# Specific in vivo detection of V2R-positive metastatic ccRCC using a toxin-based PET radioligand

## TL;DR

This study introduces a new PET imaging method using a radioligand that specifically targets V2R in metastatic clear cell renal cell carcinoma, improving detection accuracy.

## Contribution

The first radioligand targeting V2R for PET imaging of metastatic ccRCC is developed and validated.

## Key findings

- [18F]F-MQ232 shows high tumor uptake correlated with V2R expression levels in tissues.
- PET/CT imaging with [18F]F-MQ232 enables specific detection of V2R-expressing tumors with high contrast.
- Human metastatic ccRCC tissues were confirmed to express V2R, supporting the technique's clinical relevance.

## Abstract

The diagnosis of metastatic clear cell renal cell carcinoma (mccRCC) remains challenging due to the tumor's molecular heterogeneity, often resulting in low sensitivity and a high false-positive rate. In this study, we introduce and validate a new imaging modality for mccRCC based on the first radioligand targeting the type 2 vasopressin receptor (V2R) suitable for positron emission tomography (PET). V2R is ectopically expressed in mccRCC. This imaging approach utilizes [18F]F-MQ232, a radiolabeled peptide derived from snake venom which exhibits high in vivo selectivity for V2R.

The V2R-selective peptide MQ232 conjugated with either a cyanine 5 (Cy5) or a fluorine 18 (18F) group were chemically synthetized. V2R mRNA was quantified and protein expression assessed by flow cytometry using Cy5-MQ232. The selectivity and tumor targeting ability of the modified MQ232 peptides were assessed using in vivo fluorescence imagery in tumor-bearing mice using CHO-V2R tumors with graded expression. Metabolic stability and PET pharmacokinetics of [18F]F-MQ232 were assessed in rodents. Specific tumor targeting and imaging contrast were validated in vivo using V2R-expressing tumors.

[18F]F-MQ232 is a highly relevant radioligand whose tumor uptake directly correlates with V2R expression levels in tissues, demonstrating its specificity to V2R-expressing tumors. Replacing the peptide moiety by an isoform unable to interact with V2R leads to a drastic decrease in the radioligand's tumor uptake, highlighting its origin in a specific, ligand/receptor type interaction between the MQ232 moiety and V2R. PET/CT imaging of Caki-1 xenografted mice demonstrated the ability of [18F]F-MQ232 to allow specific detection of the tumor compartment associated with high tumor-to-background contrast. RT-qPCR screening of metastatic and non-metastatic ccRCC biopsies from patients confirms V2R expression.

This work validates the V2R-targeting strategy in mccRCC using [18F]F-MQ232 and demonstrates that human mccRCC tissues express V2R, confirming the suitability of this specific imaging technique for metastasis extension assessment.