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.

Backbone degradable multiblock N-(2-hydroxypropyl)methacrylamide copolymer conjugates via reversible addition-fragmentation chain transfer polymerization and thiol-ene coupling reaction

Telechelic water-soluble HPMA copolymers and HPMA copolymer-doxorubicin (DOX) conjugates have been synthesized by RAFT polymerization mediated by a new bifunctional chain transfer agent (CTA) that contains an enzymatically degradable oligopeptide sequence. Postpolymerization aminolysis followed by chain extension with a bis-maleimide resulted in linear high molecular weight multiblock HPMA copolymer conjugates. These polymers are enzymatically degradable; in addition to releasing the drug (DOX), the degradation of the polymer backbone resulted in products with molecular weights similar to the starting material and below the renal threshold. The new multiblock HPMA copolymers hold potential as new carriers of anticancer drugs.

Effect of hydrophobic interactions on properties and stability of DNA-polyelectrolyte complexes

Polyplexes are polyelectrolyte complexes of DNA and polycations, designed for potential gene delivery. We investigated the properties of new polyplexes formed from cholesterol-modified polycations and DNA. Three complexes were tested; their cholesterol contents were 1.4, 6.3, and 8.7 mol %. UV spectroscopy and fluorescence assay using ethidium bromide proved the formation of polyplexes. The kinetics of turbidity of polyplexes solutions in physiological solution showed that the colloid stability of polyplexes increases with increasing content of cholesterol in polycations. Dynamic, static, and electrophoretic light scattering, small-angle X-ray scattering, and atomic force microscopy were used for characterization of polyplexes. The observed hydrodynamic radii of polyplexes were in the range of 30-60 nm; they were related to the polycation/DNA ratio and hydrophobicity of the used polycations (the cholesterol content). The properties of polyplex particles depend, in addition to polycation structure, on the rate of polycation addition to DNA solutions.

Antitumor efficacy of colon-specific HPMA copolymer/9-aminocamptothecin conjugates in mice bearing human-colon carcinoma xenografts

The antitumor activity of a colon-specific N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer - 9-aminocamptothecin (9-AC) conjugate (P-9-AC) was assessed in orthotopic and subcutaneous animal (HT29 xenograft) tumor models. P-9-AC treatment of mice bearing orthotopic colon tumors, with a dose of 3 mg/kg of 9-AC equivalent every other day for 6 weeks, resulted in regression of tumors in 9 of 10 mice. A lower dose of P-9-AC (1.25 mg/kg of 9-AC equivalent) every other day for 8 weeks inhibited subcutaneous tumor growth in all mice. No liver metastases were observed. Colon-specific release of 9-AC from polymer conjugates enhanced antitumor activity and minimized the systemic toxicity.

Endocytic uptake of a large array of HPMA copolymers: Elucidation into the dependence on the physicochemical characteristics

Endocytic uptake and subcellular trafficking of a large array of HPMA (N-(2-hydroxypropyl)methacrylamide) based copolymers possessing positively or negatively charged residues, or hydrophobic groups were evaluated by flow cytometry and living cell confocal microscopy in cultured prostate cancer cells. The degrees of cellular uptake of various copolymer fractions with narrow polydispersities were quantified. The copolymer charge was the predominant physicochemical feature in terms of cellular uptake. Fast and efficient uptake occurred in positively charged copolymers due to non-specific adsorptive endocytosis, whereas slow uptake of negatively charged copolymers was observed. The uptake of copolymers was also molecular weight dependent. The copolymers were internalized into the cells through multiple endocytic pathways: positively charged copolymers robustly engaged clathrin-mediated endocytosis, macropinocytosis and dynamin-dependent endocytosis, while weakly negatively charged copolymers weakly employed these pathways; strongly negatively charged copolymers only mobilized macropinocytosis. HPMA copolymer possessing 4 mol% of moderately hydrophobic functional groups did not show preferential uptake. All copolymers ultimately localized in late endosomes/lysosomes via early endosomes; with varying kinetics among the copolymers. This study indicates that cell entry and subsequent intracellular trafficking of polymeric drug carriers are strongly dependent on the physicochemical characteristics of the nanocarrier, such as charge and molecular weight.

Biorecognition and subcellular trafficking of HPMA copolymer-anti-PSMA antibody conjugates by prostate cancer cells

A new generation of antibodies against the prostate specific membrane antigen (PSMA) has been proven to bind specifically to PSMA molecules on the surface of living prostate cancer cells. To explore the potential of anti-PSMA antibodies as targeting moieties for macromolecular therapeutics for prostate cancer, fluorescently labeled HPMA (N-(2-hydroxypropyl)methacrylamide) copolymer-anti-PSMA antibody conjugates (P-anti-PSMA) were synthesized and the mechanisms of their endocytosis and subcellular trafficking in C4-2 prostate cancer cells were studied. Radioimmunoassays showed the dissociation constants of P-anti-PSMA for C4-2 prostate cancer cells in the low nanomolar range, close to values for free anti-PSMA. It indicated that conjugation of anti-PSMA to HPMA copolymers did not compromise their binding affinity. The rate of endocytosis of P-anti-PSMA was much faster than that of control HPMA copolymer conjugates containing nonspecific IgG. Selective pathway inhibitors of clathrin-mediated endocytosis and of macropinocytosis inhibited the internalization of P-anti-PSMA. Inhibition of clathrin-mediated endocytosis was further evidenced by down-regulation of clathrin heavy chain expression by siRNA. Using a dominant-negative mutant of dynamin (Dyn K44A) to abolish the clathrin-, caveolae-independent endocytic pathway, we found that some of P-anti-PSMA adopted this pathway to be endocytosed into C4-2 cells. Thus multiple receptor-mediated endocytic pathways, including clathrin-mediated endocytosis, macropinocytosis, and clathrin-, caveolae-independent endocytosis, were involved in the internalization of P-anti-PSMA. The extent of the participation of each pathway in P-anti-PSMA endocytosis was estimated. Membrane vesicles containing P-anti-PSMA rapidly colocalized with membrane vesicles overexpressing Rab7, a late endosome localized protein, demonstrating that a part of P-anti-PSMA was transported to late endosomes.

