Angiotensin-(1–7) [Ang-(1–7)] is an endogenous peptide hormone of the renin-angiotensin system with vasodilator properties. Our group showed that Ang-(1–7) attenuates the growth of vascular smooth muscle cells (VSMCs) in vivo and in vitro, demonstrating the anti-proliferative effects of the peptide. We propose that growth inhibition by Ang-(1–7) is not limited to VSMCs but also extends to cancer cells. ZR-75-1 cells, a human ductal carcinoma cell line, were treated with a mitogen, in the presence and absence of Ang-(1–7), to determine whether the heptapeptide inhibits the growth of breast cancer cells in vitro. Ang-(1–7) caused a significant reduction in mitogen-stimulated growth, with an average inhibition of 50%. Treatment with Ang-(1–7) also decreased serum-stimulated DNA synthesis in ZR-75-1 or MCF-7 human breast cancer cells. The attenuation of DNA replication was dependent on the dose of Ang-(1–7) with a maximal reduction of approximately 40% of serum-stimulated 3H-thymidine incorporation and IC50s in the subnanomolar range. In contrast, Ang-(1–7) had no effect on human breast cancer cells of the MDA-MB-435 cell line, suggesting that these cells may lack the AT(1–7) receptor. Treatment of ZR-75-1 cells with Ang-(1–7) resulted in an increase in p16Ink, a cyclin-dependent kinase inhibitor which regulates cell cycle progression, while CDK4, a cyclin-dependent kinase, was reduced, as determined by Western blot hybridization. These effects correlated with a time-dependent reduction in mitogen-stimulated hyperphosphorylation of retinoblastoma which which is known to cause cell cycle arrest and inhibition of cell growth. This study provides the first evidence that Ang-(1–7) inhibits the proliferation of human breast cancer cells, suggesting that Ang-(1–7) or agents which increase endogenous Ang-(1–7) may be an effective chemotherapeutic or chemopreventive agent in breast cancer. Further, these results are in agreement with epidemiological studies showing that hypertensive patients treated with angiotensin-converting enzyme (ACE) inhibitors have a reduced risk of cancer, particularly gender-specific and lung cancers. ACE inhibitors cause a reduction in Ang II, a potent vasoconstrictor and mitogen, as well as a significant elevation in both tissue and circulating Ang-(1–7). Our results suggest that the reduced cancer risk observed in patients after administration of ACE inhibitors may be due, at least in part, to the elevated levels of Ang-(1–7). This study was support by funding from the Susan G. Komen Breast Cancer Foundation and the Women's Health Initiative at Wake Forest University School of Medicine.
[Proc Amer Assoc Cancer Res, Volume 45, 2004]