Such esters are also said to increase encapsulating capacity and stabilise the vesicle membrane against leakage of the entrapped substances toward the carrier liquid. EP-A to Eibl discloses glycerol derivatives.
Prior art is silent to the use and optimization of structural elements II or lipids I to enhance cellular uptake and cytosolic delivery of liposomes and sequestered active ingredient.
Prior art has not taught, that the combination of hydrophobic moieties with the pH sensitive hydrophilic moieties provides criticality to such function. Objects of the invention. It is therefore a general object of the present invention to provide an improved non-viral carrier system for the in vivo, in vitro or ex vivo delivery of active agents into cells, especially mammalian cells.
In particular it is an object of the invention to provide an improved non- viral carrier system for delivering nucleic acids e. Another object of the invention is the provision of a non- viral carrier system that provides improved uptake of such active agents into cells.
A different object of the present invention is to improve the uptake of liposomes and other lipid-based carrier systems that encapsulate or sequester active agents into cells. Yet another object of the invention therefore is to provide a compound that can be incorporated into a lipid assembly such, for example, as a liposome, for improving the uptake of the lipid assembly into a cell. In particular, it is an object of the present invention to provide a compound that can be incorporated into such a lipid assembly for improving the fusogenicity of the assembly with biological membranes, especially cell membranes.
Yet another object of the invention is to provide pharmaceutical compositions comprising liposomes with improved uptake into cells as carriers for the delivery of active agents or other ingredients. Yet another object of the present invention is to provide improved compositions and methods for the treatment of humans or non-human animals in which a pharmaceutical composition comprising an active agent is targeted to a specific organ or organs, tumours or sites of infection or inflammation.
The or each TEE moiety is thus incorporated in a lipid molecule. The position of the hydrophilic moiety within the or each lipid molecule may vary. In some aspects, the hydrophilic moiety may be located distally from the link between the lipid moiety and the TEE. Alternatively, the hydrophilic moiety may be located centrally within the TEE. The present invention also comprehends, in a different aspect, the use of a transfection enhancer element TEE in a lipid assembly for improving the fusogenicity of the lipid assembly with a biological membrane, especially a cell membrane, wherein the transfection enhancer element TEE may be incorporated in a lipid molecule or may be complexed with the lipid assembly by means of ionic interactions, said TEE having the formula II : II hydrophobic moiety - pH sensitive hydrophilic moiety wherein the pH sensitive hydrophilic moiety of the TEE is a weak acid having pKa of between 2 and 6 or a zwitterionic structure comprising a combination of an acidic group with a weak base and having a pKa of between 3 and 8.
Where one or more transfection enhancer elements are incorporated in a lipid molecule, said molecule may have the formula I : I lipid- [hydrophobic moiety - pH sensitive hydrophilic moiety]. Thus, in another aspect of the present invention there is provided a lipid assembly including one or more lipids according to the invention or transfection enhancer elements TEE' s that are complexed with said lipid assembly by means of ionic interactions, said TEE' s having the formula: hydrophobic moiety - pH sensitive hydrophilic moiety II said pH sensitive hydrophilic moiety of each TEE being independently a weak acid having a pka of between 2 and 6 or a zwitterionic structure comprising a combination of acidic groups with weak bases having a pKa of between 3 and 8.
And in yet another aspect of the present invention, there is provided a lipid assembly formed from a lipid phase having amphoteric character, said assembly including lipids comprising one or more transfection enhancer elements Lipid-TEE's according to the formula I , wherein said transfection enhancer elements TEE' s have the general formula II : lipid moiety- [Hydrophobic moiety - pH sensitive hydrophilic moiety] I hydrophobic moiety - pH sensitive hydrophilic moiety II and said pH sensitive hydrophilic moiety of said TEE is a weak acid having a pka of between 2 and 6 or is a zwitterionic structure comprising a combination of an acidic group with a weak base having a pKa of between 3 and 8.
Said lipid assemblies may sequester active pharmaceutical ingredients. In one embodiment said pharmaceutical ingredients are nucleic acid-based drugs, like DNA plasmids, polynucleotides and oligonucleotides.
It has been found that lipid assemblies, in particular liposomes, comprising one or more lipids incorporating one or more transfection enhancer elements TEE's or being complexed with one or more separate transfection enhancer elements by means of ionic interactions may be used efficiently to transfect cells in vitro, in vivo or ex vivo.
The present invention provides an improvement in non-viral carrier systems for active pharmaceutical ingredients based on a hydrophile-hydrophobe transition in response to acidification of the environment.
