According to a researchpublished in an article paclitexal loaded Liposomes were produced withSPC:CHOL:PEG2000- DSPE:tocopherol:PTX?16.2:3.8:1.3:0.
2:1 molar concentration bythin film hydration method (Umrethia et al. 2007). Briefly, SPC, CHOL, and PTX wereweighed correctly and then dissolved in organic phase, that is,chloroform (5 mL) in a 100-mL round bottom flask. This was assembled with arotary evaporator and the organic phase was evaporated at 45?2°C, which formsthe film on the wall of the flask. The other processing parameters , such asrotational speed of evaporating flask (100 rpm) and vacuum (250 mmHg) weremaintained constant. The round bottom flask comprising thin lipid film was left in vacuum desiccatorovernight to evaporate the solvent residualsif any. After that it was hydrated with phosphate-buffered saline (PBS), pH7.
4, employing vortex mixture for about 2 min to form conventional liposomes.This liposomal suspension was left at room temperature for about 2 h to obtain complete swelling. The resulting suspensionwas sonicated for 12 min in probe sonicator (220 W) to get small and homogenousvesicles and extruded via polycarbonatemembrane of 0.2 mm pore size. (Xuand Meng, 2016) According to anotherresearch , Both the conventional liposome consists of S100PC/CH (90:10, molarconcentration) and the PEGylated liposome consisting of S100PC/CH/MPEG2000-DSPE (90:10:5 as a molarconcentration) were produced by improved thin-film hydration technique.
Temporarily , the hydrophobic excipients, paclitaxel (3.5 mg/mL), CH andlipids 10% (w/v) S100PC and MPEG2000-DSPE, were dissolved in chloroform andtransferred into a appropriate conical flask. The flask was then connected witha BUCHI R-200 rotary evaporator ¨ (Flawil, Switzerland) and water bath (BUCHIB-490) with tem- ¨ perature maintained at 40 ?C under the aspirate vacuum. Thethin-film layer formed was washed with nitrogen gas for 5 min and maintained overnightunder vacuum to evaporate traces of chloroform. The thin-film was re-suspendedin phosphate buffer saline (PBS, pH 4.
0) with or without 3% (v/v) Tween 80 byrotating the flask at approximately t 300 rpm till the lipid film was entirely hydrated.Then, the liposome dispersion was passed through 1.2, 0.4 sequencially andfinally 0.2 m pore size filters (IsoporeTM) under nitrogen gas with an extruder(Northern Lipids, Inc., Canada). Un-entrapped paclitaxel was detached from theliposome suspensions by centrifuging at 1000 rpm for 10 min, after that the supernatant liposomal dispersion wascentrifuged at 50,000 rpm for 30 min to precipitate the liposomes. Entire precipitationof liposomes was revealed by observingthe absence of particles in the supernatant utilizing a NICOMP 370 SubmicronParticle Sizer.
The supernatant was wasted , and the liposome pellet was washedtwo times with PBS (pH 7.4). The pellet was then suspended in distilled water havingsucrose(molar ratio of sugar-to-lipid = 2.3), and freeze-dried (Laboratory Floor ModelFreeze-dryer FD5512, Ilshin, Seoul, Korea).
The concluding liposome particleswere kept in tight containers at 4 ?C for additional experiments. (Yang et al., 2007) Functionalized liposomesLiposomes speak to a versatile medicationcarrier system that may be enriched for other properties moving forward their targetingon towards those tumors. A novel amongst those approaches will be shaping anstealth liposome.Paclitaxel encapsulated in pegylated liposomes (long-circulatingliposomes)Fast freedom of the acceptedliposomes Toward RES speaks to a novel amongst those significant limitations in thedrug delivery.
This issue might have been understood eventually by utilizing the long-circulatingliposomes. Those grafting about accepted liposomes for an inactive andbiocompatible polymer for example, polyethylene glycol (PEG) prompts thoseshaping of a protective and hydrophilic layer on the liposomal surface 46. · the surface change couldlimit the abstraction of liposomes by cell of RES and clearly prolongs thosehalf-life from purporting liposomesThroughout coursing period47. · Those long-circulatingliposomes would likewise alluded should similarly as pegylated, stericallysettled alternately stealth liposomes. It might have been showed that thepermeability of the slim endothelium inthe tumors may be increased as compare to ordinary tissues 48. · the macromolecules arepassively gathered will more excellent degree to more drawn out period in thetumor over in the non-malignant capillary endothelium. This wonder may be alludedwill similarly as an improved permeability and Also provide maintenance (EPR) effect 49. · the zeta possibility of the conventionalliposome might have been Practically unbiased as anticipated since S100PCFurthermore cholesterol donot have any charge.
addition of 3% (v/v) Tween 80 inthe hydration medium, those imply zeta possibility about traditional liposomescattering might have been that’s only the tip of the iceberg negative whichwill be steady with past reports. The reason behind those lower zeta potentialwas because of the halfway hydrolysis of Tween 80. Those zeta potential fromclaiming PEGylated liposomes might have been more negative over that of conventionalliposomes because of those contrarily charged phosphate aggregation fromclaiming MPEG-DSPE, which is likewise about the outcome the reports inliterature. In this case, the impact from claiming Tween 80 for zeta-potentialappears to be unimportant since those negative charge because of thosePEGylation may be to such an extent bigger.(Yang et al.
