Selective targeting of immunoliposomal doxorubicin against human multiple myeloma in vitro and ex vivo

Targeted Approaches to Inhibit Sialylation of Multiple Myeloma in the Bone Marrow Microenvironment

Aberrant glycosylation modulates different aspects of tumor biology, and it has long been recognized as a hallmark of cancer. Among the different forms of glycosylation, sialylation, the addition of sialic acid to underlying oligosaccharides, is often dysregulated in cancer. Increased expression of sialylated glycans has been observed in many types of cancer, including multiple myeloma, and often correlates with aggressive metastatic behavior. Myeloma, a cancer of plasma cells, develops in the bone marrow, and colonizes multiple sites of the skeleton including the skull. In myeloma, the bone marrow represents an essential niche where the malignant cells are nurtured by the microenvironment and protected from chemotherapy. Here, we discuss the role of hypersialylation in the metastatic process focusing on multiple myeloma. In particular, we examine how increased sialylation modulates homing of malignant plasma cells into the bone marrow by regulating the activity of molecules important in bone marrow cellular trafficking including selectins and integrins. We also propose that inhibiting sialylation may represent a new therapeutic strategy to overcome bone marrow-mediated chemotherapy resistance and describe different targeted approaches to specifically deliver sialylation inhibitors to the bone marrow microenvironment.

Immunoliposomes: A review on functionalization strategies and targets for drug delivery

Nanoparticles, especially liposomes, have gained prominence in the field of drug delivery for the treatment of human diseases, particularly cancer; they provide several advantages, including controlled drug release, protection of the drug against degradation, improved pharmacokinetics, long circulation, and passive targeting to tumors and inflammatory sites due to the enhanced permeability and retention effect. The functionalization of liposomes with monoclonal antibodies or antibody fragments to generate immunoliposomes has emerged as a promising strategy for targeted delivery to and uptake by cells overexpressing the antigens to these antibodies, with a consequent reduction in side effects. In this review, we address functionalization strategies for the non-covalent and covalent attachment of monoclonal antibodies and their fragments to liposomal surfaces. The main reaction occurs between the sulfhydryl groups of thiolated antibodies and maleimide-containing liposomes. Furthermore, we explore the main targeting possibilities with these ligands for the treatment of a variety of pathologies, including HER2- and EGFR-positive cancers, inflammatory and cardiovascular diseases, infectious diseases, and autoimmune and neurodegenerative diseases, which have not previously been reviewed together. Overall, many studies have shown selective delivery of immunoliposomes to target cells, with promising in vivo results, particularly for cancer treatment. Although clinical trials have been conducted, immunoliposomes have not yet received clinical approval. However, immunoliposomes are promising formulations that are expected to become available for therapeutic use after clinical trials prove their safety and efficacy, and after scaling issues are resolved.

Identification of a nanobody specific to human pulmonary surfactant protein A

Nanobody (Nb) is a promising vector for targeted drug delivery. This study aims to identify an Nb that can specifically target the lung by binding human pulmonary surfactant protein A (SP-A). Human lung frozen tissue sections were used for 3 rounds of biospanning of our previously constructed Nb library for rat SP-A to establish a sub-library of Nb, which specifically bound human lung tissues. Phage-ELISA was performed to screen the sub-library to identify Nb4, which specifically bound human SP-A. The binding affinity Kd of Nb4 to recombinant human SP-A was 7.48 × 10⁻⁷ M. Nb4 (19 kDa) was stable at 30 °C–37 °C and pH 7.0–7.6 and specifically bound the SP-A in human lung tissue homogenates, human lung A549 cells, and human lung tissues, whereas didn’t react with human liver L-02 cells, kidney 293T cells, and human tissues from organs other than the lung. Nb4 accumulated in the lung of nude mice 5 minutes after a tail vein injection of Nb4 and was excreted 3 hours. Short-term exposure (one month) to Nb4 didn’t cause apparent liver and kidney toxicity in rats, whereas 3-month exposure resulted in mild liver and kidney injuries. Nb4 may be a promising vector to specifically deliver drugs to the lung.

