Chronopharmacology and controlled drug release

Effect of Circadian Rhythm Modulated Blood Flow on Nanoparticle based Targeted Drug Delivery in Virtual In Vivo Arterial Geometries

Delivery of drug using nanocarriers tethered with vasculature-targeting epitopes aims to maximize the therapeutic efficacy of the drug while minimizing the drug side effects. Circadian rhythm which is governed by the central nervous system has implications for targeted drug delivery due to sleep-wake cycle changes in blood flow dynamics. This paper presents an advanced fluid dynamics modeling method that is based on viscous incompressible shear-rate fluid (blood) coupled with an advection-diffusion equation to simulate the formation of drug concentration gradients in the blood stream and buildup of concentration at the targeted site. The method is equipped with an experimentally calibrated nanoparticle-endothelial cell adhesion model that employs Robin boundary conditions to describe nanoparticle retention based on probability of adhesion, a friction model accounting for surface roughness of endothelial cell layer, and a dispersion model based on Taylor-Aris expression for effective diffusion in the boundary layer. The computational model is first experimentally validated and then tested on engineered bifurcating arterial systems where impedance boundary conditions are applied at the outflow to account for the downstream resistance at each outlet. It is then applied to a virtual geometric model of an in vivo arterial tree developed through MRI-based image processing techniques. These simulations highlight the potential of the computational model for drug transport, adhesion, and retention at multiple sites in virtual in vivo models. The model provides a virtual platform for exploring circadian rhythm modulated blood flow for targeted drug delivery while minimizing the in vivo experimentation.

Statement of Significance

A novel integration of nanoparticle-based drug delivery framework with shear-rate dependent blood flow model is presented. The framework is comprised of a unique combination of mechanics-based dispersion model, an asperity model for endothelium surface roughness, and a stochastic nanoparticle-endothelial cell adhesion model. Simulations of MRI based in vivo carotid artery system showcase the effects of vessel geometry on nanoparticle adhesion and retention at the targeted site. Vessel geometry and target site location impact nanoparticle adhesion; curved and bifurcating regions favor local accumulation of drug. It is also shown that aligning drug administration with circadian rhythm and sleep cycle can enhance the efficacy of drug delivery processes. These simulations highlight the potential of the computational modeling for exploring circadian rhythm modulated blood flow for targeted drug delivery while minimizing the in vivo experimentation.

Construction and application of medication reminder system: intelligent generation of universal medication schedule

BACKGROUND

Patients with chronic conditions need multiple medications daily to manage their condition. However, most patients have poor compliance, which affects the effectiveness of treatment. To address these challenges, we establish a medication reminder system for the intelligent generation of universal medication schedule (UMS) to remind patients with chronic diseases to take medication accurately and to improve safety of home medication.

METHODS

To design medication time constraint with one drug (MTCOD) for each drug and medication time constraint with multi-drug (MTCMD) for each two drugs in order to better regulate the interval and time of patients' medication. Establishment of a medication reminder system consisting of a cloud database of drug information, an operator terminal for medical staff and a patient terminal.

RESULTS

The cloud database has a total of 153,916 pharmaceutical products, 496,708 drug interaction data, and 153,390 pharmaceutical product-ingredient pairs. The MTCOD data was 153,916, and the MTCMD data was 8,552,712. An intelligent UMS medication reminder system was constructed. The system can read the prescription information of patients and provide personalized medication guidance with medication timeline for chronic patients. At the same time, patients can query medication information and get remote pharmacy guidance in real time.

CONCLUSIONS

Overall, the medication reminder system provides intelligent medication reminders, automatic drug interaction identification, and monitoring system, which is helpful to monitor the entire process of treatment in patients with chronic diseases.

