1
|
Xu H, George E, Gallo D, Medvedev S, Wang X, Kryczka R, Hyer ML, Fourtounis J, Stocco R, Aguado-Fraile E, Petrone A, Yin SY, Shiwram A, Anderson M, Kim H, Liu F, Marshall CG, Simpkins F. Targeting CCNE1 amplified ovarian and endometrial cancers by combined inhibition of PKMYT1 and ATR. Res Sq 2024:rs.3.rs-3854682. [PMID: 38410486 PMCID: PMC10896384 DOI: 10.21203/rs.3.rs-3854682/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
Ovarian cancers (OVCAs) and endometrial cancers (EMCAs) with CCNE1-amplification are often resistant to standard of care treatment and represent an unmet clinical need. Previously, synthetic-lethal screening identified loss of the CDK1 regulator, PKMYT1, as synthetically lethal with CCNE1-amplification. We hypothesized that CCNE1-amplification associated replication stress will be more effectively targeted by combining the PKMYT1 inhibitor, lunresertib (RP-6306), with the ATR inhibitor, camonsertib (RP-3500/RG6526). Low dose combination RP-6306 with RP-3500 synergistically increased cytotoxicity more in CCNE1 amplified compared to non-amplified cells. Combination treatment produced durable antitumor activity and increased survival in CCNE1 amplified patient-derived and cell line-derived xenografts. Mechanistically, low doses of RP-6306 with RP-3500 increase CDK1 activation more so than monotherapy, triggering rapid and robust induction of premature mitosis, DNA damage and apoptosis in a CCNE1-dependent manner. These findings suggest that targeting CDK1 activity by combining RP-6306 with RP-3500 is a novel therapeutic approach to treat CCNE1-amplifed OVCAs and EMCAs.
Collapse
Affiliation(s)
- Haineng Xu
- Penn Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
| | - Erin George
- Penn Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
| | - David Gallo
- Repare Therapeutics, Inc., 7171 Frederick-Banting, Ville St-Laurent, QC, Canada
| | - Sergey Medvedev
- Penn Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
| | - Xiaolei Wang
- Penn Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
| | - Rosie Kryczka
- Repare Therapeutics, Inc., 7171 Frederick-Banting, Ville St-Laurent, QC, Canada
| | | | - Jimmy Fourtounis
- Repare Therapeutics, Inc., 7171 Frederick-Banting, Ville St-Laurent, QC, Canada
| | - Rino Stocco
- Repare Therapeutics, Inc., 7171 Frederick-Banting, Ville St-Laurent, QC, Canada
| | | | | | - Shou Yun Yin
- Repare Therapeutics, Inc., 7171 Frederick-Banting, Ville St-Laurent, QC, Canada
| | - Ariya Shiwram
- Repare Therapeutics, Inc., 7171 Frederick-Banting, Ville St-Laurent, QC, Canada
| | - Matthew Anderson
- Penn Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
| | - Hyoung Kim
- Penn Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
| | - Fang Liu
- Penn Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
| | | | - Fiona Simpkins
- Penn Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
- Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
| |
Collapse
|
2
|
Szychowski J, Papp R, Dietrich E, Liu B, Vallée F, Leclaire MÈ, Fourtounis J, Martino G, Perryman AL, Pau V, Yun Yin S, Mader P, Roulston A, Truchon JF, Marshall CG, Diallo M, Duffy NM, Stocco R, Godbout C, Bonneau-Fortin A, Kryczka R, Bhaskaran V, Mao D, Orlicky S, Beaulieu P, Turcotte P, Kurinov I, Sicheri F, Mamane Y, Gallant M, Black WC. Discovery of an Orally Bioavailable and Selective PKMYT1 Inhibitor, RP-6306. J Med Chem 2022; 65:10251-10284. [PMID: 35880755 PMCID: PMC9837800 DOI: 10.1021/acs.jmedchem.2c00552] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
PKMYT1 is a regulator of CDK1 phosphorylation and is a compelling therapeutic target for the treatment of certain types of DNA damage response cancers due to its established synthetic lethal relationship with CCNE1 amplification. To date, no selective inhibitors have been reported for this kinase that would allow for investigation of the pharmacological role of PKMYT1. To address this need compound 1 was identified as a weak PKMYT1 inhibitor. Introduction of a dimethylphenol increased potency on PKMYT1. These dimethylphenol analogs were found to exist as atropisomers that could be separated and profiled as single enantiomers. Structure-based drug design enabled optimization of cell-based potency. Parallel optimization of ADME properties led to the identification of potent and selective inhibitors of PKMYT1. RP-6306 inhibits CCNE1-amplified tumor cell growth in several preclinical xenograft models. The first-in-class clinical candidate RP-6306 is currently being evaluated in Phase 1 clinical trials for treatment of various solid tumors.
Collapse
Affiliation(s)
- Janek Szychowski
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Robert Papp
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Evelyne Dietrich
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Bingcan Liu
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Frédéric Vallée
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Marie-Ève Leclaire
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Jimmy Fourtounis
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Giovanni Martino
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Alexander L. Perryman
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Victor Pau
- Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, ON, M5G 1X5, Canada
| | - Shou Yun Yin
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Pavel Mader
- Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, ON, M5G 1X5, Canada
| | - Anne Roulston
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Jean-Francois Truchon
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - C. Gary Marshall
- Repare Therapeutics, 1 Broadway, 15th Floor, Cambridge, MA 02142, USA
| | - Mohamed Diallo
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Nicole M. Duffy
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Rino Stocco
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Claude Godbout
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | | | - Rosie Kryczka
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Vivek Bhaskaran
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Daniel Mao
- Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, ON, M5G 1X5, Canada
| | - Stephen Orlicky
- Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, ON, M5G 1X5, Canada
| | - Patrick Beaulieu
- OmegaChem Inc., 480 Rue Perreault, Saint-Romuald, QC, G6W 7V6, Canada
| | - Pascal Turcotte
- AdMare BioInnovations, 7171 Frederick-Banting, Montréal, QC, H4S 1Z9, Canada
| | - Igor Kurinov
- Department of Chemistry and Chemical Biology, Cornell University, NE-CAT, Argonne, Il 60439, USA
| | - Frank Sicheri
- Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, ON, M5G 1X5, Canada
- Departments of Biochemistry and Molecular Genetics, University of Toronto, Ontario M5S 1A8, Canada
| | - Yael Mamane
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - Michel Gallant
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| | - W. Cameron Black
- Repare Therapeutics, Inc., 7210 Frederick-Banting, Ville St-Laurent, QC, H4S 2A1, Canada
| |
Collapse
|
3
|
Fourtounis J, Martino J, Stocco R, Baruah P, Duffy N, Gallo D, Fournier S, Li J, Li L, Aguado E, Petrone A, Roulston A, Mamane Y, Morris S, Szychowski J, Papp R, Zinda M, Marshall CG. Abstract 5650: RP-6306, a novel PKMYT1 inhibitor, demonstrates synthetic lethality as monotherapy and in combination with gemcitabine in CCNE1 amplified cancer cells. Cancer Res 2022. [DOI: 10.1158/1538-7445.am2022-5650] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Cyclin E1, the protein product of the CCNE1 gene, complexes with CDK2 and is a key regulator of the G1-S transition in cycling cells. CCNE1 amplification has been associated with increased replication stress and genomic instability associated with tumorigenesis. The serine-threonine protein kinase family member PKMYT1 negatively regulates the G2-Mitosis transition by phosphorylating and inactivating CDK1. The aim of the current study was to evaluate the impact of RP-6306, a novel and selective PKMYT1 inhibitor, on the CCNE1 amplified human breast cancer cell line, HCC1569. RP-6306 is a highly potent PKMYT1 inhibitor that displays single digit nM potency in an in vitro enzyme assay. RP-6306 dose-dependently inhibited the phosphorylation of CDK1 on Thr14 in HCC1569 cells and had no impact on the Tyr15 phospho-site of CDK1 that is regulated by family member Wee1. Cell-based assays showed increased phosphorylation of replication stress and pre-mitotic entry biomarkers in RP-6306 treated HCC1569 cells. Micronuclei and Caspase-3 were detected in a dose-dependent manner in HCC1569 cells treated with RP-6306 indicating the onset of genomic instability and apoptosis in these cells. Growth assays confirmed irreparable damage and proliferation defects in cells treated with RP-6306. Experiments to evaluate the combination of RP-6306 with gemcitabine, an S-phase specific pyrimidine analog that inhibits DNA synthesis showed profound synergistic growth defects in HCC1569 cells. In vivo, RP-6306 inhibition of Thr14 phosphorylation of CDK1 in HCC1569 tumors was directly proportional to free circulating plasma levels and resulted in significant inhibition of tumor growth in a dose and time dependent manner. In combination with gemcitabine, RP-6306 demonstrated tumor regression and superior efficacy compared to single agent treatment of either agent alone in multiple CCNE1 amplified models, including HCC1569 and OVCAR3. Our studies show that inhibition of PKMYT1 kinase activity impairs the growth of CCNE1 amplified cancer cell lines both in vitro and in vivo and stands to benefit cancer patients with CCNE1 amplification. A Phase I clinical trial (NCT04855656- Mythic Study) is currently underway to evaluate RP-6306 in patients with advanced solid tumors.