Targeted liposomal drug delivery systems for the treatment of B cell malignancies

Nanoparticulate systems have demonstrated significant potential for overcoming the limitations of non-specific adverse effects related to chemotherapy. The treatment of blood malignancies employing targeted particulate drug delivery systems presents unique challenges and considerable research has been focused towards the development of targeted liposomal formulations for B cell malignancies. These formulations are aimed at achieving selectivity towards the malignant cells by targeting several cell surface markers which are over-expressed in that specific malignancy. CD19, CD20, CD22 and CD74 are few of such markers of which CD19, CD22 and CD74 are internalizing and CD20 is non-internalizing. Systems which have been developed to target both types of these cell surface markers are discussed. Specifically, the efficacy and development of targeted liposomes is considered. A number of studies have demonstrated the advantages of targeted liposomal systems encapsulating doxorubicin or vincristine. However, liposomal encapsulation of newer anti-neoplastic agents such as AD 198 which are superior to doxorubicin should be considered.

Monoclonal antibody-based therapies in cancer: advances and challenges

Conventional anticancer therapeutics often suffer from lack of specificity, resulting in toxicities to normal healthy tissues and poor therapeutic index. Antibody-mediated delivery of anticancer drugs or toxins to tumor cells through tumor selective or overexpressed antigens is progressively being recognized as an effective strategy for increasing the therapeutic index of anticancer drugs. In this review we focus on three therapeutic modalities in the field of antibody-mediated targeting, including antibody-drug conjugates (ADCs), immunotoxins (ITs) and immunoliposomes (ILs). Design considerations for development of each of the above therapeutic modalities are discussed. Furthermore, an overview of ADCs, ITs or ILs approved for use in clinical oncology and those currently in clinical development is provided. Challenges encountered by the field of antibody-based targeting are discussed and concepts around development of the next generation of antibody therapeutics are presented.

Paramagnetic liposome nanoparticles for cellular and tumour imaging

In this review we discuss the development of paramagnetic liposomes incorporating MRI contrast agents and show how these are utilized in cellular imaging in vitro. Bi-functional, bi-modal imaging paramagnetic liposome systems are also described. Next we discuss the upgrading of paramagnetic liposomes into bi-modal imaging neutral nanoparticles for in vivo imaging applications. We discuss the development of such systems and show how paramagnetic liposomes and imaging nanoparticles could be developed as platforms for future multi-functional, multi-modal imaging theranostic nanodevices tailor-made for the combined imaging of early stage disease pathology and functional drug delivery.

The use of single chain Fv as targeting agents for immunoliposomes: an update on immunoliposomal drugs for cancer treatment

IMPORTANCE OF THE FIELD

Targeted liposomal drugs represent the next evolution of liposomal drug delivery in cancer treatment. In various preclinical cancer models, antibody-targeted PEGylated liposomal drugs have demonstrated superior therapeutic effects over their non-targeted counterparts. Single chain Fv (scFv) has gained popularity in recent years as the targeting agent of choice over traditional targeting agents such as monoclonal antibodies (mAb) and antibody fragments (e.g., Fab').

AREAS COVERED IN THIS REVIEW

This review is focused mainly on advances in scFv-targeted liposomal drug delivery for the treatment of cancers, based on a survey of the recent literature, and on experiments done in a murine model of human B-lymphoma, using anti-CD19 targeted liposomes targeted with whole mAb, Fab' fragments and scFv fragments.

WHAT THE READER WILL GAIN

This review examines the recent advances in PEGylated immunoliposomal drug delivery, focusing on scFv fragments as targeting agents, in comparison with Fab' and mAb.

TAKE HOME MESSAGE

For clinical development, scFv are potentially preferred targeting agents for PEGylated liposomes over mAb and Fab', owing to factors such as decreased immunogenicity, and pharmacokinetics/biodistribution profiles that are similar to non-targeted PEGylated (Stealth) liposomes.

Targeting and internalization of sterically stabilized liposome modified with ZCH-4-2E8

Sterically stabilized liposome (SL) modified with 2E8 monoclonal antibody (2E8-SL) was prepared in order to evaluate its targeting ability and internalization efficiency against tumor cells with high expression of CD19. 2E8 was coupled to the surface of SL using post-insertion technique. The shape of liposomes was observed under a transmission electronic microscope. The average size of liposomes was determined by using the Zetasizer instrument. The binding and internalization of 2E8-SL against tumor cells with higher expression of CD19 were tested by flow cytometry and confocal microscopy. The mean diameter of 2E8-SL was 121.25 nm. 2E8-SL was stable after up to 24 days in various buffers. 2E8-SL showed specific binding to tumor cells with high expression of CD19, including B cells in peripheral blood mononuclear cells (PBMCs). 2E8-SL could efficiently internalize into Nalm6 cells with CD19 high expression. It is suggested that 2E8-SL may serve as useful delivery carrier of anti-cancer drugs targeting to hematological malignant tumors with CD19 high expression.