Synthesis and evaluation of multivalent branched HPMA copolymer-Fab' conjugates targeted to the B-cell antigen CD20

Several drug delivery designs combine synthetic drug carriers with covalently conjugated targeting moieties. Such modifications of monoclonal antibodies (mAb), or their Fab' fragments, inevitably result in diminished affinity for their targeted tissue. In an attempt to overcome this limitation, high molecular weight, branched N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers were synthesized and conjugated with Fab' fragments of the anti-CD20 antibody, 1F5. This produced multivalent conjugates with varying valency (amount of Fab' per macromolecule) targeted to the B-cell antigen CD20. Evaluation of a multivalent effect was done by determining the apparent K(D) at low concentrations of conjugates, the Sips heterogeneity factor, a, and the binding enhancement factors of each construct. The results clearly indicated that multivalency could improve the affinity of the HPMA copolymer-Fab' conjugates to that of unconjugated mAb.

Water-soluble HPMA copolymer—prostaglandin E1conjugates containing a cathepsin K sensitive spacer

A novel bone targeting, N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer based, prostaglandin E1 (PGE1) delivery system was designed, synthesized and characterized. PGE1 was bound to the polymer backbone via a spacer, composed of a cathepsin K sensitive tetrapeptide (Gly-Gly-Pro-Nle) and a self-eliminating 4-aminobenzyl alcohol structure. The HPMA copolymer conjugates were prepared by photo-initiated free radical copolymerization of HPMA, PGE1-containing macromonomer, and optionally a comonomer containing a reactive p-nitrophenyl ester group. The latter group was used as attachment points for the D-aspartic acid octapeptide targeting moieties. Incubation of the PGE1-containing macromonomer and HPMA copolymer-PGE1 conjugates with cathepsin K resulted in release of unmodified PGE1. The rate of release depended on the composition of the conjugate. The higher the PGE1 content in the conjugate, the slower the PGE1 release. This appeared to be the result of association of hydrophobic side-chains in aqueous media, which rendered the formation of the enzyme substrate complex more difficult. The data seems to indicate that HPMA copolymer-PGE1 conjugates have a potential in the treatment of osteoporosis and other bone diseases.

Novel HPMA copolymer-bound constructs for combined tumor and mitochondrial targeting

A wide variety of therapeutic agents may benefit by specifically directing them to the mitochondria in tumor cells. The current work aimed to design delivery systems that would enable a combination of tumor and mitochondrial targeting for such therapeutic entities. To this end, novel HPMA copolymer-based delivery systems that employ triphenylphosphonium (TPP) ions as mitochondriotropic agents were developed. Constructs were initially synthesized with fluorescent labels substituting for drug and were used for validation experiments. Microinjection and incubation experiments performed using these fluorescently labeled constructs confirmed the mitochondrial targeting ability. Subsequently, HPMA copolymer-drug conjugates were synthesized using a photosensitizer mesochlorin e 6 (Mce 6). Mitochondrial targeting of HPMA copolymer-bound Mce 6 enhanced cytotoxicity as compared to nontargeted HPMA copolymer-Mce 6 conjugates. Minor modifications may be required to adapt the current design and allow for tumor site-specific mitochondrial targeting of other therapeutic agents.

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.

Combination chemotherapy and photodynamic therapy with fab' fragment targeted HPMA copolymer conjugates in human ovarian carcinoma cells

The biological activities of sequential combinations of anticancer drugs, SOS thiophene (SOS) and mesochlorin e₆ monoethylenediamine (Mce₆), in the form of free drugs, nontargeted N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer−drug conjugates, P-GFLG-Mce₆ and P-GFLG-SOS (P is the HPMA copolymer backbone and GFLG is the glycylphenylalanylleucylglycine spacer), and Fab′-targeted HPMA copolymer−drug conjugates, P-(GFLG-Mce₆)-Fab′ and P-(GFLG-SOS)-Fab′ (Fab′ from OV-TL16 antibodies complementary to CD47), were evaluated against human ovarian carcinoma OVCAR-3 cells. Mce₆, SOS, P-GFLG-Mce₆, P-GFLG-SOS, P-(GFLG-Mce₆)-Fab′, and P-(GFLG-SOS)-Fab′, when used as single agents or in binary combination, exhibited cytotoxic activities against OVCAR-3 cells, as determined using a modified MTT assay. The binding and internalization of P-(GFLG-Mce₆)-Fab′ and P-(GFLG-SOS)-Fab′ by OVCAR-3 cells were visualized by confocal microscopy and flow cytometry. The results confirmed an enhanced biorecognition by OVCAR-3 cells of Fab′-targeted HPMA copolymer conjugates over nontargeted conjugates. The median-effect analysis and the determination of the combination index (CI) were used to describe the drug interaction and quantify the synergism, antagonism, or additivity in anticancer effects. The sequential combinations of SOS+Mce₆ and P-GFLG-SOS+P-GFLG-Mce₆ displayed very strong synergism to synergism in the entire range of cell inhibition levels (f_a = 0.5 − 0.95). The P-(GFLG-SOS)-Fab′+P-(GFLG-Mce₆)-Fab′ exhibited a strong synergism for f_a values up to about 0.85, but showed synergistic effect and nearly additive effect at f_a = 0.9 and 0.95, respectively. These observations support the continuation of in vivo investigations of these conjugates for the treatment of ovarian cancer.

