Pharmacokinetics & tissue distribution of temperature-sensitive liposomal doxorubicin in tumor-bearing mice triggered with mild hyperthermia

Pre-mixing of omega-3 fatty acid-containing liposomes enhances the drug release rate and therapeutic efficacy of anticancer drugs loaded in liposomes

The therapeutic efficacy of anticancer drugs loaded in liposomes composed of rigid phosphatidylcholine (PC) is hindered by the limited release of these drugs at the tumor site, which in turn hampers delivery of the drug to its intracellular target. In an attempt to improve the therapeutic efficacy of liposomal anticancer drugs, we here explored the use of empty liposomes as "trigger" vehicles to induce drug release from drug-loaded liposomes through liposome-liposome interactions. Empty liposomes containing PC in which omega-3 fatty acids comprised both fatty acid strands (Omega-L) showed a triggering effect on drug release from doxorubicin (DOX)-loaded liposomes (Caelyx). The effectiveness of this triggered-release effect was dependent on the Omega-L composition as well as the mixing ratio of Omega-L to Caelyx. Cryo-TEM and differential calorimetry studies revealed that the Omega-L effect was associated with liposome-liposome interactions that led to loosened membrane packing and increased fluidity of Caelyx. In cultured cells, the intracellular/intranuclear DOX uptake and anticancer efficacy of Caelyx was greatly improved by Omega-L pre-mixing. Intravenous injection of rats with Caelyx, premixed with Omega-L, decreased the area under the plasma concentration-time curve from time zero to time infinity and increased clearance without significantly changing the mean residence time or terminal half-life of DOX compared with Caelyx alone. Ex vivo bioimaging showed that DOX fluorescence in tumors, but not in other organs, was significantly increased by Omega-L premixing. In the mouse xenograft model, premixing of Omega-L with Caelyx suppressed tumor growth 2.5-fold compared with Caelyx. Collectively, the data provide preliminary evidence that the Omega-L-triggered drug release that occurs before and after dosing, particularly at tumor site, improved the therapeutic efficacy of Caelyx. The simple approach described here could enhance the therapeutic value of Caelyx and other anticancer drug-loaded liposomes.

Co-Loading of Black Phosphorus Nanoflakes and Doxorubicin in Lysolipid Temperature-Sensitive Liposomes for Combination Therapy in Prostate Cancer

Black phosphorus (BP) is one of the most promising nanomaterials for cancer therapy. This 2D material is biocompatible and has strong photocatalytic activity, making it a powerful photosensitiser for combined NIR photothermal and photodynamic therapies. However, the fast degradation of BP in oxic conditions (including biological environments) still limits its use in cancer therapy. This work proposes a facile strategy to produce stable and highly concentrated BP suspensions using lysolipid temperature-sensitive liposomes (LTSLs). This approach also allows for co-encapsulating BP nanoflakes and doxorubicin, a potent chemotherapeutic drug. Finally, we demonstrate that our BP/doxorubicin formulation shows per se high antiproliferative action against an in vitro prostate cancer model and that the anticancer activity can be enhanced through NIR irradiance.

Doxorubicin and other anthracyclines in cancers: Activity, chemoresistance and its overcoming

Anthracyclines have been important and effective treatments against a number of cancers since their discovery. However, their use in therapy has been complicated by severe side effects and toxicity that occur during or after treatment, including cardiotoxicity. The mode of action of anthracyclines is complex, with several mechanisms proposed. It is possible that their high toxicity is due to the large set of processes involved in anthracycline action. The development of resistance is a major barrier to successful treatment when using anthracyclines. This resistance is based on a series of mechanisms that have been studied and addressed in recent years. This work provides an overview of the anthracyclines used in cancer therapy. It discusses their mechanisms of activity, toxicity, and chemoresistance, as well as the approaches used to improve their activity, decrease their toxicity, and overcome resistance.

Pharmacokinetic behaviors of soft nanoparticulate formulations of chemotherapeutics

Chemotherapeutic treatment with conventional drug formulations pose numerous challenges, such as poor solubility, high cytotoxicity and serious off-target side effects, low bioavailability, and ultimately subtherapeutic tumoral concentration leading to poor therapeutic outcomes. In the field of Nanomedicine, advances in nanotechnology have been applied with great success to design and develop novel nanoparticle-based formulations for the treatment of various types of cancer. The approval of the first nanomedicine, Doxil® (liposomal doxorubicin) in 1995, paved the path for further development for various types of novel delivery platforms. Several different types of nanoparticles, especially organic (soft) nanoparticles (liposomes, polymeric micelles, and albumin-bound nanoparticles), have been developed and approved for several anticancer drugs. Nanoparticulate drug delivery platform have facilitated to overcome of these challenges and offered key advantages of improved bioavailability, higher intra-tumoral concentration of the drug, reduced toxicity, and improved efficacy. This review introduces various commonly used nanoparticulate systems in biomedical research and their pharmacokinetic (PK) attributes, then focuses on the various physicochemical and physiological factors affecting the in vivo disposition of chemotherapeutic agents encapsulated in nanoparticles in recent years. Further, it provides a review of the current landscape of soft nanoparticulate formulations for the two most widely investigated anticancer drugs, paclitaxel, and doxorubicin, that are either approved or under investigation. Formulation details, PK profiles, and therapeutic outcomes of these novel strategies have been discussed individually and in comparison, to traditional formulations. This article is categorized under: Nanotechnology Approaches to Biology > Cells at the Nanoscale Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Triggered release from thermosensitive liposomes improves tumor targeting of vinorelbine

Triggered drug delivery strategies have been shown to enhance drug accumulation at target diseased sites in comparison to administration of free drug. In particular, many studies have demonstrated improved targetability of chemotherapeutics when delivered via thermosensitive liposomes. However, most studies continue to focus on encapsulating doxorubicin while many other drugs would benefit from this targeted and localized delivery approach. The proposed study explores the therapeutic potential of a thermosensitive liposome formulation of the commonly used chemotherapy drug vinorelbine in combination with mild hyperthermia (39-43 °C) in a murine model of rhabdomyosarcoma. Rhabdomyosarcoma, the most common soft tissue sarcoma in children, is largely treated using conventional chemotherapy which is associated with significant adverse long-term sequelae. In this study, mild hyperthermia was pursued as a non-invasive, non-toxic means to improve the efficacy and safety profiles of vinorelbine. Thorough assessment of the pharmacokinetics, biodistribution, efficacy and toxicity of vinorelbine administered in the thermosensitive liposome formulation was compared to administration in a traditional, non-thermosensitive liposome formulation. This study shows the potential of an advanced formulation technology in combination with mild hyperthermia as a means to target an untargeted therapeutic agent and result in a significant improvement in its therapeutic index.

