Comprehensive radiotherapy for pediatric Ewing Sarcoma: Outcomes of a prospective proton study

BACKGROUND AND PURPOSE

Patients with Ewing Sarcoma (EWS) are treated with multimodality therapy which includes radiation therapy (RT) as an option for local control. We report on the efficacy after proton radiation therapy (PRT) to the primary site for localized and metastatic EWS.

MATERIALS AND METHODS

Forty-two children with EWS (33 localized, 9 metastatic) treated between 2007 and 2020 were enrolled on 2 prospective registry protocols for pediatric patients undergoing PRT. PRT was delivered by passive scatter (74 %), pencil-beam scanning (12 %) or mixed technique (14 %). Treated sites included the spine (45 %), pelvis/sacrum (26 %), skull/cranium (14 %), extraosseous (10 %), and chest wall (5 %). Median radiation dose was 54 Gy-RBE (range 39.6-55.8 Gy-RBE). Patients with metastatic disease received consolidative RT to metastatic sites (4 at the time of PRT to the primary site, 5 after completion of chemotherapy). Median follow-up time was 47 months after PRT.

RESULTS

The 4-year local control (LC), progression-free survival (PFS), and overall survival (OS) rates were 83 %, 71 %, and 86 %, respectively. All local failures (n = 6) were in-field failures. Tumor size ≥ 8 cm predicted for inferior 4-year LC (69 % vs 95 %, p = 0.04). 4-year PFS and OS rates were not statistically different in patients with localized versus metastatic disease (72 % vs 67 %, p = 0.70; 89 % vs 78 %, p = 0.38, respectively).

CONCLUSION

In conclusion, LC for pediatric patients with EWS treated with PRT was comparable to that of historical patients who received photon-RT. Tumor size ≥ 8 cm predicted increased risk of local failure. Patients with metastatic disease, including non-pulmonary only metastases, received radiation therapy to all metastatic sites and had favorable survival outcomes.

Intrinsic epigenetic state of primary osteosarcoma drives metastasis

Osteosarcoma (OS) is the most common primary malignant bone tumor affecting the pediatric population with high potential to metastasize to distal sites, most commonly the lung. Insights into defining molecular features contributing to metastatic potential are lacking. We have mapped the active chromatin landscapes of OS tumors by integrating histone H3 lysine acetylated chromatin (H3K27ac) profiles (n=13), chromatin accessibility profiles (n=11) and gene expression (n=13) to understand the differences in their active chromatin profiles and its impact on molecular mechanisms driving the malignant phenotypes. Primary OS tumors from patients with metastasis (primary met) have a distinct active chromatin landscape compared to primary tumors from patients without metastatic disease (localized). The difference in chromatin activity shapes the transcriptional profile of OS. We identified novel candidate genes involved in OS pathogenesis and metastasis, including PPP1R1B , PREX1 and IGF2BP1 , which exhibit increased chromatin activity in primary met along with higher transcript levels. Overall, differential chromatin activity in primary met occurs in proximity of genes regulating actin cytoskeleton organization, cellular adhesion, and extracellular matrix suggestive of their role in facilitating OS metastasis. Furthermore, chromatin profiling of tumors from metastatic lung lesions noted increases in chromatin activity in genes involved in cell migration and key intracellular signaling cascades, including the Wnt pathway. Thus, this data demonstrates that metastatic potential is intrinsically present in primary metastatic tumors and the cellular chromatin profiles further adapt to allow for successful dissemination, migration, and colonization at the distal metastatic site.

MYC regulates CSF1 expression via microRNA 17/20a to modulate tumor-associated macrophages in osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor of childhood. Approximately 20%-30% of OSs carry amplification of chromosome 8q24, which harbors the oncogene c-MYC and correlates with a poor prognosis. To understand the mechanisms that underlie the ability of MYC to alter both the tumor and its surrounding tumor microenvironment (TME), we generated and molecularly characterized an osteoblast-specific Cre-Lox-Stop-Lox-c-MycT58A p53fl/+ knockin genetically engineered mouse model (GEMM). Phenotypically, the Myc-knockin GEMM had rapid tumor development with a high incidence of metastasis. MYC-dependent gene signatures in our murine model demonstrated significant homology to the human hyperactivated MYC OS. We established that hyperactivation of MYC led to an immune-depleted TME in OS demonstrated by the reduced number of leukocytes, particularly macrophages. MYC hyperactivation led to the downregulation of macrophage colony-stimulating factor 1, through increased microRNA 17/20a expression, causing a reduction of macrophage population in the TME of OS. Furthermore, we developed cell lines from the GEMM tumors, including a degradation tag-MYC model system, which validated our MYC-dependent findings both in vitro and in vivo. Our studies utilized innovative and clinically relevant models to identify a potentially novel molecular mechanism through which MYC regulates the profile and function of the OS immune landscape.

