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Nanomedicine. 2007 Dec;3(4):297-305. Epub 2007 Sep 27.

Tumor imaging using technetium-99m bound to pH-sensitive peptides.

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  • 1Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, Oregon 97331, USA.


Solid tumors often display metabolic abnormalities that consistently produce low pH in the extracellular space of poorly perfused tissue. These acidic regions may provide a mechanism for drug targeting. Peptides have been designed in such a manner that they exist in an anionic hydrophilic form at the pH of normal tissues, but then undergo a sharp transition to a non-ionic lipophilic form at reduced pH. Peptides were labeled with fluorescein or technetium-99m (99mTc) and evaluated in vitro and in two murine models of cancer. Our studies suggest that PAP-1, an 18 amino acid pH activated peptide with a pH of transition between hydrophilic and lipophilic forms (pT) of 6.4, will deliver fluorescein and 99mTc to tumors. Activation of PAP-1 by low pH and penetration into the plasma membrane of cells and tumors were confirmed using flow cytometry, fluorescence microscopy, and gamma scintigraphy. These results support our central hypothesis that PAP-1 may enable the selective delivery of macromolecules to tumors. This technology has potential for exploiting a common property of tumors to achieve highly specific medical intervention.

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