Introduction

Niclosamide (NIC) is a generic anthelmintic drug approved by the Food and Drug Administration (FDA) which is listed in the Model List of Essential Medicines produced by the World Health Organization (WHO).1 In recent years, there has been a consistent increase in the popularity of studies exploring the potential of niclosamide for various diseases, such as cancer, bacterial infections, and viral infections.2 It was suggested that its anti-tumor activity involves blocking multiple pathways (WNT/b-catenin, mTORC1, Stat3, NF-kB, Notch) and inducing cell-cycle arrest through targeting mitochondrial enzymes, resulting in growth inhibition and programmed cell death.3 In 2004, Wu et al reported inhibitory effect of NIC on viral replication of SARS-CoV. A more recent study in 2019 demonstrated that niclosamide is highly effective in inhibiting the viral replication of MERS-CoV by over a 1000-fold, positioning it as a promising agent against viral replication.4,5 In recent years, a great effort to repurpose niclosamide has been made. Drug repurposing involves identifying new therapeutic applications for drugs that have already received approval, in order to minimize pharmaceutical research expenses6. Nevertheless, the primary constraint linked to NIC is its low water solubility, leading to restricted bioavailability.7 Improving water solubility is key for repurposing of NIC. Numerous strategies can be employed to improve the aqueous solubility and dissolution rate of an Active Pharmaceutical Ingredient (API). These approaches include particle size reduction, co-crystals, salts, amorphous solid dispersion, cyclodextrins, co-solvents, surfactants, lipid-based formulations, and others.8 This review outlines the endeavors made to enhance the water solubility and consequently the bioavailability of NIC, considering various formulation strategies and administration pathways.

NIC Properties Physicochemical Properties of NIC

NIC (5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide) is a crystalline solid with a yellowish-grey hue and odourless nature, melting within the temperature range of 224 to 229 °C.8 The solubility of NIC at 20 °C has been reported to be 5–8 μg/mL.2 For its properties of low solubility and high permeability, NIC has been classified as a class II drug in the Biopharmaceutical Classification System (BCS), meaning that its bioavailability is limited by the dissolution rate.2 NIC, classified as a weak acid, contains an ionizable phenolic -OH group, with reported pKa values ranging from 5.6 to 7.2. Consequently, the solubility of NIC and Log D is heightened at higher pH conditions.2,9 At a blood pH of 7.4, NIC predominantly exists in its anionic form. There are two obstacles hindering the oral absorption of NIC. Firstly, as a weak acid, NIC remains neutral at low pH levels, limiting its solubility in the gastric region. Secondly, while the higher pH in the small intestine enhances its solubilization, the permeation through enterocyte membranes becomes less favourable due to the increased proportion of charged species.10 Moreover, it has been reported that there is no significant difference in solubility between the acidic medium (0.1N HCl) and buffered medium (pH 6.8). This finding further exacerbates the challenge of absorption.11 Another significant aspect concerning pH is that when NIC in amorphous solid dispersion is exposed to acidic media, it undergoes crystallization.9 This results in even poorer dissolution and subsequently lowers the bioavailability of NIC. Additionally, NIC experiences chemical degradation in both acidic and basic conditions, attributed to hydrolysis.9 Furthermore, some reports have indicated that alkaline solutions promote the photooxidation of NIC.12 The degradation products of NIC exhibit toxicity to mononuclear cells, neuronal cells, and alveolar cell lines, while demonstrating non-toxicity to hepatic cell lines.13Log P was reported to be 3.912. NIC, due to its pKa and LogP values, demonstrates an affinity for and accumulates within acidic environments, including cancer cells and acidic intracellular vesicles.2 Research indicates an efficient distribution of NIC from the bloodstream to tumours, where it attains concentrations in the micromolar range.14

Besides being poorly water-soluble, it also exhibits poor glass-forming characteristics.1 The evaluation of a drug’s tendency to become amorphous is determined by its glass-forming ability (GFA), which is classified into three categories: poor (class 1), modest (class 2), and good (class 3). NIC falls under class 1, indicating a high propensity for recrystallization, implying it cannot naturally form an amorphous solid. However, it has the potential to create an amorphous solid dispersion or glass solution when dissolved in a solid matrix.1 Glassy materials possess higher thermodynamic energy compared to crystalline ones, resulting in enhanced solubility and dissolution rates.9 As mentioned earlier, a low pH environment promotes the conversion of the amorphous form to the crystalline form.

The literature describes three crystal forms of NIC: a hygroscopic anhydrous form, along with two monohydrates named HA and HB.15 In an aqueous medium, the anhydrous form swiftly transforms into HA, and subsequently transitions to the most stable and least water-soluble form, HB.10 Indeed, the solubility decreases from 13.32 μg/mL in the anhydrous form to 0.95 μg/mL and 0.61 μg/mL for the monohydrates HA and HB.10 Jara et al reported that the transition of NIC anhydrate to NIC HA during storage can be visually confirmed, as the original yellowish-white powder of NIC anhydrate turns yellow in the HA form.2 Therefore, it was recommended to subject NIC to treatment at 100 °C for 15 minutes if the raw material is exposed to high humidity.15 While both NIC anhydrate and monohydrate are options for drug formulation, each presents drawbacks. The anhydrate exhibits a high affinity for water, whereas the hydrate’s poorer solubility can lead to sedimentation during storage.15 NIC possesses several potential hydrogen-bonding sites, including NO2, OH, and carbonyl groups, along with two Cl atoms capable of forming halogen bonds. These structural characteristics generally promote the formation of solvates and co-crystals, offering promising avenues for enhancing solubility and decreasing hygroscopicity.16 The LogP value for NIC reveals its solubility being thousands of times higher in the organic phase than in the aqueous phase, indicating a preference for lipid dissolution, membrane penetration, and protein binding. However, at pH 6.9, the LogD (referring to lipophilicity at a specific pH) value of 3.6 suggests a declining trend in lipid partitioning due to increased ionization. Nevertheless, its significant lipophilicity could still encourage the development of lipid-based formulations.17,18 The most effective formulations are likely to generate moderate supersaturation close to the site of absorption. Lipid-based formulations are particularly well suited to these criteria since solubilization protects against high supersaturation ratios (and precipitation), and supersaturation initiation typically occurs in the small intestine at the absorptive membrane.19

