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Light triggered drug delivery systems offer attractive possibilities for sophisticated therapy, providing both temporal and spatial control of drug release. We have developed light triggered liposomes with clinically approved indocyanine green (ICG) as the light sensitizing compound. Amphiphilic ICG can be localized in different compartments of the liposomes, but the effect of its presence, on both triggered release and long term stability, has not been studied. In this work, we report that ICG localization has a significant effect on the properties of the liposomes. Polyethylene glycol (PEG) coating of the liposomes leads to binding and stabilization of the ICG molecules on the surface of the lipid bilayer. This formulation showed both good storage stability in buffer solution (at +4–37 °C) and adequate stability in serum and vitreous (at +37 °C). The combination of ICG within the lipid bilayer and PEG coating lead to poor stability at elevated temperatures of +22 °C and + 37 °C. The mechanisms of the increased instability due to ICG insertion in the lipid bilayer was elucidated with molecular dynamics simulations. Significant PEG insertion into the bilayer was induced in the presence of ICG in the lipid bilayer. Finally, feasibility of freeze-drying as a long term storage method for the ICG liposomes was demonstrated. Overall, this is the first detailed study on the interactions of lipid bilayer, light sensitizer (ICG) and PEG coating on the liposome stability. The localization of the light triggering agent significantly alters the structure of the liposomes and it is important to consider these aspects in triggered drug delivery system design. [ABSTRACT FROM AUTHOR]

Thermally triggered drug release from temperature-sensitive liposomes (TSL) holds great promise for cancer therapy. Different types of TSL have been designed recently for heat triggered drug release inside tumor blood vessels or after accumulation into the tumor interstitium. However, justification of drug release profiles is for far mainly based on in vitro release data. While these methods could be good enough to give early indication about the thermal sensitivity of TSL, they are still far from being optimum. This is because these methods do not take into consideration the actual adsorption of proteins onto the surface of TSL after their in vivo administration, also known as “protein corona” and the influence this could have on drug release. Therefore, in this study we compared thermal triggered drug release profile of two different types of doxorubicin encapsulated TSL; namely the lysolipid-containing TSL (LTSL) and traditional TSL (TTSL) after their in vivo recovery from the blood circulation of CD-1 mice. Ex vivo release profile at 42 °C was then tested either in the presence of full plasma or after removal of unbound plasma proteins (i.e. protein corona coated TSL). Our data showed that the influence of the environment on drug release profile was very much dependent on the type of TSL. LTSL release profile was consistently characterized by ultrafast drug release independent on the conditions tested. On the contrary, TTSL release profile changed significantly. Doxorubicin release from in vivo recovered TTSL was slow and incomplete in the presence of unbound plasma proteins, whereas very rapid drug release was detected from in vivo recovered and purified protein corona-coated TTSL in the absence of unbound proteins. Using mass spectrometry and quantification of protein adsorption, we confirmed that this discrepancy is due to the changes in protein adsorption onto TTSL when heated in the presence of unbound proteins leading to reduction in drug release. In summary this study showed that the formation of the in vivo corona on TSL will have a dramatic impact on their release profile and is dependent on both their lipid composition and the protein content of the environment in which drug release is triggered. [ABSTRACT FROM AUTHOR]

Precise delivery of antineoplastic drugs to specific tumor region has drawn much attention in recent years. Herein, a light/magnetic hyperthermia triggered drug delivery with multiple functionality is designed based on methotrexate (MTX) modified thermo-sensitive magnetoliposomes (MTX-MagTSLs). In this system, MTX and oleic acid modified magnetic nanoparticles (MNPs) can be applied in biological and magnetic targeting. Meanwhile, lipophilic fluorescent dye Cy5.5 and MNPs are encapsulated into the bilayer of liposomes, which can not only achieve dual-imaging effect to verify the MTX-MagTSLs accumulation in tumor region, but also provide an appropriate laser irradiation region to release Doxorubicin (Dox) under alternating magnetic field (AMF). Both in vitro and in vivo results revealed that MTX-MagTSLs possessed an excellent targeting ability towards HeLa cells and HeLa tumor-bearing mice. Furthermore, the heating effect of MTX-MagTSLs was amplified 4.2-fold upon combination with AMF and local precise near-infrared laser irradiation (808 nm) (DUAL-mode) to rapidly reach the phase change temperature (Tm) of MTX-MagTSLs in 5 min compared with either AMF or laser stimulation alone, resulting in a significantly enhanced release of Dox at tumor region and precise cancer synergetic theranostics. [ABSTRACT FROM AUTHOR]

