[75] Homozygous Deletion of CDKN2 in Tumorigenic Mesenchymal Stem Cells: A Key Event for Osteosarcoma Genesis

AB Mohseny, K Szuhai, S Romeo, EP Buddingh, I Briaire-de Bruijn, D de Jong, M van Pel, PCW Hogendoorn, AM Cleton-Jansen. Leiden University Medical Center, Leiden, Netherlands

Background: Osteosarcoma (OS) is a malignant bone tumour in which associations with underlying hereditary diseases or germline mutations are limited. Given the young age of occurrence, a sequential accumulation of carcinogenic hits for malignant transformation is unlikely. Moreover, OS is characterized by extreme genetic instability. So identification of its cell of origin is crucial for characterizing genetic events responsible for OS formation and identifying alternative therapeutic targets. Potential cells of origin are mesenchymal stem cells (MSCs), given their role in normal bone remodeling during growth spurt and their multipotential differentiation commitment evoking the histological spectrum observed in OS. Accordingly we investigated murine MSCs as a model for OS formation.
Design: OS deriving murine MSCs were characterized at different stages, i.e. genetically (COBRA-FISH, arrayCGH), mRNA expression (qRT-PCR), phenotypically (FACS) and functionally (differentiation, adhesion-independency and tumour formation) to recapitulate OS formation upon malignant transformation of MSCs. Findings were verified on a clinical series of 144 OS cases, including biopsies, resections and metastases.
Results: Long-term in vitro culturing induced remarkable changes: aneuploidization, loss of CDKN2 locus, loss of CDKN2A/p16 gene expression, anchorage independent growth and subcutaneous OS formation in nude mice. Intriguingly, MSC characteristics remained as substantiated by specific markers expression and they retained capacity to differentiate towards osteoblasts, chondroblasts and adipocytes. On a clinical series, expression levels of the CDKN2A/p16 protein showed a significant correlation with patients survival (logrank, p<0.000).
Conclusions: Here we established a unique and reproducible model to study different steps in OS genesis. As compared to full blown OS this model allows far better detection of driving genetic mechanisms. Furthermore this model provides substantial evidence for a MSCs origin of OS and identifies CDKN2 deletion as a key event. The importance of loss of CDKN2A expression is clinically validated by its ability to predict survival better than the currently used response to chemotherapy.
Category: Bone & Soft Tissue

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 17, Tuesday Morning