Early Whole Body PK: Anticipate Exposure and Toxicity at Lead Selection Stage

Introduction:

ImaBiotech offers an innovative early in-vivo ADME platform for identifying early pharmacokinetic profile in plasma and all organs simultaneously on rodent species. Purpose is to significantly accelerate optimiza-tion of lead molecules and selection of drug candidates. Indeed when lead candidates have been selected from a wide number of potentials hit-to-leads, it is crucial to evaluate the kinetic of absorption, distribution, metabolism, and excretion in a whole animal (usually rodents)1. It is key to understand the overall distribution of compounds, to localize drug and metabolites in targeted tissue(s) or untargeted tissue(s). With our line of services, Early Whole Body PK, we can contribute to antici-pating efficacy or potential adverse effects by looking simultaneously at the tissue distribution of drugs and metabolites. ImaBiotech offers a unique combination of two bioanalytical techniques, QMSI and LC-MS/MS, to localize and quantify drugs in all organs and plasmawithout any labelling. Our IT team has developed Multimaging software to automatically calculate all PK parameters of interest directly from the generated raw dataset.

Combination of Four Technological Platforms in One Study:

ImaBiotech offers one comprehensive vivo study design for assessing Early Whole Body PK:

• Animal model: rodent
• Number of time-points: 6
• Number of animal per time-point: 1
• Dose: One dose. A cassette dosing can perfectly be set up if several candidates need to be evaluated.
• Route of administration: oral (PO) and/or intra- venous (IV)
• Sampling: plasma samples and whole carcasses

Four technical platforms are combined to achieve the final goal:

• Histology – Microscopy: frozen whole bodies are sectioned longitudinally in two section plans in order to investigate all organs of interest. Additio- nally, optical images of sections are generated to visualize all organs.
• Bioanalysis – QMSI (Quantitative Mass Spectrometry Imaging): whole body sections are analyzed by MALDI imaging to determine biodistribution and concentration of drug and related metabolites.
• Bioanalysis – LC-MS/MS (liquid chromatogra- phy Mass Spectrometry): this platform is used to calculate drug concentration in plasma.
• IT – Multimaging software: ImaBiotech has developed his own software to manage all raw data generated by the three above-mentioned PK parameters are automatically calculated accor- ding to the combination of the bioanalytical results.

ImaBiotech is today the expert in QMSI 2–6. This technology offers several advantages compared to classical approaches (no labelling, histological integrity, quantitative, drug and metabolites differentiation).

Case study illustration:

In order to investigate in situ metabolism and disposition of a CNS drug candidate, C57Bl/6 mice were orally dosed with 25 mg/kg of drug. Plasma samples and whole-body carcasses were collected at different time points and analyzed by LC-MS/MS and QMSI respec- tively. Images obtained for both drug and metabolites are displayed in Figure 1 and show a wide distribution of the active compound, including in the brain, demonstra- ting target exposure, while main metabolite does not seem to cross the blood-brain barrier. In the latest time point, biodistribution of active compound and metabo- lites suggests renal clearance. Technical note: whole bodies can be gently curved during the snap freezing procedure in order to respect the max length of sample analyzed in the mass spectrometer. This sample preparation impacts neither organs annotation nor molecular distribution.

In situ quantitation of molecules by QMSI allows to construct concentration-time profiles at organ level (Figure 2) to go beyond the classical plasma-based pharmacokinetic approach. Multiple PK parameters can be derived from these data such as Cmax, Tmax, AUCt, AUCinf, Kp, Kel, t1/2, clearance and volume of distribution (Table 1).

This early whole-body PK study showed at an early development stage that the drug investigated presents a wide and fast distribution in mouse after oral administra- tion. Biodistribution data revealed that the brain is exposed to the drug but not to the main metabolite. In addition to the tissue analysis, the complete plasma PK profile has been characterized on the same experimental design, providing valuable complementary data.

By combining IV and PO routes bioavailability can be measured and early mass balance information can be obtained by identifying routes of excretion (renal clearance, gastric or biliary secretion) directly from the MS image.

QMSI also opens up possibility to determine partition coefficients (Kp) for both drug and metabolite(s). It has a great interest to feed, refine and finally increase the accuracy of both pharmacokinetics/pharmacodynamics (PK/PD) and physiologically-based pharmacokinetics (PBPK) models which are increasingly used in drug development for in vivo study design and eventually active dose selection for the patient.

Conclusion:

Early Whole Body PK is an easy way to obtain Bioavailability and Biodistribution information at an early stage to minimize attrition rate of drugs. Indeed it is thus possible to anticipate in situ efficacy or potential adverse effect by looking simultaneously at tissue distribution of Drugs and metabolites.

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