Selective CXCR4-Targeting Radioconjugates Derived from LY2510924: Evaluation of [18F]AlF-NOTA-SC, [177Lu]Lu-BL02, and [161Tb]Tb-BL02 for Theranostic Development

Background/Objectives: The chemokine receptor CXCR4 plays a pivotal role in tumor progression, metastasis, and therapy resistance and is frequently overexpressed in hematologic malignancies, including multiple myeloma and lymphoma. This study investigates a CXCR4-targeted theranostic platform comprising a PET imaging agent and two therapeutic radioconjugates derived from the high-affinity CXCR4 antagonist LY2510924. Methods: The PET tracer [18F]AlF-NOTA-SC and therapeutic radioconjugates [177Lu]Lu-BL02 and [161Tb]Tb-BL02 were synthesized and evaluated. Radiolabeling efficiency, molar activity, and in vitro binding affinity were assessed. Specificity and uptake were evaluated in CXCR4-expressing U87.CD4.CXCR4 and MM.1S cells, with cytotoxic potential being analyzed via clonogenic survival assays. In vivo biodistribution and pharmacokinetics were evaluated in MM.1S xenograft mouse models, supported by longitudinal SPECT imaging. Results: All radioconjugates were obtained with high radiochemical purity (>98%). The constructs showed nanomolar affinity for human CXCR4; in vitro assays confirmed specific uptake in CXCR4-positive cells, and both therapeutic agents demonstrated dose-dependent cytotoxicity. In vivo, all compounds displayed comparable tumor uptake with low off-target accumulation. Co-injection studies confirmed consistent pharmacokinetics across agents, while SPECT/CT imaging demonstrated gradual tumor clearance of [177Lu]Lu-BL02 over seven days. Conclusions: The radiopharmaceutical trio [18F]AlF-NOTA-SC, [177Lu]Lu-BL02, and [161Tb]Tb-BL02 demonstrates the feasibility of a CXCR4-targeted theranostic approach for imaging and treating hematologic malignancies. The observed tumor washout highlights the need for further structural optimization to enhance tumor retention and therapeutic efficacy, providing a clear direction for future development toward clinical translation.