Phosphoproteomic Profiling Reveals ALK and MET as Novel Actionable Targets across Synovial Sarcoma Subtypes

ALK fusions in the pan-cancer setting: another tumor-agnostic target?

Anaplastic lymphoma kinase (ALK) alterations (activating mutations, amplifications, and fusions/rearrangements) occur in ~3.3% of cancers. ALK fusions/rearrangements are discerned in >50% of inflammatory myofibroblastic tumors (IMTs) and anaplastic large cell lymphomas (ALCLs), but only in ~0.2% of other cancers outside of non-small cell lung cancer (NSCLC), a rate that may be below the viability threshold of even large-scale treatment trials. Five ALK inhibitors -alectinib, brigatinib, ceritinb, crizotinib, and lorlatinib-are FDA approved for ALK-aberrant NSCLCs, and crizotinib is also approved for ALK-aberrant IMTs and ALCL, including in children. Herein, we review the pharmacologic tractability of ALK alterations, focusing beyond NSCLC. Importantly, the hallmark of approved indications is the presence of ALK fusions/rearrangements, and response rates of ~50-85%. Moreover, there are numerous reports of ALK inhibitor activity in multiple solid and hematologic tumors (e.g., histiocytosis, leiomyosarcoma, lymphoma, myeloma, and colorectal, neuroendocrine, ovarian, pancreatic, renal, and thyroid cancer) bearing ALK fusions/rearrangements. Many reports used crizotinib or alectinib, but each of the approved ALK inhibitors have shown activity. ALK inhibitor activity is also seen in neuroblastoma, which bear ALK mutations (rather than fusions/rearrangements), but response rates are lower (~10-20%). Current data suggests that ALK inhibitors have tissue-agnostic activity in neoplasms bearing ALK fusions/rearrangements.

Recent advances on anti-angiogenic multi-receptor tyrosine kinase inhibitors in osteosarcoma and Ewing sarcoma

Osteosarcoma (OS) and Ewing sarcoma (ES) are the two most common types of primary bone cancer that predominantly affect the young. Despite aggressive multimodal treatment, survival has not improved significantly over the past four decades. Clinical efficacy has historically been observed for some mono-Receptor Tyrosine Kinase (RTK) inhibitors, albeit in small subsets of OS and ES patients. Clinical efficacy in larger groups of OS or ES patients was reported recently with several newer generation multi-RTK inhibitors. All these inhibitors combine a strong anti-angiogenic (VEGFRs) component with simultaneous inhibition of other key RTKs implicated in OS and ES progression (PDGFR, FGFR, KIT and/or MET). However, despite interesting clinical data, none of these agents have obtained a registration for these indications and are thus difficult to implement in routine OS and ES patient care. It is at present also unclear which of these drugs, with largely overlapping molecular inhibition profiles, would work best for which patient or subtype, and treatment resistance almost uniformly occurs. Here, we provide a critical assessment and systemic comparison on the clinical outcomes to the six most tested drugs in this field in OS and ES to date, including pazopanib, sorafenib, regorafenib, anlotinib, lenvatinib and cabozantinib. We pay special attention to clinical response evaluations in bone sarcomas and provide drug comparisons, including drug-related toxicity, to put these drugs into context for OS and ES patients, and describe how future trials utilizing anti-angiogenic multi-RTK targeted drugs could be designed to ultimately improve response rates and decrease toxicity.

Targeting the FAK-Src Complex in Desmoplastic Small Round Cell Tumors, Ewing Sarcoma, and Rhabdomyosarcoma

Desmoplastic small round cell tumors (DSRCTs), Ewing sarcoma (ES), and alveolar and embryonal rhabdomyosarcoma (ARMS and ERMS) are malignant sarcomas typically occurring at young age, with a poor prognosis in the metastatic setting. New treatment options are necessary. Src family kinase inhibitor dasatinib single-agent treatment has been investigated in a phase 2 study in patients with advanced sarcomas including ES and RMS but failed as a single agent in these subtypes. Since previous studies demonstrated high FAK and Src activities in RMS and ES tissue and cell lines, and dasatinib treatment was shown to upregulate activated FAK, we hypothesized that FAK-Src combination treatment could potentially be an interesting treatment option for these tumor types. We examined the effects of targeting the FAK-Src complex by addressing (p)FAK and (p)Src expressions in tumor sections of DSRCT (n = 13), ES (n = 68), ARMS (n = 21), and ERMS (n = 39) and by determining the antitumor effects of single and combined treatment with FAK inhibitor defactinib and multikinase (Abl/SFK) inhibitor dasatinib in vitro on cell lines of each subtype. In vivo effects were assessed in DSRCT and ERMS models. Concurrent pFAK and pSrc expressions (H-score >50) were observed in DSRCT (67%), ES (6%), ARMS (35%), and ERMS (19%) samples. Defactinib treatment decreased pFAK expression and reduced cell viability in all subtypes. Dasatinib treatment decreased pSrc expression and cell viability in each subtype. Combination treatment led to a complete reduction in pFAK and pSrc in each cell line and showed enhanced cell viability reduction, drug synergy, DNA damage induction, and a trend toward higher apoptosis induction in DSRCT, ERMS, and ARMS but not in ES cells. These promising in vitro results unfortunately do not translate into promising in vivo results as we did not observe a significant effect on tumor volume in vivo, and the combination did not show superior effects compared to dasatinib single-agent treatment.

