Brain Distribution of Drugs: Pharmacokinetic Considerations

Pharmacokinetics of Novel Dopamine Transporter Inhibitor CE-123 and Modafinil with a Focus on Central Nervous System Distribution

S-CE-123, a novel dopamine transporter inhibitor, has emerged as a potential candidate for cognitive enhancement. The objective of this study was to compare the tissue distribution profiles, with a specific focus on central nervous system distribution and metabolism, of S-CE-123 and R-modafinil. To address this objective, a precise liquid chromatography-high resolution mass spectrometry method was developed and partially validated. Neuropharmacokinetic parameters were assessed using the Combinatory Mapping Approach. Our findings reveal distinct differences between the two compounds. Notably, S-CE-123 demonstrates a significantly superior extent of transport across the blood-brain barrier (BBB), with an unbound brain-to-plasma concentration ratio (Kp,uu,brain) of 0.5, compared to R-modafinil's Kp,uu,brain of 0.1. A similar pattern was observed for the transport across the blood-spinal cord barrier. Concerning the drug transport across cellular membranes, we observed that S-CE-123 primarily localizes in the brain interstitial space, whereas R-modafinil distributes more evenly across both sides of the plasma membrane of the brain's parenchymal cells (Kp,uu,cell). Furthermore, our study highlights the substantial differences in hepatic metabolic stability, with S-CE-123 having a 9.3-fold faster metabolism compared to R-modafinil. In summary, the combination of improved BBB transport and higher affinity of S-CE-123 to dopamine transporters in comparison to R-modafinil makes S-CE-123 a promising candidate for further testing for the treatment of cognitive decline.

How Much is Enough? Impact of Efflux Transporters on Drug delivery Leading to Efficacy in the Treatment of Brain Tumors

The lack of effective chemotherapeutic agents for the treatment of brain tumors is a serious unmet medical need. This can be attributed, in part, to inadequate delivery through the blood-brain barrier (BBB) and the tumor-cell barrier, both of which have active efflux transporters that can restrict the transport of many potentially effective agents for both primary and metastatic brain tumors. This review briefly summarizes the components and function of the normal BBB with respect to drug penetration into the brain and the alterations in the BBB due to brain tumor that could influence drug delivery. Depending on what is rate-limiting a compound's distribution, the limited permeability across the BBB and the subsequent delivery into the tumor cell can be greatly influenced by efflux transporters and these are discussed in some detail. Given these complexities, it is necessary to quantify the extent of brain distribution of the active (unbound) drug to compare across compounds and to inform potential for use against brain tumors. In this regard, the metric, Kp,uu, a brain-to-plasma unbound partition coefficient, is examined and its current use is discussed. However, the extent of active drug delivery is not the only determinant of effective therapy. In addition to Kp,uu, drug potency is an important parameter that should be considered alongside drug delivery in drug discovery and development processes. In other words, to answer the question - How much is enough? - one must consider how much can be delivered with how much needs to be delivered.

Parenteral Lipid-Based Nanoparticles for CNS Disorders: Integrating Various Facets of Preclinical Evaluation towards More Effective Clinical Translation

Contemporary trends in combinatorial chemistry and the design of pharmaceuticals targeting brain disorders have favored the development of drug candidates with increased lipophilicity and poorer water solubility, with the expected improvement in delivery across the blood-brain barrier (BBB). The growing availability of innovative excipients/ligands allowing improved brain targeting and controlled drug release makes the lipid nanocarriers a reasonable choice to overcome the factors impeding drug delivery through the BBB. However, a wide variety of methods, study designs and experimental conditions utilized in the literature hinder their systematic comparison, and thus slows the advances in brain-targeting by lipid-based nanoparticles. This review provides an overview of the methods most commonly utilized during the preclinical testing of liposomes, nanoemulsions, solid lipid nanoparticles and nanostructured lipid carriers intended for the treatment of various CNS disorders via the parenteral route. In order to fully elucidate the structure, stability, safety profiles, biodistribution, metabolism, pharmacokinetics and immunological effects of such lipid-based nanoparticles, a transdisciplinary approach to preclinical characterization is mandatory, covering a comprehensive set of physical, chemical, in vitro and in vivo biological testing.

