Glioblastoma Cancer Stem Cells Research Articles

ADAMDEC1 and FGF2/FGFR1 signaling constitute a positive feedback loop to maintain GBM cancer stem cells

ABSTRACTIdentification of targetable mechanisms that maintain glioblastoma cancer stem cells (CSCs) remain a priority. Our study reveals a new mechanism by which a disintegrin and metalloproteinase domain-like protein decysin 1 promotes CSC maintenance through the activation of a fibroblast growth factor autocrine signaling loop, which can be blocked pharmacologically.

GENE-26. HOST GENETIC VARIATIONS IN MACROPHAGE MIGRATION INHIBITOR FACTOR CONFER WORSE PROGNOSIS IN GLIOBLASTOMA

Abstract Genetic and systemic prognostic factors have been identified in glioblastoma (GBM) that correlate with survival, but patient-specific genomic risk factors that impact prognosis or response to immunotherapies have not been elucidated. GBM promotes an immune suppressive microenvironment via many mechanisms including the production of macrophage migration inhibitory factor (MIF) by GBM cancer stem cells, which activates myeloid derived suppressor cells (MDSCs). Increased circulating and intracranial MDSCs as well as intratumoral MIF expression in GBM patients portend a worse overall prognosis. Endogenous MIF expression is dependent on two genetic microsatellite loci: single nucleotide polymorphisms (SNPs) and CATT repeats within the promoter. To determine whether these genetic variations were linked to GBM development and/or prognosis, we assessed peripheral nucleated blood from 520 GBM patients for the MIF SNPs and CATT repeats. MIF microsatellite frequencies were similar between the normal population and GBM patients indicating loci variability was not a risk factor for GBM development. However, newly diagnosed IDH wild-type GBM patients with a minor allele SNP who received standard of care therapy had a 3.1 month shorter progression free survival (PFS), and a 4.3 month shorter overall survival (OS) when compared to patients with two major allele SNPs. This association was seen also with the CATT-repeat analyses. Furthermore, in a multivariate analysis for PFS that included age, sex, Karnofsky performance status, MGMT methylation status, 1p/19q co-deletion, and SNP status as covariates, only age and SNP status were independently associated with shorter PFS. Taken together, patients with variant MIF microsatellite loci experienced shorter PFS and decreased OS compared to those with the most common loci. These results are currently being validated in a separate 1700 patient cohort with the intent of understanding how MIF expression influences myeloid populations within the GBM microenvironment and then developing novel peripheral GBM screening markers for aggressiveness.

STEM-02. GLIOBLASTOMA CANCER STEM CELLS UTILIZE ASYMMETRIC CELL DIVISION TO PROMOTE THERAPEUTIC RESISTANCE

Abstract Asymmetric cell division (ACD) enables the maintenance of a stem cell population while simultaneously generating differentiated progeny. Cancer stem cells (CSCs) undergo multiple modes of cell division during tumor expansion and in response to therapy, yet the functional consequences of these division modes has yet to be determined. Using a fluorescence-based system that reports the mitotic distribution of lipid rafts enriched in cell surface receptors, we found that ACD in glioblastoma CSCs generated a daughter cell with enhanced resistance to radiation and temozolomide. Single-cell analyses using our reporter system revealed that ACD also increased the co-inheritance of epidermal growth factor receptor (EGFR) and neurotrophin receptor (p75NTR), which was validated across four additional glioblastoma CSC models. Stimulation of both receptors maintained self-renewal under differentiation conditions, and stimulation with p75NTR ligands rescued the reduction in STAT3, AKT, and ERK induced by erlotinib-mediated EGFR inhibition. Finally, knockdown of p75NTR enhanced the therapeutic efficacy of EGFR inhibition in vivo. Taken together, our data indicate that co-inheritance of p75NTR and EGFR promotes resistance to EGFR inhibition through a redundant mechanism. Overall, these findings demonstrate that ACD produces progeny with enhanced growth factor receptors, which contributes to the generation of a more therapeutically resistant CSC population, and suggest that ACD needs to be considered in the development of next-generation targeting strategies.

