Specific labeling with potent radiolabels alters the uptake of cell‐penetrating peptides

Abstract

Radiolabeled peptides play an important role in radiopharmacy not only as tumor markers but also as transport vectors. Therefore, cell-penetrating peptides (CPP) may serve as very effective delivery tools, as well. Recently, CPP based on the human hormone calcitonin (hCT) have been developed. Especially, branched hCT-peptide sequences turned out to have highly efficient internalization capacities. Labeling these peptides with radionuclides would generate promising new tools for imaging and therapy applications in radiopharmacy. However, the influence of the metal complexation on the internalization capacity of CPP has not been elucidated yet in detail. In this study we quantified the uptake of Ga-DOTA modified hCT-carrier peptides in HeLa cells by using atomic absorption spectroscopy (AAS) and compared the results to the uptake of fluorescently-labeled peptides. Interestingly, we measured different uptake rates depending on the attached label. Unexpectedly, modification with a Ga-DOTA complex can have tremendous effects on the uptake efficiency. The results of these studies support the need of detailed analysis of each carrier peptide/cargo construct, especially in the field of metal complex modified CPP.

Specific Targeting of Hypoxic Tumor Tissue with Nitroimidazole–Peptide Conjugates

“…[8,9] Using this method, we recently reported the successful and efficient delivery of nanocrystals, [10] oligonucleotides, [11] gallium complexes [12] and bioactive metal complexes [13][14][15][16] into cancer, as well as primary cells. However, while CPPs provide a tool through which cell-impermeable compounds can reach intracellular targets, one of their major drawbacks is their lack of selectivity towards different cell lines.…”

New generation CPPs show distinct selectivity for cancer and noncancer cells

“…Walther et al 46 Although the exact mechanism of internalization is not fully clear, the TAT peptide is suitable for internalization of a myriad of covalently linked substances into different cell types and across the blood-brain barrier. The CPPs were covalently coupled to the near-infrared fluorescent dye DY676 and subjected to internalization using different cell lines.…”

Imaging the inside of a tumour: a review of radionuclide imaging and theranostics targeting intracellular epitopes

“…There is some debate on the mechanism by which CPPs, mainly TAT, are taken up into the cell, especially regarding its ability for endosomal escape . In any case, the mode of uptake and intracellular distribution seems to depend strongly on the CPP, on the type of cargo, on the chemical identity of the linker between cargo and CPP, or on the identity of the label attached to the CPP to study its intracellular distribution …”

“…58 In any case, the mode of uptake and intracellular distribution seems to depend strongly on the CPP, on the type of cargo, on the chemical identity of the linker between cargo and CPP, or on the identity of the label attached to the CPP to study its intracellular distribution. 59 The first to report the use of a CPP-targeting-label construct was Eisenhut et al, 60 who used a TAT-peptide construct in an effort to measure apoptosis. They used a DEVDG motif, which binds to caspase-3 and showed that the radioiodinated construct was taken up twofold more in apoptotic cells compared to normal controls.…”