Targeting of human and mouse T-lymphocytes by monoclonal antibody-HPMA copolymer-doxorubicin conjugates directed against different T-cell surface antigens

Targeted Delivery of Recombinant Heat Shock Protein 27 to Cardiomyocytes Promotes Recovery from Myocardial Infarction

Ischemic heart disease, especially myocardial infarction (MI), is the leading cause of death worldwide. Apoptotic mechanisms are thought to play a significant role in cardiomyocyte death after MI. Increased production of heat shock proteins (Hsps) in cardiomyocytes is a normal response to promote tolerance and to reduce cell damage. Hsp27 is considered to be a therapeutic option for the treatment of ischemic heart disease due to its protective effects on hypoxia-induced apoptosis. Despite its antiapoptotic effects, the lack of strategies to deliver Hsp27 to the heart tissue in vivo limits its clinical applicability. In this study, we utilized an antibody against the angiotensin II type 1 (AT1) receptor, which is expressed immediately after ischemia/reperfusion in the heart of MI rats. To achieve cardiomyocyte-targeted Hsp27 delivery after ischemia/reperfusion, we employed the immunoglobulin-binding dimer ZZ, a modified domain of protein A, in conjunction with the AT1 receptor antibody. Using the AT1 receptor antibody, we achieved systemic delivery of ZZ-TAT-GFP fusion protein into the heart of MI rats. This approach enabled selective delivery of Hsp27 to cardiomyocytes, rescued cells from apoptosis, reduced the area of fibrosis, and improved cardiac function in the rat MI model, thus suggesting its applicability as a cardiomyocyte-targeted protein delivery system to inhibit apoptosis induced by ischemic injury.

HPMA Copolymer-Drug Conjugates with Controlled Tumor-Specific Drug Release

Over the past few decades, numerous polymer drug carrier systems are designed and synthesized, and their properties are evaluated. Many of these systems are based on water-soluble polymer carriers of low-molecular-weight drugs and compounds, e.g., cytostatic agents, anti-inflammatory drugs, or multidrug resistance inhibitors, all covalently bound to a carrier by a biodegradable spacer that enables controlled release of the active molecule to achieve the desired pharmacological effect. Among others, the synthetic polymer carriers based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers are some of the most promising carriers for this purpose. This review focuses on advances in the development of HPMA copolymer carriers and their conjugates with anticancer drugs, with triggered drug activation in tumor tissue and especially in tumor cells. Specifically, this review highlights the improvements in polymer drug carrier design with respect to the structure of a spacer to influence controlled drug release and activation, and its impact on the drug pharmacokinetics, enhanced tumor uptake, cellular trafficking, and in vivo antitumor activity.

A new construct of antibody-drug conjugates for treatment of B-cell non-Hodgkin's lymphomas

The aim of this study was to develop a new class of antibody-drug conjugates (ADCs) with the potential to not only enhance treatment efficacy but also improve tolerability for patients with B-cell lymphomas. Classic ADCs consist of monoclonal antibodies (mAbs) linked to drugs or toxins. They selectively deliver toxic moieties to tumor cells. As such, they greatly improve the therapeutic index compared to traditional chemotherapeutic agents. However, the therapeutic efficacy and safety of ADCs are dependent on linker stability and payload toxicity. Limited payload number on a single antibody (drug-to-antibody ratio, or DAR) has been driving investigators to use extremely toxic agents; however, even very low off-target binding of these ADCs may kill patients. Herein we report a new design of ADCs that consists of rituximab (RTX) and N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-epirubicin conjugates. The latter was selectively attached to RTX via reduced disulfide bonds. Such design allows the introduction of a large payload of drug on the antibody without adding attachment sites and without compromising the antigen-targeting ability. The binding of the new conjugate, namely RTX-P-EPI, to Ramos cells (with high CD20 expression) was confirmed. The cytotoxicity of RTX-P-EPI against Raji and Ramos cells was also determined. Interestingly, two-fold inhibition of cell proliferation was observed when using RTX-P-EPI compared with their equivalent physical mixture of RTX and P-EPI. Treatment of male SCID mice bearing subcutaneous Ramos B-cell lymphoma tumors demonstrated that RTX-P-EPI possessed superior efficacy when compared to combination of RTX with chemotherapy EPI (RTX+EPI) and P-EPI (RTX+P-EPI), whereas single RTX and a non-specific conjugate IgG-P-EPI only showed marginal effect. The conjugate RTX-EPI in which EPI was directly attached to RTX demonstrated much less antitumor activity compared with RTX-P-EPI. The results suggest that this new design possesses synergistic potential of immunotherapy combined with established macromolecular therapy; moreover, a conventional chemo-agent could be utilized to generate highly effective ADCs and to achieve lower risk of off-target toxicity.

