Lipases, liposomes and lipid-prodrugs

Drug-phospholipid conjugate nano-assembly for drug delivery

Phospholipid-based liposomes are among the most successful nanodrug delivery systems in clinical use. However, these conventional liposomes present significant challenges including low drug-loading capacity and issues with drug leakage. Drug-phospholipid conjugates (DPCs) and their assemblies offer a promising strategy for addressing these limitations. In this review, we summarize recent advances in the design, synthesis, and application of DPCs for drug delivery. We begin by discussing the chemical backbone structures and various design strategies such as phosphate head embedding and mono-/bis-embedding in the sn-1/sn-2 positions. Furthermore, we highlight stimulus-responsive designs of DPCs and their applications in treating diseases such as cancer, inflammation, and malaria. Lastly, we explore future directions for DPCs development and their potential applications in drug delivery.

Lipid-conjugated nucleoside monophosphate and monophosphonate prodrugs: A versatile drug delivery paradigm

Integrating lipid conjugation strategies into the design of nucleoside monophosphate and monophosphonate prodrugs is a well-established approach for discovering potential therapeutics. The unique prodrug design endows nucleoside analogues with strong lipophilicity and structures resembling lysoglycerophospholipids, which improve cellular uptake, oral bioavailability and pharmacological activity. In addition, the metabolic stability, pharmacological activity, pharmacokinetic profiles and biodistribution of lipid prodrugs can be finely optimized by adding biostable caps, incorporating transporter-targeted groups, inserting stimulus-responsive bonds, adjusting chain lengths, and applying proper isosteric replacements. This review summarizes recent advances in the structural features and application fields of lipid-conjugated nucleoside monophosphate and monophosphonate prodrugs. This collection provides deep insights into the increasing repertoire of lipid prodrug development strategies and offers design inspirations for medicinal chemists for the development of novel chemotherapeutic agents.

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.

Translational Challenges and Prospective Solutions in the Implementation of Biomimetic Delivery Systems

Biomimetic delivery systems (BDSs), inspired by the intricate designs of biological systems, have emerged as a groundbreaking paradigm in nanomedicine, offering unparalleled advantages in therapeutic delivery. These systems, encompassing platforms such as liposomes, protein-based nanoparticles, extracellular vesicles, and polysaccharides, are lauded for their targeted delivery, minimized side effects, and enhanced therapeutic outcomes. However, the translation of BDSs from research settings to clinical applications is fraught with challenges, including reproducibility concerns, physiological stability, and rigorous efficacy and safety evaluations. Furthermore, the innovative nature of BDSs demands the reevaluation and evolution of existing regulatory and ethical frameworks. This review provides an overview of BDSs and delves into the multifaceted translational challenges and present emerging solutions, underscored by real-world case studies. Emphasizing the potential of BDSs to redefine healthcare, we advocate for sustained interdisciplinary collaboration and research. As our understanding of biological systems deepens, the future of BDSs in clinical translation appears promising, with a focus on personalized medicine and refined patient-specific delivery systems.

Expanding the toolbox of metabolically stable lipid prodrug strategies

Nucleoside- and nucleotide-based therapeutics are indispensable treatment options for patients suffering from malignant and viral diseases. These agents are most commonly administered to patients as prodrugs to maximize bioavailability and efficacy. While the literature provides a practical prodrug playbook to facilitate the delivery of nucleoside and nucleotide therapeutics, small context-dependent amendments to these popular prodrug strategies can drive dramatic improvements in pharmacokinetic (PK) profiles. Herein we offer a brief overview of current prodrug strategies, as well as a case study involving the fine-tuning of lipid prodrugs of acyclic nucleoside phosphonate tenofovir (TFV), an approved nucleotide HIV reverse transcriptase inhibitor (NtRTI) and the cornerstone of combination antiretroviral therapy (cART). Installation of novel lipid terminal motifs significantly reduced fatty acid hepatic ω-oxidation while maintaining potent antiviral activity. This work contributes important insights to the expanding repertoire of lipid prodrug strategies in general, but particularly for the delivery and distribution of acyclic nucleoside phosphonates.

Membrane composition and successful bioaugmentation. Studies of the interactions of model thylakoid and plasma cyanobacterial and bacterial membranes with fungal membrane-lytic enzyme Lecitase ultra

Cyanobacterial/bacterial consortia are frequently inoculated to soils to increase the soil fertility and to accelerate the biodegradation of organic pollutants. Moreover, such consortia can also be successfully applied in landfills especially for the biodegradation of plastic wastes. However, the bioaugmentation techniques turn out frequently inefficient due to the competition of the indigenous microorganisms attacking directly these inoculated or secreting to their surroundings cell wall and membrane-lytic enzymes. It can be hypothesized that the resistance of the microbial membrane to the enzymatic degradation is correlated with its lipid composition. To verify this hypothesis glycolipid and phospholipid Langmuir monolayers were applied as models of thylakoid and plasma cyanobacterial and bacterial membranes. Hybrid fungal enzyme Lecitase ultra joining the activity of lipase and phospholipase A1 was applied as the model of fungal membrane-lytic enzyme. It turned out that anionic thylakoid lipids sulfoquinovosyldiacylglycerol and phosphatidylglycerols were the main targets of Lecitase ultra in the model multicomponent thylakoid membranes. The resistance of the model plasma bacterial membranes to enzymatic degradation depended significantly to their composition. The resistance increased generally when the unsaturated lipids were exchanged to their saturated counterparts. However, most resistant turned out the membranes composed of unsaturated phosphatidylamine and saturated anionic phospholipids.

