Potential of Sugar Residues Attached to N-(2- Hydroxypropyl)methacryl amide Copolymers as Targeting Groups for the Selective Delivery of Drugs

Soluble copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) have already shown potential as targetable drug-carriers. Here HPMA copolymers were synthesized which contained N-linked aminosugars attached to the poly mer backbone via a diglycyl side-chain. Following radioiodination their body distribution in rats was investigated. Incorporation of mannosamine or glu cosamine caused enhanced deposition in liver macrophages following intra venous and intraperitoneal administration, and increased retention at the site of injection when the carrier was administered subcutaneously. Macrophage pinocytic uptake of certain HPMA copolymers was also assessed using rat peri toneal macrophages cultured in vitro. It was demonstrated that polymers bear ing mannosamine or glucosamine are internalized rapidly by a common recep tor and that the interaction can be inhibited by free D-mannose, L-fucose, but not by D-glucose.

Feasibility of using a bone-targeted, macromolecular delivery system coupled with prostaglandin E(1) to promote bone formation in aged, estrogen-deficient rats

PURPOSE

Macromolecular delivery systems have therapeutic uses because of their ability to deliver and release drugs to specific tissues. The uptake and localization of HPMA copolymers using Asp(8) as the bone-targeting moiety was determined in aged, ovariectomized (ovx) rats. PGE(1) was attached via a cathepsin K-sensitive linkage to HPMA copolymer-Asp(8) conjugate and was tested to determine if it could promote bone formation.

MATERIALS AND METHODS

The uptake of FITC-labeled HPMA copolymer-Asp(8) conjugate (P-Asp(8)-FITC) on bone surfaces was compared with the mineralization marker, tetracycline. Then a targeted PGE(1)-HPMA copolymer conjugate (P-Asp(8)-FITC-PGE(1)) was given as a single injection and its effects on bone formation were measured 4 weeks later.

RESULTS

P-Asp(8)-FITC preferentially deposited on resorption surfaces, unlike tetracycline. A single injection of P-Asp(8)-FITC-PGE(1) resulted in greater indices of bone formation in aged, ovx rats.

CONCLUSIONS

HPMA copolymers can be targeted to bone surfaces using Asp(8), with preferential uptake on resorption surfaces. Additionally, PGE(1) attached to the Asp(8)-targeted HPMA copolymers and given by a single injection resulted in greater bone formation measured 4 weeks later. This initial in vivo study suggests that macromolecular delivery systems targeted to bone may offer some therapeutic opportunities and advantages for the treatment of skeletal diseases.

Liberation of doxorubicin from HPMA copolymer conjugate is essential for the induction of cell cycle arrest and nuclear fragmentation in ovarian carcinoma cells

Despite intensive study, the molecular mechanism for cell toxicity of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound doxorubicin remains unclear. Moreover, the ability of the released drug to accumulate in the nucleus has also been questioned. We have hypothesized that the pattern of cell cycle progression is a useful indicator for the presence of free doxorubicin in the nucleus and its interaction with nuclear DNA. The effects of HPMA copolymer-bound doxorubicin on cell cycle progression were evaluated in this study in cultured human ovarian cancer A2780 cells. We determined that P-GFLG-DOX, but not P-GG-DOX, initiates cell cycle arrest and nuclear fragmentation in the same manner as free DOX, but with a time-delay. Our data indicate that drug release from the conjugate is required for the apoptotic activity associated with the conjugate.

Cathepsin K inhibitor–polymer conjugates: potential drugs for the treatment of osteoporosis and rheumatoid arthritis

The role of the newly discovered cysteine protease, cathepsin K, in osteoporosis and rheumatoid arthritis is reviewed. The current development of cathepsin K inhibitors and their targeted delivery using synthetic polymer carriers are discussed. Future challenges and possible strategies to improve these delivery systems are addressed.

Design of a multivalent galactoside ligand for selective targeting of HPMA copolymer–doxorubicin conjugates to human colon cancer cells

N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymers have been shown to be efficient carriers for anticancer drugs because of their versatile chemistry and good biocompatibility. As demonstrated with hepatocytes, targeting efficacy of anticancer drugs could be further improved when the drug (doxorubicin) was conjugated to HPMA copolymers with biorecognisable groups, such as simple carbohydrates. The present study was devised to learn whether the cluster (multivalent) construction of carbohydrate residues could improve the targeting capability of HPMA copolymer-doxorubicin (DOX) conjugates towards human colon adenocarcinoma cells. DOX was linked via a lysosomally degradable tetrapeptide sequence to HPMA copolymers bearing galactosamine (GalN), lactose (Lac), or multivalent galactose residues (TriGal) to produce targetable polymeric drug carriers. The effect of the type of sugar moiety and its three-dimensional cluster arrangement on biorecognition by three human colon-adenocarcinoma cell lines was studied. The role of galectin-3 in the biorecognition of HPMA copolymer conjugates was explored. Biorecognition of the targetable (glycoside-bearing) conjugates decreased their IC(50) doses in comparison to the non-targetable (non-glycosylated) conjugates. The biorecognition of the TriGal-containing HPMA copolymer-doxorubicin conjugate by the cells was superior with concomitant decrease of its IC(50) doses. It is suggested that the increased cytotoxicity of the glycosylated HPMA-copolymer-DOX conjugates toward human colon-adenocarcinoma cells was caused by their biorecognition and effective internalisation via receptor-mediated endocytosis. All three human colon adenocarcinoma cell lines tested, Colo-205, SW-480 and SW-620, expressed the galectin-3 protein and the galectin-3-specific RNA. However, contrary to expectation, Colo-205 cells did not express a detectable amount of galectin-3 on the cell surface. This suggests that the binding of the glycoside-bearing HPMA copolymer-DOX conjugates to the cells was mediated not only by galectin-3. We conclude that targeting of the anticancer agent, doxorubicin, using HPMA copolymer conjugates bearing multivalent galactoside residues can improve their cytotoxicity.

Enhanced biorecognition and internalization of HPMA copolymers containing multiple or multivalent carbohydrate side-chains by human hepatocarcinoma cells

N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing pendant saccharide moieties (galactosamine, lactose, and triantennary galactose) were synthesized. The relationship between the content of saccharide moieties and three-dimensional arrangement of galactose residues and their biorecognition and internalization by human hepatocarcinoma HepG2 cells was investigated. The results obtained clearly indicated preferential binding of the trivalent galactose and the lactose-containing copolymers to these cells. The higher the saccharide moieties content in HPMA copolymers, the higher the levels of binding. The biorecognition of the glycosylated HPMA copolymers by HepG2 cells was inhibited by free lactose. The data on the internalization and subcellular trafficking of HPMA copolymer conjugates obtained by confocal fluorescence microscopy correlated well with the flow cytometric analysis of their biorecognition by target cells. Structural features of the glycosides responsible for the specific recognition of the HPMA copolymers have been identified. The results underline the potential of glycosylated HPMA copolymers for delivery of pharmaceutical agents to hepatocarcinoma cells.

Improved synthesis and evaluation of 17-substituted aminoalkylgeldanamycin derivatives applicable to drug delivery systems

The 17-methoxy group of geldanamycin was substituted with 1,3-diaminopropane and 1,3-diamino-2-hydroxypropane to introduce a primary amino group useful for conjugation with targeting moieties and drug carriers. We have developed a procedure that has provided improved yield and reproducibility of the syntheses. Both geldanamycin derivatives demonstrated antiproliferative activity towards the human ovarian carcinoma cell line, A2780.

Biorecognizable HPMA copolymer-drug conjugates for colon-specific delivery of 9-aminocamptothecin

N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates for colon-specific delivery of 9-aminocamptothecin (9-AC) were designed. They hold 9-AC bound via spacers containing amino acid residues and aromatic azo bonds. In vitro release profiles of 9-AC from HPMA copolymer conjugates were evaluated under artificial conditions that simulated large intestinal azoreductase and peptidase activities. The studies indicated that the azo bond was reduced first, followed by the release of unmodified 9-AC from the 9-AC containing fragment by peptidases. Release profiles depended on the chemical structure of the peptide part of the spacer. Conjugates containing leucylalanine showed high colon-specific release of 9-AC when compared to alanine containing conjugates. It appears that the studied conjugates are suitable as colon-specific drug delivery systems.

