热敏靶向脂质体在肿瘤治疗中的研究进展

介绍热敏靶向脂质体在肿瘤热疗中的应用以及国内外研究的现状，并介绍热敏长循环脂质、磁性热敏脂质体、免疫热敏脂质体和多聚物热敏脂质体等新型热敏靶向脂质体的特点和应用。     

热敏长循环脂质体的研究进展

简述长循环脂质体及热敏脂质体的制备原理及国内外研究进展, 将两种脂质体结合构成新型脂质体——热敏长循环脂质体, 并展望新型脂质体的研究前景.     

聚(2-乙基丙烯酸)脂质体的制体及其热敏性研究

采用插入法以脂肪酰胺修饰的聚(2-乙基丙烯酸)衍生物构建热敏递药的高分子脂质体。用荧光分析法，借助荧光分光光度仪和粒径仪系统地研究了高分子脂质体的热敏特性。结果发现，采用脂肪胺修饰的聚(2-乙基丙烯酸)制备的脂质体具有明显的热敏释药特性，其释药特性与插入的高分子结构有关，还与制备脂质体的磷脂组成有关，同时采用聚(2-乙基丙烯酸)制备的脂质体还具有显著的酸敏释药特性。以聚(2-乙基丙烯酸)为热敏诱导介质制备的脂质体在体外实验中呈现出良好的热敏释药特性，且制剂制备方法简便、可靠。     

薄膜分散法制备白藜芦醇长循环热敏前体脂质体及其表征研究

目的:对白藜芦醇长循环热敏前体脂质体制备的研究以及对其性质进行分析。方法:先用薄膜分散法制备白藜芦醇长循环热敏脂质体后,再用冷冻干燥法来制备白藜芦醇长循环热敏脂质体的前体。采用电势测定仪、HPLC等方法对该脂质体的包封率、粒径、稳定性、载药量、电位、释放度等来展开系统的检查。结果:白藜芦醇长循环热敏前体脂质体水合后形成白藜芦醇长循环热敏脂质体,粒径均值为(107.9±3.6)nm,Zeta电位的均值为(-12.2±1.6)m V,包封率可达89.4%;该脂质体在相变温度42℃下药物释放达到94%以上。结论:采用长循环热敏来制备的白藜芦醇前体脂质体含量与包封率检查方法准确、快速、简单且方法简便易行。载药量大,包封率好,工艺比较稳定。本实验可为新型白藜芦醇静脉注射用热敏脂质体的研究提供基础。     

依托泊苷长循环热敏前体脂质体的制备工艺研究

目的:对依托泊苷(Etoposide,VP-16)长循环热敏前体脂质体的制备工艺进行研究,并对该制备工艺进行方法学及制剂质量考察。方法:应用薄膜分散法制成VP-16长循环热敏脂质体,进一步借助冷冻干燥技术进行依托泊苷长循环热敏前体脂质体的制备;采用zeta电势测定仪及HPLC等技术进行方法学考察,主要包括脂质体的包封率、粒径、载药量、电位、释放度、稳定性。结果:VP-16长循环热敏前体脂质体水合形成长循环热敏脂质体,粒径为(105.2±3.4)nm,Zeta电位为(-11.9±1.7)m V,包封率可达96.8%;该脂质体在相变温度42℃下药物释放达到96%以上。结论:VP-16长循环热敏前体脂质体的制备工艺稳定,脂质体载药量大,包封率高;药物含量及包封率的测定方法简单、快速而准确,因而,该研究可为VP-16开发成静脉注射用新制剂提供数据支持。     

热敏脂质体的研究进展

综述以二棕榈酰磷脂酰胆碱（DPPC）等为主要膜材的常规热敏脂质体以及磁性热敏脂质体、长循环热敏脂质体、多聚物热敏脂质体、热敏免疫脂质体的研究进展。以热敏脂质体为载体包埋化疗药物,可结合热疗的优势和靶向给药的特点,提高治疗靶向性,降低全身毒性,增强抗肿瘤疗效。     

电磁波控制热敏磁性脂质体靶向给药

本文从新型靶向给药系统-热敏磁性脂质体靶向给药的几个关键之处出发，介绍了目前热敏磁性脂质体的脂质材料、磁性材料、磁定位和电磁波控释研究状况，分析讨论了电磁波在热敏磁性脂质体的磁靶向和药物控释方面的作用,并提出了测量热敏磁性脂质体的电磁参数和选择合适的电磁波频段用于药物控释的必要性。     

