24. Antibody-Targeted Fusion Provides a Versatile Platform for Novel Targeted Therapies
Authors: Takafumi Nakamura, Kah-Whye Peng, Sompong Vongpunsawad, Mary Harvey, Hiroyuki Mizuguchi, Takao Hayakawa, Roberto Cattaneo, Stephen J. Russell
Journal: Molecular Therapy (2004)

Cell fusion is a basis for stem cell plasticity and has therapeutic applications in cancer gene therapy, virotherapy and the generation of novel cancer vaccines. We recently engineered the fusogenic viral membrane glycoprotein complex of measles virus to restrict and retarget membrane fusion through various antibody-receptor interactions. To ablate its natural tropism for CD46 and SLAM, mutations of positions 481 and 533 were introduced in the coding sequence of the virus attachment protein H, and three different single chain antibodies were then fused to its C-terminus. To demonstrate the potential of targeted cell fusion for cytoreductive gene therapy of human cancer, we generated bicistronic adenovirus vectors expressing measles F with EGFR-targeted, CD38-targeted or untargeted H proteins, and compared their specificity and potency against human ovarian SKOV3ip.1 tumor cells as a treatment model. The SKOV3ip.1 cells express abundant CD46 and abundant EGFR, but not CD38. Surprisingly, compared to adenoviruses expressing untargeted measles H, the EGFR-targeted adenoviruses could mediate very efficient targeted fusion and killing of SKOV3ip.1 cells. In contrast, control vectors expressing the CD38-targeted H protein showed no fusion activity in SKOV3ip.1 cells. We next evaluated the [italic]in vivo[/italic] effects of these adenoviral vectors against established SKOV3ip.1 xenografts implanted subcutaneously in athymic mice. Adenoviral vectors mediating EGFR-targeted fusion showed greatly increased therapeutic potency in this intratumoral therapy model compared to control vectors mediating fusion through CD46 (untargeted) or CD38 (P=0.0013 compared to PBS, or P≤0.05 compared to Ad H/F and Ad H481A, 533A-CD38/F with comparison on day 32). Histological analysis of explanted tumors three days after they were injected with the different adenoviral vectors showed that cell fusion was considerably more prominent in tumors inoculated with vector expressing the EGFR targeted H protein. Taken together, these data demonstrate the superior specificity and potency of vectors mediating antibody-targeted cell fusion. Increasingly, cells are exploited as therapeutic agents and antibody-targeted fusion has considerable potential to enhance the therapeutic outcome; stem cells are used for tissue repair, immune effector cells for tumor therapy, and vector-modified cells for delivery of diverse genetic payloads. To demonstrate that heterologous cell fusion between an immune effector cell and an epithelial tumor could be accurately targeted we infected K562 cells with adenoviral vectors expressing nontargeted, EGFR-targeted or CD38-targeted H proteins. K562 cells transduced with the EGFR-targeted or CD38-targeted vector did not fuse with each other but underwent heterologous fusion with EGFR-positive epithelial tumor cells (A431) or with CD38-expressing suspension Jurkat T cells, respectively. Thus, our data suggest that receptor choice is not a significant limitation for cell fusion and that it should be possible to target the process through a broad array of cell surface antigens. Antibody-targeted cell fusion offers a versatile new technology with many potential applications.