1. Development of a new antibiotic for XDR-TB

There are nearly 9 million new cases of active tuberculosis (TB) worldwide and over 1.5 million associated deaths every year. The difficulty of chemotherapy in TB/HIV co-infection and the prevalence of multi drug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) are particularly serious clinical problems.

Our institute was established in 1962 by Dr. Hamao Umezawa who discovered kanamycin, the first anti-TB drug developed in Japan. Since then, we have continued the development of new antiTB drugs. In 2003, we discovered the anti-TB antibiotics caprazamycins, which are produced by the actinomycete Streptomyces sp. MK730-62F2. We found that some of the derivatives from caprazamycin exhibited potent and selective activities against Mycobacterium tuberculosis H37Rv in vitro and have excellent water solubility, superior to the lead compound. In particular, CPZEN-45 exhibited good activity against MDR- and XDR-TB strains in vitro and showed excellent therapeutic efficacy in the treatment of mice infected with XDR-TB.

In 2008, we joined “The Lilly TB Drug Discovery Initiative” and collaborated on further studies for developing this candidate drug in a short time.

2. The antibacterial agent tripropeptin C

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MRSA (methicillin-resistant Staphylococcus aureus) and VRE (vancomycin-resistant Enterococcus) are opportunistic pathogens. These organisms cause severe infections such as sepsis, pneumonia, and endocarditis in immunocompromised hosts. Vancomycin has been the last resort for the treatment of MRSA, but its efficacy is limited because of the emergence of vancomycin intermediate resistant- and highly resistant-bacteria. Under these circumstances, new effective drugs against those pathogens are needed urgently.

The discovery of tripropeptin C (TPPC) stemmed from research on compounds which were effective against MRSA without cross-resistance to vancomycin. TPPC shows very potent antimicrobial activity against Gram-positive bacteria including resistant strains (MRSA, VRE, PRSP; penicillin-resistant Streptococcus pneumoniae) and excellent therapeutic efficacy in a mouse model of staphylococcal septicemia when administered intravenously. A study on the mode of action of TPPC revealed the blocking of peptidoglycan biosynthesis in a manner different from those of vancomycin, daptomycin, and bacitracin.

Preclinical studies of TPPC have started, and the in vivo efficacy of TPPC in a mouse MRSA-thigh, VISA-septicemia model is under evaluation.

TPPC shows excellent efficacy in a mouse-MRSA/VRE infection model, good toxicological profiles, and a distinct mode of action from other available drugs. The findings indicate that TPPC is a promising novel class of antibiotic against infections caused by MRSA and VRE.

3. The spreading mechanism of NDM-1, a novel β-lactamase

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The dissemination of drug-resistant pathogens has constituted a major threat to human life for a long period of time. Many of the genes responsible for the development of this resistance exist on movable plasmids and are transmissible between microorganisms. As a consequence, these genes have rapidly spread worldwide. Accordingly, it is considered that a study of the spreading mechanism may contribute to control of the proliferation of drug resistance in pathogens.

NDM-1 was first characterized as a novel class of β-lactamase in 2008. The gene blaNDM-1, which encodes NDM-1, exists on a mobile plasmid ; since its discovery , this gene has disseminated throughout the world, particularly in South Asia and Europe. The first case in Japan was a NDM-1 producing strain of Escherichia coli, isolated at Dokkyo Medical University Hospital in 2009. One of our goals in collaboration with Dokkyo Medical University is to determine the very effective spreading mechanism of NDM-1. Until date, a large plasmid (ca. 200 kbp) encoding blaNDM-1 has been sequenced. We are now investigating the detail of the spreading mechanism using this sequence data.

4. Functional analysis of the VEGFR-1 signaling system

VEGFR-1, the receptor for vascular endothelial growth factor (VEGF), has a cytoplasmic tyrosine kinase domain　that is expressed in not only vascular endothelial cells but also macrophages. It has been suggested that VEGFR-1 has a role as a negative regulating factor in vascularization (Fig.) although its physiological function is not well-defined.

Recent studies have shown that the growth of implanted tumor cells in VEGFR-1 tyrosine kinase–deficient mice (VEGFR-1 TK^−/−) was decreased by the suppression of macrophage infiltration into tumors(1). Bone marrow transplantation experiments showed that VEGFR-1 signaling is involved in the migration of macrophages into cancerous tissues and tumor progression.

We have investigated the function of the VEGFR-1 signaling system in macrophage lineage cells, and also elucidated its effect on tumor growth.

(1)Muramatsu, M., Yamamoto, S., Osawa, T., and Shibuya, M. (2010) Cancer Res 70:8211.

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5. Development of new compounds against sensory neuron-related disorders

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Abnormal neuronal activity of sensory afferent impulses evokes various disorders such as inflammatory and neuropathic pain, overactive bladder, and pruritus (Fig.). In particular, we have focused on bioactive substances and their receptors involved in the sensitization of dorsal root ganglion (DRG) neurons. We have screened microbial metabolites to identify compounds that affect sensory nerve functional signaling. The compounds we have discovered are expected to be used not only as chemical biological tools for the analysis of the sensitization mechanism of DRG neurons but also as starting materials for the development of drugs to treat sensory neuron-related disorders.

6. Study on aquatic and terrestrial microorganisms for drug discovery

We are expanding our culture stock library for the discovery of new bioactive metabolites. At present, we have more than 40,000 pure cultures of soil bacteria. Fermentation broths of these bacteria are used for screening of useful bioactive compounds. The screening results therefore depend directly on the quality and diversity of the library. Our library is composed mainly of actinomycetes, which are an excellent source for the discovery of novel secondary metabolites with diverse biological activities, therefore, they are regarded as the best screening sources for drug discovery. The clinically important drugs, kanamycin, bleomycin, josamycin, and aclacinomycin were discovered from secondary metabolites of actinomycetes at our institute.

High quality and as yet undiscovered isolates for screening sources are essential to the discovery of new metabolites. Our focus for isolating strains is based on poorly studied habitats within the extremobiosphere and underused samples such as deep sea sediment and aquatic organisms as well as soil bacteria.

7. Study on insect symbionts and entomopathogeic fungi

We have isolated insect symbionts and entomopathogenic fungi as screening resources for drugs. Insect symbionts produce various molecules to maintain symbiosis, and entomopathogenic fungi infect insects by evading the host defense mechanism with bioactive molecules. The molecules produced by these microbes are expected to possess unique structures and biological functions and may represent seed compounds for drugs as well as being useful tools for understanding symbiosis and pathogenesis.