Stability, pKa and plasma protein binding of roscovitine

Immobilized angiotensin II type I receptor: A powerful method of high throughput screening for antihypertensive compound identification through binding interaction analysis

The enormous growth in drug discovery paradigm has necessitated continuous exploration of new methods for drug-protein interaction analysis. To enhance the role of these methodologies in designing rational drugs, this work extended an immobilized angiotensin II type I receptor (AT1R) based affinity chromatography in antihypertensive compound identification. We fused haloalkane dehalogenase at C-terminus of AT1R and expressed the fusion receptor in E. coli. The expressed receptor was covalently immobilized onto 8.0 μm microspheres by mixing the cell lysate with 6-chlorocaproic acid-modified amino polystyrene microspheres. The immobilized AT1R was utilized for thermodynamic and kinetic interaction analysis between the receptor and four specific ligands. Following confirmation of these interactions by molecular docking, we identified puerarin and rosmarinic acid by determining their binding to the receptor. Azilsartan, candesartan, valsartan and olmesartan displayed two kinds of binding sites to AT1R by injection amount-dependent method. By molecular docking, we recognize the driving forces of the interaction as electrostatic interaction, hydrogen bonds and van der Waals force. The dissociation rate constants (kd) of azilsartan, candesartan, valsartan and olmesartan to AT1R were 0.01138 ± 0.003, 0.05142 ± 0.003, 0.07547 ± 0.004 and 0.01310 ± 0.005 min-1 by peak profiling assay. Comparing with these parameters, puerarin and rosmarinic acid presented lower affinity (KA: 0.12 × 104 and 1.5 × 104/M) and slower kinetics (kd: 0.6864 ± 0.03 and 0.3005 ± 0.01 min-1) to the receptor. These results, taking together, indicated that the immobilized AT1R has the capacity to probe antihypertensive compounds.

Graphene Oxide Tablets for Sample Preparation of Drugs in Biological Fluids: Determination of Omeprazole in Human Saliva for Liquid Chromatography Tandem Mass Spectrometry

In this study, a novel sort of sample preparation sorbent was developed, by preparing thin layer graphene oxide tablets (GO-Tabs) utilizing a mixture of graphene oxide and polyethylene glycol on a polyethylene substrate. The GO-Tabs were used for extraction and concentration of omeprazole (OME) in human saliva samples. The determination of OME was carried out using liquid chromatography-tandem mass spectrometry (LC–MS/MS) under gradient LC conditions and in the positive ion mode (ESI+) with mass transitions of m/z 346.3→198.0 for OME and m/z 369.98→252.0 for the internal standard. Standard calibration for the saliva samples was in the range of 2.0–2000 nmol L⁻¹. Limits of detection and quantification were 0.05 and 2.0 nmol L⁻¹, respectively. Method validation showed good method accuracy and precision; the inter-day precision values ranged from 5.7 to 8.3 (%RSD), and the accuracy of determinations varied from −11.8% to 13.3% (% deviation from nominal values). The extraction recovery was 60%, and GO-Tabs could be re-used for more than ten extractions without deterioration in recovery. In this study, the determination of OME in real human saliva samples using GO-Tab extraction was validated.

Reduced graphene oxide as an efficient sorbent in microextraction by packed sorbent: Determination of local anesthetics in human plasma and saliva samples utilizing liquid chromatography-tandem mass spectrometry

Herein, reduced graphene oxide (RGO) has been utilized as an efficient sorbent in microextraction by packed sorbent (MEPS). The combination of MEPS and liquid chromatography-tandem mass spectrometry has been used to develop a method for the extraction and determination of three local anesthetics (i.e. lidocaine, prilocaine, and ropivacaine) in human plasma and saliva samples. The results showed that the utilization of RGO in MEPS could minimize the matrix effect so that no interfering peaks at the retention times of the analytes or internal standard was observed. The high extraction efficiency of this method was approved by mean recoveries of 97.26-106.83% and 95.21-105.83% for the studied analytes in plasma and saliva samples, respectively. Intra- and inter-day accuracies and precisions for all analytes were in good accordance with the international regulations. The accuracy values (as percentage deviation from the nominal value) of the quality control samples were between -2.1 to 13.9 for lidocaine, -4.2 to 11.0 for prilocaine and between -4.5 to -2.4 for ropivacaine in plasma samples while the values were ranged from -4.6 to 1.6 for lidocaine, from -4.2 to 15.5 for prilocaine and from -3.3 to -2.3 for ropivacaine in human saliva samples. Lower and upper limit of quantification (LLOQ, ULOQ) were set at 5 and 2000 nmol L^-1 for all of the studied drugs. The correlation coefficients values were ≥0.995. The limit of detection values were obtained 4 nmol L^-1 for lidocaine and prilocaine, and 2 nmol L^-1 for ropivacaine.

