The combination of immunotherapy and a glutamine metabolism inhibitor represents an effective therapeutic strategy for advanced and metastatic murine pancreatic adenocarcinoma

Despite constant advances in cancer research, the treatment of pancreatic adenocarcinoma remains extremely challenging. The intratumoral immunotherapy approach that was developed by our research group and was based on a combination of mannan-BAM, TLR ligands, and anti-CD40 antibody (MBTA) showed promising therapeutic effects in various murine tumor models, including a pancreatic adenocarcinoma model (Panc02). However, the efficacy of MBTA therapy in the Panc02 model was negatively correlated with tumor size at the time of therapy initiation. Here, we aimed to further improve the outcome of MBTA therapy in the Panc02 model using the glutamine antagonist 6-diazo-5-oxo-L-norleucine (DON). The combination of intratumoral MBTA therapy and intraperitoneal administration of DON resulted in the complete elimination of advanced Panc02 subcutaneous tumors (140.8 ± 46.8 mm3) in 50% of treated animals and was followed by development of long-term immune memory. In the bilateral Panc02 subcutaneous tumor model, we observed a significant reduction in tumor growth in both tumors as well as prolonged survival of treated animals. The appropriate timing and method of administration of DON were also addressed to maximize its therapeutic effects and minimize its side effects. In summary, our findings demonstrate that the intraperitoneal application of DON significantly improves the efficacy of intratumoral MBTA therapy in both advanced and bilateral Panc02 subcutaneous tumor murine models.

Proteogenomic discovery of neoantigens facilitates personalized multi-antigen targeted T cell immunotherapy for brain tumors

Neoantigen discovery in pediatric brain tumors is hampered by their low mutational burden and scant tissue availability. Here we develop a proteogenomic approach combining tumor DNA/RNA sequencing and mass spectrometry proteomics to identify tumor-restricted (neoantigen) peptides arising from multiple genomic aberrations to generate a highly target-specific, autologous, personalized T cell immunotherapy. Our data indicate that aberrant splice junctions are the primary source of neoantigens in medulloblastoma, a common pediatric brain tumor. Proteogenomically identified tumor-specific peptides are immunogenic and generate MHC II-based T cell responses. Moreover, polyclonal and polyfunctional T cells specific for tumor-specific peptides effectively eliminate tumor cells in vitro. Targeting tumor-specific antigens obviates the issue of central immune tolerance while potentially providing a safety margin favoring combination with other immune-activating therapies. These findings demonstrate the proteogenomic discovery of immunogenic tumor-specific peptides and lay the groundwork for personalized targeted T cell therapies for children with brain tumors.

Targeting tumor-associated antigens in paediatric medulloblastomas (MB) is challenging due to their low mutational burden. Here, the authors develop a sensitive proteogenomic approach to identify tumour specific neoantigens, which may enable personalised T cell immunotherapy in paediatric MB.

Mannan-BAM, TLR ligands, and anti-CD40 immunotherapy in established murine pancreatic adenocarcinoma: understanding therapeutic potentials and limitations

Pancreatic adenocarcinoma is one of the leading causes of cancer-related deaths, and its therapy remains a challenge. Our proposed therapeutic approach is based on the intratumoral injections of mannan-BAM, toll-like receptor ligands, and anti-CD40 antibody (thus termed MBTA therapy), and has shown promising results in the elimination of subcutaneous murine melanoma, pheochromocytoma, colon carcinoma, and smaller pancreatic adenocarcinoma (Panc02). Here, we tested the short- and long-term effects of MBTA therapy in established subcutaneous Panc02 tumors two times larger than in previous study and bilateral Panc02 models as well as the roles of CD4+ and CD8+ T lymphocytes in this therapy. The MBTA therapy resulted in eradication of 67% of Panc02 tumors with the development of long-term memory as evidenced by the rejection of Panc02 cells after subcutaneous and intracranial transplantations. The initial Panc02 tumor elimination is not dependent on the presence of CD4+ T lymphocytes, although these cells seem to be important in long-term survival and resistance against tumor retransplantation. The resistance was revealed to be antigen-specific due to its inability to reject B16-F10 melanoma cells. In the bilateral Panc02 model, MBTA therapy manifested a lower therapeutic response. Despite numerous combinations of MBTA therapy with other therapeutic approaches, our results show that only simultaneous application of MBTA therapy into both tumors has potential for the treatment of the bilateral Panc02 model.

