CNS Pharmacokinetics Research Articles

Continuous evaluation of single-dose moxifloxacin concentrations in brain extracellular fluid, cerebrospinal fluid, and plasma: a novel porcine model.

Knowledge regarding CNS pharmacokinetics of moxifloxacin is limited, with unknown consequences for patients with meningitis caused by bacteria resistant to beta-lactams or caused by TB. (i) To develop a novel porcine model for continuous investigation of moxifloxacin concentrations within brain extracellular fluid (ECF), CSF and plasma using microdialysis, and (ii) to compare these findings to the pharmacokinetic/pharmacodynamic (PK/PD) target against TB. Six female pigs received an intravenous single dose of moxifloxacin (6 mg/kg) similar to the current oral treatment against TB. Subsequently, moxifloxacin concentrations were determined by microdialysis within five compartments: brain ECF (cortical and subcortical) and CSF (ventricular, cisternal and lumbar) for the following 8 hours. Data were compared to simultaneously obtained plasma samples. Chemical analysis was performed by high pressure liquid chromatography with mass spectrometry. The applied PK/PD target was defined as a maximum drug concentration (Cmax):MIC ratio >8. We present a novel porcine model for continuous in vivo CNS pharmacokinetics for moxifloxacin. Cmax and AUC0-8h within brain ECF were significantly lower compared to plasma and lumbar CSF, but insignificantly different compared to ventricular and cisternal CSF. Unbound Cmax:MIC ratio across all investigated compartments ranged from 1.9 to 4.3. A single dose of weight-adjusted moxifloxacin administered intravenously did not achieve adequate target site concentrations within the uninflamed porcine brain ECF and CSF to reach the applied TB CNS target.

Abstract B023: CNS and systemic pharmacokinetics of antibody-drug conjugate payloads through convection-enhanced delivery

Abstract B023: CNS and systemic pharmacokinetics of antibody-drug conjugate payloads through convection-enhanced delivery

Trial in Progress: A Phase I/II Study of Tafasitamab Plus Lenalidomide in Patients with Relapsed CNS Lymphoma

Background and Significance The development of novel, more effective biological strategies to prevent secondary CNS lymphoma (CNSL) and to treat primary and secondary CNSL would have significant impact. It is well established that the CD19 transmembrane glycoprotein is expressed by B-cells throughout differentiation, by the majority of B cell malignancies, and by follicular dendritic cells. Given the high incidence of neurotoxicity associated with blood-brain barrier disruption with CD19-directed CAR-T cells and bi-specific T-cell engager antibodies, Parker et al. recently investigated the possibility of CD19 expression by previously unrecognized cell population(s) in the brain. Single-cell RNA sequencing data demonstrated CD19 expression in brain mural cells, an integral component of the neurovascular unit that regulates integrity of the blood-brain barrier.(Cell, 2020; 183:126-42). Given these observations and the compelling problem of relapsed primary and secondary CNS lymphoma, we are evaluating tafasitamab, an anti-CD19 humanized monoclonal antibody, as a novel therapeutic for refractory CNS lymphomas. We hypothesize that tafasitamab may modulate blood-brain barrier integrity by perturbation of CD19 expressed on mural cells; but without recruitment of cytotoxic T cells and resultant cytokine release syndrome. Our rationale is supported by the Phase II L-MIND study, in which tafasitamab plus lenalidomide exhibited synergistic efficacy against relapsed/refractory aggressive non-Hodgkin lymphoma, with overall response rate of 60%, complete response rate of 43%, and a favorable toxicity profile compared to CAR-T without neurotoxicity. Notably, the L-MIND trial excluded patients previously treated with immunomodulatory drugs as well as CNS lymphoma. (Lancet Oncology 2020: 21:978-88). We also recently reported that tafasitamab plus lenalidomide induced brain parenchymal regressions in two consecutive CNS lymphoma patients with disease refractory to lenalidomide, pomalidomide and rituximab. (British Journal of Haematology 2023 201(1):154-157). Study Design and Methods This single-arm, open-label, multicenter Phase I/II study (NCT05351593) assesses safety, CNS pharmacokinetics and preliminary efficacy of tafasitamab plus lenalidomide in patients with relapsed primary and secondary CNSL. The Phase I portion of the study will determine tolerated dose (MTD) and recommended Phase II dose (RP2D) of lenalidomide in combination with tafasitamab. We are applying 3+3 dose escalation rules to examine lenalidomide 10mg, 15mg and 20 mg plus tafasitamab at 12 mg/kg. After the RP2D is identified, the Phase II portion of the study will begin. The primary objective of the Phase II expansion is to evaluate the clinical benefit rate (stable disease or better) via Simon's minimax two-stage design. Exploratory endpoints include assessment of effect of tafasitamab on blood-brain barrier permeability, correlation of the relationships between tumor response or resistance with tumor mutational profile, and changes in CSF and blood immune cell phenotypes. The study plans to enroll up to 35 patients. Eligibility mandates age ≥ 18 years, anticipated survival >2 months, ECOG PS 0-1, and receipt of at least one prior systemic therapy. Patients with prior exposure to lenalidomide or pomalidomide or concomitant systemic lymphoma are allowed. Patients with HIV infection, CNS PTLD, and those who previously received a CD19-targeting CAR-T product are ineligible. The study is currently enrolling at the University of California San Francisco, with plans to expand enrollment to other institutions within the United States.