The clinical use of liposomal drug delivery vehicles is often hindered by insufficient drug release. Here we present the rational design of liposomes optimized for secretory phospholipase A 2 (sPLA 2 ) triggered drug release, and test their utility in vitro and in vivo . We hypothesized that by adjusting the level of cholesterol in anionic, unsaturated liposomes we could tune the enzyme specificity based on membrane fluidity, thus obtaining liposomes with an improved therapeutic outcome and reduced side effects. Cholesterol is generally important as a component in the membranes of liposome drug delivery systems due to its stabilizing effects in vivo . The incorporation of cholesterol in sPLA 2 sensitive liposomes has not previously been possible due to reduced sPLA 2 activity. However, in the present work we solved this challenge by optimizing membrane fluidity. In vitro release studies revealed enzyme specific drug release. Treatment of two different cancer cell lines with liposomal oxaliplatin revealed efficient growth inhibition compared to that of clinically used stealth liposomes. The in vivo therapeutic effect was evaluated in nude NMRI mice using the sPLA 2 secreting mammary carcinoma cell line MT-3. Three days after first treatment all mice having received the novel sPLA 2 sensitive liposome formulation were euthanized due to severe systemic toxicity. Thus the present study demonstrates that great caution should be implemented when utilizing sPLA 2 sensitive liposomes and that the real utility can only be disclosed in vivo . The present studies have clinical implications, as sPLA 2 sensitive formulations are currently undergoing clinical trials (LiPlaCis®). [ABSTRACT FROM AUTHOR]

The first developed secretory phospholipase A 2 (sPLA 2 ) sensitive liposomal cisplatin formulation (LiPlaCis®) is currently undergoing clinical evaluation. In the present study we revisit and evaluate critical preclinical parameters important for the therapeutic potential and safety of platinum drugs, here oxaliplatin (L-OHP), formulated in sPLA 2 sensitive liposomes. We show the mole percentage of negatively charged phospholipid needed to obtain enzyme-sensitivity for saturated systems is ≥ 25% for 16-carbon chain lipid membranes, and > 40% for 18-chain lipid membranes, which was surprising as 25% is used clinically in LiPlaCis®. Efficient sPLA 2 -dependent growth inhibition of colorectal cancer cells was demonstrated in vitro , where cell membrane degradation and cytolysis depends on the sensitivity of the formulation towards the enzyme and is governed by the amount of lysolipids generated and the presence of serum proteins. We found that serum proteins did not affect the lipase activity of the enzyme towards the membranes but instead sequester the lysolipid byproducts consequently inhibiting their detergent-like cytotoxic properties. In vivo therapeutic potential and safety of the liposomes was investigated in nude mice bearing sPLA 2 -deficient FaDu squamous carcinoma and sPLA 2 -expressing Colo205 colorectal adenocarcinoma. After intravenous injections, the tumor growth was suppressed for liposomal L-OHP relative to free drug, but only a weak response was observed for both slow- and fast-releasing sPLA 2 -sensitive formulations compared to non-sensitive liposomes. Also, the mice did not show longer survival. In turn, for the highly sPLA 2 -sensitive liposomes, multiple high doses caused petechial cutaneous hemorrhages, along with multifocal hepatonecrotic lesions, suggestive of premature activation in skin and liver irrespective of sPLA 2 -status of the tumor engraft. These results indicate that although liposomal carriers can improve the antitumor efficacy of platinum drugs, sPLA 2 -triggered release suffers from a narrow therapeutic index and has safety concerns. [ABSTRACT FROM AUTHOR]