Poly(Ethylene Glycol)-Doxorubicin Conjugates with pH-Controlled Activation

The synthesis and physico-chemical characterisation of a biodegradable multiblock polymer drug carrier based on poly(ethylene glycol) (PEG) is described. The blocks of PEG ( Mw 2,000) are connected by an enzymatically degradable tripeptide derivative consisting of one lysine and two glutamic acid residues. Doxorubicin (Dox), was attached to the polymer carrier via a hydrazone bond susceptible to acid hydrolysis at pH 5.0. Human immunoglobulin (IgG) was covalently linked to the polymer-Dox conjugate by the reaction of 2-pyridyldisulfanyl groups of the polymer with thiol groups of the antibody modified with 2-iminothiolane. The resulting antibody-polymer-drug conjugates were characterised by size-exclusion chromatography, UV/VIS spectrophotometry, electrophoresis and amino acid analysis. All polymers studied (both with and without IgG) showed high anti-proliferative activity against concanavalin A-stimulated murine splenocytes and various cancer cell lines in vitro. The polymer-Dox conjugate (without IgG) exhibited a significant anti-tumor efficacy against murine EL4 T-cell lymphoma and human colorectal carcinoma SW620 in vivo.

Poly(Hpma)-coated liposomes demonstrate prolonged circulation in mice

Surface modification of liposomes with amphiphilic flexible polymers significantly prolongs their circulation time in blood and reduces uptake by cells of the reticuloendothelial system (RES). Several polymers have already been shown to provide steric protection to liposomes. Still more polymers are expected to serve this purpose, thus broadening the variability of properties of long-circulating liposomes. Poly[N-(2-hydroxypropyl)methacrylamide] (poly (HPMA)) seems to have some properties similar to polyethylene glycol (PEG), the most widely used polymer in liposome surface modification, including flexibility, hydrophilicity and low immunogenicity, which suggest that it may also function as an efficient steric protector of liposomes. Semitelechelic poly(HPMA) with single- or double-oleic acid hydrophobic terminus were synthesized and incorporated into the surface of liposomes composed of phosphatidylcholine and cholesterol. These poly(HPMA)-modified liposomes provided strong steric protection for liposomes, increasing their circulation time and decreasing liver accumulation in experimental mice. Poly(HPMA)-modified liposomes may become a useful addition to a family of long-circulating liposomes with potential to be used as a drug delivery system.

Targeting of multidrug-resistant human ovarian carcinoma cells with anti-P-glycoprotein antibody conjugates

A monoclonal antibody (mAb) to P-glycoprotein (Pgp), UIC2, is used as a targeting moiety for N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer/drug [(meso chlorin e(6) mono(N-2-aminoethylamide) (Mce(6)) or doxorubicin (DOX)] conjugates to investigate their cytotoxicity towards the Pgp-expressing human ovarian carcinoma cell line A2780/AD. The binding, internalization, and subcellular trafficking of a fluorescein labeled UIC2 targeted HPMA copolymer are studied and show localization to the plasma membrane with limited internalization. The specificity of the UIC2-targeted HPMA copolymer/drug conjugates are confirmed using the sensitive cell line A2780 that does not express Pgp.

Targetable HPMA copolymer-aminohexylgeldanamycin conjugates for prostate cancer therapy

PURPOSE

This study focuses on the synthesis and characterization of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-cyclo-RGD (Arg-Gly-Asp) conjugates for delivery of geldanamycin to prostate tumors.