Does nonlinear blood-brain barrier transport matter for (lower) morphine dosing strategies?

Morphine blood-brain barrier (BBB) transport is governed by passive diffusion, active efflux and saturable active influx. This may result in nonlinear plasma concentration-dependent brain extracellular fluid (brainECF) pharmacokinetics of morphine. In this study, we aim to evaluate the impact of nonlinear BBB transport on brainECF pharmacokinetics of morphine and its metabolites for different dosing strategies using a physiologically based pharmacokinetic simulation study. We extended the human physiologically based pharmacokinetic LeiCNS-PK3.0, model with equations for nonlinear BBB transport of morphine. Simulations for brainECF pharmacokinetics were performed for various dosing strategies: intravenous (IV), oral immediate (IR) and extended release (ER) with dose range of 0.25–150 mg and dosing frequencies of 1–6 times daily. The impact of nonlinear BBB transport on morphine CNS pharmacokinetics was evaluated by quantifying (i) the relative brainECF to plasma exposure (AUCu,brainECF/AUCu,plasma) and (ii) the impact on the peak-to-trough ratio (PTR) of concentration-time profiles in brainECF and plasma. We found that the relative morphine exposure and PTRs are dose dependent for the evaluated dose range. The highest relative morphine exposure value of 1.4 was found for once daily 0.25 mg ER and lowest of 0.1 for 6-daily 150 mg IV dosing. At lower doses the PTRs were smaller and increased with increasing dose and stabilized at higher doses independent of dosing frequency. Relative peak concentrations of morphine in relation to its metabolites changed with increasing dose. We conclude that nonlinearity of morphine BBB transport affects the relative brainECF exposure and the fluctuation of morphine and its metabolites mainly at lower dosing regimens.

Drug Distribution in Brain and Cerebrospinal Fluids in Relation to IC50 Values in Aging and Alzheimer’s Disease, Using the Physiologically Based LeiCNS-PK3.0 Model

BackgroundVery little knowledge exists on the impact of Alzheimer’s disease on the CNS target site pharmacokinetics (PK).AimTo predict the CNS PK of cognitively healthy young and elderly and of Alzheimer’s patients using the physiologically based LeiCNS-PK3.0 model.MethodsLeiCNS-PK3.0 was used to predict the PK profiles in brain extracellular (brainECF) and intracellular (brainICF) fluids and cerebrospinal fluid of the subarachnoid space (CSFSAS) of donepezil, galantamine, memantine, rivastigmine, and semagacestat in young, elderly, and Alzheimer’s patients. The physiological parameters of LeiCNS-PK3.0 were adapted for aging and Alzheimer’s based on an extensive literature search. The CNS PK profiles at plateau for clinical dose regimens were related to in vitro IC50 values of acetylcholinesterase, butyrylcholinesterase, N-methyl-D-aspartate, or gamma-secretase.ResultsThe PK profiles of all drugs differed between the CNS compartments regarding plateau levels and fluctuation. BrainECF, brainICF and CSFSAS PK profile relationships were different between the drugs. Aging and Alzheimer’s had little to no impact on CNS PK. Rivastigmine acetylcholinesterase IC50 values were not reached. Semagacestat brain PK plateau levels were below the IC50 of gamma-secretase for half of the interdose interval, unlike CSFSAS PK profiles that were consistently above IC50.ConclusionThis study provides insights into the relations between CNS compartments PK profiles, including target sites. CSFSAS PK appears to be an unreliable predictor of brain PK. Also, despite extensive changes in blood-brain barrier and brain properties in Alzheimer’s, this study shows that the impact of aging and Alzheimer’s pathology on CNS distribution of the five drugs is insignificant.

