Title of Invention

LIPID NANOVESICLES FOR IMPROVED DELIVERY OF ANTICANCER DRUGS AS AEROSOLS AND INTRAVENOUS FORMULATIONS

Abstract

The present invention describes a lipid nanovesicle encapsulating a pharmaceutical formulation of paclitaxel. The lipid nanovesicle is a combination of two phospholipids viz DPPC and DOPE. The nanovesicles achieve a stealth character without the addition of any polymers. The nanovesicles show an increased efficacy in drug resistant cancers by bypassing p glycoprotein efflux. The drug release from the nanovesicle is both temperature and pH triggered. The said formulation is administered both as an aerosol and an intravenous formulation and offers a high therapeutic efficacy.

Full Text

FORM2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See section 10; rule 13) 1. Title of the invention: "LIPID NANOVESICLES FOR IMPROVED DELIVERY OF ANTICANCER DRUGS AS AEROSOLS AND INTRAVENOUS FORMULATIONS" 2. Applicant(s) (a) NAME : (b) NATIONALITY (c) ADDRESS: INDIAN INSTITUTE OF TECHNOLOGY Created by an act of Parliament, Institute of Technologies Act, 1961 Indian Institute of Technology Bombay, Powai, Mumbai 400 076. 3. PREAMBLE TO THE DESCRIPTION The following specification particularly describes the invention and the manner in which it is to be performed: FIELD OF INVENTION The present invention relates to lipid nanovesicles for delivery of anticancer drugs. More particularly, the present invention deals with the development of lipid nanovesicles for site specific, sustained delivery of anticancer drugs. BACKGROUND OF THE INVENTION Cancer results from aberrant cell cycle progression, leading to enormous proliferation of cells. Current treatment approaches include surgery, chemotherapy, radiation therapy etc. As far as conventional chemotherapy is considered, it is characterized by the "Hill and Valley" phenomena. As the drug is administered, plasma drug concentration increases, peaks and then drops as the drug is metabolized. This cycle is repeated for each drug dose. This is not desirable as the "peak" concentrations of the drug could be toxic to normal cells and the "trough" levels could be ineffective. Thus the therapeutic concentration of the drug is reached only intermittently. For efficient treatment it is required that the plasma concentrations of the drug be within the therapeutic window for a prolonged period of time. Moreover, anticancer drugs have a low therapeutic index. This is because of the fact that these drugs are not tumor specific. Much of the drug has been found to be concentrated in normal healthy tissues and causes toxic effect. Furthermore if the drug is given by an intravenous injection, conventional formulations have a short half life in systemic circulation due to rapid uptake by the reticuloendothelial system. Despite the discovery of many new cytotoxic drugs that are potential candidates for the treatment of cancer, this life threatening disease is the major cause of more than 6 million deaths every year worldwide and the number is growing. Patients 2 under chemotherapy suffer more because of the side effects of the drugs rather than because of the actual problem. Conventional treatment strategies for cancer comprise surgery, radiation and chemotherapy. As far as conventional chemotherapy is considered, it suffers from various disadvantages such as sudden rise and fall of drug levels in plasma, low therapeutic index of the drugs and high toxicity due to non-specific accumulation in normal tissues. To circumvent the problems associated with conventional chemotherapy, the drug has to be delivered in a suitable tumor specific vehicle which should be biocompatible and should allow controlled release of the drug. Chemotherapeutic treatment of tumors is limited by the low therapeutic index of the anticancer drugs currently used. The reasons for this being low anticancer activity accompanied by severe side effects. Also the drugs accumulate not only in tumors but also in healthy tissues, which often results in no tumor targeting at all. Furthermore, some drugs are prone to enzymatic degradation during systemic circulation process; as a consequence, very high doses have to be given for sufficient tumor treatment, which also causes side effects. In this regard various drug carriers such as polymer based carriers