Consideration of Fractional Distribution Parameter fd in the Chen and Gross Method for Tissue-to-Plasma Partition Coefficients: Comparison of Several Methods.

PURPOSE: The tissue-to-plasma partition coefficient (Kp) describes the extent of tissue distribution in physiologically-based pharmacokinetic (PBPK) models. Constant-rate infusion studies are common for experimental determination of the steady-state Kp,ss, while the tissue-plasma concentration ratio (CT/Cp) in the terminal phase after intravenous doses is often utilized. The Chen and Gross (C&G) method converts a terminal slope CT/Cp to Kp,ss based on assumptions of perfusion-limited distribution in tissue-plasma equilibration. However, considering blood flow (QT) and apparent tissue permeability (fupPSin) in the rate of tissue distribution, this report extends the C&G method by utilizing a fractional distribution parameter (fd). METHODS: Relevant PBPK equations for non-eliminating and eliminating organs along with lung and liver were derived for the conversion of CT/Cp values to Kp,ss. The relationships were demonstrated in rats with measured CT/Cp and Kp,ss values and the model-dependent fd for 8 compounds with a range of permeability coefficients. Several methods of assessing Kp were compared. RESULTS: Utilizing fd in an extended C&G method, our estimations of Kp,ss from CT/Cp were improved, particularly for lower permeability compounds. However, four in silico methods for estimating Kp performed poorly across tissues in comparison with measured Kp values. Mathematical relationships between Kp and Kp,ss that are generally applicable for eliminating organs with tissue permeability limitations necessitates inclusion of an extraction ratio (ER) and fd. CONCLUSION: Since many different types/sources of Kp are present in the literature and used in PBPK models, these perspectives and equations should provide better insights in measuring and interpreting Kp values in PBPK.

Crystal structures of human NSDHL and development of its novel inhibitor with the potential to suppress EGFR activity.

NAD(P)-dependent steroid dehydrogenase-like (NSDHL), an essential enzyme in human cholesterol synthesis and a regulator of epidermal growth factor receptor (EGFR) trafficking pathways, has attracted interest as a therapeutic target due to its crucial relevance to cholesterol-related diseases and carcinomas. However, the development of pharmacological agents for targeting NSDHL has been hindered by the absence of the atomic details of NSDHL. In this study, we reported two X-ray crystal structures of human NSDHL, which revealed a detailed description of the coenzyme-binding site and the unique conformational change upon the binding of a coenzyme. A structure-based virtual screening and biochemical evaluation were performed and identified a novel inhibitor for NSDHL harboring suppressive activity towards EGFR. In EGFR-driven human cancer cells, treatment with the potent NSDHL inhibitor enhanced the antitumor effect of an EGFR kinase inhibitor. Overall, these findings could serve as good platforms for the development of therapeutic agents against NSDHL-related diseases.

Development and Validation of Analytical Method for SH-1242 in the Rat and Mouse Plasma by Liquid Chromatography/Tandem Mass Spectrometry.

SH-1242, a novel inhibitor of heat shock protein 90 (HSP90), is a synthetic analog of deguelin: It was previously reported that the treatment of SH-1242 led to a strong suppression of hypoxia-mediated retinal neovascularization and vascular leakage in diabetic retinas by inhibiting the hypoxia-induced upregulation of expression in hypoxia-inducible factor 1α (HIF-1ɑ) and vascular endothelial growth factor (VEGF). In this study, an analytical method for the quantification of SH-1242 in biological samples from rats and mice was developed/validated for application in pharmacokinetic studies. SH-1242 and deguelin, an internal standard of the assay, in plasma samples from the rodents were extracted with methanol containing 0.1% formic acid and analyzed at m/z transition values of 368.9→151.0 and 395.0→213.0, respectively. The method was validated in terms of accuracy, precision, dilution, matrix effects, recovery, and stability and shown to comply with validation guidelines when it was used in the concentration ranges of 1-1000 ng/mL for rat plasma and of 2-1000 ng/mL for mouse plasma. SH-1242 levels in plasma samples were readily determined using the developed method for up to 480 min after the intravenous administration of 0.1 mg/kg SH-1242 to rats and for up to 120 min to mice. These findings suggested that the current method was practical and reliable for pharmacokinetic studies on SH-1242 in preclinical animal species.