Such mechanism is also known in the nature. For example, influenza viruses use a specific fusion mechanism. After the virus is internalized into the cell by receptor-mediated endocytosis, the viral envelope fuses with the endosomal membrane which leads to a release of the viral genome into the cytosol of the infected cell. This fusion event is catalyzed by the viral envelope glycoprotein hemagglutinin.
The trigger of the fusion is the acidic pH within the endosomal compartment leading to a conformational change of the hemagglutinin. Concomitantly, the N-terminal fusion peptide of the HA2 chain undergoes a hydrophobic shift due to protonation of carboxyl groups in the amino acid side chain.
The hydrophobic peptide can insert into the target membrane which leads to destabilization and subsequent fusion e. In some embodiments the pH-responsive hydrophilic moiety of the TEE of the invention may comprise a weak acid having a pKa of between 3 and 5. Said weak acid may be selected from carboxyl groups, barbituric acid and derivatives thereof, xanthine and derivatives thereof.
In other embodiments, said pH-responsive hydrophilic moiety may be a zwitterionic structure comprising a combination of a weak or strong acidic group with a weak base, the latter having a pKa of between 4. Suitably said zwitterionic structure may be formed from an anionic group and a heterocyclic nitrogen atom as cationic group. To achieve specific pKa's of said hydrophilic moieties, said pH-responsive hydrophilic moiety may be substituted with structural elements, selected from the group comprising hydroxymethyl-, hydroxyethyl-, methoxymethyl-, methoxyethyl-, ethoxymethyl-, ethoxyethyl-, thiomethyl-, thioethyl-, methylthiomethyl-, methylthioethyl-, ethylthiomethyl-, ethylthioethyl-, chlorid-, chlormethyl- vinyl-, phenyl-, benzyl-, methyl-, ethyl- , propyl-, isopropyl- and tert-butyl or cyclohexyl groups.
In some embodiments said hydrophobic moiety comprise linear, branched or cyclic chains with a minimum chain length of 6 elements. In one aspect of this embodiment said hydrophobic moiety comprises more than 6 and up to 40 elements, in a second aspect said hydrophobic moiety comprises between 6 and 20 elements and in a third aspect said hydrophobic moiety comprises between 20 and 40 elements.
The chain elements of said hydrophobic moiety may be carbon atoms. In one embodiment said hydrophobic moiety can be saturated or may contain unsaturated bonds. In other embodiments said hydrophobic moiety may be substituted. In some embodiments the branching of the main chain of said hydrophobic moiety may comprise rather small building blocks. Preferred building blocks comprise methyl-, ethyl-, propyl-, isopropyl-, methoxy-, ethoxy-, methoxymethyl-, ethoxymethyl-, methoxyethyl-, ethoxyethyl- and vinyl- or halogen groups or mixtures thereof.
Alternatively, said hydrophobic moiety may derive from sterols, said sterols may be further substituted. It is possible to insert one or more heteroatoms or chemical groups into the hydrophobic moiety of the pH-responsive transfection enhancer elements TEE's.
TEE's undergo a hydrophile-hydrophobe transition in response to an acidification of the environment. This transition is mediated by the hydrophilic moieties described above that are responsive towards pH. In some embodiments of the invention logD 4. In most aspects of the invention, the logD at pH 4 of said pH-responsive transfection enhancer elements TEE's exceeds 0. Of course, said pH-responsive transfection enhancer elements TEE's may contain more than one pH responsive hydrophilic moiety.
Where the transfection enhancer elements are chemically linked to a lipid moiety in accordance with the invention, the TEE's may be linked or grafted to the polar head group of said lipid moiety.
In a further embodiment the lipids may include chemical linkers between the graft and the pH sensitive transfection enhancer elements. Furthermore the polar headgroup of the lipid moiety may be further substituted, hi yet another embodiment of this aspect said lipids may contain more than one hydrophilic polar head group or complex hydrophilic head groups that allow substitution on various positions without affecting hydrophilicity.
In one aspect of the present invention the lipid assemblies are liposomes and in a specific embodiment of this aspect the liposomes are amphoteric liposomes of various size and lamellarity. Said amphoteric liposomes may be formed from a lipid phase comprising one or more amphoteric lipids or from a lipid phase comprising i a stable cationic lipid and a chargeable anionic lipid, ii a chargeable cationic lipid and chargeable anionic lipid or iii a stable anionic lipid and a chargeable cationic lipid.
Where said TEE's are complexed with said lipid assemblies using ionic interactions in accordance with the invention, said TEE's may be linked to a polycationic element and combined with anionic lipid assemblies or linked to a polyanionic element and combined with cationic lipid assemblies.
