Experimental methods in cancer therapeutics

Technological solutions for encapsulation

Encapsulation offers broad scope of applications. It can be used to deliver almost everything from advanced drugs to unique consumer sensory experiences; it could be also employed as a protection system or a sensing material. This cutting-edge technology undergoes rapid growth in both academic and industrial conditions. Research in this matter is continuing to find a new application of microcapsules as well as to improve the methods of their fabrication. Therefore, in this review, we focus on the art of the encapsulation technology to provide the readers with a comprehensive and in-depth understanding of up-to-day development of microcapsule preparation methods. Our goal is to help identify the major encapsulation processes and by doing so maximize the potential value of ongoing research efforts.

Review : Biodegradable Microcapsular Drug Delivery Systems: Manufacturing Methodology, Release Control and Targeting Prospects

An overview of the subject of biodegradable microcapsular drug delivery systems is presented from a polymer chemist's viewpoint. Various polymerization and microencapsulation techniques (including emulsion polymerization, interfacial polycondensation, suspension crosslinking, coacer vation/phase separation and solvent evaporation/extraction) suitable for the preparation of biodegradable microcapsules based on proteins, polysaccharides, polyesters, polyamides, or cyanoacrylates are described. Drug release from biodegradable microcapsules is discussed, and examples are presented to illus trate how the rate of drug release can be controlled by adjusting parameters such as microcapsule size, porosity, and crosslinking. Prospects of site-specific chemotherapy by means of passive and active targeting of microcapsular drug carriers are also analyzed.

Toxicity of magnetic albumin microspheres bearing adriamycin

Magnetic albumin microspheres bearing adriamycin (ADM-MAM) is a novel chemotherapeutic compound with site-specific drug delivery characteristics. The acute and subacute toxic tests of the compound, local irritating test and anaphylactic test were performed on mice and guinea pigs. The results showed there was no macroscopically and microscopically direct cytotoxic injuries of the compound to the animal organs or to the cells. The LD50 value of the compound was higher than that of the single used adriamycin, indicating that the compound was less toxic than the single adriamycin and quite safe in its therapeutic dosage. Furthermore, there was also no side effects or toxic reactions to be observed on clinical patients with advanced carcinoma or gastric cancer.

Nonliposomal approach--a study of preparation of egg albumin nanospheres containing amphotericin-B

The stability of liposomes after introduction into the body is presently being discussed and needs thorough understanding. Hence, as a nonliposomal approach, egg albumin nanospheres were prepared by the pH-coacervation method, and a preliminary study was carried out of the influence of process variables on the size and shape of nanospheres by changing the pH of the albumin solution, concentration of albumin solution, and volume of cross-linking agent. The batch prepared with an albumin medium of pH 9, 2% concentration, and 100 microliters of 4% glutaraldehyde-ethanol solution was found to have a spherical uniform shape with an average size of 497.6 nm. The ideal batch was loaded with the systemic antifungal drug amphotericin-B. Drug-loaded nanospheres were evaluated to study their in vitro release. They were found to exhibit a biphasic pattern with a cumulative percentage release of 97.7%.

Niosomal plumbagin with reduced toxicity and improved anticancer activity in BALB/C mice

Plumbagin niosome were prepared using a lipid layer hydration method, and drug entrapment was measured. The acute toxicity studies were conducted following treatment with free and niosomal plumbagin. The antitumour activity of niosomal plumbagin in a solid tumor (sarcoma-180) and Ehrlich ascites model was evaluated. Niosome-encapsulated plumbagin was less toxic than free drug. The antitumour activity of the drug was also better after encapsulation. The better anticancer activity can be justified with the help of LD50 survival studies and study of tumour volume doubling time.

