in the present invention , it has been determined that using an glucocorticoid pharmacologic agent in combination with a gene of interest provides a distinct improvement in the efficiency of gene delivery to cells which express glucocorticoid receptors as well as increasing the number of cells receiving the gene . in particular , dexamethasone , one of the most potent synthetic glucocorticoids , at mole ratios up to 3 compared to the cationic lipid , has been shown to facilitate the non - viral gene delivery of a variety of genetic constructs capable of performing their function ( including apoptotic cell death ) in human cancer cells . therefore the present invention provides an aqueous formulation useful for selective targeting and delivery of genes to cancer cells , comprising : ( a ) a cationic lipid , ( b ) a steroid and ( c ) a neutral co - lipid characterized in enhancing the transfection efficiency and stability of the formulation , wherein the said cationic lipid , steroid and neutral co - lipid are mixed in the ratio in the range of 0 . 75 : 0 . 5 : 1 to 1 : 2 : 1 preferably 0 . 75 : 1 : 1 to 1 : 2 : 1 . in a preferred embodiment of the invention , genes which can induce cell death are delivered via a non - viral route combination with glucocorticoid pharmacological compounds in order to provide more complete tumor emission and more effective prevention of tumor recurrence , thus leading to improved patient survival . the glucocorticoid pharmacological agent ( e . g ., dexamethasone ) is to be administered via the same route of gene delivery , by incorporating it with the non - viral gene carrier ( e . g ., a cationic lipid coat ). in this embodiment , four classes of genes may be used . first , cytotoxic genes such a tumor necrosis factor alpha or the tumor suppressor gene p53 , which promotes apoptosis , can be provided . second , genes which sensitize cells by enzymatically activating pro - drugs can be provided . for example , thymidine kinase or cytosine deaminase which respectively activate the cytotoxic pro - drugs gancylclovir and 5 - fluorocytosine could be provided . third , genes which promote immune surveillance could be provided . for example , tumor growth factor - beta 1 could be provided in combination with interleukin - 2 and interferon - gamma . fourth , antimetastatic genes , such as 5 e1a , could be provided . the idea of making this formulation stems from the fact that dexamethasone , a glucocorticoid , has close structural resemblance with cholesterol , a commonly used co - lipid present in many of the cationic lipids used for non - viral based gene delivery . the present invention provides a method for delivering genetic constructs via a non - viral mode with enhanced efficiency by co - formulating cationic lipid based gene delivery formulation carrying a glucocorticoid based pharmacologic agent along with the common co - lipid cholesterol . cholesterol as a co - lipid has long been used in liposomal formulations . it is known that cholesterol - containing liposomes have greater stability and lower ion - permeability than when cholesterol is not used [ straubinger et al 1983 , cell , 32 , 1069 - 1079 ]. in the event of lysosomal entrapment during cellular delivery the liposomal cargo is expected to be chewed up by the lysosomal degradative enzymes , such as nucleases , that work at ph & lt ; 6 . it is very much conceivable from the above known facts that cholesterol - associated liposomes not only provide a concrete integrity to the lipid - dna complex in cytosol but also prevent diffusion of lower ph solution containing lysosomal nucleases inside the lipid - dna core . the use of cholesterol increasing the stability of the genetic cargo and transfection efficiency is documented previously [ templeton et al . 