Pediatric sarcomas are a heterogeneous group of malignant tumors of bone and soft tissue origin. Although more than 100 different histologic subtypes have been described, the majority of pediatric cases belong to the Ewing’s family of tumors, rhabdomyosarcoma and osteosarcoma. Most patients that present with localized stage are curable with surgery and/or chemotherapy; however, those with metastatic disease at diagnosis or those who experience a relapse continue to have a very poor prognosis. New therapies for these patients are urgently needed. Immunotherapy is an established treatment modality for both liquid and solid tumors, and in pediatrics, most notably for neuroblastoma and osteosarcoma. In the past, immunomodulatory agents such as interferon, interleukin-2, and Liposomal-muramyl tripeptide phosphatidyl-ethanolamine (L-MTP) have been tried, with some activity seen in subsets of patients; additionally, various cancer vaccines have been studied with possible benefit. Monoclonal antibody therapies against tumor antigens such as disialoganglioside GD2 or immune checkpoint targets such as CTLA4 and PD-1 are being actively explored in pediatric sarcomas. Building on the success of adoptive T cell therapy for EBV-related lymphoma, strategies to redirect T cells using chimeric antigen receptors and bispecific antibodies are rapidly evolving with potential for the treatment of sarcomas. This review will focus on recent preclinical and clinical developments in targeted agents for pediatric sarcomas with emphasis on the immunobiology of immune checkpoints, immunoediting, tumor microenvironment, antibody engineering, cell engineering, and tumor vaccines. The future integration of antibody based and cell based therapies into an overall treatment strategy of sarcoma will be discussed.

High-risk neuroblastoma, a pediatric tumor originating from the sympathetic nervous system, has a low mutation load but highly recurrent somatic DNA copy number variants. Previously, segmental gains and/or amplifications allowed identification of drivers for neuroblastoma development. Using this approach, combined with gene dosage impact on expression and survival, we identified ribonucleotide reductase subunit M2 (RRM2) as a candidate dependency factor further supported by growth inhibition upon in vitro knockdown and accelerated tumor formation in a neuroblastoma zebrafish model coexpressing human RRM2 with MYCN. Forced RRM2 induction alleviates excessive replicative stress induced by CHK1 inhibition, while high RRM2 expression in human neuroblastomas correlates with high CHK1 activity. MYCN-driven zebrafish tumors with RRM2 co-overexpression exhibit differentially expressed DNA repair genes in keeping with enhanced ATR-CHK1 signaling activity. In vitro, RRM2 inhibition enhances intrinsic replication stress checkpoint addiction. Last, combinatorial RRM2-CHK1 inhibition acts synergistic in high-risk neuroblastoma cell lines and patient-derived xenograft models, illustrating the therapeutic potential.

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BACKGROUND: The authors report a retrospective analysis of high‐dose ifosfamide, carboplatin, and etoposide (HD‐ICE) for patients with refractory or relapsed neuroblastoma (NB). A major reason for using this regimen was the long time since patients received previous treatment with a platinum compound. The authors also summarized the published experience on ICE in patients with NB.METHODS: Treatment comprised ifosfamide (2000 mg/m² daily for 5 days), carboplatin (500 mg/m² daily for 2 days), and etoposide (100 mg/m² daily for 5 days). Patients who had poor hematologic reserve (platelet count 36% in phase 1 and 2 studies (in which less comprehensive staging evaluations were used) that involved resistant NB and >70% in induction for newly diagnosed NB.CONCLUSIONS: HD‐ICE is appealing as salvage treatment or consolidative therapy because of its anti‐NB activity and the low risk of major nonhematologic toxicity. PBSC support is unnecessary for patients who had intact hematologic reserve. Cancer 2013. © 2012 American Cancer Society.

BACKGROUND: The authors exploited a large database to investigate the outcomes of patients with high‐risk neuroblastoma in the contemporary era.METHODS: All patients with high‐risk neuroblastoma aged 18 months with MYCN‐nonamplified [MYCN(−)] stage 4 disease.RESULTS: A complete response/very good partial response (CR/VGPR) to induction was correlated with significantly superior event‐free survival (EFS) (P < .001) and overall survival (OS) (P < .001) compared with a partial response or less. Patients with MYCN(+) and MYCN(−) disease had similar rates of CR/VGPR to induction (P = .366), and those with MYCN(+) and MYCN(−) disease who attained a CR/VGPR had similar EFS (P = .346) and OS (P = .542). In contrast, only MYCN(+) patients had progressive disease as a response to induction (P < .001), and early death from progressive disease (<366 days after diagnosis) was significantly more common (P < .001) among those with MYCN(+) disease. Overall, among patients who had a partial response or less, MYCN(+) patients had significantly inferior EFS (P < .001) and OS (P < .001) compared with MYCN(−) patients, which accounted for the significantly worse EFS (P = .008) and OS (P = .002) for the entire MYCN(+) cohort versus the MYCN(−) cohort.CONCLUSIONS: Patients with MYCN(−), high‐risk neuroblastoma display a broad, continuous spectrum with regard to response and outcome, whereas MYCN(+) patients either have an excellent response to induction associated with good long‐term outcome or develop early progressive disease with a poor outcome. This extreme dichotomy in the clinical course of MYCN(+) patients points to underlying biologic differences with MYCN(+) neuroblastoma, the elucidation of which may have far‐reaching implications, including improved risk classification at diagnosis and the identification of targets for treatment. Cancer 2014;120:2050–2059. © 2014 American Cancer Society.

High-risk neuroblastoma (NB) has a poor prognosis. Even with intensive myeloablative chemotherapy, relapse is common and almost uniformly fatal, and new treatments are needed. Translocator protein 18kDa (TSPO) ligands have been studied as potential new therapeutic agents in many cancers, but not in NB. We studied the effects of TSPO ligands on cell proliferation, cell cycle progression and apoptosis using paired cell lines derived from the same patient at the time of initial surgery and again after development of progressive disease or relapse post-chemotherapy. We found that TSPO expression was significantly increased 2- to 10-fold in post-relapse cell lines compared with pre-treatment lines derived from the same individual. Subsequently, these cell lines were treated with the specific TSPO ligand 1-(2-chlorophenyl-N-methylpropyl)-3-isoquinolinecarboxamide (PK11195) (0–160µM) as a single agent, with cytotoxic chemotherapy agents alone (carboplatin, etoposide or melphalan), or with combinations of PK11195 and chemotherapy drugs. We found that PK11195 inhibited proliferation in a dose-dependent manner, induced apoptosis and caused G1/S cell cycle arrest in all tested NB cell lines at micromolar concentrations. In addition, PK11195 significantly decreased mRNA expression of the chemotherapy resistance efflux pumps ABCA3, ABCB1 and ABCC1 in two post-relapse NB cell lines. We also found that pre-treatment with PK11195 sensitized these cell lines to treatment with cytotoxic chemotherapy agents. These results suggest that PK11195 alone or in combination with standard chemotherapeutic drugs warrants further study for the treatment of neuroblastoma.