NIR Ratiometric Fluorescent Antibody‐Drug Conjugate for Metastatic Ovarian Cancer Theranostics and Treatment Response Monitoring

Abstract In vivo optical imaging advances antibody‐drug conjugate (ADC) optimization by enabling real‐time monitoring of biological stimulus‐responsive drug behavior. Ratiometric probes, incorporating orthogonal wavelength‐encoded multicolor detection and stimuli‐cleavable linkages, are preferred over single‐color strategies. Here, the synthesis of n501‐CYMMAF (cyanine‐decorated Monomethylauristatin F) is described as a novel ratiometric theranostic agent for dual efficacy in ovarian metastasis treatment and in situ treatment response monitoring. With low‐dose administration (2.5 mg kg −1 ), exceptional target affinity (EC 50(n501‐CYMMAF) = 1.17 n m ), and favorable biosafety (delivery to tumor‐parts only), n501‐CYMMAF enables experimental verification of treatment‐evading metastatic cell populations through in situ fluorescent tracking, providing crucial insights into tumor recurrence pathways and judgement of treatment terminal point. In general, n501‐CYMMAF represents a prototype for next‐generation smart theranostics, integrating treatment and endpoint assessment to offer a platform for precision metastasis management.