Interactions of fungal phospholipase Lecitase ultra with phospholipid Langmuir monolayers - Search for substrate specificity and structural factors affecting the activity of the enzyme

Inoculation of selected microbial species into the soils is one of the most effective means of bioremediation of soils polluted by persistent organic pollutants as well as of biocontrol of plant pests. However, this procedure turns out frequently to be ineffective due to the membrane-destructive enzymes secreted to the soil by the autochthonous microorganisms. Especial role play here phospholipases and among them phospholipase A1 (PLA1), Therefore, to explain the interactions of microbial membranes and PLA1 at molecular level and to find the correlation between the composition of the membrane and its resistance to PLA1 action we applied phospholipid Langmuir monolayers as model microbial membranes. As a representative soil extracellular PLA1 we applied Lecitase ultra which is a commercially available hybrid enzyme of PLA1 activity. With the application of specific sn1-ether-sn2-ester phospholipids we proved that Lecitase ultra has solely PLA1 activity; thus, can be applied as an effective model of soil PLA1s. Our studies proved that this enzyme has vast substrate specificity and can hydrolyze structural phospholipids regardless the structure of their polar headgroup. It turned out that the hydrolysis rate was controlled by the condensation of the model membranes. These built of the phospholipids with long saturated fatty acid chains were especially resistant to the action of this enzyme, whereas these formed by the 1-saturated-2-unsaturated-sn-glycero-3-phospholipids were readily degraded. Regarding the polar headgroup we proposed the following row of substrate preference of Lecitase ultra: phosphatidylglycerols > phosphatidylcholines > phosphatidylethanolamines > cardiolipins.

Simultaneous action of microbial phospholipase C and lipase on model bacterial membranes - Modeling the processes crucial for bioaugmentation

Bioaugmentation is a promising method of the remediation of soils polluted by persistent organic pollutants (POP). Unfortunately, it happens frequently that the microorganisms inoculated into the soil die out due to the presence of enzymes secreted by autochthonous microorganisms. Especially destructive are here phospholipases C (PLC) and lipases which destruct the microorganism's cellular membrane. The composition of bacterial membranes differs between species, so it is highly possible that depending on the membrane constitution some bacteria are more resistant to PLCs and lipases than other. To shed light on these problems we applied phospholipid Langmuir monolayers as model microbial membranes and studied their interactions with α-toxin (model bacterial PLC) and the lipase isolated from soil fungus Candida rugosa. Membrane phospholipids differing in their headgroup (phosphatidylcholines, phosphatidylethanolamines, phosphatidylglycerols and cardiolipins) and in their tail structure were applied. The monolayers were characterized by the Langmuir technique, visualized by Brewster angle microscopy, and the packing mode of the phospholipid molecules was verified by the application of the diffraction of synchrotron radiation. We also studied the mutual miscibility of diacylglycerols and the native phospholipids as their interaction is crucial for the understanding of the PLC and lipase activity. It turned out that all the investigated phospholipid classes can be hydrolyzed by PLC; however, they differ profoundly in the hydrolysis degree. Depending on the effects of the initial PLC action and the mutual organization of the diacylglycerol and phospholipid molecules the lipase can ruin the model membranes or can be completely neutral to them.

Liposomal delivery of antibiotic loaded nucleic acid nanogels with enhanced drug loading and synergistic anti-inflammatory activity against S. aureus intracellular infections

The persistence of Staphylococcus aureus has been accredited to its ability to escape immune response via host cell invasion. Despite the efficacy of many antibiotics against S. aureus, the high extracellular concentrations of conventional antibiotics required for bactericidal activity is limited by their low cellular accumulation and poor intracellular retention. While nanocarriers have received tremendous attention for antibiotic delivery against persistent pathogens, they suffer daunting challenges such as low drug loading, poor retention and untimely release of hydrophilic cargos. Here, a hybrid system (Van_DNL) is fabricated wherein nucleic acid nanogels are caged within a liposomal vesicle for antibiotic delivery. The central principle of this approach relies on exploiting non-covalent electrostatic interactions between cationic cargos and polyanionic DNA to immobilize antibiotics and enable precise temporal release against intracellular S. aureus. In vitro characterization of Van_DNL revealed a stable homogenous formulation with circular morphology and enhanced vancomycin loading efficiency. The hybrid system significantly sustained the release of vancomycin over 24 h compared to liposomal or nanogel controls. Under enzymatic conditions relevant to S. aureus infections, lipase triggered release of vancomycin was observed from the hybrid. While using Van_DNL to treat S. aureus infected macrophages, a dose dependent reduction in intracellular bacterial load was observed over 24 h and exposure to Van_DNL for 48 h caused negligible cellular toxicity. Pre-treatment of macrophages with the antimicrobial hybrid resulted in a strong anti-inflammatory activity in synergy with vancomycin following endotoxin stimulation. Conceptually, these findings highlight these hybrids as a unique and universal platform for synergistic antimicrobial and anti-inflammatory therapy against persistent infections.

