Improvement of biodistribution profile of a radiogallium-labeled, αvβ6 integrin-targeting peptide probe by incorporation of negatively charged amino acids.

Ann Nucl Med

Department of Biofunction Imaging Analysis, Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, 1-1-1 Tsushima-naka, Kita-ku, Okayama, 700-8530, Japan.

Published: August 2020

AI Article Synopsis

  • Researchers aimed to improve a probe ([Ga]CG6) used for detecting pancreatic cancer by reducing its accumulation in non-target organs like the liver and spleen, which may have been caused by its positive charge.
  • A new probe ([Ga]CD6) was synthesized with a different electric charge, showing similar binding affinity to pancreatic cancer cells but significantly less uptake in the liver and spleen compared to the original probe.
  • The study concluded that the modified probe ([Ga]CD6) is more effective for targeting pancreatic ductal adenocarcinoma (PDAC) while minimizing unwanted side effects in surrounding organs.

Article Abstract

Objective: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers. Since αvβ6 integrin has been reported as a promising target for PDAC diagnosis, we previously developed H-Cys(mal-NOTA-Ga)-(Gly)6-A20FMDV2-NH ([Ga]CG6) as an αvβ6 integrin-targeting probe. Although [Ga]CG6 specifically binds to αvβ6 integrin-positive xenografts, the uptake of [Ga]CG6 in the organs surrounding the pancreas, such as the liver and spleen, was comparable to that in the αvβ6 integrin-positive xenografts. We hypothesized that the undesirable accumulation of [Ga]CG6 in those organs was caused by the positive charges of [Ga]CG6 (+ 3). In this study, we aimed to decrease [Ga]CG6 uptake in the liver and spleen by reducing the electric charges of the probe.

Methods: We synthesized H-Cys(mal-NOTA-Ga)-(Asp)6-A20FMDV2-NH ([Ga]CD6) and evaluated its affinity to αvβ6 integrin via in vitro competitive binding assay. Isoelectric points of the probes were determined by electrophoresis. Biodistribution study, autoradiography, and immunostaining for β6 integrin were conducted using αvβ6 integrin-positive and negative tumor-bearing mice.

Results: In vitro competitive binding assay showed that the alteration of the linker had a negligible impact on the affinity of [Ga]CG6 to αvβ6 integrin. The results of electrophoresis revealed that [Ga]CG6 was positively charged whereas [Ga]CD6 was negatively charged. In the biodistribution study, the uptake of [Ga]CD6 in the αvβ6 integrin-positive xenografts was significantly higher than that in the αvβ6 integrin-negative ones at 60 and 120 min. The uptake of [Ga]CD6 in the liver and spleen was more than two-fold lower than that of [Ga]CG6 at both time points. In the immunohistochemistry study, the radioactivity accumulated areas in the autoradiogram of the αvβ6 integrin-positive xenograft roughly coincided with β6 integrin-expressing areas.

Conclusion: We have successfully reduced the nonspecific uptake in the liver and spleen by altering the linker amino acid from G6 to D6. [Ga]CD6 overcame the drawbacks of [Ga]CG6 in its biodistribution.

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http://dx.doi.org/10.1007/s12149-020-01483-6DOI Listing

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