Patent Description:
Liposomes are defined as artificial microscopic vesicles consisting of an aqueous core surrounded by one or more concentric phospholipid layers (lamellas) [<NUM>]. Liposomes have gained extensive attention as carriers for a wide range of therapeutic agents because of being both nontoxic and biodegradable, as they are composed of naturally occurring substances [<NUM>]. Liposomes show extensive potential applications as they are able to incorporate hydrophilic (in the aqueous compartment), hydrophobic (within lipidic membrane) and amphiphilic substances (lipid aqueous interface) [<NUM>]. Moreover, biologically active materials encapsulated into liposomes are protected from immediate dilution or degradation. For all these reasons liposomes are the most popular nanocarrier systems used since their discovery.

The widespread use of liposomes for several purposes has created the need to develop efficient and reproducible preparation methods with the greatest simplicity as possible. There are different methods for preparation of liposomes, with numerous variants. Because of its simplicity, most laboratory use the lipid thin-film hydration method, first described in <NUM> [<NUM>]. However, the film method tends to be unsuitable for large scale production. Additionally, there are concerns about the use of chlorinated solvents.

The ethanol injection method is an interesting technique for GMP scaling-up liposomes production. It offers several advantages, e.g. simplicity, GMP friendly solvent, fast implementation and reproducibility, as well as the fact that it does not cause lipid degradation or oxidative alterations. The ethanol injection method was first reported in <NUM> by Batzri and Korn [<NUM>] as one of the first alternatives for the preparation of small unilamellar vesicles (SUVs) without sonication. By the immediate dilution of the ethanol in the aqueous phase, the lipid molecules precipitate and form bilayer planar fragments. Through energy dissipation in the system (by stirring and/or ultrasonication), the fragments of these lipid bilayers tend to decrease the exposure of the hydrophobic parts of their molecules to the aqueous environment, resulting in the curvature of these fragments which take a quasi-spherical structure. In the following years, several studies have investigated the preparation parameters of the ethanol injection technique (lipid concentration and composition, injection velocity, temperature of both phases, stirring rate, etc.) on the resulting liposome's characteristics (size distribution, zeta potential, drug encapsulation efficiency, etc.) [<NUM>].

In the classic ethanolic injection method, the ethanolic phase is in minor percentage comparatively to the aqueous phase, usually <NUM>-<NUM>%. After ethanol evaporation, the liposomal dispersion is extruded in order to reduce vesicles size. Briefly, classic ethanolic injection method comprises <NUM> key steps:.

In general, liposomal therapeutic or imaging agents loading is achieved by either passive or active methods:.

This method (active loading) however requires that molecule have a different protonation state at the extreme pHs of the buffers use inside and outside of liposomes. In such manner a given molecule will diffuse the lipid bilayer when two different pHs are set inside and outside the liposome. Thus, a pH gradient is the driving force to translocate and retain the amphiphilic weak bases and acids [<NUM>].

It also reported in the literature the active loading approach for a weakly basic amine therapeutic or imaging agents using a transmembrane ammonium sulfate gradient. In this case, the ammonia gradient drives a pH gradient, leading to active transport of the agent into the liposome. The sulfate then acts as a counterion for the ionized agent, causing it to precipitate within the liposome. This strategy has been applied to the production of liposomal doxorubicin in the case of Doxil. Myocet is another example of liposomal doxorubicin that is remotely loaded, although the pH gradient is established with citric acid [<NUM>].

In active loading process, after liposomes preparation with the classic ethanolic injection method, the extra-liposomal phase is removed, and then the agent is added to the extra-liposomal phase and the liposomes are incubated to allow the remote loading process to proceed. Briefly, active loading process comprises <NUM> key steps:.

Document <CIT>, Liposomes and its production method) describes a method of liposomal production which is the lipidic film hydration method.

Document <CIT>, High-encapsulation liposome processing method) describes a method for production of liposomes that uses chloroform. The liposomes produced present <NUM> microns or larger, needing extrusion to size reduction (where the originally encapsulated agent is lost).

Document <CIT>, Preparation of liposome and lipid complex compositions) describes a method to obtain liposomes containing compounds which exhibit poor solubility in water, alcohols, and halogenated hydrocarbon solvents. In this method the lipids are dissolved in an aprotic solvent solution, which may additionally contain a lower alkanol if needed to solubilize them. This method requires extrusion to obtain liposomes with defined size.

