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Wada S.-I.,Numazu Bio Medical Research Institute | Usami I.,Numazu Bio Medical Research Institute | Umezawa Y.,Microbial Chemistry Research Foundation | Inoue H.,Numazu Bio Medical Research Institute | And 4 more authors.
Cancer Science | Year: 2010

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 n. m, it hardly inhibited any other phosphatases examined. Rubratoxin B, a close analog, also specifically but weakly inhibits PP2A at Ki = 3.1 μ. m. The inhibition of intracellular PP2A in cultured cells is obviously observed with 20 μ. m 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. © 2009 Japanese Cancer Association. Source

Momose I.,Numazu Bio Medical Research Institute | Ohba S.-i.,Numazu Bio Medical Research Institute | Tatsuda D.,Numazu Bio Medical Research Institute | Kawada M.,Numazu Bio Medical Research Institute | And 5 more authors.
Biochemical and Biophysical Research Communications | Year: 2010

Large areas of tumor are nutrient-starved and hypoxic due to a disorganized vascular system. Therefore, we screened small molecules to identify cytotoxic agents that function preferentially in nutrient-starved conditions. We found that efrapeptin F had preferential cytotoxicity to nutrient-deprived cells compared with nutrient-sufficient cells. Because efrapeptin F acts as a mitochondrial complex V inhibitor, we examined whether inhibitors of complex I, II, III, and V function as cytotoxic agents preferentially in nutrient-deprived cells. Interestingly, these inhibitors showed preferential cytotoxicity to nutrient-deprived cells and caused cell death under glucose-limiting conditions, irrespective of the presence or absence of amino acids and/or serum. In addition, these inhibitors were preferentially cytotoxic to nutrient-deprived cells even under hypoxic conditions. Further, efrapeptin F showed antitumor activity in vivo. These data indicate that mitochondrial inhibitors show preferential cytotoxicity to cancer cells under glucose-limiting conditions, and these inhibitors offer a promising strategy for anticancer therapeutic. © 2010 Elsevier Inc. All rights reserved. Source

Iijima M.,Numazu Bio Medical Research Institute | Momose I.,Numazu Bio Medical Research Institute | Ikeda D.,Numazu Bio Medical Research Institute
Bioscience, Biotechnology and Biochemistry | Year: 2010

TP-110, a novel proteasome inhibitor, has been found to possess potent growth inhibition in human multiple myeloma cells. To enhance its therapeutic effects, we established TP-110-resistant RPMI-8226 (RPMI-8226/ TP-110) cells and elucidated their resistance mechanisms. The IC50 value for TP-110 cytotoxicity in the RPMI-8226/TP-110 cells was about 10-fold higher than that of the parental sensitive cells. The RPMI-8226/TP-110 cells exhibited distinct drug resistance to other proteasome inhibitors. Furthermore, they showed high cross-resistance to the cytotoxic effects of doxorubicin, etoposide, taxol, and vincristine. P-glycoprotein (MDR1), encoded by ABCB1, was elevated in the RPMI-8226/TP-110 cells, and the MDR1 inhibitor verapamil overcame their resistance to TP-110. The results of DNA microarray and RT-PCR suggested that the expression of ABCB1 is significantly elevated in RPMI-8226/TP-110 cells. This indicates that resistance in RPMI-8226/TP-110 cells is involved in the expression of P-glycoprotein, a drug-efflux pump. Source

Kawada M.,Numazu Bio Medical Research Institute | Inoue H.,Numazu Bio Medical Research Institute | Ohba S.-I.,Numazu Bio Medical Research Institute | Masuda T.,Numazu Bio Medical Research Institute | And 2 more authors.
International Journal of Cancer | Year: 2010

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. When DU-145 cells were coinoculated with PrSC subcutaneously in nude mice, leucinostatin A was found to significantly suppress the tumor growth more than atpenin B. The antitumor effect of leucinostatin A in vivo was not obtained against the tumors of DU-145 cells alone. RT-PCR experiments revealed that leucinostatin A specifically inhibited IGF-I expression in PrSC without effect on expressions of other IGF axis molecules. Leucinostatins and atpenins are known to abrogate mitochondrial functions. However, when we used mitochondrial DNA-depleted, pseudo-q0 cells, we found that one of leucinostain A actions certainly depended on mitochondrial function, but it actually inhibited the growth of DU-145 cells more strongly in coculture with pseudo-q0 PrSC and reduced IGF-I expression in pseudo-q0 PrSC. Taken together, our results suggested that leucinostatin A inhibited prostate cancer cell growth through reduction of IGF-I expression in PrSC. © 2009 UICC. Source

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