ADME studies with radiolabeled compounds. Biomedical Applications of Radioisotopes and Pharmacokinetics Unit

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1 ADME studies with radiolabeled compounds Miguel Ángel Morcillo Alonso Biomedical Applications of Radioisotopes and Pharmacokinetics Unit

2 CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas)

3 Biomedical Applications of Radioisotopes and Pharmacokinetics Unit 1. Production of radioisotopes for biomedicine: generators (68Ge/68Ga) and minicyclotron (future). 2. Radiolabelling compounds: labelling of small molecules, polymers, peptides, proteins and oligonuleotides with radioisotopes. Radionucleidic and radiochemical purity analysis. 3. In vitro studies: cell-based radioligand receptor-binding assays, cell proliferation assays and labelling and cell tracking. 4. Small animal molecular imaging: positron emission tomography (PET), computed tomography (CT) and quantitative whole-body autoradiography (QWBA). 5. In vivo ADME studies with radiolabelled compounds in experimental animals: bioavailability, mass-balance studies, quantitative tissue distribution studies (QWBA and traditional methods) and metabolic profiling (by HPLC and on-line radiometric detector) 6. Pharmacokinetic data analysis by standard software packages

4 Biomedical Applications of Radioisotopes and Pharmacokinetics Unit Radioactive Installation IR-08 Radiochemistry Laboratory: Hot cells, fume hoods, dose calibrator, HPLC with diode array and radioactivity detector, TLC, etc. Pharmacokinetic and Molecular Imaging Laboratory: Metabolic cages System, cryomicrotome, micropet/ct, dose calibrator, etc. Cell Culture Laboratory: Centrifuges, incubator, optic microscope, laminar flow cabinet Other facilities and equipment: Experimental Animal Facility, liquid/solid scintillation counter, gamma spectrometer, radioluminography system, etc.

ADME studies with radiolabeled compounds Drug Radiolabeling Radiolabeled drug Mass balance studies Asess organ distribution Identify the excretory pathways of a drug Asess extent and kinetics of

5 ADME studies with radiolabeled compounds Drug Radiolabeling Radiolabeled drug Mass balance studies Asess organ distribution Identify the excretory pathways of a drug Asess extent and kinetics of excretion Asess extent and kinetics of metabolism Elucidate the metabolic fate of a drug Asess extent of absorption and bioavailability Regulatory Compliance: GLPS are not neccesaries; however, SOPs should be followed European Guidelines for the Care and Use of Laboratory Animals

6 Radiolabeling Radiosynthesis provides a radiolabeled drug that is used to investigate the pharmacokinetics of a new compound in preclinical studies Important parameters in designing the ADME studies: The choice of the radioisotope The position of the radiolabel in the drug compound (it needs to be metabolically stable). The radiochemical purity and the specific activity Radioisotope Type of decay 14 C, 3 H, 131 I, 35 S ß - 125/131 I, 99m Tc, 111 In γ 68 Ga/ 18 F/ 11 C positron

7 Study designs Animal subjects: Rodents: rats or mice The specie, strain and source of animals should match those used in the toxicological studies Dosing regimen/route depends on the drug program 3-5 animals/time point and at least four time points Sample collection and analysis: Schedule: sampling should be adequately planned in order to estimate pharmacokinetic parameters Samples: Whole-body. Radioactivity detection: Autoradiography (ß - /γ/positron) PET (positron) Blood, plasma, urine, feces and organs. Radioactivity determination: Liquid scintillation counting: ß - Solid scintillation counting: positron/γ

8 1. Radiochemical purity of the radiolabeled drug HPLC with radioactivity and photodiode array/fluorescence detection Actividad (mv) Tiempo (min) UV ß

9 2. Organ distribution A) Radioactivity measurement in tissues/organs B) Quantitative whole-body autoradiography (QWBA)

10 B) Quantitative whole-body autoradiography (QWBA)

11 B) Quantitative whole-body autoradiography (QWBA) 14 C- Pipotiazine, 1 h post-iv

12 B) Quantitative whole-body autoradiography (QWBA) 14 C- Espiramicine, 24 h post-iv

13 2. Organ distribution C) PET/CT

14 B16V5 mouse

15 3. Asess extent and kinetics of excretion Radioactivity measurement in urine/feces

16 4. Metabolite profiling Samples are anayzed by HPLC

17 5. Asess extent of absorption and bioavailability Radioactivity measurement in plasma after IV/OR administration

18 Example IV administration: Group animals per time point Samples: urine and feces and QWBA (0,5 h;1h; 4h; 1d; 4d) Objectives: Organ distribution Asessment of extent and kinetics of metabolite and unchanged drug excretion Group 2 15 animals (3 animals/time point; at least 5 times) Samples: organs and blood/plasma Objectives: Organ distribution Metabolic profiling Plasma pharmacokinetics OR administration: only if asessment of absorption is necessary

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