DRES-10. TEMOZOLOMIDE-ASSOCIATED HYPERMUTATION DETECTED WITH A GENE PANEL SIGNATURE IMPROVES IMMUNE RESPONSE IN GLIOBLASTOMA

Glioblastoma (GBM) is the most common and deadly type of malignant brain cancer in adults. While current standard of care which combines resection, radiation therapy (RT) and Temozolomide (TMZ) effectively eliminates primary disease, recurrence is inevitable, occurs rapidly following treatment and is ultimately lethal due to limited therapeutic opportunities of recurrent GBM. Hypermutation has been reported to occur in a subset of both low and high-grade gliomas and emerges after exposure to TMZ. Mutational inactivation and loss of mismatch repair (MMR) gene expression lead to the accumulation of single nucleotide polymorphisms throughout the genome. To date, the gain of hypermutation and subsequent therapeutic responses are still largely unknown. We hypothesized that hypermutant (HM) and non-hypermutant (NH) tumors represent two recurrent GBM subtypes, which has distinct therapeutic vulnerabilities. In addition, given the lack of concordance between microsatellite instability (MSI) and occurrence of hypermutation in GBM, we sought to derive a limited gene panel which can be used as surrogate biomarker for hypermutation following TMZ to replace whole exome sequencing (WES). Using public datasets, we demonstrated that recurrent GBM can be clustered into two subtypes: HM and NH. We used matched primary and recurrent GBM datasets to derive a gene panel signature, which is uniquely mutated at recurrence in HM GBM and confirmed the specificity of this panel in an independent dataset. Furthermore, we utilized patient derived xenograft (PDX) models to generate pre-clinical models and demonstrated that HM recurrent GBM are more immune responsive while NH recurrent GBM maintained sensitivity to a range of alternate chemotherapies such as cisplatin and RT. Finally, we demonstrated that this signature is represented in exosomes and can be enriched by use of tumor specific antibody capture methods to improve the sensitivity of hypermutation detection in liquid biopsy.

THER-01. PRECLINICAL DEVELOPMENT OF EO1001, A NOVEL IRREVERSIBLE BRAIN PENETRATING PAN-ErbB INHIBITOR

Dysregulation of ErbB-mediated signaling is observed in up to 90% of solid tumors. ErbB family cross-talk is implicated in the development of resistance and metastasis, including CNS metastases. Inhibition of multiple ErbB receptors may result in improved patient outcomes. EO1001 is a novel, patented, oral, brain-penetrating, irreversible pan-ErbB inhibitor targeting EGFR (ErbB1), HER2 (ErbB2) and HER4 (ErbB4). METHODS: (1) In vitro testing. EO1001 demonstrates high specificity for the ErbB family of receptors with excellent, balanced equipotent activity against EGFR, HER2 and HER4 (0.4 to 7.4 nM). EO1001 inhibits signaling downstream of wild type EGFR, mutant EGFR (T790M, L858R and d746-750) and HER2. (2) PK and toxicity. In rodent studies in vivo, EO1001 exhibited a half-life of 16–20 hours. EO1001 rapidly enters the CNS and penetrates tumor tissue at higher concentrations relative to plasma. Safety of EO1001 was evaluated by repeat-dosing studies in SD rats and beagle dogs. Toxicities typical of the ErbB inhibitor class, including gastro-intestinal effects, weight loss and decreased activity were observed at higher dose groups in both species. Mortality was observed in SD rats at higher dose groups. (3) In vivo efficacy studies. EO1001 was studied following oral administration in several erbB-positive mouse xenograft models including N87 (Her2+), H1975 (EGFR/T790M), GBM12 (EGFR+), GBM39 (EGVRvIII+). Following oral administration, treatment with EO1001 resulted in a statistically significant improvement in outcomes compared to positive and negative controls in both CNS and systemic tumor models. EO1001 was well-tolerated with no gastrointestinal side effects observed at efficacious doses in these models. CONCLUSION: Based on research to date, EO1001 has the potential to be a best-in-class CNS-penetrating pan-ErbB inhibitor with a safety and pharmacokinetic profile amenable for use as a single agent and in combination with other agents. EO1001 is poised to enter phase 1-2a clinical testing in the second-half of 2019.

