Combined approach for high-throughput preparation and analysis of plasma samples from exposure studies

Rapid Bioavailability and Disposition protocol: A novel higher throughput approach to assess pharmacokinetics and steady-state brain distribution with reduced animal usage

Besides routine pharmacokinetic (PK) parameters, unbound brain-to-blood concentration ratio (K_p,uu) is an index particularly crucial in drug discovery for central nervous system (CNS) indications. Despite advantages of K_p,uu from steady state after constant intravenous (i.v.) infusion compared with one- or multiple time points after transient dosing, it is seldom obtained for compound optimization in early phase of CNS drug discovery due to requirement of prerequisite PK data to inform the study design. Here, we designed a novel rat in vivo PK protocol, dubbed as Rapid Bioavailability and Disposition (RBD), which combined oral (p.o.) dosing and i.v. infusion to obtain steady-state brain penetration, along with blood clearance, oral exposure and oral bioavailability for each discovery compound, within a 24 hour in-life experiment and only a few (e.g., 3) animals. Protocol validity was verified through simulations with a range of PK parameters in compartmental models as well as data comparison for nine compounds with distinct PK profiles. PK parameters (K_p,brain, CL_b and oral AUC) measured from the RBD protocol for all compounds, were within two-fold and/or statistically similar to those derived from conventional i.v./p.o. crossover PK studies. Our data clearly indicates that the RBD protocol offers reliable and reproducible data over a wide range of PK properties, with reduced turnaround time and animal usage.

Substituted 7-amino-5-thio-thiazolo[4,5-d]pyrimidines as potent and selective antagonists of the fractalkine receptor (CX3CR1)

We have developed two parallel series, A and B, of CX3CR1 antagonists for the treatment of multiple sclerosis. By modifying the substituents on the 7-amino-5-thio-thiazolo[4,5-d]pyrimidine core structure, we were able to achieve compounds with high selectivity for CX3CR1 over the closely related CXCR2 receptor. The structure-activity relationships showed that a leucinol moiety attached to the core-structure in the 7-position together with α-methyl branched benzyl derivatives in the 5-position displayed promising affinity, and selectivity as well as physicochemical properties, as exemplified by compounds 18a and 24h. We show the preparation of the first potent and selective orally available CX3CR1 antagonists.

The volume of distribution is an indicator of poor in vitro-in vivo extrapolation of clearance for acidic drugs in the rat

Abstract 1. We applied the regression offset approach to predict rat in vivo intrinsic clearance (CLint) for 54 new chemical acid entities with high plasma protein binding values and low renal clearance (CL). The prediction success was correlated to volume of distribution (Vd), molecular weight (Mw) and CL. 2. A correlation between poor in vitro-in vivo extrapolation (IVIVE) and Vd values distinct from the Vd of albumin (0.1-0.2 L/kg) was revealed. For compounds with a Vd value above 0.5 L/kg, 0% of the predictions of in vivo CLint was within twofold of the observed value, compared to 69% for compounds with a Vd value below 0.5 L/kg. 3.  Compounds with a Mw below 450 g/mol demonstrated more accurate in vivo CLint predictions than compounds with a Mw above 450 g/mol, i.e. 63% compared to 21% within twofold. For compounds with in vivo CL below 30% of the liver blood flow (LBF), 53% of the predictions was within twofold of the observed value, compared to 0% for compounds with CL above 30% of the LBF. 4. We show that accurate IVIVE for acidic compounds with high plasma protein binding and low renal CL can be associated with a low Vd (i.e. around the Vd of albumin) and with a low in vivo CL, and that Mw is an important optimization parameter for pharmacokinetic. This study also further demonstrates the advantages of the application of the regression method for identifying cases when metabolic CL is not the single major elimination pathway.