Citation Format: Jimmy Fourtounis, John Martino, Rino Stocco, Prasamit Baruah, Nicole Duffy, David Gallo, Sarah Fournier, JingJing Li, Li Li, Elia Aguado, Adam Petrone, Anne Roulston, Yael Mamane, Stephen Morris, Janek Szychowski, Robert Papp, Mike Zinda, C. Gary Marshall. RP-6306, a novel PKMYT1 inhibitor, demonstrates synthetic lethality as monotherapy and in combination with gemcitabine in CCNE1 amplified cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5650.
Collapse
Affiliation(s)
| | - John Martino
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | - Rino Stocco
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | | | - Nicole Duffy
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | - David Gallo
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | | | - JingJing Li
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | - Li Li
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | - Elia Aguado
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | - Adam Petrone
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | | | - Yael Mamane
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | | | | | - Robert Papp
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | - Mike Zinda
- 1Repare Therapeutics Inc., Montreal, Quebec, Canada
| | | |
Collapse
|
4
|
Gallo D, Young JTF, Fourtounis J, Martino G, Álvarez-Quilón A, Bernier C, Duffy NM, Papp R, Roulston A, Stocco R, Szychowski J, Veloso A, Alam H, Baruah PS, Fortin AB, Bowlan J, Chaudhary N, Desjardins J, Dietrich E, Fournier S, Fugère-Desjardins C, Goullet de Rugy T, Leclaire ME, Liu B, Bhaskaran V, Mamane Y, Melo H, Nicolas O, Singhania A, Szilard RK, Tkáč J, Yin SY, Morris SJ, Zinda M, Marshall CG, Durocher D. CCNE1 amplification is synthetic lethal with PKMYT1 kinase inhibition. Nature 2022; 604:749-756. [PMID: 35444283 PMCID: PMC9046089 DOI: 10.1038/s41586-022-04638-9] [Citation(s) in RCA: 58] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Accepted: 03/14/2022] [Indexed: 12/13/2022]
Abstract
Amplification of the CCNE1 locus on chromosome 19q12 is prevalent in multiple tumour types, particularly in high-grade serous ovarian cancer, uterine tumours and gastro-oesophageal cancers, where high cyclin E levels are associated with genome instability, whole-genome doubling and resistance to cytotoxic and targeted therapies1–4. To uncover therapeutic targets for tumours with CCNE1 amplification, we undertook genome-scale CRISPR–Cas9-based synthetic lethality screens in cellular models of CCNE1 amplification. Here we report that increasing CCNE1 dosage engenders a vulnerability to the inhibition of the PKMYT1 kinase, a negative regulator of CDK1. To inhibit PKMYT1, we developed RP-6306, an orally bioavailable and selective inhibitor that shows single-agent activity and durable tumour regressions when combined with gemcitabine in models of CCNE1 amplification. RP-6306 treatment causes unscheduled activation of CDK1 selectively in CCNE1-overexpressing cells, promoting early mitosis in cells undergoing DNA synthesis. CCNE1 overexpression disrupts CDK1 homeostasis at least in part through an early activation of the MMB–FOXM1 mitotic transcriptional program. We conclude that PKMYT1 inhibition is a promising therapeutic strategy for CCNE1-amplified cancers. Genome-scale CRISPR–Cas9-based synthetic lethality screens identify PKMYT1 as a potential therapeutic target in tumours with CCNE1 amplification.
Collapse
Affiliation(s)
- David Gallo
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
| | | | | | | | - Alejandro Álvarez-Quilón
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.,Repare Therapeutics, Saint-Laurent, Quebec, Canada
| | | | | | - Robert Papp
- Repare Therapeutics, Saint-Laurent, Quebec, Canada
| | | | - Rino Stocco
- Repare Therapeutics, Saint-Laurent, Quebec, Canada
| | | | | | - Hunain Alam
- Repare Therapeutics, Saint-Laurent, Quebec, Canada
| | | | | | | | - Natasha Chaudhary
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
| | | | | | | | | | - Theo Goullet de Rugy
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.,Repare Therapeutics, Saint-Laurent, Quebec, Canada
| | | | - Bingcan Liu
- Repare Therapeutics, Saint-Laurent, Quebec, Canada
| | | | - Yael Mamane
- Repare Therapeutics, Saint-Laurent, Quebec, Canada
| | - Henrique Melo
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
| | | | | | - Rachel K Szilard
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
| | - Ján Tkáč
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
| | - Shou Yun Yin
- Repare Therapeutics, Saint-Laurent, Quebec, Canada
| | | | | | | | - Daniel Durocher
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada. .,Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada.
| |
Collapse
|
5
|
Schroeder P, Fulzele K, Forsyth S, Ribadeneira MD, Guichard S, Wilker E, Marshall CG, Drake A, Fessler R, Konstantinidis DG, Seu KG, Kalfa TA. Etavopivat, a Pyruvate Kinase Activator in Red Blood Cells, for the Treatment of Sickle Cell Disease. J Pharmacol Exp Ther 2022; 380:210-219. [PMID: 35031585 DOI: 10.1124/jpet.121.000743] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 12/21/2021] [Indexed: 11/22/2022] Open
Abstract
Etavopivat is an investigational, oral, small molecule activator of erythrocyte pyruvate kinase (PKR) in development for the treatment of sickle cell disease (SCD) and other hemoglobinopathies. PKR activation is proposed to ameliorate the sickling of SCD red blood cells (RBC) through multiple mechanisms, including reduction of 2,3-diphosphoglycerate (2,3-DPG), which consequently increases hemoglobin (Hb)-oxygen affinity; increased binding of oxygen reduces HbS polymerization and sickling. In addition, PKR activation increases adenosine triphosphate (ATP) produced via glycolytic flux, which helps preserve membrane integrity and RBC deformability. We evaluated the pharmacodynamic response to etavopivat in non-human primates (NHP) and in healthy human subjects, and the effects in RBC from patients with SCD after ex vivo treatment with etavopivat. A single dose of etavopivat decreased 2,3-DPG in NHP and healthy subjects. Hb-oxygen affinity was significantly increased in healthy subjects after 24 hours. Following daily dosing of etavopivat over 5 consecutive days in NHP, ATP was increased by 38% from baseline. Etavopivat increased Hb-oxygen affinity and reduced sickling in RBC collected from SCD patients with either HbSS or HbSC disease. Collectively, these results demonstrate the ability of etavopivat to decrease 2,3-DPG and increase ATP, resulting in increased Hb-oxygen affinity and improved sickle RBC function. Etavopivat is currently being evaluated in clinical trials for the treatment of SCD. ClinicalTrials.gov identifier: NCT03815695 Significance Statement Etavopivat-a small molecule activator of the glycolytic enzyme erythrocyte pyruvate kinase -decreased 2,3-diphosphoglycerate in red blood cells (RBC) from non-human primates and healthy subjects and significantly increased hemoglobin (Hb)-oxygen affinity in healthy subjects. Using ex vivo RBC from donors with sickle cell disease (SCD) (HbSS or HbSC genotype), etavopivat increased Hb-oxygen affinity and reduced sickling under deoxygenation. Etavopivat shows promise as a treatment for SCD, that potentially might reduce vaso-occlusion and improve anemia.
Collapse
Affiliation(s)
| | | | | | | | | | | | | | | | - Rose Fessler
- Cincinnati Children's Hospital Medical Center, United States
| | | | - Katie G Seu
- Cincinnati Children's Hospital Medical Center, United States
| | | |
Collapse
|
6
|
Reutershan MH, Machacek MR, Altman MD, Bogen S, Cai M, Cammarano C, Chen D, Christopher M, Cryan J, Daublain P, Fradera X, Geda P, Goldenblatt P, Hill AD, Kemper RA, Kutilek V, Li C, Martinez M, McCoy M, Nair L, Pan W, Thompson CF, Scapin G, Shizuka M, Spatz ML, Steinhuebel D, Sun B, Voss ME, Wang X, Yang L, Yeh TC, Dussault I, Marshall CG, Trotter BW. Discovery of MK-4688: an Efficient Inhibitor of the HDM2-p53 Protein-Protein Interaction. J Med Chem 2021; 64:16213-16241. [PMID: 34714078 DOI: 10.1021/acs.jmedchem.1c01524] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Identification of low-dose, low-molecular-weight, drug-like inhibitors of protein-protein interactions (PPIs) is a challenging area of research. Despite the challenges, the therapeutic potential of PPI inhibition has driven significant efforts toward this goal. Adding to recent success in this area, we describe herein our efforts to optimize a novel purine carboxylic acid-derived inhibitor of the HDM2-p53 PPI into a series of low-projected dose inhibitors with overall favorable pharmacokinetic and physical properties. Ultimately, a strategy focused on leveraging known binding hot spots coupled with biostructural information to guide the design of conformationally constrained analogs and a focus on efficiency metrics led to the discovery of MK-4688 (compound 56), a highly potent, selective, and low-molecular-weight inhibitor suitable for clinical investigation.
