Lipid Drug Conjugates Research Articles

Lipid Drug Conjugate (LDC) Nanoparticles as Autolymphotrophs for Oral Delivery of Methotrexate

The objective of the study was to develop lipid drug conjugate nanoparticles (LDC-NPs) of anticancer drug methotrexate (MTX) for oral delivery that faces problems of low and variable bioavailability. The MTX loaded LDC-NPs significantly enhanced bioavailability and reduced MTX associated gastrointestinal toxicity even in higher doses recommended for anticancer therapy.

Lipid Nanocarriers: Influence of Lipids on Product Development and Pharmacokinetics

Lipid nanocarriers are on the forefront of the rapidly developing field of nanotechnology with several potential applications in drug delivery. Owing to their size-dependent properties, lipid nanoparticles offer the possibility for development of new therapeutics and an alternative system to other colloidal counterparts for drug administration. An important point to be considered in the selection of a lipid for the carrier system is its effect on the properties of the nanocarrier and also its intended use, as different types of lipids differ in their nature. Researchers around the globe have tapped the potential of solid lipid nanoparticles (SLNs) in developing formulation(s) that can be administered by various routes such as oral, ocular, parenteral, topical, and pulmonary. Since the start of this millennium, a new generation of lipid nanoparticles, namely nanostructured lipid carriers (NLCs), lipid drug conjugates (LDCs), and pharmacosomes, has evolved that have the potential to overcome the limitations of SLNs. The current review article presents broad considerations on the influence of various types of lipids on the diverse characteristics of nanocarriers, encompassing their physicochemical, formulation, pharmacokinetic, and cytotoxic aspects.

Solid lipid nanoparticles: a modern formulation approach in drug delivery system.

Solid lipid nanoparticles are at the forefront of the rapidly developing field of nanotechnology with several potential applications in drug delivery, clinical medicine and research, as well as in other varied sciences. Due to their unique size-dependent properties, lipid nanoparticles offer the possibility to develop new therapeutics. The ability to incorporate drugs into nanocarriers offers a new prototype in drug delivery that could be used for secondary and tertiary levels of drug targeting. Hence, solid lipid nanoparticles hold great promise for reaching the goal of controlled and site specific drug delivery and hence have attracted wide attention of researchers. This review presents a broad treatment of solid lipid nanoparticles discussing their advantages, limitations and their possible remedies. The different types of nanocarriers which were based on solid lipid like solid lipid nanoparticles, nanostructured lipid carriers, lipid drug conjugates are discussed with their structural differences. Different production methods which are suitable for large scale production and applications of solid lipid nanoparticles are described. Appropriate analytical techniques for characterization of solid lipid nanoparticles like photon correlation spectroscopy, scanning electron microscopy, differential scanning calorimetry are highlighted. Aspects of solid lipid nanoparticles route of administration and their biodistribution are also incorporated. If appropriately investigated, solid lipid nanoparticles may open new vistas in therapy of complex diseases.

Recent Advances and Patents on Solid Lipid Nanoparticles

Solid Lipid Nanoparticles (SLNs) have attracted increasing scientific and commercial attention as colloidal drug carriers during the last decade. They have emerged as a potential alternative compared to other colloidal systems like polymeric nanoparticles, liposomes and fat emulsions, as they have been claimed to combine their advantages but successfully overcome their drawbacks. SLN formulations are extensively developed and characterized for their in vitro and in vivo applications by various routes like parenteral, oral, pulmonary, ocular, and dermal. SLNs are being widely investigated as carriers for delivery of macromolecules like proteins, oligonucleotides and DNA. SLNs have already been taken up for medium and large scale production using two of its reported production methods. In fact, the first SLN based product has recently been introduced in the Poland market as a topically applied moisturizer. Newer methods for production of SLNs and their applications are being reported and patented. Nanostructured lipid carriers (NLC) are mixture of solid lipid and liquid lipid while Lipid Drug Conjugates (LDC) are water insoluble lipid carrier for loading of poorly lipid soluble drugs. These new generation of lipid nanoparticles have been claimed to overcome the shortcomings of SLNs. This article reviews the formulation, characterization, applications, and patents on the advances and research on SLNs, NLC and LDC.

