title: Combination treatments with the PKC inhibitor, enzastaurin, enhance the cytotoxicity of the anti-mesothelin immunotoxin, SS1P.
abstract: Activated protein kinase C (PKC) contributes to tumor survival and proliferation, provoking the development of inhibitory agents as potential cancer therapeutics. Immunotoxins are antibody-based recombinant proteins that employ antibody fragments for cancer targeting and bacterial toxins as the cytotoxic agent. Pseudomonas exotoxin-based immunotoxins act via the ADP-ribosylation of EF2 leading to the enzymatic inhibition of protein synthesis. Combining PKC inhibitors with the immunotoxin SS1P, targeted to surface mesothelin, was undertaken to explore possible therapeutic strategies. Enzastaurin but not two other PKC inhibitors combined with SS1P to produce synergistic cell death via apoptosis. Mechanistic insights of the synergistic killing centered on the complete loss of the prosurvival Bcl2 protein, Mcl-1, the loss of AKT and the activation of caspase 3/7. Synergy was most evident when cells exhibited resistance to the immunotoxin alone. Further, because PKC inhibition by itself was not sufficient to enhance SS1P action, enzastaurin must target other kinases that are involved in the immunotoxin pathway.
authors.affiliation: Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Abid R
authors.initials: AR
authors.lastname: Mattoo
authors.forename: Ira
authors.initials: I
authors.lastname: Pastan
authors.forename: David
authors.initials: D
authors.lastname: Fitzgerald
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D045744:Cell Line, Tumor; D003131:Combined Modality Therapy; D004357:Drug Synergism; D058851:GPI-Linked Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D007211:Indoles / Q000627:therapeutic use*; D020128:Inhibitory Concentration 50; D000090204:Mesothelin; D064546:Protein Kinase C beta / Q000037:antagonists & inhibitors*
chemical_list: D000911:Antibodies, Monoclonal; D058851:GPI-Linked Proteins; D007211:Indoles; C474515:SS1(dsFv)PE38; D064546:Protein Kinase C beta; D000090204:Mesothelin; C504878:enzastaurin