Correlating decline in left ventricular ejection fraction and longitudinal strain in pediatric cancer patients

PURPOSE

Left ventricular ejection fraction (LVEF) is routinely used to monitor cardiac function in cancer patients. Global longitudinal strain (GLS) detects subclinical myocardial dysfunction. There is no consensus on what constitutes a significant change in GLS in pediatric cancer patients. We aim to determine the change in GLS associated with a simultaneous decline in LVEF in pediatric cancer patients.

METHODS

This is a retrospective longitudinal study of pediatric cancer patients treated with anthracyclines between October 2017 and November 2019. GLS was measured by 2-dimensional speckle tracking. The study outcome was a decline in LVEF, defined as a decrease in LVEF of ≥ 10% points from baseline or LVEF < 55%. We evaluated two echocardiograms per patient, one baseline, and one follow-up. The follow-up echocardiogram was either (1) the first study that met the outcome or (2) the last echocardiogram available in patients without the outcome. Statistical analyses included receiver operator characteristic curves and univariable and multivariable Cox proportional hazards regression.

RESULTS

Out of 161 patients, 33 (20.5%) had a decline in LVEF within one year of follow-up. GLS reduction by ≥ 15% from baseline and follow-up GLS >-18% had sensitivities of 85% and 78%, respectively, and specificities of 86% and 83%, respectively, to detect LVEF decline. GLS reduction by ≥ 15% from baseline and follow-up GLS >-18% were independently associated with simultaneous LVEF decline [hazard ratio (95% confidence intervals): 16.71 (5.47-51.06), and 12.83 (4.62-35.63), respectively].

CONCLUSION

Monitoring GLS validates the decline in LVEF in pediatric cancer patients.

A Simulation Workshop for Pediatric Residents Using Team-Based Reflective Practice to Communicate Life-Altering News

Introduction

Guiding patients and their families through threat and tragedy is an essential skill for physicians. Educational opportunities to acquire this crucial expertise during medical training are limited. We describe a workshop design employing simulation and team-based reflection to enhance pediatric residents' confidence in delivering life-altering news.

Methods

Three hundred and seventy-six pediatric residents participated in an annual 2.75-hour workshop from 2011 to 2018. For each session, 24 to 28 residents were randomly assigned to learning teams of 6-7 trainees and two faculty. Each team had four different simulated parent encounters to convey life-altering news. Briefing and debriefing of encounters utilized team-based reflection. The impact of this educational intervention was evaluated using retrospective pre-post self-report questionnaires.

Results

Participants indicated that the learning experience was realistic, useful, and was provided in a safe learning environment. Residents reported increased confidence in their ability to communicate various types of life-altering news. A one-year follow-up survey indicated most respondents found the experience useful in actual practice subsequent to the workshop. The design also appears to be an efficient use of resources.

Conclusion

A workshop combining team-based reflection and simulation improves the confidence of pediatric residents in communicating life-altering news.

Patient-derived iPSCs link elevated mitochondrial respiratory complex I function to osteosarcoma in Rothmund-Thomson syndrome

Rothmund-Thomson syndrome (RTS) is an autosomal recessive genetic disorder characterized by poikiloderma, small stature, skeletal anomalies, sparse brows/lashes, cataracts, and predisposition to cancer. Type 2 RTS patients with biallelic RECQL4 pathogenic variants have multiple skeletal anomalies and a significantly increased incidence of osteosarcoma. Here, we generated RTS patient-derived induced pluripotent stem cells (iPSCs) to dissect the pathological signaling leading to RTS patient-associated osteosarcoma. RTS iPSC-derived osteoblasts showed defective osteogenic differentiation and gain of in vitro tumorigenic ability. Transcriptome analysis of RTS osteoblasts validated decreased bone morphogenesis while revealing aberrantly upregulated mitochondrial respiratory complex I gene expression. RTS osteoblast metabolic assays demonstrated elevated mitochondrial respiratory complex I function, increased oxidative phosphorylation (OXPHOS), and increased ATP production. Inhibition of mitochondrial respiratory complex I activity by IACS-010759 selectively suppressed cellular respiration and cell proliferation of RTS osteoblasts. Furthermore, systems analysis of IACS-010759-induced changes in RTS osteoblasts revealed that chemical inhibition of mitochondrial respiratory complex I impaired cell proliferation, induced senescence, and decreased MAPK signaling and cell cycle associated genes, but increased H19 and ribosomal protein genes. In summary, our study suggests that mitochondrial respiratory complex I is a potential therapeutic target for RTS-associated osteosarcoma and provides future insights for clinical treatment strategies.