Collapse
Affiliation(s)
- Michael H Reutershan
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Michelle R Machacek
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Michael D Altman
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Stephane Bogen
- Merck & Co., Inc., 2015 Galloping Hill Rd, Kenilworth, New Jersey 07032, United States
| | - Mingmei Cai
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Carolyn Cammarano
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Dapeng Chen
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Matthew Christopher
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - John Cryan
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Pierre Daublain
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Xavier Fradera
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Prasanthi Geda
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Peter Goldenblatt
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Armetta D Hill
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Raymond A Kemper
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Victoria Kutilek
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Chaomin Li
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Michelle Martinez
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Mark McCoy
- Merck & Co., Inc., 2015 Galloping Hill Rd, Kenilworth, New Jersey 07032, United States
| | - Latha Nair
- Merck & Co., Inc., 2015 Galloping Hill Rd, Kenilworth, New Jersey 07032, United States
| | - Weidong Pan
- Merck & Co., Inc., 2015 Galloping Hill Rd, Kenilworth, New Jersey 07032, United States
| | | | - Giovanna Scapin
- Merck & Co., Inc., 2015 Galloping Hill Rd, Kenilworth, New Jersey 07032, United States
| | - Manami Shizuka
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Marianne L Spatz
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Dietrich Steinhuebel
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Binyuan Sun
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Matthew E Voss
- Albany Molecular Research Inc., 61 Science Park Road, Singapore (West) 117525, Singapore
| | - Xiao Wang
- Merck & Co., Inc., 126 East Lincoln Avenue, Rahway, New Jersey 07065, United States
| | - Liping Yang
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Tammie C Yeh
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Isabelle Dussault
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - C Gary Marshall
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - B Wesley Trotter
- Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| |
Collapse
|
7
|
Turnbull AP, Ioannidis S, Krajewski WW, Pinto-Fernandez A, Heride C, Martin ACL, Tonkin LM, Townsend EC, Buker SM, Lancia DR, Caravella JA, Toms AV, Charlton TM, Lahdenranta J, Wilker E, Follows BC, Evans NJ, Stead L, Alli C, Zarayskiy VV, Talbot AC, Buckmelter AJ, Wang M, McKinnon CL, Saab F, McGouran JF, Century H, Gersch M, Pittman MS, Marshall CG, Raynham TM, Simcox M, Stewart LMD, McLoughlin SB, Escobedo JA, Bair KW, Dinsmore CJ, Hammonds TR, Kim S, Urbé S, Clague MJ, Kessler BM, Komander D. Molecular basis of USP7 inhibition by selective small-molecule inhibitors. Nature 2017; 550:481-486. [PMID: 29045389 DOI: 10.1038/nature24451] [Citation(s) in RCA: 283] [Impact Index Per Article: 40.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Accepted: 09/25/2017] [Indexed: 12/16/2022]
Abstract
Ubiquitination controls the stability of most cellular proteins, and its deregulation contributes to human diseases including cancer. Deubiquitinases remove ubiquitin from proteins, and their inhibition can induce the degradation of selected proteins, potentially including otherwise 'undruggable' targets. For example, the inhibition of ubiquitin-specific protease 7 (USP7) results in the degradation of the oncogenic E3 ligase MDM2, and leads to re-activation of the tumour suppressor p53 in various cancers. Here we report that two compounds, FT671 and FT827, inhibit USP7 with high affinity and specificity in vitro and within human cells. Co-crystal structures reveal that both compounds target a dynamic pocket near the catalytic centre of the auto-inhibited apo form of USP7, which differs from other USP deubiquitinases. Consistent with USP7 target engagement in cells, FT671 destabilizes USP7 substrates including MDM2, increases levels of p53, and results in the transcription of p53 target genes, induction of the tumour suppressor p21, and inhibition of tumour growth in mice.
Collapse
Affiliation(s)
- Andrew P Turnbull
- CRUK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, London NW1 0NH, UK
| | | | - Wojciech W Krajewski
- CRUK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, London NW1 0NH, UK
| | - Adan Pinto-Fernandez
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7FZ, UK
| | - Claire Heride
- Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Agnes C L Martin
- CRUK Therapeutic Discovery Laboratories, Jonas Webb Building, Babraham Research Campus, Cambridge CB22 3AT, UK
| | - Louise M Tonkin
- CRUK Therapeutic Discovery Laboratories, Jonas Webb Building, Babraham Research Campus, Cambridge CB22 3AT, UK
| | | | - Shane M Buker
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | - David R Lancia
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | | | - Angela V Toms
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | - Thomas M Charlton
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7FZ, UK
| | | | - Erik Wilker
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | - Bruce C Follows
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | - Nicola J Evans
- CRUK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, London NW1 0NH, UK
| | - Lucy Stead
- Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Cristina Alli
- CRUK Therapeutic Discovery Laboratories, Jonas Webb Building, Babraham Research Campus, Cambridge CB22 3AT, UK
| | | | - Adam C Talbot
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | | | - Minghua Wang
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | | | - Fabienne Saab
- CRUK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, London NW1 0NH, UK
| | - Joanna F McGouran
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7FZ, UK
| | - Hannah Century
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7FZ, UK
| | - Malte Gersch
- Medical Research Council Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Marc S Pittman
- CRUK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, London NW1 0NH, UK
| | - C Gary Marshall
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | - Tony M Raynham
- CRUK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, London NW1 0NH, UK
| | - Mary Simcox
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | - Lorna M D Stewart
- CRUK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, London NW1 0NH, UK
| | - Sheila B McLoughlin
- CRUK Therapeutic Discovery Laboratories, Jonas Webb Building, Babraham Research Campus, Cambridge CB22 3AT, UK
| | - Jaime A Escobedo
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | - Kenneth W Bair
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | | | - Tim R Hammonds
- CRUK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, London NW1 0NH, UK
| | - Sunkyu Kim
- FORMA Therapeutics, Arsenal Street, Watertown, Massachusetts 02472, USA
| | - Sylvie Urbé
- Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Michael J Clague
- Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Benedikt M Kessler
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7FZ, UK
| | - David Komander
- Medical Research Council Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| |
Collapse
|
8
|
Siu T, Kumarasinghe SE, Altman MD, Katcher M, Northrup A, White C, Rosenstein C, Mathur A, Xu L, Chan G, Bachman E, Bouthillette M, Dinsmore CJ, Marshall CG, Young JR. The discovery of reverse tricyclic pyridone JAK2 inhibitors. Part 2: lead optimization. Bioorg Med Chem Lett 2014; 24:1466-71. [PMID: 24582987 DOI: 10.1016/j.bmcl.2014.02.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 01/31/2014] [Accepted: 02/04/2014] [Indexed: 11/27/2022]
Abstract
This communication discusses the discovery of novel reverse tricyclic pyridones as inhibitors of Janus kinase 2 (JAK2). By using a kinase cross screening approach coupled with molecular modeling, a unique inhibitor-water interaction was discovered to impart excellent broad kinase selectivity. Improvements in intrinsic potency were achieved by utilizing a rapid library approach, while targeted structural changes to lower lipophilicity led to improved rat pharmacokinetics. This multi-pronged approach led to the identification of 31, which demonstrated encouraging rat pharmacokinetics, in vivo potency, and excellent off-target kinase selectivity.