Redox-sensitive dimeric camptothecin phosphatidylcholines-based liposomes for improved anticancer efficacy

Aim: A redox-triggered camptothecin (CPT) liposomal system was developed for an improved clinical potential in tumor therapy. Materials & methods: CPT–phosphorylcholine conjugates (CPT–SS–GPCs: CPT–SS–3–GPC and CPT–SS–11–GPC) were synthesized by conjugating CPT to glycerylphosphorylcholine via disulfide bond linker. CPT–SS–GPCs could be assembled into liposomes. Different in vitro and in vivo analyses were used to evaluate the anticancer activities of CPT–SS–GPCs. Results: CPT–SS–GPCs liposomes exhibited extremely high drug loading and uniform size of 150–200 nm. Moreover, the rapid release of parent CPT in reductive condition and high cellular uptake of CPT–SS–GPCs liposomes were observed. At last, in vitro and in vivo anticancer assay showed the enhanced efficacy of CPT–SS–GPCs liposomes. Conclusion: Redox-triggered CPT–SS–GPC liposomes have great potential in tumor therapy.

Synergistical Use of Electrostatic and Hydrophobic Interactions for the Synthesis of a New Class of Multifunctional Nanohybrids: Plasmonic Magneto-Liposomes

By carefully controlling the electrostatic interactions between cationic liposomes, which already incorporate magnetic nanoparticles in the bilayers, and anionic gold nanoparticles, a new class of versatile multifunctional nanohybrids (plasmonic magneto-liposomes) that could have a major impact in drug delivery and controlled release applications has been synthesized. The experimental results confirmed the successful synthesis of hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) and polyethylene glycol functionalized (PEGylated) gold nanoparticles (AuNPs). The SPIONs were incorporated in the liposomal lipidic bilayers, thus promoting the formation of cationic magnetoliposomes. Different concentrations of SPIONs were loaded in the membrane. The cationic magnetoliposomes were decorated with anionic PEGylated gold nanoparticles using electrostatic interactions. The successful incorporation of SPIONs together with the modifications they generate in the bilayer were analyzed using Raman spectroscopy. The plasmonic properties of the multifunctional nanohybrids were investigated using UV-Vis absorption and (surface-enhanced) Raman spectroscopy. Their hyperthermic properties were recorded at different frequencies and magnetic field intensities. After the synthesis, the nanosystems were extensively characterized in order to properly evaluate their potential use in drug delivery applications and controlled release as a result of the interaction with an external stimulus, such as an NIR laser or alternating magnetic field.

Molecular Modeling-Guided Design of Phospholipid-Based Prodrugs

The lipidic prodrug approach is an emerging field for improving a number of biopharmaceutical and drug delivery aspects. Owing to their structure and nature, phospholipid (PL)-based prodrugs may join endogenous lipid processing pathways, and hence significantly improve the pharmacokinetics and/or bioavailability of the drug. Additional advantages of this approach include drug targeting by enzyme-triggered drug release, blood–brain barrier permeability, lymphatic targeting, overcoming drug resistance, or enabling appropriate formulation. The PL-prodrug design includes various structural modalities-different conjugation strategies and/or the use of linkers between the PL and the drug moiety, which considerably influence the prodrug characteristics and the consequent effects. In this article, we describe how molecular modeling can guide the structural design of PL-based prodrugs. Computational simulations can predict the extent of phospholipase A₂ (PLA₂)-mediated activation, and facilitate prodrug development. Several computational methods have been used to facilitate the design of the pro-drugs, which will be reviewed here, including molecular docking, the free energy perturbation method, molecular dynamics simulations, and free density functional theory. Altogether, the studies described in this article indicate that computational simulation-guided PL-based prodrug molecular design correlates well with the experimental results, allowing for more mechanistic and less empirical development. In the future, the use of molecular modeling techniques to predict the activity of PL-prodrugs should be used earlier in the development process.

