Description

Prostate cancer,Breast cancer

Description

Zibotentan (ZD4054) is a specific Endothelin A (ET_A) antagonist with IC50 of 21 nM.

Targets

IC₅₀

In Vitro

As Zibotentan specifically inhibits ET_A-mediated antiapoptotic effects, but not ET_B-mediated proapoptotic effects in human and rat smooth muscle cells, Zibotentan binds to endothelin A receptor (ET_A) with high affinity with K_i of 13 nM, and has no affinity for endothelin B receptor (ETB) with IC50 of >10 μM. ^[1] Zibotentan treatment at 1 μM inhibits ET-1 induced mitogenic activity in ovarian carcinoma cell lines HEY and OVCA 433 secreting ET-1 and expressing ET_A and ET_B mRNA. ^[2] ZD4054 (1 μM) inhibits ET-1 induced EGFR transactivation in HEY and OVCA 433 cells. Zibotentan (1 μM) reverts ET-1 mediated epithelial-mesenchymal transition (EMT), by enhancing E-cadherin expression and promoter activity, and inhibiting vascular endothelial growth factor (VEGF) secretion and invasiveness in HEY and OVCA 433 cells. ^[3] Zibotentan also potently inhibits the basal and ET-1 induced cell proliferation in SKOV-3 and A-2780 cells, associated with the inhibition of AKT and p42/44MAPK phosphorylation, and with increased apoptosis through the inhibition of bcl-2 and activation of caspase-3 and poly(ADP-ribose) polymerase proteins. ^[4]

In Vivo

Administration of Zibotentan at 10 mg/kg/day for 21 days potently inhibits the growth of HEY ovarian carcinoma xenografts in mice by 69% with no associated toxicity, which is in association with the blocking of cell proliferation evaluated by 37% inhibition of the Ki-67 expression, and the 62% inhibition of tumor-induced vascularization. Consistently, Zibotentan treatment significantly inhibits the expression of matrix metalloproteinase-2 (MMP-2) and VEGF, as well as the activation of p42/44 MAPK and EGFR, and potently enhances the expression of E-cadherin. ^[3]

Clinical Trials

A Phase III study of Zibotentan in patients with hormone resistant prostate cancer (HRPC) and bone metastases has been completed.

Features

Description

Zibotentan (1 μM) in combination with Gefitinib (1 μM) results in a greater inhibition of ET-1 induced EGFR, MAPK, and AKT phosphorylation in HEY and OVCA 433 cells, as well as a significant decrease in cell proliferation (65%), invasion (52%), and VEGF production (50%), accompanied by a 2-fold increase in apoptosis. Zibotentan administered i.p. at 10 mg/kg/day together with oral administration of Gefitinib at 125 mg/kg/day for 21 days significantly induce tumor growth inhibition by 82% of HEY xenografts, more potently compared with each drug treatment alone with ~69% tumor growth inhibition, and the growth delay in established tumors persists for up to 4 weeks after the termination of the combined treatment. The combination of Zibotentan and Gefitinib induces more significant inhibition of tumor neovascularization (78%) compared with either Zibotentan (62%) or Gefitinib (45%) treatment alone, and markedly decreased expression of Ki-67 by 46% versus 37% or 30%, which is associated with more potent inhibition of the expression/activation of MMP-2, VEGF, MAPK and EGFR, and the enhancement of E-cadherin expression, compare with single-agent treatment. ^[3] The combination of Zibotentan (10 mg/kg/day) and Paclitaxel (three 20 mg/kg i.v. doses every 4 days) produces additive antitumor effects in HEY ovarian cancer xenografts, with 40% of mice remaining tumor-free. ^[4]

Receptor-binding assays

The inhibition by Zibotentan (varying concentrations) of ¹²⁵iodine-ET-1 binding to cloned human ETA is assessed using standard radioligand-binding techniques. Human recombinant ETA is expressed in mouse erythroleukaemic cells, and cell membranes prepared for competitive binding studies using ¹²⁵iodine-ET-1 as the radioligand. Incubations are carried out in triplicate in the presence of Zibotentan, 100 pM to 100 μM in half-log increments, and inhibition of ET-1 binding is expressed as the geometric mean pIC50 value (concentration to inhibit 50% of binding) with a 95% confidence interval (CI). The affinity of Zibotentan for cloned human ETA is also assessed using the equation of Cheng and Prusoff to determine the equilibrium dissociation constant (Ki) in a further receptor-binding screen utilizing a greater number of concentration-response curves determined in three separate studies.

Cell Lines

HEY and OVCA 433

Concentrations

Dissolved in DMSO, final concentrations 1 μM

Incubation Time

48 hours

Methods

Cells are serum starved by incubation for 24 hours in serum-free DMEM before exposed to Zibotentan for 48 hours. After the treatment, cells are lysed and the supernatant is recovered and assayed for histone-associated DNA fragments, at 405 nm by the use of a microplate reader. For detection of early apoptotic events, floating and adherent cells are collected. Cells are double stained with FITC-conjugated Annexin V and propidium iodide using the Vybrant Apoptosis Kit and are immediately analyzed by cytofluorometric analysis.

Animal Models

Female athymic (nu⁺/nu⁺) mice bearing established HEY human ovarian carcinoma xenografts

Formulation

Dissolved in DMSO, and diluted in PBS

Doses

10 mg/kg/day

Administration

Treated i.p.