Chronotherapeutic Approaches

The chapter provides a comprehensive review of current approaches to personalized chronodiagnosis and chronotherapy. We discuss circadian clock drug targets that aim to affect cellular clock machinery, circadian mechanisms of pharmacokinetics/pharmacodynamics, and chronotherapeutic approaches aimed at increasing treatment efficacy and minimizing its side effects. We explore how chronotherapy can combat acquired and compensatory drug resistance. Non-pharmacological interventions for clock preservation and enhancement are also overviewed, including light treatment, melatonin, sleep scheduling, time-restricted feeding, physical activity, and exercise.

PREGABALIN TREATMENT OF PERIPHERAL NERVE DAMAGE IN A MURINE DIABETIC PERIPHERAL NEUROPATHY MODEL

Context

Peripheral nerve lesions are a major complication of diabetes mellitus, the main clinical manifestations of which are numbness and pain involving the limbs.

Objective

To determine the correlation between pregabalin treatment and diabetic peripheral neuropathic pain.

Design

An experimental animal study in BALB/c mice.

Subjects and Methods

Diabetes models are established by injecting streptozotocin (STZ) into the abdominal cavities of mice. The correlation between the treatment effect, time, and dosage of pregabalin was determined. The effect of a type 1 organic cation transporter (Octn1) in the absorption of pregabalin was evaluated.

Results

Pregabalin reduced tactile allodynia in diabetic mice. The best analgesic effect occurred when intestinal absorption was increased. Octn1 mediated pregabalin entry into intestinal epithelial cells, which influenced the absorption of pregabalin with a time-dependent fluctuation in the small intestine. Peripheral nerve damage caused by diabetes was dependent on time and dose of pregabalin, which was related to the regular expression of Octn1 in small intestinal epithelium.

Conclusions

Peripheral nerve damage caused by diabetes was dependent on time and dosage of pregabalin, which was related to the regular expression of Octn1 in small intestinal epithelium.

Melatonin: Countering Chaotic Time Cues

Last year melatonin was 60 years old, or at least its discovery was 60 years ago. The molecule itself may well be almost as old as life itself. So it is time to take yet another perspective on our understanding of its functions, effects and clinical uses. This is not a formal review-there is already a multitude of systematic reviews, narrative reviews, meta-analyses and even reviews of reviews. In view of the extraordinary variety of effects attributed to melatonin in the last 25 years, it is more of an attempt to sort out some areas where a consensus opinion exists, and where placebo controlled, randomized, clinical trials have confirmed early observations on therapeutic uses. The current upsurge of concern about the multiple health problems associated with disturbed circadian rhythms has generated interest in related therapeutic interventions, of which melatonin is one. The present text will consider the physiological role of endogenous melatonin, and the mostly pharmacological effects of exogenous treatment, on the assumption that normal circulating concentrations represent endogenous pineal production. It will concentrate mainly on the most researched, and accepted area of therapeutic use and potential use of melatonin-its undoubted ability to realign circadian rhythms and sleep-since this is the author's bias. It will touch briefly upon some other systems with prominent rhythmic attributes including certain cancers, the cardiovascular system, the entero-insular axis and metabolism together with the use of melatonin to assess circadian status. Many of the ills of the developed world relate to deranged rhythms-and everything is rhythmic unless proved otherwise.

Optimizing the dosing schedule of l-asparaginase improves its anti-tumor activity in breast tumor-bearing mice

Proliferation of acute lymphoblastic leukemic cells is nutritionally dependent on the external supply of asparagine. l-asparaginase, an enzyme hydrolyzing l-asparagine in blood, is used for treatment of acute lymphoblastic leukemic and other related blood cancers. Although previous studies demonstrated that l-asparaginase suppresses the proliferation of cultured solid tumor cells, it remains unclear whether this enzyme prevents the growth of solid tumors in vivo. In this study, we demonstrated the importance of optimizing dosing schedules for the anti-tumor activity of l-asparaginase in 4T1 breast tumor-bearing mice. Cultures of several types of murine solid tumor cells were dependent on the external supply of asparagine. Among them, we selected murine 4T1 breast cancer cells and implanted them into BALB/c female mice kept under standardized light/dark cycle conditions. The growth of 4T1 tumor cells implanted in mice was significantly suppressed by intravenous administration of l-asparaginase during the light phase, whereas its administration during the dark phase failed to show significant anti-tumor activity. Decreases in plasma asparagine levels due to the administration of l-asparaginase were closely related to the dosing time-dependency of its anti-tumor effects. These results suggest that the anti-tumor efficacy of l-asparaginase in breast tumor-bearing mice is improved by optimizing the dosing schedule.

