PDGFRα, PDGFRβ and KIT expression/activation in conventional chondrosarcoma

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Chondrosarcomas represent 20% of all primary bone sarcomas, and many studies have attempted to unravel molecular targets for future development of new therapies. The aim of this study was to investigate the expression/activation of PDGFRα, PDGFRβ and KIT receptor tyrosine kinases (RTKs) as potential therapeutic targets inconventional central primarychondrosarcomas (CCS). The expression of PDGFRα, PDGFRβ and KIT RTKs was detected in 16 CCSs using immunohistochemistry (IHC), and their level of expression and activation status were analysed by immunoprecipitation and western blot experiments.PDGFRα,PDGFRβ andKITcDNAs were screened to verify the presence of activating mutations and the presence of the cognate ligands was analysed by means of RT-PCR.RTKgene amplification was further studied by means of fluorescencein situhybridization (FISH) analysis. The immunophenotyping and biochemical analyses showed that the CCSs co-expressed PDGFRα and PDGFRβ, with the latter showing definitively greater protein expression and phosphorylation levels. PDGFRβ was expressed but not activated in control healthy joint cartilage, in line with no PDGFB detection. Conversely, the KIT gene product did not seem to play a relevant role. These findings, in the absence of activating mutations or an abnormal genomic profile and the presence of PDGFA and PDGFB expression, are consistent with an autocrine/paracrine loop activation of the corresponding receptors. The CCS gene profile described here offers a rationale for the use of RTK inhibitors alone or in combination with chemotherapy, and supports further investigation of RTKs and their downstream signals.

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