MATERIALS AND METHODS

HPMA copolymers containing aminohexylgeldanamycin (AH-GDM) with and without the targeting peptide RGDfK were synthesized and characterized. Drug release from copolymers was evaluated using cathepsin B. Competitive binding of copolymer conjugates to alpha(v)beta(3) integrin was evaluated in prostate cancer (PC-3) and endothelial (HUVEC) cell lines and in vitro growth inhibition was assessed. The maximum tolerated dose for single i.v. injections of free drug and the conjugates was established in nude mice.

RESULTS

HPMA copolymers containing AH-GDM and RGDfK showed active binding to the alpha(v)beta(3) integrin similar to that of free peptide. Similarly, growth inhibition of cells by conjugates was comparable to that of the free drug. Single intravenous doses of HPMA copolymer-AH-GDM-RGDfK conjugates in mice were tolerated at 80 mg/kg drug equivalent, while free drug caused morbidity at 40 mg/kg. No signs of toxicity were present in mice receiving HPMA copolymer-AH-GDM-RGDfK over the 14-day evaluation period.

CONCLUSION

Results of in vitro activity and in vivo tolerability experiments hold promise for the utility of HPMA copolymer-AH-GDM-RGDfK conjugates for treatment of prostate cancer with greater efficacy and reduced toxicity.

Treatment with HPMA copolymer-based doxorubicin conjugate containing human immunoglobulin induces long-lasting systemic anti-tumour immunity in mice

Linkage of doxorubicin (Dox) to a water-soluble synthetic N-(2-hydroxypropyl)methacrylamide copolymer (PHPMA) eliminates most of the systemic toxicity of the free drug. In EL-4 lymphoma-bearing C57BL/6 mice, a complete regression of pre-established tumours has been achieved upon treatment with Dox-PHPMA-HuIg conjugate. The treatment was effective using a range of regimens and dosages, ranging from 62.5 to 100% cured mice treated with a single dose of 10-20 mg of Dox eq./kg, respectively. Fractionated dosages producing lower levels of the conjugate for a prolonged time period had substantial curative capacity as well. The cured mice developed anti-tumour protection as they rejected subsequently re-transplanted original tumour. The proportion of tumour-protected mice inversely reflected the effectiveness of the primary treatment. The treatment protocol leading to 50% of cured mice produced only protected mice, while no mice treated with early treatment regimen (i.e. starting on day 1 after tumour transplantation) rejected the re-transplanted tumour. Exposure of the host to the cancer cells was a prerequisite for developing protection. The anti-tumour memory was long lasting and specific against the original tumour, as the cured mice did not reject another syngeneic tumour, melanoma B16-F10. The immunity was transferable to naïve recipients in in vivo neutralization assay by spleen cells or CD8(+) lymphocytes derived from cured animals. We propose an effective treatment strategy which eradicates tumours without harming the protective immune anti-cancer responses.

Preparation and characterisation of antibody modified gelatin nanoparticles as drug carrier system for uptake in lymphocytes

Established methods of protein chemistry can be used for the effective attachment of drug targeting ligands to the surface of protein-based nanoparticles. In the present work gelatin nanoparticles were used for the attachment of biotinylated anti-CD3 antibodies by avidin-biotin-complex formation. These antibody modified nanoparticles represent a promising carrier system for the specific drug targeting to T-lymphocytes. The objective of this work was the comprehensive quantification of every chemical reaction step during the preparation procedure of these cell specific nanoparticles. Gelatin nanoparticles were formed by a two-step desolvation process. After the first desolvation step the remaining sediment and the supernatant were analysed for molecular weight distribution by size exclusion chromatography (SEC). Nanoparticles then were formed using the high molecular gelatin fraction and subsequently were stabilised by glutaraldehyde crosslinking. A part of the detectable amino groups on the particle surface was reacted with 2-iminothiolane in order to introduce reactive sulfhydryl groups. The thiolated nanoparticles were coupled to NeutrAvidin (NAv) which previously was activated with the heterobifunctional crosslinker sulfo-MBS. All these reaction steps were quantified by photometry or gravimetry. The functionality of NAv after covalent conjugation was confirmed by a biotin-4-fluorescein assay. The NAv-modified nanoparticles then were used for the binding of biotinylated anti-CD3 antibodies by avidin-biotin-complex formation. A highly effective attachment of the ligand was ascertained by different, indirect methods: immunoblotting and fluorimetry. Therefore, a well-defined nanoparticle system with drug targeting ligand modification was established that holds promise for further effective preclinical testing.