Circadian hormone control in a human-on-a-chip: In vitro biology's ignored component?

Organs-on-Chips (OoCs) are poised to reshape dramatically the study of biology by replicating in vivo the function of individual and coupled human organs. Such microphysiological systems (MPS) have already recreated complex physiological responses necessary to simulate human organ function not evident in two-dimensional in vitro biological experiments. OoC researchers hope to streamline pharmaceutical development, accelerate toxicology studies, limit animal testing, and provide new insights beyond the capability of current biological models. However, to develop a physiologically accurate Human-on-a-Chip, i.e., an MPS homunculus that functions as an interconnected, whole-body, model organ system, one must couple individual OoCs with proper fluidic and metabolic scaling. This will enable the study of the effects of organ-organ interactions on the metabolism of drugs and toxins. Critical to these efforts will be the recapitulation of the complex physiological signals that regulate the endocrine, metabolic, and digestive systems. To date, with the exception of research focused on reproductive organs on chips, most OoC research ignores homuncular endocrine regulation, in particular the circadian rhythms that modulate the function of all organ systems. We outline the importance of cyclic endocrine regulation and the role that it may play in the development of MPS homunculi for the pharmacology, toxicology, and systems biology communities. Moreover, we discuss the critical end-organ hormone interactions that are most relevant for a typical coupled-OoC system, and the possible research applications of a missing endocrine system MicroFormulator (MES-µF) that could impose biological rhythms on in vitro models. By linking OoCs together through chemical messenger systems, advanced physiological phenomena relevant to pharmacokinetics and pharmacodynamics studies can be replicated. The concept of a MES-µF could be applied to other standard cell-culture systems such as well plates, thereby extending the concept of circadian hormonal regulation to much of in vitro biology. Impact statement Historically, cyclic endocrine modulation has been largely ignored within in vitro cell culture, in part because cultured cells typically have their media changed every day or two, precluding hourly adjustment of hormone concentrations to simulate circadian rhythms. As the Organ-on-Chip (OoC) community strives for greater physiological realism, the contribution of hormonal oscillations toward regulation of organ systems has been examined only in the context of reproductive organs, and circadian variation of the breadth of other hormones on most organs remains unaddressed. We illustrate the importance of cyclic endocrine modulation and the role that it plays within individual organ systems. The study of cyclic endocrine modulation within OoC systems will help advance OoC research to the point where it can reliably replicate in vitro key regulatory components of human physiology. This will help translate OoC work into pharmaceutical applications and connect the OoC community with the greater pharmacology and physiology communities.

Systems Chronotherapeutics

Chronotherapeutics aim at treating illnesses according to the endogenous biologic rhythms, which moderate xenobiotic metabolism and cellular drug response. The molecular clocks present in individual cells involve approximately fifteen clock genes interconnected in regulatory feedback loops. They are coordinated by the suprachiasmatic nuclei, a hypothalamic pacemaker, which also adjusts the circadian rhythms to environmental cycles. As a result, many mechanisms of diseases and drug effects are controlled by the circadian timing system. Thus, the tolerability of nearly 500 medications varies by up to fivefold according to circadian scheduling, both in experimental models and/or patients. Moreover, treatment itself disrupted, maintained, or improved the circadian timing system as a function of drug timing. Improved patient outcomes on circadian-based treatments (chronotherapy) have been demonstrated in randomized clinical trials, especially for cancer and inflammatory diseases. However, recent technological advances have highlighted large interpatient differences in circadian functions resulting in significant variability in chronotherapy response. Such findings advocate for the advancement of personalized chronotherapeutics through interdisciplinary systems approaches. Thus, the combination of mathematical, statistical, technological, experimental, and clinical expertise is now shaping the development of dedicated devices and diagnostic and delivery algorithms enabling treatment individualization. In particular, multiscale systems chronopharmacology approaches currently combine mathematical modeling based on cellular and whole-body physiology to preclinical and clinical investigations toward the design of patient-tailored chronotherapies. We review recent systems research works aiming to the individualization of disease treatment, with emphasis on both cancer management and circadian timing system–resetting strategies for improving chronic disease control and patient outcomes.

