5-HT6 receptor antagonists. Design, synthesis, and structure-activity relationship of substituted 2-(1-methyl-4-piperazinyl)pyridines

In this study, we present the discovery and pharmacological characterization of a new series of 6-piperazinyl-7-azaindoles. These compounds demonstrate potent antagonism and selectivity against the 5-HT6 receptor. Our research primarily focuses on optimizing the lead structure and investigating the structure-activity relationship (SAR) of these compounds. Our main objective is to improve their activity and selectivity against off-target receptors. Overall, our findings contribute to the advancement of novel compounds targeting the 5-HT6 receptor. Compound 29 exhibits significant promise in terms of pharmacological, physicochemical, and ADME (Absorption, Distribution, Metabolism, and Excretion) properties. Consequently, it merits thorough exploration as a potential drug candidate due to its favorable activity profile and successful outcomes in a range of in vivo experiments.

Metabolism and Mass Balance of the Novel Nonsteroidal Androgen Receptor Inhibitor Darolutamide in Humans

The biotransformation and excretion of darolutamide were investigated in a phase I study. Six healthy male volunteers received a single dose of 300 mg ¹⁴C-darolutamide as an oral solution in the fasted state. Plasma, urine, and feces samples were analyzed for mass balance evaluation by liquid scintillation counting (LSC). Metabolite profiling and identification were determined using liquid chromatography mass-spectrometry with off-line radioactivity detection using LSC. Complete mass balance was achieved, with mean radioactivity recovery of 95.9% within 168 hours (63.4% in urine, 32.4% in feces). The administered 1:1 ratio of (S,R)- and (S,S)-darolutamide changed to approximately 1:5, respectively, in plasma. Darolutamide and the oxidation product, keto-darolutamide, were the only components quantifiable by LSC in plasma, accounting for 87.4% of total radioactivity, with a 2.1-fold higher plasma exposure for keto-darolutamide. Aside from darolutamide, the most prominent metabolites in urine were O-glucoronide (M-7a/b) and N-glucuronide (M-15a/b), as well as pyrazole sulfates (M-29, M-24) and glucuronides (M-21, M-22) resulting from oxidative cleavage of the parent. The darolutamide diastereomers were mainly detected in feces. In vitro assays showed that darolutamide metabolism involves a complex interplay between oxidation and reduction, as well as glucuronidation. Interconversion of the diastereomers involves oxidation to keto-darolutamide, primarily mediated by CYP3A4, followed by reduction predominantly catalyzed by cytosolic reductase(s), with aldo-keto reductase 1C3 playing the major role. The latter reaction showed stereoselectivity with preferential formation of (S,S)-darolutamide. SIGNIFICANCE STATEMENT: The metabolism and excretion of darolutamide in humans revealed that oxidation (CYP3A4) and glucuronidation (UGT1A9, UGT1A1) were the main metabolic routes of elimination. Direct excretion also contributed to overall clearance. The two pharmacologically equipotent diastereomers of darolutamide interconvert primarily via oxidation to the active metabolite keto-darolutamide, followed by reduction predominantly by cytosolic reductase(s). The latter reaction showed stereoselectivity with preferential formation of (S,S)-darolutamide. Data indicate a low drug-drug interaction potential of darolutamide with inducers or inhibitors of metabolizing enzymes.

Pharmacokinetics of Darolutamide, its Diastereomers and Active Metabolite in the Mouse: Response to Saini NK et al. (2020)

BACKGROUND

Saini et al. recently investigated the pharmacokinetics of darolutamide and its diastereomers in vitro and in vivo in Balb/c mice, reporting higher levels of (S,S)-darolutamide than (S,R)-darolutamide following intravenous or oral dosing, and interconversion of (S,R)-darolutamide to (S,S)-darolutamide.

OBJECTIVE

To present our in vitro and in vivo studies of darolutamide pharmacokinetics in mice, which contrast with the findings of Saini et al. Methods: Nude male Balb/c mice were orally dosed for 7 days with 25, 50, or 100 mg/kg of darolutamide twice daily. Pharmacokinetic parameters in plasma and tissue samples were assessed by liquid chromatography-tandem mass spectrometry. Metabolism and interconversion of darolutamide and its diastereomers were investigated in cryopreserved Balb/c mouse hepatocytes. Protein binding was determined in plasma samples by equilibrium dialysis.