Proteomic and Metabolomic Profiling in Soft Tissue Sarcomas

Advances in proteomic and metabolomic technologies have accelerated our understanding of multiple aspects of cancer biology across distinct tumour types. Here we review the current state-of-the-art in the use of proteomics and metabolomics in soft tissue sarcomas. We highlight the utility of these Omics-based methodologies to identify new drug targets, synthetic lethal interactions, candidate therapeutics and novel biomarkers to facilitate patient stratification. Due to the unbiased and global nature of these profiling methods to assess the levels of protein expression, post-translational modifications such as phosphorylation and glycosylation as well as key metabolites, many of these findings have broad applications not just in specific histotypes but across multiple STS subtypes. Specific examples of proteomic and metabolomic findings that have led to the development of early phase clinical trials of investigational agents will be discussed. While promising, the use of these technologies in the study of sarcoma is still limited, and there is a need for further research in this area. In particular, it would be important to integrate these approaches with other Omics strategies such as genomics and epigenomics as well as implement these tools alongside clinical trials in order to maximize the impact of these tools on our biological understanding and treatment of this group of rare diseases of unmet need.

Synchronous lung and multiple soft tissue metastases developed from osteosarcoma of tibia: a rare case report and genetic profile analysis

Background

Osteosarcoma is the most common primary malignant bone tumor with a highly metastatic propensity in children and young adolescents. The majority of metastases develope in the lung, while metastases to the extrapulmonary locations have rarely been discussed, especially in skeletal muscle.

Case presentation

We reported a young patient with pathologically diagnosed osteosarcoma of the right tibia who was initially treated with standard chemotherapy and complete surgical resection. However, pulmonary metastases and multiple soft tissue masses in skeletal muscle developed four years after the index surgical resection. Subsequently, a targeted next-generation sequencing assay based on an 806 oncogenes and tumor suppressor genes panel was performed to analyze genetic alterations in this patient with rare metastatic pattern. The genetic analysis revealed canonical somatic mutations of RB1 and germline variants of ALK (c.862 T > C), BLM (c.1021C > T), PTCH1 (c.152_154del), MSH2 (c.14C > A), RAD51C (c.635G > A). Using silico prediction programs, the germline variants of the MSH2 and RAD51C were predicted as “Possibly Damaging” by Polymorphism Phenotyping v2 (PolyPhen-2) and “Tolerated” by Sorting Intolerant from Tolerant (SIFT); BLM was classified as “Tolerated”, while the germline variant of ALK was predicted to be pathogenic by both PolyPhen-2 and SIFT.

Conclusions

Osteosarcoma with extrapulmonary metastases is rare, especially located in the skeletal muscle, which predicts a worse clinical outcome compared with lung-only metastases. The several novel variants of ALK, BLM, PTCH1 in this patient might expand the mutational spectrums of the osteosarcoma. All the results may contribute to a better understanding of the clinical course and genetic characteristics of osteosarcoma patients with metastasis.

Upregulation of ERK-EGR1-heparanase axis by HDAC inhibitors provides targets for rational therapeutic intervention in synovial sarcoma

BACKGROUND

Synovial sarcoma (SS) is an aggressive soft tissue tumor with limited therapeutic options in advanced stage. SS18-SSX fusion oncogenes, which are the hallmarks of SS, cause epigenetic rewiring involving histone deacetylases (HDACs). Promising preclinical studies supporting HDAC targeting for SS treatment were not reflected in clinical trials with HDAC inhibitor (HDACi) monotherapies. We investigated pathways implicated in SS cell response to HDACi to identify vulnerabilities exploitable in combination treatments and improve the therapeutic efficacy of HDACi-based regimens.

METHODS

Antiproliferative and proapoptotic effects of the HDACi SAHA and FK228 were examined in SS cell lines in parallel with biochemical and molecular analyses to bring out cytoprotective pathways. Treatments combining HDACi with drugs targeting HDACi-activated prosurvival pathways were tested in functional assays in vitro and in a SS orthotopic xenograft model. Molecular mechanisms underlying synergisms were investigated in SS cells through pharmacological and gene silencing approaches and validated by qRT-PCR and Western blotting.

