Toward Successful Cyclodextrin Based Solubility-Enabling

May 15, 2017 - The effective permeability (Peff) through the rat jejunum was determine .... 2) and the AUC data of the same formulations reported by H...
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Toward Successful Cyclodextrin Based Solubility-Enabling Formulations for Oral Delivery of Lipophilic Drugs: Solubility− Permeability Trade-Off, Biorelevant Dissolution, and the Unstirred Water Layer Noa Fine-Shamir,‡ Avital Beig,‡ Moran Zur,‡ David Lindley,† Jonathan M. Miller,†,§ and Arik Dahan*,‡

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‡

Department of Clinical Pharmacology, School of Pharmacy, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel † AbbVie Inc., North Chicago, Illinois 60064, United States ABSTRACT: The purpose of this work was to investigate key factors dictating the success/failure of cyclodextrin-based solubility-enabling formulations for oral delivery of low-solubility drugs. We have studied the solubility, the permeability, and the solubility−permeability interplay, of the highly lipophilic drug danazol, formulated with different levels (8.5, 10, 20, and 30%) of the commonly used hydroxypropyl-β-cyclodextrin (HPβCD), accounting for the biorelevant solubilization of the drug along the gastrointestinal tract (GIT), the unstirred water layer (UWL) adjacent to the GI membrane, and the overall absorption. HPβCD significantly increased danazol solubility, and decreased the drugs’ permeability, in a concentration-dependent manner. These Peff results were in good correlation (R2 = 0.977) to literature rat AUC data of the same formulations. Unlike vehicle without HPβCD, formulations containing 8.5% HPβCD and above were shown to successfully dissolve the drug dose during the entire biorelevant dissolution experiment. We conclude that CD-based solubility-enabling formulations should contain the minimal amount of CD sufficient to dissolve the drug dose throughout the GIT, and not more than that; excess CD does not provide solubility gain but causes further permeability loss, and the overall absorption is then impaired. Moreover, a significant UWL effect was revealed in danazol intestinal permeability, and accounting for this effect allowed an excellent prediction of the solubility−permeability trade-off vs % HPβCD. Overall, this work assessed the contribution of each individual step of the absorption cascade to the success/failure of HPβCD-based formulation, allowing a more mechanistic development process of better solubility-enabling formulations. KEYWORDS: cyclodextrins, drug absorption, intestinal permeability, low solubility, oral drug delivery, solubility-enabling formulations, solubility−permeability interplay

1. INTRODUCTION Low aqueous solubility is a central challenge in todays’ oral drug delivery.1−3 Various solubility-enabling formulations allow tackling this obstacle efficiently;4,5 however, while the apparent solubility of the drug may be significantly increased, the apparent permeability may concomitantly decrease. This solubility−permeability trade-off was shown for formulations containing cyclodextrins,6,7 surfactants,8,9 hydrotropy,10 and cosolvents.11,12 Since the solubility and the permeability together are the two key factors dictating oral drug absorption,13,14 the overall absorption of the drug becomes unpredicted due to this solubility−permeability trade-off.15,16 The formulation development process has to account for the dynamic environment that the drug product is exposed to throughout its gastrointestinal tract (GIT) journey, e.g., pH changes, residence times, and fluid volumes/dilutions. A good formulation will allow a solution mediated phase transformation or supersaturation of the drug dose throughout the © 2017 American Chemical Society

entire travel along the GIT, while an inferior one will fail to solubilize the drug dose in these dynamic surroundings, and drug precipitation will occur.17,18 Different in vitro biorelevant dissolution methods have been developed throughout the years, including systems with “gastric” and “intestinal” compartments,19,20 two-phase dissolution apparatus,21,22 the gastrointestinal simulator system,23−26 the dynamic lipolysis model for lipid-based formulations,27−29 and the dilution−dissolution approach.30,31 These (and other) in vitro models have shown significant success in predicting the in vivo ability of a given formulation to retain the drug dose in solution (or supersaturation) in the dynamic GIT environment. Received: Revised: Accepted: Published: 2138

April 4, 2017 May 11, 2017 May 15, 2017 May 15, 2017 DOI: 10.1021/acs.molpharmaceut.7b00275 Mol. Pharmaceutics 2017, 14, 2138−2146

