Hsp90 Inhibitor 17-Allylamino-17-Demethoxygeldanamycin Prevents Synovial Sarcoma Proliferation via Apoptosis in In vitro Models

Abstract

Synovial sarcoma is a soft tissue malignancy with a poor prognosis; many patients will die from this disease within 10 years of diagnosis, despite treatment. Gene expression profiling and immunohistochemistry studies have identified oncogenes that are highly expressed in synovial sarcoma. Included in this group are receptor tyrosine kinases such as epidermal growth factor receptor, insulin-like growth factor receptor 1, fibroblast growth factor receptor 3, KIT, and HER2. Inhibitors of these growth-promoting receptors are likely to inhibit proliferation of synovial sarcoma; however, the effect of receptor tyrosine kinase inhibitors on synovial sarcoma is largely unknown. We assessed the ability of the following receptor tyrosine kinase inhibitors to halt proliferation and induce apoptosis in synovial sarcoma monolayer and three dimensional spheroid in vitro models: gefitinib (Iressa), NVP-AEW541, imatinib mesylate (Gleevec), SU5402, trastuzumab (Herceptin), and 17-allylamino-17-demethoxygeldanamycin (17-AAG). Gefitinib, NVP-AEW541, and imatinib inhibited proliferation only at relatively high concentrations, which are not clinically applicable. 17-AAG, which destabilizes multiple receptor tyrosine kinases and other oncoproteins through heat shock protein 90 inhibition, prevented proliferation and induced apoptosis in synovial sarcoma monolayer models at concentrations achievable in human serum. 17-AAG treatment was also associated with receptor tyrosine kinase degradation and induction of apoptosis in synovial sarcoma spheroid models. 17-AAG was more effective than doxorubicin, particularly in the spheroid models. Here we provide in vitro evidence that 17-AAG, a clinically applicable drug with known pharmacology and limited toxicity, inhibits synovial sarcoma proliferation by inducing apoptosis, and thus has potential as a systemic therapy for this disease.Synovial sarcoma accounts for f7% to 10% of soft tissue malignancies and is associated with significant morbidity and mortality (1). Approximately 50% of patients will die from metastatic disease within 10 years of diagnosis despite treatment; the efficacy of conventional chemotherapeutics is controversial, although a recent report has suggested that combination doxorubicin/ifosfamide therapy offers a modest survival advantage in advanced cases (2,3).A translocation between SYT on chromosome 18 and SSX1 or SSX2 on chromosome X is characteristic of synovial sarcoma and is the only apparent cytogenetic abnormality in one third of cases (4). The biological roles of SYT and SSX are poorly understood; studies suggest that SYT functions as a transcriptional activator and SSX as a transcriptional repressor (4), although neither binds DNA directly. This implies that the SYT-SSX fusion protein combines these opposing activities and contributes to the pathogenesis of synovial sarcoma by dysregulating transcriptional patterns (4, 5). Expression profiling studies have identified a number of genes that are highly expressed in synovial sarcoma, including known oncog...

Editorial: The Long and Winding Road to Better Cancer Cell–Specific Therapies

“…Because no mutated HER-1 genes were found in synovial sarcomas, in retrospect, gefitinib was unlikely to exert antitumor activity in these entities, consistent with the findings from the clinical study [3]. Accordingly, gefitinib inhibited proliferation of synovial sarcoma cell lines only at high concentrations, which are too high to be reached in humans [12]. If EGFR is indeed involved in the 594 pathogenesis of synovial sarcomas, it is in its wild-type form.…”

Fibroblast Growth Factor Receptor 3 (FGFR3) Is a Strong Heat Shock Protein 90 (Hsp90) Client

“…For example, a proteomics screen for proteins that interact with the dimerized transmembrane and intracellular domains of FGFR1 detected Hsp90 and Cdc37 (51). A report that Hsp90 inhibitors destabilize oncogenes implicated in synovial sarcoma included FGFR3 as a kinase that responds to Hsp90 inhibition (52). Most recently, subtypes of FGFR3-driven multiple myeloma were shown to be sensitive to a new Hsp90 inhibitor (53).…”

Histone deacetylase inhibitors induce growth arrest, apoptosis, and differentiation in clear cell sarcoma models

“…Cell Growth Assays and Cell Cycle Analysis The growth of cells was assessed as previously described (26) by measuring the absorbance of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Monolayer cultured cells were subcultured in 24-well plates and treated in triplicate wells with media containing final concentrations of MS-275, romidepsin, doxorubicin, or vehicle control (DMSO).…”

“…Antimouse and antirabbit fluorescently labeled secondary antibodies were purchased from LI-COR Biosciences. Total cellular protein lysates were harvested, quantified, and immunoblotted as previously described (26). Western blot analysis was done using an Odyssey infrared imaging system.…”