A Novel Method for the Preparation of Poly (Acrylamide−co−Acrylonitrile) Upper Critical Solution Temperature Thermosensitive Hydrogel by the Partial Dehydration of Acrylamide Grafted Polypropylene Sheets

In an attempt to find a potential application of cell culture harvesting, a novel method for the preparation of an upper critical solution temperature (UCST) thermosensitive hydrogel was studied. An electron accelerator was used as the electron beam (EB) radiation source, and acrylamide (AAm) was first grafted onto the pre-irradiated polypropylene (PP) sheet. Then, the grafting layer of poly (acrylamide-co-acrylonitrile) (P (AAm-co-AN)) was obtained by the partial dehydration of the acylamino group into the cyano group in the solution mixture of sulfoxide chloride (SOCl₂) and dimethyl formamide (DMF). The effects of the absorbed dose, AAm concentration, reaction time, and temperature on the degree of grafting were studied, respectively. The effect of the SOCl₂ concentration on the conversion degree of the cyano group from the acylamino group was studied, followed by the temperature of the UCST. The UCST properties of the grafted samples with P (AAm-co-AN) were studied by quartz crystal microbalance (QCM) and atomic force microscope (AFM), respectively. The cytotoxicities of the hydrogels against cells were verified by CCK-8 studies.

Encapsulation of doxorubicin prodrug in heat-triggered liposomes overcomes off-target activation for advanced prostate cancer therapy

L-377,202 prodrug consists of doxorubicin (Dox) conjugated to a prostate-specific antigen (PSA) peptide substrate that can be cleaved by enzymatically active PSA at the tumor site. Despite the initial promise in phase I trial, further testing of L-377,202 (herein called Dox-PSA) was ceased due to some degree of non-specific activation and toxicity concerns. To improve safety of Dox-PSA, we encapsulated it into low temperature-sensitive liposomes (LTSL) to bypass systemic activation, while maintaining its biological activity upon controlled release in response to mild hyperthermia (HT). A time-dependent accumulation of activated prodrug in the nuclei of PSA-expressing cells exposed to mild HT was observed, showing that Dox-PSA was efficiently released from the LTSL, cleaved by PSA and entering the cell nucleus as free Dox. Furthermore, we have shown that Dox-PSA loading in LTSL can block its biological activity at 37°C, while the combination with mild HT resulted in augmented cytotoxicity in both 2D and 3D PC models compared to the free Dox-PSA. More importantly, Dox-PSA encapsulation in LTSL prolonged its blood circulation and reduced Dox accumulation in the heart of C4-2B tumor-bearing mice over the free Dox-PSA, thus significantly improving Dox-PSA therapeutic window. Finally, Dox-PSA-loaded LTSL combined with HT significantly delayed tumor growth at a similar rate as mice treated with free Dox-PSA in both solid and metastatic PC tumor models. This indicates this strategy could block the systemic cleavage of Dox-PSA without reducing its efficacy in vivo, which could represent a safer option to treat patients with locally advanced PC. STATEMENT OF SIGNIFICANCE: This study investigates a new tactic to tackle non-specific cleavage of doxorubicin PSA-activatable prodrug (L-377,202) to treat advanced prostate cancer. In the present study, we report a nanoparticle-based approach to overcome the non-specific activation of L-377,202 in the systemic circulation. This includes encapsulating Dox-PSA in low temperature-sensitive liposomes to prevent its premature hydrolysis and non-specific cleavage. This class of liposomes offers payload protection against degradation in plasma, improved pharmacokinetics and tumor targeting, and an efficient and controlled drug release triggered by mild hyperthermia (HT) (∼42°C). We believe that this strategy holds great promise in bypassing any systemic toxicity concerns that could arise from the premature activation of the prodrug whilst simultaneously being able to control the spatiotemporal context of Dox-PSA cleavage and metabolism.

Doxorubicin nanoformulations on therapy against cancer: An overview from the last 10 years

Doxorubicin (DOX) is a natural antibiotic with antineoplastic activity. It has been used for over 40 years and remains one of the most used drugs in chemotherapy for a variety of cancers. However, cardiotoxicity limits its use for long periods. To overcome this limitation, encapsulation in smart drug delivery systems (DDS) brings advantages in comparison with free drug administration (i.e., conventional anticancer drug therapy). In this review, we present the most relevant nanostructures used for DOX encapsulation over the last 10 years, such as liposomes, micelles and polymeric vesicles (i.e., polymersomes), micro/nanoemulsions, different types of polymeric nanoparticles and hydrogel nanoparticles, as well as novel approaches for DOX encapsulation. The studies highlighted here show these nanoformulations achieved higher solubility, improved tumor cytotoxicity, prolonged DOX release, as well as reduced side effects, among other interesting advantages.

Emerging nanoformulation strategies for phytocompounds and applications from drug delivery to phototherapy to imaging

Over thousands of years, natural bioactive compounds derived from plants (bioactive phytocompounds, BPCs) have been used worldwide to address human health issues. Today, they are a significant resource for drug discovery in the development of modern medicines. Although many BPCs have promising biological activities, most of them cannot be effectively utilized in drugs for therapeutic applications because of their inherent limitations of low solubility, structural instability, short half-life, poor bioavailability, and non-specific distribution to organs. Researchers have utilized emerging nanoformulation (NF) technologies to overcome these limitations as they have demonstrated great potential to improve the solubility, stability, and pharmacokinetic and pharmacodynamic characteristics of BPCs. This review exemplifies NF strategies for resolving the issues associated with BPCs and summarizes recent advances in their preclinical and clinical applications for imaging and therapy. This review also highlights how innovative NF technologies play a leading role in next-generation BPC-based drug development for extended therapeutic applications. Finally, this review discusses the opportunities to take BPCs with meaningful clinical impact from bench to bedside and extend the patent life of BPC-based medicines with new formulations or application to new adjacent diseases beyond the primary drug indications.