RESULTS

SS cell response to HDACi was consistently characterized by activation of a cytoprotective and auto-sustaining axis involving ERKs, EGR1, and the β-endoglycosidase heparanase, a well recognized pleiotropic player in tumorigenesis and disease progression. HDAC inhibition was shown to upregulate heparanase by inducing expression of the positive regulator EGR1 and by hampering negative regulation by p53 through its acetylation. Interception of HDACi-induced ERK-EGR1-heparanase pathway by cell co-treatment with a MEK inhibitor (trametinib) or a heparanase inhibitor (SST0001/roneparstat) enhanced antiproliferative and pro-apoptotic effects. HDAC and heparanase inhibitors had opposite effects on histone acetylation and nuclear heparanase levels. The combination of SAHA with SST0001 prevented the upregulation of ERK-EGR1-heparanase induced by the HDACi and promoted caspase-dependent cell death. In vivo, the combined treatment with SAHA and SST0001 potentiated the antitumor efficacy against the CME-1 orthotopic SS model as compared to single agent administration.

CONCLUSIONS

The present study provides preclinical rationale and mechanistic insights into drug combinatory strategies based on the use of ERK pathway and heparanase inhibitors to improve the efficacy of HDACi-based antitumor therapies in SS. The involvement of classes of agents already clinically available, or under clinical evaluation, indicates the transferability potential of the proposed approaches.

Enhancing the Potential of Immunotherapy in Paediatric Sarcomas: Breaking the Immunosuppressive Barrier with Receptor Tyrosine Kinase Inhibitors

Despite aggressive surgery, chemotherapy, and radiotherapy, survival of children and adolescents and young adults (AYAs) with sarcoma has not improved significantly in the past four decades. Immune checkpoint inhibitors (ICIs) are an exciting type of immunotherapy that offer new opportunities for the treatment of paediatric and AYA sarcomas. However, to date, most children do not derive a benefit from this type of treatment as a monotherapy. The immunosuppressive tumour microenvironment is a major barrier limiting their efficacy. Combinations of ICIs, such as anti-PD-1 therapy, with targeted molecular therapies that have immunomodulatory properties may be the key to breaking through immunosuppressive barriers and improving patient outcomes. Preclinical studies have indicated that several receptor tyrosine kinase inhibitors (RTKi) can alter the tumour microenvironment and boost the efficacy of anti-PD-1 therapy. A number of these combinations have entered phase-1/2 clinical trials, mostly in adults, and in most instances have shown efficacy with manageable side-effects. In this review, we discuss the status of ICI therapy in paediatric and AYA sarcomas and the rationale for co-treatment with RTKis. We highlight new opportunities for the integration of ICI therapy with RTK inhibitors, to improve outcomes for children with sarcoma.

The Biology of Synovial Sarcoma: State-of-the-Art and Future Perspectives

New molecular insights are being achieved in synovial sarcoma (SS) that can provide new potential diagnostic and prognostic markers as well as therapeutic targets. In particular, the advancement of research on epigenomics and gene regulation is promising. The concrete hypothesis that the pathogenesis of SS might mainly depend on the disruption of the balance of the complex interaction between epigenomic regulatory complexes and the consequences on gene expression opens interesting new perspectives. The standard of care for primary SS is wide surgical resection combined with radiation in selected cases. The role of chemotherapy is still under refinement and can be considered in patients at high risk of metastasis or in those with advanced disease. Cytotoxic chemotherapy (anthracyclines, ifosfamide, trabectedin, and pazopanib) is the treatment of choice, despite several possible side effects. Many possible drug-able targets have been identified. However, the impact of these strategies in improving SS outcome is still limited, thus making current and future research strongly needed to improve the survival of patients with SS.

Unraveling the IGF System Interactome in Sarcomas Exploits Novel Therapeutic Options

Aberrant bioactivity of the insulin-like growth factor (IGF) system results in the development and progression of several pathologic conditions including cancer. Preclinical studies have shown promising anti-cancer therapeutic potentials for anti-IGF targeted therapies. However, a clear but limited clinical benefit was observed only in a minority of patients with sarcomas. The molecular complexity of the IGF system, which comprises multiple regulators and interactions with other cancer-related pathways, poses a major limitation in the use of anti-IGF agents and supports the need of combinatorial therapeutic strategies to better tackle this axis. In this review, we will initially highlight multiple mechanisms underlying IGF dysregulation in cancer and then focus on the impact of the IGF system and its complexity in sarcoma development and progression as well as response to anti-IGF therapies. We will also discuss the role of Ephrin receptors, Hippo pathway, BET proteins and CXCR4 signaling, as mediators of sarcoma malignancy and relevant interactors with the IGF system in tumor cells. A deeper understanding of these molecular interactions might provide the rationale for novel and more effective therapeutic combinations to treat sarcomas.

