A multifunctional theranostic contrast agent for ultrasound/near infrared fluorescence imaging-based tumor diagnosis and ultrasound-triggered combined photothermal and gene therapy

Abstract Purpose Encapsulated microbubbles (MBs) have been reported as new theranostic carriers for simultaneous imaging and ultrasound (US)-triggered therapy. Here, we designed a dual-modality US/NIRF contrast agent and extended its applications from image contrast enhancement to combined diagnosis and therapy with US-directed and site-specific targeting. Methods Gold nanorods (AuNRs) resonant at 880 nm together with the NIR797 dye were first encapsulated in lipid-shelled MBs to construct fluorescent gold microbubbles (NIR797/AuMBs) via thin film hydration and mechanical shaking in the presence of sulfur hexafluoride (SF6) gas. Then, polyethylenimine (PEI)-DNA complexes were electrostatically conjugated onto the surface of the NIR797/AuMBs, forming theranostic encapsulated MBs (PEI-DNA/NIR797/AuMBs). The potential of the PEI-DNA/NIR797/AuMBs for use as a dual-modality contrast enhancement agent was evaluated in vitro and in vivo. The antitumor effect of US/NIR laser irradiation mediating double-fusion suicide gene and photothermal therapy was also investigated using Bel-7402 cells and xenografts. Results The developed theranostic AuMB complexes could not only provide excellent US and NIRF imaging to detect tumors but also serve as an efficient US-triggered carrier for gene delivery and photothermal ablation of tumors in xenografted nude mice. And US + laser exposure group showed a much higher rate of cell inhibition, apoptosis and necrosis as well as a higher Bel-7402 xenograft inhibition rate than the single gene therapy or single exposure (US or laser) group. Conclusions PEI-DNA/NIR797/AuMBs would be of great value for providing more comprehensive diagnostic information and to guide more accurate and effective synergistic cancer therapy. Statement of Significance This is an original paper focusing on developing a dual-modality US/NIRF contrast agent and extended its applications from image contrast enhancement to combined diagnosis and therapy with US-directed and site-specific targeting. The developed theranostic AuMB complexes could not only provide excellent US and NIRF imaging to detect tumors but also serve as an efficient US-triggered carrier for gene delivery and photothermal ablation of tumors in xenografted nude mice. PEI-DNA/NIR797/AuMBs would be of great value for providing more comprehensive diagnostic information and to guide more accurate and effective synergistic cancer therapy.