Noriyuki Takata

Prediction of passive intestinal absorption using bio-mimetic artificial membrane permeation assay and the paracellular pathway model

The purpose of this study was to construct and examine the prediction model for total passive permeation through the intestinal membrane. The paracellular pathway prediction model based on Renkin function (PP-RF) was combined with a bio-mimetic artificial membrane permeation assay (BAMPA), which is an in vitro method to predict transcellular pathway permeation, to construct the prediction model (BAMPA-PP-RF model). The parameters of the BAMPA-PP-RF model, e.g. apparent pore radius and potential drop of the paracellular pathway, were calculated from BAMPA permeability, the dissociation constant, the molecular radius and the fraction of a dose absorbed in humans consisting of 80 structurally diverse compounds. The apparent pore radius and the apparent potential drop obtained in this study were 5.61-5.65 A and 75-86 mV, respectively, and these were in accordance with the previously reported values. The mean square root error of the BAMPA-PP-RF model was 13-14%. The BAMPA-PP-RF model was shown to be able to predict the total passive permeability more adequately than BAMPA alone.

Rate-Limiting Steps of Oral Absorption for Poorly Water-Soluble Drugs in Dogs; Prediction from a Miniscale Dissolution Test and a Physiologically-Based Computer Simulation

ABSTRACTPurposeNonlinear oral absorption due to poor solubility often impedes drug development. The purpose of this study was to elucidate the rate-limiting process in oral absorption of Biopharmaceutical Classification System (BCS) class II (low solubility–high permeability) drugs in order to predict nonlinear absorption of dose caused by solubility-limited absorption.MethodsOral absorption of danazol, griseofulvin, and aprepitant was predicted from a miniscale dissolution test and a physiologically-based model. The effect of particle size reduction and dose increase on absorption was investigated in vitro and in vivo to clarify the rate-limiting steps of dissolution-rate-limited and solubility-limited absorption.ResultsThe rate-limiting steps of oral absorption were simulated and increase in the dissolution rate and administration dose showed a shift from dissolution rate-limited to solubility-limited absorption. In the study in dogs, particle size reduction improved the oral absorption of large particle drugs but had little effect on small particle drugs. Dose nonlinearity was observed with small particles at a high dose. Our model quantitatively predicted results observed in vivo, including but not exclusively, dissolution-rate-limited and solubility-limited absorption.ConclusionThe present study provides a powerful tool to predict dose nonlinearity and will aid in the success of BCS class II drug development.

Correction of Permeability with Pore Radius of Tight Junctions in Caco-2 Monolayers Improves the Prediction of the Dose Fraction of Hydrophilic Drugs Absorbed by Humans

AbstractPurpose. To improve predictions of fraction dose absorbed (Fa) for hydrophilic drugs, a correction of paracellular permeability using the pore radius of tight junctions (TJs) in Caco-2 monolayers was performed. Methods. The apparent permeability coefficient (Papp) of drugs was measured using the Caco-2 assay and the parallel artificial membrane permeation assay (PAMPA), and values were corrected with the pore radius of TJs. Results. An equation for calculating the pore radius of TJs from the Papp of lucifer yellow was obtained. The optimal pore radius of TJs in Caco-2 monolayers for predicting human Fa was calculated to be 7 Å. The correlation between the actual and predicted Fa was improved by using the Papp corrected with the pore radius of TJs. Permeability in the PAMPA, which was corrected using the pore radius and membrane potential, was well correlated with that in the Caco-2 assay. Most of the hydrophilic drugs tested in this study were absorbed mainly through the paracellular pathway. Conclusions. The results suggest the necessity of optimizing paracellular permeation for the prediction of Fa, and also the importance of the paracellular pathway to the absorption of hydrophilic drugs. This method might contribute to the setting of appropriate dosages and the development of hydrophilic drugs.

Quantitative Analysis of the Effect of Supersaturation on in Vivo Drug Absorption

The purpose of this study is to clarify the effects of intestinal drug supersaturation on solubility-limited nonlinear absorption. Oral absorption of a novel farnesyltransferase inhibitor (FTI-2600) from its crystalline free base and its HCl salt was determined in dogs. To clarify the contribution of supersaturation on improving drug absorption, in vivo intraluminal concentration of FTI-2600 after oral administration was estimated from the pharmacokinetics data using a physiologically based model. Dissolution and precipitation characteristics of FTI-2600 in a biorelevant media were investigated in vitro using a miniscale dissolution test and powder X-ray diffraction analysis. In the in vitro study, the HCl salt immediately dissolved but precipitated rapidly. The metastable amorphous free base precipitant, which did not convert into the stable crystalline free base in the simulated intestinal fluids for several hours, generated a 5-fold increase in dissolved concentration compared to the equilibrium solubility of the crystalline free base. By computer simulation, the intraluminal drug concentration after administration of the free base was estimated to reach the saturated solubility, indicating solubility-limited absorption. On the other hand, administration of the HCl salt resulted in an increased intraluminal concentration and the plasma concentration was 400% greater than that after administration of the free base. This in vivo/in vitro correlation of the increased drug concentrations in the small intestine provide clear evidence that not only the increase in the dissolution rate, but also the supersaturation phenomenon, improved the solubility-limited absorption of FTI-2600. These results indicate that formulation technologies that can induce supersaturation may be of great assistance to the successful development of poorly water-soluble drugs.

