revertant H3M27K DMG model is a useful tool to investigate the downstream epigenetic reprogramming specific to H3K27M mutation in these tumors.

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.