Suppression of Canine ATP Binding Cassette ABCB1 in Madin-Darby Canine Kidney Type II Cells Unmasks Human ABCG2-Mediated Efflux of Olaparib.

Endogenous canine ATP binding cassette B1 (cABCB1) is expressed abundantly in Madin-Darby canine kidney type II (MDCKII) cells, and its presence often complicates phenotyping of the transport process. Errors in estimating the corrected efflux ratio (cER), as a result of the variable expression of cABCB1, were examined for the dual substrates of ABCB1 and ABCG2 in MDCKII cells expressing human ABCG2 (hABCG2). cABCB1 mRNA and protein expression was 60% and 55% lower, respectively, in MDCKII cells expressing hABCG2 compared with the wild type, suggesting that the expression of endogenous cABCB1 became variable after the expression of hABCG2. To minimize the contribution of endogenous efflux, cABCB1 was suppressed kinetically (using verapamil as a selective inhibitor) or biochemically (transfecting short-hairpin RNA against cABCB1). Under these suppression conditions, cER values for irinotecan and topotecan (dual substrates of ABCB1 and ABCG2) were elevated by more than 4-fold and 2-fold, respectively, compared with cER values without the suppression. The cER of olaparib was similarly increased to 3- and 5-fold in MDCKII cells under the kinetic and biochemical suppression of cABCB1, respectively, suggesting that hABCG2-mediated efflux cannot be ruled out for olaparib. Since the substrate selectivity for ABCB1 and ABCG2 overlapped considerably, the possibility of an inaccurate estimation of cER must be considered for dual substrates in the case of the variable expression of cABCB1 in MDCKII cells.

Z-ligustilide and n-Butylidenephthalide Isolated from the Aerial Parts of Angelica tenuissima Inhibit Lipid Accumulation In Vitro and In Vivo.

Abnormal lipid metabolism, such as increased fatty acid uptake and esterification, is associated with nonalcoholic fatty liver disease (NAFLD). The aqueous extract of the aerial part of Angelica tenuissima Nakai (ATX) inhibited high-fat diet-induced hepatic steatosis in mice as well as oleic acid-induced neutral lipid accumulation in HepG2 cells. ATX decreased the mRNA and protein levels of CD36 and diglyceride acyltransferase 2 (DGAT2), the maturation of sterol regulatory element-binding proteins (SREBP), and the expression of the lipogenic target genes fasn and scd1. The ATX components, Z-ligustilide and n-butylidenephthalide, inhibited the expression of FATP5 and DGAT2 and thus oleic acid-induced lipid accumulation in HepG2 cells. These results suggest that ATX and its active components Z-ligustilide and n-butylidenephthalide inhibit fatty acid uptake and esterification in mice and have potential as therapeutics for NAFLD.

Specific Inhibition of the Distribution of Lobeglitazone to the Liver by Atorvastatin in Rats: Evidence for a Rat Organic Anion Transporting Polypeptide 1B2-Mediated Interaction in Hepatic Transport.

Cytochrome P450 enzymes and human organic anion transporting polypeptide (OATP) 1B1 are reported to be involved in the pharmacokinetics of lobeglitazone (LB), a new peroxisome proliferator-activated receptor γ agonist. Atorvastatin (ATV), a substrate for CYP3A and human OATP1B1, is likely to be coadministered with LB in patients with the metabolic syndrome. We report herein on a study of potential interactions between LB and ATV in rats. When LB was administered intravenously with ATV, the systemic clearance and volume of distribution at steady state for LB remained unchanged (2.67 ± 0.63 ml/min per kg and 289 ± 20 ml/kg, respectively), compared with that of LB without ATV (2.34 ± 0.37 ml/min per kg and 271 ± 20 ml/kg, respectively). Although the tissue-to-plasma partition coefficient (Kp) of LB was not affected by ATV in most major tissues, the liver Kp for LB was decreased by ATV coadministration. Steady-state liver Kp values for three levels of LB were significantly decreased as a result of ATV coadministration. LB uptake was inhibited by ATV in rat OATP1B2-overexpressing Madin-Darby canine kidney cells and in isolated rat hepatocytes in vitro. After incorporating the kinetic parameters for the in vitro studies into a physiologically based pharmacokinetics model, the characteristics of LB distribution to the liver were consistent with the findings of the in vivo study. It thus appears that the distribution of LB to the liver is mediated by the hepatic uptake of transporters such as rat OATP1B2, and carrier-mediated transport is involved in the liver-specific drug-drug interaction between LB and ATV in vivo.