The effects of subcellular localization of N-(2-hydroxypropyl)methacrylamide copolymer-Mce(6) conjugates in a human ovarian carcinoma

Photosensitizers, light-sensitive compounds, become activated upon illumination with a specific wavelength of light generating cytotoxic oxygen species. Due to the short half-life of singlet oxygen, the subcellular site of localization and excitation affects the type of cellular damage produced as well as cellular responses to different types of photodamage created within the cell. Here, we investigated the effects of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-mesochlorin e(6) monoethylenediamine (Mce(6)) conjugates localized to different subcellular compartments. Temperature was utilized to achieve subcellular localization of conjugates and subcellular fractionation was performed to confirm localization patterns of HPMA copolymer-Mce(6) conjugates. Cytotoxicity studies suggest plasma membrane and late endosomes were more sensitive to photodamage than lysosomal compartments as observed by an approximate 2-fold decrease in the IC(50) compared to lysosomally accumulated conjugate. Releasing Mce(6) from the polymer backbone within lysosomal compartments significantly lowered the IC(50) when compared to HPMA copolymer conjugates with Mce6 bound via a nondegradable linkage. These differences will prove useful in the future design of HPMA copolymer-Mce(6) conjugates for the treatment of ovarian cancer.

Preparation and biological evaluation of polymerizable antibody Fab' fragment targeted polymeric drug delivery system

A new polymerizable antibody Fab' fragment with a PEG spacer (MA-PEG-Fab') was prepared from OV-TL 16 antibody, specific against the OA-3 antigen expressed on most human ovarian carcinomas. The MA-PEG-Fab' possessed a higher reactivity in the copolymerization with N-(2-hydroxypropyl)methacrylamide (HPMA) than the polymerizable Fab' fragment MA-Fab' with a short spacer. The MA-PEG-Fab' was copolymerized with HPMA and MA-Gly-Phe-Leu-Gly-Mce(6) producing an Fab' targeted HPMA copolymer-Mce(6) conjugate. The number and weight average molecular weights of the copolymer were 164000 and 271000 Da, respectively. About two MA-PEG-Fab' fragments per chain were incorporated in the copolymer conjugates. Preliminary in vivo antitumor studies indicated that the Fab' targeted conjugates showed a higher efficacy of tumor growth inhibition in nude mice than the non-targeted conjugate.

Potential of lectin-N-(2-hydroxypropyl)methacrylamide copolymer-drug conjugates for the treatment of pre-cancerous conditions

N-(2-Hydroxypropyl)methacrylamide (HPMA)-lectin (wheat germ agglutinin (WGA), peanut agglutinin (PNA)) drug conjugates for treatment of the pre-cancerous conditions ulcerative colitis and Barrett's esophagus are being developed. Cell-surface glycoproteins that are altered in disease and development bind lectins. PNA binds alpha-lactose and the Thomsen-Friedenreich (TF) antigen, a disease- and development-associated glycoprotein. PNA incorporation in conjugates may allow for preferential delivery to diseased over healthy tissues. Conjugates were prepared by attaching lectins to HPMA copolymers via an amide linkage. Frontal affinity chromatography was used to measure dissociation constants (K(d)) of free and conjugated lectins. Animal models of colitis (DSS, TNBS/EtOH) were developed. Human biopsy specimens were obtained. Free and HPMA copolymer-conjugated FITC-labeled lectin and anti-TF antigen antibody binding patterns were examined in normal neonatal, adult and diseased rodent tissues and normal and diseased human tissues. K(d) values of free and conjugated lectins were similar ( approximately 10(-5) M(-1)). Free and conjugated lectins had comparable binding patterns. In health, strong WGA binding was seen in goblet cells; PNA binding was minimal, occurring only in the supranuclear goblet cell region. In disease, WGA binding was not altered, but PNA binding was increased in both human and rodent tissues; entire goblets bound the lectin. Anti-TF antigen antibody binding was minimal, but did overlap with PNA binding patterns both in normal and diseased tissues. Conjugation of lectins to HPMA copolymers does not affect binding affinity. Alterations in glycoprotein structures in development and disease resulted in modified lectin binding patterns. In development and disease, the PNA binding seen was to the TF antigen and other lactose-containing glycoproteins. The results suggest that site-specific delivery of therapeutic agents such as cyclosporin A (CsA) for ulcerative colitis and mesochlorin e(6) for Barrett's esophagus may be achieved. P(HPMA)-lectin-CsA conjugates have been prepared and preliminary in vivo studies are underway.

Synthesis and characterization of HPMA copolymer-aminopropylgeldanamycin conjugates

Geldanamycin (GDM) is a benzoquinone ansamycin antibiotic with anticancer activity. The use of drug delivery systems based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing lysosomally degradable oligopeptide (GFLG) spacers results in an increased therapeutic efficacy of anticancer drugs. The objective of this study was to synthesize HPMA copolymer-GDM conjugates with anticancer activity and reduced toxic side-effect of the compound. 17-(3-Aminopropylamino)-17-demethoxygeldanamycin (AP-GDM) was synthesized and converted into a polymerizable GDM derivative, N-methacryloylglycylphenylalanylglycyl-17-(3-aminopropylamino)-17-demethoxygeldanamycin [MA-GFLG-(AP-GDM)]. The structures of AP-GDM and MA-GFLG-(AP-GDM) were validated by mass spectroscopy, elemental analysis, and two-dimensional nuclear magnetic resonance. MA-GFLG-(AP-GDM) was copolymerized with HPMA and N-methacryloyglycylglycine p-nitrophenylester by radical precipitation polymerization. Water-soluble HPMA copolymer-AP-GDM conjugates (M(r)=16 kDa) were obtained. Monoclonal antibody OV-TL16, which recognizes the OA-3 antigen expressed on the OVCAR-3 human ovarian carcinoma cell line, was optionally attached to the HPMA copolymer-AP-GDM conjugate. Cytotoxicity of polymer-bound AP-GDM (both targeted and non-targeted) was determined using OVCAR-3 and another human ovarian carcinoma cell line, A2780. The HPMA copolymer-AP-GDM conjugate was cytotoxic toward A2780 cells. Attachment of OV-TL16 antibody enhanced cytotoxicity of the conjugate toward OVCAR-3 cells.

Combination chemotherapy and photodynamic therapy of targetable N-(2-hydroxypropyl)methacrylamide copolymer-doxorubicin/mesochlorin e(6)-OV-TL 16 antibody immunoconjugates

The aim of this study was to evaluate the combination chemotherapy and photodynamic therapy of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound doxorubicin (DOX) and mesochlorin e(6) (Mce(6)) targeted with an OV-TL 16 monoclonal antibody (P-DOX-Ab and P-Mce(6)-Ab, respectively) in nude mice bearing human ovarian OVCAR-3 carcinoma xenografts. P-DOX-Ab and P-Mce(6)-Ab were synthesized by first conjugating DOX or Mce(6) to an HPMA copolymer precursor (Mw=21000), then reacting with OV-TL 16 antibody. The immunoconjugates were purified by size exclusion chromatography on Superose 6 column and analyzed. The Mce(6) concentration in tissues was determined by a fluorescence assay. Eighteen hours after administration, the tumors received a light dose of 220 J/cm(2) from a KTP 650-nm dye-laser. P-DOX-Ab and P-Mce(6)-Ab had polymer:drug:protein weight ratios of 32:3:62 and 26:2:72, corresponding to polymer:drug:protein molecular ratios of approximately 4:14:1 and 3:8:1, respectively. The biodistribution results indicated that the percentage of total administered dose of Mce(6) in tumors reached approximately 1% for the nontargeted conjugate at 18 h after administration, while that of P-Mce(6)-Ab was approximately 13 times higher. Nude mice bearing OVCAR-3 xenografts that received one i.v. dose of P-DOX-Ab (2.2 mg/kg DOX equivalent) and P-Mce(6)-Ab (1.5 mg/kg Mce(6) equivalent) with light irradiation achieved a xenograft cure rate of more than 60%. The incorporation of OV-TL 16 antibody dramatically enhanced the accumulation in tumors with a concomitant increase in the therapeutic efficacy of P-DOX-Ab and P-Mce(6)-Ab in combination therapy, which may probably be attributed to both antibody targeting and enhanced permeability and retention (EPR) effects.