Phospholipid-Based Prodrugs for Colon-Targeted Drug Delivery: Experimental Study and In-Silico Simulations

In ulcerative colitis (UC), the inflammation is localized in the colon, and one of the successful strategies for colon-targeting drug delivery is the prodrug approach. In this work, we present a novel phospholipid (PL)-based prodrug approach, as a tool for colonic drug targeting in UC. We aim to use the phospholipase A₂ (PLA₂), an enzyme that is overexpressed in the inflamed colonic tissues of UC patients, as the PL-prodrug activating enzyme, to accomplish the liberation of the parent drug from the prodrug complex at the specific diseased tissue(s). Different linker lengths between the PL and the drug moiety can dictate the rate of activation by PLA₂, and subsequently determine the amount of free drugs at the site of action. The feasibility of this approach was studied with newly synthesized PL-Fmoc (fluorenylmethyloxycarbonyl) conjugates, using Fmoc as a model compound for testing our hypothesis. In vitro incubation with bee venom PLA₂ demonstrated that a 7-carbon linker between the PL and Fmoc has higher activation rate than a 5-carbon linker. 4-fold higher colonic expression of PLA₂ was demonstrated in colonic mucosa of colitis-induced rats when compared to healthy animals, validating our hypothesis of a colitis-targeting prodrug approach. Next, a novel molecular dynamics (MD) simulation was developed for PL-based prodrugs containing clinically relevant drugs. PL-methotrexate conjugate with 6-carbon linker showed the highest extent of PLA₂-mediated activation, whereas shorter linkers were activated to a lower extent. In conclusion, this work demonstrates that for carefully designed PL-drug conjugates, PLA₂ overexpression in inflamed colonic tissues can be used as prodrug-activating enzyme and drug targeting strategy, including insights into the activation mechanisms in a PLA₂ binding site.

Prospects and Challenges of Phospholipid-Based Prodrugs

Nowadays, the prodrug approach is used already at the early stages of drug development. Lipidic prodrug approach is a growing field for improving a number of drug properties/delivery/therapy aspects, and can offer solutions for various unmet needs. This approach includes drug moiety bound to the lipid carrier, which can be triglyceride, fatty acids, steroid, or phospholipid (PL). The focus of this article is PL-based prodrugs, which includes a PL carrier covalently bound to the active drug moiety. An overview of relevant physiological lipid processing pathways and absorption barriers is provided, followed by drug delivery/therapeutic application of PL-drug conjugates, as well as computational modeling techniques, and a modern bioinformatics tool that can aid in the optimization of PL conjugates. PL-based prodrugs have increased lipophilicity comparing to the parent drug, and can therefore significantly improve the pharmacokinetic profile and overall bioavailability of the parent drug, join the endogenous lipid processing pathways and therefore accomplish drug targeting, e.g., by lymphatic transport, drug release at specific target site(s), or passing the blood-brain barrier. Moreover, an exciting gateway for treating inflammatory diseases and cancer is presented, by utilizing the PL sn-2 position in the prodrug design, aiming for PLA₂-mediated activation. Overall, a PL-based prodrug approach shows great potential in improving different drug delivery/therapy aspects, and is expected to grow.

Construction of a Supramolecular Drug-Drug Delivery System for Non-Small-Cell Lung Cancer Therapy

Nanoscale drug delivery systems (DDSs) are generally considered to be an effective alternative to small molecular chemotherapeutics due to improved accumulation in the tumor site and enhanced retention in blood. Nevertheless, most DDSs have low loading efficiency or even pose a high threat to normal organs from severe side effects. Ideally, a supramolecular drug-drug delivery system (SDDDS) composed of pure drugs via supramolecular interaction provides a hopeful approach for cancer treatment. Herein we propose a facile method to construct SDDDS via coassembly of gefitinib (GEF) and tripeptide tyroservatide (YSV), two kinds of chemotherapeutic pharmaceuticals for non-small-cell lung cancer (NSCLC) via multiple intermolecular interactions, including hydrogen bonding and π-π stacking. As shown through transmission electron microscopy (TEM) and dynamic light scattering (DLS), GEF and YSV self-assemble into nanoparticles with regular morphology and uniform size, which facilitates the delivery of both drugs. In vitro studies demonstrate that the SDDDS is much more efficient in entering cancer cells and inhibiting the proliferation of cancer cells compared with single GEF, YSV, or GEF/YSV drug mixture. In vivo experiments show that the SDDDS can selectively accumulate in tumor tissue, resulting in much better drug efficacy without evident side effects. Considering the advantages of the SDDDS, we believe this strategy provides a promising route for enhanced anticancer therapy in nanomedicine.

Stimuli-responsive liposomes for drug delivery

The ultimate goal of drug delivery is to increase the bioavailability and reduce the toxic side effects of the active pharmaceutical ingredient (API) by releasing them at a specific site of action. In the case of antitumor therapy, association of the therapeutic agent with a carrier system can minimize damage to healthy, nontarget tissues, while limit systemic release and promoting long circulation to enhance uptake at the cancerous site due to the enhanced permeation and retention effect (EPR). Stimuli-responsive systems have become a promising way to deliver and release payloads in a site-selective manner. Potential carrier systems have been derived from a wide variety of materials, including inorganic nanoparticles, lipids, and polymers that have been imbued with stimuli-sensitive properties to accomplish triggered release based on an environmental cue. The unique features in the tumor microenvironment can serve as an endogenous stimulus (pH, redox potential, or unique enzymatic activity) or the locus of an applied external stimulus (heat or light) to trigger the controlled release of API. In liposomal carrier systems triggered release is generally based on the principle of membrane destabilization from local defects within bilayer membranes to effect release of liposome-entrapped drugs. This review focuses on the literature appearing between November 2008-February 2016 that reports new developments in stimuli-sensitive liposomal drug delivery strategies using pH change, enzyme transformation, redox reactions, and photochemical mechanisms of activation. WIREs Nanomed Nanobiotechnol 2017, 9:e1450. doi: 10.1002/wnan.1450 For further resources related to this article, please visit the WIREs website.