1997 , nature biotechnology , 15 , 647 - 652 ; xu and szoka 1996 , biochemistry , 35 , 5616 - 5623 ]. in the context the present invention stands with complete patentability because the formulation uses our own patented cationic lipid along side a secondary co - lipid dexamethasone , and a common , generic , glucocorticoid . the dexamethasone is not modified at all and is used as such . the concentration at which the dexamethasone is used did not induce any toxicity to non - cancer cells . the use of dexamethasone for the targeted gene delivery to cancer is not documented in any of these papers . moreover , we for the first time showed that upon associating dexamethasone into cationic lipid formulation , the cancer cells are alone targeted leaving non - cancer cells untouched , even though the glucocorticoid receptors , through which dexamethasone works in cells , are ubiquitously present in all cells . the following examples are given by the way of illustration of the present invention and should not be construed to limit the scope of the present invention . glucocorticoid receptor expressing cell - specific gene delivery properties of the dexamethasone - cationic liposomal formulation the in vitro transfection efficacies of dx liposome containing dexamethasone in combination with dodeac as cationic lipid and cholesterol as co - lipid at a mole ratio of 0 . 75 : 1 : 1 were evaluated by reporter gene expression assay using pcmv - sport - β - gal plasmid as the reporter gene in a549 , mcf - 7 and cho cells across the cationic lipid to dna having charge ratios 8 : 1 to 1 : 1 . dexamethasone containing liposome dx has been found to be nearly 2 - 30 folds more efficient in transfecting a549 and mcf - 7 cells ( human cancer cells expressing glucocorticoid receptor ) ( fig1 and 3 ) than cho cell line . dx was most efficient in transfecting lung cancer cells a549 at cationic lipid : dna charge ratios of 8 : 1 and 4 : 1 ( fig1 ). transfection efficiency of dx in a549 at 2 : 1 and 1 : 1 was at least 10 - 20 fold less than that of other charge ratios . however , dx was most efficient in transfecting breast cancer cells mcf - 7 at cationic lipid : dna charge ratios of 4 : 1 , 2 : 1 and 1 : 1 ( fig3 ). both in a549 and mcf - 7 cells , lipofectamine ™ mediate comparatively much less transfection in comparison to dx ( fig1 & amp ; 3 ). significantly low levels of reporter gene expression were observed for dx in the otherwise highly transfectable , non - cancerous , transformed cell cho across all the charge ratios studied with 8 : 1 and 4 : 1 giving the highest transfection efficiencies ( fig5 ). transfection efficiencies of other charge ratios are not shown . lipofectamine ™ as expected did show up very high transfection efficiency in cho with respect to dx ( fig5 ). the contrastingly enhanced □- galactosidase reporter gene expression level observed in both a549 and mcf - 7 cells ( fig1 and 3 ) strongly indicate that transfection of glucocorticoid receptor expressing cancer cells , a549 and mcf - 7 by dx is likely to be mediated by the glucocorticoid receptor - binding dexamethasone as present in formulation dx . the transfection efficiencies of the dx formulation in transfecting glucocorticoid receptor expressing lung and breast cancer cells were significantly reduced when the gene transfer experiments were carried out by pretreating the cells with the ru - 38486 , the commercially available glucocorticoid receptor antagonists ( fig2 and 4 ) ( p & lt ; 0 . 01 ). similar ru - 38486 pretreatment studies in cho cells yielded no significant change in transfection efficiencies ( fig6 ) ( p & gt ; 0 . 1 ). thus , the results summarized in fig1 - 6 provided strong evidence for the involvement of glucocorticoid receptors expression in breast and lung cancer cells for the present class of dexamethasone associated gene delivery reagents . materials used — dulbecco &# 39 ; s modified eagle medium ( dmem ), fetal bovine serum was obtained from sigma - aldrich . lipofectamine ™ was obtained from invitrogen . p - cmv -. beta .- galactosidase was a generous gift from dr n . m . rao , ccmb , india . dexamethasone , ru - 38486 were purchased from ( sigma chemical co ., st . louis , mo .) cell - culture — mcf - 7 , cho , a549 cells were purchased from national center for cell sciences ( pune , india ) and were mycoplasma free . cells were cultured in dmem medium ( sigma chemical co ., st . louis , mo .) containing 10 % fetal bovine serum ( sigma chemical co ., st . louis , mo .) and 1 % penicillin - streptomycin at 370 c in a humidified atmosphere of 5 % co2 in air . cultures of 85 - 90 % confluency were used for all of the experiments . the cells were trypsinized , counted , subcultured in 96 - well plates for transfection and viability studies . the cells were allowed to adhere overnight before they were used for experiments . all the necessary compounds ( for e . g . dodeac , cholesterol , dope , dexamethasone ) were taken as stock solutions and mixed in a sample vial in appropriate amounts . it was dried as a thin film in gentle nitrogen flow and further dried in high vacuum for 6 hrs . then it was hydrated for overnight . after that it was subjected to bath sonication for 10 - 15 min and then probe sonicated at room temperature using a ti - probe sonicator for 3 - 4 min to get suv liposome . the liposomes were kept at 4 ° c . for a typical gene transfection study in vitro , cells were first seeded at a density of 12 , 000 - 15 , 000 cells / well in a 96 well plate usually 18 - 24 h before transfection . plasmid dna was complexed with cationic liposome typically in the following manner : 0 . 