Proteins in the B cell CLL/lymphoma 2 (BCL-2) family are key regulators of the apoptotic process. This family comprises proapoptotic and prosurvival proteins, and shifting the balance toward the ...latter is an established mechanism whereby cancer cells evade apoptosis. The therapeutic potential of directly inhibiting prosurvival proteins was unveiled with the development of navitoclax, a selective inhibitor of both BCL-2 and BCL-2-like 1 (BCL-X(L)), which has shown clinical efficacy in some BCL-2-dependent hematological cancers. However, concomitant on-target thrombocytopenia caused by BCL-X(L) inhibition limits the efficacy achievable with this agent. Here we report the re-engineering of navitoclax to create a highly potent, orally bioavailable and BCL-2-selective inhibitor, ABT-199. This compound inhibits the growth of BCL-2-dependent tumors in vivo and spares human platelets. A single dose of ABT-199 in three patients with refractory chronic lymphocytic leukemia resulted in tumor lysis within 24 h. These data indicate that selective pharmacological inhibition of BCL-2 shows promise for the treatment of BCL-2-dependent hematological cancers.
The BCL-2/BCL-XL/BCL-W inhibitor ABT-263 (navitoclax) has shown promising clinical activity in lymphoid malignancies such as chronic lymphocytic leukemia. However, its efficacy in these settings is ...limited by thrombocytopenia caused by BCL-XL inhibition. This prompted the generation of the BCL-2-selective inhibitor venetoclax (ABT-199/GDC-0199), which demonstrates robust activity in these cancers but spares platelets. Navitoclax has also been shown to enhance the efficacy of docetaxel in preclinical models of solid tumors, but clinical use of this combination has been limited by neutropenia. We used venetoclax and the BCL-XL-selective inhibitors A-1155463 and A-1331852 to assess the relative contributions of inhibiting BCL-2 or BCL-XL to the efficacy and toxicity of the navitoclax-docetaxel combination. Selective BCL-2 inhibition suppressed granulopoiesis in vitro and in vivo, potentially accounting for the exacerbated neutropenia observed when navitoclax was combined with docetaxel clinically. By contrast, selectively inhibiting BCL-XL did not suppress granulopoiesis but was highly efficacious in combination with docetaxel when tested against a range of solid tumors. Therefore, BCL-XL-selective inhibitors have the potential to enhance the efficacy of docetaxel in solid tumors and avoid the exacerbation of neutropenia observed with navitoclax. These studies demonstrate the translational utility of this toolkit of selective BCL-2 family inhibitors and highlight their potential as improved cancer therapeutics.
Histone methyltransferases are epigenetic regulators that modify key lysine and arginine residues on histones and are believed to play an important role in cancer development and maintenance. These ...epigenetic modifications are potentially reversible and as a result this class of enzymes has drawn great interest as potential therapeutic targets of small molecule inhibitors. Previous studies have suggested that the histone lysine methyltransferase G9a (EHMT2) is required to perpetuate malignant phenotypes through multiple mechanisms in a variety of cancer types. To further elucidate the enzymatic role of G9a in cancer, we describe herein the biological activities of a novel peptide-competitive histone methyltransferase inhibitor, A-366, that selectively inhibits G9a and the closely related GLP (EHMT1), but not other histone methyltransferases. A-366 has significantly less cytotoxic effects on the growth of tumor cell lines compared to other known G9a/GLP small molecule inhibitors despite equivalent cellular activity on methylation of H3K9me2. Additionally, the selectivity profile of A-366 has aided in the discovery of a potentially important role for G9a/GLP in maintenance of leukemia. Treatment of various leukemia cell lines in vitro resulted in marked differentiation and morphological changes of these tumor cell lines. Furthermore, treatment of a flank xenograft leukemia model with A-366 resulted in growth inhibition in vivo consistent with the profile of H3K9me2 reduction observed. In summary, A-366 is a novel and highly selective inhibitor of G9a/GLP that has enabled the discovery of a role for G9a/GLP enzymatic activity in the growth and differentiation status of leukemia cells.
G9a is a histone lysine methyltransferase responsible for the methylation of histone H3 lysine 9. The discovery of A-366 arose from a unique diversity screening hit, which was optimized by ...incorporation of a propyl-pyrrolidine subunit to occupy the enzyme lysine channel. A-366 is a potent inhibitor of G9a (IC50: 3.3 nM) with greater than 1000-fold selectivity over 21 other methyltransferases.