Biodistribution and pharmacokinetic studies of bone-targeting N-(2-hydroxypropyl)methacrylamide copolymer-alendronate conjugates

The biodistribution and pharmacokinetics of bone-targeting N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-alendronate conjugates were evaluated following intravenous administration of radioiodinated conjugates to young healthy BALB/c mice. The synthesis of a polymerizable and cathepsin K cleavable alendronate derivative, N-methacryloylglycylglycylprolylnorleucylalendronate, enabled the preparation of HPMA copolymer-alendronate conjugates with varying composition. Using the RAFT (reversible addition-fragmentation chain transfer) polymerization technique, four conjugates with different molecular weight and alendronate content and two control HPMA copolymers (without alendronate) with different molecular weight were prepared. The results of biodistribution studies in mice demonstrated a strong binding capacity of alendronate-targeted HPMA copolymer conjugates to bone. Conjugates with low (1.5 mol%) alendronate content exhibited a similar bone deposition capacity as conjugates containing 8.5 mol % of alendronate. The molecular weight was an important factor in the biodistribution of the HPMA copolymer conjugates. More conjugate structures need to be evaluated, but the data suggest that medium molecular weights (50-100 kDa) might be effective drug carriers for bone delivery.

Self-association properties of HPMA copolymers containing an amphipathic heptapeptide

Receptor-binding peptides are suitable targeting moieties for macromolecular therapeutics. Binding several targeting peptides to one macromolecule may improve biorecognition due to the multivalency effect. On the other hand, the resulting amphipathic structure of such conjugates may result in the association of side-chains with a concomitant decrease in the accessibility of the side-chain-bound ligands. Using the one-bead one-compound combinatorial method, we have recently identified a heptapeptide (YILIHRN; HP) ligand for the CD21 receptor (Biomacromolecules 7, 3037, 2006). Here, we evaluated the relationship between structure and self-association of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-HP conjugates using fluorescence resonance energy transfer (FRET) to evaluate their conformation in solution. In addition to HP, HPMA copolymers containing side-chains terminating in tryptophan (energy donor) and dansyl (energy acceptor) were synthesized, and solutions were evaluated using an excitation wavelength of 295 nm (ratio of emission intensity 510 nm/370 nm indicated energy transfer efficiency). It was found that higher HP content correlated with higher FRET efficiency, indicating the formation of compact coils. Modification of the HPMA copolymer backbone by the incorporation of acrylic acid (AA) comonomer units resulted in decreased FRET efficiency, presumably due to the expansion of the polymer coils as a result of electrostatic repulsion. The dependence of FRET efficiency on pH was in agreement with the ionization profile of the AA residues. To determine the effect of HP content on enzymatic drug release kinetics, HPMA copolymer-HP conjugates containing GFLG side-chains terminating with doxorubicin (DOX) were incubated with papain and the release of free DOX monitored. When HP content increased above a particular threshold, the rate of DOX release decreased as a result of self-association of HPMA copolymer-GFLG-DOX-HP conjugates. The FRET data correlated well with hydrodynamic volumes determined by size exclusion chromatography (SEC), with molecular weights determined by light scattering, and with the kinetics of drug release.

Stability in plasmas of various species of HPMA copolymer-PGE1 conjugates

PURPOSE

To determine the stability of HPMA copolymer-prostaglandin E(1) (PGE(1)) conjugates in plasmas of different species and to identify the enzymes responsible for the cleavage of the ester bond.

METHODS

The conjugates were incubated in human, rat, and mouse plasma at 37 degrees C in the presence and absence of specific esterase inhibitors. The released PGE(1) was analyzed using an HPLC assay. To evaluate the effect of the conformation of the conjugate on the rate of PGE(1) release, its structure was modified by the attachment of hydrophobic side chains.

RESULTS

The rate of PGE(1) release was strongly species dependent. Whereas the conjugate was stable in human plasma, the PGE(1) release in rat or mouse plasma was substantial. In rat plasma, the ester bond cleavage was mainly catalyzed by butyrylcholinesterase; in mouse plasma, in addition to butyrylcholinesterase, carboxylesterase also contributed to the cleavage. The formation of compact polymer coils stabilized the ester bond.

CONCLUSIONS

HPMA copolymer-PGE(1) conjugates are strong candidates as novel therapeutics for the treatment of osteoporosis. The observed species differences in plasma stability of ester bonds are of importance, because the ovariectomized rat model is recommended by the FDA for pre-clinical evaluation.

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.

Osteotropic Peptide that differentiates functional domains of the skeleton

HPMA copolymer-d-aspartic acid octapeptide (D-Asp8) conjugates have been found to target the entire skeleton after systemic administration. In a recent study using the ovariectomized rat model of osteoporosis, we surprisingly discovered that D-Asp8 would favorably recognize resorption sites in skeletal tissues, while another bone-targeting moiety, alendronate (ALN), directs the delivery system to both formation and resorption sites. Atomic force microscopy (AFM) analyses reveal that ALN has a stronger binding force to hydroxyapatite (HA) than D-Asp8. In vitro HA binding studies indicate that D-Asp8 is more sensitive to change of HA crystallinity than ALN. Because the bone apatite in the newly formed bone (formation sites) usually has lower crystallinity than the resorption sites (mainly mature bone), we believe that the favorable recognition of D-Asp8 to the bone resorption sites could be attributed to its relatively weak binding to apatite, when compared to bisphosphonates, and the different levels of crystallinity of bone apatite at different functional domains of the skeleton.

