An overview on liposarcoma subtypes: Genetic alterations and recent advances in therapeutic strategies

Liposarcoma (LPS) is a rare malignancy of adipocytic differentiation. According to World Health Organization classification, LPS comprises of four principle subtypes Atypical lipomatous tumor/Well-differentiated liposarcoma (ATL/WDLPS), Dedifferentiated liposarcoma (WDLPS), Myxoid liposarcoma (MLPS), and Pleomorphic liposarcoma (PLPS). Each subtype can develop at any location and shows distinct clinical behavior and treatment sensitivity. ATL/ WDLPS subtype has a higher incidence rate, low recurrence, and is insensitive to radiation and chemotherapy. DDLPS is the focal progression of WDLPS, which is aggressive and highly metastasizing. MLPS is sensitive to radiation and chemotherapy, with a higher recurrence rate and metastasis. PLPS subtype is highly metastasizing, has a poor prognosis, and exhibiting higher recurrence rate. Initial histological analysis provides information for the characterization of LPS subtypes', further molecular and genetic analysis provides certain subtype specifications, such as gene amplifications and gene fusions. Such molecular genetic alterations will be useful as therapeutic targets in various cancers, including the LPS subtypes. A wide range of novel therapeutic agents based on genetic alterations that aim to target LPS subtypes specifically are under investigation. This review summarizes the LPS subtype classification, their molecular genetic characteristics, and the implications of genetic alterations in therapeutics.

Significant blockade of multiple receptor tyrosine kinases by MGCD516 (Sitravatinib), a novel small molecule inhibitor, shows potent anti-tumor activity in preclinical models of sarcoma

Sarcomas are rare but highly aggressive mesenchymal tumors with a median survival of 10–18 months for metastatic disease. Mutation and/or overexpression of many receptor tyrosine kinases (RTKs) including c-Met, PDGFR, c-Kit and IGF1-R drive defective signaling pathways in sarcomas. MGCD516 (Sitravatinib) is a novel small molecule inhibitor targeting multiple RTKs involved in driving sarcoma cell growth. In the present study, we evaluated the efficacy of MGCD516 both in vitro and in mouse xenograft models in vivo. MGCD516 treatment resulted in significant blockade of phosphorylation of potential driver RTKs and induced potent anti-proliferative effects in vitro. Furthermore, MGCD516 treatment of tumor xenografts in vivo resulted in significant suppression of tumor growth. Efficacy of MGCD516 was superior to imatinib and crizotinib, two other well-studied multi-kinase inhibitors with overlapping target specificities, both in vitro and in vivo. This is the first report describing MGCD516 as a potent multi-kinase inhibitor in different models of sarcoma, superior to imatinib and crizotinib. Results from this study showing blockade of multiple driver signaling pathways provides a rationale for further clinical development of MGCD516 for the treatment of patients with soft-tissue sarcoma.

Current classification, treatment options, and new perspectives in the management of adipocytic sarcomas

Sarcomas are a heterogeneous group of mesenchymal tumors arising from soft tissue or bone, with an uncertain etiology and difficult classification. Soft tissue sarcomas (STSs) account for around 1% of all adult cancers. Till date, more than 50 histologic subtypes have been identified. Adipocyte sarcoma or liposarcoma (LPS) is one of the most common STS subtypes, accounting for 15% of all sarcomas, with an incidence of 24% of all extremity STSs and 45% of all retroperitoneal STSs. The new World Health Organization classification system has divided LPS into four different subgroups: atypical lipomatous tumor/well-differentiated LPS, dedifferentiated LPS, myxoid LPS, and pleomorphic LPS. These lesions can develop at any location and exhibit different aggressive potentials reflecting their morphologic diversity and clinical behavior. Patients affected by LPS should be managed in specialized multidisciplinary cancer centers. Whereas surgical resection is the mainstay of treatment for localized disease, the benefits of adjuvant and neoadjuvant chemotherapy are still unclear. Systemic treatment, particularly chemotherapy, is still limited in metastatic disease. Despite the efforts toward a better understanding of the biology of LPS, the outcome of advanced and metastatic patients remains poor. The advent of targeted therapies may lead to an improvement of treatment options and clinical outcomes. A larger patient enrollment into translational and clinical studies will help increase the knowledge of the biological behavior of LPSs, test new drugs, and introduce new methodological studies, that is, on treatment response.

