Development of a novel radiopharmaceutical kit for radiolabeling with Lu-177 for application in breast cancer treatment

Abstract Breast cancer remains the most prevalent malignancy among women worldwide, with HER2 overexpression occurring in 20–30% of cases and representing an aggressive disease phenotype. This study aimed to develop a novel theranostic radiopharmaceutical kit for breast cancer treatment by radiolabeling trastuzumab (TRZ) with lutetium-177 (Lu-177). TRZ was conjugated with four chelating agents (EDTA, DOTA, DTPA, and MAG3) at 1:1, 1:10, and 1:100 nmol ratios and formulated as both solution (S1–S12) and lyophilized kit (L1–L12) preparations. Physicochemical characterization confirmed homogeneous particle distributions (PDI ≤ 0.38), isotonic osmolality (309–325 mOsmol/kg), and TRZ content consistent with theoretical values (893–990 µg). Radiolabeling conditions were systematically optimized across pH (5, 7, and 9), incubation time (15–60 min), and radioactivity levels (5–50 mCi), with quality control performed by dose calibrator and RP-HPLC. Cytotoxicity assessment via WST-1 assay demonstrated selective toxicity toward MCF-7 breast cancer cells (83–85% viability at 72 h) while preserving healthy CRL-10762 cells (>95% viability), supporting the therapeutic selectivity of the developed formulations. MAG3-based formulations (S11, L11) demonstrated optimal radiolabeling performance, achieving >98% efficiency at pH 7.0 with 60-minute incubation and maintaining >95% radiochemical purity for seven days at 50 mCi. In vivo SPECT/CT imaging and quantitative biodistribution studies in MCF-7 tumor-bearing Balb-C nude mice confirmed superior tumor retention for Lu-177-L11, with peak accumulation of 15.2 ± 1.8 %ID/g at 72–96 hours — representing a 5.1-fold increase over free Lu-177 — and an ROI value of 583.67 ± 18.77, significantly outperforming literature-reported DOTA-based conjugates. These findings support the clinical translation potential of the Lu-177-MAG3-TRZ lyophilized kit as a promising theranostic agent for HER2-positive breast cancer.