RESULTS

On day 7, C_max was reached 30 min after the last dose. Rapid formation and greater exposure of keto-darolutamide versus darolutamide were observed. Plasma exposure of (S,R)-darolutamide was 3-5-fold higher than that of (S,S)-darolutamide. The fraction of unbound keto-darolutamide was almost 6-fold lower than for darolutamide. In mouse hepatocytes, the conversion of (S,S)- to (S,R)-darolutamide was observed, but the conversion of (S,R)- to (S,S)-darolutamide was not detectable. Back-formation of keto-darolutamide to both diastereomers occurred at low levels.

CONCLUSION

The darolutamide diastereomer ratio changes upon administration in mice and other species due to interconversion through keto-darolutamide. This is not considered clinically relevant since both diastereomers and keto- darolutamide are pharmacologically similar in vitro. Based on the high protein binding of keto-darolutamide, its contribution in vivo in humans is considered low.

Predicting the effect of prandial stage and particle size on absorption of ODM-204

The prediction of absorption properties plays a key role in formulation development when the compound under development shows poor solubility and its absorption is therefore presumed to be solubility limited. In our work, we combined and compared data obtained from in vitro dissolution tests, transit intestinal model studies (TIM-1) and physiologically based pharmacokinetic modelling. Our aim was to determine the ability of these methods to predict performance of poorly soluble lipophilic weak base in vivo. The validity of the predictive methods was evaluated against the in vivo clinical pharmacokinetic (PK) data obtained after administration of the first test formulation, T1. The aim of our study was to utilize the models in evaluating absorption properties of the second test formulation, T2, which has not yet been clinically administered. The compound in the studies was ODM-204, which is a novel, orally administered, investigational, nonsteroidal dual inhibitor of CYP17A1 and androgen receptor. Owing to its physicochemical properties ODM-204 is prone to low or variable bioavailability. The models examined provided congruent data on dose dependent absorption, food effect at a dose of 200 mg and on the effect of API (active pharmaceutical ingredient) particle size on absorption. Our study shows that the predictive tools of in vitro dissolution, TIM-1 system and the PBPK (physiologically based pharmacokinetic) simulation, showed predictive power of different mechanisms of bioavailability and together provided valuable information for decision making.

Abstract 1753: Targeting cancer with selective cbp/p300 bromodomain inhibitors

Background: The Bromodomain (BRD) and Extra-Terminal domain (BET) family of proteins are key regulators of epigenetic control. Although pan BET Inhibitors show good clinical activity, progressive disease was seen after several months of treatment in clinical responders, likely due to secondary resistance mechanisms. The plausible resistance mechanisms are increased expression of TCF7L2, c-Myc, Survivin and PIM1. Cyclic AMP response element binding protein (CREB)-binding protein (CBP) and E1A interacting protein of 300 kDa (EP300 or p300) are two closely related histone acetyl transferases with oncogenic roles in a variety of cancers. They are known to be co-activators of several key transcription factors that contribute to tumor progression including HIF1a, BRCA-1, p53, c-Myc and androgen receptor (AR). Studies have indicated that p300 is also upregulated in SPOP-mutated prostate cancer. Thus, targeting CBP/p300 represents an attractive approach for developing novel therapies.

Methods and Results: Multiple potent and selective CBP/p300 bromodomain inhibitors that are structurally unrelated to known inhibitors were identified by iterative medicinal chemistry and SAR based approaches. The compounds were optimized towards attaining good physicochemical properties and DMPK profile. The anti-proliferative activity of the lead compounds was studied across multiple tumor types in a 3-day assay. The lead compounds potently inhibited viability of a wide range of hematological and solid tumor cell lines including prostate cancer cell lines VCaP and 22Rv1. In H929 cell line the lead compounds showed dose-dependent inhibition of cMYC and increase in cPARP. In a single dose PK-PD study in MV4-11 xenograft model, the compounds showed modulation of cMYC and Survivin.

Conclusions: In summary, our studies demonstrate that selective CBP/p300 bromodomain inhibitors are potent in models of hematologic malignancies and solid tumors in-vitro. Profiling of efficacy in xenograft models, and further toxicological evaluation are in progress.