Full utilization of a mass spectrometer using on-demand sharing with multiple LC units

The applicability of liquid chromatography-mass spectrometry (LC/MS) is often limited by throughput. The sharing of a mass spectrometer with multiple LCs significantly improves throughput; however, the reported systems have not been designed to fully utilize the MS duty cycle, and as a result to achieve maximum throughput. To fully utilize the mass spectrometer, the number of LC units that a MS will need to recruit is application dependent and could be significantly larger than the current commercial or published implementations. For the example of a single analyte, the number may approach the peak capacity to a first degree approximation. Here, the construction of a MS system that flexibly recruits any number of LC units demanded by the application is discussed, followed by the method to port a previously developed LC/MS method to the system to fully utilize a mass spectrometer. To demonstrate the performance and operation, a prototypical MS system of eight LC units was constructed. When 1-min chromatographic separations were performed in parallel on the eight LCs of the system, the average LC/MS analysis time per sample was 10.5 s when applied to the analysis of samples in 384-well plate format. This system has been successfully used to conduct large-volume biochemical assays with the analysis of a variety of molecular entities in support of drug discovery efforts. Allowing the recruitment of the number of LC units appropriate for a given application, this system has the potential to be a plug-and-play system to fully utilize a mass spectrometer.

From known knowns to known unknowns: predicting in vivo drug metabolites

'It is better to be useful than perfect'. This review attempts to critically cover and assess the currently available approaches and tools to answer the crucial question: Is it possible (and if it is, to what extent is it possible) to predict in vivo metabolites and their abundances on the basis of in vitro and preclinical animal studies? In preclinical drug development, it is possible to produce metabolite patterns from a candidate drug by virtual means (i.e., in silico models), but these are not yet validated. However, they may be useful to cover the potential range of metabolites. In vitro metabolite patterns and apparent relative abundances are produced by various in vitro systems employing tissue preparations (mainly liver) and in most cases using liquid chromatography-mass spectrometry analytical techniques for tentative identification. The pattern of the metabolites produced depends on the enzyme source; the most comprehensive source of drug-metabolizing enzymes is cultured human hepatocytes, followed by liver homogenate fortified with appropriate cofactors. For specific purposes, such as the identification of metabolizing enzyme(s), recombinant enzymes can be used. Metabolite data from animal in vitro and in vivo experiments, despite known species differences, may help pinpoint metabolites that are not apparently produced in in vitro human systems, or suggest alternative experimental approaches. The range of metabolites detected provides clues regarding the enzymes attacking the molecule under study. We also discuss established approaches to identify the major enzymes. The last question, regarding reliability and robustness of metabolite extrapolations from in vitro to in vivo, both qualitatively and quantitatively, cannot be easily answered. There are a number of examples in the literature suggesting that extrapolations are generally useful, but there are only a few systematic and comprehensive studies to validate in vitro-in vivo extrapolations. In conclusion, extrapolation from preclinical metabolite data to the in vivo situation is certainly useful, but it is not known to what extent.

Internal standard tracked dilution to overcome challenges in dried blood spots and robotic sample preparation for liquid chromatography/tandem mass spectrometry assays

Dried blood spot (DBS) technology is an emerging alternative for sample collection in bioanalysis. Dilution for DBS samples is a challenge due to its solid sample format. Currently, DBS samples requiring dilution were first extracted as regular samples and then diluted with extracted blank samples containing internal standard (IS). Since the dilution step is a volume-critical step, extra care has to be taken to achieve accurate dilution when dealing with limited volume extracted samples. Here, we introduce an alternative sample dilution for liquid chromatography/tandem mass spectrometry (LC/MS/MS) assays using IS to track the dilution step. Dilution factor-adjusted IS working solution was first added to the sample requiring dilution before sample processing; subsequently, the processed sample was approximately diluted into the assay linear response range before LC/MS/MS analysis. We define this approach as "IS-tracked dilution". The advantage of this approach is that the diluting step is tracked by the IS and is no longer a volume-critical step. Another recognized challenge related to sample dilution is automatic sample dilution using a liquid handler. This "IS-tracked dilution" may also help address some of the challenges for automatic sample dilution of liquid samples. This new dilution approach was proven to be effective and convenient in both plasma assays and DBS assays using omeprazole as a probe compound.

