The preparation and localization study of a novel sentinel lymphoscintigraphy agent 99Tcm-IT-Rituximab

Objective: To investigate labelling method of a novel sentinel lymphoscintigraphy agent 99Tcm-Rituximab, and to evaluate its ability in detection of sentinel lymph node (SLN). Methods: Rituximab was prepared indirectly via 2-iminothiolane (2-IT) conjugation and labeled with 99Tcm. The final product 99Tcm-IT-Rituximab was analysed for numbers of free sulfhydryl group, chemical and radiochemical purity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and instant thin-layer chroma- tography-silica gel (ITLC-SG) and also the immuno-reactivity by ELISA method. The localization ability of 99Tcm-IT-Rituximab and 99Tcm-sulfur colloid (SC) was compared with biological distribution in mice. Also, 10 cases of breast cancer underwent dynamic SLN mapping. Results: Optimal conditions for labelling Rituximab was a 10:1 molar ratio of 2-IT: Rituximab in 4 degree C, the number of--SH group per mole of Rituximab was 2.1. 99Tcm-IT-Rltuximab, with a yield of about 90%, was intact, and it kept full immuno reactivity. The binding rate with B lymphoma cell line Raji cell was 69.4%. Dynamic SLN mapping in mice showed that SLN visualized in 30 min to 24 h after injection, and it could visualize clearly as early as 2 h. The secondary lymph nodes were not seen even at 24 h. Generally, the localization ability of 99Tcm-IT-Rituximab was superior to 99Tcm-SC. The uptake of 99Tcm-IT-Rituximab in 24 h was 4.49%, with no uptake in secondary and tertiary lymph nodes. For the clinical result, 99Tcm-IT-Rituximab could identify SLN successfully in all 10 cases. Conclusions: The labelling method is simple with high yield rate. 99Tcm-IT-Rituximab, as a tracer to mapping SLN, demonstrate its good localization ability. Therefore it would be a potential novel SLN imaging agent. (authors)