Precision medicine and phosphoproteomics for the identification of novel targeted therapeutic avenues in sarcomas

Rapid advances in genomic technologies have enabled in-depth interrogation of cancer genomes, revealing novel and unexpected therapeutic targets in many cancer types. Identifying actionable dependencies in the diverse and heterogeneous group of sarcomas, particularly those that occur in children or adolescents and young adults (AYAs), remains especially challenging. These patients rarely harbor actionable genomic aberrations, no targeted agent is approved, and outcomes have remained poor for the past decades. This underlines a clear need to refine our methods for target identification. Phosphoproteomics studies in sarcoma showed the power of such analyses to capture novel actionable drivers that are not accompanied by mutational events or gene amplifications. This Review makes the case that incorporating phosphoproteomic molecular profiling alongside (functional) genomics technologies can significantly expand therapeutic target identification, and pinpoint drug mechanisms of action, in pediatric and AYA sarcoma patients. We explore the utility and prospects of phosphoproteomics in personalized medicine.

Focal adhesion kinase inhibition synergizes with nab-paclitaxel to target pancreatic ductal adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) is a very lethal disease, with minimal therapeutic options. Aberrant tyrosine kinase activity influences tumor growth and is regulated by phosphorylation. We investigated phosphorylated kinases as target in PDAC.

Methods

Mass spectrometry-based phosphotyrosine proteomic analysis on PDAC cell lines was used to evaluate active kinases. Pathway analysis and inferred kinase activity analysis was performed to identify novel targets. Subsequently, we investigated targeting of focal adhesion kinase (FAK) in vitro with drug perturbations in combination with chemotherapeutics used against PDAC. Tyrosine phosphoproteomics upon treatment was performed to evaluate signaling. An orthotopic model of PDAC was used to evaluate the combination of defactinib with nab-paclitaxel.

Results

PDAC cell lines portrayed high activity of multiple receptor tyrosine kinases to various degree. The non-receptor kinase, FAK, was identified in all cell lines by our phosphotyrosine proteomic screen and pathway analysis. Targeting of this kinase with defactinib validated reduced phosphorylation profiles. Additionally, FAK inhibition had anti-proliferative and anti-migratory effects. Combination with (nab-)paclitaxel had a synergistic effect on cell proliferation in vitro and reduced tumor growth in vivo.

Conclusions

Our study shows high phosphorylation of several oncogenic receptor tyrosine kinases in PDAC cells and validated FAK inhibition as potential synergistic target with Nab-paclitaxel against this devastating disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01892-z.

Establishment and characterization of NCC-SS4-C1: a novel patient-derived cell line of synovial sarcoma

Synovial sarcoma (SS) is defined as a monomorphic blue spindle cell sarcoma showing variable epithelial differentiation, and is characterized by a specific fusion gene, SS18-SSX. Although SS is rare, it accounts for approximately 8% of all soft tissue sarcomas, which occupies a significant proportion of soft tissue tumors. The prognosis of SS is unfavorable, with 5-year survival rate of 50-60%, and only a few anti-cancer agents are recommended for its treatment. Thus, we need to urgently establish novel treatment methods. Patient-derived cell lines are essential tools in basic research and pre-clinical studies. However, there are only 4 publicly available SS cell lines. Therefore, we established a novel SS cell line, NCC-SS4-C1, using surgically resected tumor tissues of a patient with SS. The cell line maintained the characteristic fusion gene, SS18-SSX1, and copy number alteration, in concordance with the original tumor. The cells also exhibited moderate cell proliferation, invasion ability, and spheroid formation ability. Moreover, a drug-screening test using 4 SS cell lines, including NCC-SS4-C1, demonstrated the significant anti-proliferative effects of ALK and HDAC inhibitors. Thus, we concluded that the NCC-SS4-C1 cell line is a useful tool for basic and pre-clinical studies of SS.

Proteomics-based interrogation of the kinome and its implications for precision oncology

The identification of specific protein kinases as oncogenic drivers in a variety of cancer types, coupled with the clinical success of particular kinase-directed targeted therapies, has cemented the human kinome as an attractive source of "actionable" targets for cancer therapy. However, "mining" of the human kinome for precision oncology applications has yet to yield its full potential. This reflects a variety of issues, including oncogenic kinase dysregulation at levels not detectable by genomic sequencing and the uncharacterized nature of a considerable fraction of the kinome. In addition, selective therapeutic targeting of specific kinases requires efficient mapping of total kinome space impacted by candidate small molecule drugs. Fortunately, recent developments in proteomics techniques, particularly in mass spectrometry-based phosphoproteomics and kinomics, provide the necessary technology platforms to address these impediments. Moreover, initiatives such as the Clinical Proteomic Tumour Analysis Consortium have enabled the generation, deposition and integration of genomic, transcriptomic and (phospho)proteomic data for many cancer types, providing unprecedented insights into oncogenic kinases and cancer cell signalling generally. These multi-omic data are identifying novel therapeutic targets, highlighting opportunities for drug re-purposing, and helping assign optimal therapies to specific tumour subtypes, heralding a new era of "enhanced" precision oncology.

