Structural Characterization of Heat Shock Protein 90ß and Molecular Interactions with Geldanamycin and Ritonavir: A Computational Study.

Drug repositioning is an important therapeutic strategy for treating breast cancer. Hsp90ß chaperone is an attractive target for inhibiting cell progression. Its structure has a disordered and flexible linker region between the N-terminal and central domains. Geldanamycin was the first Hsp90ß inhibitor to interact specifically at the N-terminal site. Owing to the toxicity of geldanamycin, we investigated the repositioning of ritonavir as an Hsp90ß inhibitor, taking advantage of its proven efficacy against cancer. In this study, we used molecular modeling techniques to analyze the contribution of the Hsp90ß linker region to the flexibility and interaction between the ligands geldanamycin, ritonavir, and Hsp90ß. Our findings indicate that the linker region is responsible for the fluctuation and overall protein motion without disturbing the interaction between the inhibitors and the N-terminus. We also found that ritonavir established similar interactions with the substrate ATP triphosphate, filling the same pharmacophore zone.

6-Carboxycellulose Acetate Butyrate: Effectiveness as an Amorphous Solid Dispersion Polymer.

Amorphous solid dispersion (ASD) in a polymer matrix is a powerful method for enhancing the solubility and bioavailability of otherwise crystalline, poorly water-soluble drugs. 6-Carboxycellulose acetate butyrate (CCAB) is a relatively new commercial cellulose derivative that was introduced for use in waterborne coating applications. As CCAB is an amphiphilic, carboxyl-containing, high glass transition temperature (Tg) polymer, characteristics essential to excellent ASD polymer performance, we chose to explore its ASD potential. Structurally diverse drugs quercetin, ibuprofen, ritonavir, loratadine, and clarithromycin were dispersed in CCAB matrices. We evaluated the ability of CCAB to create ASDs with these drugs and its ability to provide solubility enhancement and effective drug release. CCAB/drug dispersions prepared by spray drying were amorphous up to 25 wt % drug, with loratadine remaining amorphous up to 50% drug. CCAB formulations with 10% drug proved effective at providing in vitro solubility enhancement for the crystalline flavonoid drug quercetin as well as ritonavir, but not for the more soluble APIs ibuprofen and clarithromycin and the more hydrophobic loratadine. CCAB did provide slow and controlled release of ibuprofen, offering a simple and promising Long-duration ibuprofen formulation. Formulation with clarithromycin showed the ability of the polymer to protect against degradation of the drug at stomach pH. Furthermore, CCAB ASDs with both loratadine and ibuprofen could be improved by the addition of the water-soluble polymer poly(vinylpyrrolidone) (PVP), with which CCAB shows good miscibility. CCAB provided solubility enhancement in some cases, and the slower drug release exhibited by CCAB, especially in the stomach, could be especially beneficial, for example, in formulations containing known stomach irritants like ibuprofen.

Influence of Solvent Selection on the Crystallizability and Polymorphic Selectivity Associated with the Formation of the "Disappeared" Form I Polymorph of Ritonavir.

The comparative crystallizability and polymorphic selectivity of ritonavir, a novel protease inhibitor for the treatment of acquired immune-deficiency syndrome, as a function of solvent selection are examined through an integrated and self-consistent experimental and computational molecular modeling study. Recrystallization at high supersaturation by rapid cooling at 283.15 K is found to produce the metastable "disappeared" polymorphic form I from acetone, ethyl acetate, acetonitrile, and toluene solutions in contrast to ethanol which produces the stable form II. Concomitant crystallization of the other known solid forms is not found under these conditions. Isothermal crystallization studies using turbidometric detection based upon classical nucleation theory reveal that, for an equal induction time, the required driving force needed to initiate solution nucleation decreases with solubility in the order of ethanol, acetone, acetonitrile, ethyl acetate, and toluene consistent with the expected desolvation behavior predicted from the calculated solute solvation free energies. Molecular dynamics simulations of the molecular and intermolecular chemistry reveal the presence of conformational interplay between intramolecular and intermolecular interactions within the solution phase. These encompass the solvent-dependent formation of intramolecular O-H...O hydrogen bonding between the hydroxyl and carbamate groups coupled with differing conformations of the hydroxyl's shielding phenyl groups. These conformational preferences and their relative interaction propensities, as a function of solvent selection, may play a rate-limiting role in the crystallization behavior by not only inhibiting to different degrees the nucleation process but also restricting the assembly of the optimal intermolecular hydrogen bonding network needed for the formation of the stable form II polymorph.