Document <CIT>, Method of making liposomes, liposome compositions made by the methods, and methods of using the same) describes a method to obtain liposomes where the aqueous solution comprises ethylenediaminetetraacetic acid (EDTA) to encapsulate ascorbic acid or a salt thereof. The liposome composition has a selected mean particle size diameter of about <NUM>-<NUM>.

Document <CIT>, Method of amphiphatic drug loading in liposomes by ammonium ion gradient) describes active loading of weak amphiphatic drugs into liposomes using transmembrane gradient.

Document <CIT>, Stably encapsulating a weak acid drug in liposomes, at a high concentration) describes liposomes encapsulated with a weak acid drug at a high concentration. The method employed a proton shuttle mechanism involving the salt of a weak acid to generate a higher inside/lower outside pH gradient.

Document <CIT> relates to methods and compositions for producing lipid-encapsulated negatively-charged therapeutic polymers, such as nucleic acid, proteins and peptides, which are encapsulated within a lipid layer.

Document <CIT> relates to methods and compositions for producing lipid-encapsulated charged therapeutic agent particles, after mixture of preformed lipid vesicles, a charged therapeutic agent (with a charge opposite to the lipid) and a destabilizing agent. Document <CIT> discloses a method for producing nanoparticles for encapsulating an active ingredient comprising the steps of (i) preparing an ethanol solution of lipids and (ii) injecting said solution to an aqueous solution.

The method of the description has the advantage of achieving a small molecule encapsulation efficiency in a targeted liposome equal to or better than previous methods without extra processing steps to produce nanoparticles. Polycharged molecules, namely with negative charges in their structure at neutral pHs (<NUM>-<NUM>) like methotrexate
and doxorubicin encapsulate better with this method. Methotextrate has high encapsulation rates and doxorubicin with reduced number of steps. (table <NUM> and <NUM>).

In the proposed alternative method, a higher encapsulation efficiency of the therapeutic or imaging agent is achieved using a pre-concentration method with an ethanol: aqueous phase at similar volume ratio, and the liposomes may be diluted at the end. The novel proposed method presents a reduced number of steps (only <NUM>) which is desirable in an industrial process. These features are congregated for the first time on the same method, differentiating it from those reported in the literature.

The widespread use of liposomes for several purposes has created the need to develop preparation methods which should be efficient, reproducible and with the greatest simplicity possible. Existing methods remain laborious for industrial scale-up and/or achieving low encapsulation efficiency of the agent of interest. In this way, it is imperative the development of a method with a reduced number of steps and that achieves high encapsulation efficiency of the encapsulated agent.

The lipids used to produce the liposomes may be changed or modified to customize the properties of the liposomal surface and membrane layer. There are different classes of lipids, based in their charge: neutral, cationic, and anionic. The addition of organic molecules to the phosphate head group creates a variety of phospholipid species such as phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylglycerol (PG) and phosphatidylcholine (PC). All these lipids could be used in liposomes production.

Unmodified liposomes do not survive long in circulation, as they are removed by macrophages. One of the first attempts to overcome these problems was focused on the manipulation of lipid membrane components in order to modify bilayer fluidity, as example by inclusion of a steroid. In this way, our liposomal formulations may preferentially contain cholesterol (CH), which may vary from a molar ratio of <NUM>-<NUM>%, preferably <NUM>-<NUM>%. It was demonstrated that incorporation of cholesterol, into liposomes reduces interaction with blood proteins, by causing increased packing of phospholipids in the lipid bilayer.

Furthermore, in a preferential execution was included a synthetic polymer, polyethyleneglycol (PEG) to the liposomes. PEG-containing liposomes showed less binding to blood proteins, reduced RES uptake, and thus prolonged duration of liposomes in the circulatory system. This has extended the blood circulation of conventional liposomes to drug delivery, the conjugated phospholipid DSPE-MPEG was incorporated in lipidic film of these new formulations, in a molar ratio which may vary between <NUM>-<NUM>%, preferably <NUM>-<NUM>%.