Thermosensitive liposomes have been put forward as a strategy to improve upon the limited tumor drug availability associated with conventional non-thermosensitive liposomes. ThermoDox® is the first and only thermosensitive liposome formulation to reach clinical development. The initial Phase III clinical trial on ThermoDox® ( i.e. HEAT trial) evaluating the combination of ThermoDox® and radiofrequency ablation (RFA) in comparison to RFA alone for treatment of inoperable hepatocellular carcinoma (HCC) failed to reach its primary endpoint in progression-free survival (PFS). Nevertheless, a subgroup analysis demonstrated a marked improvement in PFS and a significant improvement in overall survival (OS) for patients who underwent RFA treatment for at least 45 min. Potential reasons for failure of the HEAT trial have been summarized in this review and include issues with clinical trial design, lack of supporting preclinical data, and improvements in the control arm ( i.e. RFA alone). In recent years, there have been many developments and improvements in heating infrastructure, thermometry and treatment planning of hyperthermia and ablation treatments. Still, there are many barriers to the clinical implementation and accessibility of heat treatment. This review provides an in-depth analysis of the current status, as well as potential challenges faced by continued clinical translation of thermosensitive liposomes. [ABSTRACT FROM AUTHOR]

An important limitation to successful cancer treatment with chemotherapeutics is the inability to achieve therapeutically effective drug concentrations while avoiding healthy tissue damage. In this work, a new tumor-targeting peptide iRGD (CCRGDKGPDC) was used to modify drug-loaded low temperature-sensitive liposomes (iRGD-LTSL-DOX) to explore the anti-tumor effects in combination with high intensity focused ultrasound (HIFU) in vitro and in vivo. iRGD-LTSL-DOX can specifically target to ανβ3-positive cells and locally release the encapsulated doxorubicin (DOX) in a hyperthermia-triggered manner. In vivo results showed that DOX from iRGD-LTSL-DOX was intravascularly released and rapidly penetrated into tumor interstitial space after HIFU-triggered heat treatment, thereby overcoming the limited tumor penetration of anticancer drugs. Significantly stronger anti-tumor efficacy further supported the effective combination of iRGD-LTSL-DOX with HIFU-induced hyperthermia. Our study provided a novel tumor-targeting LTSL-DOX and demonstrated its usefulness in HIFU-induced hyperthermia-triggered drug delivery. [ABSTRACT FROM AUTHOR]

The controlled release of payloads from mesoporous silica nanocapsules (SiNCs) consisting of stimulus-responsive shells is of considerable interest in applications such as self-healing materials and drug delivery. However, the release of payloads from SiNCs before application of external triggers ( i.e. non-selective release) remains a formidable challenge. In fact, the non-selective release of payloads from SiNCs occurs because of the mesoporous nature of the silica shell that cannot trap payloads in the core of SiNCs perfectly. We establish an efficient and straightforward strategy based on the encapsulation of a pro-active payload to hinder the non-selective release of small payloads from mesoporous capsules. A pro-active payload is defined as a compound that is converted to an active functional molecule in the environment where it is needed. In this sense, it is a generalization of a prodrug. Encapsulating a pro-active payload instead of a payload allowed hindering the non-selective release of the payload from SiNCs. A selective release of the payload could be achieved upon reduction of the encapsulated pro-active payload. Furthermore, the total amount of released substance is significantly enhanced by introducing responsive groups in the silica shell. These results show that the pro-active payload strategy combined with the use of stimulus-responsive materials can be successfully exploited to achieve selective release of cargo from mesoporous nanocapsules. [ABSTRACT FROM AUTHOR]

