Improvement of biodistribution profile of a radiogallium-labeled, αvß6 integrin-targeting peptide probe by incorporation of negatively charged amino acids.

OBJECTIVE: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers. Since αvß6 integrin has been reported as a promising target for PDAC diagnosis, we previously developed H-Cys(mal-NOTA-67Ga)-(Gly)6-A20FMDV2-NH2 ([67Ga]CG6) as an αvß6 integrin-targeting probe. Although [67Ga]CG6 specifically binds to αvß6 integrin-positive xenografts, the uptake of [67Ga]CG6 in the organs surrounding the pancreas, such as the liver and spleen, was comparable to that in the αvß6 integrin-positive xenografts. We hypothesized that the undesirable accumulation of [67Ga]CG6 in those organs was caused by the positive charges of [67Ga]CG6 (+ 3). In this study, we aimed to decrease [67Ga]CG6 uptake in the liver and spleen by reducing the electric charges of the probe. METHODS: We synthesized H-Cys(mal-NOTA-67Ga)-(Asp)6-A20FMDV2-NH2 ([67Ga]CD6) and evaluated its affinity to αvß6 integrin via in vitro competitive binding assay. Isoelectric points of the probes were determined by electrophoresis. Biodistribution study, autoradiography, and immunostaining for ß6 integrin were conducted using αvß6 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 [67Ga]CG6 to αvß6 integrin. The results of electrophoresis revealed that [67Ga]CG6 was positively charged whereas [67Ga]CD6 was negatively charged. In the biodistribution study, the uptake of [67Ga]CD6 in the αvß6 integrin-positive xenografts was significantly higher than that in the αvß6 integrin-negative ones at 60 and 120 min. The uptake of [67Ga]CD6 in the liver and spleen was more than two-fold lower than that of [67Ga]CG6 at both time points. In the immunohistochemistry study, the radioactivity accumulated areas in the autoradiogram of the αvß6 integrin-positive xenograft roughly coincided with ß6 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. [67Ga]CD6 overcame the drawbacks of [67Ga]CG6 in its biodistribution.

Structural features of the glycogen branching enzyme encoding genes from aspergilli.

A maltose binding protein, p78, was purified to homogeneity from Aspergillus nidulans by a single column chromatography step on cross-linked amylose. The partial amino acid sequence was highly homologous to the glycogen branching enzymes (GBEs) of human and yeast, and p78 did show branching enzyme activity. The genomic gene and its cDNA encoding GBE (p78) were isolated from the A. nidulans genomic and cDNA libraries. Furthermore, a cDNA encoding A. oryzae GBE was entirely sequenced. A. nidulans GBE shared overall and significant amino acid sequence identity with GBEs from A. oryzae (83.9%), Saccharomyces cerevisiae (61.1%) and human (63.0%), and with starch branching enzymes from green plants (55-56%).