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Molecular Pharmaceutics

(Protocol IL-08-01-2015). Animals were housed and handled according to the Ben-Gurion University of the Negev Unit for Laboratory Animal Medicine Guidelines. Male ∼300 g Wistar rats (Harlan, Israel) were used for all studies. Rats were fasted overnight (12 h) before each experiment, with free access to water. Animals were randomly assigned to the different experimental groups. Single-pass intestinal perfusion (SPIP) studies were carried out according to a previously reported protocol.40,41 Rats were anesthetized (1 mL/kg ketamine:xylazine solution) and placed on a 37 °C pad (Harvard Apparatus Inc., Holliston, MA). A proximal jejunal segment of about 10−20 cm was cannulated on two ends and was thoroughly rinsed with 37 °C normal saline solution. Danazol solutions were prepared with different concentrations of HPβCD (0, 1, 8.5, 10, 20, and 30% w/v) in MES buffer (pH 6.5), and were perfused through the intestinal segment at a flow rate of 0.2 mL/min (Watson-Marlow 205S, Wilmington, MA). To assess the UWL effect on danazol intestinal permeability, similar studies with flow rates of 2, 3, 4, or 4.5 mL/min were also carried out.42 To ensure steady-state conditions, the test solutions were first perfused for 60 min, followed by an additional 60 min, during which samples were collected at 5−10 min intervals.43 Samples were centrifuged (14,000 rpm) for 15 min and immediately assayed for danazol content (UPLC). The effective permeability (Peff) through the rat jejunum was determine by the equation44

Specifically for cyclodextrin-based solubility-enabling formulations, a tremendous improved solubility can be certainly achieved, that may also be maintained throughout the entire GIT travel; however, this advantage comes with the price of concomitant permeability decrease, which hampers the chances of the formulation to improve the overall absorption of the drug. Since cyclodextrins enable apparent solubility increase by hosting the lipophilic molecule inside their hydrophobic cavity, the free fraction of the drug dose available for absorption may decrease, explaining the apparent permeability decrease. Both simulations and experimental data demonstrated that cyclodextrins can improve, have no effect, or impair drug absorption when administered as a physical mixture with a lipophilic drug.32−36 Defining the different criteria that may allow achieving the maximal potential of cyclodextrin-based solubility enabling formulations represents an important unmet need. The purpose of this work was to investigate key factors that may dictate the success/failure of cyclodextrin-based solubilityenabling formulations for oral delivery of low-solubility drugs. We have studied the highly lipophilic drug danazol, formulated with different levels of the commonly used hydroxypropyl-βcyclodextrin (HPβCD), accounting for the solubility−permeability interplay, biorelevant solubilization of the drug along the gastrointestinal tract (GIT), the unstirred water layer (UWL) adjacent to the GI membrane, and the overall absorption. The effects of the formulations on the solubility, in vivo permeability, and biorelevant dissolution of the drug were investigated, and they were correlated with relevant literature in vivo absorption data.37 The results were mechanistically analyzed, and together with experiments of the UWL effect, an excellent prediction of the solubility−permeability trade-off was enabled. Since formulation development is often an empirical process that is based on trial and error, this work aimed to assess the contribution of each individual step of the absorption cascade to the overall success/failure of a given formulation, allowing a more mechanistic a priori development of better solubility-enabling formulations.

( )

−Q ln Peff =

C ′out C ′in

2πRL

(1)

