EXTH-11. Development of Topically Applied Fluorescent Probes for Intraoperative Diagnosis of Primary Central Nervous System Lymphoma

Abstract BACKGROUND Ring-enhancing lesions observed on gadolinium-enhanced MRI often include primary central nervous system lymphoma (PCNSL), metastatic brain tumors, and glioblastoma. Preoperative differentiation of these lesions remains challenging. As surgical strategies vary depending on the diagnosis, accurate intraoperative identification is crucial. However, real-time pathological assessment during surgery is often infeasible in institutions lacking on-site pathologists or during emergency procedures. Furthermore, the efficacy of 5-aminolevulinic acid (5-ALA), approved for glioblastoma, is inconsistent in PCNSL. Therefore, we aimed to develop a novel, topically applied fluorescent probe for real-time intraoperative identification of PCNSL, to facilitate rapid diagnosis and inform optimal surgical strategies. We previously developed a locally administered fluorescent probe based on hydroxymethyl rhodamine green (HMRG) for glioblastoma and extended its application to PCNSL. METHODS We synthesized a library of HMRG-based fluorescent probes conjugated with various amino acids and applied them topically to 14 surgical specimens from patients with PCNSL. Fluorescence intensity was measured over time and compared with that of peritumoral tissue. Based on fluorescence intensity and background signal, four candidate probes (W, X, Y, Z) were selected. These probes were subsequently evaluated in SCID beige mouse xenograft models implanted with three patient-derived PCNSL xenografts, and temporal changes in fluorescence intensity were monitored. RESULTS Necrotic tissues were excluded from analysis. A two-fold increase in fluorescence intensity was used as the evaluation cutoff. Sensitivity and specificity were as follows: W (0.67 and 0), X (1.0 and 0.67), Y (0.88 and 0.67), and Z (1.0 and 0.75). In mouse xenograft models, probe Z demonstrated a marked increase in fluorescence intensity corresponding to tumor distribution, indicating robust tumor-specific labeling capability. CONCLUSIONS The selected HMRG-based fluorescent probes, particularly probe Z, appear promising for intraoperative identification of PCNSL. These probes may serve as novel tools for surgical guidance, enabling real-time diagnosis and potentially improving intraoperative decision-making.