Water soluble polymers in tumor targeted delivery

The rationales for the use of water soluble polymers for anticancer drug delivery include: the potential to overcome some forms of multidrug resistance, preferential accumulation in solid tumors due to enhanced permeability and retention (EPR) effect, biorecognizability, and targetability. The utility of a novel paradigm for the treatment of ovarian carcinoma in an experimental animal model, which combines chemotherapy and photodynamic therapy with polymer-bound anticancer drugs is explained. Research and clinical applications as well as directions for the future development of macromolecular therapeutics are discussed.

Preliminary evaluation of caspases-dependent apoptosis signaling pathways of free and HPMA copolymer-bound doxorubicin in human ovarian carcinoma cells

The purpose of the study was to examine the role of caspases in signaling pathways of apoptosis induced by free doxorubicin (DOX) and HPMA copolymer-bound DOX (P(GFLG)-DOX) in human ovarian carcinoma cells. Sensitive A2780 and DOX resistant A2780/AD cells were exposed to different doses of drugs within 12, 18, 24 and 36 h. Caspase activity, expression of genes encoding human caspases 1-10, Apaf-1 and bcl-2 proteins and apoptosis were studied. In sensitive cells both free and P(GFLG)-DOX activated caspases 3, 7 and 9. In addition, P(GFLG)-DOX activated caspases 6 and 8. In resistant cells apoptosis induced by free DOX depended on the activation of caspases 2, 7 and 9, while caspase 3 was not involved; this explains the low degree of apoptosis induced by free DOX in resistant cells. P(GFLG)-DOX triggered the additional caspases 3, 6 and 8. A more pronounced degree of caspase activation and apoptosis after the action of P(GFLG)-DOX depended on the inhibition of bcl-2-encoded cellular defensive mechanisms and a more significant activation of Apaf-1. It was concluded that HPMA copolymer-bound DOX induced additional caspase-dependent apoptosis signaling pathways and the degree of the induction was higher, which led to more pronounced apoptosis when compared to free DOX.

The influence of a colonic microbiota on HPMA copolymer lectin conjugates binding in rodent intestine

Germ-free (GF) animals lack a colonic microflora like that seen in conventional (CV) animals. Bacterial presence plays a role in the development of glycoproteins in the gastrointestinal (GI) tract; the absence of a microbiota has been seen to suppress the production of certain glycoproteins and glycolipids. Binding patterns of lectins are modified when glycoprotein structures are altered (e.g., during development or disease). Little information on lectin binding patterns in mature GF animals is available. We examined the binding of free and N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-conjugated fluorescein isothiocyanate (FITC)-labeled wheat germ agglutinin (WGA) [P(HPMA)-(WGA-FITC)] and FITC-labeled peanut agglutinin (PNA) [P(HPMA)-(PNA-FITC)] in CV and GF mouse colon with and without neuraminidase pretreatment. Anti-Thomsen-Friedenreich (TF) antigen (a development and disease-related glycoprotein) antibody binding was also examined in these tissues. Subtle differences were seen in the binding patterns between CV and GF animals. CV animals showed strong P(HPMA)-(WGA-FITC) binding in goblet cells, but minimal P(HPMA)-(PNA-FITC) binding was visible. In GF animals, luminal surface binding of P(HPMA)-(WGA-FITC) was visible, and goblet cell binding of P(HPMA)-(PNA-FITC) was seen. These subtle changes suggest that altered glycoprotein expression occurred under GF conditions.

Biodistribution and antitumour efficacy of long-circulating N-(2-hydroxypropyl)methacrylamide copolymer-doxorubicin conjugates in nude mice

The aim of this study was to evaluate the influence of the molecular weight (mol. wt) of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin (DOX) conjugates (P-DOX) on biodistribution and therapeutic efficacy in nu/nu mice bearing human ovarian carcinoma OVCAR-3 xenografts. Copolymerisation of HPMA, a polymerisable derivative of DOX (N-methacryloylglycylphenylalanylleucylglycyl doxorubicin) and a newly designed crosslinking agent, N(2),N(5)-bis(N-methacryloylglycylphenylalanyl-leucylglycyl)ornithine methyl ester monomers resulted in novel, high mol. wt, branched, water-soluble P-DOX containing lysosomally degradable oligopeptide sequences as crosslinks and side-chains terminated in DOX. Four conjugates with mol. wt of 22, 160, 895 and 1230 kDa were prepared. The results indicated that the half-life in blood and the elimination rate from the tumour were up to 28 times longer and 25 times slower, respectively, for P-DOX (mol. wt=1230 kDa) than for free DOX. Treatment with P-DOX (mol. wt > or = 160 kDa) inhibited tumour growth more efficiently than that of 22 kDa P-DOX or free DOX (P<0.02) at a 2.2 mg/kg DOX equivalent dose. In conclusion, the administration of long circulating P-DOX resulted in enhanced tumour accumulation with a concomitant increase in therapeutic efficacy.

Modification of cyclosporin A and conjugation of its derivative to HPMA copolymers

Cyclosporin A (CsA) was epoxidized with m-chloroperoxybenzoic acid in the presence of sodium carbonate or with tert-butyl hydroperoxide in the presence of dioxomolybdenum iminodiethanoxide. The CsA epoxide was not stable and rearranged into a compound with a more stable five-member ring structure. An amino group containing cyclosporin A derivative (CsA amine) was obtained by the reaction of CsA epoxide with excess ethylenediamine. The yield of the CsA amine was 30--40% based on the CsA. An HPMA copolymer--CsA conjugate was prepared by the reaction of the CsA amine with an HPMA and MA-Gly-Phe-Leu-Gly-ONp copolymer. The content of CsA amine in the conjugate was 8.7 wt %. The CsA amine was released from the copolymer by enzymatic hydrolysis with papain.

Chronic exposure of human ovarian carcinoma cells to free or HPMA copolymer-bound mesochlorin e6 does not induce P-glycoprotein-mediated multidrug resistance

The acquisition of multidrug resistance in human ovarian carcinoma A2780 cells was investigated after chronic exposure to free mesochlorin e6 monoethylenediamine (Mce6) and N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound Mce6 (P(GG)-Mce6). The dose that inhibits growth by 50% (IC50) was determined for free Mce6 (2.09 +/- 0.32 microM) and P(GG)-Mce6 (204.15 +/- 28.97 microM) to utilize similar effective doses of drug. A total of 14 drug exposures were performed over a period of 78 days. Cells were characterized by IC50 dose, MDR1 gene expression and anti-human P-glycoprotein (P-gp) antibody binding after each drug exposure. At the conclusion of the experiment, neither the A2780 cells habitually exposed to free Mce6 or P(GG)-Mce6 were significantly different than the control A2780 cells indicating cells did not acquire a MDR phenotype. The doxorubicin (DOX)-resistant A2780/AD cells served as a positive control.

