Angiotensin-(1-7) inhibits triple negative tumor growth through the inhibition of angiogenesis and a reduction in placental growth factor PlGF.

Abstract

Abstract Abstract #901 Triple negative breast tumors are aggressive, highly metastatic forms of breast cancer that lack estrogen and progesterone receptors and have basal expression of the epidermal growth factor receptor HER2 (ERBB2). This subtype of breast cancer, which mainly affects pre-menopausal and minority women, is characterized by aggressive and highly metastatic growth and correlates with a poor prognosis and survival rate when compared with other subtypes of breast cancer. In this study, we determined whether angiotensin-(1-7) [Ang-(1-7)], an endogenous heptapeptide hormone that activates the AT(1-7) receptor mas, can be used as a targeted chemotherapeutic agent in the treatment of triple negative breast cancer. Ang-(1-7) significantly reduced the in vivo proliferation of human triple negative breast tumor growth, using an orthotopic model. Injection of MDA-MB-231 cells into the mammary fat pad of athymic mice resulted in triple negative tumors that were treated for 28 days with either saline or 1000 μg/kg Ang-(1-7), delivered by subcutaneous injection every 12 h. The average tumor volume from mice treated with the heptapeptide was approximately 3-fold less than the size of the tumors from control animals (170.8 ± 21.4 mm3 versus 546.7 ± 87.9 mm3; n = 5, p < 0.05). In addition, Ang-(1-7) administration markedly reduced tumor weight, from 1.0 ± 0.2 g in the saline-treated mice to 0.5 ± 0.1 g in Ang-(1-7)-treated mice (n = 5, p < 0.05). The decrease in tumor growth of Ang-(1-7) treated mice was associated with a reduction in the endothelial cell marker CD34 (87.8 ± 6.4 vessel density to 32.0 ± 7.0, p < 0.05), suggesting an inhibition of angiogenesis by the heptapeptide. The decrease in vessel density observed in Ang-(1-7)-treated tumors correlated with a reduction in placental growth factor (PlGF) when compared to tumors from control animals (0.38 ± 0.11 relative density units vs 0.87 ± 0.08, n = 6), as assessed by Western blot hybridization. Incubation of MDA-MB-231 cells with Ang-(1-7) caused a time-dependent reduction in PlGF with a maximum reduction of 50% at 2 h. These results are in agreement with studies reporting that patients receiving subcutaneous administration of Ang-(1-7) showed a decrease in circulating PlGF levels. Ang-(1-7) caused a significant reduction in human umbilical vascular endothelial cells (HUVECS) tubule formation by more than 40% at a 10 nM dose. The anti-angiogenic effect of Ang-(1-7) was blocked by the specific Ang-(1-7) receptor antagonist [D-Pro7]-Ang-(1-7). Moreover, the heptapeptide significantly reduced new blood vessel formation by more than 50% in chicken chorioallantoic membrane assay; D-Pro7-[Ang-(1-7)] attenuated this effect. Taken together, these results suggest that Ang-(1-7) inhibits angiogenesis in vivo through activation of an AT(1-7) receptor. Based on the anti-angiogenic properties of the heptapeptide, Ang-(1-7) may be an effective, first-in-class compound for the treatment of triple negative breast tumors targeting the specific AT(1-7) receptor mas. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 901.