HPMA copolymers containing doxorubicin bound by a proteolytically or hydrolytically cleavable bond: comparison of biological properties in vitro

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer carrier containing the anticancer drug doxorubicin bound either by a proteolytically degradable bond (non-targeted PK1 or targeted with alpha-CD71 mAb) or by a hydrolytically degradable bond were synthesised and tested in vivo for various biological properties. Mouse 38C13 B-cell lympoma was used as a well established and defined cell line for this study. 38C13 cells are sensitive to free doxorubicin and IC50 was very low, about 0.014 microM. PK1 showed a strongly decreased cytostatic effect, IC50 being 12.6 microM. alpha-CD71 targeted conjugate, which can be considered as an antibody-targeted form of PK1, had IC50 0.358 microM. HPMA copolymer with doxorubicin bound via a hydrolytically sensitive bond (HYD conjugate) showed a high cytostatic effect with IC50 about 0.052 microM. We demonstrated that HYD conjugate inhibited DNA synthesis and induced p21(Waf1/Cip1) protein expression (p21(Waf1/Cip1) is cyclin-dependent kinase inhibitor which blocks cell cycle progression) as quickly as free doxorubicin, whereas PK1 acted much more slowly. Similarly, apoptosis induction measured by Annexin V binding and Caspase 3 activity was detected later after incubation of cells with PK1 or alpha-CD71 targeted conjugate. Apoptosis was manifested by elevation of bax and bad mRNA levels, which was much more rapid and intense in the case of free doxorubicin and HYD conjugate. Expression of antiapoptotic genes as well as cyclin-dependent kinases was surprisingly not affected.

Polymeric anticancer drugs with pH-controlled activation

The paper is dealing with the synthesis and properties of new, nontargeted or antibody-targeted pH-sensitive polymer-doxorubicin (DOX) conjugates designed as anticancer drugs facilitating site-specific therapy. These conjugates are stable and inactive during transport in the body but activate inside target cells as a result of pH changes outside and inside the cells. Cytotoxicity of the conjugates depends on the detailed structure of the polymer and of the spacer between the drug and polymer carrier. In both protective and therapeutic regimes of drug administration, the in vivo antitumor activity of the pH-sensitive conjugates containing DOX was significantly enhanced (T-cell lymphoma EL 4, C57BL/16 mice) in comparison with the free DOX or classic PK1, the PHPMA-DOX conjugate clinically tested at present.

Multivalent Conjugates of Poly-γ-d-glutamic Acid fromBacillus licheniformiswith Antibody F(ab‘) and Glycopeptide Ligands

Poly-gamma-D-glutamic acid from Bacillus licheniformis is a water-soluble, nontoxic, nonimmunogenic exopolymer. Using synthetic linkers, the alpha-carboxylate side chains of PGA were conjugated to an exposed thiol side chain of an antibody F(ab') fragment, Mc109F4. Analysis of the PGA-Mc109F4 conjugate by gel filtration HPLC revealed a mixture of multivalent conjugates. The PGA-Mc109F4 conjugate retained biological activity, but showed a lower binding affinity to target BCL3B3 cells than free Mc109F4 F(ab')(2) by flow cytometry, and a lower efficacy for BCL3B3 growth inhibition than free Mc109F4 F(ab')(2). PGA was also conjugated with the free amino group of glycopeptide antibiotic vancomycin. The PGA-vancomycin conjugate showed slightly lower antibacterial activity than free vancomycin versus susceptible Bacillus subtilis, but slightly higher activity versus intrinsically resistant Leuconostoc mesenteroides.