A Complete Extension of Classical Hepatic Clearance Models Using Fractional Distribution Parameter fd in Physiologically Based Pharmacokinetics.

The classical organ clearance models have been proposed to relate the plasma clearance CLp to probable mechanism(s) of hepatic clearance. However, the classical models assume the intrinsic capability of drug elimination (CLu,int) that is physically segregated from the vascular blood but directly acts upon the unbound drug concentration in the blood (fubCavg), and do not handle the transit-time delay between the inlet/outlet concentrations in their closed-form clearance equations. Therefore, we propose unified model structures that can address the internal blood concentration patterns of clearance organs in a more mechanistic/physiological manner, based on the fractional distribution parameter fd operative in PBPK. The basic partial/ordinary differential equations for four classical models are revisited/modified to yield a more complete set of extended clearance models, i.e., the Rattle, Sieve, Tube, and Jar models, which are the counterparts of the dispersion, series-compartment, parallel-tube, and well-stirred models. We demonstrate the feasibility of applying the resulting extended models to isolated perfused rat liver data for 11 compounds and an example dataset for in vitro-in vivo extrapolation of the intrinsic to the systemic clearances. Based on their feasibilities to handle such real data, these models may serve as an improved basis for applying clearance models in the future.

Cerebrospinal Fluid Pharmacokinetics of Nicardipine Following Intrathecal Administration in Subarachnoid Hemorrhage Patients.

Subarachnoid hemorrhage (SAH) is a devastating type of stroke, leading to high mortality and morbidity rates. Cerebral vasospasm and delayed cerebral ischemia (DCI) are common complications following SAH that contribute significantly to the poor outcomes observed in these patients. Intrathecal (IT) nicardipine delivered via an existing external ventricular drain is an off-label intervention that has been shown to be correlated with reduced DCI and improved patient outcomes. The current study aims to characterize the population pharmacokinetic (popPK) properties of intermittent IT nicardipine. Following informed consent, serial cerebrospinal fluid (CSF) samples were obtained from 16 SAH patients (50.4 ± 9.3 years old; 13 females) treated with IT nicardipine every 6 h (q6h, n = 8) or every 8 h (q8h, n = 8) for an average of 72 ± 21 doses. High-performance liquid chromatography was used to quantify CSF concentration from each sample. Our popPK analysis showed that the CSF pharmacokinetics of IT nicardipine in the cohort was adequately described by a two-compartment model with a lag time. Model parameter estimates were reliable (relative standard error <50%). Intracranial pressure influenced both the total clearance and the central volume of nicardipine (i.e., negative correlation, P <-.001). Calculated PK parameters were similar between q6h and q8h dosing regimens. Despite a small cohort of SAH patients, we successfully developed a popPK model to describe the nicardipine disposition kinetics in the CSF following IT administration. These findings may help inform future clinical trials designed to examine the optimal dosing of IT nicardipine.

Theoretical Examination Seeking Tangible Physical Meanings of Slopes and Intercepts of Plasma Concentration-Time Relationships in Minimal Physiologically Based Pharmacokinetic Models.

In minimal physiologically based pharmacokinetic (mPBPK) models, physiological (e.g., cardiac output) and anatomical (e.g., blood/tissue volumes) variables are utilized in the domain of differential equations (DEs) for mechanistic understanding of the plasma concentration-time relationships [Formula: see text]. Although fundamental biopharmaceutical variables in terms of distribution (e.g., [Formula: see text] and [Formula: see text]) and elimination kinetics (e.g., [Formula: see text]) in mPBPK provide greater insights in comparison to classical compartment models, an absence of kinetic elucidation of slopes and intercepts in light of such DE model parameters hinders more intuitive appreciation of [Formula: see text]. Therefore, this study seeks the tangible physical meanings of slopes and intercepts of the plasma concentration-time relationships in one- and two-tissue mPBPK models (i.e., m2CM and m3CM), with respect to time parameters that are readily understandable in PK analyses, i.e., the mean residence ([Formula: see text]) and transit ([Formula: see text]) times. Utilizing the explicit equations (EEs) for the slopes, intercepts, and areas of each exponential phase in the m2CM and m3CM, we theoretically and numerically examined the limiting/boundary conditions of such kinetic properties, based on the ratio of the longest tissue [Formula: see text] to the [Formula: see text] in the body (i.e., [Formula: see text]) that is useful for dissecting complex PBPK systems. The kinetic contribution of the area of each exponential phase to the total drug exposure was assessed to identify the elimination phase between the terminal and non-terminal phases of the [Formula: see text] in the m2CM and m3CM. This assessment provides improved understanding of the complexities inherent in all PBPK profiles and models.