Enhanced Solubility and Bioavailability of Naringenin via Liposomal Nanoformulation: Preparation and In Vitro and In Vivo Evaluations

This study was aimed at preparing orally administered naringenin-loaded liposome for pharmacokinetic and tissue distribution studies in animal models. The liposomal system, consisting of phospholipid, cholesterol, sodium cholate, and isopropyl myristate, was prepared using the thin-film hydration method. Physicochemical characterization of naringenin-loaded liposome such as particle size, zeta potential, and encapsulation efficiency produced 70.53 ± 1.71 nm, -37.4 ± 7.3 mV, and 72.2 ± 0.8%, respectively. The in vitro release profile of naringenin from the formulation in three different media (HCl solution, pH 1.2; acetate buffer solution, pH 4.5; phosphate buffer solution, pH 6.8) was significantly higher than the free drug. The in vivo studies also revealed an increase in AUC of the naringenin-loaded liposome from 16648.48 to 223754.0 ng·mL^-1 h as compared with the free naringenin. Thus, approximately 13.44-fold increase in relative bioavailability was observed in mice after oral administration. The tissue distribution further showed that the formulation was very predominant in the liver. These findings therefore indicated that the liposomal formulation significantly improved the solubility and oral bioavailability of naringenin, thus leading to wider clinical applications.

Assembled liposomes of dual podophyllotoxin phospholipid: preparation, characterization and in vivo anticancer activity

Aim: A novel amphiphilic prodrug dual podophyllotoxin (PPT) succinate glycerophosphorylcholine (Di-PPT-GPC) assembled liposomes was developed to improve efficiency of PPT. Materials & methods: Di-PPT-GPC liposomes were prepared by thin film technique and characterized by dynamic light scattering and cryo-electron microscopy. Results: In vitro release studies showed that Di-PPT-GPC liposomes could significantly release PPT in weakly acidic environment but had good stability under biological conditions. Methyl tetrazolium assay data revealed that the liposomes have comparable cytotoxicities to free PPT against MCF-7, HeLa and U87 cells. More importantly, in vivo antitumor evaluation indicated that Di-PPT-GPC liposomes exhibited favorable tumor growth inhibition without side effects. Conclusion: Di-PPT-GPC liposomes might have potential to promote the therapeutic effect of PPT for cancer therapy.

Lipid-Drug Conjugate for Enhancing Drug Delivery

Lipid-drug conjugates (LDCs) are drug molecules that have been covalently modified with lipids. The conjugation of lipids to drug molecules increases lipophilicity and also changes other properties of drugs. The conjugates demonstrate several advantages including improved oral bioavailability, improved targeting to the lymphatic system, enhanced tumor targeting, and reduced toxicity. Based on the chemical nature of drugs and lipids, various conjugation strategies and chemical linkers can be utilized to synthesize LDCs. Linkers and/or conjugation methods determine how drugs are released from LDCs and are critical for the optimal performance of LDCs. In this review, different lipids used for preparing LDCs and various conjugation strategies are summarized. Although LDCs can be administered without a delivery carrier, most of them are loaded into appropriate delivery systems. The lipid moiety in the conjugates can significantly enhance drug loading into hydrophobic components of delivery carriers and thus generate formulations with high drug loading and superior stability. Different delivery carriers such as emulsions, liposomes, micelles, lipid nanoparticles, and polymer nanoparticles are also discussed in this review.

Dynamic formation of nanostructured particles from vesicles via invertase hydrolysis for on-demand delivery

Controlled hydrolysis via invertase action alters molecular shape and therefore lipid curvature, consequently triggering the release of encapsulated drug.

Synthesis of paramagnetic dendritic silica nanomaterials with fibrous pore structure (Fe3O4@KCC-1) and their application in immobilization of lipase from Candida rugosa with enhanced catalytic activity and stability

Paramagnetic mesoporous fibrous silica (Fe₃O₄@KCC-1) was prepared and its surface was functionalized with 3-aminopropyltriethoxysilane (APTES).

