B7-H3 as a Prognostic Biomarker and Therapeutic Target in Pediatric central nervous system Tumors

B7–H3 (CD276), a member of the B7 superfamily, is an important factor in downregulating immune responses against tumors. It is also aberrantly expressed in many human malignancies. Beyond immune regulatory roles, its overexpression has been linked to invasive metastatic potential and poor prognosis in patients with cancer. Antibody-dependent cell-mediated cytotoxicity strategies targeting B7–H3 are currently in development, and early-phase clinical trials have shown encouraging preliminary results.

To understand the role of B7–H3 in pediatric central nervous system (CNS) malignancies, a comprehensive panel of primary CNS tumors of childhood was examined by immunohistochemistry for levels and extent of B7–H3 expression. In addition, B7–H3 m-RNA expression status and association with overall survival in various pediatric CNS tumor types was accessed by curating publicly available patient gene expression data sets derived from bioinformatics analysis and visualization platforms (GlioVis).

We demonstrate that B7–H3 is broadly expressed in pediatric glial and nonglial CNS tumors, and its aberrant expression, as determined by immunohistochemical staining intensity, correlates with tumor grade. Moreover, high B7–H3 m-RNA expression is significantly associated with worse survival and could potentially improve prognostication in various brain tumor types of childhood. B7–H3 can be used as a therapeutic target, given its tumor selectivity and the availability of targeted therapeutic agents to this antigen.

An [18F]-Positron Emitting Fluorophore Allows Safe Evaluation of Small Molecule Distribution in the CSF, CSF Fistulas, and CNS Device Placement

The small molecule fluorescein is commonly used to guide the repair of cerebral spinal fluid leaks (CSFLs) in the clinic. We modified fluorescein so that it is also visible by positron emission tomography (PET). This probe was used to quantitatively track the fast distribution of small molecules in the CSF of rats. We tested this probe in models relevant to the clinical diagnosis and treatment of central nervous system (CNS) diseases that affect CSF flow. In this study, fluorescein was radiolabeled with fluorine-18 to produce Fc-AMBF3. [18/19F]-Fc-AMBF3 was introduced at trace quantities (13.2 nmols, 100 μCi) intrathecally (between L5 and L6) in rats to observe the dynamic distribution and clearance of small molecules in the CSF by both [18F]-PET and fluorescence (FL) imaging. Murine models were used to demonstrate the following utilities of Fc-AMBF3: (1) utility in monitoring the spontaneous CSFL repair of a compression fracture of the cribriform plate and (2) utility in quantifying CSF flow velocity during neurosurgical lumboperitoneal shunt placement. Fc-AMBF3 clearly delineated CSF-containing volumes based on noninvasive PET imaging and in ex vivo FL histology. In vivo morbidity (n = 16 rats, <2.7 mg/kg, 77 times the PET dose) was not observed. The clearance of the contrast agent from the CNS was rapid and quantitative (t1/2 = 33.8 ± 0.6 min by FL and t1/2 = 26.0 ± 0.5 min by PET). Fc-AMBF3 was cleared from the CSF through the vasculature and/or lymphatic system that supplies the cribriform plate and the temporal bone. Fc-AMBF3 can be used to diagnose CSFLs, image CSFL repair, and determine the CSF flow velocity in the CNS or through lumboperitoneal shunts by PET/FL imaging. In conclusion, Fc-AMBF3 PET imaging has been demonstrated to safely and dynamically quantitate CSF flow, diagnose fistulas associated with the CSF space, and approximate the clearance of small molecules in the CSF.

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.

Abstract 2073: Transcriptome profiles of cancer stem-like cells in patient-derived diffuse intrinsic pontine glioma (DIPG)

Diffuse intrinsic pontine glioma (DIPG) is a rare, but lethal childhood cancer with a 5-year survival less than 1 %. Genetic profiling of DIPG biopsies and post-mortem tissue have recently identified mutations in PI3KCA, PTEN, TP53, ATM/MPL, histones and PDGF receptor overexpression. PI3KCA and PTEN mutations as well as PDGF receptor overexpression indicate upregulation of the PI3K/AKT/mTOR signaling axis, representing druggable targets. We recently developed a multifunctional kinase inhibitor (ST-182), which targets the PI3K/AKT/mTOR and MAPK pathways which is often upregulated in various malignancies as a compensatory mechanism when PI3K is inhibited. We evaluated ST-182's efficacy for targeting these pathways in patient derived DIPG by western blotting and reverse phase protein array analysis (RPPA). Phosphorylation changes of ERK and AKT, downstream signaling inhibition as well as diminished proliferation was shown in two DIPG cell lines (SU-DIPGIV and XIII) when treated with ST-182, indicating efficacy of co-targeting these pathways as a new therapeutic advance for DIPG.

