载柚皮素壳聚糖纳米粒的制备及其体外细胞评价

目的：制备柚皮素壳聚糖纳米粒,初步探讨其对人肺腺癌细胞A549的细胞毒性和细胞摄取。方法：以壳聚糖和鱼精蛋白作为载体材料,采用离子胶凝法制备柚皮素壳聚糖纳米粒,透射电镜（TEM）观察其形态,马尔文激光粒度仪测定其粒径、分散度（PDI）和Zeta电位,离心法测定其包封率和载药量,采用恒温振荡水浴法对柚皮素壳聚糖纳米粒进行体外释放度研究,最后采用人肺癌细胞系A549细胞进行了细胞毒性、细胞摄取研究。结果：柚皮素壳聚糖纳米粒为球形或类球形粒子,结构完整,大小均一、球形度好,分散均匀,PDI、粒径、Zeta电位和包封率分别为0.268,139 nm、+15.7 mV和83.34%,柚皮素壳聚糖纳米粒体外释放呈缓释,24 h累积释放量达到了80%以上,体外释药过程用Higuchi方程拟合较好。MTT试验显示不同浓度的壳聚糖纳米粒和细胞作用72 h后,细胞活力均大于95%,本文所制备的壳聚糖纳米粒无细胞毒性。细胞摄取试验表明载FITC的壳聚糖纳米粒和A549细胞作用3 h后,可明显看到大量带绿色荧光的纳米粒穿过细胞膜进入细胞。结论：离子凝胶法成功制得粒径较小的柚皮素壳聚糖纳米粒,具有缓释性好,毒性小,壳聚糖纳米粒摄取率较高,可大大提高药物的利用率,具有广泛的应用前景。     

泊洛沙姆188-PLGA纳米给药系统对抗耐药肿瘤的研究

目的 利用泊洛沙姆188对PLGA进行化学修饰,制备包载阿霉素的纳米粒,并评价纳米粒在人耐药乳腺癌细胞中的摄取能力及毒性。方法 通过EDC/NHS法合成泊洛沙姆188-PLGA,通过核磁共振对其结构进行表征并测定临界胶束浓度;通过纳米沉淀法制备包载阿霉素的纳米粒,通过粒度仪对纳米粒的粒径及分布进行分析,通过细胞摄取实验及细胞毒性实验对纳米粒的摄取效果及毒性进行评价。结果 成功合成了泊洛沙姆188-PLGA,并制备了粒径在140 nm左右的纳米粒,该纳米粒在人耐药乳腺癌细胞中有较好的摄取效果及较强的毒性。结论 泊洛沙姆188能够逆转耐药,增强耐药细胞对化疗药物的敏感程度。     

PEG表面修饰硬脂酸脂质纳米粒的制备与体外细胞摄取

目的　研究不同分子量聚乙二醇［poly(ethylene glycol),PEG］表面修饰的硬脂酸脂质纳米粒的制备方法及体外细胞摄取的情况。方法　以亲脂端为硬脂基,亲水端为不同链长度PEG的非离子性表面活性剂,用“乳化蒸发-低温固化”的方法制备硬脂酸纳米粒。以小鼠腹腔巨噬细胞为细胞模型做体外细胞吞噬实验。结果　用Brij 78,Myrj 53和Myrj 59为表面活性剂制备了粒径分别为(162.0±67.4) nm, (50.2±28.9) nm和(326.8±195.2) nm的纳米粒。体外细胞摄取实验证明,各种纳米粒相对于硬脂酸溶液均可增加巨噬细胞对硬脂酸的摄取,其中以Myrj 59组摄取最少;在样品中加入小鼠血浆可以增加巨噬细胞对硬脂酸纳米粒的摄取。结论　用“乳化蒸发-低温固化”的方法可以制备PEG表面修饰的硬脂酸纳米粒;表面修饰PEG链的长度可以影响硬脂酸纳米粒体外细胞的摄取。     

