Pharmacokinetics of anticancer drugs in cerebrospinal fluid

Drug Clearance from Cerebrospinal Fluid Mediated by Organic Anion Transporters 1 (Slc22a6) and 3 (Slc22a8) at Arachnoid Membrane of Rats

Although arachnoid mater epithelial cells form the blood-arachnoid barrier (BAB), acting as a blood-CSF interface, it has been generally considered that the BAB is impermeable to water-soluble substances and plays a largely passive role. Here, we aimed to clarify the function of transporters at the BAB in regulating CSF clearance of water-soluble organic anion drugs based on quantitative targeted absolute proteomics (QTAP) and in vivo analyses. Protein expression levels of 61 molecules, including 19 ATP-binding-cassette (ABC) transporters and 32 solute-carrier (SLC) transporters, were measured in plasma membrane fraction of rat leptomeninges using QTAP. Thirty-three proteins were detected; others were under the quantification limits. Expression levels of multidrug resistance protein 1 (Mdr1a/P-gp/Abcb1a) and breast cancer resistance protein (Bcrp/Abcg2) were 16.6 and 3.27 fmol/μg protein (51.9- and 9.82-fold greater than in choroid plexus, respectively). Among those organic anion transporters detected only at leptomeninges, not choroid plexus, organic anion transporter 1 (oat1/Slc22a6) showed the greatest expression (2.73 fmol/μg protein). On the other hand, the protein expression level of oat3 at leptomeninges was 6.65 fmol/μg protein, and the difference from choroid plexus was within two-fold. To investigate oat1's role, we injected para-aminohippuric acid (PAH) with or without oat1 inhibitors into cisterna magna (to minimize the contribution of choroid plexus function) of rats. A bulk flow marker, FITC-inulin, was not taken up from CSF up to 15 min, whereas uptake clearance of PAH was 26.5 μL/min. PAH uptake was completely blocked by 3 mM cephalothin (inhibits both oat1 and oat3), while 17% of PAH uptake was inhibited by 0.2 mM cephalothin (selectively inhibits oat3). These results indicate that oat1 and oat3 at the BAB provide a distinct clearance pathway of organic anion drugs from CSF independently of choroid plexus.

Evaluation of postmortem drug concentrations in cerebrospinal fluid compared with blood and pericardial fluid

In forensic toxicology, body fluids are important materials not only as alternatives to blood but also for investigation of postmortem drug redistributions and pharmaco-/toxicokinetic analysis; however, there are limited data on postmortem drug distributions in cerebrospinal fluid (CSF). The present study reviewed toxicological data of autopsy cases (n=103), in which drugs were detected in CSF using gas chromatography/mass spectrometry (GC/MS), to investigate drug concentrations in CSF, compared with blood and pericardial fluid (PCF) concentrations. Oral/injected amphetamines (n=23) showed similar CSF and blood/PCF concentrations with partly lower CSF concentrations (about ×0.5-1.1). CSF concentrations of the venous anesthetic midazolam (n=7) were lower with poor correlations. Oral caffeine (n=15), acetaminophen (n=7), chlorpheniramine (n=6), dihydrocodeine (n=6), and phenobarbital (n=21) showed equivalent to lower CSF concentrations (about ×0.2-1.2), compared with blood and PCF concentrations; however, CSF phenobarbital concentrations were high in a fatal intoxication case. CSF concentrations of phenothiazine derivatives (n=29) were markedly lower (about ×0.1) than blood/PCF concentrations. The distribution of the local anesthetic lidocaine used in critical medical care (n=49) markedly varied by case. These findings suggest that CSF is useful in routine forensic toxicology as an alternative to blood as well as for investigating pharmaco-/toxicokinetics and postmortem redistributions.