Interaction of CYP3A4 with the inhibitor cobicistat: Structural and mechanistic insights and comparison with ritonavir.

Cobicistat is a derivative of ritonavir marketed as a pharmacoenhancer for anti-HIV therapy. This study investigated the interaction of cobicistat with the target protein, drug-metabolizing cytochrome P450 3A4 (CYP3A4), at the molecular level using spectral, kinetic, functional, and structural approaches. It was found that, similar to ritonavir, cobicistat directly coordinates to the heme via the thiazole nitrogen but its affinity and the binding rate are 2-fold lower: 0.030 µM and 0.72 s-1, respectively. The newly determined 2.5 Å crystal structure of cobicistat-bound CYP3A4 suggests that these changes arise from the inability of cobicistat to H-bond to the active site S119 and establish multiple stabilizing contacts with the F-F' connecting fragment, which becomes disordered upon steric clashing with the bulky morpholine moiety. Nonetheless, cobicistat inhibits recombinant CYP3A4 as potently as ritonavir (IC50 of 0.24 µM vs 0.22 µM, respectively) due to strong ligation to the heme and formation of extensive hydrophobic/aromatic interactions via the phenyl side-groups. To get insights into the inhibitory mechanism, the K257 residue, known to be solely and irreversibly modified by the reactive ritonavir metabolite, was substituted with alanine. Neither this nor control K266A mutation changed the extent of time-dependent inhibition of CYP3A4 by cobicistat and ritonavir, suggesting the existence of alternative inactivation mechanism(s). More importantly, K257 was found to be functionally important and contributed to CYP3A4 allosterism, possibly by modulating protein-ligand interactions through conformational dynamics.

In Vitro Lipolysis Model to Predict Food Effect of Poorly Water-Soluble Drugs Itraconazole, Rivaroxaban, and Ritonavir.

It is desirable to predict positive food effect of oral formulations due to food mediated dissolution enhancement of lipophilic drugs. The objective was to assess the ability of in vitro lipolysis to anticipate a positive food effect. Tested formulations included rivaroxaban and itraconazole, where some formulations, but not all, exhibit a positive food effect in vivo in humans. Amorphous solid dispersion formulations of ritonavir, which exhibit a negative food effect in vivo in humans, were also studied. Fe-lipolysis and Fa-lipolysis media representing fed and fasted intestinal conditions were used. Results show frequent agreement between in vitro lipolysis predictions and in vivo human outcomes. For rivaroxaban, food effect of unformulated active pharmaceutical ingredient (API) and products were correctly predicted where 2.5 mg and 10 mg strengths did not show any food effect; however, 20 mg did show a positive food effect. For itraconazole, all four products were correctly predicted, with Sporanox, Sempera, and generic capsules having a food effect, but Tolsura not having a positive food effect. For ritonavir, lipolysis predicted a positive food effect for API and Norvir tablet and powder, but Norvir products have negative food effect in vivo in humans. Overall, the lipolysis model showed favorable predictability and merits additional evaluation.

Physicochemical interaction of rifampicin and ritonavir-lopinavir solid dispersion: an in-vitro and ex-vivo investigation.

OBJECTIVE: To investigate the in-situ physicochemical interaction of Rifampicin and Ritonavir - Lopinavir Solid dispersion administered for the treatment of comorbid conditions i.e. Tuberculosis and HIV/AIDS. METHODS: pH-shift dissolution of Rifampicin (RIF) in presence of Ritonavir-Lopinavir solid dispersion (RL-SD) was carried out in USP phosphate buffer 6.8 and FaSSIF. Equilibrium and amorphous solubility were determined for the drugs. Pure drugs, their physical mixtures, and pH-shifted co-precipitated samples were characterized using DSC, PXRD, and FTIR. Fluorescence spectroscopy was used to investigate drug-rich and drug-lean phases. In-vitro and ex-vivo flux studies were also carried out. RESULTS: The results showed significant differences in the solubility and dissolution profiles of RTV and LOP in the presence of RIF, while RIF profile remained unchanged. Amorphicity, intermolecular interaction and aggregate formation in pH-shifted samples were revealed in DSC, XRD and FTIR analysis. Fluorescence spectroscopy confirmed the formation of drug-rich phase upon pH-shift. In-vitro and ex-vivo flux studies revealed significant reduction in the flux of all the drugs when studied in presence of second drug. CONCLUSION: RIF, RTV and LOP in presence of each other on pH-shift, results in co-precipitation in the amorphous form (miscible) which leads to reduction in the highest attainable degree of supersaturation. This reduction corresponds to the mole fraction of the RIF, RTV and LOP within the studied system. These findings suggest that the concomitant administration of these drugs may lead to physicochemical interactions and possible ineffective therapy.