Collapse
Affiliation(s)
- Tony Siu
- Department of Medicinal Chemistry, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA.
| | | | - Michael D Altman
- Department of Structural Chemistry, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Matthew Katcher
- Department of Medicinal Chemistry, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Alan Northrup
- Department of Medicinal Chemistry, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Catherine White
- Department of Medicinal Chemistry, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Craig Rosenstein
- Department of In Vitro Sciences, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Anjili Mathur
- Department of Pharmacology, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Lin Xu
- Department of Drug Metabolism, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Grace Chan
- Department of In Vitro Sciences, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Eric Bachman
- Department of Pharmacology, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Melaney Bouthillette
- Department of Basic Pharmaceutical Sciences, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Christopher J Dinsmore
- Department of Medicinal Chemistry, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - C Gary Marshall
- Department of Oncology, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Jonathan R Young
- Department of Medicinal Chemistry, Merck & Co., 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| |
Collapse
|
9
|
Kraus M, Wang Y, Aleksandrowicz D, Bachman E, Szewczak AA, Walker D, Xu L, Bouthillette M, Childers KM, Dolinski B, Haidle AM, Kopinja J, Lee L, Lim J, Little KD, Ma Y, Mathur A, Mo JR, O’Hare E, Otte RD, Taoka BM, Wang W, Yin H, Zabierek AA, Zhang W, Zhao S, Zhu J, Young JR, Marshall CG. Efficacious intermittent dosing of a novel JAK2 inhibitor in mouse models of polycythemia vera. PLoS One 2012; 7:e37207. [PMID: 22623993 PMCID: PMC3356383 DOI: 10.1371/journal.pone.0037207] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2011] [Accepted: 04/16/2012] [Indexed: 01/08/2023] Open
Abstract
A high percentage of patients with the myeloproliferative disorder polycythemia vera (PV) harbor a Val617→Phe activating mutation in the Janus kinase 2 (JAK2) gene, and both cell culture and mouse models have established a functional role for this mutation in the development of this disease. We describe the properties of MRLB-11055, a highly potent inhibitor of both the WT and V617F forms of JAK2, that has therapeutic efficacy in erythropoietin (EPO)-driven and JAK2V617F-driven mouse models of PV. In cultured cells, MRLB-11055 blocked proliferation and induced apoptosis in a manner consistent with JAK2 pathway inhibition. MRLB-11055 effectively prevented EPO-induced STAT5 activation in the peripheral blood of acutely dosed mice, and could prevent EPO-induced splenomegaly and erythrocytosis in chronically dosed mice. In a bone marrow reconstituted JAK2V617F-luciferase murine PV model, MRLB-11055 rapidly reduced the burden of JAK2V617F-expressing cells from both the spleen and the bone marrow. Using real-time in vivo imaging, we examined the kinetics of disease regression and resurgence, enabling the development of an intermittent dosing schedule that achieved significant reductions in both erythroid and myeloid populations with minimal impact on lymphoid cells. Our studies provide a rationale for the use of non-continuous treatment to provide optimal therapy for PV patients.
Collapse
Affiliation(s)
- Manfred Kraus
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Yuxun Wang
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Dan Aleksandrowicz
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Eric Bachman
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Alexander A. Szewczak
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Deborah Walker
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Lin Xu
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Melaney Bouthillette
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Kaleen M. Childers
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Brian Dolinski
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Andrew M. Haidle
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Johnny Kopinja
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Linda Lee
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Jongwon Lim
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Kevin D. Little
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Yanhong Ma
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Anjili Mathur
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Jan-Rung Mo
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Erin O’Hare
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Ryan D. Otte
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Brandon M. Taoka
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Wenxian Wang
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Hong Yin
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Anna A. Zabierek
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Weisheng Zhang
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Shuxia Zhao
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Joe Zhu
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
| | - Jonathan R. Young
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
- * E-mail: (CGM); (JRY)
| | - C. Gary Marshall
- Departments of DMPK, in vitro Sciences, in vivo Sciences, Medicinal Chemistry, Basic Pharmaceutical Sciences and Oncology, Merck Research Laboratories, Boston, Massachusetts, United States of America
- * E-mail: (CGM); (JRY)
| |
Collapse
|
10
|
Lim J, Taoka B, Otte RD, Spencer K, Dinsmore CJ, Altman MD, Chan G, Rosenstein C, Sharma S, Su HP, Szewczak AA, Xu L, Yin H, Zugay-Murphy J, Marshall CG, Young JR. Discovery of 1-amino-5H-pyrido[4,3-b]indol-4-carboxamide inhibitors of Janus kinase 2 (JAK2) for the treatment of myeloproliferative disorders. J Med Chem 2011; 54:7334-49. [PMID: 21942426 DOI: 10.1021/jm200909u] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The JAK-STAT pathway mediates signaling by cytokines, which control survival, proliferation, and differentiation of a variety of cells. In recent years, a single point mutation (V617F) in the tyrosine kinase JAK2 was found to be present with a high incidence in myeloproliferative disorders (MPDs). This mutation led to hyperactivation of JAK2, cytokine-independent signaling, and subsequent activation of downstream signaling networks. The genetic, biological, and physiological evidence suggests that JAK2 inhibitors could be effective in treating MPDs. De novo design efforts of new scaffolds identified 1-amino-5H-pyrido[4,3-b]indol-4-carboxamides as a new viable lead series. Subsequent optimization of cell potency, metabolic stability, and off-target activities of the leads led to the discovery of 7-(2-aminopyrimidin-5-yl)-1-{[(1R)-1-cyclopropyl-2,2,2-trifluoroethyl]amino}-5H-pyrido[4,3-b]indole-4-carboxamide (65). Compound 65 is a potent, orally active inhibitor of JAK2 with excellent selectivity, PK profile, and in vivo efficacy in animal models.
Collapse
Affiliation(s)
- Jongwon Lim
- Department of Chemistry, Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Katz JD, Jewell JP, Guerin DJ, Lim J, Dinsmore CJ, Deshmukh SV, Pan BS, Marshall CG, Lu W, Altman MD, Dahlberg WK, Davis L, Falcone D, Gabarda AE, Hang G, Hatch H, Holmes R, Kunii K, Lumb KJ, Lutterbach B, Mathvink R, Nazef N, Patel SB, Qu X, Reilly JF, Rickert KW, Rosenstein C, Soisson SM, Spencer KB, Szewczak AA, Walker D, Wang W, Young J, Zeng Q. Discovery of a 5H-benzo[4,5]cyclohepta[1,2-b]pyridin-5-one (MK-2461) inhibitor of c-Met kinase for the treatment of cancer. J Med Chem 2011; 54:4092-108. [PMID: 21608528 DOI: 10.1021/jm200112k] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
c-Met is a transmembrane tyrosine kinase that mediates activation of several signaling pathways implicated in aggressive cancer phenotypes. In recent years, research into this area has highlighted c-Met as an attractive cancer drug target, triggering a number of approaches to disrupt aberrant c-Met signaling. Screening efforts identified a unique class of 5H-benzo[4,5]cyclohepta[1,2-b]pyridin-5-one kinase inhibitors, exemplified by 1. Subsequent SAR studies led to the development of 81 (MK-2461), a potent inhibitor of c-Met that was efficacious in preclinical animal models of tumor suppression. In addition, biochemical studies and X-ray analysis have revealed that this unique class of kinase inhibitors binds preferentially to the activated (phosphorylated) form of the kinase. This report details the development of 81 and provides a description of its unique biochemical properties.
Collapse
Affiliation(s)
- Jason D Katz
- Department of Chemistry, Merck Research Laboratories, 33 Avenue Louis Pasteur, BMB-2-114, Boston, Massachusetts 02115, United States.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Siu T, Kozina ES, Jung J, Rosenstein C, Mathur A, Altman MD, Chan G, Xu L, Bachman E, Mo JR, Bouthillette M, Rush T, Dinsmore CJ, Marshall CG, Young JR. The discovery of tricyclic pyridone JAK2 inhibitors. Part 1: hit to lead. Bioorg Med Chem Lett 2010; 20:7421-5. [PMID: 21044843 DOI: 10.1016/j.bmcl.2010.10.031] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2010] [Revised: 10/04/2010] [Accepted: 10/06/2010] [Indexed: 10/19/2022]
Abstract
This paper describes the discovery and design of a novel class of JAK2 inhibitors. Furthermore, we detail the optimization of a screening hit using ligand binding efficiency and log D. These efforts led to the identification of compound 41, which demonstrates in vivo activity in our study.
Collapse
Affiliation(s)
- Tony Siu
- Department of Chemistry, Merck & Co., Boston, MA 02115, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Ma Y, Zhao S, Zhu J, Bettano KA, Qu X, Marshall CG, Young JR, Kohl NE, Scott ML, Zhang W, Wang Y. Real-time bioluminescence imaging of polycythemia vera development in mice. Biochim Biophys Acta Mol Basis Dis 2009; 1792:1073-9. [PMID: 19715759 DOI: 10.1016/j.bbadis.2009.08.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2009] [Revised: 07/13/2009] [Accepted: 08/20/2009] [Indexed: 10/20/2022]
Abstract
Polycythemia vera (PV) is a myeloproliferative disorder involving hematopoietic stem cells. A recurrent somatic missense mutation in JAK2 (JAK2V617F) is thought to play a causal role in PV. Therefore, targeting Jak2 will likely provide a molecular mechanism-based therapy for PV. To facilitate the development of such new and specific therapeutics, a suitable and well-characterized preclinical animal model is essential. Although several mouse models of PV have been reported, the spatiotemporal kinetics of PV formation and progression has not been studied. To address this, we created a bone marrow transplant mouse model that co-expresses mutant Jak2 and luciferase 2 (Luc2) genes. Bioluminescent imaging (BLI) was used to visualize disease cells and analyze the kinetics of PV development in vivo. To better understand the molecular mechanism of PV, we generated mice carrying a kinase inactive mutant Jak2 (Jak2K882E), demonstrating that the PV disease was dependent on constitutive activation of the Jak2 kinase activity. We further showed that the Jak2V617F mutation caused increased stem cell renewal activity and impaired cell differentiation, which was at least in part due to deregulated transcriptional programming. The Jak2V617F-Luc2 PV mice will be a useful preclinical model to characterize novel JAK2 inhibitors for the treatment of PV.