Genomic analysis and preclinical xenograft model development identify potential therapeutic targets for MYOD1-mutant soft-tissue sarcoma of childhood

The myogenic differentiation 1 gene (MYOD1) p.L122R somatic mutation was first discovered in a subset of clinically aggressive embryonal rhabdomyosarcomas and has since been described in both pediatric and adult spindle cell/sclerosing rhabdomyosarcomas. Relatively little is known about the clinical, molecular, and histopathological features of these tumors in children. In order to further characterize the genomic and clinical features of pediatric MYOD1-mutant sarcomas, we evaluated a cohort of soft-tissue sarcoma patients treated at Texas Children's Hospital. Tumor DNA was subjected to next-generation panel sequencing and/or Sanger sequencing of the MYOD1 hotspot mutation. The MYOD1 p.L122R mutation was identified in six tumors, with a variant allele fraction greater than 0.8 in three cases, suggestive of loss of heterozygosity. One sclerosing rhabdomyosarcoma lacking the MYOD1 hotspot mutation was observed to have a MYOD1 copy number gain, also with evidence of loss of heterozygosity. Cancer gene panel sequencing revealed potentially targetable alterations in six of seven (86%) patients with MYOD1 alterations, including four patients with an alteration in the PI3K-AKT pathway: two hotspot PIK3CA mutations and deletions in PTEN and TSC2. On histopathologic review, MYOD1-altered tumors exhibited spindle and/or round cells and varying degrees of hyaline sclerosis. At last follow-up, six patients had died of disease and the seventh progressed early and was subsequently lost to follow-up. Both pre- and post-therapy patient-derived xenograft models were generated from one patient's tumor. These models were confirmed to harbor the MYOD1 and PIK3CA mutations seen in the primary tumor and were shown to be sensitive to PI3K/mTOR inhibition in vitro and in vivo. In conclusion, this study adds to recent reports describing the clinicopathologic and genomic features of MYOD1-altered soft-tissue sarcomas in children, including dismal prognosis and potential molecular targets for therapy. The novel preclinical models developed will facilitate further biological and preclinical study of this rare and aggressive tumor. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Abstract 405: The role of GALNT14 in chemoresistant and metastatic osteosarcoma

Introduction: Osteosarcoma is the most common bone tumor in children and adolescents. Many patients have disease progression through standard chemotherapy regimens of methotrexate, cisplatin, and doxorubicin. Presently, there are no salvage therapies that have added significant survival benefits, leaving minimal options for relapsed and resistant disease. Additionally, there are no clinically significant biomarkers for this disease that would predict treatment failures. N-acetylgalactosaminyltransferase 14 (GALNT14) is an enzyme that initiates O-linked glycosylation to outer membrane-bound and extracellular proteins. Using transcriptomic analyses, we identified GALNT14 overexpression correlated with poor tumor necrosis and survival outcomes. Therefore, we hypothesize that GALNT14 contributes to metastatic and chemoresistant phenotypes in pediatric osteosarcoma.

Methods: Transcriptomic data from the Therapeutically Applicable Research for Generating Effective Treatments (TARGET) database and RNA-sequencing of institutional patient-derived xenografts (PDXs) revealed that overexpression of GALNT14 correlated to poor necrosis rates. Gene Set Enrichment Analysis (GSEA) also identified upregulation of glycosylation pathways. Aberrant expression of GALNT14 was confirmed using quantitative polymerase chain reaction (qPCR) and Western blot analyses in various osteosarcoma cell lines. Transient GALNT14 knockdown and overexpression were then analyzed for effects on proliferation, invasion, migration, and chemotherapy response in vitro. Kaplan-Meier curves demonstrating overall survival (OS) and event-free survival (EFS) were established using data from the TARGET database.

Results: GALNT14 expression was higher in both commercial and PDX cell lines that were known to be more prone for chemoresistance and invasiveness. The highest quartile of patients based on GALNT14 overexpression had 40% OS and 25% EFS, compared to 80% (p=0.002) and 75% (p&lt;0.001) for the lowest quartile of expression, respectively.

Summary: GALNT14 shows promise as a predictive marker of chemoresistance and metastasis for pediatric osteosarcoma. Future functional genomic studies through gain and loss-of-function assays will evaluate the role of GALNT14 in osteosarcoma chemoresistance and metastatic potential.

Citation Format: Zachary D. Prudowsky, Tajhal Patel, Kimal Rajapakshe, Christian Coarfa, Ryan Shuck, Nino Rainusso, Jason Yustein. The role of GALNT14 in chemoresistant and metastatic osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 405.

Early detection of myocardial changes with and without dexrazoxane using serial magnetic resonance imaging in a pre-clinical mouse model

Background

Cancer therapy-related cardiac dysfunction may occur in pediatric cancer survivors. Identification of early markers of myocardial damage secondary to anthracycline exposure is crucial to develop strategies that may ameliorate this complication.

Objectives

The purpose of this study was to identify early myocardial changes induced by doxorubicin with and without cardioprotection using dexrazoxane detected by serial cardiac magnetic resonance imaging (CMR) in a pre-clinical mouse model.

Methods

Serial CMR examinations were performed in 90 mice distributed in 3 groups: 45 received doxorubicin (DOX group), 30 mice received doxorubicin with dexrazoxane (DOX/DEX group) and 15 mice received saline injections (control group). We obtained the following CMR parameters in all mice: T2, extracellular volume quantification (ECV), myocardial deformation, and functional quantification.

