Thermosensitive Nanotherapeutics for Localized Photothermal Ablation of MRSA-Infected Osteomyelitis Combined with Chemotherapy

Chronic osteomyelitis is an inflammatory skeletal disease caused by a bacterial infection that affects the periosteum, bone, and bone marrow. Methicillin-resistant Staphylococcus aureus (MRSA) is the most common causative agent. The bacterial biofilm formed on the necrotic bone is a considerable challenge to treating MRSA-infected osteomyelitis. Here, we developed an all-in-one cationic thermosensitive nanotherapeutic (TLCA) for treating MRSA-infected osteomyelitis. The prepared TLCA particles were positively charged and <230 nm in size, which allowed them to diffuse effectively into the biofilm. The positive charges of the nanotherapeutic accurately targeted the biofilm, and it subsequently regulated the drug release under near-infrared (NIR) light irradiation, thereby efficiently exerting the synergistic effect of NIR light-driven photothermal sterilization and chemotherapy. More than 80% of the antibiotics were abruptly released at 50 °C, which dispersed the biofilm by up to 90%. When applied to MRSA-infected osteomyelitis, with a localized temperature of 50 °C induced by 808 nm laser irradiation, it not only eliminated the bacteria and controlled infection but also inhibited the bone tissue inflammatory response, significantly reducing TNF-α, IL-1β, and IL-6 levels. In conclusion, we constructed an all-in-one antimicrobial treatment modality that provides a new and effective strategy for the topical treatment of chronic osteomyelitis.

Preparation and Evaluation of Thermosensitive Liposomes Encapsulating I-125-Labeled Doxorubicin Derivatives for Auger Electron Therapy

Auger electrons (AEs) are very low-energy electrons emitted by radionuclides such as I-125 (¹²⁵I). This energy is deposited across a small distance (<0.5 μm), resulting in high linear energy transfer that is potent for causing lethal damage to cancer cells. Thus, AE-emitting radiotherapeutic agents have great potential for cancer treatment. In this study, thermosensitive liposomes (TSLs) encapsulating ¹²⁵I-labeled doxorubicin (DOX) derivatives were developed for Auger electron therapy, targeting the DNA of cancer cells. A radioiodinated DOX derivative [¹²⁵I]5 highly accumulated in the nuclei of cancer cells and showed potent cytotoxicity against Colon 26 cancer cells by AEs. Subsequently, [¹²⁵I]5 was loaded into the TSLs with high encapsulation efficiency. Potent release of [¹²⁵I]5 from TSLs was achieved with heating, whereas a decreased release was observed without heating. Furthermore, TSLs encapsulating [¹²⁵I]5 showed a high uptake in the nuclei at 42 °C for 1 h. We supposed that [¹²⁵I]5 was released by heating at 42 °C and accumulated in the nuclei in the cells. These results suggest that the combination of TSLs encapsulating [¹²⁵I]5 and hyperthermia is an effective cancer therapy.

NIR-Activated Thermosensitive Liposome-Gold Nanorod Hybrids for Enhanced Drug Delivery and Stimulus Sensitivity

Combinatorial photothermal therapy and chemotherapy is an extremely promising tumor therapeutic modality. However, such systems still remain challenges in stimulus sensitivity, avoiding drug leakage, and therapeutic safety. To solve these problems, we engineered actively loaded doxorubicin (DOX) and gold nanorod (GNR) liposomes through embedding stiff hollow mesoporous silica nanoparticles (HMSNs) in the liposomal water cavity (HMLGDB) to resist the influence of shear force of GNRs to prevent drug leakage. Under 808 nm laser irradiation, the ambient temperature was raised greatly because of the photothermal conversion of GNRs, thereby rupturing the lipid layer and then triggering the DOX release. The results of in vitro experiments showed that the low concentration of HMLGDB (15 μg/mL) could effectively overcome the MCF-7 cells (human breast cancer cell line) by the increase of DOX concentration intracellularly and the good photothermal effect of GNRs. After intravenous injection, HMLGDB exhibited intratumor aggregation and PTT capacity. Furthermore, the combined chemo-photothermal antitumor strategy demonstrated a high inhibition of tumor growth and low damage to normal tissues. The developed hybrids provide a paradigm for efficient combinatorial photothermal therapy (PTT) and chemotherapy (CT).

Review of the Delivery Kinetics of Thermosensitive Liposomes

Thermosensitive liposomes (TSL) are triggered nanoparticles that release the encapsulated drug in response to hyperthermia. Combined with localized hyperthermia, TSL enabled loco-regional drug delivery to tumors with reduced systemic toxicities. More recent TSL formulations are based on intravascular triggered release, where drug release occurs within the microvasculature. Thus, this delivery strategy does not require enhanced permeability and retention (EPR). Compared to traditional nanoparticle drug delivery systems based on EPR with passive or active tumor targeting (typically <5%ID/g tumor), TSL can achieve superior tumor drug uptake (>10%ID/g tumor). Numerous TSL formulations have been combined with various drugs and hyperthermia devices in preclinical and clinical studies over the last four decades. Here, we review how the properties of TSL dictate delivery and discuss the advantages of rapid drug release from TSL. We show the benefits of selecting a drug with rapid extraction by tissue, and with quick cellular uptake. Furthermore, the optimal characteristics of hyperthermia devices are reviewed, and impact of tumor biology and cancer cell characteristics are discussed. Thus, this review provides guidelines on how to improve drug delivery with TSL by optimizing the combination of TSL, drug, and hyperthermia method. Many of the concepts discussed are applicable to a variety of other triggered drug delivery systems.

