UCN-01 (7-hydroxystaurosporine) inhibits the growth of human breast cancer xenografts through disruption of signal transduction

Background: 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.

Materials and methods: 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.

Results: 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).

Conclusion: 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.