are under experimental evaluation. Anticancer drugs like paclitaxel are highly hydrophobic, and hence are not soluble in aqueous medium and relevant pharmaceutical solvents. Clinical administration of many such anticancer drugs requires adjuvants, which involves numerous side affects and sometimes could be fatal. As far as paclitaxel is considered, the current dosage form is Taxol®. It comprises paclitaxel associated with 50:50 (v/v) Cremophor® EL (polyoxyethylated castor oil) and dehydrated alcohol, to increase drug solubility. Taxol® needs to be further diluted to 0.3-1.2 mg/ml using 5% dextrose and 0.9% sodium chloride. However, this Cremophor® EL based paclitaxel formulation is marked by serious complications like severe anaphylactoid hypersensitivity reactions, neurotoxicity, cardiotoxicity, nephrotoxicity, hyperlipidaemia, abnormal lipoprotein patterns, erythrocyte aggregation, and peripheral neuropathy. 3 Patent No US7288243 claims a method of inhibiting further growth of lung metastasis by administering a dose of a lipid-drug enhancer liposomal complex followed by a dose of a lipid-anticancer drug liposomal complex, both complexes delivered by aerosolization. The liposome composed of lipid having transition temperature of about 17°C or less, specifically in this case is dilauroylphosphatidylcholine (DLPC). The aforesaid thus involves a two step process. The said patent further reports micro sized carriers for the drugs. Formulations of such sizes if delivered intravenously result in RES clearance and the loss of the vesicles from the blood. This patent relates to the use of DLPC with enhancers and drugs which is in a fluid state at body temperature. The fluid state of the lipid makes it leaky at body temperature which effects the stability of the drug. Patent No US 6200598 and US 7108863 disclose the triggered release of drug from the nanovesicles. However, in the aforesaid patents the formulations are either temperature or pH triggered and require the additional presence of polymers for the stabilisation of the formulations. The formulations can be delivered as intravenous boluses and are not developed for aerosol therapy. US 6200598 teaches temperature sensitive liposomes with active agents. Liposome is composed of DPPC and a lysophospholipid named MPPC in a ratio of 99:1 to 80:20 molar weight. Liposome bilayer is derivatized by the addition of a hydrophilic polymer which may be polyethylene glycol, polylactic acid, polyglycolic acid, copolymers of polylactic acid and polyglycolic acid, and polyvinyl alcohol. The active agents are paclitaxel and camptothecin. This system is useful for administering active agents under mild hyperthermic conditions. The long circulation time or avoidance of the reticuloendothelial system uptake is achieved by the addition of polymers. These add to complexity of the formulation and the degradation products of the polymers can lead toxic acidic end products. Further, the presence of the polymer adds to steric hindrance which attenuates the 4 intracellular internalisation at the target site. The formulation is not effective in multidrug resistant cancers which overexpress p glycoprotein efflux pumps. Further, lysophospholipids are known to adversely affect the function of pulmonary surfactant making the formulation less suitable for pulmonary applications. US 7108863 teaches pH sensitive liposomes with active agents. Liposomal composition for efficient intracellular delivery of active agents have been proposed, wherein the liposome is composed of a pH sensitive lipid and includes a targeting ligand to direct the liposomes to a target cell. The liposome also includes a polymer-derivatized lipid upto 1-20 mol%, where the polymer is attached to the lipid by a releasable linkage. The liposome is composed of DOPE (pH sensitive lipid) and a stabilizing lipid (CHEMS) where DOPE has been derivatised with the polymer polyethylene glycol. Targeting ligand is an antibody or antibody fragment chosen from a group of anti-CD 19, anti-CD20, and anti-CD22. The active agent used is doxorubicin. In some embodiments of the said patent, the polymer derivatised lipid is DSPE-mPEG. The bonds for the linkage of the polymer to the lipid include dithiobenzyl bonds. The said patent however involves the addition of a polymer derivatised