Recent advances and pathological mechanisms in photodynamic and sonodynamic therapy in the treatment of bone tumors (Review)

Given the recent advances that have been made with photodynamic therapy (PDT) combined with sonodynamic therapy (SDT) (PDT/SDT; also known as SPDT), the application of this combination therapy in the clinic has provided another major breakthrough in the medical field, especially with regard to the treatment of deep tumors. Concerning its application in the treatment of bone tumors, numerous pathological mechanisms have been taken advantage of to overcome the barrier of tissue hypoxia, and SPDT is expected to achieve radical effects, with high penetration depth and low aggressiveness. In the present review, it is comprehensively shown how, according to the histoanatomy of bone tumors, PDT and SDT target cells in a coordinated manner, affecting such processes as necrotizing apoptosis, pyroptosis, autophagy and ferroptosis on the macroscopic level, and crucially, thrombosis at the vascular level, which leads to the triggering of immunogenic cell death in local and distant locations. Additionally, PDT and SDT have been shown to have roles in: i) degrading the extracellular matrix; ii) influencing the receptor activator of nuclear factor‑κB (RANK)/RANK ligand signaling pathway; iii) disrupting the equilibrium between glutathione peroxidase 4 and reactive oxygen species (ROS); and iv) destroying the microscopic structure of the bone tumor. Upon PDT/SDT stimulation, several mechanisms act in concert to ensure that the targeted bone tumor is eliminated. Furthermore, widely distributed ROS have been revealed to promote osteoclast formation and osteogenic mineralization through the regulation of macrophages, processes that greatly improve the effects of postoperative repair. Finally, the developmental prospects of bone tumor engineering in the future are discussed in the present review.