Differences in the intracellular fate of free and polymer-bound doxorubicin

Internalization and subcellular fate of free doxorubicin or its polymeric conjugates based on poly N-(2-hydroxypropyl)methacrylamide (pHPMA), either non-targeted or targeted with anti-Thy1.2 or anti-CD71 monoclonal antibody was tested on EL-4 mouse T-cell lymphoma, SW620 human colorectal carcinoma and OVCAR-3 human ovarian adenocarcinoma. Doxorubicin fluorescence allowed us to follow the internalization and intracellular distribution of tested conjugates by laser scanning confocal microscopy and/or by fluorescent microscopy. Whereas free doxorubicin was always detectable only in the nuclei of treated cells, detectable fluorescence of doxorubicin bound to a polymeric carrier, targeted or non-targeted, was detectable up to 3 days of incubation only in the cytoplasmatic structures. While free doxorubicin causes apoptosis in the populations of tested cancer cell lines, significant number of apoptotic cells was never found in cell cultures exposed to targeted or non-targeted polymeric conjugates. In contrast to free doxorubicin, which is a strong inducer of p53 expression, increased p53 expression was never observed after the treatment with the polymeric drug. High-performance liquid chromatographic analysis shows that the percentage of cleaved doxorubicin is very low even after 48 h of incubation of tested cells with the polymeric conjugate, and cannot be the only reason for the toxicity of the conjugate. We suggest that: (a) after the treatment with pHPMA-bound drug, the cells die by necrosis and (b) the toxicity of pHPMA-based conjugates is a combination of the toxic effect of released doxorubicin and the toxic effect of doxorubicin in polymer-bound form directed against cell membranes.

Star structure of antibody-targeted HPMA copolymer-bound doxorubicin: a novel type of polymeric conjugate for targeted drug delivery with potent antitumor effect

The aim of this study was to compare the properties and antitumor potential of a novel type of antibody-targeted N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound doxorubicin conjugates with star structure with those of previously described classic antibody-targeted or lectin-targeted HPMA copolymer-bound doxorubicin conjugates. Classic antibody-targeted conjugates were prepared by aminolytic reaction of the multivalent HPMA copolymer containing side-chains ending in 4-nitrophenyl ester (ONp) reactive groups with primary NH(2) groups of the antibodies. The star structure of antibody-targeted conjugates was prepared using semitelechelic HPMA copolymer chains containing only one reactive N-hydroxysuccinimide group at the end of the backbone chain. In both types of conjugates, B1 monoclonal antibody (mAb) was used as a targeting moiety. B1 mAb recognizes the idiotype of surface IgM on BCL1 cells. The star structure of the targeted conjugate had a narrower molecular mass distribution than the classic structure. The peak in the star structure was around 300-350 kDa, while the classic structure conjugate had a peak around 1300 kDa. Doxorubicin was bound to the HPMA copolymer via Gly-Phe(D,L)-Leu-Gly spacer to ensure the controlled intracellular delivery. The release of doxorubicin from polymer conjugates incubated in the presence of cathepsin B was almost twice faster from the star structure of targeted conjugate than from the classic one. The star structure of the targeted conjugate showed a lower binding activity to BCL1 cells in vitro, but the cytostatic activity measured by [(3)H]thymidine incorporation was three times higher than that seen with the classic conjugate. Cytostatic activity of nontargeted and anti-Thy 1.2 mAb (irrelevant mAb) modified HPMA copolymer-bound doxorubicin was more than hundred times lower as compared to the star structure of B1 mAb targeted conjugate. In vivo, both types of conjugates targeted with B1 mAb bound to BCL1 cells in the spleen with approximately the same intensity. The classic structure of the targeted conjugate bound to BCL1 cells in the blood with a slightly higher intensity than the star structure. Both types of targeted conjugates had a much stronger antitumor effect than nontargeted HPMA copolymer-bound doxorubicin and free doxorubicin. The star structure of targeted conjugate had a remarkably higher antitumor effect than the classic structure: a single intravenous dose of 100 microg of doxorubicin given on day 11 completely cured five out of nine experimental animals whereas the classic structure of targeted conjugate given in the same schedule only prolonged the survival of experimental mice to 138% of control mice. These results show that the star structure of antibody-targeted HPMA copolymer-bound doxorubicin is a suitable conjugate for targeted drug delivery with better characterization, higher cytostatic activity in vitro, and stronger antitumor potential in vivo than classic conjugates.