Time- and concentration-dependent apoptosis and necrosis induced by free and HPMA copolymer-bound doxorubicin in human ovarian carcinoma cells

A2780 sensitive and A2780/AD doxorubicin (DOX) resistant human ovarian carcinoma cells were exposed to different concentrations (0.25, 0.5, 1, 5 and 10xIC(50)) of free and HPMA copolymer-bound DOX for 12, 24, 36, 48, 60 and 72 h. Apoptosis and necrosis were evaluated using the FITC-conjugated annexin V and propidium iodide staining. The data obtained showed that the induction of apoptosis and necrosis by both free DOX and HPMA copolymer-bound DOX were time- and concentration-dependent. The data also showed significant differences between the drugs. It was found that: (i) under the action of HPMA copolymer-bound doxorubicin the alterations in the plasma membrane permeability preceded disturbances in cellular metabolism; (ii) HPMA copolymer-bound doxorubicin kills the cells mainly by necrosis; (iii) HPMA copolymer-bound doxorubicin is a more effective anticancer drug than free doxorubicin.

Biorecognition of HPMA copolymer-lectin conjugates as an indicator of differentiation of cell-surface glycoproteins in development, maturation, and diseases of human and rodent gastrointestinal tissues

Lectins are proteins that bind glycoproteins; binding patterns are altered with changes in glycoprotein expression accompanying maturation or disease. Binding of two lectins, wheat germ agglutinin (WGA) and peanut agglutinin (PNA), in human and rodent colon were previously examined. Normal tissue showed intense WGA binding; PNA binding was minimal. Diseased tissues showed increased PNA binding. We hypothesized that N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-lectin-drug conjugates could deliver therapeutic agents to diseased tissues by targeting colonic glycoproteins. We examined biorecognition of free and HPMA copolymer-conjugated WGA and PNA and anti-Thomsen-Friedenreich (TF) antigen antibody binding in normal neonatal, adult, and diseased rodent tissues, human specimens of inflammation, and Barrett's esophagus. Neonatal WGA binding was comparable to the adult, with additional luminal columnar cell binding. PNA binding was more prevalent; luminal columnar cell binding existed during the first 2.5 weeks of life. WGA binding was strong in both normal and diseased adult tissues; a slight decrease was noted in disease. PNA binding was minimal in normal tissues; increases were seen in disease. Anti-TF antigen antibody studies showed that PNA did not bind to the antigen. The results suggest that HPMA copolymer-lectin-drug conjugates may provide site-specific treatment of conditions such as colitis and Barrett's esophagus.

HPMA copolymer-anticancer drug conjugates: design, activity, and mechanism of action

The design, synthesis and properties of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers as carriers of anticancer drugs are reviewed. Macromolecular therapeutics based on HPMA copolymers are biocompatible, preferentially accumulate in tumors, and possess a higher anticancer efficacy than low molecular weight drugs. Novel designs of HPMA copolymer carriers resulted in long-circulating conjugates and gene and oligonucleotide delivery systems. HPMA copolymer based macromolecular therapeutics were active against numerous cancer models and are in clinical trials. The data obtained indicated that macromolecular therapeutics activated different signaling pathways and possessed a different mechanism of action than free drugs. This bodes well for the success of future research aimed at identification of new intracellular molecular targets as a basis for the design of the second generation of macromolecular therapeutics.

Efficacy of the chemotherapeutic action of HPMA copolymer-bound doxorubicin in a solid tumor model of ovarian carcinoma

Anticancer activity and main mechanisms of action of free doxorubicin (DOX) and HPMA copolymer-bound DOX (P(GFLG)-DOX) were studied in solid tumor mice models of DOX sensitive and resistant human ovarian carcinoma. Free DOX was effective only in sensitive tumors decreasing the tumor size about three times, whereas P(GFLG)-DOX decreased the tumor size 28 and 18 times in the sensitive and resistant tumors. An enhanced accumulation of P(GFLG)-DOX in the tumor was observed, whereas only low concentrations of DOX were detected in other organs following P(GFLG)-DOX administration. This effect was dependent on the high permeability of blood vessels in untreated tumors. After treatment with P(GFLG)-DOX the permeability decreased concomitantly with the downregulation of VEGF gene expression. P(GFLG)-DOX effectively killed both types of tumors inducing apoptosis and necrosis through the activation of p53, Apaf-1, caspase 9, c-fos, or c-jun pathways, and the downregulation of the bcl-2 gene. HPMA copolymer-bound DOX preserved its activity inside cells, inhibited detoxification and defensive mechanisms encoded by GST-pi, BUDP, and HSP-70 genes, and limited DNA repair, replication, and biosynthesis by downregulation of Topo-IIalpha,beta, and TK1 genes. P(GFLG)-DOX also produced tumor tissue hypoxia and significantly activated lipid peroxidation in tumors. No damage to other organs after exposure to P(GFLG)-DOX was detectable. On the other hand, free DOX activated lipid peroxidation and led to tissue hypoxia in many organs. All data relevant to the mechanism of anticancer action of P(GFLG)-DOX indicated a higher antitumor activity and lower systemic toxicity of HPMA copolymer-bound DOX when compared with free DOX.

HPMA copolymer-modified avidin: immune response

Protein-polymer conjugates to be used in the pretargeted delivery of a photosensitizer to cells were synthesized and characterized. Avidin was modified by N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers bearing the photosensitizer, mesochlorin e6 mono(N-2-aminoethylamide) (Mce6). Synthesis of HPMA copolymer-avidin-Mce6 conjugates was carried out so that either predominantly single point attachment or multipoint attachment of copolymer chains to avidin would result. HPMA copolymer-avidin conjugates were used which retained specific binding activity to a lower affinity biotin analog. Antigen specific anti-avidin immune response was shown to be reduced six-fold in some HPMA copolymer-avidin conjugates when compared to immune response to unmodified avidin. HPMA copolymer itself was shown to elicit a very low (IgM) immune response.

Synthesis of bioadhesive lectin-HPMA copolymer-cyclosporin conjugates

An amino group containing cyclosporin A (CsA) derivative has been synthesized and conjugated to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer via an aromatic azo bond, which can be specifically cleaved by azoreductase activity in colon to release the drug for the treatment of colon diseases. Lectins, peanut (Arachis hypogea) agglutinin (PNA) and wheat germ agglutinin (WGA), have been conjugated to HPMA copolymer-CsA derivative conjugates (PCsA), respectively, to give bioadhesive conjugates. The PNA and WGA are the targeting proteins that can bind to diseased colon tissue and healthy tissue, respectively. There were on average four P(CsA) copolymer chains attached on one WGA molecule with a drug content of 16.0 wt % and five P(CsA) copolymer chains attached on one PNA molecule with a drug content of 11.5 wt %. The incubation of a P(CsA) copolymer with the rat cecal contents resulted in the cleavage of the azo bond and release of the cyclosporin derivative. The biological evaluation of the conjugates is under way.

HPMA copolymer-anticancer drug-OV-TL16 antibody conjugates. 3. The effect of free and polymer-bound adriamycin on the expression of some genes in the OVCAR-3 human ovarian carcinoma cell line

The effect of an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-Adriamycin-OV-TLl6 antibody conjugate [P(GFLG)-ADR-Ab] on OVCAR-3 human ovarian carcinoma cells was studied. A nontargeted HPMA copolymer-ADR conjugate (P(GFLG)-ADR) and free ADR were the controls. The IC(50) doses were 0.65, 3.0, and 65 microM for free ADR, targeted P(GFLG)-ADR-Ab conjugate, and nontargeted P(GFLG)-ADR conjugate, respectively. These differences reflect the different mechanisms of cell entry of the compounds evaluated. Free ADR and HPMA copolymer-ADR conjugates had different impacts on the expression of MDR1, MRP, c-fos, c-jun, and bcl-2 genes which encode the P-glycoprotein (MDR1) and the multidrug resistance-associated protein (MRP) efflux pumps, and play an important role in cell death signaling pathways (c-fos, c-jun, and bcl-2). Whereas high doses of free ADR induced MDR1 gene expression, HPMA copolymer-bound ADR appeared to be without effect. On the contrary, expression of the MRP gene was not influenced by free ADR, whereas HPMA copolymer-ADR conjugates seemed to suppress the gene expression in a concentration-dependent manner. There were differences in the expression of c-fos, c-jun, and bcl-2 genes after the incubation of OVCAR-3 cells with free and HPMA copolymer-bound ADR indicating differences in activation of cell death signaling pathways.

