title: The novel pyrrolo-1,5-benzoxazepine, PBOX-21, potentiates the apoptotic efficacy of STI571 (imatinib mesylate) in human chronic myeloid leukaemia cells.
abstract: The Bcr-Abl kinase inhibitor, STI571, is the first line treatment for chronic myeloid leukaemia (CML), but the recent emergence of STI571 resistance has led to the examination of combination therapies. In this report, we describe how a novel non-toxic G1-arresting compound, pyrrolo-1,5-benzoxazepine (PBOX)-21, potentiates the apoptotic ability of STI571 in Bcr-Abl-positive CML cells. Co-treatment of CML cells with PBOX-21 and STI571 induced more apoptosis than either drug alone in parental (K562S and LAMA84) and STI571-resistant cells lines (K562R). This potentiation of apoptosis was specific to Bcr-Abl-positive leukaemia cells with no effect observed on Bcr-Abl-negative HL-60 acute myeloid leukaemia cells. Apoptosis induced by PBOX-21/STI571 resulted in activation of caspase-8, cleavage of PARP and Bcl-2, upregulation of the pro-apoptotic protein Bim and a downregulation of Bcr-Abl. Repression of proteins involved in Bcr-Abl transformation, the anti-apoptotic proteins Mcl-1 and Bcl-(XL) was also observed. The combined lack of an early change in mitochondrial membrane potential, release of cytochrome c and cleavage of pro-caspase-9 suggests that this pathway is not involved in the initiation of apoptosis by PBOX-21/STI571. Apoptosis was significantly reduced following pre-treatment with either the general caspase inhibitor Boc-FMK or the chymotrypsin-like serine protease inhibitor TPCK, but was completely abrogated following pre-treatment with a combination of these inhibitors. This demonstrates the important role for each of these protease families in this apoptotic pathway. In conclusion, our data highlights the potential of PBOX-21 in combination with STI571 as an effective therapy against CML.
authors.affiliation: School of Biochemistry and Immunology, Trinity College, Dublin 2, Ireland. brights@tcd.ie
authors.forename: Sandra A
authors.initials: SA
authors.lastname: Bright
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Greene
authors.forename: Tom F
authors.initials: TF
authors.lastname: Greene
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Campiani
authors.forename: Stefania
authors.initials: S
authors.lastname: Butini
authors.forename: Margherita
authors.initials: M
authors.lastname: Brindisi
authors.forename: Mark
authors.initials: M
authors.lastname: Lawler
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Meegan
authors.forename: D Clive
authors.initials: DC
authors.lastname: Williams
authors.forename: Daniela M
authors.initials: DM
authors.lastname: Zisterer
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides; D015153:Blotting, Western; D002219:Carbamates / Q000494:pharmacology / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004357:Drug Synergism; D005434:Flow Cytometry; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000473:pathology*; D008564:Membrane Potentials / Q000187:drug effects; D010077:Oxazepines / Q000494:pharmacology / Q000627:therapeutic use*; D010879:Piperazines / Q000494:pharmacology / Q000627:therapeutic use*; D011743:Pyrimidines / Q000494:pharmacology / Q000627:therapeutic use*; D015854:Up-Regulation
chemical_list: C514161:7-((diethylcarbamoyl)oxy)-6-p-tolylpyrrolo(2,1-d)(1,5)benzoxazepine; D000970:Antineoplastic Agents; D001549:Benzamides; D002219:Carbamates; D010077:Oxazepines; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl