Someday, quantum dots and other nanomaterials may be components in "smart nanostructures," or nanomachines, that circulate through the body, detect cancer-associated molecular changes, deliver a drug to the disease site, and even monitor the progress of therapy. A team led by cancer researcher Erkki Ruoslahti, M.D., Ph.D., of the Burnham Institute in La Jolla, Calif., has taken one step toward this goal, as reported in the October 1, 2002, issue of the Proceedings of the National Academy of Sciences.
Ruoslahti, Sangeeta Bhatia, M.D., Ph.D., of the University of California at San Diego, and their colleagues used quantum dots coated with various "homing peptides" to target the dots to specific tissues and blood vessels or lymphatic vessels in tumors in mice. The peptides, developed in Ruoslahtis laboratory, bind to specific molecular markers that are unique to the vasculature of individual organs, tissues, and tumors.
The researchers injected mice with peptide-coated dots, allowed the dots to circulate for several minutes, and then prepared tissue samples from the animals and examined the distribution of fluorescence. Their results showed "exquisite specificity of the homing," Ruoslahti said, although the dots did not glow as brightly as expected, suggesting the dot formulation used in this study may be unstable or fluoresce poorly in living tissues.
Ruoslahti noted that the primary purpose of this study was "not to show that quantum dots could be used as a diagnostic tool," but rather to show that the homing peptides could be used to target inorganic nanoparticles to specific tissues in a living mammal. "Were beginning to see peptides that home only to the vasculature of a certain type of tumor, and were working on distinguishing between the stages of a tumor," such as early malignancy, full-blown malignancy, and metastasis, Ruoslahti said. "We are now able to target not only the blood vessels [in tumors], but also the lymphatic vessels, for the purpose of getting at those tumor cells that are close to metastasizing through the lymphatic system."
"Now were thinking of more advanced nanodevices that would do more than just be luminescent," he added. These tiny devices, which might include quantum dots as one component, would enter the circulation and accumulate in specific tissues such as tumors. When the nanodevices reach their target, Ruoslahti said, "thats when one would like to give a command to the device that it should fire" and deliver an anticancer drug or other toxic substance to the tumor.
Although multifunctional nanomachines that circulate through the human body and detect, treat, and monitor diseases such as cancer or Alzheimers disease so far remain the stuff of fictionand researchers dreamsRuoslahti said he believes this goal is achievable in the long term. It "may be a dream," he said, "but not a pipe dream."
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