Design of immuno-enzymosomes with maximum enzyme targeting capability: effect of the enzyme density on the enzyme targeting capability and cell binding properties

Review on novel targeted enzyme drug delivery systems: enzymosomes

The goal of this review is to present enzymosomes as an innovative means for site-specific drug delivery. Enzymosomes make use of an enzyme's special characteristics, such as its capacity to accelerate the reaction rate and bind to a particular substrate at a regulated rate. Enzymosomes are created when an enzyme forms a covalent linkage with a liposome or lipid vesicle surface. To construct enzymosomes with specialized activities, enzymes are linked using acylation, direct conjugation, physical adsorption, and encapsulation techniques. By reducing the negative side effects of earlier treatment techniques and exhibiting efficient medication release, these cutting-edge drug delivery systems improve long-term sickness treatments. They could be a good substitute for antiplatelet medication, gout treatment, and other traditional medicines. Recently developed supramolecular vesicular delivery systems called enzymosomes have the potential to improve drug targeting, physicochemical characteristics, and ultimately bioavailability in the pharmaceutical industry. Enzymosomes have advantages over narrow-therapeutic index pharmaceuticals as focusing on their site of action enhances both their pharmacodynamic and pharmacokinetic profiles. Additionally, it reduces changes in normal enzymatic activity, which enhances the half-life of an enzyme and accomplishes enzyme activity on specific locations.

Physicochemical Stimulus-Responsive Systems Targeted with Antibody Derivatives

The application of monoclonal antibodies and antibody fragments with the advent of recombinant antibody technology has made notable progress in clinical trials to provide a regulated drug release and extra targeting to the special conditions in the function site. Modification of antibodies has facilitated using mAbs and antibody fragments in numerous models of therapeutic and detection utilizations, such as stimuliresponsive systems. Antibodies and antibody derivatives conjugated with diverse stimuliresponsive materials have been constructed for drug delivery in response to a wide range of endogenous (electric, magnetic, light, radiation, ultrasound) and exogenous (temperature, pH, redox potential, enzymes) stimuli. In this report, we highlighted the recent progress on antibody-conjugated stimuli-responsive and dual/multi-responsive systems that affect modern medicine by improving a multitude of diagnostic and treatment strategies.

Glucuronides: From biological waste to bio-nanomedical applications

Long considered as no more than biological waste meant to be eliminated in urine, glucuronides have recently contributed to tremendous developments in the biomedical field, particularly against cancer. While glucuronide prodrugs monotherapy and antibody-directed enzyme prodrug therapy have been around for some time, new facets have emerged that combine the unique properties of glucuronides notably in the fields of antibody-drug conjugates and nanomedicine. In both cases, glucuronides are utilized as a vector to improve pharmacokinetics and confer localized activation of potent drugs at tumor sites while also decreasing systemic toxicity. Here we will discuss some of the most promising strategies using glucuronides to promote successful anti-tumor therapeutic treatments.

Recent strategies towards the surface modification of liposomes: an innovative approach for different clinical applications

Liposomes are very useful biocompatible tools used in diverse scientific disciplines, employed for the vehiculation and delivery of lipophilic, ampiphilic or hydrophilic compounds. Liposomes have gained the importance as drug carriers, as the drugs alone have limited targets, higher toxicity and develop resistance when used in higher doses. Conventional liposomes suffer from several drawbacks like encapsulation inefficiencies and partially controlled particle size. The surface chemistry of liposome technology started from simple conventional vesicles to second generation liposomes by modulating their lipid composition and surface with different ligands. Introduction of polyethylene glycol to lipid anchor was the first innovative strategy which increased circulation time, delayed clearance and opsonin resistance. PEGylated liposomes have been found to possess higher drug loading capacity up to 90% or more and some drugs like CPX-1 encapsuled in such liposomes have increased the disease control up to 73% patients suffering from colorectal cancer. The surface of liposomes have been further liganded with small molecules, vitamins, carbohydrates, peptides, proteins, antibodies, aptamers and enzymes. These advanced liposomes exhibit greater solubility, higher stability, long-circulating time and specific drug targeting properties. The immense utility and demand of surface modified liposomes in different areas have led their way to the modern market. In addition to this, the multi-drug carrier approach of targeted liposomes is an innovative method to overcome drug resistance while treating ceratin tumors. Presently, several second-generation liposomal formulations of different anticancer drugs are at various stages of clinical trials. This review article summarizes briefly the preparation of liposomes, strategies of disease targeting and exclusively the surface modifications with different entities and their clinical applications especially as drug delivery system.