Polymerizable Fab' antibody fragments for targeting of anticancer drugs

We have designed a new pathway for the synthesis of targeted polymeric drug delivery systems, using polymerizable antibody Fab' fragments (MA-Fab'). The targeted systems can be directly prepared by copolymerization of the MA-Fab', N-(2-hydroxypropyl)methacrylamide (HPMA) and drug-containing monomers. Both MA-Fab' and the Fab'-targeted copolymers can effectively bind to target cells. An MA-Fab' (from OV-TL 16 Ab) targeted HPMA copolymer containing mesochlorin e6 (Mce6) was synthesized by copolymerization of MA-Fab', HPMA, and MA-GFLG-Mce6. The targeted copolymer exhibited a higher cytotoxicity toward OVCAR-3 human ovarian carcinoma cells than the nontargeted Mce6-containing copolymer or free Mce6. The targeted copolymer was internalized more efficiently by OVCAR-3 cells than the nontargeted copolymer.

High-molecular weight HPMA copolymer-adriamycin conjugates

High-molecular weight (branched) water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing lysosomally degradable oligopeptide crosslinks were synthesized by radical copolymerization of HPMA and newly designed crosslinking agents, N(2), N(5)-bis(N-methacryloylglycylphenylalanylleucylglycyl)ornithine s with different modification of the carboxy group. The length of the primary chain was controlled by the addition of a chain transfer agent, 3-mercaptopropionic acid. A polymerizable derivative of the anticancer drug adriamycin (ADR), N-methacryloylglycylphenylalanylleucylglycyl adriamycin, was added to some polymerization mixtures. This resulted in high-molecular weight, branched, water-soluble HPMA copolymers containing oligopeptide sequences in the crosslinks as well as in side-chains terminated in ADR. The degradability of the crosslinks as well as the release of ADR by lysosomal enzymes isolated from rat liver were investigated.

Photodynamic crosslinking of proteins. III. Kinetics of the FMN- and rose bengal-sensitized photooxidation and intermolecular crosslinking of model tyrosine-containing N-(2-hydroxypropyl)methacrylamide copolymers

As part of a study on the role of Tyr residues in the photosensitized intermolecular crosslinking of proteins, we have surveyed the kinetics of the rose bengal- and flavin mononucleotide (FMN)-sensitized photooxidation and crosslinking of a water-soluble N-(2-hydroxypropyl)methacrylamide copolymer with attached 6-carbon side chains terminating in tyrosinamide groups (thus the -OH group of the Tyr is free, but both the amino and carboxyl groups are blocked, simulating the situation of a nonterminal Tyr in a protein). The intermolecular photodynamic crosslinking of the Tyr copolymer can result only from the formation of Tyr-Tyr (dityrosine) bonds, because the copolymer itself is not photooxidizable. Rose bengal, primarily a Type II (singlet oxygen) sensitizer, sensitized the rapid photooxidation of the Tyr residue in the Tyr copolymer only at high pH, where the Tyr phenolic group is ionized; crosslinking did not occur with rose bengal under any of the reaction conditions used. In contrast, FMN, which can sensitize by both Type I (free radical) and Type II processes, sensitized the photooxidation of the Tyr copolymer over the pH range 4-9.5. Also, significant photocrosslinking occurred, but only from pH 4 to 8, with a maximum rate at pH 6. Crosslinking required the presence of oxygen. Studies with inhibitors, D2O as solvent, catalase and superoxide dismutase indicated that the photooxidation and photocrosslinking of the Tyr copolymer with FMN at pH 6 were not mediated by singlet oxygen, superoxide or hydrogen peroxide. It appears that crosslinking involves the abstraction of an H atom from the Tyr phenolic group to give Tyr and FMN radicals. The Tyr radical in one Tyr copolymer can then react with a Tyr radical in another Tyr copolymer to give an intermolecular dityrosine crosslink.

Comparison of the anticancer effect of free and HPMA copolymer-bound adriamycin in human ovarian carcinoma cells

PURPOSE

To study peculiarities and the mechanism of the anticancer effect of free and HPMA copolymer-bound ADR in sensitive and resistant human ovarian carcinoma cells.

METHODS

Sensitive A2780 and ADR resistant A2780/AD cells were exposed to different doses of drugs during 12, 24, 36, 48, 60, and 72 hours. Cell viability, drug accumulation, apoptosis, cellular metabolism, lipid peroxidation, DNA content and gene expression were studied.

RESULTS

HPMA copolymer-bound ADR (P(GFLG)-ADR) possessed a comparable cytotoxicity to free ADR when comparison was based on intracellular concentrations. While free ADR up-regulated genes encoding ATP driven efflux pumps (MDR1, MRP), P(GFLG)-ADR overcame existing pumps and down regulated the MRP gene. Free ADR also activated cell metabolism and expression of genes responsible for detoxification and DNA repair. P(GFLG)-ADR down-regulated HSP-70, GST-pi, BUDP, Topo-IIalpha, beta, and TK-1 genes. Apoptosis, lipid peroxidation and DNA damage were significantly higher after exposure to P(GFLG)-ADR, as reflected by simultaneous activation of p53, c-fos in A2780 cells) or c-jun (A2780/AD) signaling pathways and inhibition of the bcl-2 gene. Differences between free ADR and P(GFLG)-ADR increased with the time of incubation and drug concentration.

CONCLUSIONS

P(GFLG)-ADR overcame drug efflux pumps, more significantly induced apoptosis and lipid peroxidation, inhibited DNA repair, replication, and biosynthesis when compared to free ADR.

Biorecognition of HPMA copolymer-adriamycin conjugates by lymphocytes mediated by synthetic receptor binding epitopes

PURPOSE

The EDPGFFNVE nonapeptide (NP) was recognized as the CD21 (CR2) binding epitope of the Epstein-Barr virus (EBV) gp350/ 220 envelope glycoprotein which mediates the virus attachment to human B lymphocytes (Nemerow et al., Cell 56:369-377, 1989). Here we evaluated the targeting potential of a synthetic receptor binding epitope (NP) covalently attached to a water-soluble polymeric drug carrier. In particular, the biorecognition of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-NP conjugates by B- and T-cells and the cytotoxicity of HPMA copolymer-NP-adriamycin (ADR) conjugates toward B-cells, T-cells, and peripheral blood lymphocytes (PBL) were evaluated.

METHODS

HPMA copolymer-NP and optionally ADR conjugates varying in the NP density and mode of NP attachment were incubated with Raji B-cells (human Burkitt's lymphoma), CCRF-CEM T-cells (acute human lymphoblastic leukemia), and CCRF-HSB-2 T-cells (human lymphoblastic leukemia). The kinetics of binding was studied, the Langmuir adsorption isotherms analyzed, binding constants calculated, and IC50 doses determined.

RESULTS

Flow cytometry studies revealed that binding was homogeneous to both cell types. The apparent binding constants to T-cells were about two times higher when compared to B-cells. The binding and cytotoxicity increased with increased amount of epitopes per polymer chain. Attachment of the NP via a GFLG spacer resulted in increased biorecognition when compared with conjugates containing NP bound via a GG spacer. HPMA copolymer-NP-ADR conjugates possessed specific cytotoxicity to T- and B-malignant cells. Concentrations, which were lethal to the latter, were not toxic for PBL.

CONCLUSIONS

The data obtained seem to indicate the potential of the HPMA copolymer-NP conjugates as polymer anticancer drug carriers targetable to immunocompetent cells.