Collapse
Affiliation(s)
- Yanhong Ma
- Department of Oncology, Merck Research Laboratories, 33 Avenue Louis Pasteur, Boston, MA 02115, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
14
|
Marshall CG, Torrent M, Williams O, Hamilton KA, Buser CA. Characterization of inhibitor binding to human kinesin spindle protein by site-directed mutagenesis. Arch Biochem Biophys 2009; 484:1-7. [PMID: 19467625 DOI: 10.1016/j.abb.2009.01.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2008] [Revised: 01/14/2009] [Accepted: 01/15/2009] [Indexed: 11/19/2022]
Abstract
A number of inhibitors of kinesin spindle protein (KSP) have been described, which are known from X-ray crystallography studies to bind to an induced fit pocket defined by the L5 loop. We describe the characterization of eight mutant forms of KSP in which six residues that line this pocket have been altered. Mutants were analyzed by measuring rates of enzyme catalysis, in the presence and absence of six KSP inhibitors of four diverse structural classes and of varied ATP-competition status. Our analysis was in agreement with the model of binding established by the structural studies and suggests that binding energy is well distributed across functional groups in these molecules. The majority of the mutants retained significant enzymatic activity while diminishing inhibitor binding, indicating potential for the development of drug resistance. These data provide detailed information on interactions between inhibitor and binding pocket at the functional group level and enable the development of novel KSP inhibitors.
Collapse
Affiliation(s)
- C Gary Marshall
- Dept. of Cancer Biology and Therapeutics, Merck Research Laboratories, 33 Avenue Louis Pasteur, Boston, MA 02115, USA.
| | | | | | | | | |
Collapse
|
15
|
Krog AJ, Marshall CG. Alkyl-Dimethyl-Benzyl-Ammonium-Chloride for Sanitization of Eating and Drinking Utensils. Am J Public Health Nations Health 2008; 30:341-8. [PMID: 18015201 DOI: 10.2105/ajph.30.4.341] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
|
16
|
Carleton M, Mao M, Biery M, Warrener P, Kim S, Buser C, Marshall CG, Fernandes C, Annis J, Linsley PS. RNA interference-mediated silencing of mitotic kinesin KIF14 disrupts cell cycle progression and induces cytokinesis failure. Mol Cell Biol 2006; 26:3853-63. [PMID: 16648480 PMCID: PMC1488988 DOI: 10.1128/mcb.26.10.3853-3863.2006] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
KIF14 is a microtubule motor protein whose elevated expression is associated with poor-prognosis breast cancer. Here we demonstrate KIF14 accumulation in mitotic cells, where it associated with developing spindle poles and spindle microtubules. Cells at later stages of mitosis were characterized by the concentration of KIF14 at the midbody. Time-lapse microscopy revealed that strong RNA interference (RNAi)-mediated silencing of KIF14 induced cytokinesis failure, causing several rounds of endoreduplication and resulting in multinucleated cells. Additionally, less efficacious KIF14-specific short interfering RNAs (siRNAs) induced multiple phenotypes, all of which resulted in acute apoptosis. Our data demonstrate the ability of siRNA-mediated silencing to generate epiallelic hypomorphs associated with KIF14 depletion. Furthermore, the link we observed between siRNA efficacy and phenotypic outcome indicates that distinct stages during cell cycle progression are disrupted by the differential modulation of KIF14 expression.
Collapse
Affiliation(s)
- Michael Carleton
- Rosetta Inpharmatics LLC, 401 Terry Ave., N. Seattle, Washington 98109, USA.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
17
|
Abstract
Nonribosomal peptide synthetases (NRPSs) use phosphopantetheine (pPant) bearing carrier proteins to chaperone activated aminoacyl and peptidyl intermediates to the various enzymes that effect peptide synthesis. Using components from siderophore NRPSs that synthesize vibriobactin, enterobactin, yersiniabactin, pyochelin, and anguibactin, we examined the nature of the interaction of such cofactor-carrier proteins with acyl-activating adenylation (A) domains. While VibE, EntE, and PchD were all able to utilize "carrier protein-free" pPant derivatives, the pattern of usage indicated diversity in the binding mechanism, and even the best substrates were down at least 3 log units relative to the native cofactor-carrier protein. When tested with four noncognate carrier proteins, EntE and VibE differed both in the range of substrate utilization efficiency and in the distribution of the efficiencies across this range. Correlating sequence alignments to kinetic efficiency allowed for the construction of eight point mutants of VibE's worst substrate, HMWP2 ArCP, to the corresponding residue in its native VibB. Mutants S49D and H66E combined to increase activity 6.2-fold and had similar enhancing effects on the downstream condensation domain VibH, indicating that the two NRPS enzymes share carrier protein recognition determinants. Similar mutations of HMWP2 ArCP toward EntB had little effect on EntE, suggesting that the position of recognition determinants varies across NRPS systems.
Collapse
Affiliation(s)
- C Gary Marshall
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | |
Collapse
|
18
|
Keating TA, Marshall CG, Walsh CT, Keating AE. The structure of VibH represents nonribosomal peptide synthetase condensation, cyclization and epimerization domains. Nat Struct Biol 2002; 9:522-6. [PMID: 12055621 DOI: 10.1038/nsb810] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Nonribosomal peptide synthetases (NRPSs) are large, multidomain enzymes that biosynthesize medically important natural products. We report the crystal structure of the free-standing NRPS condensation (C) domain VibH, which catalyzes amide bond formation in the synthesis of vibriobactin, a Vibrio cholerae siderophore. Despite low sequence identity, NRPS condensation enzymes are structurally related to chloramphenicol acetyltransferase (CAT) and dihydrolipoamide acyltransferases. However, although the latter enzymes are homotrimers, VibH is a monomeric pseudodimer. The VibH structure is representative of both NRPS condensation and epimerization domains, as well as the condensation-variant cyclization domains, which are all expected to be monomers. Surprisingly, despite favorable positioning in the active site, a universally conserved histidine important in CAT and in other C domains is not critical for general base catalysis in VibH.
Collapse
Affiliation(s)
- Thomas A Keating
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | |
Collapse
|
19
|
Pootoolal J, Thomas MG, Marshall CG, Neu JM, Hubbard BK, Walsh CT, Wright GD. Assembling the glycopeptide antibiotic scaffold: The biosynthesis of A47934 from Streptomyces toyocaensis NRRL15009. Proc Natl Acad Sci U S A 2002; 99:8962-7. [PMID: 12060705 PMCID: PMC124406 DOI: 10.1073/pnas.102285099] [Citation(s) in RCA: 151] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/13/2002] [Indexed: 11/18/2022] Open
Abstract
The glycopeptide antibiotics vancomycin and teicoplanin are vital components of modern anti-infective chemotherapy exhibiting outstanding activity against Gram-positive pathogens including members of the genera Streptococcus, Staphylococcus, and Enterococcus. These antibiotics also provide fascinating examples of the chemical and associated biosynthetic complexity exploitable in the synthesis of natural products by actinomycetes group of bacteria. We report the sequencing and annotation of the biosynthetic gene cluster for the glycopeptide antibiotic from Streptomyces toyocaensis NRRL15009, the first complete sequence for a teicoplanin class glycopeptide. The cluster includes 34 ORFs encompassing 68 kb and includes all of the genes predicted to be required to synthesize and regulate its biosynthesis. The gene cluster also contains ORFs encoding enzymes responsible for glycopeptide resistance. This role was confirmed by insertional inactivation of the d-Ala-d-lactate ligase, vanAst, which resulted in the predicted -sensitive phenotype and impaired antibiotic biosynthesis. These results provide increased understanding of the biosynthesis of these complex natural products.
Collapse
Affiliation(s)
- Jeff Pootoolal
- Antimicrobial Research Centre, Department of Biochemistry, McMaster University, Hamilton, ON, Canada L8N 3Z5
| | | | | | | | | | | | | |
Collapse
|
20
|
Abstract
The iron-chelating catechol siderophore vibriobactin of the pathogenic Vibrio cholerae is assembled by a four-subunit, ten-domain nonribosomal peptide synthetase system, VibE, VibB, VibH, and VibF, using 2,3-dihydroxybenzoate and L-threonine as precursors to two (dihydroxyphenyl)methyloxazolinyl groups in amide linkage on a norspermidine scaffold. We have utilized site-specific and domain-deletion mutagenesis to map the heterocyclization and primary and secondary amine acylation activities of the six-domain (Cy1-Cy2-A-C1-PCP-C2) VibF subunit. We have found that Cy2 is capable of and limited to the condensation (amide bond formation) step of the three-step heterocyclization process, while Cy1 is capable of and limited to the final processing (cyclization/dehydration) steps to the completed heterocycle. Additionally, we have observed that the C2 domain functions in both N(9) (primary amine) acylation and N(5) (secondary amine) acylation of the (dihydroxybenzoyl)norspermidine substrate, leaving no catalytic role for the C1 domain, a conclusion confirmed with the formation of vibriobactin in a C1-deficient system. Thus VibF is an NRPS with two domains, Cy1 and Cy2, that perform a function otherwise performed by one and with one domain, C2, that performs a function otherwise performed by two. While C2 appeared to tolerate uncyclized threonine in place of the usual heterocycle in primary amine acylation, it refused this replacement in the corresponding donor substrate in secondary amine acylation.