STEM-20. RADIO-SENSITIZING GLIOBLASTOMA CANCER STEM CELLS BY INHIBITION OF FACT

Abstract Glioblastoma (GBM) has a particularly high rate of recurrence with a 5-year overall survival rate of approximately 5%. This is in part due to a sub-population of cancer stem cells (CSC), which are both radioresistant and chemotherapeutically resistant to conventional treatments. Here we investigated CBL0137, a small molecule form of curaxin, in combination with radiotherapy as a means to radiosensitize CSCs. CBL0137 sequesters FACT (facilitates chromatin transcription) complex to chromatin, which leads to activation of p53 and inhibition of NF-κB. This sequestering of FACT results in cytotoxicity especially within tumor cells and prevents FACT from performing its primary role as a histone chaperone, as well as inhibits its part in the DNA damage response pathway. We show that when combined with radiotherapy, CBL0137 administration limited the ability of CSCs to identify and repair damaged DNA. CSCs treated in vitro with CBL0137 and irradiation showed an increased inhibition of cancer cell growth and decreased viability compared to irradiation or drug alone. Combination therapy also showed more DNA damage in the CSCs than with either agent alone. Based on our in vitro evidence for the efficacy of combination therapy to target CSCs, we moved forward to test the treatment in vivo. Using a subcutaneous model, we show that the amount of CD133+ cells (a marker for GMB CSCs) was reduced in irradiation plus CBL0137 compared to either treatment alone. Survival studies demonstrated that irradiation plus CBL0137 compared to irradiation alone or CBL0137 alone increase lifespan. Here we show the ability of CBL0137, in combination with irradiation, to target patient GBM CSCs both in vitro and in vivo. This work establishes a new treatment paradigm for GBM that inclusively targets CSCs and may ultimately reduce tumor recurrence.

STEM-07. THE ATYPICAL METALLOPROTEINASE ADAMDEC1 MAINTAINS A NOVEL FGF MEDIATED SIGNALLING NETWORK IN GLIOBLASTOMA CANCER STEM CELLS

Abstract Glioblastomas (GBM) are lethal brain tumors where poor outcome is attributed to cellular heterogeneity, therapeutic resistance, and a highly infiltrative nature. These characteristics are preferentially linked to GBM cancer stem cells (CSCs), but how CSCs maintain their stemness is incompletely understood and the subject of intense investigation. CSCs rely both on cell intrinsic programs and microenvironmental interactions to regulate their maintenance. Recent work has demonstrated that CSCs can modulate their surrounding microenvironment by metalloproteinase expression, allowing direct modification of the extracellular matrix that provides structural tissue integrity, and instructive signalling via engagement of key cell surface receptors and sequestration of essential growth factors. Here, we identify a novel growth factor signalling loop that induces and maintains CSCs via an atypical metalloproteinase, a disintegrin and metalloproteinase domain-like protein decysin 1 (ADAMDEC1), secreted by CSCs. ADAMDEC1 solubilizes fibroblast growth factor-2 (FGF2) in the tumor microenvironment. We find that CSCs exclusively express FGF receptor 1 (FGFR1), which upon binding of FGF2 induces upregulation of Zinc finger E-box-binding homeobox 1 (ZEB1). ZEB1 is a regulator of stemness and tumor initiation, and therefore ADAMDEC1-FGF2-FGFR1 signalling promotes malignancy in GBM. We further show that ERK phosphorylation drives ZEB1, which regulates ADAMDEC1 expression, creating a positive feedback loop via repression of microRNA-203. Genetic or pharmacological targeting of components of this axis attenuates self-renewal and tumor growth. These findings reveal a new signalling axis for CSC maintenance and highlight ADAMDEC1 and FGFR1 as potential therapeutic targets in GBM. In addition, these findings provide a new paradigm for GBM growth through which key growth factors embedded within the extracellular matrix can be selectively accessed by CSC for their maintenance.

ADAMDEC1 Maintains a Growth Factor Signaling Loop in Cancer Stem Cells.

Glioblastomas (GBM) are lethal brain tumors where poor outcome is attributed to cellular heterogeneity, therapeutic resistance, and a highly infiltrative nature. These characteristics are preferentially linked to GBM cancer stem cells (GSC), but how GSCs maintain their stemness is incompletely understood and the subject of intense investigation. Here, we identify a novel signaling loop that induces and maintains GSCs consisting of an atypical metalloproteinase, ADAMDEC1, secreted by GSCs. ADAMDEC1 rapidly solubilizes FGF2 to stimulate FGFR1 expressed on GSCs. FGFR1 signaling induces upregulation of ZEB1 via ERK1/2 that regulates ADAMDEC1 expression through miR-203, creating a positive feedback loop. Genetic or pharmacologic targeting of components of this axis attenuates self-renewal and tumor growth. These findings reveal a new signaling axis for GSC maintenance and highlight ADAMDEC1 and FGFR1 as potential therapeutic targets in GBM. SIGNIFICANCE: Cancer stem cells (CSC) drive tumor growth in many cancers including GBM. We identified a novel sheddase, ADAMDEC1, which initiates an FGF autocrine loop to promote stemness in CSCs. This loop can be targeted to reduce GBM growth.This article is highlighted in the In This Issue feature, p. 1469.