where Q is the perfusion flow rate (0.2−4.5 mL/min), C′out/ C′in is the ratio of danazol outlet vs inlet concentrations adjusted for water flux using the gravimetric method,45 R is the radius of the intestinal segment (0.2 cm), and L is the exact length of the perfused intestinal segment as was measured at the end point of each experiment (10−20 cm). 2.4. In Vitro pH-Dilution Dissolution Studies. A biorelevant in vitro pH-dilution dissolution method was used, aiming to mimic physiological conditions in the different segments throughout the GIT journey. The method has been shown to be successful in simulating drug dissolution from a given formulation while traveling along the GIT.30,31 Danazol dose in the different formulations (600 μL) was first diluted into 1 M HCl (pH 4.0) at a dilution factor of 1:0.66. Sample vials were agitated for 15 min, using a 100 rpm shaking water bath at 37 °C. Then, the vials were further diluted with FaSSIF (Biorelevant.com Ltd., London, U.K.) at a dilution factor of 1:0.5 and continued to be agitated for another 15 min. Further FaSSIF dilutions were carried out with a dilution factor of 1:1 (agitation time of 30 min), and then twice 1:1 dilution every 60 min, for a total agitation time of 3 h. Samples (100 μL) were taken at a set time points throughout the experiment; the samples were centrifuged (14,000 rpm) for 20 min, filtered, and immediately assayed for drug content (UPLC). The comparison of solubilized drug (obtained from the UPLC results) and total drug content (calculated from the initial dose and the subsequent dilutions) provides the insight into the solubilization performance of the formulations during the GIT travel. 2.5. True Membrane Permeability. Determination of the true membrane permeability of the drug is important for the understanding of the solubility permeability interplay. To reveal the role of the UWL vs the membrane in the overall

2. MATERIALS AND METHODS 2.1. Materials. Danazol was purchased from Carbosynth Ltd. (Compton Berkshire, U.K.). 2-Hydroxypropyl-β-cyclodextrin (HPβCD) was purchased from Glentham Life Sciences Ltd. (Corsham, U.K.). SIF powder was obtained from Biorelevant.com Ltd. (London, U.K.). MES buffer, KCl, NaCl, and DMSO were obtained from Sigma Chemical Co. (St. Louis, MO). Acetonitrile and water (Merck KGaA, Darmstadt, Germany) were UPLC grade. All other chemicals were of analytical reagent grade. 2.2. Solubility Experiments. The solubility experiments for danazol with HPβCD were conducted according to a previously described method.38,39 Excess amounts of danazol were added to a number of glass test tubes containing MES buffer solution (pH 6.5) of different HPβCD concentrations (0, 1, 2.5, 5, 8.5, 10, 20, and 30% w/v). The intrinsic solubility of danazol in MES buffer was determined from the samples without any HPβCD. The test tubes were placed in a 100 rpm shaking water bath at room temperature (25 °C) or 37 °C for 48 h. After 48 h the vials were centrifuged (14,000 rpm) for 15 min, filtered, and immediately assayed for drug content by UPLC. 2.3. Rat Jejunal Perfusion. The protocol used for all animal experiments was approved by the Ben-Gurion University of the Negev Animal Use and Care Committee 2139

DOI: 10.1021/acs.molpharmaceut.7b00275 Mol. Pharmaceutics 2017, 14, 2138−2146

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Molecular Pharmaceutics permeability of the drug, we used the above-mentioned singlepass perfusion method. Danazol solution (with 0% CD content) was perfused under five different flow rates, 0.2, 2, 3, 4, and 4.5 mL/min, and permeability was calculated. If the UWL is a barrier to the intestinal absorption, higher flow rates will result in higher Peff. Otherwise, the effective permeability should remain steady regardless of the flow rate.42,46 2.6. Permeability Predictions. The central quasi-equilibrium analysis of the effect of increased apparent solubility via complexation with cyclodextrins on apparent membrane permeability has been described in detail previously.6,7,33,42 Briefly, the apparent membrane permeability (Pm) dependence on drug apparent aqueous solubility (Saq) can be written as Pm =

Pm(0) × Saq(0) Saq

(2)

where Pm(0) is the intrinsic membrane permeability of the free drug and Saq(0) is the intrinsic aqueous solubility of the drug in the absence of cyclodextrins. 2.7. Ultraperformance Liquid Chromatography (UPLC). The concentration of danazol in the solution was determined by a Waters UPLC H-Class system equipped with a photodiode array detector and Empower software. A Waters SunFire C18 3.5 μm 4.6 × 100 mm column was used. The detection wavelength was 285 nm. A gradient mobile phase consisting of 15:85 going to 6:94 and then back to 15:85 (v/v) of water:acetonitrile (both with 0.1% TFA) over 6 min was used. The flow rate was 0.5 mL/min, and the injection volumes ranged from 20 to 100 μL. 2.8. Statistical Analysis. Solubility studies were performed in triplicate, while each group of the animal studies consisted of 4 rats. Values are expressed as mean ± standard deviation (SD). To determine statistically significant differences among the experimental groups, the nonparametric Kruskal−Wallis test was used for multiple comparisons, and the two-tailed nonparametric Mann−Whitney U-test for two-group comparison, where appropriate. p < 0.05 was termed significant.

