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Biorecognition-element labeled liposomes are simple and versatile tools used to amplify signals for the detection of analytes of environmental, clinical, food safety, and national security interest. Relying on measurement of encapsulated species via electrochemical or spectroscopic techniques, or properties inherent to liposomes themselves (such as mass, refractive index, or charge), many advances have been made in both bench-scale and microfluidic applications. Some of these measurement techniques are inherently sensitivity limited, but through the inclusion of liposomes, reduced limits of detection potentially broaden the utility towards otherwise challenging levels of analytes. Other advances took advantage of the hydrophobic environment required by many biorecognition elements to expand the target selectivity range or utilized the amphipathic nature of the lipid bilayer to provide enhanced separation capabilities. Novel handling approaches included wavelength-specific release of contents encapsulated within thermosensitive liposomes or application of electric fields to move, concentrate, and strategically lyse liposomes. These and other topics are discussed in terms of either present incorporation or adaptation to microfluidic devices.

Chromatographic and spectrophotometric methods for the qualitative and quantitative analysis of thermosensitive liposomes loaded with doxorubicin were developed. Lipids and doxorubicin in thermosensitive liposomes were separated by TLC using the two solvent systems CHCl3:MeOH:NH4OH (conc.) (65:25:4) and CHCl3:MeOH:HOAc (glacial):H2O (25:15:4:2). Chromatographic determination of sucrose in thermosensitive liposomes was performed using the solvent systems 1,2-dichloroethane:HOAc (anhydrous): MeOH:H2O (10:5:3:2) or i-PrOH:Me2CO:Et2O:H2O (7:7:2:4). The spectrophotometric assay for doxorubicin in thermosensitive liposomes was validated.

To engineer optimized near-infrared (NIR) active thermosensitive liposomes to potentially achieve image-guided delivery of chemotherapeutic agents.Thermosensitive liposomes were surface-coated with either polyethylene glycol or dextran. Differential scanning calorimetry and calcein release studies were conducted to optimize liposomal release, and flow cytometry was employed to determine the in vitro macrophage uptake of liposomes. Indocyanine green (ICG) was encapsulated as the NIR dye to evaluate the in vivo biodistribution in tumor-bearing mice.The optimized thermosensitive liposome formulation consists of DPPC, SoyPC, and cholesterol in the 100:50:30 molar ratio. Liposomes with dextran and polyethylene glycol demonstrated similar thermal release properties; however in vitro macrophage uptake was greater with dextran. Non-invasive in vivo NIR imaging showed tumor accumulation of liposomes with both coatings, and ex vivo NIR imaging correlated well with actual ICG concentrations in various organs of healthy mice.The optimized thermosensitive liposome formulation demonstrated stability at 37 °C and efficient burst release at 40 and 42 °C. Dextran exhibited potential for application as a surface coating in thermosensitive liposome formulations. In vivo studies suggest that liposomal encapsulation of ICG permits reliable, real-time monitoring of liposome biodistribution through non-invasive NIR imaging.

To increase the anti-tumor activity of paclitaxel (PTX), novel temperature-sensitive liposomes loading paclitaxel (PTX-TSL) were developed. In vitro, characteristics of PTX-TSL were evaluated. The mean particle diameter was about 100 nm, and the entrapment efficiency was larger than 95%. The phase-transition temperature of PTX-TSL determined by differential scanning calorimetry was about 42 °C. The result of in vitro drug release from PTX-TSL illustrated that release rate at 37 °C was obviously lower than that at 42 °C. Stability data indicated that the liposome was physically and chemically stable for at least 3 months at -20 °C. In vivo study, after three injections with hyperthermia in the xenograft lung tumor model, PTX-TSL showed distinguished tumor growth suppression, compared with non-temperature-sensitive liposome and free drug. The results of intratumoral drug concentration indicated that PTX-TSL combined with hyperthermia delivered more paxlitaxel into the tumor location than the other two paxlitaxel formulations. In summary, PTX-TSL combined with hyperthermia significantly inhibited tumor growth, due to the increased targeting efficiency of PTX to tumor tissues. Such approach may enhance the delivery efficiency of chemotherapeutics into solid tumors.

The combination of thermosensitive liposomes and local heating has been shown to improve anticancer drug delivery in both animal models and human patients. The lyso-lipid temperature sensitive liposomes (LTSL) consisting of DPPC, MSPC and DSPE-PEG(2000) is currently under evaluation in clinical trials. We hypothesized that Brij surfactants resembling the chemical structures of MSPC and DSPE-PEG(2000) could be utilized for generating a thermosensitive formulation with DPPC. Here, we report using a robust in vitro system to efficiently screen a series of liposomal candidates composed of DPPC and a Brij surfactant for thermosensitive delivery of doxorubicin. The data indicated that the optimal acyl chain length of the surfactant was between C(16) and C(18) with a saturated carbon chain, a PEG repeating unit ranging between 10 and 100 and a molecule weight above 600Da. The linking chemistry between the acyl chain and the PEG chain did not influence thermosensitivity. In the panel of surfactants tested, Brij78 was optimal and could be incorporated into the liposomes by the thin film hydration or the post-insertion method with an optimal range of 1 to 8mol%. Doxorubicin was incorporated into the formulation by pH gradient with >95% loading efficiency at drug/lipid of 1/20 (w/w). The transition temperature of the Brij78-liposomes was slightly lower than that of LTSL (41 v.s. 41.5°C), leading to enhanced drug release at the low end of the hyperthermic temperatures (40°C) with similar stability at 37°C, which was confirmed by cell based assays. Finally, the Brij78-liposomes and LTSL displayed comparable blood compatibility with mild hemolytic activity. This in vitro system allowed for efficient screening and optimization to produce an optimal formulation.

