Fusion-negative rhabdomyosarcoma 3D organoids to predict effective drug combinations: A proof-of-concept on cell death inducers

Rhabdomyosarcoma (RMS) is the main form of pediatric soft-tissue sarcoma. Its cure rate has not notably improved in the last 20 years following relapse, and the lack of reliable preclinical models has hampered the design of new therapies. This is particularly true for highly heterogeneous fusion-negative RMS (FNRMS). Although methods have been proposed to establish FNRMS organoids, their efficiency remains limited to date, both in terms of derivation rate and ability to accurately mimic the original tumor. Here, we present the development of a next-generation 3D organoid model derived from relapsed adult and pediatric FNRMS. This model preserves the molecular features of the patients' tumors and is expandable for several months in 3D, reinforcing its interest to drug combination screening with longitudinal efficacy monitoring. As a proof-of-concept, we demonstrate its preclinical relevance by reevaluating the therapeutic opportunities of targeting apoptosis in FNRMS from a streamlined approach based on transcriptomic data exploitation.

Conditional generation of free radicals by selective activation of alkoxyamines: towards more effective and less toxic targeting of brain tumors

Brain tumors are an important cause of suffering and death. Glioblastoma are the most frequent primary tumors of the central nervous system in adults. They are associated with a very poor prognosis, since only 10% of GBM patients survive 5 years after diagnosis. Medulloblastoma are the most frequent brain malignancies in childhood; they affect the cerebellum in children under 10 years of age in 75% of cases. The current multimodal treatment comes at the expense of serious and often long-lasting side effects. Herein, we propose the synthesis of a library of novel alkoxyamines as anticancer drug candidates. The most efficient molecule, ALK4, was selected based on its ability to inhibit both survival and migration of GBM and MB cells in 2D cultures and in 3D tumor spheroids. A fluorescent derivative was used to show the early cytosolic accumulation of ALK4 in tumor cells. Spontaneous homolysis of ALK4 led to the release of alkyl radicals, which triggered the generation of reactive oxygen species, fragmentation of the mitochondrial network and ultimately apoptosis. To control its homolytic process, the selected alkoxyamine was bioconjugated to a peptide selectively recognized by matrix metalloproteases. This bioconjugate, named ALK4-MMPp, successfully inhibited survival, proliferation, and invasion of GBM and MB tumor micromasses. We further developed innovative brain and cerebellum organotypic models to monitor treatment response over time. It confirmed that ALK4-MMPp significantly impaired tumor progression, while no significant damage was observed on normal brain tissue. Lastly, we showed that ALK4-MMPp was well-tolerated in vivo by zebrafish embryos. This study provides a new strategy to control the activation of alkoxyamines, and revealed the bioconjugate ALK4-MMPp bioconjugate as a good anticancer drug candidate.

SMAD2/3 mediate oncogenic effects of TGF-β in the absence of SMAD4

TGF-β signaling is involved in pancreatic ductal adenocarcinoma (PDAC) tumorigenesis, representing one of the four major pathways genetically altered in 100% of PDAC cases. TGF-β exerts complex and pleiotropic effects in cancers, notably via the activation of SMAD pathways, predominantly SMAD2/3/4. Though SMAD2 and 3 are rarely mutated in cancers, SMAD4 is lost in about 50% of PDAC, and the role of SMAD2/3 in a SMAD4-null context remains understudied. We herein provide evidence of a SMAD2/3 oncogenic effect in response to TGF-β1 in SMAD4-null human PDAC cancer cells. We report that inactivation of SMAD2/3 in SMAD4-negative PDAC cells compromises TGF-β-driven collective migration mediated by FAK and Rho/Rac signaling. Moreover, RNA-sequencing analyses highlight a TGF-β gene signature related to aggressiveness mediated by SMAD2/3 in the absence of SMAD4. Using a PDAC patient cohort, we reveal that SMAD4-negative tumors with high levels of phospho-SMAD2 are more aggressive and have a poorer prognosis. Thus, loss of SMAD4 tumor suppressive activity in PDAC leads to an oncogenic gain-of-function of SMAD2/3, and to the onset of associated deleterious effects.

In pancreatic ductal adenocarcinoma cells and patient tissue, SMAD2/3 is shown to mediate oncogenic effects of TGF-β in the absence of SMAD4.

