Contrast-Aided Diagnostic Ultrasound Does Not Enhance Lung Metastasis in a Mouse Melanoma Tumor Model

Abstract

Objective. The purpose of this research was to test the hypothesis that contrast-aided diagnostic ultrasound (CADUS) could exacerbate the metastatic spread of mouse melanoma tumor cells to the lungs. Methods. The melanoma cell lines B16 and B16-D5 (metastatic specifically to lung) were implanted on a hind leg of female C57/bl6 mice. Growing tumors were scanned by 1.5-MHz diagnostic ultrasound in a 37°C water bath. Four hundred image frames were triggered at a 1-Hz rate with 4 retroorbital injections of an ultrasonographic contrast agent at dosage of 10 µL/kg at 100-second intervals. Sham-treated mice received 400 frames of ultrasonography followed by the contrast agent with the ultrasound off. The primary tumor was surgically removed 1 day after ultrasound administration. Lungs were removed and evaluated blind after 2 weeks of bleaching in Fekete solution. Results. Three experiments were performed. The first experiment involved scanning sham and CADUS groups of 20 mice each with B16 tumors; B16 metastasis was not enhanced. The second experiment repeated this test with the D5 cell line; the metastasis enhancement was marginally significant for average number (0.3 and 3.2; P = .06) and incidence (3 and 9 of 19; P = .08) in mice without tumor recurrence. Finally, a third experiment was performed to clarify ambiguous results in the second experiment and consisted of 2 groups of 40 mice each. In this larger experiment, the results were essentially equal for the sham and CADUS groups. Conclusions. Overall, the results do not support the hypothesis of CADUSenhanced metastasis.

Evaluation of pulsed high intensity focused ultrasound exposures on metastasis in a murine model

“…In a preclinical study, similar results were found for ablative exposures in a highly metastatic prostate cancer line, implanted into the hind leg of rats, where increases in the number of lung metastases were not observed [14]. Furthermore, lower diagnostic levels of ultrasound exposures were not found to enhance metastases [15, 16]. In contrast, a study using non-thermal, high-amplitude ultrasound exposures (on subcutaneous tumors implanted into the hind leg of mice) did show a significant increase in the number of lung metastases, when compared to diagnostic ultrasound exposures.…”

“…Delaying or not amputating the tumor bearing leg would allow the primary tumor to seed additional metastases and increase metastatic burden, confounding the results and potentially resulting in detrimental effect on the health of the mice. [15, 16]. …”

A dedicated automated injection system for dynamic contrast‐enhanced MRI experiments in mice

“…At present, for various other studies, we routinely use the presented injection system for pre/post-CA T1w imaging and its success rate is now more than 90%. Retro-orbital injection has been reported an effective route to administer radioactive tracers for PET imaging (19) or microbubble contrast agents for ultrasonography (20) in mice. For our study, we chose the retro-orbital injection because pilot experiments with the same tumor mouse model showed that many tail vein injections failed, especially at later time points with progressed disease.…”

Biological Effects in Diagnostic Ultrasound

“…Subcutaneous melanoma tumors in mice, which have an enhanced potential for lung metastasis, were scanned intermittently with 1.5 MHz DUS during or after DEFINITY injection (Miller and Dou, 2005). Subcutaneous melanoma tumors in mice, which have an enhanced potential for lung metastasis, were scanned intermittently with 1.5 MHz DUS during or after DEFINITY injection (Miller and Dou, 2005).…”