Protein phosphatase 1 regulatory subunit 1A in ewing sarcoma tumorigenesis and metastasis

Protein phosphatase inhibitors are often considered as tumor promoters. Protein phosphatase 1 regulatory subunit 1A (PPP1R1A) is a potent protein phosphatase 1 (PP1) inhibitor; however, its role in tumor development is largely undefined. Here we characterize, for the first time, the functions of PPP1R1A in Ewing sarcoma (ES) pathogenesis. We found that PPP1R1A is one of the top ranked target genes of EWS/FLI, the master regulator of ES, and is upregulated by EWS/FLI via a GGAA microsatellite enhancer element. Depletion of PPP1R1A resulted in a significant decrease in oncogenic transformation and cell migration in vitro as well as xenograft tumor growth and metastasis in an orthotopic mouse model. RNA-sequencing and functional annotation analyses revealed that PPP1R1A regulates genes associated with various cellular functions including cell junction, adhesion and neurogenesis. Interestingly, we found a significant overlap of PPP1R1A-regulated gene set with that of ZEB2 and EWS, which regulates metastasis and neuronal differentiation in ES, respectively. Further studies for characterization of the molecular mechanisms revealed that activation of PPP1R1A by PKA phosphorylation at Thr35, and subsequent PP1 binding and inhibition, was required for PPP1R1A-mediated tumorigenesis and metastasis, likely by increasing the phosphorylation levels of various PP1 substrates. Furthermore, we found that a PKA inhibitor impaired ES cell proliferation, tumor growth and metastasis, which was rescued by the constitutively active PPP1R1A. Together, these results offered new insights into the role and mechanism of PPP1R1A in tumor development and identified an important kinase and phosphatase pathway, PKA/PPP1R1A/PP1, in ES pathogenesis. Our findings strongly suggest a potential therapeutic value of inhibition of the PKA/PPP1R1A/PP1 pathway in the treatment of primary and metastatic ES.

Predictive properties of DNA methylation patterns in primary tumor samples for osteosarcoma relapse status

Osteosarcoma is the most common primary malignant bone tumor in children. Validated biological markers for disease prognosis available at diagnosis are lacking. No genome-wide DNA methylation studies linked to clinical outcomes have been reported in osteosarcoma to the best of our knowledge. To address this, we tested the methylome at over 1.1 million loci in 15 osteosarcoma biopsy samples obtained prior to the initiation of therapy and correlated these molecular data with disease outcomes. At more than 17% of the tested loci, samples obtained from patients who experienced disease relapse were more methylated than those from patients who did not have recurrence while patients who did not experience disease relapse had more DNA methylation at fewer than 1%. In samples from patients who went on to have recurrent disease, increased DNA methylation was found at gene bodies, intergenic regions and empirically-annotated candidate enhancers, whereas candidate gene promoters were unusual for a more balanced distribution of increased and decreased DNA methylation with 6.6% of gene promoter loci being more methylated and 2% of promoter loci being less methylated in patients with disease relapse. A locus at the TLR4 gene demonstrates one of strongest associations between DNA methylation and 5 y event-free survival (P-value = 1.7 × 10(-6)), with empirical annotation of this locus showing promoter characteristics. Our data indicate that DNA methylation information has the potential to be predictive of outcome in pediatric osteosarcoma, and that both promoters and non-promoter loci are potentially informative in DNA methylation studies.

Combinatorial immunotherapy of N-803 (IL-15 superagonist) and dinutuximab with ex vivo expanded natural killer cells significantly enhances in vitro cytotoxicity against GD2+ pediatric solid tumors and in vivo survival of xenografted immunodeficient NSG mice

Background

Children with recurrent and/or metastatic osteosarcoma (OS), neuroblastoma (NB) and glioblastoma multiforme (GBM) have a dismal event-free survival (<25%). The majority of these solid tumors highly express GD2. Dinutuximab, an anti-GD2 monoclonal antibody, significantly improved event-free survival in children with GD2⁺ NB post autologous stem cell transplantation and enhanced natural killer (NK) cell-mediated antibody-dependent cell cytotoxicity. Thus, approaches to increase NK cell number and activity, improve persistence and trafficking, and enhance tumor targeting may further improve the clinical benefit of dinutuximab. N-803 is a superagonist of an interleukin-15 (IL-15) variant bound to an IL-15 receptor alpha Su-Fc fusion with enhanced biological activity.