, 2007) Smalllong-circulating liposomes (100 nm) showed An higher recurrence forencountering permeability in vessels ofthe tumor and extra-vasating under those fenestrated tumor tissue. This aggregationof long-circulating liposomes with encapsulated drugs by EPR effect representsa passive targeting mechanism enhancing the drug delivery and drug therapeuticpotential. 50.
Liposomal formulations containing 4mol% of PTX were prepared either as conventional ones made up ofPC/PG/cholesterol (molar ratio, 9:1:2) or as pegylated ones composed ofPC/PG/cholesterol/ DSPE-PEG (molar ratio, 9:1:2:0.7). However, both types ofliposomes were physically stable only for less than 1 day in the hydrated stateat 4 °C and reserved only 50% of the initial PTX content 51. Conventional andpegylated liposomes were produced by extrusion of MLVs producing PTX liposomeswith a average size of 120 nm. Theintroduction of cholesterol at more than20% caused a PTX precipitation and liposome destabilization. The conventionalPTX liposomes were more stable than previously pegylated ones 52. However,the pegylated PTX liposomes were long-circulating showing a half-life time of48.
6 h against 9.3 h for the conventional ones. It is a result of a less clearanceof the pegylated PTX liposomes. Their biodistribution established a considerabledecline in PTX uptake in RES-containing organs (liver and spleen) after 0.5 and3 h in comparison with their conventional complements in Balb/c mice model52.
The circulation result of PTX was observed after i.v.administration of 7.5 mg PTX/kg (single dose) of Taxol®, conventional andpegylated PTX liposomes in mice model having tumor xenograft. Cr-P was rapidly amassedand cleared by the liver, spleen and lung, while PTX liposomes exhibited a enhancedhalf-life of 1.
6-fold and 7.1-fold for the conventional and pegylatedformulation, respectively. In tumor, after 6 and 24 h the PTX concentration ofpegylated liposomes (0.4 and 0.1 ?g/g) was expressively higher than that of theconventional liposomes (0.
1 and 0.03 ?g/g) and Cr-P (0.05 ?g/g and cleaved). Incase of pegylated PTX liposomes, the drug concentration in tumor after 6 h was morethan that in spleen, lung, heart, kidney and brain. The aggregation of thepegylated PTX liposomes after i.v.
administration of 7.5 mg PTX/kg (3cumulative doses in 4-day intervals) in tumor resulted in a prominent inhibitionof the tumor growth as compared with the other methods at the end of theobservation period of 60 days. Long circulation time and slow delivery of PTXfrom pegylated liposomes gives opportunity for PTX to be retained at tumorthrough EPR effect and uphold the effective therapeutic level for a long-timeperiod via a depot effect. The passive tumor targeting was explained by anapplication of pegylated PTX liposomes of an suitable size of b200 nm 53. Thearrangement of lipids comprising EPC, HEPC, cholesterol and DSPEmPEG was optimizedto make better encapsulation capacity ofPTX and prepare stable pegylated liposomes.
The addition of cholesterol alloweda preparation of small-sized liposomes with high drug incorporation. Thepresence of pegylated PL gave a steric stabilization of the liposomes.Increasing portions of HEPC (25 to 82 mol%) have headed towards to an increasedaverage diameter of the liposomes (113 to 203 nm), in the mean time , theencapsulation efficacy of PTX slowly decreased (69 to 37%).
Established onthese results, the liposomal formulation of EPC/HEPC/ cholesterol/DSPE-mPEG(molar ratio, 15:5:2:1) was found to be optimum . Liposomes were made bysonication of MLVs followed by extrusion through 0.2 ?m filters. The maximumencapsulation capacity of stable liposomes during the preparation was observedto be 20 mol%.furthermore , PTX accelerated liposome destabilization, needle likeprecipitates and aggregated liposomes were detected . Liposomes encapsulatingup to 15 mol% of PTX reserved the original drug content and the actual size(about 140 nm) for 6 months at 4 °C.