Targeted drug conjugates: principles and progress

Reports of targeting drugs using antibodies have appeared in the literature since 1958, but exciting clinical results in this field have only been reported in the last few years. Progress in this field has occurred largely through an understanding how drug-immunoconjugates work. The objective of this review is to draw together the fundamental principles on which this field of work is based, to examine the evidence supporting those principles, and the effectiveness and selectivity of targeted drug conjugates. The activity of many drug-immunoconjugates can now largely be accounted for by the underlying principles. Excellent development work, both with conventional anti-cancer agents and very potent drugs have led to a number of interesting clinical trials. In the best Phase I and II trials, good evidence of effectiveness have been reported, which suggest that drug-immunoconjugates may now be heralding a new era for chemotherapy.

Doxorubicin bound to a HPMA copolymer carrier through hydrazone bond is effective also in a cancer cell line with a limited content of lysosomes

We have synthesized conjugates containing doxorubicin (DOX) bound to oligopeptide side chains (GlyGly or GlyPheLeuGly) of a water-soluble copolymer carrier based on poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) either through proteolytically (PK1 conjugates) [Synthetic polymeric drugs. U.S. Patent 5,037,883 (1991)] or hydrolytically cleavable bond (HC conjugates). Pharmacological efficacy of PK1 and HC conjugates was compared in vitro on murine: T-cell lymphoma EL4, B-cell leukemia BCL1, B-cell lymphoma 38C13, leukemia P388 and Con A-stimulated A/Ph splenocytes and on human: primary (SW480) and metastatic (SW620) colorectal cancer cell lines parent and transfected with Thy 1.2 gene [2] and on erythromyeloid leukemia cell line K 562. Inhibition of proliferation determined by 3[H]-thymidine incorporation revealed that the cytostatic effect of HC conjugates is up to two orders of magnitude higher compared to PK1 conjugates. In some cancer cell lines (SW 620/T, SW 480) the pharmacological activity of HC conjugates is in vitro comparable with the activity of the free drug. Unlike PK1 conjugates, HC conjugates with a lysosomally degradable spacer (GlyPheLeuGly) are less effective compared to HC conjugates containing lysosomally non-degradable spacer (GlyGly). Moreover, HC conjugates exert pronounced anti-proliferative activity also in erythroblastoid leukemia cell line K 562 with a limited content of lysosomes.

Antiproliferative effect of a lectin- and anti-Thy-1.2 antibody-targeted HPMA copolymer-bound doxorubicin on primary and metastatic human colorectal carcinoma and on human colorectal carcinoma transfected with the mouse Thy-1.2 gene

The aim of this study was to compare the potential of two plant lectins [peanut agglutinin (PNA) and wheat germ agglutinin (WGA)], monoclonal antibody (anti-Thy-1.2), its F(ab')(2) fragments, and galactosamine as targeting moieties bound to the polymer drug carrier to deliver a xenobiotic, doxorubicin, to selected cancer cell lines. We have used primary (SW 480, HT 29) and metastatic (SW 620) human colorectal cancer cell lines and a transfectant, genetically engineered SW 620 cell line with mouse gene Thy-1.2 (SW 620/T) to test the possibility of marking human cancer with xenogeneic mouse gene and use it for effective site-specific targeting. The targeting moieties and doxorubicin were conjugated to a water-soluble copolymer based on N-(2-hydroxypropyl)methacrylamide (HPMA) acting as a carrier responsible for controlled intracellular release of the targeted drug. FACS analysis showed a strong binding of WGA-FITC to all tested cell lines. Binding of PNA-FITC was considerably weaker. The in vitro antiproliferative effect of lectin-targeted HPMA carrier-bound doxorubicin evaluated as [(3)H]TdR incorporation reflected both the intensity of the binding and the different sensitivity of the tested cancer cells lines to doxorubicin. The antiproliferative effect of conjugates targeted with WGA was comparable to that with the conjugates targeted with the anti-Thy-1.2 monoclonal antibody or their F(ab')(2) fragments. The magnitude of the cytotoxic effect of HPMA-doxorubicin targeted with PNA was lower in all tested cell lines. While the conjugates with WGA were more cytotoxic, the conjugates with PNA were more specific as their binding is limited to cancer cells and to the sites of inflammation. Noncytotoxic conjugates with a very low concentration of doxorubicin and targeted with PNA, anti-Thy-1.2, or their F(ab')(2) fragments exerted in some lines (SW 480, SW 620) low mitogenic activity. The Thy-1.2 gene-transfected SW 620 metastatic colorectal cancer cell line was sensitive to the antiproliferative effect of Thy-1.2-targeted doxorubicin as was shown for the Thy-1. 2(+) EL4 cell line and for Thy-1.2(+) concanavalin A-stimulated mouse T lymphocytes. These results represent the first indication of the suitability of transfection of human cancer cells with selected targeting genes for site-specific therapy of malignancies.