PEG表面修饰硬脂酸脂质纳米粒的制备与体外细胞摄取

目的　研究不同分子量聚乙二醇 [poly(ethyleneglycol) ,PEG]表面修饰的硬脂酸脂质纳米粒的制备方法及体外细胞摄取的情况。方法　以亲脂端为硬脂基 ,亲水端为不同链长度PEG的非离子性表面活性剂 ,用“乳化蒸发 低温固化”的方法制备硬脂酸纳米粒。以小鼠腹腔巨噬细胞为细胞模型做体外细胞吞噬实验。结果　用Brij 78,Myrj5 3和Myrj5 9为表面活性剂制备了粒径分别为 (16 2 0± 6 7 4)nm ,(5 0 2± 2 8 9)nm和 (32 6 8± 195 2 )nm的纳米粒。体外细胞摄取实验证明 ,各种纳米粒相对于硬脂酸溶液均可增加巨噬细胞对硬脂酸的摄取 ,其中以Myrj5 9组摄取最少 ;在样品中加入小鼠血浆可以增加巨噬细胞对硬脂酸纳米粒的摄取。结论　用“乳化蒸发 低温固化”的方法可以制备PEG表面修饰的硬脂酸纳米粒 ;表面修饰PEG链的长度可以影响硬脂酸纳米粒体外细胞的摄取。     

5-FU有机金属框架纳米粒的体外细胞摄取及影响因素的研究

目的 制备5-氟尿嘧啶(5-FU)有机金属框架(BTC)纳米粒,考察体外细胞摄取率及其影响因素.方法 用室温配位调控法制备BTC纳米粒5-FU-Cu-BTC,用扫描电子显微镜观察其形态,用流式细胞仪测定其体外细胞摄取率及影响因素.结果 Cu-BTC载体的粒径约为100 nm,载药量为38％,体外细胞摄取实验表明:细胞摄取率与样品浓度和温度成正比.结论 有机金属框架纳米粒可载入抗肿瘤药物并被肿瘤细胞摄取.     

PEG-胆固醇双重修饰PBCA纳米粒脑靶向机制

目的中枢神经系统疾病目前存在的主要问题是血脑屏障(BBB)通透性的问题,本实验期望通过制备PEG-胆固醇双重修饰PBCA纳米粒,提高难透过BBB的中枢神经系统疾病的治疗及早期诊断药物的治疗作用,并对其经过BBB进入脑组织的机制进行探讨。方法采用乳化聚合法制备双重修饰PBCA纳米粒并对其理化特性进行评价。(1)双重修饰PBCA纳米粒体内药动学及脑组织分布研究:实验前12小时大鼠进行颈静脉插管手术。实验时于插管处给予原药溶液,胆固醇单修饰及PEG-胆固醇双重修饰PBCA纳米粒。给药后不同时间点取血200μL,化学/发光分析仪测定血液中香豆素-6的含量。大鼠尾静脉分别给予原药溶液、胆固醇单修饰及PEG-胆固醇双重修饰PBCA纳米粒。给药后不同时间点处死大鼠,取脑组织测定香豆素-6的含量。(2)双重修饰PBCA纳米粒体外细胞摄取及转运机制研究:采用b End.3细胞模型(永生化小鼠脑内皮细胞株)评价了载体及纳米粒的体外细胞毒性,同时选用了巨胞饮介导的内吞作用(细胞松弛素D),网格蛋白介导的内吞作用(氯丙嗪),小窝蛋白介导的内吞作用(染料木素),胆固醇耗竭(MβCD和制霉菌素),高尔基体抑制剂(布雷菲德菌素A)和耗能(叠氮钠)等七种细胞摄取抑制剂来研究载药纳米粒的细胞摄取及转运机制。结果 (1)制备的纳米粒粒径为(191.1±1.22)nm、载药量约为1.97%,包封率大于98%。同时双重修饰PBCA纳米粒在体外具有更明显的缓释效果。(2)双重修饰PBCA纳米粒在体内具有更高的血药浓度及缓释效果,能持续释放12 h,而胆固醇单修饰纳米粒仅释放8 h,原药溶液仅4 h内能检测到药物。脑组织分布研究结果表明,双重修饰PBCA纳米粒静脉给药后脑组织中药物含量显著增高且成缓慢释放的过程,说明具有成为脑靶向制剂的研究潜力。(3)载体及载药纳米粒细胞安全性良好,纳米粒在实验范围内没有明显的细胞毒性,具有较好的安全性。选择不同类型的摄取和转运抑制剂研究了载药纳米粒的细胞摄取及转运机制。结果表明,参与细胞转运和摄取的机制可以是不同的,而胆固醇-PEG双修饰PBCA纳米粒在b End.3细胞中的转运机制,是一个包括巨胞饮介导、耗能、同时需要胆固醇参与等多种机制介导的复杂过程。结论本实验制备的PEG20000-胆固醇双重修饰PBCA纳米粒,可解决中枢神经系统疾病的治疗及诊断药物体内BBB通透率低、安全性差、缓释性差等瓶颈问题,具有重要应用前景。     

