Overcoming chemoresistance in osteosarcoma: the role of autophagy in cell death or survival following chemotherapy

For the past 30 years, long-term survival rates in metastatic and recurrent osteosarcoma (OS) patients has remained unchanged. Drug resistance is thought to be the main cause and overcoming this phenomenon is a key step towards greater efficacy in OS therapy. Increasing evidence shows that autophagy, a ‘self-degradation’ pathway, can act as a protective mechanism to help cancer cells thrive under chemotherapeutic stress. The current study investigated the implication of autophagy in metastatic OS progression and further investigated the functional role of autophagy in two OS cell lines in response to two standard chemotherapy treatments, doxorubicin and cisplatin. The results from the tissue OS microarray showed that advanced grade and stage tumours express high levels of autophagy marker LC3. Bioinformatics showed how MAP1LC3B (LC3B gene) can be highly expressed in tumours associated with poor disease outcome. Drug-treated OS cell lines showed a remarkable increase in LC3 puncta (autophagy marker) detected by Immunofluorescence. Additionally, drug-treated OS cell lines showed increase autophagic flux (LC3-I/LC3-II protein conversion) that correlated with reduced p62/SQSTM1 expression, analysed by Western Blot. RT-PCR results confirmed this pattern. Combination of chloroquine (CQ) with chemotherapy had a significant effect on OS cell proliferation and cell death rate. However, the results of CQ combination could not be attributed to autophagy inhibition, due to the substantial cytotoxic effects that was associated with single CQ treatment. In conclusion, there is strong evidence to suggest advanced OS tumours highly express autophagy to aid in their progression and metastatic potential. Chemotherapy can significantly induce autophagy in OS cell lines, with more profound effect seen on the highly metastatic HOS-143B cells. Therefore, chemotherapy-induced autophagy is predominantly a survival strategy in metastatic OS, although further studies are required to understand the underlying mechanism.