Timing of Administration: For Commonly-Prescribed Medicines in Australia

Chronotherapy involves the administration of medication in coordination with the body's circadian rhythms to maximise therapeutic effectiveness and minimise/avoid adverse effects. The aim of this study is to investigate the "time of administration" recommendations on chronotherapy for commonly-prescribed medicines in Australia. This study also aimed to explore the quality of information on the timing of administration presented in drug information sources, such as consumer medicine information (CMI) and approved product information (PI). Databases were searched for original research studies reporting on the impact of "time of administration" of the 30 most commonly-prescribed medicines in Australia for 2014. Further, time of administration recommendations from drug information sources were compared to the evidence from chronotherapy trials. Our search revealed 27 research studies, matching the inclusion and exclusion criteria. In 56% (n = 15) of the research studies, the therapeutic effect of the medicine varied with the time of administration, i.e., supported chronotherapy. For some medicines (e.g., simvastatin), circadian-based optimal administration time was evident in the information sources. Overall, dedicated studies on the timing of administration of medicines are sparse, and more studies are required. As it stands, information provision to consumers and health professionals about the optimal "time" to take medications lags behind emerging evidence.

Circadian modulation in the intestinal absorption of P-glycoprotein substrates in monkeys

Recent studies in laboratory rodents have revealed that circadian oscillation in the physiologic functions affecting drug disposition underlies the dosing time-dependent change in pharmacokinetics. However, it is difficult to predict the circadian change in the drug pharmacokinetics in a diurnal human by using the data collected from nocturnal rodents. In this study, we used cynomolgus monkeys, diurnal active animals, to evaluate the relevance of intestinal expression of P-glycoprotein (P-gp) to the dosing time dependency of the pharmacokinetics of its substrates. The rhythmic phases of circadian gene expression in the suprachiasmatic nuclei (the mammalian circadian pacemaker) of cynomolgus monkeys were similar to those reported in nocturnal rodents. On the other hand, the expression of circadian clock genes in the intestinal epithelial cells of monkeys oscillated at opposite phases in rodents. The intestinal expression of P-gp in the small intestine of monkeys was also oscillated in a circadian time-dependent manner. Furthermore, the intestinal absorption of P-gp substrates (quinidine and etoposide) was substantially suppressed by administering the drugs at the times of day when P-gp levels were abundant. By contrast, there was no significant dosing time-dependent difference in the absorption of the non-P-gp substrate (acetaminophen). The oscillation in the intestinal expression of P-gp appears to affect the pharmacokinetics of its substrates. Identification of circadian factors affecting the drug disposition in laboratory monkeys may improve the predictive accuracy of pharmacokinetics in humans.

Influence of Chronobiology on the Nanoparticle-Mediated Drug Uptake into the Brain

Little attention so-far has been paid to the influence of chronobiology on the processes of nanoparticle uptake and transport into the brain, even though this transport appears to be chronobiologically controlled to a significant degree. Nanoparticles with specific surface properties enable the transport across the blood–brain barrier of many drugs that normally cannot cross this barrier. A clear dependence of the central antinociceptive (analgesic) effects of a nanoparticle-bound model drug, i.e., the hexapeptide dalargin, on the time of day was observable after intravenous injection in mice. In addition to the strongly enhanced antinociceptive effect due to the binding to the nanoparticles, the minima and maxima of the pain reaction with the nanoparticle-bound drug were shifted by almost half a day compared to the normal circadian nociception: The maximum in the pain reaction after i.v. injection of the nanoparticle-bound dalargin occurred during the later rest phase of the animals whereas the normal pain reaction and that of a dalargin solution was highest during the active phase of the mice in the night. This important shift could be caused by an enhanced endo- and exocytotic particulates transport activity of the brain capillary endothelial cells or within the brain during the rest phase.