Activity-based targeting of secretory phospholipase A2 enzymes: A fatty-acid-binding-protein assisted approach

Syntheses and enzymological characterization of fluorogenic substrate probes targeting secretory phospholipase A₂ (sPLA₂) for detection and quantitative assays are presented. Three fluorogenic phosphatidylcholine analogs PC-1, PC-2, and PC-3 each containing the duo of 7-mercapto-4-methyl-coumarin fluorophore and 2,4-dinitroanaline quencher on either tail were synthesized from (R)-3-amino-1,2-propanediol and R-(-)-2,2-dimethyl-1,3-dioxolane-4-methanol. These small reporter groups are advantageous in preserving natural membrane integrity. Phosphocholine was incorporated into the sn-3 position of the glycerol backbone. Acyl amino group at the sn-1 position in PC-1 and PC-2 is meant to block sPLA₁. The sn-1 and sn-2 positions of the glycerol backbone in PC-1 have a quencher terminated 12-carbon chain and fluorophore terminated 11-carbon chain respectively. PC-2 has a quencher terminated 3-carbon chain at the sn-2 and chain terminating fluorescent reporter at the sn-1 positions. PC-3 resembles PC-1 except for an ester instead of amide at the sn-1 position, because of which it is more similar to natural phospholipids than PC-1. It was designed to elucidate the effect of replacing the ester group with amide by comparing its hydrolysis rate with that of PC-1. Design principles apply to synthesis of other labeled phospholipids. Enzymological characterization using bee-venom sPLA₂ was performed by a fatty-acid-binding-protein fluorescence assay and by pH-Stat method in which the amount of fatty acid released by hydrolysis is given by the amount of base required to maintain a constant pH of 8.0. Hydrolytic activity toward PC-1 and PC-3 were each about 238±25μmol/mg/min and 537μmol/mg/min on unmodified phospholipid. Ester to amide change did not affect hydrolysis rates. Activity toward PC-2 was about 45-μmol/mg/min. PC-1 and PC-3 show potential for targeted real-time spectrophotometric assay of sPLA₂.

Effect of fatty acids on the permeability barrier of model and biological membranes

Because of the amphipathicity and conical molecular shape of fatty acids, they can efficiently incorporate into lipid membranes and disturb membrane integrity, chain packing, and lateral pressure profile. These phenomena affect both model membranes as well as biological membranes. We investigated the feasibility of exploiting fatty acids as permeability enhancers in drug delivery systems for enhancing drug release from liposomal carriers and drug uptake by target cells. Saturated fatty acids, with acyl chain length from C8 to C20, were tested using model drug delivery liposomes of 1,2- dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and the breast cancer MCF-7 cell line as a model cell. A calcein release assay demonstrated reduction in the membrane permeability barrier of the DPPC liposomes, proportionally to the length of the fatty acid. Differential scanning calorimetry (DSC) and dynamic light scattering (DLS) experiments revealed that C12 to C20 fatty acids can stabilize DPPC liposomal bilayers and induce the formation of large structures, probably due to liposome aggregation and bilayer morphological changes. On the other hand, the short fatty acids C8 and C10 tend to destabilize the bilayers and only moderately cause the formation of large structures. The effect of fatty acids on DPPC liposomes was not completely transferrable to the MCF-7 cell line. Using cytotoxicity assays, the cells were found to be relatively insensitive to the fatty acids at apoptotic sub-millimolar concentrations. Increasing the fatty acid concentration to few millimolar substantially reduced the viability of the cells, most likely via the induction of necrosis and cell lysis. A bioluminescence living-cell-based luciferase assay showed that saturated fatty acids in sub-cytotoxic concentrations cannot reduce the permeability barrier of cell membranes. Our results confirm that the membrane perturbing effect of fatty acids on model membranes cannot simply be carried over to biological membranes of live cells.

Responsive self-assembled nanostructured lipid systems for drug delivery and diagnostics

While stimuli-responsive polymers have received a huge amount of attention in the literature, responsive lipid-based mesophase systems offer unique opportunities in biomedical applications such as drug delivery and biosensing. The different mesophase equilibrium structures enables dynamic switching between nanostructures to facilitate drug release or as a transducer for recognition events. In drug delivery, this behavior offers researchers the means to deliver a therapeutic payload at a specific rate and time i.e. 'on-demand'. This review summarizes the distinctive features of these multifaceted materials and aggregates the current state of the art research from our groups and others into the use of these materials as bulk gels and nanostructured dispersions for drug delivery, biosensing and diagnostics.

Optimization and modeling of the remote loading of luciferin into liposomes

We carried out a mechanistic study to characterize and optimize the remote loading of luciferin into preformed liposomes of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPC/DPPG) 7:3 mixtures. The influence of the loading agent (acetate, propionate, butyrate), the metal counterion (Na(+), K(+), Ca(+2), Mg(+2)), and the initial extra-liposomal amount of luciferin (nL(add)) on the luciferin Loading Efficiency (LE%) and luciferin-to-lipid weight ratio, i.e., Loading Capacity (LC), in the final formulation was determined. In addition, the effect of the loading process on the colloidal stability and phase behavior of the liposomes was monitored. Based on our experimental results, a theoretical model was developed to describe the course of luciferin remote loading. It was found that the highest luciferin loading was obtained with magnesium acetate. The use of longer aliphatic carboxylates or inorganic proton donors pronouncedly reduced luciferin loading, whereas the effect of the counterion was modest. The remote-loading process barely affected the colloidal stability and drug retention of the liposomes, albeit with moderate luciferin-induced membrane perturbations. The correlation between luciferin loading, expressed as LE% and LC, and nL(add) was established, and under our conditions the maximum LC was attained using an nL(add) of around 2.6μmol. Higher amounts of luciferin tend to pronouncedly perturb the liposome stability and luciferin retention. Our theoretical model furnishes a fair quantitative description of the correlation between nL(add) and luciferin loading, and a membrane permeability coefficient for uncharged luciferin of 1×10(-8)cm/s could be determined. We believe that our study will prove very useful to optimize the remote-loading strategies of moderately polar carboxylic acid drugs in general.