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Natural bioactive phytocompounds derived from plants have been used worldwide to address human health issues. However, most of them cannot be effectively utilized in drugs for therapeutic applications because of their inherent limitations.

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Nanoformulation approach has recently been underlined as an emerging pharmaceutical strategy to overcome the intrinsic drawbacks of bioactive phytocompounds.

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Various types of nanoformulation and their up-to-date applications for targeted delivery, phototherapy, and imaging are reviewed. Finally, their clinical implications for the repurposing of bioactive phytocompounds are deliberated.

Drug development of lyso-thermosensitive liposomal doxorubicin: Combining hyperthermia and thermosensitive drug delivery

We review the drug development of lyso-thermosensitive liposomal doxorubicin (LTLD) which is the first heat-activated formulation of a liposomal drug carrier to be utilized in human clinical trials. This class of compounds is designed to carry a payload of a cytotoxic agent and adequately circulate in order to accumulate at a tumor that is being heated. At the target the carrier is activated by heat and releases its contents at high concentrations. We summarize the preclinical and clinical experience of LTLD including its successes and challenges in the development process.

Furin-responsive triterpenine-based liposomal complex enhances anticervical cancer therapy through size modulation

The accumulation and penetration of antitumor drugs in tumor tissues are directly related to their antitumor effects. The particle size of the nanodrug delivery system is one of the most important factors for the accumulation and penetration of antitumor drugs within tumor tissues. Generally, nanodelivery systems of intermediate size (100–120 nm) are capable of efficient accumulation owing to prolonged circulation and enhanced permeability and retention (EPR) effect; however, smaller ones (20–40 nm) are effective for deep penetration within tumor tissue. Currently a conventional drug delivery system cannot possess two types of optimal sizes, simultaneously. To solve this and to enhance cervical cancer treatment, a furin-responsive triterpenine-based liposomal complex (PEGcleavable Tf-CTM/L), with Tf-CTM (transferrin-modified tripterine-loaded coix seed oil microemulsion) in core, coated with a thermo-sensitive lipid and a kind of PEG shell modified with a furin-cleavable peptide was developed to improve tumor-specific accumulation and penetration. Herein, PEGcleavable Tf-CTM/L was capable of efficient accumulation because of EPR effect. The PEG shells could timely detach under stimulation of overexpressed furin protein to solve the problem of the steric hindrance dilemma. The small-sized Tf-CTM released under stimulation of tumor microthermal environment in cervical cancer, which was efficient with regards to deep penetration at tumor sites. Notably, compared to the use of triterpenine alone, PEGcleavable Tf-CTM/L promoted anticervical efficacy and displayed diminished systemic toxicity by efficient accumulation and deep penetration of antitumor drugs within tumor tissues. Our study provides a new strategy, and holds promising potential for anticervical cancer treatment.

PD1 blockade potentiates the therapeutic efficacy of photothermally-activated and MRI-guided low temperature-sensitive magnetoliposomes

This study investigates the effect of PD1 blockade on the therapeutic efficacy of novel doxorubicin-loaded temperature-sensitive liposomes. Herein, we report photothermally-activated, low temperature-sensitive magnetoliposomes (mLTSL) for efficient drug delivery and magnetic resonance imaging (MRI). The mLTSL were prepared by embedding small nitrodopamine palmitate (NDPM)-coated iron oxide nanoparticles (IO NPs) in the lipid bilayer of low temperature-sensitive liposomes (LTSL), using lipid film hydration and extrusion. Doxorubicin (DOX)-loaded mLTSL were characterized using dynamic light scattering, differential scanning calorimetry, electron microscopy, spectrofluorimetry, and atomic absorption spectroscopy. Photothermal experiments using 808 nm laser irradiation were conducted. In vitro photothermal DOX release studies and cytotoxicity was assessed using flow cytometry and resazurin viability assay, respectively. In vivo DOX release and tumor accumulation of mLTSL(DOX) were assessed using fluorescence and MR imaging, respectively. Finally, the therapeutic efficacy of PD1 blockade in combination with photothermally-activated mLTSL(DOX) in CT26-tumor model was evaluated by monitoring tumor growth, cytokine release and immune cell infiltration in the tumor tissue. Interestingly, efficient photothermal heating was obtained by varying the IO NPs content and the laser power, where on-demand burst DOX release was achievable in vitro and in vivo. Moreover, our mLTSL exhibited promising MR imaging properties with high transverse r₂ relaxivity (333 mM^-1 s^-1), resulting in superior MR imaging in vivo. Furthermore, mLTSL(DOX) therapeutic efficacy was potentiated in combination with anti-PD1 mAb, resulting in a significant reduction in CT26 tumor growth via immune cell activation. Our study highlights the potential of combining PD1 blockade with mLTSL(DOX), where the latter could facilitate chemo/photothermal therapy and MRI-guided drug delivery.

Image-guided thermosensitive liposomes for focused ultrasound enhanced co-delivery of carboplatin and SN-38 against triple negative breast cancer in mice

Triggerable nanocarriers have the potential to significantly improve the therapeutic index of existing anticancer agents. They allow for highly localised delivery and release of therapeutic cargos, reducing off-target toxicity and increasing anti-tumour activity. Liposomes may be engineered to respond to an externally applied stimulus such as focused ultrasound (FUS). Here, we report the first co-delivery of SN-38 (irinotecan's super-active metabolite) and carboplatin, using an MRI-visible thermosensitive liposome (iTSL). MR contrast enhancement was achieved by the incorporation of a gadolinium lipid conjugate in the liposome bilayer along with a dye-labelled lipid for near infrared fluorescence bioimaging. The resulting iTSL were successfully loaded with SN-38 in the lipid bilayer and carboplatin in the aqueous core - allowing co-delivery of both. The iTSL demonstrated both thermosensitivity and MR-imageability. In addition, they showed effective local targeted co-delivery of carboplatin and SN-38 after triggered release with brief FUS treatments. A single dosage induced significant improvement of anti-tumour activity (over either the free drugs or the iTSL without FUS-activation) in triple negative breast cancer xenografts tumours in mice.