Design and synthesis of an androgen receptor pure antagonist (CH5137291 ) for the treatment of castration-resistant prostate cancer

A series of 5,5-dimethylthiohydantoin derivatives were synthesized and evaluated for androgen receptor pure antagonistic activities for the treatment of castration-resistant prostate cancer. Since CH4933468, which we reported previously, had a problem with agonist metabolites, novel thiohydantoin derivatives were identified by applying two strategies. One was the replacement of the alkylsulfonamide moiety by a phenylsulfonamide to avoid the production of agonist metabolites. The other was the replacement of the phenyl ring with a pyridine ring to improve in vivo potency and reduce hERG affinity. Pharmacological assays indicated that CH5137291 (17b) was a potent AR pure antagonist which did not produce the agonist metabolite. Moreover, CH5137291 completely inhibited in vivo tumor growth of LNCaP-BC2, a castration-resistant prostate cancer model.

Characterizing the dissolution profiles of supersaturable salts, cocrystals, and solvates to enhance in vivo oral absorption

The purposes of this study were to elucidate the type-specific characteristics of salt, cocrystal, and solvate formulations upon dissolution and precipitation, and to clarify their effect on enhancing oral absorption. Several types of solid formulations (dantrolene sodium salt [DAN-NA], pioglitazone hydrochloride salt [PIO-HCL], megestrol acetate saccharin cocrystal [MEG-SA], and an in-house compound ZR ethanolate [ZR-ETH]) that induce supersaturation of BCS class II drugs were compared to their crystalline free forms. An in vitro miniscale dissolution test in biorelevant media was used to characterize their dissolution profiles and residue forms. Both salts (DAN-NA and PIO-HCL) rapidly reached the maximum concentration within 5min, whereas the cocrystal (MEG-SA) did so slowly. After the maximum concentration had been reached, the dissolved concentrations of DAN-NA, PIO-HCL, and MEG-SA decreased, but that of ZR-ETH did not. Time-dependent XRPD analysis revealed that the initial solid state of each salt dissolved within 5min, whereas the cocrystal remained for more than 10min, and the solvate remained for 4h. It also revealed that PIO-HCL and MEG-SA precipitated to the stable free form, while DAN-NA precipitated to the metastable form, which maintains a higher concentration than the stable free form continuously. In vivo absorption in beagle dogs was also examined. The plasma AUC of DAN-NA, MEG-SA, and ZR-ETH was respectively 1.5-, 2.1-, and 11-fold more than each free form. On the other hand, the absorption of PIO-HCL was not enhanced compared with its free form. The results in the present study clarified that not only the precipitation rate and the form of precipitation but also the retention of the initial solid state in the absorption process contribute to enhancing the in vivo absorption of Class II drugs from solid formulations such as salts, solvates, and cocrystals.

Cocrystal structure design for CH5134731 based on isomorphism

We succeeded in forming a benzoic acid cocrystal of CH5134731 by focusing on the isomorphism shown by its solvates. As a result of evaluation, the benzoic acid cocrystal showed good solubility. This crystal engineering approach made it possible to reduce the amount of compound and study time in the early stage of research and development.

Abstract A220: Design and synthesis of an androgen receptor pure antagonist (CH5137291) for treatment of castration‐resistant prostate cancer

Background: We hypothesized that the androgen receptor (AR) pure antagonists, which exhibit no agonist activities, would inhibit AR signaling completely and would be efficacious against castration‐resistant prostate cancer (CRPC). Based on our understanding of estrogen receptor pure antagonists, we designed dihydrotestosterone (DHT) derivatives and nonsteroidal RU56187 derivatives that inhibit the folding of helix 12 of AR and screened AR pure antagonists. Although a non‐steroidal derivative (CH4933468) showed improved metabolic stability compared with DHT derivatives, it metabolized into an extremely small amount of a dealkylated metabolite with strong agonist effect. Therefore, CH4933468 did not show antitumor activity against the CRPC xenograft model. Methods: For metabolic stability, we designed and synthesized sulfonamide‐substituted aryl compounds without dealkylated agonist metabolites. The production of agonist metabolites was examined in rat, mouse, monkey and dog. The efficacy of our compounds was measured using an in vitro reporter assay, a cell growth assay and in vivo prostate cancer xenograft models. Results: As a result of our optimization, CH5137291 was discovered and found to be an orally‐active androgen receptor pure antagonist without agonistic activities derived from dealkylated agonist metabolites in vivo in rat, mouse, monkey and dog. CH5137291 exhibited AR antagonistic activities of IC50 of 300 nM and no agonist activity even at 30,000 nM in the reporter gene assay. In LNCaP‐BC2 cells (AR overexpression CRPC model), CH5137291 was more efficient than bicalutamide. CH5137291 completely inhibited cell growth, in contrast to the partial inhibition of bicalutamide. Furthermore, CH5137291 inhibited the tumor growth and PSA production in the LNCaP‐BC2 xenograft model. CH5137291 also inhibited AR nuclear translocation in the presence of R1881. According to the binding models of CH5137291 and bicalutamide to wild type AR, the sulfonamide of CH5137291 directly collided with M895 and thus prevented the folding of helix 12 completely. On the other hand, bicalutamide did not collide with M895 from helix 12 and inhibited helix 12 folding indirectly through W741. Hence, CH5137291 might act as an AR pure antagonist, but bicalutamide apparently does not. Conclusions: CH5137291, a novel AR pure antagonist without agonistic activities derived from dealkylated agonist metabolites, has shown antitumor activities in both in vitro and in vivo CRPC models. Our experimental results for clinical candidate CH5137291 corroborate our hypothesis that pure antagonists inhibit the folding of helix 12 completely, leading to the complete inhibition of the transcription activity of AR. Based on the strong efficacy against CRPC xenograft model and the inhibition of AR nuclear translocation, CH5137291 may offer more benefit than bicalutamide. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A220.