DOPE for steric hindrance to avoid uptake by the reticulo-endothelial system. The derivatised lipid is bonded chemically and needs to be broken in vivo for the efficacy of the formulation. This leads to uncertainties as the presence of the polymer can otherwise attenuate the intracellular internalisation at the target site. Moreover, the formulation is not effective in multidrug resistant cancers that overexpress p glycoprotein efflux pumps. Also the invention is not developed for aerosol therapy and does not mimic the function of pulmonary surfactant. Patent No US 5683715 teaches a liposomal taxane formulation given intravenously for the treatment of animals afflicted with cancer. The cancer may be brain, breast, colon, liver, lung, ovarian or prostate cancer. The liposome is composed of lipid and paclitaxel with one or more protective sugars at the inside 5 and outside surfaces of the bilayer. Liposomal lipid is an unsaturated or partially unsaturated phosphatidylcholine like DOPC, POPC, or egg phosphatidylcholine. Such lipids are susceptible to peroxidative damage due to unsaturation of the phospholipids. Further, the lipids used have transition temperatures less than 37 degrees indicating their fluid and leaky nature at body temperature. This in turn leads to low stability of the drug. The said patent requires the additional use of mono and disaccharides for the stabilisation of the formulation and for preventing its aggregation. Further, unsaturated phosphatidylcholines may destabilise the pulmonary surfactant in the lungs. The formulation does not contain any non-lamellar or pH sensitive lipids that can increase intracellular internalisation. US20070160658 teaches pharmaceutical drug delivery system comprising a particulate delivery vehicle wherein the delivery vehicle is a liposome. The liposome is composed of distereoylphosphoethanolamine polyethyleneglycoi 2000(DSPE-PEG), dipalmitoylphosphatidylcholine (DPPC), cholesterol (CHOL) and stearylamine (SA). The method is used in the treatment of Cancer of the CNS. The aforesaid prior art however teaches the uses of cholesterol and PEG modified components in its embodiments. The use of high cholesterol levels in the said patent is associated with cisplatin resistance. Also high density of caveolae (associated with cholesterol transport) is found in paclitaxel resistant lung adenocarcinoma cells. Moreover high cholesterol can cause an increase in the efflux from p glycoprotein pumps. Prior art methods for the treatment of cancer employing lipid based nanovesicles or liposomes have certain shortcomings. Most of the patents describing vesicular anticancer formulations relate to formulations which contain cholesterol or the lipids are derivatised with polymers or PEGylated. PEGylation causes steric hindrance which though desirable for avoiding the uptake by the liver, leads to decreased intracellular uptake at the target sites. In many instances the pH sensitive lipid is itself derivatised with PEG which then needs to be cleaved to 6 allow intracellular internalisation of the formulation. Further, the bulky molecule can hinder aerosolisation of the formulation. Therefore, there is a need for an improved method for the treatment of cancer employing nanovesicles. The present inventors have surprisingly developed a lipid based nanovesicle with reduced side effects and which overcomes drawbacks found in the prior art. The present inventors have developed a biocompatible phospholipid nanovesicles which carry the anticancer drug and targets it specifically to the cancerous region. This results in a reduced drug dosage as well as increased therapeutic index of the drug. Moreover, it also solves the solubility problem of hydrophobic anticancer drugs like paclitaxel. The present inventors have further surprisingly found that by using a simple combination of two phospholipids provides following advantages: 1. The nanovesicles formed can avoid uptake by the liver when given intravenously thus achieving a long circulation without the addition of any polymers to achieve a stealth character. 2. Administration as intravenous formulation, the combination of 60-70 mol% DPPC along with 30-40 mol% DOPE, surprisingly shows a specific targeted accumulation in the lungs. 3. Increased efficacy in multidrug resistant cancers by bypassing the pglycoprotein efflux pumps. 