Phase I feasibility study of Magnetic Resonance guided High Intensity Focused Ultrasound-induced hyperthermia, Lyso-Thermosensitive Liposomal Doxorubicin and cyclophosphamide in de novo stage IV breast cancer patients: study protocol of the i-GO study

INTRODUCTION

In breast cancer, local tumour control is thought to be optimised by administering higher local levels of cytotoxic chemotherapy, in particular doxorubicin. However, systemic administration of higher dosages of doxorubicin is hampered by its toxic side effects. In this study, we aim to increase doxorubicin deposition in the primary breast tumour without changing systemic doxorubicin concentration and thus without interfering with systemic efficacy and toxicity. This is to be achieved by combining Lyso-Thermosensitive Liposomal Doxorubicin (LTLD, ThermoDox, Celsion Corporation, Lawrenceville, NJ, USA) with mild local hyperthermia, induced by Magnetic Resonance guided High Intensity Focused Ultrasound (MR-HIFU). When heated above 39.5°C, LTLD releases a high concentration of doxorubicin intravascularly within seconds. In the absence of hyperthermia, LTLD leads to a similar biodistribution and antitumour efficacy compared with conventional doxorubicin.

METHODS AND ANALYSIS

This is a single-arm phase I study in 12 chemotherapy-naïve patients with de novo stage IV HER2-negative breast cancer. Previous endocrine treatment is allowed. Study treatment consists of up to six cycles of LTLD at 21-day intervals, administered during MR-HIFU-induced hyperthermia to the primary tumour. We will aim for 60 min of hyperthermia at 40°C-42°C using a dedicated MR-HIFU breast system (Profound Medical, Mississauga, Canada). Afterwards, intravenous cyclophosphamide will be administered. Primary endpoints are safety, tolerability and feasibility. The secondary endpoint is efficacy, assessed by radiological response.This approach could lead to optimal loco-regional control with less extensive or even no surgery, in de novo stage IV patients and in stage II/III patients allocated to receive neoadjuvant chemotherapy.

ETHICS AND DISSEMINATION

This study has obtained ethical approval by the Medical Research Ethics Committee Utrecht (Protocol NL67422.041.18, METC number 18-702). Informed consent will be obtained from all patients before study participation. Results will be published in an academic peer-reviewed journal.

TRIAL REGISTRATION NUMBERS

NCT03749850, EudraCT 2015-005582-23.

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.

Encapsulated doxorubicin crystals influence lysolipid temperature-sensitive liposomes release and therapeutic efficacy in vitro and in vivo

Doxorubicin (DOX)-loaded lysolipid temperature-sensitive liposomes (LTSLs) are a promising stimuli-responsive drug delivery system that rapidly releases DOX in response to mild hyperthermia (HT). This study investigates the influence of loaded DOX crystals on the thermosensitivity of LTSLs and their therapeutic efficacy in vitro and in vivo. The properties of DOX crystals were manipulated using different remote loading methods (namely (NH₄)₂SO₄, NH₄-EDTA and MnSO₄) and varying the lipid:DOX weight ratio during the loading step. Our results demonstrated that (NH₄)₂SO₄ or NH₄-EDTA remote loading methods had a comparable encapsulation efficiency (EE%) into LTSLs in contrast to the low DOX EE% obtained using the metal complexation method. Cryogenic transmission electron microscopy (cryo-TEM) revealed key differences in the nature of DOX crystals formed inside LTSLs based on the loading buffer or/and the lipid:DOX ratio used, resulting in different DOX release profiles in response to mild HT. The in vitro assessment of DOX release/uptake in CT26 and PC-3 cells revealed that the use of a high lipid:DOX ratio exhibited a fast and controlled release profile in combination with mild HT, which correlated well with their cytotoxicity studies. Similarly, in vivo DOX release, tumour growth inhibition and mice survival rates were influenced by the physicochemical properties of LTSLs payload. This study demonstrates, for the first time, that the characteristics of DOX crystals loaded into LTSLs, and their conformational rearrangement during HT, are important factors that impact the TSLs performance in vivo.

An acoustic/thermo-responsive hybrid system for advanced doxorubicin delivery in tumor treatment

The efficiency of drug delivery and bioavailability to tumor cells are crucial for effective cancer chemotherapy. Herein, a doxorubicin (DOX) encapsulated lysolipid-based thermosensitive liposome decorated with cRGD peptide (RTSL) is conjugated on the surface of an IR780-loaded microbubble (IMB) to synthesize RTSL-IMBs. Sequentially taking advantage of acoustic-assisted early extravasation and thermo-triggered interstitium ultrafast drug release, RTSL-IMBs combine with ultrasound (US) and laser irradiation can advance drug delivery and bioavailability. In vitro experiments demonstrate that RTSL-IMBs associated with a two-step protocol (subsequently US irradiation for 1 min and laser irradiation for 5 min) can dramatically enhance the cellular uptake and bioavailability of DOX. In vivo fluorescence imaging studies reveal that the combination of RTSL-IMBs and US shows a 2.8-fold intratumoral drug accumulation increase at 0.5 h post-injection, while it will take 48 h to reach the same level of intratumoral drug accumulation for the RTSL-IMB group alone. Interestingly, the following localized application of a laser can further increase drug accumulation and slow tumor clearance. Histological analysis demonstrates that the combinational RTSL-IMBs, US and laser significantly improve the drug penetration distance and delivery efficiency in the tumor core. In this study, the acoustic/thermo-responsive hybrid system shows potential for advancing DOX chemotherapy in breast cancer cell MCF-7 xenograft nude mice.

Emerging hyperthermia applications for pediatric oncology

Local application of hyperthermia has a myriad of effects on the tumor microenvironment as well as the host's immune system. Ablative hyperthermia (typically > 55 °C) has been used both as monotherapy and adjuvant therapy, while mild hyperthermia treatment (39-45 °C) demonstrated efficacy as an adjuvant therapy through enhancement of both chemotherapy and radiation therapy. Clinical integration of hyperthermia has especially great potential in pediatric oncology, where current chemotherapy regimens have reached maximum tolerability and the young age of patients implies significant risks of late effects related to therapy. Furthermore, activation of both local and systemic immune response by hyperthermia suggests that hyperthermia treatments could be used to enhance the anticancer effects of immunotherapy. This review summarizes the state of current applications of hyperthermia in pediatric oncology and discusses the use of hyperthermia in the context of other available treatments and promising pre-clinical research.

