Revisiting Concurrent Radiation Therapy, Temozolomide, and the Histone Deacetylase Inhibitor Valproic Acid for Patients with Glioblastoma-Proteomic Alteration and Comparison Analysis with the Standard-of-Care Chemoirradiation

BACKGROUND

Glioblastoma (GBM) is the most common brain tumor with an overall survival (OS) of less than 30% at two years. Valproic acid (VPA) demonstrated survival benefits documented in retrospective and prospective trials, when used in combination with chemo-radiotherapy (CRT).

PURPOSE

The primary goal of this study was to examine if the differential alteration in proteomic expression pre vs. post-completion of concurrent chemoirradiation (CRT) is present with the addition of VPA as compared to standard-of-care CRT. The second goal was to explore the associations between the proteomic alterations in response to VPA/RT/TMZ correlated to patient outcomes. The third goal was to use the proteomic profile to determine the mechanism of action of VPA in this setting.

MATERIALS AND METHODS

Serum obtained pre- and post-CRT was analyzed using an aptamer-based SOMAScan® proteomic assay. Twenty-nine patients received CRT plus VPA, and 53 patients received CRT alone. Clinical data were obtained via a database and chart review. Tests for differences in protein expression changes between radiation therapy (RT) with or without VPA were conducted for individual proteins using two-sided t-tests, considering p-values of <0.05 as significant. Adjustment for age, sex, and other clinical covariates and hierarchical clustering of significant differentially expressed proteins was carried out, and Gene Set Enrichment analyses were performed using the Hallmark gene sets. Univariate Cox proportional hazards models were used to test the individual protein expression changes for an association with survival. The lasso Cox regression method and 10-fold cross-validation were employed to test the combinations of expression changes of proteins that could predict survival. Predictiveness curves were plotted for significant proteins for VPA response (p-value < 0.005) to show the survival probability vs. the protein expression percentiles.

RESULTS

A total of 124 proteins were identified pre- vs. post-CRT that were differentially expressed between the cohorts who received CRT plus VPA and those who received CRT alone. Clinical factors did not confound the results, and distinct proteomic clustering in the VPA-treated population was identified. Time-dependent ROC curves for OS and PFS for landmark times of 20 months and 6 months, respectively, revealed AUC of 0.531, 0.756, 0.774 for OS and 0.535, 0.723, 0.806 for PFS for protein expression, clinical factors, and the combination of protein expression and clinical factors, respectively, indicating that the proteome can provide additional survival risk discrimination to that already provided by the standard clinical factors with a greater impact on PFS. Several proteins of interest were identified. Alterations in GALNT14 (increased) and CCL17 (decreased) (p = 0.003 and 0.003, respectively, FDR 0.198 for both) were associated with an improvement in both OS and PFS. The pre-CRT protein expression revealed 480 proteins predictive for OS and 212 for PFS (p < 0.05), of which 112 overlapped between OS and PFS. However, FDR-adjusted p values were high, with OS (the smallest p value of 0.586) and PFS (the smallest p value of 0.998). The protein PLCD3 had the lowest p-value (p = 0.002 and 0.0004 for OS and PFS, respectively), and its elevation prior to CRT predicted superior OS and PFS with VPA administration. Cancer hallmark genesets associated with proteomic alteration observed with the administration of VPA aligned with known signal transduction pathways of this agent in malignancy and non-malignancy settings, and GBM signaling, and included epithelial-mesenchymal transition, hedgehog signaling, Il6/JAK/STAT3, coagulation, NOTCH, apical junction, xenobiotic metabolism, and complement signaling.

CONCLUSIONS

Differential alteration in proteomic expression pre- vs. post-completion of concurrent chemoirradiation (CRT) is present with the addition of VPA. Using pre- vs. post-data, prognostic proteins emerged in the analysis. Using pre-CRT data, potentially predictive proteins were identified. The protein signals and hallmark gene sets associated with the alteration in the proteome identified between patients who received VPA and those who did not, align with known biological mechanisms of action of VPA and may allow for the identification of novel biomarkers associated with outcomes that can help advance the study of VPA in future prospective trials.

Bench to bedside radiosensitizer development strategy for newly diagnosed glioblastoma

Glioblastoma is the most common primary brain malignancy and carries with it a poor prognosis. New agents are urgently needed, however nearly all Phase III trials of GBM patients of the past 25 years have failed to demonstrate improvement in outcomes. In 2019, the National Cancer Institute Clinical Trials and Translational Research Advisory Committee (CTAC) Glioblastoma Working Group (GBM WG) identified 5 broad areas of research thought to be important in the development of new herapeutics for GBM. Among those was optimizing radioresponse for GBM in situ. One such strategy to increase radiation efficacy is the addition of a radiosensitizer to improve the therapeutic ratio by enhancing tumor sensitivity while ideally having minimal to no effect on normal tissue. Historically the majority of trials using radiosensitizers have been unsuccessful, but they provide important guidance in what is required to develop agents more efficiently. Improved target selection is essential for a drug to provide maximal benefit, and once that target is identified it must be validated through pre-clinical studies. Careful selection of appropriate in vitro and in vivo models to demonstrate increased radiosensitivity and suitable bioavailability are then necessary to prove that a drug warrants advancement to clinical investigation. Once investigational agents are validated pre-clinically, patient trials require consistency both in terms of planning study design as well as reporting efficacy and toxicity in order to assess the potential benefit of the drug. Through this paper we hope to outline strategies for developing effective radiosensitizers against GBM using as models the examples of XPO1 inhibitors and HDAC inhibitors developed from our own lab.