Figure 1. Apparent solubility of danazol as a function of HPβCD level at 37 °C (circles) and at room temperature (25 °C; triangles). Average ± SD; n = 4 in each experimental group.

Figure 2. In vivo rat intestinal permeability of danazol from the different HPβCD-based formulations. Average ± SD; n = 6 in the 0% HPβCD group, and n = 4 in all other experimental groups.

3. RESULTS 3.1. Danazol−HPβCD Solubility Studies. Danazol solubility at 37 °C and at room temperature (25 °C) is presented in Figure 1. It can be seen that a significant and linear increase in danazol solubility was obtained with increasing amounts of HPβCD. At room temperature (25 °C) the solubility increased ∼1500-fold, from 2.2 μg/mL in the absence of HPβCD to 3256 μg/mL in the presence of 30% HPβCD. At 37 °C the solubility increased even more, up to 4366 μg/mL in the presence of 30% HPβCD. A binding constant (K1:1) of 373 M−1 was calculated from the 37 °C phase solubility diagram presented in Figure 1. The binding constant, K1:1, was calculated from the slope/(intercept·[1 − slope]) of the phase solubility diagram.47 3.2. Danazol−HPβCD in Vivo Permeability in Rats. Rat intestinal permeability data of danazol in the presence of various HPβCD levels are presented in Figure 2. The decrease in the permeability of the drug with increasing HPβCD concentrations and drug solubility can be clearly seen. The highest permeability of 7.7 × 10−4 cm/s was obtained in the absence of HPβCD, and the lowest permeability of 2.6 × 10−5 cm/s was obtained in the presence of 30% HPβCD, representing a 30-fold drop in the drug’s intestinal permeability. These results show that the solubility−permeability interplay in

this case is of a trade-off nature, which means that any HPβCDmediated solubility gain is accompanied by permeability loss. 3.3. Danazol AUC−P eff Correlation. In a recent publication, Holm et al.37 examined the oral bioavailability of four danazol−HPβCD formulations in rats. Danazol (14 mg/ kg) in aqueous vehicles containing 8.5, 10, 20, or 30% HPβCD (% w/v), was orally administrated to rats, and the results revealed significantly higher danazol AUC and bioavailability for the two low HPβCD level formulations (8.5% and 10%) vs the two high HPβCD level vehicles (20% and 30%). Figure 3 illustrates the correlation between our rat permeability data (presented in Figure 2) and the AUC data of the same formulations reported by Holm et al.37 It can be seen that a very good correlation (R2 = 0.977) was obtained between these parameters. 3.4. Biorelevant Dilution−Dissolution Study. To further compare the different danazol−HPβCD formulations, we have run a biorelevant dissolution study for all of them, simulating the ability of the formulations to solubilize the drug dose in the dynamic GIT environment (Figure 4). The 0% HPβCD formulation exhibited poor dissolution ability, as can 2140

DOI: 10.1021/acs.molpharmaceut.7b00275 Mol. Pharmaceutics 2017, 14, 2138−2146

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are presented in Figure 7. Excellent correlation between the predicted and the experimental permeability for all % HPβCD conditions was obtained.