Identifying the antiasthmatic target of doxofylline using immobilized β2 -adrenoceptor based high-performance affinity chromatography and site-directed molecular docking

As a xanthine derivative, doxofylline is believed to be dominant for fighting against asthma in practice. Unlike other xanthines, the antiasthmatic effects of doxofylline lack any definite proof of target and mediating mechanism according to previous reports. In this work, the interaction between doxofylline and β2 -AR was investigated by high performance affinity chromatography using frontal analysis and nonlinear model. The methodology involved the immobilization of β2 -AR on the silica gel by a random linking method, the determination of the binding parameters by frontal analysis and nonlinear chromatography and the exploration of the binding mechanism by site-directed molecular docking. The association constant for doxofylline binding to immobilized β2 -AR was determined to be 7.70 × 10(4)  M(-1) by nonlinear chromatography and 5.91 × 10(4)  M(-1) by frontal analysis. Ser(169) and Ser(173) were the binding sites for the receptor-drug interaction on which hydrogen bond was believed to be the main driven force during the interaction. These results indicated that the antiasthmatic effects of doxofylline may be behind the mediating mechanism of β2 -AR. High performance affinity chromatography based on immobilized receptor has potential to become an alternative for drug target confirmation and drug-receptor interaction analysis. Copyright © 2016 John Wiley & Sons, Ltd.

Microextraction by packed sorbent

Microextraction by packed sorbent (MEPS) is a miniaturized form of SPE. MEPS can handle small sample volumes and be connected on-line with LC or GC without any modifications. In addition, the MEPS sorbent bed is integrated into an injection syringe and can be used for more than 100 extractions. The key aspect of MEPS is that the solvent volume used for the elution of the analytes is of a suitable order of magnitude to be injected directly into GC or LC systems. MEPS has been used in many research fields such as environmental, biological and food analysis. This article gives an overview of the MEPS technique, including fields of application and common formats.

The effect of circadian rhythm on pharmacokinetics and metabolism of the Cdk inhibitor, roscovitine, in tumor mice model

Roscovitine is a selective Cdk-inhibitor that is under investigation in phase II clinical trials under several conditions, including chemotherapy. Tumor growth inhibition has been previously shown to be affected by the dosing time of roscovitine in a Glasgow osteosarcoma xenograft mouse model. In the current study, we examined the effect of dose timing on the pharmacokinetics, biodistribution and metabolism of this drug in different organs in B6D2F1 mice. The drug was orally administered at resting (ZT3) or activity time of the mice (ZT19) at a dose of 300 mg/kg. Plasma and organs were removed at serial time points (10, 20 and 30 min; 1, 2, 4, 6, 8, 12 and 24 h) after the administration. Roscovitine and its carboxylic metabolite concentrations were analyzed using HPLC-UV, and pharmacokinetic parameters were calculated in different organs. We found that systemic exposure to roscovitine was 38% higher when dosing at ZT3, and elimination half-life was double compared to when dosing at ZT19. Higher organ concentrations expressed as (organ/plasma) ratio were observed when dosing at ZT3 in the kidney (180%), adipose tissue (188%), testis (132%) and lungs (112%), while the liver exposure to roscovitine was 120% higher after dosing at ZT19. The metabolic ratio was approximately 23% higher at ZT19, while the intrinsic clearance (CLint) was approximately 67% higher at ZT19, indicating faster and more efficient metabolism. These differences may be caused by circadian differences in the absorption, distribution, metabolism and excretion processes governing roscovitine disposition in the mice. In this article, we describe for the first time the chronobiodistribution of roscovitine in the mouse and the contribution of the dosing time to the variability of its metabolism. Our results may help in designing better dosing schedules of roscovitine in clinical trials.