Chronopharmacokinetics of drugs in toxicological aspects: A short review for pharmacy practitioners

A rough 24-hour cycle driven endogenously in biochemical, physiological or behavioral processes is called circadian rhythm. Chronobiology is the study of biological temporal rhythms. For decades, we know that the biological rhythm and the drug metabolism are also affected from daylight and chronopharmacology became recognized by scientists in the early 1970s. Its lateral branch chronocopharmacokinetics is the study of rhythmic, predictable-in-time differences in the pharmacokinetics of drugs. Chronopharmacokinetic studies are performed at every step of the biotransformation i.e., absorption, distribution, metabolism and excretion. Feeding schedules, sex and phenotype must be taken into consideration while applying pharmacotherapy to increase the efficiency and to decrease side effects. The impact of drugs on circadian rhythm should be not neglected. On the other hand, new special drug delivery systems can be used to synchronize drug concentrations according to circadian rhythms. “Chronopharmaceuticals” can identify the proper dosing time and this amelioration will lead to improved progress and diffusion of pharmacotherapy. Chronopharmaceuticals coupled with nanotechnology could be the future of drug delivery systems, and lead to safer and more efficient disease therapy in the future. In this review, we will discuss the pharmacokinetic effects of circadian rhythm and its toxicological outcomes. Besides, we will try to give some practical points for clinical pharmacist/pharmacy practitioners, concerning chronopharmacokinetics.

Population pharmacokinetic analysis of diurnal and seasonal variations of plasma concentrations of cilostazol in healthy volunteers

BACKGROUND

The background of this study was (1) to examine factors influencing cilostazol pharmacokinetics by developing a population model incorporating diurnal variation and other covariate effects and (2) to assess the feasibility of applying the developed model to determine the optimal dosing times.

METHODS

Data obtained from a cilostazol pharmacokinetic study consisting of 2 clinical trials (a single twice-a-day (BID) dosing trial in winter and a multiple BID dosing trial in summer) conducted in healthy Korean subjects were used for model building. A basic model was built, followed by a diurnal variation model, and then a final model was built incorporating covariates, including a seasonal difference. The optimal morning and evening dosing times were determined from simulations.

RESULTS

Diurnal variation in cilostazol pharmacokinetics was explained by the morning absorption rate constant being faster than in the evening, yielding values of 0.278 versus 0.234/h in summer, when 24- and 12-hour circadian rhythms were included in the model. The seasonal variation was explained by a 26.9% and a 31.8% decrease in the absorption rate constant and clearance, respectively, in winter compared with summer. Based on twice-a-day (BID) dosing, dosing times of 9 AM and 5 PM in summer and 10 AM and 7 PM in winter were expected to produce the smallest peak-to-peak fluctuations in cilostazol concentration, possibly minimizing unwanted effects of the drug.

CONCLUSIONS

This study demonstrated the intraday and interseasonal time-varying nature of cilostazol pharmacokinetics using a population modeling approach and developed a strategy for optimizing dosing times. It is suggested that these methods can be similarly applied to analyses and controls of other drugs that exhibit characteristics of time-varying pharmacokinetics.

Influence of dosing time on the efficacy and safety of finasteride in rats

Finasteride (FIN), a widely used medication for the treatment of androgen-dependent diseases, blocks the conversion of testosterone to a more potent androgen, dihydrotestosterone (DHT). In this study, we investigated a dosing time-dependent effect and safety of FIN in rats. Androgen receptor (AR) mRNA and nuclear protein levels exhibited clear daily rhythms with the peak during the dark period in the prostate and during the light period in the liver. Repeated oral administration of FIN (5 or 100 mg/kg) at 3 h after lights on (HALO) for 2 weeks decreased serum DHT concentration throughout a 24-h period, whereas the dosing of the agent at 15 HALO decreased its level only transiently even in the higher dose group. FIN caused laboratory abnormalities in the 3 HALO group but not in the 15 HALO group. However, the effect of FIN on the prostate weight was not influenced by the dosing time. These results suggest that the safety, but not effect, of FIN depends on its dosing time in rats. The dosing of FIN in the active period might be a rational dosage regimen, which is needed to be confirmed in human subjects.