Current developments in drug delivery with thermosensitive liposomes

Thermosensitive liposomes (TSLs) have been an important research area in the field of tumor targeted chemotherapy. Since the first TSLs appeared that using 1,2-dipalmitoyl-sn-glyce-ro-3-phosphocholine (DPPC) as the primary liposomal lipid, many studies have been done using this type of liposome from basic and practical aspects. While TSLs composed of DPPC enhance the cargo release near the phase transition temperature, it has been shown that many factors affect their temperature sensitivity. Thus numerous attempts have been undertaken to develop new TSLs for improving their thermal response performance. The main objective of this review is to introduce the development and recent update of innovative TSLs formulations, including combination of radiofrequency ablation (RFA), high-intensity focused ultrasound (HIFU), magnetic resonance imaging (MRI) and alternating magnetic field (AMF). In addition, various factors affecting the design of TSLs, such as lipid composition, surfactant, size and serum components are also discussed.

Hyperthermia-triggered release of hypoxic cell radiosensitizers from temperature-sensitive liposomes improves radiotherapy efficacy in vitro

Hypoxia is a characteristic feature of solid tumors and an important cause of resistance to radiotherapy. Hypoxic cell radiosensitizers have been shown to increase radiotherapy efficacy, but dose-limiting side effects prevent their widespread use in the clinic. We propose the encapsulation of hypoxic cell radiosensitizers in temperature-sensitive liposomes (TSL) to target the radiosensitizers specifically to tumors and to avoid unwanted accumulation in healthy tissues. The main objective of the present study is to develop and characterize TSL loaded with the radiosensitizer pimonidazole (PMZ) and to evaluate the in vitro efficacy of free PMZ and PMZ encapsulated in TSL in combination with hyperthermia and radiotherapy. PMZ was actively loaded into TSL at different drug/lipid ratios, and the physicochemical characteristics and the stability of the resulting TSL-PMZ were evaluated. PMZ release was determined at 37 °C and 42 °C in HEPES buffer saline and fetal bovine serum. The concentration-dependent radiosensitizing effect of PMZ was investigated by exposing FaDu cells to different PMZ concentrations under hypoxic conditions followed by exposure to ionizing irradiation. The efficacy of TSL-PMZ in combination with hyperthermia and radiotherapy was determined in vitro, assessing cell survival and DNA damage by means of the clonogenic assay and histone H2AX phosphorylation, respectively. All TSL-PMZ formulations showed high encapsulation efficiencies and were stable for 30 d upon storage at 4 °C and 20 °C. Fast PMZ release was observed at 42 °C, regardless of the drug/lipid ratio. Increasing the PMZ concentration significantly enhanced the effect of ionizing irradiation. Pre-heated TSL-PMZ in combination with radiotherapy caused a 14.3-fold increase in cell death as compared to radiotherapy treatment alone. In conclusion, our results indicate that TSL-PMZ in combination with hyperthermia can assist in improving the efficacy of radiotherapy under hypoxic conditions.

Near-Infrared Light-Activated Thermosensitive Liposomes as Efficient Agents for Photothermal and Antibiotic Synergistic Therapy of Bacterial Biofilm

Biofilm is closely related to chronic infections and is difficult to eradicate. Development of effective therapy strategies to control biofilm infection is still challenging. Aiming at biofilm architecture, we designed and prepared near-infrared-activated thermosensitive liposomes with photothermal and antibiotic synergistic therapy capacity to eliminate Pseudomonas aeruginosa biofilm. The liposomes with positive charge and small size aided to enter the biofilm microchannels and locally released antibiotics in infection site. The liposomes could remain stable at 37 °C and release about 80% antibiotics over 45 °C. The biofilm dispersion rate was up to 80%, which was a 7- to 8-fold rise compared to excess antibiotic alone, indicating that the localized antibiotic release and photothermal co-therapy improved the antimicrobial efficiency. In vivo drug-loaded liposomes in treating P. aeruginosa-induced abscess exhibited an outstanding therapeutic effect. Furthermore, photothermal treatment could stimulate the expression of bcl2-associated athanogene 3 to prevent normal tissue from thermal damage. The near-infrared-activated nanoparticle carriers had the tremendous therapeutic potential to dramatically enhance the efficacy of antibiotics through thermos-triggered drug release and photothermal therapy.

Radiolabeled cholesteryl ethers: A need to analyze for biological stability before use

Radiolabeled cholesteryl ethers are widely used as non-metabolizable tracers for lipoproteins and lipid emulsions in a variety of in vitro and in vivo experiments. Since cholesteryl ethers do not leave cells after uptake and are not hydrolyzed by mammalian cellular enzymes, these compounds can act as markers for cumulative cell uptakes of labeled particles. We have employed [³H]cholesteryl oleoyl ether to study the uptake and distribution of triglyceride-rich emulsion particles on animal models. However, questionable unexpected results compelled us to analyze the stability of these ethers. We tested the stability of two commercially available radiolabeled cholesteryl ethers - [³H]cholesteryl oleoyl ether and [³H]cholesteryl hexadecyl ether from different suppliers, employing in vitro, in vivo and chemical model systems. Our results show that, among the two cholesteryl ethers tested, one ether was hydrolyzed to free cholesterol in vitro, in vivo and chemically under alkaline hydrolyzing agent. Free cholesterol, unlike cholesteryl ether, can then re-enter the circulation leading to confounding results. The other ether was not hydrolyzed to free cholesterol and remained as a stable ether. Hence, radiolabeled cholesteryl ethers should be analyzed for biological stability before utilizing them for in vitro or in vivo experiments.

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Tested stability of two commercially available radiolabeled cholesteryl ethers.

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One ether was hydrolyzed to free cholesterol (FC) in vitro and in vivo.

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FC, re-entered circulation giving questionable unexpected results in experiments.