Old Polymorph, New Technique: Assessing Ritonavir Crystallinity Using Low-Frequency Raman Spectroscopy.

Two decades ago, postmarket discovery of a second crystal form of ritonavir with lower solubility had major implications for drug manufacturers and patients. Since then, ritonavir has been reformulated via the hot-melt-extrusion process in an amorphous form. Here, quantitative low- and mid-frequency Raman spectroscopy methods were developed to characterize polymorphs, form I and form II, in commercial ritonavir 100 mg oral tablets as an alternate analysis approach compared to X-ray powder diffraction (XRPD). Crystallization in three lots of ritonavir products obtained from four separate manufacturers was assessed after storage under accelerated conditions at 40 °C and 75% relative humidity (RH). Results were compared with quantitative XRPD methods developed and validated according to ICH Q2 (R1) guidelines. In a four-week open-dish study, form I crystallization occurred in two of the four products and form II crystallization was detected in another ritonavir product. The limits of detection for XRPD, low-frequency Raman (LFR), and mid-frequency Raman (MFR) were determined to be 0.7, 0.8, and 0.5% for form I and 0.6, 0.6, and 1% for form II, respectively. Root-mean-squared-error of predictions were 0.6-1.0 and 0.6-2.5% for LFR- and MFR-based partial least-squares models. Further, ritonavir polymorphs could also be identified and detected directly from ritonavir tablets using transmission LFR. In summary, LFR was applied for the assessment of polymorphism in real-world samples. While providing analytical performance similar to conventional techniques, LFR reduced the single measurement time from 66 min (XRPD) to 10 s (LFR) without the need for tedious sample preparation procedures.

Drug Release from Surfactant-Containing Amorphous Solid Dispersions: Mechanism and Role of Surfactant in Release Enhancement.

PURPOSE: To understand how surfactants affect drug release from ternary amorphous solid dispersions (ASDs), and to investigate different mechanisms of release enhancement. METHODS: Ternary ASDs containing ritonavir (RTV), polyvinylpyrrolidone/vinyl acetate (PVPVA) and a surfactant (sodium dodecyl sulfate (SDS), Tween 80, Span 20 or Span 85) were prepared with rotary evaporation. Release profiles of ternary ASDs were measured with surface normalized dissolution. Phase separation morphologies of ASD compacts during hydration/dissolution were examined in real-time with a newly developed confocal fluorescence microscopy method. The water ingress rate of different formulations was measured with dynamic vapor sorption. Microscopy was employed to check for matrix crystallization during release studies. RESULTS: All surfactants improved drug release at 30% DL, while only SDS and Tween 80 improved drug release at higher DLs, although SDS promoted matrix crystallization. The dissolution rate of neat polymer increased when SDS and Tween 80 were present. The water ingress rate also increased in the presence of all surfactants. Surfactant-incorporation affected both the kinetic and thermodynamics factors governing phase separation of RTV-PVPVA-water system, modifying the phase morphology during ASD dissolution. Importantly, SDS increased the miscibility of RTV-PVPVA-water system, whereas other surfactants mainly affected the phase separation kinetics/drug-rich barrier persistence. CONCLUSION: Incorporation of surfactants enhanced drug release from RTV-PVPVA ASDs compared to the binary system. Increased drug-polymer-water miscibility and disruption of the drug-rich barrier at the gel-solvent interface via plasticization are highlighted as two key mechanisms underlying surfactant impacts based on direct visualization of the phase separation process upon hydration and release.

Effect of different seed crystals on the supersaturation state of ritonavir tablets prepared by hot-melt extrusion.

