Therapeutic targeting of the endothelin a receptor in human ovarian carcinoma.

The endothelin A receptor (ET(A)R) autocrine pathway is overexpressed in many malignancies, including ovarian carcinoma. In this tumor, engagement of ET(A)R triggers tumor growth, survival, neoangiogenesis, and invasion. To evaluate whether ET(A)R represents a new target in cancer treatment, we examine in vitro and in vivo the effect of the selective ET(A)R antagonist ABT-627 (atrasentan), a small p.o. bioavailable molecule, in mono- and combination therapy with taxane. ABT-627 effectively inhibits cell proliferation, vascular endothelial growth factor (VEGF) secretion of ovarian carcinoma cell lines, and primary cultures. ET(A)R blockade also results in the sensitization to paclitaxel-induced apoptosis. In ovarian carcinoma xenografts, in which the ET-1/ET(A)R autocrine pathway is overexpressed, tumor growth was significantly inhibited in ABT-627-treated mice compared with control. The therapeutic efficacy of ABT-627 was associated with a significant reduction in microvessel density, expression of VEGF, and matrix metalloproteinase-2, and increased the percentage of apoptotic tumor cells. Combined treatment of ABT-627 with paclitaxel produced additive antitumor, apoptotic, and antiangiogenic effects. These findings demonstrate that the small molecule ABT-627 is a candidate for clinical testing as an antitumor agent in ovarian cancer patients, especially in combination with taxane therapy. Interruption of ET(A)R signaling therefore, represents, a promising therapeutic strategy in ovarian carcinoma.

Growth inhibition of cervix carcinoma cells in vivo by endothelin A receptor blockade.

In human papillomavirus (HPV)-positive cervical cancer cells, the endothelin A receptor (ET(A)R) mediates an endothelin-1-induced mitogenic effect, thus representing a relevant target for antitumor therapy. Here, we describe the complete inhibition of human cervix carcinoma growth by blocking the ET(A)R. In nude mice, the ET(A)R-selective antagonist atrasentan inhibits the growth and the neoangiogenesis of cervical carcinoma cell xenografts. Two cycles of treatment completely revert tumor growth. Atrasentan displays additive effects when administered in combination with the cytotoxic drug paclitaxel. These results demonstrate that by inhibiting cell proliferation and angiogenesis, this small molecule may help to control cervical cancer by either monotherapy or combination therapy.

Endothelin-1 promotes proteolytic activity of ovarian carcinoma.

Endothelin-1 (ET-1) is a potent mitogenic and angiogenic factor for ovarian carcinoma cell lines, which acts selectively through the ET(A) receptor (ET(A)R). A previous study demonstrated that ET-1 is present at high concentrations in ovarian cancer ascites, indicating a direct role in the progression and metastasis of ovarian carcinoma. In this study, we investigated whether ET-1 could induce production and activation of tumour-associated proteinases in ovarian carcinoma cells. As demonstrated by ELISA, we found that the secretion of matrix metalloproteinase (MMP)-2 and MMP-9, urokinase-type plasminogen activator and plasminogen activator inhibitor type-1 and -2 was upregulated by ET-1 in a dose-dependent manner in the HEY cell line. In addition, the MMPs in ET-1-treated cells are consistently active, as shown by MMP gelatinase activity assay. Finally, we demonstrated that BQ-123, an antagonist of ET(A)R, inhibited the ET-1-induced tumour protease secretion and activity, suggesting that ET-1/ET(A)R may play an important role in the progression and metastasis of ovarian carcinoma, activating multiple proteinase cascades.

Endothelin-1 acts as a survival factor in ovarian carcinoma cells.

The aim of this study was to evaluate the role of endothelin-1 (ET-1) in the sensitivity of ovarian carcinoma to paclitaxel, one of the most common drugs used for the management of this tumour histotype. ET-1 is a powerful mitogenic peptide produced by ovarian carcinomas and it acts as an autocrine growth factor, selectively through ET(A) receptor (ET(A)R), which is predominantly expressed in this tumour. OVCA 433 and HEY, two ovarian carcinoma cell lines, which produce elevated amounts of ET-1 and express abundantly high-affinity ET(A)Rs, were used. As demonstrated by sub-G(1) peak in DNA content histograms and terminal transferase deoxytidyl uridine end labelling assay, we found that paclitaxel induces cytotoxic effect through the activation of apoptosis in both cell lines. When the treatment with paclitaxel was performed in association with ET-1, paclitaxel-induced apoptosis was inhibited. In order to evaluate which ET-1 receptor mediated the effect of ET-1 on protection from paclitaxel-induced apoptosis, we performed experiments using two selective antagonists for ET(A)R (BQ-123) and for ET(B)R (BQ-788). We showed that ET(A)R blockade inhibits the ET-1-induced survival activity against paclitaxel-mediated apoptosis. However, no effect was observed on blocking ET(B)R with BQ-788. Our results establish a novel role for ET-1 in determining survival of ovarian carcinoma cells and suggest that pharmacological ET(A)R blockade using a specific ET(A)R antagonist may provide a novel approach to the treatment of ovarian carcinoma in combination therapy.

Endothelin receptor blockade inhibits the growth of human papillomavirus-associated cervical carcinoma.