重组人干扰素α-2b纳米粒小鼠体内药物动力学及组织分布

目的考察小鼠静脉注射重组人干扰素α2b纳米粒后的体内药动学及组织分布。方法小鼠尾静脉注射给药后,采集不同时间血液、肝、肺和肾样品,经处理后,应用双抗体夹心酶联免疫吸附法(ELISA)测定重组人干扰素α2b的血浆及组织中浓度。结果重组人干扰素α2b纳米粒及溶液注射给药,血浆药时数据经3p97药动学程序拟合,均符合一级消除动力学双隔室模型。给予重组人干扰素α2b纳米粒小鼠体内消除半衰期(t1/2β=2.786 h)是溶液剂消除半衰期的(t1/2β=0.599 h)的4.7倍;血药浓度时间曲线下面积纳米粒组是溶液剂组的3.95倍,肝组织中药时曲线下面积纳米粒制剂是溶液剂组的3.8倍。与溶液剂组相比,纳米粒组在肺、肾中的药物分布也显著增加(P<0.001)。结论纳米粒作为重组人干扰素α2b的载体,能够显著延长重组人干扰素α2b小鼠体内消除半衰期,增加其在肝、肺、肾组织中的分布。     

羧甲基壳聚糖-聚乙二醇作为胰岛素载体的研究

目的：制备胰岛素-羧甲基壳聚糖-聚乙二醇纳米粒。方法：利用红外光谱（FTIR）和核磁共振氢谱（¹H-NMR）对羧甲基壳聚糖-聚乙二醇的结构进行表征,用粒度分析仪测定纳米粒的粒径分布及电位,采用动态透析法考察纳米粒的释药性能,用CCK-8试剂盒检测纳米粒细胞毒性,以糖尿病小鼠为模型,研究纳米粒的降血糖作用。结果：聚乙二醇成功接枝到羧甲基壳聚糖上,包埋胰岛素的纳米粒的平均粒径为（257.5±12.1）nm,Zeta电位为（-15.2±0.3）mV,负载胰岛素的羧甲基壳聚糖-聚乙二醇纳米粒在中性释放介质中,5 h内胰岛素的释放速度较快,之后8 h趋于平稳,胰岛素的累计释放量可达到80%,CCK-8试剂盒显示纳米粒对L929细胞基本无细胞毒性,50 U·kg^-1的纳米粒溶液经灌胃给药后,血糖浓度明显降低。结论：胰岛素-羧甲基壳聚糖-聚乙二醇纳米粒基本无毒性,具有良好的生物相容性,对糖尿病小鼠有效发挥降血糖作用。     

