Anti-MUC-1 immunoliposomal doxorubicin in the treatment of murine models of metastatic breast cancer

Targeted Liposomal Drug Delivery: Overview of the Current Applications and Challenges

In drug development, it is not uncommon that an active substance exhibits efficacy in vitro but lacks the ability to specifically reach its target in vivo. As a result, targeted drug delivery has become a primary focus in the pharmaceutical sciences. Since the approval of Doxil® in 1995, liposomes have emerged as a leading nanoparticle in targeted drug delivery. Their low immunogenicity, high versatility, and well-documented efficacy have led to their clinical use against a wide variety of diseases. That being said, every disease is accompanied by a unique set of physiological conditions, and each liposomal product must be formulated with this consideration. There are a multitude of different targeting techniques for liposomes that can be employed depending on the application. Passive techniques such as PEGylation or the enhanced permeation and retention effect can improve general pharmacokinetics, while active techniques such as conjugating targeting molecules to the liposome surface may bring even further specificity. This review aims to summarize the current strategies for targeted liposomes in the treatment of diseases.

Canonical and truncated transglutaminase-2 regulate mucin-1 expression and androgen independency in prostate cancer cell lines

Androgen independency is associated with poor prostate cancer (PCa) survival. Here we report that silencing of transglutaminase-2 (TG2) expression by CRISPR-Cas9 is associated with upregulation of androgen receptor (AR) transcription in PCa cell lines. Knockout of TG2 reversed the migratory potential and anchorage independency of PC3 and DU145 cells and revealed a reduced level of mucin-1 (MUC1) RNA transcript through unbiased multi-omics profiling, which was restored by selective add-back of the truncated TG2 isoform (TGM2_v2). Silencing of AR resulted into increased MUC1 in TG2KO PC3 cells showing that TG2 affects transcriptional regulation of MUC1 via repressing AR expression. Treatment of PC3 WT cell line with TG2 inhibitor ZDON led to a significant increase in AR expression and decrease in MUC1. ZDON also blocked the formation of MUC1-multimers labelled with TG amine-donor substrates in reducing conditions, revealing for the first time a role for TG2, which we show to be externalised via extracellular vesicles, in MUC1 stabilisation via calcium-dependent transamidation. A specific antibody towards TGM2_v2 revealed its restricted nuclear location compared to the canonical long form of TG2 (TGM2_v1), which is predominantly cytosolic, suggesting that this form contributes to the previously suggested TG2-mediated NF-κB activation and AR transcriptional repression. As TGM2_v2 transcription was increased in biopsies of early-stage prostate adenocarcinoma (PRAD) patients compared to subjects presenting inflammatory prostatitis, and total TG2 protein expression significantly increased in PRAD versus normal tissue, the role of TG2 and its truncated form as a prostate malignancy marker is suggested. In conclusion, this investigation has provided the first unbiased discovery of a novel pathway mediated by TG2 via MUC1, which is shown to contribute to androgen insensitivity and malignancy of PCa cells and be upregulated in PCa biopsies, with potential relevance to cancer immune evasion.

Identification of an ALK-2 inhibitor as an agonist for intercellular exchange and tumor delivery of nanomaterial

Inefficient extravasation and penetration in solid tissues hinder the clinical outcome of nanoparticles (NPs). Recent studies have shown that the extravasation and penetration of NPs in solid tumor was mostly achieved via an active transcellular route. For this transport process, numerous efforts have been devoted to elucidate the endocytosis and subcellular trafficking of NPs. However, how they exit from one cell and re-enter into neighboring ones (termed intercellular exchange) remains poorly understood. We previously developed cellular assays that exclusively quantify the intercellular exchange of NPs in vitro. Our study showed that a significant portion of NPs are transferred inside extracellular vesicles (EVs). Pharmacological inhibition of EV biogenesis significantly reduced the tumor accumulation and vascular penetration of both inorganic and organic NPs in vivo. Intrigued by this result, we performed here a manual chemical screen with our assay, which identified that LDN-214117 (an inhibitor for activin receptor-like kinase-2, ALK-2) is an agonist of NP intercellular exchange. We further showed that LDN-214117 regulates the intercellular exchange by increasing the EV biogenesis. Mechanistic investigation showed that LDN-214117 functions via BMP (bone morphogenetic protein)-MAPK (mitogen-activated protein kinase) signaling pathway to increase EV biogenesis. We further demonstrated that LDN-214117 treatment in vivo enhanced the tumor accumulation and vascular penetration of a variety of NPs in multiple tumor models, which improves their antitumor efficacy. Overall, we showcase here the identification of a novel chemical compound with our intercellular exchange assays to modulate EV biogenesis and EV-mediated transport, thus boosting up the delivery and therapeutic efficacy of nanomaterial.

Antitumor efficacy of MUC1-derived variable epitope library treatments in a mouse model of breast cancer

The identification of novel targets for cancer immunotherapy and the development of new vaccine immunogens are subjects of permanent interest. MUC1 is an overexpressed antigen found in most tumors, and its overexpression correlates with poor prognosis. Many attempts to direct the immune response against MUC1 in tumor cells have failed, including several clinical trials. We have previously developed an innovative Variable Epitope Library (VEL) vaccine platform that carries massively substituted mutant variants of defined epitopes or epitope regions as an alternative to using wild-type peptide sequences-based immunogens. Here, two murine MUC1-derived epitopes equivalent to the previously tested in cancer immunotherapy human MUC1 regions were used to generate VELs. We observed that vaccination with the 23L VEL immunogens, encompassing the entire signal peptide region of MUC1, reduces the tumor area compared to the wild-type sequence treatment. Contrastingly, vaccination with the MUC1 signal peptide-derived predicted CD8⁺+ T cell epitope-based VEL, 9MUC1spL, showed similar tumor area reduction as the wild-type treatment; however, a decrease in lung metastasis after 9MUC1spL treatment was observed. In addition, vaccination induced a large pool of CD8⁺ T cells which recognized most variant epitopes from 9MUC1spL. Also, we generated MUC1 variable number tandem repeat (VNTR)-based VELs that reduced the metastatic burden when dendritic cells and M13 recombinant bacteriophages were used as vaccine carriers. Collectively, our data demonstrate the immunogenic and antitumor properties of MUC1 signal peptide- and VNTR-derived VEL immunogens.

