title: Selective CDK9 inhibition overcomes TRAIL resistance by concomitant suppression of cFlip and Mcl-1.
abstract: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can induce apoptosis in many cancer cells without causing toxicity in vivo. However, to date, TRAIL-receptor agonists have only shown limited therapeutic benefit in clinical trials. This can, most likely, be attributed to the fact that 50% of all cancer cell lines and most primary human cancers are TRAIL resistant. Consequently, future TRAIL-based therapies will require the addition of sensitizing agents that remove crucial blocks in the TRAIL apoptosis pathway. Here, we identify PIK-75, a small molecule inhibitor of the p110α isoform of phosphoinositide-3 kinase (PI3K), as an exceptionally potent TRAIL apoptosis sensitizer. Surprisingly, PI3K inhibition was not responsible for this activity. A kinome-wide in vitro screen revealed that PIK-75 strongly inhibits a panel of 27 kinases in addition to p110α. Within this panel, we identified cyclin-dependent kinase 9 (CDK9) as responsible for TRAIL resistance of cancer cells. Combination of CDK9 inhibition with TRAIL effectively induced apoptosis even in highly TRAIL-resistant cancer cells. Mechanistically, CDK9 inhibition resulted in downregulation of cellular FLICE-like inhibitory protein (cFlip) and Mcl-1 at both the mRNA and protein levels. Concomitant cFlip and Mcl-1 downregulation was required and sufficient for TRAIL sensitization by CDK9 inhibition. When evaluating cancer selectivity of TRAIL combined with SNS-032, the most selective and clinically used inhibitor of CDK9, we found that a panel of mostly TRAIL-resistant non-small cell lung cancer cell lines was readily killed, even at low concentrations of TRAIL. Primary human hepatocytes did not succumb to the same treatment regime, defining a therapeutic window. Importantly, TRAIL in combination with SNS-032 eradicated established, orthotopic lung cancer xenografts in vivo. Based on the high potency of CDK9 inhibition as a cancer cell-selective TRAIL-sensitizing strategy, we envisage the development of new, highly effective cancer therapies.
authors.affiliation: 1] Centre for Cell Death, Cancer and Inflammation, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK [2] Clinic of General and Visceral Surgery, University of Ulm, Albert-Einstein-Allee 23, 89081 Ulm, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Lemke
authors.affiliation: Centre for Cell Death, Cancer and Inflammation, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK.
authors.forename: S
authors.initials: S
authors.lastname: von Karstedt
authors.affiliation: Centre for Cell Death, Cancer and Inflammation, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK.
authors.forename: M
authors.initials: M
authors.lastname: Abd El Hay
authors.affiliation: 1] Centre for Cell Death, Cancer and Inflammation, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK [2] Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, 20133 Milan, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Conti
authors.affiliation: Cancer Immunology Unit, University College London, 72 Huntley Street, London WC1E 6DD, UK.
authors.forename: F
authors.initials: F
authors.lastname: Arce
authors.affiliation: Centre for Cell Death, Cancer and Inflammation, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK.
authors.forename: A
authors.initials: A
authors.lastname: Montinaro
authors.affiliation: Centre for Cell Death, Cancer and Inflammation, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK.
authors.forename: K
authors.initials: K
authors.lastname: Papenfuss
authors.affiliation: Department of Histopathology, Imperial College London, Du Cane Road, London W12 0NN, UK.
authors.forename: M A
authors.initials: MA
authors.lastname: El-Bahrawy
authors.affiliation: Centre for Cell Death, Cancer and Inflammation, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK.
authors.forename: H
authors.initials: H
authors.lastname: Walczak
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D042863:Cyclin-Dependent Kinase 9 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D005260:Female; D045325:HCT116 Cells; D006367:HeLa Cells; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D016513:Mice, SCID; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000235:genetics / Q000378:metabolism*; D011897:Random Allocation; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D014162:Transfection; D023041:Xenograft Model Antitumor Assays
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C579095:MCL1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9