Is P‐glycoprotein functionally active at the Blood‐CSF Barrier?

The brain is protected from circulating metabolites and xenobiotics by two major barriers: the blood‐brain barrier (BBB) and the blood‐cerebrospinal fluid (CSF) barrier (BCSFB). The drug efflux transporter P‐glycoprotein (P‐gp) is known to be expressed luminally at the BBB where it limits the entry of circulating drugs and toxins into the brain. The BCSFB, formed by the choroid plexus epithelial cells, similarly expresses membrane transporters to mediate solute efflux or influx into the CSF. There are conflicting findings on P‐gp activity at the BCSFB, and limited studies of P‐gp localization posit the transporter is expressed apically or subapically, implying a paradoxical function to mediate a blood‐to‐CSF transport of xenobiotics and endobiotics. The objective of this study is to clarify the localization and function of P‐gp at the BCSFB utilizing a quantitative fluorescence microscopy approach. Calcein‐AM, commonly used to evaluate P‐gp‐mediated efflux, is a permeable, non‐fluorescent P‐gp substrate that is converted by intracellular esterases into calcein, a fluorescent and impermeable compound. Time‐dependent uptake of 250 nM calcein‐AM was performed in lateral ventricle choroid plexus isolated from adult FVB mice, and confocal imaging was utilized to observe the accumulation of calcein formed in the choroid plexus epithelial cells. Image segmentation was performed using ImageJ to individually quantify choroid plexus cell and blood capillary accumulation of calcein. Coincubation with 2 µM elacridar, a potent P‐gp inhibitor, increased accumulation of calcein in the choroid plexus cells by 5.7‐fold and increased blood capillary accumulation by 11.2‐fold, indicating inhibition of apical efflux transport. Our data suggests that that P‐gp is indeed functionally active at the apical, CSF‐facing membrane of the BCSFB. As CSF drug concentrations are frequently used as a surrogate measure of CNS drug exposure, elucidating the functional role of P‐gp at the BCSFB is critical for understanding the interplay of BBB and BCSFB transporters and their impact on CNS pharmacokinetics and pharmacodynamics.

Enhancing CDK4/6 inhibitor therapy for medulloblastoma using nanoparticle delivery and scRNA-seq-guided combination with sapanisertib.

The therapeutic potential of CDK4/6 inhibitors for brain tumors has been limited by recurrence. To address recurrence, we tested a nanoparticle formulation of CDK4/6 inhibitor palbociclib (POx-Palbo) in mice genetically-engineered to develop SHH-driven medulloblastoma, alone or in combination with specific agents suggested by our analysis. Nanoparticle encapsulation reduced palbociclib toxicity, enabled parenteral administration, improved CNS pharmacokinetics, and extended mouse survival, but recurrence persisted. scRNA-seq identified up-regulation of glutamate transporter Slc1a2 and down-regulation of diverse ribosomal genes in proliferating medulloblastoma cells in POx-Palbo–treated mice, suggesting mTORC1 signaling suppression, subsequently confirmed by decreased 4EBP1 phosphorylation. Combining POx-Palbo with the mTORC1 inhibitor sapanisertib produced mutually enhancing effects and prolonged mouse survival compared to either agent alone, contrasting markedly with other tested drug combinations. Our data show the potential of nanoparticle formulation and scRNA-seq analysis of resistance to improve brain tumor treatment and identify POx-Palbo + Sapanisertib as effective combinatorial therapy for SHH medulloblastoma.