IMMU-15. PROTEOGENOMIC DISCOVERY OF NOVEL TUMOR PEPTIDES AS NEOANTIGENS FOR PERSONALIZED T CELL IMMUNOTHERAPY IN MEDULLOBLASTOMA

T cell immunotherapies are promising new tools to combat high-risk subgroups of medulloblastoma without increasing the late effects burden. The ideal target antigen of an effective antitumor T-cell response is abundantly expressed by tumor cells but not by normal tissues, in order to limit off-target effects. Tumors translate a host of highly novel transcripts that are the result of aberrations in tumor DNA and the unmasking of alternative or novel exons. We developed a novel proteogenomic approach to identify tumor-restricted peptides and used them to select and expand T cells capable of mounting a tumor-specific cytotoxic immune response. Using RNA-seq and WGS data, we created personalized custom searchable databases containing predicted novel proteins from somatic mutations, novel junctions and fusion transcripts from 56 medulloblastoma tumors. By searching these databases with raw mass spectrometry data from paired medulloblastoma tumors, we identified tens of neoantigen peptides arising from the translation of tumor-specific transcripts; novel isoforms being the predominant source. We tested these peptides for their ability to select and expand autologous polyclonal populations of T cells and tested the immunogenicity of each individual peptide. Flow cytometry revealed populations of CD4+ and CD8+ cells with an activation profile marked by IFN-γ and TNF-α. Immunosuppressive marker profiles were also characterized. Using cytotoxicity assays, we demonstrated that tumor specific T cells can eliminate neoantigen bearing tumor cells. Thus, proteogenomics can identify immunogenic tumor specific peptides that can be used to create a personalized, targeted T cell therapy for children with high risk medulloblastoma.

Abstract 1067: Proteogenomic discovery of novel tumor proteins as neoantigens for personalized T cell immunotherapy in pediatric medulloblastoma

Medulloblastoma is a common childhood brain tumor for which current therapies fail to cure high-risk subgroups, including metastatic and recurrent disease. Toxicity limits further intensification of conventional chemo-radiation therapy and most survivors endure significant lifelong sequelae from treatment. There is an urgent need to develop new tools to combat this cancer without increasing the late effects burden. Neoantigens exclusively expressed on tumor cells, are one of the main targets of an effective antitumor T-cell response. The ideal target antigen is abundantly expressed by tumor cells but not by normal tissues, in order to limit off-target effects. Tumors translate a host of unique transcripts that are the result of aberrations in tumor DNA and the unmasking of alternative or novel exons. We used a novel proteogenomic approach to identify tumor-restricted peptides and used them to select and expand T cells capable of mounting a tumor-specific cytotoxic immune response, with no off-target effects for patients with MB. Using RNA-seq and WGS data, we created personalized custom searchable databases containing predicted novel proteins from somatic mutations, novel isoforms and fusion proteins from 46 medulloblastoma tumors. By searching this database with raw mass spectrometry data from the paired medulloblastoma tumor, we have identified tens of peptides arising from the translation of tumor-specific transcripts; these peptides are potential neoantigens. Our data indicates that in cases of tumors with low mutation rates, such as pediatric brain tumors, novel isoforms are the main source of neoantigens. In a pilot study, we tested these peptides for their ability to select and expand polyclonal populations of T cells from a patient whose tumor was the source of the peptides. The immunogenicity of each individual peptide was then determined. Flow cytometry cellular characterization reveals populations of both CD4+ and CD8+ cells with an activation profile marked by IFN-γ and TNF-α production. Inhibitory co-receptor profiles were also characterized for these cells. Using cytotoxicity assays, we demonstrated that tumor specific T cells can eliminate neoantigen bearing tumor cells. These findings demonstrate an initial proof of principle that proteogenomics can be used to identify immunogenic tumor specific peptides and lay the groundwork for a personalized, targeted T cell therapy for children with high risk medulloblastoma.