Concomitant delivery of doxorubicin and cisplatin through liposome-based thermosensitive nanoparticles: perspective in the treatment of cancer in animal models

The temperature sensitive liposomal formulations are a promising tool to improve the therapeutic index of the drugs with minimal toxicity. The aim of this study was to investigate the potential of concomitant delivery of cisplatin (Cis) and doxorubicin (Dox) containing thermosensitive liposomes (TSLs) with mild hyperthermia against cancer in vitro and in vivo. The polyethylene glycol coated DPPC/DSPC, thermosensitive and DSPC, non-thermosensitive liposomes incorporating Cis and Dox were prepared and characterized. A conventional Differential Scanning Calorimetry (DSC) technique and Fourier Transform Infrared Spectroscopy (FT-IR) were applied to study drug-phospholipid interaction and compatibility. The chemotherapeutic efficacy of these formulations was evaluated in benzo[a]pyrene (BaP) induced fibrosarcoma under hyperthermic condition. The size diameter of prepared thermosensitive liposomes was measured to be 120 ± 10 nm. The DSC data exhibited the changes in the curves of DSPC + Dox and DSPC + Cis while comparing the pure DSPC and drugs. However, the FITR showed same spectrum of phospholipids and drugs individually and in the mixture as well. The data showed higher efficacy of Cis-Dox-TSL as 84% inhibition in tumor growth was recorded in this group of animals in hyperthermic condition. The Kaplan-Meir curve revealed, 100% and 80% survival of the animals in the groups treated with Cis-Dox-TSL under hyperthermia and Cis-Dox-NTSL without hyperthermia, respectively. However, Cis-TSL as well as Dox-TSL exhibited 50% survival, while only 20% survival was recorded in the groups of animals treated with Dox-NTSL and Cis-NTSL. The flow cytometry analysis revealed that Cis-Dox-NTSL augments the induction of apoptosis in the tumor cells which was recorded as 18%. As expected, Cis-Dox-TSL showed great potential as 39% of cells were measured as apoptotic cells, significantly very high in comparison to Cis-Dox-NTSL, Dox-TSL and Cis-TSL as well. The apoptotic analysis of the cells by flow cytometry clearly indicated the effect of hyperthermia during the treatment while Cis-Dox-TSL formulation was administered. Finally, the immunohistochemical analysis of the tumor tissues by confocal microscopy exhibited several fold increases in the expression of pAkt in the animals treated with vehicles in Sham-NTSL as well as Sham-TSL. However, Cis-Dox-TSL showed great reduction in the expression of Akt, as it declined by 11-fold. The results of the present study directed the role of concomitant delivery doxorubicin and cisplatin containing thermosensitive liposomes under hyperthermic conditions for the development of a novel therapeutic strategy for the treatment of cancer.

Doxorubicin Loaded Thermosensitive Magneto-Liposomes Obtained by a Gel Hydration Technique: Characterization and In Vitro Magneto-Chemotherapeutic Effect Assessment

The combination of magnetic hyperthermia with chemotherapy is considered a promising strategy in cancer therapy due to the synergy between the high temperatures and the chemotherapeutic effects, which can be further developed for targeted and remote-controlled drug release. In this paper we report a simple, rapid, and reproducible method for the preparation of thermosensitive magnetoliposomes (TsMLs) loaded with doxorubicin (DOX), consisting of a lipidic gel formation from a previously obtained water-in-oil microemulsion with fine aqueous droplets containing magnetic nanoparticles (MNPs) dispersed in an organic solution of thermosensitive lipids (transition temperature of ~43 °C), followed by the gel hydration with an aqueous solution of DOX. The obtained thermosensitive magnetoliposomes (TsMLs) were around 300 nm in diameter and exhibited 40% DOX incorporation efficiency. The most suitable MNPs to incorporate into the liposomal aqueous lumen were Zn ferrites, with a very low coercive field at 300 K (7 kA/m) close to the superparamagnetic regime, exhibiting a maximum absorption rate (SAR) of 1130 W/gFe when dispersed in water and 635 W/gFe when confined inside TsMLs. No toxicity of Zn ferrite MNPs or of TsMLs was noticed against the A459 cancer cell line after 48 h incubation over the tested concentration range. The passive release of DOX from the TsMLs after 48h incubation induced a toxicity starting with a dosage level of 62.5 ug/cm². Below this threshold, the subsequent exposure to an alternating magnetic field (20-30 kA/m, 355 kHz) for 30 min drastically reduced the viability of the A459 cells due to the release of incorporated DOX. Our results strongly suggest that TsMLs represent a viable strategy for anticancer therapies using the magnetic field-controlled release of DOX.

Aptamer-functionalized Quercetin Thermosensitive Liposomes for Targeting Drug Delivery and Antitumor Therapy

Chemo-thermotherapy, as a promising cancer combination therapy strategy, has attracted widespread attention. In this study, a novel aptamer functionalized thermosensitive liposome encapsulating hydrophobic drug quercetin was fabricated as an efficient drug delivery system. This aptamer-functionalized quercetin thermosensitive liposomes (AQTSL) combined the merits of high-loading yield, sustained drug release, long-term circulation in the body of PEGylated liposomes, passive targeting provided by 100-200 nm nanoparticles, active targeting and improved internalization effects offered by AS1411 aptamer, and temperature-responsive of quercetin release. In addition, AQTSL tail vein injection combined with 42℃ water bath heating on tumor site (AQTSL+42℃)treatment inhibited the tumor growth significantly compared with the normal saline administration (p<0.01), and the inhibition rate reached 75%. Furthermore, AQTSL+42℃ treatment also slowed down the tumor growth significantly compared with QTSL combined with 42℃ administration (p<0.05), confirming that AS1411 decoration on QTSL increased the active targeting and internalization effects of the drug delivery system, and AS1411 aptamer itself might also contribute to the tumor inhibition. These data indicate that AQTSL is a potential carrier candidate for different hydrophobic drugs and tumor targeting delivery, and this kind of targeted drug delivery system combined with temperature responsive drug release mode is expected to achieve an ideal tumor therapy effect.

