Inhibition of the autophagy pathway modulates osteosarcoma chemoresistance

Osteosarcoma is the most common primary malignant bone tumour. Although the introduction of chemotherapy has improved the survival rate of osteosarcoma patients, chemoresistance remains a major clinical problem underlying poor survival outcome. Previous studies have shown that deregulation of a cell survival process called autophagy is closely associated with this phenomenon. This study aims to further investigate the role of autophagy in osteosarcoma chemoresistance.

Activation of autophagy in HOS-143B cells following chemotherapy was confirmed by an increased autophagic flux and autophagic clearance of p62. Autophagy-related microRNA (miRNA) expression was found to be decreased in chemotherapy-treated HOS-143B cells. To investigate the role of the key autophagy gene ATG7, CRISPR/Cas9 technology was employed to disrupt ATG7 (ATG7-/-), resulting in the inhibition of autophagy and increased sensitivity to cisplatin. A kinase screen revealed a reduction in the phosphorylation of p53 (S15) in ATG7-/-HOS-143B cells (with/without cisplatin treatment), and ATR inhibition (ATR phosphorylates p53 at S15 responsible for DNA Damage Response; DDR) increased cisplatin sensitivity of HOS-143B cells by inducing cell death via apoptosis. Subsequent protein analysis verified that ATR inhibition decreased phosphorylation of p53 at S15 and reduced ATG7 levels/blocked autophagy in cisplatin-treated HOS-143B cells.

In summary, autophagy is activated in HOS-143B cells following chemotherapy, facilitating the recycling of damaged cellular components for sustained cell survival and proliferation. Knockout of ATG7 inhibited the autophagy pathway and enhanced cisplatin sensitivity, and ATR inhibition mimicked this effect of autophagy inhibition. These findings could ultimately lead to novel adjuvant therapy for osteosarcoma, lowering the dosage of cisplatin required. This could reduce the harsh side effects of cisplatin treatment and prevent tumour progression, potentially improving overall survival rate of osteosarcoma patients.