Ultrasound Microbubble Delivery For Cancer Drugs


A new way to deliver cancer drugs deep into cancer tumor cells has been developed by scientists at Nanyang Technological University in Singapore. The method involves creating micro-sized gas bubbles coated with cancer drug particles and iron oxide nanoparticles, and then using magnets to direct these bubbles to gather around a specific tumor.

Then, ultrasound is employed to vibrate the microbubbles, giving them energy to direct the drug particles into a targeted area. Asst Prof Xu Chenjiefrom, who co-led the team of researchers, said the new method may solve some of the most pressing problems faced in chemotherapy used to treat cancer.

The big issue is that today’s chemotherapy drugs are mostly non-targeted. The drug particles flow in the bloodstream, damaging both healthy and cancerous cells. These drugs are usually flushed away quickly in organs such as the lungs and liver, limiting their effectiveness.

The remaining drugs are also not able to penetrate deep into the core of the tumor, leaving some cancer cells alive, which could lead to a resurgence in tumour growth.

Asst Prof Xu, who has been working on cancer diagnosis and drug delivery systems since 2004, explained:

“The first unique characteristic of our microbubbles is that they are magnetic. After injecting them into the bloodstream, we are able to gather them around the tumour using magnets and ensure that they don’t kill the healthy cells.

More importantly, our invention is the first of its kind that allows drug particles to be directed deep into a tumour in a few milliseconds. They can penetrate a depth of 50 cell layers or more – which is about 200 micrometres, twice the width of a human hair. This helps to ensure that the drugs can reach the cancer cells on the surface and also inside the core of the tumour.”

Tumour Penetration

Xu Chenjie
Asst Prof Xu Chenjie (left) and Assoc Prof Claus-Dieter Ohl (right) looking at the magnetic bubbles on a petri dish

Clinical Associate Professor Chia Sing Joo, a Senior Consultant at the Tan Tock Seng Hospital’s Endoscopy Centre and the Urology & Continence Clinic, and one of the consultants for this study, added:

“For anticancer drugs to achieve their best effectiveness, they need to penetrate into the tumour efficiently in order to reach the cystoplasm of all the cancer cells that are being targeted without affecting the normal cells.

Currently, these can be achieved by means of a direct injection into the tumour or by administering a large dosage of anticancer drugs, which can be painful, expensive, impractical and might have various side effects.”

Driving this research project is the need to find alternative solutions for drug delivery systems that are non-invasive and safe. Ultrasound, for example, uses sound waves with frequencies higher than those heard by the human ear. It is commonly used for medical imaging such as to get diagnostic images.

And magnets, which can draw and attract the microbubbles, are already in use in diagnostic machines such as Magnetic Resonance Imaging (MRI).

Moving forward, the team will be adopting this new drug delivery system in studies on lung and liver cancer using animal models, and eventually clinical studies. They estimate that it will take another eight to ten years before it reaches human clinical trials.

Yu Gao et al. Controlled nanoparticle release from stable magnetic microbubble oscillations, NPG Asia Materials (2016). DOI: 10.1038/am.2016.37

Image: Annie Cavanagh, Wellcome Images