4. DISCUSSION Key factors that may dictate the success/failure of cyclodextrinbased solubility-enabling formulations for oral delivery of lowsolubility drugs were investigated in this work. Danazol solubility increased substantially with increasing HPβCD concentration, and a strong molecular complexation (as demonstrated by the high binding constant of 373 M−1) was obtained. Such significant solubility increase when using cyclodextrins is the main reason for their common use as pharmaceutical solubilizers. However, the use of cyclodextrins should be done with caution because the advantage of the solubility increase is accompanied by the undesired effect of a decreased intestinal permeability, attributable to decreased free fraction of the drug dose available for absorption. In a recent publication, Holm et al.37 reported a decreased danazol AUC and bioavailability values for the two high HPβCD level formulations (20% and 30%) vs the two low HPβCD level formulations (8.5% and 10%). Very good correlation was detected between these in vivo results and our rat permeability data as illustrated in Figure 3. These results demonstrate the care that must be taken when formulating oral lipophilic drugs with cyclodextrins; in spite of dramatic solubility increase, an unbalanced formulation may not only fail to improve bioavailability but even have a negative effect on the overall absorption of the drug. The next critical question that may dictate the formulation success/failure is what is the optimal cyclodextrin formulation content that will maximize bioavailability? How can the formulator avoid undesired excess amounts of HPβCD in the formulation? We posit that the optimal formulation should contain the minimal CD level sufficient to solubilize the drug dose throughout the GIT journey, and not more than that. We have shown that all four formulations (8.5, 10, 20, and 30% HPβCD) completely solubilize the drug dose in conditions mimicking the GIT travel (Figure 4), indicating that the three higher % HPβCD formulations are not balanced; hence, they are not expected to improve, and may even decrease, the overall drug absorption. Indeed the pharmacokinetic study published by Holm et al. reported these very outcomes.37 Whether 8.5% HPβCD is a balanced quantity or also represents excess of solubilizer was the next question we dealt with. A pH-dilution dissolution study for four additional danazol formulations (0, 1, 2.5, and 5% HPβCD) is presented in Figure 8. It can be seen that the 0 and 1% HPβCD formulations demonstrated poor solubilizing capacity, resulting in significant and quick drug precipitation. On the other hand, the 2.5% HPβCD formulation, and obviously the 5% as well, were able to solubilize the entire danazol dose throughout the whole experiment. Therefore, HPβCD above 1% but below 2.5% may represent the minimal HPβCD level sufficient to allow complete solubilization of the drug dose throughout the GIT journey. HPβCD levels higher than 2.5% do not contribute to danazol solubilization, have unnecessary “price” of decreased intestinal permeability, and hence may impair the bioavailability of the drug. It should be noted that the minimal amount of CD needed to dissolve a given drug is influenced by the type and strength of the drug−CD interaction, which can be appreciated from the phase−solubility diagram and the K1:1 coefficient; therefore, the 1−2.5% found in Figure 8 is specific solely to this

Figure 3. Correlation between our rat permeability data (presented in Figure 2) and the AUC data of the same formulations reported by Holm et al.37

be seen from the immediate gap between total and dissolved danazol plots of this formulation, indicating that the drug precipitated quickly during the first 15 min of the experiment. All four danazol−HPβCD formulations (8.5%, 10%, 20%, and 30%) were successful in dissolving the drug dose during the entire dissolution experiment, as can be appreciated from the overlay of the total and dissolved danazol plots for all four formulations throughout the entire time course. These results illustrate the reason for using HPβCD in oral solubilityenabling formulations for lipophilic drugs. 3.5. The Solubility−Permeability Interplay. The solubility of danazol, as well as the drugs’ permeability, both theoretical (based on reversed correlation to the increased solubility) and experimental, as a function of HPβCD concentration, are presented in Figure 5. Increased solubility and decreased intestinal permeability with increasing amounts of HPβCD was obtained, in line with the solubility− permeability trade-off associated with cyclodextrin-based formulations.48,49 However, a significant gap between the predicted decreased Peff and the experimental permeability values was obtained, indicating the involvement of a further complexity. 3.6. The Unstirred Water Layer (UWL) Effect. Next, we evaluated whether the UWL adjacent to the intestinal membrane is a significant barrier to danazol permeability, and responsible for the lack of correlation between the predicted and experimental Peff values. Danazol effective permeability as a function of the flow rate of the perfused solution (without HPβCD) is presented in Figure 6. It can be seen that the perfusion flow rate (Q) has a significant effect on danazol effective permeability, showing increasing Peff with increasing Q, indicating a significant UWL effect. However, at perfusion flow rate of 4 mL/min and above, this effect is plateaued, indicating a membrane-controlled intestinal permeability at these conditions. A Peff value of 8 × 10−3 cm/s could be readily identified as the true membrane permeability of danazol. This permeability value was then used for the improved prediction of the drugs’ Peff vs HPβCD level. Danazol theoretical permeability, based on reversed correlation to the increased solubility while accounting for the true membrane permeability (8 × 10−3 cm/s), and the drugs’ experimental Peff, as a function of HPβCD concentration, 2141

DOI: 10.1021/acs.molpharmaceut.7b00275 Mol. Pharmaceutics 2017, 14, 2138−2146

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Figure 4. Ability of the five HPβCD formulations to achieve and maintain dissolution of the danazol dose in the dynamic GIT environment, using the pH-dilution dissolution method. Circles, total danazol concentration; diamonds, solubilized danazol concentration.