4. Addition of non-lamellar lipid (DOPE) to dissaturated lipid (DPPC) makes the formulation function like the pulmonary surfactant, even in the absence of surfactant specific proteins. Thereby, delivering anticancer drugs to the lungs directly as an aerosol without adverse effects. 5. Nanovesicles are both temperature and pH sensitive and show enhanced drug release at temperature of 42 C and pH 5, which are associated with hyperthermia and drug resistant cancers respectively. 6. The lipid nanovesicles of the present invention are in the diameter range of 100-120 nm and exhibit a sustained delivery of the anti-cancer drugs 7 specifically to the cancerous tissues. This improves the therapeutic efficacy of drugs thereby minimizing the drug dosage and hence the side effects of chemotherapy. 7. Simpler than existing prior arts, avoids the use of polymers and can be delivered as an aerosol or as intravenous bolus. The simplicity of the present invention can also be appreciated by the fact that unlike most of the formulations which consist of three or more lipids including cholesterol, the present invention is composed of only two lipids i.e. DPPC and DOPE. OBJECT OF INVENTION It is an object of the present invention to provide a lipid nanovesicle encapsulating a pharmaceutical formulation for the sustained delivery of the hydrophobic anticancer drugs paclitaxel, but is also suited for other hydrophobic anticancer drugs like camptothecin, adriamycin, rapamycin etoposide. It is an object of the present invention to provide a lipid nanovesicle which is a combination of dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylethanolamine (DOPE) only. It is an object of the present invention to achieve prolong circulation of the drug with decreased uptake by the liver without the use of polymers for steric hindrance It is an object of the present invention to achieve specific targeted accumulation in the lungs. It is an object of the present invention to effectively deliver drugs in multidrug resistant cancers. It is an object of the invention to provide a lipid nanovesicle that can function like a pulmonary surfactant. It is an object of the invention to provide a phospholipid nanovesicle that can deliver anticancer drugs in the lungs directly as an aerosol and also as an intravenous injection. 8 It is an object of the invention to provide a lipid nanovesicle which facilitates both pH and temperature triggered drug release. It is an object of the present invention to provide a lipid nanovesicle which has a particle size in the range of 100 to 200 nm, preferably in the range of 100-120 nm. It is an object of the present invention to provide a lipid nanovesicle which is free from cholesterol. SUMMARY OF THE INVENTION According to an aspect of the present invention there is provided a lipid nanovesicle encapsulating a pharmaceutical formulation of paclitaxel. According to an aspect of the present invention there is provided process for preparation of lipid nanovesicles comprising steps i. Formation of a solution of DPPC and DOPE in chloroform- methanol 2;1 with the drug in a drug to lipid molar ratio of 1:2 ii. Evaporation of the solvent under vacuum at 40 C for ten minutes to form a thin film of phospholipids iii. Hydration of the thin film formed for a limited period of 1 hour at 45 °C using phosphate buffered saline as the hydrating medium iv. Centrifugation at 25000 g for ten minutes at 4 C v. Reconstitution of the pellet formed using phosphate buffered saline at a pH of 7.4 vi. Sonication at 20 kHz at 50% power output or equivalent for two minutes or extrusion of the vesicles formed through a polycarbonate membrane having 200nm pore size BRIEF DESCRIPTION OF FIGURES • Figure 1: Particle size distribution of ISV-PTX as obtained by photon correlation spectroscopy (PCS) 9 Figure 2: Percent opening time of capillary simulating lung airways under the effect of different formulations as studied by Capillary Surfactometer (n=3) Figure 3: Cumulative release of free paclitaxel compared with the release of paclitaxel from ISV-PTX at 37°C and pH 7.4 Figure 4: Cumulative release of paclitaxel from ISV-PTX at 37°C and 42°C and pH 7.4 (n=3) Figure 5; Cumulative release of paclitaxel from ISV-PTX at pH 7.4 and pH5.0andat37°C(n=3) Figure 