Turning sledgehammers into picks

August 6, 2009

They are so small the name “particle” doesn’t do them justice. They are called instead “nanoparticles,” tiny bits of matter—liposomes, actually—being groomed to carry cancer-treating radioisotopes to tumors. Last week in Anaheim, CA, at the American Association of Physicists in Medicine meeting, a group of researchers from Johns Hopkins University reported progress with this new type of nano-killers

They are so small the name "particle" doesn't do them justice. They are called instead "nanoparticles," tiny bits of matter-liposomes, actually-being groomed to carry cancer-treating radioisotopes to tumors. Last week in Anaheim, CA, at the American Association of Physicists in Medicine meeting, a group of researchers from Johns Hopkins University reported progress with this new type of nano-killers.

It's as easy to be skeptical as it is to recognize the need for such focused weapons against cancer. For the better part of 30 years, oncologists have embraced and then become disenchanted with magic bullets that promised specificity to cancer. Always these have encountered some problem that made them less than it was hoped they would be.

Adding to the disappointment has been oncologists' half-century dependence on sledgehammer protocols, ones built around toxins such as methotrexate, that poison healthy cells as well as cancerous ones, playing on the special vulnerability of cancer cells that comes from uncontrolled cell division.

Like so many of the magic bullets of the past, the nanoparticles developed at Johns Hopkins are driven to tumors by cancer-specific antibodies. But it is here that the present breaks away from the past. These antibodies have been built into liposomes, tiny naturally occurring spheres made of fatty molecules that biopharma companies have recently succeeded in turning into packages for delivery of drugs and other chemicals. Johns Hopkins' breed of "immunoliposomes" are designed to use their antibody component to find tumors inside the body, then deliver a hefty dose of radioisotopes, called alpha-particle emitters, to the cancerous tumor. Results in mice have been encouraging.

But mice and humans are a long way apart in the evolutionary chain. Failure to remember this has led to the dashing of some of biomedicine's greatest hopes. But just the simple technical success of reproducibly loading a delivery system with high doses of radioisotope and making it land much more frequently at the metaphorical feet of cancerous cells than healthy ones is reason enough to be encouraged that the Johns Hopkins folks might be onto something.

This prospective and still unproven treatment has the potential to be much less toxic than chemotherapy, according to Dr. George Sgouros, the Johns Hopkins radiology professor who led the research. It may be particularly helpful when fighting metastatic disease, he added. And the Hopkins team is not alone in believing this may be so. Similar studies by other groups have demonstrated how such immunoliposomes could carry tiny radioactive tracers for imaging tumors.

It is this nexus of imaging and therapy, its specificity and elegance, that is so intriguing. Whether it will pan out is impossible to say until clinical trials begin. But, clearly, the specificity for cancer is what oncology and cancer patients need.