Citation Format: Mahaboobi Jaleel, Ramesh S. Senaiar, Chandrasekhar Abbineni, Girish A. Renukappa, Subhendu Mukherjee, Sivapriya Marappan, DS Samiulla, AB Aravind, Naveen R. Kumar, Venkata Siva N. Reddy, Asha Babu, Akhila P. Srinivas, Prasad Yadlapalli, Suraj Tgore, Raghavendra NR, Chandranath D. Naik, Sanjeev Giri, Thomas Antony, Kavitha Nellore, Shekar Chelur, Girish Daginakatte, laura Ravanti, Mikko Myllymäki, Gerd Wohlfahrt, Elina Mattila, Stefan Karlsson, Mari Björkman, Reetta Riikonen, Tarja Ikonen, Laura Leimu, Chira Mälmström, Timo Korjamo, Anu Moilanen, Murali Ramachandra, Susanta Samajdar. Targeting cancer with selective cbp/p300 bromodomain inhibitors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1753.

Drug-Drug Interaction Potential of Darolutamide: In Vitro and Clinical Studies

Background and Objectives

Darolutamide is a novel androgen receptor (AR) antagonist approved for the treatment of nonmetastatic castration-resistant prostate cancer (nmCRPC). Accordingly, the drug–drug interaction (DDI) potential of darolutamide was investigated in both nonclinical and clinical studies.

Methods

In vitro studies were performed to determine the potential for darolutamide to be a substrate, inducer or inhibitor for cytochrome P450 (CYP) isoforms, other metabolizing enzymes and drug transporters. A phase I drug-interaction study in healthy volunteers evaluated the impact of co-administering rifampicin [CYP3A4 and P-glycoprotein (P-gp) inducer] and itraconazole [CYP3A4, P-gp and breast cancer resistance protein (BCRP) inhibitor] on the pharmacokinetics of darolutamide. Two further phase I studies assessed the impact of co-administering oral darolutamide on the pharmacokinetics of midazolam (sensitive CYP3A4 substrate) and dabigatran etexilate (P-gp substrate) and the impact on the pharmacokinetics of co-administered rosuvastatin [a substrate for BCRP, organic anion-transporting polypeptide (OATP)1B1, OATP1B3 and organic anion transporter (OAT)3].

Results

In vitro, darolutamide was predominantly metabolized via oxidative biotransformation catalyzed by CYP3A4 and was identified as a substrate for P-gp and BCRP. The enzymatic activity of nine CYP isoforms was not inhibited or slightly inhibited in vitro with darolutamide, and a rank order and mechanistic static assessment indicated that risk of clinically relevant DDIs via CYP inhibition is very low. In vitro, darolutamide exhibited no relevant induction of CYP1A2 or CYP2B6 activity. Inhibition of BCRP-, P-gp-, OAT3-, MATE1-, MATE2-K-, OATP1B1- and OATP1B3-mediated transport was observed in vitro. Phase I data showed that darolutamide exposure increased 1.75-fold with co-administered itraconazole and decreased by 72% with rifampicin. Co-administration of darolutamide with CYP3A4/P-gp substrates showed no effect or only minor effects. Rosuvastatin exposure increased 5.2-fold with darolutamide because of BCRP and probably also OATPB1/OATPB3 inhibition.

Conclusions

Darolutamide has a low potential for clinically relevant DDIs with drugs that are substrates for CYP or P-gp; increased exposure of BCRP and probably OATP substrates was the main interaction of note.

Electronic supplementary material

The online version of this article (10.1007/s13318-019-00577-5) contains supplementary material, which is available to authorized users.

Drug-drug interaction (DDI) of darolutamide with cytochrome P450 (CYP) and P-glycoprotein (P-gp) substrates: Results from clinical and in vitro studies