6: Lung deposition of paclitaxel in BALB/c mice after 2 hours of 60 minute inhalation of our formulation compared with lung deposition after 2 hours of i/v administration of paclitaxel solution. (n=3) Figure 7: Liver deposition of paclitaxel in BALB/c mice after 2 hours of 60 min inhalation of our formulation comapared with liver deposition after 2 hours of i/v administration of paclitaxel solution. (n=3) Figure 8: Lung deposition of paclitaxel in BALB/c mice after 30 minutes and 2 hours of i/v administration of our formulation compared with lung deposition after 30 minutes and 2 hours of i/v administration of paclitaxel solution, (n-3) Figure 9: Ratio of lung to liver deposition of paclitaxel in BALB/c mice after 30 minutes and 2 hours of i/v administration of our formulation compared with the ratio achieved after 30 minutes and 2 hours of i/v administration of paclitaxel solution. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nanovesicle system for the delivery of anticancer drugs wherein components of the nanovesicle consist of dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylethanolamine (DOPE). The size of the nanovesicle is between 100-200 nm and helps to evade 10 the reticuloendothelial system without the aid of any other polymer or PEGylation. The present invention relates to lipid nanovesicles which encapsulate an anticancer drug and have diameters of lOOnm to 200 nm. The drug used is paclitaxel, which is a potent anticancer drug, but has limited application due to its poor solubility in aqueous solutions. The phospholipid nanovesicles developed are non-toxic and biodegradable. The nanovesicles when suitably sized tend to accumulate significantly in the tumor tissues due to a leaky vasculature and the lack of an effective lymphatic drainage system (passive targeting). This is called the enhanced permeability and retention effect (EPR effect). Specifically, the lipids involved are DPPC (dipalmitoylphosphatidylcholine) and DOPE (dioleoylphosphatidylethanolamine) in a molar ratio of 60-70% DPPC and 30-40% DOPE. This combination of two phospholipids allows the nanovesicles to avoid uptake by the liver when given intravenously thus achieving a prolonged circulation without the addition of any polymers to achieve a stealth character. DPPC is a dissaturated phospholipid and forms the main component of the nanovesicles of present invention. DPPC is the major component of lung surfactant and forms highly surface active surfactant monolayers at physiological temperature (37°C). However, due to its high phase transition temperature (42 °C) it is in the gel state at 37°C leading to a very slow adsorption of the lipid to the air-aqueous interface of the lungs. Hence, DPPC alone cannot function as a lung surfactant which is required to open up collapsed alveoli and maintain airway patency. Hence the prior art requires the addition of surfactant specific proteins to enhance the adsorption of DPPC and allow it to maintain airway patency. In the present invention, the addition of the non-lamellar lipid (DOPE) to the desaturated lipid (DPPC) makes the formulation function like the pulmonary surfactant, even in the absence of surfactant specific proteins. The invention can thus act as an exogenous surfactant similar to the pulmonary surfactant and deliver anticancer drugs in the lungs directly as an aerosol without adverse effects. 11 In addition the nanovesicles are both temperature and pH sensitive and show enhanced drug release at temperature of 42 C and pH 5, which are associated with hyperthermia and drug resistant cancers respectively. The present invention uses 60 to 70 mol% DPPC and 30 to 40 mol% DOPE. There is essentially no use of lysolipids or polymer derivatised lipids or cholesterol derivative The size of the vesicle is important in preventing the drug as well as the vesicle itself from being recognized and engulfed by the reticuloendothelial system (RES). The unique composition of the present invention along with its preferred size The formulation of the present invention are effective at low dose. At a dose of lOmg/kg i/v, the formulation of the of the present invention shows a 100-fold increase in paclitaxel concentration in lungs as compared to lOmg/kg of the standard formulation of paclitaxel in cremaphor (Figure 8). Anticancer