Collapse
Affiliation(s)
- C Gary Marshall
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | |
Collapse
|
21
|
Walsh CT, Chen H, Keating TA, Hubbard BK, Losey HC, Luo L, Marshall CG, Miller DA, Patel HM. Tailoring enzymes that modify nonribosomal peptides during and after chain elongation on NRPS assembly lines. Curr Opin Chem Biol 2001; 5:525-34. [PMID: 11578925 DOI: 10.1016/s1367-5931(00)00235-0] [Citation(s) in RCA: 228] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nonribosomal peptide synthetases are large enzyme complexes that synthesize a variety of peptide natural products through a thiotemplated mechanism. Assembly of the peptides proceeds through amino acid loading, amide-bond formation and chain translocation, and finally thioester lysis to release the product. The final products are often heavily modified, however, through methylation, epimerization, hydroxylation, heterocyclization, oxidative cross-linking and attachment of sugars. These activities are the province of specialized enzymes (either embedded in the multidomain nonribosomal peptide synthetase structure or standalone).
Collapse
Affiliation(s)
- C T Walsh
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Marshall CG, Burkart MD, Keating TA, Walsh CT. Heterocycle formation in vibriobactin biosynthesis: alternative substrate utilization and identification of a condensed intermediate. Biochemistry 2001; 40:10655-63. [PMID: 11524010 DOI: 10.1021/bi010937s] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The iron-chelating peptide vibriobactin of the pathogenic Vibrio cholerae is assembled by a four-subunit nonribosomal peptide synthetase complex, VibE, VibB, VibH, and VibF, using 2,3-dihydroxybenzoate and L-threonine as precursors to two 2,3-dihydroxyphenyl- (DHP-) methyloxazolinyl groups in amide linkage on a norspermidine scaffold. We have tested the ability of the six-domain VibF subunit (Cy-Cy-A-C-PCP-C) to utilize various L-threonine analogues and found the beta-functionalized amino acids serine and cysteine can function as alternate substrates in aminoacyl-AMP formation (adenylation or A domain), aminoacyl-S-enzyme formation (A domain), acylation by 2,3-dihydrobenzoyl- (DHB-) S-VibB (heterocyclization or Cy domain), heterocyclization to DHP-oxazolinyl- and DHP-thiazolinyl-S-enzyme forms of VibF (Cy domain) as well as transfer to DHB-norspermidine at both N(5) and N(9) positions (condensation or C domain) to make the bis(oxazolinyl) and bis(thiazolinyl) analogues of vibriobactin. When L-threonyl-S-pantetheine or L-threonyl-S-(N-acetyl)cysteamine was used as a small-molecule thioester analogue of the threonyl-S-VibF acyl enzyme intermediate, the Cy domain(s) of a CyCyA fragment of VibF generated DHB-threonyl-thioester products of the condensation step but not the methyloxazolinyl thioesters of the heterocyclization step. This clean separation of condensation from cyclization validates a two-stage mechanism for threonyl, seryl, and cysteinyl heterocyclization domains in siderophore and antibiotic synthetases. Full heterocyclization activity could be restored by providing CyCyA with the substrate L-threonyl-S-peptidyl carrier protein (PCP)-C2, suggesting an important role for the protein scaffold component of the heterocyclization acceptor substrate. We also examined heterocyclization donor substrate specificity at the level of acyl group and protein scaffold and observed intolerance for substitution at either position.
Collapse
Affiliation(s)
- C G Marshall
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | |
Collapse
|
23
|
Keating TA, Ehmann DE, Kohli RM, Marshall CG, Trauger JW, Walsh CT. Chain termination steps in nonribosomal peptide synthetase assembly lines: directed acyl-S-enzyme breakdown in antibiotic and siderophore biosynthesis. Chembiochem 2001; 2:99-107. [PMID: 11828432 DOI: 10.1002/1439-7633(20010202)2:2<99::aid-cbic99>3.0.co;2-3] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- T A Keating
- Harvard Medical School, Department of Biological Chemistry and Molecular Pharmacology, 240 Longwood Avenue, Boston, MA 02115, USA
| | | | | | | | | | | |
Collapse
|
24
|
Keating TA, Ehmann DE, Kohli RM, Marshall CG, Trauger JW, Walsh CT. Chain termination steps in nonribosomal peptide synthetase assembly lines: directed acyl-S-enzyme breakdown in antibiotic and siderophore biosynthesis. Chembiochem 2001. [PMID: 11828432 DOI: 10.1002/1439-7633(20010202)2:23.0.co;2-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Affiliation(s)
- T A Keating
- Harvard Medical School, Department of Biological Chemistry and Molecular Pharmacology, 240 Longwood Avenue, Boston, MA 02115, USA
| | | | | | | | | | | |
Collapse
|
25
|
Keating TA, Ehmann DE, Kohli RM, Marshall CG, Trauger JW, Walsh CT. Cover Picture. Chembiochem 2001. [DOI: 10.1002/1439-7633(20010202)2:2<91::aid-cbic91>3.0.co;2-e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
26
|
Keating TA, Marshall CG, Walsh CT. Reconstitution and characterization of the Vibrio cholerae vibriobactin synthetase from VibB, VibE, VibF, and VibH. Biochemistry 2000; 39:15522-30. [PMID: 11112538 DOI: 10.1021/bi0016523] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Vibriobactin [N(1)-(2,3-dihydroxybenzoyl)-N(5),N(9)-bis[2-(2, 3-dihydroxyphenyl)-5-methyloxazolinyl-4-carboxamido]norspermidine] , is an iron chelator from the cholera-causing bacterium Vibrio cholerae. The six-domain, 270 kDa nonribosomal peptide synthetase (NRPS) VibF, a component of vibriobactin synthetase, has been heterologously expressed in Escherichia coli and purified. VibF has an unusual NRPS domain organization: cyclization-cyclization-adenylation-condensation-peptidyl carrier protein-condensation (Cy(1)-Cy(2)-A-C(1)-PCP-C(2)). VibF activates and covalently loads its PCP with L-threonine, and together with vibriobactin synthetase proteins VibE (adenylation) and VibB (aryl carrier protein) condenses and heterocyclizes 2, 3-dihydroxybenzoyl-VibB with L-Thr to 2-dihydroxyphenyl-5-methyloxazolinyl-4-carboxy-VibF in the first demonstration of oxazoline formation by an NRPS cyclization domain. This enzyme-bound aryl oxazoline can be transferred by VibF to various amine acceptors but most efficiently to N(1)-(2, 3-dihydroxybenzoyl)norspermidine (k(cat) = 122 min(-1), K(m) = 1.7 microM), the product of 2,3-dihydroxybenzoyl-VibB, norspermidine, and VibH. This diacylated product undergoes a second aryl oxazoline acylation on its remaining secondary amine, also catalyzed by VibF, to yield vibriobactin. Vibriobactin biosynthesis in vitro has thus been accomplished from four proteins, VibE, VibB, VibF, and VibH, with the substrates 2,3-dihydroxybenzoic acid, L-Thr, norspermidine, and ATP. Vibriobactin synthetase is an unusual NRPS in that all intermediates are not covalently tethered as PCP thioesters and in that it represents an NRPS pathway with two branch points.