Thermoresponsive Liposomes for Photo-Triggered Release of Hypericin Cyclodextrin Inclusion Complex for Efficient Antimicrobial Photodynamic Therapy

Antimicrobial strategies with high efficacy against bacterial infections are urgently needed. The development of effective therapies to control bacterial infections is still a challenge. Herein, near-infrared (NIR)-activated thermosensitive liposomes (TSL) were loaded with the NIR-dye 1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide (DiR) and the water-soluble hypericin (Hyp) β-cyclodextrin inclusion complex (Hyp-βCD). DiR and Hyp-βCD loaded thermosensitive liposomes (DHβCD-TSL) are functionalized for photothermal triggered release and synergistic photodynamic therapy to eliminate the gram-positive Staphylococcus saprophyticus. The dually active liposomes allow the production of heat and singlet oxygen species with the help of DiR and Hyp, respectively. The elevated temperature, generated by the NIR irradiation, irreversibly damages the bacterial membrane, increases the permeation, and melts the liposomes via a phase-transition mechanism, which allows the release of the Hyp-βCD complex. The photodynamic effect of Hyp-βCD eradicates the bacterial cells owing to its toxic oxygen species production. DHβCD-TSL measured the size of 130 nm with an adequate encapsulation efficiency of 81.3% of Hyp-βCD. They exhibited a phase transition temperature of 42.3 °C, while they remained stable at 37 °C, and 44% of Hyp-βCD was released after NIR irradiation (T > 47 °C). The bacterial viability dropped significantly after the synergistic treatment (>4 log₁₀), indicating that the NIR-activated TSL have immense therapeutic potential to enhance the antibacterial efficacy. The liposomes showed good biocompatibility, which was confirmed by the cellular viability of mouse fibroblasts (L929).

Macrophage membrane- and cRGD-functionalized thermosensitive liposomes combined with CPP to realize precise siRNA delivery into tumor cells

Despite the success of small interfering RNAs (siRNAs) in clinical settings, their fast clearance and poor delivery efficiency to target cells still hinder their therapeutic effect. Herein, a new treatment system was constructed by combining thermosensitive liposomes with the macrophage membrane, tumor-targeting cyclic Arg-Gly-Asp peptide, a cell-penetrating peptide, and thermotherapy. The constructed system was found to be thermosensitive and stable; the proteins were inherited from the macrophage membrane. This new system combined with thermotherapy displayed the least uptake by macrophages, the greatest uptake by HepG2 cells, the most obvious HepG2 cell apoptosis, and the strongest inhibition of Bcl-2 mRNA and Bcl-2 protein in HepG2 cells. Moreover, 24 h after system administration in tumor-bearing mice, the most prominent distribution of siRNA was observed in tumors, while almost no siRNA was found in other organs. The strongest inhibition of Bcl-2 mRNA, Bcl-2 protein, and tumors was found in mice that had received the proposed system. In summary, when using the constructed system both in vitro and in mice, less uptake by the reticuloendothelial system, greater accumulation in tumor cells, and improved therapeutic efficacy were observed. Therefore, this new system can deliver siRNA selectively and efficiently, and it is a promising therapeutic candidate for precise tumor-targeted therapy.

Untargeted Large Volume Hyperthermia Reduces Tumor Drug Uptake From Thermosensitive Liposomes

Goal: The impact of hyperthermia (HT) method on tumor drug uptake with thermosensitive liposomes (TSL) is not well understood. Methods: We created realistic three-dimensional (3-D) computer models that simulate TSL-encapsulated doxorubicin (TSL-DOX) delivery in mouse tumors with three HT methods (thermistor probe (T), laser (L) and water bath (WB), at 15 min and 60 min HT duration), with corroborating in vivo studies. Results: Average computer model-predicted tumor drug concentrations (μg/g) were 8.8(T, 15 min), 21.0(T, 60 min), 14.1(L, 15 min), 25.2(L, 60 min), 9.4(WB, 15 min), and 8.7(WB, 60 min). Tumor fluorescence was increased by 2.6 × (T) and 1.6 × (L) when HT duration was extended from 15 to 60 min (p < 0.05), with no increase for WB HT. Pharmacokinetic analysis confirmed that water bath HT causes rapid depletion of encapsulated TSL-DOX in systemic circulation due to the large heated tissue volume. Conclusions: Untargeted large volume HT causes poor tumor drug uptake from TSL.

Liposome Photosensitizer Formulations for Effective Cancer Photodynamic Therapy

Photodynamic therapy (PDT) is a promising non-invasive strategy in the fight against that which circumvents the systemic toxic effects of chemotherapeutics. It relies on photosensitizers (PSs), which are photoactivated by light irradiation and interaction with molecular oxygen. This generates highly reactive oxygen species (such as ¹O₂, H₂O₂, O₂, ·OH), which kill cancer cells by necrosis or apoptosis. Despite the promising effects of PDT in cancer treatment, it still suffers from several shortcomings, such as poor biodistribution of hydrophobic PSs, low cellular uptake, and low efficacy in treating bulky or deep tumors. Hence, various nanoplatforms have been developed to increase PDT treatment effectiveness and minimize off-target adverse effects. Liposomes showed great potential in accommodating different PSs, chemotherapeutic drugs, and other therapeutically active molecules. Here, we review the state-of-the-art in encapsulating PSs alone or combined with other chemotherapeutic drugs into liposomes for effective tumor PDT.

Effects of Surface Charge, PEGylation and Functionalization with Dipalmitoylphosphatidyldiglycerol on Liposome-Cell Interactions and Local Drug Delivery to Solid Tumors via Thermosensitive Liposomes

Purpose

Previous studies demonstrated the possibility of targeting tumor-angiogenic endothelial cells with positively charged nanocarriers, such as cationic liposomes. We investigated the active targeting potential of positively charged nanoparticles in combination with the heat-induced drug release function of thermosensitive liposomes (TSL). This novel dual-targeted approach via cationic TSL (CTSL) was thoroughly explored using either a novel synthetic phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphodiglycerol (DPPG₂) or a conventional polyethylene glycol (PEG) surface modification. Anionic particles containing either DPPG₂ or PEG were also included in the study to highlight difference in tumor enrichment driven by surface charge. With this study, we aim to provide a deep insight into the main differences between DPPG₂- and PEG-functionalized liposomes, focusing on the delivery of a well-known cytotoxic drug (doxorubicin; DOX) in combination with local hyperthermia (HT, 41–43°C).