Poly(2-oxazoline) nanoparticle delivery enhances the therapeutic potential of vismodegib for medulloblastoma by improving CNS pharmacokinetics and reducing systemic toxicity

We report a nanoparticle formulation of the SHH-pathway inhibitor vismodegib that improves efficacy for medulloblastoma, while reducing toxicity. Limited blood–brain barrier (BBB) penetration and dose-limiting extitle/citraneural toxicities complicate systemic therapies for brain tumors. Vismodegib is FDA-approved for SHH-driven basal cell carcinoma, but implementation for medulloblastoma has been limited by inadequate efficacy and excessive bone toxicity. To address these issues through optimized drug delivery, we formulated vismodegib in polyoxazoline block copolymer micelles (POx-vismo). We then evaluated POx-vismo in transgenic mice that develop SHH-driven medulloblastomas with native vasculature and tumor microenvironment. POx-vismo improved CNS pharmacokinetics and reduced bone toxicity. Mechanistically, the nanoparticle carrier did not enter the CNS, and acted within the vascular compartment to improve drug delivery. Unlike conventional vismodegib, POx-vismo extended survival in medulloblastoma-bearing mice. Our results show the broad potential for non-targeted nanoparticle formulation to improve systemic brain tumor therapy, and specifically to improve vismodegib therapy for SHH-driven cancers.

Characterizing the pharmacokinetics of panobinostat in a non-human primate model for the treatment of diffuse intrinsic pontine glioma.

Diffuse intrinsic pontine glioma (DIPG) is one of the deadliest forms of childhood cancers. To date, no effective treatment options have been developed. Recent drug screening studies identified the HDAC inhibitor panobinostat as an active agent against DIPG cells lines and animal models. To guide in the clinical development of panobinostat, we evaluated the CNS pharmacokinetics of panobinostat using CSF as a surrogate to CNS tissue penetration in a pre-clinical nonhuman primate (NHP) model after oral administration. Panobinostat was administered orally to NHP (n = 3) at doses 1.0, 1.8, 2.4, and 3.0mg/kg (human equivalent dose: 20, 36, 48, 60mg/m2, respectively). The subjects served as their own controls where possible. Serial, paired CSF and plasma samples were collected for 0-48h. Panobinostat was quantified via a validated uHPLC-MS/MS method. Pharmacokinetic (PK) parameters were calculated using non-compartmental methods. CSF penetration of panobinostat after systemic delivery was low, with levels detectable in only two subjects. The CSF penetration of panobinostat was low following oral administration in this pre-clinical NHP model predictive of human PK.

1 What constitutes evidence of target engagement in AD trials? ELND005 CNS pharmacokinetics, biomarker, and safety profile

1 What constitutes evidence of target engagement in AD trials? ELND005 CNS pharmacokinetics, biomarker, and safety profile

Antiretroviral drug treatment of CNS HIV-1 infection

The advent of combination antiretroviral treatment has had a profound impact on CNS HIV infection and its clinical complications, but neurological impairment still occurs in patients on systemically effective combination therapy, and in some patients it may be important to consider antiretroviral drug entry and effects within the CNS. There are now data on the CNS exposure for most antiretroviral drugs. This review focuses on the CNS pharmacokinetics and pharmacodynamics of antiretroviral drugs in humans, and also discusses controversies in this field.

CNS pharmacokinetics of antifungal agents

The goal in treatment of infections is to achieve a beneficial effect while minimizing toxicity. It is widely recognized that the principles of pharmacokinetics and pharmacodynamics are critical to determining an adequate dose–response relationship. There has been an increased involvement of the CNS to infection from opportunistic and endemic fungi over the last several decades due to establishment of solid-organ and bone marrow transplantation as well as immunosuppression from HIV. In this regard it has become critical to define optimal dosing regimens by an understanding of the processes which govern delivery of an antifungal agent to the targeted CNS site of involvement. The objective of this review is to: i) summarize published experimental and clinical antifungal pharmacokinetics; and ii) examine the relationship between CNS antifungal pharmacokinetics and efficacy. Examination of these studies reveal marked variability among antifungal drugs with regard to cerebrospinal fluid and brain parenchymal penetration. Formal examination of the relationship between CNS antifungal pharmacokinetics and efficacy are limited. The few experimental studies available suggest that brain parenchymal kinetics is a superior predictor of antifungal efficacy than cerebrospinal fluid concentrations.