Chronic exposure to HPMA copolymer-bound adriamycin does not induce multidrug resistance in a human ovarian carcinoma cell line

The influence of free and N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound adriamycin (ADR) on the induction of multidrug resistance in the A2780 human ovarian carcinoma cell line was studied in vitro. It was found that chronic exposure to free ADR led to an increase in resistance to ADR and Taxol and overexpression of the MDR1 gene. No significant changes in the expression of the MRP gene were found during adaptation to free ADR. In addition to MDR1 gene-encoded multidrug resistance, a significant increase in the resistance against ADR was found before the overexpression of the MDR1 gene was measurable. This non-P-glycoprotein resistance does not appear to be connected with MRP gene-encoded resistance. During adaptation to free ADR, changes in cellular metabolism such as increased rate of glucose uptake, oxidation and glycolysis were detected. Adapted sensitive A2780 cells expressed the MDR1 gene and possessed almost the same decreased sensitivity toward ADR as the ADR-resistant human ovarian carcinoma A2780/AD cells. However, they significantly differed in proliferation rate, cellular metabolism and MRP gene expression. On the contrary, multidrug resistance was not induced after repeated exposure of sensitive A2780 cells to HPMA copolymer-bound adriamycin. The cells did not express the MDR1 gene, the expression of the MRP gene was partially inhibited, and the resistance against Taxol was decreased. Differences were also observed in metabolic changes. In summary, the data indicate that, contrary to free ADR, HPMA copolymer-bound ADR does not induce multidrug resistance in A2780 cell culture after repeated exposure.

Degradation and aggregation of human calcitonin in vitro

PURPOSE

To investigate the degradation of human calcitonin (hCT) by enzymes or mucosa from different gastrointestinal (GI) compartments and evaluate the stabilization effect of a synthetic ionizable copolymer on the stability of hCT in an aqueous solution. These data are a prerequisite for the development of a hydrogel based colon-specific hCT delivery system.

METHODS

Luminal and brush border membrane (BBM) enzymes from the colon and small intestine (SI) of the rabbit were isolated and their enzymatic activity toward hCT in vitro was evaluated. Human fecalase was used to mimic the luminal enzymatic activity in the human colon and its degradation ability was assessed. Excised intact rabbit intestinal tissues from both the colon and the SI were used to study the degradation patterns of hCT by intact mucosa. Detection of intact human calcitonin was performed using gradient elution, reverse phase high-pressure liquid chromatography (RP-HPLC). The structure of the hCT fragments was determined by Matrix Assisted Laser Desorption/lonization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) analysis. UV/VIS and fluorescence spectroscopy methods were used to evaluate the influence of a copolymer, possessing the same structure as the primary chains in hydrogels degradable in the colon, on the fibrillation process of hCT.

RESULTS

In vitro results showed that isolated luminal enzymes and BBM enzymes from the SI were more potent in degrading intact hCT, as expected. Moreover, BBM enzymes were far more abundant in the SI than in the colon. Compared with rabbit colonic luminal enzymes, the degradation potency of human fecalase was further abated. Intact mucosal studies revealed extensive degradation by the SI mucosa but not by the colonic mucosa. The primary structures of the peptide fragments were identified by MALDI-TOF MS analysis. Fibrillation studies of hCT indicated that acrylic acid-containing polymeric materials were able to decrease the aggregation of hCT in aqueous solutions.

CONCLUSIONS

Reduced proteolytic activity suggests that the colon is an advantageous site for peptide delivery. The structures of hCT degradation products were identified and the participation of particular enzymes in the degradation process was suggested. In addition, it was determined that an acrylic acid-containing copolymer improved the physical stability of hCT in aqueous solution.

Functionalized semitelechelic poly[N-(2-hydroxypropyl)methacrylamide] for protein modification

Semitelechelic poly[N-(2-hydroxypropyl)methacrylamide]s (ST-PHPMA) with different functional end groups, namely carboxyl, methyl ester, hydrazide, and amino groups, were prepared by chain transfer free-radical polymerization. 2,2'-Azobisisobutyronitrile (AIBN) was used as an initiator and 3-mercaptopropionic acid, methyl 3-mercaptopropionate, 3-mercaptopropionic hydrazide, and 2-mercaptoethylamine were used as chain-transfer agents. The semitelechelic polymers have been characterized by end-group analysis, size-exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The effects of the concentrations of the mercaptans and the initiator on the molecular weight of the polymers have been investigated. The higher the concentration of mercaptan, the lower the molecular weight of ST-PHPMA. The concentration of initiator did not have a significant effect on the molecular weight of the semitelechelic polymers. The end groups of the ST polymers can be readily transformed by polymeranalogous reactions. A model protein, alpha-chymotrypsin, has been modified with ST-PHPMA-CONHNH2 and ST-PHPMA-COOSu and the conjugates characterized by MALDI-TOF MS. The activity of modified chymotrypsins toward a high molecular weight substrate, P-Gly-Leu-Phe-NAp (where P is the HPMA copolymer backbone, and NAp is p-nitroanilide), was slightly lower than the activity of the native enzyme. The cleavage of a low molecular weight substrate, Z-Gly-Leu-Phe-NAp, by modified chymotrypsins was dependent on their structure. Whereas the activity of the amino group modified chymotrypsins was higher than that of the native enzyme, the activity of carboxyl-modified chymotrypsins was lower than that of the native enzyme. In summary, the data seem to indicate that ST-PHPMA is an effective protein-modifying agent.

HPMA copolymer bound adriamycin overcomes MDR1 gene encoded resistance in a human ovarian carcinoma cell line

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer-adriamycin (ADR) conjugate containing lysosomally degradable oligopeptide (GFLG) side chains terminated in ADR was synthesized. The effect of free and HPMA copolymer-bound ADR on the viability of A2780 sensitive and A2780/AD multidrug resistant human ovarian carcinoma cells was studied in vitro. As expected, the IC50 dose for the HPMA copolymer-ADR conjugate was higher than for free ADR reflecting the difference in the mechanism of cell entry. The resistant A2780/AD cells demonstrated about 40-times higher resistance to free ADR than the sensitive A2780 cells. On the contrary, there was only a small difference in cytotoxicity of the HPMA copolymer-ADR conjugate toward sensitive A2780 or MDR resistant A2780/AD cells. The IC50 value for A2780/AD was only about 20% higher than the value for sensitive A2780 cells. These data seem to indicate that the HPMA copolymer-ADR conjugate may, at least partially, avoid the ATP driven P-glycoprotein (Pgp) efflux pump. The analysis of the expression of the MDR1 gene which encodes the Pgp, has shown that free ADR in high doses stimulated MDR1 gene expression in sensitive A2780 cells. At the same time both free and HPMA copolymer-ADR conjugate partially inhibited the expression of the MDR1 and beta 2 m genes in multidrug resistant A2780/AD cells.

Novel pH-sensitive hydrogels with adjustable swelling kinetics

Novel pH-sensitive hydrogels were synthesized by copolymerization of N,N-dimethylacrylamide, tert.-butylacrylamide, acrylic acid, 4,4'-di(methacryloylamino)azobenzene, and N-alkanoyl, O-methacryloylhydroxylamines. The influence of the length (and consequently hydrophobicity) of the alkanoyl (propionyl, hexanoyl, and lauroyl), and its content in the hydrogel on the kinetics of swelling were investigated. Upon change in the pH from acidic to neutral, N-alkanoyl, O-acylhydroxylamine moieties were hydrolyzed. The rate of side-chain hydrolysis was dependent on the length of the alkyl and the content of the hydrolyzable comonomer in the network structure. Further, chemical control of kinetics of swelling was coupled to biophysical control of kinetics of swelling by synthesizing hydrogels containing two types of cross-linking agents, one hydrolyzable, the other enzymatically degradable. The kinetics of swelling of cross-linked polymers was compared with the kinetics of hydrolysis of N-alkanoyl, O-methacryloylhydroxylaminemoieties incorporated into linear soluble copolymers of similar structures.

