Dr. Noboru Yamazaki, senior research scientist of the Nanotechnology Research Institute (Dr. Hiroshi Yokoyama, Director) of the AIST, and Dr. Nobuyuki Ohguro, senior lecturer of the Department of Ophthalmology (Dr. Yasuo Tano, Professor) of the Medical School at Osaka University, have successfully created the world's first DDS nanoparticles with sugar-chain ligands that can enable active targeting for the treatment of various diseases with inflammatory symptoms. Using a mouse with retinochoroiditis (eye inflammation) developed as a model animal of inflammatory diseases, their experiments have proven that targeting DDS nanoparticles utilize lectins that exist on vascular endothelial cell membranes to actively target the inflammation-inducing tissues of various diseases.

Numerous studies have already been conducted on DDS nanostructured materials such as liposomes that bear various types of ligands (antibodies, peptides, saccharides, etc.) for active targeting. Unfortunately, although these materials can be bound to target cells in vitro, they have rarely been successful in targeting tissues and target cells in vivo as would be expected. In order to address this issue, the technology of active targeting DDS nanoparticle with sugar-chain ligands developed at the Nanotechnology Research Institute of the AIST was combined with the technology for analyzing the active targeting functions on target molecules on inflammation tissues developed at the Department of Ophthalmology of Osaka University. The resulting interdisciplinary technology is accelerating the pharmaceutical development of DDS that can be applied to both general inflammatory diseases (encephalitis, retinochoroiditis, pneumonia, hepatitis, arthritis, etc.) and diseases or conditions that cause continuous inflammatory symptoms (malignant tumors, rheumatism, cerebral infarction, diabetes mellitus, Alzheimer's disease, etc.).

Future plans call for this new technology to be applied to the practical development of delivery systems required for new fields such as cancer and gene therapies, and tissue engineering.

Figure 1 One procedure for preparing novel DDS nanoparticles

Figure 2 Diagram of the active targeting

Drug Delivery Systems, or DDS for short, are divided into various subsystems. One of these, targeting DDS, recognizes target cells and tissues of diseases such as cancer and sends drugs and genes to the target site. Current research in this field is focusing on the development and/or marketing of DDS nanomaterials for passive targeting. Work is also being done on so-called "missile drugs" for active targeting DDS which can enhance the functionality of targeting. Missile drugs are showing promise as the "wonder drugs" of the 21st century.

With the aging of society, the number of cancer cases and cancer-related deaths has been increasing year by year, and there are great expectations for the development of targeting DDS as a new nanomaterial for treatment. The development of DDS nanomaterial technology is also gaining attention in other disease treatments that are seeking active targeting DDSs that do not produce side-effects. The market value of such a product could easily exceed 10 trillion yen. The establishment and development of this technology can allow target cells and tissues of diseases and conditions such as cancer and inflammations to be recognized by a drug delivery system that can send drugs, genes, etc., to local areas for treatment. The technology also enables the development of targeting nanoparticle technology that can be used in diagnoses as a cell and tissue sensing probe. Success in these endeavors will accelerate Japan’s entry into new applied nanotech industries and help to enhance its global competitiveness in commercially important fields of medicine.

The present research focuses on molecule and cell recognition functions related to sugar chains that are currently gaining attention in the life sciences as the so-called third chain, after the nucleic acid and protein chains. It is designed to develop the basis for synthesizing highly functional, targeting DDS nanomaterials with sugar-chain ligand applications as a new type of molecular recognition element. The present researchers are also aiming to establish the fundamental technology for building new DDS nanomaterials by synthesizing the present nanomaterials with highly varied DDS particles having different sugar-chain structures and using these products to study the molecular recognition functions and internal in vivo dynamics of the nanomaterials, among other things. In addition, they are undertaking fundamental and practical research with the Osaka University School of Medicine to understand the functions of these new DDS nanoparticles in the body and develop drugs for new treatments.

(1) Technology for producing active targeting DDS nanoparticles: Themes include providing liposomes that introduce sugar chains having an array of specific binding properties into different types of lectins (proteins that recognize sugar chains) that exist on the surfaces of various types of cells in the body, and liposomes that can distinguish tissues and cells in a living body andeffectively send drugs, genes, etc., to where they are needed. In order to achieve these goals, the present researchers are conducting a number of experiments and investigations into the properties of liposome surfaces, and sugar chains and linker proteins that are bound on these surfaces. In addition, their research has completed by controlling target orientation toward different structures by changing the design of these combining sugar chain molecules (see Fig. 1).

