Drug-carrying nanoparticles not reaching targets

Much research has gone into developing carefully engineered nanoparticles to carry drugs directly to specific sites in the body, such as cancerous tumours. Now, an international team has shown that, despite many nanoparticle designs and animal trials conducted over the past decade, the delivery efficiency of nanoparticles to solid tumour targets is still too low for effective treatment in humans.  

Medical nanoparticles carry drugs on their surface or have a drug-filled core. They release medication in response to triggers such as light or chemical reactions. Certain artificial nanostructures show particular promise in seeking out cancer cells in cell cultures and mouse models.  

“We wanted to know why, despite exciting research over the last decade, very few nanoparticles have been used in patients.” says Warren Chan at the Donnelly Center for Cellular and Biomolecular Research at the University of Toronto. “We decided to look at the field more closely.” 

There are myriad obstacles to overcome as nanoparticles travel through the body, such as passing through major organs without being destroyed or avoiding the premature release of their drug cargo. As a result, the percentage of administered nanoparticles that reach their destination is far lower than the original dose. Low ‘delivery efficiency’ results in a need to increase dosage, increasing costs and the potential for toxicity. 

To investigate current nanoparticle delivery efficiency for cancer tumours, Chan and his team collated and analyzed data from 117 relevant research projects from the last ten years. 

“We were really surprised by what we uncovered,” says Chan. “We thought the average delivery efficiency would probably be low, say 5-10%, but we were astonished to find that it was actually less than 1%.” 

The researchers found that the mid-point – or median – of all the collated data suggested only 0.7% of the administered dose reached solid tumours during animal trials. In response to this discovery, Chan and his team are recommending a new 30-year research strategy for perfecting medical nanoparticles.  

“Ultimately, we all want to see nanotechnology used in patient care,” says Chan. “We have built an open-access database into which researchers can input and share new data. The database automatically calculates delivery efficiency and conducts other key statistical analyses. This will help us determine progress more easily.”

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