Oncolytic Effect of Adenoviruses Serotypes 5 and 6 Against U87 Glioblastoma Cancer Stem Cells.

Oncolytic adenoviruses are promising therapeutic agents against both the bulk of tumor cells and cancer stem cells. The present study intended to test the oncolytic capability of adenovirus serotype 6 (Ad6), which has a lower seroprevalence and hepatotoxicity relatively to adenovirus 5 (Ad5), against the glioblastoma and its cancer stem cells. Oncolytic efficacy of Ad6 was compared to widespread Ad5 both in vitro and in vivo, using the U87 and U251 human glioblastoma cell lines and subcutaneously transplanted U87 cells in SCID mice, respectively. Ad6 had a dose-dependent cytotoxicity toward glioblastoma cells in vitro and its intratumoral injections lead to a significant (p<0.05) decrease in volume of U87 xenografts, similarly to Ad5. Based on the innate capability of glioblastoma cancer stem cells to internalize a fluorescent-labeled double-stranded DNA probe, the spatial localization of these cells was estimated and it was shown that the number of cancer stem cells tended to decrease under adenovirus therapy as compared to the control group. Ad6 was shown to be a promising agent for treating glioblastomas.

Therapeutic Targeting of Cancer Stem Cells in Human Glioblastoma by Manipulating the Renin-Angiotensin System.

Patients with glioblastoma (GB), a highly aggressive brain tumor, have a median survival of 14.6 months following neurosurgical resection and adjuvant chemoradiotherapy. Quiescent GB cancer stem cells (CSCs) invariably cause local recurrence. These GB CSCs can be identified by embryonic stem cell markers, express components of the renin-angiotensin system (RAS) and are associated with circulating CSCs. Despite the presence of circulating CSCs, GB patients rarely develop distant metastasis outside the central nervous system. This paper reviews the current literature on GB growth inhibition in relation to CSCs, circulating CSCs, the RAS and the novel therapeutic approach by repurposing drugs that target the RAS to improve overall symptom-free survival and maintain quality of life.

Prion Protein in Glioblastoma Multiforme.

The cellular prion protein (PrPc) is an evolutionarily conserved cell surface protein encoded by the PRNP gene. PrPc is ubiquitously expressed within nearly all mammalian cells, though most abundantly within the CNS. Besides being implicated in the pathogenesis and transmission of prion diseases, recent studies have demonstrated that PrPc contributes to tumorigenesis by regulating tumor growth, differentiation, and resistance to conventional therapies. In particular, PrPc over-expression has been related to the acquisition of a malignant phenotype of cancer stem cells (CSCs) in a variety of solid tumors, encompassing pancreatic ductal adenocarcinoma (PDAC), osteosarcoma, breast cancer, gastric cancer, and primary brain tumors, mostly glioblastoma multiforme (GBM). Thus, PrPc is emerging as a key in maintaining glioblastoma cancer stem cells’ (GSCs) phenotype, thereby strongly affecting GBM infiltration and relapse. In fact, PrPc contributes to GSCs niche’s maintenance by modulating GSCs’ stem cell-like properties while restraining them from differentiation. This is the first review that discusses the role of PrPc in GBM. The manuscript focuses on how PrPc may act on GSCs to modify their expression and translational profile while making the micro-environment surrounding the GSCs niche more favorable to GBM growth and infiltration.

The metalloproteinase ADAMDEC1 maintains a novel growth factor signalling loop in glioblastoma cancer stem cells

Abstract Glioblastomas (GBM) are lethal brain tumours where poor outcome is attributed to cellular heterogeneity, therapeutic resistance, and a highly infiltrative nature. These characteristics are preferentially linked to GBM cancer stem cells (GSCs), but how GSCs maintain their stemness is incompletely understood and the subject of intense investigation. Here, we identify a novel growth factor signalling loop that induces and maintains GSCs. This loop consists of an atypical metalloproteinase, a disintegrin and metalloproteinase domain-like protein decysin 1 (ADAMDEC1), secreted by GSCs. ADAMDEC1 solubilizes fibroblast growth factor-2 (FGF2) in the tumour microenvironment. We find that GSCs exclusively express FGF receptor 1 (FGFR1), which upon binding of FGF2 induces upregulation of Zinc finger E-box-binding homeobox 1 (ZEB1). ZEB1 is a regulator of stemness and tumour initiation, and therefore ADAMDEC1-FGF2-FGFR1 signalling promotes malignancy in GBM. We further show that ZEB1 regulates ADAMDEC1 expression, creating a positive feedback loop. Genetic or pharmacological targeting of components of this axis attenuates self-renewal and tumour growth. These findings reveal a new signalling axis for GSC maintenance and highlight ADAMDEC1 and FGFR1 as potential therapeutic targets in GBM.