A549细胞对壳寡糖及其纳米粒的摄取作用

目的研究壳寡糖及其纳米粒的A549肺上皮细胞摄取作用,探讨壳寡糖纳米粒作为药物载体的可能性。方法溶剂扩散法制备壳寡糖纳米粒,以A549肺上皮细胞评价壳寡糖及其纳米粒的细胞毒性,由荧光倒置显微镜、流式细胞仪研究A549细胞对壳寡糖及其纳米粒的摄取作用。结果壳寡糖及其纳米粒的细胞毒性均较低,IC₅₀分别为944.36和643.16 mg·L^-1。壳寡糖及其纳米粒的细胞摄取作用与其浓度及细胞孵育时间相关;在同一孵育时间壳寡糖纳米粒的摄取量比等浓度的壳寡糖增加0.49～13.9倍。结论壳寡糖及其纳米粒的细胞毒性较低。壳寡糖形成纳米粒后,可显著增加A549细胞的摄取作用。     

无稳定剂修饰的汉防己甲素PLGA纳米粒制备及体外评价

目的:制备无稳定剂修饰的汉防己甲素PLGA纳米粒,研究其理化性质及细胞毒和细胞摄取特性。方法:以聚乳酸-羟基醋酸共聚物(PLGA)为载体材料,采用无稳定剂修饰的纳米沉淀法制备汉防己甲素纳米粒;通过单因素试验考察不同制备工艺对纳米粒理化性质的影响;通过载药量、包封率、累积释药量等指标考察其载药特性;采用MTT比色法检测其对人肺腺癌细胞株A549的细胞毒性;采用共聚焦显微镜技术考察其细胞摄取特性。结果:无稳定剂修饰的汉防己甲素PLGA纳米粒平均粒径169.3 nm,与有稳定剂的汉防己甲素PLGA纳米粒相比外观无明显改变。在一定范围内,随着PLGA用量的增加,纳米粒的粒径呈上升趋势;随着投药量的增加,纳米粒的载药量显著增加,包封率下降。在pH7.4的释放介质中,纳米粒释慢释药,96 h累积释药率60.44%。细胞毒试验显示,当培养时间为8 h时,汉防己甲素组的细胞毒性大于汉防己甲素纳米粒组;当培养时间延长至24 h时,汉防己甲素纳米粒组的细胞活性明显低于纯药物组;高剂量的空白纳米粒组始终表现较低的细胞毒性。激光共聚焦电镜断层扫描显示汉防己甲素纳米粒能够较好的被细胞摄取。结论:制备的无稳定剂修饰的汉防己甲素PLGA纳米粒大小均一,包封率高,体外释药表现出较好的缓释效果,易被细胞摄取,对A549细胞的增殖有明显的抑制作用。     

Cellular uptake and elimination of lipophilic drug delivered by nanocarriers

To investigate the cellular uptake and elimination process of a lipophilic drug loaded in different nanocarriers, emulsions, liposomes and poly (DL-lactide-co-glycolide) (PLGA) nanoparticles loaded with a model drug, coumarin 6, were prepared and their transportation in HeLa cells compared. After 4 h incubation, liposomes and nanoparticles mediated significantly higher intracellular drug levels, which were 3 or 2.5 times that of the emulsion group, into cells. A novel kinetic model was established to analyze the cellular elimination process. Emulsions had the longest intracellular mean residence time (MRT), which was about 1-2 times longer than other nanocarriers. The endocytosis inhibition experiment suggested that the coumarin 6 in liposomes and nanoparticles entered cells directly via diffusion, while part of the intracellular coumarin 6 was taken up through clathrin-mediated endocytosis in emulsions. Combined with the results on uptake pathway and kinetic parameters, it can be concluded that different nanocarriers bring about diverse mechanisms of cellular uptake and elimination.     

