Forkhead box class O1 (FOXO1) and fas-associated death domain (FADD) regulate cell death pathways and homeostatic processes such as cell cycle progression and apoptosis. FADD phosphorylation promotes nuclear localization of FOXO1, and FOXO1 regulates FADD expression. Therefore, it is plausible that FOXO1 and FADD have synergistic or antagonistic effects on cell cycle regulation and the response to anticancer drug treatment in cancer cells. In the present study, we report that AS1842856-mediated inhibition of FOXO1 reverses anticancer drug-induced cytotoxicity, while FADD knockdown increases anticancer drug-induced cytotoxicity in osteosarcoma (OS). Reversed anticancer drug-induced cytotoxicity was accompanied by G2/M cell cycle arrest and increased expression of p21. The anticancer function of FOXO1 was further supported by the observation that OS cells that express higher basal levels of FOXO1 had increased sensitivity to camptothecin-induced cytotoxicity. FADD knockdown reversed the FOXO1 inhibition-induced increase in p21 expression. The results presented in this study indicate that FOXO1 has a tumor suppressor function, while FADD has a tumor-promoting function in OS following anticancer drug treatment. The experimental approach used in this investigation also indicates that FADD antagonizes the effect of FOXO1 on p21 expression in OS.

Abstract Osteosarcoma (OS) is the most common primary malignant bone tumor in children with lung metastases representing the leading cause of mortality. Survival rates have remained unchanged for over three decades. Immunotherapy with natural killer (NK) cells has shown limited efficacy in solid tumors including OS. We previously demonstrated that natural killer (NK) cells have anti-tumor activity against OS. However, efficacy was limited due to poor infiltration and proliferation within the immunosuppressive and metabolically hostile tumor microenvironment (TME). Tumor-associated hypoxia and acidosis impair immune cell infiltration and cytolytic function. We hypothesize that metabolic reprogramming of the lung TME can overcome these barriers and enhance NK cell-mediated antitumor activity. We have shown that Pramlintide, an FDA-approved drug for Type I and II diabetes, modulates OS metabolism by reducing glycolytic activity and hypoxia, through decreased HIF1-α expression, and suppresses tumor growth. In this study, we evaluated whether Pramlintideenhances the efficacy of adoptive NK cell therapy against OS. Pramlintide treated CCH-OS-D cells and tumor samples from mice labeled with glucose and glutamine tracers were subjected to ion chromatography mass spectrometry (IC-MS) and metabolic profiling was determined. Mice bearing CCH-OS-D OS tumors were subjected to hyperpolarized pyruvate (HP) MRI to assess in vivo metabolic changes prior to sacrife. We also evaluated the effect of pramlintide on NKG2D ligand expression and intracellular lactate levels across multiple OS cell lines including SJSA, MG63.2, OS17, LM7 and CCH-OS-D. NK cell cytotoxicity was assessed following co-culture with pramlintide-treated tumor cells under both concurrent and pre-treatment conditions. Therapeutic efficacy of the combination pramlintide + NK cells was further assessed in a pilot in vivo CCH-OS-D OS lung metastasis model. Pramlintide treatment resulted in time-dependent increases in intracellular lactate and pyruvate in CCH-OS-D cells in vitro. In vivo, lactate levels measured from tumors were reduced within the TME. Together, these results support a model in which pramlintide limits lactate efflux from tumor cells, leading to reduced extracellular lactate accumulation and consequently a less acidic TME. In addition, pramlintide upregulated NKG2D ligands (MIC A/B, CD155, ULBP1 and ULBP2/5/6) across several OS cell lines. While concurrent treatment did not impair NK cell cytotoxicity, pre-treatment enhanced NK-mediated tumor cell lysis. In vivo, NK cell therapy alone and in combination with pramlintide significantly reduced lung metastases compared to pramlintide monotherapy or untreated control. These findings demonstrate that pramlintide modulates OS tumor metabolism and enhances susceptibility to NK cell-mediated cytotoxicity. Further studies are needed to define the mechanisms underlying these metabolic effects, particularly those related to intracellular lactate accumulation and transport, to optimize NK cell-based immunotherapy strategies. Citation Format: Nancy Gordon, Ariana Anjier, Yan Zheng, Yuanzheng Yang, Valerie Barrera Estrada, Heping Wang, Qing Wang, Jim Bankson, Lin Tan, Bao Tran, Sara Martinez, Eugenie Kleinerman. The anti-diabetic drug Pramlintide modulates osteosarcoma tumor metabolism and improves NK cell therapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Breaking Barriers in the Fight against Rare Cancers; 2026 Jul 18-20; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86(14_Suppl):Abstract nr A008.

