Improved Oral Bioavailability and Gastrointestinal Stability of Amphotericin B through Fatty Acid Conjugation Approach

Conjugates of amphotericin B to resolve challenges associated with its delivery

INTRODUCTION

Amphotericin B (AmB), a promising antifungal and antileishmanial drug, acts on the membrane of microorganisms. The clinical use of AmB is limited due to issues associated with its delivery including poor solubility and bioavailability, instability in acidic media, poor intestinal permeability, dose and aggregation state dependent toxicity, parenteral administration, and requirement of cold chain for transport and storage, etc.

AREAS COVERED

Scientists have formulated and explored various covalent conjugates of AmB to reduce its toxicity with increase in solubility, oral bioavailability, and payload or loading of AmB by using various polymers, lipids, carbon-based nanocarriers, metallic nanoparticles, and vesicular carriers, etc. In this article, we have reviewed various conjugates of AmB with polymers and nanomaterials explored for its delivery to give a deep insight regarding further exploration in future.

EXPERT OPINION

Covalent conjugates of AmB have been investigated by scientists, and preliminary in vitro and animal investigations have given successful results, which are required to be validated further with systematic investigation on safety and therapeutic efficacy in animals followed by clinical trials.

The role of alkyl chain length in the melt and solution crystallization of paliperidone aliphatic prodrugs

Fatty acid-derivative prodrugs have been utilized extensively to improve the physicochemical, biopharmaceutical and pharmacokinetic properties of active pharmaceutical ingredients. However, to our knowledge, the crystallization behavior of prodrugs modified with different fatty acids has not been explored. In the present work, a series of paliperidone aliphatic prodrugs with alkyl chain lengths ranging from C4 to C16 was investigated with respect to crystal structure, crystal morphology and crystallization kinetics. The paliperidone derivatives exhibited isostructural crystal packing, despite the different alkyl chain lengths, and crystallized with the dominant (100) face in both melt and solution. The rate of crystallization for paliperidone derivatives in the melt increases with alkyl chain length owing to greater molecular mobility. In contrast, the longer chains prolong the nucleation induction time and reduce the crystal growth kinetics in solution. The results show a correlation between difficulty of nucleation in solution and the interfacial energy. This work provides insight into the crystallization behavior of paliperidone aliphatic prodrugs and reveals that the role of alkyl chain length in the crystallization behavior has a strong dependence on the crystallization method.

Potential lipid-based strategies of amphotericin B designed for oral administration in clinical application

Amphotericin B (AmB) is regarded as a first-line therapy against life-threatening invasive fungal infections. Due to its poor oral bioavailability, AmB is restricted to intravenous administration in clinical practice. As science continues to move forward, two lipid-based formulations are successfully developed for oral AmB administration, currently undergoing phase I clinical trials. Encouragingly, lipid-AmB conjugates with emulsions also exhibit a better bioavailability, which may be another strategy to design oral AmB formulation in clinical practice. Thus, this review mainly focused on the two lipid-based formulations in clinical trials, and discussed the potential perspectives of AmB-lipid conjugation-loaded nanocochleates and emulsions.

Exploring the permeability of Amphotericin B trough serum albumin dispersions and lipid nanocarriers for oral delivery

Amphotericin B (AmB) is a potent polyenic antifungal agent with leishmanicidal activity. Due to its low solubility and permeability in the gastrointestinal tract, AmB is usually administered intravenously. In this context, various approaches have been used to try to improve these properties. Some of the systems developed have shown proven successful, but there is still a lack of knowledge about the pathways AmB takes after oral administration. Therefore, the aim of this work was not only to obtain aqueous dispersions containing AmB at different aggregation states, but also to entrap this molecule in nanocarriers, and evaluate the influence of these conditions on the jejunal permeability of AmB. To observe the aggregation states of AmB, physicochemical characterization of AmB-albumin complexes and AmB-loaded formulations was performed. Different degrees of AmB aggregation states were obtained. Thus, permeability tests were performed in the Ussing chamber and a decrease in AmB concentration in the donor compartment was observed. Electrophysiological measurements showed different responses depending on the AmB formulation. In conclusion, although control of the AmB aggregation state was observed by physicochemical characterization, this approach does not seem to have a sufficient effect on AmB permeability, but on its toxicity. For a complete understanding of AmB-loaded nanocarriers, other pathways, such as lymphatic absorption, should also be investigated.