The lipid assemblies of the present invention may be sequester active pharmaceutical ingredients and in a specific embodiment said pharmaceutical ingredients are nucleic acid- based drugs, like oligonucleotides, polynucleotides or DNA plasmids. In a preferred embodiment of the invention said lipids are selected from the group comprising compounds 30 to 69 below.
In yet another aspect of the present invention there is provided a pharmaceutical composition comprising active agent-sequestered lipid assemblies or amphoteric liposomes in accordance with the present invention and a pharmaceutically acceptable vehicle therefor. For clarity, the following definitions and understandings are used for important terms of the invention: Transfection It comprises transport across, or diffusion through, penetration or permeation of biological membranes irrespective of the actual mechanism by which said processes occur.
The octanol-water partition coefficient logP is used to describe the lipophilic or hydrophobic properties of a compound. LogD differs from logP in that ionized species are considered as well as the neutral form of the molecule. LogD is therefore the logP at a given pH of the medium. LogD at pH 7. Experimental values have been generated for a vast amount of individual compounds and expert systems allow extrapolating logP and logD values for novel species.
Thus, for instance, polynucleotides as used herein refers to, among others, single-and double-stranded DNA, DNA that is a mixture of single- and double-stranded regions, single- and double-stranded RNA, and RNA that is mixture of single- and double-stranded regions, hybrid molecules comprising DNA and RNA that may be single-stranded or, more typically, double-stranded or a mixture of single- and double-stranded regions.
The exact size of an oligonucleotide will depend on many factors, including the ultimate function or use of the oligonucleotide.
Oligonucleotides can be prepared by any suitable method, including, for example, cloning and restriction of appropriate sequences and direct chemical synthesis by a method such as the phosphotriester method of Narang et al. Soc, , , or automated synthesis methods; and the solid support method of US 4,, Lipid assemblies In some aspects the amphipathic substances are known as lipids or as detergents, in other aspects such substances are known to form biological membranes or to insert into biological membranes.
The supramolecular assemblies may further comprise oils from apolar molecules. The supramolecular assemblies of the current invention therefore comprise liposomes of various size and lamellarity, micelles, inverted micelles, cubic or hexagonal lipid phases, cochleates, emulsions, double emulsions or other multimeric assemblies that are substantially build from lipids, oils or amphiphiles. Detailed description of the invention As described above it was found that lipid assemblies comprising one or more lipids with one or more transfection enhancer elements may be used to efficiently transfect cells.
This in turn leads to a decrease of the polarity of the functional group. It is possible, that the lipids I or parts thereof, e. It is also possible that the structural element II upon acidification inserts into its own lipid bilayer, thereby creating structural defects that improve fusogenicity and cellular transfection.
Liposomal delivery of drugs e. So, within the scope of the present invention such lipids with structural element II may enable or improve the transfection ability of liposomes, irrespective of their charge. Although a number of explanations can be given to explain the findings of the invention, an understanding of the exact mechanism whereby the enhanced fusion or transfection is achieved is not necessary for practicing the invention and even other mechanisms, not described here, may be involved.
Hvdrophilic moieties of TEE' s In one aspect of this invention the hydrophilic moieties are weak acids that provide a response in hydrophilicity between pH values of about 4 and the physiological pH of 7. Carboxyl groups, barbituric acid or derivatives thereof, in particular xanthine or derivatives thereof of formula 1 to 3 in table Ia represent, but do not limit such pH-responsive hydrophilic moieties.
Table Ia: Compounds Lo gD values for hydrophilic head groups derived from 1 to 3 are high at low pH and low at neutral or higher pH. Other derivatives of xanthins, pyrimidins uracils or barbituric acids are disclosed below in table Ib and analyzed with respect to their logD values at pH 4. The methoxyethyl moiety in compounds to represents or may be replaced by the hydrophobic moieties of the TEE as described above.
Table Ib: Compounds IS In another aspect of the invention, the hydrophilic moieties comprise zwitterionic groups that respond to changes in the pH of the environment.
Zwitterionic structures exist at pH values where both the cationic and the anionic group are charged and a generalized logD plot is shown in figure 1. It is apparent that the zwitterions have higher logD values than the charged parent groups. The desired increase in logD upon acidification is represented by the right flank of the logD curve and depends on the pKa of the cationic charge group; it is rather independent from the pKa of the anionic group itself.
As an example, the anionic group maybe a carboxyl group and the cationic group maybe a heterocyclic nitrogen atom two to five carbon atoms apart from that group e.
Pyridylcarboxylic acids, imidazolcarboxylic acids or the like are a few representations of such pH-responsive hydrophilic moieties. The zwitterion exists between pH 4 and pH 7, thereby providing the pH-responsive hydrophilic headgroups of the invention.