A robust post-insertion method for the preparation of targeted siRNA LNPs

Targeted delivery of nucleic acids is gaining momentum due to improved efficacy, selectivity, increased circulation time and enhanced tissue retention in target cells. Using nucleic acid-based therapies previously undruggable targets have proven now to be amenable for treatment. Currently, several methods for preparing targeted or labelled delivery vehicles for nucleic acids are based on liposomal formulations. Lipid nanoparticles (LNPs) are structurally different from liposomes and these methods should therefore be evaluated before being translated to siRNA LNPs preparation protocols. Here, we describe a robust and facile method for the preparation of targeted or fluorescently labelled siRNA LNPs. Using a copper free strain-promoted azide-alkyne cycloaddition (SPAAC) we demonstrate that post-insertion of ligand-lipid conjugates into preformed LNPs is superior to direct-surface modification because it preserves the physicochemical parameters of the LNPs. We found that the time point of solvent removal by dialysis is critical and affects the hydrodynamic diameter of the LNPs; post-insertion after dialysis shows the smallest increase in hydrodynamic diameter and polydispersity index (PDI). The post-insertion of ligand-lipid conjugates also proceeded with rapid kinetics and high efficacy over a wide temperature range. Using this optimised protocol, we generated siRNA LNPs containing both targeting and fluorescent tracking ligands allowing us to monitor siRNA LNP uptake kinetics in dependence of the targeting ligand. In aggregate, we describe a robust approach for the generation of targeted and labelled siRNA LNPs that allows their controlled and facile decoration with ligand combinations.

Current understandings and clinical translation of nanomedicines for breast cancer therapy

Breast cancer is one of the most frequently diagnosed cancers that is threatening women's life. Current clinical treatment regimens for breast cancer often involve neoadjuvant and adjuvant systemic therapies, which somewhat are associated with unfavorable features. Also, the heterogeneous nature of breast cancers requires precision medicine that cannot be fulfilled by a single type of systemically administered drug. Taking advantage of the nanocarriers, nanomedicines emerge as promising therapeutic agents for breast cancer that could resolve the defects of drugs and achieve precise drug delivery to almost all sites of primary and metastatic breast tumors (e.g. tumor vasculature, tumor stroma components, breast cancer cells, and some immune cells). Seven nanomedicines as represented by Doxil® have been approved for breast cancer clinical treatment so far. More nanomedicines including both non-targeting and active targeting nanomedicines are being evaluated in the clinical trials. However, we have to realize that the translation of nanomedicines, particularly the active targeting nanomedicines is not as successful as people have expected. This review provides a comprehensive landscape of the nanomedicines for breast cancer treatment, from laboratory investigations to clinical applications. We also highlight the key advances in the understanding of the biological fate and the targeting strategies of breast cancer nanomedicine and the implications to clinical translation.

Liposomal doxorubicin as targeted delivery platform: Current trends in surface functionalization

Liposomal delivery systems have significantly enhanced the efficacy and safety of chemotherapeutic agents compared to free (non-liposomal) formulations. Liposomes are vesicles made up of lipophilic bilayer and a hydrophilic core which provides perfect opportunity for their application as transport vehicle for various therapeutic and diagnostic agents. Doxorubicin is the most exploited chemotherapeutic agent for evaluation of different liposomal applications, as its physicochemical properties permit high drug entrapment and easy remote loading in pre-formulated liposomes. Pegylated liposomal doxorubicin clinically approved and, on the market, Doxil®, exemplifies the benefits offered upon the surface modification of liposome with polyethylene glycol. This unique formulation prolonged the drug residence time in the circulation and increased accumulation of doxorubicin in tumor tissue via passive targeting (enhanced permeability and retention effect). However, there is ample scope for further improvement in the efficiency of targeting tumors by coupling biological active ligands onto the liposome surface to generate intelligent drug delivery systems. Small biomolecules such as peptides, fraction of antibodies and carbohydrates have the potential to target receptors present on the surface of the malignant cells. Hence, active targeting of malignant cells using functionalised nanocarrier (liposomes encapsulated with doxorubicin) have been attempted which is reviewed in this article.

Antibody Conjugation of Nanoparticles as Therapeutics for Breast Cancer Treatment

Breast cancer is the most common invasive tumor in women and the second leading cause of cancer-related death. Nanomedicine raises high expectations for millions of patients as it can provide better, more efficient, and affordable healthcare, and it has the potential to develop novel therapeutics for the treatment of solid tumors. In this regard, targeted therapies can be encapsulated into nanocarriers, and these nanovehicles are guided to the tumors through conjugation with antibodies-the so-called antibody-conjugated nanoparticles (ACNPs). ACNPs can preserve the chemical structure of drugs, deliver them in a controlled manner, and reduce toxicity. As certain breast cancer subtypes and indications have limited therapeutic options, this field provides hope for the future treatment of patients with difficult to treat breast cancers. In this review, we discuss the application of ACNPs for the treatment of this disease. Given the fact that ACNPs have shown clinical activity in this clinical setting, special emphasis on the role of the nanovehicles and their translation to the clinic is placed on the revision.

Conditional internalization of PEGylated nanomedicines by PEG engagers for triple negative breast cancer therapy

Triple-negative breast cancer (TNBC) lacks effective treatment options due to the absence of traditional therapeutic targets. The epidermal growth factor receptor (EGFR) has emerged as a promising target for TNBC therapy because it is overexpressed in about 50% of TNBC patients. Here we describe a PEG engager that simultaneously binds polyethylene glycol and EGFR to deliver PEGylated nanomedicines to EGFR⁺ TNBC. The PEG engager displays conditional internalization by remaining on the surface of TNBC cells until contact with PEGylated nanocarriers triggers rapid engulfment of nanocargos. PEG engager enhances the anti-proliferative activity of PEG-liposomal doxorubicin to EGFR⁺ TNBC cells by up to 100-fold with potency dependent on EGFR expression levels. The PEG engager significantly increases retention of fluorescent PEG probes and enhances the antitumour activity of PEGylated liposomal doxorubicin in human TNBC xenografts. PEG engagers with specificity for EGFR are promising for improved treatment of EGFR⁺ TNBC patients.

