ABT-737 overcomes resistance to immunotoxin-mediated apoptosis and enhances the delivery of pseudomonas exotoxin-based proteins to the cell cytosol.
Pseudomonas exotoxin (PE)-based immunotoxins (antibody-toxin fusion proteins) have achieved frequent complete remissions in patients with hairy cell leukemia but far fewer objective responses in other cancers. To address possible mechanisms of resistance, we investigated immunotoxin activity in a model system using the colon cancer cell line, DLD1. Despite causing complete inhibition of protein synthesis, there was no evidence that an immunotoxin targeted to the transferrin receptor caused apoptosis in these cells. To address a possible protective role of prosurvival Bcl-2 proteins, the BH3-only mimetic, ABT-737, was tested alone or in combination with immunotoxins. Neither the immunotoxin nor ABT-737 alone activated caspase 3, whereas the combination exhibited substantial activation. In other epithelial cell lines, ABT-737 enhanced the cytotoxicity of PE-related immunotoxins by as much as 20-fold, but did not enhance diphtheria toxin or cycloheximide. Because PE translocates to the cytosol via the endoplasmic reticulum (ER) and the other toxins do not, ABT-737-mediated effects on the ER were investigated. ABT-737 treatment stimulated increased levels of ER stress response factor, ATF4. Because of its activity in the ER, ABT-737 might be particularly well suited for enhancing the activity of immunotoxins that translocate from the ER to the cell cytosol.
Traini
Roberta
R
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, NIH, Department of Health and Human Services, Bethesda, Maryland 20892, USA.
Ben-Josef
Gal
G
Pastrana
Diana V
DV
Moskatel
Elizabeth
E
Sharma
Ashima K
AK
Antignani
Antonella
A
Fitzgerald
David J
DJ
D051701:Activating Transcription Factor 4 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D001713:Biphenyl Compounds / Q000494:pharmacology*; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004357:Drug Synergism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005098:Exotoxins / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D000922:Immunotoxins / Q000494:pharmacology*; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D009596:Nitrophenols / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology; D014176:Protein Biosynthesis / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D011549:Pseudomonas / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology*
C501332:ABT-737; C497109:ATF4 protein, human; D001713:Biphenyl Compounds; D005098:Exotoxins; D000922:Immunotoxins; D009596:Nitrophenols; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides; D051701:Activating Transcription Factor 4; D020169:Caspases