Methods

The anti-tumor combinatorial effects of N-803, dinutuximab and ex vivo expanded peripheral blood NK cells (exPBNK) were performed in vitro using cytoxicity assays against GD2⁺ OS, NB and GBM cells. Perforin and interferon (IFN)-γ levels were measured by ELISA assays. Multiple cytokines/chemokines/growth factors released were measured by multiplex assays. Human OS, GBM or NB xenografted NOD/SCID/IL2rγnull (NSG) mice were used to investigate the anti-tumor combinatorial effects in vivo.

Results

N-803 increased the viability and proliferation of exPBNK. The increased viability and proliferation are associated with increased phosphorylation of Stat3, Stat5, AKT, p38MAPK and the expression of NK activating receptors. The combination of dinutuximab and N-803 significantly enhanced in vitro cytotoxicity of exPBNK with enhanced perforin and IFN-γ release against OS, GBM and NB. The combination of exPBNK+N-803+dinutuximab significantly reduced the secretion of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), platelet-derived growth factor-BB (PDGF-BB), and stem cell growth factor beta (SCGF-β) from OS or GBM tumor cells. Furthermore, OS or GBM significantly inhibited the secretion of regulated on activation, normal T cell expressed and presumably secreted (RANTES) and stromal cell-derived factor-1 alpha (SDF-1α) from exPBNK cells (p<0.001) but significantly enhanced monokine induced by gamma interferon (MIG) secretion from exPBNK cells (p<0.001). N-803 combined with dinutuximab and exPBNK cells significantly extended the survival of OS, GBM or NB xenografted NSG mice.

Conclusions

Our results provide the rationale for the development of a clinical trial of N-803 in combination with dinutuximab and ex vivo exPBNK cells in patients with recurrent or metastatic GD2⁺ solid tumors.

Novel cytokine-antibody fusion protein, N-820, to enhance the functions of ex vivo expanded natural killer cells against Burkitt lymphoma

BACKGROUND

The prognosis of patients with relapsed or progressive B cell (CD20⁺) non-Hodgkin's lymphoma (B-NHL), including Burkitt lymphoma (BL), is dismal due to chemoradiotherapy resistance. Novel therapeutic strategies are urgently needed. N-820 is a fusion protein of N-803 (formerly known as ALT-803) to four single-chains of rituximab. This agent has tri-specific binding activity to CD20 and enhanced antibody-dependent cell-mediated cytotoxicity.

METHODS

We investigated the anti-tumor combinatorial effects of N-820 with ex vivo expanded peripheral blood natural killer (exPBNK) cells against rituximab-sensitive and rituximab-resistant CD20⁺ BL in vitro using cytoxicity assays and in vivo using human BL xenografted NOD/SCID/IL2rγnull (NSG) mice. We also investigated the cytokines/chemokines/growth factors released using ELISA and multiplex assay. Gene expression changes were examined using real-time PCR arrays.

RESULTS

N-820 significantly enhanced the expression of NK activating receptors (p<0.001) and the proliferation of exPBNK cells with enhanced Ki67 expression and Stat5 phosphorylation (p<0.001). N-820 significantly enhanced the secretion of cytokines, chemokines, and growth factors including GM-CSF, RANTES, MIP-1B (p<0.001) from exPBNK cells as compared with the combination of rituximab+N-803. Importantly, N-820 significantly enhanced in vitro cytotoxicity (p<0.001) of exPBNK with enhanced granzyme B and IFN-γ release (p<0.001) against BL. Gene expression profiles in exPBNK stimulated by N-820+Raji-2R showed enhanced transcription of CXCL9, CXCL1, CSF2, CSF3, GZMB, and IFNG. Moreover, N-820 combined with exPBNK significantly inhibited rituximab-resistant BL growth (p<0.05) and extended the survival (p<0.05) of BL xenografted NSG mice.