On the contrary, a simple amino group having a high pKa of about 9 e. Table 2: Compounds The hydrophilic moieties can further be substituted with polar or apolar groups. In one aspect of the invention, substitutions are selected to achieve a specific pKa of the hydrophilic moiety. Rules to achieve such adjustment of pKa values are known to the skilled artisan and comprise for example substitutions at nitrogen atoms of barbituric acid or xanthine with hydroxymethyl-, hydroxyethyl-, methoxymethyl-, methoxyethyl-, ethoxymethyl-, ethoxyethyl-, thiomethyl-, thioethyl-, methylthiomethyl-, methylthioethyl-, ethylthiomethyl-, ethylthioethyl-, chloro-, chloromethyl- vinyl-, phenyl- or benzyl groups or mixtures thereof to achieve a lower pK of the structure.
Substitutions at the positions Rm, Rn or R0 in formula 2 or 3 are in particular suitable to achieve such shift in pK values. Of course, pK values can be shifted towards higher values with substitutents comprising methyl-, ethyl- , propyl-, isopropyl- and tert-butyl or cyclohexyl groups or mixtures therof. An excellent overview for substituted xanthins and their respective pK values is found in Kulikowska et al. Acta Pol. It is known, that the pKa value for carboxyl groups is also affected by substitutions or chemical alterations in spatial proximity.
Specific examples of substituted hydrophilic moieties include, but are not limited to formula 4 to 9 of table 3, wherein R identifies the hydrophobic moiety of the TEE: Table 3: Compounds Further chemical representations for the hydrophilic moieties can be identified from the group of weak acids using the relationship between logD, pH and the pKa of the substance.
The equation reflects conditions of zero ionic strength and extremely low values for logD are calculated for acids at high pH. Under physiological conditions, where the ionic strength is about 0,15M, salt formation is limiting such extremes in logD.
Figure 2 shows the logD calculations for a number of hydrophilic moieties. Further analysis reveals identical shifts in logD when curves are plotted against pH-pKa see figure 3.
Once standardized with respect to their pKa values the logD plots become similar for all hydrophilic moieties analyzed here. However the functional importance of PS scrambling for secretion is still under debate and the precise kinetics of this translocation is not established.
An interesting possibility lies in the fact that PS contributes substantially to the negative charge of the inner leaflet of the plasma membrane.
Phosphoinositides for priming secretory vesicles Phosphoinositides are a class of phospholipids characterized by an inositol head group that can be phosphorylated on the three, four, and five positions to generate seven distinct species key in cell signaling and trafficking. Much of the work carried out on exocytosis has focused on the role played by PtdIns 4,5 P2.
Indeed a number of pioneer studies indicated that PtdIns 4,5 P2 positively modulates secretion in neuroendocrine cells 16 — Using patch clamp experiments on intact chromaffin cells and in parallel analyzing images of plasma membrane lawns, it was subsequently shown that over-expression of the kinase that generates PtdIns 4,5 P2 causes an increase in the plasmalemmal PtdIns 4,5 P2 level and secretion, whereas over-expression of a membrane-tagged PtdIns 4,5 P2 phosphatase eliminates plasmalemmal PtdIns 4,5 P2 and inhibits secretion Thus, the balance between the generation and degradation rates of the plasmalemmal PtdIns 4,5 P2 directly regulates the extent of exocytosis from chromaffin cell.
Wen et al. Importantly, such an inhibition promotes a transient rise in PtdIns 4,5 P2 that was sufficient to mobilize secretory vesicles to the plasma membrane via activation of the small GTPase Cdc42 and actin polymerization.
More recently, a functional link between PtdIns 4,5 P2 signaling and secretory vesicle dynamics through de novo remodeling of the actin cytoskeleton was also described These observations are consistent with a function of PtdIns 4,5 P2 as an acute regulator of secretion. PtdIns 4,5 P2 seems to lie in a key position controlling the size and refilling rate of the primed vesicle pools, but not the fusion rate constants per se.
In line with this model, we recently reported that the HIV PtdIns 4,5 P2-binding protein Tat is able to penetrate neuroendocrine cells and accumulate at the plasma membrane through its binding to PtdIns 4,5 P2.
By sequestering plasma membrane PtdIns 4,5 P2, Tat alters neurosecretion, reducing the number of exocytotic events without significantly affecting kinetic parameters fusion pore opening, dilatation, and closure of individual events Other phosphoinositides seem to act as signaling or recruitment factors to prime secretory vesicles for exocytosis. For instance, experiments carried out on permeabilized chromaffin cells reveal that PtdIns 3 P located on a subpopulation of chromaffin granules positively regulates secretion 21 , Hence, these studies highlight a complex regulation of neuroexocytosis by phosphoinositides, with PtdIns 4,5 P2 and PtdIns 3 P being essential factors promoting ATP-dependent priming in neurosecretory cells.
