The serine protease matriptase has been implicated in epithelial cancers, has been found in ∼45% of node-negative breast cancers at high levels, and is indicated as a biomarker for survival independent of HER-2/ neu. Specifically, the overexpression of matriptase per se may not be associated with cancer progression, but the increased presence of activated matriptase instead. While in vitro methods are invaluable, few breast cancer cell-lines express matriptase though most breast cancer tissues are positive for matriptase. The disconnect between the in vitro and in vivo expression of matriptase suggests that in vivo imaging may aid in understanding its role in the context of the tumor. Therefore, radioimmunoconjugates have been developed against the cancer-specific target activated matriptase for in vivo imaging using small-animal positron emission tomography (PET).
M69, an antibody (mAb) against activated matriptase, was radiolabeled with [64Cu]copper or [89Zr]zirconium via the chelating agents TETA-based BAT and desferal (DFO), respectively. 64Cu-BAT-2IT-M69 and 89Zr-DFO-M69 were found to immunoreactive and were evaluated in mouse models for human breast cancer. A pair of polyoma middle T (PyVmT) cell-lines was bilaterally introduced into female mice to generate matriptase-positive and control tumors (paired tumors). Mice were administered radioimmunoconjugate and imaged using small-animal PET at 1-4d p.i. (through 14d for 89Zr). Small-animal PET images showed retention in matriptase-positive tumors, and expression was confirmed with immunohistochemistry. Biodistribution at 4d revealed both 64Cu-BAT-2IT-M69 and 89Zr-DFO-M69 retained two-fold higher uptake for positive-expressing tumor over control. This was also observed at 14d for 89Zr-DFO-M69. Corresponding biodistribution studies were also performed.
In addition, DOTA- and TETA-based radioimmunoconjugates for mAbs M69 and M32 (total matriptase) were radiolabeled with [64Cu]copper, and imaged in a tetracycline-inducible murine (single tumor) model. Immunohistochemistry was again used to confirm for protein expression. Pilot studies were also performed in an immune intact murine model. General linear modeling (GLM) is proposed as a means to resolve specific and nonspecific tumor uptake, with the use of biodistribution and PET-derived data. In summary, we have developed novel radioimmunoconjugates and performed the first in vivo nuclear imaging of activated matriptase. This approach has the potential for cancer diagnosis and for evaluating treatment response.
|Advisor:||Sutcliffe, Julie L.|
|Commitee:||Beckett, Laurel A., Cherry, Simon R., Louie, Angelique Y., Revzin, Alexander|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 72/08, Dissertation Abstracts International|
|Subjects:||Biomedical engineering, Medicine, Medical imaging|
|Keywords:||Cancer progression, Copper-64, Matriptase, Pet molecular imaging, Serine protease, Zirconium-89|
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