Liposomes as nanocarriers of lipid-conjugated antitumor drugs melphalan and methotrexate

The inclusion of antitumor agents into nanodimensional carriers such as 100- to 150-nm liposomes makes it possible to reduce the general toxicity of chemotherapeutic drugs by decreasing the free drug concentration in the blood flow and by increasing the passive transport and accumulation of nanocarriers in tumors due to enhanced permeability of defective capillary vessel walls. On the other hand, biodegradable lipid-drug conjugates (lipophilic prodrugs) possess improved pharmacokinetics. In this study, we have determined detailed characteristics of the liposomal formulations of the antitumor drugs melphalan and methotrexate conjugated to rac-1,2-dioleoylglycerol, which contain the drugs in amounts (∼4 mM) sufficient for systemic injections into experimental animals. The liposomes were prepared from a mixture of natural phospholipids and prodrugs (phosphatidylcholine-phosphatidylinositol-prodrug molar ratio, 8 : 1 : 1) by the standard method of extrusion through polycarbonate membranes with 100-nm pores. The liposome size, lamellarity, and degree of aggregation were determined by methods of dynamic (laser) light scattering and transmission electron microscopy (using negative contrasting and freeze fracture techniques), while the liposome composition was checked using gel chromatography with subsequent UV spectrophotometry. It has been established that both diglyceride lipid-drug conjugates are completely included into unilamellar liposomes (bounded by a single lipid bilayer) with an average size of 50–150 nm and this dispersion can be stored for several days without any signs of significant aggregation. The possibility of obtaining liposomal preparations for long-term storage has been studied. It is demonstrated that liposomal drug dispersions can be subjected to deep freezing in liquid nitrogen and then stored for a long period of time at −70°C. For subsequent usage, the dispersion should be defrozen and treated for a short time in an ultrasonic bath, which completely restores the composition and size of the initial particles. Experiments in vitro have shown that a liposomal methotrexate conjugate is capable of overcoming tumor cell resistance to the drug, which is related to impaired transmembrane transport. The drug resistance of human leukemia cells related to a decreased activity of a transport protein (reduced folate carrier) has been decreased 114 times for methotrexate conjugate in liposomal formulation compared to the initial drug.

Lipid Nanoparticles with a Solid Matrix (SLN®, NLC®, LDC®) for Oral Drug Delivery

Solid lipid nanoparticles (SLN®), nanostructured lipid carriers (NLC®), and lipid–drug conjugates (LDC®), commonly produced by high-pressure homogenization, are interesting vectors for oral delivery of lipophilic and, to a certain extent, hydrophilic substances. Their production can be done without the use of organic solvents. Techniques to make them a physically stable delivery system have been developed. Scaling up of the production process from lab-size to large-scale dimensions using high-pressure homogenization can be easily achieved by using a different type of homogenizer. The machines used for large-scale production often yield an even better product quality than the lab-scale types. This review article covers the methods of production, characterization, mechanisms of oral bioavailability enhancement, scale-up, final oral dosage forms, and regulatory aspects of lipid nanoparticles for oral drug delivery. It focuses mainly on high-pressure homogenization production methods.

Challenges and solutions for the delivery of biotech drugs – a review of drug nanocrystal technology and lipid nanoparticles

Biotechnology allows tailor-made production of biopharmaceuticals and biotechnological drugs; however, many of them require special formulation technologies to overcome drug-associated problems. Such potential challenges to solve are: poor solubility, limited chemical stability in vitro and in vivo after administration (i.e. short half-life), poor bioavailability and potentially strong side effects requiring drug enrichment at the site of action (targeting). This review describes the use of nanoparticulate carriers, developed in our research group, as one solution to overcome such delivery problems, i.e. drug nanocrystals, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC) and lipid–drug conjugate (LDC) nanoparticles, examples of drugs are given. As a recently developed targeting principle, the concept of differential protein adsorption is described (PathFinder Technology) using as example delivery to the brain.

