Combined Therapy of AXL and HDAC Inhibition Reverses Mesenchymal Transition in Diffuse Intrinsic Pontine Glioma

PURPOSE

Diffuse intrinsic pontine glioma (DIPG) is an incurable type of pediatric brain cancer, which in the majority of cases is driven by mutations in genes encoding histone 3 (H3K27M). We here determined the preclinical therapeutic potential of combined AXL and HDAC inhibition in these tumors to reverse their mesenchymal, therapy-resistant, phenotype.

EXPERIMENTAL DESIGN

We used public databases and patient-derived DIPG cells to identify putative drivers of the mesenchymal transition in these tumors. Patient-derived neurospheres, xenografts, and allografts were used to determine the therapeutic potential of combined AXL/HDAC inhibition for the treatment of DIPG.

RESULTS

We identified AXL as a therapeutic target and regulator of the mesenchymal transition in DIPG. Combined AXL and HDAC inhibition had a synergistic and selective antitumor effect on H3K27M DIPG cells. Treatment of DIPG cells with the AXL inhibitor BGB324 and the HDAC inhibitor panobinostat resulted in a decreased expression of mesenchymal and stem cell genes. Moreover, this combination treatment decreased expression of DNA damage repair genes in DIPG cells, strongly sensitizing them to radiation. Pharmacokinetic studies showed that BGB324, like panobinostat, crosses the blood-brain barrier. Consequently, treatment of patient-derived DIPG xenograft and murine DIPG allograft-bearing mice with BGB324 and panobinostat resulted in a synergistic antitumor effect and prolonged survival.

CONCLUSIONS

Combined inhibition of AXL and HDACs in DIPG cells results in a synergistic antitumor effect by reversing their mesenchymal, stem cell-like, therapy-resistant phenotype. As such, this treatment combination may serve as part of a future multimodal therapeutic strategy for DIPG.

Culture methods of diffuse intrinsic pontine glioma cells determine response to targeted therapies

Diffuse intrinsic pontine glioma (DIPG) is an aggressive type of brainstem cancer occurring mainly in children, for which there currently is no effective therapy. Current efforts to develop novel therapeutics for this tumor make use of primary cultures of DIPG cells, maintained either as adherent monolayer in serum containing medium, or as neurospheres in serum-free medium. In this manuscript, we demonstrate that the response of DIPG cells to targeted therapies in vitro is mainly determined by the culture conditions. We show that particular culture conditions induce the activation of different receptor tyrosine kinases and signal transduction pathways, as well as major changes in gene expression profiles of DIPG cells in culture. These differences correlate strongly with the observed discrepancies in response to targeted therapies of DIPG cells cultured as either adherent monolayers or neurospheres. With this research, we provide an argument for the concurrent use of both culture conditions to avoid false positive and false negative results due to the chosen method.

Multiregional Tumor Drug-Uptake Imaging by PET and Microvascular Morphology in End-Stage Diffuse Intrinsic Pontine Glioma

Inadequate tumor uptake of the vascular endothelial growth factor antibody bevacizumab could explain lack of effect in diffuse intrinsic pontine glioma. Methods: By combining data from a PET imaging study using ⁸⁹Zr-labeled bevacizumab and an autopsy study, a 1-on-1 analysis of multiregional in vivo and ex vivo ⁸⁹Zr-bevacizumab uptake, tumor histology, and vascular morphology in a diffuse intrinsic pontine glioma patient was performed. Results: In vivo ⁸⁹Zr-bevacizumab measurements showed heterogeneity between lesions. Additional ex vivo measurements and immunohistochemistry of cervicomedullary metastasis samples showed uptake to be highest in the area with marked microvascular proliferation. In the primary pontine tumor, all samples showed similar vascular morphology. Other histologic features were similar between the samples studied. Conclusion: In vivo ⁸⁹Zr-bevacizumab PET serves to identify heterogeneous uptake between tumor lesions, whereas subcentimeter intralesional heterogeneity could be identified only by ex vivo measurements. ⁸⁹Zr-bevacizumab uptake is enhanced by vascular proliferation, although our results suggest it is not the only determinant of intralesional uptake heterogeneity.