It is intriguing that PtdIns 3,5 P2 displays an opposite effect, but reveals how fine-tuning of exocytosis by phosphoinositides could potentially control the number of vesicles undergoing priming in response to a stimulation. Phosphatidic acid for fusion The local formation of PA is a recurring theme in intracellular membrane traffic and its involvement in regulated exocytosis has been suggested in various models, including neuroendocrine cells 14 , The development of molecular tools has enabled the identification of phospholipase D1 PLD1 as the key enzyme responsible for PA synthesis during exocytosis 14 , Capacitance recordings from chromaffin cells silenced for PLD1 suggest that PLD1 controls the number of fusion competent secretory granules at the plasma membrane without affecting earlier recruitment or docking steps, leading to the idea that PA acts directly in membrane fusion In agreement with this concept, a molecular sensor for PA revealed local PA accumulation at the plasma membrane near morphologically docked granules at sites of active exocytosis Other lipids Various other lipids are suspected to take part in regulated exocytosis.
Although most of them have been implicated based on in vitro membrane fusion assays, some have also been studied in neuroendocrine cells. For instance, diacylglycerol DAG increases stimulus-coupled secretion by recruiting vesicles to the immediately releasable pool through the regulation of the vesicle priming protein Munc Furthermore by activating protein kinase C, DAG may modulate the phosphorylation level of various proteins contributing or regulating the exocytotic machinery, including SNAP and Munc18 30 , Modulating PS levels also directly affects the rate of exocytosis in PC12 cells.
Finally, arachidonic acid produced from different phospholipids by phospholipase A2 and from DAG by DAG-lipase potentiates exocytosis from chromaffin cells 33 , Lipids as Recruiting Components of the Exocytotic Machinery Within membranes, the ability of microdomains to sequester specific proteins and exclude others makes them ideally suited to spatially organize cellular pathways.
For instance, numerous studies of the distribution of SNARE proteins in various cell types suggest that SNAREs partially associate with detergent resistant, cholesterol-enriched microdomains Palmitoylation appears to be the major targeting signal in these microdomains, as in the case of SNAP, although it is likely that other elements contribute to the enrichment of constituents of the exocytotic machinery within these cholesterol microdomains.
However despite intense research there is still little known about what lipid or protein molecules are actually present at sites of exocytosis.
Hydrogen or halogen atoms can substitute the chain, but are not elements of the chain. Moreover, its metabolite lysophosphatidic acid is recognized as a key signalling molecule with a myriad of biological effects mediated through specific receptors. They showed that many genes involved in phospholipid synthesis and metabolism were upregulated in differentiating mammary cells and also correlated with breast cancer survival. These correlations also show the significant role of phospholipids as a factor determining fat content and fat globule size.
Phospholipase D: a lipid centric review. After crossing the membrane, fatty acids under the influence of acyl-CoA synthetase are activated into the form of an acyl CoA. In some embodiments the branching of the main chain of said hydrophobic moiety may comprise rather small building blocks. Similarly, injection in Aplysia neurons blocked ACh release by reducing the number of active presynaptic releasing sites supporting evidence that PLD1 also plays a major role in neurotransmission, most likely by controlling the fusogenic status of presynaptic release sites Humeau et al. During lactation, the level of LPL is increased in the mammary gland and decreased in adipose tissue, indicating increased utilization of fatty acids in the mammary gland [ 41 ]. Lipid Res.
In addition, it inhibits the platelet aggregation induced by lysophosphatidic acid, possibly by inhibiting autotaxin. We performed a quantitative cell-to-cell comparison in the same field fluorescence from nontransfected cells compared with that of transfected cells expressing GFP. Accordingly, it has been known for decades that lipids, especially those coming from diet, are important to maintain normal physiological functions and good health. Another object of the invention is the provision of a non- viral carrier system that provides improved uptake of such active agents into cells. Indeed a number of pioneer studies indicated that PtdIns 4,5 P2 positively modulates secretion in neuroendocrine cells 16 — Biochim Biophys Acta.
Of course, mixtures of hydrophilic moieties can be combined with a single hydrophobic moiety. Gaussian distributions of the data were verified. DOI: Accordingly, the lipid-modifying enzyme PLD, which produces cone-shaped PA, emerges as a major actor in various cellular processes that have in common membrane fusion 6 — Agglomerations of sphingolipids with cholesterol may serve as an example in this case.