PDF file - 3091K, Supplemental Figure 1: Cell cycle progression occurs more rapidly in CD15+ cells than in CD15- cells.

BackgroundDiffuse intrinsic pontine glioma (DIPG), or high-grade brainstem glioma (BSG), is one of the major causes of brain tumor-related deaths in children. Its prognosis has remained poor despite numerous efforts to improve survival. Panobinostat, a histone deacetylase inhibitor, is a targeted agent that has recently shown pre-clinical efficacy and entered a phase I clinical trial for the treatment of children with recurrent or progressive DIPG.MethodsA collaborative pre-clinical study was conducted using both a genetic BSG mouse model driven by PDGF-B signaling, p53 loss, and ectopic H3.3-K27M or H3.3-WT expression and an H3.3-K27M orthotopic DIPG xenograft model to confirm and extend previously published findings regarding the efficacy of panobinostat in vitro and in vivo.ResultsIn vitro, panobinostat potently inhibited cell proliferation, viability, and clonogenicity and induced apoptosis of human and murine DIPG cells. In vivo analyses of tissue after short-term systemic administration of panobinostat to genetically engineered tumor-bearing mice indicated that the drug reached brainstem tumor tissue to a greater extent than normal brain tissue, reduced proliferation of tumor cells and increased levels of H3 acetylation, demonstrating target inhibition. Extended consecutive daily treatment of both genetic and orthotopic xenograft models with 10 or 20 mg/kg panobinostat consistently led to significant toxicity. Reduced, well-tolerated doses of panobinostat, however, did not prolong overall survival compared to vehicle-treated mice.ConclusionOur collaborative pre-clinical study confirms that panobinostat is an effective targeted agent against DIPG human and murine tumor cells in vitro and in short-term in vivo efficacy studies in mice but does not significantly impact survival of mice bearing H3.3-K27M-mutant tumors. We suggest this may be due to toxicity associated with systemic administration of panobinostat that necessitated dose de-escalation.

Diffuse intrinsic pontine glioma (DIPG) is a rare and incurable brain tumor that arises predominately in children and involves the pons, a structure that along with the midbrain and medulla makes up the brainstem. We have previously developed genetically engineered mouse models of brainstem glioma using the RCAS/Tv-a system by targeting PDGF-B overexpression, p53 loss, and H3.3K27M mutation to Nestin-expressing brainstem progenitor cells of the neonatal mouse. Here we describe a novel mouse model targeting these same genetic alterations to Pax3-expressing cells, which in the neonatal mouse pons consist of a Pax3 +/Nestin +/Sox2 + population lining the fourth ventricle and a Pax3 +/NeuN + parenchymal population. Injection of RCAS-PDGF-B into the brainstem of Pax3-Tv-a mice at postnatal day 3 results in 40% of mice developing asymptomatic low-grade glioma. A mixture of low- and high-grade glioma results from injection of Pax3-Tv-a;p53fl/fl mice with RCAS-PDGF-B and RCAS-Cre, with or without RCAS-H3.3K27M. These tumors are Ki67 +, Nestin +, Olig2 +, and largely GFAP − and can arise anywhere within the brainstem, including the classic DIPG location of the ventral pons. Expression of the H3.3K27M mutation reduces overall H3K27me3 as compared with tumors without the mutation, similar to what has been previously shown in human and mouse tumors. Thus, we have generated a novel genetically engineered mouse model of DIPG, which faithfully recapitulates the human disease and represents a novel platform with which to study the biology and treatment of this deadly disease.

Diffuse intrinsic pontine gliomas (DIPGs) represent a particularly lethal type of pediatric brain cancer with no effective therapeutic options. Our laboratory has previously reported the development of genetically engineered DIPG mouse models using the RCAS/tv-a system, including a model driven by PDGF-B, H3.3K27M, and p53 loss. These models can serve as a platform in which to test novel therapeutics prior to the initiation of human clinical trials. In this study, an in vitro high-throughput drug screen as part of the DIPG preclinical consortium using cell-lines derived from our DIPG models identified BMS-754807 as a drug of interest in DIPG. BMS-754807 is a potent and reversible small molecule multi-kinase inhibitor with many targets including IGF-1R, IR, MET, TRKA, TRKB, AURKA, AURKB. In vitro evaluation showed significant cytotoxic effects with an IC50 of 0.13 μM, significant inhibition of proliferation at a concentration of 1.5 μM, as well as inhibition of AKT activation. Interestingly, IGF-1R signaling was absent in serum-free cultures from the PDGF-B; H3.3K27M; p53 deficient model suggesting that the antitumor activity of BMS-754807 in this model is independent of IGF-1R. In vivo, systemic administration of BMS-754807 to DIPG-bearing mice did not prolong survival. Pharmacokinetic analysis demonstrated that tumor tissue drug concentrations of BMS-754807 were well below the identified IC50, suggesting that inadequate drug delivery may limit in vivo efficacy. In summary, an unbiased in vitro drug screen identified BMS-754807 as a potential therapeutic agent in DIPG, but BMS-754807 treatment in vivo by systemic delivery did not significantly prolong survival of DIPG-bearing mice.