Adriamycin (ADM)-encapsulated thermosensitive liposomes (ts-lip-ADM) and common liposomes (lip-ADM) were developed and evaluated. The encapsulation efficiency of the two liposomes were above 99%, and the average sizes of liposomes were about 120 nm. Temperature-dependent drug release from loaded liposomes in vitro was investigated: more than 90% of loaded ADM was released from ts-lip-ADM within 30 min at 42°C, while less than 3% was released from lip-ADM at 42°C beyond 120 min. An in vitro model of blood brain barrier (BBB) was established and evaluated by permeability and transendothelial electrical resistance (TEER). The model was employed to study the permeability of liposomes in vitro. The permeability of ts-lip-ADM could be increased significantly after the temperature was raised to 42°C, which was about 10-16, 22-38, 38-45, 50-105 fold to that of ts-lip-ADM (37°C), lip-ADM (42°C), lip-ADM (37°C) and free ADM, respectively. C6 glioma-bearing mice model was developed and used to evaluate body distribution and anti-tumor efficacy in vivo. Mice were IV injected at a drug dose of 10 mg/kg. After administration the heads of mice were heated in water bath at 42°C for 30 min. The maximum brain concentration of ts-lip-ADM was 6.4, 3.7 fold compared with that of ADM solution and lip-ADM, respectively. The survival time of mice administered ts-lip-ADM (44 d) was remarkably longer than that of other three groups. This study indicates that ADM-encapsulated thermosensitive liposomes combined hyperthermia could enhance ADM delivery across BBB and prolong survival time of glioma-bearing mice.

International audience; Background: Superficial vascular anomalies such as port wine stains are commonly treated by selective photothermolysis (SP). The endovascular laser-tissue interactions underlying SP are governed by a photothermal response (thermocoagulation of blood) and a hemodynamic response (thrombosis). Currently it is not knownwhether the hemodynamic response encompasses both primary and secondary hemostasis, which platelet receptors are involved, and what the SP-induced thrombosis kinetics are in low-flow venules.Objectives: To (1) define the role and kinetics of primary and secondary hemostasis in laser-induced thrombus formation and (2) determine which key platelet surface receptors are involved in the hemodynamic response.Methods: 532-nm laser-irradiated hamster dorsal skin fold venules were studied by intravital fluorescence microscopy following fluorescent labeling of platelets with 5(6)-carboxyfluorescein. Heparin and fluorescently labeled anti-glycoprotein Ib-a (GPIba) and anti-P-selectin antibodies were administered to investigate the role of coagulation and platelet receptors, respectively. Lesional sizes were quantified by software.Results: Laser irradiation consistently produced sub-occlusive thermal coagula. Thrombosis was triggered in all irradiated venules in a thermal coagulum-independent manner and peaked at 6.25 min post-irradiation. Heparin decreased the maximum thrombus size and caused thrombosis to reach a maximum at 1.25 min. Immunoblocking of GPIba abated the extent of thrombosis, whereas immunoblocking of P-selectin had no effect.Conclusions: The hemodynamic response ensues the photothermal response in a thermal coagulumindependent manner and involves primary and secondary hemostasis. Primary hemostasis is mediated by constitutively expressed GPIba but not by activation-dependent P-selectin.

A novel delivery system for the anticancer drug arsenic trioxide (ATO) is characterized. The release of ATO from DPPC liposomes with MPPC lysolipid incorporated into the bilayer is measured. There is negligible leakage of ATO from all systems at 25°C. Upon heating the liposomes to 37°C, there is 15% to 25% release over a 24 h time period. The ATO release from the DPPC and DPPC:MPPC(5%) systems levels off after 10 h at 37°C, whereas the DPPC:MPPC(10%) liposomes continue to release ATO over the 24 h timespan. Upon heating the liposomes rapidly to 42°C, through the gel to liquid-crystalline (LC) phase transition, the release rate is substantially increased. The two systems containing lysolipids, DPPC:MPPC(5%) and DPPC:MPPC(10%), exhibit a very rapid release of a significant amount of arsenic in the first hour. In the first hour, the DPPC:MPPC(5%) liposomes release 40% of the arsenic and the DPPC:MPPC(10%) liposomes release 55% of the arsenic. Arsenic release from pure DPPC liposomes is comparable at 37°C and 42°C, indicating presence of lysolipid is necessary for a significant enhancement of the release rate. A coarse-grained molecular dynamics (CGMD) model is used to investigate the enhanced permeability of lysolipid-incorporated liposomes and lipid bilayers. The CG liposomes did not form a gel phase when cooled due to the high curvature, however permeability was still significantly lower at 12°C, below what would be the liquid to gel phase transition temperature. At 50°C and 77°C, above Tm, we find water permeability coefficients on the order of 1.0×10−3 cm s−1, in good agreement with experiment. From simulations of flat DPPC:MPPC bilayers we find that a peak in the permeability does coincide with the phase transition from the gel to LC state when the lysolipid MPPC is present. No pores are observed in the simulations, however due to limitations in the model, we cannot rule out the possibility of lysolipid-stabilized pores enhancing the permeability in the experiments.

