Supramolecular Rotaxane-Based Multi-Modal Probes for Cancer Biomarker Imaging**

Abstract

Mechanically interlocked molecules present opportunities to construct therapeutic drugs and diagnostic imaging agents but harnessing supramolecular chemistry to make biologically active probes in water is a challenge. Here, we describe a rotaxane-based approach to synthesise radiolabelled proteins and peptides for molecular imaging of cancer biomarkers in vivo. Host–guest chemistry using β-cyclodextrin- and cucurbit[6]uril-catalysed cooperative capture synthesis produced gallium-68 or zirconium-89 radiolabelled metallo[4]rotaxanes. Photochemical conjugation to trastuzumab led to a viable positron emission tomography (PET) radiotracer. The rotaxane architecture can be tuned to accommodate different radiometal ion complexes, other protein- or peptide-based drugs, and fluorophores for optical detection. This technology provides a platform to explore how mechanical bonding can improve drug delivery, enhance tumour specificity, control radiotracer pharmacokinetics, and reduce dosimetry.