Fatty diacid-modified FAP-targeted NIR fluorescent probes with modulated pharmacokinetics for enhanced tumor imaging

-Glu (AG) linker, we evaluated the impact of diacid chain length on tumor accumulation and background clearance. In a U87MG xenograft model, fatty diacid modification prolonged systemic circulation and enhanced tumor-associated fluorescence compared with Cy7-FAPi. Notably, the longer-chain probe Cy7-FAPi-AG-C16D produced higher absolute tumor fluorescence but showed slower background clearance, whereas Cy7-FAPi-AG-C12D achieved superior tumor-to-background contrast with the highest tumor-to-muscle ratio at 24 h (T/M ratio = 31.3 ± 7.6). These results demonstrate that fatty diacid modification provides a practical strategy to tune the exposure-clearance balance of small-molecule FAP-targeted probes, enabling high-contrast tumor imaging within clinically relevant time windows.