The effects of NK cells and drug combination therapy on glioblastoma tumor growth

Background and Hypothesis: Glioblastoma (GB) is an aggressive primary brain malignancy with a mean survival time of 15-16 months. Initial therapy is limited to surgery, radiation and temozolamide (TMZ) chemotherapy with up to seventy percent of GBs recurring in the first year and only five percent of patients still alive after five years. A reason these tumors are difficult to treat is the effect that the GB tumor microenvironment has on recurrence. One major cell type in this microenvironment is GB cancer stem cells and these cells play a major role in recurrence of the GB tumor. Our approach is that if we reduced tumor volume with the standard of care and treat with NK-cell based treatment and combination drug therapy we can improve the remission and prognosis of GB tumors.&#x0D; Experimental Design or Project Methods: To explore the killing potential of NK cells as well as combination drug treatment we set up a caspase assay that would indicate DNA damage and cell health. We set up in a 96-well plate with GB43 or Cancer stem cells with increasing consideration of either drug over 72 hours or NK cells over 48 hours. After we create, dose curves to find LD50 of both Cell based and drug based treatment. &#x0D; Results: We are still assessing the cell-based therapy and calculating LD50 for both treatments. However, we have found that in the drug based combination therapy we were able to show that paclitaxel and RG3788 both alone and in combination with the standard of care,TMZ, showed significantly reduced GB43 cell viability as concentration increased at the 72 hour time point. However, cancer stem cell remain at around 80% viability across all drug combinations and concentrations.&#x0D; Conclusion and Potential Impact: In conclusion at this point these data indicate that GB43 with the standard of care TMZ in combination with paclitaxel and RG3788 have the ability to kill cells in vitro. Moving forward we plan to package paclitaxel and RG3788 in nanoparticles for more efficient targeting of cells to target tumors. In addition, we plan to create lethal dose curves for NK cells and control neuronal cell tissue to better assess drug toxicity and efficacy.

P11.19 Glioblastoma cancer stem cells proliferation and cell cycle arrest under TTFields influence

Abstract BACKGROUND Glioblastoma (GBM) is the most aggressive and fastest growing-type among brain tumours. The current standard of care is a combination of surgery, radio- and chemotherapy. However, GBM is characterized by a poor prognosis and an average life expectancy of 15 months under current treatment. Tumor treating fields (TTFields) are low-intensity electric fields alternating at an intermediate frequency (200kHz), which have been demonstrated to block cell division and interfere with organelle assembly. It has been evaluated in randomized phase 3 trials in GBM and demonstrated to prolong progression-free survival and overall survival when administered together with standard maintenance temozolomide (TMZ) chemotherapy in patients. This technology represents the biggest step forward against GBM in more than a decade. METHODS Primary cultures of human glioblastoma enriched in cancer stem cells (GSCs) were stimulated using the InovitroTM System (NOVOCURE) for 72 hours. Remaining cells were collected for further experiments. RESULTS Our investigation has targeted GSCs, a subset of cells that are considered responsible for tumour recurrence and confer resistance to chemotherapy and radiotherapy. Our data show that after 72 hours of TTFields exposure, more than 60% of the cellular population are dead. The residual GSCs were able to recover proliferation as soon as TTFields application had ended. We used different combinations of TTFields exposure times and pharmacological treatments with the main objective to impair cell proliferation relapse. Prolong TTF stimulation kills more cells but survivor cells are still able to resume proliferation. The addition of 10 mM TMX increase drastically the efficacy of the TTFields treatment even if the few cells left were able to slowly form colonies in a single cell cloning assay. CONCLUSION GCSs are sensitive to TTFields and to the combining pharmacological treatment with TMZ. The strategy to optimize the antiproliferative action on GCSs relapse will be to find a best combination of anticancer drugs concentration, together with TTFields exposure.