Exposure to total and protein-unbound rifampin is not affected by malnutrition in Indonesian tuberculosis patients

Nutritional status may have a profound impact on the pharmacokinetics of drugs, yet only few data are available for tuberculosis (TB) drugs. As malnutrition occurs frequently among TB patients, we assessed the effect of malnutrition on the steady-state pharmacokinetics of total and protein-unbound rifampin during the intensive phase of TB treatment. In a descriptive pharmacokinetic study in Bandung, Indonesia, patients received a fixed standard rifampin dose of 450 mg once daily during the intensive phase of TB treatment. A full pharmacokinetic curve for rifampin was recorded, and total and unbound concentrations of rifampin were analyzed in all samples. Rifampin pharmacokinetic parameters were compared between severely malnourished (BMI of <16.0 kg/m(2)), malnourished (BMI of <18.5 kg/m(2)), and well-nourished (BMI of ≥18.5 kg/m(2)) individuals. No difference in total and protein-unbound pharmacokinetic parameters between severely malnourished (n = 7), malnourished (n = 11), and well-nourished (n = 25) patients could be demonstrated. In addition, no significant correlation between BMI and exposure (area under the concentration-time curve from 0 to 24 h [AUC0-24] and maximum concentration of drug in serum [Cmax]) was found. Females had significantly higher total AUC0-24 (geometric mean, 59.2 versus 48.2 h · mg/liter; P = 0.02) and higher unbound AUC0-24 (geometric mean, 6.2 versus 4.8 h · mg/liter; P = 0.02) than males. Overall, a marked 2-fold interindividual variation in the free fraction was observed (7.6 to 15.0%; n = 36). Nutritional status and BMI do not appear to have a major effect on total and protein-unbound pharmacokinetic parameters of rifampin in Indonesian subjects. The large interindividual variability in the free fraction of rifampin suggests that protein-unbound rather than total rifampin concentrations should preferably be used to study exposure-response relationships.

Solid phase microextraction and related techniques for drugs in biological samples

In drug discovery and development, the quantification of drugs in biological samples is an important task for the determination of the physiological performance of the investigated drugs. After sampling, the next step in the analytical process is sample preparation. Because of the low concentration levels of drug in plasma and the variety of the metabolites, the selected extraction technique should be virtually exhaustive. Recent developments of sample handling techniques are directed, from one side, toward automatization and online coupling of sample preparation units. The primary objective of this review is to present the recent developments in microextraction sample preparation methods for analysis of drugs in biological fluids. Microextraction techniques allow for less consumption of solvent, reagents, and packing materials, and small sample volumes can be used. In this review the use of solid phase microextraction (SPME), microextraction in packed sorbent (MEPS), and stir-bar sorbtive extraction (SBSE) in drug analysis will be discussed. In addition, the use of new sorbents such as monoliths and molecularly imprinted polymers will be presented.

Monolithic packed 96-tips set for high-throughput sample preparation: determination of cyclophosphamide and busulfan in whole blood samples by monolithic packed 96-tips and LC-MS

A monolithic methacrylate packed 96-tips device was used for the extraction of the busulfan and cyclophosphamide in whole blood samples. Using a packed 96-tips set, a 96-well plate could be handled in about 2 min. The key aspect of the monolithic phase is that monolithic material can offer both good extraction capacity and low-back-pressure properties. The validation of the methodology showed that the accuracy values of quality-control samples were between 99 and 113% for busulfan, and between 103 and 110% for cyclophosphamide. The inter-day precision ranged from 7.0 to 12% for busulfan and from 13 to 16% for cyclophosphamide. The standard calibration curves were obtained within the concentration range 5-2000 nm for busulfan and from 10 to 5000 nm for cyclophosphamide in blood samples. The coefficients of determination were ≥0.99.

Monitoring free drug concentrations: challenges

Measurement of drug concentrations in biological samples is of utmost importance in many research areas. The information about the amount of drug in a biological sample can be given as either total concentration, which ignores the interaction of the drug with the sample matrix, or as free concentration, which shows the portion of molecules able to diffuse through membranes and exert biological activity. Although the historical trend has been towards determining total concentrations, measurement of free concentrations is becoming more important since it correlates better with pharmacological and toxicological effects. This review will discuss the most popular experimental approaches for monitoring free drug concentrations, based on the type of sample to be investigated and the kind of information to be collected. It is shown that the current challenges in measuring free concentrations are: convenience, accuracy, precision, wide applicability, availability of accurate and precise reference methods, ruggedness, and standardized sample conditions.