CNS pharmacokinetics of antifungal agents

The goal in treatment of infections is to achieve a beneficial effect while minimizing toxicity. It is widely recognized that the principles of pharmacokinetics and pharmacodynamics are critical to determining an adequate dose-response relationship. There has been an increased involvement of the CNS to infection from opportunistic and endemic fungi over the last several decades due to establishment of solid-organ and bone marrow transplantation as well as immunosuppression from HIV. In this regard it has become critical to define optimal dosing regimens by an understanding of the processes which govern delivery of an antifungal agent to the targeted CNS site of involvement. The objective of this review is to: i) summarize published experimental and clinical antifungal pharmacokinetics; and ii) examine the relationship between CNS antifungal pharmacokinetics and efficacy. Examination of these studies reveal marked variability among antifungal drugs with regard to cerebrospinal fluid and brain parenchymal penetration. Formal examination of the relationship between CNS antifungal pharmacokinetics and efficacy are limited. The few experimental studies available suggest that brain parenchymal kinetics is a superior predictor of antifungal efficacy than cerebrospinal fluid concentrations.

The Role of Blood-Brain Barrier Studies in the Pharmaceutical Industry

The blood-brain barrier (BBB) remains one of the greatest challenges for the discovery and development of treatments for CNS disorders, which to this day remains one of the riskiest disease areas in terms of clinical success rates. Although the BBB is currently seen predominantly as a permeability obstacle for CNS drug delivery, it is becoming increasingly clear that the BBB has many more implications for the pharmaceutical industry impacting on CNS pharmacology and pathology, CNS pharmacokinetics and pharmacodynamics, and adverse CNS effects, to name but a few areas. The present review does not intend to summarize the activities in the field of BBB research per se, which has been accomplished by a number of excellent recent reviews, but instead to provide an overview of the role of BBB studies from a pharmaceutical industry perspective. This review will elaborate on the specific needs in terms of BBB-related issues across the different drug discovery and development phases, i.e. target identification and validation, lead generation and optimization, candidate selection and profiling, preclinical development and clinical studies. The specific approaches taken will be discussed in terms of specific requirements, questions to be asked, feasibility, interpretability, and impact. It becomes clear that few of the existing BBB models fully meet the requirements of the industrialized drug discovery process, highlighting the need for an array of new or modified tools and approaches that are more effective in helping make decisions which are more specifically tailored to the various stages of the lengthy process from target to the clinic. In looking at the numerous ongoing activities in the area of BBB research from the drug discovery and development point of view, an attempt has been made to place a stronger emphasis on the applicability of particular techniques and approaches, to identify gaps and areas for future activities. In order to materialize the considerable knowledge gained in recent years, the review is intended to foster an increased awareness of the need to better integrate basic academic research with the specific requirements of the pharmaceutical industry for the search of effective and safe new CNS medicines.

Physiology of the blood–brain barrier and its consequences for drug transport to the brain

The brain endothelium forms the blood–brain barrier (BBB) and is the chief site regulating molecular traffic between blood and brain. The ‘barrier phenotype’ includes tight junctions restricting paracellular flux and a range of transport mechanisms controlling transcellular flux. The barrier is induced by cell types associated with the microvessels and is subject to regulation. The composition of the BBB membranes will influence the permeability of lipid-soluble compounds. Specific transporter systems for solute uptake are present on both the apical (luminal) and basal (abluminal) membranes and efflux transporters of broader specificity are also present. Certain larger molecules may cross via transcytotic vesicular mechanisms. Potential drug molecules designed to enter the brain may use or interact with one or more of these routes—better understanding is needed before it will be possible to establish the optimal means of delivery for specific compounds and to design or modify them accordingly. Many lipid-soluble drugs are substrates for efflux transporters, making it difficult to guarantee CNS delivery or calculate free concentration in the brain interstitial fluid (ISF). The dynamics of the flowing ISF also complicate modelling and prediction of CNS pharmacokinetics. Finally, many disease states involve BBB dysfunction, which needs to be taken into account in designing appropriate therapies.