Lipid-based nanocarriers or liposomes have been proven successful in the delivery of chemotherapeutic agents and are currently applied clinically in the treatment of various types of cancer. Liposomes offer the advantage of a high drug payload, decreased drug toxicity and enhanced drug accumulation at tumor sites. Increased accumulation is due to the relatively leaky tumor vasculature that allows liposome extravasation. Between different types of tumors and even within one tumor, vascular permeability and thus liposome extravasation may differ greatly. Furthermore, upon accumulation of liposomes in the tumor area, drug bioavailability is not guaranteed. At present, these are the major issues for clinically used liposomal drugs. Mild hyperthermia (HT), the heating of tumor tissue to temperatures of up to 43°C, has been developed in the past decades as an established and efficacious treatment modality in combination with chemo- and radiotherapy. HT can be used to further improve liposomal chemotherapy in two ways: HT is known to increase vascular permeability in solid tumors and may therefore increase levels of liposome accumulation, and thermosensitive liposomes have been developed that can be triggered to release their contents upon hyperthermia. By applying these two strategies, drug delivery to tumors can be strongly enhanced.

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.

Thermal dose in tumor tissue is a key factor for regional hyperthermia (HT) combined with chemotherapy and for drug delivery using thermosensitive liposomes (TSL). It influences therapy outcome, affects the accumulation of liposomes, and triggers the content release from TSL in the target tissue. For the development and clinical application of TSL, noninvasive visualization is of critical importance. For this purpose, TSL loaded with MRI contrast agent (CA) have been developed. With increase in temperature, the CA is released from TSL at the phase transition temperature Tm resulting in a relaxation time change, which allows MRI monitoring. The purpose of this study was to examine the feasibility of an in vivo application and MR characterization of Gd-DTPA-BMA-loaded phosphatidylglyceroglycerol-TSL (Gd-TSL) at mild HT conditions in tumor tissue using a clinically relevant setting.Gd-TSL were characterized in vitro with varying thermal doses between 37 degrees C and 45 degrees C and distinct solvents by MR at 0.5 T and 1.5 T. In vivo studies were performed in C57BL/6 mice bearing BFS-1 fibrosarcomas at 1.5 T. One tumor-bearing leg was immersed in a temperature-controlled water bath (T). Gd-TSL (Tm = 43.5 +/- 0.2 degrees C) were injected either intratumorally or intravenously at T = 37.3 +/- 0.1 degrees C or T = 42.5 +/- 0.3 degrees C. As a control, nonliposomal Gd-DTPA-BMA was injected intravenously at T = 43.1 +/- 0.3 degrees C. A second tumor on the contralateral limb, which remained unheated, served as a control. CA release was monitored by T1-weighted spin-echo.The in vitro characterization demonstrated at heated and unheated samples a strong increase in T1-relaxivity of Gd-TSL solutions from 0.4 mM-1 s-1 (37.5 degrees C) to 4.2 mM-1 s-1 (43.3 degrees C) at 0.5 T. Thermal dose and solvent affected the rate of relaxation time change significantly. A fast and complete release was observed in samples with serum, whereas Gd-TSL in glucose was only partially released within 1 hour. A dedicated experimental setup was developed for standardized in vivo investigation. Tumor signal intensity changes were detectable in all animals. After intratumoral injection of Gd-TSL, the signal increased heterogeneously (max., +52% +/- 25%) within 3 minutes after temperature increase and decreased strongly thereafter, whereas after i.v. injection, the signal increased homogeneously (+19% +/- 3%) within 2 minutes persisting thereafter. The unheated control tumors on the contralateral legs showed a 10% +/- 3% signal increase within 2 minutes. Injection at 37 degrees C showed a continuous signal increase in "heated" and unheated tumors of up to 8% to 10%. Nonliposomal CA injection demonstrated that tumors were well perfused during HT.HT-induced CA release from Gd-TSL was monitored and characterized by MRI after i.v. injection in tumor-bearing mice. Higher temperatures resulted in higher signal changes. Immediately after i.v. injection, heated tumor tissue was distinguishable from unheated tumor tissue. The Gd-TSL appears to be suitable for MR monitoring of HT tumor treatment in a clinical MRI setting independent of field strength.