It has also been demonstrated that surface-modified liposomes with gangliosides have a prolonged circulation time in the blood stream compared to non-modified ones. These characteristics are potentially useful for applications of gangliosides in immunotherapies. Several glycolipids have been tested in studies of RES uptake of liposomes after intravenous injection: the glycolipid GM1 (a brain-tissue-derived monosialoganglioside) significantly decreased RES uptake when incorporated on the liposome surface, and the formulation remained in blood circulation for several hours.

Active targeting exploits specific modification of liposomal surface with a targeting ligand, which can lead to their accumulation at the target site or intracellular delivery to target cells. The inclusion of certain ligands in liposomes allows the release of their contents intracellularly by receptor-mediated endocytosis. Targeting agent integration at membrane surface could be achieved by conjugation to phospholipid or fatty acyl chains or incorporated in the lipidic membrane.

There are different methods for preparation of liposomes, with numerous variants. In the ethanol injection method (<NUM>% ethanol), a fraction of the aqueous solution with water-soluble substances is passively encapsulated inside the vesicles. The advantage of this method is its simplicity, but only a very small percentage of water-soluble therapeutic or imaging agents can be encapsulated in this way.

In the remote loading, empty liposomes are generally prepared in an initial salt or low pH buffer. The extra-liposomal phase is then removed using dialysis or size exclusion chromatography, or by titrating the pH to slightly basic conditions. Finally, the agent is added to the extra-liposomal phase and the liposomes are incubated to allow the remote loading process to proceed [<NUM>]. The number of steps involved makes the production process difficult to scale up, constituting a barrier to further development of this standard approach.

Hence, we focus our efforts in the optimization of agent encapsulation inside liposomes, with reduced production steps. Indeed, only a low amount of the agent used was encapsulated (e.g. <NUM>-<NUM>% to methotrexate drug), being a high amount of agent wasted and this could be an issue in a scale-up process. In order to increase the encapsulated agent numerous conditions were tested in several steps of the production method. Namely: aqueous phase in organic phase containing the phospholipids (instead the opposite), do not remove ethanol, to perform the injection at room temperature instead of at <NUM>, to test different speeds of injection and several concentrations of organic phase (<NUM>% until <NUM>%). The present invention is directed to a method for encapsulating an active ingredient in a liposome consisting of the following sequential steps:.

One embodiment of the present invention consists in a new method of production of liposomes,
wherein the hydrophobic components of liposomes are dissolved in ethanol, and injected in an aqueous phase at a rate of approximately <NUM> - <NUM>/min. under vigorous agitation. The initial volume ratio ethanol: aqueous phase is <NUM>/<NUM>. After evaporation of ethanol or tangential flow filtration the liposomal dispersion should be diluted <NUM> to <NUM>-fold, to the desirable final concentration.

The pre-concentration method comprises <NUM> key steps:.

In an embodiment, this method allows the achievement of high encapsulation efficiencies (e.g. ~<NUM>%) for polycharged agent like methotrexate, with a reduced number of steps (only <NUM>). The initial pre-concentration (use of a lower aqueous volume) increases the phospholipid concentration and, consequently allows a higher encapsulation efficiency. Additionally, the use of initial <NUM>:<NUM> of ethanol:aqueous phase volume ratio allows a balance between two phases with different polarities, increasing the encapsulation of the agents.

In another embodiment, the disclosure relates to a method, wherein it further comprises the step of diluting of the liposomal dispersion <NUM> to <NUM>-fold in further diluted aqueous phase.

In a further embodiment, the disclosure relates to a method, wherein the ethanolic phase is injected at a rate of approximately <NUM>-<NUM>/minute.

In a further embodiment, the disclosure relates to a method, wherein the injecting step is performed under agitation.

In a further embodiment, the disclosure relates to a method, wherein the active ingredient is a drug, in particular an anticancer drug, antirheumatic drug, anti-neurodegenerative diseases drug, antioxidant drug, anti-inflammatory drug, antipyretic drug, antibiotic drug, antiviral drug, analgesic drug or combinations thereof.

In another embodiment, the disclosure relates to a method, wherein the targeting agent is a peptide selected from the following list with a degree of identity of at least <NUM>% of the following sequence: SEQ- ID. NO <NUM>, SEQ- ID. NO <NUM>, SEQ- ID. NO <NUM>, or mixtures thereof; comprising at least a sequence <NUM>%, preferably or at least <NUM>% identical, or at least <NUM>% identical, or at least <NUM>% identical, or at least <NUM>% identical, identical to SEQ- ID. NO <NUM>, SEQ- ID. NO <NUM>, SEQ- ID. NO <NUM>, or mixtures thereof.

