Heat therapy tackles tumours
from the inside has shown promise in animal studies conducted at
Rice University in the US, writes Phil Taylor.
The treatment is based on tiny nanoparticles made out of gold - called nanoshells - that are heated from outside the body using harmless near-infrared light, and has already been shown to eradicate tumours in animal experiments.
Jennifer West, professor of bioengineering and chemical engineering at Rice, said that the results confirm the promise of the photothermal treatment for in vivo tumours.
The nanoshells consist of a silica core covered in a gold coating, and are about 200 times as small as a red blood cell. They can be tailored to respond to different wavelengths of light and, when exposed to the right wavelength, heat up sufficiently to destroy nearby cells.
A study published in the Proceedings of the National Academy of Sciences last year revealed that direct injection of the nanoshells into tumours and exposure to NIR light could be used to destroy tumours without harming healthy tissue. But in the latest research, published in the 25 June issue of the journal Cancer Letters, suggests that the particles can also be administered systemically.
Shining the light on the tumour - either through the skin or down a fibre optic catheter for deeper cancers, activates nanoshells in the vicinity of the lesion. Nanoshells have a tendency to accumulate in tumours because their blood vessels are more permeable.
The latest animal trial involved 25 mice with tumours ranging in size from 3-5.5 millimetres. The mice were divided into three groups. The first group was given no treatment. The second received saline injections, followed by three minutes exposure to near-infrared laser light. The final group received nanoshell injections and laser treatments.
In the test, researchers injected nanoshells into the mice, waited six hours to give the nanoshells time to accumulate in the tumours and then applied a 5 millimetre wide laser on the skin above each tumour.
All signs of tumours disappeared in the nanoshells group within 10 days. These mice remained cancer-free after treatment.
Tumours in the other two test groups continued to grow rapidly. All mice in these groups were sacrificed when the cancers reached 10 millimetres in size. The mean survival time of the mice receiving no treatment was 10.1 days, while the mean survival time for the group receiving saline injections and laser treatments was 12.5 days.
Surface temperature measurements taken on the skin above the tumours during the laser treatments showed a marked increase that averaged about 46 degrees Fahrenheit (7 degrees Centigrade) for the nanoshells group. There was no measurable temperature increase at the site of laser treatments in the saline group. Likewise, sections of laser-treated skin located apart from the tumour sites in the nanoshells group also showed no increase in temperature, indicating that the nanoshells had accumulated as expected within the tumours.
"The results of these first animal studies are very promising, and while we don't yet have a target date for our first human trial, our entire team is working hard to make this treatment available to cancer patients as soon as possible," said Naomi Halas of Rice, who invented the nanoshells in the 1990s.
"We have licensed the technology to the Nanospectra Biosciences, which will obtain the necessary approvals and funding for human trials," she added. It is expected that the first indications for the treatment will be in hard-to-access tumours, such as brain cancers.
The technology bears some similarities to so-called photodynamic therapy (PDT), in which dyes are injected into the circulation, accumulate in tumours and are activated using lasers to create cell-killing compounds.
This type of therapy is already commercialised, with products on the market including Axcan's Photofrin (porfimer sodium) for superficial cancers and Barrett's oesophagus and PhotoCure's MetVix (methyl aminolaevulinate) for basal cell carcinoma.
The Rice researchers believe that the nanoshells could be more flexible than dye-based PDT, as it can be tailored to tackle tumours of different depths using light of different wavelengths.