Citation Format: Samuel Rivero-Hinojosa, Melanie Grant, Aswini Panigrahi, Huizhen Zhang, Veronika Caisova, Catherine M. Bollard, Brian R. Rood. Proteogenomic discovery of novel tumor proteins as neoantigens for personalized T cell immunotherapy in pediatric medulloblastoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1067.

Abstract B90: Improved mice survival by reducing pheochromocytoma burden through activation of innate immunity using mannan and toll-like receptors

Background and Purpose: Pheochromocytomas (PHEOs) and paragangliomas (PGLs) are rare neuroendocrine/neural crest cell tumors. Therapeutic options for PHEOs/PGLs are limited, particularly in metastatic patients. Therefore, efforts to find new and more effective therapies are crucial in PHEO/PGL research. Recently, immunotherapy based on activation of innate immunity via pathogen-associated molecular patterns (PAMPs) has been tested in melanoma. PAMPs-based immunotherapy uses mannan, a simple polysaccharide from Saccharomyces cerevisiae, as a ligand stimulating phagocytosis in combination with toll-like receptor (TLR) ligands. Thus, in the present study we evaluated (1) the effect of intratumorally administered mannan-BAM + TLR ligands in a PHEO mouse model, (2) the participation of innate immunity on the PHEO growth reduction, (3) the leukocyte infiltration in treated PHEO, and (4) in vitro interactions of PHEO cells (with or without mannan) with neutrophils.

Methods: PHEO cells were subcutaneously transplanted into mice and mannan-BAM + TLR ligands were intratumorally administered. CD45+ infiltration in tumors was measured using flow cytometry. In vitro experiments were performed using mouse/human PHEO cell lines incubated with mouse/human neutrophils.

Results: The intratumoral administration of mannan-BAM and TLR ligands into PHEO resulted in 90% tumor growth reduction. The survival median increased from 16 days in the control group to 50 days in the group treated with mannan-BAM + TLR ligands. Subsequently, mice lacking functional T and B cells were used. Intratumoral administration of mannan-BAM + TLR ligands resulted in 86% reduction of tumor growth, which proved the key role of innate immunity in PHEO tumor elimination. The flow cytometry analysis of tumor-infiltrating CD45+ cells revealed higher levels of CD45+ cells in the group treated by mannan-BAM + TLR ligands. Significant increase in the levels of granulocytes was observed on days 3 and 18 of the treatment. Cytotoxic experiments using PHEO cell lines revealed increased cytotoxic effect of neutrophils toward PHEO cells labeled with mannan-BAM compared to the cells without mannan-BAM. Microscopic evaluation of neutrophils and PHEO cells labeled with mannan-BAM revealed enhanced frustrated phagocytosis and neutrophils rosette formation dependent on the presence of mannan-BAM.

Conclusion: We demonstrate excellent therapeutic effects of enhanced innate immunity using intratumorally administered PAMPs and TLR ligands in a subcutaneous PHEO mouse model.

Citation Format: Veronika Caisova, Garima Gupta, Ivana Jochmanova, Abhishek Jha, Liping Li, Thanh Truc Huynh, Ying Pang, Hans Kumar Ghayee, David Taïeb, Jan Zenka, Karel Pacak. Improved mice survival by reducing pheochromocytoma burden through activation of innate immunity using mannan and toll-like receptors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B90.

Therapeutic Targeting of SDHB-Mutated Pheochromocytoma/Paraganglioma with Pharmacologic Ascorbic Acid

PURPOSE

Pheochromocytomas and paragangliomas (PCPG) are usually benign neuroendocrine tumors. However, PCPGs with mutations in the succinate dehydrogenase B subunit (SDHB) have a poor prognosis and frequently develop metastatic lesions. SDHB-mutated PCPGs exhibit dysregulation in oxygen metabolic pathways, including pseudohypoxia and formation of reactive oxygen species, suggesting that targeting the redox balance pathway could be a potential therapeutic approach.

