Aberrant activation of the Hedgehog (Hh) signalling pathway is known to play an oncogenic role in a wide range of cancers; in the particular case of rhabdomyosarcoma, this pathway has been demonstrated to be an important player for both oncogenesis and cancer progression. In this review, after a brief description of the pathway and the characteristics of its molecular components, we describe, in detail, the main activation mechanisms that have been found in cancer, including ligand-dependent, ligand-independent and non-canonical activation. In this context, the most studied inhibitors, i.e., SMO inhibitors, have shown encouraging results for the treatment of basal cell carcinoma and medulloblastoma, both tumour types often associated with mutations that lead to the activation of the pathway. Conversely, SMO inhibitors have not fulfilled expectations in tumours—among them sarcomas—mostly associated with ligand-dependent Hh pathway activation. Despite the controversy existing regarding the results obtained with SMO inhibitors in these types of tumours, several compounds have been (or are currently being) evaluated in sarcoma patients. Finally, we discuss some of the reasons that could explain why, in some cases, encouraging preclinical data turned into disappointing results in the clinical setting.

The identification of novel therapeutic targets for specific cancer molecular subtypes is crucial for the development of precision oncology. In the last few years, CRISPR/Cas9 screens have accelerated the discovery and validation of new targets associated with different tumor types, mutations, and fusions. However, there are still many cancer vulnerabilities associated with specific molecular features that remain to be explored. Here, we used data from CRISPR/Cas9 screens in 954 cancer cell lines to identify gene dependencies associated with 16 common cancer genomic amplifications. We found that high-copy-number genomic amplifications generate multiple collateral dependencies within the amplified region in most cases. Further, to prioritize candidate targets for each chromosomal region amplified, we integrated gene dependency parameters with both druggability data and subcellular location. Finally, analysis of the relationship between gene expression and gene dependency led to the identification of genes, the expression of which may constitute predictive biomarkers of dependency. In conclusion, our study provides a set of druggable targets specific for each amplification, opening the possibility to specifically target amplified tumors on this basis.

Background: Rhabdomyosarcoma (RMS), such as other childhood tumors, has witnessed treatment advancements in recent years. However, high-risk patients continue to face poor survival rates, often attributed to the presence of the PAX3/7-FOXO1 fusion proteins, which has been associated with metastasis and treatment resistance. Despite efforts to directly target these chimeric proteins, clinical success remains elusive. In this study, the main aim was to address this challenge by investigating regulators of FOXO1. Specifically, we focused on TRIB3, a potential regulator of the fusion protein in RMS. Methods: TRIB3 expression was examined through the analysis of patient datasets, including gene expression profiling and gene set enrichment analyses. In cell lines, the DepMap dataset for RMS was utilized alongside Western blot analysis to assess TRIB3 expression. The functional significance of TRIB3 in RMS was assessed through constitutive and inducible shRNA-mediated knockdowns. Subsequent in vitro and in vivo analyses, including orthotopic tumor models in immune-compromised mice, were conducted to delineate the role and underlying molecular mechanisms exerted by TRIB3 in RMS Results: Our findings revealed a prominent TRIB3 expression in RMS tumors, highlighting its correlation with several clinical features. By conducting TRIB3 genetic inhibition experiments, we observed an impairment on cell proliferation. Notably, the knockdown of TRIB3 led to a decrease in PAX3-FOXO1 and its target genes at protein level, accompanied by a reduction in the activity of the Akt signaling pathway. Furthermore, TRIB3 influenced posttranslational modifications, such as phosphorylation together with proteasomal degradation of PAX3-FOXO1 protein. Additionally, inducible silencing of TRIB3 significantly delayed tumor growth and improved overall survival in vivo . Conclusions: Based on our comprehensive analysis, we propose that TRIB3 holds therapeutic potential for treating the most aggressive subtype of RMS. The findings herein reported contribute to our understanding of the underlying molecular mechanisms driving RMS progression and provide novel insights into the potential use of TRIB3 as a therapeutic intervention for high-risk RMS patients.

Targeting MDM2-p53 interaction to enhance p53 activity represents a promising antitumoral strategy for p53 wild-type pediatric tumors, including soft-tissue sarcomas. However, results from early-phase clinical trials in hematological and solid cancers have shown limited efficacy of MDM2 inhibitors, underscoring the necessity to explore more effective combinations with other agents. In this study, we provide results from a 22-drug combination screening demonstrating the therapeutic potential of combining siremadlin (MDM2 inhibitor) and olaparib (PARP inhibitor) for treating p53 wild-type rhabdomyosarcoma (p53 WT RMS). Cell survival, cell death, and apoptosis analysis revealed synergistic effects of combining siremadlin plus olaparib in vitro . The combination of both drugs led to a significant increase in p53 activity, as evidenced by p53 accumulation and K382 acetylation, along with an increased expression of bona fide p53 targets. Furthermore, treatment with both drugs resulted in significant reduction of tumor growth and increased mice overall survival when compared to single treatments and control in cell line-derived orthotopic xenograft models. Overall, our study demonstrates, for the first time, the synergistic effect of combining siremadlin plus olaparib in inhibiting p53 WT RMS tumor growth in vitro and in vivo . Our findings support the potential to study the combination of both drugs in clinical trials and warrants further investigation in other tumors with similar molecular features.

The identification of novel therapeutic targets for specific cancer molecular subtypes is crucial for the development of precision oncology. In the last years, CRISPR/Cas9 screens have accelerated the discovery and validation of new targets associated with different tumor types, mutations or fusions. However, there are still many cancer vulnerabilities associated with specific molecular features that remain to be explored. Here we used data from CRISPR/Cas9 screens in 954 cancer cell lines to identify gene dependencies associated with 16 common cancer genomic amplifications. We found that high-copy number genomic amplifications generate multiple collateral dependencies within the amplified region in 94% of cases. Further, to prioritize candidate targets for each chromosomal region amplified, we integrated gene dependency parameters with both druggability data and subcellular location. Finally, analysis of the relationship between gene expression and gene dependency leads to the identification of genes, the expression of which may constitute predictive biomarkers of dependency.