Role of Silica Intrawall Microporosity on Abiraterone Acetate Solubilization and In Vivo Oral Absorption.

SBA-15 mesoporous silica (MPS) has been widely used in oral drug delivery; however, it has not been utilized for solidifying lipid-based formulations, and the impact of their characteristic intrawall microporosity remains largely unexplored. Here, we derive the impact of the MPS microporosity on the in vitro solubilization and in vivo oral pharmacokinetics of the prostate cancer drug abiraterone acetate (AbA) when coencapsulated along with medium chain lipids into the pores. AbA in lipid (at 80% equilibrium solubility) was imbibed within a range of MPS particles (with comparable morphology and mesoporous structure but contrasting microporosity ranging from 0-247 m2/g), and their solid-state properties were characterized. Drug solubilization studies during in vitro lipolysis revealed that microporosity was the key factor in facilitating AbA solubilization by increasing the surface area available for drug-lipid diffusion. Interestingly, microporosity hindered hydrolysis of AbA to its active metabolite, abiraterone (Ab), under simulated intestinal conditions. This unique relationship between microporosity and AbA/Ab aqueous solubilization behavior was hypothesized to have significant implications on the subsequent bioavailability of the active metabolite. In vivo oral pharmacokinetics studies in male Sprague-Dawley rats revealed that MPS with moderate microporosity attained the highest relative bioavailability, while poor in vitro-in vivo correlations (IVIVC) existed between in vitro drug solubilization during lipolysis and in vivo AUC. Despite this, a reasonable IVIVC was established between the in vitro solubilization and in vivoCmax, providing evidence for an association between silica microporosity and oral drug absorption.

Arylacetamide deacetylase as a determinant of the hydrolysis and activation of abiraterone acetate in mice and humans.

AIM: Abiraterone acetate for metastatic castration-resistant prostate cancer is an acetylated prodrug to be hydrolyzed to abiraterone. Abiraterone acetate is known to be hydrolyzed by pancreatic cholesterol esterase secreted into the intestinal lumen. This study aimed to investigate the possibility that arylacetamide deacetylase (AADAC) expressed in enterocytes contributes to the hydrolysis of abiraterone acetate based on its substrate preference. MATERIALS AND METHODS: Abiraterone acetate hydrolase activity was measured using human intestinal (HIM) and liver microsomes (HLM) as well as recombinant AADAC. Correlation analysis between activity and AADAC expression was performed in 14 individual HIMs. The in vivo pharmacokinetics of abiraterone acetate was examined using wild-type and Aadac knockout mice administered abiraterone acetate with or without orlistat, a pancreatic cholesterol esterase inhibitor. KEY FINDINGS: Recombinant AADAC showed abiraterone acetate hydrolase activity with similar Km value to HIM and HLM. The positive correlation between activity and AADAC levels in individual HIMs supported the responsibility of AADAC for abiraterone acetate hydrolysis. The area under the plasma concentration-time curve (AUC) of abiraterone after oral administration of abiraterone acetate in Aadac knockout mice was 38% lower than that in wild-type mice. The involvement of pancreatic cholesterol esterase in abiraterone formation was revealed by the decreased AUC of abiraterone by coadministration of orlistat. Orlistat potently inhibited AADAC, implying its potential as a perpetrator of drug-drug interactions. SIGNIFICANCE: AADAC is responsible for the hydrolysis of abiraterone acetate in the intestine and liver, suggesting that concomitant use of abiraterone acetate and drugs potently inhibiting AADAC should be avoided.

Systematic Development and Validation of a RP-HPLC Method for Estimation of Abiraterone Acetate and its Degradation Products.

The present study described the development of a reversed-phase liquid chromatographic method for the estimation of abiraterone acetate by Quality by Design (QbD) approach. Using an isocratic solvent system for the mobile phase, the chromatographic estimation of analyte was performed on a Hypersil BDS C18 column using mobile phase mixture containing acetonitrile and water with pH adjusted with 0.1% v/v orthophosphoric acid (15:85%v/v ratio), flow rate 1.0 mL.min-1 and detection at 250 nm using photodiode array detector. Systematic development of the chromatographic method was carried out by factor screening using a half-factorial design which suggested organic modifier (%), flow rate (mL.min-1) and autosampler temperature (°C) as influential variables. Further, the method was optimized by Box-Behnken design and trials performed were evaluated for the area under peak, retention time, theoretical plate count and tailing factor as the responses. Validation of the developed method showed good linearity, accuracy, precision and sensitivity. Evaluation of the stability-indicating profile of the method using forced degradation studies revealed the formation of a possible degradation product under acidic and alkaline conditions, while no such degradation product peaks were observed under the oxidative environment. Overall, the study construed the successful development of HPLC assay method for pharmaceutical applications.

