HOUSTON (The New York Times News Service) -- Scientists hold in their hands a powerful therapy for many diseases.

The trouble is they have never been able to deliver these fragile drugs, tiny bits of genetic material similar to DNA, safely to the location of the disease.

Until now.

For the first time, scientists have successfully transported these medicines inside the human body to the source of melanoma, a form of skin cancer.

The work, reported by Mark Davis of the California Institute of Technology recently in the journal Nature, is at the vanguard of several efforts, including labs in Houston, to devise tiny, elaborate capsules in which to safely transport these drugs beyond the body's immune system to their intended targets. Like cancer cells.

"These are very sophisticated ways of sending biological messages to the body," said Mauro Ferrari, chairman of NanoMedicine and Biomedical Engineering at The University of Texas Medical School at Houston.

"It will change medicine completely."

The drugs, actually snippets of RNA, stop the actions of genes inside cells. The practice is called RNA interference, because the short bits of RNA interfere with the process by which genes signal cells to produce proteins.

Proteins are the chief actors within cells. Without them, tumor cells would lose the ability to become tumors and spread throughout the body. Turn off specific genes, then, and you can stop many diseases.

It's such a powerful idea that the discoverers of RNA interference, Andrew Fire and Craig Mello, won a Nobel Prize in 2006, just eight years after reporting their find in 1998.

Since that time, researchers have grappled with how to deliver RNA-interfering drugs inside the body.

The body's immune system immediately recognizes them as invaders and destroys them. Previous efforts to deliver these drugs into the body have either failed to bypass the body's immune system or, more commonly, have proven toxic.

"A number of delivery methods have been hampered by safety issues," said Dr. Anil Sood, a researcher at the University of Texas M.D. Anderson Cancer Center. "Even before efficacy, safety has to obviously be the primary goal of any delivery method."

Sood said there are a number of delivery approaches showing promise. One of them is in his lab.

Working with Dr. Gabriel Lopez-Berestein, also at M.D. Anderson, Sood has developed tiny liposomes -- about 60 billionths of a meter wide -- that are made of the same bubble-like material in a cell membrane.

Animal tests have led Sood to believe they're effective at transporting RNA interference drugs into ovarian cancer tumors, and he hopes to begin clinical trials soon.

Sood is also working with Ferrari, at UT-Houston, to take the concept a step further.

Ferrari's approach builds on Sood's liposomes by adding a time-release function.

His lab has developed a porous silicon material in which Sood's liposomes are embedded. Over time the silicon material breaks down, gradually releasing the liposomes into the body's bloodstream.

"This allows us to do one injection as opposed to multiple injections," Ferrari said.

The Houston-based approaches are at least a couple of years behind the California-based work of Davis, a chemical engineer.

Davis' infiltrating particles are actually two large molecules bound together, with a protein on the surface that binds to cancer cells. They're slightly larger than Sood's liposomes.

In theory, the particles enter the bloodstream and circulate until they find blood vessels leading to tumor cells. Once inside the cell, the particle essentially falls apart and releases the RNA-interfering drugs.

In reality, Davis said, that appears to be exactly what happened when they tried the drug in 15 patients.

The more of the drug they injected into patients, the more of the RNA-interfering compound that accumulated in their tumor cells.

"This is the first time ever to show that as you increase the dose in a patient, you could see increased accumulation in tumor cells in patients," Davis said.

As part of the tests, the scientists broke the tumor cells open.

They found evidence that the RNA-interfering drugs had shut down precisely the genes they were hoping to stop.

"It's really the smoking gun we were looking for," Davis said.

At least two more rounds of human testing, likely requiring several years, remain before the drugs could be approved for widespread use in patients.

Copyright 2010 The New York Times News Service. All rights reserved.