Methods for the alignment of sequences for comparison are well known in the art, such methods include GAP, BESTFIT, BLAST, FASTA and TFASTA. GAP uses the algorithm of <NPL>) to find the global (over the whole sequence) alignment of two sequences that maximizes the number of matches and minimizes the number of gaps. The BLAST algorithm (Altschul et al.

(<NPL>) calculates percent sequence identity and performs a statistical analysis of the similarity between the two sequences. The software for performing BLAST analysis is publicly available through the National Centre for Biotechnology Information (NCBI). Global percentages of similarity and identity may also be determined using one of the methods available in the MatGAT software package (<NPL>. MatGAT: an application that generates similarity/identity matrices using protein or DNA sequences). Minor manual editing may be performed to optimise alignment between conserved motifs, as would be apparent to a person skilled in the art. The sequence identity values, which are indicated in the present subject matter as a percentage were determined over the entire amino acid sequence, using BLAST with the default parameters.

The invention relates to a method, wherein the ethanol concentration, relative to the initial aqueous volume, is between <NUM>% and <NUM>%, preferably <NUM>%.

In another embodiment, the disclosure relates to a method, wherein the temperature is <NUM> or <NUM>.

In another embodiment, the disclosure relates to a method, wherein the active ingredient is a polycharged molecule containing at least one negative charge at a pH of around <NUM> to around <NUM>, particularly methotrexate or doxorubicin.

In a further embodiment, the disclosure relates to a method, wherein the aqueous phase is phosphate buffered saline, PBS.

In another embodiment, the disclosure relates to a method wherein the ethanolic phase comprises anionic, neutral or cationic phospholipids.

In a further embodiment, the disclosure relates to a method, wherein the ethanolic phase comprises phosphatidylcholines, phosphatidylethanolamines, phosphatidylserines, phosphatidylglycerols and/or their derivates or mixtures thereof, in particular <NUM>,<NUM>-dioleoyl-sn-glycero-<NUM>-phosphoethanolamine.

In another embodiment, the disclosure relates to a method wherein the ethanolic phase comprises a steroid, a stealth agent, a targeting agent, or mixtures thereof. According to the invention, a steroid is present in the ethanolic phase.

In a further embodiment, the disclosure relates to a method wherein the steroid is cholesterol, and/or their derivate, in particular cholesteryl hemisuccinate.

In another embodiment, the disclosure relates to a method wherein the stealth agent is polyethylene glycol, PEG, or gangliosides.

In a further embodiment, the disclosure relates to a method wherein the polyethylene glycol, PEG, is bound to a phospholipid, in particular distearoylphosphatidylethanolamine.

In another embodiment, the disclosure relates to a method wherein the targeting agent is incorporated in the lipidic membrane.

In another embodiment, the disclosure relates to a method wherein the active ingredient is an imaging or therapeutic agent.

In a further embodiment, the disclosure relates to a method wherein the imaging or therapeutic agent is hydrophobic or hydrophilic.

In another further embodiment, the disclosure relates to a method, wherein the imaging agent is a dye.

The present disclosure relates to a method for production of liposomes, in order to obtain high encapsulation efficiency of encapsulated agents with a reduced number of production steps, namely avoiding the extrusion step of the classical liposomal production process. The liposomes of the invention are intended to carry a therapeutic agent like an anticancer agent, antioxidant, anti-inflammatory, antipyretic, antibiotic, antiviral, antirheumatic, analgesic, growth-factor, or mixtures thereof.

The method of the description has the advantage of achieving a small molecule encapsulation efficiency in a targeted liposome equal to or better than previous methods without extra processing steps to produce nanoparticles.