CD (HPβCD) and drug (danazol). These relatively simple in vitro studies demonstrate the optimization process we propose the formulator to take during CD-based formulation development, to avoid excess of solubilizer in the formulation, and to maximize the overall drug absorption afforded by the formulation. It should be noted that the presence of bile salts in the intestinal lumen may also affect the optimal formulation CD content; bile salts have high affinity to HPβCD and have the propensity to displace drugs from the cyclodextrin cavity,50 and hence the CD concentration required to achieve full solubilization may be higher in vivo.51

High quality a priori prediction of the solubility− permeability trade-off can be very helpful throughout the formulation development process. We have shown before that a simple reversed correlation to the increased solubility often allows a good prediction of the permeability at a given % CD, according to eq 2,42,49 where the apparent membrane permeability (Pm) at a given % HPβCD is equal to the intrinsic permeability of danazol in the absence of solubilizer (Pm(0)) times the aqueous solubility of danazol in the absence of solubilizer (Saq(0)) divided by the apparent solubility of the drug at the relevant % HPβCD (Saq). 2142

DOI: 10.1021/acs.molpharmaceut.7b00275 Mol. Pharmaceutics 2017, 14, 2138−2146

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Figure 7. Theoretical vs experimental apparent permeability of danazol as a function of increasing HPβCD concentrations, when taking into account the true membrane permeability of the drug. Experimental data are presented as mean ± SD; n = 4−6 in each experimental group.

Figure 5. Illustration of the solubility−permeability interplay, as well as the theoretical vs experimental permeability decrease vs HPβCD level. Experimental data are presented as mean ± SD; n = 4−6. Empty circles, experimental Peff; gray circles, predicted Peff; triangles, danazol solubility.

UWL is not a barrier to the drug absorption, a lack of effect of the flow rate on the intestinal permeability is expected. However, if the UWL is indeed a barrier to the intestinal permeability of the drug, then the increasing flow rates will lead to increased permeability values, attributable to decreased thickness of the UWL by the perfusion flow speed. This will continue until the UWL is no longer an effective barrier, indicated by plateaued Peff vs Q plot, and the true membrane permeability of the drug is obtained under these conditions. It can be seen in Figure 6 that increasing the perfusion flow rate significantly increased the permeability of danazol, revealing the considerable involvement of the UWL in the absorption of danazol. At a flow rate of 4 mL/min and above, Q no longer affected Peff, and a permeability value of ∼8 × 10−3 cm/s could be readily identified as the true membrane permeability of danazol. Indeed, taking this true Pm value for the solubility−permeability trade-off predictions resulted in the excellent correlation between the predicted and experimental values presented in Figure 7. Overall, in this work we assessed the contribution of each individual step of the absorption cascade to the success/failure of HPβCD-based formulation, allowing a more mechanistic development process of better solubility-enabling formulations. The trade-off between the solubility and the permeability when using cyclodextrins is intuitively attributable to the decreased free fraction of the drug; however, this trade-off also exists regardless of free fraction considerations, e.g., with cosolvents30 or hydrotropy10 due to decreased partition coefficient.15 Since the apparent permeability is equal to the diffusion coefficient of the drug through the membrane, times the apparent membrane/aqueous partition coefficient of the drug, divided by the membrane thickness, the presence of solubilizer decreases the drugs’ apparent membrane/aqueous partition coefficient and, hence, the apparent permeability goes down. It should be noted that using the amorphous form of the drug may allow increasing the apparent solubility without concomitant permeability decrease.52−55 This advantageous solubility−permeability interplay is attributable to the fact that amorphous solid dispersions do not affect the equilibrium

Figure 6. Plot of the effective permeability coefficient of danazol and the perfusion flow rate, to determine the effective barrier function of the UWL to danazol intestinal permeability. Average ± SD; 0.2 mL/ min, n = 6; and n = 4 in all other experimental groups.

