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Nano technology
US researchers have developed tiny nanoparticle robots that can
travel through a patient's blood and into tumours where they
deliver a therapy that turns off an important cancer gene.
The finding, reported in the journal Nature on Sunday, offers early
proof that a new treatment approach called RNA interference or RNAi
might work in people.
RNA stands for ribonucleic acid - a chemical messenger that is
emerging as a key player in the disease process.
Dozens of biotechnology and pharmaceutical companies including
Alnylam, Merck, Pfizer, Novartis and Roche are looking for ways to
manipulate RNA to block genes that make disease-causing proteins
involved in cancer, blindness or AIDS.
But getting the treatment to the right target in the body has
presented a challenge.
A team at the California Institute of Technology in Pasadena used
nanotechnology - the science of really small objects - to create
tiny polymer robots covered with a protein called transferrin that
seek out a receptor or molecular doorway on many different types of
tumours.
"This is the first study to be able to go in there and show it's
doing its mechanism of action," said Mark Davis, a professor of
chemical engineering, who led the study.
"We're excited about it because there is a lot of scepticism
whenever any new technology comes in," said Davis, a consultant to
privately held Calando Pharmaceuticals Inc, which is developing the
therapy.
Other teams are using fats or lipids to deliver the therapy to the
treatment target. Pfizer last week announced a deal with Canadian
biotech Tekmira Pharmaceuticals Corp for this type of delivery
vehicle for its RNAi drugs, joining Roche and Alnylam.
In the approach used by Davis and colleagues, once the particles
find the cancer cell and get inside, they break down, releasing
small interfering RNAs or siRNAs that block a gene that makes a
cancer growth protein called ribonucleotide reductase.
"In the particle itself, we've built what we call a chemical
sensor," Davis said in a telephone interview.
"When it recognizes that it's gone inside the cell, it says OK,
now it's time to disassemble and give off the RNA."
In a phase 1 clinical trial in patients with various types of
tumours, the team gave doses of the targeted nanoparticles four
times over 21 days in a 30-minute intravenous infusion.
Tumour samples taken from three people with melanoma showed the
nanoparticles found their way inside tumour cells.
And they found evidence that the therapy had disabled
ribonucleotide reductase, suggesting the RNA had done its
job.
Davis could not say whether the therapy helped shrink tumours in
the patients, but one patient did get a second cycle of treatment,
suggesting it might be.
Nor could he say if there were any safety concerns.
Davis said that part of the study will be presented at the American
Society of Clinical Oncology meeting in June.