Abstract 1671: Engineering new cellular models to decipher H3.3K27M mutation role in DIPGs' resistance to therapies

Among pediatric brain tumors, Diffuse Intrinsic Pontine Gliomas (DIPGs) display a particularly dismal prognosis, highlighted by their median survival lower than one year. Indeed, DIPGs’ location and infiltrative properties preclude their surgical resection. Moreover, DIPGs poorly respond to chemotherapeutic agents. In this context, the only treatment for these tumors remains palliative radiotherapy, systematically followed by tumor progression. In addition to their resistance to therapies, DIPGs are characterized by recurrent histone H3 mutations. The H3.3K27M mutation is the most frequent and results from a heterozygous single nucleotide variant in the H3F3A gene, inducing the lysine 27 substitution by a methionine. Although H3.3K27M’s driver role in DIPGs tumorigenesis is now established, its role in their chemo- and radioresistance remains unclear. Aiming to decipher the potential role of this mutation in pediatric gliomas’ resistance to therapies, we established isogenic cellular models of H3.3K27M induction and reversion.We first induced H3.3K27M mutation in three initially non-mutated supratentorial pediatric glioma cell lines. Thus, we generated models that stably expressed the dominant-negative H3.3K27M or the wild type H3.3 as controls. Complementarily, to study H3.3K27M roles in a DIPG cell context, we also developed H3.3K27M reversion models in two initially mutated DIPG cell lines by applying a gene-editing strategy based on the combinatorial use of the CRISPR/Cas9 technology and an insert.We showed that H3.3K27M induction in Res259 and KNS42 cells conferred a radioresistant phenotype to a fractionated radiotherapy schedule. Besides, we performed a screening of 80 anti-cancer drugs, which revealed a differential impact of the mutation on the drug sensitivity profiles of our three H3.3K27M-induced cell lines. These results indicate that H3.3K27M can control pediatric glioma cells’ resistance to therapies, but in a heterogeneous way depending on the cellular context. Along this line, we are currently characterizing the chemo- and radiotherapy response of our new DIPG H3.3K27M-reversed models. Altogether, our first results support a role for H3.3K27M in pediatric gliomas resistance to treatments, and our complementary models pave the way for identifying new H3.3K27M-dependent mechanisms and promising targets to sensitize DIPGs to therapies.

Citation Format: Andria Rakotomalala, Paul Lewandowski, Quentin Bailleul, Clara Savary, Mélanie Arcicasa, Christine Bal, Maud Hamadou, Paul Huchedé, Audrey Restouin, Remy Castellano, Yves Collette, Audrey Vincent, Pierre-Olivier Angrand, Eric Adriaenssens, Xuefen Le Bourhis, Pierre Leblond, Marie Castets, Eddy Pasquier, Alessandro Furlan, Samuel Meignan. Engineering new cellular models to decipher H3.3K27M mutation role in DIPGs' resistance to therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1671.

Low expression of ANT1 confers oncogenic properties to rhabdomyosarcoma tumor cells by modulating metabolism and death pathways

Rhabdomyosarcoma (RMS) is the most frequent form of pediatric soft-tissue sarcoma. It is divided into two main subtypes: ERMS (embryonal) and ARMS (alveolar). Current treatments are based on chemotherapy, surgery, and radiotherapy. The 5-year survival rate has plateaued at 70% since 2000, despite several clinical trials. RMS cells are thought to derive from the muscle lineage. During development, myogenesis includes the expansion of muscle precursors, the elimination of those in excess by cell death and the differentiation of the remaining ones into myofibers. The notion that these processes may be hijacked by tumor cells to sustain their oncogenic transformation has emerged, with RMS being considered as the dark side of myogenesis. Thus, dissecting myogenic developmental programs could improve our understanding of RMS molecular etiology. We focused herein on ANT1, which is involved in myogenesis and is responsible for genetic disorders associated with muscle degeneration. ANT1 is a mitochondrial protein, which has a dual functionality, as it is involved both in metabolism via the regulation of ATP/ADP release from mitochondria and in regulated cell death as part of the mitochondrial permeability transition pore. Bioinformatics analyses of transcriptomic datasets revealed that ANT1 is expressed at low levels in RMS. Using the CRISPR-Cas9 technology, we showed that reduced ANT1 expression confers selective advantages to RMS cells in terms of proliferation and resistance to stress-induced death. These effects arise notably from an abnormal metabolic switch induced by ANT1 downregulation. Restoration of ANT1 expression using a Tet-On system is sufficient to prime tumor cells to death and to increase their sensitivity to chemotherapy. Based on our results, modulation of ANT1 expression and/or activity appears as an appealing therapeutic approach in RMS management.