Stimulus-triggered drug release based on the liposomal drug delivery platform has been studied vigorously to increase drug release at the target site. Although the delivery system has been developed, an effective carrier system is needed to achieve effective therapeutic efficacy. Therefore, we focused on the development of gold cluster bound thermosensitive liposomes (G-TSL), which are capable of triggered drug release when stimulated by external near-infrared (NIR) irradiation in the tumor microenvironment. The size of doxorubicin (DOX)-loaded G-TSL (DOX/G-TSL) was 171.5 ± 8.3 nm, and the efficiency of DOX encapsulation was up to 90%. The release of DOX from DOX/G-TSL was increased 70% by NIR irradiation (1.50 W/cm 2 for 0.5 min) compared to non-gold-coated TSL. Consequentially, the gold cluster on the TSL enabled the light-controlled DOX release through the photothermal conversion of the energy of NIR-absorbed light, leading to membrane destabilization. Cell cytotoxicity of DOX/G-TSL was also increased by their NIR irradiation-triggered DOX release compared to non-NIR-irradiated DOX/G-TSL. In addition, we demonstrated the therapeutic efficacy of DOX/G-TSL against the MDA-MB-231 tumor model. The NIR-irradiated DOX/G-TSL treatment showed greater therapeutic efficacy than that of the non-NIR-irradiated DOX/G-TSL and control ( p < 0.05). Taken together, DOX/G-TSL has the potential for remote-triggered drug release upon stimulation with NIR irradiation in the tumor microenvironment, and may be applied to a broad range of photothermal-based disease therapies. [ABSTRACT FROM AUTHOR]

The redox responsive nanocarriers have made a considerable progress in achieving triggered drug release by responding to the endogenous occurring difference between the extra- and intra- cellular redox environments. Despite the promises, this redox difference exists both in normal and tumor tissue. So a non-selective redox responsive drug delivery system may result in an undesired drug release in normal cells and relevant side-effects. To overcome these limitations, we have developed a chitosan based glycolipid-like nanocarrier (CSO-ss-SA) which selectively responded to the reducing environment in tumor cells. The CSO-ss-SA showed an improved reduction-sensitivity which only fast degraded and released drug in 10 mM levels of glutathione (GSH). The CSO-ss-SA could transport the drug fast into the human ovarian cancer SKOV-3 cells and human normal liver L-02 cells by internalization, but only fast release drug in SKOV-3 cells. By regulating the intracellular GSH concentration in SKOV-3 cells, it indicated that the cellular inhibition of the PTX-loaded CSO-ss-SA showed a positive correlation with the GSH concentration. The CSO-ss-SA was mainly located in the liver, spleen and tumor in vivo, which evidenced the passive tumor targeting ability. Despite the high uptake of liver and spleen, drug release was mainly occurred in tumor. PTX-loaded CSO-ss-SA achieved a remarkable tumor growth inhibition effect with rather low dose of PTX. This study demonstrates that a smartly designed glycolipid-like nanocarrier with selective redox sensitivity could serve as an excellent platform to achieve minimal toxicity and rapid intracellular drug release in tumor cells. [ABSTRACT FROM AUTHOR]

Externally triggered drug release at defined targets allows site- and time-controlled drug treatment regimens. We have developed liposomal drug carriers with encapsulated gold nanoparticles for triggered drug release. Light energy is converted to heat in the gold nanoparticles and released to the lipid bilayers. Localized temperature increase renders liposomal bilayers to be leaky and triggers drug release. The aim of this study was to develop a drug releasing system capable of releasing its cargo to cell cytosol upon triggering with visible and near infrared light signals. The liposomes were formulated using either heat-sensitive or heat- and pH-sensitive lipid compositions with star or rod shaped gold nanoparticles. Encapsulated fluorescent probe, calcein, was released from the liposomes after exposure to the light. In addition, the pH-sensitive formulations showed a faster drug release in acidic conditions than in neutral conditions. The liposomes were internalized into human retinal pigment epithelial cells (ARPE-19) and human umbilical vein endothelial cells (HUVECs) and did not show any cellular toxicity. The light induced cytosolic delivery of calcein from the gold nanoparticle containing liposomes was shown, whereas no cytosolic release was seen without light induction or without gold nanoparticles in the liposomes. The light activated liposome formulations showed a controlled content release to the cellular cytosol at a specific location and time. Triggering with visual and near infrared light allows good tissue penetration and safety, and the pH-sensitive liposomes may enable selective drug release in the intracellular acidic compartments (endosomes, lysosomes). Thus, light activated liposomes with gold nanoparticles are an attractive option for time- and site-specific drug delivery into the target cells. [ABSTRACT FROM AUTHOR]