Hot-melt extrusion (HME) is a technology increasingly common for the commercial production of pharmaceutical amorphous solid dispersions (ASDs), especially for poorly water-soluble active pharmaceutical ingredients (APIs). However, recrystallization of the APIs during dissolution must be prevented to maintain the supersaturation state enabled by ASD. Unfortunately, the amorphous formulation may be contaminated by seed crystals during the HME manufacturing process, which could lead to undesirable crystal growth during the dissolution process. In this study, the dissolution behavior of ritonavir ASD tablets prepared using both Form I and Form II polymorphs was examined, and the effects of different seed crystals on crystal growth rates were investigated. The aim was to understand how the presence of seed crystals can impact the dissolution of ritonavir, and to determine the optimal polymorph and seeding conditions for the production of ASDs. The results showed that both Form I and Form II ritonavir tablets had similar dissolution profiles, which were also similar to the reference listed drug (RLD). However, it was observed that the presence of seed crystals, particularly the metastable Form I seed, led to more precipitation compared to the stable Form II seed in all formulations. The Form I crystals that precipitated from the supersaturated solution were easily dispersed in the solution and could serve as seeds to facilitate crystal growth. On the other hand, Form II crystals tended to grow more slowly and presented as aggregates. The addition of both Form I and Form II seeds could affect their precipitation behaviors, and the amount and form of the seeds had significant effects on the precipitation process of the RLD tablets, as are the tablets prepared with different polymorphs. In conclusion, the study highlights the importance of minimizing the contamination risk of seed crystals during the manufacturing process and selecting the appropriate polymorph for the production of ASDs.

Impact of Crystal Nuclei on Dissolution of Amorphous Drugs.

Amorphous drugs are used to improve bioavailability of poorly water-soluble drugs. Crystallization must be managed to take full advantage of this formulation strategy. Crystallization of amorphous drugs proceeds in a sequence of crystal nucleation and growth, with different kinetics. At low temperatures, crystal nucleation is fast, but crystal growth is slow. Therefore, amorphous drugs may generate dense but nanoscale crystal nuclei. Such tiny nuclei cannot be detected using routine powder X-ray diffraction (PXRD) and polarized light microscopy (PLM). However, they may negate the dissolution advantage of amorphous drugs. In this work, for the first time, the impact of crystal nuclei on dissolution of amorphous drugs was studied by monitoring the real-time dissolution from amorphous drug films, with and without crystal nuclei, and the evolving crystallinity in the films. Three model drugs (ritonavir/RTV, posaconazole/POS, and nifedipine/NIF) were chosen to represent different crystallization tendencies in the supercooled liquid state, namely, slow-nucleation-and-slow-growth (SN-SG), fast-nucleation-and-slow-growth (FN-SG), and fast-nucleation-and-fast-growth (FN-FG), respectively. We find that although the amorphous films containing nuclei do not show obvious differences from the nuclei-free films under PLM and PXRD before dissolution, they have inferior dissolution performance relative to the nuclei-free amorphous films. For SN-SG drug RTV, crystal nuclei have negligible impact on the crystallization of amorphous films, dissolution rate, and supersaturation achieved. However, they cause earlier de-supersaturation by inducing crystallization in solution as heterogeneous seeds. For FN-SG drug POS and FN-FG drug NIF, crystal nuclei accelerate crystallization in the amorphous films leading to lower supersaturation achieved with POS, and elimination of any supersaturation with NIF. Dissolution profiles of amorphous films can be further analyzed using a derivative function of the apparent dissolution rate, which yields amorphous solubility, initial intrinsic dissolution rate, and onset of crystallization in the amorphous films. This study highlights that although crystal nuclei are undetectable with routine analytical methods, they can significantly negate, or even eliminate, the dissolution advantage of amorphous drugs. Hence, understanding crystal nucleation process and developing approaches to prevent it are necessary to fully realize the benefits of amorphous solids.

Ritonavir Form III: A New Polymorph After 24 Years.

Polymorphism occurs widely in pharmaceutical solids, and must be thoroughly studied during product development. Twenty-four years after ritonavir (RTV) Form II materialized, we report a new polymorph, Form III, discovered via melt crystallization. Form III has a unique PXRD pattern, Raman spectrum, lower melting point and heat of fusion, compared to the known polymorphs, Form I and Form II. It is the least stable form, monotropically, among the three polymorphs. Form III differs from Form I and Form II in molecular conformation and hydrogen bonding motifs in crystal lattice. Nucleation from RTV supercooled liquid is slow, and selected Form III exclusively. The discovery of RTV Form III demonstrates the importance of crystal nucleation studies. Crystallization from supercooled liquids should be incorporated as part of polymorph screening workflow.