Diffuse intrinsic pontine gliomas (DIPGs) represent a particularly lethal type of pediatric brain cancer with no effective therapeutic options. Our laboratory has previously reported the development of genetically engineered DIPG mouse models using the RCAS/tv-a system, including a model driven by PDGF-B, H3.3K27M, and p53 loss. These models can serve as a platform in which to test novel therapeutics prior to the initiation of human clinical trials. In this study, an in vitro high-throughput drug screen as part of the DIPG preclinical consortium using cell-lines derived from our DIPG models identified BMS-754807 as a drug of interest in DIPG. BMS-754807 is a potent and reversible small molecule multi-kinase inhibitor with many targets including IGF-1R, IR, MET, TRKA, TRKB, AURKA, AURKB. In vitro evaluation showed significant cytotoxic effects with an IC50 of 0.13 μM, significant inhibition of proliferation at a concentration of 1.5 μM, as well as inhibition of AKT activation. Interestingly, IGF-1R signaling was absent in serum-free cultures from the PDGF-B; H3.3K27M; p53 deficient model suggesting that the antitumor activity of BMS-754807 in this model is independent of IGF-1R. In vivo, systemic administration of BMS-754807 to DIPG-bearing mice did not prolong survival. Pharmacokinetic analysis demonstrated that tumor tissue drug concentrations of BMS-754807 were well below the identified IC50, suggesting that inadequate drug delivery may limit in vivo efficacy. In summary, an unbiased in vitro drug screen identified BMS-754807 as a potential therapeutic agent in DIPG, but BMS-754807 treatment in vivo by systemic delivery did not significantly prolong survival of DIPG-bearing mice.

High-grade Brainstem Glioma (BSG), also known as Diffuse Intrinsic Pontine Glioma (DIPG), is an incurable pediatric brain cancer. Increasing evidence supports the existence of regional differences in gliomagenesis such that BSG is considered a distinct disease from glioma of the cerebral cortex (CG). In an effort to elucidate unique characteristics of BSG, we conducted expression analysis of mouse PDGF-B-driven BSG and CG initiated in Nestin progenitor cells and identified a short list of expression changes specific to the brainstem gliomagenesis process, including abnormal upregulation of paired box 3 (Pax3). In the neonatal mouse brain, Pax3 expression marks a subset of brainstem progenitor cells, while it is absent from the cerebral cortex, mirroring its regional expression in glioma. Ectopic expression of Pax3 in normal brainstem progenitors in vitro shows that Pax3 inhibits apoptosis. Pax3-induced inhibition of apoptosis is p53-dependent, however, and in the absence of p53, Pax3 promotes proliferation of brainstem progenitors. In vivo, Pax3 enhances PDGF-B-driven gliomagenesis by shortening tumor latency and increasing tumor penetrance and grade, in a region-specific manner, while loss of Pax3 function extends survival of PDGF-B-driven;p53-deficient BSG-bearing mice by 33%. Importantly, Pax3 is regionally expressed in human glioma as well, with high PAX3 mRNA characterizing 40% of human BSG, revealing a subset of tumors that significantly associates with PDGFRA alterations, amplifications of cell cycle regulatory genes, and is exclusive of ACVR1 mutations. Collectively, these data suggest that regional Pax3 expression not only marks a novel subset of BSG but also contributes to PDGF-B-induced brainstem gliomagenesis.