Poly(ethylene glycol) multiblock copolymer as a carrier of anti-cancer drug doxorubicin

The synthesis of a novel water-soluble polymer drug carrier system based on biodegradable poly(ethylene glycol) block copolymer is described in this paper. The copolymer consisting of PEG blocks of molecular weight 2000 linked by means of an oligopeptide with amino end groups was prepared by interfacial polycondensation of the diamine and PEG bis(succinimidyl carbonate). The structure of the oligopeptide diamine consisting of glutamic acid and lysine residues was designed as a substrate for cathepsin B, a lysosomal enzyme, which was assumed to be one of the enzymes responsible for the degradation of the polymer carrier in vivo. Each of the oligopeptide blocks incorporated in the carrier contained three carboxylic groups of which some were used for attachment of an anti-cancer drug, doxorubicin (Dox), via a tetrapeptide spacer Gly-Phe-Leu-Gly. This tetrapeptide spacer is susceptible to enzymatic hydrolysis. In vitro release of Dox and the degradation of the polymer chain by cathepsin B as well as preliminary evaluation of in vivo anti-cancer activity of the conjugate are also demonstrated.

Polymeric drugs based on conjugates of synthetic and natural macromolecules. I. Synthesis and physico-chemical characterisation

This paper describes the synthesis, physico-chemical characteristics and results of selected biological tests of conjugates of antibodies or proteins with poly(HPMA) or with poly(HPMA) carriers of anti-cancer drug doxorubicin, designed for targeted cancer therapy. Two types of conjugates differing in the method of conjugation of polymer with protein were synthesized. In the first, protein is attached to the polymer via an oligopeptide sequence in the side chain of the polymer backbone and, in the second, the polymer is attached to protein via its end-chain functional group. Conjugation of an antibody with poly(HPMA) does not influence the binding activity of the antibody for cell surface antigen. The physico-chemical characteristics and biological activity of both systems depend on the detailed structure of the polymer, the type of antibody or protein moiety and the structure of the whole system.

A versatile method for the conjugation of proteins and peptides to poly[2-(dimethylamino)ethyl methacrylate]

Random copolymers of 2-(dimethylamino) ethyl methacrylate (DMAEMA) with aminoethyl methacrylate (AEMA) were synthesized by radical polymerization. The amount of incorporated primary amino groups could be controlled by the feed ratio of AEMA to DMAEMA, and was varied from 2 to 6 mol %. Subsequently, protected thiol groups were introduced in a derivatization step with N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) and subsequent treatment with dithiothreitol (DTT). The obtained thiolated p(DMAEMA-co-AEMA) was conjugated to transferrin (Tf) or the F(ab') fragment of mAb 323/A3 via a disulfide linkage. Moreover, the maleimide derivative of the nuclear localization signal (NLS) decapeptide Gly-Pro-Lys-Lys-Lys-Arg-Lys-Val-Glu-Asp-NH(2) was coupled to the thiolated polymer via a thioether linkage. The coupling efficiency, as determined by GPC (Tf), SDS-PAGE [F(ab')], or (1)H NMR (NLS peptide) was 90-95% for the Tf conjugate, and more than 95% for the F(ab') conjugate and the NLS conjugate. The synthetic strategy described in this paper is a universal method for the preparation of conjugates of proteins and peptides with pDMAEMA in particular. This method can possibly be used to synthesize protein-polymethacrylate conjugates in general.