Cellular uptake and transport of gold nanoparticles incorporated in a liposomal carrier

Recent interest in using gold nanoparticles (Au NPs) for therapy in radiation medicine has motivated development of a liposome-based system to enhance their delivery to cells. In this study, liposomes were demonstrated to perform like a “Trojan Horse” to deliver small (1.4 nm) Au NPs into tumor cells by overcoming the energetically unfavorable endocytosis process for small NPs. The results reveal that the liposomal approach provides a thousand-fold enhancement in the cellular uptake of the small Au NPs. Real-time intracellular tracking of the Au NP–liposomes revealed an average speed of 12.48 ± 3.12 μm/hr for their intracellular transport. Analysis of the time-dependent intracellular spatial distribution of the Au NP–liposomes demonstrated that they reside in lysosomes (final degrading organelles) within 40 minutes of incubation. Knowledge gained in these studies opens the door to pursuing liposomes as a viable strategy for delivery of Au NPs in radiation therapy applications.From the Clinical EditorGold nanoparticles (Au NPs) as part of an optimized liposome-based delivery system have been proposed for therapy in radiation medicine. The approach resulted in a thousand-fold enhancement in the cellular uptake of Au NPs compared to conventional delivery methods, with the nanoparticles residing in lysosomes within 40 minutes of incubation.     

Impact of Surface-Engineered ZnO Nanoparticles on Protein Corona Configuration and Their Interactions With Biological System

In biological system, the interaction between nanoparticles (NPs) and serum biomolecules results in the formation of a dynamic corona of different affinities. The formed corona enriched with opsonin protein is recognized by macrophages and immune effector cells, resulting in rapid clearance with induced toxicity. Hence, to reduce corona genesis, surface-engineered ZnO (c-ZnO) NPs were in situ synthesized using a polyacrylamide-grafted guar gum (PAm-g-GG) polymer that provided surface neutrality to the NPs. Furthermore, we studied the characteristics of the corona formed onto uncapped anionic ZnO (bared ZnO [b-ZnO]) NPs and c-ZnO NPs by serum incubation. The result shows that b-ZnO NPs were wrapped with a high amount of serum proteins, particularly opsonin (IgG and complement), compared with c-ZnO NPs. These corona findings helped us substantially in interpretation of in vivo biokinetics studies. The in vivo study was accomplished by oral administration of NPs to Swiss mice at doses of 300 and 2000 mg/kg body weight. The studies performed on the cellular uptake, intracellular particle distribution, cytotoxicity, and pharmacokinetics of NPs indicated that b-ZnO NPs experienced higher immune cell recognition, hepatic inflammation, and resultant rapid clearance from the system, unlike c-ZnO NPs. Thus, capping of NPs by a neutral polymer has provided limited binding sites for undesired proteins around NPs, which limits immune system activation.     

Cellular elimination of nanoparticles

Exposure of the general population to nanoparticles (NPs) occurs mainly by dermal and oral uptake of consumer products, food and pharmaceutical applications and by inhalation. While cellular uptake mechanisms have been intensely studied it is less well known how NPs are eliminated from the cells. Quantification of the amount of excreted particles is complicated by inherent limitations of the technologies that are suitable to study excretion. Among the mechanisms to decrease intracellular particle concentration active excretion by lysosomal exocytosis appears to be the most important. Lysosomal localization, small particle size and high intracellular and low extracellular particle levels facilitate exocytosis. Transporting epithelia, cells with secretory function and highly proliferative cells are expected to be able to decrease intracellular particle concentrations more efficiently than cells lacking these characteristics. As NPs can influence the extent of exocytosis it is possible that NPs can stimulate their excretion.     

