Development of LRRC15-binding disulfide-constrained peptides for PET imaging of cancer-associated fibroblasts.

Tombling, Benjamin J; Cai, Fei; Wendorff, Timothy J; Ogasawara, Annie; Gill, Herman S; Tinianow, Jeff N; Chang, Andrew; Balana, Aaron T et al. · Nat Commun · 2026

basic_science · Level V

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Abstract

Leucine-rich-repeat-containing protein 15 (LRRC15) is selectively expressed on cancer-associated fibroblasts (CAFs) and constitutes a promising biomarker for imaging the tumor microenvironment. Using a combinatorial library approach, assisted by machine learning, we developed disulfide-constrained peptides (DCPs), notably ML-YSD-07 and ML-PD-03, that demonstrate subnanomolar affinities for murine LRRC15 (muLRRC15) and specifically localize onto muLRRC15-expressing fibroblasts. PET imaging with <sup>18</sup>F-radiolabeled ML-YSD-07 exhibits specific tumor accumulation in a murine pancreatic cancer model highly enriched with LRRC15-expressing CAFs. Crystal structures of apo-muLRRC15 and of ML-YSD-07-bound muLRRC15 show that the DCPs evolved to adopt a distinct binding conformation that efficiently interacts with a flat epitope on muLRRC15. Collectively, this work identifies potent, molecularly engineered LRRC15-binding peptides and further highlights LRRC15 as a valuable CAF biomarker for cancer imaging applications.