Therapies for macular degeneration and diabetic retinopathy require intravitreal injections every 4–8 weeks. Injections are uncomfortable, time-consuming, and carry risks of infection and retinal damage. However, drug delivery via noninvasive methods to the posterior segment of the eye has been a major challenge due to the eye's unique anatomy and physiology. Here we present a novel nanoparticle depot platform for on-demand drug delivery using a far ultraviolet (UV) light-degradable polymer, which allows noninvasively triggered drug release using brief, low-power light exposure. Nanoparticles stably retain encapsulated molecules in the vitreous, and can release cargo in response to UV exposure up to 30 weeks post-injection. Light-triggered release of nintedanib (BIBF 1120), a small molecule angiogenesis inhibitor, 10 weeks post-injection suppresses choroidal neovascularization (CNV) in rats. Light-sensitive nanoparticles are biocompatible and cause no adverse effects on the eye as assessed by electroretinograms (ERG), corneal and retinal tomography, and histology. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we have developed an albumin-camouflaged/thrombin-triggered delivery system for site-specific delivery of tissue plasminogen activator (tPA). The camouflaged construct is expected to suppress tPA's enzymatic activity in the systemic circulation but regenerate its thrombolytic action upon contact with thrombin present on the thrombus. tPA was camouflaged with human serum albumin (HSA) via a thrombin-cleavable peptide (GFPRGFPAGGCtPA). The surface of the albumin molecule was decorated with a homing peptide (CQQHHLGGAKQAGDV) that binds with GPIIb/IIIa expressed on activated platelets. To avoid non-specific interactions, the unpaired cysteine-34 of HSA was permanently blocked by iodoacetamide and the primary amines were temporarily masked with citraconic anhydride. Shielding with HSA suppressed 75% of tPA's activity which, upon contact with 25nM thrombin, was regenerated to ~90% of that of native tPA. The fibrin agar plate assay further confirmed the thrombin-mediated release of tPA from the camouflaged construct. The integrity of camouflaged construct was maintained in human plasma or blood. The fluorescence microscopic studies confirmed the binding affinity of camouflaged tPA with the activated platelets. Furthermore, when evaluated in a rat thrombosis model, the thrombolytic activity of camouflaged tPA was similar to that of native tPA. However, the degradation of circulating fibrinogen was reduced by 2-fold with HSA-decorated tPA compared with that of native tPA, which is an indication of reduced risk of hemorrhagic incidence. This proof-of-principle study suggests that the activity of tPA can be suppressed by HSA and regenerated by thrombin present at the thrombus. [Copyright &y& Elsevier]

Abstract: The clinical applicability of polymers as gene delivery systems depends not only on their efficiency, but also on their safety. The cytotoxicity of these systems remains a major issue, mainly due to their cationic nature. Therefore, it is highly preferable to have a system based on biocompatible neutral polymers, lacking polycations, without compromising the DNA condensing and protecting capacities. Here, we introduce a concept to obtain a neutral polymeric gene delivery system, through a 3-step process (charge-driven condensation; stabilization through disulfide crosslinking; polyplex decationization) to generate polyplexes with a core of disulfide crosslinked poly(hydroxypropyl methacrylamide) (pHPMA) in which plasmid DNA (pDNA) is entrapped and a shell of poly(ethylene glycol) (PEG). The resulting polyplexes combine beneficial features of high and stable DNA loading capacity, stealth behavior and reduced toxicity. The nanoparticles are designed to release the pDNA after cellular uptake through cleavage of disulfide crosslinks within the intracellular reducing environment. This was shown by forced introduction of the polyplexes into the cytosol of HeLa cells by electroporation, which resulted in a high level of expression of the reporter gene. Additionally, the decationized polyplexes showed no interference on the cellular cell viability or metabolic activity (even at high dose) and no complex-induced membrane destabilization. Furthermore, decationized polyplexes showed a low degree of non-specific uptake, which is a highly favorable property for targeted therapy. Summarizing, the stabilized, decationized polyplexes presented here contribute to solve the high toxicity, low stability and lack of cellular/tissue specificity of cationic polymer based gene delivery systems. [Copyright &y& Elsevier]