A Compartment Model for the Membrane-Coated Fiber Technique Used for Determining the Absorption Parameters of Chemicals into Lipophilic Membranes

PURPOSE: The purpose of this work was to develop a compartment model for the membrane-coated fiber (MCF) technique for determining the absorption parameters of chemicals into lipophilic membranes. METHODS: A polymer membrane coated onto a section of inert fiber was used as a permeation membrane in the MCF technique. When MCFs were immersed into a donor solution, the compounds in the solution partitioned into the membrane. At a given permeation time, a fiber was removed from the solution and transferred into a gas chromatography injector for quantitative analysis. The permeation process of a given chemical from the donor phase into the membrane was described by a one-compartment model by assuming first-order kinetics. RESULTS: A mathematical model was obtained that describes the cumulative amount of a chemical permeated into the membrane as a function of the permeation time in an exponential equation. Two constants were introduced into the compartment model that were clearly defined by the physiochemical parameters of the system (a kinetic parameter and the equilibrium absorption amount) and were obtained by regression of the experimental data sampled over a limited time before equilibrium. The model adequately described the permeation kinetics of the MCF technique. All theoretical predictions were supported by the experimental results. The experimental data correlated well with the mathematical regression results. The partition coefficients, initial permeation rate, uptake, and elimination rate constants were calculated from the two constants. CONCLUSIONS: The compartment model can describe the absorption kinetics of the MCF technique. The regression method based on the model is a useful tool for the determination of the partition coefficients of lipophilic compounds when it takes too long for them to reach permeation equilibrium. The kinetic parameter and the initial permeation rate are unique parameters of the MCF technique that could be used in the development of quantitative structure-activity relationship models.     

Preparation of folate-modified pullulan acetate nanoparticles for tumor-targeted drug delivery

The purpose of this work was to develop a novel nano-carrier with targeting property to tumor. In this study, pullulan acetate (PA) was synthesized by the acetylation of pullulan to simplify the preparation technique of nanoparticles. Folic acid (FA) was conjugated to PA in order to improve the cancer-targeting activity. The products were characterized by proton nuclear magnetic resonance (1H NMR) spectroscopy. Epirubicin-loaded nanoparticles were prepared by a solvent diffusion method. The loading efficiencies and EPI content increased with the amount of triethylamine (TEA) increasing in some degree. FPA nanoparticles could incorporate more epirubicin than PA nanoparticles. The folate-modified PA nanoparticles (FPA/EPI NPs) exhibited faster drug release than PA nanoparticles (PA/EPI NPs) in vitro. Confocal image analysis and flow cytometry test revealed that FPA/EPI NPs exhibited a greater extent of cellular uptake than PA/EPI NPs against KB cells over-expressing folate receptors on the surface. FPA/EPI NPs also showed higher cytotoxicity than PA/EPI NPs. The cytotoxic effect of FPA/EPI NPs to KB cells was inhibited by an excess amount of folic acid, suggesting that the binding and/or uptake were mediated by the folate receptor.     

Preparation of folate-modified pullulan acetate nanoparticles for tumor-targeted drug delivery

The purpose of this work was to develop a novel nano-carrier with targeting property to tumor. In this study, pullulan acetate (PA) was synthesized by the acetylation of pullulan to simplify the preparation technique of nanoparticles. Folic acid (FA) was conjugated to PA in order to improve the cancer-targeting activity. The products were characterized by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Epirubicin-loaded nanoparticles were prepared by a solvent diffusion method. The loading efficiencies and EPI content increased with the amount of triethylamine (TEA) increasing in some degree. FPA nanoparticles could incorporate more epirubicin than PA nanoparticles. The folate-modified PA nanoparticles (FPA/EPI NPs) exhibited faster drug release than PA nanoparticles (PA/EPI NPs) in vitro. Confocal image analysis and flow cytometry test revealed that FPA/EPI NPs exhibited a greater extent of cellular uptake than PA/EPI NPs against KB cells over-expressing folate receptors on the surface. FPA/EPI NPs also showed higher cytotoxicity than PA/EPI NPs. The cytotoxic effect of FPA/EPI NPs to KB cells was inhibited by an excess amount of folic acid, suggesting that the binding and/or uptake were mediated by the folate receptor.     