Evolution and prognosis of breast osteosarcoma: A case report

Breast osteosarcoma is a rare malignancy of unknown etiology, with no standard adjuvant treatment at present. The prognosis of the disease is poor, and it has a high propensity for recurrence and metastasis. The current report presents the case of a 52-year-old woman, in whom adenomyoepithelioma gradually developed into breast osteosarcoma following three separate surgeries. The patient survived for 41 months from the initial lesion occurrence and resection in the left breast; during this time, she underwent surgery and chemotherapy (liposomal doxorubicin and cisplatin) for the treatment of disease recurrence and lung metastasis, along with molecular-targeted therapy (sunitinib). However, the patient eventually succumbed to respiratory failure due to progressive disease. The present case underwent a clear pathological transformation process, and may provide a basis for an improved understanding of the clinical characteristics and treatment of breast osteosarcoma.

The Potential of panHER Inhibition in Cancer

Purpose: Hyper-activation of the HER (erbB) family receptors, HER 1-4, leads to up-regulation of the three vital signaling pathways: mitogen activated protein kinase, phosphoinositide 3-kinase/AKT, and Janus kinase/signal transducer and activator of transcription pathways. Blocking HER1/EGFR has a limited anticancer effect due to either secondary mutation e.g., T790M or by-pass signaling of other HER members. The emergence of an anti-panHER approach to blockade of these pathways as a cancer treatment may provide a solution to this resistance. This review aimed to provide an overview of the HER signaling pathways and their involvement in tumor progression and examine the current progress in panHER inhibition.

Methods: Recent literature associated with HER signaling pathways and panHER inhibition was reviewed through PubMed and Medline database, followed by critical comparison and analysis.

Results: Pre-clinical studies and clinical trials of panHER inhibitors show promising results, and the potential to improve patient outcomes in solid cancers.

Conclusion: The use of panHER inhibitors in cancers with HER-family hyper-activation, such as other epithelial cancers and sarcoma, is a new direction to research and has potential in clinical cancer therapy in the future.

Sustained inhibition of receptor tyrosine kinases and macrophage depletion by PLX3397 and rapamycin as a potential new approach for the treatment of MPNSTs

PURPOSE

Malignant peripheral nerve sheath tumor (MPNST) is a highly aggressive tumor type that is resistant to chemotherapy and there are no effective therapies. MPNSTs have been shown to have gene amplification for receptor tyrosine kinases (RTK), PDGFR and c-Kit. We tested the c-Kit inhibitor, imatinib, and PLX3397, a selective c-Fms and c-Kit inhibitor, to evaluate their efficacy against MPNST cells in vitro and in vivo.

EXPERIMENTAL DESIGN

We tested the efficacy of imatinib or PLX3397 either alone or in combination with TORC1 inhibitor rapamycin in a cell proliferation assay in vitro and by immunoblotting to determine target inhibition. Immunoblotting and immunohistochemical analysis was further carried out using xenograft samples in vivo.

RESULTS

Our in vitro studies show that imatinib and PLX3397 similarly inhibit cell growth and this can be enhanced with rapamycin with comparable target specificity. However, in vivo studies clearly demonstrate that compared with imatinib, PLX3397 results in sustained blockade of c-Kit, c-Fms, and PDGFRβ, resulting in significant suppression of tumor growth. Moreover, staining for Iba-1, a marker for macrophages, indicates that PLX3397 results in significant depletion of macrophages in the growing tumors. The combination of PLX3397 and rapamycin results in even greater macrophage depletion with continued growth suppression, even when the drug treatment is discontinued.

CONCLUSIONS

Taken together, our data strongly suggest that PLX3397 is superior to imatinib in the treatment of MPNSTs, and the combination of PLX3397 with a TORC1 inhibitor could provide a new therapeutic approach for the treatment of this disease.