30 μg of pcmv - sport - β - gal dna , a negatively charged entity ( diluted to 50 μl with plain dmem ) was electrostatically complexed with varying amount of cationic liposomes ( a positively charged entity , diluted to 50 μl with plain dmem ) for 30 min . the molar ratios ( lipid : dna ) were 8 : 1 , 4 : 1 , 2 : 1 and 1 : 1 . after the complexation of plasmid dna and cationic liposome was completed , 200 μl of dmem containing 10 % fbs ( cm1 ×) were added to the resulting lipoplexes for triplicate experiments . thus the final concentration of serum became 6 . 7 %. cells were washed with phosphate - buffered saline ( pbs ), ph 7 . 4 ( 1 × 200 μl ) and then with lipoplex ( 100 μl ). after incubation of the cell plates at a humidified atmosphere containing 5 % co 2 at 37 ° c . for 4 hr , 100 μl of dmem containing 10 % fbs ( cm1 ×) were added to cells . the reporter gene activity was assayed after 48 hr . the media were removed completely from the wells and cells were lysed with 50 μl of 1 × lysis buffer ( np - 40 ) for 30 min . the beta - galactosidase activity per well was estimated by adding 50 μl of 2 × substrate ( 1 . 33 mg / ml of onpg , 0 . 2 m sodium phosphate , ph 7 . 3 and 2 mm magnesium chloride ) to the cell - lysate in the 96 well plate . absorption of the product ortho - nitrophenol at 405 nm was converted to absolute μ - galactosidase units using a calibration curve constructed with commercial μ - galactosidase enzyme . ru 38486 was dissolved in dmso at a concentration of 10 mm . 1 μl of it were added to each well plate where cells were plated previously in 100 μl of dmem + 10 % fbs . after 2 hr media were removed and cells were washed with pbs ( 1 × 100 μl ) and treated with lipoplexes . statistical analysis — all experiments were repeated at least once . data were expressed as mean ± standard derivation and statistically analyzed by the two - tailed unpaired student t - test using the microsoft excel software program ( microsoft , seattle , wash .). data were primarily considered significant if p & lt ; 0 . 01 . an experiment has been conducted to prove that indeed the cholesterol inclusion increases the stability of the liposomal formulation . the optimal formulation concentration that we used in our examples was 1 : 0 . 75 : 1 for dodeac : dex : chol . we made a formulation devoid of cholesterol but having the same ratio of cationic lipid and dexamethasone . the new formulation is hence dodeac : dex , 1 : 0 . 75 . the formulations were made 1 mm in concentration with respect to cationic lipid . 50 μl of each formulation was dispersed in 2 ml of phosphate buffer saline ( pbs ). pbs contains similar ionic strength and ph that prevails in a cellular environment . then we proceeded to measure the size in zetasizer ( malvern instruments , u . k .) over the period of time as indicated in fig7 . the data here indeed proves that the absence of cholesterol in cationic lipid formulation is detrimental for the size - stability of the liposome . the cholesterol - less formulation tends to increase in its size which might render it precipitate out in due course . in fact after 20 h it is noticed that the dodeac : dex ( 1 : 0 . 75 ) formulation indeed precipitated out , while the cholesterol - containing formulation [ dodeac dex : cholesterol :: 1 : 0 . 75 : 1 ] remained intact and showed no signs of precipitation . the wide range of literature related with cationic lipid mediated , gene transfection shows that the optimal size of the liposome showing efficient transfection should be in submicron level primarily because the lipid formulations with more than micron size will tend to precipitate out in long run rendering them incapable of carrying any bioactive molecules such as dna in a near - soluble form . moreover , a very big particulate matter will not be compatible in fusing with cellular membrane and hence will not be able to penetrate the membrane . in the same scenario , our cholesterol - formulated liposome does not change its size showing tremendous amount of stability and structural integrity of the formulation . two dexamethasone ( dex ) associated cationic liposome formulations comprising with or without cholesterol ( chol ) were made and proceeded to check their gene transfection efficiencies . the formulations were dodeac : dex : chol ( 1 : 0 . 