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The other ether was unhydrolyzed in all model systems.

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Radiolabeled cholesteryl ethers should be analyzed for stability before use.

Injectable PLGA/Fe3O4 implants carrying cisplatin for synergistic magnetic hyperthermal ablation of rabbit VX2 tumor

Magnetic hyperthermia ablation has attracted wide attention in tumor therapy for its minimal invasion. Although the chemo-hyperthermal synergism has been proven to be effective in subcutaneously xenografted tumors of nude mice in our previous experiment, the occurrence of residual tumors due to incomplete ablation is more common in relatively larger and deeper-seated tumors in anti-tumor therapy. Thus, a larger tumor and larger animal model are needed for further study of the therapeutic efficacy. In this study, we tested the efficiency of this newly developed technique using a rabbit tumor model. Furthermore, we chose cisplatin (DDP), which has been confirmed with high efficiency in enhancing hyperthermia therapy as the chemotherapeutic drug for the synergistic magnetic hyperthermal ablation therapy of tumors. In vitro studies demonstrated that developed DDP-loaded magnetic implants (DDP/PLGA-Fe₃O₄) have great heating efficacy and the drug release can be significantly boosted by an external alternating magnetic field (AMF). In vivo studies showed that the phase-transitional DDP/PLGA-Fe₃O₄ materials that are ultrasound (US) and computerized tomography (CT) visible can be well confined in the tumor tissues after injection. When exposed to AMF, efficient hyperthermia was induced, which led to the cancer cells’ coagulative necrosis and accelerating release of the drug to kill residual tumors. Furthermore, an activated anti-tumor immune system can promote apoptosis of tumor cells. In conclusion, the DDP/PLGA-Fe₃O₄ implants can be used efficiently for the combined chemotherapy and magnetic-hyperthermia ablation of rabbit tumors.

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 stimuli responsive liposome loaded hydrogel provides flexible on-demand release of therapeutic agents

Lysolipid-based thermosensitive liposomes (LTSL) embedded in a chitosan-based thermoresponsive hydrogel matrix (denoted Lipogel) represents a novel approach for the spatiotemporal release of therapeutic agents. The entrapment of drug-loaded liposomes in an injectable hydrogel permits local liposome retention, thus providing a prolonged release in target tissues. Moreover, release can be controlled through the use of a minimally invasive external hyperthermic stimulus. Temporal control of release is particularly important for complex multi-step physiological processes, such as angiogenesis, in which different signals are required at different times in order to produce a robust vasculature. In the present work, we demonstrate the ability of Lipogel to provide a flexible, easily modifiable release platform. It is possible to tune the release kinetics of different drugs providing a passive release of one therapeutic agent loaded within the gel and activating the release of a second LTSL encapsulated agent via a hyperthermic stimulus. In addition, it was possible to modify the drug dosage within Lipogel by varying the duration of hyperthermia. This can allow for adaption of drug dosing in real time. As an in vitro proof of concept with this system, we investigated Lipogels ability to recruit stem cells and then elevate their production of vascular endothelial growth factor (VEGF) by controlling the release of a pro-angiogenic drug, desferroxamine (DFO) with an external hyperthermic stimulus. Initial cell recruitment was accomplished by the passive release of hepatocyte growth factor (HGF) from the hydrogel, inducing a migratory response in cells, followed by the delayed release of DFO from thermosensitive liposomes, resulting in a significant increase in VEGF expression. This delayed release could be controlled up to 14days. Moreover, by changing the duration of the hyperthermic pulse, a fine control over the amount of DFO released was achieved. The ability to trigger the release of therapeutic agents at a specific timepoint and control dosing level through changes in duration of hyperthermia enables sequential multi-dose profiles.

STATEMENT OF SIGNIFICANCE

This paper details the development of a heat responsive liposome loaded hydrogel for the controlled release of pro-angiogenic therapeutics. Lysolipid-based thermosensitive liposomes (LTSLs) embedded in a chitosan-based thermoresponsive hydrogel matrix represents a novel approach for the spatiotemporal release of therapeutic agents. This hydrogel platform demonstrates remarkable flexibility in terms of drug scheduling and sequencing, enabling the release of multiple agents and the ability to control drug dosing in a minimally invasive fashion. The possibility to tune the release kinetics of different drugs independently represents an innovative platform to utilise for a variety of treatments. This approach allows a significant degree of flexibility in achieving a desired release profile via a minimally invasive stimulus, enabling treatments to be tuned in response to changing symptoms and complications.

Chemophototherapy: An Emerging Treatment Option for Solid Tumors

Near infrared (NIR) light penetrates human tissues with limited depth, thereby providing a method to safely deliver non-ionizing radiation to well-defined target tissue volumes. Light-based therapies including photodynamic therapy (PDT) and laser-induced thermal therapy have been validated clinically for curative and palliative treatment of solid tumors. However, these monotherapies can suffer from incomplete tumor killing and have not displaced existing ablative modalities. The combination of phototherapy and chemotherapy (chemophototherapy, CPT), when carefully planned, has been shown to be an effective tumor treatment option preclinically and clinically. Chemotherapy can enhance the efficacy of PDT by targeting surviving cancer cells or by inhibiting regrowth of damaged tumor blood vessels. Alternatively, PDT-mediated vascular permeabilization has been shown to enhance the deposition of nanoparticulate drugs into tumors for enhanced accumulation and efficacy. Integrated nanoparticles have been reported that combine photosensitizers and drugs into a single agent. More recently, light-activated nanoparticles have been developed that release their payload in response to light irradiation to achieve improved drug bioavailability with superior efficacy. CPT can potently eradicate tumors with precise spatial control, and further clinical testing is warranted.