Lysolipid-based thermosensitive liposomes have been successfully introduced as efficient drug delivery system with fast drug release upon heat treatment. Hexadecylphosphocholine (HePC) is structurally related to 1-palmitoyl-2-lyso-sn-glycero-3-phosphocholine (P-lyso-PC) but chemically and metabolically more stable, thereby offering strong antineoplastic, antiprotozoal and antifungal activity. We investigated the properties of HePC in low temperature sensitive (LTSL) and high temperature sensitive liposomes (HTSL) based on 1,2-dipalmitoyl-sn-glycero-3-phosphoglyceroglycerol (DPPGOG). Therefore liposomes composed of DPPC/DSPC=8:2 (molar ratio), DPPC/DSPC/DPPGOG=5:2:3, HePC/DPPC/DSPC/DPPGOG=1:4:2:3, HePC/DSPC/DPPGOG=1:6:3 and P-lyso-PC/DPPC/DSPC/DPPGOG=1:4:2:3 were prepared by the lipid film hydration and extrusion method and compared with regard to stability at 37 degrees C and the release kinetics under heating conditions (38 degrees C-45 degrees C) in the presence of fetal calf serum. Each formulation was characterized for size distribution, zeta-potential, encapsulation efficiency and phase transition temperature (T(m)). The influence of heat on the cytotoxic activity of HePC in TSL was investigated using the WST-1 assay in BFS-1 fibrosarcoma and C6 glioma cells for the low (HePC-LTSL, T(m)=42.9 degrees C) and the high (HePC-HTSL, T(m)=48.5 degrees C) temperature sensitive formulations and compared to micellar HePC or plain TSL. The cellular HePC uptake after 15 min incubation at 37 degrees C or 42 degrees C was determined by liquid chromatography tandem-mass spectrometry (LC-MS/MS). As expected, HePC increases the release rate of TSL similar to lysolipid. The cytotoxicity of HePC in TSL was heat inducible and stronger than the one induced by micellar HePC which did not respond to heat. A possible explanation for this raise in cytotoxicity of HePC in TSL is the increased cellular transfer of HePC under heating conditions demonstrated by LC-MS/MS.

Lysolipid-containing thermosensitive liposomes (LTSL) release their contents instantly when heated to temperatures close to their gel to liquid-crystalline phase transition temperature (TC). We have recently shown that during the melting transition these liposomes undergo major morphology changes, including the formation of open liposomes, bilayer discs, and pore-like defects. The hyperthermia-induced release of liposomal contents appears to depend on the presence and accumulation of membrane additives in grain boundaries, which enhance packing defects and, in the case of micelle-forming membrane additives, stabilize the bilayer rim of open liposome structures and transient membrane pores. In the present study, we used the fluorescent label 1-pyrenehexadecanoicacid (PHDA) and a radiolabelled lysolipid as markers for lysolipid membrane distribution and retention, respectively. PHDA dimer formation indicated local PHDA accumulation in cholesterol-free liposomes but not in cholesterol-containing liposomes. When LTSL were incubated at a temperature of 37 degrees C together with egg-phosphatidylcholine (EPC) multilamellar vesicles (MLVs) approximately 50% of the lysolipids transferred rapidly from LTSL to EPC MLVs. This transfer led to a significant reduction in the amount of carboxyfluorescein released from LTSL upon heating. Our results imply that poor retention of lysolipids in the LTSL membrane could also affect drug release characteristics of LTSL in vivo.

Cryogenic transmission electron microscopy (cryo-TEM) images of lysolipid-containing thermosensitive liposomes (LTSL) revealed that open liposomes and bilayer discs appeared when liposomes were cycled through the gel (Lβ′) to liquid-crystalline (Lα) phase transition. The amount of bilayer discs generated was dependent on the combined presence of PEG-lipid and lysolipid in the membrane. We hypothesize that micelle-forming membrane components stabilize the rim of bilayer openings and membrane discs that form when liposomes are cycled through TC.

Thermosensitive liposomes have emerged as a viable strategy for localized delivery and triggered release of chemotherapy. MR-guided focused ultrasound (MRgFUS) has the capability of heating tumors in a controlled manner, and when combined with thermosensitive liposomes can potentially reduce tumor burden in vivo. However, the impact of this drug delivery strategy has rarely been investigated. We have developed a unique liposome formulation modified with p(NIPAAm-co-PAA), a polymer that confers sensitivity to both temperature and pH. These polymer-modified thermosensitive liposomes (PTSL) demonstrated sensitivity to focused ultrasound, and required lower thermal doses and were more cytotoxic than traditional formulations in vitro. A set of acoustic parameters characterizing optimal release from PTSL in vitro was applied in the design of a combined MRgFUS/PTSL delivery platform. This platform more effectively reduced tumor burden in vivo when compared to free drug and traditional formulations. Histological analysis indicated greater tumor penetration, more extensive ECM remodeling, and greater cell destruction in tumors administered PTSL, correlating with improved response to the therapy.

A novel drug delivery system, enabling an in situ, thermally triggered drug release is described, consisting of an injectable thermoresponsive chitosan hydrogel containing doxorubicin-loaded thermosensitive liposomes. The design, fabrication, characterization, and an assessment of in vitro bioactivity of this formulation is detailed. Combining on-demand drug delivery with in situ gelation results in a promising candidate for local chemotherapy.

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.