drug used is paclitaxel but the invention is not limited to it. Other hydrophobic anticancer drugs of the present invention include camptothecin, adriamycin, rapamycin, etoposide. Drug and lipids are preferably in 1:2 molar ratio though lower amounts of drug may also be used. The encapsulation efficiency of paclitaxel is 95 %. The formulation shows both pH and temperature sensitivity. Statistically significant increase in the release has been observed at pH 5 and high temperature 42°C as compared to physiological temperature and pH. The sustained release of drug from the nanovesicles is achieved with 17% release over a period of 48 hours as shown in Figure 3. 12 The formulation exhibits in vitro cytotoxicity with an IC50 which is several folds lower than that of the standard formulation of paclitaxel in cremaphor as per prior art for numerous cancers including lung cancer, colon carcinoma, ovarian carcinoma and glioblastoma (Table 1 and 2). The formulation is effective even in drug resistant cancers like the drug resistant colon carcinoma, glioblastoma and drug resistant ovarian carcinoma where the standard formulation of paclitaxel in cremaphor is ineffective as per the prior art. (IC50 of 750 nM for the present invention for drug resistant colon carcinoma HCT15 as seen in Table 2 opposed to 0% killing at 1 micromolar concentration of the the standard paclitaxel in cremaphor [4]). The standard paclitaxel formulation is known to have to IC50 values of 1.4 to 6 micromolar concentration for drug resistant lung cancer cell lines [5]and 24 micromolar for drug resistant H449 and H1870 lung cancer cell lines [6]. Similarly, the present invention has an IC50 of 60 nM for the OVCAR3 ovarian carcinoma (Table 2) whereas the standard paclitaxel formulation in prior art is reported to have an IC50 of 240 nM for the same cell line [7]. In drug resistant A2780 ovarian carcinoma the standard paclitaxel formulation has IC50 of around 10 micromolar as per the prior art. [8] The formulation can be nebulized as an aerosol and has two folds higher levels in the lungs than conventional i/v taxol preparations. The formulation can be nebulized as an aerosol and reaches negligible levels in the liver, a 35 fold lower drug level in the liver as compared to the conventional i/v taxol. The formulation has been intended but not limited for lung cancer. The formulation when given as an intravenous bolus leads to a hundred fold increase in levels in the lungs as compared to the conventional i/v taxol. The formulation when given as an intravenous bolus leads to a four fold lower ratio of drug in the liver as compared to the lungs whereas the conventional i/v taxol leads to a four fold higher concentration in the liver than the lungs 13 Process of preparation of paclitaxel loaded nanovesicles: Weighed amounts of DPPC and DOPE in the desired ratios were dissolved in a chloroform-methanol 2:1 solution. The solvent was evaporated under vacuum at 40 °C for ten minutes and a thin film of the lipid was formed. This film was further hydrated for a limited period of 1 hour at 45°C with continuous rotation using phosphate buffered saline as the aqueous hydrating medium. The vesicle suspension thus formed was sonicated at 20kHz with 50% power output or equivalent for two minutes to obtain the nanovesicles. In another embodiment, the vesicle suspension can be extruded through polycarbonate membranes of 200 run pore size to form the nanovesicles. Other solvents like methanol may be used instead of the chloroform-methanol solution. For the drug encapsulated formulation, paclitaxel was added to chloroform-methanol solution containing the phospholipids in a drug to lipid molar ratio of 1:2. The solvents were evaporated under vacuum at 40 °C for ten minutes to form a thin film. This film was further hydrated for a limited period of 1 hour at 45°C with continuous rotation using phosphate buffered saline as the aqueous hydrating medium. After formation of vesicles the unencapsulated paclitaxel was removed by centrifugation at 25,000 g for fifteen minutes at 4 °C. The pellet thus obtained was reconstituted using phosphate buffered saline having a pH of 7.4. The vesicle suspension thus formed was sonicated at 20kHz with 50% power output or equivalent for two minutes to obtain the nanovesicles. In an