Novel Inhibitors for PRMT1 Discovered by High-Throughput Screening Using Activity-Based Fluorescence Polarization

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1 Novel Inhibitors for PRMT1 Discovered by High-Throughput Screening Using Activity-Based Fluorescence Polarization Myles B. C. Dillon, Daniel A. Bachovchin, Steven J. Brown, M. G. Finn, Hugh Rosen, Benjamin F. Cravatt and Kerri A. Mowen ACS Chem. Biol. 2012, DOI: /cb300024c 2012/05/28 Organic Seminar Bioorganic Chemistry Laboratory Megumi Iseki 1

2 This work PRMT Protein arginine (R) methyltransferase PRMTs catalyze the posttranslational methylation of arginine. PRMT1 Responsible for over 85% of the arginine methylation Involved in Transcription Chromatin modification Signal transduction Research and therapeutic value Known inhibitors for PRMT1 lack specificity across PRMT family. High-throughput screening assay was developed and two novel selective inhibitors for PRMT1 were identified. Fackelmayer, F. O. et. al. J. Cell Sci., 2009, 122,

3 Fluorescence polarization-activity based protein profiling assay Competitive activity-based protein profiling Powerful platform to identify inhibitors of enzymes Probe Probe Enzyme Fluorescent moiety Enzyme Inhibitor Enzyme Fluorescence polarization Fast rotation Probe Saghatelian, A. et.al. J. Am. Chem. Soc., 2011, 133, Dispersion of polarization Low polarization Polarized light Slow rotation Probe High polarization Enzyme Cravatt, B. F. et. al. Nat. Biotechnol., 2009, 27,

4 Methylation reaction catalyzed by PRMT1 Methyl donor: S-adenosylmethionine (SAM) Methylation reaction turns SAM into SAH (S-adenosylhomocysteine). PRMT1 is classified as type I PRMTs which catalyze assymmetric dimethylarginine. SAM SAH SAM SAH Gehring, H. et. al. Biochim. Biophys. Acta, 2006, 1764,

5 Covalent labeling of Cys101 PRMT1 contains a hyper-reactive cysteine (Cys101, C101). The homologous cysteine is absent in all other PRMTs except PRMT8. An activity-based probe that specifically labels Cys101 could provide a basis to monitor active PRMT1 protein. PRMT1 Cys101 AF488 maleimid e Wild-type Mutant without Cys101 SDS-PAGE Fluorescently labeled protein All protein Novel Fluorescent probe: Maleimide-Alexa Fluor (AF) 488 PRMT1 Cravatt, B. F. et.al. Nature, 2010, 468, 790 Wild-type PRMT1 showed stronger signal of labeling. Even the mutant without Cys101 showed reactivity with the probe. 5

6 Optimization of the Protein concentration by fluorescence polarization assay PRMT1 1.3 M PRMT1 4 M PRMT1 0.4 M PRMT1-C101A 1.3 M PRMT1-C101A 4 M PRMT1-C101A 0.4 M Maleimide-AF488 (probe) With 0.4 M conditions, the fluorescent signal was reduced to similar levels as detected by probe alone. 0.4 M is suitable for the screening. 6

7 Screening of compound library using PRMT1 fluorescence polarization assay Maybridge Hitfinder Collection: Compound library which consists of 16,000 compounds 100% inhibition: PRMT1-C101A Compounds screened 0% inhibition: DMSO treated 789 compounds (4.9 %): greater than 50% inhibition The result was compared to a counter screen using different proteins containing active-cysteine. This counter-screen identified false positives, cross-reactive compounds, and/or thiol-reactive compounds, which were discarded from further analysis. 98 compounds (0.6% of total) remained. The top 19 inhibitors with greater than 50% inhibition were selected. 7

8 Further selection using in vitro methylation assay A radiolabeled SAM substrate was used to methylate an arginine residue of Histone4. Inhibited PRMT1 cannot catalyze the methylation, and observation of faint or no bands indicates poor radiolabling of Histone4. Conc. of inhibitors are 100 M Four of the top compounds Negative control DMSO: Negative control, AMI-1, AMI-408: known small molecule inhibitor Bedford, M. T. et.al. J. Biol. Chem., 2004, 279,

9 Four of the top compounds Dose-response study The two strongest inhibitor IC 50 ( M) Negative control Nitroalkene and other electrophilic groups are likely to form a covalent bond with sulfhydryl group of the Cys101. 9

10 Dose-dependent study of the two members of Type I PRMTs Type I PRMTs cysteine residue close to active site Inhibitory activity PRMT8 CARM1 Two novel inhibitors specific for PRMT1 and PRMT8 over other SAM-dependent methyltransferase were obtained. 10

11 Conclusion A high-throughput fluorescence polarization assay has been developed to screen for novel PRMT1 inhibitors. Two novel inhibitors specific for PRMT1 and PRMT8 over other SAM-dependent methyltransferase were obtained. 11