EXPERIMENTAL DESIGN

We studied the genetic alterations of cluster I PCPGs compared with cluster II PCPGs, which usually present as benign tumors. By targeting the signature molecular pathway, we investigated the therapeutic effect of ascorbic acid on PCPGs using in vitro and in vivo models.

RESULTS

By investigating PCPG cells with low SDHB levels, we show that pseudohypoxia resulted in elevated expression of iron transport proteins, including transferrin (TF), transferrin receptor 2 (TFR2), and the divalent metal transporter 1 (SLC11A2; DMT1), leading to iron accumulation. This iron overload contributed to elevated oxidative stress. Ascorbic acid at pharmacologic concentrations disrupted redox homeostasis, inducing DNA oxidative damage and cell apoptosis in PCPG cells with low SDHB levels. Moreover, through a preclinical animal model with PCPG allografts, we demonstrated that pharmacologic ascorbic acid suppressed SDHB-low metastatic lesions and prolonged overall survival.

CONCLUSIONS

The data here demonstrate that targeting redox homeostasis as a cancer vulnerability with pharmacologic ascorbic acid is a promising therapeutic strategy for SDHB-mutated PCPGs.

Abstract A23: Proteogenomic discovery of novel tumor proteins as neoantigens for personalized T-cell immunotherapy in pediatric medulloblastoma

Medulloblastoma is a common childhood brain tumor for which current therapies fail to cure high-risk subgroups, including metastatic and recurrent disease. Toxicity limits further intensification of conventional chemo-radiation therapy, and most survivors endure significant lifelong sequelae from treatment. There is an urgent need to develop new tools to combat this cancer without increasing the late effects burden. Neoantigens, which are exclusively expressed on tumor cells, are one of the main targets of an effective antitumor T-cell response. The ideal target antigen is abundantly expressed by tumor cells but not by normal tissues, in order to limit off-target effects. Tumors translate a host of highly novel transcripts that are the result of aberrations in tumor DNA and the unmasking of alternative or novel exons. We used a novel proteogenomic approach to identify tumor-restricted peptides and used them to select and expand T cells capable of mounting a tumor-specific cytotoxic immune response, with no off-target effects for patients with MB. Using RNA-seq and WGS data, we created personalized custom searchable databases containing predicted novel proteins from somatic mutations, novel isoforms, and fusion proteins from 56 medulloblastoma tumors. By searching this database with raw mass spectrometry data from the paired medulloblastoma tumor, we have identified tens of peptides arising from the translation of tumor-specific transcripts; these peptides are potential neoantigens. Our data indicate that in cases of tumors with low mutation rates, such as pediatric brain tumors, novel isoforms are the main source of neoantigens. In a pilot study, we have tested these peptides for their ability to select and expand polyclonal populations of T cells from the same patient whose tumor was the source of the peptides. The immunogenicity of each individual peptide was then determined. Flow cytometry cellular characterization reveals populations of both CD4+ and CD8+ cells with an activation profile marked by IFN-γ and TNF-α production. Immunosuppressive marker profiles have also been characterized for these cells. Using cytotoxicity assays, we demonstrated that tumor-specific T cells can eliminate neoantigen-bearing tumor cells. These findings demonstrate an initial proof of principle that proteogenomics can be used to identify immunogenic tumor specific peptides and lay the groundwork for a personalized, targeted T-cell therapy for children with high-risk medulloblastoma.

Citation Format: Samuel Rivero-Hinojosa, Melanie Grant, Aswini Panigrahi, Huizhen Zhang, Veronika Caisova, Catherine Bollard, Brian Rood. Proteogenomic discovery of novel tumor proteins as neoantigens for personalized T-cell immunotherapy in pediatric medulloblastoma [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A23.