Targetable HPMA copolymer-adriamycin conjugates. Recognition, internalization, and subcellular fate

Recognition, internalization, and subcellular trafficking of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates containing N-acylated galactosamine (GalN) or monoclonal OV-TL16 antibodies (Ab) have been investigated in human hepatocarcinoma HepG2 and ovarian carcinoma OVCAR-3 cells, respectively. The intrinsic fluorescence of fluorescein or adriamycin (ADR) attached to HPMA copolymers permitted us to follow the subcellular fate of HPMA copolymer conjugates by confocal fluorescence microscopy and fluorescence spectroscopy. The pattern of fluorescence during incubation of HPMA copolymer-ADR-GalN conjugate containing lysosomally degradable tetrapeptide (GFLG) side-chains with HepG2 cells was consistent with conjugate recognition, internalization, localization in lysosomes, followed by the release of ADR from the polymer chains and ultimately diffusion via the cytoplasm into the cell nuclei. A similar pattern was observed in OVCAR-3 cells for Ab targeted HPMA copolymer conjugates. To test our hypothesis that HPMA-copolymer-bound anticancer drugs will be inaccessible to the energy-driven P-glycoprotein efflux pump in multidrug resistant (MDR) cells, we have compared the internalization of the HPMA copolymer-ADR conjugates by sensitive (A2780) and ADR-resistant (A2780/AD) ovarian carcinoma cell lines. Preliminary data on relative retention of ADR in MDR (A2780/AD) cells indicate a higher intracellular ADR concentration after incubation with HPMA copolymer-ADR conjugate when compared to incubation with free (unbound) ADR.

HPMA copolymer-anticancer drug-OV-TL16 antibody conjugates. II. Processing in epithelial ovarian carcinoma cells in vitro

The binding, internalization, subcellular trafficking and in vitro cytotoxicity of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-anti-cancer drug-OV-TL16 antibody (Ab) conjugates in the ovarian carcinoma OVCAR-3 cell line have been investigated. Adriamycin (ADR) and meso chlorin e6 mono(N-2-aminoethylamide) (Mce6) photosensitizer were used as anti-cancer drugs. Targeted (Ab-containing) conjugates were compared with non-targeted HPMA copolymer-drug conjugates and with free drugs. Targeted conjugates were taken up rapidly by cells and detected within lysosomes by confocal fluorescence microscopy. The ADR attached to polymer chains via a degradable GFLG spacer was released from the conjugate, diffused via the lysosomal membrane into the cytoplasm and ultimately accumulated in the cell nuclei. In contrast, conjugates containing ADR bound via the GG spacer accumulated in the lysosomes, but no fluorescence could be detected in the cell nuclei. Binding the drugs to a non-targeted HPMA copolymer decreased their cytotoxicity in vitro. The IC50 dose increased from 2 microM for free ADR to 150 microM for P(GFLG)-ADR (P is the HPMA copolymer backbone) and from 0.34 microM for free Mce6 (with light) to 290 microM for P-(GG)-Mce6. However, attachment of OV-TL16 Abs rendered HPMA copolymer-drug conjugates biorecognizable by OVCAR-3 cells and markedly increased their cytotoxicity. The IC50 doses were 4.4 and 0.38 microM for the targeted conjugates P(GFLG)-ADR-Ab and P(GG)-Mce6-Ab (with light), respectively. Biorecognition was shown to be specific by inhibition experiments with free Ab. The findings indicate the potential of these conjugates as effective agents in the treatment of ovarian cancer.

In vitro degradation of pH-sensitive hydrogels containing aromatic azo bonds

Biodegradable and pH-sensitive hydrogels containing azoaromatic moieties were synthesized from the same polymeric precursors by two synthetic methods, namely a polymer-polymer reaction and cross-linking of polymeric precursors. The effect of the synthetic route employed and the detailed network structure on in vitro degradation of hydrogels was studied. Regardless of the synthetic method used, two patterns of degradation were observed. Hydrogels with lower cross-linking density underwent a surface erosion process and degraded at a faster rate. Hydrogels with higher cross-linking densities degraded at a slower rate by a process where a colourless degradation front moved inward to the yellow core. It appears that hydrogels synthesized by a polymer-polymer reaction degraded at a slightly faster rate than their analogues synthesized by cross-linking of polymeric precursors. The degradation rate of a hydrogel was compared with those of a linear azopolymer and a low-molecular-weight azosubstrate (methyl orange) respectively. The degradation rates were in the order of hydrogel < linear azopolymer < low-molecular-weight azosubstrate.

Lysosomal degradability of poly(alpha-amino acids)

The lysosomal degradability of poly(alpha-amino acids) based on poly(L-glutamic acid) and its derivatives/copolymers was evaluated to gain insight into the subcellular fate of the macromolecules as water soluble polymeric drug carriers. The results indicate that both the incorporation of hydrophobic comonomers and modification of the carboxylic groups of glutamic acid side chains with hydroxyalkylamine increase the lysosomal degradability of the copolymers. Decreased lysosomal degradability of L-glutamic acid copolymers containing tripeptides terminated in p-nitroanilide (drug model) in the side chains confirmed that drug conjugation alters the degradation pattern of the polymeric carriers. The percentages of the enzymatic release of p-nitroaniline from its polymeric complex with time is relatively independent of the contents of the tripeptidyl p-nitroanilides attached to the polymeric conjugates. Determination of the degradation products by electrospray mass spectroscopy showed that no fragments less than 10(3) D were generated by lysosomal enzymes, whereas the main degradation products by papain and chymotrypsin were tripeptides and tetrapeptides. The conclusions derived from these data strongly suggest that these macromolecules, if used as lysosomotropic drug carriers, may accumulate in the lysosomes and limit their usefulness in some applications.

Photodynamic crosslinking of proteins. II. Photocrosslinking of a model protein-ribonuclease A

Illumination of bovine pancreatic ribonuclease A (RNase A) in solution in the presence of rose bengal as a photosensitizer resulted in the progressive formation of enzyme dimers, trimers, tetramers and higher oligomers, as measured by gel electrophoresis and size exclusion chromatography. Oxygen was necessary for crosslink formation, and azide inhibition studies indicated that singlet oxygen was involved in the process. Chemical modification of His residues (with diethyl pyrocarbonate) and/or Lys residues (with acetic acid N-hydroxysuccinimide ester) in the enzyme decreased crosslinking, suggesting the participation of these two amino acid residues in the reaction. Met and cystine residues did not appear to be involved. Similar studies have shown that model N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing epsilon-aminocaproic acid side chains terminating in His or Lys residues are photodynamically crosslinked via His-His or His-Lys interactions. Treatment of crosslinked RNase A and its His, Lys and Lys-His derivatives for 5 min at 97 degrees C in a dithiothreitol-sodium dodecyl sulfate mixture efficiently ruptured a major part of the photodynamically formed crosslinks; treatment with the detergent alone had no effect. Similar results were obtained with the crosslinked amino acid-containing HPMA copolymers, suggesting that photodynamic crosslinks involving His-His and His-Lys interaction are chemically the same in RNase A and the copolymer model.

HPMA copolymer-anticancer drug-OV-TL16 antibody conjugates. 1. influence of the method of synthesis on the binding affinity to OVCAR-3 ovarian carcinoma cells in vitro

The influence of different methods of binding the OV-TL16 antibody and its Fab' fragment to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer--drug (adriamycin [ADR] or meso chlorin e6 mono(N-2-aminoethylamide) (Mce6)) conjugates on the affinity of conjugates to an ovarian carcinoma (OVCAR-3) cell associated antigen was investigated. The binding of the antibody to HPMA copolymer--drug (ADR or Mce6) conjugates via amino groups resulted in conjugates which were heterogeneous in their antigen binding. Coupling, the HPMA copolymer--Mce6 conjugate to the carbohydrate region of the antibody resulted in conjugates with a more homogeneous distribution of affinity constants than conjugates prepared by linking the antibody to the polymer via amino groups. However, both methods resulted in a decrease in the affinity constant compared to the native antibody. Conjugates prepared with the Fab' frgment of the OV-TL16 antibody demonstrated a more homogenous affinity than either conjugate prepared with the whole antibody. To verify the hypothesis that the changes in the binding affinity and homogeneity are a consequence of conformational changes in the antibody structure, a series of physiocochemical methods were employed to characterize the conjugates. The excitation energy transfer between OV-TL16 antibody and drugs (ADR and Mce6) and the spectral properties of Mce6 were used to monitor the interactions between the antibody and drugs. The quenching of the intrinsic fluorescence of the antibody was also employed to study its conformational changes. An attempt has been made to correlate the biorecognition at the cellular surface with the interactions of drug with the antibody molecule and with the changes in antibody conformation.

