Myxoid liposarcoma and the mammalian target of rapamycin pathway

Crosstalk between Macrophages and Myxoid Liposarcoma Cells Increases Spreading and Invasiveness of Tumor Cells

Myxoid liposarcoma (MLPS) is the second most common subtype of liposarcoma and has tendency to metastasize to soft tissues. To date, the mechanisms of invasion and metastasis of MLPS remain unclear, and new therapeutic strategies that improve patients' outcomes are expected. In this study, we analyzed by immunohistochemistry the immune cellular components and microvessel density in tumor tissues from patients affected by MLPS. In order to evaluate the effects of primary human MLPS cells on macrophage polarization and, in turn, the ability of macrophages to influence invasiveness of MLPS cells, non-contact and 3D organotypic co-cultures were set up. High grade MLPS tissues were found heavily vascularized, exhibited a CD3, CD4, and CD8 positive T lymphocyte-poor phenotype and were massively infiltrated by CD163 positive M2-like macrophages. Conversely, low grade MLPS tissues were infiltrated by a discrete amount of CD3, CD4, and CD8 positive T lymphocytes and a scarce amount of CD163 positive macrophages. Kaplan-Meier analysis revealed a shorter Progression Free Survival in MLPS patients whose tumor tissues were highly vascularized and heavily infiltrated by CD163 positive macrophages, indicating a clear-cut link between M2-like macrophage abundance and poor prognosis in patients. Moreover, we documented that, in co-culture, soluble factors produced by primary human MLPS cells induce macrophage polarization toward an M2-like phenotype which, in turn, increases MLPS cell capability to spread into extracellular matrix and to cross endothelial monolayers. The identification of M2-like polarization factors secreted by MLPS cells may allow to develop novel targeted therapies counteracting MLPS progression.

Recent advances in the understanding and management of liposarcoma

Liposarcomas are a common subfamily of soft tissue sarcoma with several subtypes recognized by the World Health Organization: atypical lipomatous tumors (ALT)/well-differentiated liposarcoma (WDLPS), dedifferentiated liposarcoma (DDLPS), myxoid liposarcoma (MLPS), pleomorphic liposarcoma (PLPS), and myxoid pleomorphic liposarcoma (MPLPS). Despite shared adipocytic features among liposarcomas, the clinical approach to each subtype differs based on histology, location, clinical behavior, and specific oncogenic drivers. In this review, we highlight subtype-specific molecular features with the potential to generate novel therapies. We discuss recent clinical trials investigating the use of preoperative radiation therapy for retroperitoneal liposarcoma, chemotherapy, small molecule inhibitors, and innovative immunotherapy approaches and describe how we incorporate these advancements into the management of liposarcoma.

The PTEN Tumor Suppressor Gene in Soft Tissue Sarcoma

Soft tissue sarcoma (STS) is a rare malignancy of mesenchymal origin classified into more than 50 different subtypes with distinct clinical and pathologic features. Despite the poor prognosis in the majority of patients, only modest improvements in treatment strategies have been achieved, largely due to the rarity and heterogeneity of these tumors. Therefore, the discovery of new prognostic and predictive biomarkers, together with new therapeutic targets, is of enormous interest. Phosphatase and tensin homolog (PTEN) is a well-known tumor suppressor that commonly loses its function via mutation, deletion, transcriptional silencing, or protein instability, and is frequently downregulated in distinct sarcoma subtypes. The loss of PTEN function has consequent alterations in important pathways implicated in cell proliferation, survival, migration, and genomic stability. PTEN can also interact with other tumor suppressors and oncogenic signaling pathways that have important implications for the pathogenesis in certain STSs. The aim of the present review is to summarize the biological significance of PTEN in STS and its potential role in the development of new therapeutic strategies.

Precision Oncology in Sarcomas: Divide and Conquer

Sarcomas are a heterogeneous group of rare malignancies that exhibit remarkable heterogeneity, with more than 50 subtypes recognized. Advances in next-generation sequencing technology have resulted in the discovery of genetic events in these mesenchymal tumors, which in addition to enhancing understanding of the biology, have opened up avenues for molecularly targeted therapy and immunotherapy. This review focuses on how incorporation of next-generation sequencing has affected drug development in sarcomas and strategies for optimizing precision oncology for these rare cancers. In a significant percentage of soft tissue sarcomas, which represent up to 40% of all sarcomas, specific driver molecular abnormalities have been identified. The challenge to evaluate these mutations across rare cancer subtypes requires the careful characterization of these genetic alterations to further define compelling drivers with therapeutic implications. Novel models of clinical trial design also are needed. This shift would entail sustained efforts by the sarcoma community to move from one-size-fits-all trials, in which all sarcomas are treated similarly, to divide-and-conquer subtype-specific strategies.