The regulatory roles of phosphatases in cancer

The relevance of potentially reversible post-translational modifications required for controlling cellular processes in cancer is one of the most thriving arenas of cellular and molecular biology. Any alteration in the balanced equilibrium between kinases and phosphatases may result in development and progression of various diseases, including different types of cancer, though phosphatases are relatively under-studied. Loss of phosphatases such as PTEN (phosphatase and tensin homologue deleted on chromosome 10), a known tumour suppressor, across tumour types lends credence to the development of phosphatidylinositol 3-kinase inhibitors alongside the use of phosphatase expression as a biomarker, though phase 3 trial data are lacking. In this review, we give an updated report on phosphatase dysregulation linked to organ-specific malignancies.

Pazopanib in the treatment of soft tissue sarcoma

Patients with advanced metastatic soft tissue sarcoma (STS) have a poor prognosis, and in the last two decades of the 20th century their overall survival has remained unchanged. Improved treatments are needed for these patients and for preventing metastases in earlier stages of disease. Numerous novel agents and new combination regimens are undergoing clinical testing in STS. Some of these agents show promising activity. Pazopanib is one such agent that has undergone Phase II and III evaluations in advanced STS. Pazopanib is a multi-tyrosine kinase inhibitor, blocking various signaling pathways, thereby preventing angiogenesis and metastasis, and inhibiting tumor cell growth and survival. In a Phase II study, pazopanib demonstrated activity in patients with advanced leiomyosarcomas, synovial sarcomas and other eligible STSs. This activity was confirmed in a Phase III trial, where pazopanib significantly extended the median progression-free survival versus placebo in a variety of STS subtypes.

Phosphoproteomics identifies driver tyrosine kinases in sarcoma cell lines and tumors

Driver tyrosine kinase mutations are rare in sarcomas, and patterns of tyrosine phosphorylation are poorly understood. To better understand the signaling pathways active in sarcoma, we examined global tyrosine phosphorylation in sarcoma cell lines and human tumor samples. Anti-phosphotyrosine antibodies were used to purify tyrosine phosphorylated peptides, which were then identified by liquid chromatography and tandem mass spectrometry. The findings were validated with RNA interference, rescue, and small-molecule tyrosine kinase inhibitors. We identified 1,936 unique tyrosine phosphorylated peptides, corresponding to 844 unique phosphotyrosine proteins. In sarcoma cells alone, peptides corresponding to 39 tyrosine kinases were found. Four of 10 cell lines showed dependence on tyrosine kinases for growth and/or survival, including platelet-derived growth factor receptor (PDGFR)α, MET, insulin receptor/insulin-like growth factor receptor signaling, and SRC family kinase signaling. Rhabdomyosarcoma samples showed overexpression of PDGFRα in 13% of examined cases, and sarcomas showed abundant tyrosine phosphorylation and expression of a number of tyrosine phosphorylated tyrosine kinases, including DDR2, EphB4, TYR2, AXL, SRC, LYN, and FAK. Together, our findings suggest that integrating global phosphoproteomics with functional analyses with kinase inhibitors can identify drivers of sarcoma growth and survival.

Novel targeted therapies in the treatment of soft-tissue sarcomas

Systemic therapy options for sarcomas historically have been limited once these tumors become resistant to traditional cytotoxic chemotherapy. Ongoing preclinical research into their biology and clinical trials based on rational biologic targeting have identified novel therapies. For example, the success of imatinib in gastrointestinal stromal tumor has led to the use of other tyrosine kinase inhibitors in other sarcoma subtypes. Other novel therapies include targeting of the mTOR pathway, and IGF-1 receptor. The heterogeneity of these tumors demands intelligently designed protocols in recognizing efficacy that may be restricted to certain histologic subtypes. This article will cover recent trials of new biologic agents in sarcomas that have exhibited promising activity.