Cerebrospinal Fluid Pharmacokinetics of Nicardipine Following Intrathecal Administration in Subarachnoid Hemorrhage Patients.

Subarachnoid hemorrhage (SAH) is a devastating type of stroke, leading to high mortality and morbidity rates. Cerebral vasospasm and delayed cerebral ischemia (DCI) are common complications following SAH and contribute significantly to the poor outcomes observed in these patients. Intrathecal (IT) nicardipine delivered via an existing external ventricular drain has been shown to be correlated with reduced DCI and improved patient outcomes. The current study aims to characterize population pharmacokinetic (popPK) properties of intermittent IT nicardipine. Following informed consent, serial cerebrospinal fluid (CSF) samples were obtained from 16 SAH patients (50.4 ± 9.3 years old; 12 females) treated with IT nicardipine every 6 hours (n=8) or every 8 hours (n=8), which were subject to high-performance liquid chromatography for measurement of its CSF concentration. Our popPK analysis showed that the CSF PK of IT nicardipine in the cohort was adequately described by a two-compartment model with a lag time, with reliable parameter estimates (relative standard error < 50%). The intracranial pressure influenced both the total clearance and the central volume. Calculated PK parameters were similar between q6h and q8h dosing regimens. Despite a small cohort of SAH patients, we successfully developed a popPK model to describe the nicardipine disposition kinetics in the CSF following IT administration. These findings may help inform future clinical trials designed to examine the optimal dosing of IT nicardipine.

Determinants of Biological Half-Lives and Terminal Slopes in Physiologically Based Pharmacokinetic Systems: Assessment of Limiting Conditions.

In pharmacokinetic (PK) analyses, the biological half-life T1/2 is usually determined in the terminal phase after drug administration, which is readily calculated from the relationship T1/2 = ln2/λz where λz is the terminal-phase slope obtainable from non-compartmental analysis (NCA). Since kinetic understanding of λz has been limited to the theory of a one-compartment model, this study seeks kinetic determinants of λz in more complex plasma concentration-time profiles. We utilized physiologically based pharmacokinetic (PBPK) systems that are consistent with the assumptions of NCA (e.g., linear PK and elimination occurring from plasma) to interrelate λz and disposition kinetic parameters of PBPK models. In a mammillary form of PBPK models, the two boundary conditions of λz are the inverses of the mean residence time in the body (1/MRTB = CL/VSS) and the mean transit time through the kinetically largest tissue (1/MTTmax = QTfdRb/VTKp). Importantly, the limiting conditions of λz between 1/MRTB and 1/MTTmax are dependent on a simple product MRTBλz (Pdet) and a simple ratio MTTmax/MRTB (Kdet), leading to introduction of the unitless product-ratio plot for determination of the limiting condition of λz in linear PK. We found that the MRTBλz value of 0.5 serves as a practical threshold determining whether λz is more closely associated with 1/MRTB or 1/MTTmax. The current theory was applied for assessment of the terminal slope λz for observed PK data of various compounds in man and rat.

Determination of the Number of Tissue Groups of Kinetically Distinct Transit Time in Whole-Body Physiologically Based Pharmacokinetic (PBPK) Models I: Theoretical Consideration of Bottom-Up Approach of Lumping Tissues in Whole-Body PBPK.