Targeting the vasculature of colorectal carcinoma with a fused protein of (RGD)₃-tTF

Purpose. Truncated tissue factor (tTF) fusion protein targeting tumor vasculature can induce tumor vascular thrombosis and necrosis. Here, we generated (RGD)₃-tTF in which three arginine-glycine-aspartic (RGD) targeting integrin α_vβ₃ and tTF induce blood coagulation in tumor vessels. Methods. The bioactivities of (RGD)₃-tTF including coagulation activity, FX activation, and binding with integrin α_vβ₃ were performed. The fluorescent labeled (RGD)₃-tTF was intravenously injected into tumor-bearing mice and traced in vivo. The tumor growth, volume, blood vessel thrombosis, tumor necrosis, and survival time of mice treated with (RGD)₃-tTF were evaluated. Results. The clotting time and FX activation of (RGD)₃-tTF were similar to that of TF (P > 0.05) but different with that of RGD (P < 0.05). (RGD)₃-tTF presented a higher binding with α_vβ₃ than that of RGD and TF at the concentration of 0.2 μmol/L (P < 0.05). (RGD)₃-tTF could specifically assemble in tumor and be effective in reducing tumor growth by selectively inducing tumor blood vessels thrombosis and tumor necrosis which were absent in mice treated with RGD or TF. The survival time of mice treated with (RGD)₃-tTF was higher than that of mice treated with TF or RGD (P < 0.05). Conclusion. (RGD)₃-tTF may be a promising strategy for the treatment of colorectal cancer.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Liposome-mediated targeting of enzymes to cancer cells for site-specific activation of prodrugs: comparison with the corresponding antibody-enzyme conjugate

PURPOSE

Immunoenzymosomes are tumor-targeted immunoliposomes bearing enzymes on their surface. These enzymes are capable of converting relatively nontoxic prodrugs into active cytostatic agents. The aims of this study were to compare the enzyme delivery capability of immunoenzymosomes with that of the corresponding antibody-enzyme conjugate and to evaluate whether immunoenzymosomes are able to mount a strong bystander effect.

METHODS

Immunoenzymosomes exposing Fab' fragments of the monoclonal antibody 323/A3 and the bacterial enzyme beta-glucuronidase or the corresponding antibody-enzyme conjugate were incubated with OVCAR-3 cells (human ovarian carcinoma cells). Cell-associated enzymatic activity and the in vitro antiproliferative effect of a glucuronide prodrug of doxorubicin (DOX-GA3) were determined.

RESULTS

At equal numbers of carrier units, the cell-associated enzymatic activity achieved by using immunoenzymosomes was 15-fold higher than that obtained after incubation with the corresponding antibody-enzyme conjugate. Increasing the amount of antibody-enzyme conjugate added to the cells could not compensate for their lower enzyme delivery capability. Immunoenzymosomes were able to induce inhibition of cell growth not only of tumor cells to which immunoenzymosomes were bound but also of a large number of neighboring cells.

CONCLUSIONS

Immunoenzymosomes are able (a) to target prodrug-converting enzymes more efficiently to tumor cells than the corresponding antibody-enzyme conjugate and (b) to mount a strong bystander effect.

Quantitative immunoblot assay for assessment of liposomal antibody conjugation efficiency

Routine direct assessment of immunoglobulin (Ig)-liposome(lp) conjugation efficiency has been impeded by phospholipid interference with standard protein and immunoassay methods. Rabbit IgG conjugated to anionic liposomes was quantitated in immunoblots using computer image analysis techniques. Lp-coupled Ig was separated from free Ig by dialysis in disposable Spectra/Por units (MWCO 300 kDa). Differential Lowry protein assay (DLA) of the thiolated Ig reactant and the dialyzate provided an estimate of conjugation efficiency that was compared to the results of the immunoblot assay (IBA). The color response of Ig-lp in the IBA was about an order of magnitude greater than rabbit IgG alone, requiring the synthesis of an Ig-lp standard in which the Ig conjugation efficiency was assessed by radiotracer methodology. The use of the same standard in three colorimetric protein assays verified the accuracy of the IBA and demonstrated that the colorimetric assays could be employed to determine Ig-lp conjugation efficiency. In terms of sensitivity and specificity, however, the IBA is better suited for routine assessment of laboratory-scale Ig-lp conjugation efficiencies. The DLA was found to be an unsatisfactory measure of conjugation efficiencies because an interfering substance was apparently released by Ig-lp preparations.

