Real-Time Detection of Colorectal Cancer Using Topical Application of a pH-Activatable Fluorophore

INTRODUCTION: Standard treatment for locally advanced rectal cancer involves neoadjuvant chemoradiation therapy (nCRT) followed by total mesorectal excision, but this approach carries significant morbidity and often results in incomplete resections owing to poor intraoperative tumor visualization. For patients with complete response to nCRT, a watch-and-wait (W&W) strategy can spare surgery, but current imaging techniques inadequately identify complete responders, leading to regrowth in ~ 30% of cases. To improve nCRT response assessment and guide resections, we developed PH10, a topically applied, pH-activatable near-infrared (NIR) fluorescent probe for rapid, tumor-specific imaging. METHODS: PH10, a small-molecule cyanine analog, was tested in murine models and on human tumor specimens (n = 11). Fluorescence activation, tumor specificity, and tumor-to-background ratio (TBR) were evaluated in vivo and ex vivo within clinically relevant timeframes. RESULTS: PH10 enabled rapid and specific tumor visualization, achieving a median TBR of 3.2 within 1 min in vivo in murine models and 2.2 within 10 min ex vivo on human samples. The probe demonstrated high specificity for tumor tissue within the acidic tumor microenvironment without requiring systemic administration or prolonged incubation. CONCLUSIONS: PH10 is a promising, fast-acting topical NIR agent for real-time tumor detection during colorectal cancer endoscopy and surgery. Its simplicity and rapid kinetics support potential clinical translation. Moreover, its pH-activatable mechanism may extend its utility to other solid cancers with acidic microenvironments.