Ex-vivo Imaging of Upper Tract Urothelial Carcinoma Using Novel pH Low Insertion Peptide (Variant 3), a Molecular Imaging Probe

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Objective: To improve visualization of upper tract urothelial carcinomas. Previous studies using the novel pH low insertion peptide (pHLIP) variant 3 (Var3) conjugated to indocyanine green (ICG) have demonstrated high sensitivity and specificity for imaging of bladder urothelial carcinoma. Here, we describe a novel approach for the imaging of upper tract urothelial carcinomas using ICG-Var3 pHLIP. Methods: Twelve ex-vivo upper urinary tract specimens were irrigated with ICG-Var 3 pHLIP for 15 minutes and then examined using a white light laparoscopic camera followed by near infrared fluorescent (NIRF) imaging using a Stryker 1588 AIM imaging system. Standard histopathologic evaluation was performed and findings were correlated with white light and ICG-Var3 NIRF imaging. One patient who underwent radical nephrectomy for renal cell carcinoma was used as a negative control. Results: Nineteen lesions were identified on histopathologic evaluation in 10 patients, including 82% high-grade urothelial carcinoma and 18% low-grade urothelial carcinoma. Nineteen (100%) malignant lesions were identified using NIRF imaging, while 15 (78.9%) lesions were identified using conventional white light examination. The sensitivity of ICG-Var3 pHLIP NIRF imaging was 100% compared to 78.9% white light examination. Both modalities are 100% specific. Benign collecting systems and ureters did not show uptake of the pHLIP construct. Conclusion: In this feasibility study, the ICG-Var3 pHLIP imaging agent demonstrated superior diagnostic performance compared to conventional white light examination. While additional studies are required for validation and in-vivo translation, pHLIP-based imaging represents a promising tool to improve the evaluation and management of upper tract urothelial carcinoma.

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