Hybrid hydrogels self-assembled from HPMA copolymers containing peptide grafts

Graft copolymers were designed that self-assemble into hydrogels mediated by the interaction of coiled-coil peptide domains. A linear hydrophilic polymer of HPMA was chosen as the backbone, and coiled-coil forming peptides, covalently attached to the backbone, formed the grafts. Microrheology was used to evaluate the self-assembly of graft copolymers into hydrogels. The results revealed that the length and the number of coiled-coil grafts per chain had a significant influence on the gelation process. At least 4 heptads were needed to achieve the association of graft copolymers into hydrogels. CD spectra of the copolymer containing 5 heptad grafts further suggested that coiled-coil formation may contribute to the self-assembly. Gelation of graft copolymers containing CC4 peptides indicated that a threshold amount of grafts per macromolecule is needed to form a three-dimensional structure. These studies demonstrated a potential of the graft copolymers to create self-assembling hydrogels with desirable and controllable structures.

Synthesis and characterization of novel aromatic azo bond-containing pH-sensitive and hydrolytically cleavable IPN hydrogels

Novel interpenetrating network (IPN) hydrogels, composed of pH-sensitive, aromatic azo group containing network as one component (Network A), and a hydrolyzable network as the other (Network B), were prepared by a sequential process. The first network was formed by crosslinking of a reactive polymer precursor (copolymer of N,N-dimethylacrylamide, acrylic acid, N-tert.butylacrylamide, and N-methacryloylglycylglycine p-nitrophenyl ester) with an aromatic azo group containing diamine ((N,N'-epsilon-aminocaproyl)-4,4'-diaminoazobenzene). The second network was formed by radical crosslinking copolymerization of N-(2-hydroxypropyl)methacrylamide with N,O-dimethacryloylhydroxylamine. The composition of the hydrogels was manipulated to determine the influence of hydrogel composition on the equilibrium degree of swelling, modulus of elasticity in compression, and on the rate of degradation of Network B. Modeling of network structure was accomplished using the statistical branching theory. The major advantage of IPN hydrogels, when compared to traditional pH-sensitive networks, is the linear swelling profile following abrupt change of pH from 2 to 7.4. This indicates the suitability of IPN as carriers for oral drug delivery.

Bone-targeting macromolecular therapeutics

Musculoskeletal diseases such as osteoporosis are recognized as major public health problems worldwide. Many novel therapeutic agents have been identified for the treatment of these diseases. However, the majority of them are not specific to hard tissue, resulting significant toxicity. Bone-targeting drug delivery systems based on water-soluble polymers can specifically direct candidate drugs to bone thereby reducing side effects due to non-specific tissue interactions. Incorporation of a targeting moiety, a drug release mechanism, drug selection and optimization of the polymer carrier are all essential elements in the development of bone-targeting macromolecular therapeutics. Successful clinical application of this approach can significantly contribute to the development of treatments for many musculoskeletal diseases.

Biopolymer-based delivery systems for advanced imaging and skeletal tissue-specific therapeutics

There is considerable advantage in developing tissue-specific delivery systems for therapeutic and diagnostic applications. Synthetic water-soluble polymeric delivery systems have been developed to allow selective delivery of therapeutic and imaging agents to musculoskeletal tissues. For mineralized tissues, bone-targeting agents such as aspartic acid octapeptide could concentrate the polymer conjugates to bone surfaces including resorption sites, which was demonstrated with routine bone histomorphometry. For bone-associated soft tissues, other targeting approaches based on pathophysiological properties unique to the local tissue environment, such as the leaky vasculature in arthritic joints, were utilized to achieve the selective deposition of the polymeric delivery systems to the desired sites. For this study, magnetic resonance imaging (MRI) was used to assess real-time pharmacokinetics and biodistribution of the MRI contrast agent conjugated polymer in major organs including skeletal tissues. The MRI data were then correlated with other standard imaging methods such as pQCT and DXA as well as routine histopathology and skeletal histomorphometry. Clearly, biopolymeric delivery systems may be used to improve the pharmacological and pharmacokinetic properties of different therapeutic agents for musculoskeletal diseases such as osteoporosis and arthritis. In addition, this or related technologies may also be useful to improve diagnosis and medical imaging with positron emission tomography, gamma scintigraphy, or other technologies.

The Arthrotropism of Macromolecules in Adjuvant-Induced Arthritis Rat Model: A Preliminary Study

PURPOSE

To study the accumulation of macromolecules into the arthritic joints and the possible applications of such phenomenon.

METHODS

The accumulation of plasma albumin in the joints of adjuvant-induced arthritis (AIA) rat model was first visualized with Evans blue injection. A N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer contrast agent was then synthesized and injected into the AIA rats to allow qualitative examination of biodistribution and pharmacokinetics of the injected macromolecule with magnetic resonance imaging (MRI). Vital organs and the diseased joints were isolated and examined histologically to correlate with the MRI findings.

RESULTS

Deep blue color developed around the arthritic joints of the AIA rat a few hours after the injection of Evans blue. MR imaging of the AIA rats injected with polymer contrast agent demonstrated a gradual but very strong accumulation of the injected polymer in the arthritic joints, which lasted for 1-2 days. Observed differences in the concentration of the injected polymer in the joints correlated with disease severity as assessed histologically.

CONCLUSIONS

Profound arthrotropism of macromolecules in the AIA rat model was demonstrated with various imaging tools. These observations should help in the conceptual and practical design of novel macromolecular delivery systems for the imaging and treatment of rheumatoid arthritis.

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.