NIR-Laser-Controlled Drug Release from DOX/IR-780-Loaded Temperature-Sensitive-Liposomes for Chemo-Photothermal Synergistic Tumor Therapy

NIR laser-induced photothermal therapy (PTT) through near-infrared agents has demonstrated the great potential in solid tumor ablation. However, the nonuniform heat distribution over tumors from PTT makes it insufficient to kill all tumor cells, resulting in tumor recurrence and inferior outcomes. To improve the tumor treatment efficacy, it is highly desirable to develop the combinational treatment of PTT with other modalities, especially with chemotherapeutic agents. Here we report a smart DOX/IR-780-loaded temperature-sensitive-liposome (DITSL) which can achieve NIR-laser-controlled drug release for chemo-photothermal synergistic tumor therapy. In this system, the liposoluble IR-780 was incorporated into the temperature-sensitive lipid bilayer and the soluble chemotherapeutic doxorubicin (DOX) was encapsulated in the hydrophilic core. The resulting DITSL is proved to be physiologically stable and can provide a fast and laser irradiation-controllable DOX release in the PBS and cellular conditions. We further employed this nanoparticle for tumor treatment, demonstrating significantly higher tumor inhibition efficacy than that of DOX-loaded temperature-sensitive-liposome (DTSL) or IR780-loaded temperature-sensitive-liposome (ITSL) in the in vitro cells and in vivo animals. Histological analysis further revealed much more apoptotic cells, confirming the advantageous anti-tumor effect of DITSL over DTSL or ITSL. Our study provides a promising strategy to realize chemo-photothermal synergistic combination therapy for breast tumors.

Anticancer nanoparticulate polymer-drug conjugate

We review recent progress in polymer-drug conjugate for cancer nanomedicine. Polymer-drug conjugates, including the nanoparticle prepared from these conjugates, are designed to release drug in tumor tissues or cells in order to improve drugs' therapeutic efficacy. We summarize general design principles for the polymer-drug conjugate, including the synthetic strategies, the design of the chemical linkers between the drug and polymer in the conjugate, and the in vivo drug delivery barriers for polymer-drug conjugates. Several new strategies, such as the synthesis of polymer-drug conjugates and supramolecular-drug conjugates, the use of stimulus-responsive delivery, and triggering the change of the nanoparticle physiochemical properties to over delivery barriers, are also highlighted.

Gold Nanoantenna-Mediated Photothermal Drug Delivery from Thermosensitive Liposomes in Breast Cancer

In this work, we demonstrate controlled drug delivery from low-temperature-sensitive liposomes (LTSLs) mediated by photothermal heating from multibranched gold nanoantennas (MGNs) in triple-negative breast cancer (TNBC) cells in vitro. The unique geometry of MGNs enables the generation of mild hyperthermia (∼42 °C) by converting near-infrared light to heat and effectively delivering doxorubicin (DOX) from the LTSLs in breast cancer cells. We confirmed the cellular uptake of MGNs by using both fluorescence confocal Z-stack imaging and transmission electron microscopy (TEM) imaging. We performed a cellular viability assay and live/dead cell fluorescence imaging of the combined therapeutic effects of MGNs with DOX-loaded LTSLs (DOX-LTSLs) and compared them with free DOX and DOX-loaded non-temperature-sensitive liposomes (DOX-NTSLs). Imaging of fluorescent live/dead cell indicators and MTT assay outcomes both demonstrated significant decreases in cellular viability when cells were treated with the combination therapy. Because of the high phase-transition temperature of NTSLs, no drug delivery was observed from the DOX-NTSLs. Notably, even at a low DOX concentration of 0.5 μg/mL, the combination treatment resulted in a higher (33%) cell death relative to free DOX (17% cell death). The results of our work demonstrate that the synergistic therapeutic effect of photothermal hyperthermia of MGNs with drug delivery from the LTSLs can successfully eradicate aggressive breast cancer cells with higher efficacy than free DOX by providing a controlled light-activated approach and minimizing off-target toxicity.

In vivo pharmacokinetics, biodistribution and the anti-tumor effect of cyclic RGD-modified doxorubicin-loaded polymers in tumor-bearing mice

In our previous study, we successfully produced and characterized a multifunctional drug delivery system with doxorubicin (RC/GO/DOX), which was based on graphene oxide (GO) and cyclic RGD-modified chitosan (RC). Its characteristics include: pH-responsiveness, active targeting of hepatocarcinoma cells, and efficient loading with controlled drug release. Here, we report the pharmacokinetics, biodistribution, and anti-tumor efficacy of RC/GO/DOX polymers in tumor-bearing nude mice. The objective of this study is to assess its targeting potential for tumors. Pharmacokinetic and biodistribution profiles demonstrated that tumor accumulation of RC/GO/DOX polymers was almost three times higher than the others, highlighting the efficacy of the active targeting strategy. Furthermore, the tumor inhibition rate of RC/GO/DOX polymers was 56.64%, 2.09 and 2.93 times higher than that of CS/GO/DOX polymers (without modification) and the DOX solution, respectively. Anti-tumor efficacy results indicated that the tumor growth was better controlled by RC/GO/DOX polymers than the others. Hematoxylin and eosin (H&E) staining showed remarkable changes in tumor histology. Compared with the saline group, the tumor section from the RC/GO/DOX group revealed a marked increase in the quantity of apoptotic and necrotic cells, and a reduction in the quantity of the blood vessels. Together, these studies show that this new system could be regarded as a suitable form of DOX-based treatment of the hepatocellular carcinoma.

Time-evolution of in vivo protein corona onto blood-circulating PEGylated liposomal doxorubicin (DOXIL) nanoparticles

Nanoparticles (NPs) are instantly modified once injected in the bloodstream because of their interaction with the blood components. The spontaneous coating of NPs by proteins, once in contact with biological fluids, has been termed the 'protein corona' and it is considered to be a determinant factor for the pharmacological, toxicological and therapeutic profile of NPs. Protein exposure time is thought to greatly influence the composition of protein corona, however the dynamics of protein interactions under realistic, in vivo conditions remain unexplored. The aim of this study was to quantitatively and qualitatively investigate the time evolution of in vivo protein corona, formed onto blood circulating, clinically used, PEGylated liposomal doxorubicin. Protein adsorption profiles were determined 10 min, 1 h and 3 h post-injection of liposomes into CD-1 mice. The results demonstrated that a complex protein corona was formed as early as 10 min post-injection. Even though the total amount of protein adsorbed did not significantly change over time, the fluctuation of protein abundances observed indicated highly dynamic protein binding kinetics.