alternate procedure, the vesicle suspension can be extruded through polycarbonate membranes of 200 nm pore size or homogenised to form the nanovesicles. Alternatively, other methods of preparing nanovesicles like freeze thawing, reverse phase evaporation may also be used. For aerosol formation, the lipid nanovesicles suspension was nebulised using a jet nebuliser generated with a blend of 5 % C02 and 95 % 02 at the air flow rate of 10 L/min 14 EXAMPLES Example 1: Preparation of formulation Weighed amounts o£DPPC and DOPE in a ratio of 60 to 40 mol% were dissolved in a chloroform-methanol 2;1 solution. The solvent was evaporated under vacuum and a thin film of the lipid was formed. This film was further hydrated for a limited period of 1 hour at 45°C with continuous rotation using phosphate buffered saline as the aqueous hydrating medium. The vesicle suspension thus formed was extruded through polycarbonate membranes of 100 nm diameter to form the nanovesicles. In an alternate procedure, the vesicle suspension was sonicated at Hz for ten minutes to obtain the nanovesicles. For the drug encapsulated formulation, paclitaxel was added to the chloroform-methanol solution containing the phospholipids in a drug to lipid molar ratio of 1:2. This film was further hydrated for a limited period of 1 hour at 45°C with continuous rotation using phosphate buffered saline as the aqueous hydrating medium. After formation of nanovesicles the unencapsulated paclitaxel was removed by centrifugation. The vesicle suspension thus formed was extruded through polycarbonate membranes of 200 nm diameter to form the nanovesicles. In an alternate procedure, the vesicle suspension was sonicated at Hz for ten minutes to obtain the nanovesicles. The nanovesicles obtained were 100-200nm in size (preferred embodiment with diameters of 100-120 nm) and had a drug encapsulation efficiency of 95%. Example 2: The in vitro cytotoxicity of the formulation was tested on nine different cancer cell lines. Table 1: IC50 of the present invention on different cancer cell lines Compound H-460 HCT-116 A-549 PC-3 A2780 Present invention (nM) 50nM 62nM 140nM 150nM 43nM Blank (nM) - - - - - 15 Example 3: The in vitro cytotoxicity of the invented formulation was tested on drug resistant cancer cell lines. Table 2: IC50 of the present invention on different drug resistant cancer cell lines Compound AsPC-1 HCT-15 U373 MG OVCAR-3 Present invention (nM) 350nM 720nM 500nM 60nM Blank (nM) - - - - As can be observed from Table 1 and Table 2, for all the nine cell lines, the formulation showed a low IC50 value Example 4: Figure 4 compares the in vitro release profiles of paclitaxel from nanovesicles at 37°C and 42°C at pH 7.4 (physiological pH). Statistically significant and marked increase in the cumulative release of paclitaxel from nanovesicle has been observed at 42°C as compared to 37°C. Example 5: Figure 5 shows the comparative in vitro release profile of paclitaxel at pH 7 and 5. Statistically significant and marked increase in the cumulative release of paclitaxel from nanovesicle has been observed at lower pH. Therefore, by using a simple lipid combination, the present invention provides a dual triggered release at higher temperature (42°C) and low pH (5), which can be 16 useful for endosomal drug release, drug release in resistant cancers and under hyperthermic conditions. Example 6: Pharmacokinetic studies were done on tumor free BALB/c mice (~ 20 gm). Mice were divided into three separate groups with each having 6 mice for delivering the formulation by aerosol, the formulation as an intravenous bolus and for receiving free paclitaxel as intravenous bolus. The aerosol was generated with a blend of 5% CO2 and 95% O2. The nebulizer generated aerosol particles at the air flow rate of 10 L/min. Dose of the formulation given was 1 mg drug/ml. Concentration of drug achieved in the chamber after nebulization was 20 jig/mL. Intravenous administration of free paclitaxel and formulation of the present invention was done via tail vein with a dosage of 10 mg/kg. The formulation showed higher levels of drug deposition in the lungs than the free drug and lower levels of drug in the liver. This is beneficial as the intended use of the formulation is for lung cancers. Figure 6 shows that the deposition of the drug in