title: Synergism between staurosporine and drugs inducing endoplasmic reticulum stress.
abstract: Drugs causing endoplasmic reticulum or mitochondrial dysfunction may trigger apoptosis in eukaryotic cells. The thiol reagent dithiothreitol (DTT) belongs to the first group whereas the protein kinases inhibitor staurosporine acts on mitochondria. Since the endoplasmic reticulum and the mitochondrial pathways of apoptosis may converge in common steps, we examined the possibility of synergism between these two drugs. Using the activation of caspase-3 as indicator of apoptosis, we found that in two cell lines, Jurkat and Mono-Mac 6, staurosporine and DTT elicited apoptosis with a different pattern: staurosporine acted rapidly and at nanomolar concentrations while DTT acted slowly and at higher concentrations (1mM). When staurosporine and DTT were combined, the proapoptotic action was increased. This was confirmed examining late apoptotic events such as the translocation of phosphatidylserine across the plasma membrane and the cleavage of the antiapoptotic protein Mcl-1. The use of subthreshold DTT concentrations and isobologram analysis demonstrated the synergic nature of the interaction. Tunicamycin, a drug that, like DTT, inhibits protein folding in the endoplasmic reticulum also increased the proapoptotic effect of staurosporine. In agreement with the interplay between the mitochondrial and the endoplasmic reticulum pathways it was found that both staurosporine and DTT induced cytochrome c release. Furthermore, 90min incubation with DTT did not induce caspase-4 activation while staurosporine alone or in combination with DTT stimulated caspase-4 activity. We conclude that staurosporine is more active in cells undergoing endoplasmic reticulum stress. This synergism may warrant evaluation to establish whether the anticancer activity of staurosporine is also enhanced.
authors.affiliation: Department of Pharmacology and Anaesthesiology, University of Padua, Padua, Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Cusinato
authors.forename: Isabella
authors.initials: I
authors.lastname: Pighin
authors.forename: Sisto
authors.initials: S
authors.lastname: Luciani
authors.forename: Lucia
authors.initials: L
authors.lastname: Trevisi
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D053471:Caspases, Initiator; D004229:Dithiothreitol / Q000494:pharmacology; D004357:Drug Synergism; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology*; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014415:Tunicamycin; C505407:CASP3 protein, human; C093516:CASP4 protein, human; D053148:Caspase 3; D020169:Caspases; D053471:Caspases, Initiator; D019311:Staurosporine; D004229:Dithiothreitol