NIC Plasma Protein Binding, Permeability, Metabolism, CYP Inhibition and Safety

A recent study revealed that NIC, at concentrations of 1 and 10 µM, displayed an extensive binding affinity to plasma proteins, surpassing 99% in both rat and human plasma. This significant plasma protein binding raises considerable concerns regarding potential drug-drug interactions. With multiple drugs co-administered, there’s a risk of competition for the same binding sites, potentially altering free drug concentrations and subsequent therapeutic outcomes.20 The permeability of NIC (1µM) was assessed using Caco-2 cells in the apical to basolateral direction (AB→BL), revealing a Papp value of 28.33×10−6 cm/s. Notably, NIC permeability closely resembles that of the control with high permeability, propranolol (27.5 x 10−6 cm/s), rather than the control for low permeability, atenolol (1.75 x 10−6).20 The same research group further investigated the efflux ratio (P app BL→AP / P app AP→BL). The ratio was determined to be 0.98, indicating no involvement of efflux transporters. Consequently, intestinal permeability is unlikely to be a contributing factor to the low bioavailability.20 Nevertheless, as the concentration of NIC increased to 10 µM, the Papp value dropped by 10-fold (2.90 x 10−6 cm/s), indicating that its low solubility might impede intestinal absorption.20

NIC undergoes significant Phase I metabolism by Cytochrome P450 enzymes (CYP), with notable Phase II metabolism by UDP-glycuronosyltransferases (UGTs). The primary metabolizers for both phases I and II are CYP1A2, primarily located in the liver, and UGT1A1, predominantly found in the liver and small intestine. CYP1A2 catalyzes the formation of 3-hydroxy NIC metabolites, while UGT1A1 generates the NIC-2-O-glucuronide metabolite.2,21 The production of 3-hydroxy NIC in the liver is minimal compared to the synthesis of NIC-2-O-glucuronide in both the intestine and liver.22 Therefore, the primary metabolic pathway for NIC is intestinal and hepatic glucuronidation, with the intestinal metabolism rate being approximately 10 times higher than hepatic metabolism. This indicates that UGT metabolization might significantly contribute to the reduced bioavailability of NIC.2 The distribution and relative abundance of these enzymes vary across different tissues and animal models.21,22 Among dogs, monkeys, mice, and rats, microsomes in monkeys exhibit glucuronidation parameters that are closest to humans.21

The half-lives of NIC in rat, dog, and human hepatic microsomes were determined to be 44.9, 16.0, and 11.8 minutes, respectively. These results suggest that NIC is metabolically unstable, with a half-life of approximately 45 minutes, and that the half-life tends to be shorter in larger mammals.23 This also indicates that human metabolization is more challenging and complex with respect to preclinical models.2 In humans, these enzymes are predominantly localized in the liver, colon, and small intestine.24 While in rats and mice, being the most common animal models, NIC primarily targets the liver and small intestine during its biodistribution.25,26 Several studies have observed a second peak in the plasma concentration profile following both oral and intravenous administration of NIC. Some authors have linked this phenomenon to enterohepatic circulation. Molecules exhibiting this phenomenon typically display multiple peaks in their pharmacokinetic profiles. However, only a few formulations of NIC have demonstrated this behavior. It remains unclear whether NIC undergoes enterohepatic circulation.10

In a study conducted by Seo et al20 the impact of NIC on seven CYP isoenzymes was examined. Results indicated that NIC showed negligible inhibitory activity on most of the tested isoenzymes, except for CYP1A2 and CYP2C8. The IC50 values for these two isoenzymes were found to be 6.66 uM and 6.34 uM, respectively, signifying that NIC has a potent inhibitory effect on these specific CYP enzymes. Therefore, it is essential to highlight the need for careful consideration of potential drug-drug interactions mediated by CYP enzymes, particularly those involving these two isoforms.20 The authors concluded that NIC is improbable to display time-dependent inhibitory effects on CYP1A2 and CYP2C8. Consequently, careful consideration is crucial when selecting drugs for co-medication with NIC to prevent adverse reactions.

Regarding NIC safety, several studies have reported that the oral administration of NIC is safe.2 However, clinical trials also present conflicting findings. For instance, in their review, Jara and Williams2 reported differing maximum tolerated doses. In the phase I clinical trial NCT02532114 of 2018, Schweizer et al observed that patients tolerated doses of up to 500 mg three times daily (TID), totaling 1500 mg/day in solid capsule form. Furthermore, it was concluded by the authors that the administered dose of NIC per os (PO) should not be above 500 mg TID.27 Conversely, in the subsequent phase Ib clinical trial conducted by Parikh et al in 2021 (NCT02807805), patients were administered 1200 mg of a NIC formulation orally twice a day, reporting favorable patient tolerance.28 However, it must be noted that in the above-cited studies, NIC was administered along with another drug (enzalutamide and abiraterone/prednisone, respectively).

It can be said that safety profile of systemic delivery of NIC remains largely unexplored, necessitating future studies for a clearer understanding of its toxicity. The oral dose of NIC as a cestocidal agent is 2g as a single dose, resulting in a wide range of serum concentrations due to variable absorption rates. Consequently, the efficacy of clinical studies is unpredictable due to low oral bioavailability and substantial variations in serum concentrations. Further investigations utilizing formulations with high bioavailability are necessary before NIC can be more widely utilized.29

Pharmacokinetics of NIC

Pharmacokinetic data was collected from a study conducted by Choi et al, where NIC was administered to rats and dogs via intravenous (IV), oral (PO), and intramuscular (IM) routes at various doses.23 The dosing solutions were prepared using a solvent mixture comprising 10% DMSO, 30% PEG, 20% of 0.05N NaOH, and 40% saline.23 Following intravenous (IV) administration to rats, the authors observed that increasing the nominal dose of NIC by 3.3 and 10 times led to dose-dependent increases in Cmax and AUClast, specifically by 3.0 and 11.5 times, respectively. The clearance (CL) values were moderate compared to the hepatic blood flow rate of rats and did not show significant changes with the NIC dose. This implies that NIC was primarily confined to the plasma pool with limited tissue distribution due to its high plasma-protein binding properties. Indeed, the authors found that plasma protein binding in rat, dog, and human plasma samples was remarkably high, with values of 99.86% ± 0.006%, 99.83% ± 0.015%, and 99.84% ± 0.042%, respectively.23 This is in accordance with Seo et al20 NIC presented a linear pharmacokinetic profile in an IV gavage. In rats, the oral bioavailability of NIC was measured at 5.51% ± 1.02%, with very low plasma exposure, suggesting limited absorption. This is the result of the moderate clearance (CL) value in comparison to the hepatic blood flow rate of rats. The authors stated that NIC presented flip-flop kinetics. This implies that the rate of absorption is lower compared to the rate of elimination. Conversely, the absorption rate of NIC via intramuscular (IM) administration in rats was high, with a Tmax of 5 minutes, and the bioavailability was higher than that achieved via oral (PO) administration.