T cells expressing NKG2D chimeric antigen receptors efficiently eliminate glioblastoma and cancer stem cells

BackgroundTraditional therapies fail to cure most glioblastoma patients and the 5-year survival rate is less than 10%, highlighting need for new therapeutic approaches. The natural killer group 2 member D ligands (NKG2DLs) are highly expressed in glioblastomas and are considered promising targets for chimeric antigen receptor (CAR) T-cell therapy. The aim of this study was to investigate the effect of NKG2D-expressing CAR-T cells on glioblastomas and glioblastoma stem cells.MethodsThe expression of NKG2DLs was analyzed by flow cytometry and immunohistochemistry. NKG2D-BBz CAR, containing the extracellular domain of NKG2D, was constructed and delivered into T cells by lentiviral particles. In vitro cytotoxicity of the CAR-T cells was assessed by flow cytometry. Release of cytokine, perforin and granzyme B was quantified using enzyme-linked immunosorbent assay kits. The therapeutic efficacy of NKG2D-BBz CAR-T cells in vivo was evaluated using subcutaneous tumor models. The safety of the CAR was analyzed by investigating the effects on proliferation, apoptosis, and karyotype.ResultsOur data confirmed the high expression of NKG2DLs in human glioblastoma cells, cancer stem cells, and tumor samples. Further, the NKG2D-BBz CAR-T cells efficiently lysed glioblastoma cells and cancer stem cells in vitro and produced high levels of cytokines, perforin, and granzyme B. The CAR-T cells markedly eliminated xenograft tumors in vivo and did not exhibit significant treatment-related toxicity in the treated mice. The CAR expression also did not exert any obvious effects on cell proliferation, apoptosis, and genomic stability.ConclusionOur findings demonstrated that NKG2D CAR-T cells targeted glioblastoma cells and cancer stem cells in an NKG2D-dependent manner, supporting the use of CAR-T therapy in glioblastoma therapeutic strategies.

Abstract 4284: Targeting notch signaling in glioblastoma cancer stem cells through modulation of Connexin43 function

Abstract Glioblastoma (GBM) is a highly malignant and lethal cancer of the central nervous system for which there has been limited progress in improving patient outcomes despite intensive research efforts. The current multimodal therapy for newly diagnosed GBM patients includes surgical resection, radiotherapy and cytotoxic chemotherapy with temozolomide (TMZ), conferring a median survival time of just 14.6 months. Failure to generate more effective treatment strategies is due to 1) the infiltrative nature of GBM tumor cells preventing complete surgical resection, and 2) the cellular heterogeneity within GBM tumors, which often comprise a sub-population of GBM cancer stem cells (GSCs) characterized by self-renewal characteristics and resistance to chemotherapeutic alkylating agents including TMZ. Multiple signaling pathways, including Notch, participate to the formation and maintenance of GSCs. Recent studies, including our research, have shown that increased levels of gap junction protein Connexin43 (Cx43) correlate with TMZ resistance in GBM cells and inversely correlated with GBM patient survival. Importantly, Cx43 has also been associated with anti-proliferative effects in glioma, and reduced levels of Cx43 protein occur in high-grade gliomas. Therefore, we hypothesized that altering Cx43 localization and/or activity rather than Cx43 expression represents a potent strategy for GBM treatment. Regulating Cx43 function is primarily associated with the multiple sites for post-translational modifications and protein-protein interactions within the Cx43 carboxy-terminus. Our research identifies crosstalk between Cx43 and Notch signaling in GSCs. Using a Cx43 carboxy-terminus mimetic peptide that modulates non-junctional functions of Cx43, we observe a decrease in Notch1 protein expression and reduced transcription of its downstream targets Hes1 and Hey1 in GSCs derived from patient tumors. Most importantly, our Cx43 mimetic peptide decreases cell survival in TMZ-resistant GSCs, limits GSC neurosphere formation in vitro, and inhibits GSC-derived tumor growth in vivo. Our current research aims at dissecting the molecular mechanisms of Cx43 functions on Notch signaling in GSCs using this Cx43 mimetic peptide. In conclusion, we have identified a novel therapeutic opportunity to decrease the tumorigenic potential of GSCs through altering Cx43 activity and Notch signaling to target chemoresistant GSCs in GBM treatment. Citation Format: Michael Lunski, James Smyth, Jennifer Vaughn, Zhi Sheng, Robert Gourdie, Benjamin Purow, Samy Lamouille. Targeting notch signaling in glioblastoma cancer stem cells through modulation of Connexin43 function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4284.

