KS04.5.A Development of a somatostatin receptor type 2 (SSTR2)-targeted probe for near infrared fluorescence guided meningioma surgery

Abstract Background Meningioma mostly recur at the primary resection bed requiring improvement in the intraoperative tumor visualization and surgical technique. This study aims to develop a highly specific and sensitive optical probe for intraoperative meningioma imaging to guide the tumor resection. Fluorescent dyes in the near infrared (NIR I, 700-1000nm) and shortwave infrared (NIR II, 1000-2000nm) allow detection by suitable cameras up to few millimeters in depth in real time. Our objective is to invent a fluorescent NIR I and II probe specifically targeting the somatostatin receptor type 2 (SSTR2) reliably overexpressed in meningioma independently of WHO grade and subtype. Material and Methods By linking a somatostatin analogue (TATE, Tyr(3)Thr(8)-Octreotid) to a new developed dye (sNIR), we synthesized a SSTR2 specific probe. Its optical properties are comparable to indocyanine green and stability as well as bleaching kinetic were observed in vitro. The probe was intravenously injected in native mice to evaluate pharmacokinetics and biodistribution and detected by a custom-built camera setup focusing on physiologically highly expressing SSTR2 tissues validated by immunohistochemistry (IHC). As proof-of-principle fluorescence guided tumor resection was performed in an ectopic and orthotopic meningioma IOMM-Lee mouse model. Results The SSTR2-sNIR probe is stable in aqueous solution up to 12h with favorable optical properties regarding kinetics, biodistribution and photostability compared to its IRDye800 analogue. In vivo, we observed a highly specific physiological signal uptake in the gastric epithelium, the pancreas and pituitary (they are highly expressing SSTR2 on IHC) compared to autofluorescence and negative controls (unlabeled dye and scrambled version). Given the moderate SSTR2 expression in the preclinical meningioma model we could still detect a mean tumor-to-brain ratio of 6.12 (n = 5; SD 1.8) in the orthotopic meningioma mouse model, allowing the fluorescence guidance to be feasible. Conclusion Our preclinical results demonstrate that the innovative SSTR2-targeted fluorescent probe is stable in various biological media over time and capable of specifically targeting the SSTR2 in vitro and in vivo potentially enabling sensitive and specific meningioma fluorescent guided surgery in the future.