In dogs, following intravenous (IV) administration, a high mean clearance (CL) was observed, along with a low volume of distribution at steady state (Vss), indicating poor distribution of NIC in tissues. Additionally, after oral administration, flip-flop kinetics were observed, and the oral bioavailability of NIC was only 0.54%, attributed to the high CL value.

Regarding biodistribution, NIC initially accumulates in the intestines, kidneys, liver, and spleen. Levels of NIC in the heart and lungs are negligible following intravenous (IV) administration after an IV administration in rats (2 mg/kg).2,25 On the other hand, after oral administration of NIC ethanolamine to mice, Tao et al observed that the biodistribution of the NIC salt was higher in the liver and kidneys, with lower levels detected in the heart and lungs. Concentration in the spleen was undetected. The authors did not evaluate the concentration in the intestine.26 These discrepancies could be attributed to variations in the routes of administration, diverse animal models, and the distinct forms of NIC (such as salt) utilized in the studies.

Additionally, Yang et al introduced a novel NIC prodrug (PDNIC).30 Their research revealed that following both intravenous (IV) and oral (PO) administrations of PDNIC, there was a notably high tissue-to-plasma AUC0- ∞ ratio in well-perfused tissues such as the heart, lung, kidney, liver, spleen, and intestine. Conversely, distribution to adipose tissue and the brain was comparatively lower.

NIC Modifications for Solubility Enhancement NIC Derivatives

The literature reports various NIC derivatives and their superior biological activity. However, the main focus of this review will be the solubility and pharmacokinetic improvement of the new derivatives. Some of the derivatives with the most prominent improvement in solubility, biological activity and ADME (Absorption, Distributions, Metabolism, Excretion) characteristics are presented in Figures 1 and 2.

Figure 1 Chemical structure of NIC (A) and derivatives with enhanced solubility and biological activity prepared by Chen et al31 (B), Xu et al32 (C), Ma et al33 (D), He et al34 (E), Wu et al35 (F), Li et al36 (G), Mook et al37 (H) and Yang et al38(I).

Figure 2 The chemical structure of NIC (A) and selected derivatives (B-E) synthesized by Shamim et al38 that show activity against the SARS-CoV-2 infection and Zika virus with significantly improved in vitro drug-like properties such as microsomal stability, solubility, and PAMPA permeability compared to NIC.

Chen et al modified the hydroxyl group on the phenol ring of NIC, introducing an O-alkylamino side chain (Figure 1B).31 The author stated that scaffolds containing amino groups are crucial motifs for structural tuning, possessing the capability to engage in hydrogen bonding, and are therefore expected to have better solubility. The most successful derivatives were produced through the Mitsunobu coupling of NIC with N-Boc-protected amino alcohols, followed by Boc deprotection. Compounds HJC0125 and HJC0152, among all derivatives, not only showed improved anticancer activity but also displayed a notable increase in aqueous solubility. Indeed, compound HJC0125, with a pentylamine side chain, showed a saturated concentration of 248 μg/mL, indicating a 1080-fold improvement in water solubility. Compound HJC0152 with an ethylamine side chain, exhibited a saturated concentration of 762 μg/mL, improving water solubility of NIC by 3300-fold. Additionally, it was demonstrated that in MDA-MB-231 cells, the novel derivative HJC0152 suppressed STAT3 promoter activity, increased active caspase-3 expression, halted cell-cycle progression, and induced apoptosis. Furthermore, in nude mice presenting breast tumor xenografts, HJC0152 significantly inhibited the growth of MDA-MB-231 xenograft tumors in vivo.

Xu et al further synthesized O-alkylamino-tethered derivatives of NIC.32 The most successful compound (HJC0431) with 4-aminobutyl moiety (Figure 1C), was also synthesized via the Mitsunobu coupling reaction, as described earlier. Compound HJC0431 revealed a saturated concentration of 650 μg/mL. In this study, aiming to develop novel antibacterial derivatives this compound also showed the broadest antibacterial activity, being effective against 6 strains.

The ethanolamine salt of NIC was also synthesized. It was reported that the solubility of ethanolamine salt increases to 180–280 mg/L at 20 °C compared to 5–8 mg/L of NIC and that this form of NIC has an excellent safety profile8,39. The synthesis of NIC ethanolamine salt (NEN) is reported by Kapale as by patent CN106496060A.8 Tao et al discovered that NEN exhibits a remarkable antidiabetic effect in mice. Following oral administration, the LD50 value of NEN remained consistent or even higher compared to NIC. This observation indicates that pro-longed oral therapy with NEN does not present any toxic effects.26 Ma et al synthesized pegylated NIC with mPEG-5000 (mPEG5000-nic, Figure 1D)) by reversible addition-fragmentation chain transfer polymerization (RAFT) method.33 It was designed for injectable administration. The authors reported that the water solubility of the pegylated NIC was over 1.8 mg/mL, representing an 8000-fold increase with respect to pure NIC. The authors attributed the enhanced solubility to the self-assembly of mPEG5000-NIC in water. This self-assembly improved the water solubility of NIC, as the hydrophilic chain segment mPEG mutually entangled and enveloped the hydrophobic group NIC. Consequently, NIC was evenly distributed in the water without precipitation. The in vitro release experiment was conducted in phosphate-buffered saline (PBS) with a pH of 7.4 and a concentration of 0.01M, supplemented with 0.5% (wt/wt) Tween 80. NIC, grafted onto the copolymer, exhibited a gradual and sustained release extending up to 11 days, with cumulative drug release exceeding 80%. The novel formulation demonstrated antitumor efficacy both in vitro and in vivo, showing comparable antitumor activity to 5-fluorouracil but with lower toxicity.

In another investigation, He et al created a set of degradable NIC derivatives to target small-cell lung cancer.34 The authors modified the hydroxyl group on the phenol ring of NIC, introducing a phosphate and disodium phosphate moiety (Figure 1E). The water solubility of the new derivatives was reported to be 7.2 mg/mL and 22.1 mg/mL respectively, while the water solubility of NIC was reported to be 0.06 mg/mL. This represents a 120-fold and 368-fold increase in aqueous solubility, respectively. These two compounds displayed anti-small cell lung cancer (SCLS) activity comparable to the most potent compound among the new derivatives, which had very limited solubility.