Bioavailability Enhancement and Food Effect Elimination of Abiraterone Acetate by Encapsulation in Surfactant-Enriched Oil Marbles.

Abiraterone acetate has limited bioavailability in the fasted state and exhibits a strong positive food effect. We present a novel formulation concept based on the so-called oil marbles (OMs) and show by in vitro and in vivo experiments that the food effect can be suppressed. OMs are spherical particles with a core-shell structure, formed by coating oil-based droplets that contain the dissolved drug by a layer of powder that prevents the cores from sticking and coalescence. OMs prepared in this work contained abiraterone acetate in the amorphous form and showed enhanced dissolution properties during in vitro experiments when compared with originally marketed formulation of abiraterone acetate (Zytiga®). Based on in vitro comparison of OMs containing different oil/surfactant combinations, the most promising formulation was chosen for in vivo studies. To ensure relevance, it was verified that the food effect previously reported for Zytiga® in humans was translated into the rat animal model. The bioavailability of abiraterone acetate formulated in OMs in the fasted state was then found to be enhanced by a factor of 2.7 in terms of AUC and by a factor of 4.0 in terms of Cmax. Crucially, the food effect reported in the literature for other abiraterone acetate formulations was successfully eliminated and OMs showed comparable extent of bioavailability in a fed-fasted study. Oil marbles therefore seem to be a promising formulation concept not only for abiraterone acetate but potentially also for other poorly soluble drugs that reveal a positive food effect.

Preclinical evaluation of new formulation concepts for abiraterone acetate bioavailability enhancement based on the inhibition of pH-induced precipitation.

Abiraterone acetate is a potent drug used for the treatment of metastatic castration resistant prostate cancer. However, currently marketed product containing crystalline abiraterone acetate exhibits strong positive food effect which results in strict dosing regimen. In the present work, a rational approach towards design of novel abiraterone acetate formulations that would allow increased bioavailability on a fasting stomach and thus decreased food effect is presented. Precipitation experiments in biorelevant media were designed to assess pH induced precipitation of the drug and a pool of polymeric excipients was then screened for their potential to inhibit precipitation. The best performing polymeric excipients were subsequently used as carriers for the preparation of amorphous solid dispersions. Two main approaches were followed in order to formulate the drug. The first approach relies on the suppression of precipitation from a supersaturated solution whereas the second one is based on the hypothesis that when the release of the drug is tuned, optimal uptake of the drug can be reached. Optimized formulation prototypes were tested in a rat animal model in an incomplete block, randomized bioequivalence study to assess their relative bioavailability under fasting conditions. We show that both formulation approaches lead to increased bioavailability of abiraterone acetate on a fasting stomach with bioavailability in rats being enhanced up to 250% compared to the original drug product containing crystalline drug.

Supersaturated-Silica Lipid Hybrids Improve in Vitro Solubilization of Abiraterone Acetate.

PURPOSE: Abiraterone acetate (AbA) is a poorly water-soluble drug with an oral bioavailability of <10% and a significant pharmaceutical food effect. We aimed to develop a more efficient oral solid-state lipid-based formulation for AbA using a supersaturated silica-lipid hybrid (super-SLH) approach to achieve high drug loading, improve in vitro solubilization and mitigate the food effect, while gaining a mechanistic insight into how super-SLH are digested and release drug. METHODS: The influence of super-SLH saturation level and lipid type on the physicochemical properties and in vitro solubilization during lipolysis of the formulations was investigated and compared to the commercial product, Zytiga. RESULTS: Super-SLH achieved significantly greater levels of AbA solubilization compared to Zytiga. Solubilization was influenced by the AbA saturation level, which determined the solid state of AbA and the relative amount of lipid, and the lipid utilized, which determined its degree of digestion and the affinity of the lipid and digestion products to the silica. A fine balance existed between achieving high drug loads using supersaturation and improving performance using the lipid-based formulation approach. The non-supersaturated SLH prepared with Capmul PG8 mitigated the 3-fold in vitro food effect. CONCLUSION: SLH and super-SLH improve in vitro solubilization of AbA, remove the food effect and demonstrate potential to improve oral bioavailability in vivo. Graphical Abstract Abiraterone acetate was formulated as silica-lipid hybrids and demonstrated enhanced in vitro solubilization in comparison to pure abiraterone acetate and commercial product, Zytiga.