Results

Myocardial edema assessed by T2 time was the earliest parameter demonstrating evidence of myocardial injury, most notable in the DOX group at week 4 and 8 compared with DOX/DEX group. Similarly, global longitudinal strain was abnormal in both the DOX and DOX/DEX groups. However, this change persisted only in the DOX group. The ECV was significantly elevated in the DOX group at the final CMR, while only minimally elevated in the DOX/DEX group. The right and left ejection fraction was decreased, along with the mass to volume ratio in the DOX group. The T2 time, ECV, and deformation correlated with ejection fraction and left ventricular volume.

Conclusions

T2 time and deformation by CMR identifies early myocardial injury from anthracyclines. Dexrazoxne did not prevent the initial edema, but the inflammatory changes were not sustained. CMR may be useful for early detection of cardiac dysfunction. Serial CMR demonstrates dexrazoxane minimizes cardiac dysfunction and aids recovery in a mouse model.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40959-021-00109-8.

Targeting PAK4 Inhibits Ras-Mediated Signaling and Multiple Oncogenic Pathways in High-Risk Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most prevalent pediatric soft-tissue sarcoma. Multimodal treatment, including surgery and traditional chemotherapy with radiotherapy, has contributed to improvements in overall survival rates. However, patients with recurrent or metastatic disease have 5-year survival rates of less than 30%. One reason for the lack of therapeutic advancement is identification and targeting of critical signaling nodes. p21-activated kinases (PAK) are a family of serine/threonine kinases downstream of multiple critical tumorigenic receptor tyrosine kinase receptors and oncogenic regulators, including IGFR and RAS signaling, that significantly contribute to aggressive malignant phenotypes. Here, we report that RMS cell lines and tumors exhibit enhanced PAK4 expression levels and activity, which are further activated by growth factors involved in RMS development. Molecular perturbation of PAK4 in multiple RMS models in vitro and in vivo resulted in inhibition of RMS development and progression. Fusion-positive and -negative RMS models were sensitive to two PAK4 small-molecule inhibitors, PF-3758309 and KPT-9274, which elicited significant antitumor and antimetastatic potential in several primary and metastatic in vivo models, including a relapsed RMS patient-derived xenograft model. Transcriptomic analysis of PAK4-targeted tumors revealed inhibition of the RAS-GTPase, Hedgehog, and Notch pathways, along with evidence of activation of antitumor immune response signatures. This PAK4-targeting gene signature showed prognostic significance for patients with sarcoma. Overall, our results show for the first time that PAK4 is a novel and viable therapeutic target for the treatment of high-risk RMS. SIGNIFICANCE: These data demonstrate a novel oncogenic role for PAK4 in rhabdomyosarcoma and show that targeting PAK4 activity is a promising viable therapeutic option for advanced rhabdomyosarcoma.

Tegavivint and the β-Catenin/ALDH Axis in Chemotherapy-Resistant and Metastatic Osteosarcoma

BACKGROUND

The Wnt/β-catenin pathway is closely associated with osteosarcoma (OS) development and metastatic progression. We investigated the antitumor activity of Tegavivint, a novel β-catenin/transducin β-like protein 1 (TBL1) inhibitor, against OS employing in vitro, ex vivo, and in vivo cell line and patient-derived xenograft (PDX) models that recapitulate high risk disease.

METHODS

The antitumor efficacy of Tegavivint was evaluated in vitro using established OS and PDX-derived cell lines. Use of an ex vivo three-dimensional pulmonary metastasis assay assessed targeting of β-catenin activity during micro- and macrometastatic development. The in vivo activity of Tegavivint was evaluated using chemoresistant and metastatic OS PDX models. Gene and protein expression were quantified by quantitative Reverse transcription polymerase chain reaction or immunoblot analysis. Bone integrity was determined via microCT. All statistical tests were two-sided.

RESULTS

Tegavivint exhibited antiproliferative activity against OS cells in vitro and actively reduced micro- and macrometastatic development ex vivo. Multiple OS PDX tumors (n = 3), including paired patient primary and lung metastatic tumors with inherent chemoresistance, were suppressed by Tegavivint in vivo. We identified that metastatic lung OS cell lines (n = 2) exhibited increased stem cell signatures, including enhanced concomitant aldehyde dehydrogenase (ALDH1) and β-catenin expression and downstream activity, which were suppressed by Tegavivint (ALDH1: control group, mean relative mRNA expression = 1.00, 95% confidence interval [CI] = 0.68 to 1.22 vs Tegavivint group, mean = 0.011, 95% CI = 0.0012 to 0.056, P < .001; β-catenin: control group, mean relative mRNA expression = 1.00, 95% CI = 0.71 to 1.36 vs Tegavivint group, mean = 0.45, 95% CI = 0.36 to 0.52, P < .001). ALDH1high PDX-derived lung OS cells, which demonstrated enhanced metastatic potential compared with ALDHlow cells in vivo, were sensitive to Tegavivint. Toxicity studies revealed decreased bone density in male Tegavivint-treated mice (n = 4 mice per group).