Materials and Methods

DPPG₂- and PEG-based cationic TSLs (PG₂-CTSL/PEG-CTSL) were thoroughly analyzed for size, surface charge, and heat-triggered DOX release. Cancer cell targeting and DOX delivery was evaluated by FACS, fluorescence imaging, and HPLC. In vivo particle behavior was analyzed by assessing DOX biodistribution with local HT application in tumor-bearing animals.

Results

The absence of PEG in PG₂-CTSL promoted more efficient liposome–cell interactions, resulting in a higher DOX delivery and cancer cell toxicity compared with PEG-CTSL. By exploiting the dual-targeting function of CTSLs, we were able to selectively trigger DOX release in the intracellular compartment by HT. When tested in vivo, local HT promoted an increase in intratumoral DOX levels for all (C)TSLs tested, with DOX enrichment factors ranging from 3 to 14-fold depending on the type of formulation.

Conclusion

Cationic particles showed lower hemocompatibility than their anionic counterparts, which was partially mitigated when PEG was grafted on the liposome surface. DPPG₂-based anionic TSL showed optimal local drug delivery compared to all other formulations tested, demonstrating the potential advantages of using DPPG₂ lipid in designing liposomes for tumor-targeted applications.

Polar Lipid Fraction E from Sulfolobus acidocaldarius and Dipalmitoylphosphatidylcholine Can Form Stable yet Thermo-Sensitive Tetraether/Diester Hybrid Archaeosomes with Controlled Release Capability

Archaeosomes have drawn increasing attention in recent years as novel nano-carriers for therapeutics. The main obstacle of using archaeosomes for therapeutics delivery has been the lack of an efficient method to trigger the release of entrapped content from the otherwise extremely stable structure. Our present study tackles this long-standing problem. We made hybrid archaeosomes composed of tetraether lipids, called the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius, and the synthetic diester lipid dipalmitoylphosphatidylcholine (DPPC). Differential polarized phase-modulation and steady-state fluorometry, confocal fluorescence microscopy, zeta potential (ZP) measurements, and biochemical assays were employed to characterize the physical properties and drug behaviors in PLFE/DPPC hybrid archaeosomes in the presence and absence of live cells. We found that PLFE lipids have an ordering effect on fluid DPPC liposomal membranes, which can slow down the release of entrapped drugs, while PLFE provides high negative charges on the outer surface of liposomes, which can increase vesicle stability against coalescence among liposomes or with cells. Furthermore, we found that the zeta potential in hybrid archaeosomes with 30 mol% PLFE and 70 mol% DPPC (designated as PLFE/DPPC(3:7) archaeosomes) undergoes an abrupt increase from −48 mV at 37 °C to −16 mV at 44 °C (termed the ZP transition), which we hypothesize results from DPPC domain melting and PLFE lipid ‘flip-flop’. The anticancer drug doxorubicin (DXO) can be readily incorporated into PLFE/DPPC(3:7) archaeosomes. The rate constant of DXO release from PLFE/DPPC(3:7) archaeosomes into Tris buffer exhibited a sharp increase (~2.5 times), when the temperature was raised from 37 to 42 °C, which is believed to result from the liposomal structural changes associated with the ZP transition. This thermo-induced sharp increase in drug release was not affected by serum proteins as a similar temperature dependence of drug release kinetics was observed in human blood serum. A 15-min pre-incubation of PLFE/DPPC(3:7) archaeosomal DXO with MCF-7 breast cancer cells at 42 °C caused a significant increase in the amount of DXO entering into the nuclei and a considerable increase in the cell’s cytotoxicity under the 37 °C growth temperature. Taken together, our data suggests that PLFE/DPPC(3:7) archaeosomes are stable yet potentially useful thermo-sensitive liposomes wherein the temperature range (from 37 to 42–44 °C) clinically used for mild hyperthermia treatment of tumors can be used to trigger drug release for medical interventions.

Thermosensitive Exosome-Liposome Hybrid Nanoparticle-Mediated Chemoimmunotherapy for Improved Treatment of Metastatic Peritoneal Cancer

Metastatic peritoneal carcinoma (mPC) is a deadly disease without effective treatment. To improve treatment of this disease, a recently developed hyperthermic intraperitoneal chemotherapy (HIPEC) has emerged as the standard of care. However, the efficacy of this approach is limited by inefficient drug penetration and rapidly developed drug resistance. Herein, a nanotechnology approach is reported that is designed to improve drug delivery to mPC and to augment the efficacy of HIPEC through delivery of chemoimmunotherapy. First, the drug delivery efficiency of HIPEC is determined and it is found that chemotherapy agents cannot be efficiently delivered to large tumors nodules. To overcome the delivery hurdle, genetically engineered exosomes-thermosensitive liposomes hybrid NPs, or gETL NPs, are then synthesized, and it is demonstrated that the NPs after intravenous administration efficiently penetrates into mPC tumors and releases payloads at the hypothermia condition of HIPEC. Last, it is shown that, when granulocyte-macrophage colony-stimulating factor (GM-CSF) and docetaxel are co-delivered, gETL NPs effectively inhibit tumor development and the efficacy is enhanced when HIPEC is co-administered. The study provides a strategy to improve drug delivery to mPCs and offers a promising approach to improve treatment of the disease through combination of locoregional delivery of HIPEC and systemic delivery of chemoimmunotherapy via gETL NPs.

Indocyanine Green-Parthenolide Thermosensitive Liposome Combination Treatment for Triple-Negative Breast Cancer

Background

Certain patients with triple-negative breast cancer cannot tolerate the serious adverse effects of cytotoxic chemotherapy agents, which significantly affect the disease prognosis.

