Abstract: Objective To evaluate the feasibility of integrating cancer gene therapy with therapeutic effect evaluation using
siRNA-loaded nano-scale microbubbles (siRNA-NBs). Methods siRNA-NBs were prepared by hetero-assembly of polymeric
siRNA micelles and liposomal microbubbles, and the particle sizes and surface potentials were examined with dynamic light
scattering. The distributions of cy3-labled siRNA in the tumor tissues were evaluated using confocal laser scanning
microscopy. A siRNA targeting the anti-apoptosis gene SIRT2 was designed and its gene silencing effects was tested in vivo
using siRNA-NBs with ultrasound exposure. The therapeutic effect of the loaded siRNA-NBs was evaluated by
contrast-enhanced ultrasonography. Results The siRNA-NBs had a mean diameter of 400.7 ± 30.5 nm with a weak positive
charge of +8.8±0.8 mV. With ultrasound exposure, siRNA-NBs effectively delivered cy3-siRNA into the cytoplasm of cancer
cells and caused SIRT2 suppression and cell apoptosis in tumor tissues, resulting in significantly suppressed tumor growth. In
addition, contrast-enhanced ultrasonography of siRNA-NBs provided good imaging quality to allow real-time observation of
blood supply during gene therapy. Conclusions As a novel ultrasound contrast agent, siRNA-NBs make possible the
integration of tumor gene therapy and therapeutic effect evaluation for cancer.