NOTCH3 expression is linked to breast cancer seeding and distant metastasis

Background

Development of distant metastases involves a complex multistep biological process termed the invasion-metastasis cascade, which includes dissemination of cancer cells from the primary tumor to secondary organs. NOTCH developmental signaling plays a critical role in promoting epithelial-to-mesenchymal transition, tumor stemness, and metastasis. Although all four NOTCH receptors show oncogenic properties, the unique role of each of these receptors in the sequential stepwise events that typify the invasion-metastasis cascade remains elusive.

Methods

We have established metastatic xenografts expressing high endogenous levels of NOTCH3 using estrogen receptor alpha-positive (ERα⁺) MCF-7 breast cancer cells with constitutive active Raf-1/mitogen-associated protein kinase (MAPK) signaling (vMCF-7^Raf-1) and MDA-MB-231 triple-negative breast cancer (TNBC) cells. The critical role of NOTCH3 in inducing an invasive phenotype and poor outcome was corroborated in unique TNBC cells resulting from a patient-derived brain metastasis (TNBC-M25) and in publicly available claudin-low breast tumor specimens collected from participants in the Molecular Taxonomy of Breast Cancer International Consortium database.

Results

In this study, we identified an association between NOTCH3 expression and development of metastases in ERα⁺ and TNBC models. ERα⁺ breast tumor xenografts with a constitutive active Raf-1/MAPK signaling developed spontaneous lung metastases through the clonal expansion of cancer cells expressing a NOTCH3 reprogramming network. Abrogation of NOTCH3 expression significantly reduced the self-renewal and invasive capacity of ex vivo breast cancer cells, restoring a luminal CD44^low/CD24^high/ERα^high phenotype. Forced expression of the mitotic Aurora kinase A (AURKA), which promotes breast cancer metastases, failed to restore the invasive capacity of NOTCH3-null cells, demonstrating that NOTCH3 expression is required for an invasive phenotype. Likewise, pharmacologic inhibition of NOTCH signaling also impaired TNBC cell seeding and metastatic growth. Significantly, the role of aberrant NOTCH3 expression in promoting tumor self-renewal, invasiveness, and poor outcome was corroborated in unique TNBC cells from a patient-derived brain metastasis and in publicly available claudin-low breast tumor specimens.

Conclusions

These findings demonstrate the key role of NOTCH3 oncogenic signaling in the genesis of breast cancer metastasis and provide a compelling preclinical rationale for the design of novel therapeutic strategies that will selectively target NOTCH3 to halt metastatic seeding and to improve the clinical outcomes of patients with breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1020-0) contains supplementary material, which is available to authorized users.

Abstract 1956: miR-181d degradation mediated genetic heterogeneity and acquired resistance