Human papillomaviruses (HPVs) are associated with cervical cancer and interact with growth factors that may enhance malignant transformation of cervical carcinoma cells. Endothelin-1 (ET-1) is released from HPV-transfected keratinocytes and induces increased growth response in these cell lines in comparison with normal cells. HPV-positive cancer cells secrete ET-1 and express mRNA for ET-1 and its receptors, whereas HPV-negative carcinoma cell lines express only the ET(B) receptor (ET(B)R) mRNA and do not secrete ET-1. In HPV-positive cancer cells, ET(A)R mediates the ET-1-induced mitogenic effect and sustains the basal growth rate of unstimulated cervical tumour cells. Therefore, ET-1 may be involved in the neoplastic growth of HPV-associated cervical carcinoma, where the increased ET-1 autocrine loop can be targeted for antitumour therapy. In the present work, the action of specific antagonists of ET(A)R (BQ-123 and ABT-627), was analysed in CaSki and C33A cells that are derived from human cervical carcinoma. CaSki cells are HPV-16-positive, produce ET-1 and possess ET(A)R and ET(B)R, whereas the C33A line is HPV-negative, does not secrete ET-1 and has no ET(A)R. In HPV-positive cancer cells ABT-627 strongly inhibited the proliferation induced by ET-1 and substantially reduced the basal growth rate of unstimulated cervical tumour cells, whereas the ET(B)R antagonist had no effect. These results demonstrate that ET-1 participates in the progression of neoplastic growth in HPV-associated carcinoma, in which ET(A)R expression is increased and could be targeted for antitumour therapy. In conclusion, an ET-1 autocrine loop is involved in tumour cell proliferation via ET(A)R, and ABT-627 is effective in controlling proliferation of cervical carcinoma cells.

ABT-627, a potent endothelin receptor A antagonist, inhibits ovarian carcinoma growth in vitro.

Endothelin-1 (ET-1) is present at high concentrations in ovarian cancer ascites and is overexpressed in primary and metastatic ovarian carcinomas. In these tumours the presence of ET-1 is associated with enhanced neovascularization and with vascular endothelial growth factor (VEGF) expression. In these tumour cells, ET-1 acts as an autocrine growth factor selectively through the receptor ET(A), which is predominantly expressed in tumour cells. Furthermore, ET-1 produced by ovarian tumour cells stimulates VEGF production and VEGF-mediated angiogenic effects through ET(A) binding. These results demonstrate that activation of the ET(A) in ovarian carcinoma cells promotes cell proliferation, neovascularization and invasion, which are the principal hallmarks of malignant transformation. The present study was designed to investigate the effects of the ET(A)-selective antagonist ABT-627 on the ET-1-induced mitogenic effect in both primary cultures (PMOV1 and PMOV2) and cell lines (OVCA 433 and HEY) of ovarian carcinoma. All tumour cells express the components of the ET-1 system and secrete ET-1. ET(A) blockade by ABT-627 inhibits ET-1-induced mitogenic effects. The ET(B) antagonist BQ-788 is ineffective although all cell lines express both ET(A) and ET(B) mRNAs. In conclusion, our results demonstrate that ABT-627 is capable of inhibiting the proliferative activity of ET-1, suggesting that this potent ET(A) antagonist may provide a novel approach to the multidisciplinary treatment of ovarian carcinoma.

Endothelin-1 protects ovarian carcinoma cells against paclitaxel-induced apoptosis: requirement for Akt activation.

Endothelin-1 (ET-1) is a powerful mitogenic peptide produced by different tumors. In ovarian carcinoma cells, ET-1 acts as an autocrine growth factor, selectively through ET(A) receptor (ET(A)R), which is predominantly expressed in tumor cells. The aim of this study was to examine whether ET-1 plays a role in the sensitivity of three ovarian carcinoma cell lines (OVCA 433, HEY, and SK-OV-3) to apoptosis induced by two different stimuli. Our results demonstrated that the addition of ET-1 markedly inhibited serum withdrawal and paclitaxel-induced apoptosis in a concentration-dependent manner, as demonstrated by Annexin-V assay, sub-G(1) peak in DNA content histograms, internucleosomal DNA fragmentation, and terminal deoxynucleotidyl transferase-mediated dUTP biotin nick-end labeling method. Pretreatment of the cells with an ET(A)R antagonist, BQ 123, reversed the ET-1-induced protective effect. Paclitaxel-induced apoptosis resulted in the phosphorylation of Bcl-2 that was suppressed by the addition of ET-1. Further analysis of the signaling pathway demonstrated that ET-1 stimulated Akt activation. The phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin blocked ET-1-induced Akt phosphorylation. Inhibition of ET-1-stimulated mitogen-activated protein kinase activity did not affect ET-1 protection from paclitaxel-mediated apoptosis. Moreover, BQ 123 blocked the Akt-mediated pathway activated by ET-1, sensitizing ovarian carcinoma cells to paclitaxel treatment. These results establish a novel role for ET-1 in determining protection of ovarian carcinoma cells against paclitaxel-induced apoptosis through Bcl-2-dependent and PI3-K-mediated Akt pathways and suggest that ET-1 and ET(A)R could represent important targets for anticancer therapy.