Liposomes as in-vivo carriers for citicoline: effects on rat cerebral post-ischaemic reperfusion

Citicoline is a therapeutic agent widely used in the treatment of brain injury, for example in cerebrovascular disease or traumatic accidents. Unfortunately, the strong polar nature of this drug prevents it crossing the blood-brain barrier. In this paper, the possibility of efficiently trapping citicoline in liposomes to improve its therapeutic effects is reported. The citicoline-encapsulation efficiency, drug leakage and size analysis of various liposome systems were studied. The real therapeutic effectiveness of these citicoline liposome formulations was evaluated by biological assay. The effects of free and liposome encapsulated citicoline on survival rate of ischaemic reperfused male Wistar rats (80-100 g) were investigated. Of the phospholipid mixtures used in citicoline liposome formulation the best in terms of delivery and therapeutic effects was 1,2-dipalmitoyl-sn-glycero-phosphocholine: dipalmitoyl-DL-alpha-phosphatidyl-L-serine:cholesterol (7:4:7 molar ratio). This phospholipid mixture was also assayed for brain conjugated diene levels in rats, since this parameter is an index of lipid peroxidation in rat cerebral cortex during post-ischaemic reperfusion. A citicoline-loaded phospholipid mixture has produced an increase in rat survival rate of about 24% and a reduction in diene levels of 60%, compared to the free drug.

Macrophages loaded with doxorubicin by ATP-mediated permeabilization: potential carriers for antitumor therapy

In many cell types extracellular ATP (ATPe) has been shown to cause reversible plasma membrane permeabilization to low molecular weight (< 900 Da) water-soluble compounds. In the present report we have exploited this technique to incorporate the anticancer drug doxorubicin (DXR), molecular mass 543 Da, into the cytoplasm of two mouse cell lines that had previously been shown to express the ATPe-gated pore, J774 macrophages and tumor necrosis factor (TNF)-resistant L929 fibroblasts. Compared to passively loaded cells, ATPe-mediated reversible permeabilization allowed an at least 4-fold increase in DXR intracellular trapping (0.5 pg/cell versus 2 pg/cell). Analysis of the release kinetics at 37 degrees C showed that about 40% of total intracellular DXR was discharged during the first hour from both ATPe-permeabilized and passively loaded cells; about 15% further release was observed upon incubation up to 4 h. DXR release profiles were similar in ATPe-permeabilized and passively loaded cells. ATPe-permeabilized, DXR-loaded (ATPe-DXR) cells strongly inhibited the proliferation of K562 tumor cells. Taken together these results indicate that ATPe-mediated reversible plasma membrane permeabilization can be effectively used to load cells of different histotypes with high concentrations of DXR. This approach could permit to vehicle high doses of anticancer agents by using living cells while reducing systemic toxic effects.

Microspheres for biomedical applications: preparation of reactive and labelled microspheres

This review describes the synthesis and physico-chemical properties of reactive and labelled microspheres useful for biomedical applications. Preparation of microspheres with specific functional groups, fluorescent species, radionuclides and magnetite particles (Fe2O3) are discussed. Physico-chemical properties of microspheres, including surface charge and hydrophilicity/hydrophobicity, are also briefly covered.

Magnetic fields, brain and immunity: effect on humoral and cell-mediated immune responses

Magnetic fields (MF) can influence biological systems in a wide range of animal species and humans. We report here on the influence of static MF, locally applied to the brain area, on immune system performances in the rat. In the first series of experiments two AKMA micromagnets (M) with the influx density of 600 Gauss were bilaterally implanted (with "N" polarity facing the cranial bones) and fixed to the skull posterior to the fronto-parietal suture (parietal brain exposure). Rats implanted with iron beads (I) and sham-operated (SO) rats served as controls. Animals were exposed to MF or I during different periods of time before and after immunization with several soluble or cellular antigens. We report here on the in vivo immunoregulating effects of centrally applied MF on plaque-forming cell (PFC) response, local hypersensitivity skin reactions and experimental allergic encephalomyelitis. The selective influence of MF applied to different brain regions on PFC response was evaluated, as well. For this purpose, two M were bilaterally implanted in the area of (a) frontal, (b) parietal and (c) occipital brain regions. Rats were under the influence of MF for 20 days before and 4 days after immunization with sheep red blood cells. Groups of nonimmunized rats were exposed for 14, 24 and 34 days to parietally implanted M or I, and the number of peripheral blood CD4+ and CD8+ cells determined by mouse anti-rat W3/25 and MRC OX 8 monoclonal antibodies. The results show an overall in vivo immunopotentiation of humoral and cell-mediated immune responses in rats exposed to MF. Furthermore, these immunomodulating effects of centrally applied MF depend on at least two basic parameters, time of exposure and brain region exposed. The highest immune performance was obtained after exposure of the occipital brain region for a total period of 24 days. The results provide further evidence of the complex interrelationship between the environment, the central nervous system and the immune system.