Purpose

Research into the combined use of photosensitizers and non-cytotoxic antineoplastic drugs for the safe treatment of triple-negative breast cancer is vital.

Methods

In this study, the photosensitizer indocyanine green and the natural drug parthenolide were co-loaded into thermosensitive liposomes. Under a near-infrared irradiation, indocyanine green reached excitation levels, releasing heat, and the liposome underwent a phase transition, releasing the drug were researched.

Results

Thus, indocyanine green and parthenolide exert synergistic antineoplastic effects. In the nude mice xenograft MDA-MB-231 tumor model, the tumor inhibition rate of indocyanine green-parthenolide thermosensitive liposomes was approximately 2.08-fold than that of paclitaxel and demonstrated a good initial safety evaluation.

Conclusion

Photosensitizers and non-cytotoxic antineoplastic agents in combination with nanoscale carriers should be further investigated for the treatment of tumors.

Real-time fluorescence imaging for visualization and drug uptake prediction during drug delivery by thermosensitive liposomes

Objective: Thermosensitive liposomal doxorubicin (TSL-Dox) is a promising stimuli-responsive nanoparticle drug delivery system that rapidly releases the contained drug in response to hyperthermia (HT) (>40 °C). Combined with localized heating, TSL-Dox allows highly localized delivery. The goals of this study were to demonstrate that real-time fluorescence imaging can visualize drug uptake during delivery, and can predict tumor drug uptake. Methods: Nude mice carrying subcutaneous tumors (Lewis lung carcinoma) were anesthetized and injected with TSL-Dox (5 mg/kg dose). Localized HT was induced by heating tumors for 15, 30 or 60 min via a custom-designed HT probe placed superficially at the tumor location. In vivo fluorescence imaging (excitation 523 nm, emission 610 nm) was performed before, during, and for 5 min following HT. After imaging, tumors were extracted, drug uptake was quantified by high-performance liquid chromatography, and correlated with in vivo fluorescence. Plasma samples were obtained before and after HT to measure TSL-Dox pharmacokinetics. Results: Local drug uptake could be visualized in real-time during HT. Compared to unheated control tumors, fluorescence of heated tumors increased by 4.6-fold (15 min HT), 9.3-fold (30 min HT), and 13.2-fold (60 min HT). HT duration predicted tumor drug uptake (p = .02), with tumor drug concentrations of 4.2 ± 1.3 µg/g (no HT), 7.1 ± 5.9 µg/g (15 min HT), 14.1 ± 6.7 µg/g (30 min HT) and 21.4 ± 12.6 µg/g (60 min HT). There was good correlation (R² = 0.67) between fluorescence of the tumor region and tumor drug uptake. Conclusions: Real-time in vivo fluorescence imaging can visualize drug uptake during delivery, and can predict tumor drug uptake.

Sonosensitive MRI Nanosystems as Cancer Theranostics: A Recent Update

In the tireless search for innovative and more efficient cancer therapies, sonosensitive Magnetic Resonance Imaging (MRI) agents play an important role. Basically, these systems consist of nano/microvesicles composed by a biocompatible membrane, responsive to ultrasound-induced thermal or mechanical effects, and an aqueous core, filled up with a MRI detectable probe and a therapeutic agent. They offer the possibility to trigger and monitor in real time drug release in a spatio-temporal domain, with the expectation to predict the therapeutic outcome. In this review, the key items to design sonosensitive MRI agents will be examined and an overview on the different approaches available so far will be given. Due to the extremely wide range of adopted ultrasound settings and formulations conceived, it is hard to compare the numerous preclinical studies reported. However, in general, a significantly better therapeutic outcome was noticed when exploiting ultrasound triggered drug release in comparison to traditional therapies, thus paving the way to the possible clinical translation of optimized sonosensitive MRI agents.

Nanoplatform Assembled from a CD44-Targeted Prodrug and Smart Liposomes for Dual Targeting of Tumor Microenvironment and Cancer Cells

The tumor microenvironment (TME) plays a critical role in tumor initiation, progression, invasion, and metastasis. Therefore, a therapy that combines chemotherapeutic drugs with a TME modulator could be a promising route for cancer treatment. This paper reports a nanoplatform self-assembled from a hyaluronic acid (HA)-paclitaxel (PTX) (HA-PTX) prodrug and marimastat (MATT)-loaded thermosensitive liposomes (LTSLs) (MATT-LTSLs) for the dual targeting of the TME and cancer cells. Interestingly, the prodrug HA-PTX can self-assemble on both positively and negatively charged liposomes, forming hybrid nanoparticles (HNPs, 100 nm). Triggered by mild hyperthermia, HA-PTX/MATT-LTSLs HNPs rapidly release their payloads into the extracellular environment, and the released HA-PTX quickly enters 4T1 cells through a CD44-HA affinity. The HNPs possess promoted tumor accumulation (1.6-fold), exhibit deep tumor penetration, and significantly inhibit the tumor growth (10-fold), metastasis (100%), and angiogenesis (10-fold). Importantly, by targeting the TME and maintaining its integrity via inhibiting the expression and activity of matrix metalloproteinases (>5-fold), blocking the fibroblast activation by downregulating the TGF-β1 expression (5-fold) and suppressing the degradation of extracellular matrix, the HNPs allow for significant metastasis inhibition. Overall, these findings indicate that a prodrug of an HA-hydrophobic-active compound and liposomes can be self-assembled into a smart nanoplatform for the dual targeting of the TME and tumor cells and efficient combined treatment; additionally, the co-delivery of MATT and HA-PTX with the HNPs is a promising approach for the treatment of metastatic cancer. This study creates opportunities for fabricating multifunctional nanodevices and offers an efficient strategy for disease therapy.