Microextraction by packed sorbent (MEPS): a tutorial

This tutorial provides an overview on a new technique for sample preparation, microextraction by packed sorbent (MEPS). Not only the automation process by MEPS is the advantage but also the much smaller volumes of the samples, solvents and dead volumes in the system. Other significant advantages such as the speed and the simplicity of the sample preparation process are provided. In this tutorial the main concepts of MEPS will be elucidated. Different practical aspects in MEPS are addressed. The factors affecting MEPS performance will be discussed. The application of MEPS in clinical and pre-clinical studies for quantification of drugs and metabolites in blood, plasma and urine will be provided. A comparison between MEPS and other extraction techniques such as SPE, LLE, SPME and SBSE will be discussed.

Preclinical characterization of BI 201335, a C-terminal carboxylic acid inhibitor of the hepatitis C virus NS3-NS4A protease

BI 201335 is a hepatitis C virus (HCV) NS3-NS4A (NS3 coexpressed with NS4A) protease inhibitor that has been shown to have potent clinical antiviral activity. It is a highly optimized noncovalent competitive inhibitor of full-length NS3-NS4A proteases of HCV genotypes 1a and 1b with K(i) values of 2.6 and 2.0 nM, respectively. K(i) values of 2 to 230 nM were measured against the NS3-NS4A proteases of HCV genotypes 2 to 6, whereas it was a very weak inhibitor of cathepsin B and showed no measurable inhibition of human leukocyte elastase. BI 201335 was also shown to be a potent inhibitor of HCV RNA replication in vitro with 50% effective concentrations (EC(50)s) of 6.5 and 3.1 nM obtained in genotype 1a and 1b replicon assays. Combinations of BI 201335 with either interferon or ribavirin had additive effects in replicon assays. BI 201335 had good permeability in Caco-2 cell assays and high metabolic stability after incubation with human, rat, monkey, and dog liver microsomes. Its good absorption, distribution, metabolism, and excretion (ADME) profile in vitro, as well as in rat, monkey, and dog, predicted good pharmacokinetics (PK) in humans. Furthermore, drug levels were significantly higher in rat liver than in plasma, suggesting that distribution to the target organ may be especially favorable. BI 201335 is a highly potent and selective NS3-NS4A protease inhibitor with good in vitro and animal ADME properties, consistent with its good human PK profile, and shows great promise as a treatment for HCV infection.

Seliciclib in malignancies

Cyclins and cyclin-dependent kinases (CDK) form a key part of the regulatory proteins that govern the cell cycle. Aberrancy in their function can lead to uncontrolled growth and proliferation of the cells which forms the basis of many human diseases, especially cancers. Seliciclib (CYC202, R-roscovitine) is a second-generation CDK inhibitor that competes for ATP binding sites on these kinases, reducing tumor growth and inducing cell death. It is a direct inhibitor of cyclin E/CDK2 and also has inhibitory effects on cyclin H/CDK7 and cyclin T/CDK9. Seliciclib leads to growth arrest and apoptosis of cell lines through activation of the p53 gene, inhibition of RNA processing and blockage of the RNA polymerase II-dependent transcription, and reduction of anti-apoptotic proteins. Seliciclib has good oral bioavailability, although its absorption is slowed by food. It is distributed rapidly to the body tissues and metabolized rapidly to a carboxylated derivative that is excreted by the kidneys. The major adverse effects of seliciclib are electrolyte disturbances (hypokalemia, hyponatremia), gastrointestinal side effects (nausea, emesis, anorexia), fatigue, transient hyperglycemia, elevation of liver enzymes and reversible elevation of serum creatinine. At present, it is in Phase II trials for non-small cell lung cancer and nasopharyngeal carcinoma.

A novel roscovitine derivative potently induces G1-phase arrest in platelet-derived growth factor-BB-activated vascular smooth muscle cells