聚(2-乙基丙烯酸)脂质体的制体及其热敏性研究

采用插入法以脂肪酰胺修饰的聚(2-乙基丙烯酸)衍生物构建热敏递药的高分子脂质体.用荧光分析法,借助荧光分光光度仪和粒径仪系统地研究了高分子脂质体的热敏特性.结果发现,采用脂肪胺修饰的聚(2-乙基丙烯酸)制备的脂质体具有明显的热敏释药特性,其释药特性与插入的高分子结构有关,还与制备脂质体的磷脂组成有关,同时采用聚(2-乙基丙烯酸)制备的脂质体还具有显著的酸敏释药特性.以聚(2-乙基丙烯酸)为热敏诱导介质制备的脂质体在体外实验中呈现出良好的热敏释药特性,且制剂制备方法简便、可靠.     

新型脂质体研究进展

目的:介绍新型脂质体研究进展。方法:查阅国内外新近文献资料,并加以分析、整理和归纳。结果:综述了几种新型的热敏脂质体、pH敏脂质体、免疫脂质体的优点和目前存在的问题。结论:随着科学技术的发展、制剂工艺研究的深入,以及多种方法的综合运用,必将有更好的脂质体问世而用于临床。     

磁性热敏脂质体的研究进展

磁性热敏脂质体是近年来兴起的一种新型靶向药物载体,它可以在外加磁场的作用下随血液循环聚集到靶器官,在不加磁场或正常体温条件下应使包裹在脂质体中的药物缓慢、平稳释放并起到药品储库作用;而在体外交变磁场作用下产热达到热敏脂质体相变温度而控制包裹在脂质体中的药物迅速释放,以达到在肿瘤组织靶向、多次和脉冲式给药的效果。与普通脂质体相比,磁性热敏脂质体具有更强的组织靶向性和控释特性。本文综述了磁性热敏脂质体的制备、磁定位靶向性和热敏释药性。     

Targeted thermosensitive liposomes: an attractive novel approach for increased drug delivery to solid tumors

Introduction: Currently available chemotherapy is hampered by a lack in tumor specificity and resulting toxicity. Small and long-circulating liposomes can preferentially deliver chemotherapeutic drugs to tumors upon extravasation from tumor vasculature. Although clinically used liposomal formulations demonstrated significant reduction in toxicity, enhancement of therapeutic activity has not fully met expectations.

Areas covered: Low drug bioavailability from liposomal formulations and limited tumor accumulation remain major challenges to further improve therapeutic activity of liposomal chemotherapy. The aim of this review is to highlight strategies addressing these challenges. A first strategy uses hyperthermia and thermosensitive liposomes to improve tumor accumulation and trigger liposomal drug bioavailability. Image-guidance can aid online monitoring of heat and drug delivery and further personalize the treatment. A second strategy involves tumor-specific targeting to enhance drug delivery specificity and drug internalization. In addition, we review the potential of combinations of the two in one targeted thermosensitive-triggered drug delivery system.

Expert opinion: Heat-triggered drug delivery using thermosensitive liposomes as well as the use of tumor vasculature or tumor cell-targeted liposomes are both promising strategies to improve liposomal chemotherapy. Preclinical evidence has been encouraging and both strategies are currently undergoing clinical evaluation. A combination of both strategies rendering targeted thermosensitive liposomes (TTSL) may appear as a new and attractive approach promoting tumor drug delivery.     

Development of a bone targeted thermosensitive liposomal doxorubicin formulation based on a bisphosphonate modified non-ionic surfactant

Bone is among the most common sites of metastasis in cancer patients, so it is an urgent need to develop drug delivery systems targeting tumor bone metastasis with the feature of controlled release. This study aimed to delivery of thermosensitive liposomal doxorubicin to bone for tumor metastasis treatment. First, Brij78 (polyoxyethylene stearyl ether) was conjugated with Pamidronate (Pa). By incorporating Pa-Brij78 to DPPC/Chol liposomes, we developed Pa surface functionalized liposomes. The Pa-Brij78/DPPC/Chol liposomes (PB-liposomes) exhibited a stronger binding affinity to hydroxyapatite (HA), a major component of bone, than Brij78/DPPC/Chol liposomes (B-liposomes). Doxorubicin (Dox) was then encapsulated in PB-liposomes and the results demonstrated complete release of Dox from PB-liposomes or the complex of HA/PB-liposomes within 10?min at 42?°C. Next, human lung cancer A549 cells were treated with the thermosensitive complex of HA/PB-liposomes/Dox to mimic tumor bone metastasis treatment through bone targeted delivery of therapeutic agents. Pre-incubation of HA/PB-liposomes/Dox with mild heat at 42?°C induced subsequent higher cytotoxicity to A549 cells than incubation of the same complex at 37?°C, suggesting more active drug release triggered by heat. In conclusion, we synthesized a novel surfactant Pa-Brij78 and it has the potential to be used for development of a bone targeted thermosensitive liposome formulation for treatment of tumor bone metastasis.     