Enhancement of abiraterone acetate oral bioavailability by supersaturated-silica lipid hybrids.

Abiraterone acetate (AbA) has an oral bioavailability of <10% due to its poor water solubility. Here we investigate the performance of silica-lipid hybrids (SLH) and supersaturated SLH (super-SLH) in improving oral bioavailability of AbA. Specifically, we investigate the influence of lipid type and AbA saturation level of the equilibrium solubility in the lipid (Seq), and explore in vitro-in vivo correlation (IVIVC). An oral pharmacokinetic study was conducted in fasted Sprague-Dawley rats. Suspensions of the formulations were administered via oral gavage at an AbA dose of 25 mg/kg. Plasma samples were collected and analyzed for drug content. SLH with a saturation level of 90% Seq enhanced the oral bioavailability of unformulated AbA by 31-fold, and super-SLH with saturation levels of 150, 200 and 250% Seq, enhanced the bioavailability by 11, 10 and 7-fold, respectively. In comparison with the commercial product Zytiga, SLH (90% Seq) increased the oral bioavailability 1.43-fold whereas super-SLH showed no improvement. A reasonable IVIVC existed between the performance of unformulated AbA, SLH and super-SLH, in the in vitro lipolysis and in vivo oral pharmacokinetic studies. SLH and super-SLH significantly enhanced the oral bioavailability of AbA. Additionally, supersaturation of SLH improved drug loading but did not correlate with enhanced AbA bioavailability.

Abiraterone acetate exerts a cytotoxic effect in human prostate cancer cell lines.

To study the capability of the CYP17A1 inhibitor abiraterone acetate (AER) to antagonize the androgen receptor (AR) activation in human prostate cancer (PCa) cell lines. T877A-AR-LNCaP, WT-AR-VCaP, AR-negative DU145, and PC3 PCa cell lines were used by MTT and cell count to study the ability of AER and enzalutamide (ENZ) to modify cell viability. The role of ARs in LNCaP was demonstrated through a gene-silencing experiment. The mechanism of AER cytotoxicity in LNCaP cells was studied, as well as the ability of AER to modulate AR gene expression. The in silico docking approach was applied to study the interaction of AER and ENZ with T877A-AR. Through high-performance liquid chromatography, the production of the AER main metabolite Δ4A was studied. AER bound AR in an almost identical manner to that of dihydrotestosterone (DHT). The higher binding energy for AER in T877A-AR could explain the major cytotoxic effect observed in LNCaP cells. The capability of LNCaP cells to synthesize Δ4A could mediate, at least in part, this effect. AER cytotoxicity in LNCaP cells was mainly due to the activation of apoptosis. Further, AER induced modification of AR target gene expression, suggesting a direct effect on AR activity. AER-induced cytotoxicity on PCa cell lines seemed to be mediated by binding with AR. The higher affinity of AER for T877A-AR may suggest a potential role of AER in the management of CRPC carrying this mutation; however, T877A-AR expressing CRPC patients developed AER resistance, probably due to the increase of progesterone.

Identification, Characterization and High-Performance Liquid Chromatography Quantification for Process-Related Impurities in Abiraterone Acetate Bulk Drug.