Candidate Biomarkers for Specific Intraoperative Near-Infrared Imaging of Soft Tissue Sarcomas: A Systematic Review

Simple Summary

Near-infrared imaging of tumors during surgery facilitates the oncologic surgeon to distinguish malignant from healthy tissue. The technique is based on fluorescent tracers binding to tumor biomarkers on malignant cells. Currently, there are no clinically available fluorescent tracers that specifically target soft tissue sarcomas. This review searched the literature to find candidate biomarkers for soft tissue sarcomas, based on clinically used therapeutic antibodies. The search revealed 7 biomarkers: TEM1, VEGFR-1, EGFR, VEGFR-2, IGF-1R, PDGFRα, and CD40. These biomarkers are abundantly present on soft tissue sarcoma tumor cells and are already being targeted with humanized monoclonal antibodies. The conjugation of these antibodies with a fluorescent dye will yield in specific tracers for image-guided surgery of soft tissue sarcomas to improve the success rates of tumor resections.

Abstract

Surgery is the mainstay of treatment for localized soft tissue sarcomas (STS). The curative treatment highly depends on complete tumor resection, as positive margins are associated with local recurrence (LR) and prognosis. However, determining the tumor margin during surgery is challenging. Real-time tumor-specific imaging can facilitate complete resection by visualizing tumor tissue during surgery. Unfortunately, STS specific tracers are presently not clinically available. In this review, STS-associated cell surface-expressed biomarkers, which are currently already clinically targeted with monoclonal antibodies for therapeutic purposes, are evaluated for their use in near-infrared fluorescence (NIRF) imaging of STS. Clinically targeted biomarkers in STS were extracted from clinical trial registers and a PubMed search was performed. Data on biomarker characteristics, sample size, percentage of biomarker-positive STS samples, pattern of biomarker expression, biomarker internalization features, and previous applications of the biomarker in imaging were extracted. The biomarkers were ranked utilizing a previously described scoring system. Eleven cell surface-expressed biomarkers were identified from which 7 were selected as potential biomarkers for NIRF imaging: TEM1, VEGFR-1, EGFR, VEGFR-2, IGF-1R, PDGFRα, and CD40. Promising biomarkers in common and aggressive STS subtypes are TEM1 for myxofibrosarcoma, TEM1, and PDGFRα for undifferentiated soft tissue sarcoma and EGFR for synovial sarcoma.

Cabozantinib as an emerging treatment for sarcoma

PURPOSE OF REVIEW

Sarcomas are a diverse group of rare solid tumors with limited treatment options for patients with advanced, inoperable disease. Cabozantinib is a tyrosine kinase inhibitor currently approved for advanced renal cell, hepatocellular, and medullary thyroid carcinoma. Cabozantinib has potent activity against a variety of kinases, including MET, vascular endothelial growth factor receptor, and AXL, that are associated with sarcoma growth and development. Here we review the preclinical findings and clinical development of cabozantinib in the treatment of soft tissue sarcoma, gastrointestinal stromal tumors (GIST), osteosarcoma, and Ewing sarcoma.

RECENT FINDINGS

In vitro, cabozantinib has shown relevant activity in inhibiting the growth and viability of soft tissue sarcoma, GIST, osteosarcoma, and Ewing sarcoma tumor cell lines. Cabozantinib also promoted the regression of GIST in various murine xenografts, including imatinib-resistant models. More than 10 prospective trials with cabozantinib that included patients with sarcomas have been completed or are currently ongoing. Clinical activity with cabozantinib has been recently reported in phase 2 clinical trials for patients with GIST and for patients with osteosarcoma or Ewing sarcoma.

SUMMARY

Cabozantinib has shown promising activity for the treatment of various sarcomas, supporting further evaluation in this setting.

Synovial Sarcoma: A Complex Disease with Multifaceted Signaling and Epigenetic Landscapes

PURPOSE OF REVIEW

Aside from a characteristic SS18-SSX translocation identified in almost all cases, no genetic anomalies have been reliably isolated yet to drive the pathogenesis of synovial sarcoma. In the following review, we explore the structural units of wild-type SS18 and SSX, particularly as they relate to the transcriptional alterations and cellular pathway changes imposed by SS18-SSX.

RECENT FINDINGS

Native SS18 and SSX contribute recognizable domains to the SS18-SSX chimeric proteins, which inflict transcriptional and epigenetic changes through selective protein interactions involving the SWI/SNF and Polycomb chromatin remodeling complexes. Multiple oncogenic and developmental pathways become altered, collectively reprogramming the cellular origin of synovial sarcoma and promoting its malignant transformation. Synovial sarcoma is characterized by complex epigenetic and signaling landscapes. Identifying the operational pathways and concomitant genetic changes induced by SS18-SSX fusions could help develop tailored therapeutic strategies to ultimately improve disease control and patient survivorship.