Abstract 4742: The influence of cellular developmental state on response to therapeutics in glioblastoma

Abstract Glioblastoma (GBM) is an aggressive tumor treated with ionizing radiation (IR) and temozolomide (TMZ). Here we investigate how developmental state of glioblastoma cells: cancer stem cells (CSC) or differentiated cells, influences cellular response to treatment. Tissue from untreated primary GBM tumors representing diverse genotype were dissociated and cultured in conditions selective for CSCs, which were subsequently differentiated into an astrocytic phenotype by culturing in media supplemented with 2% FBS. Stemness index was evaluated using a machine learning predictive algorithm. Sensitivity of both isogenic CSC and serum differentiated cell (SDC) populations to TMZ and IR was determined by non-linear fitting of dose-response curves, using CellTiterGlo to measure cell viability (n=5) . CSCs and SDCs were then subjected to sub-lethal TMZ, IR (4 Gy), or control treatments, in triplicate. Cells were harvested, and DNA was isolated and Illumina 450k DNA methylation array data was analyzed by using the Methylumi package in R software. RNA was isolated for sequencing, and differentially expressed genes were determined by NOISeq R package. Our results show that GBM CSCs are more vulnerable to both TMZ and IR treatment than the isogenic SDCs. Transcriptome profiling show that IR leads to increase in p53 mediated expression of pro-apoptotic genes such as MDM2, PUMA and BCL2 binding protein relative to control in CSCs. In differentiated cells, IR lead to an increase in WNT signaling, DNA-repair activity and histone modification /remodeling proteins. Enrichment analysis using Fisher’s exact test identified significant enrichment in lipid, fatty acid and metabolic processes as well as receptor tyrosine signaling. Globally, CSCs exhibited a decrease in protein coding genes and increase in regulatory RNA expression. DNA methylation show a global increase in CpG promoter methylation in differentiated cells relative to isogenic stem-like counterparts. We recovered significant differentially methylated probes between treatment groups (Wilcoxon signed rank test) as well as a global increase in CpG promoter methylation in IR treated cells relative to control. These findings underscore the challenge of treating a highly heterogeneous tumor and challenge a strategy of inducing differentiation to increase GBM sensitivity to treatment. Citation Format: Oluwademilade Nuga, Ana deCarvalho, Douglas Ruden, Stephen Brown, Indrani Datta, Tathianne Malta. The influence of cellular developmental state on response to therapeutics in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4742.

Abstract CT116: Phase I/II study of dianhydrogalactitol (VAL-083) with radiation therapy in patients with newly diagnosed, MGMT-unmethylated glioblastoma

Abstract Glioblastoma (GBM) is the most common and aggressive primary brain cancer. Current standard-of-care includes surgery followed by chemo-radiation and temozolomide. An unmethylated promoter for O6-methylguanine-DNA-methyltransferase (MGMT) is a validated biomarker for temozolomide-resistance and is strongly correlated with poor outcomes. Unmethylated MGMT represents the majority of newly diagnosed GBM tumors. VAL-083 is a first-in-class bi-functional DNA-targeting agent that has shown activity against GBM in NCI-sponsored clinical trials both as single agent and in combination with radiotherapy. VAL-083 induces interstrand cross-links at N7-guanine, leading to DNA double-strand breaks and cell-death. VAL-083’s unique mechanism-of-action circumvents MGMT-mediated chemoresistance, and it has demonstrated cytotoxicity in MGMT-unmethylated GBM cell-lines, cancer stem cells (CSCs) and in vivo models. Furthermore, VAL-083 acts as a radiosensitizer in GBM CSCs and non-CSCs. We completed a dose-escalation trial of VAL-083 in recurrent GBM, and a generally well-tolerated dosing regimen was selected for further clinical development. The present trial is an ongoing open-label, biomarker-driven, Phase I/II study to evaluate the tolerability and efficacy of VAL-083 in combination with radiotherapy in newly diagnosed MGMT-unmethylated GBM patients. A treatment regimen, consisting of a 6-week induction period of VAL-083 and concurrent radiation (2 Gy daily, 5 days/week) followed by up to 24 weeks of maintenance therapy with single-agent VAL-083, is being evaluated. The study is being conducted in two parts. The dose-confirmation part (20, 30, and 40 mg/m2/day IV infusion on days 1-3 of a 21-day cycle) has been completed, and the expansion part has been initiated in up to 20 additional patients at 30 mg/m2/day IV infusion on days 1-3 of a 21-day cycle. Tumor response will be assessed by MRI, according to RANO criteria. Efficacy endpoints include progression-free survival (PFS) and overall survival (OS). Additional endpoints include safety evaluations and pharmacokinetic assessments of plasma and CSF samples. Trial design, enrollment and safety data update will be provided at the meeting. Clinicaltrials.gov identifier: NCT03050736. Citation Format: Zhong-ping Chen, Chengcheng Guo, Jeffrey Bacha, John Langlands, Anne Steino, Claire Kwan, Sarath Kanekal, Richard Schwartz, Lorena Lopez, Dennis Brown. Phase I/II study of dianhydrogalactitol (VAL-083) with radiation therapy in patients with newly diagnosed, MGMT-unmethylated glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT116.