The folate receptor: what does it promise in tissue-targeted therapeutics?

For over a decade the folate receptor has been intensively investigated as a means for tumor-specific delivery of a broad range of experimental therapies including several conceptually new treatments. Despite a few set backs in clinical trials, the literature is replete with encouraging in vitro and pre-clinical studies of gynecological and other tumors and more therapeutic approaches are ready for clinical testing. Recent studies have added myelogenous leukemias to the list of candidate cancers for FR-targeted therapies. Each approach faces unique challenges in translation that could be addressed through a mechanistic understanding of the function and expression of the receptor in the appropriate experimental systems and by improvements in the technology. This review discusses FR in the context of positive recent developments in broad areas of FR-targeted therapy and attempts to highlight its potential and the anticipated challenges.

Expression and purification of two anti-CD19 single chain Fv fragments for targeting of liposomes to CD19-expressing cells

Antibody-targeted liposomal anticancer drugs combine the specificity of antibodies with large payloads of entrapped drugs. We previously showed that liposomal doxorubicin (DXR) targeted via anti-CD19 monoclonal antibodies (mAb) or their Fab' fragments against the B-cell antigen CD19 led to improved therapeutic effects in murine B-cell lymphoma models relative to non-targeted liposomal DXR. We now are examining the use of anti-CD19 single chain fragments of the antibody variable region (scFv) as a targeting moiety, to test the hypothesis that scFv have advantages over full-sized mAb or Fab' fragments. We expressed two different anti-CD19 scFv constructs, HD37-C and HD37-CCH in E. coli, and purified the scFvs using two different methods. The HD37-CCH construct was selected for coupling studies due to its relative stability and activity in comparison to HD37-C. When coupled to liposomes, the HD37-CCH scFv showed increased binding in vitro to CD19-positive Raji cells, compared to non-targeted liposomes. Cytotoxicity data showed that HD37-CCH scFv-targeted liposomes loaded with DXR were more cytotoxic than non-targeted liposomal DXR. Our results suggest that anti-CD19 scFv constructs should be explored further for their potential in treating B-lymphoid leukemias and lymphomas.

Development and application of CD19-specific T cells for adoptive immunotherapy of B cell malignancies

The graft-versus-leukemia (GVL)-effect achieved by donor-derived T cells arising from transplanted allogeneic hematopoietic stem cells or given as donor-leukocyte infusions (DLI) after allogeneic transplant, demonstrates that donor-derived T cells can eradicate B-lineage malignancies. However, graft-versus-host-disease (GVHD) occurring after allogeneic hematopoietic stem-cell transplant (HSCT) or polyclonal DLI can limit the efficacy of these interventions. This toxicity can be avoided by using autologous T cells and/or tumor-specific cytotoxic T lymphocytes (CTLs). To generate antigen-specific T cells that can be derived from the allogeneic donor or the patient, we have genetically manipulated T cells to express a CD19-specific chimeric immunoreceptor. This renders T cells specific for CD19, a cell surface molecule found on B-lineage leukemia and lymphoma. This review will demonstrate the redirected specificity of CD19-specific T cells and implementation of clinical trials using these cellular agents.

Drug delivery systems for oestrogenic hormones and antagonists: the need for selective targeting in estradiol-dependent cancers

The pleiotropic activity of oestrogens and their mechanism of action via their binding to the two oestrogen receptors alpha (ER alpha) and beta (ER beta) subtypes in the different tissues where oestrogens exert their action have been briefly described. The fate of these compounds trapped into different galenic forms is discussed with regard to their therapeutic applications. Firstly, the advantages and disadvantages of the different forms (pills, i.v. forms and transdermal patches) used in contraception are compared. Secondly, the therapeutic use of formulated oestrogens for the post-menopausal hormone replacement therapy (HRT) is analysed through the various results obtained in different trials. The link between HRT and the risks of breast cancer and cardiovascular disease is underlined. Finally, comparing the activity of selective oestrogen receptor modulators such as tamoxifen and pure anti-oestrogens such as RU58668 and ICI182780, we analysed the reasons leading to the need for a tumor targeting of the latters, but not of the former for the treatment of oestrogen-dependent breast cancer. Different injectable and biodegradable formulations, that lead to a remarkable anti-tumor efficiency in xenografts, have been recently developed and we believe that they may represent promising new administration ways of added therapeutic values for anti-oestrogens. Such devices could be extended to the delivery of other anti-cancer drugs with more aggressive activities than anti-oestrogens.

