Insight into the Etiology of Undifferentiated Soft Tissue Sarcomas from a Novel Mouse Model

Bioinformatics Screen Reveals Gli-Mediated Hedgehog Signaling as an Associated Pathway to Poor Immune Infiltration of Dedifferentiated Liposarcoma

Liposarcomas are the most diagnosed soft tissue sarcoma, with most cases consisting of well-differentiated (WDLPS) or dedifferentiated (DDLPS) histological subtypes. While both tumor subtypes can have clinical recurrence due to incomplete resections, DDLPS often has worse prognosis due to a higher likelihood of metastasis compared to its well-differentiated counterpart. Unfortunately, targeted therapeutic interventions have lagged in sarcoma oncology, making the need for molecular targeted therapies a promising future area of research for this family of malignancies. In this work, previously published data were analyzed to identify differential pathways that may contribute to the dedifferentiation process in liposarcoma. Interestingly, Gli-mediated Hedgehog signaling appeared to be enriched in dedifferentiated adipose progenitor cells and DDLPS tumors, and coincidentally Gli1 is often co-amplified with MDM2 and CDK4, given its genomic proximity along chromosome 12q13-12q15. However, we find that Gli2, but not Gli1, is differentially expressed between WDLPS and DDLPS, with a noticeable co-expression signature between Gli2 and genes involved in ECM remodeling. Additionally, Gli2 co-expression had a noticeable transcriptional signature that could suggest Gli-mediated Hedgehog signaling as an associated pathway contributing to poor immune infiltration in these tumors.

Challenges in modeling EWS-FLI1-driven transgenic mouse model for Ewing sarcoma

EWS-FLI1 is a master regulator of Ewing sarcoma (ES) oncogenesis. Although EWS-FLI1 represents a clear therapeutic target, targeted therapeutic inhibitors are lacking. Scientific literature has indicated accumulating information pertaining to EWS-FLI1 translocation, pathogenesis, function, oncogenic partnerships, and potential clinical relevance. However, attempts to develop EWS-FLI1-driven human-like ES mouse models or in vivo systems ended up with limited success. Establishing such models as preclinical screening tools may accelerate the development of EWS-FLI1 targeted therapeutic inhibitors. This review summarizes the current scenario, which focuses on the limitations, challenges, and possible reasons for past failures in model development and also plausible interim alternatives.

NKX6-1 mediates cancer stem-like properties and regulates sonic hedgehog signaling in leiomyosarcoma

Background

Leiomyosarcoma (LMS), the most common soft tissue sarcoma, exhibits heterogeneous and complex genetic karyotypes with severe chromosomal instability and rearrangement and poor prognosis.

Methods

Clinical variables associated with NKX6-1 were obtained from The Cancer Genome Atlas (TCGA). NKX6-1 mRNA expression was examined in 49 human uterine tissues. The in vitro effects of NXK6-1 in LMS cells were determined by reverse transcriptase PCR, western blotting, colony formation, spheroid formation, and cell viability assays. In vivo tumor growth was evaluated in nude mice.

Results

Using The Cancer Genome Atlas (TCGA) and human uterine tissue datasets, we observed that NKX6-1 expression was associated with poor prognosis and malignant potential in LMS. NKX6-1 enhanced in vitro tumor cell aggressiveness via upregulation of cell proliferation and anchorage-independent growth and promoted in vivo tumor growth. Moreover, overexpression and knockdown of NKX6-1 were associated with upregulation and downregulation, respectively, of stem cell transcription factors, including KLF8, MYC, and CD49F, and affected sphere formation, chemoresistance, NOTCH signaling and Sonic hedgehog (SHH) pathways in human sarcoma cells. Importantly, treatment with an SHH inhibitor (RU-SKI 43) but not a NOTCH inhibitor (DAPT) reduced cell survival in NKX6-1-expressing cancer cells, indicating that an SHH inhibitor could be useful in treating LMS. Finally, using the TCGA dataset, we demonstrated that LMS patients with high expression of NKX6-1 and HHAT, an SHH pathway acyltransferase, had poorer survival outcomes compared to those without.

Conclusions

Our findings indicate that NKX6-1 and HHAT play critical roles in the pathogenesis of LMS and could be promising diagnostic and therapeutic targets for LMS patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00726-6.

Preclinical In Vivo Modeling of Pediatric Sarcoma-Promises and Limitations

Pediatric sarcomas are an extremely heterogeneous group of genetically distinct diseases. Despite the increasing knowledge on their molecular makeup in recent years, true therapeutic advancements are largely lacking and prognosis often remains dim, particularly for relapsed and metastasized patients. Since this is largely due to the lack of suitable model systems as a prerequisite to develop and assess novel therapeutics, we here review the available approaches to model sarcoma in vivo. We focused on genetically engineered and patient-derived mouse models, compared strengths and weaknesses, and finally explored possibilities and limitations to utilize these models to advance both biological understanding as well as clinical diagnosis and therapy.

Sarcoma treatment in the era of molecular medicine

Sarcomas are heterogeneous and clinically challenging soft tissue and bone cancers. Although constituting only 1% of all human malignancies, sarcomas represent the second most common type of solid tumors in children and adolescents and comprise an important group of secondary malignancies. More than 100 histological subtypes have been characterized to date, and many more are being discovered due to molecular profiling. Owing to their mostly aggressive biological behavior, relative rarity, and occurrence at virtually every anatomical site, many sarcoma subtypes are in particular difficult-to-treat categories. Current multimodal treatment concepts combine surgery, polychemotherapy (with/without local hyperthermia), irradiation, immunotherapy, and/or targeted therapeutics. Recent scientific advancements have enabled a more precise molecular characterization of sarcoma subtypes and revealed novel therapeutic targets and prognostic/predictive biomarkers. This review aims at providing a comprehensive overview of the latest advances in the molecular biology of sarcomas and their effects on clinical oncology; it is meant for a broad readership ranging from novices to experts in the field of sarcoma.

Anatomic Origin of Osteochondrogenic Progenitors Impacts Sensitivity to EWS-FLI1-Induced Transformation

Ewing sarcomas predominantly arise in pelvic and stylopod bones (i.e., femur and humerus), likely as a consequence of EWS-FLI1 oncogene-induced transformation of mesenchymal stem/progenitor cells (MSCs). MSCs located in the embryonic superficial zone cells (eSZ) of limbs express anatomically distinct posterior Hox genes. Significantly, high expression of posterior HOXD genes, especially HOXD13, is a hallmark of Ewing sarcoma. These data drove our hypothesis that Hox genes in posterior skeleton MSCs contribute to Ewing sarcoma tumorigenesis. We isolated eSZ cells from stylopod and zeugopod (i.e., tibia/fibula, radius/ulna) bones, from wild-type and Hoxd13 mutant embryos, and tested the impact of EWS-FLI1 transduction on cell proliferation, gene expression, and tumorigenicity. Our data demonstrate that both stylopod and zeugopod eSZ cells tolerate EWS-FLI1 but that stylopod eSZ cells are relatively more susceptible, demonstrating changes in proliferation and gene expression consistent with initiation of malignant transformation. Significantly, loss of Hoxd13 had no impact, showing that it is dispensable for the initiation of EWS-FLI1-induced transformation in mouse MSCs. These findings show that MSCs from anatomically distinct sites are differentially susceptible to EWS-FLI1-induced transformation, supporting the premise that the dominant presentation of Ewing sarcoma in pelvic and stylopod bones is attributable to anatomically-defined differences in MSCs.