Stability and interconversion of duocarmycins were studied in relation to their cytotoxicities and antimicrobial activities. The compounds studied included duocarmycin A and SA, which have a spirocyclopropylhexadienone moiety, and four halogenated seco-compounds of duocarmycin A: duocarmycin B1, B2, C1 and C2, from which the cyclopropane ring structure is absent. Duocarmycins were potent cytotoxic compounds to cells. The cytotoxic activity seen on Balb 3T3/H-ras cells after 72 h drug exposure was in the following order (IC50 (nM): concentration for 50% growth inhibition); SA (0.05) > A (0.3) > B2 (1.5) > B1 (3.0) > C2 (20) > C1 (40). Average minimum inhibitory concentrations (MICs) of duocarmycins against microorganisms showed essentially the same ranking order as that of cytotoxicity. There was a large difference between SA and A in their stability in aqueous solvents. For halogenated seco-compounds, a good correlation was found between their cytotoxicities in vitro and their conversion rate to duocarmycin A, suggesting that halogenated seco-compounds undergo closure to the spirocyclopropylhexadienone structure, the pertinent active form, in cells.
Lck is a Src-family tyrosine kinase that is expressed predominantly in T cells, where it plays important roles in T-cell activation. Lymphostin was isolated from Streptomyces sp. as an inhibitor of Lck. As previously reported, lymphostin inhibited Lck (IC50 0.05 microM) and the mixed lymphocyte reaction (IC50 0.009 microM). We have now examined the mechanism of inhibition by lymphostin. Lymphostin inhibited protein-tyrosine kinase activity in Jurkat T cells, demonstrating the effectiveness of the compound at the cellular level. Furthermore, lymphostin suppressed delayed-type hypersensitivity in mice. However, the inhibitory activity against Lck at the cellular level was weaker than that against the mixed lymphocyte reaction. Thus, we examined the effects of lymphostin on other kinases. Interestingly, lymphostin also inhibited phosphatidylinositol 3-kinase (IC50 0.001 microM). Consequently, we conclude that lymphostin inhibits the mixed lymphocyte reaction and delayed-type hypersensitivity not only through the blockade of Lck, but through the blockade of phosphatidylinositol 3-kinase as well.
UCN-01 is a staurosporine-related compound that was isolated from the culture broth of Streptomyces sp. and shows potent and selective inhibitory activity against protein kinase C. Cellular inhibitory activity of UCN-01 against protein kinase C and cytotoxicity of UCN-01 were compared with those of staurosporine. When the mechanism of inhibitory activity was investigated in vitro, UCN-01 as well as staurosporine inhibited the activity of the catalytic domain of protein kinase C. In spite of direct inhibition against the catalytic domain of protein kinase C, cytotoxicity of UCN-01 was much lower than that of staurosporine. In addition, UCN-01 showed more selective inhibitory activity against protein kinase C than did staurosporine because of the sole structural difference at C-7. Therefore, a series of 7-O-alkyl derivatives of UCN-01 was synthesized and investigated. Interestingly, one of the compounds, the beta-methoxy derivative, showed 3-fold greater potency and 17-fold more selective inhibitory activity against protein kinase C than did UCN-01.
Seven novel potent antitumor antibiotics, duocarmycins A (1), C1 (2), C2 (3), D (4), B1 (5), B2 (6) and SA (7), were isolated from three independently collected Streptomyces sp. The complete structures, including absolute stereochemistry, were determined by spectral and chemical studies of those duocarmycins and several derivatives. Duocarmycins A (1) and SA (7) possess a 1,2,7,7a-tetrahydrocycloprop[1,2-c]indol-4-one subunit, a common pharmacophore with that of CC-1065 (10) found from Streptomyces zelensis.
A total number of 57 strains of Erysipelothrix insidiosaisolated from swine erysipelas (including 3 strains of stock cultures) were examined for sensitivity to 26 antibacterial drugs by means of a plate dilution method.1) All the strains tested were completely sensitive to penicillin G, aminobenzyl penicillin, phenoxyethyl penicillin, methylchlorophenylisoxazolyl penicillin, erythromycin, and tylosin. Most of them were fairly sensitiveto spiramycin, leucomycin, oleandomycin, mikamycin, and the tetracyclines, as compared with the other drugs.2) A very few of the strains tested were sensitive to chloramphenicol, thiophenicol, streptomycin, and dihydrostreptomycin. Furthermore, few of them were sensitive to novobiocin, fradiomycin, kanamycin, polymyxin, colistin, and sulfa drugs.3) There were no differences in sensitivity to many of the drugs tested among the strains isolated from septicemic, endocardiac, and arthritic forms.4) It was difficult to make anyof the strains resistant to penicillin G by means of an artificial process in vitro.
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