Figure 3 Selective distribution of DDS nanoparticles administered to a model inflammation disease mouse (in this case, an eye inflammation disease mouse). (Distribution to each organ is shown as a relative % to that of a normal mouse; 30 minutes after injection into the tail vein).

(2) Clarification of the active targeting of diseased tissues with inflammation regions using target lectin molecules: In the present study, a functional analysis was conducted on the active targeting DDS nanoparticles that accumulate target tissues at the locations of inflammation and can be used as therapeutic or diagnostic DDS to send drugs, genes, etc., to local areas. Specifically, this entailed the introduction of multiple target lectin molecules that appear on vascular endothelial cells at inflammation sites and sugar chains with special combination properties in an effort to understand how inflammation structures are targeted. In order to achieve these goals, the present researchers diligently investigated the application of these targeting liposomes to inflammation regions in the body, and created an eye inflammation mouse as an inflammation model animal. With this innovation, they discovered how these targeting liposomes were selectively taken to the location of an eye inflammation, helping to bring this technological development to successful conclusion (see Figs. 2, 3 and 4).

Figure 4 Fluorescent microscope photos showing active targeting (Photo D) of DDS nanoparticles toward the diseased cells, i.e., retina and chorioid cells, of the model inflammation disease mouse.

Applications have been completed for basic patents. The present researchers now plan to establish a consortium to promote the practical application of this technology, and conduct joint research with pharmaceutical companies to strengthen alliances among government, industry and academia.

• DDS
  DDS is the abbreviation for Drug Delivery System, which is called "Yakubutsu sotatsu shisutemu" in Japanese. DDS is divided into absorption-control, release-control, and targeting types. Ideally, DDS should be a system which sends drugs" to the point where they are needed in the body", "in the required amount", and "only at the required time".
• Targeting DDS
  Targeting DDS is divided into passive and active types. Passive targeting DDS uses the physicochemical properties (particle diameter, hydrophilic properties, etc.) of a carrier (transporter of the drug) to control behavior inside the body. Active targeting DDS adds special mechanisms to the passive type to tightly control the directionality toward the target tissue. For example, there are so-called "missile drugs" that use carriers consisting of combinations of ligands, e.g. antibodies, peptides, sugar chains, etc., that have specific molecular recognition features that can find target molecules of certain cells that make up the target tissue.
• Sugar chains
  Sugar chains are substances consisting of about 20 monosaccharides (such as glucose) joined together in a chain which are attached to proteins and lipids on the inside and outside of living cells. The function of sugar chains depends on the arrangement of their monosaccharide components. Normally, they branch off into complex patterns. It is estimated that the human body contains hundreds of sugar chains with widely varying structures. Sugar chains attached to proteins and lipids that recognize cells and molecules between cells appear to be involved in primary functions inside the body, but much is still unknown about the mechanism. Sugar chains, which are attracting attention in life sciences as the third life chain (after nucleic acids and proteins), show particular promise as ligands in cell recognition, and research is being conducted to apply them to the development of associated high performance materials.
• Lectin
  Lectin is known as a protein that recognizes sugar chains. Vegetable lectin has long been a topic of research, and there are now about 300 types that have been discovered. Recently, there has also been much research on animal lectin, and new lectins are constantly being discovered. Research is progressing on varied sugar chain recognition functions based on lectin groups (about 100 types) of main lectin families that exist on animal cell membranes. Of particular interest is its function as a receptor which receives structural information from sugar chains that have different structures.
• Ligands
  In biochemistry, ligands are substances which uniquely combine with proteins. For example, there are ligand substrates that combine with enzymes, and ligands such as peptides, hormones, neurotransmitters, etc. that combine various types of receptor proteins on cell membranes. The present researchers wanted to use different types of lectin proteins (which function as a kind of receptor) that exist on certain cell membranes of target tissues. Therefore, they introduced a sugar chain, that is the ligand for this protein, onto the liposome surface to produce DDS nanoparticles that would provide active targeting.
• Liposomes
  Liposomes are a type of artificial lipid membrane. When the lipids are suspended in an aqueous salt solution at a temperature higher than the phase transition point which is specific to the lipid, closed vesicles are formed spontaneously from bilayer membranes called smectic liquid crystals. These closed vesicles are called liposomes. They can also combine cholesterols, glycolipids and so on. Because liposomes are small closed spores that contain water, they can be made to store water-soluble drugs. Therefore, liposomes are used to send drugs, genes, etc., to cells which have an otherwise impermeable membrane. In addition, because of their good biocompatibility, they show great promise as nanoparticulate carrier materials for DDS.