Minimal physiologically based pharmacokinetic (mPBPK) models, consisting of system-specific (e.g., tissue volume and blood flow) and drug-related (e.g., tissue-to-plasma partition coefficient) parameters, are practically useful for pharmacokinetic analyses. However, biopharmaceutical principles were not clear on how peripheral tissues, adopted in whole-body physiologically based pharmacokinetic (WB-PBPK) models, could be kinetically consolidated into one or two tissue groups in the mPBPK models. In this theoretical examination, we studied the relationship between the progressive tissue lumping in the direction from the longest mean transit time (MTTmax) to the shorter one(s) and the slopes of the terminal (λter)/distributional phases, assuming tissues with comparable MTTs are kinetically combined. The appropriateness of lumping was ascertained by evaluating the impact of difference in tissue MTTs during the lumping on the analytical solution of WB-PBPK models. We found that the ratio of MTTmax to the mean residence time in the body, viz., Kdet, is related to the change in λter by the progressive lumping and can serve as an index for the robustness of λter. Calculations with two extreme cases revealed that, for caffeine at Kdet < 0.03, the change in λter was minimal even when all peripheral tissues were collectively lumped, whereas for artesunic acid at Kdet > 50, the tissue of MTTmax could not be kinetically combined even with the tissue having the second-longest MTT without significantly affecting λter. Therefore, we proposed Kdet as an index for the robustness of λter during tissue lumping and for the number of tissue groups with distinct transit times in WB-PBPK.

Determination of the Number of Tissue Groups of Kinetically Distinct Transit Time in Whole-Body Physiologically Based Pharmacokinetic (PBPK) Models II: Practical Application of Tissue Lumping Theories for Pharmacokinetics of Various Compounds.

In our companion paper, we described the theoretical basis for tissue lumping in whole-body physiologically based pharmacokinetic (WB-PBPK) models and found that Kdet, a coefficient for determining the number of tissue groups of distinct transit time in WB-PBPK models, was related to the fractional change in the terminal slope (FCT) when tissues were progressively lumped from the longest transit time to shorter ones. This study was conducted to identify the practical threshold of Kdet by applying the lumping theory to plasma/blood concentration-time relationships of 113 model compounds collected from the literature. We found that drugs having Kdet < 0.3 were associated with FCT < 0.1 even when all peripheral tissues were lumped, resulting in comparable plasma concentration-time profiles between one-tissue minimal PBPK (mPBPK) and WB-PBPK models. For drugs with Kdet ≥ 1, WB-PBPK profiles appeared similar with two-tissue mPBPK models by applying the rule of FCT < 0.1 for lumping slowly equilibrating tissues. The two-tissue mPBPK model also appeared appropriate in terms of concentration-time profiles for drugs with 0.3 ≤ Kdet < 1, although, some compounds (15.9% of the total cases), but not all, in this range showed a slight (maximum of 18.9% of the total AUC) deviation from WB-PBPK models, indicating that the two-tissue model, with caution, could still be used for those cases. Comparison of kinetic parameters between traditional (model-fitting) and current (theoretical calculation) mPBPK analyses revealed their significant correlations. Collectively, these observations suggest that the number of tissue groups could be determined based on the Kdet/FCT criteria, and plasma concentration-time profiles from WB-PBPK could be calculated using equations significantly less complex.

Prediction of Pharmacokinetics of IDP-73152 in Humans Using Physiologically-Based Pharmacokinetics.

IDP-73152, a novel peptide deformylase inhibitor with an antibacterial effect against Gram-positive bacteria, is in phase I development. The objective of this study was to develop a physiologically-based pharmacokinetic model (PBPK) for IDP-73152 in animals, and to extend the model to humans. Biopharmaceutical properties of IDP-73152 are determined using in vitro/in vivo experimentations for the PBPK model. A transit model consisting of gastrointestinal segments is applied for an estimation of the intestinal absorption kinetics. The PBPK model of IDP-73152 in rats is able to appropriately predict the plasma concentration-time profiles after the administration of IDP-73152 at different doses and by different routes (combined absolute average fold error (cAAFE), 1.77). The model is also found to be adequate in predicting the plasma concentration-time profiles of IDP-73152 in mice (cAAFE 1.59) and dogs (cAAFE 1.42). Assuming the oral administration of IDP-73152 to humans at doses of 640 and 1280 mg, the model is able to reproduce the concentration-time profiles obtained in humans (cAAFE 1.38); therefore, these observations indicate that the PBPK model used for IDP-73152 is applicable to animal species and humans. This model may be useful in predicting efficacious doses of IDP-73152 for the management of infectious disease in humans.

Metronomic dose-finding approach in oral chemotherapy by experimentally-driven integrative mathematical modeling.