Wu et al synthesized a new NIC derivative, B17, obtained by the fusion of hydroxybenzamide NIC’s ring (Figure 1F), targeting urological cancers.35 The authors stated that B17 exhibited increased solubility (10.6 mg/mL) compared to NIC (1.6 mg/mL) in DMSO.

Another NIC derivative JMX0207, with a 3-NO2 group, (without the 5-Cl moiety, Figure 1G) was tested in vivo and in vitro for antiviral efficacy against the Zika virus. The derivative showed improved pharmacokinetic properties. When given orally to B6 mice at a dose of 40 mg/kg, JMX0207 exhibited Cmax of 145±18 μM (242-fold improvement), T1/2 of 4.6±1.0 hours (2.39-fold increase) and an AUC0-∞ of 2719± 1018 (777-fold increase).36

Mook et al synthesized a series of NIC derivatives and discovered an acyl derivative, DK-520 (Figure 1H), which substantially increased both the plasma concentration and the duration of exposure to NIC when administered orally.37 This results from the capacity of the derivative DK-520, which has a octanoyl moiety instead of the -OH, to metabolize into NIC, thereby increasing the exposure of NIC after oral administration. The derivatives were synthesized by coupling substituted anilines with 5-chloro-2-hydroxybenzoic acid. The authors reported that administering a 200 mg/kg solution of DK-520 to mice in corn oil resulted in higher plasma exposure compared to published studies on NIC orally dosed at 200 mg/kg, as referenced in the study by Osada et al14 The Cmax, AUC and the duration of exposure all increased with the new derivate. Plasma concentrations of NIC, following the administration of DK-520 at 200 mg/kg, surpassed the IC50 for inhibiting Wnt signalling in the TOPFlash assay for nearly 24 hours. In comparison, the reported plasma levels of NIC dosed as a solution at 200 mg/kg were only above the IC50 for Wnt inhibition in the TOPFlash assay for less than 1 hour. Moreover, this elevated NIC exposure did not lead to any observed toxicity.

Yang et al introduced a novel NIC prodrug (PDNIC) called NCATS-SM4705 (Figure 1I).30 The prodrug exhibits an acyloxy piperazine moiety on the -OH group. PDNIC exhibited a remarkable 40-fold increase in solubility at pH 7.4 when compared to NIC. The in vitro metabolic stability of PDNIC was assessed using plasma and liver fractions from mice, hamsters, and humans. PDNIC exhibited rapid biotransformation to NIC in mouse and hamster plasma, but a significantly slower biotransformation in human plasma. In mouse and human liver microsomes, only a minor fraction of PDNIC was converted to NIC, whereas a slightly higher proportion of NIC was converted to NIC in hamster microsomes. In vivo studies conducted in mice following both intravenous (IV) and oral (PO) administration demonstrated high oral absorption of PDNIC, with a bioavailability of 85.6% and a moderate clearance. The formulation used was composed as follows: 5% ethanol, 60% PEG-300 and 35% of 20% HP-β-CD solution in water. The administered doses were 3 and 10 mg/kg for IV and 10 mg/kg for PO gavage. The authors noted that PDNIC can be effectively converted to NIC in vivo following both intravenous (IV) and oral (PO) doses, with the plasma AUC0-∞ ratio of NIC to PDNIC ranging from 0.34 to 0.48. The dose-normalized AUC0-∞ of NIC was 216 (h*ng/mL)/(mg/kg) after a PO dose of PDNIC (10 mg/kg), which was 8-fold higher compared to a PO dose of NIC at 40 mg/kg as the authors compare to the study reported by Fan et al22 As stated before, PDNIC was highly distributed in well-perfused tissues (heart, lungs, kidney, liver, spleen and intestine) and presented a low distribution in adipose and brain. The Vdss was 0.28–0.33L. Additionally, following an oral dose of 10 mg/kg PDNIC, the lung-to-plasma AUC0-last ratio of NIC was approximately 0.97, marking a 3.6-fold increase compared to 0.27 reported after an oral dose of NIC (40 mg/kg).22 Following intravenous doses of PDNIC, the formed NIC exhibited a terminal half-life (T1/2) ranging from 2.7 to 4.5 hours in plasma and similar half-lives in other tissues, except for the liver, where the elimination of NIC was notably 4-fold slower than in all other tissues, with terminal half-lives ranging from 11.6 to 21.2 hours. Similar profiles were observed in the 10 mg/kg oral group. In vivo studies were conducted in hamsters using both intravenous (IV) and oral (PO) doses. The IV dose administered was 3 mg/kg, while the PO dose was 30 mg/kg. The formulation used for both IV and PO administration was 20% HP-β-CD in water (0.6 mg/mL for IV and 3 mg/kg for PO). PDNIC demonstrated efficient conversion to NIC in vivo, with plasma AUC0-∞ ratios (NIC/PDNIC) of 0.32 and 0.44 after both IV and PO doses, showing similarity to observations in mice. The dose-normalized AUC0-∞ of NIC was 88 (h*ng/mL)/(mg/kg) after the PO dose of PDNIC (30 mg/kg), slightly lower than that observed in mice. The prodrug exhibited a Vdss of 0.74 L in hamsters. Additionally, after both IV and PO doses of PDNIC, the lung to plasma AUC0-∞ ratio of NIC was 72 and 107 respectively. This value is quite higher than that in mice. Following an oral dose of 30 mg/kg, the bioavailability of PDNIC in hamsters is approximately 64%, slightly lower than that observed in mice. It’s worth mentioning that the formulation media for mice and hamsters differed. The mice formulation contained 60% PEG-300. This raises questions about whether PEG might impact the formulation outcome in some way and be also responsible for some differences in pharmacokinetic parameters.

