Ultrasound-targeted
microbubble destruction (UTMD) can be used to deliver silencing gene
therapy to
tumors. We hypothesized that UTMD would be effective in suppressing angiogenesis within
tumors, and that modulation of the ultrasound pulsing intervals (PI) during UTMD would affect the magnitude of target knockdown. We performed UTMD of
vascular endothelial growth factor receptor-2 (VEGFR2) short hairpin (sh)
RNA plasmid in an heterotopic mammary
adenocarcinoma model in rats, evaluating PIs of 2, 5, 10, and 20 seconds. We demonstrated that UTMD with a PI of 10 seconds resulted in the greatest knockdown of VEGFR2 by PCR, immunostaining, western blotting, smaller
tumor volumes and perfused areas, and lower
tumor microvascular blood volume (MBV) and flow by contrast-enhanced ultrasound (CEU) compared with UTMD-treated
tumors at 2, 5, and 20 seconds, control
tumors,
tumors treated with intravenous
shRNA plasmid and scrambled plasmid. CEU perfusion assessment using the therapeutic probe demonstrated that
tumors were fully replenished with
microbubbles within 10 seconds, but incompletely replenished at PI-2 and PI-5 seconds. In conclusion, for anti-VEGFR2 cancer gene
therapy by UTMD, PI of 10 seconds results in higher target knockdown and a greater anti-angiogenic effect. Complete replenishment of
tumor vasculature with silencing gene-bearing
microbubbles in between destructive pulses of UTMD is required to maximize the efficacy of anti-angiogenic cancer gene
therapy.Molecular
Therapy -
Nucleic Acids (2013) 2, e94; doi:10.1038/mtna.2013.20; published online 21 May 2013.