Integrated pharmacokinetics and pharmacodynamics in drug development

Drug development is a complex, lengthy and expensive process. Pharmaceutical companies and regulatory authorities have recognised that the drug development process needs optimisation for efficiency in view of the return on investments. Pharmacokinetics and pharmacodynamics are the two main principles determining the relationship between dose and response. This article provides an update on integrated approaches towards drug development by linking pharmacokinetics, pharmacodynamics and disease aspects into mathematical models. Gradually, a transition is taking place from a rather empirical approach towards a modelling- and simulation-based approach to drug development. The main learning phases should be phases 0, I and II, whereas phase III studies should merely have a confirmatory purpose. In model-based drug development, mechanism-based mathematical models, which are iteratively refined along the path of development, incorporate the accumulating knowledge of the investigational drug, the disease and their mutual interference in different subsets of the target population. These models facilitate the design of the next study and improve the probability of achieving the projected efficacy and safety endpoints. In this article, several theoretical and practical aspects of an integrated approach towards drug development are discussed, together with some case studies from different therapeutic areas illustrating the application of pharmacokinetic/pharmacodynamic disease models at different stages of drug development.

Considerations in the use of cerebrospinal fluid pharmacokinetics to predict brain target concentrations in the clinical setting: implications of the barriers between blood and brain

In the clinical setting, drug concentrations in cerebrospinal fluid (CSF) are sometimes used as a surrogate for drug concentrations at the target site within the brain. However, the brain consists of multiple compartments and many factors are involved in the transport of drugs from plasma into the brain and the distribution within the brain. In particular, active transport processes at the level of the blood-brain barrier and blood-CSF barrier, such as those mediated by P-glycoprotein, may lead to complex relationships between concentrations in plasma, ventricular and lumbar CSF, and other brain compartments. Therefore, CSF concentrations may be difficult to interpret and may have limited value. Pharmacokinetic data obtained by intracerebral microdialysis monitoring may be used instead, providing more valuable information. As non-invasive alternative techniques, positron emission tomography or magnetic resonance spectroscopy may be of added value.

Pharmacokinetics of nimustine, cytosine arabinoside, and methotrexate in cerebrospinal fluid during cerebrospinal fluid perfusion chemotherapy

This report investigates the pharmacokinetics of nimustine (ACNU), cytosine arabinoside (Ara-C), and methotrexate (MTX) in cerebrospinal fluid (CSF) during CSF perfusion chemotherapy. A 47-year-old Japanese man with spinal cord, cerebellum and brain stem dissemination of oligo-astrocytoma received nine courses of CSF perfusion chemotherapy with ACNU, Ara-C, and MTX. A CSF perfusion chemotherapy solution was perfused via an Ommaya reservoir in the ventricle, and was discharged by drainage though another Ommaya reservoir in the lumbar spinal canal. CSF samples via Ommaya reservoirs in the lumbar spinal canal were obtained during the fifth and eighth courses of treatment. The concentrations of ACNU and Ara-C in CSF were measured by HPLC, and the MTX concentrations by fluorescence polarization immunoassay. In the fifth course of treatment, a CSF injection chemotherapy solution, consisting of 5 mg of ACNU dissolved in 20 ml of artificial CSF, was injected over a few minutes using the Ommaya reservoir. Next, a CSF perfusion chemotherapy solution, consisting of 10 mg of Ara-C and 5 mg of MTX dissolved in 100 ml of artificial CSF, was perfused over 2 h. In the eighth course of treatment, a CSF perfusion chemotherapy solution, consisting of 5 mg of ACNU, 10 mg of Ara-C and 5 mg of MTX dissolved in 100 ml of artificial CSF, was perfused over 2 h. In both treatments, the highest concentrations of Ara-C and MTX in CSF were observed 1 or 2 h after the end of perfusion, with the values of each drug being similar. The CSF AUCs of Ara-C and MTX in each treatment were of similar values. Although the highest concentration of ACNU in CSF was observed in the fifth treatment 1 h after injection (an injection chemotherapy of ACNU plus a perfusion chemotherapy of Ara-C and MTX), the concentration of ACNU in CSF was undetectable in the eighth treatment (a perfusion chemotherapy of ACNU, Ara-C and MTX). We were successful in administering all anticancer drugs, and reaching a level of over 1.0 microg/ml concentration in CSF of the lumbar spinal canal, using an injection chemotherapy of ACNU plus a perfusion chemotherapy of Ara-C and MTX; this was done even though the drugs, in particular ACNU, underwent some perfusion-period dependent decomposition.