CONCLUSIONS

Our results provide the rationale for the development of a clinical trial of N-820 alone or in combination with endogenous or ex vivo expanded NK cells in patients with CD20⁺ B-NHL failing prior rituximab containing chemoimmunotherapy regimens.

Protein phosphatase 1 regulatory subunit 1A regulates cell cycle progression in Ewing sarcoma

Ewing sarcoma (ES) is a malignant pediatric bone and soft tissue tumor. Patients with metastatic ES have a dismal outcome which has not been improved in decades. The major challenge in the treatment of metastatic ES is the lack of specific targets and rational combinatorial therapy. We recently found that protein phosphatase 1 regulatory subunit 1A (PPP1R1A) is specifically highly expressed in ES and promotes tumor growth and metastasis in ES. In the current investigation, we show that PPP1R1A regulates ES cell cycle progression in G1/S phase by down-regulating cell cycle inhibitors p21^Cip1 and p27^Kip1, which leads to retinoblastoma (Rb) protein hyperphosphorylation. In addition, we show that PPP1R1A promotes normal transcription of histone genes during cell cycle progression. Importantly, we demonstrate a synergistic/additive effect of the combinatorial therapy of PPP1R1A and insulin-like growth factor 1 receptor (IGF-1R) inhibition on decreasing ES cell proliferation and migration in vitro and limiting xenograft tumor growth and metastasis in vivo. Taken together, our findings suggest a role of PPP1R1A as an ES specific cell cycle modulator and that simultaneous targeting of PPP1R1A and IGF-1R pathways is a promising specific and effective strategy to treat both primary and metastatic ES.

Circumventing resistance within the Ewing sarcoma microenvironment by combinatorial innate immunotherapy

BACKGROUND

Pediatric patients with recurrent/metastatic Ewing sarcoma (ES) have a dismal 5-year survival. Novel therapeutic approaches are desperately needed. Natural killer (NK) cell number and function are low in ES patient tumors, in large part due to the immunosuppressive tumor microenvironment (TME). Melanoma cell adhesion molecule (MCAM) is highly expressed on ES and associated with ES metastasis. NKTR-255 is a polymer-conjugated recombinant human interleukin-15 (IL-15) agonist improving NK cell activity and persistence. Magrolimab (MAG) is a CD47 blockade that reactivates the phagocytic activity of macrophages.

METHODS

Transcriptome profiling coupled with CIBERSORT analyses in both ES mouse xenografts and human patient tumors were performed to identify mechanisms of NK resistance in ES TME. A chimeric antigen receptor (CAR) NK cell targeting MCAM was engineered by CAR mRNA electroporation into ex vivo expanded NK cells. In vitro cytotoxicity assays were performed to investigate the efficacy of anti-MCAM-CAR-NK cell alone or combined with NKTR-255 against ES cells. Interferon-γ and perforin levels were measured by ELISA. The effect of MAG on macrophage phagocytosis of ES cells was evaluated by in vitro phagocytosis assays. Cell-based and patient-derived xenograft (PDX)-based xenograft mouse models of ES were used to investigate the antitumor efficacy of CAR-NK alone and combined with NKTR-255 and MAG in vivo.

RESULTS

We found that NK cell infiltration and activity were negatively regulated by tumor-associated macrophages (TAM) in ES TME. Expression of anti-MCAM CAR significantly and specifically enhanced NK cytotoxic activity against MCAMhigh but not MCAM-knockout ES cells in vitro, and significantly reduced lung metastasis and extended animal survival in vivo. NKTR-255 and MAG significantly enhanced in vitro CAR-NK cytotoxicity and macrophage phagocytic activity against ES cells, respectively. By combining with NKTR-255 and MAG, the anti-MCAM-CAR-NK cell significantly decreased primary tumor growth and prolonged animal survival in both cell- and PDX-based ES xenograft mouse models.

CONCLUSIONS

Our preclinical studies demonstrate that immunotherapy via the innate immune system by combining tumor-targeting CAR-NK cells with an IL-15 agonist and a CD47 blockade is a promising novel therapeutic approach to targeting MCAMhigh malignant metastatic ES.