Preclinical evaluation of convection-enhanced delivery of liposomal doxorubicin to treat pediatric diffuse intrinsic pontine glioma and thalamic high-grade glioma

OBJECTIVE Pediatric high-grade gliomas (pHGGs) including diffuse intrinsic pontine gliomas (DIPGs) are primary brain tumors with high mortality and morbidity. Because of their poor brain penetrance, systemic chemotherapy regimens have failed to deliver satisfactory results; however, convection-enhanced delivery (CED) may be an alternative mode of drug delivery. Anthracyclines are potent chemotherapeutics that have been successfully delivered via CED in preclinical supratentorial glioma models. This study aims to assess the potency of anthracyclines against DIPG and pHGG cell lines in vitro and to evaluate the efficacy of CED with anthracyclines in orthotopic pontine and thalamic tumor models. METHODS The sensitivity of primary pHGG cell lines to a range of anthracyclines was tested in vitro. Preclinical CED of free doxorubicin and pegylated liposomal doxorubicin (PLD) to the brainstem and thalamus of naïve nude mice was performed. The maximum tolerated dose (MTD) was determined based on the observation of clinical symptoms, and brains were analyzed after H & E staining. Efficacy of the MTD was tested in adult glioma E98-FM-DIPG and E98-FM-thalamus models and in the HSJD-DIPG-007-Fluc primary DIPG model. RESULTS Both pHGG and DIPG cells were sensitive to anthracyclines in vitro. Doxorubicin was selected for further preclinical evaluation. Convection-enhanced delivery of the MTD of free doxorubicin and PLD in the pons was 0.02 mg/ml, and the dose tolerated in the thalamus was 10 times higher (0.2 mg/ml). Free doxorubicin or PLD via CED was ineffective against E98-FM-DIPG or HSJD-DIPG-007-Fluc in the brainstem; however, when applied in the thalamus, 0.2 mg/ml of PLD slowed down tumor growth and increased survival in a subset of animals with small tumors. CONCLUSIONS Local delivery of doxorubicin to the brainstem causes severe toxicity, even at doxorubicin concentrations that are safe in the thalamus. As a consequence, the authors could not establish a therapeutic window for treating orthotopic brainstem tumors in mice. For tumors in the thalamus, therapeutic concentrations to slow down tumor growth could be reached. These data suggest that anatomical location determines the severity of toxicity after local delivery of therapeutic agents and that caution should be used when translating data from supratentorial CED studies to treat infratentorial tumors.

Bevacizumab Targeting Diffuse Intrinsic Pontine Glioma: Results of 89Zr-Bevacizumab PET Imaging in Brain Tumor Models

The role of the VEGF inhibitor bevacizumab in the treatment of diffuse intrinsic pontine glioma (DIPG) is unclear. We aim to study the biodistribution and uptake of zirconium-89 ((89)Zr)-labeled bevacizumab in DIPG mouse models. Human E98-FM, U251-FM glioma cells, and HSJD-DIPG-007-FLUC primary DIPG cells were injected into the subcutis, pons, or striatum of nude mice. Tumor growth was monitored by bioluminescence imaging (BLI) and visualized by MRI. Seventy-two to 96 hours after (89)Zr-bevacizumab injections, mice were imaged by positron emission tomography (PET), and biodistribution was analyzed ex vivo High VEGF expression in human DIPG was confirmed in a publically available mRNA database, but no significant (89)Zr-bevacizumab uptake could be detected in xenografts located in the pons and striatum at an early or late stage of the disease. E98-FM, and to a lesser extent the U251-FM and HSJD-DIPG-007 subcutaneous tumors, showed high accumulation of (89)Zr-bevacizumab. VEGF expression could not be demonstrated in the intracranial tumors by in situ hybridization (ISH) but was clearly present in the perinecrotic regions of subcutaneous E98-FM tumors. The poor uptake of (89)Zr-bevacizumab in xenografts located in the brain suggests that VEGF targeting with bevacizumab has limited efficacy for diffuse infiltrative parts of glial brain tumors in mice. Translating these results to the clinic would imply that treatment with bevacizumab in patients with DIPG is only justified after targeting of VEGF has been demonstrated by (89)Zr-bevacizumab immuno-PET. We aim to confirm this observation in a clinical PET study with patients with DIPG. Mol Cancer Ther; 15(9); 2166-74. ©2016 AACR.