Detection of metabolic change in glioblastoma cells after radiotherapy using hyperpolarized 13 C-MRI

Dynamic nuclear polarization (DNP) of 13 C-labeled substrates enables the use of magnetic resonance imaging (MRI) to monitor specific enzymatic reactions in tumors and offers an opportunity to investigate these differences. In this study, DNP-MRI chemical shift imaging with hyperpolarized [1-13 C] pyruvate was conducted to evaluate the metabolic change in glycolytic profiles after radiation of two glioma stem-like cell-derived gliomas (GBMJ1 and NSC11) and an adherent human glioblastoma cell line (U251) in an orthotopic xenograft mouse model. The DNP-MRI showed an increase in Lac/Pyr at 6 and 16 h after irradiation (18% ± 4% and 14% ± 3%, respectively; mean ± SEM) compared with unirradiated controls in GBMJ1 tumors, whereas no significant change was observed in U251 and NSC11 tumors. Metabolomic analysis likewise showed a significant increase in lactate in GBMJ1 tumors at 16 h. An immunoblot assay showed upregulation of lactate dehydrogenase-A expression in GBMJ1 following radiation exposure, consistent with DNP-MRI and metabolomic analysis. In conclusion, our preclinical study demonstrates that the DNP-MRI technique has the potential to be a powerful diagnostic method with which to evaluate GBM tumor metabolism before and after radiation in the clinical setting.

Abstract IA-002: Microenvironmental regulation of glioblastoma radioresistance

Glioblastomas (GBM) have long been recognized as radioresistant tumors. Defining the mechanisms mediating their radioresistance should provide a rational basis for designing target-based strategies that enhance GBM radiosensitivity. Towards this end, a major barrier is the availability of an experimental model system that replicates the molecules and processes that determine GBM radioresponse. Laboratory studies have suggested that the brain microenvironment plays a role in GBM radioresistance. Moreover, it is well established that GBMs comprise a diverse set of tumors that are highly variable in terms of histology, mutations, and gene expression profiles. Yet, despite this extensive biological heterogeneity, although some GBMs respond better than others, they all essentially fail radiotherapy. This relatively "homogeneous" clinical response in a background of inter-tumor heterogeneity further suggests that the microenvironment plays a significant role in determining GBM radioresponse. Complicating this proposed role for the microenvironment, however, is that the brain is comprised of structurally and functionally diverse microenvironments; whether each contributes in a similar manner to GBM radioresistance is unclear. To investigate the role of specific brain microenvironments in determining tumor cell radioresponse, we used orthotopic xenografts initiated from GBM stem-like cells (GSCs) as a model system. After implantation of GSCs into the right striatum of nude mice, tumor cells were detectable throughout the striatum, the corpus callosum and the olfactory bulb. To measure radiosensitivity, the proliferation status of individual tumor cells was defined according to the incorporation of 5-chloro-2'-deoxyuridine (CldU), which was delivered at 4-20 days after brain irradiation. After an initial loss of proliferating tumor cells in the corpus callosum and striatum after irradiation, there was only a minor recovery. In contrast, the proliferation of tumor cells located in the olfactory bulb began to recover at 4 days and returned to unirradiated levels by day 12 post-irradiation. These results suggest that tumor cells in olfactory bulb are relatively radioresistant. Using ddPCR to define the percent human cells in the right hemisphere and the olfactory bulb as a function of time after irradiation also suggested that the tumor cells in the olfactory bulb were relatively radioresistant. RNAseq analysis showed that the gene expression profile for NSC11 tumor cells in the olfactory bulb as compared to those growing in the right hemisphere included signaling pathways and processes associated with radioresistance. Overall, these results indicate that the murine olfactory bulb, which is highly enriched in neurons and interneurons, provides a radioprotective niche for tumor cells. In addition, these data suggest that human tumor cells grown in the murine olfactory bulb may provide an experimental model that simulates GBM radioresistance.

Citation Format: Philip Tofilon. Microenvironmental regulation of glioblastoma radioresistance [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr IA-002.

Radiosensitizers in the temozolomide era for newly diagnosed glioblastoma

Glioblastoma (GBM) is a challenging diagnosis with almost universally poor prognosis. Though the survival advantage of postoperative radiation (RT) is well established, around 90% of patients will fail in the RT field. The high likelihood of local failure suggests the efficacy of RT needs to be improved to improve clinical outcomes. Radiosensitizers are an established method of enhancing RT cell killing through the addition of a pharmaceutical agent. Though the majority of trials using radiosensitizers have historically been unsuccessful, there continues to be interest with a variety of approaches having been employed. Epidermal growth factor receptor inhibitors, histone deacetylase inhibitors, antiangiogenic agents, and a number of other molecularly targeted agents have all been investigated as potential methods of radiosensitization in the temozolomide era. Outcomes have varied both in terms of toxicity and survival, but some agents such as valproic acid and bortezomib have demonstrated promising results. However, reporting of results in phase 2 trials in newly diagnosed GBM have been inconsistent, with no standard in reporting progression-free survival and toxicity. There is a pressing need for investigation of new agents; however, nearly all phase 3 trials of GBM patients of the past 25 years have demonstrated no improvement in outcomes. One proposed explanation for this is the selection of agents lacking sufficient preclinical data and/or based on poorly designed phase 2 trials. Radiosensitization may represent a viable strategy for improving GBM outcomes in newly diagnosed patients, and further investigation using agents with promising phase 2 data is warranted.