Collapse
Affiliation(s)
- T A Keating
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | |
Collapse
|
27
|
Keating TA, Marshall CG, Walsh CT. Vibriobactin biosynthesis in Vibrio cholerae: VibH is an amide synthase homologous to nonribosomal peptide synthetase condensation domains. Biochemistry 2000; 39:15513-21. [PMID: 11112537 DOI: 10.1021/bi001651a] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Vibrio cholerae siderophore vibriobactin is biosynthesized from three molecules of 2,3-dihydroxybenzoate (DHB), two molecules of L-threonine, and one of norspermidine. Of the four genes positively implicated in vibriobactin biosynthesis, we have here expressed, purified, and assayed the products of three: vibE, vibB, and vibH. All three are homologous to nonribosomal peptide synthetase (NRPS) domains: VibE is a 2,3-dihydroxybenzoate-adenosyl monophosphate ligase, VibB is a bifunctional isochorismate lyase-aryl carrier protein (ArCP), and VibH is a novel amide synthase that represents a free-standing condensation (C) domain. VibE and VibB are homologous to EntE and EntB from Escherichia coli enterobactin synthetase; VibE activates DHB as the acyl adenylate and then transfers it to the free thiol of the phosphopantetheine arm of VibB's ArCP domain. VibH then condenses this DHB thioester (the donor) with the small molecule norspermidine (the acceptor), forming N(1)-(2, 3-dihydroxybenzoyl)norspermidine (DHB-NSPD) with a k(cat) of 600 min(-1) and a K(m) for acyl-VibB of 0.88 microM and for norspermidine of 1.5 mM. Exclusive monoacylation of a primary amine of norspermidine was observed. VibH also tolerates DHB-acylated EntB and 1,7-diaminoheptane, octylamine, and hexylamine as substrates, albeit at lowered catalytic efficiencies. DHB-NSPD possesses one of three acylations required for mature vibriobactin, and its formation confirms VibH's role in vibriobactin biosynthesis. VibH is a unique NRPS condensation domain that acts upon an upstream carrier-protein-bound donor and a downstream amine, turning over a soluble amide product, in contrast to an archetypal NRPS-embedded C domain that condenses two carrier protein thioesters.
Collapse
Affiliation(s)
- T A Keating
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | |
Collapse
|
28
|
Marshall CG, Zolli M, Wright GD. Molecular mechanism of VanHst, an alpha-ketoacid dehydrogenase required for glycopeptide antibiotic resistance from a glycopeptide producing organism. Biochemistry 1999; 38:8485-91. [PMID: 10387095 DOI: 10.1021/bi982843x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The vancomycin resistance enzyme VanH is an alpha-ketoacid dehydrogenase that stereospecifically reduces pyruvate to D-lactate, which is required for the synthesis of the depsipeptide D-alanine-D-lactate. This compound then forms an integral part of the bacterial cell wall replacing the vancomycin target dipeptide D-alanine-D-alanine, thus the presence of VanH is essential for glycopeptide resistance. In this work, the VanH homologue from the glycopeptide antibiotic producing organism Streptomyces toyocaensis NRRL 15009, VanHst, has been overexpressed in Escherichia coli and purified, and its substrate specificity and mechanism were probed by steady-state kinetic methods and site-directed mutagenesis. The enzyme is highly efficient at pyruvate reduction with kcat/Km = 1.3 x 10(5) M-1 s-1 and has a more restricted alpha-ketoacid substrate specificity than VanH from vancomycin resistant enterococci (VRE). Conversely, VanHst shows no preference between NADH and NADPH while VanH from VRE prefers NADPH. The kinetic mechanism for VanHst was determined using product and dead-end inhibitors to be ordered BiBi with NADH binding first followed by pyruvate and products leaving in the order D-lactate, NAD+. Site-directed mutagenesis indicated that Arg237 plays a role in pyruvate binding and catalysis and that His298 is a candidate for an active-site proton donor. Glu266, which has been suggested to modulate the pKa of the catalytic His in other D-lactate dehydrogenases, was found to fulfill a similar role in VanHst, lowering a pKa value of kcat/Km nearly 2 units. These results now provide the framework for additional structure and inhibitor design work on the VanH family of antibiotic resistance enzymes.
Collapse
Affiliation(s)
- C G Marshall
- Antimicrobial Research Centre, Department of Biochemistry, McMaster University, Hamilton, ON, Canada
| | | | | |
Collapse
|
29
|
Abstract
Vancomycin-resistant enterococci acquire high-level resistance to glycopeptide antibiotics through the synthesis of peptidoglycan terminating in D-alanyl-D-lactate. A key enzyme in this process is a D-alanyl-D-alanine ligase homologue, VanA or VanB, which preferentially catalyzes the synthesis of the depsipeptide D-alanyl-D-lactate. We report the overexpression, purification, and enzymatic characterization of DdlN, a VanA and VanB homologue encoded by a gene of the vancomycin-producing organism Amycolatopsis orientalis C329.2. Evaluation of kinetic parameters for the synthesis of peptides and depsipeptides revealed a close relationship between VanA and DdlN in that depsipeptide formation was kinetically preferred at physiologic pH; however, the DdlN enzyme demonstrated a narrower substrate specificity and commensurately increased affinity for D-lactate in the C-terminal position over VanA. The results of these functional experiments also reinforce the results of previous studies that demonstrated that glycopeptide resistance enzymes from glycopeptide-producing bacteria are potential sources of resistance enzymes in clinically relevant bacteria.
Collapse
Affiliation(s)
- C G Marshall
- Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada L8N 3Z5
| | | |
Collapse
|
30
|
Abstract
The mechanism of high-level resistance to vancomycin in enterococci consists of the synthesis of peptidoglycan terminating in D-alanyl-D-lactate instead of the usual D-alanyl-D-alanine. This alternate cell wall biosynthesis pathway is ensured by the collective actions of three enzymes: VanH, VanA, and VanX. The origin of this resistance mechanism is unknown. We have cloned three genes encoding homologs of VanH, VanA, and VanX from two organisms which produce glycopeptide antibiotics: the A47934 producer Streptomyces toyocaensis NRRL 15009 and the vancomycin producer Amycolatopsis orientalis C329.2. The predicted amino acid sequences are highly similar to those found in VRE: 54 to 61% identity for VanH, 59 to 63% identity for VanA, and 61 to 64% identity for VanX. Furthermore, the orientations of the genes, vanH, vanA, and vanX, are identical to the orientations found in vancomycin-resistant enterococci. Southern analysis of total DNA from other glycopeptide-producing organisms, A. orientalis 18098 (chloro-eremomycin producer), A. orientalis subsp. lurida (ristocetin producer), and Amycolatopsis coloradensis subsp. labeda (teicoplanin and avoparcin producer), with a probe derived from the vanH, vanA, and vanX cluster from A. orientalis C329.2 revealed cross-hybridizing DNA in all strains. In addition, the vanH, vanA, vanX cluster was amplified from all glycopeptide-producing organisms by PCR with degenerate primers complementary to conserved regions in VanH and VanX. Thus, this gene sequence is common to all glycopeptide producers tested. These results suggest that glycopeptide-producing organisms may have been the source of resistance genes in vancomycin-resistant enterococci.
Collapse
Affiliation(s)
- C G Marshall
- Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada L8N 3Z5
| | | | | | | |
Collapse
|
31
|
Marshall CG, Wright GD. The glycopeptide antibiotic producer Streptomyces toyocaensis NRRL 15009 has both D-alanyl-D-alanine and D-alanyl-D-lactate ligases. FEMS Microbiol Lett 1997; 157:295-9. [PMID: 9435111 DOI: 10.1111/j.1574-6968.1997.tb12788.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
High level resistance to vancomycin and other glycopeptide antibiotics requires the synthesis of peptidoglycan terminating in the depsipeptide D-Ala-D-lactate, rather the usual D-Ala-D-Ala. We report the purification and enzymatic characterization of two D-Ala ligases from Streptomyces toyocaensis NRRL 15009 which produces the glycopeptide antibiotic A47934. One of these enzymes catalyzes only D-Ala-D-Ala peptide formation and is recovered from mid-exponential phase cell cultures. The other enzyme is a D-Ala-D-lactate ligase which can be detected in actively antibiotic producing stationary phase cultures or mid-exponential phase cultures grown in the presence of A47934. These results imply that peptidoglycan components of S. toyocaensis NRRL 15009 change upon induction of antibiotic production and predict the existence of a VanX-like D-Ala-D-Ala DD-dipeptidase activity.
Collapse
Affiliation(s)
- C G Marshall
- Department of Biochemistry, McMaster University, Hamilton, Ont., Canada
| | | |
Collapse
|
32
|
Marshall CG, Broadhead G, Leskiw BK, Wright GD. D-Ala-D-Ala ligases from glycopeptide antibiotic-producing organisms are highly homologous to the enterococcal vancomycin-resistance ligases VanA and VanB. Proc Natl Acad Sci U S A 1997; 94:6480-3. [PMID: 9177243 PMCID: PMC21075 DOI: 10.1073/pnas.94.12.6480] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The crisis in antibiotic resistance has resulted in an increasing fear of the emergence of untreatable organisms. Resistance to the glycopeptide antibiotic vancomycin in the enterococci, and the spread of these pathogens throughout the environment, has shown that this scenario is a matter of fact rather than fiction. The basis for vancomycin resistance is the manufacture of the depsipeptide D-Ala-D-lactate, which is incorporated into the peptidoglycan cell wall in place of the vancomycin target D-Ala-D-Ala. Pivotal to the resistance mechanism is the production of a D-Ala-D-Ala ligase capable of ester formation. Two highly efficient depsipeptide ligases have been cloned from vancomycin-resistant enterococci: VanA and VanB. These ligases show high amino acid sequence similarity to each other ( approximately 75%), but less so to other D-Ala-D-X ligases (<30%). We have cloned ddls from two glycopeptide-producing organisms, the vancomycin producer Amycolatopsis orientalis and the A47934 producer Streptomyces toyocaensis. These ligases show strong predicted amino acid homology to VanA and VanB (>60%) but not to other D-Ala-D-X ligases (<35%). The D-Ala-D-Ala ligase from S. toyocaensis shows D-Ala-D-lactate synthase activity in cell-free extracts of S. lividans transformed with the ddl gene and confirms the predicted enzymatic activity. These results imply a close evolutionary relationship between resistance mechanisms in the clinics and in drug-producing bacteria.