We optimized thermosensitive liposomes encapsulating an anticancer drug, 5-Fluorouracil (5-FU), in order to trigger the release upon focused ultrasound-mediated mild hyperthermia at the tumor. This approach would improve drug efficacy and would lower side effects. Liposomes were prepared by the lipid hydration method by mixing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) for its temperature sensitivity at 41.5 ± 0.5°C, cholesterol (CHOL) to promote liposome stability towards blood components, and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG) to confer stealthiness to the formulation. The experiments confirmed that the liposomes formulated with DPPC/CHOL/DSPE-PEG in a molar ratio 90:5:5 mol% are thermosensitive, while liposomes composed of the same lipid mixture in a ratio 65:30:5 mol% were considered non thermosensitive negative control. The optimization of passive encapsulation of 5-FU yielded an encapsulation efficacy (encapsulated 5-FU/total 5-FU) of 13%. 5-FU was, however, very weakly retained (12%) in the aqueous core of liposomes following dilution due to the generation of an osmotic gradient. The retention of 5-FU has been optimized (93%) by the active encapsulation technique based on the intraliposomal complexation of 5FU with copper-polyethylenimine complex encapsulated beforehand into liposomes. This technique also improved 5-FU encapsulation efficacy by 3-fold (37%), yielding a loading efficiency (final drug/lipid ratio, mol/mol) of approximately 50%. The resulting thermosensitive liposomes and non thermosensitive liposomes have a hydrodynamic diameter and a surface charge around 65 nm and -10 mV, and 105 nm and -4.9 mV, respectively. Heat-triggered drug delivery was evaluated using focused ultrasound, and showed a release of 68% of the encapsulated 5-FU from thermosensitive liposomes, within 10 min, whereas release remained below 20% for the non thermosensitive formulation. Furthermore, the cytotoxicity of 5-FU-copper-polyethylenimine complex-loaded liposomes towards HT-29 human colorectal carcinoma cell line was evaluated. Results revealed that lipids at a concentration of 800 µM are not cytotoxic (80% viability). Moreover, 5-FU complexation has no impact on its cytotoxic activity, disclosing that liposomes toxicity arose from 5-FU and not from the excipients. Nevertheless, 5-FU-copper-polyethylenimine complex-loaded liposomes exhibited a lower half maximal inhibitory concentration of 49 µM compared to 115 µM for complex solution. This enhancement of cytotoxicity was attributed to the cellular internalization of liposomes. Pharmacokinetics in mice bearing HT-29 xenograft tumor showed that liposomes can extend the plasma distribution half-life of 5-FU by a factor 1.4. Furthermore, areas under the concentration-time curve over 24 h were higher by 1.9- and 2.9-fold when the drug was encapsulated into thermosensitive and non thermosensitive liposomes, respectively, compared to free 5-Fluorouracil. Finally, non thermosensitive liposomes significantly increased 5-FU accumulation in tumor by 2-fold, compared to 5-FU solution. In conclusion, these 5-FU-loaded thermosensitive liposomes represent valuable carriers to investigate the therapeutic efficacy following focused ultrasound-mediated heat application., Nous avons optimisé des liposomes thermosensibles, encapsulant un principe actif anticancéreux, le 5-Fluorouracile (5-FU), afin de déclencher sa libération par une hyperthermie locale modérée (39-42°C) induite par des ultrasons focalisés. L'hyperthermie sera appliquée au niveau de la tumeur, afin d'améliorer l’efficacité thérapeutique et de réduire la toxicité systémique. Les liposomes ont été formulés par hydratation du film lipidique en mélangeant la 1,2-dipalmitoyl-sn-glycéro-3-phosphocholine (DPPC) pour sa thermosensibilité à 41,5 ± 0,5°C, le cholestérol (CHOL) pour favoriser la stabilité des liposomes vis-à-vis des composants du sang, et le 1,2-distéaroyl-sn-glycéro-3-phosphoéthanolamine-N-[méthoxy(polyéthylène glycol)-2000] (DSPE-PEG) pour assurer la furtivité de la formulation. Les expériences ont confirmé que les liposomes formulés à base de DPPC/CHOL/DSPE-PEG dans un ratio molaire 90 : 5 : 5 mol% sont thermosensibles. Des liposomes composés du même mélange lipidique dans un rapport 65 : 30 : 5 mol% ont été considérés comme contrôle négatif non thermosensible. L’optimisation de l’encapsulation passive du 5-FU a permis d’obtenir une efficacité d’encapsulation (5-FU encapsulé/5-FU total) de 13%, mais le 5-FU est très faiblement retenu (12%) dans la cavité aqueuse des liposomes du fait du gradient osmotique à la dilution. La rétention du 5-FU a été optimisée (93%) par la technique d’encapsulation active basée sur la complexation intraliposomale du 5-FU avec le complexe cuivre-polyéthylèneimine préalablement encapsulé dans les liposomes. Cette technique a également permis d’améliorer l’efficacité d’encapsulation d’un facteur trois environ (37%), avec un taux de charge (ratio final 5-FU/lipides, mole/mole) de 50% environ. Nous avons alors obtenu des liposomes thermosensibles d'un diamètre hydrodynamique de 65 nm et de charge de surface de -10 mV. Les liposomes non thermosensibles, ont été caractérisés par un diamètre hydrodynamique de 105 nm et une charge de surface de -4,9 mV. La libération du 5-FU déclenchée par une hyperthermie induite par des ultrasons focalisés a été mesurée in vitro. En réponse à une hyperthermie de 42°C, les liposomes thermosensibles libèrent 68% de leur contenu, au bout de 10 min, alors que les liposomes non thermosensibles en libèrent moins de 20%. En outre, la cytotoxicité des liposomes encapsulant le complexe 5-FU-cuivre-polyéthylèneimine a été évaluée vis-à-vis de la lignée cellulaire HT-29 du carcinome colorectal humain. Les résultats ont révélé que les lipides à une concentration de 800 µM ne sont pas cytotoxiques (80% de viabilité). De plus, la complexation du 5-FU n’influence pas sa cytotoxicité ce qui prouve que la toxicité provient du 5-FU et non des excipients. En revanche, l’encapsulation du complexe 5-FU-cuivre-polyéthylèneimine dans les liposomes induit une diminution de la concentration inhibitrice médiane de 115 (solution du complexe) à 49 µM environ, corrélée à leur internalisation cellulaire. La pharmacocinétique chez des souris porteuses d’un modèle de tumeur colorectale HT-29 xénogreffée a montré que les liposomes permettent de prolonger d’un facteur 1,4 la demi-vie plasmatique de distribution du 5-FU. De plus, les aires sous la courbe des concentrations plasmatiques sur 24 h sont 1,9 et 2,9 fois plus élevées lorsque le 5-FU est administré sous forme de liposomes thermosensibles et non thermosensibles, respectivement, par rapport à la solution de 5-FU. Enfin, les liposomes non thermosensibles augmentent significativement d'un facteur 2 l'accumulation du 5-FU dans la tumeur par rapport à la solution de 5-FU. En conclusion, les liposomes thermosensibles développés présentent un fort intérêt pour une application thérapeutique en combinaison avec des ultrasons focalisés.

