Biological Role and Clinical Implications of MYOD1L122R Mutation in Rhabdomyosarcoma

Major progress in recent decades has furthered our clinical and biological understanding of rhabdomyosarcoma (RMS) with improved stratification for treatment based on risk factors. Clinical risk factors alone were used to stratify patients for treatment in the European Pediatric Soft Tissue Sarcoma Study Group (EpSSG) RMS 2005 protocol. The current EpSSG overarching study for children and adults with frontline and relapsed rhabdomyosarcoma (FaR-RMS NCT04625907) includes FOXO1 fusion gene status in place of histology as a risk factor. Additional molecular features of significance have recently been recognized, including the MYOD1L122R gene mutation. Here, we review biological information showing that MYOD1L122R blocks cell differentiation and has a MYC-like activity that enhances tumorigenesis and is linked to an aggressive cellular phenotype. MYOD1L122R mutations can be found together with mutations in other genes, such as PIK3CA, as potentially cooperating events. Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, ten publications in the clinical literature involving 72 cases were reviewed. MYOD1L122R mutation in RMS can occur in both adults and children and is frequent in sclerosing/spindle cell histology, although it is also significantly reported in a subset of embryonal RMS. MYOD1L122R mutated tumors most frequently arise in the head and neck and extremities and are associated with poor outcome, raising the issue of how to use MYOD1L122R in risk stratification and how to treat these patients most effectively

Chemosensitivity profiling of osteosarcoma tumour cell lines identifies a model of BRCAness

Osteosarcoma (OS) is an aggressive sarcoma, where novel treatment approaches are required. Genomic studies suggest that a subset of OS, including OS tumour cell lines (TCLs), exhibit genomic loss of heterozygosity (LOH) patterns reminiscent of BRCA1 or BRCA2 mutant tumours. This raises the possibility that PARP inhibitors (PARPi), used to treat BRCA1/2 mutant cancers, could be used to target OS. Using high-throughput drug sensitivity screening we generated chemosensitivity profiles for 79 small molecule inhibitors, including three clinical PARPi. Drug screening was performed in 88 tumour cell lines, including 18 OS TCLs. This identified known sensitivity effects in OS TCLs, such as sensitivity to FGFR inhibitors. When compared to BRCA1/2 mutant TCLs, OS TCLs, with the exception of LM7, were PARPi resistant, including those with previously determined BRCAness LoH profiles. Post-screen validation experiments confirmed PARPi sensitivity in LM7 cells as well as a defect in the ability to form nuclear RAD51 foci in response to DNA damage. LM7 provides one OS model for the study of PARPi sensitivity through a potential defect in RAD51-mediated DNA repair. The drug sensitivity dataset we generated in 88 TCLs could also serve as a resource for the study of drug sensitivity effects in OS

The long non-coding RNA MYCNOS-01 regulates MYCN protein levels and affects growth of MYCN-amplified rhabdomyosarcoma and neuroblastoma cells

BACKGROUND: MYCN is amplified in small cell lung cancers and several pediatric tumors, including alveolar rhabdomyosarcomas and neuroblastomas. MYCN protein is known to play a key oncogenic role in both alveolar rhabdomyosarcomas and neuroblastomas. MYCN opposite strand (MYCNOS) is a gene located on the antisense strand to MYCN that encodes alternatively spliced transcripts, two of which (MYCNOS-01 and MYCNOS-02) are known to be expressed in neuroblastoma and small cell lung cancer with reciprocal regulation between MYCNOS-02 and MYCN reported for neuroblastomas. We sought to determine a functional role for MYCNOS-01 in alveolar rhabdomyosarcoma and neuroblastoma cells and identify any associated regulatory effects between MYCN and MYCNOS-01.METHODS: MYCNOS-01, MYCNOS-02 and MYCN expression levels were assessed in alveolar rhabdomyosarcoma and neuroblastoma cell lines and tumor samples from patients using Affymetrix microarray data and quantitative RT-PCR. Following MYCNOS-01 or MYCN siRNA knockdown and MYCNOS-01 overexpression, transcript levels were assayed by quantitative RT-PCR and MYCN protein expression assessed by Western blot and immunofluorescence. Additionally, effects on cell growth, apoptosis and cell cycle profiles were determined by a metabolic assay, caspase activity and flow cytometry, respectively.RESULTS: MYCNOS-01 transcript levels were generally higher in NB and RMS tumor samples and cell lines with MYCN genomic amplification. RNA interference of MYCNOS-01 expression did not alter MYCN transcript levels but decreased MYCN protein levels. Conversely, MYCN reduction increased MYCNOS-01 transcript levels, creating a negative feedback loop on MYCN protein levels. Reduction of MYCNOS-01 or MYCN expression decreased cell growth in MYCN-amplified alveolar rhabdomyosarcoma and neuroblastoma cell lines. This is consistent with MYCNOS-01-mediated regulation of MYCN contributing to the phenotype observed.CONCLUSIONS: An alternative transcript of MYCNOS, MYCNOS-01, post-transcriptionally regulates MYCN levels and affects growth in MYCN-amplified rhabdomyosarcoma and neuroblastoma cells.</p

Aurora A kinase inhibition destabilizes PAX3-FOXO1 and MYCN and synergizes with Navitoclax to induce Rhabdomyosarcoma cell death