Collapse
Affiliation(s)
- C G Marshall
- Department of Biochemistry, McMaster University, 1200 Main Street West, Hamilton, ON, Canada, L8N 3Z5
| | | | | | | |
Collapse
|
33
|
Abstract
1. Single-ion-channel recording has been used to estimate the equilibrium concentration-response relationship for several acetylcholine analogues. The response, corrected for desensitization, was taken as the probability of a channel being open during clusters of openings that were separated by desensitized periods. 2. All agonists were able to block the channels which they themselves opened. Carbachol, suberyldicholine and the sulphonium analogue of acetylcholine were all found to be efficacious agonists in the sense that the results indicate that all of them, in sufficiently high concentration, would be able to open 90% or more of channels if it were not for channel block. 3. In the case of suberyldicholine the results are much as predicted by the interpretation of the fine structure of channel openings at low agonist concentrations. 4. The maximum probability of opening that could be obtained with decamethonium and with phenyltrimethylammonium was low (below 4%), and it was not possible to distinguish whether this was wholly a result of the powerful (relative to activation potency) channel-blocking action of these agonists, or whether it was to some extent attributable to their being genuine partial agonists. 5. The results suggest that, for a range of agonists, differences in equilibrium potency are usually more strongly influenced by affinity for binding to the resting state of the receptor than by ability to activate the receptor once bound, though in the case of suxamethonium (relative to acetylcholine) the contributions of each factor are similar.
Collapse
Affiliation(s)
- C G Marshall
- Department of Pharmacology, University College London
| | | | | |
Collapse
|
34
|
Marshall CG, Ogden DC, Colquhoun D. The actions of suxamethonium (succinyldicholine) as an agonist and channel blocker at the nicotinic receptor of frog muscle. J Physiol 1990; 428:155-74. [PMID: 2133043 PMCID: PMC1181640 DOI: 10.1113/jphysiol.1990.sp018205] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
1. Patch clamp methods were used to study the equilibrium and kinetic properties of the acetylcholine analogue, succinyldicholine (suxamethonium), which is used clinically as a neuromuscular blocking agent. 2. The equilibrium concentration-response curve, corrected for desensitization was estimated by measuring as the response the probability of being open of single ion channels during clusters of activity that occur between long desensitized periods. Suxamethonium (Sux) was about 7.6-fold less potent than acetylcholine (ACh) (at low concentrations), partly because of 2.9-fold lower affinity for the resting receptor, and partly because of a lower ability to activate the receptor once bound. 3. Sux was a more potent blocker of the open ion channel than ACh (equilibrium constant about 200 microM); this limited the maximum open probability to about 0.36 (at 12 degrees C and -120 mV). Individual channel blockages lasted about 65 microseconds on average. They appeared to get longer at high agonist concentration; however, a simulation method was used to show that this effect could be accounted for by the fact that at higher concentrations there are more openings that are too brief to be detected. Over the concentration range tested the effects were described by a simple open channel block mechanism. 4. No component of brief shut times could be detected other than those resulting from channel blockages. However, the results suggest that multiple channel openings (the nachschlag phenomenon) should be rare, so this is not inconsistent with previous results with other agonists. 5. Sux differed from ACh and carbachol in that it had a somewhat lower efficacy and a greater channel blocking action. However, in clinical practice channel block is unlikely to contribute to neuromuscular block to any significant extent; the main mechanism of paralysis, at least in the early stages, is probably a result of prolonged depolarization of the region of membrane surrounding the motor endplate leading to inactivation of the sodium channels therein.
Collapse
Affiliation(s)
- C G Marshall
- Department of Pharmacology, University College London
| | | | | |
Collapse
|
35
|
Affiliation(s)
- D Colquhoun
- MRC Receptor Mechanisms Group, Department of Pharmacology, University College London, U.K
| | | | | | | | | |
Collapse
|
36
|
Abstract
1. Voltage-activated currents have been recorded from cerebellar granule neurones in explant cultures from young rats (1-9 days old). Cells were examined with whole-cell patch-clamp methods. Depolarizing pulses from a pre-pulse potential of -100 mV evoked a rapidly activated transient inward current, and an outward current which decayed in two phases. The ionic dependence, kinetics and pharmacological properties of these currents have been studied. 2. Peak inward Na+ currents in cells from 7-day-old rats were in the range 350-450 pA. No evidence was found for the presence of calcium currents. Thus, inward current was unchanged in zero Ca2+, 1 mM-EGTA solution. No inward current was obtained in medium containing 10 mM-Ba2+ and tetrodotoxin (TTX). Supplementing the pipette (i.e. intracellular) solution with Mg-ATP did not reveal any Ca2+ current. 3. Depolarizing steps (from -100 mV) in TTX-containing solution gave an early transient outward current and a late outward current. The transient current resembled IA described in other cells, and reversed close to EK in both normal and elevated potassium concentrations, indicating that K+ is the predominant charge carrier. Depolarizing steps from -50 mV failed to give a transient outward current, and gave only a slowly rising current which resembled the late potassium current, IK. 4. Inactivation of the transient current was examined by applying test depolarizations from increasingly negative pre-pulse potentials (-50 to -120 mV): half-inactivation occurred at -72 mV. Transient outward currents decayed exponentially with time constants, tau, of 7.3-25.3 ms at 0 mV. The time course of removal of inactivation in cells held at -50 mV, and given increasingly long pre-pulses to -100 mV, was exponential with tau = 35 ms. 5. Both transient and late outward currents were reversibly abolished by addition to the bathing medium of 10 mM-Ba2+ or 1 mM-quinine. Outward K+ current was not dependent on external calcium. Tetraethylammonium (20 mM) selectively reduced the late outward current; the peak transient current was reduced by less than 20%. 4-Aminopyridine (2 mM) showed little selectivity between transient and late outward currents. 6. It is concluded that cerebellar granule cells from young rats possess voltage-activated inward Na+ current as well as two types of K+ current, IA and IK. In terms of neuronal functioning, the properties of the transient outward current may confer a role in regulating excitability and in repolarization, but a definitive statement will require knowledge of the cellular location and relative densities of channels in granule cells in vivo.
Collapse
|
37
|
Abstract
Thousands of salivary cells fill the interstices throughout the anterior ends of jawed leeches. The somata are large (30–200 micron in diameter). They project single processes (ductules) into the three jaws, and were found to fire overshooting action potentials of 50–85 mV amplitude and 100–200 ms duration at low spontaneous rates. The action potentials were not detected in the presence of cobalt (10 mmol l-1), but could be recorded when sodium was absent from the Ringer, so they appear to be calcium-dependent. Salivary material is transported by the long processes of these unicellular glands and secreted into ducts which alternate with paired teeth on the jaws. Secretion is activated reliably by 10(−6) mol l-1 serotonin, but not by other neurotransmitters found in the leech nervous system. Each jaw secretes at an average rate of 230 nl min-1 in the presence of serotonin, and secretion is completely abolished by cobalt. Perfusion with serotonin excites the salivary gland cells into impulse activity, and often evokes bursting. Impulse activity of the peripherally projecting, serotonergic Retzius cells evokes both depolarizations and action potentials in the salivary gland cells. In jawed leeches, central neurones appear to control salivation by a peripheral release of serotonin. This neurotransmitter evokes calcium-dependent action potentials and calcium, in turn, stimulates secretion.
Collapse
Affiliation(s)
- C G Marshall
- Department of Pharmacology, University College London, UK
| | | |
Collapse
|
38
|
Abstract
Two pairs of discrete salivary glands are located at the base of the muscular proboscis of the sanguivorous Glossiphoniid leeches Haementeria ghilianii and Haementeria officinalis. Each anterior gland is 0.8 cm to 2 cm in length, and comprises over 200 giant salivary cell bodies ranging from 150 microns to over 1000 microns in diameter, depending on the size of the animal. The salivary cells are neither electrically nor dye coupled, and there is no acinar structure or common duct, but instead each cell extends an individual ductule. The cells fire action potentials of 100–200 ms duration and 70–100 mV amplitude in response to depolarizing pulses, or at the cessation of a hyperpolarizing pulse. The impulse is abolished by procedures known to antagonize calcium currents, and persists in sodium-free solution, or when calcium is replaced with strontium or barium. Our results support the hypothesis of a purely calcium-dependent impulse.
Collapse
|