Enhanced tumor targeting and penetration of fluorophores via iRGD peptide conjugation: a strategy for the precision targeting of lung cancer.

Background: Accurate real-time tumor delineation is essential for achieving curative resection (R0 resection) during non-small cell lung cancer (NSCLC) surgery. The unique characteristics of lung tissue structure significantly challenge the use of video-assisted thoracoscopic surgery in the identification of lung nodules. This difficulty often results in an inability to discern the margins of lung nodules, necessitating either an expansion of the resection scope, or a transition to open surgery. Due to its high spatial resolution, ease of operation, and capacity for real-time observation, near-infrared fluorescence (NIRF) navigation in oncological surgery has emerged as a focal point of clinical research. Targeted NIRF probes, which accumulate preferentially in tumor tissues and are rapidly cleared from normal tissues, enhance diagnostic sensitivity and surgical outcomes. The imaging effect of the clinically approved NIRF probe indocyanine green (ICG) varies significantly from person to person. Therefore, we hope to develop a new generation of targeted NIRF probes targeting lung tumor-specific targets.

Methods: First, the peptide iRGD (sequence: CRGDKGPDC) fluorescent tracer was synthesized, and characterized through mass spectrometry (MS), proton nuclear magnetic resonance (¹H NMR), and high-performance liquid chromatography (HPLC). Fluorescence properties were tested subsequently. Safety was performed in vitro using both human normal liver cells and human normal breast cells. Second, Metabolism and optimal imaging time were determined by tail vein injection of iRGD fluorescent tracer. Finally, Orthotopic and metastatic lung tumor models were used to evaluate the targeting properties of the iRGD fluorescent tracer.

Results: We successfully synthesized an iRGD fluorescent tracer specifically designed to target NSCLC. The molecular docking analyses indicated that this tracer has receptor affinity comparable to that of iRGD for αvβ3 integrin, with a purity ≥98%. Additionally, the tracer is highly soluble in water, and its excitation and emission wavelengths are 767 and 799 nm, respectively, positioning it within the near-infrared spectrum. The cellular assays confirmed the tracer's minimal cytotoxicity, underscoring its excellent biosafety profile. In vivo studies further validated the tracer's capacity for specific NSCLC detection at the cellular level, alongside a prolonged imaging window of 6 days or more. Notably, the tracer demonstrated superior specificity in localizing very small lung nodules, which are otherwise clinically indiscernible, outperforming non-targeted ICG. Fluorescence intensity analyses across various organs revealed that the tracer is predominantly metabolized by the liver and kidneys, with excretion via bile and urine, and exhibits minimal toxicity to these organs as well as the lungs.

Conclusions: The iRGD fluorescent tracer selectively accumulates in NSCLC tissues by specifically targeting αvβ3 receptors, which are overexpressed on the surface of tumor cells. This targeted approach facilitates the real-time intraoperative localization of NSCLC, presenting an improved strategy for intraoperative tumor identification with significant potential for clinical application.