Theranostic Nanoplatform: Triple-Modal Imaging-Guided Synergistic Cancer Therapy Based on Liposome-Conjugated Mesoporous Silica Nanoparticles

Mesoporous silica nanoparticles (MSNs) have long since been investigated to provide a versatile drug-delivery platform due to their multitudinous merits. Presently, gadolinium (Gd), a T1 magnetic resonance imaging (MRI) contrast agent, was doped into MSNs as a newly emerging theranostic nanocomposite, which has received much research attention. However, it is still concerned about the dispersibility and drug leakage of MSNs. Hence, in this project, we constructed an near-infrared (NIR) irradiation-triggered, triple-modal imaging-guided nanoplatform based on doxorubicin (DOX)@Gd-doped MSNs, conjugating with indocyanine green (ICG)-loaded thermosensitive liposomes (designated as DOX@GdMSNs-ICG-TSLs). In this platform, ICG could contribute to both photodynamic therapy and photothermal therapy effects; meanwhile, it could also give play to near-infrared fluorescence imaging (NIRFI) as well as photoacoustic imaging (PAI). Consequently, NIRFI and PAI from ICG combined with the MRI function of Gd, devoted to triple-modal imaging with success. At the same time, folic acid-modified thermosensitive liposomes were explored to be coated onto the surface of DOX@GdMSNs, to solve the DOX leakage as well as improve cellular uptake. Under NIR irradiation, ICG could generate heat, thus leading to the rupture of ICG-TSLs and the release of DOX. Accordingly, the multifunctional nanocomposite appeared to be a promising meritorious theranostic nanoplatform to pave a way for treating cancer.

Drug release kinetics of temperature sensitive liposomes measured at high-temporal resolution with a millifluidic device

PURPOSE

Current release assays have inadequate temporal resolution ( ∼ 10 s) to characterise temperature sensitive liposomes (TSL) designed for intravascular triggered drug release, where release within the first few seconds is relevant for drug delivery.

MATERIALS AND METHODS

We developed a novel release assay based on a millifluidic device. A 500 µm capillary tube was heated by a temperature-controlled Peltier element. A TSL solution encapsulating a fluorescent compound was pumped through the tube, producing a fluorescence gradient along the tube due to TSL release. Release kinetics were measured by analysing fluorescence images of the tube. We measured three TSL formulations: traditional TSL (DPPC:DSPC:DSPE-PEF2000,80:15:5), MSPC-LTSL (DPPC:MSPC:DSPE-PEG2000,85:10:5) and MPPC-LTSL (DPPC:MMPC:PEF2000,86:10:4). TSL were loaded with either carboxyfluorescein (CF), Calcein, tetramethylrhodamine (TMR) or doxorubicin (Dox). TSL were diluted in one of the four buffers: phosphate buffered saline (PBS), 10% bovine serum albumin (BSA) solution, foetal bovine serum (FBS) or human plasma. Release was measured between 37-45 °C.

RESULTS

The millifluidic device allowed measurement of release kinetics within the first few seconds at ∼5 ms temporal resolution. Dox had the fastest release and highest release %, followed by CF, Calcein and TMR. Of the four buffers, release was fastest in human plasma, followed by FBS, BSA and PBS.

CONCLUSIONS

The millifluidic device allows measurement of TSL release at unprecedented temporal resolution, thus allowing adequate characterisation of TSL release at time scales relevant for intravascular triggered drug release. The type of buffer and encapsulated compound significantly affect release kinetics and need to be considered when designing and evaluating novel TSL-drug combinations.

Thermosensitive Liposomal Codelivery of HSA-Paclitaxel and HSA-Ellagic Acid Complexes for Enhanced Drug Perfusion and Efficacy Against Pancreatic Cancer

Fibrotic stroma and tumor-promoting pancreatic stellate cells (PSCs), critical characters in the pancreatic ductal adenocarcinoma (PDA) microenvironment, promote a tumor-facilitating environment that simultaneously prevents drug penetration into tumor foci and stimulates tumor growth. Nab-PTX, a human serum albumin (HSA) nanoparticle of paclitaxel (PTX), indicates enhanced matrix penetration in PDA probably due to its small size in vivo and high affinity of HSA with secreted protein acidic and rich in cysteine (SPARC), overexpressed in the PDA stroma. However, this HSA nanoparticle shows poor drug blood retention because of its weak colloidal stability in vivo, thus resulting in insufficient drug accumulation within tumor. Encapsulating HSA nanoparticles into the internal aqueous phase of ordinary liposomes improves their blood retention and the following tumor accumulation, but the large 200 nm size and shielding of HSA in the interior might make it difficult for this hybrid nanomedicine to penetrate the fibrotic PDA matrix and promote bioavailability of the payload. In our current work, we prepared ∼9 nm HSA complexes with an antitumor drug (PTX) and an anti-PSC drug (ellagic acid, EA), and these two HSA-drug complexes were further coencapsulated into thermosensitive liposomes (TSLs). This nanomedicine was named TSL/HSA-PE. The use of TSL/HSA-PE could improve drug blood retention, and upon reaching locally heated tumors, these TSLs can rapidly release their payloads (HSA-drug complexes) to facilitate their further tumor accumulation and matrix penetration. With superior tumor accumulation, impressive matrix penetration, and simultaneous action upon tumor cells and PSCs to disrupt PSCs-PDA interaction, TSL/HSA-PE treatment combined with heat exhibited strong tumor growth inhibition and apoptosis in vivo.

Focused Ultrasound Hyperthermia Mediated Drug Delivery Using Thermosensitive Liposomes and Visualized With in vivo Two-Photon Microscopy

The future of nanomedicines in oncology requires leveraging more than just the passive drug accumulation in tumors through the enhanced permeability and retention effect. Promising results combining mild hyperthermia (HT) with lyso-thermosensitive liposomal doxorubicin (LTSL-DOX) has led to improved drug delivery and potent antitumor effects in pre-clinical studies. The ultimate patient benefit from these treatments can only be realized when robust methods of HT can be achieved clinically. One of the most promising methods of non-invasive HT is the use of focused ultrasound (FUS) with MRI thermometry for anatomical targeting and feedback. MRI-guided focused ultrasound (MRgFUS) is limited by respiratory motion and large blood vessel cooling. In order to translate exciting pre-clinical results to the clinic, novel heating approaches capable of overcoming the limitations on clinical MRgFUS+HT must be tested and evaluated on their ability to locally release drug from LTSL-DOX.