The Role of Tyrosine Kinases as a Critical Prognostic Parameter and Its Targeted Therapies in Ewing Sarcoma

Ewing sarcoma (ES) is a rare, highly aggressive, bone, or soft tissue-associated tumor. Although this sarcoma often responds well to initial chemotherapy, 40% of the patients develop a lethal recurrence of the disease, with death recorded in 75-80% of patients with metastatic ES within 5 years, despite receiving high-dose chemotherapy. ES is genetically well-characterized, as indicated by the EWS-FLI1 fusion protein encoded as a result of chromosomal translocation in 80-90% of patients with ES, as well as in ES-related cancer cell lines. Recently, tyrosine kinases have been identified in the pathogenesis of ES. These tyrosine kinases, acting as oncoproteins, are associated with the clinical pathogenesis, metastasis, acquisition of self-renewal traits, and chemoresistance of ES, through the activation of various intracellular signaling pathways. This review describes the recent progress related to cellular and molecular functional roles of tyrosine kinases in the progression of ES.

The landscape of tyrosine kinase inhibitors in sarcomas: looking beyond pazopanib

Introduction: Tyrosine kinases are key mediators of intracellular signaling cascades and aberrations in these proteins have been implicated in driving oncogenesis through the dysregulation of fundamental cellular processes including proliferation, migration, and apoptosis. As such, targeting these proteins with small molecule tyrosine kinase inhibitors (TKI) has led to significant advances in the treatment of a number of cancer types.Areas covered: Soft tissue sarcomas (STS) are a heterogeneous and challenging group of rare cancers to treat, but the approval of the TKI pazopanib for the treatment of advanced STS demonstrates that this class of drugs may have broad utility against a range of different sarcoma histological subtypes. Since the approval of pazopanib, a number of other TKIs have entered clinical trials to evaluate whether their activity in STS matches the promising results seen in other solid tumors. In this article, we review the emerging role of TKIs in the evolving landscape of sarcoma treatment.Expert opinion: As our biological understanding of response and resistance of STS to TKIs advances, we anticipate that patient management will move away from a 'one size fits all' paradigm toward personalized, multi-line, and patient-specific treatment regimens where patients are treated according to the underlying biology and genetics of their specific disease.

Targeted Therapy-based Combination Treatment in Rhabdomyosarcoma

Targeted therapies have revolutionized cancer treatment; however, progress lags behind in alveolar (ARMS) and embryonal rhabdomyosarcoma (ERMS), a soft-tissue sarcoma mainly occurring at pediatric and young adult age. Insulin-like growth factor 1 receptor (IGF1R)-directed targeted therapy is one of the few single-agent treatments with clinical activity in these diseases. However, clinical effects only occur in a small subset of patients and are often of short duration due to treatment resistance. Rational selection of combination treatments of either multiple targeted therapies or targeted therapies with chemotherapy could hypothetically circumvent treatment resistance mechanisms and enhance clinical efficacy. Simultaneous targeting of distinct mechanisms might be of particular interest in this regard, as this affects multiple hallmarks of cancer at once. To determine the most promising and clinically relevant targeted therapy-based combination treatments for ARMS and ERMS, we provide an extensive overview of preclinical and (early) clinical data concerning a variety of targeted therapy-based combination treatments. We concentrated on the most common classes of targeted therapies investigated in rhabdomyosarcoma to date, including those directed against receptor tyrosine kinases and associated downstream signaling pathways, the Hedgehog signaling pathway, apoptosis pathway, DNA damage response, cell-cycle regulators, oncogenic fusion proteins, and epigenetic modifiers. Mol Cancer Ther; 17(7); 1365-80. ©2018 AACR.

Overactive IGF1/Insulin Receptors and NRASQ61R Mutation Drive Mechanisms of Resistance to Pazopanib and Define Rational Combination Strategies to Treat Synovial Sarcoma

Pazopanib is approved for treatment of advanced soft tissue sarcomas, but primary and secondary drug resistance limits its clinical utility. We investigated the molecular mechanisms mediating pazopanib resistance in human synovial sarcoma (SS) models. We found reduced cell sensitivity to pazopanib associated with inefficient inhibition of the two critical signaling nodes, AKT and ERKs, despite strong inhibition of the main drug target, PDGFRα. In the CME-1 cell line, overactivation of IGF1 and Insulin receptors (IGF1R/InsR) sustained AKT activation and pazopanib resistance, which was overcome by a combination treatment with the double IGF1R/InsR inhibitor BMS754807. In the highly pazopanib resistant MoJo cell line, NRASQ61R mutation sustained constitutive ERK activation. Transfection of the NRAS mutant in the pazopanib sensitive SYO-1 cell line increased the drug IC₅₀. MoJo cells treatment with pazopanib in combination with the MEK inhibitor trametinib restored ERK inhibition, synergistically inhibited cell growth, and induced apoptosis. The combination significantly enhanced the antitumor efficacy against MoJo orthotopic xenograft abrogating growth in 38% of mice. These findings identified two different mechanisms of intrinsic pazopanib resistance in SS cells, supporting molecular/immunohistochemical profiling of tumor specimens as a valuable approach to selecting patients who may benefit from rational drug combinations.

