The impact of the DiI fluorescent probe on the in vivo fate of paclitaxel-loaded methoxy polyethylene glycol-block-poly (d,l-lactide) micelles.

Fluorescent probes are extensively used for tracking the in vivo behavior of nanocarriers. However, the impact of fluorescent probes on the in vivo fate of nanomedicines remains uncertain. Potential interference from the probes may lead to misleading conclusions. This study investigated the influence of a commonly used fluorescent probe, DiI, on the in vivo fate of paclitaxel (PTX)-loaded polymeric micelles (PMs) in rats. The drug release kinetics of PTX-loaded PMs (PTX-PM) with DiI/PTX coloaded PMs (DiI/PTX-PM) in rat plasma was quantitatively compared. The results indicate that coencapsulation with DiI significantly exacerbated drug release and altered the protein binding of PTX through competitive binding, resulting in an increased proportion of free PTX. DiI enhanced diffusion-driven drug leakage without affecting the micelle dissociation kinetics. Notably, DiI inhibited elimination and increased the systemic exposure of both the free micelle material and the nanocarrier. This study provides evidence that DiI can potentially interfere with the in vivo fate of both the therapeutic payload and the nanocarrier, highlighting the necessity for rigorous validation when using it for nanocarrier tracking. SIGNIFICANCE STATEMENT: This study reveals that the common fluorescent probe DiI significantly alters the in vivo fate of paclitaxel-loaded polymeric micelles by accelerating drug release, competing for plasma protein binding, and inhibiting carrier elimination. These findings highlight the critical need for rigorous validation when using fluorescent probes to track nanomedicines.