The Quiescent Metabolic Phenotype of Glioma Stem Cells

Introduction

Glioblastoma (GBM) is the most common primary malignant brain tumor in humans and, even with aggressive treatment that includes surgical resection, radiation (IR), and chemotherapy administration, prognosis is poor due to tumor recurrence. There is evidence that within GBMs a small number of glioma stem-like cells (GSLCs) exist, which are thought to be therapy resistant and are thus capable of repopulating a tumor after treatment. Like most cancers, GBMs largely employ aerobic glycolysis to create ATP, a phenomenon known as the Warburg Effect. There is no consensus on the metabolic characteristics of cancer stem cells. GSLCs have been shown to rely more heavily on oxidative phosphorylation, but there is also evidence that cancer stem cells can adapt their metabolism by fluctuating between energy pathways or acquiring intermediate metabolic phenotypes. We hypothesized that the metabolism of GSLCs differs from that of differentiated GBM tumor cell lines, and that the steady state metabolism would be differentially altered following radiation treatment.

Materials and Methods

We evaluated the oxygen consumption rate, extracellular acidification rate, and metabolic enzyme levels of GBM cell lines and GSLCs before and after irradiation using extracellular flux assays. We also measured absolute metabolite levels in these cells via mass spectroscopy with and without radiation treatment.

Results

GSLCs were found to be significantly more quiescent in comparison to adherent GBM cell lines, highlighted by lower glycolytic and maximal respiratory capacities as well as lower oxygen consumption and extracellular acidification rates. Analysis of individual metabolite concentrations revealed lower total metabolite concentrations overall but also elevated levels of metabolites in different energy pathways for GSLCs compared to GBM cell lines. Additionally, the metabolism of both GSLCs and GBM cell lines were found to be altered by IR.

Conclusions

While there is not one metabolic alteration that distinguishes irradiated GSLC metabolism from that of GBM cell lines, therapies targeting more metabolically quiescent tumor cells and thus the resistant GSLC population may increase a cancer's sensitivity to radiotherapy.

4E-BP1 Is a Tumor Suppressor Protein Reactivated by mTOR Inhibition in Head and Neck Cancer

Aberrant activation of the PI3K-mTOR signaling pathway occurs in >80% of head and neck squamous cell carcinomas (HNSCC), and overreliance on this signaling circuit may in turn represent a cancer-specific vulnerability that can be exploited therapeutically. mTOR inhibitors (mTORi) promote tumor regression in genetically defined and chemically induced HNSCC animal models, and encouraging results have been recently reported. However, the mTOR-regulated targets contributing to the clinical response have not yet been identified. Here, we focused on EIF4E-BP1 (4E-BP1), a direct target of mTOR that serves as key effector for protein synthesis. A systematic analysis of genomic alterations in the PIK3CA-mTOR pathway in HNSCC revealed that 4E-BP1 is rarely mutated, but at least one 4E-BP1 gene copy is lost in over 35% of the patients with HNSCC, correlating with decreased 4E-BP1 protein expression. 4E-BP1 gene copy number loss correlated with poor disease-free and overall survival. Aligned with a tumor-suppressive role, 4e-bp1/2 knockout mice formed larger and more lesions in models of HNSCC carcinogenesis. mTORi treatment or conditional expression of a mutant 4E-BP1 that cannot be phosphorylated by mTOR was sufficient to disrupt the translation-initiation complex and prevent tumor growth. Furthermore, CRISPR/Cas9-targeted 4E-BP1 HNSCC cells resulted in reduced sensitivity to mTORi in vitro and in vivo. Overall, these findings indicate that in HNSCC, mTOR persistently restrains 4E-BP1 via phosphorylation and that mTORi can restore the tumor-suppressive function of 4E-BP1. Our findings also support 4E-BP1 expression and phosphorylation status as a mechanistic biomarker of mTORi sensitivity in patients with HNSCC. SIGNIFICANCE: These findings suggest that EIF4E-BP1 acts as a tumor suppressor in HNSCC and that 4E-BP1 dephosphorylation mediates the therapeutic response to mTORi, providing a mechanistic biomarker for future precision oncology trials.

Abstract 1389: Inhibition of the histone H3K27 demethylase UTX enhances tumor cell radiosensitivity

