IMMU-55. GD2 IS A MACROPHAGE CHECKPOINT MOLECULE AND COMBINED GD2/CD47 BLOCKADE RESULTS IN SYNERGISTIC EFFECTS AGAINST GD2 POSITIVE MALIGNANCIES

GD2 is a disialoganglioside expressed on a variety of tumors including DIPG, neuroblastoma and osteosarcoma. Anti-GD2 antibodies have demonstrated some success in neuroblastoma and they have either not proven to be effective or have not been evaluated in other GD2 positive malignancies. CD47 is the dominant “Don’t Eat Me” signal expressed by cancer cells to inhibit macrophages and blocking CD47 leads to phagocytosis of tumor cells. We hypothesized that CD47 blockade synergizes with anti-GD2. We measured in vitro phagocytosis of DIPG and NBL cells and observed a synergy of anti-GD2/CD47 compared to the single agents. In vivo, this combination led to the complete clearance of both orthotopic and metastatic models of NBL. Additionally, the combination significantly enhanced survival of OS xenografts. Finally, in a murine model of metastatic pulmonary OS, the combination led to a near elimination of all metastatic burden. To understand the underlying biologic basis, we studied the effects of GD2 crosslinking on tumor cells and the effects of GD2 blockade on macrophages. A portion of DIPG or NBL cells die when treated with dinutuximab, and those that survive upregulate surface calreticulin, an important pro-phagocytic (“Eat Me”) signal. Additionally, we have identified the ligand for GD2, a molecule expressed on macrophages known to inhibit phagocytosis. In summary, we have identified a novel combination of anti-GD2 and anti-CD47 antibodies that is highly effective in preclinical models and will soon be tested in children. Furthermore, we have shown that GD2 itself is a macrophage checkpoint or “Don’t Eat Me” signal.

Abstract PR04: GD2-directed chimeric antigen receptor T cells mediate potent antitumor effect and cure in xenograft models of diffuse intrinsic pontine glioma

Introduction: Diffuse intrinsic pontine glioma (DIPG) is a universally fatal pediatric brainstem tumor with a median survival of less than one year. Despite advances in the understanding of the molecular origins of DIPG, improvement in clinical outcomes has yet to materialize. To date, there has been little target exploration for immunotherapy applications in DIPG.

Methods: Patient-derived DIPG cell cultures were screened for expression of more than 350 surface antigens as potential immunotherapeutic targets. The disialoganglioside GD2 was found to have the highest expression across cell cultures and was verified by IHC on post-mortem samples. Chimeric antigen receptor (CAR) T-cell therapy against this target was explored both in vitro and in vivo.

Results: We found high levels of the disialoganglioside GD2 expressed on cell cultures derived from post-mortem samples of DIPG. Quantification of the number of GD2 molecules per cell demonstrated higher GD2 expression on DIPG than any other tumors, including neuroblastoma, for which GD2 targeted immunotherapy is part of the standard of care.

Most cases of DIPG are caused by a mutation in Histone 3.3 (H3K27M). GD2 is highly and uniformly expressed in patient-derived H3K27M DIPG cultures, whereas H3 wild-type pediatric high-grade gliomas, including those diagnosed as DIPG, do not express significant levels of GD2. The H3K27M mutation is associated with increased levels of enzymes in the ganglioside synthesis pathway, suggesting that expression of the target antigen is driven by H3K27M-induced transcriptional dysregulation.

Anti-GD2 CAR T cells with a 4-1BB costimulatory domain demonstrate remarkable preclinical activity against H3K27M DIPG. GD2 CAR T cells specifically kill DIPG cells and produce cytokines IL-2 and IFN- upon coculture with tumor. Systemic administration of anti-GD2 CAR T cells achieves potent and durable cure compared to control T cells in multiple orthotopic xenograft models of DIPG. Using a CAR fluorescent protein fusion construct, we demonstrate significant T-cell trafficking to the brainstem where the antitumor effect is mediated. Universal response was observed across multiple cohorts, and treatment-associated toxicity was transient and tolerated during the period of peak antitumor activity.

