A previous study reported that moderate thermal effects (42 ℃) could significantly enhance the efficacy of PDT by increasing the photosensitization reaction rate and improving tumor hypoxia[
105-
107]. In light of these findings, Ju
et al.[
46] investigated whether the combination of SDT and thermal therapy could synergistically contribute to tumor ablation. They found that the group that received SDT plus thermal therapy had significantly high Bax and cleaved caspase-3, -8, and -9 expression levels, which indicated the apoptosis of tumor cells and excellent tumor ablation ability. Subsequently, MRI was introduced to monitor the thermal therapy of the tumor region during SDT and thermal treatment to achieve more accurate control of GBM treatment. Yoshida
et al.[
49] explored the combination of 5-ALA and transcranial MRI-guided FUS for SDT-thermal therapy
via in vitro and
in vivo experiments. The combination strategy could induce apoptosis and inhibit tumor growth and progression with minimal injury to healthy brain tissue. To improve the MRI imaging ability, Mn
2+ ions were introduced by Wan
et al.[
80], who developed Mn
2+-conjugated human serum albumin—Ce6 nanoassemblies (HCM NAs). HCM NAs with an average diameter of (75±2) nm were obtained. The HCM NAs exhibited similar ultraviolet—visible absorption spectra as those of free Ce6. Furthermore, the r
1 values were nearly three times higher than those of Magnevist [4.3 mmol/(L•s)]. U87 glioma cells incubated with NAs for 3 h and irradiated with SDT (1 W/cm
2, 2 min) at 42 ℃ tended to induce greater ROS generation, resulting in a higher percentage of apoptosis to achieve more efficient tumor cell eradication. Finally, the combination of SDT (1 W/cm
2) and moderate thermal therapy (42 ℃, 20 min, 1st and 4th day) completely inhibited tumor proliferation in a subcutaneous glioma mouse model, which significantly delayed tumor growth in an orthotopic U87 glioma mouse model after 5 weeks. To further investigate the tumor eradication function of MRgFUS, Wu
et al.[
81] explored the efficiency of different parameters of transcranial MRgFUS and real-time MRI thermometry monitoring using 5-ALA in combination in a rat brain tumor model. They found that the maximum temperature increase was (2.5±1.0) ℃ and (3.3±1.2) ℃ for 32 ℃ and 37 ℃, respectively, with core body temperatures corresponding to 20 min of MRgFUS at an ISPTA of 5.5 W/cm
2. Both regimens achieved significant inhibition of tumor growth and an increase in OS in an intracranial rat glioma tumor model, and there was no significant difference between the two groups. The author explained that the possible mechanism of SDT at these low intensities is not thermal but mechanical interaction of US and 5-ALA within the tumor, possibly
via the bursting of gas bubbles. We believe that the differences in the obtained results may be due to the efficiency of thermal generation of the sonosensitizers. 5-ALA cannot effectively generate sufficient thermal energy compared with HCM NAs. Therefore, by integrating MRI temperature monitoring and SDT-based thermal therapy, this comprehensive platform demonstrated certain advantages. First, with the application of an MRI temperature monitoring system, safety was well guaranteed. Second, the nanosonosensitizers not only achieved SDT effects but also contributed to accurate tumor imaging (e.g., HCM NAs). Finally, the synergistic tumor elimination effect was fulfilled with good biosafety. This platform might be a promising and effective therapeutic strategy for GBM treatment.