The majority of treatment options for cancers are ineffective due to limited therapeutic targeting. Here, the authors develop bispecific antibodies that effectively target nanomaterials to triple-negative breast cancer cell receptors and deliver therapeutics leading to inhibition of tumour growth.

Monoclonal antibody-targeted, temperature-sensitive liposomes: in vivo tumor chemotherapeutics in combination with mild hyperthermia

The development of actively targeted, responsive delivery vectors holds great promise for cancer therapy. Here, we investigated whether enhanced therapeutic activity of temperature sensitive liposomes (TSL) could be obtained by mild hyperthermia-triggered release of the chemotherapeutic drug doxorubicin (DOX) after hCTMO1 monoclonal antibody (anti-MUC-1) binding and uptake into cancer cells. We showed that traditional TSL (TTSL) liposome systems maintained their physicochemical and thermal properties after conjugation to hCTMO1 full IgG. Receptor-mediated cellular uptake and cytotoxic efficacy of antibody-targeted TTSL (TTSL-Ab) were investigated using 2D and 3D cell culture models. Significant enhancement in cellular uptake and cytotoxic activity after 1h of heating at 42 °C was observed for TTSL-Ab compared to non-targeted liposomes in MUC-1 over-expressing breast cancer cells (MDA-MB-435). Tissue distribution and in vivo therapeutic activity were studied using different heating protocols to explore the effect of mild hyperthermia on the tumor accumulation of targeted TTSL and their therapeutic effect. Application of local, mild hyperthermia (42°C) significantly increased the tumor accumulation of targeted TSL compared to non-targeted liposomes, associated with a moderate improvement in therapeutic activity and survival.

Liposomal drug delivery systems: from concept to clinical applications

The first closed bilayer phospholipid systems, called liposomes, were described in 1965 and soon were proposed as drug delivery systems. The pioneering work of countless liposome researchers over almost 5 decades led to the development of important technical advances such as remote drug loading, extrusion for homogeneous size, long-circulating (PEGylated) liposomes, triggered release liposomes, liposomes containing nucleic acid polymers, ligand-targeted liposomes and liposomes containing combinations of drugs. These advances have led to numerous clinical trials in such diverse areas as the delivery of anti-cancer, anti-fungal and antibiotic drugs, the delivery of gene medicines, and the delivery of anesthetics and anti-inflammatory drugs. A number of liposomes (lipidic nanoparticles) are on the market, and many more are in the pipeline. Lipidic nanoparticles are the first nanomedicine delivery system to make the transition from concept to clinical application, and they are now an established technology platform with considerable clinical acceptance. We can look forward to many more clinical products in the future.

Challenges in development of targeted liposomal therapeutics

Liposomes, phospholipid vesicles with a bilayered membrane structure, have been widely used as pharmaceutical carriers for drugs and genes, in particular for treatment of cancer. To enhance the efficacy of the liposomal drugs, drug-loaded liposomes are targeted to the tumors by means of passive (enhanced permeability and retention mediated) targeting, based on the longevity of liposomes in blood and its accumulation in pathological sites with compromised vasculature, and active targeting, based on the attachment of specific ligands to the liposomal surface to bind certain antigens on the target cells. Antibody-targeted liposomes loaded with anticancer drugs demonstrate high potential for clinical applications. This review highlights evolution of liposomes for both passive and active targeting and challenges in development of targeted liposomal therapeutics specifically antibody-targeted liposomes.

Self-assemble gene delivery system for molecular targeting using nucleic acid aptamer

We have developed a novel vector constructed with pDNA, polyethylenimine (PEI), and mucin 1 (MUC1) aptamer for tumor-targeted gene delivery. The MUC1 aptamer and non-specific aptamer were employed to coat the pDNA/PEI complexes electrostatically and stable nanoparticles were formed. The addition of a non-specific aptamer to the pDNA/PEI complex decreased gene expression in the human lung cancer cell line, A549 cells expressing MUC1 regularly. At the same time, the pDNA/PEI/MUC1 aptamer complex showed higher gene expression than pDNA/PEI/non-specific aptamer complex. Furthermore, the pDNA/PEI/MUC1 aptamer complex showed markedly high gene expression in tumor-bearing mice; thus, pDNA/PEI/MUC1 aptamer complexes are useful as a tumor-targeted gene delivery system with high transfection efficiency.

Liposomal nanomedicine for breast cancer therapy

Liposomes are well-established nanocarriers for improving the therapeutic index of anticancer agents. A remarkable understanding in the pathophysiology of breast cancer progression has emerged with information on the involved specific biomolecules, which may serve as molecular targets for its therapy. Hormonal and nonhormonal receptors can both be exploited for targeting to breast cancer cells. Targeted delivery of cytotoxic drugs using liposomes is a novel approach for breast cancer therapy. In the present article, we summarize molecular targets present on the breast cancer cells. Recent developments in liposome-based delivery of bioactives for selective treatments of breast cancer are discussed. In addition, utilization of bioenvironmental conditions of tumor for liposome-based targeted delivery is also summed up.

Prevention of metastasis in a 4T1 murine breast cancer model by doxorubicin carried by folate conjugated pH sensitive polymeric micelles

This study primarily focused on the anti-metastatic activity of doxorubicin (DOX) loaded in a pH-sensitive mixed polymeric micelle formed from two block polymers: poly(L-lactide) (PLLA) (Mn 3000)-b-poly(ethylene glycol) (PEG) (Mn 2000)-folate and poly(L-histidine) (PHis) (Mn 4700)-b-PEG (Mn 2000). Tumor formation and metastasis in mice were examined using a murine mammary carcinoma cell of 4T1 which is one of the most aggressive metastatic cancer cell lines. The efficacy was evaluated by tumor size, body weight change, survival rate, dorsal skin fold window chamber model, and histological observation of the lung, heart, liver and spleen after treatment with various DOX formulations. When the tumor reached 50-100 mm³ in size, the mice were treated 4 times at a 3-day interval at a dose of 10 mg DOX/kg. The mixed micelle formulation resulted in retarded tumor growth, no weight loss, and no death for 4-5 weeks. In another set of the in vivo test for histological evaluation of the organs, the mice were similarly treated but the formulations were injected one day after 4T1 cell inoculation. The treatment by DOX loaded mixed micelle showed no apparent metastasis till 28 days. However, significant metastasis to the lung and heart was observed on Day 28 when the mice were treated with DOX carried by PBS, PLLA-b-PEG micelle and PHis-b-PEG micelle.