High-Throughput Screening of Myxoid Liposarcoma Cell Lines: Survivin Is Essential for Tumor Growth

Myxoid liposarcoma (MLS) is a soft tissue sarcoma characterized by a recurrent t(12;16) translocation. Although tumors are initially radio- and chemosensitive, the management of inoperable or metastatic MLS can be challenging. Therefore, our aim was to identify novel targets for systemic therapy. We performed an in vitro high-throughput drug screen using three MLS cell lines (402091, 1765092, DL-221), which were treated with 273 different drugs at four different concentrations. Cell lines and tissue microarrays were used for validation. As expected, all cell lines revealed a strong growth inhibition to conventional chemotherapeutic agents, such as anthracyclines and taxanes. A good response was observed to compounds interfering with Src and the mTOR pathway, which are known to be affected in these tumors. Moreover, BIRC5 was important for MLS survival because a strong inhibitory effect was seen at low concentration using the survivin inhibitor YM155, and siRNA for BIRC5 decreased cell viability. Immunohistochemistry revealed abundant expression of survivin restricted to the nucleus in all 32 tested primary tumor specimens. Inhibition of survivin in 402-91 and 1765-92 by YM155 increased the percentage S-phase but did not induce apoptosis, which warrants further investigation before application in the treatment of metastatic MLS. Thus, using a 273-compound drug screen, we confirmed previously identified targets (mTOR, Src) in MLS and demonstrate survivin as essential for MLS survival.

Establishment and characterization of a new human myxoid liposarcoma cell line (DL-221) with the FUS-DDIT3 translocation

Myxoid liposarcoma has the pathognomonic fusion oncogene FUS-DDIT3 encoding a chimeric transcription factor. Metastatic risk is higher with an increased round cell component and has been linked to aberrations involving the IGFR/PI3K/AKT pathway. These molecular insights have yet to translate to targeted therapies, and the lack of experimental models is a major hindrance. We describe the initial in-depth characterization of a new cell line (DL-221) and establishment of a mouse xenograft model. The cell line DL-221 was derived from a metastatic pleural lesion showing myxoid and round cell histology. This newly established cell line was characterized for phenotypic properties and molecular cytogenetic profile, using PCR, COBRA-FISH, and western blot. Next-generation whole-exome sequencing was performed to further characterize the cell line and the parent tumor. NOD-SCID-IL2R gamma knockout mice were xenograft hosts. DL-221 cells grew an adhering monolayer and COBRA-FISH showed an aneuploid karyotype with t(12;16)(q13;p11) and several other rearrangements; RT-PCR demonstrated a FUS-DDIT3 fusion transcript type 1. Both the cell line and the original tumor harbored a TP53 compound heterozygous mutation in exon 4 and 7, and were wild-type for PIK3CA. Moreover, among the 1254 variants called by whole-exome sequencing, there was 77% concordance between the cell line and parent tumor. The recently described hotspot mutation in the TERT promoter region in myxoid liposarcomas was also found at C228T in DL-221. Xenografts suitable for additional preclinical studies were successfully established in mice after subcutaneous injection. The established DL-221 cell line is the only published available myxoid liposarcoma cell line that underwent spontaneous immortalization, without requiring SV40 transformation. The cell line and its xenograft model are unique and helpful tools to study the biology and novel potential-targeted treatment approaches for myxoid liposarcoma.

HDACi inhibits liposarcoma via targeting of the MDM2-p53 signaling axis and PTEN, irrespective of p53 mutational status

The MDM2-p53 pathway plays a prominent role in well-differentiated liposarcoma (LPS) pathogenesis. Here, we explore the importance of MDM2 amplification and p53 mutation in LPS independently, to determine whether HDACi are therapeutically useful in LPS. We demonstrated that simultaneous knockdown of MDM2 and p53 in p53-mutant LPS lines resulted in increased apoptosis, anti-proliferative effects, and cell cycle arrest, as compared to either intervention alone. HDACi treatment resulted in the dephosphorylation and depletion of MDM2 and p53 without affecting CDK4 and JUN expression, irrespective of p53 mutational status in MDM2-amplified LPS. In control mesothelioma cell lines, HDACi treatment resulted in down-regulation of p53 in the p53 mutant cell line JMN1B, but resulted in no changes of MDM2 and p53 in two mesothelioma lines with normal MDM2 and wild-type p53. HDACi treatment substantially decreased LPS and mesothelioma proliferation and survival, and was associated with upregulation of PTEN and p21, and inactivation of AKT. Our findings indicate that wild-type p53 depletion by HDACi is MDM2 amplification-dependent. These findings underscore the importance of targeting both MDM2 and p53 in LPS and other cancers harboring p53 mutations. Moreover, the pro-apoptotic and anti-proliferative effect of HDACi warrants further evaluation as a therapeutic strategy in MDM2-amplified LPS.

Metastasis of myxoid liposarcoma to fat-bearing areas: A case report of unusual metastatic sites and a hypothesis

Sarcoma is a rare disease that always metastasizes to the lungs and bones. Myxoid liposarcoma (MLPS), in comparison with other sarcomas, has a distinct biological characteristic. Recent studies have suggested that MLPS expresses high levels of adipophilin and chemokine (C-X-C motif) receptor 4 (CXCR4), which are correlated with adipogenesis and metastasis. In addition, the Ewing sarcoma breakpoint region 1-DNA damage-inducible transcript 3 (EWSR1-DDIT3) fusion transcript, recently identified in MLPS, was shown to selectively repress the osteoblastic transcription in multipotent mesenchymal cells. The present study reported a rare case of MLPS with metastasis in fat-bearing areas, including the bones, epidural region, orbits and abdominal cavity, while the lungs were not involved. Bone metastasis was diagnosed by magnetic resonance imaging and proven by histology. However, bone scanning lacked sufficient sensitivity to detect the bone metastasis. Based on these findings, we hypothesized that molecular adipophilin and molecular CXCR4 may contribute to the fat-bearing area metastasis pattern. Furthermore, the EWSR1-DDIT3 fusion transcript may repress the osteoblastic activity in the bone metastases, ultimately resulting in a low detection rate by bone scans.