In vitro cytotoxic study of immunoliposomal doxorubicin targeted to human CD34+ leukemic cells

The expression of CD34 antigen in acute myelogenous leukemias is considered an unfavourable prognosis marker for response to anticancer drugs and duration of remission. This study investigated the applicability of long-circulating immunoliposomes loaded with doxorubicin targeted to CD34 antigen present on MDR(+) human myelogenous leukemia KG-1a cell line. Immunoliposomal doxorubicin showed a higher cytotoxicity against KG-1a cells than non-targeted liposomal doxorubicin, but it did not improve over that of free drug. Although no reversal of doxorubicin resistance was found to occur through its liposomal encapsulation, a therapeutic benefit can be obtained by the selective cytotoxicity observed. Endocytosis studies demonstrated that, after binding to CD34 antigen, the immunoliposomes are not internalized by the KG-1a cells and so the cytotoxic effect might be due to drug released into the space near the cell membrane. Thus, immunotargeting of liposomal doxorubicin to CD34(+) leukemic cells may only provide an ex vivo strategy for site-selective CD34(+) leukemia cell killing.

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.

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.

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.

Receptor induction and targeted drug delivery: a new antileukaemia strategy

Strategic modalities of drug delivery have the potential to greatly improve the therapeutic efficacy of available drugs in acute myelogenous leukaemia (AML). Folate receptor (FR) type beta is selectively expressed on the surface of approximately 70% of AMLs. Increased FR-beta expression in these cells can be induced by all-trans retinoic acid (ATRA) and other retinoid compounds in the absence of terminal differentiation or cell growth inhibition. An apparent post-transcriptional modification prevents FR-beta in normal haematopoietic cells from binding folate, in contrast to AML cells. FR-beta may, therefore, be used as a target for the selective delivery of chemotherapeutic drugs to AML cells; this treatment modality appears to be particularly efficacious when administered in conjunction with retinoid-induction of FR-beta. FR-targeted liposomal drug delivery can also bypass the P-glycoprotein (P-gp)-mediated drug efflux pump commonly associated with multiple drug resistance in AML. The rationale and merits of this novel experimental treatment for AML and the current status of this research are provided.

Tumor-cell targeted epiderimal growth factor liposomes loaded with boronated acridine: uptake and processing

PURPOSE

The aim of this work was to investigate the cellular binding and processing of polyethylene glycol-stabilized epidermal growth factor (EGF) liposomes. The liposomes were actively loaded with water-soluble boronated acridine (WSA), primarily developed for boron neutron capture therapy.

METHODS

The uptake, internalization, and retention of EGF-liposome conjugates were studied in two cultured monolayer cell-lines, A-431 and U-343, with regard to the nuclide-label on the targeting agent, the carrier, and the load. The subcellular localization of WSA was studied using confocal microscopy.

RESULTS

We found that the liposome complex was internalized after specific binding to the EGF receptor. After internalization in the tumor cells, WSA was distributed mainly in the cytoplasm and was shown to have long cellular retention, with 80% of the boron remaining after 48 h.

CONCLUSIONS

The long retention of the compound and the cellular boron concentration reached makes these targeted liposomes interesting for further development toward boron neutron capture therapy.

Ligand-targeted therapeutics in anticancer therapy

Cytotoxic chemotherapy or radiotherapy of cancer is limited by serious, sometimes life-threatening, side effects that arise from toxicities to sensitive normal cells because the therapies are not selective for malignant cells. So how can selectivity be improved? One strategy is to couple the therapeutics to antibodies or other ligands that recognize tumour-associated antigens. This increases the exposure of the malignant cells, and reduces the exposure of normal cells, to the ligand-targeted therapeutics.