Preparation and characterization of Tegafur magnetic thermosensitive liposomes

The purpose was to study the preparation and properties of tegafur magnetic thermosensitive liposomes. The method was to employ an improved chemical coprecipitation method for preparing nano-magnetic particles and a reverse-phase evaporation and ultrasonic method for preparing tegafur magnetic thermosensitive liposomes. The results showed that tegafur magnetic thermosensitive liposomes were prepared successfully. They had comparatively strong magnetism and superparamagnetism, and their temperature showed a linear positive correlation with dosages and the field strength under a current value. The conclusion was that tegafur magnetic thermosensitive liposomes with comparatively small particle size, superparamagnetism and comparatively strong magnetism were prepared successfully.     

热敏脂质体

目的:综述热敏脂质体的原理和它作为靶向药物载体的应用。方法:论述了脂质体相变的原理和热敏脂质体的研究概况,以及携带化疗药物的热敏脂质体和肿瘤热疗结合后治疗效果的增强作用,指出了热敏脂质体的发展前景。结果:热敏脂质体有良好的热靶向性,在肿瘤治疗方面效果明显。结论:热敏脂质体是新一代热靶向药物载体,有重要的开发价值。     

Listeriolysin O enhances cytoplasmic delivery by Her-2 targeting liposomes

To enhance cytoplasmic delivery of liposomal contents to breast cancer cells, the authors have attached the pore-forming protein, listeriolysin O (LLO), to thermosensitive liposomes. The antibody trastuzumab (Herceptin^®) was also conjugated with the outer surface of the liposomes, resulting in highly specific binding and internalization into mammary epithelial cells that overexpress the human epidermal growth factor receptor 2 (Her-2). The liposomes were preloaded with a marker fluorescent dye, and the effect of LLO on the distribution of dye within the cells was monitored using fluorescence microscopy. Owing to the thermosensitive nature of the liposomes, hyperthermia at 42°C triggered the release of the encapsulated fluorescent calcein from the endocytosed liposomes into the interior of the endosomes. LLO, when conjugated to these liposomes, subsequently formed pores in the endosomal membrane, allowing calcein to flow out of the endosomal compartment into the cytoplasm. Her-2–targeted liposomes bearing LLO delivered a 22-fold greater concentration of calcein to mammary epithelial cells that overexpress Her-2 compared to cells with normal Her-2 expression. Thus, the addition of LLO to preformed liposomes offers a method for significantly enhancing delivery of liposomal contents to the cytoplasm of targeted cells.     

Hydroxycamptothecin liposomes based on thermal and magnetic dual-responsive system: preparation,in vitro and in vivo antitumor activity,microdialysis-based tumor pharmacokinetics

Due to the absence of lactone form of hydroxycamptothecin, the commercially available hydroxycamptothecin injection exhibits inefficient therapeutic effects. In this study, we constructed a novel delivery system (thermosensitive magnetic liposomes) that protects lactone form of hydroxycamptothecin from blood or water. After hydroxycamptothecin was loaded into the thermosensitive magnetic liposome (HCPT/TML), its in vitro and in vivo antitumor activity and microdialysis-based tumour pharmacokinetics were determined. The results demonstrated that HCPT/TMLs possessed favourable physicochemical features and significant cytotoxicity against the Huh-7 cells in vitro. In the in vivo antitumor study and tumour pharmacokinetics, HCPT/TMLs displayed effective targeting delivery and antitumor effects, which corresponded to the determined hydroxycamptothecin concentration in tumour tissue. In conclusion, this thermal and magnetic dual-responsive system can efficiently deliver hydroxycamptothecin to tumour tissue and has great potential application in cancer treatment.     