Shamin et al synthesized a series of NIC derivatives (Figure 2), concentrating on the anilide and salicylic regions of NIC to enhance physicochemical properties and target the inhibition of Zika virus and SARS-CoV-2 infection.38 The objective was to investigate the impact of electron-donating and electron-withdrawing substitutions in both regions of NIC. The authors aimed to identify a suitable replacement for the aniline 4-NO2 group, which could undergo reduction and glucuronidation in vivo. Among all tested compounds, the 5-bromo substitution in the salicylic acid region demonstrated retained potency along with improved ADME properties. It exhibited enhanced solubility (8 µg/mL), good rat liver microsomal stability (t1/2 greater than 30 min), and increased PAMPA permeability (6.7 x 10−5 cm/s). Moreover, the alterations in the anilide region with 2-OMe and 2-H substitutions demonstrated comparable IC50 values to NIC in the NS-1 assay, while exhibiting markedly improved physicochemical properties compared to NIC. Through modifications in the anilide region, it was discovered that 4-CN and 4-CF3 served as suitable replacements for 4-NO2. These compounds exhibited similar potencies to NIC in the NS-1 inhibition assay while offering enhanced physico-chemical properties, such as microsomal stability, solubility, and PAMPA permeability.38

Amorphous Solid Dispersions

The use of hydrophilic polymers in creating amorphous solid dispersions (ASDs) is a well-established method to enhance the aqueous solubility of poorly soluble drugs, directly impacting bioavailability.40 ASDs, generally, are dispersions where the drug is dissolved within a solid matrix, typically a polymer.41 Amorphous materials enhance the apparent solubility of the drug by increasing its thermodynamic activity when it is dispersed in a molecularly and randomly distributed manner within the polymer.42,43 NIC has a limited ability to form an amorphous solid on its own, as it is a poor glass former with a high tendency to recrystallize. However, it can form an amorphous solid dispersion (ASD) when dissolved in a solid matrix, such as a polymer.2 Furthermore, the addition of a third component (surfactant, polymer, or excipient) prevents drug precipitation and stability issues, offering advantages like controlled drug release, heightened drug loading, and improved stability compared to binary ASDs.40 Jara et al developed an amorphous solid dispersion (ASD) of NIC that generates nanoparticles during dissolution.1 It was prepared by the hot melt extrusion method wherein the drug was formulated with poly (1-vinyl pyrrolidone-co-vinyl acetate (PVA-VA). The NIC ASD produced nanoparticles with an average particle size of approximately 100 nm in fasted simulated intestinal fluid (FaSSIF) media. The ASD not only raised NIC apparent solubility from 6.6±0.4 to 481.7 ± 22.2 μg/mL in FaSSIF, representing a 60-fold increase but also enhanced its oral availability by 2.6 times in Sprague-Dawley rats when administered as a suspension. The same formulation was also administered as capsules containing sodium bicarbonate to counteract the acidic stomach pH, but, there was no statistically significant increase in bioavailability. Furthermore, in a side-by-side diffusion test, where the media was FaSSIF and decanol, a four-fold increase in NIC diffusion was reported. However, the same authors stated that NIC ASD in acidic media, undergoes recrystallization, suggesting that an enteric coating would be necessary to avoid this problem. In a further study of the same group, the overall formulation contained NaCl to facilitate the dissolution of the tablets, croscarmellose sodium as a disintegrant, and microcrystalline cellulose, and was sealed with the poly(vinyl alcohol)-based coating known as Opadry® II Clear.9 After that, the tablets were enteric coated with Acryl-EZE® 93 A. The enteric-coated tablets were administered to fasted beagle dogs. The administration dose was 75 mg/kg. The detected plasma concentrations were up to 149 ± 79.2 ng/mL. The plasma concentrations achieved were superior to those documented with NIC dissolved in a blend of solvents, polymers, and pH modifiers (DMSO, PEG, NaOH, and saline buffer) given at a higher dose (100 mg/kg) to beagle dogs.23 This proves the success of the enteric coat in protecting the formulation from the acidic environment.

Bhanushali et al developed a variety of binary and ternary amorphous solid dispersions of NIC with various polymers and polymer to NIC ratios.40 The most successful was the one containing NIC and hydroxyethyl cellulose (HEC) in a NIC-to-polymer ratio of 1:4. The p-XRD findings confirmed the amorphous trans-formation of NIC within the formulation. The water solubility of NIC increased significantly by 70 times (428.333±14.142 μg/mL) compared to pure NIC (6.14 ± 0.67 μg/mL). The pharmacokinetics of NIC and the ASD formulation of NIC were compared in healthy female Wistar rats at a dose of 25 mg/kg administered orally. The authors reported a 4-fold improvement in Cmax. The AUC0-t presented a 4.41-fold increase while the AUC0-∞ presented a 4.17-fold increase.

NIC Co-Crystals

Co-crystal engineering provides an alternative approach to modify the physicochemical properties of a drug, thereby enhancing drug delivery. Co-crystals consist of two components with a fixed stoichiometric ratio, connected by non-covalent bonds. One component is the pharmaceutically active drug, and the other is the inactive co-former, typically considered a Generally Recognized as Safe (GRAS) molecule.44 Co-crystals are documented to effectively improve the solubility, dissolution rate, bioavailability, and physical stability of active pharmaceutical biomaterials.45

Ray et al developed an inhalable co-crystal formulation of NIC-nicotinamide (NIC-NCT) via a rapid and continuous spray drying method (SDC) and a solvent evaporation method (SEC) for comparison.44 Needle-shaped co-crystals with a mean particle size of 11.52 ±6.65 μm were obtained from the solvent evaporation method. In contrast, spherical co-crystals, with a mean particle size of 4.76 ±1.26 μm were obtained by the spray drying method. The yields for NIC-NCT co-crystals, produced via spray drying and solvent evaporation methods, were 71.4% ± 8.46% and 66.4% ± 7.33%, respectively. DSC analysis indicated that a glassy transition was observed in the case of spray-dried NIC-NCT co-crystal powder. Such transitions are primarily characteristic of amorphous powders. The co-crystals of the drug exhibited a substantial improvement in solubility. Furthermore, SEC NIC-NCT co-crystals showed a 5.9-fold increase, while SDC NIC-NCT demonstrated a 14.8-fold increase in the dissolution of NIC. Furthermore, SDC improved aerodynamic parameters, including MMAD (median mass aerodynamic diameter) and FPF (fine particle fraction), enhancing its suitability for inhalation and deposition within the deep lung. In contrast, needle-shaped SEC co-crystals exhibited a larger mass median aerodynamic diameter size and lower fine particle fraction compared to spherical SDC. These findings suggest the inadequacy of the SEC formulation for in vitro inhalation. Moreover, SDC demonstrated higher anti-proliferative activity against human lung adenoma cells in a dose-dependent manner, surpassing both NIC alone and SEC co-crystals. However, the poor glass-forming ability of NIC demonstrated previously1 may lead to physical instability of the spray-dried system. In this light, the recrystallisation of amorphous NIC-NCT spray-dried product should be further examined.