A promising approach for local drug delivery is high-intensity focused ultrasound (HIFU)-triggered release of drugs from stimuli-responsive nanoparticles such as liposomes. The aim of this study was to investigate whether another release mechanism is involved with HIFU-triggered release from liposomes beside cavitation and temperature. Furthermore, it was studied whether this new release mechanism allows the release of lipophilic compounds. Therefore, both a lipophilic (Nile red) and a hydrophilic (fluorescein) compound were loaded into thermosensitive (TSL) or non-thermosensitive liposomes (NTSL) and the liposomes were subjected both to continuous wave (CW)- and pulsed wave (PW)-HIFU. The mean liposome size varied from 97 to 139nm with a polydispersity index (PDI)≤0.06 for the different formulations. The T m of the phospholipid bilayer of the TSL was around 42°C. Approximately 80% of fluorescein was released within 15min from TSL at temperatures≥42°C. In contrast, no fluorescein release from NTSL and NR release from both TSL and NTSL was observed at temperatures up to 60°C. CW-HIFU exposure of TSL resulted in rapid temperature elevation up to 52°C and subsequently almost quantitative fluorescein release. Fluorescein release from NTSL was also substantial (~64% after 16min at 20W). Surprisingly, CW-HIFU exposure (20W for 16min) resulted in the release of NR from TSL (~66% of the loaded amount), and this was even higher from NTSL (~78%). PW-HIFU exposure did not result in temperatures above the T m of TSL. However, nearly 85% of fluorescein was released from TSL after 32min at 20W of PW-HIFU exposure, whereas the release from NTSL was around 27%. Interestingly, NR release from NTSL was~30% after 2min PW-HIFU exposure and increased to~70% after 32min. Furthermore, addition of microbubbles to the liposomes prior to PW-HIFU exposure did not result in more release, which suggests that cavitation can be excluded as the main mechanism responsible for the triggered release of both a hydrophilic and a lipophilic model compound from liposomes. Dynamic light scattering analysis showed that the mean size and PDI of the liposomes did not significantly change after CW- and PW-HIFU exposure. Taken together, it is therefore concluded that neither temperature elevation nor inertial cavitation is essential for the release of both hydrophilic and lipophilic compounds from liposomes. It is assumed that the release originates from radiation force-induced acoustic streaming, causing the liposomes to collide at the walls of the exposure chamber leading to shear forces which in turn results in reversible liposome destabilization and release of both hydrophilic and lipophilic compounds. [ABSTRACT FROM AUTHOR]

Abstract: Particulate drug delivery via hair follicles represents a promising concept, although requirements are high. This process must be realized at the desired depth and at the appropriate time, due to the fact that the particles themselves are not able to overcome the follicular skin barrier. In the present study, a novel triggering concept for the release of a model drug from the delivering particles is presented based on the application of two different particle types of the same size, where one particle type is the drug carrier, and the second one is loaded with a protease. The latter particle type is supposed to interact with the drug-carrying particles to trigger the drug release. A mixture of both particles was applied onto porcine skin samples, followed by follicular analysis. As a control, the particles were applied unaided without protease, whereas one skin area remained untreated. The investigations revealed that the protease was able to release the model drug from the delivering particles in significant depths within the hair follicle (866±62nm). Additionally, an uptake of the model drug in the sebaceous gland was observed after release providing a promising novel approach for the development of treatment strategies for different skin diseases. [Copyright &y& Elsevier]