Molecular basis for the dosing time-dependency of anti-allodynic effects of gabapentin in a mouse model of neuropathic pain

BACKGROUND

Neuropathic pain is characterized by hypersensitivity to innocuous stimuli (tactile allodynia) that is nearly always resistant to NSAIDs or even opioids. Gabapentin, a GABA analogue, was originally developed to treat epilepsy. Accumulating clinical evidence supports the effectiveness of this drug for diverse neuropathic pain. In this study, we showed that the anti-allodynic effect of gabapentin was changed by the circadian oscillation in the expression of its target molecule, the calcium channel α2δ-1 subunit.

RESULTS

Mice were underwent partial sciatic nerve ligation (PSL) to create a model of neuropathic pain. The paw withdrawal threshold (PWT) in PSL mice significantly decreased and fluctuated with a period length about 24 h. The PWT in PSL mice was dose-dependently increased by intraperitoneal injection of gabapentin, but the anti-allodynic effects varied according to its dosing time. The protein levels of α2δ-1 subunit were up-regulated in the DRG of PSL mice, but the protein levels oscillated in a circadian time-dependent manner. The time-dependent oscillation of α2δ-1 subunit protein correlated with fluctuations in the maximal binding capacity of gabapentin. The anti-allodynic effect of gabapentin was attenuated at the times of the day when α2δ-1 subunit protein was abundant.

CONCLUSIONS

These findings suggest that the dosing time-dependent difference in the anti-allodynic effects of gabapentin is attributable to the circadian oscillation of α2δ-1 subunit expression in the DRG and indicate that the optimizing its dosing schedule helps to achieve rational pharmacotherapy for neuropathic pain.

Preparation and evaluation of a novel delayed-onset sustained-release system of propranolol hydrochloride

The objective of this work was to prepare and evaluate a new delayed-onset sustained-release system, comprising a sustained-release core tablet with hydroxypropyl methylcellulose as polymer matrix and an ethylcellulose/Eudragit L coating capable of delaying the drug release. The sustained core containing propranolol hydrochloride as the model drug was prepared by granulate tableting and the polymer coating was applied in a computer-controlled coating pan. The dissolution tests demonstrated that the in-vitro drug release was pH-dependent with sufficient gastric resistance, and the lag time (t10%) could be controlled by adjusting the coating level. Three dosage forms including commercial tablet, sustained-release tablet and the delayed-onset sustained-release tablet were administrated to six beagle dogs and the plasma levels of propranolol hydrochloride were measured with high-performance liquid chromatography. The delayed-onset sustained-release tablet had a lag time of 3.0 h in-vitro and 3.5 h in-vivo, and a tmax of 7.0 h. The relative bioavailability for delayed-onset sustained-release tablet was 96.98% compared with commercial tablets. The results indicate that the new propranolol delayed-onset sustained-release system could achieve a relatively constant drug release followed by a programmed lag time, and this may provide a promising drug delivery form for chronopharmacotherapy of certain cardiovascular diseases.

Tone-induced sleep fragmentation in persons with Alzheimer's disease: a feasibility study

Sleep fragmentation increases as Alzheimer's disease (AD) progresses. Its effects on cognition, specifically vigilant attention, are profoundly important because vigilant attention is thought to be the first step in memory acquisition. To our knowledge, no one has experimentally studied the effect of sleep fragmentation on vigilant attention in persons with AD. Therefore, this study piloted an experimental method using sound (tones produced by an audiometer) to induce sleep fragmentation. Participants enrolled in the University of Arkansas for Medical Sciences Memory Research Center ([MRC] n = 4) underwent one night of undisturbed and one of fragmented sleep. All participants tolerated the earphone needed for the tone-induced sleep fragmentation (TISF) method, and we were able to score awakenings in real time. However, only 50% of tones produced awakenings. The findings suggest that this experimental method is feasible for use in persons with mild AD. Based on the results, we will increase the duration, intensity, and frequency of tones delivered for optimal result.

