Biotin-guided NIR fluorescent probe for in situ imaging of fibroblast activation protein in human breast cancer tissues

Breast cancer continues to be the malignant tumor with the highest incidence and mortality rates among women. Fibroblast activation protein (FAP) is a leading diagnostic and therapeutic biomarker associated with immune suppression, cancer metastasis, and poor prognosis in solid cancers, particularly in breast cancer. Therefore, developing a FAP-activated fluorescent probe holds considerable promise for the early detection and therapy of breast cancer. In this work, we designed a tumor-targeted near-infrared (NIR) fluorescent probe, DCIP-Biotin, to detect FAP activity in human breast cancer cells, tumor-bearing mice and human breast cancer tissue samples. The probe incorporated a novel NIR fluorophore (dicyanoisophorone) with an FAP recognition substrate linked to a biotin tag. The probe exhibited a wider linear range, high sensitivity, good selectivity, and robust anti-interference capability. DCIP-Biotin could be specifically activated at 660 nm when FAP was present, enabling it to efficiently recognize and image FAP-expressing cells. Furthermore, excellent fluorescence imaging performance of DCIP-Biotin was observed in MDA-MB-231 tumor-bearing mice and human breast cancer tissues, including high specificity, a high tumor-to-background ratio, deep tissue penetration, and stable fluorescence signal. DCIP-Biotin exhibits such good performance that it allows for clear demarcation between human breast cancer and adjacent non-cancerous regions, demonstrating considerable promise for use in intraoperative navigation.