Methods: In this work, a new system is described to integrate focused ultrasound (FUS) into a two-photon microscopy (2PM) setting to image the release of drug from LTSL-DOX in real-time during FUS+HT in vivo. A candidate scheme for overcoming the limitations of respiratory motion and large blood vessel cooling during MRgFUS+HT involves applying FUS+HT to 42°C in short ~30s bursts. The spatiotemporal drug release pattern from LTSL-DOX as a result is quantified using 2PM and compared against continuous (3.5min and 20min at 42°C) FUS+HT schemes and unheated controls.

Results: It was observed for the first time in vivo that these short duration temperature elevations could produce substantial drug release from LTSL-DOX. Ten 30s bursts of FUS+HT was able to achieve almost half of the interstitial drug concentration as 20min of continuous FUS+HT. There was no significant difference between the intravascular area under the concentration-time curve for ten 30s bursts of FUS+HT and 3.5min of continuous FUS+HT.

Conclusion: We have successfully combined 2PM with FUS+HT for imaging the release of DOX from LTSL-DOX in vivo in real-time, which will permit the investigation of FUS+HT heating schemes to improve drug delivery from LTSL-DOX. We have evaluated the ability to release DOX in short 30s FUS+HT bursts to 42°C as a method to overcome limitations on clinical MRgFUS+HT and have found that such exposures are capable of releasing measurable amounts of drug. Such an exposure has the potential to overcome limitations that hamper conventional MRgFUS+HT treatments in targets that are associated with substantial tissue motion.

Therapeutic Efficacy of Cisplatin Thermosensitive Liposomes upon Mild Hyperthermia in C26 Tumor Bearing BALB/c Mice

This study reports on the activity of thermosensitive liposomes (TSLs) incorporating different HSPC ratios in DPPC/MSPC/PEG₂₀₀₀-DSPE matrix (90/10/4) plus mild hyperthermia (HT) (42 °C). TSLs were loaded with a poorly membrane permeable anticancer drug, cisplatin, through the passive equilibration method. The addition of HSPC to the corresponding DPPC lipid matrix increased the transition temperature. In vitro data demonstrated >90% cisplatin leakage from nanosized DPPC 90-lyso-TSL (LTSL) within 10 min at 42 °C, while other TSLs bearing HSPC showed greater stability. The plasma kinetics of cisplatin demonstrated higher cisplatin leakage from DPPC 90-LTSL in the first 4 h (from 17.4 to 0.4 μg/mL) compared to other formulations. Indeed, increasing HSPC fraction in liposome bilayers significantly improved drug retention in blood. Though DPPC 90-LTSL plus one-step HT was expected to provide a unique drug release, the premature drug leakage as well as the likely wash-back of a great portion of drug into the blood circulation resulted in reduced survival. On the other hand, stabilized DPPC 30/HSPC 60/MSPC 10/PEG₂₀₀₀-DSPE 4 liposomes plus two-step HT greatly enhanced the survival of animals. In particular, the improved delivery of cisplatin through stabilized DPPC 30/HSPC 60/MSPC 10/PEG₂₀₀₀-DSPE 4 liposomes in two-step mild HT enhanced antitumor efficacy compared to other formulations. Thus, prolonged exposure of cancer cells to cisplatin through stabilized liposomes would be an efficient approach in improving the survival of animals.

A pilot trial of doxorubicin containing phosphatidyldiglycerol based thermosensitive liposomes in spontaneous feline soft tissue sarcoma

PURPOSE

Doxorubicin (DOX)-loaded phosphatidyldiglycerol-based thermosensitive liposomes (DPPG₂-TSL-DOX) combined with local hyperthermia (HT) was evaluated in cats with locally advanced spontaneous fibrosarcomas (soft tissue sarcoma [STS]). The study was designed to evaluate the safety and pharmacokinetic profile of the drug. Results from four dose-levels are reported.

METHODS

Eleven client-owned cats with advanced STS were enrolled. Five cats received escalating doses of 0.1-0.4 mg/kg DOX (group I), three received 0.4 mg/kg constantly (group II) and three 0.6 mg/kg (group III) IV over 15 min. HT with a target temperature of 41.5 °C was started 15 min before drug application and continued for a total of 60 min. Six HT treatments were applied every other week using a radiofrequency applicator. Tumour growth was monitored by magnetic resonance imaging (MRI) and for dose level III also with ¹⁸F-FDG PET.

RESULTS

Treatment was generally well tolerated and reasons for premature study termination in four cats were not associated with drug-induced toxicity. No DPPG₂-TSL-DOX based hypersensitivity reaction was observed. One cat showed simultaneous partial response (PR) in MRI and positron emission tomography (PET) whereas one cat showed stable disease in MRI and PR in PET (both cats in dose level III). Pharmacokinetic measurements demonstrated DOX release triggered by HT.

CONCLUSION

DPPG₂-TSL-DOX + HT is a promising treatment option for advanced feline STS by means of targeted drug delivery. As MTD was not reached further investigation is warranted to determine if higher doses would result in even better tumour responses.

Thermosensitive liposomal cisplatin in combination with local hyperthermia results in tumor growth delay and changes in tumor microenvironment in xenograft models of lung carcinoma

Treatment efficacy of a heat-activated thermosensitive liposome formulation of cisplatin (CDDP), known as HTLC, was determined in xenograft models of non-small-cell lung carcinoma. The short-term impact of local hyperthermia (HT) on tumor morphology, microvessel density and local inflammatory response was also evaluated. The HTLC formulation in combination with local HT resulted in a significant advantage in therapeutic effect in comparison with free drug and a non-thermosensitive liposome formulation of CDDP (i.e. Lipoplatin^TM) when administered at their maximum tolerated doses. Local HT-induced widespread cell necrosis and a significant reduction in microvessel density in the necrotic regions of tumors. CD11b-expressing innate leukocytes were demonstrated to infiltrate and reside preferentially at the necrotic rim of tumors, likely as a means to phagocytose-damaged tissue. Colocalization of CD11b with a marker of DNA damage (i.e. γH2AX) revealed a small portion of CD11b-expressing leukocytes that were possibly undergoing apoptosis as a result of HT-induced damage and/or the short lifespan of leukocytes. Overall, HT-induced tissue damage (i.e. at 24-h post-treatment) alone did not result in significant improvements in treatment effect, rather, the enhancement in tumor drug availability was correlated with improved therapeutic outcomes.