HPMA Copolymer-Bound Doxorubicin Induces Apoptosis in Human Ovarian Carcinoma Cells by a Fas-Independent Pathway

The mechanism of cell death in A2780 human ovarian carcinoma cells induced by free doxorubicin (DOX) and N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound DOX [P-(GFLG)-DOX] was investigated. In particular, the involvement of the Fas receptor system in drug-induced apoptosis was evaluated. P-(GFLG)-DOX was shown to effect apoptosis-induced tumor cell death as manifested by positive Annexin V-FITC staining, cleavage of procaspase 3 and its physiological substrate, poly(ADP-ribose) polymerase (PARP), and cleavage of procaspase 8. Using the fluorochrome-labeled caspase inhibitor assay, it was found that both free DOX and P-(GFLG)-DOX activated caspases 3 and 9, but both forms of DOX did not have an effect on the activity of caspase 8, when compared to untreated cells. It was shown that free DOX and P-(GFLG)-DOX upregulated Fas receptor expression at the cell membrane in a time-dependent manner. Triggering the drug-induced Fas receptor with an exogeneous soluble Fas ligand (sFasL) resulted in an increase in the extent of apoptotic cell death, indicating that the Fas signaling pathway remained functionally active. Also, antagonistic anti-Fas ZB4 antibody blocked the increase in the level of apoptosis following the application of sFasL, but did not interfere with drug-induced apoptosis. The study of the functional activity of the Fas receptor and of the activation of the most proximal effector of the caspase cascade, caspase 8, indicated that the Fas receptor pathway was not decisive in the induction of cell death by free DOX and P-(GFLG)-DOX in A2780 cells. This study suggests further investigation of the involvement of the mitochondrial pathway in A2780 cell apoptotic death, induced by free and HPMA copolymer-bound DOX.

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.

Free and N-(2-hydroxypropyl)methacrylamide copolymer-bound geldanamycin derivative induce different stress responses in A2780 human ovarian carcinoma cells

The effects of geldanamycin (GA), 17-(3-aminopropylamino)-17-demethoxygeldanamycin (AP-GA), and N-(2-hydroxypropyl)methacrylamide copolymer-AP-GA conjugate [P(AP-GA)] on A2780 human ovarian carcinoma cells at an equitoxic dose (2x IC(50)) were compared by the gene expression array analysis. All treatments resulted in similar gene expression profiles up to 12 h (e.g., down-regulation of CDK4 and up-regulation of APAF-1), although P(AP-GA)-treated cells showed delayed gene expression because of time-dependent internalization of the conjugate and intracellular drug release from P(AP-GA). However, AP-GA-treated cells showed elevated expression of HSP70 and HSP27 after 6 h compared with that observed by GA and P(AP-GA) treatments. Depletion of C-Raf, an HSP90 client protein, was observed in all treatments up to 12 h. Confocal microscopy using mesochlorin e(6) as a model drug revealed that drug release caused by the lysosomal cleavage of glycylphenylalanylleucylglycine oligopeptide spacer, used as GA derivative copolymer attachment/release point, was moderately fast. These results suggested that AP-GA treatment may activate stress-response pathways, whereas P(AP-GA) treatment may suppress them and trigger signaling pathways essential to cell growth arrest and death by inducing an HSP90-active factor. Although GA and P(AP-GA) treatments induced a time-dependent increase in HSP70 and HSP27 protein expression (detected by Western blotting analysis), AP-GA treatment resulted in more rapid and more intense expression of both proteins. Our results suggest that conjugation of AP-GA to N-(2-hydroxypropyl)methacrylamide copolymer may be able to modulate the cell stress responses induced by AP-GA because of differences in its internalization mechanism, subcellular localization, and intracellular concentration gradients.

Pegylated polyethylenimine-Fab' antibody fragment conjugates for targeted gene delivery to human ovarian carcinoma cells

Specific targeting of ovarian carcinoma cells using pegylated polyethylenimine (PEG-PEI) conjugated to the antigen binding fragment (Fab') of the OV-TL16 antibody, which is directed to the OA3 surface antigen, was the objective of this study. OA3 is expressed by a majority of human ovarian carcinoma cell lines. To demonstrate the ability of the PEG-PEI-Fab' to efficiently complex DNA, an ethidium bromide exclusion assay was performed. Comparison with PEG-PEI or PEI 25 kDa showed only minor differences in the ability to condense DNA. Since conjugation of Fab' to PEG-PEI might influence complex stability, this issue was addressed by incubating the complexes with increasing amounts of heparin. This assay revealed stability similar to that of unmodified PEG-PEI/DNA or PEI 25 kDa/DNA complexes. Complexes displayed a size of approximately 150 nm with a zeta potential close to neutral. The latter property is of particular interest for potential in vivo use, since a neutral surface charge reduces nonspecific interactions. Binding studies using flow cytometry and fluorescently labeled DNA revealed a more than 6-fold higher degree of binding of PEG-PEI-Fab'/DNA complexes to epitope-expressing cell lines compared to unmodified PEG-PEI/DNA complexes. In OA3-expressing OVCAR-3 cells, luciferase reporter gene expression was elevated up to 80-fold compared to PEG-PEI and was even higher than that of PEI 25 kDa. The advantage of this system is its specificity, which was demonstrated by competition experiments with free Fab' in the cell culture media during transfection experiments and by using OA3-negative cells. In the latter case, only a low level of reporter gene expression could be achieved with PEG-PEI-Fab'.

Synthesis and evaluation of water-soluble polymeric bone-targeted drug delivery systems

Four polymeric bone-targeting conjugates were synthesized based on poly(ethylene glycol) (PEG, two conjugates) and poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA, two conjugates). The well-known bone-targeting compounds, alendronate and aspartic acid peptide, were used as bone-targeting moieties. Fluorescein isothiocyanate (FITC) was attached to the conjugates as a model drug for detection purposes. The bone-targeting potential of these conjugates was tested in vitro with hydroxyapatite (HA) and in mice. The data obtained indicated that these novel delivery systems could specifically accumulate in the bone tissue.

