No abstract

To elucidate the mechanisms behind the high sensitivity of myxoid/round cell liposarcoma (MRCL) to trabectedin and the suggested selectivity for specific subtypes, we have developed and characterized three MRCL xenografts, namely ML017, ML015 and ML004 differing for the break point of the fusion gene FUS-CHOP, respectively of type I, II and III. FUS-CHOP binding to the promoters of some target genes such as Pentraxin 3 or Fibronectin 1, assessed by chromatin immunoprecipitation, was strongly reduced in the tumor 24 h after the first or the third weekly dose of trabectedin, indicating that the drug at therapeutic doses causes a detachment of the FUS-CHOP chimera from its target promoters as previously shown in vitro. Moreover, the higher sensitivity of MRCL types I and II appears to be related to a more prolonged block of the transactivating activity of the fusion protein. Doxorubicin did not affect the binding of FUS-CHOP to target promoters. Histologically, the response to trabectedin in ML017 and ML015 was associated with a marked depletion of non-lipogenic tumoral cells and vascular component, as well as lipidic maturation as confirmed by PPARγ2 expression in western Blot. By contrast, in ML004 no major changes either in the cellularity or in the amount of mature were found, and consistently PPARγ2 was null. In conclusion, the data support the view that the selective mechanism of action of trabectedin in MRCL is specific and related to its ability to cause a functional inactivation of the oncogenic chimera with consequent derepression of the adypocytic differentiation.

We have previously demonstrated that chordomas express activated platelet-derived growth factor receptor (PDGFRB) and that treatment with imatinib, which is capable of switching off the activation of various receptor tyrosine kinases (RTKs) including PDGFRB, benefits a number of patients. The aim of this study was to identify the possible presence of other activated RTKs and their downstream signaling effectors. Cryopreserved material from 22 naïve sporadic chordomas was investigated for the presence of activated RTKs and their cognate ligands and downstream signaling effectors by means of human phospho-RTK antibody arrays, Western blotting, and molecular analysis; immunohistochemistry and fluorescence in situ hybridization were used to analyze the corresponding formalin-fixed and paraffin-embedded samples. We detected activated PDGFRB, FLT3, and colony stimulating factor 1 receptor (CSF1R) of the PDGFR family and highly phosphorylated EGFR, HER2/neu, and (to a lesser extent) HER4 of the EGFR family. The detection of PDGFRB/PDGFB confirmed our previous data. The presence of activated EGFR was paralleled by the finding of high levels of epidermal growth factor (EGF) and transforming growth factor alpha (TGFalpha) and PDGFB co-expression and PDGFRB co-immunoprecipitation. Of the downstream effectors, the PI3K/AKT and RAS/MAPK pathways were both activated, thus leading to the phosphorylation of mammalian target of rapamycin (mTOR) and 4E-BP1 among the regulators involved in translational control. Taken together, our results (i) provide a rationale for tailored treatments targeting upstream activated receptors, including the PDGFR and EGFR families; (ii) support the idea that a combination of upstream antagonists and mTOR inhibitors enhances the control of tumor growth; and (iii) indicate that the 4E-BP1/eIF4E pathway is a major regulator of protein synthesis in chordoma.

Purpose: Alveolar soft part sarcoma (ASPS) is a rare, chemoresistant soft tissue sarcoma. ASPS harbors the t(17-X) (p11.2;q25) translocation, resulting in the ASPACR1-TFE3 fusion protein, causing MET autophosphorylation and activation of downstream signaling. The tumor vascular pattern prompted us to use sunitinib malate (SM), a tyrosine kinase inhibitor with antiangiogenic properties. Experimental Design: Since July 2007, five patients with progressive metastatic ASPS have been treated with continuous SM 37.5 mg/d on a named basis. Four patients are evaluable for response. In four cases, cryopreserved material was available. Upstream and downstream targets of receptor tyrosine kinase (RTK) pathways, as well as mechanisms of activation, were investigated by biochemical profiles, including human phospho-receptor RTK antibody arrays and immunoprecipitation/Western blotting, molecular analyses, immunohistochemistry, and fluorescence in situ hybridization analyses. Results: After 3 months, two patients had RECIST (response evaluation criteria in solid tumor) partial response, as well as positron emission tomography response and subjective improvement. One had a RECIST stable disease. One progressed and stopped treatment. One patient is still responding after 12 months. The upstream analysis showed activation of all the platelet-derived growth factor receptor (PDGFR) family members, as well as epidermal growth factor receptor, MET families, and RET. Vascular endothelial growth factor receptors (VEGFR1 and VEGFR2) were activated only in one case. The downstream target analysis showed strong activation of phosphatidylinositol 3-kinase/AKT, extracellular signal-regulated kinase 1/2, and mTOR and its targets (S6K and S6).The absence of any upstream mTOR effector deregulation and the presence of RTK cognate ligands support an autocrine-paracrine activation loop mechanism. Conclusion: SM may have antitumor activity in ASPS, possibly through a mechanism involving PDGFR and RET.The role of MET, epidermal growth factor receptor, and mTOR, as well as PDGFR inhibition, needs to be further explored.