Besides conventional chondrosarcoma, several rare chondrosarcoma subtypes are described, comprising about 15% of all chondrosarcomas. Clear cell chondrosarcoma (CCS) is a low-grade malignant tumour, often recurring after curettage, and showing overall survival of about 85%. Mesenchymal chondrosarcoma (MCS) is a highly malignant tumour occurring in bone and soft tissue of relatively young patients. The tumour shows differentiated cartilage mixed with undifferentiated small round cells. It often metastasises and shows a 5-year overall survival of 55%. Dedifferentiated chondrosarcoma (DDCS) is a tumour containing a high-grade non-cartilaginous sarcoma (DD), and a usually low-grade malignant cartilage-forming tumour (WD).

The prognosis is poor. The lack of efficacious treatment of these rare tumours emphasises the need to learn more about their characteristics and to unravel potential targets for therapy.

We constructed tissue microarrays (TMAs) with 2mm cores of 45 DDCS (WD and DD), 24 CCS, and 25 MCS, in triplicate.

Using immunohistochemistry, we investigated protein expression of estrogen-signaling molecules, growth plate-signaling molecules, and other molecules which might be potential targets for therapy. In addition, we gathered genomic information using Agilent 44K oligo arrays.

30% of the WD components were positive for Cox-2. Almost all others were negative. For Bcl2, 88% of the small cells and 32% of the cartilage in MCS were positive. In CCS, WD, and DD 48%, 4%, and 12% were positive, respectively. We demonstrated the presence of ESR1 and aromatase protein in the majority of tumours in all subtypes. Using array CGH, we observed similar aberrations in the two components of DDCS, with additional aberrations in the DD.

Celecoxib treatment is not recommended, as most of the tumours are negative for Cox-2. However, the presence of ESR1 and aromatase support a possible effect of anti-estrogen treatment in all subtypes, and application of Bcl2 inhibitors might chemosensitise MCS.

Chondrosarcomas are malignant hyaline cartilage tumours of bone. They are clinically resistant to conventional chemo- and radiotherapy and the underlying mechanism is poorly studied. Chemoresistance is a multifactorial process and the inaccessibility due to abundant hyaline cartilaginous matrix surrounding the cells, presence of multi-drug resistance pumps, and expression of anti-apoptotic proteins such as BCL2, have been suggested. Our aim was to study chemoresistance mechanisms in chondrosarcoma.

We first studied the sensitivity of chondrosarcoma cell lines (SW1353, CH2879, JJ012, OUMS27) and 2 primary cultures for doxorubicin and cisplatin. We used a 3D pellet model of CH2879 to study doxorubicin incorporation. To investigate whether chondrosarcoma cells could be resensitised to chemotherapy we tested the BH3 mimetic ABT737 inhibiting anti-apoptotic BCL2 family proteins. Cell viability was assessed using a WST assay for mitochondrial activity.

Dose response curves showed that chondrosarcoma cell lines and cultures are partially resistant to doxorubicin, while primary cultures were completely resistant to cisplatin. In 3D cell pellets, with morphology strongly resembling high grade chondrosarcoma, doxorubicin incorporation was confirmed. Chondrosarcoma cells responded to ABT737 with a >60% reduction in cell viability at high concentrations (25μM). Combination treatment allowing 2 days between ABT737 and chemotherapy addition led to a complete reduction of cell viability in all cell cultures.

In conclusion, chondrosarcoma cell lines show a partial response to doxorubicin and less response to cisplatin. The incorporation of doxorubicin in the cells in a 3D pellet model indicates that resistance is not caused by inaccessibility of the cells for the drugs nor by multi-drug resistance pump activity. By combining BCL2 inhibition with Doxorubicin treatment, a complete reduction of cell viability was obtained. This suggests that BCL2 overexpression plays an important role in chemoresistance of chondrosarcoma, and turning on the apoptotic machinery by BCL 2 inhibition can render them chemosensitive.