Abnormal differentiation of thymocytes induced by free cyclosporine is avoided when cyclosporine bound to N-(2-hydroxypropyl)methacrylamide copolymer carrier is used

Beyond oncology--application of HPMA copolymers in non-cancerous diseases

Macromolecular drug conjugates have been developed to improve the efficacy and safety profile of various therapeutic agents for many years. Among them, N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-drug conjugates are the most extensively studied delivery platforms for the effective treatment of cancer. In recent years, the applications of HPMA copolymers for the treatment of a broader range of non-cancerous diseases have also been explored. This review highlights the recent developments in the rational design, synthesis, and evaluation of novel HPMA copolymer-drug conjugates for non-cancerous diseases, such as musculoskeletal diseases, infectious diseases and spinal cord injury. The translation potential of these applications is also briefly discussed.

Clinical experience with anthracycline antibiotics-HPMA copolymer-human immunoglobulin conjugates

This paper reviews an early clinical experience with anthracycline (epirubicin; Epi or doxorubicin; Dox) containing an N-(2-hydroyxypropyl)methacrylamide copolymer carrier targeted with autologous or commercial human immunoglobulin in six patients aged 28-55 suffering from therapy-resistant metastatic cancer. More than 100 biochemical, hematological and immunological parameters, including nine tumor markers, were tested in blood samples taken 24 h after the first and up to 10 months after the last application. The intravenous application proceeded without serious adverse or side effects and did not require hospitalization. Cardiotoxicity was not observed. Four of six monitored patients attained stabilization of disease (liver ultrasound scan and bone computer tomography) with a very good quality of life lasting from seven up to 18 months. Positive response to the treatment was, among others, evaluated as decreased CA 15-3 and CEA tumor markers. In three of five tested patients the serum level of C-reactive protein was temporarily increased 72 h after the treatment. A stable or elevated number of peripheral blood reticulocytes together with activation of natural killer (NK) cells and lymphokine-activated killer (LAK) cells supports the data previously obtained in experimental animals pointing to a dual role, i.e. the cytotoxic and immunomobilizing character of doxorubicin-HPMA conjugates.

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.

Acquired and specific immunological mechanisms co-responsible for efficacy of polymer-bound drugs

We present data providing new evidence that poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA)-bound drugs, unlike free drugs, have both cytostatic and immunomobilizing activity (CIA). Immediately after injection, due to the high level of the drug, the main activity of the polymeric conjugate is cytotoxic and cytostatic. Later on, long-term circulating PHPMA-bound drug, at concentrations lower than its minimal inhibitory levels, mobilizes the defense mechanisms of the host. Cytotoxic and cytostatic effects of drug-PHPMA were repeatedly confirmed. The following data support the concept of the immunomobilizing activity of the N-(2-hydroxypropyl)methacrylamide (HPMA) conjugates: (a) pre-treatment with free drugs (doxorubicin, cyclosporin A) accelerates the appearance of EL4 mouse T-cell lymphoma while a similar pre-treatment with doxorubicin-PHPMA induces limited but definitive mobilization of the host's defense mechanisms; (b) mice cured of EL4 mouse T-cell lymphoma, BCL1 mouse B-cell leukemia and 38C13 mouse B-cell lymphoma by injection of doxorubicin-PHPMA conjugate targeted with monoclonal antibodies (anti-Thy 1.2 for EL4, anti-B1 for BCL1 and anti-CD71 for 38C13) and re-transplanted with a lethal dose of the same cancer cells survive without any treatment considerably longer than control mice; (c) increased NK activity and anti-cancer antibody was detected only in animals treated with doxorubicin-PHPMA conjugate; and (d) considerably increased NK and LAK activity was seen in a human patient treated for generalized breast carcinoma with doxorubicin-PHPMA-IgG.

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.

Polymeric drugs based on conjugates of synthetic and natural macromolecules. II. Anti-cancer activity of antibody or (Fab')(2)-targeted conjugates and combined therapy with immunomodulators

We provide data on in vivo targeting of the Thy 1.2 (CDw90) cell surface receptor expressed on neoplastic T cells, mouse EL4 T cell lymphoma. The targeting antibody and the anticancer drug, doxorubicin (DOX) 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 conjugated drug. The in vivo therapeutic efficacy of HPMA copolymer-bound DOX targeted with anti-EL4 antibody, polyclonal anti-thymocyte globulin (ATG), monoclonal anti-Thy 1.2 antibody or its F(ab')(2) fragment was compared with the efficacy of DOX conjugated to HPMA copolymer containing nonspecific IgG or bovine serum albumin (BSA). Anti-EL4 antibody-targeted conjugate caused a significant retardation of tumor growth and an extension of the life span of treated mice. The effect was comparable with that of HPMA copolymer-bound DOX targeted with ATG, anti-Thy 1.2 antibody or its F(ab')(2) fragment. However, considerable antitumor effect was seen also in conjugates targeted instead of specific antibodies with syngeneic nonspecific IgG or BSA. Patients with advanced cancer are often immunocompromised due to dysfunction of their immune system induced by cancer and cytotoxic drugs. A significant decrease of unwanted side-effects of targeted drugs against a number of vital organs was already documented. In this study we have compared immunotoxic effects of free DOX with those of its antibody-targeted form on NK cells and cytolytic T lymphocytes (CTLs) isolated from C57BL/10 mice bearing EL4 T cell lymphoma. In the same model we have tested the combination therapy with immunomodulators (beta-glucan or AM-2) injected together with targeted daunomycin. We have observed a significant protective effect of targeted DOX against NK cells and CTLs. Moreover, the data revealed that combination therapy considerably enhances antitumor efficacy of the targeted anticancer drug.