A Pilot Study of RNA Sequencing to Improve the Diagnostic Yield of Bronchoalveolar Lavage Specimens in Pediatric Allogeneic Hematopoietic Stem Cell Transplant Recipients

BACKGROUND

Pulmonary complications often cause morbidity and mortality in pediatric allogeneic hematopoietic stem cell transplant (HSCT) recipients. While detection of infection and initiation of appropriate antimicrobial therapy improves survival, present techniques oftentimes do not detect infections in bronchoalveolar lavage (BAL) samples because of pretreatment with antimicrobial therapies and the need for a priori knowledge of likely viral pathogens, decreasing the yield of BAL.

OBJECTIVE

We evaluated whether RNA-based massively parallel sequencing (MPS) would improve detection of infections in BAL fluid in pediatric allogeneic HSCT recipients.

RESULTS

Nine patients underwent 10 BAL (1 patient underwent 2 BAL) and had sufficient BAL fluid for inclusion in this study. Clinical microbiological testing identified infections in 7 patients, and MPS identified infections in 5 patients, although some of these detected organisms were not detected by clinical testing. Results were fully concordant in 5 patients, fully discordant in 3 patients, and partially discordant in 2 patients. Bacterial, viral, and fungal infections were detected via both techniques.

CONCLUSION

This suggests that MPS in conjunction with routine clinical testing increases the yield of detection of infectious organisms in the BAL fluid.

Consensus recommendations in the management of Ewing sarcoma from the National Ewing Sarcoma Tumor Board

Ewing sarcoma (ES) is a malignant tumor of bone and soft tissue that most often occurs in adolescents and young adults. Despite an international coordinated approach, several nuances, discrepancies, and debates remain in defining the standard of care for treating ES. In this review, the authors leverage the expertise assembled by formation of the National Ewing Sarcoma Tumor Board, a multi-institution, multidisciplinary virtual tumor board that meets monthly to discuss complicated and challenging cases of ES. This report is focused on select topics that apply to the management of patients with newly diagnosed ES. The specific topics covered include indications for bone marrow aspirate and biopsy for initial evaluation compared with fluorodeoxyglucose-positron emission tomography, the role of interval compressed chemotherapy in patients aged 18 years and older, the role of adding ifosfamide/etoposide to vincristine/doxorubicin/cyclophosphamide for patients with metastatic disease, the data on and role of high-dose chemotherapy with autologous stem cell transplantation, maintenance therapy, and whole-lung irradiation. The data referenced are often limited to subgroup analyses and/or compiled from multiple sources. Although not intended to replace the clinical judgement of treating physicians, the guidelines are intended to provide clarity and recommendations for the upfront management of patients with ES. PLAIN LANGUAGE SUMMARY: Ewing sarcoma is a malignant tumor of bone and soft tissue that most often occurs in adolescents and young adults. For this review, the authors used the experience of the National Ewing Sarcoma Tumor Board, a multi-institution, multidisciplinary virtual tumor board that meets monthly to discuss complicated and challenging cases of Ewing sarcoma. Although not intended to replace the clinical judgement of treating physicians, the guidelines will focus on the development of consensus statements for the upfront management of patients with Ewing sarcoma.

Combinatorial immunotherapy of anti-MCAM CAR-modified expanded natural killer cells and NKTR-255 against neuroblastoma

Pediatric patients with recurrent metastatic neuroblastoma (NB) have a dismal 5-year survival. Novel therapeutic approaches are urgently needed. The melanoma cell adhesion molecule (MCAM/CD146/MUC18) is expressed in a variety of pediatric solid tumors, including NB, and constitutes a novel target for immunotherapy. Here, we developed a chimeric antigen receptor (CAR) expressing natural killer (NK) cell-targeting MCAM by non-viral electroporation of CAR mRNA into ex vivo expanded NK cells. Expression of anti-MCAM CAR significantly enhanced NK cell cytotoxic activity compared to mock NK cells against MCAMhigh but not MCAMlow/knockout NB cells in vitro. Anti-MCAM-CAR-NK cell treatment significantly decreased tumor growth and prolonged animal survival in an NB xenograft mouse model. NKTR-255, a polymer-conjugated recombinant human interleukin-15 agonist, significantly stimulated NK cell proliferation and expansion and further enhanced the in vitro cytotoxic activity and in vivo anti-tumor efficacy of anti-MCAM-CAR-NK cells against NB. Our preclinical studies demonstrate that ex vivo expanded and modified anti-MCAM-CAR-NK cells alone and/or in combination with NKTR-255 are promising novel alternative therapeutic approaches to targeting MCAMhigh malignant NB.