FACS analysis of DIPG cells (SU-DIPGXIII) identified a large percentage (&gt;10%) of DIPG cells as ALDH positive indicating aggressive stem like features. Characterization of these distinct DIPG populations (ALDH+,-) at the transcriptome level was performed to understand differences in pathway signaling and to identify potential drug resistance mechanisms to ST-182. Utilizing an innovative transcriptome analysis approach, we identified elevated levels of MYC, E2F and DNA repair genes in ALDH+ cells, supporting stem like phenotype of ALDH+ DIPG cells. MYC has long been identified as a crucial player in maintaining embryonic stem cell pluripotency and self-renewal, whereas E2F provide transcriptional control of stem cell fate and DNA repair mechanisms maintain and regulate cancer stem cells. Pharmacological targeting of MAPK/PI3K/mTOR by ST-182 demonstrated up regulation of NFkB, apoptosis, hypoxia, p53 and inflammatory response in ALDH+ and ALDH- cells and down-regulation of MYC, E2F and DNA replication indicating efficacy of targeting these pathways in preventing/reversing stem-like phenotypes in the ALDH+ cell population.

Our findings indicate efficacy of ST-182 for the treatment of ALDH+ cancer stem cells providing impetus for evaluation of molecularly targeted MAPK/PI3K/mTOR therapy. Our comprehensive transcriptome studies provide a new direction for the treatment of DIPG through novel insights into the underlying transcriptomic basis of drug resistant cancer stem cells. Development of new compounds such as ST-182 provides opportunities to implement precision medicine to improve treatment outcomes for DIPG patients.

Citation Format: Stefanie Galbán, Carlos Espinoza, Karan Bedi, Uday B. Maachani, Mark M. Souweidane, Mats Ljungman, Marcian Van Dort, Brian D. Ross. Transcriptome profiles of cancer stem-like cells in patient-derived diffuse intrinsic pontine glioma (DIPG) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2073.

FOXM1 and STAT3 interaction confers radioresistance in glioblastoma cells

Glioblastoma multiforme (GBM) continues to be the most frequently diagnosed and lethal primary brain tumor. Adjuvant chemo-radiotherapy remains the standard of care following surgical resection. In this study, using reverse phase protein arrays (RPPAs), we assessed the biological effects of radiation on signaling pathways to identify potential radiosensitizing molecular targets. We identified subsets of proteins with clearly concordant/discordant behavior between irradiated and non-irradiated GBM cells in vitro and in vivo. Moreover, we observed high expression of Forkhead box protein M1 (FOXM1) in irradiated GBM cells both in vitro and in vivo. Recent evidence of FOXM1 as a master regulator of metastasis and its important role in maintaining neural, progenitor, and GBM stem cells, intrigued us to validate it as a radiosensitizing target. Here we show that FOXM1 inhibition radiosensitizes GBM cells by abrogating genes associated with cell cycle progression and DNA repair, suggesting its role in cellular response to radiation. Further, we demonstrate that radiation induced stimulation of FOXM1 expression is dependent on STAT3 activation. Co-immunoprecipitation and co-localization assays revealed physical interaction of FOXM1 with phosphorylated STAT3 under radiation treatment. In conclusion, we hypothesize that FOXM1 regulates radioresistance via STAT3 in GBM cells. We also, show GBM patients with high FOXM1 expression have poor prognosis. Collectively our observations might open novel opportunities for targeting FOXM1 for effective GBM therapy.

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.

Modulation of miR-21 signaling by MPS1 in human glioblastoma

Monopolar spindle 1 (MPS1) is an essential spindle assembly checkpoint (SAC) kinase involved in determining spindle integrity. Beyond its mitotic functions, it has been implicated in several other signaling pathways. Our earlier studies have elaborated on role of MPS1 in glioblastoma (GBM) radiosensitization. In this study using reverse phase protein arrays (RPPAs), we assessed MPS1 mediated cell signaling pathways and demonstrated that inhibiting MPS1 could upregulate the expression of the tumor suppressor PDCD4 and MSH2 genes, by down regulating micro RNA-21 (miR-21). In GBMs miR-21 expression is significantly elevated and is associated with chemo and radioresistance. Both MPS1 and miR-21 depletion suppressed GBM cell proliferation, whereas, ectopic expression of miR-21 rescued GBM cell growth from MPS1 inhibition. Further, we demonstrate that MPS1 mediates phosphorylation of SMAD3 but not SMAD2 in GBM cells; A possible mechanism behind miR-21 modulation by MPS1. Collectively, our results shed light onto an important role of MPS1 in TGF-β/SMAD signaling via miR-21 regulation. We also, show the prognostic effect of miR-21, PDCD4 and MSH2 levels to patient survival across different GBM molecular subtypes. This scenario in which miR-21 is modulated by MPS1 inhibition may be exploited as a potential target for effective GBM therapy.

