Prostate cancer shows high expression of type I insulin-like growth factor (IGF-I) receptor (IGF-IR) and prostate stromal cells (PrSC) produce IGF-I. Although high plasma level of IGF

Screening of new insecticidal and acaricidal antibiotics was carried out with reference to anti-brine shrimp activity from actinomycete strains isolated from marine environments. Of 200 actinomycete isolates, one isolate was found to produce a newsubstance, altemicidin. The strain was isolated from sea mudcollected at Gamo, Miyagi Prefecture, Japan, and identified as Streptomyces sioyaensis SA-1758. Altemicidin was purified by Diaion CHP-20P and Sephadex LH-20 column chromatographies. The molecular formula was determined as C13H20N4O7Sby elemental analysis, MSand 13C NMR spectrum. Altemicidin showed not only acaricidal activity but also antitumor activity. The compound showed no antimicrobial activity except the inhibitory activity to Xanthomonas strains.

Taken together, our results emphasize that achievement of a clinical benefit upon treatment with novel readthrough-inducing agents would require several favourable conditions including PTC nucleotide context, intrinsic and induced stability of mRNA and correct synthesis of a full-length active protein.

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Regions of hypoxia are present in the majority of solid tumors mainly because of poor and defective vascularization.1,2) Evidence indicating that hypoxic cells exist in the tumors has been obtained from microscopic analysis of histological sections 3,4) and radiobiological studies. 5) Oxygen is required for the cytotoxic effects of many cancer chemotherapeutic drugs and radiation, and hypoxic tumor cells are resistant to the conventional chemotherapy and radiotherapy. 6)Moreover, hypoxia also selects for more aggressive and metastatic cancer phenotypes that are associated with poor prognosis. 7)To conquer the therapeutic resistance induced by hypoxia, several compounds have been developed as prodrugs that are preferentially bioactivated in the hypoxic cells. The most advanced bioreductive drug, tirapazamine, is in phase III clinical trials in combination with cisplatin. 8)To identify a novel hypoxia-selective cytotoxin, we screened 20000 cultured broths of microorganisms and found that rakicidin A showed significant hypoxia-selective cytotoxicity. Rakicidin A was approximately 17.5-fold more cytotoxic under hypoxic than under normoxic conditions. In this paper, we describe the hypoxia-selective cytotoxicity of rakicidin A. MATERIALS AND METHODSCell Culture CHO chinese hamster ovary cells were maintained in minimum essential medium alpha medium (a-MEM) supplemented with 10% fetal bovine serum (ICN Biomedicals, Costa Mesa, CA, U.S.A.) and kanamycin (50 mg/ml). Human colorectal adenocarcinoma cell lines HCT-8 and DLD-1, human glioblastoma cell lines U251 and SF268, human prostate cancer cell lines PC-3 and LNCaP, human pancreatic adenocarcinomas cell line PANC-1 were maintained in RPMI1640 with 10% fetal bovine serum and kanamycin (50 mg/ml). A stable transformant of CHO cells was established by the transfection of the HIF-1-dependent luciferase (5ϫHRE/pGL3/VEGF/E1b) and neomycin resistant genes as previously described.9) Stably transfected cells were maintained in a-MEM supplemented with 10% fetal bovine serum and kanamycin (50 mg/ml). Cells were cultured at 37°C in a humidified incubator containing 5% CO 2 (normoxia).Materials Materials used were as follows: [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT), CoCl 2 , actinomycin D, bleomycin, camptothecin, chlorambucil, doxorubicin, etoposide, melphalan, mitomycin C, streptonigrin, taxol and tubercidin from Sigma Aldrich, St. Louis, U.S.A.; cisplatin from BioVision, California, U.S.A.; neocarzinostatin from Astellas Pharma, Inc., Japan; glutathione from Cayman Chemical Company, Michigan, U.S.A.; a-tocopherol and N-acetyl-L-cysteine from LKT Laboratories, Inc., Minnesota, U.S.A. All reagents were initially dissolved in dimethyl sulfoxide (DMSO) (Sigma) and diluted with the medium for assay.Screening CHO cells were seeded at a density of 1ϫ10 4 /100 ml medium per well into a pair of 96-well microplates and cultured for 24 h to assure complete adherence of the cells to the plates. The cultured cells were treated with fermentation broths of microor...

Although cytostatin analog protein phosphatase 2A (PP2A)-specific inhibitors are promising candidates of a new type of anticancer drug, their development has been hindered because of their liability. To find new classes of PP2A-specific inhibitors, we conducted a screening with microbial metabolites and found that rubratoxin A, a classical mycotoxin, is a highly specific and potent inhibitor of the enzyme. While rubratoxin A inhibits PP2A at Ki = 28.7 nM, it hardly inhibited any other phosphatases examined. Rubratoxin B, a close analog, also specifically but weakly inhibits PP2A at Ki = 3.1 lM. The inhibition of intracellular PP2A in cultured cells is obviously observed with 20 lM rubratoxin A treatment for 3 h, inducing the overphosphorylation in PP2A substrate proteins. Although rubratoxins and cytostatin differ in the apparent structures, these compounds share similarities in the structures in detail and PP2A-binding manners. Rubratoxin A showed higher suppression of tumor metastasis and reduction of the primary tumor volume than cytostatin in mouse experiments. As a successor of cytostatin analogs, rubratoxin A should be a good compound leading to the development of antitumor drugs targeting PP2A. (Cancer Sci 2010; 101: 743-750) T he phosphorylation of intracellular protein plays a central role in the regulation of eukaryotic cell function and metabolism. Protein phosphatase (PP)2A is a ubiquitous serine ⁄ threonine phosphatase in eukaryotic cells, which regulates the phosphorylation state and function of a broad range of proteins.(1,2) We previously isolated a PP2A-specific inhibitor, cytostatin, from an actinomycete culture.(3-5) Its analog, fostriecin, and other PP2A-specific inhibitors have also been reported since mid 1990s.(6-11) These new inhibitors have higher specificities to PP2A than okadaic acid, a previously identified inhibitor (PP1 IC 50 ⁄ PP2A IC 50 : fostriecin, 10 4

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Targeting stroma in tumor tissues is an attractive new strategy for cancer treatment. We developed in vitro coculture system, in which the growth of human prostate cancer DU-145 cells is stimulated by prostate stromal cells (PrSC) through insulin-like growth factor I (IGF-I). Using this system, we have been searching for small molecules that inhibit tumor growth through modulation of tumor-stromal cell interactions. As a result, we have found that leucinostatins and atpenins, natural antifungal antibiotics, inhibit the growth of DU-145 cells cocultured with PrSC more strongly than that of DU-145 cells alone. In this study we examined the antitumor effects of these small molecules in vitro and in vivo. Growing evidence indicates that the stroma plays a critical role in the growth and metastasis of various cancers, including colorectal, 1 breast, 2,3 pancreatic 4 and prostate cancer.