Drug targeting using non-magnetic and magnetic albumin-globulin mix microspheres of mefenamic acid

Optimum conditions for the preparation of non-magnetic and magnetic microspheres of albumin-globulin mix (alglomix) containing mefenamic acid have been standardized. The effect of various parameters has been investigated with regard to the appearance, yield, drug content and encapsulation efficiency. The physicochemical parameters of the microspheres such as density, particle size distribution, surface topography and wall thickness, as well as the magnetite contained within the magnetic microspheres, have been determined. The infrared spectroscopic analysis confirmed the encapsulation of the drug and absence of free drug on the surface of the microspheres. The X-ray diffraction analysis confirmed that the crystallinity of the drug remained unchanged indicating thereby that no complex formation had taken place between core and coat materials. The in vitro release profiles of the microspheres have been studied. An attempt has also been made to check the in vivo efficacy in rats.

Biodegradable poly(lactic acid) and poly(lactide-co-glycolide) microcapsules: problems associated with preparative techniques and release properties

Poly(lactic acid) [PLA] and its co-polymers with glycolic acid [PLCG] have been known to be biodegradable and histocompatible for the past 20 years. Their physico-chemical and biological properties have been found suitable, in many instances, for sustaining drug release in vivo for days or months. Several dosage forms for parenteral administration have been investigated using these polymers and a microencapsulation technique is chosen frequently for its unique properties. There are a limited number of published papers concerning preparation and characterization of PLA or PLCG microcapsules, possibly because of commercial unavailability and difficulties in the synthesis of reproducible batches of these polymers. However, microcapsules can be made using different traditional and non-traditional techniques containing core materials ranging from biological proteins to synthetic drugs. An attempt is made here to review problems associated with the different microencapsulation techniques using PLA or PLCG. In vivo and in vitro drug release from these microcapsules is also reviewed.

Internalization and shedding of Lym-1 monoclonal antibody following interaction with surface antigens of a cultured human B cell lymphoma

Modulation of surface antigens of Raji Burkitt's lymphoma cells by monoclonal antibody Lym-1 was investigated by flow cytometry and radioimmunoassay (RIA). Raji cells, treated with antibody conjugated with FITC, became bright green as determined by FACS and the FITC-labeled Lym-1 remained associated with target cells for up to 48 hr after incubation at either 4 or 37 degrees C. Lym-1 antibody linked with biotin also bound to Raji cells and rendered these cells highly reactive with avidin-phycoerythrin (APE). However, the APE fluorescence intensity measured by FACS decreased substantially when Raji cells were cultured at 37 degrees C for 1 hr prior to APE exposure but not when incubation was carried out at 4 degrees C, indicating a disappearance of antibody from the surface of the metabolically active cells. This process was time dependent with a total loss of surface-bound biotinylated antibody occurring over a period of approximately 2 hr. Raji cells exposed to both fluoresceinated and biotinylated Lym-1 in a double labeling experiment became positive to both reagents. The flow cytometric profile was not altered when these cells were incubated for 1 hr at 4 degrees C followed by reaction with APE. However, they failed to react with APE when the 1-hr incubation took place at 37 degrees C despite the fact that they remained FITC positive, suggesting that the antibody with its fluorescent label had entered the cells. Utilizing 131I-labeled Lym-1 it was determined that approximately 50% of initially bound antibody had dissociated from the cells within the first 2 hr of incubation at 37 degrees C, although the remainder persisted with targets for up to 48 hr. The HPLC protein profile indicated that the radioactivity found in the culture supernatants and cytoplasm was associated with whole antibody, degradation products, and Ig complexes with antigen. Therefore, the present findings suggest that Lym-1 Ig molecules react with cell surface antigens and are rapidly internalized and shed, resulting in the disappearance of antibody from the surface membrane of Raji cells.