Abnormal vascular smooth muscle cell (VSMC) proliferation contributes to the pathogenesis of restenosis. Thus, drugs interfering with cell cycle progression in VSMC are promising candidates for an antirestenotic therapy. In this study, we pharmacologically characterize N-5-(2-aminocyclohexyl)-N-7-benzyl-3-isopropyl-1(2)H-pyrazolo[4,3-d]pyrimidine-5,7-di-amine (LGR1406), a novel derivative of the cyclin-dependent kinase (CDK) inhibitor roscovitine (ROSC), in PDGF-BB-activated VSMC. Cell proliferation was quantified measuring DNA synthesis via 5-bromo-2'-deoxyuridine incorporation. Analysis of cell cycle distribution was done by flow cytometry using propidium iodide-stained nuclei. Key regulators of the cell cycle and relevant signaling pathways were dissected by Western blot analyses. In addition, in vitro kinase assays and in silico studies regarding the pharmacokinetic profile of both compounds were performed. LGR1406 shows a stronger (IC(50) = 3.0 muM) antiproliferative activity than ROSC (IC(50) = 16.9 muM), halting VSMCs in G(0)/G(1) phase of the cell cycle, whereas ROSC does not arrest but rather delays cell cycle progression. Neither of the compounds interferes with early PDGF-BB-induced signaling pathways (p38, extracellular signal-regulated kinase 1/2, c-Jun NH(2)-terminal kinase, Akt, signal transducer and activator of transcription 3), and both inhibit CDKs, with LGR1406 exerting a slightly higher potency against CDK1/2 and 4 than ROSC. Expression of cyclins A and E as well as hyperphosphorylation of the pocket proteins retinoblastoma protein and p107 are negatively affected by both compounds, although to a different extent. In silico calculations predicted a much higher metabolic stability for LGR1406 compared with ROSC. Altogether, ROSC derivatives, such as LGR1406 seem to be promising compounds for further development in antirestenotic therapy.

Screening of cocaine and its metabolites in human urine samples by direct analysis in real-time source coupled to time-of-flight mass spectrometry after online preconcentration utilizing microextraction by packed sorbent

Microextraction by packed sorbent (MEPS) has been evaluated for fast screening of drugs of abuse with mass spectrometric detection. In this study, C8 (octyl-silica, useful for nonpolar to moderately polar compounds), ENV(+) (hydroxylated polystyrene-divinylbenzene copolymer, for extraction of aliphatic and aromatic polar compounds), Oasis MCX (sulfonic-poly(divinylbenzene-co-N-polyvinyl-pyrrolidone) copolymer), and Clean Screen DAU (mixed mode, ion exchanger for acidic and basic compounds) were used as sorbents for the MEPS. The focus was on fast extraction and preconcentration of the drugs with rapid analysis using a time-of-flight (TOF) mass spectrometer as the detector with direct analysis in a real-time (DART) source. The combination of an analysis time of less than 1 min and accurate mass of the first monoisotopic peak of the analyte and the relative abundances of the peaks in the isotopic clusters provided reliable information for identification. Furthermore, the study sought to demonstrate that it is possible to quantify the analyte of interest using a DART source when an internal standard is used. Of all the sorbents used in the study, Clean Screen DAU performed best for extraction of the analytes from urine. Using Clean Screen DAU to extract spiked samples containing the drugs, linearity was demonstrated for ecgonine methyl ester, benzoylecgonine, cocaine, and cocaethylene with average ranges of: 65-910, 75-1100, 95-1200, and 75-1100 ng/mL (n = 5), respectively. The limits of detection (LOD) for ecgonine methyl ester, benzoylecgonine, cocaine, and cocaethylene were 22.9 ng/mL, 23.7 ng/mL, 4.0 ng/mL, and 9.8 ng/mL respectively, using a signal-to-noise ratio of 3:1.

Rapid analysis of the interactions between drugs and human serum albumin (HSA) using high-performance affinity chromatography (HPAC)

This study used a combination of zonal elution and frontal affinity chromatography on immobilized human serum albumin (HSA) high-performance affinity chromatography (HPAC) column to examine the association constants of various compounds that have been studied by equilibrium dialysis or ultra filtration. A standard plot was generated from retention factors of reference compounds using zonal elution chromatography against association constants of reference compounds using frontal affinity chromatography. The linear relationship was established (r2=0.9993) between retention factors and association constants of reference compounds. This standard plot was later used for rapid determination of association constants of various drugs which show low to medium binding affinity to HSA. Association constants of those drugs from this study were compared to that of more generally used methods (i.e., equilibrium dialysis or ultra filtration) from literature and resulted in a relatively high correlation (r2=0.945) value. This combination of zonal elution and frontal affinity chromatography method for determining association constants showed several advantages against traditional methods. Depending on drugs of interest, an association constant of drug to HSA can be measured as fast as 1.5 min. Other notable advantages include an ease of automation and its ability to distinguish association constants of chiral compounds at the same time. The same approach could be used for studying interaction of other drugs and proteins and should further improve overall drug screening process.