In conventional chemotherapy, maximum tolerated dose approach is considered as a first-line medication for cancer treatment in clinics. In contrast to the conventional chemotherapy which has heavy tumor burdens arising from high dose treatment, metronomic chemotherapy (MCT) engages relatively low dose without drug-free breaks, and is recognized as a promising strategy for a long-term management of the disease. Although doxorubicin (DOX), an anthracycline anti-cancer drug, showed a potential of maintenance effect in vitro, further study on in vivo-relevant concentration to achieve tumor suppression with no toxicity is required to apply the MCT in clinicals. Therefore, the objective of this study was to identify an optimal MCT regimen of DOX by determining concentration-response relationships of tumor suppression (pharmacodynamic; PD) and cardiac toxicity (toxicodynamic; TD). Utilizing an oral DOX formulation complexed with deoxycholic acid (DOX/DOCA complex) which has enhanced bioavailability, physiologically-based pharmacokinetic (PBPK) model was linked to TD and PD models to generate drug profiles from the combined PK, TD, and PD parameters. The integrated model was validated for various scenarios of administration route, formulation, dose, and frequency. The established mathematical model facilitated calculations of adequate in vivo-relevant dosages and intervals, suggesting the optimum oral metronomic regimen of DOX. It is expected to serve as a useful guideline for the design and evaluation of oral DOX formulations in future preclinical/clinical studies.

Meta-Assessment of Metformin Absorption and Disposition Pharmacokinetics in Nine Species.

The objective of this study was to systematically assess literature datasets and quantitatively analyze metformin PK in plasma and some tissues of nine species. The pharmacokinetic (PK) parameters and profiles of metformin in nine species were collected from the literature. Based on a simple allometric scaling, the systemic clearances (CL) of metformin in these species highly correlate with body weight (BW) (R2 = 0.85) and are comparable to renal plasma flow in most species except for rabbit and cat. Reported volumes of distribution (VSS) varied appreciably (0.32 to 10.1 L/kg) among species. Using the physiological and anatomical variables for each species, a minimal physiologically based pharmacokinetic (mPBPK) model consisting of blood and two tissue compartments (Tissues 1 and 2) was used for modeling metformin PK in the nine species. Permeability-limited distribution (low fd1 and fd2) and a single tissue-to-plasma partition coefficient (Kp) value for Tissues 1 and 2 were applied in the joint mPBPK fitting. Nonlinear regression analysis for common tissue distribution parameters along with species-specific CL values reasonably captured the plasma PK profiles of metformin across most species, except for rat and horse with later time deviations. In separate fittings of the mPBPK model to each species, Tissue 2 was considered as slowly-equilibrating compartment consisting of muscle and skin based on in silico calculations of the mean transit times through tissues. The well-fitted mPBPK model parameters for absorption and disposition PK of metformin for each species were compared with in vitro/in vivo results found in the literature with regard to the physiological details and physicochemical properties of metformin. Bioavailability and absorption rates decreased with the increased BW among the species. Tissues such as muscle dominate metformin distribution with low permeability and partitioning while actual tissue concentrations found in rats and mice show likely transporter-mediated uptake in liver, kidney, and gastrointestinal tissues. Metformin has diverse pharmacologic actions, and this assessment revealed allometric relationships in its absorption and renal clearance but considerable variability in actual and modeled tissue distribution probably caused by transporter differences.

Effects of 1α,25-Dihydroxyvitamin D3 on the Pharmacokinetics of Procainamide and Its Metabolite N-Acetylprocainamide, Organic Cation Transporter Substrates, in Rats with PBPK Modeling Approach.

In this study, possible changes in the expression of rat organic cationic transporters (rOCTs) and rat multidrug and toxin extrusion proteins (rMATEs) following treatment with 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) were investigated. Rats received intraperitoneal administrations of 1,25(OH)2D3 for four consecutive days, and the tissues of interest were collected. The mRNA expression of rOCT1 in the kidneys was significantly increased in 1,25(OH)2D3-treated rats compared with the control rats, while the mRNA expressions of rOCT2 and rMATE1 in the kidneys, rOCT1 and N-acetyltransferase-II (NAT-II) in the liver, and rOCT3 in the heart were significantly decreased. Changes in the protein expression of hepatic rOCT1 and renal rOCT2 and rMATE1 were confirmed by western blot analysis. We further evaluated the pharmacokinetics of procainamide (PA) hydrochloride and its major metabolite N-acetyl procainamide (NAPA) in the presence of 1,25(OH)2D3. When PA hydrochloride was administered intravenously at a dose 10 mg/kg to 1,25(OH)2D3-treated rats, a significant decrease in renal and/or non-renal clearance of PA and NAPA was observed. A physiological model for the pharmacokinetics of PA and NAPA in rats was useful for linking changes in the transcriptional and translational expressions of rOCTs and rMATE1 transporters to the altered pharmacokinetics of the drugs.