Diffuse Intrinsic Pontine Glioma (DIPG) is a type of incurable pediatric brain tumor with a dismal outcome. With overall survival of less than one year, and no therapeutic advancements over the last three decades, gaining a better understanding of how to treat these deadly tumors is crucial. Recent genomic analysis has revealed that nearly 80% of DIPGS harbor a K27M mutation in histone H3.3 (K27M H3.3) or histone H3.1 (K27M H3.1). In an effort to elucidate novel therapeutics to treat DIPG, we examined Panobinostat, a potent pan-histone deacetylase inhibitor (HDACi) currently in clinical trials for a variety of different cancers. HDACi are a promising new class of agents known to have multiple target effects. Panobinostat targets HDACs in Classes I, II and IV and can cause disruption of genes involved in cell cycle control, apoptosis, DNA damage repair, and differentiation. To determine the effect of Panobinostat on DIPG, we utilized cell lines derived from a genetically engineered DIPG mouse model driven by PDGF-B overexpression, p53 loss, and either K27M or WT H3.3. Our results indicate that Panobinostat is highly effective at low nanomolar concentrations (<50nM), decreasing proliferation and viability, and increasing apoptosis in a dose dependent manner. Furthermore, utilizing isogenic lines we found the sensitivity of DIPG cells to Panobinostat to be independent of their H3.3 mutational status and that both K27M H3.3 and WT H3.3 lines were equally susceptible to treatment. In conclusion, murine DIPG cell lines, both with and without the K27M H3.3 mutation, show high sensitivity to Panobinostat in vitro. We are currently investigating its efficacy in vivo with hopes of translation to the clinic as a new therapeutic avenue for DIPG.

Diffuse intrinsic pontine glioma (DIPG) is an incurable tumor that arises in the brainstem of children. To date there is not a single approved drug to effectively treat these tumors and thus novel therapies are desperately needed. Recent studies suggest that a significant fraction of these tumors contain alterations in cell cycle regulatory genes including amplification of the D-type cyclins and CDK4/6, and less commonly, loss of Ink4a-ARF leading to aberrant cell proliferation. In this study, we evaluated the therapeutic approach of targeting the cyclin-CDK-Retinoblastoma (Rb) pathway in a genetically engineered PDGF-B-driven brainstem glioma (BSG) mouse model. We found that PD-0332991 (PD), a CDK4/6 inhibitor, induces cell-cycle arrest in our PDGF-B; Ink4a-ARF deficient model both in vitro and in vivo. By contrast, the PDGF-B; p53 deficient model was mostly resistant to treatment with PD. We noted that a 7-day treatment course with PD significantly prolonged survival by 12% in the PDGF-B; Ink4a-ARF deficient BSG model. Furthermore, a single dose of 10 Gy radiation therapy (RT) followed by 7 days of treatment with PD increased the survival by 19% in comparison to RT alone. These findings provide the rationale for evaluating PD in children with Ink4a-ARF deficient gliomas.

Abstract Medulloblastoma is the most common malignant brain tumor in children. Although aggressive surgery, radiation, and chemotherapy have improved outcomes, survivors suffer severe long-term side effects, and many patients still succumb to their disease. For patients whose tumors are driven by mutations in the sonic hedgehog (SHH) pathway, SHH antagonists offer some hope. However, many SHH-associated medulloblastomas do not respond to these drugs, and those that do may develop resistance. Therefore, more effective treatment strategies are needed for both SHH and non-SHH–associated medulloblastoma. One such strategy involves targeting the cells that are critical for maintaining tumor growth, known as tumor-propagating cells (TPC). We previously identified a population of TPCs in tumors from patched mutant mice, a model for SHH-dependent medulloblastoma. These cells express the surface antigen CD15/SSEA-1 and have elevated levels of genes associated with the G2–M phases of the cell cycle. Here, we show that CD15+ cells progress more rapidly through the cell cycle than CD15− cells and contain an increased proportion of cells in G2–M, suggesting that they might be vulnerable to inhibitors of this phase. Indeed, exposure of tumor cells to inhibitors of Aurora kinase (Aurk) and Polo-like kinases (Plk), key regulators of G2–M, induces cell-cycle arrest, apoptosis, and enhanced sensitivity to conventional chemotherapy. Moreover, treatment of tumor-bearing mice with these agents significantly inhibits tumor progression. Importantly, cells from human patient-derived medulloblastoma xenografts are also sensitive to Aurk and Plk inhibitors. Our findings suggest that targeting G2–M regulators may represent a novel approach for treatment of human medulloblastoma. Cancer Res; 73(20); 6310–22. ©2013 AACR.