Treatment of H. pylori infection and gastric ulcer: Need for novel Pharmaceutical formulation

Peptic ulcer disease (PUD) is one of the most prevalent gastro intestinal disorder which often leads to painful sores in the stomach lining and intestinal bleeding. Untreated Helicobacter pylori (H. pylori) infection is one of the major reasons for chronic PUD which, if left untreated, may also result in gastric cancer. Treatment of H. pylori is always a challenge to the treating doctor because of the poor bioavailability of the drug at the inner layers of gastric mucosa where the bacteria resides. This results in ineffective therapy and antibiotic resistance. Current treatment regimens available for gastric ulcer and H. pylori infection uses a combination of multiple antimicrobial agents, proton pump inhibitors (PPIs), H2-receptor antagonists, dual therapy, triple therapy, quadruple therapy and sequential therapy. This polypharmacy approach leads to patient noncompliance during long term therapy. Management of H. pylori induced gastric ulcer is a burning issue that necessitates alternative treatment options. Novel formulation strategies such as extended-release gastro retentive drug delivery systems (GRDDS) and nanoformulations have the potential to overcome the current bioavailability challenges. This review discusses the current status of H. pylori treatment, their limitations and the formulation strategies to overcome these shortcomings. Authors propose here an innovative strategy to improve the H. pylori eradication efficiency.

Synthesis and Biological Evaluation of Amphotericin B Formulations Based on Organic Salts and Ionic Liquids against Leishmania infantum

Nowadays, organic salts and ionic liquids (OSILs) containing active pharmaceutical ingredients (APIs) are being explored as drug delivery systems in modern therapies (OSILs-API). In that sense, this work is focused on the development of novel OSILs-API based on amphotericin B through an innovative procedure and the evaluation of the respective biological activity against Leishmania infantum. Several ammonium, methylimidazolium, pyridinium and phosphonium organic cations combined with amphotericin B as anion were synthesized in moderate to high yields and high purities by the water-reduced buffer neutralization method. All prepared compounds were characterized to confirm the desired chemical structure and the specific optical rotation ([α]_D²⁵) was also determined. The biological assays performed on L. infantum promastigotes showed increased activity against this parasitic disease when compared with the starting chloride forms and amphotericin B alone, highlighting [P_6,6,6,14][AmB] as the most promising formulation. Possible synergism in the antiprotozoal activity was also evaluated for [P_6,6,6,14][AmB], since it was proven to be the compound with the highest toxicity. This work reported a simple synthetic method, which can be applied to prepare other organic salts based on molecules containing fragile chemical groups, demonstrating the potential of these OSILs-AmB as possible agents against leishmaniasis.

Limitations of current chemotherapy and future of nanoformulation-based AmB delivery for visceral leishmaniasis-An updated review

Visceral leishmaniasis (VL) is the most lethal of all leishmaniasis diseasesand the second most common parasiticdisease after malaria and,still, categorized as a neglected tropical disease (NTD). According to the latest WHO study, >20 Leishmania species spread 0.7-1.0 million new cases of leishmaniasis each year. VL is caused by the genus, Leishmania donovani (LD), which affects between 50,000 and 90,000 people worldwide each year. Lack of new drug development, increasing drug resistance, toxicity and high cost even with the first line of treatmentof Amphotericin B (AmB), demands new formulation for treatment of VLFurther the lack of a vaccine, allowedthe researchers to develop nanofomulation-based AmB for improved delivery. The limitation of AmB is its kidney and liver toxicity which forced the development of costly liposomal AmB (AmBisome) nanoformulation. Success of AmBisome have inspired and attracted a wide range of AmB nanoformulations ranging from polymeric, solid lipid, liposomal/micellar, metallic, macrophage receptor-targetednanoparticles (NP) and even with sophisticated carbon/quantum dot-based AmBnano delivery systems. Notably, NP-based AmB delivery has shown increased efficacy due to increased uptake, on-target delivery and synergistic impact of NP and AmB. In this review, we have discussed the different forms of leishmaniasis disease and their current treatment options with limitations. The discovery, mechanism of action of AmB, clinical status of AmB and improvement with AmBisome over fungizone (AmB-deoxycholate)for VL treatment was further discussed. At last, the development of various AmB nanoformulation was discussed along with its adavantages over traditional chemotherapy-based delivery.