In order to increase the encapsulated agent, with reduced production steps, numerous conditions were tested in several steps of the production method. The results demonstrate that the initial percentage of ethanol significantly affected the encapsulation efficiency. A drastic increase in encapsulation efficiency has been noticed as the ethanol volume was higher than the classic <NUM>% (<NUM>% relative to the initial aqueous phase), and also using a lower volume of aqueous solution of agent (the sample is afterwards diluted five times to get the usual agent concentration after ethanol evaporation or tangential flow filtration). Vesicles' size has been positively affected by the ethanol volume after this ratio is achieved. Indeed, batches having a higher ethanol volume (><NUM>%) showed larger vesicles (< <NUM>) than liposome batches previously produced. These results may be attributed to the slower diffusion of ethanol related to its volume increase in aqueous phase, leading to the formation of higher sized liposomes due to the slow self-assembly of phospholipids. Accordingly, the smaller the vesicles' size, the smaller the aqueous core volume and the lower obtained encapsulation efficiencies, knowing that the hydrophilic agent is mainly encapsulated in the liposome aqueous core [<NUM>, <NUM>]. However, a compromise between the encapsulation efficiency and size was obtained using <NUM>% of initial ethanol volume. Liposomes obtained with this percentage of ethanol present small size (<<NUM>) and PDI values (<<NUM>). Moreover, with these conditions, the extrusion process usually needed to decrease, and uniform vesicles' size is perfectly expendable.

In an embodiment, liposomes composed of DOPE/Cholesterol/DSPE-MPEG (<NUM>:<NUM>:<NUM>, molar ratio) were prepared using the ethanolic injection method. Briefly, lipids (DOPE, cholesterol and DSPE-MPEG) were dissolved in ethanol (<NUM>% in the classic ethanol injection method; <NUM>% in the new proposed pre-concentration method, relative to the initial <NUM>% aqueous phase) at <NUM>.

The solution was injected under stirring to an aqueous solution (phosphate buffered saline, PBS). This process is done at <NUM>, remaining during the necessary time to evaporate all the ethanol volume.

In the classic ethanolic injection method liposomes are extruded to reduce their size. In the pre-concentration method, after ethanol evaporation or tangential flow filtration, liposomal dispersion is diluted five times in PBS (remaining <NUM>% of volume is added). The free therapeutic or imaging agent that was not incorporated into liposomes was removed from the samples after passage through a gel filtration chromatography column (GE Healthcare) with <NUM> kDa cut-off (PD-<NUM> Desalting Columns containing <NUM> of Sephadex G-<NUM> Medium). Hydrophilic therapeutic or imaging agents (e.g. methotrexate and doxorubicin) are present in this aqueous phase in the classic ethanol injection method and in the new proposed pre-concentration method. In remote/active loading, after production in ammonium sulfate (<NUM>, pH=<NUM>), the buffer is changed to Trizma®Base sucrose (<NUM>%, w/v, buffered at pH <NUM>) and empty liposomes are incubated with the therapeutic or imaging agents.

Characterization of liposomes encapsulating methotrexate: comparative study between several production methods.

Where ranges are given, endpoints are included. Furthermore, it is to be understood that unless otherwise indicated or otherwise evident from the context and/or the understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value within the stated ranges in different embodiments of the invention, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise. It is also to be understood that unless otherwise indicated or otherwise evident from the context and/or the understanding of one of ordinary skill in the art, values expressed as ranges can assume any subrange within the given range, wherein the endpoints of the subrange are expressed to the same degree of accuracy as the tenth of the unit of the lower limit of the range.

The disclosure is of course not in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof without departing from the disclosure as defined in the appended claims.

The above described embodiments are obviously combinable.

Claim 1:
Method for encapsulating an active ingredient in a liposome consisting of the following sequential steps:
preparing an ethanolic phase by mixing hydrophobic molecules of phospholipids and a steroid with ethanol,
preparing an aqueous phase with an active ingredient and a targeting agent in a buffer solution;
obtaining the liposomes by injecting the ethanolic phase in the aqueous phase, at a temperature from around <NUM> to around <NUM>, wherein the ethanolic/aqueous phase volume ratio is between <NUM>:<NUM> and <NUM>:<NUM>;
removing the ethanol;
removing the remaining free active ingredient in a suitable way, namely by tangencial flow filtration;
optionally, the step of diluting of the liposomal dispersion <NUM> to <NUM>-fold in further diluted aqueous phase;
wherein the targeting agent is a peptide that is conjugated with a liposomal component or incorporated in the lipidic membrane;
wherein the ethanol concentration, relative to initial aqueous volume, is between <NUM>% and <NUM>%.