Release Mechanisms of Amorphous Solid Dispersions: Role of Drug-Polymer Phase Separation and Morphology.

Formulating poorly soluble molecules as amorphous solid dispersions (ASDs) is an effective strategy to improve drug release. However, drug release rate and extent tend to rapidly diminish with increasing drug loading (DL). The poor release at high DLs has been postulated to be linked to the process of amorphous-amorphous phase separation (AAPS), although the exact connection between phase separation and release properties remains somewhat unclear. Herein, release profiles of ASDs formulated with ritonavir (RTV) and polyvinylpyrrolidone/vinyl acetate (PVPVA) at different DLs were determined using surface normalized dissolution. Surface morphologies of partially dissolved ASD compacts were evaluated with confocal fluorescence microscopy, using Nile red and Alexa Fluor 488 as fluorescence markers to track the hydrophobic and hydrophilic phases respectively. ASD phase behavior during hydration and release of components were also visualized in real time using a newly developed in situ confocal fluorescence microscopy method. RTV-PVPVA ASDs showed complete and rapid drug release below 30% DL, partial drug release at 30% DL and no drug release above 30% DL. It was observed that formation of discrete drug-rich droplets at lower DLs led to rapid and congruent release of both drug and polymer, whereas formation of continuous drug-rich phase at the ASD matrix-solution interface was the cause of poor release above certain DLs. Thus, the domain size and interconnectivity of phase separated drug-rich domains appear to be critical factors impacting drug release from RTV-PVPVPA ASDs.

Discovery of Novel HIV Protease Inhibitors Using Modern Computational Techniques.

The human immunodeficiency virus type 1 (HIV-1) has continued to be a global concern. With the new HIV incidence, the emergence of multi-drug resistance and the untoward side effects of currently used anti-HIV drugs, there is an urgent need to discover more efficient anti-HIV drugs. Modern computational tools have played vital roles in facilitating the drug discovery process. This research focuses on a pharmacophore-based similarity search to screen 111,566,735 unique compounds in the PubChem database to discover novel HIV-1 protease inhibitors (PIs). We used an in silico approach involving a 3D-similarity search, physicochemical and ADMET evaluations, HIV protease-inhibitor prediction (IC50/percent inhibition), rigid receptor-molecular docking studies, binding free energy calculations and molecular dynamics (MD) simulations. The 10 FDA-approved HIV PIs (saquinavir, lopinavir, ritonavir, amprenavir, fosamprenavir, atazanavir, nelfinavir, darunavir, tipranavir and indinavir) were used as reference. The in silico analysis revealed that fourteen out of the twenty-eight selected optimized hit molecules were within the acceptable range of all the parameters investigated. The hit molecules demonstrated significant binding affinity to the HIV protease (PR) when compared to the reference drugs. The important amino acid residues involved in hydrogen bonding and п-п stacked interactions include ASP25, GLY27, ASP29, ASP30 and ILE50. These interactions help to stabilize the optimized hit molecules in the active binding site of the HIV-1 PR (PDB ID: 2Q5K). HPS/002 and HPS/004 have been found to be most promising in terms of IC50/percent inhibition (90.15%) of HIV-1 PR, in addition to their drug metabolism and safety profile. These hit candidates should be investigated further as possible HIV-1 PIs with improved efficacy and low toxicity through in vitro experiments and clinical trial investigations.

In Silico Evaluation of Natural Flavonoids as a Potential Inhibitor of Coronavirus Disease.

The recent coronavirus disease (COVID-19) outbreak in Wuhan, China, has led to millions of infections and the death of approximately one million people. No targeted therapeutics are currently available, and only a few efficient treatment options are accessible. Many researchers are investigating active compounds from natural plant sources that may inhibit COVID-19 proliferation. Flavonoids are generally present in our diet, as well as traditional medicines and are effective against various diseases. Thus, here, we reviewed the potential of flavonoids against crucial proteins involved in the coronavirus infectious cycle. The fundamentals of coronaviruses, the structures of SARS-CoV-2, and the mechanism of its entry into the host's body have also been discussed. In silico studies have been successfully employed to study the interaction of flavonoids against COVID-19 Mpro, spike protein PLpro, and other interactive sites for its possible inhibition. Recent studies showed that many flavonoids such as hesperidin, amentoflavone, rutin, diosmin, apiin, and many other flavonoids have a higher affinity with Mpro and lower binding energy than currently used drugs such as hydroxylchloroquine, nelfinavir, ritonavir, and lopinavir. Thus, these compounds can be developed as specific therapeutic agents against COVID-19, but need further in vitro and in vivo studies to validate these compounds and pave the way for drug discovery.