Anaplastic Lymphoma Kinase (ALK) Receptor Tyrosine Kinase: A Catalytic Receptor with Many Faces

The anaplastic lymphoma kinase (ALK) receptor is a membrane-bound tyrosine kinase. The pathogenesis of several cancers is closely related to aberrant forms of ALK or aberrant ALK expression, including ALK fusion proteins, ALK-activated point mutations, and ALK amplification. Clinical applications of different ALK inhibitors represent significant progress in targeted therapy. Knowledge of different aspects of ALK biology can provide significant information to further the understanding of this receptor tyrosine kinase. In this mini-review, we briefly summarize different features of ALK. We also summarize some recent research advances on ALK fusion proteins in cancers.

Antitumor profile of the PI3K inhibitor ZSTK474 in human sarcoma cell lines

Treatment of patients with advanced sarcoma remains challenging due to lack of effective medicine, with the development of novel drugs being of keen interest. A pan-PI3K inhibitor, ZSTK474, has been evaluated in clinical trials against a range of advanced solid tumors, with clinical benefit shown in sarcoma patients. In the present study, we developed a panel of 14 human sarcoma cell lines and investigated the antitumor effect of 24 anticancer agents including ZSTK474, other PI3K inhibitors, and those clinically used for sarcoma treatment. ZSTK474 exhibited a similar antiproliferative profile to other PI3K inhibitors but was clearly different from the other drugs examined. Indeed, ZSTK474 inhibited PI3K-downstream pathways, in parallel to growth inhibition, in all cell lines examined, showing proof-of-concept of PI3K inhibition. In addition, ZSTK474 induced apoptosis selectively in Ewing's sarcoma (RD-ES and A673), alveolar rhabdomyosarcoma (SJCRH30) and synovial sarcoma (SYO-1, Aska-SS and Yamato-SS) cell lines, all of which harbor chromosomal translocation and resulting oncogenic fusion genes, EWSR1-FLI1, PAX3-FOXO1 and SS18-SSX, respectively. Finally, animal experiments confirmed the antitumor activity of ZSTK474 in vivo, with superior efficacy observed in translocation-positive cells. These results suggest that ZSTK474 could be a promising drug candidate for treating sarcomas, especially those harboring chromosomal translocation.

In silico and in vitro screening of small molecule Inhibitors against SYT-SSX1 fusion protein in synovial sarcoma

Synovial sarcoma (SS) is characterized by a tumour specific chromosomal translocation t(X;18) (p11;q11) which results in the formation of SYT-SSX1 fusion protein. This fusion protein represents a clear therapeutic target and molecules specifically targeting SYT-SSX1 fusion protein are currently not available. In this study, SYT-SSX1 fusion protein sequence was retrieved from Uniprot and 3D structure was generated using I-TASSER modeling program. A structure based computational screening approach has been employed using Glide docking software to identify potential SYT-SSX1 small molecule inhibitors that bind to the junction region of the fusion protein. The obtained inhibitors were further filtered based on the docking score and ADME/T properties. Ten best fit compounds were chosen for in vitro studies. The anti-proliferative activities of these 10 compounds were screened in Yamato, ASKA (carries SYT-SSX1 fusion protein) and other sarcoma cell lines such as A673, 143B to understand the specificity of inhibition of the chosen compounds. The in vitro activity was compared against HEK293 cell lines. The compound 5-fluoro-3-(1-phenyl-1H-tetraazol-5-yl)-1H-indole (FPTI) was found to be selectively cytotoxic in synovial sarcoma cell lines (Yamato and ASKA) and this compound also showed insignificant anti proliferative activity on other cell lines. Further, target gene expression study confirmed that FPTI treatment down-regulated SYT-SSX1 and modulated its downstream target genes. Cell cycle analysis revealed the involvement of an apoptotic mechanism of cell death. Further experimental validations may elucidate the therapeutic potentials of FPTI against SYT-SSX1 fusion protein.

Preclinical Evaluation of Nintedanib, a Triple Angiokinase Inhibitor, in Soft-tissue Sarcoma: Potential Therapeutic Implication for Synovial Sarcoma

Sarcomas are rare cancers that make up about 1% of all cancers in adults; however, they occur more commonly among children and young adolescents. Sarcomas are genetically complex and are often difficult to treat given the lack of clinical efficacy of any of the currently available therapies. Receptor tyrosine kinases (RTK) such as c-Kit, c-Met, PDGFR, IGF-1R, as well as FGFR have all been reported to be involved in driving tumor development and progression in adult and pediatric soft-tissue sarcoma. These driver kinases often act as critical determinants of tumor cell proliferation and targeting these signal transduction pathways remains an attractive therapeutic approach. Nintedanib, a potent triple angiokinase inhibitor, targets PDGFR, VEGFR, and FGFR pathways critical for tumor angiogenesis and vasculature. In this study, we evaluated the preclinical efficacy of nintedanib in soft-tissue sarcoma cell lines. Nintedanib treatment resulted in significant antiproliferative effect in vitro in cell lines with high expression of RTK drug targets. Furthermore, treatment with nintedanib showed significant downregulation of downstream phosphorylated AKT and ERK1/2. Finally, treatment with nintedanib resulted in significant tumor growth suppression in mouse xenograft model of synovial sarcoma. Notably, both the in vitro and in vivo efficacy of nintedanib was superior to that of imatinib, another multikinase inhibitor, previously tested with minimal success in clinical trials in sarcoma. Overall, the data from this study provide a strong rationale to warrant further clinical exploration of this drug in patients with synovial sarcoma. Mol Cancer Ther; 17(11); 2329-40. ©2018 AACR.