Development of Physiologically Based Pharmacokinetic Model for Orally Administered Fexuprazan in Humans.

Fexuprazan is a new drug candidate in the potassium-competitive acid blocker (P-CAB) family. As proton pump inhibitors (PPIs), P-CABs inhibit gastric acid secretion and can be used to treat gastric acid-related disorders such as gastroesophageal reflux disease (GERD). Physiologically based pharmacokinetic (PBPK) models predict drug interactions as pharmacokinetic profiles in biological matrices can be mechanistically simulated. Here, we propose an optimized and validated PBPK model for fexuprazan by integrating in vitro, in vivo, and in silico data. The extent of fexuprazan tissue distribution in humans was predicted using tissue-to-plasma partition coefficients in rats and the allometric relationships of fexuprazan distribution volumes (VSS) among preclinical species. Urinary fexuprazan excretion was minimal (0.29-2.02%), and this drug was eliminated primarily by the liver and metabolite formation. The fraction absorbed (Fa) of 0.761, estimated from the PBPK modeling, was consistent with the physicochemical properties of fexuprazan, including its in vitro solubility and permeability. The predicted oral bioavailability of fexuprazan (38.4-38.6%) was within the range of the preclinical datasets. The Cmax, AUClast, and time-concentration profiles predicted by the PBPK model established by the learning set were accurately predicted for the validation sets.

Investigation of the Factors Responsible for the Poor Oral Bioavailability of Acacetin in Rats: Physicochemical and Biopharmaceutical Aspects.

Acacetin, an important ingredient of acacia honey and a component of several medicinal plants, exhibits therapeutic effects such as antioxidative, anticancer, anti-inflammatory, and anti-plasmodial activities. However, to date, studies reporting a systematic investigation of the in vivo fate of orally administered acacetin are limited. Moreover, the in vitro physicochemical and biopharmaceutical properties of acacetin in the gastrointestinal (GI) tract and their pharmacokinetic impacts remain unclear. Therefore, in this study, we aimed to systematically investigate the oral absorption and disposition of acacetin using relevant rat models. Acacetin exhibited poor solubility (≤119 ng/mL) and relatively low stability (27.5-62.0% remaining after 24 h) in pH 7 phosphate buffer and simulated GI fluids. A major portion (97.1%) of the initially injected acacetin dose remained unabsorbed in the jejunal segments, and the oral bioavailability of acacetin was very low at 2.34%. The systemic metabolism of acacetin occurred ubiquitously in various tissues (particularly in the liver, where it occurred most extensively), resulting in very high total plasma clearance of 199 ± 36 mL/min/kg. Collectively, the poor oral bioavailability of acacetin could be attributed mainly to its poor solubility and low GI luminal stability.

A novel small molecule STAT3 inhibitor SLSI-1216 suppresses proliferation and tumor growth of triple-negative breast cancer cells through apoptotic induction.

Triple-negative breast cancer (TNBC) is the most aggressive type of breast cancer, characterized by the lack of expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Owing to the absence of molecular targets, there are limited treatment options, and TNBC patients exhibit high mortality rates. Signal transducer and activator of transcription 3 (STAT3) is overexpressed and aberrantly activated in TNBC cells. Therefore, inhibition of STAT3-mediated signaling provides a potential strategy for the treatment of TNBC. In this study, A series of synthetic derivatives of SLSI-1 (a STAT3 inhibitor) were designed and evaluated for antitumor activity in TNBC cells. A novel derivative (SLSI-1216) exhibited the most potent anti-proliferative activity. SLSI-1216 effectively inhibited STAT3 activity and activation of STAT3, leading to the downregulation of AXL, a downstream target of STAT3 and epithelial-mesenchymal transition (EMT) progression. The inhibition of EMT by SLSI-1216 was associated with modulation of E-cadherin and N-cadherin. Furthermore, SLSI-1216 induced apoptosis by targeting STAT3 and effectively inhibited tumor growth in vivo. These findings suggest that SLSI-1216, as a potential inhibitor of STAT3, may be a promising therapeutic agent for TNBC.