Improved Immuno-PET Imaging of HER2-Positive Tumors in Mice: Urokinase Injection-Triggered Clearance Enhancement of 64Cu-Trastuzumab.

Abstract

Immuno-positron emission tomography (immuno-PET) is expected to improve the specificity of small chemical tracers such as 18F-fluorodeoxyglucose. Whole antibodies significantly accumulate in target molecule-expressing tumors but frequently persist too long in the blood circulation for imaging purposes. We investigated the utility of whole antibodies, 64Cu-labeled via a urokinase-substrate linker, and their exogenous urokinase-responsive cleavage to enhance clearance of immuno-PET probes from the blood and shorten the time required to develop adequate imaging contrast. Specifically, we used 64Cu-labeled trastuzumab in human epidermal growth factor receptor 2 (HER2)-positive tumor-bearing mice. 64Cu-labeled trastuzumab with a urokinase-cleavage site (64Cu-CB-TE1A1P-USL-trastuzumab) was synthesized using a bifunctional chelator incorporating an urokinase substrate peptide. Urokinase cleavage was analyzed in vitro by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and radio-gel permeation-high-performance liquid chromatography. Improvements in radioisotope clearance and HER2-imaging by urokinase injection were evaluated by PET imaging and ex vivo biodistribution studies in A431 tumor-bearing mice. 64Cu-CB-TE1A1P-USL-trastuzumab was cleaved into smaller radioactive fragments by 20 000 IU/mL urokinase treatment in vitro at an efficacy of ∼95%. The probe targeted HER2 in A431 tumors in mice within 24 h post-injection, and approximately two-thirds of the probe in the blood circulation was eliminated via renal clearance of radioactive fragments after three urokinase injections. Therefore, the tumor/blood ratio increased 3.0-fold. Without urokinase injection, the tumor accumulation of 64Cu-CB-TE1A1P-USL-trastuzumab slowly increased, and the blood radioactivity decreased over 72 h. However, the tumor/blood ratios in mice after three urokinase injections were higher at 24 h than those in mice without injections at 72 h. The results indicate that our approach shortened the time required to develop adequate imaging contrast of immuno-PET by >2 days. Therefore, this approach can benefit high-sensitivity imaging under lower radioactive decay conditions and can decrease patient radiation exposure. In addition, it could reduce other adverse effects of radioimmunotherapy.

• Authors: Qin Ren, Kohta Mohri, Shota Warashina, Yasuhiro Wada, Yasuyoshi Watanabe, Hidefumi Mukai
• Journal: Molecular pharmaceutics (Mol Pharm) Vol. 16 Issue 3 Pg. 1065-1073 (03 04 2019) ISSN: 1543-8392 [Electronic] United States
• PMID: 30633529 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• 1,4,8,11-tetraazacyclotetradecane-1-(methanephosphonic acid)-8-(methane carboxylic acid)
• Chelating Agents
• Copper Radioisotopes
• Heterocyclic Compounds, 2-Ring
• Organophosphonates
• Fluorodeoxyglucose F18
• ERBB2 protein, human
• Receptor, ErbB-2
• Urokinase-Type Plasminogen Activator
• Trastuzumab

Topics

• Animals
• Cell Line, Tumor
• Chelating Agents (chemistry)
• Copper Radioisotopes (chemistry)
• Fluorodeoxyglucose F18
• Heterocyclic Compounds, 2-Ring (chemistry)
• Heterografts
• Humans
• Injections, Intravenous
• Male
• Mice
• Mice, Inbred BALB C
• Mice, Nude
• Neoplasm Transplantation
• Neoplasms (diagnostic imaging, pathology)
• Organophosphonates (chemistry)
• Positron-Emission Tomography (methods)
• Receptor, ErbB-2 (metabolism)
• Tissue Distribution
• Trastuzumab (chemistry, metabolism)
• Urokinase-Type Plasminogen Activator (administration & dosage, pharmacology)