furthermore , i.v. administration ofliposomal PTX (40 mg/kg) triggered neither acute toxicity nor mice death, whichTaxol® at the consistent dose did 54. For the in vivo studies utilizing Colon-26solid tumor-bearing mice, it was customary that PEG-coated PTX liposomesdelivered a significantly higher amount of PTX to tumor tissue and gave moreexcellent anti-tumor effect than PEG uncoated PTX liposomes 55. These resultsproposes that PEG liposomes would aid as a potent PTX delivery carrier for thefuture cancer chemotherapy and implies appropriate platform for the advancementof targeted liposomal PTX systems (Koudelka and Turánek, 2012) In yet one more revision where long circulating and targeted liposomesof paclitexal for FGF receptors were arranged employing a thin filmevaporation-extrusion method .Provisonally , paclitaxel, eggphosphatidylcholine, cholesterol, COOH-PEG2000-cholesterol,and DSPE-PEG2000 (2:60:30:5:3mol/mol) were dissolved in 4 mL of methanol and chloroform (1:3, v/v) as a mixedsolvent at 37 Celsius and dried to a thin film, firstly withnitrogen gas and after that under vacuum for several hours. The lipid film washydrated with 2 mL of 10 mM2-(N-morpholino) ethanesulfonic acid (MES) buffer (pH 5.0) at 40°C for one hour.
To obtainsmall and homogeneous vesicles, the liposome suspension was sonicated for 10minutes in a bath-type sonicator (Bransonic 12) along with three extrusion cycles via polycarbonate filters with 0.2 ?m pores(Lipex™ Extruder, Northern Lipids Inc, Vancouver, BC).40 For CL-PTX, paclitaxel, egg phosphatidylcholine, and cholesterol (molarratio, 2:60:30) were dissolved in chloroform/methanol (3:1, v/v), and then readyas for the above description of paclitaxel-loaded targeted PEGylated liposomes(TL-PTX) to obtain persistent CL-PTX. The resultant liposomes were purified ona Sephadex G-75 column to remove the non-encapsulated drug particles.(Cai et al.,2012) Application of pegylated paclitaxel-containing liposomes inmetronomic chemotherapy Metronomic chemotherapy or commonadministration at doses much less than MTDrepresents an alternate method of treatment with respect to common strategyutilizing MTDchemotherapy of the drug. As an advantage , this strategy shows a lowerdestructive effect and metronomic regimen could exploit the growth-limitingeffects as well as the anti-angiogenic properties.
The pegylated PTX liposomesand Taxol® formulation were used to predict the influence of metronomic and MTD action on the tumor growth inhibition andantiangiogenic activity. The uncoated Balb/c mice bearing MDA-MB-231cells were in developing stage to be treated after 11th day of xenograftimplantation. PTX formulations were administered at 15 mg PTX/kg on the 11th,15th, 19th and 23rd day and at 6 mg PTX/kg every day from the 11th to 15th day inaddition to the 22nd to 26th day for MTDand metronomic chemotherapy, respectively. On the 32nd day, mice weresacrificed and the tumor volume was measured .Mostly , the tumor growth in thegroups of metronomic and MTDpegylated PTX liposomes as well as MTDTaxol® showed the same inhibition effect, while important tumor progression wasobserved for the metronomic administration of Taxol®.
The metronomic application of pegylated PTX liposomes was moreeffective in anti-angiogenic action as determined by micro-vessel compactness calculation.These results postulates that conventional administration of pegylated PTXliposomes had an anti-angiogenic effect that disrupts the blood stream and maybe more effective in overcoming tumor growth in vivo 56.(Koudelka and Turánek, 2012)Tissue distribution study:· In case of Taxol®, plasma absorptionof paclitaxel was nearly negligible at 6 h, and it was readily uptake and cleanby the liver, spleen and lung.Though , when paclitaxel was encapsulated inliposomes, the plasma concentration was sustained for up to 24 h. · Furthermore , PEGylatedliposomes gave greater plasma level thanthat of conventional liposomes, which is consistent with the results from thepharmacokinetic study in rats.
In tumor tissue, paclitaxel concentration inPEGylated liposomes was significantly higher than that in conventionalliposomes and in Taxol® at 6 and 24 h. Also, in the case of PEGylatedliposomes, the paclitaxel concentration in tumor was higher than that inspleen, lung, heart, kidney and brain tissues from 6 h. These results proposedthat PEGylated liposomes were noticeably localized in the tumor tissues.· It seems that long-circulatingtime and slow discharge of PEGylated liposomes might offer sufficient chancefor paclitaxel to be achieved at the tumor site by EPR effect and preserve theeffective therapeutic concentration for a long period of time through the depoteffect. · Therefore, these results designatethat our PEGylated liposomal formulation successfully increased the antitumor effectivenesswhile overcoming the potential side-effects.Inhibition of tumorgrowth:· Since the paclitaxel loadedclassical liposomes and PEGylated liposomes were highly stored in the tumortissues of MDA-MB-231 human breast cancer xenograft model, the tumor growthinhibition effect was further observed. The study on the control (saline) groupterminated on the 35th day reason is that the tumor capacity was extremelyenlarged (about 2000 mm3), while other groups lasted until the 60th day.
· The PEGylated liposomes inhibitedtumor growth most efficiently, followed by the conventional liposomes andTaxol® (p < 0.05). This better anti-tumor activity of the PEGylatedliposomes can be clarified by the increased local concentration of pacltiaxelnear the tumor via EPR effect.(Yang et al., 2007)