Abstract The growth of many tumors has been suggested to depend on a subset of tumor cells with an extensive capacity for self-renewal, termed cancer stem cells or tumor-initiating cells (TICs). These cells are not necessarily abundant or proliferative, but because they are long-lived and often resistant to conventional therapies, they are thought to contribute to tumor resistance and recurrence. Therefore, identifying these cells and finding approaches to targeting them has become an important goal in cancer research. We recently identified a population of TICs in a mouse model of medulloblastoma, the most common malignant brain tumor in children. These cells, marked by expression of the cell surface antigen CD15, are capable of propagating tumors following transplantation, whereas CD15– cells from the same donors cannot. To gain insight into the molecular mechanisms underlying the increased tumorigenic potential of CD15+ cells, we compared their gene expression profile to that of CD15– cells. Among the genes most consistently elevated in CD15+ cells were regulators of the G2/M phases of the cell cycle. This observation led us to hypothesize that CD15+ cells display altered cell cycle regulation, and that these cells might be particularly vulnerable to inhibitors of cell cycle progression. Here we show that CD15+ cells move more quickly through the G1 and S phases of the cell cycle, and as a result contain an increased proportion of cells in G2/M. Consistent with this cell cycle skewing, CD15+ cells express higher levels of the G2/M regulators Aurora Kinase (Aurk) and Polo-like Kinase (Plk). Treatment of tumor cells with small molecule antagonists of Aurk or Plk inhibits cell cycle progression, promotes apoptosis and enhances sensitivity to other modes of chemotherapy. Treatment of tumor-bearing mice with these agents also significantly inhibits tumor progression. Importantly, cells from medulloblastoma patient-derived xenografts are also sensitive to Aurk and Plk inhibitors. These findings suggest that inhibitors of Aurk and Plk may be useful for targeting TICs and may represent a novel avenue for therapy of human medulloblastoma. Citation Format: Shirley Markant, Lourdes Adriana Esparza, Kelly Barton, Jesse Sun, Robert Wechsler-Reya,. Targeting tumor-initiating cells in medulloblastoma. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr CN07-02.

Medulloblastoma is the most common malignant brain tumor in children. While the current treatment strategy of surgery plus radiation has a 60–80% cure rate, the survivors suffer severe side effects, including growth delays and cognitive deficits. Therefore, more effective, less toxic treatments are needed. One approach to achieving this is targeting the cells within a tumor that are capable of re-populating the tumor, known as tumor-propagating cells (TPCs). These cells are thought to be responsible for tumor resistance to conventional therapies. In the patched mutant mouse model of medulloblastoma, TPCs are marked by expression of the cell surface carbohydrate antigen CD15. Our previous studies have suggested that CD15+ cells display increased expression of genes associated with the G2/M phases of the cell cycle. Cell cycle analysis suggests that CD15+ cells move quickly through the G1 and S phases of the cell cycle, but accumulate in the G2/M phases. This accumulation in G2/M may represent a vulnerability of CD15+ TPCs, and inhibition of G2/M regulators, such as Aurora kinases, may represent one approach for targeting TPCs and overcoming therapeutic resistance. Treatment of tumor cells from patched mutant mice or human Hedgehog-associated medulloblastoma with Aurora kinase inhibitors in vitro leads to inhibition of proliferation, arrest in G2/M and apoptosis. Furthermore, in vivo treatment of tumor-bearing mice with Aurora kinase inhibitors significantly delays tumor progression and prolongs survival. Our findings suggest that targeting Aurora kinases in TPCs may represent a new approach for the treatment of human medulloblastoma.

Abstract Medulloblastoma is the most common malignant brain tumor in children. While the current treatment strategy of surgery, radiation and chemotherapy has a 60-80% cure rate, the survivors suffer severe side effects, including growth delays and cognitive deficits. Therefore, more effective, less toxic treatments are needed. One approach to achieving this is targeting the cells within a tumor that are capable of re-populating the tumor, known as tumor-propagating cells (TPCs). In the patched mutant mouse model of medulloblastoma, TPCs are marked by expression of the cell surface carbohydrate antigen CD15. Our previous studies suggest that CD15+ cells display increased expression of genes associated with G2/M phase of the cell cycle. Cell cycle analysis suggests that these CD15+ cells move quickly through the G1 and S phases of the cell cycle, but accumulate in G2/M phase. Therefore, inhibition of G2/M regulators, such as Aurora kinases, may represent one approach to targeting TPCs in these tumors. Treatment of tumor cells with the Aurora kinase inhibitor VX-680 (tozasertib) leads to inhibition of proliferation in vitro, with arrest in G2/M and apoptosis. Preliminary studies suggest that patched mutant tumors are also sensitive to Aurora kinase inhibition in vivo. Our findings suggest that targeting Aurora kinases may represent a novel approach for the treatment of hedgehog-associated human medulloblastoma. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3443. doi:10.1158/1538-7445.AM2011-3443