Endocytosis of immuno-ricin A chain specific for gastric cancer and its implications in antibody targeting therapy

In the present study,ricin A chain（RTA）was first biotinylated,and then chemicallyintroduced to a monoclonal antibody against gastric cancer,MGb2 to generate an immuno-ricin Achain conjugate（I-RTA）specific for gastric cancer.Subsequently,its endocytosis in human gas-tric cancer cell line SGC-7901 was investigated by double dynamic EM labeling technique utilizingstreptavidin-gold and sheep anti-mouse IgG-gold probes.In addition,the effects of verapamil onI-RTA endocytosis process were also observed.Our findings demonstrated that the main entryroute of I-RTA was non-coated microinvagination,followed by coated pits and interiorization ofmicrovilli.Intracellularly,the endocytosed I-RTA was quickly transported from tubulovesicularstrueutres to multivesicular bodies,and finally to lysosomes where it was degraded,while in thenon-membranous structures I-RTA was scanty.In the presence of verapamil,however,I-RTAwas found to stay longer in tubulovesicular structures and to move in a less amount and moreslowly into lysosomes.In the meantime,I-RTA was seen to be increased in the non-membranousstructures of the cytosol,and the in vitro killing efficacy was greatly augmented.