Targeting Anaplastic Lymphoma Kinase (ALK) in Rhabdomyosarcoma (RMS) with the Second-Generation ALK Inhibitor Ceritinib

Background

The receptor tyrosine kinase (RTK) anaplastic lymphoma kinase (ALK) has been implicated in the tumorigenesis of rhabdomyosarcoma (RMS). However, the exact role of ALK in RMS is debatable and remains to be elucidated.

Objective

To determine the in vitro and in vivo effects and mechanism of action of the second-generation ALK inhibitor ceritinib on RMS cell growth.

Methods

Effects of ceritinib on cell proliferation, wound healing, cell cycle, and RTK signaling were determined in alveolar and embryonal rhabdomyosarcoma (ARMS, ERMS). In addition, possible synergistic effects of combined treatment with ceritinib and the Abl/Src family kinase inhibitor dasatinib were determined.

Results

Ceritinib treatment led to decreased cell proliferation, cell cycle arrest, apoptosis, and decreased in vivo tumor growth for the ARMS subtype. ERMS cell lines were less affected and showed no cell cycle arrest or apoptosis. Both subtypes lacked intrinsic ALK phosphorylation, and ceritinib was shown to affect the IGF1R signaling pathway. High levels of phosphorylated Src (Tyr416) were present following ceritinib treatment, making combined treatment with a Src inhibitor a potential treatment option. Combined treatment of ceritinib and dasatinib showed synergistic effects in both ERMS and ARMS cell lines.

Conclusion

This study shows that monotherapy with an ALK inhibitor, such as ceritinib, in RMS, has no effect on ALK signaling. However, the synergistic effects of ceritinib and dasatinib are promising, most probably due to targeting of IGF1R and Src.

Electronic supplementary material

The online version of this article (10.1007/s11523-017-0528-z) contains supplementary material, which is available to authorized users.

Systemic Treatment for Adults with Synovial Sarcoma

OPINION STATEMENT

Synovial sarcoma (SS) is a rare, yet highly malignant, type of soft tissue sarcoma (STS), for which survival has not improved significantly during the past years. In this review, we focus on systemic treatment in adults. Compared to other STS, SS are relatively chemosensitive. Ifosfamide and ifosfamide combinations are active in different lines of treatment. In high-risk extremity and chest wall STS, neoadjuvant doxorubicin and ifosfamide has shown as much activity as high-dose ifosfamide. There are indications that combination chemotherapy with doxorubicin and ifosfamide in this setting improves outcome. In the first-line metastatic setting, combination treatment with doxorubicin and ifosfamide is a preferred option in fit patients, while in other patients, sequential doxorubicin and ifosfamide can be considered. In second and later lines, pazopanib and trabectedin have shown activity. Many new approaches to treat metastatic SS are currently under investigation, both preclinical as well as clinical, including other receptor tyrosine kinase inhibitors, epigenetic modulators, compounds interfering with DNA damage response (DDR), and immunotherapy.

Synovial Sarcoma: Current Concepts and Future Perspectives

Synovial sarcoma (SS) is a rare sarcoma driven by a translocation between SS18 and SSX 1, 2, or 4. With approximately 800 to 1,000 cases a year in the United States, it most commonly affects young adults between the ages of 15 and 30 years. The resultant tumors are either monophasic (pure sarcomas), biphasic (a combination or epithelioid and sarcomatous components), or poorly differentiated. The hybrid transcription factor SS18:SSX alters SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling and global methylation patterns that may allow for future therapeutic opportunities. In this review, we focus on the pharmacologic management of SS, both in the curative setting, where the standard approach is wide surgical excision combined with radiotherapy and/or (neo)adjuvant chemotherapy as appropriate, and in the palliative setting. In advanced disease, chemotherapy with anthracyclines and/or ifosfamide, trabectedin, or pazopanib has been demonstrated to be more active compared with other soft tissue sarcomas. In addition, a better understanding of the molecular and immunologic characteristics of SS has allowed for the identification of new potential targets and the development of novel biology-driven therapies that are all at different stages of testing. There include targeted agents, immunotherapy, and metabolic therapies. Because the impact of these strategies for improving SS outcome is still limited, current and future research is strongly needed to better understand the tumor biology, to identify predictive biomarkers, and to improve the outcomes for patients with SS.