Ludeker et al employed solvent-assisted solid grinding and/or slow solvent evaporation to produce new co-crystals of NIC.46 NIC-aminothiazole 1:1 co-crystal (NIC-AT) proved to be the most successful among them. The other candidates were NIC-benzamide, NIC-isoniazide and NIC-acetamide. The equilibrium solubility of NIC-AT co-crystals was reported to be 2.8 times higher than that of NIC. Furthermore, the newly developed NIC-AT co-crystal exhibits notable stability, lasting for over 18 months, likely attributed to its robust hydrogen bonding motifs.

Grifasi et al obtained a new series of salt co-crystals by grinding NIC with carbonates and bicarbonates. Additionally, a mechanochemical reaction with imidazole yielded a classical co-crystal. Furthermore, two new salts were generated via the salification of NIC with NaOH and subsequent kneading with DMSO.47 According to the authors, a “salt co-crystal” refers to the concurrent existence of a neutral molecule and its salt within the same unit cell, engaging in hydrogen bonding interactions. The dissolution tests were conducted in an ethanolic aqueous solution (1:1). The most soluble sample was found to be ‘NaNIC·HNIC·2H2O’, which was synthesised by kneading (absolute ethanol) NIC with sodium carbonate, in a 4:1 stoichiometric ratio, at room temperature for 35 minutes. The intrinsic dissolution rate of NaNIC·HNIC·2H2O increased by a factor of 5. The concentration of NIC after 72 hours has been reported as 24 mg/L for the NaNIC·HNIC·2H2O and 3.5 mg/L for pure NIC.

Sanphui et al prepared 1:1 co-crystals of NIC with caffeine, urea, p-aminobenzoic acid, theophylline, nicotinamide, and isonicotinamide.48 The preparation of NIC co-crystals was achieved through dry grinding, wet granulation, and slow evaporation methods. Dry solvents (ethyl acetate and acetonitrile) were used to avoid hydrate formation. NIC-theophylline acetonitrile solvate (NIC-THPHS) showed the highest solubility in 40% i-PrOH-water after 24 h, followed by NIC theophylline co-crystals (NIC-THPH). The improvements in solubility were 1.4- and 1.31-fold respectively. Powder dissolution in the same medium was carried out and after 2 hours, NIC-THPHS showed the fastest dissolution rate (6.3-fold increase) followed by NIC-THPT (5.1-fold increase). The authors noted that all crystalline forms transformed into NIC mono-hydrate (HA) within 24 hours, leading to a very similar solubility for all co-crystals.

In a recent paper, D’Abbrunzo et al prepared the novel NIC co-crystal by combining it with praziquantel (PZQ), another anthelminthic drug.49 Such dual-drug antiparasitic co-crystals were obtained through a sustainable one-step mechanochemical process by grinding a PZQ/NIC molar ratio of 1:3 in the presence of micromolar amounts of methanol for 120 min at 25 Hz, resulting in pure solid products, without any traces of the starting reagents or solvent. Also, both drugs retained their chemical stability during the grinding procedure, regardless of the typical tendency of PZQ to degrade during the grinding. The novel solid phase crystallizes in the monoclinic space group of P21/c, showing one PZQ and three NCM molecules linked through homo- and heteromolecular hydrogen bonds in the asymmetric unit, showing a plate-like habitus ranging in size from 150 to 15000 nm. PZQ/NIC co-crystal presented a melting point of 202.89°C, which is intermediate to those of the parent compounds (ie 141.9 and 229.98°C for PZQ and NIC, respectively). The supramolecular interactions confer favorable properties to the co-crystal, preventing NIC transformation into the insoluble monohydrate both in the solid state and in the aqueous solution. After 72 h of exposure, PZQ/NIC co-crystal exhibits higher anthelmintic activity against adult Schistosoma mansoni in vitro than the corresponding physical mixture of the APIs (IC50 0.02123 and 0.09610 µM, respectively) Such prominent efficiency of PZQ/NIC co-crystals was further confirmed on the mice models with chronic S. mansoni infection.

Nano-Based Drug Delivery Systems

Nanosized materials possess unique physicochemical properties, featuring a significant surface area-to-mass ratio and enhanced permeability and solubility. These characteristics offer potential solutions to the limitations of traditional therapeutic and diagnostic agents.50 Heightened surface area improves particle adhesion to biological membranes, enhancing cellular uptake. Drug incorporation into nanocarriers helps reduce degradation and toxicity. Nanomaterials play a crucial role in drug targeting, where nanocarrier surfaces can be coated with ligands binding to receptors overexpressed by target cells, like in cancer disease.10 Despite the numerous advantageous features of nanocarriers, a primary drawback or challenge is their stability. These systems exhibit high total surface energy, rendering them thermodynamically unstable and prone to agglomeration, resulting in an increase in particle size. Hence, the utilization of polymers and/or surfactants are commonly employed strategies to maintain the stability of the system.10 Various strategies have been employed to develop nanostructured systems, as listed below.

Nanocrystals

Drug nanocrystals, are created by reducing the particle size of the micronized compound to the nanoscale. These colloidal dispersion systems are stabilized in water using surfactants or polymers.10,25 One advantageous aspect of nanocrystals is that the formulation does not necessitate the incorporation of the drug into a matrix system, allowing for 100% drug loading in the nanoparticles.10 Drug nanocrystals represent an intermediate stage in the preparation process, adaptable for further formulation into tablets, capsules, sprays, injections, and various administration routes.25

Ye et al formulated an injectable nanocrystal formulation of NIC was developed using a top-down wet milling technique.25 Tween 80 was chosen as a stabilizer. The final formulation comprised one aliquot of Tween 80 and five aliquots of NIC. The obtained nanocrystals had a mean particle size of 235.6 nm with a unimodal distribution. The nanocrystal formulation exhibited no significant difference in the drug release profile, as determined by the reverse bulk equilibrium method using a pH 7.4 buffer with 0.2% Tween-80 as the medium. Sprague-Dawley rats were administered a NIC-nanocrystal suspension or a NIC solution (dissolved in 30% alcohol/45% PEG400/20% water) through the jugular vein at a dose of 2 mg/kg. The newly formulated product did not demonstrate a significant enhancement in the plasma concentration versus time profile when compared to pure NIC. The authors postulated that the rapid release of drug molecules into the bloodstream upon intravenous administration could be a contributing factor. However, there was a significant difference in the biodistribution. The nanocrystal formulation exhibited higher drug levels in the heart, spleen, and lungs after 4 hours, indicating ongoing distribution at that time point. The most significant difference was observed at 2 hours, with NIC solution showing higher tissue drug levels than the nanocrystal formulation, in all tissues, implying longer blood residence time for NIC nanocrystals. The physical and chemical stability of the NIC nanocrystals was satisfactory after 60 days of storage.