Abstract: Photothermal ablation (PTA) is an emerging technique that uses near-infrared (NIR) laser light-generated heat to destroy tumor cells. However, complete eradication of tumor cells with PTA is difficult because of uneven heat distribution in the treatment volume. We hypothesized that combining PTA with chemotherapy using a single multifunctional nanoconstruct that mediates simultaneous photothermal cell killing and drug release (photothermal-chemotherapy) would result in enhanced antitumor activity and reduced toxicity compared to chemotherapy alone. Doxorubicin (DOX) was loaded to hollow gold nanospheres (HAuNS) coated with polyethylene glycol (PEG). The pharmacokinetics and biodistribution of both DOX and HAuNS in the resulting nanoconstruct, DOX@PEG-HAuNS having different DOX:PEG:HAuNS ratios, were evaluated using dual isotope labeling techniques. The antitumor activity of DOX@PEG-HAuNS with DOX:PEG:HAuNS weight ratio of 1:3:1 (NP3) in combination with NIR laser was studied in vitro and in vivo using human MDA-MB-231 breast cancer and A2780 ovarian cancer cells. In vitro, NP3 mediated PTA of both cancer cells and DOX release upon NIR laser treatment. In vivo, NP3 showed slower clearance in blood and greater accumulation in tumors than free DOX. NP3-plus-NIR laser demonstrated greater antitumor activity than free DOX, NP3, or liposomal DOX. Moreover, NP3 displayed significantly decreased systemic toxicity compared to free DOX or liposomal DOX. Enhanced antitumor effect with NP3-plus-laser can be attributed to both the cytotoxic effect of DOX released from NP3 and the photothermal effect mediated by HAuNS. Slow release of DOX from NP3 in normal tissues contributed to reduced systemic toxicity. Photothermal-chemotherapy exemplified by a single-agent nanoconstruct NP3 is a promising approach to anticancer therapy. [Copyright &y& Elsevier]

Abstract: Due to its versatility and ease of use the layer-by-layer (LbL) assembly technique has been under intensive investigation for drug and gene delivery applications. Especially the development of responsive LbL materials has advanced significantly in recent years. Responsiveness plays an important role in many delivery applications, either for loading of therapeutics or controlled and triggered release. In general four basic mechanisms within responsive LbL films have been identified: disruption of layer interactions, degradation of the LbL film, multilayer destruction via physical stimuli, and phase transitions or polymer rearrangements within the LbL film. This review will outline these different mechanisms and highlight recent advances in these fields. [Copyright &y& Elsevier]

Abstract: A targetable, heparin-triggered release system for tissue plasminogen activator (tPA) was designed to prevent the excessive ‘lytic’ state associated with the current tPA therapy for acute thrombotic conditions, such as myocardial infarction (MI). The strategy is, upon target accumulation, to trigger tPA release from a prodrug construct by a usual heparin dose. A relatively inactive form of tPA was constructed by conjugating tPA with low-molecular weight heparin followed by complexation with albumin-protamine conjugate, termed ‘camouflage’. The modified tPA was ~97% as active as native tPA. The prodrug construct of tPA significantly masked the enzymatic activity, which was fully recovered upon heparin addition. The camouflaged tPA was stable in human blood for at least 30min and was able to trigger enzyme activation in vitro at heparin level of 0.4U/mL. In vivo studies on jugular vein rat thrombosis model showed that the clot lysis of the heparin-triggered camouflaged tPA group was equivalent to the tPA+heparin group without prolongation of activated partial thromboplastin time (aPTT) before and after the treatment. This proof-of-principle study suggests that the activity of the tPA prodrug construct can be triggered at the thrombus site at therapeutic heparin concentration conjunctively used for MI with reduced bleeding risk. [Copyright &y& Elsevier]