Cancer cells have an unusually high requirement for the central and intermediary metabolite nicotinamide adenine dinucleotide (NAD+), and NAD+ depletion ultimately results in cell death. The rate ...limiting step within the NAD+ salvage pathway required for converting nicotinamide to NAD+ is catalyzed by nicotinamide phosphoribosyltransferase (NAMPT). Targeting NAMPT has been investigated as an anti-cancer strategy, and several highly selective small molecule inhibitors have been found to potently inhibit NAMPT in cancer cells, resulting in NAD+ depletion and cytotoxicity. To identify mechanisms that could cause resistance to NAMPT inhibitor treatment, we generated a human fibrosarcoma cell line refractory to the highly potent and selective NAMPT small molecule inhibitor, GMX1778. We uncovered novel and unexpected mechanisms of resistance including significantly increased expression of quinolinate phosphoribosyl transferase (QPRT), a key enzyme in the de novo NAD+ synthesis pathway. Additionally, exome sequencing of the NAMPT gene in the resistant cells identified a single heterozygous point mutation that was not present in the parental cell line. The combination of upregulation of the NAD+ de novo synthesis pathway through QPRT over-expression and NAMPT mutation confers resistance to GMX1778, but the cells are only partially resistant to next-generation NAMPT inhibitors. The resistance mechanisms uncovered herein provide a potential avenue to continue exploration of next generation NAMPT inhibitors to treat neoplasms in the clinic.
•Upregulation of QPRT in cancer cell is a novel resistance mechanism to NAMPT inhibitor.•Single amino acid mutation of NAMPT (Y18C) confers resistance to NAMPT inhibitor.•A novel NAMPT inhibitor (A-1293201) overcomes the NAMPT(Y18C) resistance mechanism.
Cystic fibrosis (CF) is a genetic disorder that affects multiple tissues and organs. CF is caused by mutations in the CFTR gene, resulting in insufficient or impaired cystic fibrosis transmembrane ...conductance regulator (CFTR) protein. The deletion of phenylalanine at position 508 of the protein (F508del-CFTR) is the most common mutation observed in CF patients. The most effective treatments of these patients employ two CFTR modulator classes, correctors and potentiators. CFTR correctors increase protein levels at the cell surface; CFTR potentiators enable the functional opening of CFTR channels at the cell surface. Triple-combination therapies utilize two distinct corrector molecules (C1 and C2) to further improve the overall efficacy. We identified the need to develop a C2 corrector series that had the potential to be used in conjunction with our existing C1 corrector series and provide robust clinical efficacy for CF patients. The identification of a pyrrolidine series of CFTR C2 correctors and the structure–activity relationship of this series is described. This work resulted in the discovery and selection of (2S,3R,4S,5S)-3-(tert-butyl)-4-((2-methoxy-5-(trifluoromethyl)pyridin-3-yl)methoxy)-1-((S)-tetrahydro-2H-pyran-2-carbonyl)-5-(o-tolyl)pyrrolidine-2-carboxylic acid (ABBV/GLPG-3221), which was advanced to clinical trials.
Cancer cells are highly reliant on NAD
-dependent processes, including glucose metabolism, calcium signaling, DNA repair, and regulation of gene expression. Nicotinamide phosphoribosyltransferase ...(NAMPT), the rate-limiting enzyme for NAD
salvage from nicotinamide, has been investigated as a target for anticancer therapy. Known NAMPT inhibitors with potent cell activity are composed of a nitrogen-containing aromatic group, which is phosphoribosylated by the enzyme. Here, we identified two novel types of NAM-competitive NAMPT inhibitors, only one of which contains a modifiable, aromatic nitrogen that could be a phosphoribosyl acceptor. Both types of compound effectively deplete cellular NAD
, and subsequently ATP, and produce cell death when NAMPT is inhibited in cultured cells for more than 48 hours. Careful characterization of the kinetics of NAMPT inhibition
allowed us to optimize dosing to produce sufficient NAD
depletion over time that resulted in efficacy in an HCT116 xenograft model. Our data demonstrate that direct phosphoribosylation of competitive inhibitors by the NAMPT enzyme is not required for potent
cellular activity or
antitumor efficacy.
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The aim of this project was to determine research priorities, barriers, and enablers for adult primary brain tumour research in Australia and New Zealand. Consumers, health professionals, and ...researchers were invited to participate in a two-phase modified Delphi study. Phase 1 comprised an initial online survey (
= 91) and then focus groups (
= 29) which identified 60 key research topics, 26 barriers, and 32 enablers. Phase 2 comprised two online surveys to (1) reduce the list to 37 research priorities which achieved consensus (>75% 2-point agreement) and had high mean importance ratings (
= 116 participants) and (2) determine the most important priorities, barriers, and enablers (
= 90 participants). The top ten ranked research priorities for the overall sample and sub-groups (consumers, health professionals, and researchers) were identified. Priorities focused on: tumour biology, pre-clinical research, clinical and translational research, and supportive care. Variations were seen between sub-groups. The top ten barriers to conducting brain tumour research related to funding and resources, accessibility and awareness of research, collaboration, and process. The top ten research enablers were funding and resources, collaboration, and workforce. The broad list of research priorities identified by this Delphi study, together with how consumers, health professionals, and researchers prioritised items differently, and provides an evidence-based research agenda for brain tumour research that is needed across a wide range of areas.
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