The processes mediating the repair of DNA double strand breaks (DSBs) are critical determinants of radiosensitivity and provide a source of potential targets for tumor radiosensitization. Among the events required for efficient DSB repair are a variety of post-translational histone modifications including methylation. Because trimethylation of histone H3 on lysine 27 (H3K27me3) has been associated with chromatin condensation, which can influence DSB repair, we determined the effects of radiation on H3K27me3 levels in three in three human tumor cell lines: U251; MDA-MB-231 and A549, and two normal cell lines. Irradiation (10Gy) of tumor cells resulted in a rapid loss of H3K27me3. According to immunoblot analysis, tumor cells had significant higher levels of the histone demethylase UTX compared to JMJD3, suggesting a more prominent role for UTX in the demethylation of H3K27me3 after irradiation. The rapid loss of H3K27me3 was prevented by the siRNA-mediated knockdown UTX and enhanced the radiosensitivity of each tumor cell line, whereas the knockdown of JMJD3 had no effect. To investigate whether inhibition of UTX could serve as a potential target to target to radiosensitize tumor cells, we focused on GSKJ4 a H3K27 demethylase inhibitor. GSKJ4 treatment (4 μM) of tumor cells was found to block the radiation-induced decrease of H3K27me3. Further, based on clonogenic survival analysis addition of GSKJ4 immediately prior to irradiation significantly enhanced the radiosensitivity of tumor cells but not that of normal cells. To begin to investigate the mechanism responsible for this radiosensitization tumor cells were irradiated (10Gy), treated with GSKJ4 and collected at 0.5-24h later for neutral comet assay, a measure of DNA double strand breaks (DSBs). GSKJ4 had no effect on the initial comet-tail moment, yet significantly increased the comet tail-moment up to 24h after radiation, suggestive of an inhibition of DSB repair. Analysis of γH2AX nuclear foci, a surrogate marker for DNA DSBs 16h after irradiation (6Gy) and treatment of tumor cells with GSKJ4 (4μM) increased the percentage of cells expressing γH2AX as compared to radiation alone suggesting that GSKJ4 inhibits DSB repair. Thus, data generated from the neutral comet and γH2AX assays suggest that the inhibition of H3K27m3 demethylation mediated by GSKJ4 inhibits the repair of radiation-induced DSBs, which could then account for the observed radiosensitization. Consistent with in vitro results radiation reduced the H3K27me3 methylation in mice bearing leg tumor xenografts. Treatment of mice bearing leg tumor xenografts with GSKJ4 and radiation significantly enhanced radiation-induce tumor growth delay. These data suggest that H3K27me3 demethylation contributes to DSB repair in tumor cells and that UTX, the demethylase responsible, provides a target for selective tumor cell radiosensitization in vivo.

Citation Format: Barbara H. Rath, Isabella Waung, Kevin Camphausen, Philip Tofilon. Inhibition of the histone H3K27 demethylase UTX enhances tumor cell radiosensitivity [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 1389.

Abstract 5427: Distinctions between the metabolic changes in glioblastoma cells and glioma stem-like cells following irradiation

Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor in adults and, even with aggressive treatment that includes surgical resection, radiation, and temozolomide administration, prognosis is poor due to tumor recurrence. There is evidence that within GBMs a small number of glioma stem- like cells (GSCs) exist, which are thought to be radiation resistant and may be capable of repopulating a tumor after treatment. Like most cancers, GBMs largely employ aerobic glycolysis to create ATP, a phenomenon known as the Warburg effect. Experiments have shown that the cellular metabolism of GSCs differs from that of differentiated cells, making them an attractive target for novel therapeutic approaches. Much work has been done to analyze the metabolic profiles of GSCs with the goal of identifying potential therapeutic targets, but little data exists linking metabolic changes to radiation resistance. The purpose of this study is to characterize the metabolic differences between glioma stem- like cells and traditional GBM tumor cells with and without radiation treatment (IR).

To this end, we compared the metabolism of a human derived GSC line with two commonly used GBM cell lines before and after IR. At baseline, we find that glioma stem-like cells are more quiescent than GBM cells, which have higher levels of both glycolysis and oxidative phosphorylation. GBM lines show higher levels of both basal and maximal respiration, as well as basal glycolysis and glycolytic capacity than GSCs. They also express higher levels of energy, glycolysis, and TCA cycle metabolites than GSCs. Inversely, GSCs demonstrate metabolic signs of quiescence such as decreased NEAA synthesis.

After IR, the radiation- sensitive GBM tumor cell line (U251) exhibits increases in all metabolic pathways, whereas the levels of glycolytic and oxidative metabolites in the GSCs remain unchanged. All cell lines show an increase of ATP and NAD production following IR. These findings indicate that the metabolism of GSCs undergoes different alterations than that of GBM tumor cells after IR, making them an attractive target for novel therapeutic approaches in conjunction with radiation therapy. Additionally, differences in metabolic signatures between GSC lines could be useful for non-invasive diagnostic modalities such as 13C MR spectroscopy.

Citation Format: Elizabeth I. Spehalski, Cord Peters, Philip Tofilon, Kevin Camphausen. Distinctions between the metabolic changes in glioblastoma cells and glioma stem-like cells following irradiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5427. doi:10.1158/1538-7445.AM2017-5427

Abstract 2017: The CEBPD transcription factor, a marker of good prognosis in breast cancer, becomes a signaling hub for promotion of cancer cell stemness by hypoxia and interleukin-6

