Reversal of MPPa-PDT Resistance in Osteosarcoma by Targeting ROCK2-Mediated Autophagy.

Osteosarcoma (OS) is a primary bone tumour that occurs mostly in adolescents and is associated with a high degree of malignancy, early metastasis, and poor prognosis. Pyropheophorbide-a methyl ester-Photodynamic therapy (MPPa-PDT) is a new approach for the clinical treatment of osteosarcoma that develops after surgery and radiotherapy; however, the presence of MPPa-PDT resistance in osteosarcoma greatly limits its efficacy. In this study, we found that Rho-associated coiled-coil containing protein kinase 2 (ROCK2) expression increased in osteosarcoma cells after MPPa-PDT treatment. ROCK2 inhibition results in osteosarcoma sensitivity to MPPa-PDT and is accompanied by a decrease in cellular autophagy levels. Rescue experiments further showed that ROCK2 mediates MPPa-PDT resistance in osteosarcoma by regulating autophagy. Mechanistic studies have shown that ROCK2 mediates autophagy in osteosarcoma cells by regulating the Hippo signalling pathway. ROCK2 overexpression resulted in increased levels of the ROCK2-Salvador homology 1 (SAV1) complex and decreased levels of the mammalian STE20-like protein kinase 1 (MST1)-SAV1 complex, thereby inhibiting activation of the Hippo pathway, which in turn led to osteosarcoma MPPa-PDT resistance by regulating cellular autophagy. ROCK2 competes with MST1 for binding to the aa 28-198 region of SAV1. We also confirmed from a clinical perspective that ROCK2 is an independent prognostic factor in patients with osteosarcoma, is associated with worse patient prognosis, and correlates with the Hippo pathway. Targeted inhibition of ROCK2 by screening for J059-0149 increases the sensitivity of osteosarcoma to MPPa-PDT. In conclusion, our study establishes a novel mechanism to reverse MPPa-PDT resistance in osteosarcoma by targeting ROCK2-mediated autophagy, providing new targets and research ideas for the clinical treatment of osteosarcoma MPPa-PDT resistance.