Relapsed resectable osteosarcoma carries a dismal prognosis of 30% 12-month post-relapse event-free survival (PREFS-12). Surgery remains the primary therapy for metastatic pulmonary osteosarcoma with the role for adjuvant therapy still undefined. There is an urgent need for effective nontoxic adjuvant therapies to improve PREFS following complete resection of metastases. Viscum album extract (Iscador® P, Iscador AG, Arlesheim, Switzerland) is a fermented aqueous extract manufactured from the leaves, stems, and berries of the white-berried hemiparasitic plant from the European mistletoe (Viscum album L.) grown on pine trees (P = Pini). It is a promising therapeutic antineoplastic agent with preclinical and clinical evidence of benefit in osteosarcoma. This includes a pilot study showing 55% PREFS in 9 pediatric, adolescent and young adult (AYA) patients with a median follow-up of 84 months. Viscum album extract has a long history of use in Europe and a track record of safety in children which allowed for the opening of a Phase II trial in the US to test the efficacy of Viscum album extract to improve PREFS in children and AYAs with relapsed osteosarcoma. Secondary outcomes include effects on quality of life and changes in immune profiling of tumor and serum samples.

Cluster markers for each of the MTL clusters

Document containing supplementary figures

Abstract The RE1 silencing transcription factor (REST) is a driver of sonic hedgehog (SHH) medulloblastoma genesis. Our previous studies showed that REST enhances cell proliferation, metastasis and vascular growth and blocks neuronal differentiation to drive progression of SHH medulloblastoma tumors. Here, we demonstrate that REST promotes autophagy, a pathway that is found to be significantly enriched in human medulloblastoma tumors relative to normal cerebella. In SHH medulloblastoma tumor xenografts, REST elevation is strongly correlated with increased expression of the hypoxia-inducible factor 1-alpha (HIF1α)—a positive regulator of autophagy, and with reduced expression of the von Hippel-Lindau (VHL) tumor suppressor protein – a component of an E3 ligase complex that ubiquitinates HIF1α. Human SHH-medulloblastoma tumors with higher REST expression exhibit nuclear localization of HIF1α, in contrast to its cytoplasmic localization in low-REST tumors. In vitro, REST knockdown promotes an increase in VHL levels and a decrease in cytoplasmic HIF1α protein levels, and autophagy flux. In contrast, REST elevation causes a decline in VHL levels, as well as its interaction with HIF1α, resulting in a reduction in HIF1α ubiquitination and an increase in autophagy flux. These data suggest that REST elevation promotes autophagy in SHH medulloblastoma cells by modulating HIF1α ubiquitination and stability in a VHL-dependent manner. Thus, our study is one of the first to connect VHL to REST-dependent control of autophagy in a subset of medulloblastomas.

Introduction Clinical adoption of NK cell immunotherapy is underway for medulloblastoma and osteosarcoma, however there is currently little feedback on cell fate after administration. We propose magnetic particle imaging (MPI) for the detection, localization, and quantification of VivoTrax-labeled NK cells. Methods Human-derived NK-92 cells were labeled by co-incubation with VivoTrax for 24 hours then the excess nanoparticles were washed with centrifugation. Cytolytic activity of labeled vs. unlabeled NK-92 cells was assessed after 4 hours of co- incubation with medulloblastoma cells (DAOY) or osteosarcoma cells (LM7 or OS17) using bioluminescent or GFP counts. Labeled NK-92 cells at two different doses (0.5 or 1 x 106) were administered to excised mouse brains (cerebellum), tibias, and lungs then imaged by 3D preclinical MPI (MOMENTUM imager) and localized relative to fiducial markers. NK-92 cells were imaged by clinical-scale MPI under development at Magnetic Insight Inc. Results NK-92 cells were labeled with an average of 3.17 pg Fe/cell with no measured effects on cell viability or cytolytic activity against 3 tumor cell lines. MPI signal was directly quantitative with the number of VivoTrax-labeled NK-92 cells, with preclinical limit of detection of 3.1 x 104 cells on MOMENTUM imager. Labeled NK-92 cells could be accurately localized in mouse brains, tibias, and lungs within < 1 mm of stereotactic injection coordinates with preclinical scanner. Feasibility for detection of a clinically relevant dose of 4 x 107 labeled NK-92 cells was demonstrated on clinical-scale MPI. Conclusion MPI can provide sensitive, quantitative, and accurate spatial information on NK cell delivery, showing its potential to resolve a significant unmet clinical need to track NK cell treatments in patients. ### Competing Interest Statement Olivia C. Sehl, Kelvin Guo, Benjamin Fellows, A. Rahman Mohtasebzadeh, Erica E. Mason, Toby Sanders, Petrina Kim, David Trease, Patrick W. Goodwill, and Joan M Greve report relationship with Magnetic Insight Inc. that includes: employment and stock ownership.