The transcription factor C/EBPdelta (CEBPD) is expressed in normal mammary epithelial cells and high expression in breast cancer correlates with hormone receptors and good prognosis (Mendoza-Villanueva et al., submitted). In the MMTV-Neu mouse model, deletion of CEBPD increases tumor multiplicity, but “paradoxically” reduces metastatic progression, suggesting that CEBPD has dual tumor suppressing and metastasis promoting functions (Balamurugan et al., 2010). Here, we identify a molecular mechanism for the tumor promoting function of CEBPD that may reach beyond breast cancer. We show that CEBPD serves as a signaling hub that integrates and amplifies pathways that promote stemness in breast cancer, glioblastoma and embryonic cancer cells. This work identifies a mechanism by which hypoxia and inflammation promote cancer stem-like cells (CSCs), which are implicated in tumor progression and resistance. Our earlier studies showed that CEBPD promotes inflammatory signaling and hypoxia adaptation by inhibiting the expression of FBXW7 (Balamurugan et al., 2010 and 2013), which can target several oncoproteins for degradation. Using a variety of established breast and glioblastoma tumor cell lines/xenografts, primary mouse mammary tumor cells and tissues, recent patient-derived glioblastoma cell lines, as well as embryonic stem/cancer cell lines, we find that deletion or depletion of CEBPD reduced the number of stem cells as determined by surface markers, sphere formation, limiting dilution xenografts, and by expression of stemness genes. Mechanistic studies in culture models show that CEBPD is expressed in CSCs and connects and amplifies both hypoxia (HIF-1) and inflammation (IL-6/STAT3) pathways to increase Notch1/NICD expression and cell stemness. CEBPD induces NICD expression transcriptionally through HIF-1 and at the level of the protein by inhibition of FBXW7-mediated degradation. In addition to its known role as a target of STAT3 and activator of IL-6 gene expression, we identified an additional role for CEBPD in promoting expression of the IL-6 receptor. Furthermore, we found that CEBPD also directly activates the expression of stemness-promoting genes such as OCT4, Sox2, KLF4, Myc, Nanog, CD44 and CD133. Taken together, this study provides novel insights into the molecular mechanisms that promote cancer cell stemness. Because CEBPD integrates and amplifies multiple stemness promoting pathways, CEBPD may represent a unique point of vulnerability in cancer stem cells, strongly suggesting that pharmacological inhibition of CEBPD signaling may effectively target CSCs. Results from current efforts to pharmacologically downregulate CEBPD in cancer stem cells will also be presented.

Citation Format: Kuppusamy Balamurugan, Daniel Mendoza-Villanueva, Barbara Rath, Philip Tofilon, Shikha Sharan, Esta Sterneck. The CEBPD transcription factor, a marker of good prognosis in breast cancer, becomes a signaling hub for promotion of cancer cell stemness by hypoxia and interleukin-6. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2017.

Abstract A51: Targeting mTOR metabolism for glioblastoma cancer therapy

Aerobic glycolysis (the Warburg effect), first recognized almost a century ago, by Otto Warburg is a core hallmark of cancer. The Warburg effect describes a switch in glucose metabolism from oxidative phosphorylation to glycolysis. Recently links have been established between the oncogenic pathways that drive tumorigenesis and the mechanistic basis of tumor cell metabolism. The kinase mTOR is a major driver of tumor metabolism and proliferation of cancer cells, acts downstream of numerous oncogenic pathways. Several drugs targeting the mTOR pathway are being developed, however the most common drug rapamycin does not inhibit mTOR complex-2. Therefore in the current study, we examined the potential benefit of MLN0128, a novel potent mTOR ATP competitive inhibitor, as a therapeutic strategy for glioblastoma (GBM), one of the deadliest brain tumors.

We studied the action of MLN0128 in human GBM tumor cells and patient derived stem cells. We show the inhibitory effect of MLN0128 in nanomolar concentrations on tumor proliferation in multiple GBM cell lines via the blockage of phospho-AKT, -ribosomal protein, -4EBP1 inhibiting both mTORC1 and mTORC2 signaling in GBM. Reduction of invasive potential and disruption of paxillin localization to focal adhesions was observed in vitro. MLN0128 treatment decreased glucose consumption and lactate production. It inhibited rate of glycolysis, glycolytic capacity and glycolytic reserve. It also inhibited ATP production, mitochondrial respiration and spare respiratory capacity. MLN0128 was superior in inhibiting metabolism compared to rapamycin. On clonogenic survival assay MLN0128 decreased GBM cell survival and increased radiosensitivity. In vivo treatment of mouse xenografts with MLN0128 downregulated mTOR targets and significantly inhibited tumor volume compared to drug and irradiation alone. Combination treatment of GBM cells with MLN0128 and other chemotherapeutic agents like carboplatin, irinotecan and TMZ showed synergistic effects when combination index was calculated in GBM tumor cells and stem cells. However, the therapeutic efficacy of TMZ combination was greater than MLN0128 combination with either carboplatin or irinotecan. Moreover, similar TMZ chemosensitivity was observed in MGMT non-methylated, TMZ in-sensitive GBM stem cells and MGMT methylated GBM cells. These findings support the rationale for clinical testing of MLN0128 in patients with GBM to provide insight towards optimizing therapeutic efficacy of mTOR kinase inhibitors with standard care.

Citation Format: Anita Tandle, Tamalee Kramp, Philip Tofilon, Kevin Camphausen. Targeting mTOR metabolism for glioblastoma cancer therapy. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr A51.