Molecular recognition in a reconstituted tumor cell membrane

The design of an immunoliposome system for molecular recognition using reconstituted, hydrogel-supported bilayer lipid membranes (sb-BLMs) is described. By monitoring the electrical properties, two kinds of recognition are feasible: (i) the human bladder tumor cells, Ej and its antibody BDI-1, the lifetime of the reconstituted membrane is 42 min; and (ii) the human rectum tumor cells, LOVO, the life of the reconstructed membrane is more than 40 min, the same as conventional BLM. Further, the anticancer drug, Adriamycin (Anticancer Res., 20 (2000) 1391), was shown to be effective in such reconstituted systems, the life of which is less than 5 min. In these experiments, the active ingredients of the Ej and LOVO cells were determined on reconstituted sb-BLMs. The key point is that the component part being recognized on the BLM must be kept in its native state.

Theoretically-derived molecular descriptors important in human intestinal absorption

A quantitative structure-human intestinal absorption relationship was developed using artificial neural network (ANN) modeling. A set of 86 drug compounds and their experimentally-derived intestinal absorption values used in this study was gathered from the literature and a total of 57 global molecular descriptors, including constitutional, topological, chemical, geometrical and quantum chemical descriptors, calculated for each compound. A supervised network with radial basis transfer function was used to correlate calculated molecular descriptors with experimentally-derived measures of human intestinal absorption. A genetic algorithm was then used to select important molecular descriptors. Intestinal absorption values (IA%) were used as the ANN's output and calculated molecular descriptors as the inputs. The best genetic neural network (GNN) model with 15 input descriptors was chosen, and the significance of the selected descriptors for intestinal absorption examined. Results obtained with the model that was developed indicate that lipophilicity, conformational stability and inter-molecular interactions (polarity, and hydrogen bonding) have the largest impact on intestinal absorption.

Cationic polymeric gene delivery of beta-glucuronidase for doxorubicin prodrug therapy

BACKGROUND

An approach to improve current chemotherapy is the selective transduction of tumor cells with suicide genes to sensitize these cells to prodrugs of cytostatic agents.

METHODS

In this study, gene transfer was accomplished with the cationic polymer poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), able to condense plasmid-DNA by electrostatic interaction. OVCAR-3 cells were transfected with plasmids encoding E. coli-derived or human beta-glucuronidase and the transfection efficiency and inhibition by serum was determined. Next, we measured the sensitivity of OVCAR-3 cells transiently expressing beta-glucuronidase to the glucuronide prodrug of doxorubicin (DOX-GA3) or to doxorubicin.

RESULTS

OVCAR-3 cells were efficiently transfected with a plasmid encoding E. coli-derived beta-glucuronidase. The degree of transfection (30% of cells) was higher than that achieved with commercially available cationic lipids (DOTAP, Lipofectamine) without inhibition by serum. OVCAR-3 cells transiently expressing beta-glucuronidase were equally sensitive to the glucuronide prodrug of doxorubicin (DOX-GA3) or to doxorubicin itself, indicating complete conversion of prodrug to drug. Similar studies were performed with the plasmid encoding for human beta-glucuronidase, which is likely to be less immunogenic. Also in this case, OVCAR-3 cells showed an increased sensitivity to the prodrug DOX-GA3, although less pronounced than when the bacterial enzyme was used. A strong bystander effect was observed when OVCAR-3 cells transfected with beta-glucuronidase were mixed with non-transfected cells at different ratios. Complete tumor cell growth inhibition was already observed when only 15% of the cells expressed the activating enzyme.

CONCLUSION

These studies suggest that beta-glucuronidase gene therapy using PDMAEMA as a carrier system and DOX-GA3 as the prodrug has a potential application in cancer gene therapy.