Design of double functionalized carbon nanotube for amphotericin B and genetic material delivery

In the present work, single wall carbon nanotubes (SWCNT) were successively functionalized with phospholipid DSPE-PEG carboxylic acid, and then, with ethylenediamine (EDA), to obtain double functionalized single wall carbon nanotube (DFSWCNT). Then, DFSWCNT was applied as a carrier for delivering amphotericin B (Amb) and EGFP plasmid. FSWCNT's concentration obtained via UV-visible analysis was 0.99 mg/mL. The TGA analysis results provided the lost weights of DSPE-PEG-COOH, EDA, Amb and SWCNT impurities. XPS results showed that carbon atoms' percentage decreased during the functionalization processes from 97.2% (SWCNT) to 76.4% (FSWCNT) and 69.9% (DFSWNCT). Additionally, the oxygen atoms' percentage increased from 2.3% (SWCNT) to 21% and 22.5% for FSWCNT and DFSWCNT, respectively. New bonds such as C-N and N-C=O appeared in the synthesized nanocarrier. The I_G/I_D ratio in Raman analysis decreased from 7.15 (SWCNT) to 4.08 (FSWCNT). The amount of Amb released to phosphate buffer saline medium was about 33% at pH = 5.5 and 75% at pH = 7.4 after 48 h. CCK8 results confirmed that the toxicity of functionalized SWCNT had decreased. In a 2:1 ratio of DFSWCNT/EGFP plasmid, the cell viability (87%) and live transfected cells (56%) were at their maximum values. The results indicate that carbon nanotubes have the potential to be applied as drug/gene delivery systems with outstanding properties such as high loading capacity and easy penetration to cell membrane.

Review of Novel Oral Amphotericin B Formulations for the Treatment of Parasitic Infections

Amphotericin B (AmpB) is a polyene macrolide antibiotic used in the treatment of blood-borne parasitic and fungal infections. However, its use, particularly in the developing world, has been limited by dose-dependent kidney toxicity, other systemic-related toxicity issues following injection, the inconvenience of parenteral administration, and accessibility. Oral formulation approaches have focused on the dual problem of solubility and permeability of AmpB, which is poorly water soluble, amphoteric and has extremely low oral bioavailability. Therefore, to enhance oral absorption, researchers have employed micellar formulations, polymeric nanoparticles, cochleates, pro-drugs, and self-emulsifying drug delivery systems (SEDDS). This paper will highlight current uses of AmpB against parasitic infections such as leishmaniasis, preclinical and clinical formulation strategies, applications in veterinary medicine and the importance of developing a cost-effective and safe oral AmpB formulation.

Chemical and physical approaches for improved biopharmaceutical activity of amphotericin B: Current and future prospective

Over the last 50 years, the number of patients with mycotic infections has been increasing gradually. Amphotericin-B is a gold standard drug used in serious systemic fungal infections. However, limited solubility and permeability are challenging issues associated with Amphotericin-B. Chemical modification is one of the ways to get its broader applicability along with improved physicochemical properties. The review article provides a comprehensive overview of the chemical modification approach for investigation of the mechanism of action, biological activity, bioavailability, toxicity of Amphotericin B. Further, several drug delivery approaches have also been utilized to provide better therapeutic outcomes. This gives an overview of chemical approaches for the exploration of various factors associated with Amphotericin B and information on its drug delivery approaches for improved biopharmaceutical outcomes.

Engineering of small-molecule lipidic prodrugs as novel nanomedicines for enhanced drug delivery

A widely established prodrug strategy can effectively optimize the unappealing properties of therapeutic agents in cancer treatment. Among them, lipidic prodrugs extremely uplift the physicochemical properties, site-specificity, and antitumor activities of therapeutic agents while reducing systemic toxicity. Although great perspectives have been summarized in the progress of prodrug-based nanoplatforms, no attention has been paid to emphasizing the rational design of small-molecule lipidic prodrugs (SLPs). With the aim of outlining the prospect of the SLPs approach, the review will first provide an overview of conjugation strategies that are amenable to SLPs fabrication. Then, the rational design of SLPs in response to the physiological barriers of chemotherapeutic agents is highlighted. Finally, their biomedical applications are also emphasized with special functions, followed by a brief introduction of the promising opportunities and potential challenges of SLPs-based drug delivery systems (DDSs) in clinical application.