The application of local hypobaric pressure - A novel means to enhance macromolecule entry into the skin

The local application of controlled hypobaric stress represents a novel means to facilitate drug delivery into the skin. The aims of this work were to understand how hypobaric stress modified the properties of the skin and assess if this penetration enhancement strategy could improve the percutaneous penetration of a macromolecule. Measurements of skin thickness demonstrated that the topical application of hypobaric stress thinned the tissue (p<0.05), atomic force microscopy showed that it shrunk the corneocytes in the stratum corneum (p<0.001) and the imaging of the skin hair follicles using multiphoton microscopy showed that it opened the follicular infundibula (p<0.001). Together, these changes contributed to a 19.6-fold increase in in vitro percutaneous penetration of a 10,000 molecular weight dextran molecule, which was shown using fluorescence microscopy to be localized around the hair follicles, when applied to the skin using hypobaric stress. In vivo, in the rat, a local hemodynamic response (i.e. a significant increase in blood flow, p<0.001) was shown to contribute to the increase in follicular transport of the dextran to produce a systemic absorption of 7.2±2.81fg·mL(-1). When hypobaric stress was not applied to the rat there was no detectable absorption of dextran and this provided evidence that this novel penetration enhancement technique can improve the percutaneous penetration of macromolecules after topical application to the skin.

MRI monitoring of nanocarrier accumulation and release using Gadolinium-SPIO co-labelled thermosensitive liposomes

Encapsulation of anticancer drugs in triggerable nanocarriers can beneficially modify pharmacokinetics and biodistribution of chemotherapeutic drugs, and consequently increase tumor drug concentration and efficacy, while reducing side effects. Thermosensitive liposomes release their contents triggered by hyperthermia, which can be, for example, precisely delivered using an MR Imaging-guided focused ultrasound procedure. In such a scenario, it is attractive to demonstrate the accumulation of liposomes before applying hyperthermia, as well as to document the release of liposome content using MRI. To address this need, thermosensitive liposomes were developed and characterized, which were doubly loaded by iron oxide nanoparticles and Gd-chelate, as opposed to loading with a single contrast agent. When intact, the transverse relaxivity of the liposomes is high allowing detection of carriers in tissue. After heating the longitudinal relaxivity steeply increases indicating release of the small molecular contents. By choosing the appropriate MR sequences, availability and release can be evaluated without interference of one contrast agent with the other. Copyright © 2016 John Wiley & Sons, Ltd.

Theranostic liposomes containing conjugated polymer dots and doxorubicin for bio-imaging and targeted therapeutic delivery

This work was devoted to the development of a lipid-based theranostic nanoparticle able to simultaneously host conjugated polymer dots, doxorubicin (Dox) and folate acid (FA).

Alginate Microspheres Containing Temperature Sensitive Liposomes (TSL) for MR-Guided Embolization and Triggered Release of Doxorubicin

Objective

The objective of this study was to develop and characterize alginate microspheres suitable for embolization with on-demand triggered doxorubicin (DOX) release and whereby the microspheres as well as the drug releasing process can be visualized in vivo using MRI.

Methods and Findings

For this purpose, barium crosslinked alginate microspheres were loaded with temperature sensitive liposomes (TSL/TSL-Ba-ms), which release their payload upon mild hyperthermia. These TSL contained DOX and [Gd(HPDO3A)(H₂O)], a T₁ MRI contrast agent, for real time visualization of the release. Empty alginate microspheres crosslinked with holmium ions (T₂* MRI contrast agent, Ho-ms) were mixed with TSL-Ba-ms to allow microsphere visualization. TSL-Ba-ms and Ho-ms were prepared with a homemade spray device and sized by sieving. Encapsulation of TSL in barium crosslinked microspheres changed the triggered release properties only slightly: 95% of the loaded DOX was released from free TSL vs. 86% release for TSL-Ba-ms within 30 seconds in 50% FBS at 42°C. TSL-Ba-ms (76 ± 41 μm) and Ho-ms (64 ± 29 μm) had a comparable size, which most likely will result in a similar in vivo tissue distribution after an i.v. co-injection and therefore Ho-ms can be used as tracer for the TSL-Ba-ms. MR imaging of a TSL-Ba-ms and Ho-ms mixture (ratio 95:5) before and after hyperthermia allowed in vitro and in vivo visualization of microsphere deposition (T₂*-weighted images) as well as temperature-triggered release (T₁-weighted images). The [Gd(HPDO3A)(H₂O)] release and clusters of microspheres containing holmium ions were visualized in a VX₂ tumor model in a rabbit using MRI.

Conclusions

In conclusion, these TSL-Ba-ms and Ho-ms are promising systems for real-time, MR-guided embolization and triggered release of drugs in vivo.

Pharmacokinetics, Tissue Distribution and Therapeutic Effect of Cationic Thermosensitive Liposomal Doxorubicin Upon Mild Hyperthermia

PURPOSE

To evaluate pharmacokinetic profile, biodistribution and therapeutic effect of cationic thermosensitive liposomes (CTSL) encapsulating doxorubicin (Dox) upon mild hyperthermia (HT).

METHODS

Non-targeted thermosensitive liposomes (TSL) and CTSL were developed, loaded with Dox and characterized. Blood kinetics and biodistribution of Dox-TSL and Dox-CTSL were followed in B16BL6 tumor bearing mice upon normothermia (NT) or initial hyperthermia conditions. Efficacy study in B16BL6 tumor bearing mice was followed with Dox-TSL or Dox-CTSL upon NT or HT. Efficacy study in LLC tumor bearing mice was performed upon two HT conditions. Intravital microscopy was performed on B16BL6 tumors implanted in dorsal-skin fold window-bearing mice.

RESULTS

Targeting did not cause faster blood clearance of CTSL compared to TSL. Highest uptake of liposomes was observed in spleen, kidneys and liver. Applying HT prior to CTSL administration increased drug delivery to the tumor and CTSL delivered ~1.7 fold higher Dox concentration compared to TSL. Efficacy in B16BL6 murine melanoma showed that HT had a significant effect on CTSL in tumor suppression and prolonged survival. Efficacy in LLC Lewis lung carcinoma tumor model demonstrates that two HT treatments hold promises for a successful treatment option.

CONCLUSION

CTSL have potency to increase drug efficacy in tumors due to their targeted and drug release functions.