Enzymatic activity of chymotrypsin and its poly(ethylene glycol) conjugates toward low and high molecular weight substrates

Native chymotrypsin and its polyethylene glycol (PEG) conjugates, obtained using the succinimidyl carbonate of methoxy-PEG (SC-PEG) as the amino group modifying reagent, were tested for their activity toward several low and high molecular weight substrates. Tripeptide and tetrapeptide p-nitroanilides either as N alpha-benzyloxycarbonyl derivatives or attached via their N-terminals to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers or to PEG, as well as the proteins albumin and azoalbumin, were used as substrates. Extensively modified chymotrypsin bearing on average of 14 PEG chains per chymotrypsin molecule (PEG14CHT) and a moderately modified one containing 10 PEG chains (PEG10CHT) both degraded the low molecular weight p-nitroanilides at rates comparable to, and in the case of PEG10CHT, greater than, the rates exhibited by the native enzyme. Synthetic high molecular weight substrates and azoalbumin were also degraded by the PEG-modified enzymes. However, rates of such enzymatic reactions were lower for the PEG-enzymes than for the native one. Native albumin, as compared to azoalbumin, resisted degradation by both PEGCHTs yet was readily digested by the native chymotrypsin. The results obtained indicate that substrate-size-dependent specificity of PEG-modified enzymes cannot be explained solely by steric hindrance considerations. The decreased activity of PEG-enzymes toward protein substrates is consistent with the well-documented ability of PEG to exclude proteins from its surroundings and with the influence of protein unfolding on the susceptibility to degradation.

Evaluation of protein-N-(2-hydroxypropyl)methacrylamide copolymer conjugates as targetable drug carriers. 1. Binding, pinocytic uptake and intracellular distribution of transferrin and anti-transferrin receptor antibody conjugates

The transferrin receptor of human skin fibroblasts was studied as an in vitro model target antigen receptor for interaction with protein-polymer conjugates having potential for targeted drug delivery. Pinocytic uptake of 125I-labelled N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugated to monoclonal antibody B3/25 (specific for the transferrin receptor) or transferrin was up to 9-fold greater than uptake of the parent HPMA copolymer. The ability of these conjugates to bind specifically was confirmed by Scatchard analysis. Pinocytic internalisation was dependent on the molecular mass of the conjugate. Intracellular routing following internalisation was evaluated using density-gradient centrifugation. Unmodified HPMA copolymer was transferred via the endosomal compartment into secondary lysosomes, where, being resistant to degradation, it accumulated. Although the majority of endocytosed transferrin is recycled via the endosome, it was shown that any transferrin reaching the lysosomes was rapidly degraded and low-molecular-weight degradation products were released. Monoclonal antibody B3/25 showed a subcellular distribution consistent with prolongation on the cell surface, followed by internalisation and subcellular trafficking, via endosomes, into the lysosomal compartment, with subsequent degradation. Conjugation of protein to HPMA copolymer increased lysosomal accumulation of polymer up to 9-fold, with no detectable degradation of conjugate. The data presented here have implications regarding clinical potential of protein-HPMA copolymer conjugates designed for lysosomotropic drug delivery.

Effect of galactose on interaction of N-(2-hydroxypropyl)methacrylamide copolymers with hepatoma cells in culture: preliminary application to an anticancer agent, daunomycin

A series of copolymers were prepared containing 1,2:3,4-di-O-isopropylidene-6-O-methacryloyl-alpha-D-galactopyranose (0 to 99 mol %), methacryoyltyrosinamide and N-(2-hydroxypropyl)methacrylamide (99 to 0 mol %). The effect of galactose content on interaction with hepatoma cells in vitro was studied. Increased galactose content caused increased accumulation of N-(2-hydroxypropyl)methacrylamide copolymers by two human hepatoma cell lines (Hep G2 and SAH), but accumulation by rat and mouse hepatoma (HTC and NCTC) was not galactose dependent. Accumulation of N-(2-hydroxypropyl)methacrylamide copolymers by Hep G2 was shown to be an active process, being inhibited by low temperature and by the metabolic inhibitor 2,4-dinitrophenol. Addition of N-acetylgalactosamine and polymer-galactose to the incubation medium resulted in a concentration-dependent inhibition of accumulation of galactose-containing polymers. Addition of fucose or galactose was without effect at the concentrations used. Polymers bearing galactosamine or fucosylamine residues and, in addition, daunomycin were evaluated for cytotoxicity against Hep G2 and SAH. N-(2-Hydroxypropyl)methacrylamide copolymer-bound daunomycin produced a dose-dependent inhibition of DNA synthesis (measured by incorporation of [3H]thymidine), and the galactose-containing polymer showed greatest inhibition.

Anticancer agents coupled to N-(2-hydroxypropyl)methacrylamide copolymers. II. Evaluation of daunomycin conjugates in vivo against L1210 leukaemia

DBA2 mice were inoculated i.p. with 10(5)L1210 cells. Animals subsequently treated with daunomycin (single i.p. dose, 0.25-5.0 mg kg-1) all died. The maximum increase in mean survival time observed was approximately 135%. Animals treated with N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers conjugated to daunomycin (DNM) showed a significant increase in mean survival time when the polymer-drug linkage was biodegradable (i.e., Gly-Phe-Leu-Gly). Such treatment also produced a number of long term survivors (greater than 50 days). In contrast, HPMA copolymer conjugated to DNM via a non-degradable linkage (Gly-Gly) produced no increase in survival time relative to untreated control animals. The effect observed with biodegradable HPMA copolymer-DNM conjugates was dependent on the concentration of conjugated drug administered (optimum greater than 5 mg kg-1); the frequency of administration (multiple doses were more effective than single); the timing of administration (single doses given on days 1 and 3 were most effective); and the site of tumour inoculation and route of drug administration. Biodegradable HPMA copolymer-DNM conjugates administered i.p. were active against L1210 inoculated s.c. at higher doses than required to curb a peritoneal tumour. Under certain experimental conditions polymer-DNM conjugates containing fucosylamine or galactosamine proved more active than conjugates without the carbohydrate moeity. The mechanism of drug-conjugate action in vivo is at present unclear. Radioiodination of polymer showed approximately 75% of polymer-drug conjugate to be excreted 24 h after i.p. administration. Synthesis of HPMA conjugates containing [3H]DNM showed that polymer containing Gly-Gly-[3H]DNM was excreted (60% of radioactivity in the urine, 24 h) in macromolecular form. In contrast polymer containing Gly-Phe-Leu-Gly-[3H]DNM was largely excreted in the form of low molecular weight species.

Antibody-directed affinity therapy applied to the immune system: in vivo effectiveness and limited toxicity of daunomycin conjugated to HPMA copolymers and targeting antibody

The applicability of targeting therapy intervention in lymphatic tissue was studied. The effect was measured as the inhibition of anti-sheep red blood cell antibody response expressed in plaque-forming cells. Daunomycin was used as the effective drug and polyclonal and monoclonal anti-Thy 1.2 or anti-Iak antibody served for targeting. Both components were coupled to a soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer with oligopeptidic side sequences which permitted a controlled release of the drug in the target tissue. HPMA copolymer conjugates with side sequences Gly-Phe-Leu-Gly cleavable by lysosomal enzymes decreased in vivo the antibody reaction by 60-85%. A comparable amount of free targeting antibody was without a significant effect. Injection of targeted daunomycin decreased the toxicity of the drug against hematopoietic precursors in bone marrow colony-forming unit-spleen 80 times compared to the same amount of free drug. The in vivo effectiveness of targeted daunomycin was confirmed morphologically. Application of free daunomycin lead to a significant irritation of Kupffer cells in liver while none of the daunomycin-antibody-copolymer conjugate had such an effect.