Consensus recommendations for systemic therapies in the management of relapsed Ewing sarcoma: A report from the National Ewing Sarcoma Tumor Board

Ewing sarcoma (ES) is a malignant tumor of bone and soft tissue that most often occurs in children, adolescents, and young adults. Debate and controversy remain in the management of relapsed/refractory ES (RR-ES). The authors leveraged the expertise assembled by the National Ewing Sarcoma Tumor Board, a multidisciplinary virtual tumor board that meets monthly to discuss challenging cases of ES. In this review, they focus on select topics that apply to the management of patients with RR-ES. The specific topics covered include the initial approach of such patients and discussion of the goals of care, the role of molecular testing, chemotherapy regimens and novel agents to consider, the role of maintenance therapy, and the use of high-dose chemotherapy with autologous stem cell rescue. The data referenced are often limited to subgroup analyses and/or compiled from multiple sources. Although not intended to replace the clinical judgement of treating physicians, these guidelines are intended to support clinicians and provide some clarity and recommendations for the management of patients with RR-ES. PLAIN LANGUAGE SUMMARY: Ewing sarcoma (ES) is a bone and soft tissue cancer that most often occurs in teenagers and young adults. This article uses the experience of the National Ewing Sarcoma Tumor Board, a multi-institution, multidisciplinary virtual tumor board that meets monthly to discuss challenging cases of ES and to address questions related to the treatment of patients with relapsed ES. Although not intended to replace the clinical judgement of treating physicians and limited by available data, these consensus recommendations will support clinicians who treat patients with this challenging malignancy, made even more difficult when it recurs.

Abstract 6594: Targeting Ewing sarcoma and osteosarcoma with anti-MCAM chimeric antigen receptor modified NK cells

Ewing sarcoma and osteosarcoma are the two most common pediatric malignant bone tumors. Patients who present with metastatic disease or relapse have a dismal average 5-year survival of only 20%. Novel therapeutic approaches are desperately needed. The melanoma cell adhesion molecule (MCAM/CD146/MUC18) is highly expressed in sarcoma and metastatic pediatric tumors. MCAM depletion inhibits Ewing sarcoma cell migration in vitro and tumor metastasis in vivo. High MCAM levels in patient tumors are associated with poor survival in Ewing sarcoma. MCAM therefore constitutes a unique and novel target for immunotherapy against MCAM+ sarcomas. We previously demonstrated that natural killer (NK) cell engineered to express chimeric antigen receptor (CAR) against CD20 significantly reduced tumor burden, prevented tumor dissemination, and extended survival of treated mice compared to mock NK treatment in humanized Burkitt lymphoma xenograft mouse model. We hypothesize that anti-MCAM CAR NK cell will enhance the inherent NK-sarcoma cytotoxicity by better targeting sarcoma cells. Here we develop an anti-MCAM CAR NK cell and investigate its efficacy in promoting NK cell cytotoxicity against Ewing sarcoma and osteosarcoma. MCAM expression in sarcoma cell lines and tumor samples were validated by flow cytometry and western blotting. Peripheral blood mononuclear cells (PBMCs) are expanded into NK cells ex vivo using K562-mbIL21-41BBL artificial antigen presenting cells (aAPC). Anti-MCAM CAR NK cells are generated by non-viral electroporation of anti-MCAM CAR mRNA into expanded NK cells. Anti-MCAM CAR NK cytotoxicity is evaluated in vitro by luciferase based cytotoxicity assay. We detected various levels of MCAM expression in Ewing sarcoma and osteosarcoma cell lines and tumors. In addition, we noticed an interesting patchy expression pattern of MCAM in the Ewing sarcoma tumor sample. Importantly, we found a significantly increased cytotoxicity of anti-MCAM CAR NK cells compared to mock NK cells (59.9±10 vs 13.3±3.7 at E:T ratio of 5:1, p=0.006; and 65.6±7 vs 13.7±3.4 at 10:1, p=0.004) against Ewing sarcoma TC71 cells after co-culturing for 4 hours. A similar result was observed at the time point of 48 hours (91.5±8 vs 59±0.5 at E:T of 5:1, p=0.018). Anti-MCAM CAR NK cells also showed significantly enhanced cytotoxicity against U2OS osteosarcoma cells compared to mock NK cells (32.6±23.2 vs 0.5±19.5 at E:T of 0.5:1, p=0.004; 47.1±27.4 vs 10.2±24 at E:T of 1:1, p=0.001) at the time point of 48 hours. In summary, these findings demonstrated enhanced efficacy of anti-MCAM CAR NK cells compared to mock NK cells against Ewing sarcoma and osteosarcoma cells and support a further preclinical investigation whether targeting MCAM by CAR NK will limit sarcoma growth and/or metastasis and increase survival in vivo.