Interaction of CYP3A4 with Rationally Designed Ritonavir Analogues: Impact of Steric Constraints Imposed on the Heme-Ligating Group and the End-Pyridine Attachment.

Controlled inhibition of drug-metabolizing cytochrome P450 3A4 (CYP3A4) is utilized to boost bioavailability of anti-viral and immunosuppressant pharmaceuticals. We investigate structure-activity relationships (SARs) in analogues of ritonavir, a potent CYP3A4 inhibitor marketed as pharmacoenhancer, to determine structural elements required for potent inhibition and whether the inhibitory potency can be further improved via a rational structure-based design. This study investigated eight (series VI) inhibitors differing in head- and end-moieties and their respective linkers. SAR analysis revealed the multifactorial regulation of inhibitory strength, with steric constraints imposed on the tethered heme-ligating moiety being a key factor. Minimization of these constraints by changing the linkers' length/flexibility and N-heteroatom position strengthened heme coordination and markedly improved binding and/or inhibitory strength. Impact of the end-pyridine attachment was not uniform due to influence of other determinants controlling the ligand-binding mode. This interplay between pharmacophoric determinants and the end-group enlargement can be used for further inhibitor optimization.

Role of Surfactants on Release Performance of Amorphous Solid Dispersions of Ritonavir and Copovidone.

PURPOSE: To understand the role of different surfactants, incorporated into amorphous solid dispersions (ASDs) of ritonavir and copovidone, in terms of their impact on release, phase behavior and stabilization of amorphous precipitates formed following drug release. METHODS: Ternary ASDs with ritonavir, copovidone and surfactants (30:70:5 w/w/w) were prepared by rotary evaporation. ASD release performance was tested using Wood's intrinsic dissolution rate apparatus and compared to the binary drug-polymer ASD with 30% drug loading. Size measurement of amorphous droplets was performed using dynamic light scattering. Solid state characterization was performed using attenuated total reflectance-infrared spectroscopy, differential scanning calorimetry and scanning electron microscopy. RESULTS: All surfactant-containing ASDs showed improvement over the binary ASD. Span 85 and D-α-tocopheryl polyethylene glycol succinate (TPGS) showed complete release with no evidence of AAPS or crystallization whereas Span 20 and Tween 80 showed < 50% release with amorphous amorphous phase separation (AAPS). Span 20 also induced solution crystallization. Sodium dodecyl sulfate (SDS) showed very rapid, albeit incomplete (~ 80%) release. AAPS was not observed with SDS. However, crystallization on the dissolving solid surface was noted. Span 20 and TPGS formed the smallest and most size-stable droplets with ~ 1 µm size whereas coalescence was noted with other surfactants. CONCLUSIONS: Surfactants improved the release performance relative to the binary ASD. Different surfactant types impacted overall performance to varying extents and affected different attributes. Overall, Span 85 showed best performance (complete release, no crystallization/AAPS and small droplet size). Correlation between physicochemical properties and surfactant performance was not observed.

Investigation of binding characteristics of ritonavir with calf thymus DNA with the help of spectroscopic techniques and molecular simulation.

The binding behavior of ritonavir (RTV), a HIV/AIDS protease inhibitor, with ct-DNA was characterized through multiple testing technologies and theoretical calculation. The findings revealed that the RTV-DNA complex was formed through the noncovalent interaction mainly including conventional hydrogen bonds and carbon hydrogen bonds as well as hydrophobic interactions (pi-alkyl interactions). The stoichiometry and binding constant of the RTV-DNA complex were 1:1 and 1.87 × 103 M-1 at 298 K, respectively, indicating that RTV has moderate affinity with ct-DNA. The findings confirmed that RTV binds to the minor groove of DNA. The outcomes of CD experiments showed that the binding with RTV changed the conformation of DNA slightly. However, the conformation of RTV had obvious changes after binding to DNA, meaning that the flexibility of RTV molecule played an important role in stabilizing the RTV-DNA complex. Meanwhile, the results of DFT calculation revealed that the RTV and DNA interaction caused the changes in the frontier molecular orbitals, dipole moment and atomic charge distribution of RTV, altering the chemical properties of RTV when it bound to DNA. Communicated by Ramaswamy H. Sarma.