When unrepaired, alkylated DNA can induce cell death or trigger mutagenesis. Cellular capacity for repair of these lesions by O6-methylguanine methyltransferase (MGMT) dictates the equilibrium between cell viability and genetic diversity. Treatment of glioblastoma cells with temozolomide (TMZ) induced ATM- and Rad3-related (ATR) kinase dependent polyribonucleotide nucleotidyltransferase 1 (PNPT1) degradation of miR-181d. miR-181d suppresses MGMT expression; its degradation increases the mean MGMT expression of the cell population. miR-181d degradation also magnifies the cell-to-cell variability in MGMT expression, expanding the genetic heterogeneity of the population. This expanded heterogeneity enhances the “fitness” of the population and constitutes a novel form of chemotherapeutic resistance. These effects can be suppressed by overexpression of miR-181d, suggesting miRNA delivery as a strategy for glioblastoma therapy. To characterize the mechanism of acquired resistance, we profiled the expression of 2400 miRNAs before and after TMZ treatment. In independent patient-derived neurosphere lines, the majority of miRNAs remained unchanged after treatment. However, miR-181d was consistently suppressed after TMZ treatment. Our previous work demonstrated miR-181d as the master regulator of MGMT. We confirmed TMZ-induced suppression of miR-181d using independent in vitro and in vivo models as well as matched pre- and post-TMZ treated clinical specimens. TMZ-induced miR-181d suppression persisted after transcriptional inhibition, suggesting degradation as the primary mechanism. We performed an siRNA screen and identified polyribonucleotide nucleotidyltransferase 1 (PNPT1) as the gene responsible for miR-181d degradation. CRISPR inactivation of PNPT1 eliminated TMZ-induced suppression of miR-181d; this was rescued by wild-type PNPT1 but not by PNPT1 harboring RNAse-inactivating mutations. TMZ-induced degradation of miR-181d requires ATR kinase. Silencing or inhibition of ATR eliminated binding of PNPT1 to miR-181d and prevented degradation of miR-181d. TMZ-sensitizing effects of ATR inhibition were reversed by anti-miR-181d, suggesting miR-181d is essential in this process. In addition to elevating the mean MGMT expression of the population, single-cell analysis revealed that miR-181d degradation broadened the cell-to-cell variability in MGMT expression in vitro. In matched clinical pre- and post-TMZ treated specimens, variability in MGMT expression was significantly elevated in post-TMZ samples. This was recapitulated using The Cancer Genome Atlas (TCGA) database. We propose that miR-181d degradation-mediated expansion of genetic heterogeneity enhances the “fitness” of the population, constituting a novel form of chemotherapeutic resistance. These effects are suppressed by miR-181d overexpression, suggesting miRNA delivery as a strategy for glioblastoma therapy.

Citation Format: Valya Ramakrishnan, Johnny Akers, Thien Nguyen, Aaron Wang, Bandita Adhikari, Brian Hirshman, Jie Li, Jann Sarkaria, Wei Hua, Mao Ying, Masayuki Nitta, Tao Jiang, Bob Carter, Clark C. Chen. miR-181d degradation mediated genetic heterogeneity and acquired resistance [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 1956.

Immunovirotherapy with measles virus strains in combination with anti-PD-1 antibody blockade enhances antitumor activity in glioblastoma treatment

Background

Glioblastoma (GBM) is the most common primary malignant brain tumor and has a dismal prognosis. Measles virus (MV) therapy of GBM is a promising strategy due to preclinical efficacy, excellent clinical safety, and its ability to evoke antitumor pro-inflammatory responses. We hypothesized that combining anti- programmed cell death protein 1 (anti-PD-1) blockade and MV therapy can overcome immunosuppression and enhance immune effector cell responses against GBM, thus improving therapeutic outcome.

Methods

In vitro assays of MV infection of glioma cells and infected glioma cells with mouse microglia ± aPD-1 blockade were established to assess damage associated molecular pattern (DAMP) molecule production, migration, and pro-inflammatory effects. C57BL/6 or athymic mice bearing syngeneic orthotopic GL261 gliomas were treated with MV, aPD-1, and combination treatment. T2* weighted immune cell-specific MRI and fluorescence activated cell sorting (FACS) analysis of treated mouse brains was used to examine adaptive immune responses following therapy.

Results

In vitro, MV infection induced human GBM cell secretion of DAMP (high-mobility group protein 1, heat shock protein 90) and upregulated programmed cell death ligand 1 (PD-L1). MV infection of GL261 murine glioma cells resulted in a pro-inflammatory response and increased migration of BV2 microglia. In vivo, MV+aPD-1 therapy synergistically enhanced survival of C57BL/6 mice bearing syngeneic orthotopic GL261 gliomas. MRI showed increased inflammatory cell influx into the brains of mice treated with MV+aPD-1; FACS analysis confirmed increased T-cell influx predominantly consisting of activated CD8+ T cells.

Conclusions

This report demonstrates that oncolytic measles virotherapy in combination with aPD-1 blockade significantly improves survival outcome in a syngeneic GBM model and supports the potential of clinical/translational strategies combining MV with αPD-1 therapy in GBM treatment.