Characterization of drug-loaded poly(d,l-lactide) microspheres

Lomustine and progesterone have been incorporated in biodegradable poly(d,l-lactide) microspheres by evaporating dichloromethane from stirred dichloromethane-in-water emulsions. Spherical microspheres with lomustine or progesterone payloads less than or equal to 23% were obtained. Higher lomustine payloads gave irregularly shaped particles. Microspheres with less than or equal to 68% progesterone were obtained, but free drug crystals formed on the surface of such microspheres. Increased agitation rates decreased mean microsphere size. Addition of drug to the dichloromethane phase increased average particle size relative to that obtained with drug-free microspheres prepared under the same experimental conditions. Complete evaporation of the dichloromethane, while the medium was continuously stirred, promoted formation of free drug crystals in the aqueous phase. Increased emulsifier concentrations did not significantly enhance drug incorporation efficiency within the microspheres. Shelf-life stability of lomustine and progesterone was reduced by incorporation in the microspheres, presumably due to their molecular dispersion in the poly(d,l-lactide).

Enzyme-albumin polymers. New approaches to the use of enzymes in medicine

The widespread use of enzymes as drugs or therapeutic agents has been limited by (a) enzyme availability, (b) biodegradation of administered enzyme, (c) immunogenecity of the enzyme as a foreign protein, and (d) accessibility of the enzyme to the appropriate site of action. It has become obvious that due to these limitations, the administration of free or native enzyme is not likely to be effective. Various mechanisms of protecting or packaging enzymes to offset some of these drawbacks have been described. We have been successful in producing conjugates of a number of different enzymes with a molar excess of homologous albumin. The resulting enzyme-albumin complex is resistant to proteolytic and heat inactivation and is apparently non-immunogenic. Using specific ligands crosslinked to the enzyme-albumin conjugate we have been able to target these conjugates to specific receptor sites and specific tissues. Ligands including cell surface-recognizing antibodies and hormones such as insulin have been used. These approaches offer new possibilities for the increased use of enzymes in medicine.

Susceptibility of the prostate cancer cell to different physical, hormonal, and chemical agents: present status and theoretical prospects for improved prostate cancer therapy

The benefits and limitations of present modes of treatment of prostatic cancer with physical, hormonal, and chemical agents are briefly reviewed. The theoretical possibility that the heterogeneous clones that comprise prostatic cancer might be killed or controlled by selective targeting of cytotoxic agents (actual or potential) to malignant cells is discussed in terms of two types of delivery vehicles to provide for cell selectivity: (1) monoclonal antibodies against specific cell surface markers on cancer cells and (2) steroid ligands for receptors present in clones of malignant cells. The problems and prospects of these selective delivery systems as potential therapeutic modalities for prostatic cancer are considered.

Immunoglobulins as targeting agents for liposome encapsulated drugs

Recent literature dealing with the immunoglobulin-liposome combination as a tool for drug targeting is reviewed. Mechanisms for binding of immunoglobulins to liposomes are discussed. Results obtained so far by using this concept both to induce specific liposome-cell interactions in in vitro cell cultures and to target drug containing liposomes to selected tissues in animal studies are evaluated.

Antitumor monoclonal antibodies for radioimmunodetection of tumors and drug targeting

Developments in hybridoma technology leading to the production of monoclonal antibodies recognizing tumor-associated antigens are providing new approaches for the radioimmunodetection of, and drug targeting to, metastases. These developments are illustrated in a series of studies on the in vivo localization of an antihuman-osteogenic sarcoma monoclonal antibody (791T/36) in human tumor xenografts maintained in immunodeprived mice. 131I-labelled 791T/36 antibody localized specifically in osteogenic sarcomas but not in xenografts of other tumors, such as bladder carcinoma T24, which do not express the antigen identified by this antibody. Developing from these studies, various parameters influencing antibody localization in tumors were examined including the kinetics of antibody uptake, the relationship between tumor size and antibody binding, and the site of antibody deposition. This provides a basis for considering the potential of antitumor monoclonal antibodies for targeting antitumor agents. Of particular importance here is the observation that antibody is principally located at the periphery of tumors since this will influence the population of cells within a tumor which can be attacked by antibody-drug or antibody-toxin conjugates. Experiments with human tumor xenografts demonstrate tumor localization of radioisotope-labelled 791T/36 monoclonal antibody. Tumor localization by external gamma camera imaging of osteogenic sarcoma xenograft-bearing mice was also demonstrated. These studies illustrate the potential of antitumor monoclonal antibodies for imaging primary and metastatic tumors. This approach is further emphasized by the radioimmunodetection of primary and metastatic colorectal carcinomas.