Our laboratories have been working together in close collaboration for over 10 years concerning the design and performance of lipid-based drug delivery systems. Over the past 3 years we have conceived of, developed, and tested pre-clinically, a new liposome-based temperature-sensitive drug delivery system for the treatment of solid tumors. This work is reported in a series of four publications: "J. Liposome Res. 9 (1999) 491; Cancer Res. Adv. Brief 60(5) (2000) 1197; Cancer Res. 6(9) (2000) 748; and Cancer Res. 60 (2000) 6950". Following a brief introduction concerning the motivations behind the work, this article will review these studies, including some of our earlier work that led to these ideas, and will present the rational design of the new liposome formulation from a materials engineering perspective.

The antitumor activity of dextran magnetite (DM)-incorporating thermosensitive liposomes, namely thermosensitive magnetoliposomes (TMs), as a new hyperthermic material was examined in rats bearing AH60C tumors. TMs were injected at an iron concentration of 15 mg per cm3 tumor into AH60C tumors placed subcutaneously in the backs of Donryu rats. After injection, the whole body of the rat (treated group) was exposed to a 500-kHz electromagnetic field generated by inductive heating. The treated group was further divided into once- and twice-treated groups in order to examine whether repetitive hyperthermia is possible after a single TM injection. A control group also received a TM injection but was not treated with hyperthermia. In the heated groups, there was a marked temperature rise inside the tumor up to 42°C within 7 min, but surrounding tissues were not heated. The inhibition of the growth of AH60C tumor in the treated groups was significantly greater than in the control group (P

There is a need for therapies that can effectively treat primary hepatocellular carcinoma (HCC) as well as metastases to the liver. HCC is the fifth most common cancer worldwide and the fourth most common cause for cancer death.1 Metastasis to the liver occurs commonly from primary cancers of the gastrointestinal track and other solid tumors. Surgical resection is an option for less than 30% of patients presenting with metastases.1,2 These patients are often not good surgical candidates, because of the location of the tumor or because of intercurrent disease, such as cirrhosis.2 However, thermal ablation is a cost-effective, nonsurgical option for treatment of patients with HCC and liver metastases3 and is currently practiced worldwide. In this review, a new approach is discussed, combining thermal ablation with drug-carrying thermosensitive liposomes. The rationale for this approach is presented and discussed in light of current liposome formulations and methods to achieve thermal ablation. A summary of preclinical and clinical studies that are relevant to treatment of primary and metastatic liver cancer is also presented.

✓ Thermosensitive liposomes are microscopic vesicles that can contain drugs and release them effectively in response to hyperthermia. To deliver an antitumor drug specifically to brain tumor, the authors used thermosensitive liposomes containing cis-diamminedichloroplatinum (CDDP) in conjunction with localized brain heating. The authors then investigated the antitumor effect on rat malignant glioma. Rous sarcoma virus—induced malignant glioma cells were transplanted into the brains of Fisher rats. Ten days after tumor inoculation, the rats were assigned to one of six treatment groups: control, free CDDP, hyperthermia, free CDDP + hyperthermia, liposomes containing CDDP (CDDP—liposome), and CDDP—liposome + hyperthermia. Liposomes containing CDDP or free CDDP were injected via the tail vein. Brain tumor heating was administered by means of a radiofrequency antenna designed at our institute. The rats treated with CDDP—liposome + hyperthermia had the longest survival time and the tumor CDDP level of this group was the highest when compared to the other groups. Histopathological examination showed that tumor cells were necrotized but surrounding normal brain tissue remained undamaged. On the basis of these findings we suggest that the combination of thermosensitive liposome and localized hyperthermia may better focus antitumor drugs to the tumor, providing a significantly greater antitumor effect.