Dosing-time dependent effect of dexamethasone on bone density in rats

AIMS

While glucocorticoids are widely used to treat patients with various diseases, they often cause adverse effects such as bone fractures. In this study, we investigated whether the decrease in bone density induced by glucocorticoid therapy was ameliorated by optimizing a dosing-time.

MAIN METHODS

Rats were administered with dexamethasone (Dex) orally (1mg/kg/day) for 6weeks at a resting or an active period. After the end of the treatment, bone density of femur, biomarkers of bone formation and resorption, and other biomedical variables were measured.

KEY FINDINGS

Bone density of femur was significantly decreased by the 6-week treatment with Dex, and the degree of decrease in the 14 HALO (hours after light on) dosing group (an active period) was larger than that in the 2 HALO dosing group (a resting period). Although urinary calcium excretion was accelerated by Dex treatment, secondary hyperparathyroidism was not detected. Histomorphometry analysis showed that Dex suppressed bone resorption, which was larger in the 2 HALO than in the 14 HALO groups. These data indicate that Dex equally suppressed bone formation in the 2 and 14 HALO groups, but inhibited bone resorption more in the 2 HALO than in the 14 HALO groups.

SIGNIFICANCE

This study shows that the decrease in bone density induced by Dex was changed by its dosing-time.

Circadian clock-controlled intestinal expression of the multidrug-resistance gene mdr1a in mice

BACKGROUND & AIMS

P-glycoprotein, the product of the multidrug resistance (mdr) gene, functions as a xenobiotic transporter contributing to the intestinal barrier. Although intestinal expression of the mdr1a gene and its efflux pump function has been shown to exhibit 24-hour variation, the mechanism of the variations remains poorly understood. Here, we demonstrated that the molecular components of the circadian clock act as regulators to control 24-hour variation in the expression of the mdr1a gene.

METHODS

Luciferase reporter assay and gel mobility shift assay were used to study the mechanism of transcriptional regulation of the mdr1a gene by clock gene products. The messenger RNA levels and protein abundances in colon 26 cells and mouse intestine were measured by quantitative real-time polymerase chain reaction and Western blotting, respectively.

RESULTS

Hepatic leukemia factor (HLF) and E4 promoter binding protein-4 (E4BP4) regulated transcription of the mdr1a gene by competing with each other for the same DNA binding site. Molecular and biochemical analyses of HLF- and E4BP4-down-regulated colon 26 cells and the intestinal tract of Clock mutant mice suggested that these 2 proteins consisted of a reciprocating mechanism in which HLF activated the transcription of the mdr1a gene, whereas E4BP4 periodically suppressed transcription at the time of day when E4BP4 was abundant.

CONCLUSIONS

The intestinal expression of the mdr1a gene is influenced by the circadian organization of molecular clockwork. Our present findings provide a link between the circadian timekeeping system and xenobiotic detoxification.