The clinically aggressive alveolar rhabdomyosarcoma subtype is characterized by expression of the oncogenic fusion protein PAX3-FOXO1, which is critical for tumorigenesis and cell survival. Here we studied the mechanism of cell death induced by loss of PAX3-FOXO1 expression and identified a novel pharmacological combination therapy that interferes with PAX3-FOXO1 biology at different levels. Depletion of PAX3-FOXO1 in fusion positive (FP)-RMS cells induced intrinsic apoptosis in a NOXA-dependent manner. This was pharmacologically mimicked by the BH3 mimetic navitoclax, identified as a top compound in a screen of 208 targeted compounds. In a parallel approach, and to identify drugs that alter the stability of PAX3-FOXO1 protein, the same drug library was screened and fusion protein levels were directly measured as a read-out. This revealed that inhibition of Aurora kinase A most efficiently negatively affected PAX3-FOXO1 protein levels. Interestingly, this occurred through a novel specific phosphorylation event in and binding to the fusion protein. Aurora kinase A inhibition also destabilized MYCN, which is both a functionally important oncogene and transcriptional target of PAX3-FOXO1. Combined treatment with an Aurora kinase A inhibitor and navitoclax in FP-RMS cell lines and patient-derived xenografts synergistically induced cell death and significantly slowed tumor growth. These studies identify a novel functional interaction of Aurora kinase A with both PAX3-FOXO1 and its effector MYCN, and reveal new opportunities for targeted combination treatment of FP-RMS

Role for the histone demethylase KDM4B in rhabdomyosarcoma via CDK6 and CCNA2: compensation by KDM4A and Apoptotic Response of Targeting Both KDM4B and KDM4A

Histone demethylases are epigenetic modulators that play key roles in regulating gene expression related to many critical cellular functions and are emerging as promising therapeutic targets in a number of tumor types. We previously identified histone demethylase family members as overexpressed in the pediatric sarcoma, rhabdomyosarcoma. Here we show high sensitivity of rhabdomyosarcoma cells to a pan-histone demethylase inhibitor, JIB-04 and identify a key role for the histone demethylase KDM4B in rhabdomyosarcoma cell growth through an RNAi-screening approach. Decreasing KDM4B levels affected cell cycle progression and transcription of G1/S and G2/M checkpoint genes including CDK6 and CCNA2, which are bound by KDM4B in their promoter regions. However, after sustained knockdown of KDM4B, rhabdomyosarcoma cell growth recovered. We show that this can be attributed to acquired molecular compensation via recruitment of KDM4A to the promoter regions of CDK6 and CCNA2 that are otherwise bound by KDM4B. Furthermore, upfront silencing of both KDM4B and KDM4A led to RMS cell apoptosis, not seen by reducing either alone. To circumvent compensation and elicit stronger therapeutic responses, our study supports targeting histone demethylase sub-family proteins through selective poly-pharmacology as a therapeutic approach.</p

Endosialin expression in soft tissue sarcoma as a potential marker of undifferentiated mesenchymal cells

Background: Soft tissue sarcomas are a group of neoplasms with differentiation towards mesenchymal tissue, many of which are aggressive and chemotherapy resistant. Histology and immunoprofiles often overlap with neoplasms of other lineages, and establishing an accurate histopathological diagnosis is crucial for correct management, and therapeutic stratification. The endosialin cell surface glycoprotein is predominantly expressed by stromal fibroblasts and pericytes in epithelial neoplasms; however, tumour cell expression has been reported in small series of sarcomas. Methods: We assessed endosialin expression by immunohistochemistry in a large set of 514 human soft tissue sarcomas. Results: Tumour cell endosialin expression was seen in 89% of undifferentiated pleomorphic sarcomas (104/117), 77% adult fibrosarcomas/spindle cell sarcomas (20/26), 62% synovial sarcomas (37/60), 51% leiomyosarcomas (94/185) and 31% rhabdomyosarcomas (39/126). Conclusions: Endosialin immunohistochemistry has potential to distinguish undifferentiated and poorly differentiated sarcomas from other poorly differentiated, non-mesenchymal neoplasms. A Phase II trial randomising patients with advanced sarcomas to receive chemotherapy with/without an endosialin therapeutic antibody has recently completed enrolment. Endosialin expression could be used to select patients for such clinical trials. Based on our results, patients with undifferentiated pleomorphic sarcoma may be particularly suitable for such a therapeutic approach

Germline and Somatic Genetic Variants in the p53 Pathway Interact to Affect Cancer Risk, Progression, and Drug Responsep53 Pathway SNPs and Mutations Interact to Affect Cancer

Insights into oncogenesis derived from cancer susceptibility loci (SNP) hold the potential to facilitate better cancer management and treatment through precision oncology. However, therapeutic insights have thus far been limited by our current lack of understanding regarding both interactions of these loci with somatic cancer driver mutations and their influence on tumorigenesis. For example, although both germline and somatic genetic variation to the p53 tumor suppressor pathway are known to promote tumorigenesis, little is known about the extent to which such variants cooperate to alter pathway activity. Here we hypothesize that cancer risk-associated germline variants interact with somatic TP53 mutational status to modify cancer risk, progression, and response to therapy. Focusing on a cancer risk SNP (rs78378222) with a well-documented ability to directly influence p53 activity as well as integration of germline datasets relating to cancer susceptibility with tumor data capturing somatically-acquired genetic variation provided supportive evidence for this hypothesis. Integration of germline and somatic genetic data enabled identification of a novel entry point for therapeutic manipulation of p53 activities. A cluster of cancer risk SNPs resulted in increased expression of prosurvival p53 target gene KITLG and attenuation of p53-mediated responses to genotoxic therapies, which were reversed by pharmacologic inhibition of the prosurvival c-KIT signal. Together, our results offer evidence of how cancer susceptibility SNPs can interact with cancer driver genes to affect cancer progression and identify novel combinatorial therapies. SIGNIFICANCE: These results offer evidence of how cancer susceptibility SNPs can interact with cancer driver genes to affect cancer progression and present novel therapeutic targets