Pulsed high-intensity focused ultrasound enhances systemic administration of naked DNA in squamous cell carcinoma model: initial experience.
OBJECTIVE
To determine whether exposures to pulsed high-intensity focused ultrasound can enhance local delivery and expression of a reporter gene, administered with systemic injection of naked DNA, in tumors in mice.


METHODS
The study was performed according to an approved animal protocol and in compliance with guidelines of the institutional animal care and use committee. Squamous cell carcinoma (SCC7) tumors were induced subcutaneously in both flanks of female C3H mice (n = 3) and allowed to grow to average size of 0.4 cm(3). In each mouse, one tumor was exposed to pulsed high-intensity focused ultrasound while a second tumor served as a control. Immediately after ultrasound exposure, a solution containing a cytomegalovirus-green fluorescent protein (GFP) reporter gene construct was injected intravenously via the tail vein. The mouse was sacrificed 24 hours later. Tissue specimens were viewed with fluorescence microscopy to determine the presence of GFP expression, and Western blot analysis was performed, at which signal intensities of expressed GFP were quantitated. A paired Student t test was used to compare mean values in controls with those in treated tumors. Histologic analyses were performed with specific techniques (hematoxylin-eosin staining, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling) to determine whether tumor cells had been damaged by ultrasound exposure.


RESULTS
GFP expression was present in all sections of tumors that received ultrasound exposure but not in control tumors. Results of signal intensity measurement at Western blot analysis showed expressed GFP to be nine times greater in ultrasound-exposed tumors (160.2 +/- 24.5 [standard deviation]) than in controls (17.4 +/- 11.8) (P = .004, paired Student t test). Comparison of histologic sections from treated tumors with those from controls revealed no destructive effects from ultrasound exposure.


CONCLUSIONS
Local exposure to pulsed high-intensity focused ultrasound in tumors can enhance the delivery and expression of systemically injected naked DNA.
Dittmar
Kristin M
KM
Department of Radiology, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA.
Xie
Jianwu
J
Hunter
Finie
F
Trimble
Cameron
C
Bur
Monica
M
Frenkel
Victor
V
Li
King C P
KC
D000818:Animals; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000473:pathology*; D045744:Cell Line, Tumor; D003587:Cytomegalovirus / Q000235:genetics; D004274:DNA, Recombinant / Q000008:administration & dosage*; D005260:Female; D015870:Gene Expression / Q000502:physiology; D018014:Gene Transfer Techniques; D017930:Genes, Reporter / Q000235:genetics*; D015316:Genetic Therapy; D049452:Green Fluorescent Proteins / Q000235:genetics*; D020287:In Situ Nick-End Labeling; D007275:Injections, Intravenous; D051379:Mice; D008809:Mice, Inbred C3H; D008856:Microscopy, Fluorescence; D009374:Neoplasms, Experimental / Q000235:genetics / Q000473:pathology*; D012983:Soft Tissue Neoplasms / Q000235:genetics / Q000473:pathology*; D040521:Subcutaneous Tissue / Q000473:pathology; D014464:Ultrasonic Therapy
D004274:DNA, Recombinant; D049452:Green Fluorescent Proteins