IMMU-23. TARGETING METASTATIC AND CNS TUMORS VIA MANNAN-BAM, TLR LIGANDS AND ANTI-CD40 ANTIBODY

Immunotherapy based on activation of innate immunity has been tested in syngeneic mouse tumor models via intratumoral administration of the following components: phagocytosis-stimulating ligands (Mannan-BAM), toll-like receptor (TLR) agonists, and immunostimulant anti-CD40 antibody (abbreviated as MBTA). In this study, syngeneic colon carcinoma (CT26) and glioma (GL261) models were established to assess MBTA’s efficacy in generating immune responses against distal metastatic lesions and CNS tumors. Additionally, we investigated if therapeutic delivery of MBTA could be optimized beyond intratumoral delivery. In the colon carcinoma model, intratumoral injection of MBTA significantly reduced all metastatic CT26 tumor growth rate and induced complete remission (CR) in 33% (3/9) of treated animals. In the glioma model, subcutaneous injection of GL261 cells incubated with MBTA resulted in the complete regression of intracranial gliomas in 87.5% (7/8) of treated animals. Therapeutic effect of MBTA was abrogated in CD4+ and CD8+ lymphocyte depleted mice. Tumor infiltrating leukocyte analyses demonstrated significantly increased CD8+ cytotoxic T-lymphocytes (CTL) in metastatic tumors with higher percentages of TNFα and IFNγ positive cells. Further assessments with MHC I tetramers revealed significantly increased CT26-associated peptide (AH1) specific CTLs in the blood of MBTA treated animals. All animals that achieved complete remission in the colon carcinoma model resisted subsequent peripheral and intracranial challenges with CT26 cells, confirming the induction of immunological memory against CT26 tumors. Collectively, our investigation demonstrates that MBTA can effectively induce a tumor-specific adaptive immune response that can target tumors located in the periphery and within the CNS.

Coley's immunotherapy revived: Innate immunity as a link in priming cancer cells for an attack by adaptive immunity

There is no doubt that immunotherapy lies in the spotlight of current cancer research and clinical trials. However, there are still limitations in the treatment response in certain types of tumors largely due to the presence of the complex network of immunomodulatory and immunosuppressive pathways. These limitations are not likely to be overcome by current immunotherapeutic options, which often target isolated steps in immune pathways preferentially involved in adaptive immunity. Recently, we have developed an innovative anti-cancer immunotherapeutic strategy that initially elicits a strong innate immune response with subsequent activation of adaptive immunity in mouse models. Robust primary innate immune response against tumor cells is induced by toll-like receptor ligands and anti-CD40 agonistic antibodies combined with the phagocytosis-stimulating ligand mannan, anchored to a tumor cell membrane by biocompatible anchor for membrane. This immunotherapeutic approach results in a dramatic therapeutic response in large established murine subcutaneous tumors including melanoma, sarcoma, pancreatic adenocarcinoma, and pheochromocytoma. Additionally, eradication of metastases and/or long-lasting resistance to subsequent re-challenge with tumor cells was also accomplished. Current and future advantages of this immunotherapeutic approach and its possible combinations with other available therapies are discussed in this review.

Abstract 5853: Targeting NAD+/PARP DNA repair pathway as a novel therapeutic approach to SDHB-mutated cluster I pheochromocytoma and paraganglioma

Background: Cluster I pheochromocytomas and paragangliomas (PCPGs) tend to develop malignant transformation, tumor recurrence, and multiplicity. Transcriptomic profiling suggests that cluster I PCPGs and other related tumors exhibit distinctive changes in the tricarboxylic acid (TCA) cycle, the hypoxia signaling pathway, mitochondrial electron transport chain, and methylation status, suggesting that therapeutic regimen might be optimized by targeting these signature molecular pathways.

Experimental design: We investigated molecular signatures in clinical specimens from cluster I and II PCPGs, with a focus on the therapeutic resistance mechanisms. Further, we tested the applicability of a combination therapy including an FDA approved PARP inhibitor olaparib (Ola) and temozolomide (TMZ) in both in vitro cellular model and an in vivo allograft animal model.

Results: Our findings showed that cluster I PCPGs develop a distinctive dependency on mitochondrial complex I, evidenced by the upregulation of complex I components and enhanced NADH dehydrogenation. Mechanistically, alteration in mitochondrial function resulted in strengthened NAD+ metabolism, which provides essential cofactor for PARP catalytic activity, prompting base excision repair and chemo resistance. Combining PARP inhibitor Ola with TMZ not only improved cytotoxicity but also reduced metastatic lesions, with prolonged overall survival in a mouse model with PCPG allograft.