Cell cycle score for each cluster in the MTL

Abstract Introduction: Medulloblastoma (MB) is the most common malignant brain tumor in children. It is categorized into four molecular subgroups, each with unique genetic and epigenetic alterations, molecular signatures, and differences in clinical features and treatment responses. Targeted therapy for MB has failed in the clinic, prompting new studies of mechanisms involved in MB tumorigenesis and progression. Experimental Procedure: The transcriptomic information of the MB patients was obtained from the publicly available RNAseq datasets and was analyzed for differential expression and clustering analysis. Patient-derived orthotopic xenografts of medulloblastoma tumors with high- and low-REST expression were histologically and biochemically studied for autophagy markers. Furthermore, the SHH-MB cell lines were studied to get a mechanistic understanding of the REST-driven autophagy in this MB subgroup. Summary: Our data showed that autophagy, a process responsible for cellular recycling, and genes associated with this pathway exhibit distinctive expression patterns in human MB subgroups. Specifically, we demonstrate that autophagy is induced in one of the MB subgroups (Sonic Hedgehog-SHH) in response to elevated expression of the RE1-silencing transcription factor (REST), a transcriptional repressor and a canonical regulator of neuronal differentiation genes. REST is also a driver of SHH-MB metastasis. Pharmacological inhibition of autophagy decreases MB cell growth, suggesting it is a pro-survival pathway in REST-driven SHH MBs. In mechanistic studies, we found REST-dependent autophagy induction to involve upregulation of the hypoxia-inducible factor 1-alpha (HIF1α) due to REST-mediated silencing of the von Hippel-Lindau (VHL) gene. The VHL gene product promotes HIF1α ubiquitination and proteasomal degradation, and its loss in SHH-MBs with elevated REST expression drives HIF1α stabilization and nuclear localization to activate target autophagy-related genes. Conclusion: Our work is the first to link VHL to MB pathology. VHL loss of function in cancers has been mainly attributed to mutational events. Here, we report a novel mechanism of VHL loss, namely its epigenetic silencing by REST. Our findings provide the foundation for future pre-clinical investigations to examine the feasibility of autophagy blockade as a therapeutic strategy for REST-driven SHH MBs. Citation Format: Ashutosh Singh, Donghang Cheng, Jyothishmathi Swaminathan, Yan Zheng, Nancy Gordon, Vidya Gopalakrishnan. Transcriptional repressor REST controls autophagy in Sonic Hedgehog medulloblastoma through the VHL-HIF1α axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2864.

Purpose: The genetic intratumoral heterogeneity observed in human osteosarcomas poses challenges for drug development and the study of cell fate, plasticity, and differentiation, which are processes linked to tumor grade, cell metastasis, and survival.Experimental Design: To pinpoint errors in osteosarcoma differentiation, we transcriptionally profiled 31,527 cells from a tissue-engineered model that directs mesenchymal stem cells toward adipogenic and osteoblastic fates. Incorporating preexisting chondrocyte data, we applied trajectory analysis and non-negative matrix factorization to generate the first human mesenchymal differentiation atlas.Results: This "roadmap" served as a reference to delineate the cellular composition of morphologically complex osteosarcoma tumors and quantify each cell's lineage commitment. Projecting a bulk RNA-sequencing osteosarcoma dataset onto this roadmap unveiled a correlation between a stem-like transcriptomic phenotype and poorer survival outcomes.Conclusions: Our study quantifies osteosarcoma differentiation and lineage, a prerequisite to better understanding lineage-specific differentiation bottlenecks that might someday be targeted therapeutically.

Clinical adoption of NK cell immunotherapy is underway for medulloblastoma and osteosarcoma, however there is currently little feedback on cell fate after administration. We propose magnetic particle imaging (MPI) may have applications for the quantitative detection of NK cells. Human-derived NK-92 cells were labeled by co-incubation with iron oxide nanoparticles (VivoTrax™) for 24 h then excess nanoparticles were washed with centrifugation. Cytolytic activity of labeled versus unlabeled NK-92 cells was assessed after 4 h of co-incubation with medulloblastoma cells (DAOY) or osteosarcoma cells (LM7 or OS17). Labeled NK-92 cells at two different doses (0.5 or 1 × 106) were administered to excised mouse brains (cerebellum), fibulas, and lungs then imaged by 3D preclinical MPI (MOMENTUM™) for detection relative to fiducial markers. NK-92 cells were also imaged by clinical-scale MPI under development at Magnetic Insight Inc. NK-92 cells were labeled with an average of 3.17 pg Fe/cell with no measurable effects on cell viability or cytolytic activity against 3 tumor cell lines. MPI signal was directly quantitative with the number of labeled NK-92 cells, with preclinical limit of detection of 3.1 × 104 cells on MOMENTUM imager. Labeled NK-92 cells could be accurately localized in mouse brains, fibulas, and lungs within < 1 mm of stereotactic injection coordinates with preclinical scanner. Feasibility for detection on a clinical-scale MPI scanner was demonstrated using 4 × 107 labeled NK-92 cells, which is in the range of NK cell doses administered in our previous clinical trial. MPI can provide sensitive, quantitative, and accurate spatial information on NK cells soon after delivery, showing initial promise to address a significant unmet clinical need to track NK cell fate in patients.

