Pulsed focused ultrasound exposures enhance locally administered gene therapy in a murine solid tumor model

Abstract

Gene therapy by intratumoral injection is a promising approach for treating solid tumors. However, this approach has limited success due to insufficient distribution of gene vectors used for gene delivery. Previous studies have shown that pulsed-focused ultrasound (pFUS) can enhance both systemic and local delivery of therapeutic agents in solid tumors and other disease models. Here, murine squamous cell carcinoma flank tumors were treated with single intratumoral injection of naked tumor necrosis factor-alpha (TNF-a) plasmid, either with or without a preceding pFUS exposure. The exposures were given at 1 MHz, at a spatial average, temporal peak intensity of 2660 W cm -2 , using 50 ms pulses, given at a pulse repetition frequency of 1 Hz. One hundred pulses were given at individual raster points, spaced evenly over the projected surface of the tumor at a distance of 2 mm. Exposures alone had no effect on tumor growth. Significant growth inhibition was observed with injection of TNF-a plasmid, and tumor growth was further inhibited with pFUS. Improved results with pFUS correlated with larger necrotic regions in histological sections and improved distribution and penetration of fluorescent surrogate nanoparticles. Electron microscopy demonstrated enlarged gaps between cells in exposed tissue, and remote acoustic palpation showed decreases in tissue stiffness after pFUS. Combined, these results suggest pFUS effects may be reducing barriers for tissue transport and additionally lowering interstitial fluid pressure to further improve delivery and distribution of injected plasmid for greater therapeutic effects. This suggests that pFUS could potentially be beneficial for improving local gene therapy treatment of human malignancies.

Pulsed ultrasound expands the extracellular and perivascular spaces of the brain

“…Notably, pulsed ultrasound has been used to modulate brain tissue in selected cortical and subcortical regions without evidence of neurological damage or significant histopathologic injury (Downs et al, 2015; McDannold et al, 2012). In addition, pulsed ultrasound can safely produce mechanical changes in the ECS of various tissues including fish epidermis (Frenkel et al, 2000b; Frenkel et al, 2001), murine flank muscle (Hancock et al, 2009), and squamous cell carcinoma xenografts (Ziadloo et al, 2013), resulting in increased tissue permeability. The structural changes in the ECS resulted in larger distributions of systemically and locally delivered nanoparticles, and enhanced the efficacy of a locally administered gene therapy in a solid tumor model (Ziadloo et al, 2013).…”

“…In addition, pulsed ultrasound can safely produce mechanical changes in the ECS of various tissues including fish epidermis (Frenkel et al, 2000b; Frenkel et al, 2001), murine flank muscle (Hancock et al, 2009), and squamous cell carcinoma xenografts (Ziadloo et al, 2013), resulting in increased tissue permeability. The structural changes in the ECS resulted in larger distributions of systemically and locally delivered nanoparticles, and enhanced the efficacy of a locally administered gene therapy in a solid tumor model (Ziadloo et al, 2013). Pulsed ultrasound exposures are thought to enlarge the interstitial spaces within the tissue through non-thermal mechanisms.…”

Localized, non-viral delivery of nucleic acids: Opportunities, challenges and current strategies

“…Bottom: Therefore, a larger region of necrosis is observed, ultimately leading to reduced tumor growth. Reprinted with permission from [123], Acoustic Society of America. a s i a n j o u r n a l o f p h a r m a c e u t i c a l s c i e n c e s x x x ( 2 0 1 5 ) 1 e1 7 with the body for an extended duration, NA delivery might be a promising alternative to protein or peptide delivery due to higher stability of NA and the ability to employ resident cells as bioreactors.…”

“…Ziadloo, Xie and Frenkel recently presented an alternative approach to gene delivery through sonoporation [123]. In contrast to many studies in the field, no microbubbles were used to improve ultrasound efficiency.…”

Emerging Applications of Therapeutic Ultrasound in Neuro-oncology

“…Electron microscopy revealed gaps, sometimes microns in size, between the tumor cells exposed to pFUS. 88 …”