ABSTRACT
We previously established a model of acquired oxaliplatin resistance derived from the HCT116 oxaliplatin-sensitive cell line (HCT116S) and consisting in two resistant clones (HCT116R1, HCT116R2) and their total or partial revertants (HCT116Rev1 and HCT116Rev2, respectively). Using this cellular model, we explored the contribution of mitochondrial apoptosis and nuclear DNA to oxaliplatin-mediated apoptosis induction and oxaliplatin resistance. We showed that the activity of oxaliplatin is mediated by the induction of Bax/Bak-dependent mitochondrial apoptosis and that oxaliplatin resistance is mediated by a defect in Bax/Bak activation correlating with a reduced loss of the mitochondrial transmembrane potential (DeltaPsim). In addition, we observed that p53 only contributed marginally to oxaliplatin-induced cytotoxicity and was not involved in oxaliplatin resistance. Moreover and surprisingly, depletion of the nucleus in HCT116S cells did not abolish the oxaliplatin-induced DeltaPsim loss indicative of imminent apoptosis. Enucleation abolished the oxaliplatin resistance of HCT116R1 cells, while HCT116R2 cytoplasts conserved their resistant phenotype. Altogether, these data demonstrate that oxaliplatin exerts its cytotoxic effects by inducing mitochondrial apoptosis and that these effects can be initiated by interacting on other cellular structures than nuclear DNA. Resistance to oxaliplatin may imply both nuclear and cytoplasmic compartments.
Subject(s)
Antineoplastic Agents/pharmacology , Apoptosis/drug effects , Colonic Neoplasms/pathology , DNA/physiology , Organoplatinum Compounds/pharmacology , Cell Line, Tumor , Colonic Neoplasms/genetics , Drug Resistance, Neoplasm , Humans , OxaliplatinABSTRACT
Overcoming drug resistance has become an important issue in cancer chemotherapy. Among all known mechanisms that confer resistance, active efflux of chemotherapeutic agents by proteins from the ATP-binding cassette family has been extensively reported. The aim of the present study was to determine the involvement of ABCG2 in resistance to SN38 (the active metabolite of irinotecan) in colorectal cancer. By progressive exposure to increasing concentrations of SN38, we isolated 2 resistant clones from the human colon carcinoma cell line HCT116. These clones were 6- and 53-fold more resistant to SN38 than the HCT116-derived sensitive clone. Topoisomerase I expression was unchanged in our resistant variants. The highest resistance level correlated with an ABCG2 amplification. This overexpression was associated with a marked decrease in the intracellular accumulation of SN38. The inhibition of ABCG2 function by Ko143 demonstrated that enhanced drug efflux from resistant cells was mediated by the activity of ABCG2 protein and confirmed that ABCG2 is directly involved in acquired resistance to SN38. Furthermore, we show, for the first time in clinical samples, that the ABCG2 mRNA content in hepatic metastases is higher after an irinotecan-based chemotherapy than in irinotecan-naive metastases. In conclusion, this study supports the potential involvement of ABCG2 in the development of irinotecan resistance in vivo.
Subject(s)
ATP-Binding Cassette Transporters/metabolism , Adenocarcinoma/drug therapy , Camptothecin/analogs & derivatives , Camptothecin/therapeutic use , Colonic Neoplasms/drug therapy , Drug Resistance, Neoplasm , Liver Neoplasms/drug therapy , Neoplasm Proteins/metabolism , ATP Binding Cassette Transporter, Subfamily G, Member 2 , ATP-Binding Cassette Transporters/antagonists & inhibitors , ATP-Binding Cassette Transporters/genetics , Adenocarcinoma/metabolism , Adenocarcinoma/secondary , Antineoplastic Agents, Phytogenic/therapeutic use , Colon/metabolism , Colonic Neoplasms/metabolism , Colonic Neoplasms/pathology , DNA Topoisomerases, Type I/metabolism , Gene Expression Regulation, Neoplastic , Humans , Irinotecan , Liver Neoplasms/metabolism , Liver Neoplasms/secondary , Neoplasm Proteins/antagonists & inhibitors , Neoplasm Proteins/genetics , RNA, Messenger/metabolism , RNA, Neoplasm , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
N-(4-hydroxyphenyl)retinamide (4-HPR, fenretinide) is a potent chemopreventive agent whose effect has been suggested to involve apoptosis induction. 4-HPR induces a loss of the mitochondrial transmembrane potential and the mitochondrial release of cytochrome c before caspase activation. Inhibition of mitochondrial membrane permeabilization (MMP) by transfection with Bcl-2 or the Cytomegalovirus UL37 gene product vMIA prevented caspase activation and cell death. In contrast to other retinoid derivatives, 4-HPR has no direct MMP-inducing effects when added to isolated mitochondria or when added to proteoliposomes containing the MMP-regulatory permeability transition pore complex (PTPC). Moreover, although reactive oxygen species (ROS) overproduction appears to be instrumental for 4-HPR-induced MMP and apoptosis, inhibition of the NF-kappaB or p53-mediated signal transduction pathways failed to modulate 4-HPR-induced apoptosis. 4-HPR was found to cause an antioxidant-inhibitable conformational change of both Bax and Bak, leading to the exposure of their N-termini and to the mitochondrial relocalization of Bax. Cells with a Bax(-/-) Bak(-/-) genotype were resistant against the 4-HPR-induced MMP, overproduction of ROS and cell death. Altogether, these data indicate that 4-HPR induces MMP through an ROS-mediated pathway that involves the obligatory contribution of the proapopotic Bcl-2 family members Bax and/or Bak.
Subject(s)
Anticarcinogenic Agents/pharmacology , Apoptosis/drug effects , Fenretinide/pharmacology , Mitochondria/metabolism , Proto-Oncogene Proteins c-bcl-2/metabolism , Caspase Inhibitors , Caspases/metabolism , Cytochrome c Group/drug effects , Enzyme Activation/drug effects , HeLa Cells , Humans , Membrane Proteins/genetics , Membrane Proteins/metabolism , Mitochondria/drug effects , Permeability/drug effects , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , Proto-Oncogene Proteins c-bcl-2/genetics , Signal Transduction , Tumor Cells, Cultured , bcl-2 Homologous Antagonist-Killer Protein , bcl-2-Associated X ProteinABSTRACT
To investigate acquired resistance to oxaliplatin, we selected two resistant clones from the HCT116 cell line. We found that the resistant phenotype was associated with resistance to oxaliplatin-induced apoptosis as demonstrated by FACS analysis and by Western blotting of caspase 3 activation. In addition, the resistant phenotype showed a concomitant resistance to lonidamine and arsenic trioxide which are inducers of mitochondrial apoptosis. Furthermore, a complete loss of Bax expression due to a frameshift mutation was observed in the most resistant clone. Taken together, these findings suggest that altered mitochondrial-mediated apoptosis could play a role in oxaliplatin resistance.