Background Single-cell RNA-seq has emerged as an innovative technology used to study complex tissues and characterize cell types, states, and lineages at a single-cell level. Classification of bulk tumors by their individual cellular constituents has also created new opportunities to generate single-cell atlases for many organs, cancers, and developmental models. Despite the tremendous promise of this technology, recent evidence studying epithelial tissues and diverse carcinomas suggests the methods used for tissue processing, cell disaggregation, and preservation can significantly bias gene expression and alter the observed cell types. To determine whether sarcomas – tumors of mesenchymal origin – are subject to the same technical artifacts, we profiled patient-derived tumor explants (PDXs) propagated from three aggressive subtypes: osteosarcoma (OS), Ewing sarcoma (ES), desmoplastic small round cell tumor (DSRCT). Given the rarity of these sarcoma subtypes, we explored whether single-nuclei RNA-seq from more widely available archival frozen specimens could accurately be identified by gene expression signatures linked to tissue phenotype or pathognomonic fusion proteins. Results We systematically assessed dissociation methods across different sarcoma subtypes. We compared gene expression from single-cell and single-nucleus RNA-sequencing of 125,831 whole-cells and nuclei from ES, DSRCT, and OS PDXs. We detected warm dissociation artifacts in single-cell samples and gene length bias in single-nucleus samples. Classic sarcoma gene signatures were observed regardless of the dissociation method. In addition, we showed that dissociation method biases could be computationally corrected. Conclusions We highlighted transcriptional biases, including warm dissociation and gene-length biases, introduced by the dissociation method for various sarcoma subtypes. This work is the first to characterize how the dissociation methods used for sc/snRNA-seq may affect the interpretation of the molecular features in sarcoma PDXs.

Osteosarcoma is a primary malignant bone tumor. Effective chemotherapy regimens for refractory disease are scarce, accounting for no improvement in survival. Immune-based cell therapies have emerged as novel alternatives. However, advancements with these therapies have been seen mostly when immune cells are armed to target specific tumor Ags. Recent studies identified cluster of differentiation 70 (CD70) as a promising target to osteosarcoma particularly because CD70 is highly expressed in osteosarcoma lung metastases (Pahl et al. 2015. Cancer Cell Int. 15: 31), and its overexpression by tumors has been correlated with immune evasion and tumor proliferation (Yang et al. 2007. Blood 110: 2537-2544). However, the limited knowledge of the overall CD70 expression within normal tissues and the potential for off-target effect pose several challenges (Flieswasser et al. 2022. J. Exp. Clin. Cancer Res. 41: 12). Nonetheless, CD70-based clinical trials are currently ongoing and are preliminarily showing promising results for patients with osteosarcoma. The present review sheds light on the recent literature on CD70 as it relates to osteosarcoma and highlights the benefits and challenges of targeting this pathway.

Abstract Background Cure rates for osteosarcoma (OS) have not improved in >30 years and no new effectivetherapies have been identified for metastatic disease. Natural killer (NK) cells have become an attractive tool for cancer immunotherapy. Efficay is improved by direct tumor targeting introducing a specific chimeric antigen receptor (CAR). Emerging knowledge suggests CD70 to be a viable candidate as expression is higher in lung metastases and it has been correlated with tumor escape from immune surveillance. Objective To assess whether using CD70 CAR-NK cells we can enhance trafficking, homing and proliferation of NK cells and therefore therapeutic efficacy against OS. Methods We analyzed the cBioportal database to verify CD70 expression in OS. Surface expression of CD70 on human OS cell lines and normal osteoblasts was determined by flow cytometry. CD70 CAR constructs were sequenced, verified and transduced into NK cells. CD70 CAR NK and control NK cells cytolytic activity against OS cells was evaluated by IncuCyte. In vitro cytokine release was measured upon CD70 CAR NK/NK cells exposure to OS cells (IsoPlexis). Results Database analysis confirmed OS CD70 gene amplification. Flow cytometry showed variable expression of CD70 on OS cells and no expression on human osteoblasts. There was an increase in CD70 CAR NK percent lysis against OS cells at the highest effector:target ratios compared to control NK cells. We found a predominant release in the chemoattractive/stimulatory cytokines upon OS cells exposure to CD70 CAR NK cells. Conclusion CD70 has immunotherapy potential against OS. CD70 CAR NK cells have increased cytolytic activity against OS cells in vitro. Cytolytic activity may be influenced by the release of specific cytokines.