Abstract 1237: Anti-cancer activity of a stable, orally active angiotensin-(1-7) analog
Authors: Patricia E. Gallagher, Kenneth A. Gruber, Michael Callahan, E. Ann Tallant
Journal: Cancer Research (2016)

Abstract Angiotensin-(1-7) [Ang-(1-7)] is an endogenous, peptide hormone that reduces tumor growth through effects on proliferation, inflammation, angiogenesis, fibrosis and metastasis. Ang-(1-7) mediates biological responses by activating mas, a unique G protein-coupled receptor, thereby providing specific targeted actions when used as a therapeutic agent. Unfortunately, Ang-(1-7) has unfavorable pharmacokinetic properties, resulting in a plasma half-life of about 30 min. In this study, TCAng05, a modified cyclic analog of Ang-(1-7), was compared to the parent compound Ang-(1-7) for efficacy, stability, and oral bioavailability. Ang-(1-7) or TCAng05 was incubated with human A549 lung or MDA-MB-231 breast cancer cells for 6 to 10 days, to assess the effect on tumor cell growth. A single dose of TCAng05 significantly reduced the growth of both MDA-MB-231 and A549 cells, while daily doses of Ang-(1-7) were required due to rapid degradation. Growth inhibition by either compound was blocked by the Ang-(1-7) receptor antagonist D-Ala7-Ang-(1-7) [Dala], showing a receptor-mediated response. Ang-(1-7) was rapidly degraded following incubation in rat plasma with a half-life of about 30 min, while TCAng05 was stable under the same conditions for approximately 50 h. The oral efficacy of TCAng05 to inhibit tumor growth in vivo was assessed by injecting 4T1 cells into the mammary fat pad of BALB/C mice. Once the tumors reached 100 mm3, the mice received daily gavage of TCAng05 at 12 μg/kg/day (low), 60 μg/kg/day (medium) or 300 μg/kg/day (high). Tumors in mice with no treatment continued to grow until sacrifice at day 19, reaching a size of 671.2 ± 127.2 mm3. Oral treatment with TCAng05 at the medium or high dose reduced tumor volume, by 56.8% and 43.6%, respectively, to final tumor volumes of 289.7 ± 64.2 mm3 and 378.3 ± 151.2 mm3. Tumor weight was also reduced by treatment with the medium or high dose of oral TCAng05. TCAng05 had no effect on mouse weight, heart or kidney weight, indicating that oral administration of the Ang-(1-7) analog was well-tolerated. TCAng05 caused a dose-dependent decrease in Ki67 immunoreactivity in tumor tissue sections from mice treated with the analog, suggesting reduced tumor cell proliferation. TCAng05 administration to mice with breast tumors also caused a significant decrease in tumor blood vessel density, as measured by CD34 labeling, suggesting that the analog inhibits angiogenesis to decrease tumor size. Collagen staining with Picrosirius red was markedly decreased in human breast tumor xenografts by oral administration of TCAng05, demonstrating that the analog reduces tumor associated fibrosis. These results indicate that oral administration of TCAng05 to mice with breast tumors reduced tumor size, by decreasing tumor cell proliferation, angiogenesis and fibrosis, as previously observed with the native Ang-(1-7), and suggest that the modified analog may serve as an effective, orally active, targeted chemotherapeutic. Citation Format: Patricia E. Gallagher, Kenneth A. Gruber, Michael Callahan, E. Ann Tallant. Anti-cancer activity of a stable, orally active angiotensin-(1-7) analog. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1237.