"We are introducing here the idea of personalized nanomedicine," explains team leader Warren Chan in Toronto.

Nanotechnology is promising for delivering drugs and treating cancer, and nanomaterials can be fabricated with different sizes, shapes and surface chemistries as well as designed with unique properties. For instance, they can be engineered to emit light so that they can be detected by fluorescence imaging; to be magnetic for MRI; and to emit heat so that they can destroy cancer cells photothermally. However, despite their potential, less than 5% of an administered dose of nanoparticles actually reaches a tumour site because the materials either do not remain in the tumour for long enough and leak out, or because they are preferentially taken up by organs like the skin, spleen and liver.

Account for tumour properties

Changing the size, shape and surface chemistry has improved the tumour-targeting efficiency of many nanomaterials. But Chan and colleagues say that present-day nanomedicine is wrongly adhering to an ideology that nanoparticles and other nano-agents should have a "universal" design, regardless of the type or stage of a cancer they are meant to treat. "A tumour is a pretty complex structure and has different biological properties depending on the type of tumour, its size and how mature it is. These properties can in fact become barriers to nanoparticle transport and retention in the tumour."

One example of a tumour's property is its porosity: if the pores in a tumour are smaller than the size of the nanoparticles administered, the particles cannot enter and move within the tumour. "A tumour is also heterogeneous and this heterogeneity affects and/or prevents chemotherapeutic drugs from reaching it," explains Chan.

"If nanoparticles could instead be tailored according to the physiological state of each individual tumour, cancer detection and treatment might be drastically improved," he tells our sister site nanotechweb.org.

Tumour biology is equally important

In their experiments on mice with breast and prostate tumours, the researchers studied how methoxy-PEG-coated spherical gold nanoparticles (AuNPs) entered tumours of varying volumes and sizes and how long the particles remained at the different tumour sites. They also studied how AuNPs with different diameters (15, 30, 45, 60, and 100 nm) were taken up in a tumour. The particles were tracked thanks to fluorescent labels.

The researchers say that tumour biology is equally important as nanoparticle size when it comes to determining how efficient a nanoparticle is for treating a tumour. By thoroughly assessing the composition of different types of tumours, the team has also succeeded in developing a simple algorithm to rationally select the best AuNP composition/shape for treating individual tumours – taking their size, and how mature they are, into account.

For more on the latest developments in the application of physical sciences in cancer research, visit the journal Convergent Science Physical Oncology.

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