An optimized strategy for the mild and efficient solution phase iodination of tyrosine residues in bioactive peptides

C-H radiocyanation of bioactive molecules via sequential iodination/copper-mediated cross-coupling

This report describes a net C-H radiocyanation reaction for the transformation of electron rich (hetero)aromatic substrates into 11CN-labeled products. Electrophilic C(sp2)-H iodination of the (hetero)arene with N-iodosuccinimide is followed by Cu-mediated radiocyanation with K11CN. This sequence is applied to a variety of substrates, including the nucleobases uracil and cytosine, the amino acids tyrosine and tryptophan, and the peptide LYRAGWRAFS, which undergoes selective C-H radiocyanation at the tryptophan (W) residue.

CXCR4 peptide-based fluorescence endoscopy in a mouse model of Barrett's esophagus

Background

Near-infrared (NIR) fluorescence imaging has been emerging as a promising strategy to overcome the high number of early esophageal adenocarcinomas missed by white light endoscopy and random biopsy collection. We performed a preclinical assessment of fluorescence imaging and endoscopy using a novel CXCR4-targeted fluorescent peptide ligand in the L2-IL1B mouse model of Barrett’s esophagus.

Methods

Six L2-IL1B mice with advanced stage of disease (12–16 months old) were injected with the CXCR4-targeted, Sulfo-Cy5-labeled peptide (MK007), and ex vivo wide-field imaging of the whole stomach was performed 4 h after injection. Before ex vivo imaging, fluorescence endoscopy was performed in three L2-IL1B mice (12–14 months old)  by a novel imaging system with two L2-IL1B mice used as negative controls.

Results

Ex vivo imaging and endoscopy in L2-IL1B mice showed that the CXCR4-targeted MK007 accumulated mostly in the dysplastic lesions with a mean target-to-background ratio > 2. The detection of the Sulfo-Cy5 signal in dysplastic lesions and its co-localization with CXCR4 stained cells  by confocal microscopy further confirmed the imaging results.

Conclusions

This preliminary preclinical study shows that CXCR4-targeted fluorescence endoscopy using MK007 can detect dysplastic lesions in a mouse model of Barrett’s esophagus. Further investigations are needed to assess its use in the clinical setting.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00875-7.

Efficient 125I-radiolabeling of biomolecules using a strain-promoted oxidation-controlled cyclooctyne-1,2-quinone cycloaddition reaction

We report a novel 1,2-catechol based radioiodinated precursor for radioiodination of bicyclo[6.1.0]nonyne (BCN) installed biologically active molecules using a strain-promoted oxidation-controlled cyclooctyne-1,2-quinone cycloaddition reaction (SPOCQ) under ambient conditions. Compared to the reported methodologies, the new strategy demonstrates some clear advantages, including high in vitro and in vivo stability, high radiochemical yield, and exceptionally fast reaction kinetics at micro-molar concentration.

Validation of [125I]CPCR4.3 as an investigative tool for the sensitive and specific detection of hCXCR4 and mCXCR4 expression in vitro and in vivo

BACKGROUND

The development and clinical translation of [⁶⁸Ga] Pentixafor has substantially promoted the relevance of non-invasive PET imaging of CXCR4 expression in a broad spectrum of diseases, including cancer and inflammation. Its pronounced selectivity for the human receptor (hCXCR4), however, precludes the use of [⁶⁸Ga] Pentixafor for imaging receptor expression and dynamics in CXCR4-related diseases in endogenous mouse models. To overcome this restriction, [¹²⁵I]CPCR4.3, a structurally related pentapeptide ligand, has been evaluated as a preclinical tool for efficient in vitro and in vivo targeting of hCXCR4 and mCXCR4.

RESULTS

Compared to the reference [⁶⁸Ga] Pentixafor, [¹²⁵I]CPCR4.3 showed 2.4- to 11-fold increased specific binding to human cancer cell lines with different hCXCR4 expression levels (Jurkat, Daudi, HT-29, SH-5YSY, MCF-7, LNCaP) as well as strong and highly specific binding to mCXCR4 expressing cells (mCXCR4-transfected CHO cells, Eμ-myc 1080, 4 T1), which was not detectable for [⁶⁸Ga]Pentixafor. This is the consequence of the equally high affinity of iodo-CPCR4 to hCXCR4 and mCXCR4 (IC₅₀ = 5.4 ± 1.5 and 4.9 ± 1.7 nM, respectively) as opposed to [^natGa] Pentixafor (hCXCR4: 42.4 ± 11.6 nM, mCXCR4: > 1000 nM). Additionally, [¹²⁵I]CPCR4.3 showed enhanced tracer internalization (factor of 1.5-2 compared to the reference). In vivo biodistribution studies in immunocompetent Black Six and immunocompromised CD-1 nude mice showed predominant hepatobiliary excretion of [¹²⁵I]CPCR4.3 (logP = 0.51), leading to high activity levels in liver and intestines. However, [¹²⁵I]CPCR4.3 also showed high and specific accumulation in organs with endogenous mCXCR4 expression (spleen, lung, adrenals), even at low receptor expression levels.

CONCLUSIONS

Due to its excellent hCXCR4 and mCXCR4 targeting efficiency, both in vitro and in vivo, [¹²⁵I]CPCR4.3 represents a sensitive and reliable tool for the species-independent quantification of CXCR4 expression. Its suboptimal clearance properties will certainly restrict its use for in vivo imaging applications using ¹²³I (for SPECT) or ¹²⁴I (for PET), but due to its high and specific accumulation in mCXCR4 expressing tissues, [¹²⁵I]CPCR4.3 holds promise as a powerful preclinical tool for the investigation and quantification of CXCR4 involvement and kinetics in various murine disease models via, e.g., biodistribution and autoradiography studies.

Mild and Selective Mono-Iodination of Unprotected Peptides as Initial Step for the Synthesis of Bioimaging Probes

Chemoselective functionalization of peptides and proteins to selectively introduce residues for detection, capture, or specific derivatization is of high interest to the synthetic community. Here we report a new method for the mild and effective mono-iodination of tyrosine residues in fully unprotected peptides. This method is highly chemoselective and compatible with a wide variety of functional groups. The introduced iodine can subsequently serve as a handle for further functionalization such as introduction of fluorescent dyes and thus be used for chemoselective labeling of isolated peptides.