The effect of internalizing human single chain antibody fragment on liposome targeting to epithelioid and sarcomatoid mesothelioma

Immunoliposomes (ILs) anchored with internalizing human antibodies capable of targeting all subtypes of mesothelioma can be useful for targeted imaging and therapy of this malignant disease. The objectives of this study were to evaluate both the in vitro and in vivo tumor targeted internalization of novel internalizing human single chain antibody (scFv) anchored ILs on both epithelioid (M28) and sarcomatoid (VAMT-1) subtypes of human mesothelioma. ILs were prepared by post-insertion of mesothelioma-targeting human scFv (M1) onto preformed liposomes and radiolabeled with (111)In ((111)In-IL-M1), along with control non-targeted liposomes ((111)In-CL). Incubation of (111)In-IL-M1 with M28, VAMT-1, and a control non-tumorigenic cell line (BPH-1) at 37 °C for 24 h revealed efficient binding and rapid internalization of ILs into both subtypes of tumor cells but not into the BPH-1 cells; internalization accounted for approximately 81-94% of total cell accumulation in mesothelioma cells compared to 37-55% in control cells. In tumor-bearing mice intravenous (i.v.) injection of (111)In-IL-M1 led to remarkable tumor accumulation: 4% and 4.7% injected dose per gram (% ID/g) for M28 and VAMT-1 tumors, respectively, 48 h after injection. Furthermore, tumor uptake of (111)In-IL-M1 in live xenograft animal models was verified by single photon emission computed tomography (SPECT/CT). In contrast, i.v. injection of (111)In-CL in tumor-bearing mice revealed very low uptake in both subtypes of mesothelioma, 48 h after injection. In conclusion, M1 scFv-anchored ILs showed selective tumor targeting and rapid internalization into both epithelioid and sarcomatoid subtypes of human mesothelioma, demonstrating its potential as a promising vector for enhanced tumor drug targeting.

Morphological changes in vesicles and release of an encapsulated compound triggered by a photoresponsive Malachite Green leuconitrile derivative

Photoinduced morphological changes in phosphatidylcholine vesicles are triggered by a Malachite Green leuconitrile derivative dissolved in the lipidic membrane, and are observed at Malachite Green derivative/lipid ratios <5 mol %. This Malachite Green derivative is a photoresponsive compound that undergoes ionization to afford a positive charge on the molecule by UV irradiation. The Malachite Green derivative exhibits amphiphilicity when ionized photochemically, whereas it behaves as a lipophilic compound under dark conditions. Cryo-transmission electron microscopy was used to determine vesicle morphology. The effects of the Malachite Green derivative on vesicles were studied by dynamic light scattering and fluorescence resonance energy transfer. Irradiation of vesicles containing the Malachite Green derivative induces nonspherical vesicle morphology, fusion of vesicles, and membrane solubilization, depending on conditions. Furthermore, irradiation of the Malachite Green derivative induces the release of a vesicle-encapsulated compound.

RGD-modified polymeric micelles as potential carriers for targeted delivery to integrin-overexpressing tumor vasculature and tumor cells

Integrins alphavbeta3 and alphavbeta5 are overexpressed in angiogenic tumor endothelial cells and malignant tumor cells, making them attractive targets for cancer therapy. In this study, an integrin alphavbeta3 and alphavbeta5 binding tripeptide, RGD (Arg-Gly-Asp), was conjugated with the surface of poly(ethylene glycol)-block-poly(D,L-lactide) (PEG-PLA) micelles. A lipophilic fluorescent probe, DiI, was loaded into both the nontargeted methoxy PEG-PLA (mPEG-PLA) micelles and the targeted RGD-modified PEG-PLA micelles. The DiI-loaded targeted micelles had a size of 24.2 nm. The targeted micelles were stable in phosphate buffered saline and exhibited a negligible leakage in culture medium. Transmission electron microscopy analysis showed that targeted micelles were spherical in shape. Cell uptake of DiI-labeled targeted micelles by human umbilical vein endothelial cells and melanoma B16 cells was investigated by spectrophotofluorometry and confocal microscopy techniques. Results revealed that RGD-modified micelles significantly facilitated the intracellular delivery of the encapsulated agents via integrin-mediated endocytosis. This study suggests that RGD-modified PEG-PLA micelles are promising drug carriers for targeted delivery to both angiogenic tumor endothelial cells and tumor cells and that the targeted micelles may be attractive carriers for combination cancer therapy against both targets.

Nanovehicular intracellular delivery systems

This article provides an overview of principles and barriers relevant to intracellular drug and gene transport, accumulation and retention (collectively called as drug delivery) by means of nanovehicles (NV). The aim is to deliver a cargo to a particular intracellular site, if possible, to exert a local action. Some of the principles discussed in this article apply to noncolloidal drugs that are not permeable to the plasma membrane or to the blood-brain barrier. NV are defined as a wide range of nanosized particles leading to colloidal objects which are capable of entering cells and tissues and delivering a cargo intracelullarly. Different localization and targeting means are discussed. Limited discussion on pharmacokinetics and pharmacodynamics is also presented. NVs are contrasted to micro-delivery and current nanotechnologies which are already in commercial use. Newer developments in NV technologies are outlined and future applications are stressed. We also briefly review the existing modeling tools and approaches to quantitatively describe the behavior of targeted NV within the vascular and tumor compartments, an area of particular importance. While we list "elementary" phenomena related to different level of complexity of delivery to cancer, we also stress importance of multi-scale modeling and bottom-up systems biology approach.