A possibility to overcome P-glycoprotein (PGP)-mediated multidrug resistance by antibody-targeted drugs conjugated to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer carrier

N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing doxorubicin (DOX) and different targeting moieties were developed with the aim of specific chemotherapy. Two of them, HPMA-conjugated DOX and galactosamine-targeted DOX, are in phase II clinical trials in the U.K. We studied the effect of conjugates with different targeting moieties (anti-CD71, antithymocyte globulin, anti-CD4, transferrin) on human or mouse multidrug resistance (MDR) cell lines (CEM/VLB, P388-MDR). It was shown that targeting decreases the level of MDR for DOX and the level of MDR depends on the targeting moiety used. The combination of these conjugates with chemosensitisers (cyclosporin A, D, G) restored almost completely the sensitivity of MDR cell lines to that of parental sublines. These results suggest that different intracellular trafficking of these conjugates (in membrane-limited organelles) in contrast to free diffusion for low molecular weight compounds might partially overcome P-glycoprotein (Pgp)-mediated MDR. We also report here the development of biodegradable HPMA hydrogels suitable for prolonged release of the cytostatic drug and chemosensitiser as a potential approach to overcome MDR mediated by Pgp.

Synthesis and pharmacokinetics of a novel macromolecular prodrug of Tacrolimus (FK506), FK506-dextran conjugate

A novel macromolecular prodrug of Tacrolimus (FK506), FK506-dextran conjugate, was developed and its physico-chemical, biological and pharmacokinetic characteristics were studied. The conjugate was estimated to contain 0.45% of FK506 and the coupling molar ratio was approximately 1:1 (dextran-FK-506). Adsorption experiments using ion exchangers indicated that FK506-dextran conjugate acted as a weakly negatively charged macromolecule. Low molecular weight radioactive compound(s), which was eluted in the same fractions as [(3)H]FK506, was released from [(3)H]FK506-dextran conjugate by chemical hydrolysis with a half-life of 150 h in phosphate buffer. In vitro immunosuppressive activity of the conjugate, as assessed by the rat lymphocyte stimulation test, was almost comparable to that of free FK506, suggesting that biologically active FK506 could be liberated from the conjugate. In vitro biodistribution studies demonstrated that conjugation with the dextran derivative dramatically changed the pharmacokinetic properties of FK506 after intravenous injection in rats. AUC of the FK506-dextran conjugate was almost 2000 times higher than that of free FK506 and organ uptake clearances of the conjugate were significantly smaller than those of the free drug. Thus, the present study has demonstrated that the FK506-dextran conjugate behaves as a prodrug of FK506 with an extended blood circulating time and can be expected to have an improved therapeutic potency.

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

Binding of HPMA copolymer-conjugated doxorubicin targeted with monoclonal antibodies directed against various T-cell surface receptors, i.e. Thy1.2 (CDw90), I-A (MHC class II. glycoprotein), L3T4 (CD4), IL-2R (CD25) and CD3, is considerably increased in Con A stimulated T-lymphocytes. FACS analysis showed that the binding is most intensive with anti-Thy1.2 and anti-L3T4 targeted derivatives and it is proportional to the antiproliferative effect of the antibody-targeted drug. No binding and no antiproliferative capacity was observed after in vitro incubation of mouse T-cells with a nonspecific mouse IgG-HPMA-DOX conjugate. [3H]-TdR incorporation was inhibited considerably more in Con A stimulated T-cell culture and in EL4 mouse T-cell lymphoma as compared with the culture of nonactivated T-lymphocytes. This proves that intensively proliferating cells are more susceptible to the inhibitory action of an antibody-targeted drug. The cytotoxic efficacy of HPMA copolymer with GlyPheLeuGly or GlyLeuPheGly side-chains to which the drug is conjugated was superior to HPMA copolymer with GlyPheGly or GlyLeuGly side-chains. However, there is no direct correlation between the rate of in vitro drug release and the in vitro cytotoxicity of the respective conjugates. This suggests that the rate of drug release from the conjugate is only one factor responsible for the pharmacological efficacy of the preparation. Furthermore, we detected substantial and prolonged inhibition of proliferation of Con A activated T-cells only if doxorubicin was injected in vivo in the form of an anti-Thy1.2-targeted conjugate.