Abstract 4906: mTOR kinase inhibition enhances radiosensitivity in glioblastoma

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor and predicts a poor prognosis despite current treatment modalities. Aberrant activation of the phosphatidyl-inositol-3-kinase (PI3K) pathway is observed in nearly 90% of GBMs making the downstream effector, mammalian target of rapamycin (mTOR), a potential drug target. mTOR is a serine/threonine kinase that regulates cell growth, proliferation, survival, protein translation and metabolism by integrating signals received from the PI3 K/Akt signaling pathway. The allosteric mTOR inhibitor rapamycin has failed in the clinic as a treatment for GBM patients. Therefore, in the current study, we examined the potential benefit of MLN0128, a novel potent mTOR ATP competitive inhibitor, as a therapeutic strategy for GBM. We assessed in vitro antiproliferative activity of MLN0128 in a panel of GBM tumor and stem cell lines. MLN0128 significantly inhibited cell proliferation of both GBM tumor and stem cells. It decreased the phosphorylation of mTOR, Akt, S6, 4E-BP1, and NDRG1, inhibiting both mTORC1 and mTORC2 signaling in GBM. Thus, MLN0128 appears to be superior in blocking mTORC1/2 signaling in contrast to rapamycin. It inhibited migration and invasion of GBM cells in a matrigel coated chamber assay. On clonogenic survival assay MLN0128 decreased GBM cell survival and increased radiosensitivity. To investigate the mechanism of radiosensitization, the induction and repair of DNA double-strand breaks were evaluated by γH2AX foci formation. MLN0128 exposure significantly delayed the dispersal of radiation induced γH2AX foci formation in both tumor and stem cells. These results indicate that MLN0128 enhances tumor cell radiosensitivity by inhibiting DNA repair. Next we combined MLN0128 with temozolomide (TMZ), a FDA approved radiosensitizer for GBM therapy. Although, we did not observe any synergy in inhibition, addition of TMZ did not adversely affect MLN0128 inhibitory effects. These findings support the rationale for clinical testing of MLN0128 in patients with GBM to provide insight towards optimizing therapeutic efficacy of mTOR kinase inhibitors with standard care.

Note: This abstract was not presented at the meeting.

Citation Format: Anita T. Tandle, Philip Tofilon, Kevin Camphausen. mTOR kinase inhibition enhances radiosensitivity in glioblastoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4906. doi:10.1158/1538-7445.AM2014-4906

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

Molecular profiling indicates orthotopic xenograft of glioma cell lines simulate a subclass of human glioblastoma

Cell line models have been widely used to investigate glioblastoma multiforme (GBM) pathobiology and in the development of targeted therapies. However, GBM tumours are molecularly heterogeneous and how cell lines can best model that diversity is unknown. In this report, we investigated gene expression profiles of three preclinical growth models of glioma cell lines, in vitro and in vivo as subcutaneous and intracerebral xenografts to examine which cell line model most resembles the clinical samples. Whole genome DNA microarrays were used to profile gene expression in a collection of 25 high-grade glioblastomas, and comparisons were made to profiles of cell lines under three different growth models. Hierarchical clustering revealed three molecular subtypes of the glioblastoma patient samples. Supervised learning algorithm, trained on glioma subtypes predicted the intracerebral cell line model with one glioma subtype (r = 0.68; 95% bootstrap CI –0.41, 0.46). Survival analysis of enriched gene sets (P < 0.05) revealed 19 biological categories (146 genes) belonging to neuronal, signal transduction, apoptosis- and glutamate-mediated neurotransmitter activation signals that are associated with poor prognosis in this glioma subclass. We validated the expression profiles of these gene categories in an independent cohort of patients from ‘The Cancer Genome Atlas’ project (r = 0.62, 95% bootstrap CI: –0.42, 0.43). We then used these data to select and inhibit a novel target (glutamate receptor) and showed that LY341595, a glutamate receptor specific antagonist, could prolong survival in intracerebral tumour-implanted mice in combination with irradiation, providing an in vivo cell line system of preclinical studies.

Radiosensitization by the novel DNA intercalating agent vosaroxin

Purpose

Vosaroxin is a first in class naphthyridine analog structurally related to quinolone antibacterials, that intercalates DNA and inhibits topoisomerase II. Vosaroxin is not a P-glycoprotein receptor substrate and its activity is independent of p53, thus evading common drug resistance mechanisms. To evaluate vosaroxin as a clinically applicable radiation sensitizer, we investigated its effects on tumor cell radiosensitivity in vitro and in vivo.

Methods

Vosaroxin's effect on post-irradiation sensitivity of U251, DU145, and MiaPaca-2 cells was assessed by clonogenic assay. Subsequent mechanistic and in vivo studies were performed with U251 cells. Cell cycle distribution and G2 checkpoint integrity was analyzed by flow cytometry. DNA damage and repair was evaluated by a high throughput gamma-H2AX assay. Apoptosis was assessed by flow cytometry. Mitotic catastrophe was assessed by microscopic evidence of fragmented nuclei by immunofluorescence. In vivo radiosensitization was measured by subcutaneous tumor growth delay.

Results

50-100 nmol/L treatment with vosaroxin resulted in radiosensitization of all 3 cell lines tested with a dose enhancement factor of 1.20 to 1.51 measured at a surviving fraction of 0.1. The maximal dose enhancement was seen in U251 cells treated with 75 nmol/L vosaroxin (DEF 1.51). Vosaroxin exposure did not change cell cycle distribution prior to irradiation nor alter G2 checkpoint integrity after irradiation. No difference was seen in the apoptotic fraction regardless of drug or radiation treatment. The number of cells in mitotic catastrophe was significantly greater in irradiated cells treated with vosaroxin than cells receiving radiation only at 72 hr (p = 0.009). Vosaroxin alone did not significantly increase mitotic catastrophe over control (p = 0.53). Cells treated with vosaroxin and radiation maintained significantly higher gamma-H2AX levels than cells treated with vehicle control (p = 0.014), vosaroxin (p = 0.042), or radiation alone (p = 0.039) after 24 hr. In vivo tumor growth delay was 1.5 days for vosaroxin alone (IV 10 mg/kg), 1.0 days for radiation (3 Gy) alone, and 8.6 days for the group treated with vosaroxin 4 hours prior to radiation.