Abstract 1051: Dianhydrogalactitol (VAL-083) reduces glioblastoma tumor growth upon bevacizumab-induced hypoxia, in vivo

Abstract Background: Standard-of-care for glioblastoma (GBM) includes surgery, radiation and temozolomide (TMZ). Nearly all tumors recur and 5-year survival is less than 3%. Unmethylated promoter status for O6-methylguanine-DNA-methyltransferase (MGMT) is a validated biomarker for TMZ-resistance. Second-line treatment with bevacizumab has not only failed to improve survival, but has also been shown to induce intratumor hypoxia, which is implicated in increased chemoresistance. VAL-083 is a bi-functional DNA-targeting agent that readily crosses the blood-brain barrier and accumulates in brain tumor tissue. VAL-083 induces DNA double-strand breaks at N7-guanine and cancer cell-death in GBM cancer stem cells (CSCs) and non-CSCs, independent of MGMT. We have previously shown that bevacizumab treatment upregulates expression of glucose transporters GLUT-1/GLUT-3 on GBM cells. We hypothesized that, based on its unique monosaccharide backbone structure, VAL-083 may benefit from bevacizumab-induced GLUT transporter upregulation leading to enhanced VAL-083 uptake and anti-tumor activity. Methods: To investigate the in vivo anti-tumor effect of VAL-083+bevacizumab, we used a orthotopic patient-derived xenograft GBM model. All mice carried MGMT-unmethylated, temozolomide-resistant recurrent T16 GBM tumors as detected by MRI 35 days post-implantation. Mice were grouped into control, bevacizumab, VAL-083, and VAL-083+bevacizmab. Tumor progression was measured by MRI on days 49 and 56, and tumor growth rate was calculated for the entire study (day 35 vs. 56) and for the last 7 days (day 49 vs. 56). Results: Tumors were significantly smaller in VAL-083-treated mice both compared to control (-83%, p&amp;lt;0.001) and compared to bevacizumab-treated (-75%, p&amp;lt;0.001) mice. Additionally, analysis of tumor growth in-time showed significantly reduced tumor growth rate for VAL-083+bevacizumab compared to VAL-083 alone (p&amp;lt;0.01). Conclusions: These results show strong in vivo anti-tumor efficacy of VAL-083 against MGMT-unmethylated, TMZ-resistant recurrent GBM. This effect was further augmented in combination with bevacizumab, providing rationale of clinical investigation of VAL-083 in combination with bevacizumab in the treatment of GBM. Citation Format: Anna Golebiewska, Anais Oudin, Anne Steino, Simone P. Niclou, Jeffrey Bacha, Dennis M. Brown. Dianhydrogalactitol (VAL-083) reduces glioblastoma tumor growth upon bevacizumab-induced hypoxia, in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1051.

Abstract 182: Cancer stem cells and tumor angiogenesis in serous adenocarcinoma of ovary

Abstract The traditional view of tumour vascularization is that tumours acquire blood supply from the neighbouring normal stroma. However, recently the origin of tumour endothelial cells or pericytes in part has been shown to be derived from cancer stem cells (CSCs) in glioblastoma. In high grade serous ovarian cancer (HGSOC), the origin of endothelial cells is not known. Our objective was to determine if components of a tumour blood vessel and lymphatic vessel are derived from CSCs in ovarian cancer. Using spheroids as an in vitro model, we have evaluated the role of CSCs in primary malignant cells (PMCs) from patients with serous adenocarcinoma of ovary cultured under specific conditions. The expression of endothelial, pericyte and lymphatic endothelial markers was evaluated by flow cytometry. In addition, functional assays were performed to assess the endothelial phenotype. Further, the ability of CSCs to express endothelial markers under appropriate growth conditions was also evaluated with Bevacizumab which antagonize VEGF. PMCs grown in endothelial growth medium (EGM) showed significantly higher expression of CD105 (n=32, p = 0.002) and CLEC14A (n=10, p = 0.012) and co-expression of CD105/CLEC14A (n=10, p= 0.012) than that of spheroids. Primary malignant cells when grown in pericyte and lymphatic endothelial specific conditions, showed significantly higher expression of desmin (n=10, p=0.03), Smooth muscle actin (SMA) (n=10, p=0.017) and VEGFR3 (n=10, p=0.028) than that of the spheroids. When the PMCs were grown as spheroids in endothelial conditions in the presence or absence of Bevacizumab (1 μg/μl), there was a reduction in the co-expression of CD105 and CLEC14A (P=0.04). The cells grown in endothelial conditions showed formation of tubes, uptake of Dil-ac-LDL and expressed eNOS, confirming their endothelial phenotype. GFP transduced spheroids from PMCs formed tumours in mice and the blood vessels in the tumour co-expressed CD31, SMA, VEGFR3 and GFP, suggesting that these cells are derived from CSCs. These results prove that a proportion of endothelial cells, pericytes and lymphatic endothelial cells are derived from CSCs in serous ovarian carcinoma and the VEGF pathway has a key role. This property of CSCs to contribute to tumour angiogenesis can be inhibited. Citation Format: S Krishnapriya, C Sidhanth, P Manasa, S Sneha, S Bindhya, R P. Nagare, T S. Ganesan. Cancer stem cells and tumor angiogenesis in serous adenocarcinoma of ovary [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 182.