Graphical Abstract

Cochleate formulations of Amphotericin b designed for oral administration using a naturally occurring phospholipid

The purpose of this work was to formulate the poor soluble antifungal and antiparasitic agent Amphotericin B (AmB) in cost-effective lipid-based formulations suitable for oral use in developing countries, overcoming the limitations of poor water solubility, nephrotoxicity and low oral bioavailability. The antifungal agent was formulated, at different molar proportions, in cochleate nanocarriers prepared using an accessible naturally occurring phospholipid rich in phosphatidylserine (Lipoid PSP70). These nanoassemblies were prepared by condensation of negatively charged phospholipid membrane vesicles with divalent cations (Ca²⁺). Small-angle X-ray scattering studies revealed the Ca²⁺-triggered condensation of loosely packed multilamellar vesicles into tightly packed bilayers of strongly dehydrated multilamellar organization characterized by narrow Bragg peaks. Transmission electron microscopy and quasi-elastic light scattering studies demonstrated the formation of nanosized particles. AmB drug loading was above 55% in all formulations. Circular dichroism demonstrated the prevalence of monomeric and complexed forms of AmB over toxic aggregates. The stability of AmB in gastric medium was improved by loading in cochleates and its release in gastrointestinal media was retarded. Confocal microscopy studies revealed the in-vitro interactions of Lipoid PSP70-based cochleates with Caco2 intestinal cell monolayers. The results suggest that the low-cost AmB-loaded cochleates may increase the therapeutic range of this drug.

Enabling Oral Amphotericin B Delivery by Merging the Benefits of Prodrug Approach and Nanocarrier-Mediated Drug Delivery

Amphotericin B (AmB) is gold standard therapy for leishmaniasis and fungal infections. Considering the global disease burden, nearly 90% of cases occur in economically vulnerable countries, making the cost of AmB therapy a critical healthcare challenge in controlling disease burden. All currently marketed AmB products are administered through an intravenous (i.v.) route and involve high treatment costs. Designing an orally effective AmB formulation can substantially reduce the cost of therapy and improve patient compliance. However, it is a challenging task because of the distinctive physicochemical properties of AmB. Previously, we developed a lipid-based prodrug of AmB, AmB-oleyl conjugate (AmB-OA), which showcased remarkable stability in the gastrointestinal (GI) environment and improved intestinal permeation. Hereby, we have developed self-nanoemulsifiying drug delivery system (SNEDDS) of AmB-OA to further enhance the oral bioavailability of AmB and potentiate its therapeutic benefits. SNEDDS was developed by screening a wide range of oils, surfactants, and cosurfactants, and formulation composition was optimized using extreme vertices design. AmB-OA SNEDDS possessed the ability of quick self-nanoemulsification on dilution (droplet size ∼56 nm) along with remarkable stability in the GI environment. Accelerated stability (40 °C/75% relative humidity) studies and freeze-thaw cycling studies proved that the formulation was stable at tropical conditions as well as temperature cycling stress. Drug transport analysis in Caco-2 cells revealed a remarkable increase in drug transport for AmB-OA SNEDDS compared to AmB along with minimal cellular toxicities. AmB-OA SNEDDS showcased ∼8.9-fold higher AUC_Tot than AmB in in vivo pharmacokinetic study, proving the effectiveness of formulation to enhance oral bioavailability. In vivo toxicity analysis highlighted the ameliorated toxicity risk associated with SNEDDS formulation. Therefore, the AmB-OA SNEDDS formulation may provide a cost-friendly and effective strategy to resolve the oral AmB drug delivery challenge.