During the synthesis of abiraterone acetate bulk drug in some laboratory batches, two unreported impurities were detected by high-performance liquid chromatography analysis at levels ranging from 0.05 to 0.10% according to the United States Pharmacopeia method. The structures of two impurities were characterized and confirmed by NMR and MS, which were proposed to be [3ß-acetoxy-16-(3ß-acetoxy-androsta-5,16-dien-17-yl)-17-(3-pyridyl)-androsta-5,16-di-ene] and [3ß-acetoxy-16-(3ß-acetoxy-androsta-5,16-dien-17-yl)-17-androsta-5,16-di-ene]. It was proved that these impurities come into being during the preparation process of penultimate intermediate (abiraterone). The newly developed LC-UV method was used to monitor the impurity profile in the penultimate intermediate (abiraterone), which was validated by its satisfactory specificity, precision, accuracy and sensitivity. The probable origin of the impurity was also discussed.

Comparison of a Novel Formulation of Abiraterone Acetate vs. the Originator Formulation in Healthy Male Subjects: Two Randomized, Open-Label, Crossover Studies.

BACKGROUND AND OBJECTIVE: Abiraterone acetate is approved for the treatment of metastatic castration-resistant prostate cancer. The originator abiraterone acetate (OAA) formulation is poorly absorbed and exhibits large pharmacokinetic variability in abiraterone exposure. Abiraterone acetate fine particle (AAFP) is a proprietary formulation (using SoluMatrix Fine Particle Technology™) designed to increase the oral bioavailability of abiraterone acetate. Here, we report on two phase I studies in healthy male subjects aged 18-50 years. METHODS: In Study 101, 20 subjects were randomized in a crossover design to single doses of AAFP 100, 200, or 400 mg or OAA 1000 mg taken orally under fasting conditions. Results suggested that AAFP 500 mg would be bioequivalent to OAA 1000 mg in the fasted state. To confirm the bioequivalence hypothesis and to further expand the AAFP dose range, in Study 102, 36 subjects were randomized in a crossover design to single doses of AAFP 125, 500, or 625 mg or OAA 1000 mg. Both studies included a 7-day washout period between administrations. RESULTS: Dose-dependent increases in the area under the plasma concentration-time curve and maximum plasma concentration with AAFP were observed in both studies. The AAFP 500-mg bioavailability relative to OAA 1000 mg measured by the geometric mean ratio for area under the plasma concentration-time curve from time zero to the time of the last quantifiable concentration was 93.4% (90% confidence interval 85.3-102.4), area under the plasma concentration-time curve from time zero to infinity was 91.0% (90% confidence interval 83.3-99.4), and maximum plasma concentration was 99.8% (90% confidence interval 86.3-115.5). Dose proportionality was seen across all AAFP dose levels (100-625 mg). Abiraterone acetate fine particle was found to be safe and well tolerated in this study. CONCLUSION: Abiraterone acetate fine particle 500 mg was demonstrated to be bioequivalent to OAA 1000 mg in healthy volunteers under fasted conditions.

Steroid 17-hydroxylase and 17,20-lyase deficiencies, genetic and pharmacologic.

Steroid 17-hydroxylase 17,20-lyase (cytochrome P450c17, P450 17A1, CYP17A1) catalyzes two major reactions: steroid 17-hydroxylation followed by the 17,20-lyase reactions. The most severe mutations in the cognate CYP17A1 gene abrogate all activities and cause combined 17-hydroxylase/17,20-lyase deficiency (17OHD), a biochemical phenotype that is replicated by treatment with the potent CYP17A1 inhibitor abiraterone acetate. The adrenals of patients with 17OHD synthesize 11-deoxycorticosterone (DOC) and corticosterone but no 19-carbon steroids, similar to the rodent adrenal, and DOC causes hypertension and hypokalemia. Loss of 17,20-lyase activity precludes sex steroid synthesis and leads to sexual infantilism. Rare missense CYP17A1 mutations minimally disrupt 17-hydroxylase activity but cause isolated 17,20-lyase deficiency (ILD), Mutations in the POR gene encoding the required cofactor protein cytochrome P450-oxidoreductase causes a spectrum of disease from ILD to 17OHD combined with 21-hydroxylase and aromatase deficiencies, sometimes including skeletal malformations. Mutations in the CYB5A gene encoding a second cofactor protein cytochrome b5 also selectively disrupt 17,20-lyase activity and cause the purest form of ILD. The clinical manifestations of these conditions are best understood in the context of the biochemistry of CYP17A1.