Impact of Polymer Type on Thermal Degradation of Amorphous Solid Dispersions Containing Ritonavir.

High-temperature exposure during hot melt extrusion processing of amorphous solid dispersions may result in thermal degradation of the drug. Polymer type may influence the extent of degradation, although the underlying mechanisms are poorly understood. In this study, the model compound, ritonavir (Tm = 126 °C), undergoes thermal degradation upon high-temperature exposure. The extent of degradation of ritonavir in amorphous solid dispersions (ASDs) formulated with poly(vinylpyrrolidone) (PVP), poly(vinylpyrrolidone) vinyl acetate copolymer (PVP/VA), hydroxypropyl methylcellulose acetate succinate (HPMCAS), and hydroxypropyl methylcellulose (HPMC) following isothermal heating and hot melt extrusion was evaluated, and mechanisms related to molecular mobility and intermolecular interactions were assessed. Liquid chromatography-mass spectrometry (LC-MS/MS) studies were used to determine the degradation products and pathways and ultimately the drug-polymer compatibility. The dominant degradation product of ritonavir was the result of a dehydration reaction, which then catalyzed a series of hydrolysis reactions to generate additional degradation products, some newly reported. This reaction series led to accelerated degradation rates with protic polymers, HPMCAS and HPMC, while ASDs with aprotic polymers, PVP and PVP/VA, had reduced degradation rates. This work has implications for understanding mechanisms of thermal degradation and drug-polymer compatibility with respect to the thermal stability of amorphous solid dispersions.

Impact of Simulated Intestinal Fluids on Dissolution, Solution Chemistry, and Membrane Transport of Amorphous Multidrug Formulations.

The solution behavior and membrane transport of multidrug formulations were herein investigated in a biorelevant medium simulating fasted conditions. Amorphous multidrug formulations were prepared by the solvent evaporation method. Combinations of atazanavir (ATV) and ritonavir (RTV) and felodipine (FDN) and indapamide (IPM) were prepared and stabilized by a polymer for studying their dissolution (under non-sink conditions) and membrane transport in fasted state simulated intestinal fluid (FaSSIF). The micellar solubilization by FaSSIF enhanced the amorphous solubility of the drugs to different extents. Similar to buffer, the maximum achievable concentration of drugs in combination was reduced in FaSSIF, but the extent of reduction was affected by the degree of FaSSIF solubilization. Dissolution studies of ATV and IPM revealed that the amorphous solubility of these two drugs was not affected by FaSSIF solubilization. In contrast, RTV was significantly affected by FaSSIF solubilization with a 30% reduction in the maximum achievable concentration upon combination to ATV, compared to 50% reduction in buffer. This positive deviation by FaSSIF solubilization was not reflected in the mass transport-time profiles. Interestingly, FDN concentrations remain constant until the amount of IPM added was over 1000 µg/mL. No decrease in the membrane transport of FDN was observed for a 1:1 M ratio of FDN-IPM combination. This study demonstrates the importance of studying amorphous multidrug formulations under physiologically relevant conditions to obtain insights into the performance of these formulations after oral administration.

Cellulose derivatives as effective recrystallization inhibitor for ternary ritonavir solid dispersions: In vitro-in vivo evaluation.

Amorphous solid dispersions (ASDs) are regarded as one of the most promising techniques for poorly-soluble active pharmaceutical ingredients (API). However, the thermodynamic instability of ASDs at supersaturated state makes them easy to recrystallize in aqueous media. In this study, ritonavir (RTV) was selected as a model drug for evaluating the solubility enhancement and recrystallization inhibition effect of various cellulose derivatives and the combinations of them with typical surfactants. Combination of HPMCAS-HF/SLS was filtrated for preparing ternary RTV solid dispersions (RTV SD) via solvent evaporation method. RTV SD exhibited enhanced dissolution manner, while the oral bioavailability of RTV SD was equivalent with the Reference Standard Norvir® but increased significantly compared to the ternary physical mixture. Thus, the ternary SD system might be promisingly employed as efficient drug delivery system for RTV, while the HPMCAS-HF/SLS combination could be recommended as effective excipient for fabricating steady solid dispersions loading poorly soluble API.