Opportunities and challenges of fatty acid conjugated therapeutics

Instability, poor cellular uptake and unfavorable pharmacokinetics and biodistribution of many therapeutic molecules require modification in their physicochemical properties. The conjugation of these APIs with fatty acids has demonstrated an enhancement in their lipophilicity and stability. The improvement in the formulations that resulted from the conjugation of a drug with a fatty acid includes increased half-life, enhanced cellular uptake and retention, targeted tumor delivery, reduced chemoresistance in cancer, and improved blood-brain-barrier (BBB) penetration. In this review, various therapeutic molecules, including small molecules, peptides and oligonucleotides, that have been conjugated with fatty acid have been thoroughly discussed along with various conjugation strategies. The application of nano-system based delivery is gaining a lot of attention due to its ability to provide controlled drug release, targeting and reducing the extent of side effects. This review also covers various nano-carriers that have been utilized for the delivery of fatty acid drug conjugates. The enhanced lipophilicity of the drug-fatty acid conjugate has shown to enhance the affinity of the drug towards these carriers, thereby increasing the entrapment efficiency and formulation performance.

Recuperating Biopharmaceutical Aspects of Amphotericin B and Paromomycin Using a Chitosan Functionalized Nanocarrier via Oral Route for Enhanced Anti-leishmanial Activity

The design and development of new pharmaceutical formulations for the existing anti-leishmanial is a new strategic alternate to improve efficacy and safety rather than new drug discovery. Herein hybrid solid lipid nanoparticles (SLN) have been engineered to direct the oral delivery of two anti-leishmanial drugs amphotericin B (AmB) and paromomycin (PM). The combinatorial nanocarriers consist of conventional SLN, antileishmanial drugs (AmB and PM) which have been functionalized with chitosan (Cs) grafted onto the external surface. The Cs-SLN have the mean particle size of 373.9 ± 1.41 nm, polydispersity index (PDI) of 0.342 ± 0.02 and the entrapment efficiency for AmB and PM was found to be 95.20 ± 3.19% and 89.45 ± 6.86 %, respectively. Characterization of SLN was performed by scanning electron microscopy and transmission electron microscopy. Complete internalization of the formulation was observed in Caco-2 cells. Cs-SLN has shown a controlled and slow drug release profile over a period of 72 h and was stable at gastrointestinal fluids, confirmed by simulated gastro-intestinal fluids study. Cs coating enhanced the mucoadhesive property of Cs-SLN. The in-vitro anti-leishmanial activity of Cs-SLN (1 μg/ml) has shown a maximum percentage of inhibition (92.35%) on intra-cellular amastigote growth of L. donovani.

Exploring the Promising Potential of High Permeation Vesicle-Mediated Localized Transdermal Delivery of Docetaxel in Breast Cancer To Overcome the Limitations of Systemic Chemotherapy

The currently available systemic chemotherapy for treating breast cancer often results in serious systemic side effects and compromises patient compliance. The distinct anatomical features of human breasts (e.g., embryological origin of breast skin, highly developed internal lymphatic and venous circulation, and the presence of mammary fat layers) help in preferential accumulation of drugs into breasts after topical application on breast region. This unique feature is termed as localized transdermal delivery which could be utilized for effectively delivering anticancer agents to treat breast cancer and reducing the systemic side effects by limiting their presence in blood. However, the clinical effectiveness of this drug delivery approach is highly limited by barrier properties of skin reducing the permeation of anticancer drugs. In the present work, we have developed high permeation vesicles (HPVs) using phospholipids and synergistic combination of permeation enhancers (SCOPE) to improve the skin permeation of drugs. Docetaxel (DTX) was used as a model drug for hypothesis testing. The optimized SCOPE mixture composed of sodium oleate/sodium lauryl ether sulfate/propylene glycol in 64:16:20% w/w ratio. DTX HPVs were prepared using phospholipid: SCOPE, 8:2% w/w ratio. DTX HPVs exhibited as a uniform deformable vesicles with size range 124.2 ± 7.6 nm, significantly improved skin permeation profile, and sustained drug release until 48 h. Superior vesicle deformability, better vesicle membrane fluidization, and SCOPE mediated enhancement in skin fluidization were the prime factors behind enhancement of DTX permeation. The improved cellular uptake, reduced IC₅₀ values, and higher apoptotic index of DTX HPVs in MCF-7 and MDA-MB-231 cells ensured the therapeutic effectiveness of HPV based therapy. Also, HPVs were found to be predominantly internalized inside cells through clathrin and caveolae-dependent endocytic pathways. Bioimaging analysis in mice confirmed the tumor penetration potential and effective accumulation of HPVs inside tumors after topical application. In vivo studies were carried out in comparison with marketed intravenous DTX injection (Taxotere) to compare the effectiveness of topical chemotherapy. The topical application of DTX HPV gel in tumor bearing mice resulted in nearly 4-fold tumor volume reduction which was equivalent to intravenous Taxotere therapy. Toxicity analysis of DTX HPV gel in comparison with intravenous Taxotere dosing showcased remarkably lower levels of toxicity biomarkers (aspartate transaminase (AST), alanine transaminase (ALT), blood urea nitrogen (BUN), and creatinine), indicating improved safety of topical chemotherapy. Overall results warranted the effectiveness of topical DTX chemotherapy to reduce tumor burden with substantially reduced risk of systemic toxicities in breast cancer.

