Central chondrosarcoma progression is associated with pRb pathway alterations: CDK4 down-regulation and p16 overexpression inhibit cell growth in vitro

Chondrosarcomas are highly resistant to conventional radiation and chemotherapy, and surgical removal is the only option for curative treatment. Consequently, there is nothing to offer patients with inoperable tumours and metastatic disease. The aim of this study is to investigate genes involved in cell cycle control: CDK4, CDKN2A/p16, cyclin D1, p21, p53, MDM2 and c-MYC, which may point towards new therapeutic strategies. The pRb pathway was targeted using CDKN2A/p16 overexpressing vectors and shRNA against CDK4 in chondrosarcoma cell lines OUMS27, SW1353, and CH2879. Cell survival and proliferation were assessed. CDK4, MDM2 and c-MYC expression levels were investigated by qPCR and immunohistochemistry (IHC) in 34 fresh frozen and 90 FFPE samples of enchondroma and chondrosarcoma patients. On a subset of 29 high-grade chondrosarcomas IHC for cyclin D1, p21 and p53 was performed. The overexpression of CDKN2A/p16 and knockdown of CDK4 by shRNA in OUMS27, SW1353 and CH2879 resulted in a significant decrease in cell viability and proliferation and a decreased ability to form colonies in vitro. Expression of CDK4 and MDM2 was associated with high-grade chondrosarcoma both at the mRNA and protein level. Combining these results with the expression of cyclin D1 and the previously shown loss of CDKN2A/p16 expression show that the majority (96%; 28/29) of high-grade chondrosarcomas contain alterations in the pRb pathway. This suggests a role for the use of CDK4 inhibitors as a treatment of metastatic or inoperable high-grade chondrosarcoma.