Hideyuki Onodera

Conformational significance of EH21A1-A4, phenolic derivatives of geldanamycin, for Hsp90 inhibitory activity.

Hsp90 is an attractive chemotherapeutic target because it is essential to maturation of multiple oncogenes. We describe the conformational significance of EH21A1-A4, phenolic derivatives of geldanamycin isolated from Streptomyces sp. Their native free structures are similar to the active form of geldanamycin bound to Hsp90 protein. Their conformational character is a probable reason for their high-affinity binding. Lack of toxic benzoquinone in EH21A1-A4 also adds to their potential as lead compounds for anti-tumor drugs.

Paraphaeosphaeride D and berkleasmin F, new circumventors of arbekacin resistance in MRSA, produced by Paraphaeosphaeria sp. TR-022

Two new compounds, designated paraphaeosphaeride D (1) and berkleasmin F (2) together with a previously known compound, berkleasmin A (3), isolated from a culture broth of the fungus Paraphaeosphaeria sp. TR-022, proved to be new circumventors of arbekacin (ABK) resistance in methicillin-resistant Staphylococcus aureus (MRSA). The structures of 1 and 2 were elucidated by spectroscopic analyses, including various NMR experiments. All compounds showed 10–100 times ABK circumvention activities using the paper disc method and reduced the MIC values of ABK against MRSA from 16 μg ml−1 to 4 μg ml−1 (fourfold) using the agar dilution method. These new compounds might be promising lead compounds for developing circumventors of ABK resistance in MRSA.

In vitro antitrypanosomal activity of five low-MW antibiotics.

As part of our screening program to find new antitrypanosomal compounds, we evaluate isolates from soil-dwelling microorganisms as well as compounds from existing antibiotic libraries. We have previously published findings of various microbial metabolites exhibiting potent antitrypanosomal properties.1–7 We have recently investigated five compounds of low MW from Kyowa Hakko Kirin Co., Ltd, with MWs ranging from 238 to 511 Da. The compounds, all known to possess antibiotic properties, are EI-1507-1, EI-1941-1, EI1941-2, leinamycin (DC 107) and UCS1025A. All showed antitrypanosomal activity in vitro. Here, we report the antitrypanosomal profiles of these antibiotics (Figure 1), in comparison with two clinically used antitrypanosomal drugs, eflornithine and suramin. We also present some insights with regard to structure–activity relationships. Test compounds were obtained from the antibiotic library of the Medicinal Chemistry Research Laboratories, Kyowa Hakko Kirin Co., Ltd (Tokyo, Japan). In vitro antitrypanosomal activity against Trypanosoma brucei brucei strain GUTat 3.1 and cytotoxicity against human diploid embryonic cell line MRC-5 were measured, as described previously.1 Table 1 shows the in vitro antitrypanosomal activities of the compounds tested, as well as the two leading antitrypanosomals. EI1941-1 showed the highest trypanocidal activity, with an IC50 value of 14 nM. This compound was 79–891-fold more potent than eflornithine and suramin. Leinamycin was slightly less active than EI-1941-1, showing an IC50 value of 17 nM. EI-1507-1, EI-1941-2 and UCS1025A were 42–145-fold less active than EI-1941-1, showing IC50 values of 593–2029 nM. Although the antitrypanosomal activities of these compounds were similar to that of suramin, those activities were 6–21-fold more effective than that of eflornithine. The in vitro cytotoxicity of all compounds tested is also presented in Table 1. Leinamycin showed the highest cytotoxicity against MRC-5 cells, with an IC50 value of 313 nM. EI-1507-1, EI-1941-1 and EI-19412 were found to be only slightly cytotoxic, demonstrating IC50 values of 9.6–12.7mM, whereas UCS1025A had an IC50 value of 425mM, exhibiting very low cytotoxicity but still far more than eflornithine and suramin. For a more relevant comparison of the suitability of these compounds for possible development as human medicaments, we devised a Selectivity Index (SI), determined by (cytotoxicity [IC50 for the MRC-5 cells]/antitrypanosomal activity [IC50 for the GUTat 3.1

The synthesis and evaluation of the antiproliferative activity of deacidified GEX1A analogues

GEX1A/herboxidiene (1) is a natural product isolated from Streptomyces sp. and has been reported to target the pre-mRNA splicing process. Although 1 was shown to have antitumor activity in vivo, weight loss was observed in mice when 1 was consecutively administered. We assumed that the carboxylic acid moiety was one of the causes of this toxicity. In this study, a series of amide, carbamate and urea analogues of 1 were synthesized and their antiproliferative activity was evaluated in vitro. The synthesis of urea analogues featured Curtius rearrangement following amine treatment with the one-pot procedure from 1. Furthermore, a structure–activity relationship study of the urea analogues revealed that the pharmacologically preferable basic side chains were acceptable and that compound 9g was equipotent to parent 1. These basic urea analogues would be promising leads for the development of novel antitumor agents.

Simplifungin and Valsafungins, Antifungal Antibiotics of Fungal Origin

The targets of antifungal antibiotics in clinical use are more limited than those of antibacterial antibiotics. Therefore, new antifungal antibiotics with different mechanisms of action are desired. In the course of our screening for antifungal antibiotics of microbial origins, new antifungal antibiotics, simplifungin (1) and valsafungins A (2) and B (3), were isolated from cultures of the fungal strains Simplicillium minatense FKI-4981 and Valsaceae sp. FKH-53, respectively. The structures of 1 to 3 including their absolute stereochemistries were elucidated using various spectral analyses including NMR and collision-induced dissociation (CID)-MS/MS as well as chemical approaches including modifications to the Moshers method. They were structurally related to myriocin. They inhibited the growth of yeast-like and zygomycetous fungi with MICs ranging between 0.125 and 8.0 μg/mL. An examination of their mechanisms of action by the newly established assay using LC-MS revealed that 1 and 2 inhibited serine palmitoyltransferase activity, which is involved in sphingolipid biosynthesis, with IC50 values of 224 and 24 nM, respectively.

Habiterpenol, a novel abrogator of bleomycin-induced G2 arrest in Jurkat cells, produced by Phytohabitans suffuscus 3787_5.

A small molecule named habiterpenol produced by actinomycete Phytohabitans suffuscus 3787_5 was found to abrogate bleomycin-induced G2 arrest in Jurkat cells. Habiterpenol showed no cytotoxic effect on Jurkat cells even at 273 μM; however, the compound inhibited bleomycin-induced G2 arrest in Jurkat cells with an IC50 value of 3.55 μM, while it showed no effect on colchicine-induced M arrest even at 273 μM. These results indicated that habiterpenol selectively abrogated bleomycin-induced G2 arrest in Jurkat cells.

Naphthacemycins, novel circumventors of .BETA.-lactam resistance in MRSA, produced by Streptomyces sp. KB-3346-5. I. The taxonomy of the producing strain, and the fermentation, isolation and antibacterial activities

Screening for circumventors of β-lactam resistance in methicillin-resistant Staphylococcus aureus (MRSA) led us to find 17 novel antibiotics, naphthacemycins A1–A11, B1–B4 and C1–C2. The naphthacemycins were isolated from a cultured broth of Streptomyces sp. KB-3346-5 by repeated silica gel column chromatography and HPLC. Naphthacemycins enhanced imipenem activity 100–500 times against MRSA at 0.5 μg ml−1, and naphthacemycins A4–A11 themselves showed MIC50 values of 1–4 μg ml−1 against 22 MRSA strains.