Amphotericin B loaded ethyl cellulose nanoparticles with magnified oral bioavailability for safe and effective treatment of fungal infection

Amphotericin B is a gold standard drug used in various fungal and parasitic infection treatment. Most of the marketed formulations are administered intravenously, but show dose-dependent adverse effects i.e., nephrotoxicity and hemolysis. Oral route eliminates the toxic concern but exhibits poor bioavailability. Therefore, ethylcellulose nanoparticles (EC-NPs) have been used for magnified oral delivery of AmB, where EC provides gastrointestinal stability. These nanoparticles were synthesized by high-pressure emulsification solvent evaporation (HPESE) method and evaluated for in vitro and in vivo studies. This method yields small, monodisperse AmB-EC-NPs along with smooth surface morphology and improved encapsulation efficiency. The developed formulation showed a sustained release pattern following Higuchi diffusion kinetics along with gastric and storage stability. Aggregation study revealed that AmB was present in its monomeric form inside the biocompatible EC matrix. The antifungal result demonstrated that the MIC of AmB-EC-NPs was reduced ∼1/3rd than AmB and Fungizone® at 24 h whereas it was observed ∼1/8th at 48 h. in vivo pharmacokinetic analysis demonstrated 1.3-fold higher AUC than Fungizone® even at a 4.5-time lesser dose via the oral route and a ∼15-fold rise in the bioavailability in contrast to the native AmB. The hemolytic study revealed that the developed formulation exhibited 8-fold lesser hemolysis than Fungizone®. Furthermore, the biosafety profile of AmB-EC-NPs was ensured by the significantly lesser level of blood urea nitrogen and plasma creatinine along with the normal pattern of renal tubules in comparison to AmB and Fungizone®. In conclusion, the results stipulated that the AmB-EC-NPs could be effective, viable and a better alternative to currently existing iv formulations, for magnified oral delivery of AmB in the treatment of fungal infection without associated adverse effects.

Lipid Systems for the Delivery of Amphotericin B in Antifungal Therapy

Amphotericin B (AmB), a broad-spectrum polyene antibiotic in the clinic for more than fifty years, remains the gold standard in the treatment of life-threatening invasive fungal infections and visceral leishmaniasis. Due to its poor water solubility and membrane permeability, AmB is conventionally formulated with deoxycholate as a micellar suspension for intravenous administration, but severe infusion-related side effects and nephrotoxicity hamper its therapeutic potential. Lipid-based formulations, such as liposomal AmB, have been developed which significantly reduce the toxic side effects of the drug. However, their high cost and the need for parenteral administration limit their widespread use. Therefore, delivery systems that can retain or even enhance antimicrobial efficacy while simultaneously reducing AmB adverse events are an active area of research. Among those, lipid systems have been extensively investigated due to the high affinity of AmB for binding lipids. The development of a safe and cost-effective oral formulation able to improve drug accessibility would be a major breakthrough, and several lipid systems for the oral delivery of AmB are currently under development. This review summarizes recent advances in lipid-based systems for targeted delivery of AmB focusing on non-parenteral nanoparticulate formulations mainly investigated over the last five years and highlighting those that are currently in clinical trials.