Abstract B27: Toxicity of convection-enhanced delivery with doxorubicin to treat pediatric brain-tumors depends on anatomical location

Introduction and Aim: Diffuse Intrinsic Pontine Glioma (DIPG) and pediatric High Grade Glioma (pHGG) are primary pediatric brain tumors that have a very high mortality and morbidity. Especially tumors that are not (DIPG) or only partially (midline pHGG) eligible for surgical resection have a very poor prognosis. Systemic chemotherapy regimens have failed to deliver satisfactory results but convection enhanced delivery (CED) is a promising technique that delivers chemotherapeutics directly to the tumor. Determining the best agent to deliver via CED is a challenge. Doxorubicin has shown to be highly effective when delivered via CED in preclinical glioma models, and against pHGG and DIPG cells in vitro. Liposomal doxorubicin is thought to improve distribution, bio-availability and subsequent efficacy of CED in glioma models. This preclinical study aims to determine the feasibility of performing CED with free doxorubicin or pegylated liposomal doxorubicin (PLD) in the brainstem and thalamus, and to study the efficacy of PLD and free doxorubicin when treating preclinical DIPG and pHGG models.

Methods: Preclinical CED was performed with 15μl doxorubicin in the brainstem and thalamus of 6-week-old nude mice. Maximal tolerated dose was determined by treating mice with doxorubicin concentrations ranging from 2 mg/ml to 0.02 mg/ml. The efficacy study was performed with the highest possible dose and using the orthotopic diffusely growing E98-FM-DIPG model in the brainstem. Mice (n=12) were treated at day 9 after injection of cells. Follow-up consisted of BLI measurements, and determination of body weight and clinical symptoms.

Results: Maximal tolerated dose was 0.02 mg/ml in the brainstem and 0.2 mg/ml in the thalamus for both free doxorubicin and PLD. Clinical toxicity after CED with higher concentrations consisted of weight loss and neurological deficits including paresis and loss of balance. Symptoms occurred after three (free doxorubicin) or six days (PLD). E98FM-DIPG bearing mice treated with 0.02 mg/ml of free doxorubicin, or PL-doxorubicin via CED did not show any survival benefit compared to vehicle treated animals. 0.2 mg/ml has previously shown to be effective in treating preclinical glioma models.

Conclusions: Local drug delivery of concentrations that are safe in the thalamus show severe toxicity when delivered to the brainstem. No therapeutic window existed for treating orthotopic brainstem tumors in mice. However, therapeutic concentrations could be reached in the thalamus. This data suggest that anatomical location of the tumor is of vital importance when considering the best drugs to deliver via CED.

Citation Format: A. Charlotte P. Sewing, Susanna J.E. Veringa, Tonny Lagerweij, David P. Noske, Dannis G. van Vuurden, Gertjan J.L. Kaspers, Esther Hulleman. Toxicity of convection-enhanced delivery with doxorubicin to treat pediatric brain-tumors depends on anatomical location. [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 B27.

Convection enhanced delivery of carmustine to the murine brainstem: a feasibility study

BACKGROUND

Systemic delivery of therapeutic agents remains ineffective against diffuse intrinsic pontine glioma (DIPG), possibly due to an intact blood-brain-barrier (BBB) and to dose-limiting toxicity of systemic chemotherapeutic agents. Convection-enhanced delivery (CED) into the brainstem may provide an effective local delivery alternative for DIPG patients.

NEW METHOD

The aim of this study is to develop a method to perform CED into the murine brainstem and to test this method using the chemotherapeutic agent carmustine (BiCNU). To this end, a newly designed murine CED catheter was tested in vitro and in vivo. After determination of safety and distribution, mice bearing VUMC-DIPG-3 and E98FM-DIPG brainstem tumors were treated with carmustine dissolved in DW 5% or carmustine dissolved in 10% ethanol.

RESULTS

Our results show that CED into the murine brainstem is feasible and well tolerated by mice with and without brainstem tumors. CED of carmustine dissolved in 5% DW increased median survival of mice with VUMC-DIPG-3 and E98FM-DIPG tumors with 35% and 25% respectively. Dissolving carmustine in 10% ethanol further improved survival to 45% in mice with E98FM-DIPG tumors.