Conclusions

Vosaroxin enhanced tumor cell radiosensitivity in vitro and in vivo. The mechanism appears to be related to inhibition of DNA repair and increased mitotic catastrophe.

Vorinostat enhances the radiosensitivity of a breast cancer brain metastatic cell line grown in vitro and as intracranial xenografts

Vorinostat (suberoylanilide hydroxamic acid), a histone deacetylase inhibitor, is currently undergoing clinical evaluation as therapy for cancer. We investigated the effects of vorinostat on tumor cell radiosensitivity in a breast cancer brain metastasis model using MDA-MB-231-BR cells. In vitro radiosensitivity was evaluated using clonogenic assay. Cell cycle distribution and apoptosis was measured using flow cytometry. DNA damage and repair was evaluated using gammaH2AX. Mitotic catastrophe was measured by immunostaining. Growth delay and intracranial xenograft models were used to evaluate the in vivo tumor radiosensitivity. Cells exposed to vorinostat for 16 hours before and maintained in the medium after irradiation had an increase in radiosensitivity with a dose enhancement factor of 1.57. gammaH2AX, as an indicator of double-strand breaks, had significantly more foci per cell in the vorinostat plus irradiation group. Mitotic catastrophe, measured at 72 hours, was significantly increased in cells receiving vorinostat plus irradiation. Irradiation of s.c. MDA-MB-231-BR tumors in mice treated with vorinostat resulted in an increase in radiation-induced tumor growth delay. Most importantly, animals with intracranial tumor implants lived the longest after combination treatment. These results indicate that vorinostat enhances tumor cell radiosensitivity in vitro and in vivo. There was a greater than additive improvement in survival in our intracranial model. Combining vorinostat with radiation may be a potential treatment option for patients with breast cancer who develop brain metastases.

Adenoviral-mediated p53 transgene expression sensitizes both wild-type and null p53 prostate cancer cells in vitro to radiation

PURPOSE/OBJECTIVE

The effect of adenoviral-mediated p53 transgene expression on the radiation response of two human prostate cancer cell lines, the p53(wild-type) LNCaP and p53(null) PC3 lines, was examined. The objective was to determine if this vector sensitizes cells to radiation independently of their p53 status.

METHODS AND MATERIALS

A recombinant adenovirus-5 vector (RPR/INGN 201, Introgen Therapeutics, Houston, TX) containing a CMV promoter and wild-type p53-cDNA (Ad5-p53) was used to facilitate p53 transgene expression. A multiplicity of infection (MOI) of 10-40 viral particles per cell was used, based on Ad5/CMV/lacz infection and staining for the beta-galactosidase reporter gene product. Clonogenic assays were performed to evaluate the degree of sensitization to radiation of viral-transduced cells compared with irradiated nontransduced controls. The relative efficacy of these treatments to induce apoptotic cell death was determined using the TUNEL assay.

RESULTS

The delivery of Ad5-p53 (10 MOI) reduced control plating efficiency from 36.5% to 0.86% in the LNCaP cell line and from 75.1% to 4.1% in the PC3 cell line. After correcting for the effect of Ad5-p53 on plating efficiency, the surviving fraction after 2 Gy (SF2) of gamma-irradiation was reduced over 2.5-fold, from 0.187 to 0.072, with transgene p53 expression in the LNCaP cell line. Surviving fraction after 4 Gy (SF4) was reduced over 4.5-fold, from 0.014 to 0.003, after Ad5-p53 treatment. In the PC3 cell line, Ad5-p53 (40 MOI) reduced SF2 over 1.9-fold from 0.708 to 0.367, and SF4 over 6-fold from 0.335 to 0.056. In both the LNCaP and PC3 cell lines, the combination of Ad5-p53 plus radiation (2 Gy) resulted in supra-additive apoptosis (approximately 20% for LNCaP and approximately 15% for PC3 at 50 MOI), above that seen from the addition of the controls; control vector Ad5-pA plus RT (0.15% for LNCaP and 1.44% for PC3), Ad5-p53 alone (28.6% for LNCaP and 21.7% for PC3), RT alone (0% for LNCaP and 0.23% for PC3), or Ad5-pA alone (0.1% for LNCaP and 0.29% for PC3).

CONCLUSION

The clonogenic survival and apoptosis data demonstrate that p53 transgene expression sensitizes human prostate adenocarcinoma cells in vitro to irradiation. As this effect was observed in both the p53(wild-type) LNCaP and p53(null) PC3 lines, radiosensitization was independent of p53 status.

An implantable guide-screw system for brain tumor studies in small animals

OBJECT

To overcome the problems associated with using stereotactic techniques to establish intracranial xenografts in nude mice and to treat engrafted tumors with intratumoral therapies (such as gene or viral therapies), the authors developed an implantable guide-screw system. In this study, they describe the guide-screw system, its method of implantation, and their experience with establishing xenografts and delivering intratumoral therapy.