CONCLUSIONS

Tegavivint is a promising therapeutic agent for advanced stages of OS via its targeting of the β-catenin/ALDH1 axis.

Risk factors associated with delayed methotrexate clearance and increased toxicity in pediatric patients with osteosarcoma

High-dose methotrexate (HD-MTX; 12 g/m² ) is part of standard therapy for pediatric osteosarcoma (OS). Risk factors associated with MTX toxicity in children with OS are not well defined. We investigated the association between peak MTX levels (four-hour) and delayed MTX clearance or treatment toxicity. Information was retrieved from electronic medical records of 33 OS patients treated with HD-MTX at Texas Children's Hospital from 2008 to 2015. We found that the four-hour MTX level did not contribute to toxicity or delayed MTX clearance. We demonstrated that certain demographic characteristics are associated with delayed clearance and increased toxicity.

Neuroblastoma of the Bone and Bone Marrow Without an Apparent Primary Site: Report of 4 Cases With Long-term Follow-up

Children with neuroblastoma rarely present with metastatic disease without identifiable primary tumors. We describe the clinical and histopathologic characteristics of 4 patients aged 1, 7, 7, and 11 years with neuroblastoma involving bone or bone marrow without an apparent primary site. One patient presented with a periorbital bone lesion, 1 presented with a distal femoral lesion, and 2 presented with diffuse bone marrow involvement. All tumors were negative for MYCN amplification. All patients were alive without evidence of disease 5 years after completion of multimodality therapy. Patients with neuroblastoma of the bone and bone marrow without an apparent primary site may constitute a unique group characterized by older age at diagnosis, nonamplified MYCN tumors, and good response to treatment.

Generation of patient-derived tumor xenografts from percutaneous tumor biopsies in children with bone sarcomas

One of the limitations of performing percutaneous biopsies in patients with bone sarcomas is the small amount of tumor that can be obtained for research purposes. Here, we describe our experience developing patient-derived tumor xenografts (PDXs) using percutaneous tumor biopsies in children with bone sarcomas. We generated 14 bone sarcoma PDXs from percutaneous tumor biopsies. We also developed eight bone sarcoma PDXs from surgical resection of primary bone tumors and pulmonary metastases. A multidisciplinary team approach was critical to establish an accurate diagnosis and to provide adequate tumor samples for PDX generation.

TEM8/ANTXR1-Specific CAR T Cells as a Targeted Therapy for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive disease lacking targeted therapy. In this study, we developed a CAR T cell-based immunotherapeutic strategy to target TEM8, a marker initially defined on endothelial cells in colon tumors that was discovered recently to be upregulated in TNBC. CAR T cells were developed that upon specific recognition of TEM8 secreted immunostimulatory cytokines and killed tumor endothelial cells as well as TEM8-positive TNBC cells. Notably, the TEM8 CAR T cells targeted breast cancer stem-like cells, offsetting the formation of mammospheres relative to nontransduced T cells. Adoptive transfer of TEM8 CAR T cells induced regression of established, localized patient-derived xenograft tumors, as well as lung metastatic TNBC cell line-derived xenograft tumors, by both killing TEM8⁺ TNBC tumor cells and targeting the tumor endothelium to block tumor neovascularization. Our findings offer a preclinical proof of concept for immunotherapeutic targeting of TEM8 as a strategy to treat TNBC.Significance: These findings offer a preclinical proof of concept for immunotherapeutic targeting of an endothelial antigen that is overexpressed in triple-negative breast cancer and the associated tumor vasculature. Cancer Res; 78(2); 489-500. ©2017 AACR.

Metabolic modulation of Ewing sarcoma cells inhibits tumor growth and stem cell properties

Ewing sarcoma (EWS) is a highly aggressive and metabolically active malignant tumor. Metabolic activity can broadly be characterized by features of glycolytic activity and oxidative phosphorylation. We have further characterized metabolic features of EWS cells to identify potential therapeutic targets. EWS cells had significantly more glycolytic activity compared to their non-malignant counterparts. Thus, metabolic inhibitors of glycolysis such as 2-deoxy-D-glucose (2DG) and of the mitochondrial respiratory pathway, such as metformin, were evaluated as potential therapeutic agents against a panel of EWS cell lines in vitro. Results indicate that 2DG alone or in combination with metformin was effective at inducing cell death in EWS cell lines. The predominant mechanism of cell death appears to be through stimulating apoptosis leading into necrosis with concomitant activation of AMPK-α. Furthermore, we demonstrate that the use of metabolic modulators can target putative EWS stem cells, both in vitro and in vivo, and potentially overcome chemotherapeutic resistance in EWS. Based on these data, clinical strategies using drugs targeting tumor cell metabolism present a viable therapeutic modality against EWS.