Drug Delivery to the Brain – Realization by Novel Drug Carriers

Delivery of drugs to the brain is still a major challenge. Successful delivery across the bloodbrain barrier has only been achieved in some cases, e.g., using pro-drugs. The review describes the delivery to the brain using nanoparticulate drug carriers in combination with the novel targeting principle of "differential protein adsorption" (PathFinder technology). The PathFinder technology exploits proteins in the blood which adsorb onto the surface of intravenously injected carriers for targeting. Apolipoprotein E is the targeting moiety for the delivery of particles to the endothelials of the blood-brain barrier. To reach therapeutic drug level in the brain, nanoparticulate drug carriers with sufficiently high loading capacity are reviewed, including drug nanocrystals (nanosuspensions), lipid drug conjugate (LDC) nanoparticles and lipid nanoparticles (solid lipid nanoparticles-SLN, nanostructured lipid carriers-NLC). The features are described, including regulatory aspects and large scale production.

Lipid–drug conjugate nanoparticles of the hydrophilic drug diminazene—cytotoxicity testing and mouse serum adsorption

Sleeping sickness is a widely distributed disease in great parts of Africa. It is caused by Trypanosoma brucei gambiense and rhodiense, transmitted by the Tse–Tse fly. After a hemolymphatic stage, the parasites enter the central nervous system where they cannot be reached by hydrophilic drugs. To potentially deliver the hydrophilic antitrypanosomal drug diminazene diaceturate to the brain of infected mice, the drug was formulated as lipid–drug conjugate (LDC) nanoparticles (NP) by combination with stearic- (SA) and oleic acid (OA). To estimate the in vivo compatibility, the particles were incubated with human granulocytes. Because as potential delivery mechanism the absorption of specific serum proteins (ApoE, Apo AI and Apo AIV) was found to be responsible for the delivery of nanoparticles to the brain, demonstrated using PBCA nanoparticles coated with polysorbate 80 (LDL uptake mechanism) the nanoparticles were incubated with mouse serum and the adsorption pattern was determined using the 2-D PAGE technique. As a result of this study, the cytotoxic potential was shown to decrease when diminazene is part of the particle matrix compared to pure fatty acid nanoparticles and the mouse serum protein adsorption pattern differs from the samples studied earlier in human serum. Especially, the fact concerning Apo-E that could be detected when the particles were incubated in human serum is absent after the mouse serum incubation, potentially, is a critical point for the delivery via the LDL-uptake mechanism but the data demonstrate that LDC nanoparticles, with 33% (wt/wt) drug loading capacity possess the potential to act as a delivery system for hydrophilic drugs like diminazene diaceturate and that further studies have to demonstrate the usability as a brain delivery system.

Solid lipid nanoparticles for parenteral drug delivery

This review describes the use of nanoparticles based on solid lipids for the parenteral application of drugs. Firstly, different types of nanoparticles based on solid lipids such as “solid lipid nanoparticles” (SLN), “nanostructured lipid carriers” (NLC) and “lipid drug conjugate” (LDC) nanoparticles are introduced and structural differences are pointed out. Different production methods including the suitability for large scale production are described. Stability issues and drug incorporation mechanisms into the particles are discussed. In the second part, the biological activity of parenterally applied SLN and biopharmaceutical aspects such as pharmacokinetic profiles as well as toxicity aspects are reviewed.