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Background: Maintaining quality of survival, by delaying disease progression and minimizing therapy burden, is critical for patients and has been evaluated in the pivotal phase III ARAMIS study in patients with non-metastatic castration-resistant prostate cancer. Due to comorbidity, elderly men often receive multiple comedications, including CYP and P-gp substrates, eg, simvastatin and digoxin. Enzalutamide and apalutamide, approved androgen receptor (AR) inhibitors, are strong CYP3A4 inducers and thus have potential for CYP-mediated DDIs. The effect of darolutamide, a structurally unique AR antagonist, on CYP activity ( in vitro and in vivo) and P-gp activity ( in vivo) was assessed. Methods: Inhibition of CYP isoforms by Daro was investigated in human liver microsomes using standard substrates. In addition, CYP and P-gp activity during darolutamide treatment was studied in a phase I trial of 15 healthy men who received 75 mg dabigatran etexilate (DABE, P-gp substrate) + 1 mg midazolam (MDZ, CYP3A4 substrate) once followed by 600 mg darolutamide (two 300 mg tablets) twice daily (BID) given with food for 9 days. On day 9, darolutamide was concomitantly administered with a single dose of 75 mg DABE + 1 mg MDZ. Results: Based on in vitro data, no clinically relevant inhibition of CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, or 3A4 by darolutamide is expected. In 13 evaluable subjects in the phase I study, concomitant darolutamide reduced MDZ Cmax by ~32% and AUC by ~29% vs MDZ alone. Concomitant darolutamide reduced non-conjugated dabigatran Cmax by 16% and AUC by 9% vs DABE alone. The observed treatment-emergent adverse events were consistent with the known safety profile of darolutamide. No new safety risks were revealed by co-administration of darolutamide and DABE or MDZ. Safety data for patients in ARAMIS who received darolutamide, including those with concomitant CYP or P-gp substrates, will be presented. Conclusions: Darolutamide showed only weak effects or none on P-gp, CYP3A4, or any other relevant CYP enzyme. Thus, darolutamide is not expected to cause any clinically relevant DDI with CYP or P-gp substrates, minimizing complications of polypharmacy. Clinical trial information: NCT03237416.

ODM-203, a Selective Inhibitor of FGFR and VEGFR, Shows Strong Antitumor Activity, and Induces Antitumor Immunity

Alterations in the gene encoding for the FGFR and upregulation of the VEGFR are found often in cancer, which correlate with disease progression and unfavorable survival. In addition, FGFR and VEGFR signaling synergistically promote tumor angiogenesis, and activation of FGFR signaling has been described as functional compensatory angiogenic signal following development of resistance to VEGFR inhibition. Several selective small-molecule FGFR kinase inhibitors are currently in clinical development. ODM-203 is a novel, selective, and equipotent inhibitor of the FGFR and VEGFR families. In this report we show that ODM-203 inhibits FGFR and VEGFR family kinases selectively and with equal potency in the low nanomolar range (IC₅₀ 6-35 nmol/L) in biochemical assays. In cellular assays, ODM-203 inhibits VEGFR-induced tube formation (IC₅₀ 33 nmol/L) with similar potency as it inhibits proliferation in FGFR-dependent cell lines (IC₅₀ 50-150 nmol/L). In vivo, ODM-203 shows strong antitumor activity in both FGFR-dependent xenograft models and in an angiogenic xenograft model at similar well-tolerated doses. In addition, ODM-203 inhibits metastatic tumor growth in a highly angiogenesis-dependent kidney capsule syngenic model. Interestingly, potent antitumor activity in the subcutaneous syngenic model correlated well with immune modulation in the tumor microenvironment as indicated by marked decrease in the expression of immune check points PD-1 and PD-L1 on CD8 T cells and NK cells, and increased activation of CD8 T cells. In summary, ODM-203 shows equipotent activity for both FGFR and VEGFR kinase families and antitumor activity in both FGFR and angigogenesis models.

TRPA1: a transducer and amplifier of pain and inflammation

The transient receptor potential ankyrin 1 (TRPA1) ion channel on peripheral terminals of nociceptive primary afferent nerve fibres contributes to the transduction of noxious stimuli to electrical signals, while on central endings in the spinal dorsal horn, it amplifies transmission to spinal interneurons and projection neurons. The centrally propagating nociceptive signal that is induced and amplified by TRPA1 not only elicits pain sensation but also contributes to peripheral neurogenic inflammation through a peripheral axon reflex or a centrally mediated back propagating dorsal root reflex that releases vasoactive agents from sensory neurons in the periphery. Endogenous TRPA1 agonists that are generated under various pathophysiological conditions both in the periphery and in the spinal cord have TRPA1-mediated pro-nociceptive and pro-inflammatory effects. Among endogenous TRPA1 agonists that have been shown to play a role in the pathogenesis of pain and inflammatory conditions are, for example, methylglyoxal, 4-hydroxynonenal, 12-lipoxygenase-derived hepoxilin A3, 5,6-epoxyeicosatrienoic acid and reactive oxygen species, while mustard oil and cinnamaldehyde are most commonly used exogenous TRPA1 agonists in experimental studies. Among selective TRPA1 antagonists are HC-030031, A-967079, AP-14 and Chembridge-5861528. Recent evidence indicates that TRPA1 plays a role also in transition of acute to chronic pain. Due to its location on a subpopulation of pain-mediating primary afferent nerve fibres, blocking the TRPA1 channel is expected to have antinociceptive, antiallodynic and anti-inflammatory effects.