Subcellular trafficking of HPMA copolymer-Tat conjugates in human ovarian carcinoma cells

One of the main obstacles to efficient intracellular delivery of therapeutic macromolecules is the barrier posed by the plasma membrane. In this study, the cell penetrating peptide Tat was conjugated to a synthetic macromolecule based on N-(2-hydroxypropyl)methacrylamide (HPMA) and its subcellular distribution in human ovarian carcinoma cell lines was studied. The Tat peptide mediated uptake resulted in cytoplasmic and nuclear localization and was found to be energy independent. Time and concentration studies verified the rapidity and dependence of the transport process on these parameters. Enhanced uptake of a polymer bound anticancer drug doxorubicin was also demonstrated. These results were corroborated independently by subcellular fractionation.

HPMA copolymer delivery of chemotherapy and photodynamic therapy in ovarian cancer

Our studies document a unique and unexpected advantage of the combination of HPMA copolymer bound doxorubicin with mesochlorin e6/photodynamic therapy in the treatment of ovarian cancer. Each drug's activity is individually enhanced when compared with free (low molecular weight) drugs, furthermore, in combination these HPMA copolymer bound agents act synergistically to create an unexpected biological effect. Figure 8 depicts the known activities of each agent which may play synergistic roles. HPMA copolymer-doxorubicin has been widely evaluated in preclinical and clinical studies. It demonstrates marked advantages over free doxorubicin: control of biodistribution and accumulation via molecular weight restrictions, biodegradability, minimal immunogenicity, subcellular localization, anticancer activity, enhanced permeability and retention, increased apoptosis, lipid peroxidation, DNA damage, and reduced nonspecific toxicity. Recent clinical trials in the UK provide "proof of principle" of the "enhanced permeability and retention effect" for solid tumors and the unique advantages of this novel drug delivery system for the treatment of ovarian cancer. With regards to photodynamic therapy using the photosensitizer mesochlorin e6, the preclinical evaluations thus far document: control of biodistribution and accumulation via molecular weight restrictions, biodegradability, subcellular localization, anticancer activity, enhanced permeability and retention, and reduced nonspecific toxicity. Ongoing microarray studies document unique cellular pathways and new pharmaceutical properties which are initiated by the HPMA copolymer delivery delivery of these agents, and predict an exciting future for this novel drug delivery system.

Mechanisms of cytotoxicity in human ovarian carcinoma cells exposed to free Mce6 or HPMA copolymer-Mce6 conjugates

It is essential to understand cellular responses on photodynamic therapy (PDT) to design delivery systems that maximize cytotoxic effects coupled with minimal induction of side effects or protective mechanisms (or both). Here, we investigated mechanisms of toxicity in human ovarian carcinoma A2780 cells treated with structurally diverse N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer (P)-mesochlorin e6 monoethylenediamine (Mce6) conjugates that possessed differential subcellular accumulation or covalent attachments of photosensitizers (or both). Apoptosis and necrosis were observed after photoactivation, with increased apoptotic responses observed in cells exposed to conjugates possessing Mce6 linkage via a lysosomally degradable tetrapeptide spacer (HPMA copolymer-Mce6 conjugates containing Mce6 bound via glycylphenylalanylleucylglycine [GFLG] linker [P-GFLG-Mce6], HPMA copolymer-Mce6 conjugates containing Mce6 bound via a GFLG spacer and containing nuclear localization sequence, PKKKRKV132K(FITC)C [NLS(fluorescein-5-isothiocyanate [FITC])] bound via a thioether linkage [P-NLS(FITC)-GFLG-Mce6]). Furthermore, the induction of necrosis was more pronounced in cells exposed to conjugates containing both a nuclear localization sequence (NLS) and Mce6 bound by a degradable linker (P-NLS(FITC)-GFLG-Mce6). Caspase-independent mechanisms of cell death were identified in cells treated with nuclear-targeted conjugates possessing Mce6 attached using a nondegradable tether (HPMA copolymer-Mce6 conjugates containing Mce6 bound via a GG spacer and containing NLS(FITC) bound via a thioether linkage [P-NLS(FITC)-GG-Mce6]), whereas low levels of apoptosis and necrosis were detected in cells exposed to photoactivated nontargeted HPMA copolymer-Mce6 conjugates containing Mce6 coupled through a nondegradable spacer (HPMA copolymer-Mce6 conjugates containing Mce6 bound via GG linker [P-GG-Mce6]). Variations in gene expression were observed in cells on PDT. Specifically, HSP70 expression was solely detected in cells treated with P-GFLG-Mce6, whereas the loss of detection of several genes were observed in cells treated with P-NLS(FITC)-GFLG-Mce6. Variations in cellular responses on PDT using different HPMA copolymer-Mce6 conjugates will prove useful in the design of optimal HPMA copolymer PDT delivery systems.

Correlation of subcellular compartmentalization of HPMA copolymer-Mce6 conjugates with chemotherapeutic activity in human ovarian carcinoma cells

PURPOSE

Intracellular targets sensitive to oxidized damage generated by photodynamic therapy (PDT) utilizing N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-mesochlorin e6 monoethylenediamine (Mce6) conjugates was explored to aid in the design of second generation PDT delivery systems.

METHODS

Low temperature, metabolic inhibitor, and nuclear localization sequences (NLS(FITC)) were used to achieve desired subcellular localization that was evaluated by confocal analysis and subcellular fractionation. Mce6 was bound to HPMA copolymer conjugates via non-degradable dipeptide linkers (P-GG-Mce6, P-NLS(FITC)-GG-Mce6) or lysosomally degradable tetrapeptide spacers (P-GFLG-Mce6, P-NLS(FITC)-GFLG-Mce6). Chemotherapeutic efficacy was assessed by the concentration that inhibited growth by 50% (IC50), cell associated drug concentration (CAD) and confocal microscopy.