Abstract B24: Patient-derived tumor xenograft to study cancer stem cells is pediatric sarcomas

Tumor heterogeneity is recognized as an important hallmark in cancer. This characteristic allows cancer cells to evolve in time, to survive radiation and cyotoxic therapies, and to thrive in different organ microenvironments. Therefore, the presence of distinct tumor subpopulations, as mainstay feature of tumor heterogeneity, may play a role in tumor progression and treatment resistance. Patient-derived xenografts (PDXs) have been used to discover the molecular signaling pathways involved in tumorigenesis, metastasis formation and radiation/chemotherapy resistance in different epithelial-adult cancers. Our research interest in pediatric sarcomas is to understand the processes that drive tumor heterogeneity, to isolate and characterize cancer stem cells (CSCs), and to elucidate the mechanisms of chemoresistance using a PDX model.

Pediatric patients with suspected or established diagnosis of sarcoma evaluated at Texas Children's Hospital signed an informed consent to provide tumor samples for subcutaneous implantation of tumor explants in the flank of nonobese diabetic severe combined immunodeficient gamma (NSG) mice. Tumor explants were implanted on the same day of collection when was possible. First and subsequent PDX generations were harvested for tumor propagation, tumor histology, tumor cell karyotyping , RNA/DNA extraction for genetic studies and fluorescent activated cell sorting (FACS) analysis for ALDH, CD133, EphA2 and CD47.

Forty-six tumor samples have been collected since June 2013. Half of tumor samples (n=21) corresponded to osteosarcoma patients and 59% of all tumor specimens were obtained at the time of the initial biopsy. Approximately 66% of biopsies have been performed by Interventional Radiology in our institution. All PDXs maintained the same histological characteristics that original tumors, and also presented specific genetic translocations associated with the different sarcoma types. Chemotherapy resistant and very aggressive tumors (metastatic) had short tumor latency and generate tumors in all transplanted mice. We did not observe the formation of metastases (lungs or liver) in any of the transplanted PDX mice.

PDXs significantly increased the amount of tumor material necessary to perform cell culture under stem-like cell conditions and to analyze the expression of CSC markers by FACS. These studies would be very difficult to perform directly from patient tumor biopsies. All tumors harvested (n=15) contained 2-9% of ALDH Hi or stem-like cells. None of the PDXs analyzed expressed CD133 but synovial sarcoma. We found that &gt;90% of sarcoma cells expressed CD47 and EphA2 at different intensity levels. Whole genome sequencing of different tumor cell subpopulations and limiting dilution experiments to validate the presence of CSCs are ongoing.

Core needle biopsies would represent the most common source to obtain tumor specimens before treatment in pediatric sarcomas. The development of PDXs allows the propagation of tumor cell subpopulations, including CSCs, without the biological changes impose by cell culture. PDXs resemble the original tumor and constitute a powerful tool to study tumor heterogeneity. We plan to perform orthotopic transplantation and tail vein injection of PDX cells in an attempt to develop a PDX model of metastatic disease in pediatric sarcomas.

Citation Format: Nino Rainusso, Jose Hernandez, Rex Marco, Sanjeev Vasudevan, Norma Quintanilla, John Hicks, Wendy Allen-Rhoades, Matteo Trucco, Jason Yustein. Patient-derived tumor xenograft to study cancer stem cells is pediatric sarcomas. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr B24.

Abstract 2312: TEM8/ANTXR1 specific T cells co-target tumor stem cells and tumor vasculature in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with no approved targeted therapies. Tumor endothelial marker 8 (TEM8), initially identified as a marker of tumor endothelial cells in colorectal cancer and other solid tumors has recently been shown to be upregulated in TNBC and breast cancer stem cells (BCSCs). We investigated whether TEM8 specific chimeric antigen receptor (CAR) T cells recognize and kill both tumor endothelial cells as well as TNBC tumor cells. TEM8 specific CAR molecules were generated using single chain variable fragment derived from the monoclonal antibody, L2. L2 CAR T cells selectively recognized TEM8, secreted immunostimulatory cytokines and effectively killed both TEM8 positive TNBC and tumor endothelial cell lines. Moreover, L2 CAR T cells targeted breast cancer stem cells significantly reducing the number of mammospheres relative to non-transduced T cells. In vivo, adoptive transfer of L2 CAR T cells induced regression of established vascularized TNBC xenografts. Hence, TEM8 may serve as an attractive target for immunotherapy of TNBC.

Citation Format: Tiara Byrd, Kristen Fousek, Antonella Pignata, Christopher Szot, Kevin Bielamowicz, Steven Seaman, Daniel Landi, Nino Rainusso, Poul Sorensen, Joachim Koch, Winfried Wels, Bradley Fletcher, Meenakshi Hegde, Brad St Croix, Nabil Ahmed. TEM8/ANTXR1 specific T cells co-target tumor stem cells and tumor vasculature in triple-negative breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2312.