Mechanism of interaction between human serum albumin and N-alkyl phenothiazines studied using spectroscopic methods

The binding characteristics of human serum albumin (HSA) with N-alkyl phenothiazines derivatives (NAP) viz., levomepromazine monomaleate (LMM) and propericiazine (PPC) have been studied by employing fluorescence, absorption, circular dichroism and FT-IR techniques. The Stern-Volmer quenching constant, K(SV) values were found to decrease with increase in temperature thereby indicating the presence of static quenching mechanism in the interactions of NAP with HSA. The number of binding sites, n and the binding constant, K were noticed to be, respectively, 1.11 and (5.188+/-0.034)x10(4) M(-1) for LMM and 1.06 and (4.436+/-0.066)x10(4) M(-1) for PPC at 298 K. The negative value of enthalpy change and positive value of entropy change in the present study indicated that the hydrophobic forces played a major role in the binding of NAP to HSA. The circular dichroism and FT-IR spectral data revealed the conformational changes in the structure of protein upon its interaction with NAP. The binding distances and the energy transfer efficiency between NAP and protein were determined based on Förster's theory of energy transfer. The decreased binding constants of HAS-LMM and HAS-PPC systems in presence of common ions indicated the availability of higher concentration of free drug in plasma.

A phase I trial of the selective oral cyclin-dependent kinase inhibitor seliciclib (CYC202; R-Roscovitine), administered twice daily for 7 days every 21 days

Seliciclib (CYC202; R-roscovitine) is the first selective, orally bioavailable inhibitor of cyclin-dependent kinases 1, 2, 7 and 9 to enter clinical trial. Preclinical studies showed antitumour activity in a broad range of human tumour xenografts. A phase I trial was performed with a 7-day b.i.d. p.o. schedule. Twenty-one patients (median age 62 years, range: 39-73 years) were treated with doses of 100, 200 and 800 b.i.d. Dose-limiting toxicities were seen at 800 mg b.i.d.; grade 3 fatigue, grade 3 skin rash, grade 3 hyponatraemia and grade 4 hypokalaemia. Other toxicities included reversible raised creatinine (grade 2), reversible grade 3 abnormal liver function and grade 2 emesis. An 800 mg portion was investigated further in 12 patients, three of whom had MAG3 renograms. One patient with a rapid increase in creatinine on day 3 had a reversible fall in renal perfusion, with full recovery by day 14, and no changes suggestive of renal tubular damage. Further dose escalation was precluded by hypokalaemia. Seliciclib reached peak plasma concentrations between 1 and 4 h and elimination half-life was 2-5 h. Inhibition of retinoblastoma protein phosphorylation was not demonstrated in peripheral blood mononuclear cells. No objective tumour responses were noted, but disease stabilisation was recorded in eight patients; this lasted for a total of six courses (18 weeks) in a patient with ovarian cancer.

Roscovitine differentially affects CaV2 and Kv channels by binding to the open state

Roscovitine potently inhibits cyclin-dependent kinases (CDK) and can independently slow the closing of neuronal (CaV2.2) calcium channels. We were interested if this drug could affect other ion channels similarly. Using whole cell recordings, we found that roscovitine specifically slows deactivation of all CaV2 channels (N, P/Q and R) by binding to the open state. This effect had a rapid onset and EC(50)=54, 120 and 54microM for N-, P/Q-, and R-type channels, respectively. Deactivation of other channel types was not slowed, including L-type calcium channels (CaV1.2, CaV1.3), potassium channels (native, Kv4.2, Kv2.1 and Kv1.3), and native sodium channels. However, most of the channels tested were inhibited by roscovitine. The inhibition was characterized by slow development and a lower affinity (EC(50)=100-300microM). Surprisingly, potassium channels were rapidly inhibited with an EC(50)=23microM, which is similar to the EC(50) for roscovitine block of cell division [Meijer, L., Borgne, A., Mulner, O., Chong, J., Blow, J., Inagaki, N., Inagaki, M., Delcros, J., Moulinoux, J., 1997. Biochemical and cellular effects of roscovitine, a potent and selective inhibitor of the cyclin-dependent kinases cdc2, cdk2 and cdk5. Eur. J. Biochem. 243, 527-536]. Potassium current inhibition seemed to result from open channel block. The high potency of these two rapid onset effects makes them complicating factors for ongoing clinical trials and research using roscovitine. Thus, the physiology and pharmacology of slow CaV2 deactivation and potassium channel block must be explored.