Polyethyleneimine-based immunopolyplex for targeted gene transfer in human lymphoma cell lines

BACKGROUND

Specific and efficient delivery of genes into targeted cells is a priority objective in non-viral gene therapy. Polyethyleneimine-based polyplexes have been reported to be good non-viral transfection reagents. However, polyplex-mediated DNA delivery occurs through a non-specific mechanism. This article reports the construction of an immunopolyplex, a targeted non-viral vector based on a polyplex backbone, and its application in gene transfer over human lymphoma cell lines.

METHODS

Targeting elements (biotin-labeled antibodies), which should recognize a specific element of the target cell membrane and promote nucleic acid entry into the cell, were attached to the polyplex backbone through a bridge protein (streptavidin). Immunopolyplex transfection activity was studied in several hematological cell lines [Jurkat (CD3+/CD19-), Granta 519 (CD3-/ CD19+), and J.RT3-T3.5 (CD3-/CD19-)] using the EGFP gene as a reporter gene and anti-CD3 and anti-CD19 antibodies as targeting elements. Transfection activity was evaluated via green fluorescence per cell and the percentage of positive cells determined by flow cytometry.

RESULTS

A significant selectivity of gene delivery was observed, since the anti-CD3 immunopolyplex worked only in Jurkat cells while the anti-CD19 immunopolyplex worked only in the Granta cell line. Moreover, transfection of a CD3+/CD3- cell mixture with anti-CD3 immunopolyplexes showed up to 16-fold more transfection in CD3+ than in CD3- cells. Several non-specific transfection reagents showed poor or no transfection activity.

CONCLUSION

It is concluded that immunopolyplex is a good non-viral vector for specific and selective nucleic acid delivery. Immunopolyplex design allows easy replacement of the targeting element (antibody) - the streptavidin-polyplex backbone remaining intact - thereby conferring high versatility.

Targeted delivery and triggered release of liposomal doxorubicin enhances cytotoxicity against human B lymphoma cells

Dioleoylphosphatidylethanolamine (DOPE)-containing liposomes that demonstrated pH-dependent release of their contents were stabilized in the bilayer form through the addition of a cleavable lipid derivative of polyethylene glycol (PEG) in which the PEG was attached to a lipid anchor via a disulfide linkage (mPEG-S-S-DSPE). Liposomes stabilized with either a non-cleavable PEG (mPEG-DSPE) or mPEG-S-S-DSPE retained an encapsulated dye at pH 5.5, but treatment at pH 5.5 of liposomes stabilized with mPEG-S-S-DSPE with either dithiothreitol or cell-free extracts caused contents release due to cleavage of the PEG chains and concomitant destabilization of the DOPE liposomes. While formulations loaded with doxorubicin (DXR) were stable in culture media, DXR was rapidly released in human plasma. pH-Sensitive liposomes, targeted to the CD19 epitope on B-lymphoma cells, showed enhanced DXR delivery into the nuclei of the target cells and increased cytotoxicity compared to non-pH-sensitive liposomes. Pharmacokinetic studies suggested that mPEG-S-S-DSPE was rapidly cleaved in circulation. In a murine model of B-cell lymphoma, the therapeutic efficacy of an anti-CD19-targeted pH-sensitive formulation was superior to that of a stable long-circulating formulation of targeted liposomes despite the more rapid drug release and clearance of the pH-sensitive formulation. These results suggest that targeted pH-sensitive formulations of drugs may be able to increase the therapeutic efficacy of entrapped drugs.

Possibility of the reversal of multidrug resistance and the avoidance of side effects by liposomes modified with MRK-16, a monoclonal antibody to P-glycoprotein

For cancer chemotherapy, avoiding the side effects of chemotherapeutic agents is difficult. Multidrug resistance is one of the major obstacles to successful cancer chemotherapy. P-Glycoprotein (P-gp) serves as an efflux pump and plays a key role in the multidrug resistance. We examined the effect of MRK-16, a monoclonal antibody against P-gp, modified liposomes (MRK-Lip) on the human myelogenous leukemia K-562 cells and its adriamycin resistance cell line K-562/ADM cells to avoid the side effects and to reverse the multidrug resistance. The uptake of vincristine (VCR) by K-562/ADM cells was lower than that by K-562 cells. This low uptake was increased in the presence of verapamil and MRK-16, however, it was not increased in the presence of control antibody, IgG2A. The binding of MRK-Lip to K-562/ADM cells was higher than that of IgG2A-modified liposome (IgG-Lip) and liposome without modification (Cont-Lip). Moreover, the cytotoxicity of VCR-encapsulated MRK-Lip to K-562/ADM cells was higher than that of VCR-encapsulated IgG-Lip and Cont-Lip. These results suggest that the interaction between liposomes and multidrug resistance cells was increased by the modification of liposomes with MRK-16. Consequently, the usefulness of MRK-Lip in cancer chemotherapy as a potent carrier was suggested.