75 : 1 ) and dodeac : dex ( 1 : 0 . 75 ). the said formulations were respectively complexed with plasmid encoding β - galactosidase gene and fed to the cells . following 4 h of lipid / dna complex treatment the cells were washed and kept at normal cell culture conditions for 48 h , on completion of which the cells were washed , lysed and assayed for the β - galactosidase gene using o - nitrophenol - b - d - galactopyrano side ( onpg ) substrate . the formation of o - nitrophenol is measured by measuring absorbance at 405 nm . the efficiency of transfection is directly proportional to the expression of transgene ( here , β - galactosidase enzyme ) that produces o - nitrophenol upon exposure with onpg substrate . the results are shown in fig8 . as the result shows that the cholesterol formulated cationic liposome could induce more transfection ( 2 - 4 folds ) than cholesterol - less formulation . the process of the present invention can be exploited for preparing cationic lipid based gene transfer reagents containing glucocorticoid receptor binding dexamethasone in the formulation . the invention of this dexamethsone associated cationic lipid based gene delivery vehicle is useful for delivering polyanions , polypeptides or nucleopolymers into cells via glucocorticoid receptors . the formulation disclosed herein can be used to deliver an expression vector into a cell for manufacturing or therapeutic use . the expression vectors can be used in gene therapy protocols to deliver a therapeutically useful protein to a cell or for delivering nucleic acids encoding therapeutically useful protein molecules . the dexamethasone associated lipid based formulation can be formulated with anionic , zwitterionic and lipophilic therapeutic agents including anticancer agents such as doxorubicin hydrochloride , a hydrophilic compound , or taxol ™, a lipophilic compound to obtain complexes comprising the invented dexamethasone - associated formulation and a therapeutic agent ( s ). in the invented dexamethasone - associated cationic lipid based formulation , two classes of genes may be used . first , cytotoxic genes such a tumor necrosis factor alpha or the tumor suppressor gene p53 , which promotes apoptosis , can be provided . second , those genes can be provided which sensitize cells by enzymatically activating pro - drugs . for example , thymidine kinase or cytosine deaminase , which respectively activates the cytotoxic pro - drugs gancylclovir and 5 - fluorocytosine . third , genes that promote immune surveillance could also be provided . for example , tumor growth factor - beta 1 could be provided in combination with interleukin - 2 and interferon - gamma . fourth , antimetastatic genes , such as 5 e1a , could also be provided for killing metastatic cells .
the present invention relates to a cationic lipid based aqueous formulation comprising cationic lipid , dexamethasone and a neutral co - lipid , wherein the said formulation is useful for selective targeting and delivering gene to glucocorticoid receptor expressing cancer cells . glucorticoid receptors express in various normal and cancer cells . a lot of ligand activated physiological functions are known involving gr but its role in cancer progression is not clearly understood . synthetic gr antagonist , dexamethasone finds use as anti - inflammatory drug and is known to induce apoptosis in cancer cells . this dex is included in a cationic lipid - based formulation as a co - lipid to deliver to and express genes specifically in cancer cells possibly through expressed gr . gene delivery to cancer cells is independent of the gene construct , and tumor cell line . normal transformed cells expressing gr but with no cancer lineage show much smaller level of transfection . the composition of the formulation is optimized . the formulation may have particular application to the enhanced delivery of anticancer genetic constructs to cancer , with the synergistic effect of dex in inducing apoptosis as such .