Conclusions: Our results suggest that the NAD+/PARP pathway is a crucial targetable therapeutic resistance mechanism in SDHB-mutated PCPG. Combination therapy using TMZ and Ola could become an effective strategy against these and other advanced cluster I tumors.

Disclosure Statement: The authors have nothing to disclose.

Citation Format: Ying Pang, Yanxin Lu, Veronika Caisova, Yang Liu, Petra Bullova, Thanh-Truc Huynh, Zdenek Frysak, Igor Hartmann, David Taïeb, Karel Pacak, Chunzhang Yang. Targeting NAD+/PARP DNA repair pathway as a novel therapeutic approach to SDHB-mutated cluster I pheochromocytoma and paraganglioma [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 5853.

Targeting NAD+/PARP DNA Repair Pathway as a Novel Therapeutic Approach to SDHB-Mutated Cluster I Pheochromocytoma and Paraganglioma

Purpose: Cluster I pheochromocytomas and paragangliomas (PCPGs) tend to develop malignant transformation, tumor recurrence, and multiplicity. Transcriptomic profiling suggests that cluster I PCPGs and other related tumors exhibit distinctive changes in the tricarboxylic acid (TCA) cycle, the hypoxia signaling pathway, mitochondrial electron transport chain, and methylation status, suggesting that therapeutic regimen might be optimized by targeting these signature molecular pathways.Experimental Design: In the present study, we investigated the molecular signatures in clinical specimens from cluster I PCPGs in comparison with cluster II PCPGs that are related to kinase signaling and often present as benign tumors.Results: We found that cluster I PCPGs develop a dependency to mitochondrial complex I, evidenced by the upregulation of complex I components and enhanced NADH dehydrogenation. Alteration in mitochondrial function resulted in strengthened NAD⁺ metabolism, here considered as a key mechanism of chemoresistance, particularly, of succinate dehydrogenase subunit B (SDHB)-mutated cluster I PCPGs via the PARP1/BER DNA repair pathway. Combining a PARP inhibitor with temozolomide, a conventional chemotherapeutic agent, not only improved cytotoxicity but also reduced metastatic lesions, with prolonged overall survival of mice with SDHB knockdown PCPG allograft.Conclusions: In summary, our findings provide novel insights into an effective strategy for targeting cluster I PCPGs, especially those with SDHB mutations. Clin Cancer Res; 24(14); 3423-32. ©2018 AACR.

Anthracyclines suppress pheochromocytoma cell characteristics, including metastasis, through inhibition of the hypoxia signaling pathway

Pheochromocytomas (PHEOs) and paragangliomas (PGLs) are rare, neuroendocrine tumors derived from adrenal or extra-adrenal chromaffin cells, respectively. Metastases are discovered in 3-36% of patients at the time of diagnosis. Currently, only suboptimal treatment options exist. Therefore, new therapeutic compounds targeting metastatic PHEOs/PGLs are urgently needed. Here, we investigated if anthracyclines were able to suppress the progression of metastatic PHEO. We explored their effects on experimental mouse PHEO tumor cells using in vitro and in vivo models, and demonstrated that anthracyclines, particularly idarubicin (IDA), suppressed hypoxia signaling by preventing the binding of hypoxia-inducible factor 1 and 2 (HIF-1 and HIF-2) to the hypoxia response element (HRE) sites on DNA. This resulted in reduced transcriptional activation of HIF target genes, including erythropoietin (EPO), phosphoglycerate kinase 1 (PGK1), endothelin 1 (EDN1), glucose transporter 1 (GLUT1), lactate dehydrogenase A (LDHA), and vascular endothelial growth factor (VEGFA), which consequently inhibited the growth of metastatic PHEO. Additionally, IDA downregulated hypoxia signaling by interfering with the transcriptional activation of HIF1A and HIF2A. Furthermore, our animal model demonstrated the dose-dependent suppressive effect of IDA on metastatic PHEO growth in vivo. Our results indicate that anthracyclines are prospective candidates for inclusion in metastatic PHEO/PGL therapy, especially in patients with gene mutations involved in the hypoxia signaling pathway.