Heat-directed tumor cell fusion.
In previous studies we demonstrated that a modified human HSP70b promoter (HSE.70b) directs high levels of gene expression to tumor cells after mild hyperthermia treatment in the range of 41.5-44 degrees C. This transcriptional targeting system exhibits low basal activity at 37 degrees C, is highly induced (950-fold) after mild heat treatment (43 degrees C/30 min), and returns to basal activity levels within 12-24 hours of activation. Here we describe heat-directed targeting of an activated form of the Gibbon ape leukemia virus env protein (GALV FMG) to tumor cells. GALV FMG mediates cell-cell fusion, and when expressed in tumor cells can produce bystander effects of up to 1:200. Transient transfection of a HSE70b.GALV FMG minigene caused extensive syncytia formation in HeLa and HT-1080 cells following mild heat treatment (44 degrees C/30 min). Stable transfection into HT-1080 cells produced a cell line (HG5) that exhibits massive syncytia formation and a 60% reduction in viability relative to a vector-only control (CI1) following heat treatment in vitro. Mild hyperthermia also resulted in syncytia formation, necrosis, and complete macroscopic regression of HG5 xenograft tumors grown in the footpads of mice with severe combined immunodeficiency disorders (SCID). Median survival increased from 12.5 (in heated CI1 controls) to 52 days after a single heat treatment. Heat-directed tumor cell fusion may prove to be a highly beneficial adjunct to existing cancer treatment strategies that take advantage of the synergistic interaction between mild hyperthermia and radiation or chemotherapeutic drugs.
Brade
Anthony M
AM
Division of Experimental Therapeutics, Ontario Cancer Institute, University Health Network, University of Toronto, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada.
Szmitko
Paul
P
Ngo
Duc
D
Liu
Fei-Fei
FF
Klamut
Henry J
HJ
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002459:Cell Fusion; D002470:Cell Survival; D003673:Defective Viruses / Q000235:genetics; D005260:Female; D015686:Gene Products, env / Q000235:genetics; D005822:Genetic Vectors; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D006358:Hot Temperature; D006801:Humans; D017989:Leukemia Virus, Gibbon Ape / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D016513:Mice, SCID; D023421:Models, Animal; D009374:Neoplasms, Experimental / Q000473:pathology / Q000628:therapy*; D010957:Plasmids; D012074:Remission Induction; D014162:Transfection; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D015686:Gene Products, env; D018840:HSP70 Heat-Shock Proteins