the lungs on nebulization of the formulation was twice as compared to the lung deposition after 2 hours of i/v administration of free paclitaxel solution. Example 7: The deposition of paclitaxel on nebulization of the nanovesicles was significantly less as compared to the liver levels achieved on i/v administration of free paclitaxel solution (Figure 7). Example 8: Moreover, as can be observed from Figure 8, lung deposition of paclitaxel after i/v administration of our formulation was about 100-200 folds higher as compared to the lung deposition after i/v administration of free paclitaxel solution 17 Example 9: Figure 9 shows that the deposition of paclitaxel was 3-5 times higher in lungs as compared to its deposition in liver with our formulation given intravenously. In contrast, when paclitaxel solution was given intravenously, lung deposition was significantly less as compared to its deposition in the liver. Example 10: Table 3 shows the comparison of lethal dose estimation for the standard paclitaxel in cremaphor and the present nanovesicles invention. The LD50 or dose for 50% lethal effect is > lOOmg/kg for the present invention and is Table 3 Percentage survival and lethal dose estimation of the present invention and standard paclitaxel in cremaphor Compound % survival on day 2 % survival on day 15 LD50 Present invention (nM) 100 (at lOOmg/kg dose) 80 (at 100 mg/kg dose) > 100 mg/kg Standard paclitaxel 0 (at 30mg/kg dose) 0 (at 30 mg/kg dose) 18 We Claim: 1. A lipid nanovesicle comprising dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylethanolamine (DOPE) encapsulating a pharmaceutical formulation of hydrophobic anticancer drugs. 2. The lipid nanovesicle as claimed in claim 1 comprising 60 to 70 mol% DPPC. 3. The lipid nanovesicle as claimed in claim 1 comprising 40 to 30 mol% DOPE 4. The lipid nanovesicle as claimed in claim 1 having a size of 100-200 run. 5. The lipid nanovesicle as claimed in claim 4 wherein the most preferred size of the said vesicle is 100-120 nm. 6. The lipid nanovesicle as claimed in claim 1 which is temperature sensitive 7. The lipid nanovesicle as claimed in claim 6 wherein the said vesicle is sensitive at a temperature of 42°C. 8. The lipid nanovesicle as claimed in claim 1 which is pH sensitive. 9. The lipid nanovesicle as claimed in claim 8 wherein the said vesicle is sensitive at pH of 5. 10. The lipid nanovesicle as claimed in claim 1 is a pulmonary surfactant mimetic and the stealth character is achieved without use of any polymer. 11. The lipid nanovesicle encapsulating the pharmaceutical formulation of hydrophobic anticancer drugs as claimed in claim 1 wherein the anticancer is selected from paclitaxel, docetaxel, camptothecin, adriamycin, rapamycin and etoposide. 3 2. The lipid nanovesicle encapsulating the pharmaceutical formulation as claimed in claim 11 wherein the most preferred hydrophobic anticancer drug is paclitaxel. 13. A process for the preparation of the lipid nanovesicle as claimed in claim 1 which comprises the steps of: 19 a. Formation of a solution of DPPC and DOPE in chloroform- methanol 2; 1 with the drug in a drug to lipid molar ratio of 1:2 b. Evaporation of the solvent under vacuum at 40 °C for ten minutes to form a thin film of phospholipids c. Hydration of the thin film formed for a limited period of 1 hour at 45 °C using phosphate buffered saline as the hydrating medium d. Centrifugation at 25000 g for ten minutes at 4 °C. e. Reconstitution of the pellet formed using phosphate buffered saline at a pH of 7.4 f. Sonication at 20 kHz at 50% power output or equivalent for two minutes or extrusion of the vesicles formed through a polycarbonate membrane having 200nm pore size. 14. The lipid nanovesicle encapsulating the pharmaceutical formulation as claimed in claim 1 is effective in drug resistant cancers over expressing p glycoprotein. 15. The lipid nanovesicle as claimed in claim 1 is adapted to be administered by intraperitoneal, oral, intranasal or rectal routes. 16. The lipid nanovesicle as claimed in claim 1 is adapted to be administered either as an aerosol or an intravenous injection. 17. The lipid nanovesicle as claimed in claim 1 is adapted for the treatment of lung cancer, ovarian cancer, colon cancer, pancreatic cancer,

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