Purpose. Dextran magnetite (DM)-incorporated thermosensitive liposomes, namely thermosensitive magnetoliposomes (TMs), were prepared and characterized in order to investigate their possibility for magnetic drug targeting.

It is useful if the bioactive macromolecules, such as cytokines, could be delivered to the desired site. Liposomes have been used successfully as carriers for various agents. Targeting of liposomes to the desirable site has been also achieved to some extent, and the release of the contents at the target site has been attempted by means of thermosensitive liposomes utilizing phase transition of lipid bilayer. Thermosensitiye Iiposomes with internal solution of 2-fold higher osmotic pressure and sized through 200 nm-pore, released encapsulated macromolecules effectively when they were incubated at 40∼42°C, since transient swelling during phase transition of liposomes with hyper-osmotic internal aqueous phase causes permeation of large molecules through lipid bilayer. Long-circulating, serum stable, type of thermosensitive liposomes were also attemped to be prepared for practical usage of liposomes as a tool for macromolecule delivery.

Liposomes are a promising class of nanomedicine with the potential to provide site-specific chemotherapy, thus improving the quality of cancer patient care. First-generation liposomes have emerged as one of the first nanomedicines used clinically for localized delivery of chemotherapy. Second-generation liposomes, i.e. stimuli-responsive liposomes, have the potential to not only provide site-specific chemotherapy, but also triggered drug release and thus greater spatial and temporal control of therapy. Temperature-sensitive liposomes are an especially attractive option, as tumors can be heated in a controlled and predictable manner with external energy sources. Traditional thermosensitive liposomes are composed of lipids that undergo a gel-to-liquid phase transition at several degrees above physiological temperature. More recently, temperature-sensitization of liposomes has been demonstrated with the use of lysolipids and synthetic temperature-sensitive polymers. The design, drug release behavior, and clinical potential of various temperature-sensitive liposomes, as well as the various heating modalities used to trigger release, are discussed in this review.

Combining localized heating with thermosensitive liposomes provides a means for triggering the rapid release of active drug in a targeted region. The objective of this research was to demonstrate the feasibility of using MRI-controlled focused ultrasound hyperthermia in rabbit VX2 tumors and bone to achieve thermally-mediated localized drug delivery. To generate a uniform region of mild heating, a focused ultrasound transducer was mechanically scanned in a circular trajectory by an MRI-compatible positioner. MRI temperature images were continuously acquired during scanned heating, and applied power was adjusted in a multi-point feedbackcontrol loop based on temperatures measured in tumors or in soft tissue adjacent to bone. Lysothermosensitive liposomal doxorubicin was infused intravenously during hyperthermia. Two hours post-treatment, unabsorbed liposomes were flushed from the vasculature with saline. Drug concentrations in homogenized tissues sampled from heated and unheated regions were measured by do...

Long-circulating, thrmosensitive liposomes (TSL, 200 nm in mean diameter) were prepared from GM1/DPPC/DSPC or PEG-PE/DPPC/DSPC. Doxorubicin (DXR) was encapsulated into GM1-TSL with >98% or PEG-TSL with >90% in trapping efficiency by pH gradient method, respectively. DXR was released from both type of TSL in a temperature-dependent manner in vitro. Inclusion of 6 mol% of GM1 or 3 mol% of PEG-PE endowed TSL with prolonged circulation ability resulting in increased blood levels of liposomes and decreased RES uptake after injection to mice. Concomitantly, high DXR levels in blood were maintained for long time. The combination of DXR-long-circulating TSL and the local hyperthermia have been tested for their utility as a temperature sensitive release for DXR in colon 26 tumor-bearing mice. Accumulation of DXR into tumor tissue by local hyperthermia after injection of DXR-long-circulating TSL was significantly higher than that of DXR-bare TSL or free DXR, and resulted in effective tumor growth retardation and increased survival time. These results indicate that long circulating ability is effective for thermosensitive liposomal drug delivery in combination with hyperthermia. This system is expected to be very useful for antitumor therapy.

A thermosensitive liposome with embedded AuNPs in a bilayer was prepared using supercritical CO(2). The AuNPs-liposome can absorb a certain wavelength light, convert optical energy into heat, induce phase transition, and release drug. The results show that drug release from the liposome is due to the photothermic effects inducing phase transition of the liposome rather than destruction of the liposome structure.

