Fat bubbles to fight cancer

Microscopic fat bubbles packed with anticancer drugs can target and kill tumour cells quickly with few side effects, a new study in rats suggests.

Tracking these tumour-zapping "liposomes" with magnetic resonance imaging (MRI) in real time may also help guide cancer treatment, the researchers added.

Using MRI, "you can move around your heat source, so you can put the drug where you want it to go," explained study senior author Dr Mark Dewhirst, a professor of radiation oncology and director of the hyperthermia program at Duke University Medical Centre, in Durham, North Carolina.

His team, collaborating with scientists elsewhere, reported the findings in the January 2 issue of the Journal of the National Cancer Institute.

Bubbles packed with chemo
The fat bubbles - microscopic globules of fat manufactured to enclose and transport medications - were packed with a chemotherapy drug and infused into the body.

Liposomes are naturally attracted to heat sources, so when heat is applied to the tumour area, the bubbles naturally migrate to these areas, leaving healthy tissue alone. This type of highly targeted approach bring patients better cancer-killing effects with less drug toxicity.

In the study, researchers administered heat to rats with tumours before, during or after they gave them intravenous infusions of the fat bubbles. They then tracked the drug's progress with MRI.

Rodents that got both the fat bubbles and the heat together had the best treatment outcomes, with two of the seven animals displaying a complete shrinkage of the tumours. The five other rats showed significant delays in tumour growth.

30 times more chemo delivered
Delivering the drugs in liposomes helps scientists deliver 30 times more chemotherapy to the site than they could before, according to Dewhirst.

The new study was conducted only in animals. However, the liposomes are already being tested in clinical trials, including one Duke study in which researchers used the bubbles to deliver drugs to women whose breast cancers had recurred in the chest wall. "Only about 10 percent of women with breast cancer get this [recurrence]," Dewhirst said.

In the current study, using MRI to track the fat bubbles and the drug delivery helped immensely, Dewhirst added.

"If you can measure how much drug is being delivered with the MRI, you could see how much drug is going to that patient's tumour and then say, 'OK, is this patient going to respond to the treatment?'" he explained.

Controlling where the drug goes
By adjusting the heat at the tumour site - which attracts the fat bubbles - they could effectively control where the drug went. "We could make all the drug go to the outside [of the tumour], the inside, or even [between both]," Dewhirst said.

"What we know about this liposome is, this one destroys blood vessels," Dewhirst said. "We found that this drug was most effective on the periphery of the tumour." That makes sense, he said, because it's the tumour's outer edges that are richest in those blood vessels that help the tumour grow.

Using heat-sensitive liposomes to deliver drugs is not a new idea, Dewhirst said. But the liposome used in the current study - developed by another Duke scientist, David Needham - is capable of melting at a lower temperature, resulting in a faster release of the drug.

"They release the drug in less than 20 seconds," Dewhirst said, compared to the half-hour or so required of some older liposomes.

"The truly unique aspect [of this research] is the temperature-sensitive liposomes," added Dennis Leeper, a professor of radiation oncology at the Kimmel Cancer Centre at Thomas Jefferson University, in Philadelphia.

Also unique, he said, is the researchers' use of the MRI in real time and a contrast material that tells the scientists exactly where the fat bubbles are releasing their anticancer payload. – (HealthDayNews)

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Cancer Centre

January 2007