[Cerebrolysin in the treatment of cognitive impairment]

Cognitive impairment is one of the most important problems of modern health care. Currently, according to WHO, more than 55 million people worldwide are living with dementia. Dementia is one of the leading causes of disability and addiction among older people worldwide. Even more significant is the number of patients with mild cognitive impairment who have an increased risk of progression to dementia compared to people of the same age without cognitive impairment. The number of patients with cognitive impairment has also increased due to the consequences of COVID-19. It is necessary to use drugs that not only improve cognitive functions, but also slow down their progression. One of these drugs is cerebrolysin, the effectiveness of which has been confirmed in various types of cognitive impairment. Cerebrolysin, being a preparation from the brain of a pig, belongs to the group of biological drugs. In the production of Cerebrolysin very strict measures are taken to comply with the technology, which ensures the quality and identity of the product from batch to batch. The experience of many years of clinical use of Cerebrolysin testifies not only to its high efficiency, but also to its safety. It should be taken into account that similar substances can be developed in relation to biological products - biosimilars or biosimilars, which can be considered comparable only in case of equivalent pharmacokinetic parameters, efficacy and safety.

Shedding Light on the Blood-Brain Barrier Transport with Two-Photon Microscopy In Vivo

Treatment of brain disorders relies on efficient delivery of therapeutics to the brain, which is hindered by the blood-brain barrier (BBB). The work of Prof. Margareta Hammarlund-Udenaes was instrumental in understanding the principles of drug delivery to the brain and developing new tools to study it. Here, we show how some of the concepts developed in her research can be translated to in vivo 2-photon microscopy (2PM) studies of the BBB. We primarily focus on the methods developed in our laboratory to characterize the paracellular diffusion, adsorptive-mediated transcytosis, and receptor-mediated transcytosis of drug nanocarriers at the microscale, illustrating how 2PM can deepen our understanding of the mechanisms of drug delivery to the brain.

Acting centrally or peripherally: A renewed interest in the central nervous system penetration of disease-modifying drugs in multiple sclerosis

With the recent approval of cladribine tablets, siponimod and ozanimod, there has been a renewed interest into the extent to which these current generation disease-modifying therapies (DMTs) are able to cross into the central nervous system (CNS), and how this penetration of the blood-brain barrier (BBB) may influence their ability to treat multiple sclerosis (MS). The integrity of the CNS is maintained by the BBB, blood-cerebrospinal fluid barrier, and the arachnoid barrier, which all play an important role in preserving the immunological environment and homeostasis within the CNS. The integrity of the BBB decreases during the course of MS, with a putative temporal relationship to disease worsening. Furthermore, it is currently considered that progression of the disease is mediated mainly by resident cells of the CNS. The existing literature provides evidence to show that some of the current generation DMTs for MS are able to penetrate the CNS and potentially exert direct effects on CNS-resident cells, in particular the CNS-penetrating prodrugs cladribine and fingolimod, and other sphingosine-1 phosphate receptor modulators; siponimod and ozanimod. Other current generation DMTs appear to be restricted to the periphery due to their high molecular weight or physicochemical properties. As more effective brain penetrant therapies are developed for the treatment of MS, there is a need to understand whether the potential for direct effects within the CNS are of significance, and whether this brings additional benefits over and above treatment effects mediated in the periphery. In turn, this will require an improved understanding of the structure and function of the BBB, the role it plays in MS and subsequent treatments. This narrative review summarizes the data supporting the biological plausibility of a potential benefit from therapeutic molecules entering the CNS, and discusses the potential significance in the current and future treatment of MS.

A Review of Mathematics Determining Solute Uptake at the Blood-Brain Barrier in Normal and Pathological Conditions

The blood-brain barrier (BBB) limits movement of solutes from the lumen of the brain microvascular capillary system into the parenchyma. The unidirectional transfer constant, K_in, is the rate at which transport across the BBB occurs for individual molecules. Single and multiple uptake experiments are available for the determination of K_in for new drug candidates using both intravenous and in situ protocols. Additionally, the single uptake method can be used to determine K_in in heterogeneous pathophysiological conditions such as stroke, brain cancers, and Alzheimer's disease. In this review, we briefly cover the anatomy and physiology of the BBB, discuss the impact of efflux transporters on solute uptake, and provide an overview of the single-timepoint method for determination of K_in values. Lastly, we compare preclinical K_in experimental results with human parallels.