Abstract: We report an efficient strategy to conjugate methacrylamide moieties to the lysine units of lysozyme for co-polymerization and subsequent triggered release from hydrogels. Two novel linker molecules, containing an ester bond and/or a disulfide bond for temporary immobilization, were synthesized and conjugated to lysozyme. Lysozyme was successfully modified with on average 2.5 linker molecules per protein molecule, as evidenced by MALDI-TOF and by titration of the free amine groups, while spectral analysis verified the preservation of the protein structure. Next, methacrylated dextran (Dex-MA) was polymerized in presence of native or modified lysozyme to yield hydrogels. The release of native and modified lysozyme from Dex-MA hydrogels was studied in acetate buffer (pH 5, in absence of any trigger) and only a minor fraction (~15%) of the modified lysozyme was released, whereas ~74% of the native lysozyme was released. This indicates successful immobilization of the majority of the modified lysozyme in the hydrogel network. Upon hydrolysis of the ester bonds or incubation with glutathione to reduce disulfide bonds of the linker molecules that conjugate the lysozyme to the gel network, the modified lysozyme was mobilized and released from the hydrogel to the same extent as native lysozyme. These data were confirmed by fluorescence recovery after photobleaching experiments. This approach appeared to be highly interesting for temporary immobilization and subsequent glutathione triggered intracellular delivery of proteins from hydrogels. [Copyright &y& Elsevier]

Abstract: We investigated the preparation of ultrasound-triggered drug delivery system, based on a pendant complex of microbubble coated with liposomes. Biotinylated decafluorobutane microbubbles were coated with biotinylated liposomes via a streptavidin linker. Liposomes were prepared incorporating calcein and thrombin. Based on initial concentration of calcein, over 1um3 payload volume per each microbubble–liposome particle was achieved, when 100nm liposomes were used. Insonation of microbubble–liposome pendants in vitro resulted in the complete destruction of microbubbles and triggered release of a significant fraction of the entrapped material. Treatment with 1MHz ultrasound (5 pulses, 100ms, 7MPa peak negative acoustic pressure) resulted in the release of ~30% of entrapped calcein, as estimated by the fluorescence quenching assay. Thrombin release from liposomes complexed with microbubbles (11% of entrapped material) due to ultrasound treatment was estimated by a chromogenic substrate study. Prior to insonation, substrate hydrolysis was at background level. Ultrasound-triggered release of thrombin from the pendant complexes caused an acceleration of blood clotting. [ABSTRACT FROM AUTHOR]

Abstract: Liposomes are potent nanocarriers to deliver chemotherapeutic drugs to tumors. However, the inefficient drug release hinders their application. Thermosensitive liposomes (TSL) can release drugs upon heat. This study aims to identify the optimum 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-PEG2000 (DSPE-PEG2000) concentration in stealth TSL to improve content release efficiency under mild hyperthermia (HT). TSL were prepared with DSPE-PEG2000 from 1 to 10mol%, around 80nm in size. Quenched carboxyfluorescein (CF) in aqueous phase represented encapsulated drugs. In vitro temperature/time-dependent CF release and TSL stability in serum were quantified by fluorometry. In vivo CF release in dorsal skin flap window chamber models implanted with human BLM melanoma was captured by confocal microscopy. In vitro heat triggered CF release increased with increasing DSPE-PEG2000 density. However, 6mol% and higher DSPE-PEG2000 caused CF leakage at physiological temperature. TSL with 5mol% DSPE-PEG2000 were stable at 37°C, while released 60% CF in 1min and almost 100% CF in 1h at 42°C. In vivo optical intravital imaging showed immediate massive CF release above 41°C. In conclusion, incorporation of 5mol% DSPE-PEG2000 optimized stealth TSL content release triggered by HT. [Copyright &y& Elsevier]

Abstract: A novel proof of principle demonstration for contents release from liposomes that can be selectively activated by light irradiation is presented. The content release temperature was adjusted to slightly above body temperature, and hydrophobic or hydrophilic gold nanoparticles were incorporated into the lipid bilayer or the core of the liposomes, respectively. The release of a fluorescent marker was monitored upon exposure of the liposomes to UV light. Gold nanoparticle-containing liposomes remained intact at 37 °C but contents release was triggered by UV light-induced heating of the gold nanoparticles. This light-induced release is mediated by heat transfer from the gold nanoparticles to the lipids and subsequent phase transition. Heating is highly localized in the liposomes and the gold nanoparticles act as energy collectors that sensitize the liposomes to the light signal. This kind of selectivity is very advantageous as it can potentially make the drug delivery mechanism biologically more compatible. The triggered contents release could also be extended to other applications where local contents release is needed. [Copyright &y& Elsevier]