title: Short hairpin RNAs targeting Bcl-xL modulate senescence and apoptosis following SN-38 and irinotecan exposure in a colon cancer model.
abstract: Bcl-xL is an anti-apoptotic protein over-expressed in colorectal cancers acting on both the intrinsic and extrinsic pathways. We stably expressed four different short hairpin RNA (pSNG-xL1-4) targeting Bcl-xL in HCT 116 cells. HCT 116 pSNG-xL#1 produced a modest (30%) decrease in Bcl-xL expression whilst Bcl-2 levels were similar to the parental cell line, HCT 116 pSNG-xL#2 and 3 showed 50% decrease in Bcl-xL and stable Bcl-2. HCT 116 pSNG-xL#3 showed a concomitant decrease (50%) in Bcl-2. A decrease in Bcl-xL sensitised cells to the small molecule inhibitor of Bcl-xL, Antimycin A3 and the DNA topoisomerase I inhibitors, SN-38 and camptothecin, but not to doxorubicin. HCT 116 pSNG-xL#1 produced a moderate increase in both senescence and apoptosis and a limited increase in SN-38 induced cell death while HCT 116 pSNG-xL#2 produced an increase in apoptosis but reduced senescence. Finally, when both Bcl-xL and Bcl-2 were decreased to a similar degree (HCT 116 pSNG-xL#3), senescence was significantly increased but apoptosis was limited. This effect was confirmed in vivo after administration of irinotecan and was associated with greater anti-tumour effect. Optimal growth inhibitory effect was therefore observed when both Bcl-xL and Bcl-2 were decreased to a similar extent. Antimycin A3, in combination with SN-38 recapitulated this phenotype in HCT 116 cells, suggesting a potential role for small molecule inhibitors of Bcl-xL/Bcl-2 in the treatment of colorectal cancer, potentially in combination with irinotecan.
authors.affiliation: CRUK Pharmacology and Drug Development Group, Cancer Research UK Centre, University of Edinburgh, Crewe Road, Edinburgh, EH4 2XR, UK. Sylvie.guichard@cancer.org.uk
authors.forename: S M
authors.initials: SM
authors.lastname: Guichard
authors.forename: M L
authors.initials: ML
authors.lastname: Hua
authors.forename: P
authors.initials: P
authors.lastname: Kang
authors.forename: J S
authors.initials: JS
authors.lastname: Macpherson
authors.forename: D I
authors.initials: DI
authors.lastname: Jodrell
mesh_terms: D000818:Animals; D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology; D016923:Cell Death; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D015536:Down-Regulation; D004317:Doxorubicin / Q000494:pharmacology; D045325:HCT116 Cells; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology*; D014162:Transfection; D023041:Xenograft Model Antitumor Assays; D051020:bcl-X Protein / Q000235:genetics* / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D051020:bcl-X Protein; D000968:Antimycin A; D000077146:Irinotecan; C004510:blastmycin; D004317:Doxorubicin; D002166:Camptothecin