High-throughput analysis of standardized pharmacokinetic studies in the rat using sample pooling and UPLC-MS/MS

As a consequence of a continuous demand for increased throughput of pharmacokinetic (PK) studies, industries have introduced strategies to reduce the number of samples such as cassette analysis (pooling of samples after the in-life phase). Here, we have investigated whether relevant PK parameters change as a consequence of cassette analysis, and whether there are circumstances that disqualify this technique from being used. 22 compounds were intravenously and orally administered to parallel groups of 3 rats. Each compound was administered discretely. Equal volumes of three plasma samples corresponding to each time point of three discretely dosed rats with different compounds were pooled (cassette analysis). Samples were prepared by protein precipitation followed by UPLC-MS/MS analysis using pos/neg switching when required. With cassette analysis, 4 compounds, morphine, phenytoin, rofecoxib and diclofenac, showed high limit of quantification (LOQ) values after pooling, which led to less reliable PK analyses. Of all samples with contents above LOQ, about 5% could not be detected in pool samples compared to single samples. However, an excellent correlation was seen for all PK parameters when comparing the parameters obtained from discrete analysis versus those obtained from cassette analysis, although half life showed somewhat more scatter than the others. When PK parameters were grouped as low-medium-high, clearance, volume of distribution, half life and bioavailability were similar between discrete and cassette analysis for 90%, 86%, 95% and 90% of the total number of compounds tested, respectively. Some additional improvement was achieved if compounds with a low MS response were excluded. In summary, cassette analysis is an effective strategy to reduce samples without affecting the estimated PK parameters that are important for decision-making.

Reduction of Carry over in Liquid-Handling Systems with a Decontamination Step Integrated in the Washing Procedure

Robotic liquid-handling systems can be equipped with disposable pipetting tips or fixed reusable pipetting tips. The use of disposable tips is perceived as the best option to avoid carry over (CO) of analyte from sample to sample. We recently developed standardized CO test procedures that allow precise and reproducible quantification of CO for fixed reusable tips. We used these test procedures to reduce CO of the analytes fluorescein, IgG, and hepatitis B surface antigen (HBsAg) to minimal levels. Variations of washing intensity, using water as a washing solution, did not lower CO below acceptable target levels. These target levels would preclude a false-positive detection of IgG and HBsAg in human serum when a negative sample is measured subsequent to a sample with a high analyte concentration. We therefore integrated a decontamination step into the washing procedure. Screening of 12 decontamination solutions showed that sodium hypochlorite solution was very efficient in reducing CO. Optimization led to a final washing routine in which tips are exposed for 0.2 s to 0.17 M NaOCI and subsequently rinsed with 2 mL of water to remove any remaining decontaminant solution. The washing procedure only takes 15 s and is thus suitable for high-throughput applications. The procedure was able to lower CO of IgG and HBsAg in human sera below relevant levels. The decontamination step with hypochlorite can easily be integrated into different liquid-handling systems and is likely to be effective against CO of most proteins and peptides.

Liquid chromatography-mass spectrometry in in vitro drug metabolite screening

A combination of high performance liquid chromatography (HPLC) and mass spectrometry (LC/MS) has proven its status as the most powerful analytical tool for screening and identifying drug metabolites in modern drug discovery. These techniques have become irreplaceable for drug metabolism laboratories, providing high amounts of information from a wide variety of samples. This review focuses on the most common and useful applications of these techniques when working on in vitro metabolism, more specifically with screening and identification of chemically stable or reactive metabolites formed via biotransformation reactions. Matching specific tasks and suitable instruments is a recurring consideration; for many reasons, the time-of-flight or orbitrap mass spectrometry provides clearly increased efficiency in metabolite profiling compared to other types of mass spectrometry.