Increase of therapeutic effects by treating melanoma with targeted combinations of c-myc antisense and doxorubicin

Patients with advanced or metastatic melanoma have a very poor prognosis, due to the resistance of melanoma cells to conventional chemotherapy. We previously reported that coated cationic liposomes targeted with a monoclonal antibody against the disialoganglioside GD(2) and containing c-myc antisense oligodeoxynucleotides (alpha GD(2)-CCL[c-myc-as]) induced partial tumor growth arrest in melanoma xenografts. Here we addressed the role of c-myc-asODN treatment in the susceptibility to doxorubicin (DXR) in human melanoma cells. Cytotoxicity studies revealed that growth of melanoma cells was inhibited to a greater extent by alpha GD(2)-CCL[c-myc-as] than by the corresponding non-targeted formulations or by free c-myc-as. Targeted c-myc-as sensitized cells to DXR, reducing the IC(50) by approximately 10-fold. Scrambled ODNs had no effect on the IC(50) of DXR. Compared to either treatment alone, combination of targeted c-myc-as and DXR resulted in earlier apoptosis and in cell death after 2 days of treatment. In vivo experiments revealed that liposomal formulations of c-myc-as and DXR, both targeted via GD(2), led to the most pronounced delay in tumor growth when administered in a sequential manner. As a result, their combination translates into a statistically significant suppression of blood vessel density and an enhanced apoptosis, compared to all treatments given separately. Our data indicate the increasing cell sensitivity to DXR by c-myc-asODNs as a promising basis for developing novel anti-tumor strategy against advanced melanoma.

Transition from long- to short-lived transient pores in giant vesicles in an aqueous medium

We have observed large pores in the membrane of giant vesicles in an aqueous medium. The lifetime of the pores can reach 2 min and their size (a few micrometers) enables their visualization by fluorescence microscopy. These pores are obtained thanks to a destabilization of the membrane due to the synergistic action of a cone-shaped and nitrobenzodiazole (NBD) labeled phospholipid illuminated in the presence of dithionite. The opening of the pore occurs immediately after illumination starts so that it can be accurately triggered. A concomitant decrease of the vesicle radius is observed; we interpret it as a solubilization of the membrane. Depending on the rate of this solubilization, long- or short-lived pores were observed. At the transition between both regimes for a 30 microm vesicle, the solubilization rate was about 1/300 s{-1} . In order to interpret these observations, we have revisited the current model of pore opening to take into account this solubilization. This proposed model along with simulations enables us to prove that solubilization explains why the large long-lived pores are observed even in an aqueous medium. The model also predicts the solubilization rate at the transition between a single long-lived pore and a cascade of short-lived pores.

Determination of doxorubicin levels in whole tumor and tumor nuclei in murine breast cancer tumors

PURPOSE

Pharmacokinetic studies on liposomal drugs have previously measured total drug levels in tumors, which include non-bioavailable drug. However, drugs must be released from liposomes to have activity. We have developed a method for measuring levels of bioavailable (released) doxorubicin in vivo in tumors that will allow therapeutic activity to be correlated with bioavailable drug levels.

EXPERIMENTAL DESIGN

Mice orthotopically implanted with mammary carcinoma (4T1) were injected i.v. 10 days after implantation with free doxorubicin or formulations of liposomal doxorubicin with different drug release rates. Tumors were excised at various times after injection, and total tumor doxorubicin levels were determined by acidified isopropanol extraction of whole tumor homogenates. Bioavailable doxorubicin levels were determined by extraction of doxorubicin from isolated tumor nuclei.

RESULTS

Free doxorubicin had high levels of bioavailability in tumor tissue; 95% of the total doxorubicin in tumors was bound to nuclear DNA by 24 hours after injection. Administration of Doxil, a slow release liposomal formulation of doxorubicin, gave an area under the time-versus-concentration curve (AUC) for total doxorubicin 7 days after injection that was 87-fold higher than that obtained for free doxorubicin, and 49% of the liposomal doxorubicin was bioavailable. For liposomes with a more rapid doxorubicin release rate, by 7 days after injection, the AUC(0-7 days) for total doxorubicin was only 14-fold higher than that for free doxorubicin and only 27% of liposomal doxorubicin was bioavailable.

CONCLUSIONS

This technique allows correlations to be made between drug bioavailability and therapeutic activity and will help in the rational design of drug carriers.

Development of ligand-targeted liposomes for cancer therapy

The continued evolution of targeted liposomal therapeutics has resulted in new agents with remarkable antitumour efficacy and relatively mild toxicity profiles. A careful selection of the ligand is necessary to reduce immunogenicity, retain extended circulation lifetimes, target tumour-specific cell surface epitopes, and induce internalisation and subsequent release of the therapeutic substance from the liposome. Methods for assembling targeted liposomes, including a novel micellar insertion technology, for incorporation of targeting molecules that efficiently transforms a non-targeted liposomal therapeutic to a targeted one, greatly assist the translation of targeted liposome technology into the clinic. Targeting strategies with liposomes directed at solid tumours and vascular targets are discussed. The authors believe the development of ligand-targeted liposomes is now in the advanced stage and offers unique and important advantages among other targeted therapies. Anti-HER2 immunoliposomal doxorubicin is awaiting Phase I clinical trials, the results of which should provide new insights into the promise of ligand-targeted liposomal therapies.

Advantages of liposomal delivery systems for anthracyclines

Liposomes, closed vesicular structures consisting of one or more lipid bilayers, have generated a great deal of interest as drug delivery vehicles. In particular, they have been investigated for their ability to improve the delivery of chemotherapeutic agents to tumors, in efforts to increase therapeutic efficacy and decrease toxicity to normal cells. Development of liposomal chemotherapeutic agents has, in the past, been hindered primarily by the rapid uptake of liposomes by the reticuloendothelial system. Numerous strategies that seek to either exploit or avoid this phenomenon have been used. As a result, several liposomal chemotherapeutic agents are now available in the clinic. STEALTH, a novel liposomal system coated with polyethylene glycol, avoids uptake by the reticuloendothelial system, thus improving drug delivery to the tumor while decreasing toxicity. In pegylated liposomal doxorubicin (Doxil/Caelyx [PLD]), this delivery system encapsulates doxorubicin within polyethylene glycol-coated liposomes, leading to promising new applications for a well-established drug. Liposome-encapsulated doxorubicin citrate complex (Myocet [NPLD]), another liposomal delivery system for doxorubicin, lacks the polyethylene glycol coating, resulting in much shorter circulation times than those of PLD. Daunorubicin citrate liposome (DaunoXome [DNX]) contains daunorubicin encapsulated in a smaller liposome of a different lipid composition. It has circulation times between those of PLD and NPLD. This article reviews the advantages of liposomal delivery systems in general and the divergent approaches that have been taken in developing these agents.

