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.
