LOS ANGELES, May 7 (Xinhua) -- U.S. researchers have developed nanometer-sized "nanoworms" that can cruise through the bloodstream without significant interference from the body's immune defense system and home in on tumors like tiny anti-cancer missiles.

    The study, detailed in this week's issue of the journal Advanced Materials, was conducted by scientists at University of California in San Diego (UCSD), University of California in Santa Barbara (UCSB) and the Massachusetts Institute of Technology (MIT).

    Using nanoworms, doctors should eventually be able to target and reveal the location of developing tumors that are too small to detect by conventional methods.

    Carrying payloads targeted to specific features on tumors, these microscopic vehicles could also one day provide the means to more effectively deliver toxic anti-cancer drugs to these tumors in high concentrations without negatively impacting other parts of the body.

    "Most nanoparticles are recognized by the body's protective mechanisms, which capture and remove them from the bloodstream within a few minutes," said Michael Sailor, a professor at the UCSD who headed the research team.

    "The reason these worms work so well is due to a combination of their shape and to a polymer coating on their surfaces that allows the nanoworms to evade these natural elimination processes. As a result, our nanoworms can circulate in the body of a mouse for many hours."

    When attached to drugs, these nanoworms could offer physicians the ability to increase the efficacy of drugs by allowing them to deliver them directly to the tumors, said Sangeeta Bhatia, an MIT professor who was part of the team.

    "They could decrease the side effects of toxic anti-cancer drugs by limiting their exposure of normal tissues and provide a better diagnosis of tumors and abnormal lymph nodes."

    The scientists constructed their nanoworms from spherical iron oxide nanoparticles that join together, like segments of an earthworm, to produce tiny gummy worm-like structures about 30 nanometers long -- or about 3 million times smaller than an earthworm. Their iron-oxide composition allows the nanoworms to show up brightly in diagnostic devices, specifically the MRI, or magnetic resonance imaging, machines that are used to find tumors.

    "The iron oxide used in the nanoworms has a property of super paramagnetism, which makes them show up very brightly in MRI," said Sailor.

    "The magnetism of the individual iron oxide segments, typically eight per nanoworm, combine to provide a much larger signal than can be observed if the segments are separated. This translates toa better ability to see smaller tumors, hopefully enabling physicians to make their diagnosis of cancer at earlier stages of development."

    In addition to the polymer coating, which is derived from the biopolymer dextran, the scientists coated their nanoworms with a tumor-specific targeting molecule, a peptide called F3, developed in the laboratory of Erkki Ruoslahti, professor at the UCSB. This peptide allows the nanoworms to target and home in on tumors.

    "Because of its elongated shape, the nanoworm can carry many F3molecules that can simultaneously bind to the tumor surface," said Sailor. "And this cooperative effect significantly improves the ability of the nanoworm to attach to a tumor."

    The scientists were able to verify in their experiments that their nanoworms homed in on tumor sites by injecting them into the bloodstream of mice with tumors and following the aggregation of the nanoworms on the tumors. They found that the nanoworms, unlike the spherical nanoparticles of similar size that were shuttled out of the blood by the immune system, remained in the bloodstream for hours.

    "This is an important property because the longer these nanoworms can stay in the bloodstream, the more chances they have to hit their targets, the tumors," said one of Sailor's research assistants.

    The researchers are now working on developing ways to attach drugs to the nanoworms and chemically treat their exteriors with specific chemical "zip codes," which will allow them to be delivered to specific tumors, organs and other sites in the body.