Metabolism of oxycodone in human hepatocytes from different age groups and prediction of hepatic plasma clearance

Oxycodone is commonly used to treat severe pain in adults and children. It is extensively metabolized in the liver in adults, but the maturation of metabolism is not well understood. Our aim was to study the metabolism of oxycodone in cryopreserved human hepatocytes from different age groups (3 days, 2 and 5 months, 4 years, adult pool) and predict hepatic plasma clearance of oxycodone using these data. Oxycodone (0.1, 1, and 10 μM) was incubated with hepatocytes for 4 h, and 1 μM oxycodone also with CYP3A inhibitor ketoconazole (1 μM). Oxycodone and noroxycodone concentrations were determined at several time points with liquid chromatography–mass spectrometry. In vitro clearance of oxycodone was used to predict hepatic plasma clearance, using the well-stirred model and published physiological parameters. Noroxycodone was the major metabolite in all batches and ketoconazole inhibited the metabolism markedly in most cases. A clear correlation between in vitro oxycodone clearance and CYP3A4 activity was observed. The predicted hepatic plasma clearances were typically much lower than the published median total plasma clearance from pharmacokinetic studies. The data suggests that there are no children-specific metabolites of oxycodone. Moreover, CYP3A activity seems to be the major determinant in metabolic clearance of oxycodone regardless of age group or individual variability in hepatocyte batches.

Effects of experimental setup on the apparent concentration dependency of active efflux transport in in vitro cell permeation experiments

P-Glycoprotein mediated efflux is one of the barriers limiting drug absorption from the intestine. Predictions of the intestinal P-glycoprotein function need to take into account the concentration dependency because high intestinal drug concentrations may saturate P-glycoprotein. However, the substrate binding site of P-glycoprotein lies inside the cells and the drug concentration at the binding site cannot be measured directly. Therefore, rigorous determination of concentration dependent P-glycoprotein kinetics is challenging. In this study, the effects of the aqueous boundary layers, extracellular pH and cellular retention on the apparent saturation kinetics of P-glycoprotein mediated transport of quinidine in an in vitro cell permeation setting were explored. The changes in the experimental conditions caused 1 order of magnitude variation in the apparent affinity to P-glycoprotein (K(m,app)) and a 5-fold difference in the maximum effective P-glycoprotein mediated transport rate of quinidine (V(max,app)). However, fitting the concentration data into a compartmental model which accounted for the aqueous boundary layers, cell membranes and cellular retention suggested that the P-glycoprotein function per se was not altered, it was the differences in the passive transfer of quinidine which changed the apparent transport kinetics. These results provide further insight into the dynamics of the P-glycoprotein mediated transport and on the roles of several confounding factors involved in in vitro experimental setting. Further, the results confirm the applicability of compartmental model based data analysis approach in the determination of active transporter kinetics.

Analysis of unstirred water layer in in vitro permeability experiments

In vitro permeability experiments are used widely in drug discovery and other areas of pharmaceutical research. Much effort has been expended in developing novel epithelial models but generally much less attention has been paid to the hydrodynamic barrier in the actual experiments. The restricted liquid flow in the vicinity of solid surfaces leads to a zone where the diffusional movement of molecules exceeds the convection. This leads to formation of a concentration gradient between the bulk solution and the surface. The formed unstirred water layer (UWL) reduces the apparent permeability (P(app)) of compounds that rapidly pass through the actual epithelial layer. This lowers the resolution of P(app) versus fraction-absorbed assay, complicates the structure-permeability analysis and skews apparent kinetic parameters of transporter substrates. This review describes the techniques that can be used to determine the UWL thickness in permeability experiments and apparatuses described in the literature to control the in vitro hydrodynamics.