Nanoparticles Suitable for BCAA Isolation Can Serve for Use in Magnetic Lipoplex-Based Delivery System for L, I, V, or R-rich Antimicrobial Peptides

This paper investigates the synthesis of paramagnetic nanoparticles, which are able to bind branched chain amino acids (BCAAs)—leucine, valine, and isoleucine and, thus, serve as a tool for their isolation. Further, by this, we present an approach for encapsulation of nanoparticles into a liposome cavity resulting in a delivery system. Analyses of valine and leucine in entire complex show that 31.3% and 32.6% recoveries are reached for those amino acids. Evaluation of results shows that the success rate of delivery in Escherichia coli (E. coli) is higher in the case of BCAAs on nanoparticles entrapped in liposomes (28.7% and 34.7% for valine and leucine, respectively) when compared to nanoparticles with no liposomal envelope (18.3% and 13.7% for valine and leucine, respectively). The nanoparticles with no liposomal envelope exhibit the negative zeta potential (−9.1 ± 0.3 mV); however, their encapsulation results in a shift into positive values (range of 28.9 ± 0.4 to 33.1 ± 0.5 mV). Thus, electrostatic interactions with negatively-charged cell membranes (approx. −50 mV in the case of E. coli) leads to a better uptake of cargo. Our delivery system was finally tested with the leucine-rich antimicrobial peptide (FALALKALKKALKKLKKALKKAL) and it is shown that hemocompatibility (7.5%) and antimicrobial activity of the entire complex against E. coli, Staphylococcus aureus (S. aureus), and methicilin-resistant S. aureus (MRSA) is comparable or better than conventional penicillin antibiotics.

Development of a cell-based bioassay for phospholipase A2-triggered liposomal drug release

The feasibility of exploiting secretory phospholipase A₂ (sPLA₂) enzymes, which are overexpressed in tumors, to activate drug release from liposomes precisely at the tumor site has been demonstrated before. Although the efficacy of the developed formulations was evaluated using in vitro and in vivo models, the pattern of sPLA₂-assisted drug release is unknown due to the lack of a suitable bio-relevant model. We report here on the development of a novel bioluminescence living-cell-based luciferase assay for the monitoring of sPLA₂-triggered release of luciferin from liposomes. To this end, we engineered breast cancer cells to produce both luciferase and sPLA₂ enzymes, where the latter is secreted to the extracellular medium. We report on setting up a robust and reproducible bioassay for testing sPLA₂-sensitive, luciferin remote-loaded liposomal formulations, using 1,2-distearoyl-sn-glycero-3-phosphatidylcholine/1,2-distearoyl-sn-glycero-3-phosphatidylglycerol (DSPC/DSPG) 7:3 and DSPC/DSPG/cholesterol 4:3:3 as initial test systems. Upon their addition to the cells, the liposomes were degraded almost instantaneously by sPLA₂ releasing the encapsulated luciferin, which provided readout from the luciferase-expressing cells. Cholesterol enhanced the integrity of the formulation without affecting its susceptibility to sPLA₂. PEGylation of the liposomes only moderately broadened the release profile of luciferin. The provided bioassay represents a useful tool for monitoring active drug release in situ in real time as well as for testing and optimizing of sPLA₂-sensitive lipid formulations. In addition, the bioassay will pave the way for future in-depth in vitro and in vivo studies.

Liposomes assembled from a dual drug-tailed phospholipid for cancer therapy

We report a novel dual drug-tailed phospholipid which can form liposomes as a combination of prodrug and drug carrier. An amphiphilic dual chlorambucil-tailed phospholipid (DCTP) was synthesized by a straightforward esterification. With two chlorambucil molecules as hydrophobic tails and one glycerophosphatidylcholine molecule as a hydrophilic head, the DCTP, a phospholipid prodrug, undergoes assembly to form a liposome without any additives by the thin lipid film technique. The DCTP liposomes, as an effective carrier of chlorambucil, exhibited a very high loading capacity and excellent stability. The liposomes had higher cytotoxic effects to cancer cell lines than free DCTP and chlorambucil. The in vivo antitumor activity assessment indicated that the DCTP liposomes could inhibit the tumor growth effectively. This novel strategy of dual drug-tailed phospholipid liposomes may be also applicable to other hydrophobic anticancer drugs which have great potential in cancer therapy.