Citation Format: Aliza Gardenswartz, Wen Luo, Jeremy M. Rosenblum, Janet Ayello, Mitchell S. Cairo. Targeting Ewing sarcoma and osteosarcoma with anti-MCAM chimeric antigen receptor modified NK cells [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 6594.

Combinatorial macrophage induced innate immunotherapy against Ewing sarcoma: Turning "Two Keys" simultaneously

BACKGROUND

Macrophages play important roles in phagocytosing tumor cells. However, tumors escape macrophage phagocytosis in part through the expression of anti-phagocytic signals, most commonly CD47. In Ewing sarcoma (ES), we found that tumor cells utilize dual mechanisms to evade macrophage clearance by simultaneously over-expressing CD47 and down-regulating cell surface calreticulin (csCRT), the pro-phagocytic signal. Here, we investigate the combination of a CD47 blockade (magrolimab, MAG) to inhibit the anti-phagocytic signal and a chemotherapy regimen (doxorubicin, DOX) to enhance the pro-phagocytic signal to induce macrophage phagocytosis of ES cells in vitro and inhibit tumor growth and metastasis in vivo.

METHODS

Macrophages were derived from human peripheral blood monocytes by granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF). Flow cytometry- and microscopy-based in-vitro phagocytosis assays were performed to evaluate macrophage phagocytosis of ES cells. Annexin-V assay was performed to evaluate apoptosis. CD47 was knocked out by CRISPR/Cas9 approach. ES cell-based and patient-derived-xenograft (PDX)-based mouse models were utilized to assess the effects of MAG and/or DOX on ES tumor development and animal survival. RNA-Seq combined with CIBERSORTx analysis was utilized to identify changes in tumor cell transcriptome and tumor infiltrating immune cell profiling in MAG and/or DOX treated xenograft tumors.

RESULTS

We found that MAG significantly increased macrophage phagocytosis of ES cells in vitro (p < 0.01) and had significant effect on reducing tumor burden (p < 0.01) and increasing survival in NSG mouse model (p < 0.001). The csCRT level on ES cells was significantly enhanced by DOX in a dose- and time-dependent manner (p < 0.01). Importantly, DOX combined with MAG significantly enhanced macrophage phagocytosis of ES cells in vitro (p < 0.01) and significantly decreased tumor burden (p < 0.01) and lung metastasis (p < 0.0001) and extended animal survival in vivo in two different mouse models of ES (p < 0.0001). Furthermore, we identified CD38, CD209, CD163 and CD206 as potential markers for ES-phagocytic macrophages. Moreover, we found increased M2 macrophage infiltration and decreased expression of Cd209 in the tumor microenvironment of MAG and DOX combinatorial therapy treated tumors.

CONCLUSIONS

By turning "two keys" simultaneously to reactivate macrophage phagocytic activity, our data demonstrated an effective and highly translatable alternative therapeutic approach utilizing innate (tumor associated macrophages) immunotherapy against high-risk metastatic ES.