METHODS

The system consists of a 2.6-mm guide screw with a central 0.5-mm diameter hole that accepts the 26-gauge needle of a Hamilton syringe. The screw is implanted into a small drill hole made 2.5 mm lateral and 1 mm anterior to the bregma. A stylet is used to cap the screw between treatments. Tumor cells or therapeutic agents are injected in a freehand fashion by using a Hamilton syringe and a 26-gauge needle fitted with a cuff to determine the depth of injection. To test this system, guide screws were successfully implanted in 44 (98%) of 45 nude mice. After 1 to 2 weeks of recovery, 38 mice were inoculated with U87MG cells and killed 5 days later. On histological studies in 37 (97%) of these animals, xenografts were evident within the caudate nucleus (mean diameter 2.5 mm). To determine whether injections into the center of an established xenograft could be reproducibly achieved with the guide-screw system, an adenovirus vector containing the beta-galactosidase gene was injected 3 days after cell implantation in 15 of the mice. All of these animals demonstrated transduced cells within the tumor. To demonstrate that engrafted animals have a uniform survival time that is indicative of reproducible tumor growth, the survival of six mice was assessed after engraftment with U87MG cells. All six animals died within 28 to 35 days.

CONCLUSIONS

The guide-screw system allows a large number of animals to be rapidly and reproducibly engrafted and for intratumoral treatments to be accurately delivered into established xenografts.

Neuregulin in neuron/glial interactions in the central nervous system. GGF2 diminishes autoimmune demyelination, promotes oligodendrocyte progenitor expansion, and enhances remyelination

Glial growth factor 2 (GGF2) is a neuronal signal that promotes the proliferation and survival of the oligodendrocyte, the myelinating cell of the central nervous system (CNS). This study has focused on recombinant human GGF2 (rhGGF2) and it's potential to affect clinical recovery and repair to damaged myelin in chronic relapsing experimental autoimmune encephalomyelitis (EAE) in the mouse, a major animal model for the human demyelinating disease, multiple sclerosis (MS). Mice with EAE were treated with rhGGF2 during both the acute and relapsing phases, and GGF2 treatment led to delayed signs, decreased severity and resulted in statistically significant reductions in relapse rate. Further, rhGGF2-treated groups displayed CNS lesions with more remyelination than in controls. This correlated with increased expression of myelin basic protein exon 2, a marker for remyelination, and with an increase of the regulatory cytokine, IL-10. Thus, a beneficial effect of a neurotrophic growth factor has been demonstrated upon the clinical, pathologic and molecular manifestations of autoimmune demyelination, an effect that was associated with increased expression of a Th2 cytokine. rhGGF2 treatment may represent a novel approach to the treatment of MS (Cannella et al., 1998).

Modulation of fibrinolysis by ionizing radiation

Radiation-induced damage to the central nervous system is believed to be targeted to glial or endothelial cells or both, although the pathophysiology of this process is still poorly understood. A series of experiments were, therefore, conducted, including irradiation to primary rat astrocytes (in vitro) and rat spinal cords (in vivo). The levels of plasminogen activators (uPA and tPA) and their inhibitors (PNI and PAI-1) were determined by fibrin zymography, ELISA, amidolytic activity assay, complex formation, and Western blot analysis. Fibrin zymography revealed the presence of M(r) 48,000 (uPA) and M(r) 68,000 (tPA) lytic bands that were increased in irradiated samples. Three- to four-fold higher levels of tPA and 8- to 10-fold higher levels of uPA were detected in irradiated samples. Western blot analysis confirmed the presence of a 51-kDa band (PAI-1) in irradiated samples. PAI-1 is undetectable in nonirradiated spinal cord. Serum-free medium and cell and spinal cord extracts of nonirradiated samples showed a 43-kDa band (PNI), the intensity of which is decreased in irradiated samples. Four- to five-fold decreased levels of PNI were detected in irradiated serum-free media and cell extracts, but no levels of PNI were detected in irradiated spinal cord extracts. This study provides additional information regarding the proposed roles of plasminogen activators and their inhibitors in the development of CNS damage after irradiation.

Role of plasminogen activator and of 92-KDa type IV collagenase in glioblastoma invasion using an in vitro matrigel model

The invasive nature of human gliomas represents a major factor in preventing their total resection. The exact nature of the underlying mechanisms of tumor cell invasion are still unclear. In this study, we have quantitatively assayed a glioblastoma cell line for its ability to migrate through a polycarbonate filter coated with matrigel which contains a complex of multiple basement membrane components. At 48 h the glioblastoma cell line (U251) showed a rate of invasiveness of 42% and also dependent on the concentration of matrigel. The U251 cell line produced a urokinase type plasminogen activator and a 92-KDa type IV collagenase. Both enzymes were inhibited by the addition of uPA and 92-KDa type IV collagenase antibodies. Those same antibodies reduced the invasion rate of U251 cells from 42% to 12 and 21%, respectively. Similarly, the addition of epsilon-aminocaproic acid (a plasmin inhibitor) or tissue inhibitor of metalloprotease (TIMP2, a collagenase inhibitor) reduced the invasiveness of U251 cells from 42% to 14% and 10%, respectively. Additionally, the other two glioblastoma cell lines (LG11, UWR1) and astrocytes showed a rate of invasiveness at 41%, 61% and 12%, respectively. Finally, the addition of hyaluronic acid to the matrigel, a constituent of brain extracellular matrix, enhanced the rate of invasion. These findings provide evidence for the role of serine proteases and metalloproteases in facilitating the invasion of extracellular matrix components by glioblastoma cell line and suggest a therapeutic role for protease inhibitors in attempting to minimize the invasive propensity of gliomas.