Human Epidermal Growth Factor Receptor 2 (HER2) -Specific Chimeric Antigen Receptor-Modified T Cells for the Immunotherapy of HER2-Positive Sarcoma

PURPOSE

The outcome for patients with metastatic or recurrent sarcoma remains poor. Adoptive therapy with tumor-directed T cells is an attractive therapeutic option but has never been evaluated in sarcoma.

PATIENTS AND METHODS

We conducted a phase I/II clinical study in which patients with recurrent/refractory human epidermal growth factor receptor 2 (HER2) -positive sarcoma received escalating doses (1 × 10(4)/m(2) to 1 × 10(8)/m(2)) of T cells expressing an HER2-specific chimeric antigen receptor with a CD28.ζ signaling domain (HER2-CAR T cells).

RESULTS

We enrolled 19 patients with HER2-positive tumors (16 osteosarcomas, one Ewing sarcoma, one primitive neuroectodermal tumor, and one desmoplastic small round cell tumor). HER2-CAR T-cell infusions were well tolerated with no dose-limiting toxicity. At dose level 3 (1 × 10(5)/m(2)) and above, we detected HER2-CAR T cells 3 hours after infusion by quantitative polymerase chain reaction in 14 of 16 patients. HER2-CAR T cells persisted for at least 6 weeks in seven of the nine evaluable patients who received greater than 1 × 10(6)/m(2) HER2-CAR T cells (P = .005). HER2-CAR T cells were detected at tumor sites of two of two patients examined. Of 17 evaluable patients, four had stable disease for 12 weeks to 14 months. Three of these patients had their tumor removed, with one showing ≥ 90% necrosis. The median overall survival of all 19 infused patients was 10.3 months (range, 5.1 to 29.1 months).

CONCLUSION

This first evaluation of the safety and efficacy of HER2-CAR T cells in patients with cancer shows the cells can persist for 6 weeks without evident toxicities, setting the stage for studies that combine HER2-CAR T cells with other immunomodulatory approaches to enhance their expansion and persistence.

Cross-species identification of a plasma microRNA signature for detection, therapeutic monitoring, and prognosis in osteosarcoma

Osteosarcoma (OS) is the primary bone tumor in children and young adults. Currently, there are no reliable, noninvasive biologic markers to detect the presence or progression of disease, assess therapy response, or provide upfront prognostic insights. MicroRNAs (miRNAs) are evolutionarily conserved, stable, small noncoding RNA molecules that are key posttranscriptional regulators and are ideal candidates for circulating biomarker development due to their stability in plasma, ease of isolation, and the unique expressions associated with specific disease states. Using a qPCR-based platform that analyzes more than 750 miRNAs, we analyzed control and diseased-associated plasma from a genetically engineered mouse model of OS to identify a profile of four plasma miRNAs. Subsequent analysis of 40 human patient samples corroborated these results. We also identified disease-specific endogenous reference plasma miRNAs for mouse and human studies. Specifically, we observed plasma miR-205-5p was decreased 2.68-fold in mice with OS compared to control mice, whereas, miR-214, and miR-335-5p were increased 2.37- and 2.69-fold, respectively. In human samples, the same profile was seen with miR-205-5p decreased 1.75-fold in patients with OS, whereas miR-574-3p, miR-214, and miR-335-5p were increased 3.16-, 8.31- and 2.52-fold, respectively, compared to healthy controls. Furthermore, low plasma levels of miR-214 in metastatic patients at time of diagnosis conveyed a significantly better overall survival. This is the first study to identify plasma miRNAs that could be used to prospectively identify disease, potentially monitor therapeutic efficacy and have prognostic implications for OS patients.

The adolescent and young adult with cancer: state of the art -- bone tumors

Primary malignant bone tumors in the pediatric to young adult populations are relatively uncommon and account for about 6 % of all cancers in those less than 20 years old [1] and 3 % of all cancers in adolescents and young adults (AYA) within the age range of 15 to 29 years [2]. Osteosarcoma (OS) and Ewing's sarcoma (ES) comprise the majority of malignant bone tumors. The approach to treatment for both tumors consists of local control measures (surgery or radiation) as well as systemic therapy with high-dose chemotherapy. Despite earlier advances, there have been no substantial improvements in outcomes over the past several decades, particularly for patients with metastatic disease. This review summarizes the major advances in the treatment of OS and ES and the standard therapies available today, current active clinical trials, and areas of investigation into molecularly targeted therapies.

