We use bacterial toxins as killing agents to eliminate cancer cells. To accomplish this, we modify the toxin so it no longer binds via its own cell-binding domain and substitute in place of the binding domain a monoclonal antibody. The antibody is chosen to bind cancer cells preferentially over normal cells. These toxin-antibody molecules are called immunotoxins. Immunotoxins are promising but imperfect anticancer agents. Our goal is to understand the interaction of various toxins with eukaryotic cells and use this information to design better agents for treating cancer. To study interactions, we add toxins to mammalian cells and study the pathway of death. In tracking the killing of cancer cells by immunotoxins, we made the observation that cells grown to high density are resistant to killing. We wish to understand this phenomenon and determine its relevance for cancer therapy in general. A convenient and potentially useful way to study cell-killing pathways is to use RNA interference to identify pathways that participate in toxin delivery to the cytosol - where it acts. Recently, we initiated studies with a newly described toxin from V cholera, called Vibrio Cholera Exotoxin (CET). This toxin is related to the exotoxin from Pseudomonas, exhibiting about 50% identity in selected domains (domains II and III). However, antibodies that neutralize the exotoxin from Pseudomonas do not neutralize CET, despite the close similarity. Truncated versions of Pseudomonas Exotoxin (PE) have been fused with antibody fragments to produce potent cytotoxic agents termed recombinant immunotoxins. These agents are targeted to kill cancer cells based on the binding specificity of the antibody fragment. Potency is derived from the enzymatic nature of the toxin as it translocates to the cytosol, ADP-ribosylates elongation factor 2 and terminates the synthesis of new cellular protein. Most prior investigations reported that PE and PE-immunotoxins kill cells via apoptosis. Here we report that PE and PE immunotoxin inhibit protein synthesis and cell growth of colon cancer cell lines but do not provoke an apoptotic response. However, the addition of the BH3-only mimetic, ABT-737 in combination with the immunotoxin produces a profound apoptotic response in these cells that neither agent alone can achieve.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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National Cancer Institute Division of Basic Sciences
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Iadarola, Michael J; Sapio, Matthew R; Wang, Xunde et al. (2017) [EXPRESS]Analgesia by Deletion of Spinal Neurokinin 1 Receptor Expressing Neurons Using a Bioengineered Substance P-Pseudomonas Exotoxin Conjugate. Mol Pain 13:1744806917727657
Antignani, A; Segal, D; Simon, N et al. (2017) Essential role for Bim in mediating the apoptotic and antitumor activities of immunotoxins. Oncogene 36:4953-4962
Ali-Rahmani, Fatima; FitzGerald, David J; Martin, Scott et al. (2016) Anticancer Effects of Mesothelin-Targeted Immunotoxin Therapy Are Regulated by Tyrosine Kinase DDR1. Cancer Res 76:1560-8
Antignani, Antonella; Mathews Griner, Lesley; Guha, Rajarshi et al. (2016) Chemical Screens Identify Drugs that Enhance or Mitigate Cellular Responses to Antibody-Toxin Fusion Proteins. PLoS One 11:e0161415
Antignani, Antonella; Sarnovsky, Robert; FitzGerald, David J (2014) ABT-737 promotes the dislocation of ER luminal proteins to the cytosol, including pseudomonas exotoxin. Mol Cancer Ther 13:1655-63
Hollevoet, Kevin; Antignani, Antonella; Fitzgerald, David J et al. (2014) Combining the antimesothelin immunotoxin SS1P with the BH3-mimetic ABT-737 induces cell death in SS1P-resistant pancreatic cancer cells. J Immunother 37:8-15
Onda, Masanori; Ghoreschi, Kamran; Steward-Tharp, Scott et al. (2014) Tofacitinib suppresses antibody responses to protein therapeutics in murine hosts. J Immunol 193:48-55
Liu, Xiu-Fen; Xiang, Laiman; FitzGerald, David J et al. (2014) Antitumor effects of immunotoxins are enhanced by lowering HCK or treatment with SRC kinase inhibitors. Mol Cancer Ther 13:82-9
FitzGerald, David J (2014) Targeted diphtheria toxin to treat BPDCN. Blood 124:310-2
Haso, Waleed; Lee, Daniel W; Shah, Nirali N et al. (2013) Anti-CD22-chimeric antigen receptors targeting B-cell precursor acute lymphoblastic leukemia. Blood 121:1165-74

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