In vitro and in vivo comparison of immunoliposomes made by conventional coupling techniques with those made by a new post-insertion approach

Ligand-targeted liposomes have the potential to increase the therapeutic efficacy of antineoplastic agents. Recently, a combinatorial approach to the preparation of ligand-targeted liposomes has been developed, termed the post-insertion technique, which will facilitate the production of targeted liposomes. In this paper, Stealth immunoliposomes (SIL) coupled to anti-CD19 made by either a conventional coupling technique (SIL[anti-CD19]), or by the post-insertion technique (PIL[anti-CD19], were compared with respect to their in vitro binding and cytotoxicity and their ability to improve in vivo survival in tumor-bearing mice. The in vitro binding and uptake of PIL[anti-CD19] by CD19-expressing, B-cell lymphoma (Namalwa) cells was similar to that of SIL[anti-CD19] and both were significantly higher than binding of non-targeted liposomes (SL). In addition, no significant differences were found between the respective in vitro cytotoxicities of doxorubicin-loaded PIL[anti-CD19] or SIL[anti-CD19], or in their in vivo therapeutic efficacy in a murine model of human B-lymphoma. Overall, the results demonstrate that the post-insertion technique is a simple, flexible and effective means for preparing targeted liposomal drugs for clinical applications.

p-Nitrophenylcarbonyl-PEG-PE-liposomes: fast and simple attachment of specific ligands, including monoclonal antibodies, to distal ends of PEG chains via p-nitrophenylcarbonyl groups

We have attempted to simplify the procedure for coupling various ligands to distal ends of liposome-grafted polyethylene glycol (PEG) chains and to make it applicable for single-step binding of a large variety of a primary amino group-containing substances, including proteins and small molecules. With this in mind, we have introduced a new amphiphilic PEG derivative, p-nitrophenylcarbonyl-PEG-1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (pNP-PEG-DOPE), synthesized by reaction of DOPE with excess of bis(p-nitrophenylcarbonyl)-PEG in a chloroform/triethylamine mixture. pNP-PEG-DOPE readily incorporates into liposomes via its PE residue, and easily binds primary amino group-containing ligands via its water-exposed pNP groups, forming stable and non-toxic urethane (carbamate) bonds. The reaction between the pNP group and the ligand amino group proceeds easily and quantitatively at pH around 8.0, and remaining free pNP groups are promptly eliminated by spontaneous hydrolysis. Therefore, pNP-PEG-DOPE could serve as a very convenient tool for protein attachment to the distal ends of liposome-grafted PEG chains. To investigate the applicability of the suggested protocol for the preparation of long-circulating targeted liposomes, we have coupled several proteins, such as concanavalin A (ConA), wheat germ agglutinin (WGA), avidin, monoclonal antimyosin antibody 2G4 (mon2G4), and monoclonal antinucleosome antibody 2C5 (mon2C5) to PEG-liposomes via terminal pNP groups and studied whether the specific activity of these immobilized proteins is preserved. The method permits the binding of several dozens protein molecules per single 200 nm liposome. All bound proteins completely preserve their specific activity. Lectin-liposomes are agglutinated by the appropriate polyvalent substrates (mannan for ConA-liposomes and glycophorin for WGA-liposomes); avidin-liposomes specifically bind with biotin-agarose; antibody-liposomes demonstrate high specific binding to the substrate monolayer both in the direct binding assay and in ELISA. A comparison of the suggested method with the method of direct membrane incorporation was made. The effect of the concentration of liposome-grafted PEG on the preservation of specific protein activity in different coupling protocols was also investigated. It was also shown that pNP-PEG-DOPE-liposomes with and without attached ligands demonstrate increased stability in mouse serum.