Effects of selective serotonin reuptake inhibitors on timolol metabolism in human liver microsomes and cryo-preserved hepatocytes

Timolol has been widely used in the treatment of glaucoma. Topically applied, timolol may cause adverse cardiovascular effects due to systemic absorption through the nasolacrimal duct. Timolol is mainly metabolized by cytochrome P450 2D6 (CYP2D6) in the liver. The aim of the present study was to characterize further the metabolism of timolol in vitro. Especially the effect of several drugs such as selective serotonin reuptake inhibitors on the metabolism of timolol was evaluated. In human liver microsomes, four timolol metabolites were identified, in cryo-preserved hepatocytes nine. In both in vitro experiments, the hydroxy metabolite M1 was the main metabolite. The in vivo half-life predicted for timolol was 3.7 hr. in cryo-preserved hepatocytes, corresponding to the half-life of timolol in humans in vivo. Fluoxetine, paroxetine, sertraline, citalopram and fluvoxamine inhibited the formation of M1 in microsomes with IC(50) values of 1.4, 2.0, 3.5, 21 and 20 microM, respectively. In human cryo-preserved hepatocytes, the IC(50) values for fluoxetine, paroxetine and fluvoxamine were 0.7, 0.5 and 5.9 microM, respectively. In conclusion, compounds known to be potent CYP2D6 inhibitors inhibited timolol metabolism in in vitro experiments. The present results strongly suggest that fluoxetine and paroxetine may significantly affect the metabolism of timolol also in vivo and may thus potentiate the adverse cardiovascular effects of topically administered timolol.

Comparison of drug transporter gene expression and functionality in Caco-2 cells from 10 different laboratories

Caco-2 cells, widely used to study carrier mediated uptake and efflux mechanisms, are known to have different properties when cultured under different conditions. In this study, Caco-2 cells from 10 different laboratories were compared in terms of mRNA expression levels of 72 drug and nutrient transporters, and 17 other target genes, including drug metabolising enzymes, using real-time PCR. The rank order of the top five expressed genes was: HPT1>GLUT3>GLUT5>GST1A>OATP-B. Rank correlation showed that for most of the samples, the gene ranking was not significantly different. Functionality of transporters and the permeability of passive transport markers metoprolol (transcellular) and atenolol (paracellular) were also compared. MDR1 and PepT1 function was investigated using talinolol and Gly-Sar transport, respectively. Sulfobromophthalein (BSP) was used as a marker for MRP2 and OATP-B functionality. Atenolol permeability was more variable across laboratories than metoprolol permeability. Talinolol efflux was observed by all the laboratories, whereas only five laboratories observed significant apical uptake of Gly-Sar. Three laboratories observed significant efflux of BSP. MDR1 expression significantly correlated to the efflux ratio and net active efflux of talinolol. PepT1 mRNA levels showed significant correlation to the uptake ratio and net active uptake of Gly-Sar. MRP2 and OATP-B showed no correlation to BSP transport parameters. Heterogeneity in transporter activity may thus be due to differences in transporter expression as shown for PepT1 and MDR1 which in turn is determined by the culture conditions. Absolute expression of genes was variable indicating that small differences in culture conditions have a significant impact on gene expression, although the overall expression patterns were similar.

Effect of N-betainate and N-piperazine derivatives of chitosan on the paracellular transport of mannitol in Caco-2 cells

The effects of novel quaternary chitosan derivatives on the paracellular transport of mannitol and cell viability were studied in the Caco-2 cell model. The N-betainate derivative with the degree of substitution of 0.05 was very effective at 1.0% (w/v) concentration. The activity decreased as the degree of substitution increased. The cytotoxicity of N-betainates was rather low. The N-piperazines were at least equally effective as the N-betainates with a similar degree of substitution (>0.15). Most of the N-piperazines did not exert toxic effects on the cell monolayers. Overall, the inverse proportionality between the degree of substitution and activity suggests that an intact chitosan backbone is essential for the bioactivity of chitosan derivatives. The quaternary group does not substitute for the activity of the free amine group. In particular, the N-betainate derivatives of chitosan should contain only the minimum number of substituents required for water solubility.

The asymmetry of the unstirred water layer in permeability experiments

PURPOSE

To elucidate the apical and basolateral components of the total unstirred water layer in regular permeability experiment.

METHODS

A novel stirring apparatus was constructed to remove the basolateral unstirred water layer. Caco-2 cells were used as the permeability barrier both in Transwell-type and side-by-side apparatuses. Permeability experiments were done with several ionisable compounds at various pH and stirring conditions. The permeabilities of the cell monolayer, the unstirred water layer and the polycarbonate filter were calculated either from experimental data or theoretically.