Lipid-Drug-Conjugate (LDC) Nanoparticles as Novel Carrier System for the Hydrophilic Antitrypanosomal Drug Diminazenediaceturate

The objective of the present study was to incorporate the hydrophilic drug diminazenediaceturate at a high loading into lipid nanoparticles by creating nanoparticles from lipid-drug conjugates (LDC). IR and DSC data showed that the antitrypanosomal drug diminazene is able to react with fatty acids to form water-insoluble salts like diminazenedistearate and -dioleate. The salts could be transformed into nanoparticles using high-pressure homogenization technique, established for solid lipid nanoparticles (SLN). By using polysorbate 80 as surfactant, physically stable LDC nanoparticle dispersions of both salts could be obtained. The mean PCS diameters and polydispersity indices were 364 nm and 0.233 for diminazenedistearate and 442 nm and 0.268 for diminazenedioleate, respectively. Due to the composition of the LDC bulk materials, nanoparticles with a high drug load of 33% (w/w) were obtained even for this highly water-soluble drug diminazenediaceturate. The new carrier system of LDC nanoparticles overcomes one limitation of SLN, i.e. the limited loading capacity for hydrophilic drugs. Transforming water-soluble hydrophilic drugs into LDC and formation of nanoparticles allows prolonged drug release and targeting to specific sites by i.v. injection. These results provide a first basis of using LDC-polysorbate 80 nanoparticles for brain delivery of diminazene to treat second stage human African trypanosomiasis (HAT).

The role of plasma proteins in brain targeting: species dependent protein adsorption patterns on brain-specific lipid drug conjugate (LDC) nanoparticles

The in vivo organ distribution of particulate drug carriers is decisively influenced by the interaction with plasma proteins after i.v. administration. Serum protein adsorption on lipid drug conjugate nanoparticles, a new carrier system for i.v. application, was investigated by 2-dimensional electrophoresis (2-DE). The particles were surface-modified to target them to the brain. To assess the protein adsorption pattern after i.v. injection in mice prior to in vivo studies, the particles were incubated in mouse serum. Incubation in human serum was carried out in parallel to investigate similarities or differences in the protein patterns obtained from men and mice. Distinct differences were found. Particles incubated in human serum showed preferential adsorption of apolipoproteins A-I, A-IV and E. Previously, preferential adsorption of ApoE was reported as one important factor for targeting of Tween®80 modified polybutylcyanoacrylate nanoparticles to the brain. Preferential adsorption of ApoA-I and A-IV took place after incubation in mouse serum, adsorption of ApoE could not be clearly confirmed. In vivo localization of the LDC nanoparticles at the blood-brain barrier and diffusion of the marker Nile Red into the brain could be shown by confocal laser-scanning microscopy. Differences of the obtained adsorption patterns are discussed with regard to their relevance for correlations of in vitro and in vivo data obtained from different species.

Rationale and applications of lipids as prodrug carriers

Lipidic prodrugs, also called drug–lipid conjugates, have the drug covalently bound to a lipid moiety, such as a fatty acid, a diglyceride or a phosphoglyceride. Drug–lipid conjugates have been prepared in order to take advantage of the metabolic pathways of lipid biochemistry, allowing organs to be targeted or delivery problems to be overcome. Endogenous proteins taking up fatty acids from the blood stream can be targeted to deliver the drug to the heart or liver. For glycerides, the major advantage is the modification of the pharmacokinetic behavior of the drug. In this case, one or two fatty acids of a triglyceride are replaced by a carboxylic drug. Lipid conjugates exhibit some physico–chemical and absorption characteristics similar to those of natural lipids. Non-steroidal, anti-inflammatory drugs such as acetylsalicylic acid, indomethacin, naproxen and ibuprofen were linked covalently to glycerides to reduce their ulcerogenicity. Mimicking the absorption process of dietary fats, lipid conjugates have also been used to target the lymphatic route (e.g., l-Dopa, melphalan, chlorambucil and GABA). Based on their lipophilicity and resemblance to lipids in biological membranes, lipid conjugates of phenytoin were prepared to increase intestinal absorption, whereas glycerides or modified glycerides of l-Dopa, glycine, GABA, thiorphan and N-benzyloxycarbonylglycine were designed to promote brain penetration. In phospholipid conjugates, antiviral and antineoplasic nucleosides were attached to the phosphate moiety. After presenting the biochemical pathways of lipids, the review discusses the advantages and drawbacks of lipidic prodrugs, keeping in mind the potential pharmacological activity of the fatty acid itself.