Lin et al utilized the electrospray technique to create NIC nanoparticles for assessing their anticancer activity against ovarian cancer cells.50 The nanosuspension included 1% polyvinyl alcohol (PVA) in a phosphate-buffered saline solution. The average particle diameter was 105 nm. The dosing solution, formed by dissolving nano-NIC in PBS, was orally administered or intravenously (IV) injected to female Sprague-Dawley rats at doses of 5 mg/kg and 2 mg/kg, respectively. The AUC was calculated to be 669.5 and 1058 h(ng·mL) for the oral and IV routes, respectively. The estimated oral bioavailability was 25%, surpassing the reported 10% bioavailability of NIC. The authors noted a swift rise in NIC plasma concentration for both oral and IV routes, followed by a rebound peak at 4 hours. Since the second peak was also observed for the IV route, the authors attributed this phenomenon to an enterohepatic recycling mechanism. They mentioned that this observation aligns with the findings of a prior study in mice14. The nanosuspension effectively inhibited the metabolism and in vitro growth of CP70 and SKOV3 cells, achieving IC50 values of 3.59µM and 3.38 µM, respectively.

Bai et al also developed novel NIC suspensions using a single- or dual-capillary electrospray system (ES) addressed in ovarian cancer treatment, in vitro.51 The ES technique is employed to reduce the size of raw NIC powder particles (Nano-NIC), which are subsequently suspended in PBS containing a stabilizer. Homogeneous suspensions of pure NIC or NIC-encapsulated poly (D, L-lactic-co-glycolide) (PLGA) particles were developed. The single- or dual-capillary ES system offers versatile fabrication, enabling control over drug carrier configurations, including nanocrystalline, matrix type, or core-shell type. This is exemplified by the creation of Matrix-type NIC-PLGA and core-shell type NIC-PLGA nanoparticles using single- and dual-capillary electrospray (ES), respectively. The suggested electrospray (ES) was operated in a cone-jet mode to generate particles of NIC, with or without a PLGA shell that can be readily suspended in a water-based solution to form a suspension. This strategy minimizes the utilization and remnants of organic solvents in drug formulation. Pure NIC nanoparticles were rod-shaped (105 nm x 493 nm), while NIC-encapsulated PLGA particles are spherical, with a diameter of approximately 584–662 nm. Nano-NIC particles, without PLGA encapsulation, release NIC faster than PLGA-encapsulated particles and raw NIC powder within 500 hours. They show approximately 1.6-fold increased water solubility compared to raw NIC, possibly due to enhanced surface area. Nano-NIC particles released 31.6%, compared to raw NIC powder which released 19% of the total amount of NIC within 500 hours of test time. Interestingly, the core-shell NIC-PLGA nanoparticles displayed a two-stage release profile, while the matrix NIC-PLGA nanoparticles exhibited a faster and gradually elevated release over the 500-hour test. Beyond 500 hours, the release kinetics of NIC-PLGA particles accelerate more than nano-NIC particles. This is believed to be due to the degradation of PLGA, leading to the abrupt release of embedded NIC molecules. The authors suggested, according to Sardo et al52 that reducing particle size would be advantageous, as the release kinetics of drug-encapsulated PLGA particles are closely tied to their particle size. Nano-NIC and NIC-PLGA suspensions showed a stronger anti-proliferative ability than the conventional NIC. The matrix NIC-PLGA nanoparticles exhibited an IC50 of 1.37 µM in the treatment of CP70 cells. It is important to mention that the generated NIC (pure or encapsulated) was present as a mono-hydrate and not as an anhydrous form.

Costabile et al developed an inhalable formulation of NIC through nanosuspension technology for the therapy of Pseudomonas aeruginosa.53 The group created dry powders containing NIC nanoparticles, which can be reconstituted in saline solution to produce inhalable nanosuspensions. NIC nanoparticles were generated through high-pressure homogenization (HPH), with polysorbates employed as stabilizers. Following 20 cycles of HPH, all formulations exhibited comparable characteristics, appearing as needle-shaped nanocrystals with a hydrodynamic diameter of around 450 nm. The nanosuspensions stabilized with 10% w/w polysorbate 80 to NIC (T80_10) displayed an optimal solubility profile in interstitial lung fluid. T80_10 was effectively converted into a mannitol-based dry powder using the spray-drying technique. (T80_10 DP). Dry powder was reconstituted in saline solution. The results from in vitro release studies of NIC, conducted using a dialysis membrane from simulated cystic fibrosis (CF) mucus to simulated interstitial lung fluid (SILF), indicated no significant difference in the percentage of NIC diffused after 8 hours between T80_10 DP (58.1 ± 6.5%) and T80_10 (63.3 ± 8.0%). Conversely, the diffusion rate of Micro NIC (raw NIC micronized through a colloidal mill) considerably slowed down (22.9 ± 1.3%). The reconstituted spray-dried particles in saline solution were efficiently delivered via commonly used nebulizers, with optimal performance observed using the PARI TurboBOY and Aeroneb Pro nebulizers. The nanosuspensions demonstrated in vitro quorum sensing inhibition of P. aeruginosa at non-toxic concentrations for CF bronchial cells. In vivo data affirmed the absence of acute toxicity at therapeutic doses. Despite these positive results, Brunaugh et al54 noted that the amount of polysorbate used exceeds what is currently FDA-approved for inhaled products. Furthermore, they pointed out that the utilization of mannitol as the carrier system may induce bronchospasm and cough.54