Immune cell-mediated antitumor activities of GD2-targeted liposomal c-myb antisense oligonucleotides containing CpG motifs

BACKGROUND

Expression of the c-myb proto-oncogene in neuroblastoma, the most common extracranial solid tumor of infancy, is linked with cell proliferation and differentiation. Neuroblastoma can be selectively targeted via monoclonal antibodies against the disialoganglioside (GD2) tumor-associated antigen. Liposomes coated with anti-GD2 antibodies (targeted liposomes) and entrapping a c-myb antisense oligonucleotide have antitumor activity. Because antisense oligonucleotides containing CpG motifs can stimulate immune responses, we evaluated the effect of CpG-containing c-myb antisense oligonucleotides encapsulated within targeted liposomes.

METHODS

Antisense (myb-as) and scrambled (myb-scr) control oligonucleotides with CpG motifs were encapsulated within GD2-targeted and non-targeted liposomes. Two murine (nude and SCID-bg) xenograft models of neuroblastoma were established. Mice (groups of 10) were injected intravenously with various oligonucleotide and liposome formulations, and life span, long-term survival, immune cell activation, and cytokine release were measured over time.

RESULTS

Tumor-bearing mice injected with targeted liposome-CpG-myb-as or targeted liposome-CpG-myb-scr lived longer than mice in any other group, although long-term survival (i.e., more than 120 days) was obtained only in mice injected with targeted liposome-CpG-myb-as. Splenocytes isolated from mice injected with targeted liposome-CpG-myb-as contained activated macrophages, B cells, and natural killer (NK) cells, but only activated NK cells were associated with antitumor cytotoxic activity. In vivo immune cell activation was accompanied by the time-dependent increases in plasma levels of the cytokines interleukin 12 (IL-12; maximum level reached by 2 hours) and interferon gamma (IFN-gamma; maximum level reached by 18 hours) and was dependent on the oligonucleotide CpG motif. Ablation of macrophages or NK cells resulted in a loss of in vivo antitumor activity.

CONCLUSION

Immune cell activation, involving the time-dependent activation of macrophages and NK cells, contributes to the antitumor activity of targeted liposome-CpG-myb-as against neuroblastoma and could improve the effectiveness of antitumor targeted liposomes.

Active targeting with particulate drug carriers in tumor therapy: fundamentals and recent progress

Drug therapy for the treatment of tumors is often limited by a narrow therapeutic index. One approach that overcomes this limitation is the active targeting of tumors with particulate drug carriers. The derivatization of particulate drug carriers with a ligand leads to the selective targeting of the particulate to selected cells, thereby focusing drug delivery. In addition, particulate drug carriers have a high loading capacity, do not need covalent conjugation of the drug and the formulation protects the entrapped drug from enzymatic inactivation. Despite these favorable properties, their therapeutic efficacy in animal models has been reported only in recent years. The use of internalizing ligands and the targeting of intravascular tumor cells and endothelial cells of tumor blood vessels have been instrumental in demonstrating the clinical effectiveness of particulate drug carriers in animal models. As a result, several actively targeted particulate carriers have now entered, or are about to enter, clinical investigation. Recent findings, for example, the identification of cell-penetrating peptides with restricted cell selectivity, suggest that further improvements in this approach are likely in the near future.

Anthracyclines: Molecular Advances and Pharmacologic Developments in Antitumor Activity and Cardiotoxicity

The clinical use of anthracyclines like doxorubicin and daunorubicin can be viewed as a sort of double-edged sword. On the one hand, anthracyclines play an undisputed key role in the treatment of many neoplastic diseases; on the other hand, chronic administration of anthracyclines induces cardiomyopathy and congestive heart failure usually refractory to common medications. Second-generation analogs like epirubicin or idarubicin exhibit improvements in their therapeutic index, but the risk of inducing cardiomyopathy is not abated. It is because of their janus behavior (activity in tumors vis-à-vis toxicity in cardiomyocytes) that anthracyclines continue to attract the interest of preclinical and clinical investigations despite their longer-than-40-year record of longevity. Here we review recent progresses that may serve as a framework for reappraising the activity and toxicity of anthracyclines on basic and clinical pharmacology grounds. We review 1) new aspects of anthracycline-induced DNA damage in cancer cells; 2) the role of iron and free radicals as causative factors of apoptosis or other forms of cardiac damage; 3) molecular mechanisms of cardiotoxic synergism between anthracyclines and other anticancer agents; 4) the pharmacologic rationale and clinical recommendations for using cardioprotectants while not interfering with tumor response; 5) the development of tumor-targeted anthracycline formulations; and 6) the designing of third-generation analogs and their assessment in preclinical or clinical settings. An overview of these issues confirms that anthracyclines remain "evergreen" drugs with broad clinical indications but have still an improvable therapeutic index.

Drug release rate influences the pharmacokinetics, biodistribution, therapeutic activity, and toxicity of pegylated liposomal doxorubicin formulations in murine breast cancer

The pharmacokinetics (PK), biodistribution (BD), and therapeutic activity of pegylated liposomal doxorubicin formulations with different drug release rates were studied in an orthotopic 4T1 murine mammary carcinoma model. The focus of these experiments was to study the effects of different release rates on the accumulation of liposomal lipid and doxorubicin (DXR) into the tumor and cutaneous tissues of mice (skin and paws). These tissues were chosen because the clinical formulation of pegylated liposomal doxorubicin (Caelyx)/Doxi) causes mucocutaneous reactions such as palmar-plantar erythrodysesthesia (PPE). Liposomes with different doxorubicin (DXR) leakage rates were prepared by altering liposome fluidity through changing the fatty acyl chain length and/or degree of saturation of the phosphatidylcholine component of the liposome. Liposomes with fast, intermediate, and slow rates of drug release were studied. The plasma PK of the liposomal lipid was similar for all formulations, while the plasma PK of the DXR component was dependent on the liposome formulation. Liposomal lipid accumulated to similar levels in tumor and cutaneous tissues for all three formulations tested, while the liposomes with the slowest rates of DXR release produced the highest DXR concentrations in both cutaneous tissues and in tumor. Liposomes with the fastest drug release rates resulted in low DXR concentrations in cutaneous tissues and tumor. The formulation with intermediate release rates produced unexpected toxicity that was not related to the lipid content of the formulation. The liposomes with the slowest rate of drug leakage had the best therapeutic activity of the formulations tested.

