Ultrasonic waves used to target drugs to tumours
Biomedical engineers at the University of Southern California (USC) have proposed a new ultrasonic method to enable acoustic control and real-time tracking of cancer drugs within the body, in a study led by Qifa Zhou and published in the journal Applied Physics Letters.
Accurate drug delivery is crucial to ensure tumour obliteration, while avoiding the toxic side effects of cancer therapeutics on healthy tissue. The lack of a clinically viable method to track and direct cancer drugs to tumours is currently a big problem for targeted therapeutics.
Ultrasound is a popular method for non-invasively imaging inside the body, but because the conventional method lacks sensitivity, it has not been used in drug delivery previously. Zhou’s team adapted a new, ultrafast ultrasound method that eliminates background noise to accurately track a drug delivery vehicle within a phantom blood vessel.
“In conventional drug delivery, tissue is examined ex vivo under the microscope or radioactive materials are used to trace drugs in vivo,” said postdoctoral researcher Xuejun Qian. “We propose a new way to image and move the drug precisely inside the human body by combining the new plane wave imaging method with a focused ultrasound transducer.”
Hanmin Peng, a visiting scholar from Nanjing University of Aeronautics and Astronautics, and co-workers pumped water through a narrow silicone tube to mimic blood flow through a blood vessel. They placed the tube beneath real pig tissue and imaged across this to make the set-up more realistic. Microbubbles — tiny pockets of air that can be used as vehicles for drug delivery — were introduced into the fake blood vessels.
In recent years, there’s been much excitement over the ability to focus sound waves into ‘acoustic tweezers’ that can manipulate particles. Zhou’s team applied a focused ultrasound transducer to trap the microbubbles identified by their ultrafast imaging system.
The team predicted microbubble motion and calculated the acoustic radiation forces required to trap and move the bubbles to specific areas in the phantom blood vessel. By balancing the acoustic radiation force from the transducer, the team moved the trapped microbubbles to a specific location on the tube wall and turned up the acoustic power to burst the bubbles.
Ultrasound waves vibrate the air contained within microbubbles, which enabled Peng and co-workers to use their ultrafast ultrasound imaging system to precisely track the microbubbles at depths of up to 10 mm within the tissue. They hope this combination of ultrasound tracking and targeting can be translated to non-invasively directing drug-containing microbubbles to blood vessels adjacent to tumour locations in the body.
“We want to try in vivo studies on rat or rabbit to see whether the proposed method can monitor and release microbubble-based drug delivery in a real body,” Qian said. “We hope to further improve the imaging resolution, sensitivity and speed within a real case, and if it works, the long-term goal would be to move towards a human study.”
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