RESULTS

The unstirred water layer was thicker in the Transwell apparatus than in the side-by-side chamber even in the presence of vigorous basolateral magnetic stirring. Calculations indicated that the apical unstirred water layer is thicker than the basolateral layer. Different cellular permeability coefficients were obtained from the two permeability apparatuses.

CONCLUSIONS

An orbital shaker does not produce symmetric hydrodynamics in both chambers of Transwell apparatus. The asymmetric unstirred water layer may complicate the exact analysis of polarized transport.

Decrease in intracellular concentration causes the shift in Km value of efflux pump substrates

Passive permeability and active efflux are parallel processes in transcellular flux. Therefore, the observed kinetics of a transporter substrate depends on both of these factors. The transporter expression has been shown to affect both the apparent K(m) and V(max) values. Kinetic parameters can be obtained from various experimental settings, but these do not necessarily reflect the situation in transcellular flux. Kinetic absorption models need reliable estimates of saturable kinetics when accurate in silico predictions are to be made. The effect of increasing P-glycoprotein expression on apparent transport kinetics was studied using quinidine and digoxin as model compounds. The intracellular concentrations of drugs during the transport process were also measured. A dynamic simulation model was constructed to study the observed data. The apparent K(m) and V(max) values increased as the P-glycoprotein expression increased. Simulations reproduced the shift in both kinetic parameters as a function of efflux pump expression. In addition, the apparent K(m) value showed a strong inverse relationship to the passive permeability. In contrast, the apparent V(max) value reached a maximum at intermediate passive permeability and declined above and below this passive permeability. The true V(max) and K(m) values were never reached. The shift in K(m) was assigned to a decrease in intracellular concentration at the P-glycoprotein interaction site with both experimental and simulation data. In conclusion, the apparent kinetic parameters in transcellular permeability assays depend on passive permeability and efflux pump activity. Therefore, parameters that are obtained from in vitro assays should be cautiously applied to in vivo predictions.

Drug adsorption to plastic containers and retention of drugs in cultured cells under in vitro conditions

Loss of drug content during cell culture transport experiment can lead to misinterpretations in permeability analysis. This study analyses drug adsorption to various plastic containers and drug retention in cultured cells under in vitro conditions. The loss of various drugs to polystyrene tubes and well plates was compared to polypropylene and glass tubes both in deionised water and buffer solution. In cellular uptake experiments, administered drugs were obtained from cultured cells by liquid extraction. Samples were collected at various time points and drug concentrations were measured by a new HPLC-MS/MS method. Acidic drugs (hydrochlorothiazide, naproxen, probenicid, and indomethacin) showed little if any sorption to all tested materials in either water or buffer. In the case of basic drugs, substantial loss to polystyrene tubes and well plates was observed. After 4.5 h, the relative amount remaining in aqueous test solution stored in polystyrene tubes was 64.7 +/- 6.8%, 38.4 +/- 9.1%, 31.9 +/- 6.7%, and 23.5 +/- 6.1% for metoprolol, medetomidine, propranolol, and midazolam, respectively. Interestingly, there was no significant loss of drugs dissolved in buffer to any of the tested materials indicating that buffer reduced surficial interaction. The effect of drug concentration to sorption was also tested. Results indicated that the higher the concentration in the test solution the lower the proportional drug loss, suggesting that the polystyrene contained a limited amount of binding sites. Cellular uptake studies showed considerable retention of drugs in cultured cells. The amounts of absorbed drugs in cellular structures were 0.45%, 4.88%, 13.15%, 43.80%, 23.57% and 11.22% for atenolol, metoprolol, medetomidine, propranolol, midazolam, and diazepam, respectively. Overall, these findings will benefit development and validation of further in vitro drug permeation experiments.

Metabolic and Efflux Properties of Caco-2 Cells Stably Transfected with Nuclear Receptors

PURPOSE

To characterise in detail the patterns of expression and functional activities of CYP and efflux pump genes in Caco-2 cells stably transfected with human Pregnane X Receptor or murine Constitutive Androstane Receptor.