Improved Therapeutic Responses in a Xenograft Model of Human B Lymphoma (Namalwa) for Liposomal VincristineversusLiposomal Doxorubicin Targeted via Anti-CD19 IgG2a or Fab′ Fragments

PURPOSE

Monoclonal antibody-mediated targeting of liposomal anticancer drugs to surface antigens expressed on malignant B cells can be an effective strategy for treating B-cell malignancies. In a murine model of human B-cell lymphoma, we have made in vitro and in vivo comparisons of long-circulating sterically stabilized (Stealth) immunoliposome (SIL) formulations of two anticancer drugs, vincristine (VCR) and doxorubicin (DXR), with different mechanisms of action and drug release rates.

EXPERIMENTAL DESIGN

SIL formulations of VCR or DXR were conjugated to the monoclonal antibody anti-CD19 (SIL[alphaCD19]) or its Fab' fragments (SIL[Fab']). Specific binding of SILs to Namalwa cells was studied using radiolabeled liposomes, and cytotoxicities of DXR- or VCR-loaded SILs were quantitated by a tetrazolium assay. Pharmacokinetic and drug leakage experiments were performed in mice using dual-labeled liposomes, and the therapeutic responses of SILs were evaluated in a Namalwa (human B lymphoma) cell xenograft model.

RESULTS

SIL[alphaCD19] or SIL[Fab'] had higher association with and cytotoxicity against Namalwa cells than nontargeted liposomes. SIL[Fab'] had longer circulation times than SIL[alphaCD19], and VCR had faster release rates from the liposomes than DXR. SIL formulations of either VCR or DXR had significantly better therapeutic outcomes than nontargeted liposomes or free drugs. SILs loaded with VCR were superior to those loaded with DXR. SIL[Fab'] had better therapeutic outcomes than SIL[alphaCD19] for the drug DXR but were equally efficacious for the drug VCR.

CONCLUSIONS

Treatment of a B lymphoma model with single injections of anti-CD19-targeted liposomal formulations of VCR resulted in high levels of response and long-term survivors. Responses to anti-CD19-targeted liposomal DXR were more modest, although the longer circulation times of SIL[Fab'] versus SIL[alphaCD19] led to superior therapeutics for DXR-loaded immunoliposomes.

Cellular association and cytotoxicity of anti-CD74-targeted lipid drug-carriers in B lymphoma cells

The ability to selectively target anti-cancer drugs via specific ligands against antigens expressed on malignant cells could greatly improve the therapeutic indices of the drugs. In this paper an anti-CD74 antibody (Ab), LL1, was covalently attached to the surface of sterically stabilized lipid drug-carriers (emulsions and liposomes) by use of a PEG-based heterobifunctional coupling agent. Target cells internalize LL1 very fast and that was found to be true for the LL1-lipid drug-carrier complexes as well. During a 24 h in vitro incubation with the target Raji B-lymphoma cells about 30% of the added complexes were associated with the cells. The corresponding value for drug-carrier without targeting ligand was near 0.6%. Displacement experiments showed that free LL1 competed well with LL1-complexes indicating preserved immunoreactivity. Non-target cells showed only unspecific association of LL1-complexes. A dioleoylated derivative of the anti-cancer drug 3',5'-O-dioleoyl-FUdR (FUdR) (FUdR-dO) loaded into LL1-lipid drug-carriers showed good cytotoxic activity. In vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity tests against neoplastic B-cells gave IC30 values of 0.45, 1.25, 5.30 and 7.30 microM for the prodrug FUdR-dO in LL1-emulsions, LL1-liposomes, emulsions and liposomes, respectively. The value for the parent drug FUdR was calculated to 4.35 microM. In the light of the extensive and specific delivery of LL1-lipid drug-carriers to B-cells and the selective cytotoxicity of the incorporated drug, we infer that the complexes may be useful in the selective elimination of circulating malignant B-cells in vivo.

Ligand-targeted liposomal anticancer drugs

Antibody or ligand-mediated targeting of liposomal anticancer drugs to antigens expressed selectively or over-expressed on tumor cells is increasingly being recognized as an effective strategy for increasing the therapeutic indices of anticancer drugs. This review summarizes some recent advances in the field of ligand-targeted liposomes (LTLs) for the delivery of anticancer drugs. New approaches used in the design and optimization of LTLs is discussed and the advantages and potential problems associated with their therapeutic applications are described. New technologies are widening the spectrum of ligands available for targeting and are allowing choices to be made regarding affinity, internalization and size. The time is rapidly approaching where we will see translation of anticancer drugs entrapped in LTLs to the clinic.

Multiple injections of pegylated liposomal Doxorubicin: pharmacokinetics and therapeutic activity

Effects of multiple injections of liposomal doxorubicin on pharmacokinetics, therapeutic outcome, and toxicity were studied in mice using different dosing schedules and dose intensities. Biodistribution of doxorubicin to the cutaneous tissues of mice (skin and paws) and to orthotopically implanted mammary tumors (4T1) was examined. Weekly intravenous administration of pegylated (STEALTH) liposomal doxorubicin (SL-DXR) at a dose of 9 mg/kg (every week x 4 doses) resulted in accumulation of doxorubicin in cutaneous tissues of mice and development of lesions resembling palmar-plantar erythrodysesthesia (PPE). Lengthening the dose interval to every 2 weeks x 4 doses reduced the accumulation of doxorubicin and lowered the incidence of PPE-like lesions. A dose interval of every 4 weeks x 4 resulted in complete clearance of doxorubicin from tissues between subsequent doses and a negligible incidence of PPE-like lesions. Doses of 9 mg/kg SL-DXR given at every week x 2 or every 2 weeks x 2 had similar therapeutic activities, whereas prolonging the dose interval to every 4 weeks x 2 reduced therapeutic activity. Pharmacokinetics, biodistribution, and therapeutic activity were studied in tumor-bearing mice for three dose schedules having the same dose intensity (4.5 mg/kg every 3 days x 4, 9 mg/kg every week x 2, or 18 mg/kg every 2 weeks x 1). For these schedules, larger doses administered less often tended to be superior therapeutically to smaller doses given more often. These data provide the first pharmacokinetic measurements of doxorubicin concentrations in cutaneous tissues and tumors with repeat administration of liposomal formulations, and they provide a useful model for the study of factors leading to PPE in humans.

