Evaluation of novel MUC1-c targeted near-infrared imaging agent for fluorescence-guided surgery of cancer.

e15072 Background: Tumor-targeted, near-infrared (NIR) fluorescent is an emerging field of real-time intraoperative imaging. Targeted NIR dyes contain NIR fluorophores and specific binding ligands such as antibodies, peptides and small molecules. Smaller ligands contribute to quicker imaging and clearance which both wanted to improve tumor background ratio (TBR). Therefore, peptide conjugates and small-molecule conjugates are more suitable for intraoperatively optical imaging even though individual difference in pharmacokinetics. However, it is difficult or impossible to generate small molecule ligands for many protein targets, such as those with flat, featureless surfaces or important protein-protein interactions (PPIs). Macrocyclic peptides are a molecular class with the potential to bridge the gap between small molecules and antibodies. Mucin 1 (MUC1) is an attractive target for the development of targeted therapeutics, but previous anti-MUC1 agents targeting the shed MUC1 N-terminal have shown limited clinical efficacy. Herein, We report the generation of a MUC1-C (cleaved MUC1) targeted peptidomimetic-NIR conjugate (SAG602) that concentrates specifically in cancer tissues and clears rapidly from healthy tissues. Methods: Fifteen combinatorial single or double cyclic peptide libraries, which produce on phage and cyclized with different chemical linkers, were used for preliminary identification of high-affinity MUC1-C binders. After several rounds structure activity relationship studies, the substitution of individual amino acids in parent compounds to unnatural ones further improved the affinity, thermal and proteolytic stabilities. Binding affinities, high thermal and plasma stabilities, optical properties, transvascular extravasation, intratumoral penetration, in vitro and in vivo specificity, tumor background ratio (TBR), and pharmacokinetics (PKs) properties were evaluated in requisite models. Results: SAG602 binds to MUC1-C-expressing cells with ∼10 nM affinity, high thermal stability (90 ℃, 20 min), concentrates selectively to MUC1-C-positive cancer tissues, and clears rapidly from healthy tissues with a half-time of < 1 hour. It also exhibits an excellent TBR (5:1) as well as safety profile in animals. Conclusions: SAG602 has shown promising affinity, specificity, stability, and tumor-targeted imaging capabilities in all in vitro and in vivo studies. Based on the excellent tumor contrast in murine tumor models, we conclude that SAG602 holds great potential for fluorescence-guided surgery of MUC1-C positive malignant lesions, and is a candidate for translation into human use.