Thermosensitive magnetic liposomes with doxorubicin cell-penetrating peptides conjugate for enhanced and targeted cancer therapy

To specifically deliver cytotoxic drug to tumor cells and enhance cellular uptake is the key for effective cancer therapy. In this paper, we described a novel drug targeting system, which is designed to combine features of biological (cell-penetrating peptides, CPPs) and physical (magnetic) drug targeting for use in the magnetic hyperthermia-triggered release. A doxorubicin–CPPs conjugate (DOX-CPPs) was loaded into thermosensitive magnetic liposomes (TSMLs) (DOX-CPPs/TSMLs), and in vitro DOX-CPPs thermosensitive release activity, anti-proliferation effect, in vivo targeted delivery as well as in vivo antitumor activity were determined. The results demonstrated that the DOX-CPPs/TSMLs showed good physicochemical properties, effective anti-proliferation effect in MCF-7 cells in vitro. Additionally, in vivo study, DOX-CPPs/TSMLs under AC magnetic field displayed superior in vivo targeted delivery efficacy, antitumor efficacy in an MCF-7 xenograft murine model. In conclusion, the application of DOX-CPPs/TSMLs under AC magnetic field may provide a strategy for the selective and efficient delivery of drug.     

Enhanced Delivery and Antitumor Activity of Doxorubicin Using Long-Circulating Thermosensitive Liposomes Containing Amphipathic Polyethylene Glycol in Combination with Local Hyperthermia

Enhanced delivery of doxorubicin (DXR) to a solid tumor subjected to local hyperthermia was achieved by using long-circulating, thermosensitive liposomes (TSL) composed of dipalmitoyl phosphatidylcholine (DPPC)/distearoyl phosphatidylcholine (DSPC) (9:1, m/m) and 3 mol% amphipathic polyethylene glycol (PEG) in colon 26-bearing mice. Inclusion of 3 mol% of distearoyl phosphatidylethanolamine derivatives of PEG (DSPE-PEG, amphipathic PEG) with a mean molecular weight of 1000 or 5000 in DPPC/DSPC liposomes resulted in decreased reticuloendothelial system (RES) uptake and a concomitant prolongation of circulation time, affording sustained increased blood levels of the liposomes. Concomitantly, DXR levels in blood were also kept high over a long period. The presence of amphipathic PEG did not interfere with the encapsulation of DXR by the pH gradient method (>90% trapping efficiency) or with the temperature-dependent drug release from the liposomes. The optimal size of these liposomes was 180 – 200 nm in mean diameter for thermosensitive drug release and prolonged circulation time. The DXR levels in the tumor after injection of long-circulating TSL (DXR-PEG1000TSL or DXR-PEG5000TSL, at a dose of 5 mg DXR/ kg) with local hyperthermia were much higher than after treatment with DXR-TSL lacking PEG or with free DXR, reaching 7.0 – 8.5 DXR µg/g tumor (approximately 2 times or 6 times higher than that of DXR-TSL or free DXR, respectively). Furthermore, the combination of DXR-PEGTSL and hyperthermia effectively retarded tumor growth and increased survival time. Our results indicate that the combination of drug-loaded, long-circulating, thermosensitive liposomes with local hyperthermia at the tumor site could be clinically useful for delivering a wide range of chemotherapeutic agents in the treatment of solid tumors.     

Heat-Induced Drug Release Rate and Maximal Targeting Index of Thermosensitive Liposome in Tumor-Bearing Mice

To evaluate the rate of drug release at the tumor and maximal drug targeting after administration of thermosensitive liposomes with hy-perthermia, a theoretical and experimental method was derived assessing the fraction of drug released from liposomes in a single pass through the heated tumor, F, and the drug targeting index when drug release occurs completely in response to heat (F = 1), DTI_max. The F and DTImax were evaluated for four types of liposomes (LUV-1 and LUV-2, thermosensitive large unilamellar liposomes; LUV-3, a nonthermosensitive large unilamellar liposome; and SUV-1, a thermosensitive small unilamellar liposome) using reported data on blood liposome levels and tumor drug levels after the liposomes were administered to tumor bearing mice. DTI_max values for LUV-1 and SUV-1 were approximately 6, while the value for LUV-2 with a relatively large systemic clearance was only 2.3. The F values for LUV-1, LUV-2, and SUV-1 with hyperthermia were 0.71, 1.17, and 0.34, respectively, whereas the values for these liposomes without hyperthermia and for LUV-3 with or without hyperthermia were nearly zero. These results confirm earlier findings that LUV-1 and LUV-2 release CDDP almost completely at the heated tumor and that the large DTI value obtained in LUV-1 (DTI = 4.6) was due to its high heat sensitivity and its small systemic clearance.