Thermosensitive, near-infrared-labeled nanoparticles for topotecan delivery to tumors

Liposomal nanoparticles have proven to be versatile systems for drug delivery. However, the progress in clinic has been slower and less efficient than expected. This suggests a need for further development using carefully designed chemical components to improve usefulness under clinical conditions and maximize therapeutic effect. For cancer chemotherapy, PEGylated liposomes were the first nanomedicine to reach the market and have been used clinically for several years. Approaches toward targeted drug delivery using next generation "thermally triggered" nanoparticles are now in clinical trials. However, clinically tested thermosensitive liposomes (TSLs) lack the markers that allow tumor labeling and improved imaging for tissue specific applied hyperthermia. Here we describe the development of optically labeled TSLs for image guidance drug delivery and proof-of-concept results for their application in the treatment of murine xenograft tumors using the anticancer drug topotecan. These labeled TSLs also allow the simultaneous, real-time diagnostic imaging of nanoparticle biodistribution using a near-infrared (NIR; 750-950 nm) fluorophore coupled to a lipidic component of the lipid bilayer. When combined with multispectral fluorescence analysis, this allows for specific and high sensitivity tracking of the nanoparticles in vivo. The application of NIR fluorescence-labeled TSLs could have a transformative effect on future cancer chemotherapy.

Focused ultrasound influence on calcein-loaded thermosensitive stealth liposomes

Focused ultrasound (FUS) is a versatile technology for non-invasive thermal therapies in oncology. Indeed, this technology has great potential for local heat-mediated drug delivery from thermosensitive liposomes (TSLs), thus improving therapeutic efficacy and reducing toxicity profiles. In the present study we evaluated the influence of FUS parameters on the release of calcein from TSLs used to model a hydrophilic drug. Quantitative calcein release from TSLs (DPPC/CHOL/DSPE-PEG2000: 90/5/5) and non-thermosensitive liposomes (NTSLs) (DPPC/CHOL/DSPE-PEG2000: 65/30/5) was measured by spectrofluorimetry after both water bath and FUS-induced in vitro heating. The heating of TSLs at 42 °C in a water bath resulted in a maximum calcein release of 45%. No additional calcein release was observed at temperatures above 42 °C. A similar percentage of calcein release was achieved when TSLs were exposed to 1 MHz sinusoidal waves at peak negative pressure of 1.5 MPa, 40% duty cycle, for 10 min (i.e. above 42 °C). No release was detected when NTSLs were heated in a water bath. For both TSLs and NTSLs, the calcein release was increased by more than 10% for acoustic pressures ranging from 1.5 MPa to 2 MPa. This additional release was attributed to the mechanical stress generated by FUS, which was sufficient to disrupt the liposomal membrane. Furthermore, analysis of cryo-TEM images showed a significant decrease in liposome size (14%) induced by the thermal effect, whereas the liposome diameter remained unaffected by the FUS-triggered non-thermal effects.

Thermosensitive liposomal drug delivery systems: state of the art review

Thermosensitive liposomes are a promising tool for external targeting of drugs to solid tumors when used in combination with local hyperthermia or high intensity focused ultrasound. In vivo results have demonstrated strong evidence that external targeting is superior over passive targeting achieved by highly stable long-circulating drug formulations like PEGylated liposomal doxorubicin. Up to March 2014, the Web of Science listed 371 original papers in this field, with 45 in 2013 alone. Several formulations have been developed since 1978, with lysolipid-containing, low temperature-sensitive liposomes currently under clinical investigation. This review summarizes the historical development and effects of particular phospholipids and surfactants on the biophysical properties and in vivo efficacy of thermosensitive liposome formulations. Further, treatment strategies for solid tumors are discussed. Here we focus on temperature-triggered intravascular and interstitial drug release. Drug delivery guided by magnetic resonance imaging further adds the possibility of performing online monitoring of a heating focus to calculate locally released drug concentrations and to externally control drug release by steering the heating volume and power. The combination of external targeting with thermosensitive liposomes and magnetic resonance-guided drug delivery will be the unique characteristic of this nanotechnology approach in medicine.

Targeting chemotherapy to solid tumors with long-circulating thermosensitive liposomes and local hyperthermia

The effectiveness of the combination of long-circulating, thermosensitive liposomes and hyperthermia is described. Small-sized, thermosensitive liposomes that encapsulate doxorubicin (DXR-PEG-TSL (SUV)) have a prolonged circulation time and are extravasated to targeted solid tumors in vivo, where they preferentially release the agent in an anatomical site subjected to local hyperthermia. Liposomes were prepared by the incorporation of amphipathic polyethyleneglycol (PEG) to prolong their circulation time. DXR-PEG-TSL (SUV) was retained longest and was accumulated most efficiently in solid tumors in Balb/c mice. The combination of DXR-PEG-TSL (SUV) and hyperthermia at the tumor sites 3 h after injection, gave high concentrations of doxorubicin in tumor tissue and resulted in more effective tumor retardation and increased survival time. A large amount of DXR-PEG-TSL (SUV) was extravasated into the tumors during circulation for 3 h after injection, suggesting that the encapsulated drug was released into the interstitial spaces of the lesions by local hyperthermia. This system is expected to be clinically valuable for the delivery of a wide range of chemotherapeutic agents in the treatment of solid tumors.