Chronobiology, drug delivery, and chronotherapeutics

Biological processes and functions are organized in space, as a physical anatomy, and time, as a biological time structure. The latter is expressed by short-, intermediate-, and long-period oscillations, i.e., biological rhythms. The circadian (24-h) time structure has been most studied and shows great importance to the practice of medicine and pharmacotherapy of patients. The phase and amplitude of key physiological and biochemical circadian rhythms contribute to the known predictable-in-time patterns in the occurrence of serious and life-threatening medical events, like myocardial infraction and stroke, and the manifestation and severity of symptoms of chronic diseases, like allergic rhinitis, asthma, and arthritis. Moreover, body rhythms can significantly affect responses of patients to diagnostic tests and, most important to the theme of this special issue, medications. Rhythmicity in the pathophysiology of disease is one basis for chronotherapeutics--purposeful variation in time of the concentration of medicines in synchrony with biological rhythm determinants of disease activity--to optimize treatment outcomes. A second basis is the control of undesired effects of medications, especially when the therapeutic range is narrow and the potential for adverse effects high, which is the case for cancer drugs. A third basis is to meet the biological requirements for frequency-modulated drug delivery, which is the case for certain neuroendocrine peptide analogues. Great progress has been realized with hydrogels, and they offer many advantages and opportunities in the design of chronotherapeutic systems for drug delivery via the oral, buccal, nasal, subcutaneous, transdermal, rectal, and vaginal routes. Nonetheless, innovative delivery systems will be necessary to ensure optimal application of chronotherapeutic interventions. Next generation drug-delivery systems must be configurable so they (i) require minimal volitional adherence, (ii) respond to sensitive biomarkers of disease activity that often vary in time as periodic (circadian rhythmic) and non-periodic (random) patterns to release medication to targeted tissue(s) on a real time as needed basis, and (iii) are cost-effective.

Circadian rhythms: mechanisms and therapeutic implications

The mammalian circadian system is organized in a hierarchical manner in that a central pacemaker in the suprachiasmatic nucleus (SCN) of the brain's hypothalamus synchronizes cellular circadian oscillators in most peripheral body cells. Fasting-feeding cycles accompanying rest-activity rhythms are the major timing cues in the synchronization of many, if not most, peripheral clocks, suggesting that the temporal coordination of metabolism and proliferation is a major task of the mammalian timing system. The inactivation of noxious food components by hepatic, intestinal, and renal detoxification systems is among the metabolic processes regulated in a circadian manner, with the understanding of the involved clock output pathways emerging. The rhythmic control of xenobiotic detoxification provides the molecular basis for the dosing time-dependence of drug toxicities and efficacy. This knowledge can in turn be used in improving or designing chronotherapeutics for the patients who suffer from many of the major human diseases.

Basis for dosing time-dependent change in the anti-tumor effect of imatinib in mice

Because a variety of receptor tyrosine kinases are involved in the mechanism of tumor progression, the development of a clinically useful tyrosine kinase inhibitor is expected as a therapeutic agent for the treatment of malignant cancers. Imatinib mesylate, known as Gleevec or STI-571, is a molecule that inhibits the function of various receptors with tyrosine kinase activity, such as Abl, the bcr-abl chimeric product, KIT, and platelet-derived growth factor (PDGF) receptors. In this study, we investigated the influence of dosing time on the ability of imatinib to inhibit tumor growth in mice. Tumor-bearing mice were housed under standardized light/dark cycle conditions (lights on at 07:00 h, off at 19:00 h) with food and water ad libitum. The growth of tumor cells implanted in mice was more severely inhibited by the administration of imatinib (50 mg/kg, i.p.) in the early light phase than when it was administered in the early dark phase. The dosing time-dependency of anti-tumor effects was parallel to that of imatinib-induced anti-angiogenic effect. The inhibitory effect of imatinib on tyrosine kinase activity of PDGF receptors, but not of KIT and Abl, varied according to its administration time. The dosing time-dependency of imatinib-induced inhibition of PDGF receptor activity was closely related to that of its anti-tumor effects. Our results suggest that the anti-tumor efficacy of imatinib is enhanced by administering the drug when PDGF receptor activity was increased. The potent therapeutic efficacy of the drug could be expected by optimizing the dosing schedule.

Pulsed drug delivery

Modern drug delivery aims to develop drug delivery systems that are able to meet specific therapeutic requirements. Whereas sustained drug release aims to maintain a constant drug level within the body, pulsed drug delivery intends to release the drug rapidly within a short period of time, as a result of a biological or external trigger, after a specific lag time. This editorial highlights some of the recent advances in new concepts for pulsed drug delivery and proposes some future strategies.