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

Thanks to the recent advances in the development of chemotherapeutics, the morbidity and mortality of many cancers has decreased significantly. However, compared to oncology in general, the field of neuro-oncology has lagged behind. While new molecularly targeted chemotherapeutics have emerged, the impermeability of the blood–brain barrier (BBB) renders systemic delivery of these clinical agents suboptimal. To circumvent the BBB, novel routes of administration are being applied in the clinic, ranging from intra-arterial infusion and direct infusion into the target tissue (convection enhanced delivery (CED)) to the use of focused ultrasound to temporarily disrupt the BBB. However, the current system depends on a “wait-and-see” approach, whereby drug delivery is deemed successful only when a specific clinical outcome is observed. The shortcomings of this approach are evident, as a failed delivery that needs immediate refinement cannot be observed and corrected. In response to this problem, new theranostic agents, compounds with both imaging and therapeutic potential, are being developed, paving the way for improved and monitored delivery to central nervous system (CNS) malignancies. In this review, we focus on the advances and the challenges to improve early cancer detection, selection of targeted therapy, and evaluation of therapeutic efficacy, brought forth by the development of these new agents.

Biomarker-Based PET Imaging of Diffuse Intrinsic Pontine Glioma in Mouse Models

Diffuse intrinsic pontine glioma (DIPG) is a childhood brainstem tumor with a universally poor prognosis. Here, we characterize a positron emission tomography (PET) probe for imaging DIPG in vivo In human histological tissues, the probes target, PARP1, was highly expressed in DIPG compared to normal brain. PET imaging allowed for the sensitive detection of DIPG in a genetically engineered mouse model, and probe uptake correlated to histologically determined tumor infiltration. Imaging with the sister fluorescence agent revealed that uptake was confined to proliferating, PARP1-expressing cells. Comparison with other imaging technologies revealed remarkable accuracy of our biomarker approach. We subsequently demonstrated that serial imaging of DIPG in mouse models enables monitoring of tumor growth, as shown in modeling of tumor progression. Overall, this validated method for quantifying DIPG burden would serve useful in monitoring treatment response in early phase clinical trials. Cancer Res; 77(8); 2112-23. ©2017 AACR.

Abstract 1584: Targeting the mitotic checkpoint with inhibition of MPS1 kinase enhances radiosensitivity of glioblastoma cancer cells

During the cell cycle, genomic stability requires accurate chromosome segregation. Errors in this process can cause aneuploidy and lead to tumorigenesis. To ensure faithful chromosome segregation, cells develop a mechanism called the spindle assembly checkpoint (SAC). Cancer cells are addicted to the components of SAC machinery for a faithful entry of the cell into anaphase. Thus, targeting the molecular mechanisms required for the growth of aneuploid cells may be a more cancer cell specific therapeutic approach applicable to broader tumor histologies. Previously, using a siRNA based RNAi screen we identified MPS1 kinase, (also known as TTK) as an important kinase for GBM cell survival. MPS1 is an essential SAC enzyme aberrantly overexpressed in a wide range of tumors and necessary for tumor cell proliferation.

We observed inhibition of GBM cell growth when MPS1 was downregulated by number of MPS1 specific siRNAs. This was further validated using a selective and orally bioavailable MPS1 inhibitor NMS-P715 in various in-vitro cell assays. The inhibition of cell death was induced partly by apoptosis; however, the major mechanism was mitotic catastrophe. Cells treated with NMS-P715 showed an increase in cells in G2-M phase of cell cycle compared to control cells followed by mitotic catastrophe. Moreover, inhibition of MPS1 resulted in radiosensitization of GBM cells. We observed decrease in DNA damage repair and significant retention of γH2AX foci after combination of radiation (RT) with NMS-P715 compared to individual treatments. Next, radiation in combination with NMS-P715 inhibited cell survival ability of GBM cells in a colony formation assay. Further, NMS-P715 could inhibit GBM tumor growth in an orthotopic brain tumor model. Finally, in order to determine MPS1 associated molecular pathways, we compared gene expression profile in MPS1 knockdown cells compared to the control by microarray analysis. Ingenuity pathway and Gene Set Enrichment Analysis were used to investigate the biological relevance of the MPS1 modulated genes. We identified genes important in cell assembly, cell organization, DNA repair and cell death pathways. Thus, inhibiting MPS1 kinase in combination with radiation could represent a promising new approach to GBM therapy.

Citation Format: Anita T. Tandle, Ryan Hanson, Uday B. Maachani, Tamalee Meushaw, Shuping Zhao, Uma Shankavaram, Philip Tofilon, Natasha J. Caplen, Kevin Camphausen. Targeting the mitotic checkpoint with inhibition of MPS1 kinase enhances radiosensitivity of glioblastoma cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1584. doi:10.1158/1538-7445.AM2013-1584