Rapid internalization of novel single chain antibody targeting human prostate cancer cells

Objectives Antibodies targeting internalizing cell surface epitopes are promising targeting agents for cancer imaging. One internalizing single chain antibody (UA20) specific for prostate cancer was investigated for rapid internalization and tumor targeting.

Methods The antibodies were engineered to contain a hexahistidine tag to accommodate the 99mTc tricarbonyl labeling. For in vitro cell study, the labeled UA20 was incubated at 4^oC and 37^oC for 1h and 3 hs with two prostate cancer cell lines (DU145 and PC3) and one control cell line (BPH) to assess the total cellular uptake and the intracellular uptake. For animal study, the labeled UA20 and control antibody (N3M2) were administered to athymic mice implanted subcutaneously with the Du-145. Mice were imaged with microSPECT/CT at 1h, 2h and 3h post-injection and sacrificed at 3h to assess biodistribution.

Results The labeled UA20 was rapidly internalized into the targeted tumor cells but not the non-targeted cells and 80-85% and 55-65% of total cell accumulation were accounted to internalization at 37^oC and 4^oC respectively as early as within 1 hour. In initial animal studies, the 99mTc-UA20 was rapidly eliminated from the blood and most normal tissues (except the kidneys) giving tumor uptake above 4%ID/g and remarkable contrast at 3h post-injection. In contrast, the control antibody only exhibited tumor uptake of 0.26%ID/g.

Conclusions The UA20 showed strong rapid internalization and tumor targeting in the human prostate cancer cells, demonstrating potential use in targeted imaging and therapy.

Research Support This work is partially supported by NIH/NCI R01CA 135358-01 and Grant #IRG-97-150-10 from the American Cancer Society.