Lipid prodrug nanocarriers in cancer therapy

Application of nanotechnology in the medical field (i.e., nanomedicine) plays an important role in the development of novel drug delivery methods. Nanoscale drug delivery systems can indeed be customized with specific functionalities in order to improve the efficacy of the treatments. However, despite the progresses of the last decades, nanomedicines still face important obstacles related to: (i) the physico-chemical properties of the drug moieties which may reduce the total amount of loaded drug; (ii) the rapid and uncontrolled release (i.e., burst release) of the encapsulated drug after administration and (iii) the instability of the drug in biological media where a fast transformation into inactive metabolites can occur. As an alternative strategy to alleviate these drawbacks, the prodrug approach has found wide application. The covalent modification of a drug molecule into an inactive precursor from which the drug will be freed after administration offers several benefits such as: (i) a sustained drug release (mediated by chemical or enzymatic hydrolysis of the linkage between the drug-moiety and its promoiety); (ii) an increase of the drug chemical stability and solubility and, (iii) a reduced toxicity before the metabolization occurs. Lipids have been widely used as building blocks for the design of various prodrugs. Interestingly enough, these lipid-derivatized drugs can be delivered through a nanoparticulate form due to their ability to self-assemble and/or to be incorporated into lipid/polymer matrices. Among the several prodrugs developed so far, this review will focus on the main achievements in the field of lipid-based prodrug nanocarriers designed to improve the efficacy of anticancer drugs. Gemcitabine (Pubchem CID: 60750); 5-fluorouracil (Pubchem CID: 3385); Doxorubicin (Pubchem CID: 31703); Docetaxel (Pubchem CID: 148124); Methotrexate (Pubchem CID: 126941); Paclitaxel (Pubchem CID: 36314).

Lipid-based drug carriers for prodrugs to enhance drug delivery

The combination of lipid drug delivery systems with prodrugs offers several advantages including improved pharmacokinetics, increased absorption, and facilitated targeting. Lipidization and use of lipid carriers can increase the pharmacological half-life of the drug, thus improving pharmacokinetics and allowing less frequent dosing. Lipids also offer advantages such as increased absorption through the intestines for oral drug absorption and to the CNS for brain delivery. Furthermore, the use of lipid delivery systems can enhance drug targeting. Endogenous proteins bind lipids in the blood and carry them to the liver to enable targeting of this organ. Drugs with significant side effects in the stomach can be specifically delivered to enterocytes by exploiting lipases for prodrug activation. Finally, lipids can be used to target the lymphatic system, thus bypassing the liver and avoiding first-pass metabolism. Lymphatic targeting is also important for antiviral drugs in the protection of B and T lymphocytes. In this review, both lipid-drug conjugates and lipid-based carriers will be discussed. An overview, including the chemistry and assembly of the systems, as well as examples from the clinic and in development, will be provided.

Improved oral bioavailability of capsaicin via liposomal nanoformulation: preparation, in vitro drug release and pharmacokinetics in rats

This study innovatively prepared an effective capsaicin-loaded liposome, a nanoformulation with fewer irritants, for oral administration. The in vitro and in vivo properties of the liposomal encapsulation were investigated and the potential possibility of oral administration evaluated. The liposomal agent composed of phospholipid, cholesterol, sodium cholate and isopropyl myristate was prepared using film-dispersion method. A level A in vitro-in vivo correlation (IVIVC) was established for the first time, which demonstrated an excellent IVIVC of both formulated and free capsaicin in oral administration. Physicochemical characterizations including mean particle size, zeta (ζ) potential and average encapsulation efficiency of capsaicin-loaded liposome were found to be 52.2 ± 1.3 nm, -41.5 ± 2.71 mv and 81.9 ± 2.43 %, respectively. In vivo, liposomal encapsulation allowed a 3.34-fold increase in relative bioavailability compared to free capsaicin. The gastric mucosa irritation studies indicated that the liposomal system was a safe carrier for oral administration. These results support the fact that capsaicin, an effective drug for the treatment of neuropathic pain, could be encapsulated in liposome for improved oral bioavailability. The excellent IVIVC of capsaicin-loaded liposome could also be a promising tool in liposomal formulation development with an added advantage of reduced animal testing.

Peptidophospholipids: synthesis, phospholipase A2 catalyzed hydrolysis, and application to development of phospholipid prodrugs

New phospholipid analogues incorporating sn-2-peptide substituents have been prepared to probe the fundamental structural requirements for phospholipase A2 catalyzed hydrolysis of PLA2-directed synthetic substrates. Two structurally different antiviral oligopeptides with C-terminal glycine were introduced separately at the sn-2-carboxylic ester position of phospholipids to assess the role of the α-methylene group adjacent to the ester carbonyl in allowing hydrolytic cleavage by the enzyme. The oligopeptide-carrying phospholipid derivatives were readily incorporated into mixed micelles consisting of natural phospholipid (dipalmitoyl phosphatidylcholine, DPPC) and Triton X-100 as surfactant. Hydrolytic cleavage of the synthetic peptidophospholipids by the phospholipase A2 occurred slower, but within the same order of magnitude as the natural substrate alone. The results provide useful information toward better understanding the mechanism of action of the enzyme, and to improve the design and synthesis of phospholipid prodrugs targeted at secretory PLA2 enzymes.