RESULTS

P-GFLG-Mce6 possessed enhanced chemotherapeutic activ ity compared to P-GG-Mce6 indicating enzymatically released Mce6 was more active than copolymer-bound Mce6. Lysosomes appeared less sensitive to photodamage as observed by a higher IC50. Nuclear-directed HPMA copolymer-Mce6 conjugates (P-NLS(FITC)-GG-Mce6, P-NLS(FITC)-GFLG-Mce6) possessed enhanced chemotherapeutic activity. However, control cationic HPMA copolymer-Mce6 conjugates containing a scrambled NLS (P-scNLS(FITC)-GG-Mce6) or amino groups (P-NH2-GG-Mce6) also displayed increased chemotherapeutic activity.

CONCLUSIONS

Nuclear delivery was observed for P-NLS(FITC)-GG-Mce6 and P-NLS(FITC)-GFLG-Mce6 indicating NLS was a feasible approach for nuclear delivery. Due to the cationic nature of NLS, increased membrane binding of PDT systems incorporating cationic nuclear targeting moieties must be addressed.

The role of galactose, lactose, and galactose valency in the biorecognition of N-(2-hydroxypropyl)methacrylamide copolymers by human colon adenocarcinoma cells

PURPOSE

To examine the beta-galactoside and beta-lactoside binding capacity of three human colon-adenocarcinoma cell lines and their sugar specificity, using N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates of galactosamine, lactose, and triantennary galactose.

METHODS

Three types of HPMA copolymers containing the saccharide epitopes galactosamine (P-Gal), lactose (P-Lac), or triantennary galactose (P-TriGal) were synthesized. The relationship between the content of the saccharide moieties, the valency of the galactose residues, and their biorecognition by the cell lines (Colo-205, SW-480, and SW-620) was investigated using flow cytometry and confocal fluorescence microscopy analysis.

RESULTS

The binding of the glycoconjugates to the human colonadenocarcinoma cell lines was dependent on the type and the number of bound sugar residues per macromolecule. The higher the sugar contents in the HPMA copolymers, the higher the extent of binding. Although introduction of galactoside residues into the HPMA copolymer resulted in a significant increase in the binding of the copolymers to the cells, low biorecognition of the lactoside-containing HPMA copolymers by all cell lines used was observed. The trivalent galactoside-containing HPMA copolymers did not yield a notable glycoside cluster effect for the beta-galactoside-binding lectin expressed on human colon-adenocarcinoma cells. Among the various cell line little differences in the extent of binding of the glycopolymers to the cells were observed. The data on the internalization of HPMA copolymer conjugates obtained by confocal fluorescence microscopy correlated well with the flow cytometry analysis of their biorecognition by target cells.

CONCLUSIONS

The lectin-mediated endocytosis of the HPMA glycoconjugates in human colon cancer cell lines suggests their potential use as targeting tools of cytotoxic drugs to colon adenocarcinoma.

Cytoplasmic delivery and nuclear targeting of synthetic macromolecules

Delivery of macromolecular drugs (e.g. antisense oligonucleotides, polymer-drug conjugates, etc.) designed to work in specific sites inside cells is complicated as macromolecules typically have access to fewer biological compartments than small molecules. To better understand the fate of macromolecules in cells and begin to alter that fate, we investigated the internalization and subcellular fate of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers and HPMA copolymer-drug conjugates in Hep G2 and A2780 cells. The subcellular fate of fluorescently labeled polymers was monitored by confocal microscopy and subcellular fractionation. Initially, the HPMA copolymers and HPMA copolymer-drug conjugates were internalized by endocytosis and remained in endosomes/lysosomes. At longer incubation times (>8 h), small amounts of the HPMA copolymers were observed to enter the cytoplasm and accumulate in the nucleus of the cells. Nuclear accumulation was confirmed after cytoplasmic microinjection. Oligonucleotides conjugated via lysosomally degradable spacers entered into the cytoplasm and nucleus of the cells faster than the polymers. The effect of the subcellular location was correlated to the toxicity of the photosensitizer, mesochlorin e(6) (Mce(6))-HPMA copolymer conjugates. The plasma membrane and late endosomes were more sensitive to damage by Mce(6). Targeting the polymer conjugates to the nucleus with the nuclear localization sequence (NLS) as well as conjugating the Mce(6) via a degradable spacer increased cell adhesion and uptake, promoted their entry into the cytoplasm and nucleus of the cells, and increased their toxicity. To further promote entry of the polymers into the cytoplasm and nucleus of the cells, the protein transduction domain, Tat peptide, was conjugated to the HPMA copolymers. This resulted in high binding to the cell membrane, but also facilitated rapid (<5 min) entry of the macromolecules into the cytoplasm and nucleus of cells. These results will prove valuable in the future design of macromolecular therapeutics.

Tat-conjugated synthetic macromolecules facilitate cytoplasmic drug delivery to human ovarian carcinoma cells

We have synthesized N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-cell penetrating peptide Tat conjugates and evaluated their subcellular distribution in A2780 human ovarian carcinoma cells by confocal fluorescence microscopy and subcellular fractionation. Our data indicate the transport of these conjugates by a single Tat molecule to both the cytoplasm and nucleus via a nonendocytotic and concentration independent process. The uptake was observed to occur within 3 min, as confirmed by live cell microscopy. In contrast, HPMA copolymers lacking the Tat peptide were internalized solely by endocytosis. For the first time, Tat-mediated cytoplasmic delivery of a polymer bound anticancer drug, doxorubicin, was also demonstrated. These findings establish the feasibility of overcoming major cellular and subcellular obstacles to intracellular macromolecular delivery and hold great promise for the development of polymer-based systems for the cytoplasmic delivery of therapeutic molecules.