COMPARISON WITH EXISTING METHODS

Since genetically engineered and primary DIPG models are currently only available in mice, murine CED studies have clear advantages over CED studies in other animals.

CONCLUSION

CED in the murine brainstem can be performed safely, is well tolerated and can be used to study efficacy of chemotherapeutic agents orthotopically. These results set the foundation for more CED studies in murine DIPG models.

Human pontine glioma cells can induce murine tumors

Diffuse intrinsic pontine glioma (DIPG), with a median survival of only 9 months, is the leading cause of pediatric brain cancer mortality. Dearth of tumor tissue for research has limited progress in this disease until recently. New experimental models for DIPG research are now emerging. To develop preclinical models of DIPG, two different methods were adopted: cells obtained at autopsy (1) were directly xenografted orthotopically into the pons of immunodeficient mice without an intervening cell culture step or (2) were first cultured in vitro and, upon successful expansion, injected in vivo. Both strategies resulted in pontine tumors histopathologically similar to the original human DIPG tumors. However, following the direct transplantation method all tumors proved to be composed of murine and not of human cells. This is in contrast to the indirect method that included initial in vitro culture and resulted in xenografts comprising human cells. Of note, direct injection of cells obtained postmortem from the pons and frontal lobe of human brains not affected by cancer did not give rise to neoplasms. The murine pontine tumors exhibited an immunophenotype similar to human DIPG, but were also positive for microglia/macrophage markers, such as CD45, CD68 and CD11b. Serial orthotopic injection of these murine cells results in lethal tumors in recipient mice. Direct injection of human DIPG cells in vivo can give rise to malignant murine tumors. This represents an important caveat for xenotransplantation models of DIPG. In contrast, an initial in vitro culture step can allow establishment of human orthotopic xenografts. The mechanism underlying this phenomenon observed with direct xenotransplantation remains an open question.

Therapeutic hypercapnia prevents bleomycin-induced pulmonary hypertension in neonatal rats by limiting macrophage-derived tumor necrosis factor-α

Bleomycin-induced lung injury is characterized in the neonatal rat by inflammation, arrested lung growth, and pulmonary hypertension (PHT), as observed in human infants with severe bronchopulmonary dysplasia. Inhalation of CO2 (therapeutic hypercapnia) has been described to limit cytokine production and to have anti-inflammatory effects on the injured lung; we therefore hypothesized that therapeutic hypercapnia would prevent bleomycin-induced lung injury. Spontaneously breathing rat pups were treated with bleomycin (1 mg/kg/d ip) or saline vehicle from postnatal days 1–14 while being continuously exposed to 5% CO2 (PaCO2 elevated by 15–20 mmHg), 7% CO2 (PaCO2 elevated by 35 mmHg), or normocapnia. Bleomycin-treated animals exposed to 7%, but not 5%, CO2, had significantly attenuated lung tissue macrophage influx and PHT, as evidenced by normalized pulmonary vascular resistance and right ventricular systolic function, decreased right ventricular hypertrophy, and attenuated remodeling of pulmonary resistance arteries. The level of CO2 neither prevented increased tissue neutrophil influx nor led to improvements in decreased lung weight, septal thinning, impaired alveolarization, or decreased numbers of peripheral arteries. Bleomycin led to increased expression and content of lung tumor necrosis factor (TNF)-α, which was found to colocalize with tissue macrophages and to be attenuated by exposure to 7% CO2. Inhibition of TNF-α signaling with the soluble TNF-2 receptor etanercept (0.4 mg/kg ip from days 1–14 on alternate days) prevented bleomycin-induced PHT without decreasing tissue macrophages and, similar to CO2, had no effect on arrested alveolar development. Our findings are consistent with a preventive effect of therapeutic hypercapnia with 7% CO2 on bleomycin-induced PHT via attenuation of macrophage-derived TNF-α. Neither tissue macrophages nor TNF-α appeared to contribute to arrested lung development induced by bleomycin. That 7% CO2 normalized pulmonary vascular resistance and right ventricular function without improving inhibited airway and vascular development suggests that vascular hypoplasia does not contribute significantly to functional changes of PHT in this model.