Pharmacokinetic and Pharmacodynamic Evaluation for Tissue-Selective Inhibition of Cholesterol Synthesis by Pravastatin

The tissue-selective inhibition of cholesterol synthesis by pravastatin was evaluated pharmacokinetically and pharmacodynamically. Plasma, tissue, urine, and bile concentrations were measured after iv bolus injection of pravastatin to rats at various doses. The total body clearance and steady state volume of distribution decreased with increasing dose. A saturable biliary excretion was also observed. The time course of plasma and liver concentrations was described by a three-compartment model, consisting of a central compartment, a deep compartment with an nonsaturable uptake process, and a shallow compartment with saturable uptake and nonsaturable elimination processes. It suggests that a mechanism for the decrease in the total body clearance and distribution volume might be explained by a saturation of pravastatin uptake into the liver. Plasma concentration data after oral administration was also fitted to the same model by connecting an absorption compartment to the shallow compartment. The inhibitory activity of pravastatin against cholesterol synthesis in liver could be related to the concentration in the shallow compartment via a sigmoidal Emax model and the obtained pharmacodynamic parameters were comparable to those in vitro. Results suggest that the carrier-mediated hepatic uptake of pravastatin is actually responsible for the hepatoselective inhibition of cholesterol synthesis under physiological conditions.     

Pharmacokinetic and pharmacodynamic evaluation for tissue-selective inhibition of cholesterol synthesis by pravastatin

The tissue-selective inhibition of cholesterol synthesis by pravastatin was evaluated pharmacokinetically and pharmacodynamically. Plasma, tissue, urine, and bile concentrations were measured after i.v. bolus injection of pravastatin to rats at various doses. The total body clearance and steady state volume of distribution decreased with increasing dose. A saturable biliary excretion was also observed. The time course of plasma and liver concentrations was described by a three-compartment model, consisting of a central compartment, a deep compartment with an nonsaturable uptake process, and a shallow compartment with saturable uptake and nonsaturable elimination processes. It suggests that a mechanism for the decrease in the total body clearance and distribution volume might be explained by a saturation of pravastatin uptake into the liver. Plasma concentration data after oral administration was also fitted to the same model by connecting an absorption compartment to the shallow compartment. The inhibitory activity of pravastatin against cholesterol synthesis in liver could be related to the concentration in the shallow compartment via a sigmoidal Emax model and the obtained pharmacodynamic parameters were comparable to those in vitro. Results suggest that the carrier-mediated hepatic uptake of pravastatin is actually responsible for the hepatoselective inhibition of cholesterol synthesis under physiological conditions.     

Enhanced antiproliferative activity of transferrin-conjugated paclitaxel-loaded nanoparticles is mediated via sustained intracellular drug retention

We studied the molecular mechanism of greater efficacy of paclitaxel-loaded nanoparticles (Tx-NPs) following conjugation to transferrin (Tf) ligand in breast cancer cell line. NPs were formulated using biodegradable polymer, poly(lactic-co-glycolide) (PLGA), with encapsulated Tx and conjugated to Tf ligand via an epoxy linker. Tf-conjugated NPs demonstrated greater and sustained antiproliferative activity of the drug in dose- and time-dependent studies compared to that with drug in solution or unconjugated NPs in MCF-7 and MCF-7/Adr cells. The mechanism of greater antiproliferative activity of the drug with conjugated NPs was determined to be due to their greater cellular uptake and reduced exocytosis compared to that of unconjugated NPs, thus leading to higher and sustained intracellular drug levels. The increase in antiproliferative activity of the drug with incubation time in MCF-7/Adr cells with Tf-conjugated NPs suggests that the drug resistance can be overcome by sustaining intracellular drug retention. The intracellular disposition characteristics of Tf-conjugated NPs following their cellular uptake via Tf receptors could have been different from that of unconjugated NPs via nonspecific endocytic pathway, thus influencing the NP uptake, their intracellular retention, and hence the therapeutic efficacy of the encapsulated drug.