Characterization of an inversion on the long arm of chromosome 10 juxtaposing D10S170 and RET and creating the oncogenic sequence RET/PTC

RET/PTC is a transforming sequence created by the fusion of the tyrosine kinase domain of the RET protooncogene with the 5\u2032 end of the locus D10S170 designated by probe H4 and is frequently found activated in human papillary thyroid carcinomas. RET and D10S170 have been mapped to contiguous regions of the long arm of chromosome 10: q11.2 and q21, respectively. To identify the mechanism leading to the generation of the oncogenic sequence RET/PTC, a combined cytogenetic and molecular analysis of several cases of papillary thyroid carcinomas was done. In four cases the results indicated that these tumors had RET/PTC activation and a paracentric inversion of the long arm of chromosome 10, inv(10)(q11.2q21), with breakpoints coincident with the regions where RET and D10S170 are located. Therefore, a chromosome 10q inversion provides the structural basis for the D10S170-RET fusion that forms the hybrid transforming sequence RET/PTC

The modifier role of RET-G691S polymorphism in hereditary medullary thyroid carcinoma : functional characterization and expression/penetrance studies

Background: Hereditary medullary thyroid carcinoma (MTC) is caused by germ-line gain of function mutations in the RET proto-oncogene, and a phenotypic variability among carriers of the same mutation has been reported. We recently observed this phenomenon in a large familial MTC (FMTC) family carrying the RET-S891A mutation. Among genetic modifiers affecting RET-driven MTC, a role has been hypothesized for RET-G691S non-synonymous polymorphism, though the issue remains controversial. Aim of this study was to define the in vitro contribution of RET-G691S to the oncogenic potential of the RET-S891A, previously shown to harbour low transforming activity. Methods: The RET-S891A and RET-G691S/S891A mutants were generated by site-directed mutagenesis, transiently transfected in HEK293T cells and stably expressed in NIH3T3 cells. Their oncogenic potential was defined by assessing the migration ability by wound healing assay and the anchorage-independent growth by soft agar assay in NIH3T3 cells stably expressing either the single or the double mutants. Two RET-S891A families were characterised for the presence of RET-G691S. Results: The functional studies demonstrated that RET-G691S/S891A double mutant displays a higher oncogenic potential than RET-S891A single mutant, assessed by focus formation and migration ability. Moreover, among the 25 RET-S891A carriers, a trend towards an earlier age of diagnosis was found in the MTC patients harboring RET-S891A in association with RET-G691S. Conclusions: We demonstrate that the RET-G691S non-synonymous polymorphism enhances in vitro the oncogenic activity of RET-S891A. Moreover, an effect on the phenotype was observed in the RET-G691S/S891A patients, thus suggesting that the analysis of this polymorphism could contribute to the decision on the more appropriate clinical and follow-up management

Response to sunitinib malate in advanced alveolar soft part sarcoma

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

Identification of thyroid tumor cell vulnerabilities through a siRNA-based functional screening

The incidence of thyroid carcinoma is rapidly increasing. Although generally associated with good prognosis, a fraction of thyroid tumors are not cured by standard therapy and progress to aggressive forms for which no effective treatments are currently available. In order to identify novel therapeutic targets for thyroid carcinoma, we focused on the discovery of genes essential for sustaining the oncogenic phenotype of thyroid tumor cells, but not required to the same degree for the viability of normal cells (non-oncogene addiction paradigm). We screened a siRNA oligonucleotide library targeting the human druggable genome in thyroid cancer BCPAP cell line in comparison with immortalized normal human thyrocytes (Nthy-ori 3-1). We identified a panel of hit genes whose silencing interferes with the growth of tumor cells, while sparing that of normal ones. Further analysis of three selected hit genes, namely Cyclin D1, MASTL and COPZ1, showed that they represent common vulnerabilities for thyroid tumor cells, as their inhibition reduced the viability of several thyroid tumor cell lines, regardless the histotype or oncogenic lesion. This work identified non-oncogenes essential for sustaining the phenotype of thyroid tumor cells, but not of normal cells, thus suggesting that they might represent promising targets for new therapeutic strategies

Imatinib mesylate in chordoma

BACKGROUND. To the authors' knowledge, no effective medical therapy currently is available for advanced chordoma. Imatinib mesylate is a tyrosine kinase inhibitor targeting platelet-derived growth factor receptor-\u3b2 (PDGFRB), BCR-ABL, and KIT. METHODS. Six patients with advanced chordoma were treated with imatinib mesylate at a dose of 800 mg daily. In all patients, the tumor was found to be positive for PDGFRB, and in four patients PDGFRB was shown to be phosphorylated/ expressed. RESULTS. After a treatment period of 65 1 year, overt tumor liquefaction was evident on computed tomography (CT) scan in the first patient. In previous months, a decrease in contrast enhancement on magnetic resonance imaging (MRI) and a decrease in glucose uptake on positron emission tomography (PET) were detected. Similar signs on MRI and PET were observed in subsequent patients, who had a shorter treatment period. One of these patients initially was removed from therapy and then was readmitted to therapy because of difficulties with regard to tumor response assessment; 1 month after the reinitiation of therapy, an overt decrease in tumor density was visible on CT scan in this patient. In four of five symptomatic patients, a subjective improvement was observed early in the course of treatment. The first patient died after 17 months, with a sizeable, mostly liquefied mass. Another patient died early, apparently of unrelated causes. The remaining patients were on therapy at the time of last follow-up. CONCLUSIONS. Imatinib mesylate has been found to have antitumor activity in patients with chordoma. This activity might be mediated by inactivation of PDG-FRB. Tumor response manifests through patterns that are similar to those observed in patients with gastrointestinal stromal tumors who respond to molecular-targeted therapy, but evolves more slowly. The benefit to the patient entailed by this pattern of tumor response in chordoma needs to be elucidated, but may be limited in the presence of significant local disease

RET inhibition : implications in cancer therapy

Introduction: The RET gene encodes a receptor tyrosine kinase essential for ontogenesis of the enteric nervous system and kidney. Following identification of RET, it was found that somatic rearrangements of this gene, conventionally designated as RET/PTC, are frequently present in papillary thyroid carcinoma. Subsequently, activating germ line point mutations of RET were identified as being responsible for the hereditary medullary thyroid carcinoma syndromes MEN2A, MEN2B and FMTC. RET rearrangements have recently been identified in a small fraction of lung adenocarcinomas.Area covered: The authors review the current field concerning the RET gene and protein, its involvement in cancer and the preclinical and clinical studies which highlight its role as a potentially important therapeutic target for several cancers.Expert opinion: Many multitargeted inhibitors which crossreact with RET have been developed and investigated in clinical trials targeting many cancer indications. In particular, VEGFR/PDGFR inhibitors, widely explored as antiangiogenics, have been intensively studied in thyroid carcinoma patients. Notwithstanding the efficacy observed with such agents, their common clinical activity in thyroid carcinoma is of short duration and includes frequent and severe side effects, limiting their therapeutic action. These findings are discussed and the need for improved, more specific RET-targeting drugs is highlighted