Mitsumasa Hashimoto

Publications (3)3.95 Total impact

• Article: Combined antitumor activity of 7-hydroxystaurosporine (UCN-01) and tamoxifen against human breast carcinoma in vitro and in vivo.

  Junichi Koh, Tetsuro Kubota, Toshiko Koyama, Tomofusa Migita, Mitsumasa Hashimoto, Yoichiro Hosoda, Masaki Kitajima
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  ABSTRACT: 7-Hydroxystaurosporine (UCN-01) was originally isolated as a protein kinase C inhibitor and has shown antitumor activity against several human cancer cell lines. UCN-01 inhibits cell cycle progression from the G1 to the S phase and is associated with inhibition of cyclin-dependent kinase (CDK) activity and induction of intrinsic CDK inhibitor p21, leading to dephosphorylation of retinoblastoma (Rb) protein. Tamoxifen (TAM) traps cancer cells in the G1 phase, suggesting that the mechanism of action of TAM is similar to that of UCN-01. The present study was conducted to assess the antitumor activity of UCN-01 combined with TAM against human breast carcinoma cells in vitro and in vivo. MCF-7 cells were treated with UCN-01, TAM, or UCN-01 combined with TAM at various concentrations in vitro. The antitumor effect was evaluated as the inhibition rate (I.R.%) by MTT assay. Two human breast carcinoma xenografts in nude mice, MCF-7 and Br-10, were treated with UCN-01, TAM or both agents together. The expression of p21 and the phosphorylation status of Rb protein in MCF-7 cells were detected by Western blotting. UCN-01 or TAM alone inhibited the proliferation of MCF-7 cells in a concentration-dependent manner. Combined treatment with UCN-01 followed by TAM inhibited the growth of MCF-7 cells synergistically and no significant differences in cytotoxicity were observed between the different sequences of UCN-01/TAM and TAM/UCN-01. Combination treatment with UCN-01 and TAM against MCF-7 and Br-10 in vivo exhibited superior antitumor effects compared with either agent treatment alone. Although 0.1 microg UCN-01 per ml (I.R.: 48.1%) or 2 microM TAM (I.R.: 31%) induced p21 expression, phosphorylation of Rb protein was not inhibited. However, combination treatment with UCN-01 and TAM at the same concentrations resulted in an I.R. of 67% and dephosphorylation of Rb protein. The present study suggests that combining UCN-01 and TAM could result in augmented cytotoxicity because of their similar mechanism of action. This combination may have potential clinical applications for breast cancer treatment, by reducing the toxicity of UCN-01.
  Breast Cancer 02/2003; 10(3):260-7. · 1.36 Impact Factor
• Article: UCN-01 (7-hydroxystaurosporine) inhibits the growth of human breast cancer xenografts through disruption of signal transduction.

  Junichi Koh, Tetsuro Kubota, Tomofusa Migita, Sadanori Abe, Mitsumasa Hashimoto, Yoichiro Hosoda, Masaki Kitajima
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  ABSTRACT: 7-Hydroxystaurosporine (UCN-01), originally isolated as a phospholipid-dependent protein kinase C inhibitor, has been shown to have antitumor activity against several human cancer cell lines. UCN-01 inhibits cell cycle progression from the G1 to S phase by inhibition of cyclin-dependent kinase (CDK) activity and induction of intrinsic CDK inhibitor protein, leading to dephosphorylation of retinoblastoma (Rb) protein. The antitumor activity of UCN-01 has been investigated against three human breast carcinoma strains serially transplanted into nude mice, including estrogen-dependent MCF-7, Br-10, and estrogen-independent MX-1. When the inoculated tumors started growing exponentially, UCN-01 (7.5 mg/kg) was administered intraperitoneally on five consecutive days a week for 2 weeks. The antitumor effect was evaluated as the lowest T/C ratio (%) during the experiments, where T was the relative mean tumor weight of the treated group and C was that of the control group. At the end of UCN-01 administration expression of p21, a protein of the CDK inhibitor family, and phosphorylated and dephosphorylated Rb protein was detected by Western blotting using treated and control tumors. UCN-01 had activity against MCF-7 and Br-10, with the lowest T/C ratios of 25.0% and 27.0%, respectively, while MX-1 was resistant to UCN-01 with a T/C ratio of 65.9%. The antitumor spectrum of UCN-01 was different from that of other conventional agents such as doxorubicin and cyclophosphamide which were ineffective against Br-10 but were active against MX-1. Although p21 was induced in three tested strains by UCN-01, little dephosphorylated Rb protein was expressed in MX-1 compared with Br-10 and MCF-7 (in vitro). UCN-01 appeared to be a promising agent for the treatment of breast cancer, with a different mode of action and antitumor spectrum from other currently available antitumor drugs.
  Breast Cancer 02/2002; 9(1):50-4. · 1.36 Impact Factor
• Article: Changes in the hormone receptors of human breast carcinoma xenografts in nude mice by treatment with cytotoxic agents

  Jun-ichi Koh, Eiichi Shiina, Yoichiro Hosoda, Mitsumasa Hashimoto, Osami Yamamoto, Shoji Sakai, Tetsuro Kubota, Koji Enomoto, Osahiko Abe
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  ABSTRACT: We examined the effect of chemotherapeutic agents on the estrogen receptors (ER) of breast carcinomasin vivo using human breast carcinoma strains (Br-10, T-61) serially transplanted into nude mice. When the tumor size reached approximately 1×1×1 cm, mitomycin C (MMC) at doses of 1, 2 and 4.5 mg/kg and cyclophosphamide (CPA) at a dose of 120 mg/kg, were administered once intraperitoneally, and the ERs of the tumors were measured sequentially by the dextran-coated charcoal method. Four days after the MMC administration at above doses, the binding sites of ER in Br-10 were not reduced and binding affinity was not affected. When the changes in ER content with time after the treatment with 4.5 mg/kg MMC and 120 mg/kg CPA were investigated, the ER content was found to be stable until 4 days after the treatment with both drugs, although the growth of T-61 had been significantly inhibited by the drugs. From these findings, it seems reasonable to initiate chemotherapy before endocrine therapy, since the chemotherapeutic agents did not reduce the ER content of the breast cancer strains.
  Surgery Today 04/1990; 20(1):89-96. · 1.22 Impact Factor