Engineered conformation-dependent VEGF peptide mimics are effective in inhibiting VEGF signaling pathways

Angiogenesis, or formation of new blood vessels, is crucial to cancer tumor growth. Tumor growth, progression, and metastasis are critically influenced by the production of the pro-angiogenic vascular endothelial growth factor (VEGF). Promising anti-angiogenic drugs are currently available; however, their susceptibilities to drug resistance and long term toxicity are serious impediments to their use, thus requiring the development of new therapeutic approaches for safe and effective angiogenic inhibitors. In this work, peptides were designed to mimic the VEGF-binding site to its receptor VEGFR-2. The VEGF conformational peptide mimic, VEGF-P3(CYC), included two artificial cysteine residues, which upon cyclization constrained the peptide in a loop native-like conformation to better mimic the anti-parallel structure of VEGF. The engineered cyclic VEGF mimic peptide demonstrated the highest affinity to VEGFR-2 by surface plasmon resonance assay. The VEGF peptide mimics were evaluated as inhibitors in several in vitro assays in which VEGF-dependent signaling pathways were observed. All VEGF mimics inhibited VEGFR-2 phosphorylation with VEGF-P3(CYC) showing the highest inhibitory effects when compared with unstructured peptides. Additionally, we show in several angiogenic in vitro assays that all the VEGF mimics inhibited endothelial cell proliferation, migration, and network formation with the conformational VEGF-P3 (CYC) being the best. The VEGF-P3(CYC) also caused a significant delay in tumor development in a transgenic model of VEGF(+/-)Neu2-5(+/-). These results indicate that the structure-based design is important for the development of this peptidomimetic and for its anti-angiogenic effects.

Ewing's sarcoma

PURPOSE

The current treatments of and new therapeutic options for the management of Ewing's sarcoma (ES) are reviewed.

SUMMARY

ES is the second most common primary bone malignancy in pediatric patients and is numbered among the cancers that result in the greatest risk of mortality and morbidity in children and young adults. Much progress has been made in the treatment of ES since the disease was first described in the 1920s. With current multimodality treatment including chemotherapy, radiation, and surgery, patients with localized disease have a long-term survival rate of approximately 50%. Survival rates for patients with metastatic disease or those with early relapse remain poor. New combinations of cytotoxic agents such as cyclophosphamide, topotecan, irinotecan, and temozolomide have shown efficacy and tolerability in patients with relapsed or refractory disease. To date, the role of high-dose chemotherapy supported by stem cell rescue as a consolidation therapy for high-risk ES tumors has yet to be conclusively determined. Much effort is being invested in treating cancer with targeted therapies, and the EWS-ETS fusion gene would likely provide an important tumor-specific target. Tyrosine kinases (TKs) are overexpressed in human sarcoma tumors, and cell lines may serve as potential targets for new therapies. One TK receptor that is a promising therapeutic target is insulinlike growth factor-1 receptor.

CONCLUSION

Treatments for ES include surgery, radiation, and cytotoxic regimens, many of which include vincristine. Treatment for recurrent ES has included topotecan, cyclophosphamide, temozolomide, and irinotecan. Angiogenesis inhibitors, TK inhibitors, and bisphosphonates have also been studied.

Inhibitor hijacking of Akt activation

The kinase Akt plays a central role as a regulator of multiple growth factor input signals, making it an attractive anti-cancer drug target. A-443654 is an ATP-competitive Akt inhibitor. Unexpectedly, treatment of cells with A-443654 causes paradoxical hyperphosphorylation of Akt at its two regulatory sites (Thr308 and Ser473). We explore whether inhibitor-induced hyperphosphorylation of Akt by A-443654 is a consequence of disrupted feedback regulation at a pathway level or whether it is a direct consequence of inhibitor binding to the ATP binding site of Akt. Catalytically inactive mutants of Akt reveal that binding of an inhibitor to the ATP site of Akt is sufficient to directly cause hyperphosphorylation of the kinase in the absence of any pathway feedback effects. We conclude that ATP-competitive Akt inhibitors impart regulatory phosphorylation of their target kinase Akt providing new insights into both natural regulation of Akt activation and Akt inhibitors entering the clinic.