MATERIALS AND METHODS

Cell lines transfected with nuclear receptors were treated with established ligands, and gene expression of CYP and efflux pump genes were quantified by qRT-PCR and Western blot. P-glycoprotein activity was assessed by measuring calcein-AM accumulation and bidirectional permeability coefficients of digoxin and quinidine. CYP activities were measured with both fluorescent and non-fluorescent substrates.

RESULTS

hPXR and mCAR upregulated some CYP and efflux pump genes ligand dependently. P-glycoprotein level was increased, but CYP3A4 protein remained below the limit of detection. P-glycoprotein activity was markedly elevated in Caco/mCAR cells and more modestly in Caco/hPXR cells. CYP3A4 activity remained lower than that in vitamin D-treated Caco-2 cells.

CONCLUSIONS

Nuclear receptors can modulate the expression of metabolic genes in Caco-2 cells, but the overall level of metabolism could not be efficiently controlled. P-glycoprotein activity increased, but CYP activities remained very low.

Absorption properties and P-glycoprotein activity of modified Caco-2 cell lines

Caco-2 cell line is extensively used as an in vitro model in studying small intestinal absorption but it lacks proper expression of efflux pumps and cytochrome P450 enzymes that are involved in absorption and first pass metabolism of drugs. We created two novel Caco-2 cell lines expressing orphan nuclear receptors pregnane X receptor and constitutive androstane receptor that regulate many genes involved in xenobiotic metabolism. We conducted a systematic study on expression of some metabolic genes, P-glycoprotein activity and absorption properties of several drugs with these new cell lines and previously described modified Caco-2 cell lines (MDR1 transfection, vincristine treatment and 1alpha,25-dihydroxyvitamin D3 treatment). A short culture time medium was also included in the study. Most modified cell lines formed tight differentiated monolayers. MDR1, CYP2C9 and CYP3A4 genes were upregulated in some cell lines. Elevated P-glycoprotein activities were observed by calcein-AM uptake experiments but this did not affect significantly the permeability of selected P-glycoprotein substrates. Some cell lines had similar passive and active permeability properties to Caco/WT cells while in few cell lines these were altered. Passive transcellular permeability was modestly elevated in all modified cell lines. In addition, several compounds showed pH-dependent permeability properties.

Effect of temporin A modifications on its cytotoxicity and antimicrobial activity

Temporin A (TA), a short alpha-helical antimicrobial peptide isolated from the skin of the frog Rana temporaria, is effective against a broad spectrum of Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium strains. TA interacts directly with the cell membrane of the microorganism and it has been reported to be non-toxic to erythrocytes at concentrations that are antimicrobial. Less is known about the effects on the viability and growth of nucleated eukaryotic cells. In this study we have tested antibacterial and growth-inhibitory properties of TA, its dimeric analogue (TAd), and all-L (TAL L512) and all-D (TAD L512) enantiomeric derivatives of modified TA towards S. aureus and cultured human keratinocytes, respectively. All molecules were antibacterial at concentrations from 1.5 microM to 10 microM. In keratinocyte cultures, TAD L512, as well as TAd, showed cytotoxicity. The original TA and TAL L512 did not affect the viability of the cells at their bacteriolytic concentrations. The growth of keratinocytes in low- and high-calcium media was only slightly inhibited by temporins at concentrations which were antibacterial to S. aureus. This suggests that original TA and its modification, TAL L512, are promising molecules against multiresistant bacterial infections.

Synthesis and antimicrobial activity of the symmetric dimeric form of Temporin A based on 3-N,N-di(3-aminopropyl)amino propanoic acid as the branching unit

Dimeric derivative of antimicrobial peptide amide Temporin A (TA) was synthesized by using a new branching unit 3-N,N-di(3-aminopropyl)amino propanoic acid (DAPPA), which allows building of the parallelly symmetric alpha-helical structures. Antimicrobial effect of the original peptide amide, its monomeric carboxy (TAc) and novel dimeric (TAd) analogues were tested against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). Both TA and TAd completely inhibited the growth of S. aureus at the concentrations of 5 and 10 microM, respectively, whereas TAc did not show any inhibitory activity. The activities of TAc, TA and TAd correlate directly with the net charges of the molecules, +1, +2 and +4, respectively. Interestingly, TAd displayed antibacterial effect against E. coli at a concentration of 10 microM, where as monomeric TA did not show any activity at concentration as high as 20 microM. The results indicate that the novel structural modification improves the antibacterial properties of Temporin A especially towards Gram-negative bacteria.