title: HMBA induces activation of a caspase-independent cell death pathway to overcome P-glycoprotein-mediated multidrug resistance.
abstract: Multidrug resistance (MDR) is often characterized by the expression of P-glycoprotein (P-gp), a 170-kd ATP-dependent drug efflux protein. As well as effluxing xenotoxins, functional P-gp can confer resistance to caspase-dependent apoptosis induced by a range of different stimuli, including Fas ligand, tumor necrosis factor, UV irradiation, and serum starvation. However, P-gp-positive cells remain sensitive to caspase-independent death induced by cytotoxic T-cell granule proteins, perforin, and granzyme B. It is, therefore, possible that agents that induce cell death in a caspase-independent manner might circumvent P-gp-mediated MDR. We demonstrated here that hexamethylene bisacetamide (HMBA) induced equivalent caspase-independent cell death in both P-gp-positive and -negative cell lines at concentrations of 10 mmol/L and above. The HMBA-induced death pathway was marked by release of cytochrome c from the mitochondria and reduction of Bcl-2 protein levels. In addition, we show that functional P-gp specifically inhibits the activation of particular caspases, such as caspases-8 and -3, whereas others, such as caspase-9, remain unaffected. These studies greatly enhance our understanding of the molecular cell death events that can be regulated by functional P-gp and highlight the potential clinical use of drugs that function via a caspase-independent pathway for the treatment of MDR tumors.
authors.affiliation: Austin Research Institute, Austin Hospital, Heidelberg, Victoria, Australia.
authors.forename: A A
authors.initials: AA
authors.lastname: Ruefli
authors.forename: M J
authors.initials: MJ
authors.lastname: Smyth
authors.forename: R W
authors.initials: RW
authors.lastname: Johnstone
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis / Q000494:pharmacology / Q000502:physiology*; D000081:Acetamides / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism; D018432:Drug Resistance, Multiple; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000378:metabolism / Q000473:pathology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000081:Acetamides; D003574:Cytochrome c Group; D019253:Proto-Oncogene Proteins c-bcl-2; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; C014026:hexamethylene bisacetamide