The adolescent and young adult with cancer: state of the art -- bone tumors

Primary malignant bone tumors in the pediatric to young adult populations are relatively uncommon and account for about 6 % of all cancers in those less than 20 years old [1] and 3 % of all cancers in adolescents and young adults (AYA) within the age range of 15 to 29 years [2]. Osteosarcoma (OS) and Ewing's sarcoma (ES) comprise the majority of malignant bone tumors. The approach to treatment for both tumors consists of local control measures (surgery or radiation) as well as systemic therapy with high-dose chemotherapy. Despite earlier advances, there have been no substantial improvements in outcomes over the past several decades, particularly for patients with metastatic disease. This review summarizes the major advances in the treatment of OS and ES and the standard therapies available today, current active clinical trials, and areas of investigation into molecularly targeted therapies.

Abstract C80: Characterization of metastatic cancer stem cells in osteosarcoma

Pulmonary metastasis is the leading cause of death in osteosarcoma (OS), the most common malignant bone tumor in children and young adults. The molecular mechanisms that regulate the formation of metastases in OS remain mostly unknown. A subset of cancer stem cells (CSCs) with metastatic potential has been identified in breast, colon and pancreatic cancers. Therefore, we hypothesize that CSCs drive the metastatic process in OS by their ability to migrate, adapt to a different microenvironment, and subsequently generate distal metastatic lesions in the lungs. Using a novel mutant p53 mouse model of metastatic OS, which has been developed in Dr. Jason Yustein's laboratory, we have identified putative OS CSCs in primary bone tumors and metastatic lesions.

Cancer stem cells have been cultured from solid tumors growing as sphere-like structures under serum-free conditions. This method has been validated as a surrogate of their self-renewal capacity. We have observed that murine tumor cells obtained from both primary bone tumors and pulmonary nodules developed sarcospheres. Notably, sarcophere-forming efficiency was significantly increased (2-3 times) in tumor cells obtained from metastatic lesions.

Aldehyde dehydrogenase 1 (ALDH1) activity has been used as a functional stem cell marker to isolate CSCs in numerous solid tumors. We have found that both primary bone tumors and metastatic pulmonary nodules contain ALDH Hi (stem-like cells). The high expression of ALDH1 in murine OS tumors ranged from 0.7 to 17%. Further analysis of derived cell lines generated from primary OS tumor, circulating tumor cells (CTCs) and metastatic tumors showed that distal metastases have 4-5 times more ALDH Hi cells than CTCs and up to 10 times more ALDH Hi cells than the primary bone tumors. The isolation of OS CSCs by fluorescent activated cell sorting (FACS) facilitates the analysis of the molecular pathways and biological process that regulates this tumor cell compartment. Our initial data has shown that the Insulin-like Growth Factor (IGF) family members were differentially expressed between OS primary and metastatic cells. Furthermore, we are actively utilizing these mouse derived cell lines to perform orthotopic transplants in immunocompetent (syngeneic) mice aiming to better understand the biology and genetics of CSCs in OS. Subsequent studies will be performed to determine the functional significance of the unique OS CSC genetic alterations.

In summary, we have identified putative metastatic OS CSCc in a mutant p53 mouse model of metastatic OS. Our preliminary data has shown that CSC content seems to be increased in metastases. Our studies using an OS mouse model that parallels the biological behavior of human disease in addition to provide freshly isolated tumor specimens constitute a strong pre-clinical model to test the effect of novel anti-cancer therapies in the CSC compartment.

Citation Format: Nino Rainusso, Lyazat Kurenbekova, Lawrence Donehower, Jeffrey Rosen, Jason Yustein. Characterization of metastatic cancer stem cells in osteosarcoma. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C80.

Identification and gene expression profiling of tumor-initiating cells isolated from human osteosarcoma cell lines in an orthotopic mouse model

In the cancer stem cell model a cell hierarchy has been suggested as an explanation for intratumoral heterogeneity and tumor formation is thought to be driven by this tumor cell subpopulation. The identification of cancer stem cells in osteosarcoma (OS) and the biological processes dysregulated in this cell subpopulation, also known as tumor-initiating cells (TICs), may provide new therapeutic targets. The goal of this study, therefore, was to identify and characterize the gene expression profiles of TICs isolated from human OS cell lines. We analyzed the self-renewal capacity of OS cell lines and primary OS tumors based upon their ability to form sphere-like structures (sarcospheres) under serum-starving conditions. TICs were identify from OS cell lines using the long-term label retention dye PKH26. OS TICs and the bulk of tumor cells were isolated and used to assess their ability to initiate tumors in NOD/SCID mice. Gene expression profiles of OS TICs were obtained from fresh orthotopic tumor samples. We observed that increased sarcosphere efficiency correlated with an enhanced tumorigenic potential in OS. PKH26Hi cells were shown to constitute OS TICs based upon their capacity to form more sarcospheres, as well as to generate both primary bone tumors and lung metastases efficiently in NOD/SCID mice. Genomic profiling of OS TICs revealed that both bone development and cell migration processes were dysregulated in this tumor cell subpopulation. PKH26 labeling represents a valuable tool to identify OS TICs and gene expression analysis of this tumor cell compartment may identify potential therapeutic targets.