Cascades of transient pores in giant vesicles: line tension and transport

Under ordinary circumstances, the membrane tension of a giant unilamellar vesicle is essentially nil. Using visible light, we stretch the vesicles, increasing the membrane tension until the membrane responds by the sudden opening of a large pore (several micrometers in size). Only a single pore is observed at a time in a given vesicle. However, a cascade of transient pores appear, up to 30-40 in succession, in the same vesicle. These pores are transient: they reseal within a few seconds as the inner liquid leaks out. The membrane tension, which is the driving force for pore opening, is relaxed with the opening of a pore and the leakage of the inner liquid; the line tension of the pore's edge is then able to drive the closure of a pore. We use fluorescent membrane probes and real-time videomicroscopy to study the dynamics of the pores. These can be visualized only if the vesicles are prepared in a viscous solution to slow down the leakout of the internal liquid. From measurements of the closure velocity of the pores, we are able to infer the line tension,. We have studied the effect of the shape of inclusion molecules on. Cholesterol, which can be modeled as an inverted cone-shaped molecule, increases the line tension when incorporated into the bilayers. Conversely, addition of cone-shaped detergents reduces. The effect of some detergents can be dramatic, reducing by two orders of magnitude, and increasing pore lifetimes up to several minutes. We give some examples of transport through transient pores and present a rough measurement of the leakout velocity of the inner liquid through a pore. We discuss how our results can be extended to less viscous aqueous solutions which are more relevant for biological systems and biotechnological applications.

Rate of biodistribution of STEALTH liposomes to tumor and skin: influence of liposome diameter and implications for toxicity and therapeutic activity

The influence of diameter on the pharmacokinetic and biodistribution of STEALTH liposomes into the tumor (4T1 murine mammary carcinoma) and cutaneous tissues (skin and paws) of mice was studied to ascertain the time course of liposome accumulation and to determine if a preferential accumulation of liposomes into tumor over skin or paws could be achieved by altering liposome size. These tissues were chosen as the dose-limiting toxicity for Caelyx/Doxil in humans is palmar-plantar erythrodysesthesia, a cutaneous toxicity. We examined liposomes of four diameters: 82, 101, 154, or 241 nm. Liposomes with the three smallest diameters showed similar accumulation profiles that were significantly higher than the largest liposomes in all three tissues of interest. We were unable to achieve a preferential accumulation of liposomes into tumor over skin or paws based on size alone, as evidenced by the tumor to skin and tumor to paw ratios. However, there were differences in the time courses of liposome accumulation in these three tissues. Liposome levels plateaued in tumors and paws within 24 h, whereas skin levels plateaued between 24 and 48 h. The therapeutic activity of liposomal doxorubicin of three diameters (100, 157, and 255 nm) was tested in the same model. All formulations delayed tumor growth, with liposomes of 100 or 157 nm being equally efficacious and superior to liposomes of 255 nm.

Adventures in targeting

An overview of our experiences in the field of immunoliposomal anticancer drugs is provided with respect to choice of ligand, and choice of model system, in order to provide some guidance as to the rational use of this new technology. Liposomes targeted by either peptide or monoclonal antibodies showed significantly higher binding to their respective target cells in vitro compared to non-targeted liposomes in all model systems examined. This higher binding led to higher cytotoxicities relative to non-targeted liposomes. For the immunoliposomes to deliver their entrapped drug to target cell in vivo, long circulations half-lives are required. We have evaluated the pharmacokinetics of liposomes prepared by several different coupling techniques, and have found significant differences in the clearance of these immunoliposomes from the circulation. Immunoliposomes prepared with whole anti-CD19 IgG coupled by the Mal-PEG-DSPE method demonstrated a short plasma half-life, which may reflect the random orientation of the MAb on the liposome surface. Coupling methods that mask or eliminate the Fc region result in immunoliposomes that have clearance rates more similar to untargeted liposomes. Insertion of peptides or antibodies into pre-formed liposomes through incubation with ligand-coupled PEG micelles resulted in immunoliposomes, termed post-insertion liposomes, that demonstrated comparable in vitro binding, pharmacokinetic profiles and in vivo therapeutic efficacy to liposomes made by conventional coupling methods. The therapeutic efficacy of liposomes, prepared by various coupling methods and targeted by different ligands, was compared in several different animal models of either haematological malignancies, pseudometastatic disease or solid tumours. In our hands, successful in vivo targeting has been obtained when the target is either small or readily accessible from the vasculature, where the liposomes have longer circulating half-lives and/or where a ligand against an internalizing epitope has been chosen. These results should aid in the rational design of applications for immunoliposomal drugs in the future.

Targeting Stealth liposomes in a murine model of human small cell lung cancer

Tumor accumulation and therapeutic activity of Stealth liposomes loaded with doxorubicin (DXR) were examined in Balb/c nude mice xenografts inoculated subcutaneously with the human small cell lung cancer (SCLC) cell line, H69. Mice were treated with non-targeted liposomes (SL) or liposomes targeted with antagonist G coupled to the liposome surface (SLG). SLG showed 30-44-fold higher binding to H69 cells harvested from H69 xenografts than SL. At 48 and 72 h post injection, tumor accumulation of [(125)I]tyraminylinulin-containing liposomes was shown to be dependent on liposome size but independent of the presence of the targeting ligand. Maximum tumor uptake of either SLG or SL ranged from 2 to 4% of injected dose/g of tissue. In therapeutic studies, mice received three weekly injections of 3 or 6 mg free DXR/kg or 3 or 10 mg liposomal DXR/kg at initial tumor volumes of either 7 or 33 mm(3). The therapeutic efficacy of DXR-containing SL or SLG was significantly improved over free DXR, but SLG did not improve anti-tumor efficacy relative to SL. Stealth liposomes containing DXR have potential as a therapy against human SCLC tumors.