title: Evaluation and critical assessment of putative MCL-1 inhibitors.
abstract: High levels of BCL-2 family proteins are implicated in a failed/ineffective apoptotic programme, often resulting in diseases, including cancer. Owing to their potential as drug targets in cancer therapy, several inhibitors of BCL-2 family proteins have been developed. These primarily target specific members of the BCL-2 family, particularly BCL-2 and BCL-XL but are ineffective against MCL-1. Major efforts have been invested in developing inhibitors of MCL-1, which is commonly amplified in human tumours and associated with tumour relapse and chemoresistance. In this report, the specificity of several BCL-2 family inhibitors (ABT-263, UCB-1350883, apogossypol and BH3I-1) was investigated and compared with putative MCL-1 inhibitors designed to exhibit improved or selective binding affinities for MCL-1 (TW-37, BI97C1, BI97C10, BI112D1, compounds 6 and 7, and MCL-1 inhibitor molecule (MIM-1)). ABT-263, BI97C1, BI112D1, MIM-1 and TW-37 exhibited specificity in inducing apoptosis in a Bax/Bak- and caspase-9-dependent manner, whereas the other agents showed no killing activity, or little or no specificity. Of these inhibitors, only ABT-263 and UCB-1350883 induced apoptosis in a BCL-2- or BCL-XL-dependent system. In cells that depend on MCL-1 for survival, ABT-263 and TW-37 induced extensive apoptosis, suggesting that at high concentrations these inhibitors have the propensity to inhibit MCL-1 in a cellular context. TW-37 induced apoptosis, assessed by chromatin condensation, caspase processing and phosphatidylserine externalisation, in a BAK-dependent manner and in cells that require MCL-1 for survival. TW-37-mediated apoptosis was also partly dependent on NOXA, suggesting that derivatives of TW-37, if engineered to exhibit better selectivity and efficacy at low nanomolar concentrations, may provide useful lead compounds for further synthetic programmes. Expanded medicinal chemistry iteration, as performed for the ABT series, may likewise improve the potency and specificity of the evaluated MCL-1 inhibitors.
authors.affiliation: MRC Toxicology Unit, University of Leicester, Leicester, UK.
authors.forename: S
authors.initials: S
authors.lastname: Varadarajan
authors.forename: M
authors.initials: M
authors.lastname: Vogler
authors.forename: M
authors.initials: M
authors.lastname: Butterworth
authors.forename: D
authors.initials: D
authors.lastname: Dinsdale
authors.forename: L D
authors.initials: LD
authors.lastname: Walensky
authors.forename: G M
authors.initials: GM
authors.lastname: Cohen
mesh_terms: D000814:Aniline Compounds / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001549:Benzamides / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D006801:Humans; D019169:Jurkat Cells; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology*; D013450:Sulfones / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D000814:Aniline Compounds; D001549:Benzamides; C579095:MCL1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D034741:RNA, Small Interfering; D013449:Sulfonamides; D013450:Sulfones; C515128:TW-37 compound; D051028:bcl-2-Associated X Protein; C528561:navitoclax