Furthermore, Hobson et al developed a long-acting injectable solid dispersible nanoparticulate formulation (SDN) for the treatment of Covid-19, intended for intramuscular administration.55 The advantage of SDNs lies in their composition, consisting solely of the active pharmaceutical ingredient (API), and their ability to be stored in solid form, and then easily re-dispersed in water before use. Briefly, this formulation was obtained by inducing nanoprecipitation of NIC when NIC is pumped into an aqueous solution of stabilizers (HPMC) and sugars (sucrose), sonicating the dispersion and pumping it into a spray-dryer. The obtained nanoparticles can be dispersed in aqueous media for injection. The sustained-release characteristics of NIC delivery via nanoprecipitation were assessed in vivo over 28 days in Sprague Dawley rats. Three distinct intramuscular doses: 50, 100, and 200 mg/kg were administered. All injected doses achieved a maximum concentration (Cmax) within 3 hours. The bioavailability increased with higher doses. The Cmax values were reported to be 1408.6, 2041.3, 3125.3 ng/mL and AUC of 28955, 55,734, 74584 ng h /mL for 50, 100, and 200 mg/kg doses. A sustained plasma exposure was unmistakably attained, and the release kinetics were characterized as “flip-flop.” As stated by the authors, his phenomenon is particularly beneficial for long-acting therapeutics, as it often occurs when drug absorption from extravascular routes appears slower than the rate of drug elimination. Furthermore, the authors reported that no obvious local toxicity was observed during the 28 days of the in vivo study.

Micelles

Polymeric micelles have demonstrated the ability to enhance drug solubility and reduce toxicities when compared to traditional carriers.56 These micelles comprise hydrophilic and hydrophobic chain segments, forming core-shell nanomicelles with an inner lipophilic and outer hydrophilic structure.57 Hang et al prepared micelles named PEG2K-FIbu/NIC by a thin film dispersion method. They incorporate a hydrophilic PEG chain segment, a Fmoc motif, and the hydrophobic structural domain of ibuprofen while encapsulating NIC.57 Ibuprofen was chosen for its ability to enhance the stability of micelles. The particle size of PEG2K-FIbu was 11.11 nm while the encapsulation rate was 70.4% The tumor inhibition rate was 55.98%.

Bhattacharyya et al developed a formulation in which NIC is covalently conjugated to a genetically-encoded elastin-based chimeric polypeptide (CP).58 This CP comprises an elastin-like polypeptide, a disordered and highly water-soluble recombinant peptide polymer, fused to a short peptide segment containing thiol-reactive sites for the chemical conjugation of chemotherapeutic drugs. The resulting prodrug spontaneously self-assembles into 100 nm near-monodisperse micelles. The new formulation increased NIC half-life to 4.2 hours from 1 h. CP-NIC dissolved in PBS was injected in CD1 mice vein at a dose of 128 mg/kg. The plasma AUC of the CP-NIC was 36.9 ± 7.34 µg/mL/h compared to 3.3±1.3 µg/mL/h of unconjugated NIC. The plasma levels of CP-NIC at the dose of 128 mg/kg body weight stayed above the IC50 of Wnt signaling inhibition by NIC in the TOPFlash assay for nearly 24 hours, whereas unconjugated NIC remained above the IC50 for less than 1 hour. Unfortunately, the new conjugate expressed a low drug loading of 2% NIC only.

Russo et al designed biotin-targeted Pluronic P123/F127 mixed micelles (PMM) delivering NIC via intravenous injection to treat drug-resistant lung cancer cells.6 Pluronic F127 was biotin-conjugated for tumour targeting, and Pluronic 123 was labelled with rhodamine B for fluorescence tracking of micelles in a biological environment. NIC was encapsulated in the PMM. Approximately 8.3% of the micelle surface was covered with biotin. The Biotin-PMM were almost spherical in shape with a diameter in the range of 25–35 nm. The optimal formulation condition for NIC encapsulation was at 40 mg/mL for the Pluronic mixture and 0.7 mg/mL for NIC. The release profile of NIC from NIC-loaded Bio-PMM in phosphate-buffered saline (PBS) at pH 7.4 was assessed using the dialysis method. NIC demonstrated a biphasic release profile, with an initial burst (first 6 hours) followed by a sustained release phase lasting up to 48 hours. In Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (FBS), the release profile followed a biphasic pattern again, occurring at a slower rate, lasting up to approximately 75 hours. The results showed an increased presence of biotin-decorated PMM in cancer cells compared to normal cells. The enhanced cytotoxicity of biotin-targeted micelles loaded with NIC was clearly observed in A549 cells resistant to cisplatin and 5-FU.

Misra et al innovated the “niclocelle” by integrating NIC into well-defined rigid core polymeric micelles using a solvent evaporation method, following a mixed micellar approach.59 A tetrahydrofuran (THF) solution containing amphiphilic diblock co-polymer (polystyrene-block-polyacrylic acid) and a micellar suspension of polyethylene glycol cetyl ether (PEGCE) were co-self-assembled, incorporating NIC in the process. Control particles, called nanocelles are rigid core mixed micelles, without the inclusion of NIC, prepared with the same procedure. Incorporating PEGCE is crucial for limiting particle size to below 100 nm and enhancing micellar stability. The nanocelles had a size of approximately 100 nm, whereas the niclocells measured around 60 nm. This size reduction is likely attributed to the T-T interactions occurring between the aromatic moieties of the outer shell and NIC. The findings revealed an 87% loading of NIC in niclocelles. The drug release profile, in Dulbecco’s Phosphate-Buffered Saline (DPBS) at pH 7.4, showed an initial release of approximately 41% within the first 12 hours, followed by sustained release leading to a total release of about 82% over the 96-hour observation period. A significant enhancement in IC50 values ranging from 2.5- to 4-fold was observed for niclocelle compared to NIC across MCF-7, MDA-MB231, and MCF-7 cells.

Nanohybrids

Nanohybrids consist of composite or hybrid materials comprising two or more components, with at least one component existing at the nanoscale.60 The favorable properties and promising biomedical applications of organic/inorganic nanohybrids have garnered significant attention. Considerable efforts have been devoted to creating adaptable nanohybrids, with a variety of polymers emerging as notable organic components among them. These polymers provide distinct pathways for creating multifunctional systems with collective properties.61 In the domain of inorganic nanomaterials, clay-based nanoparticles, particularly layered double hydroxide (LDH) and montmorillonite (MMT), have received considerable attention for their applications in nanomedicine. Additionally, a variation of LDH known as hydrotalcite (HT) has been found to possess biocompatibility and mucoadhesive properties.62 Enhancing the dissolution of poorly soluble drugs through drug adsorption on silica materials represents a feasible and appealing strategy. This is attributed to several factors, including the substantial surface area, adjustable pore volume, controllable structural and textural parameters, and the abundance of silanol groups on the surface, which serve as potential sites for func