Bioavailability of phenytoin following oral administration of phenytoin-lipid conjugates to rats.

The bioavailability of phenytoin was evaluated in rats upon oral administration of phenytoin-lipid conjugates obtained by covalent binding of 3-hydroxymethylphenytoin to 1,3-dimyristoylglyceride via a succinidyl linkage, to 2-(1,3-dimyristoyl-2-glyceryl)butyric acid and to 3-myristoyloxy-2-methylpropionic acid. Despite differences of the phenytoin plasma concentrations all three compounds approximately doubled the AUC compared with the dosing of phenytoin itself. The early onset and the long duration of the anticonvulsant activity after administration of the triglyceride-derived conjugate could be correlated to the increased phenytoin plasma levels. It is concluded that drug-lipid conjugates may be useful prodrugs for the oral delivery of poorly water-soluble drugs.

Glyceride Conjugates as Drug Carriers

Abstract: Drug-lipid conjugates have been prepared in order to confer the attached drugs to the metabolic pathways of natural lipids. The drug can be covalently bound either to a fatty acid or to a glyceride. In glycerides, one or two fatty acid moieties have been replaced by a drug realizing pseudoglycerides. These pseudoglycerides exhibited some physicochemi­ cal properties and absorption characteristics similar to those of natural triglycerides resulting in a different pharmacokinetic and/or pharmacodynamic profile compared that of the parent drug. Non-steroidal anti-inflammatory drugs such as aspirin, indomethacin, ibuprofen, naproxen and aclofenac were covalently bound to diglycerides in order to reduce the ulcerogenicity of the compounds. Employing the absorption process of dietary fat, pseudoglycerides have been used for the targeting of the lymphatic route in order to avoid the first-pass metabolism of a drug (L-DOPA) and I or to target the lymphatic system for the treatment of lymphatic metastasis (chlorambucil, melphalan) or filiariasis (melphalan and GABA). Pseudoglycerides and other glyceride-like structures have been evaluated in order to increase the intestinal absorption of poorly water-soluble drugs such as phenytoin. An improvement of the blood-brain barrier penetration of GABA covalently bound to glycerides has been reported in the 80's, A similar approach was followed for L-dopa, glycine, valproate, and the enkephalinase inhibitor thiorphan including amide bio-isosteres of glycerides. Radioiodinated agents containing fluoride and nitroxyl moieties were coupled to glycerides and fatty acids as potential hepatographic agents in nuclear medicine, 19F- and 1H-nuclear magnetic resonance imaging, respectively. A variety of phospholipid-linked cytotoxic nucleosides and nucleoside analogues such as ara-C, AZT and acyclovir have been prepared. Compared to the parent drugs the phospholipid analogs exhibited increased antineoplastic activity in vitro and in vivo. The conjugates were also active against tumors and viruses that were resistant against the drug itself.

Adenosine analogs with covalently attached lipids have enhanced potency at A 1-adenosine receptors

Chemically functionalized congeners of N 6-phenyladenosine and 1,3-dipropyl-8-phenylxanthine have been covalently coupled to fatty acids, diglycerides, and a phospholipid. The lipid-drug conjugates inhibit R-[ 3H]-phenylisopropyladenosine binding to A 1-adenosine receptors in rat cerebral cortex membranes. A xanthine-phosphatidylethanolamine conjugate bound with a K i value of 19 nM. Various xanthine esters of low potency are potential prodrugs. Amides of an adenosine amine congener (ADAC) with 18-carbon fatty acids exhibited K i values at A 1-adenosine receptors of 70 pM, representing a 130-fold enhancement over the affinity of the corresponding acetyl amide. The very high affinity of adenosine-lipid conjugates may be due to stabilization of these adducts in the phospholipid microenvironment of the receptor protein.