According The thin-film was re-suspended in phosphate buffer

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Last updated: May 20, 2019

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.

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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 processingparameters , 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 molaconcentration) 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 thenassembled 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) impact 49. ·        the zeta possibility of the conventionalliposome might have been Practically unbiased as anticipated since S100PCFurthermore cholesterol donot havea any charge.

addition of 3% (v/v) Tween 80in the hydration medium, those imply zeta possibility about traditionalliposome scattering might have been that’s only the tip of the iceberg negativewhich will be steady with past reports. The reason behind those lower zetapotential was because of the halfway hydrolysis of Tween 80. Those zetapotential from claiming PEGylated liposomes might have been more negative overthat of conventional liposomes because of those contrarily charged phosphateaggregation from claiming MPEG-DSPE, which is likewise about the outcome thereports in literature.

In this case, the impact from claiming Tween 80 forzeta-potential appears to be unimportant since those negative charge because ofthose PEGylation 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.

The additionof cholesterol at more than 20% caused a PTX precipitation and liposomedestabilization. The conventional PTX liposomes were more stable than previouslypegylated ones 52. However, the pegylated PTX liposomes were long-circulatingshowing a half-life time of 48.6 h against 9.3 h for the conventional ones. Itis a result of a less clearance of the pegylated PTX liposomes. Theirbiodistribution established a                                                                                                                       considerabledecline in PTX relapse in RES-containing organs (liver and spleen) after 0.5and 3 h in comparison with their conventional complements in Balb/c mice model52.

The circulation   result of PTX was assessed 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 rapidlyaccumulated and cleared by the liver, spleen and lung, while PTX liposomesexhibited a prolong half-life of 1.6-fold and 7.1-fold for the conventional andpegylated formulation, respectively.

In tumor, after 6 and 24 h the PTXconcentration of pegylated liposomes (0.4 and 0.1 ?g/g) was expressively higherthan that of the conventional liposomes (0.1 and 0.03 ?g/g) and Cr-P (0.05 ?g/gand cleaved). In case of pegylated PTX liposomes, the drug concentration intumor after 6 h was more than that in spleen, lung, heart, kidney and brain.

The aggregation of the pegylated PTX liposomes after i.v. administration of 7.5mg PTX/kg (3 cumulative doses in 4-day intervals) in tumor resulted in a prominentinhibition of the tumor growth as compared with the other methods at the end ofthe observation period of 60 days. Long circulation time and slow delivery ofPTX from 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 the encapsulation capacity of PTX and prepare stable pegylatedliposomes. The addition of cholesterol allowed a preparation of small-sizedliposomes with high drug incorporation. The presence of pegylated PL gave asteric stabilization of the liposomes. Increasing portions of HEPC (25 to 82mol%) have headed towards to an increased average diameter of the liposomes(113 to 203 nm), in the mean time , the encapsulation efficacy of PTX slowly decreased(69 to 37%). Established on these results, the liposomal formulation ofEPC/HEPC/ cholesterol/DSPE-mPEG (molar ratio, 15:5:2:1) was found to be optimum.

Liposomes were made by sonication of MLVs followed by extrusion through 0.2?m filters. The maximum encapsulation capacity of stable liposomes during thepreparation was observed to be 20 mol%.furthermore , PTX accelerated liposomedestabilization, needle like precipitates and aggregated liposomes were detected. Liposomes encapsulating up to 15 mol% of PTX reserved the initial drugcontent and the real size (about 140 nm) for 6 months at 4 °C.furthermore ,i.v. administration of liposomal PTX (40 mg/kg) triggered neither acutetoxicity nor mice death, which Taxol® at the consistent dose did 54.

For thein vivo studies employing Colon-26 solid tumor-bearing mice, it was establishedthat PEG-coated PTX liposomes delivered a significantly higher amount of PTX totumor tissue and gave more excellent anti-tumor effect than PEG uncoated PTXliposomes 55. These results proposes that PEG liposomes would aid as a potentPTX delivery carrier for the future cancer chemotherapy and signifies a appropriateplatform for the advancement of 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 use of pegylatedPTX liposomes was more effective in anti-angiogenic action as determined bymicro-vessel compactness calculation. These results postulates that conventionaladministration of pegylated PTX liposomes had an anti-angiogenic effect that disruptsthe blood stream and may be more effective in overcoming tumor growth in vivo56.(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 improved 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)            

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