Angiotensin-(1-7) inhibition of human breast tumors with distinct hormone receptor expression results in a differential regulation of Akt.

CTRC-AACR San Antonio Breast Cancer Symposium: 2008 Abstracts Abstract #3127 Angiotensin-(1-7) [Ang-(1-7)] is an endogenous, seven amino acid peptide hormone with anti-proliferative and anti-angiogenic properties that mediates biological effects through activation of a specific AT(1-7) receptor, mas . We previously showed that the heptapeptide significantly reduced the growth of human lung cancer cells in vitro and human A549 lung tumor xenografts. The purpose of this study was to determine whether Ang-(1-7) can be used as an effective chemotherapeutic agent for breast cancer. Ang-(1-7) significantly inhibited the growth of ZR-75-1 cells, a human ER positive breast cancer cell line, BT-474 cells, a human HER2-amplified breast cancer cell line, and MDA-MB-231 cells, a triple negative breast cancer cell line. More importantly, Ang-(1-7) decreased ZR-75-1, BT-474, and MDA-MB-231 tumor growth in vivo . Cells were injected into the mammary fat pad of athymic female mice that were ovariectomized and implanted with estrogen pellets for continuous hormone deliver. Once the tumors reached a size of 100-200 mm3, osmotic minipumps were implanted to provide subcutaneous delivery of either saline or Ang-(1-7) in saline at a rate of 24 µg/kg/h, and tumor size was measured using a caliper. A marked reduction in tumor volume of Ang-(1-7) treated mice was observed when compared to saline treated animals (ZR-75-1 tumors from 322 ± 29.7 mm3 to 74 ± 13.6 mm3 , BT-474 tumors from 5209 ± 419 mm3 to 1656 ± 124 mm3, and MDA-MB-231 tumors from 492 ± 89.0 mm3 to 191 ± 8.8 mm3 , n = 5, p < 0.05). Tumor weight at the end of treatment was also decreased significantly by Ang-(1-7) administration (ZR-75-1 tumors from 0.26 ± 0.04 g to 0.13 ± 0.02 g, BT-474 tumors from 3.6 ± 0.2 g to 2.2 ± 0.1 g, MDA-MB-231 tumors from 1.00 ± 0.21 g to 0.49 ± 0.04 g, n = 5, p < 0.05). Although Ang-(1-7) inhibited the growth of all three breast tumors types, the heptapeptide was more effective in tumors that did not over-express HER2. Analysis of the orthotopic tumors by Western blot hybridization demonstrated that Ang-(1-7) significantly decreased phosphorylated Akt in ZR-75-1 and MDA-MB-231 tumors (from 0.90 ± 0.09 densitometric units to 0.03 ± 0.01 and 0.96 ± 0.05 to 0.47 ± 0.13, respectively, p < 0.05) while there was a significant increase (from 0.40 ± 0.12 to 1.55 ± 0.22, p < 0.05) in phosphorylated Akt in Ang-(1-7)-treated BT-474 tumors. Similarly, Ang-(1-7) treatment of the parent ZR-75-1 and MDA-MB-231 cells resulted in a time-dependent reduction (4-fold and 3-fold, respectively) in phosphorylated Akt, while incubation with the heptapeptide increased phosphorylated Akt 1.8-fold in BT-474 cells. These data indicate that Ang-(1-7) effectively reduces the growth of three different human breast tumors each expressing distinctive hormone receptor profiles and thus may serve as a first in class treatment for breast cancer. Further, Ang-(1-7) was more efficacious in preventing the proliferation of tumors that do not over-express the HER2 receptor, indicating that a combinatorial therapeutic modality may be more successful in treating HER2 amplified breast cancer. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3127.