Antibody-Targeted Chemotherapy with the Calicheamicin Conjugate hu3S193-N-Acetyl γ Calicheamicin Dimethyl Hydrazide Targets Lewisy and Eliminates Lewisy-Positive Human Carcinoma Cells and Xenografts

Purpose: Linking a cytotoxic anticancer drug to an antibody that recognizes a tumor-associated antigen can improve the therapeutic index of the drug. We asked whether a conjugate of the cytotoxic antibiotic N -acetyl γ calicheamicin dimethyl hydrazide (CalichDMH) and an antibody recognizing Lewis y (Le y ) antigen could eliminate carcinomas that express Le y . Because Le y is highly expressed on carcinomas of colon, breast, lung, ovary, and prostate, a CalichDMH conjugate targeting Le y could provide a treatment option for various cancers. Experimental Design: The humanized anti-Le y antibody hu3S193 was conjugated to CalichDMH via the bifunctional AcBut linker. Selectivity and avidity of the conjugate (hu3S193-CalichDMH) for Le y -BSA or Le y+ cells was tested by BIAcore or flow cytometry. Cytotoxicity of hu3S193-CalichDMH was compared with toxicity of a control conjugate on monolayers of Le y+ and Le y− carcinoma cells. Inhibition of tumor growth by hu3S193-CalichDMH was assessed on three types of s.c. xenografts. Results: Hu3S193-CalichDMH had similar selectivity as hu3S193. The conjugate had lower affinity for Le y -BSA but not for Le y+ cells. When tested on monolayers of human Le y+ carcinoma cells, hu3S193-CalichDMH was more cytotoxic than a control conjugate. This difference in efficacy was not noted on Le y− cells. Efficacy of hu3S193-CalichDMH depended on the expression of Le y and on the sensitivity of the cells to CalichDMH. In vivo , hu3S193-CalichDMH inhibited growth of xenografted human gastric (N87), colon (LOVO), and prostate carcinomas (LNCaP). When used against N87 xenografts, hu3S193-CalichDMH arrested tumor growth for at least 100 days. Conclusion: Hu3S193-CalichDMH can specifically eliminate Le y+ tumors. These results support development of this conjugate for treatment of carcinomas.