Conclusion: We have previously demonstrated that antigen density drives CAR efficacy. Extremely high expression of GD2 on DIPG makes this a particularly good disease for CAR T-cell therapy. If these results are predictive of human response, CAR T cells could have a transformative impact upon DIPG outcomes. A clinical trial of second generation anti-GD2 CAR T cells in relapsed and progressive DIPG is planned.

Citation Format: Robbie G. Majzner, Christopher Mount, Shree Sundaresh, Evan Arnold, Meena Kadapakkam, Louai Labanieh, Pamelyn Woo, Michelle Monje, Crystal L. Mackall. GD2-directed chimeric antigen receptor T cells mediate potent antitumor effect and cure in xenograft models of diffuse intrinsic pontine glioma [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr PR04.

Developmental and oncogenic programs in H3K27M gliomas dissected by single-cell RNA-seq

Gliomas with histone H3 lysine27-to-methionine mutations (H3K27M-glioma) arise primarily in the midline of the central nervous system of young children, suggesting a cooperation between genetics and cellular context in tumorigenesis. Although the genetics of H3K27M-glioma are well characterized, their cellular architecture remains uncharted. We performed single-cell RNA sequencing in 3321 cells from six primary H3K27M-glioma and matched models. We found that H3K27M-glioma primarily contain cells that resemble oligodendrocyte precursor cells (OPC-like), whereas more differentiated malignant cells are a minority. OPC-like cells exhibit greater proliferation and tumor-propagating potential than their more differentiated counterparts and are at least in part sustained by PDGFRA signaling. Our study characterizes oncogenic and developmental programs in H3K27M-glioma at single-cell resolution and across genetic subclones, suggesting potential therapeutic targets in this disease.

Decoupling genetics, lineages, and microenvironment in IDH-mutant gliomas by single-cell RNA-seq

Tumor subclasses differ according to the genotypes and phenotypes of malignant cells as well as the composition of the tumor microenvironment (TME). We dissected these influences in isocitrate dehydrogenase (IDH)-mutant gliomas by combining 14,226 single-cell RNA sequencing (RNA-seq) profiles from 16 patient samples with bulk RNA-seq profiles from 165 patient samples. Differences in bulk profiles between IDH-mutant astrocytoma and oligodendroglioma can be primarily explained by distinct TME and signature genetic events, whereas both tumor types share similar developmental hierarchies and lineages of glial differentiation. As tumor grade increases, we find enhanced proliferation of malignant cells, larger pools of undifferentiated glioma cells, and an increase in macrophage over microglia expression programs in TME. Our work provides a unifying model for IDH-mutant gliomas and a general framework for dissecting the differences among human tumor subclasses.

Abstract 4770: Delivery of doxorubicin to multi-drug resistant murine xenografts via drug-loaded micelles formed from mixtures of amphiphilic triblock copolymers