However, a significant gap between the predicted and experimental Peff values was evident (Figure 5) when taking the permeability value in the absence of HPβCD (∼7 × 10−4 cm/s) as the true intrinsic membrane permeability of the drug. This lack of correlation suggested that a further complexity is involved in the intestinal absorption process of danazol. We decided to examine whether the UWL is responsible for the gap between the predicted and the experimental values; if the UWL serves as a significant barrier to the permeability of danazol, the experimental Peff value obtained in the absence of HPβCD is actually not the true membrane permeability of the drug, rather, it is the permeability of the drug across the UWL, which may result in the gap between the predicted and experimental values. The role of the UWL in the intestinal absorption of danazol was investigated by the method of Komiya et al.46 The method involves performing rat permeability studies of the drug (in the absence of any solubilizer) at increasing flow rates (Q); if the 2143

DOI: 10.1021/acs.molpharmaceut.7b00275 Mol. Pharmaceutics 2017, 14, 2138−2146

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Figure 8. Ability of different HPβCD formulations to achieve and maintain dissolution of the danazol dose in the dynamic GIT environment, using the pH-dilution method. Circles, total danazol concentration; diamonds, solubilized danazol concentration.

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ACKNOWLEDGMENTS This work was supported by a research grant from AbbVie incorporation.

solubility of the drug, rather, they enable a temporary supersaturated phase that does not affect the membrane/ aqueous partition coefficient, hence avoiding the solubility− permeability trade-off.

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5. CONCLUSIONS

(1) Cherniakov, I.; Domb, A. J.; Hoffman, A. Self-nano-emulsifying drug delivery systems: an update of the biopharmaceutical aspects. Expert Opin. Drug Delivery 2015, 12 (7), 1121−33. (2) Lipinski, C. A.; Lombardo, F.; Dominy, B. W.; Feeney, P. J. Experimental and computational approaches to estimate solubility and permeability in drug discovery and development settings. Adv. Drug Delivery Rev. 2001, 46 (1−3), 3−26. (3) Takano, R.; Kataoka, M.; Yamashita, S. Integrating drug permeability with dissolution profile to develop IVIVC. Biopharm. Drug Dispos. 2012, 33 (7), 354−65. (4) Bergstrom, C. A.; Charman, W. N.; Porter, C. J. Computational prediction of formulation strategies for beyond-rule-of-5 compounds. Adv. Drug Delivery Rev. 2016, 101, 6−21. (5) Buckley, S. T.; Frank, K. J.; Fricker, G.; Brandl, M. Biopharmaceutical classification of poorly soluble drugs with respect to ″enabling formulations″. Eur. J. Pharm. Sci. 2013, 50 (1), 8−16. (6) Beig, A.; Agbaria, R.; Dahan, A. Oral delivery of lipophilic drugs: the tradeoff between solubility increase and permeability decrease when using cyclodextrin-based formulations. PLoS One 2013, 8 (7), e68237. (7) Miller, J. M.; Dahan, A. Predicting the solubility-permeability interplay when using cyclodextrins in solubility-enabling formulations: model validation. Int. J. Pharm. 2012, 430 (1−2), 388−91. (8) Hens, B.; Brouwers, J.; Corsetti, M.; Augustijns, P. Gastrointestinal behavior of nano- and microsized fenofibrate: In vivo

In conclusion, CD-based solubility-enabling formulations should contain the minimal amount of CD sufficient to dissolve the drug dose throughout the GIT, and not more than that; excess CD does not provide solubility gain but causes further permeability loss, and the overall absorption may then be impaired.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Department of Clinical Pharmacology, School of Pharmacy, Faculty of Health Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel. Tel: +972-86479483. Fax: +972-8-6479303. E-mail: [email protected]. ORCID

Arik Dahan: 0000-0002-3498-3514 Present Address §

J.M.M.: Vertex Pharmaceuticals Inc., 50 Northern Ave., Boston, MA 02210.

Notes

The authors declare no competing financial interest. 2144

DOI: 10.1021/acs.molpharmaceut.7b00275 Mol. Pharmaceutics 2017, 14, 2138−2146

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DOI: 10.1021/acs.molpharmaceut.7b00275 Mol. Pharmaceutics 2017, 14, 2138−2146