Tag lite: assessment of compound dissociation from GPCRs. Israel Ramos Villullas Group leader of GPCRs and Ion Channels unit BRADS Department

Transcription

1 Tag lite: assessment of compound dissociation from GPCRs Israel Ramos Villullas Group leader of GPCRs and Ion Channels unit BRADS Department 1

2 INTRODUCTION Compound residence time at protein targets is an important parameter in the Drug Discovery process: Efficacy Selectivity Side effects associated to different aspects as epitope formation or target associated toxicity. To assess residence time, different indirect methods have been developed using radioactive binding assays that combine the use of a radioligand excess with a dilution or separation step after the compound is bound to the target. These methods have several drawbacks such as the use of radioactivity, difficult results interpretation, assay price and assay logistics that justify a switch to alternative technologies. Label free methods as SPR are also used to assess dissociation but they need: Access to very expensive instrumentation They are difficult for GPCRs because they need GPCR immobilization.

3 OBJECTIVE To develop a dissociation assay : Non radioactive Simple Cost effective With a reasonable throughput that does not require specialized equipment The technology evaluated has been the new fluorescence-based Tag-lite technology, from Cisbio Bioassays A dissociation assay for human M 3 receptor has been developed. Results and assay advantages and disadvantages over the current methods, will be presented.

4 Radiolabeled dissociation assay Membranes + Antagonists (5-20Ki) Between 2 and 3 hours Dilute well content + addition of radioligand excess Dissociation starts The antagonist s dissociation from receptors is estimated indirectly by measuring the radioligand association to the receptor binding sites, as they become available, after compound dissociation Take samples at different times

5 Radiolabeled dissociation assays ( drawbacks) Radioactive and heterogeneous Membranes Each data point needs a filtration plate: Cost: Each plate costs 20 Assay logistics Assay price: 58.4 / compound (10 data points in duplicate) 2.9 / data point

6 Radiolabeled dissociation assays ( drawbacks) Dissociation is initiated by a dilution step combined with an excess of radioligand. Preincubation Preincubation < 5 Ki Preincubation 5 20 Ki Preincubation >20 Ki Dissociation < 0.5 Ki 0.5 ki 2 ki > 2 Ki We use internal controls to validate results If we run the assay at one compound concentration, 30% of the compounds assayed fail. We always assay compounds at 2 concentrations and in some cases at three.

7 Ideal dissociation assays Preincubation: High compound concentration > 20 Ki to ensure receptor occupancy > 90 % in a relatively short time. No controls. The compound concentration is high so approximately 100% occupancy is ensured Dissociation: General aspects: Non radioactive, Physiological environment (cells), microplate compatible, cheap Homogeneous Obtain all time points from the same well Initiate dissociation by complete compound removal from the well. No controls. The compound concentration is too low to interfere in the dissociation phase. Easy results interpretation.

8 Tag-Lite: a new way to do dissociation assays PREINCUBATION Adhere cells to the plate Add compounds after adhesion Use 100 Ki. Cells are adhered so Compound can be removed afterwards using a washer!!!!

9 Tag-Lite: a new way to do dissociation assays DISSOCIATION Assess dissociation meassuring changes in FRET in the same well

10 Tag-Lite: a new way to do dissociation assays Assay development steps Can we obtain several time points from the same wells? Red ligand characterization Red Ligand saturation assays: Kd Choose red ligand concentration for dissociation assay: Red Ligand occupancy >80% Kinetics: Determine Kon and check the association rate of the chosen red-ligand concentration. There is a need to quickly reveal the binding sites as soon as they become available Antagonist potency: To determine compound concentration in the preincubation step Can we wash the cells?

11 Red ligand characterization Kd and Kobs Saturation studies were ran in two different modes: Incubating the plate at RT on the bench Reading assay plate in kinetic mode in the Envision from Perkin Elmer: 25 readings during 5 hours To answer different questions: Which is the Red-Ligand Kd? Is it possible to read the same well several times without affecting the Red Ligand potency? Which is the ideal Red Ligand concentration to run dissociation assays?

12 Red ligand characterization Kd and Kobs Red Ligand saturation assay. 3 hours RT incubation. Plate on the bench Technician Kd: 202 ± 47 (n=3) Red Ligand saturation and association assay. Kinetic read Technician Kd: 199 ± 5 (n=2) Technician Kd: 102 nm (n=2) CISBIO Kd: 70 nm Time (Minutes)

13 Can we take several readings from the same well? Red ligand potency does not change when the same wells are read several times: Plate incubated 3 hours on the bench and read one time on the Envision. Kd: 202 nm Plate incubated in the Envision and read it in kinetic mode. Kd: 199 nm. Total binding is stable more than 15 hours: Ratio Time (hours)

14 Red ligand characterization Red ligand concentration for dissociation assays Assay window: 1.3 Assay window: 2.2; Kobs: 0.14 min -1 Assay window: 2.2 ; Kobs: 0.07 min - Time (Minutes)

15 Antagonists characterization Potency % Inhibition Tiotropium Ipratropium Glycopirrolate Log [Compound] (M) Compound Ki nm 10 x Ki nm 100 Ki nm 1000 Ki nm Ipratropium Glycopyrrolate Tiotropium

16 Antagonists characterization Dissociation Compound concentration during pre-incubation step can be used at more than 10 Ki ensuring receptor occupancy.

17 Antagonists characterization Dissociation Dissociation profiles for the antagonists tested are in good agreement with those obtained internally using the radioactive method. Compound Radioactive assay Tag lite assay Ipratropium t ½ : 0.2 h t ½ : 0.2 h Glycopyrrolate t ½ : 2.6 h t ½ : 2 h Tiotropium t ½ : 16 h t ½ : 17 h

18 Cellullar non radioactive assay. Tag lite dissociation assay Advantages Allows easy assay design and results interpretation Assay logistics is simple From one 384 plate, using two columns for controls (Total Binding and NSB), 352 compounds can be assayed in kinetic mode. 20 time points / cmpd data points / 352 cpds Considering plate, buffer, cells (10 K/well) and Red Ligand (800 nm final concentration) list price: 10 / compound. 0.5 / time point compared with 2.9 from radioactive assay.

19 Tag lite dissociation Disadvantages Assay window is low at high Red-Ligand concentrations. Red-Ligand associates slowly to M 3 receptor.

20 Eventhough preliminar data looks encouraging, cell handling must be improved: Cell recovery is not 100% Adhesion protocol need to be improved for HEK cells (Some cells are lost after washing): Consider plate coating Optimization of adhesion time. Tag lite dissociation Pending

21 This work has been done by Joaquim Botta Nodar

22 Questions? Thanks for your attention!!!