BACKGROUND: The toxicity of chemotherapeutic drugs is often the limiting factor in patient dosing and can be the source of severe discomfort and suffering for patients undergoing chemotherapy. For example, the anthracycline antibiotic doxorubicin (DOX) is a potent chemotherapeutic but prolonged use can also lead to permanent heart damage. Tumors can also develop resistance to DOX by increased expression of drug efflux pumps. Nanoparticle formulations of DOX have been reported to improve tumor-specific delivery via the enhanced permeability and retention (EPR) effect. METHODS: In this work, we have encapsulated DOX in polymeric micelles formed from mixtures of amphiphilic triblock copolymers. The copolymers are composed of a hydrophobic polymer segment flanked by two hydrophilic blocks. Two different copolymers were used to form the mixed micelles: a copolymer of poly(ethylene oxide) and poly(hydroxybutyrate) (PEO-PHB-PEO), and a copolymer of poly(ethylene oxide) and poly(propylene oxide) (Pluronic F127). We hypothesize that forming mixed micelles will improve drug loading and enable preparation at room temperature (where Pluronic F127 micelles are highly unstable), while facilitating drug delivery by utilizing the stability of Pluronic F127 micelles at physiological temperatures. RESULTS: We have demonstrated that the micelles formed from the mixtures of PEO-PHB-PEO and Pluronic F127 triblock copolymers provide a combination of high drug loading content and drug delivery capabilities. DOX loading for mixed micelles was greater than that for Pluronic F127-only micelles (p<0.05 for all mixture ratios). DOX encapsulated in mixed micelles demonstrated increased uptake in a drug resistant MDA-435-MDR cell line over free doxorubicin (p<.05 for all mixture ratios), while cytotoxicity of the micelle treatment was approximately equivalent to that of the free drug. Tumor treatment efficacy was assessed in mice with subcutaneous dual xenografts of MDA-435 and MDA-435-MDR (drug resistant) cell lines. Tumor suppression of drug resistant tumors was similar for encapsulated and free drug, but mice treated with micellar DOX showed no significant weight loss after treatment, while mice treated with unencapsulated DOX experienced severe weight loss after one week when compared to initial time point (18.2% +/− 2.1% weight loss, p = .0009). CONCLUSION: The cytotoxicity, drug uptake, and tumor suppression properties demonstrated by PEO-PHB-PEO/Pluronic F127 mixed micelles supports their viability as chemotherapeutic drug delivery systems for drug resistant tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4770. doi:1538-7445.AM2012-4770

Abstract 5293: Mixed micelles of triblock copolymers enhance delivery of indocyanine green for fluorescent tumor imaging

The goal of this study is to develop formulations for non-invasive, near-infrared detection of tumors. Indocyanine green (ICG) is an FDA-approved near-infrared (NIR) imaging agent that is clinically used for angiography and evaluation of liver function. ICG could potentially be used as a NIR fluorescence imaging agent for shallow tumors such as breast cancers. To fulfill this potential, formulations that improve the stability of ICG and direct its accumulation in tumors are necessary. We have previously described Pluronic F127 copolymer micelles that stabilize ICG, enhance its stability, and facilitate tumor accumulation in vivo after systemic administration. A major advantage of Pluronic F127 is its temperature-sensitive behavior that results in more stable micelle formulations at body temperature. However, Pluronic F127 micelles are not stable at room temperature, making micelle preparation and handling challenging. We hypothesized that mixed micelles formed from both Pluronic F127 and a temperature insensitive triblock copolymer composed of poly(ethylene oxide) and poly(3-hydroxybutyrate) (PEO-PHB-PEO), would result in micelles that are both easy to formulate at room temperature and that demonstrate increased stability at body temperature. Micelle formulations with various ratios of Pluronic F127: PEO-PHB-PEO were prepared and loaded with ICG. The micelle stability was determined by assessment of critical micelle concentration measurements, and time-course fluorescence assays were conducted to assess the ability of each micelle formulation to stabilize ICG fluorescence in buffer conditions. The ICG-loaded micelles were administered to tumor-bearing mice by tail vein injection and tumor localization was monitored by non-invasive fluorescence imaging in live mice. The polymer ratio used in micelle formulation was found to play a significant role in the ability of each preparation to stabilize ICG fluorescence Mixed micelles were found to enhance the stability of ICG fluorescence in buffer conditions, and CMC was shown to be dependent on polymer ratios. In vivo, mixed micelles were found to be more effective at maintaining ICG fluorescence in the bloodstream and achieved higher fluorescence signals in the tumor tissues compared with either PEO-PHB-PEO or Pluronic 127 micelles. These results suggest that the mixed micelle formulations offer a promising route to stabilizing these nanoparticles for improved delivery of NIR fluorescent contrast agents to tumors for imaging applications.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5293. doi:10.1158/1538-7445.AM2011-5293