Angiosarcoma of the retroperitoneum: report on a patient treated with sunitinib

A 52 year-old woman presented with an incidentally detected retroperitoneal angiosarcoma and multiple hepatic metastases. After chemotherapy with weekly paclitaxel and doxorubicin, angiosarcoma had progressed rapidly. Because few chemotherapeutic options were available for her, sunitinib (37.5 mg/day, daily) as a salvage regimen was administered. Although sunitinib was interrupted after two weeks due to hematologic abnormalities, some metastatic nodules were regressed. Therefore, sunitinib was recommenced at a reduced dose (25 mg/day, daily). Serial computed tomography scans showed variable response in each tumor, however, sunitinib at least delayed tumor progression, compared to previous chemotherapy. With this case report, we suggest sunitinib may be effective against angiosarcomas. When sunitinib is administered to patients with angiosarcomas, hematologic abnormalities should be monitored frequently as severe hematologic toxicity may be caused either by sunitinib per se or angiosarcoma.

Non-surgical treatment of pulmonary and extra-pulmonary metastases

Studies have demonstrated that chemotherapy alone is usually unsuccessful as exclusive therapy for osteosarcoma (Cancer 95:2202-2201, 2002). Information will be presented for situations where non-surgical alternatives could be considered as useful, if not necessary, adjuncts to chemotherapy. In the thorax these include treatment of pleural effusions, chest wall lesions, central lung or mediastinal osteosarcoma, as well as recurrences in patients with limited pulmonary reserve. Other situations include too many metastases to easily resect, axial osteosarcomas, bone metastases, liver and brain metastases. Non-surgical local control measures include radiation with chemotherapy for radiosensitization, bone-seeking radioisotopes (e.g., 153Sm-EDTMP, 223Ra), bisphosphonates, heat (radiofrequency ablation), freezing and thawing (cryoablation), and intracavitary or regional (aerosol) therapy. Because of the predictable and common pattern of pulmonary metastases in osteosarcoma, aerosol therapy also offers an attractive regional treatment strategy. Principles and use of aerosol cytokines (e.g., GM-CSF, IL-2), and aerosol chemotherapy with gemcitabin will be discussed. Individual cases illustrating strategy and techniques will be presented.

Promises and challenges of positron emission tomography for assessment of sarcoma in daily clinical practice

A correct histological diagnosis, careful staging and detection of tumour response to treatment are all crucial in the management of sarcomas. Imaging is important in all of these stages. Sarcomas have distinct biological and treatment-related features posing challenges for imaging. For example, size measurements may not adequately reflect response rates. Techniques which can measure tissue function rather than generate merely anatomical data such as positron emission tomography (PET) are rapidly gaining interest. We discuss the importance of imaging in different stages of patient management, emphasising the unique characteristics of sarcoma. Furthermore, we discuss the potential of PET for the various indications, focussing on therapy evaluation.

Recurrent, refractory, metastatic and/or unresectable pediatric sarcomas: treatment options for young people ‘off the roadmap’

Although sarcoma surgery is very important for cancer control, it is not always possible or practical to offer in some situations, including sarcoma recurrences, metastatic disease and/or unacceptable loss of function. We review some pragmatic approaches and examples of how to balance indications, risks and alternatives to control cancer in young people with sarcomas that are no longer using ‘front-line’ therapy. Radiotherapy combined with chemotherapy and outpatient ‘continuation’ chemotherapy regimens using drugs that cause less alopecia can improve function and quality of life. Some effective strategies to help cope when cure is not possible may include tumor ablation techniques performed in interventional radiology and percutaneous nerve blocks. Family centered care and effective problem solving of difficult issues can be greatly facilitated by consultation with a multidisciplinary team experienced in the management of very difficult cases. Treatment of young people with recurrent, relapsed and/or metastatic sarcoma still remains an art very much in the realm of compassion not protocol and persistent advocacy is required for the young person for whom cure may not be possible. A reduction of suffering and assistance in writing more chapters of a rich life narrative is the goal.