Abstract LB-110: Proteasome addiction a new therapeutic opportunity to treat PTEN-deficient brain tumors

Abstract One of the most common genetic alterations in glioblastoma (30-40%) occurs in the tumor suppressor gene PTEN (phosphatase and tensin homolog), where loss of function has been mechanistically linked to increased tumor cell invasion, and to a lack of radio- and chemo-therapy response. To identify new drug compounds that target PTEN-deficient brain tumors we performed a high throughput drug screening using patient-derived GBM spheres and found that PTEN-deficient samples were highly sensitive to proteasome inhibitors. We confirmed PTEN dependency to proteasome inhibition by genetically overexpressing or deleting PTEN in GBM cells and established that the drug inhibition response relied on PTEN enzymatic activity. Additionally, proteasome inhibition specifically suppressed tumor growth and increased survival of mice orthotopically engrafted with human PTEN-null glioblastoma cancer stem cells. Mechanistically, we determined that PTEN-deficient cells were more sensitive to proteasome inhibition due to an increase in protein synthesis rate and loss of autophagy activity associated with activation of the PI3K/mTOR pathway. Finally, integrated in silico analysis of the Samsung Medical Center dataset corroborated that samples with PTEN/EGFR/PI3K alterations were significantly more sensitive to Carfilzomib, an FDA-approved proteasome inhibitor. This study reveals that PTEN-deficient cells are "proteasome addictive" and opens a new therapeutic opportunity to treat glioblastoma PTEN-deficient patients. Citation Format: Jorge A. Benitez, Darren Finlay, Alexandre Rosa-Campos, Jianhui Ma, Tomoyuki Koga, Kristiina Vuori, Frank Furnari. Proteasome addiction a new therapeutic opportunity to treat PTEN-deficient brain tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-110.

Abstract 5215: Targeting of HOX-PBX binding in glioblastoma multiforme as a novel therapeutic treatment

Abstract The HOX genes encode a family of transcription factors that play an essential role in embryonic patterning. They are also aberrantly expressed in numerous cancers, including glioblastoma (GBM). Three Amino Acid Loop Extension Homeobox (TALE) proteins act as important co-factors for HOX proteins, modulating their binding affinities to genomic targets. TALE proteins include the Pre-B-cell leukemia homeobox (PBX) proteins 1-4, which bind anterior HOX proteins, facilitating their nuclear entry and limiting their degradation. HTL00-1 is a 2nd generation hexapeptide drug that inhibits HOX-PBX dimer formation, and has been shown to induce rapid apoptosis in cancer cells, but not normal cells, through the rapid upregulation of genes including cFos, DUSP1, and EGR1. We have found that both HOX and TALE genes are markedly dysregulated in primary GBM tumors as well as in murine (GL261), adult (LN18, U87-MG, U251-MG) and pediatric (KNS42, SF188) GBM cell lines, all of which are sensitive to HTL-001. These genes were even more highly expressed in experimentally induced GBM cancer stem cells (CSCs) compared with parental lines, with a corresponding increase in sensitivity to HTL-001. We also investigated the in vivo activity of HTL-001 in Black 6 mice carrying GL-261 subcutaneous and orthotropic tumors with twice weekly intraperitoneal delivery. HTL-001 was shown to cross the blood brain barrier using Alexa660 labelled peptide, and significant anti-tumor activity was observed in both subcutaneous and orthotropic models with increased survival (p&amp;lt;0.02 and p&amp;lt;0.0078, respectively). Resected tumors from HTL-001 treated mice showed marked evidence of apoptosis, tumor vasculature disruption and focal necrosis compared to untreated tumors. Taken together, our findings indicate that HOX-PBX inhibition is a potential therapeutic target for adult and pediatric GBM patients. Citation Format: Richard Morgan, Monika Primon, Steven Shnyder, Susan Short, Balveen Kaur, Bangxing Hong, Izhar Bagwan, William Rogers, Hardev S. Pandha. Targeting of HOX-PBX binding in glioblastoma multiforme as a novel therapeutic treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5215.