Ferrous Selenide Stabilized Black Phosphorus Heterojunction Sonosensitizer for MR Imaging-Guided Sonodynamic Therapy of Bladder Cancer

Abstract

It is urgent to develop an alternative dynamic therapy-based method to overcome the limited efficacy of traditional therapy methods for bladder cancer and the damage caused to patients. Sonodynamic therapy (SDT) has the advantages of high tissue penetration, high spatiotemporal selectivity, and being non-invasive, representing an emerging method for eradicating deep solid tumors. However, the effectiveness of SDT is often hindered by the inefficient production of reactive oxygen species and the nondegradability of the sonosensitizer. To improve the anti-tumor effect of SDT on bladder cancer, herein, a BP-based heterojunction sonosensitizer (BFeSe₂) was synthesized by anchoring FeSe₂ onto BP via P-Se bonding to enhance the stability and the effect of SDT. As a result, BFeSe₂ showed great cytotoxicity to bladder cancer cells under ultrasound (US) irradiation. BFeSe₂ led to a notable inhibition effect on tumor growth in subcutaneous tumor models and orthotopic tumor models under US irradiation. In addition, BFeSe₂ could also enhance T2-weighted magnetic resonance imaging (MRI) to achieve monitoring and guide treatment of bladder cancer. In general, BFeSe₂ sonosensitizer integrates MRI functions for precise treatment, promising great clinical potential for the theranostics of bladder cancer.

Fig. 1.

Schematic illustration of the BFeSe₂ as an MRI-guided agent for SDT. (A) This schematic outlines the simple preparation of BP-FeSe₂-CS (BFeSe₂) and (B) reveals its mechanism of enhanced SDT for bladder cancer.

Fig. 2.

Characterization of BFeSe₂. (A) TEM images of BP, FeSe₂, and BFeSe₂. (B) Corresponding elemental mapping images of BFeSe₂. (C) Zeta potential and (D) Raman spectra of BP, FeSe₂, and BFeSe₂. (E) XPS spectra of FeSe₂, BP, or BFeSe₂. (F to H) High-resolution XPS spectra of Fe 2p, Se 3d, and P 2p_, and the P–Se bond was formed.

Fig. 3.

Sonodynamic mechanism of BFeSe₂. (A) ESR spectra of •OH in H₂O, FeSe₂, BP, and BFeSe₂ with US (1.5 W/cm², 5 min). (B to D) The fluorescence imaging and corresponding quantitative statistical maps of total ROS and O₂^−· of MB49 cells after different treatments (n = 3). (E) The diagram of the mechanism of BFeSe₂ for enhanced SDT. Band gaps of (F) BP and (G) BFeSe₂. (H) Cyclic voltammetry curves of H₂O, FeSe₂, BP, and BFeSe₂. G1, Control; G2, BP; G3, FeSe₂; G4, BFeSe₂; G5, US; G6, BP + US; G7, FeSe₂ + US; G8, BFeSe₂ + US. **P < 0.01, ***P < 0.001.

Fig. 4.

In vitro cytotoxicity and SDT efficacy. (A) Fluorescence images of the coumarin-6-labeled BFeSe₂ in MB49 cells. (B to D) The cell viability of different treatment groups (n = 3). (E) Bio-TEM images of MB49 cells treated with BFeSe₂ for 4 and 24 h. (F) Bio-TEM images of MB49 cells treated with US and BFeSe₂ +US. G1, Control; G2, US; G3, BP; G4, BP + US; G5, FeSe₂; G6, FeSe₂ + US; G7, BFeSe₂; G8, BFeSe₂ + US. *P < 0.05, ***P < 0.001.

Fig. 5.

Untargeted metabolomics analysis of MB49 cells after different treatments. (A) Venn diagrams of various metabolites of different treatment groups. (B) PCA of metabolites extracted from MB49 cells with different treatments. (C) Volcanic diagrams of metabolites in MB49 cells treated with different treatments. (D) The heat maps of metabolites in MB49 cells were significantly different among different treatment groups. (E) KEGG bubble diagram of differential metabolites enrichment in pathways related to cell metabolism.

Fig. 6.

The antitumor effect in the MB49 subcutaneous tumor model. (A) Schematic diagram of the treatment plan of BFeSe₂ in MB49 tumor-bearing mice. The photograph of (B) mice and (C) tumor, (D) MRI images and tumor area statistical charts, (E) tumor relative volume, (F) tumor weight, and (G) body weight of the MB49 tumor-bearing model in each group. (H) Representative images of H&E staining, TUNEL histochemical, and Ki-67 immune histochemical. G1, Control; G2, BP; G3, FeSe₂; G4, BFeSe₂; G5, US; G6, BP + US; G7, FeSe₂ + US; G8, BFeSe₂ + US. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001.

Fig. 7.

The antitumor effect in the MB49 orthotopic bladder cancer model. (A) Schematic diagram of the treatment plan of BFeSe₂ in the MB49 orthotopic bladder cancer model. (B) The ultrasound images of the orthotopic bladder tumor. (C) Relative fluorescence intensity, (D) in vivo bioluminescence images, (E) survival rate, and (F) body weight of MB49 orthotopic cancer model in each group. (G) MRI images and the intensity of MRI signals of the MB49 orthotopic bladder cancer model before and after perfusion of BFeSe₂. (H) Representative images of H&E staining of the bladder tumors (scale bar, 500 μm). G1, Control; G2, BP; G3, FeSe₂; G4, BFeSe₂; G5, US; G6, BP + US; G7, FeSe₂ + US; G8, BFeSe₂ + US. *P < 0.05, ***P < 0.001.