Antisense oligonucleotides delivered to the lysosome escape and actively inhibit the hepatitis B virus

The subcellular fate and activity in inhibiting the hepatitis B virus of free and N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-phosphorothioate oligonucleotides were studied. Their internalization and subcellular fate were monitored with confocal microscopy. A fraction of the internalized free oligonucleotides escaped into the cytoplasm and nucleus of Hep G2 cells but were not active antiviral agents. Covalently attaching the oligonucleotides to the HPMA copolymers via nondegradable dipeptide GG spacers resulted in sequestering the oligonucleotides in vesicles after internalization. Conjugation of the oligonucleotides to an HPMA copolymer via a lysosomally cleavable tetrapeptide GFLG spacer resulted in release of the oligonucleotide in the lysosome and subsequent translocation into the cytoplasm and nucleus of the cells. The HPMA copolymer-oligonucleotide conjugate possessed antiviral activity, indicating that phosphorothioate oligonucleotides released from the carrier in the lysosome were able to escape into the cytoplasm and nucleus and remain active. The Hep G2 cells appeared to actively internalize the phosphorothioate oligonucleotides as oligonucleotide-HPMA copolymer conjugates were internalized to a greater extent than unconjugated polymers.

Inhibition of cathepsin K with lysosomotropic macromolecular inhibitors

Cathepsin K is the major enzyme responsible for the degradation of the protein matrix of bone and probably for the destruction of articular cartilage in rheumatoid arthritis joints. These processes occur mainly in the resorption lacuna and within the lysosomal compartment. Here, we have designed, synthesized, and evaluated new lysosomotropic (water-soluble) polymer-cathepsin K inhibitor conjugates. In particular, we characterized the relationship between conjugate structures and their activity to inhibit cathepsins K, B, L, and papain. A potent selective cathepsin K inhibitor, 1,5-bis(N-benzyloxycarbonylleucyl)carbohydrazide, was modified to 1-(N-benzyloxycarbonylleucyl)-5-(phenylalanylleucyl)carbohydrazide (I) to facilitate polymer conjugation. It was conjugated to the polymer chain termini of two water-soluble polymers [alpha-methoxy poly(ethylene glycol), abbreviated as mPEG-I; semitelechelic poly[N-(2-hydroxypropyl)methacrylamide], abbreviated as ST-PHPMA-I]. The conjugation of inhibitor I to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer side chains was accomplished via either a Gly-Gly spacer (PHPMA-GG-I) or with no spacer between I and the copolymer backbone (PHPMA-I). Kinetic analysis revealed that free inhibitor I possessed an apparent second-order rate constant against cathepsin K (k(obs)/[I] = 1.3 x 10(6) M(-1) s(-1)) similar to that of unmodified 1,5-bis(Cbz-Leu) carbohydrazide, while I conjugated to the chain termini of mPEG and ST-PHPMA-COOH had slightly lower values (about 5 x 10(5) M(-1) s(-1)). The k(obs)/[I] values for I attached to the side chains of HPMA copolymers (PHPMA-GG-I and PHPMA-I) were about 3 x 10(4) M(-1) s(-1). When tested against cathepsin L, inhibitor I and all its polymer conjugates produced k(obs)/[I] values 1-2 orders of magnitude less than those determined for cathepsin K, while for cathepsin B and papain, the values were 2-4 orders of magnitude lower. The ability of mPEG-I and ST-PHPMA-I to inhibit cathepsin K activity in synovial fibroblasts was also evaluated. Both polymer-bound inhibitors were internalized by endocytosis and were ultimately trafficked to the lysosomal compartment. ST-PHPMA-I was internalized faster than mPEG-I. The inhibitory activity in the synovial fibroblast assay correlated with the rate of internalization.

Influence of the structure of drug moieties on the in vitro efficacy of HPMA copolymer-geldanamycin derivative conjugates

PURPOSE

To optimize the structure of geldanamycin (GDM) derivative moieties attached to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers via an enzymatically degradable spacer.

METHODS

HPMA copolymers containing different AR-GDM (AR = 3-aminopropyl (AP), 6-aminohexyl (AH), and 3-amino-2-hydroxypropyl AP(OH)) were synthesized and characterized. Their cytotoxicity towards the A2780 human ovarian carcinoma cells was evaluated.

RESULTS

The cytotoxic efficacy of HPMA copolymer-AR-GDM conjugates depended on the structure of AR-GDM. Particularly, HPMA copolymer-bound AH-GDM, which possessed the longest substituent at the 17-position, demonstrated the highest efficacy among the polymer-bound GDM derivatives; however the activity of free AH-GDM was lower than that of the other free AR-GDMs. The relative increase of the activity of macromolecular AH-GDM when compared to AP-GDM or AP(OH)-GDM correlated with the enhanced recognition of AH-GDM terminated oligopeptide side-chains by the active site of the lysosomal enzyme, cathepsin B. Drug stability and further stabilization upon binding to HPMA copolymer also contributed to the observed phenomena.

CONCLUSIONS

AH-GDM was found to be a suitable GDM derivative for the design of a drug delivery system based on HPMA copolymers and enzymatically-degradable spacers.

Design of novel bioconjugates for targeted drug delivery

This paper summarizes recent work on the design and development of targeted polymeric bioconjugates based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers. Polymerizable antibody Fab' fragment (MA-Fab') has been developed and used in the preparation of targeted HPMA copolymer-mesochlorin e6 conjugates for the treatment of human ovarian carcinomas. The reactivity of the MA-Fab' in copolymerization with HPMA depended on the length of the spacer between the monomer double bond and the antibody Fab' fragment. The biological activity of the antibody Fab' fragment was maintained after incorporation into the HPMA copolymer. Novel aromatic azo spacers were designed and incorporated into HPMA copolymer-drug (cyclosporin A, 9-aminocamptothecin) conjugates for the colon-specific drug delivery and for the treatment of colon diseases. The colon-specific drug release from the conjugates was controlled by the structures of both drug and spacers. Lectins, wheat germ agglutinin (WGA) and peanut agglutinin (PNA), were conjugated to the colon-specific polymer drug conjugates to enhance specific adhesion onto colon tissues.

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.