We describe folate receptor targeted thermosensitive magnetic liposomes, which are designed to combine features of biological and physical (magnetic) drug targeting for use in magnetic hyperthermia-triggered drug release. The optimized liposome formulation DPPC:cholesterol:DSPE-PEG(2000):DSPE-PEG(2000)-Folate at 80:20:4.5:0.5 molar ratio showed calcein release of about 70% both in PBS and in 50% FBS (fetal bovine serum) at 43 degrees C and less than 5% release at 37 degrees C following 1 h incubation. Folate-targeted doxorubicin-containing magnetic liposomes of the above lipid composition (MagFolDox) showed encapsulation efficiencies of about 85% and 24% for doxorubicin and magnetic nanoparticles (mean crystallite size 10 nm), respectively. This magnetic formulation displayed the desired temperature sensitivity with 52% doxorubicin release in 50% fetal bovine serum (FBS) following 1 h incubation at 43 degrees C. MagFolDox, when physically targeted to tumor cells in culture try a permanent magnetic field yielded a substantial increase in cellular uptake of doxorubicin as compared to Caelyx(R) (a commercially available liposomal doxorubicin preparation), non-magnetic folate-targeted liposomes (FolDox) and free doxorubicin in folate receptor expressing tumor cell lines (KB and HeLa cells). This resulted in a parallel increase in cytotoxicity over Caelyx(R) and FolDox. Magnetic hyper-thermia at 42.5 degrees C and 43.5 degrees C synergistically increased the cytotoxicity of MagFolDox. The results suggest that an integrated concept of biological and physical drug targeting, triggered drug release and hyperthermia based on magnetic field influence can be used advantageously for thermo-chemotherapy of cancers. (C) 2009

Phosphatidylglyceroglycerol (DPPGOG)-based thermosensitive liposomes (TSL) with either encapsulated proton (1H) magnetic resonance (MR) contrast agent gadodiamide (Gd-DTPA-BMA) or doxorubicin (DOX) have been proposed for noninvasive online temperature monitoring and drug release respectively during tumor treatment using chemotherapy combined with hyperthermia. The technique exploits the fact that water exchange between the TSL interior and exterior is increased and/or the encapsulated Gd-DTPA-BMA or DOX is released near the gel-to-liquid crystalline phase transition temperature of TSL, and thus shortens the 1H MR longitudinal relaxation time (T1) of tissue and increases drug delivery to tissue. In this work, DPPGOG-TSL with encapsulated Gd-DTPA-BMA were mixed with those with encapsulated DOX. The resulting suspension was characterized in vitro by measuring the temperature dependence of the T1 and DOX fluorescence intensity while temperature was increased from 30 and 46 °C. The measurements revealed that from 37 to 44 °C, the T1 markedly decreased and DOX fluorescence intensity increased since encapsulated Gd-DTPA-BMA and DOX were simultaneously rapidly released.

A major challenge in HIFU mediated Image Guided Drug Delivery (IGDD) is developing accurate means to implement real-time drug delivery control, and to optimize intratumoral drug distribution. To facilitate clinical translation, objectives of this study were to: 1) develop echogenic E-LTSL, a low temperature sensitive liposome co-loaded with an US contrast agent (Perfluoropentane, PFP) and doxorubicin, 2) determine stability of contrast agent encapsulation and characterize doxorubicin release from E-LTSL and 3) investigate the ability of E-LTSL to report on real-time doxorubicin distribution with Ultrasound (US)-guided hyperthermia.

Drug delivery using focused ultrasound (focal drug delivery) has attracted significant interest during the last few years. Focused Ultrasound (FUS) can induce local tissue hyperthermia, increasing blood flow and vascular permeability, which then enhances the uptake of therapeutics by target tissues. Although a number of studies have focused on nanoparticles (e.g. thermosensitive liposomes) little work has been done on the effects of FUS on the uptake of macromolecular drugs into tumours. In this study we aim to understand the effect of FUS-induced hyperthermia on tumour vascular permeability, as measured by the increased uptake of labelled macromolecules in the tumour. Using optical imaging we monitor the labelled macromolecules tumour localisation in real time in both short (minutes to hours) and long (weeks) term.

The objective of this study was to prepare and characterize alginate microgels loaded with temperature sensitive liposomes, which release their payload after mild hyperthermia. It is further aimed that by using these microgels both the drug release and the microgel deposition can be visualized by magnetic resonance imaging (MRI) after their administration (e.g. in the vicinity of a tumor). To this end, temperature sensitive (TSL) and non-temperature sensitive liposomes (NTSL) loaded with fluorescein (drug mimicking dye) and a T-1 MRI contrast agent (Prohance,(R)[Gd(HPDO3A)(H2O)]) were encapsulated in alginate microgels crosslinked by holmium ions (73 MRI contrast agent). The drug release could be monitored by the release of [Gd(HPDO3A)(H2O)] while the microgels could be visualized using MRI via the holmium ions in the microgels. The microgels were prepared with a JetCutter and had an average size of 325 mu m and contained similar to 0.6 wt% Ho3+. Microgels loaded with NTSL (NTSL-Ho-microgels) were stable at 37 and 42 degrees C with only a minimal release of fluorescein and [Gd(HPDO3A)(H2O)]. Microgels encapsulating TSL (TSL-Ho-microgels) released fluorescein and [Gd(HPDO3A)(H2O)] only marginally at 37 degrees C while, importantly, their payload was co-released within 2 min at 42 degrees C. TSL-Ho-microgels were administered in an ex vivo sheep kidney via a catheter. Clusters of TSL-Ho-microgels could be visualized via MRI and were deposited in the interlobular blood vessels. In conclusion, these alginate TSL-Ho-microgels are promising systems for real-time, MR-guided embolization and triggered release of drugs in vivo. (C) 2015 Elsevier Ltd. All rights reserved.