Abstract 4594: Estrogen mimetic effect of a polyamine analogue in MCF-7 breast cancer cells

Abstract

Abstract Table of Contents • Estrogen mimetic effect of a polyamine analogue in MCF-7 breast cancer cells Estrogen mimetic effect of a polyamine analogue in MCF-7 breast cancer cells Bis(ethyl) polyamine analogues have been synthesized and tested as chemotherapeutic agents for different subsets of cancer. 1,15-bis(ethylamino)4,8,12-triazapentadecane (BE-3-3-3-3) is a polyamine analogue with therapeutic potential for breast cancer. We examined the effect of BE-3-3-3-3 on estrogen receptor α (ERα) positive MCF-7 cells in the presence and absence of 4 nM estradiol (E2). In the presence of E2, a concentration-dependent decrease in DNA synthesis was observed using [3H]-thymidine incorporation assay. In the absence of E2, low concentrations (1.25 to 5 µM) of BE-3-3-3-3 increased [3H]-thymidine incorporation at 24 and 48 hours of treatment. However, growth inhibition was observed by 96 hours of treatment. In order to elucidate the mechanism of analogue action, we examined the expression of two E2 sensitive oncogenes, c-myc and c-fos, using real-time quantitative polymerase chain reaction (qPCR) method. Treatment with BE-3-3-3-3 for 2 hours induced the expression of c-myc (∼2.4-fold) and c-fos (∼4.5-fold) compared to untreated control. BE-3-3-3-3's estrogen-mimetic action was also evidenced by the increased occupancy of the pS2/Tff1 gene promoter by ERα and its co-activator, steroid receptor co-activator 3 (SRC-3), as assessed by chromatin immunoprecipitation (ChIP) assay. Confocal microscopic visualization of BE-3-3-3-3- treated cells revealed co-localization of ERα in a manner similar to that induced by E2. Western blotting analysis showed that delayed growth inhibition in the absence of E2 was associated with the induction of autophagy, as evidenced by elevated levels of autophagy-related proteins, Beclin 1 and MAP LC3 II. Electron microscopic investigation demonstrated the presence of autophagic vacuoles in analogue-treated cells. Additionally, BE-3-3-3-3 inhibited polyamine synthesis and induced catabolism, resulting in significantly decreased levels of putrescine, spermidine and spermine. Analogue treatment reduced the activity of a key enzyme in the polyamine biosynthetic pathway, ornithine decarboxylase (ODC), by ∼ 23-fold after 24 hours, and stimulated the catabolic activity of spermidine/spermine N1-acetyltransferase (SSAT) by 180-fold after 48 hours. These results provide evidence of BE-3-3-3-3's ability to modulate gene expression and stimulate proliferation of breast cancer cells under conditions of low E2 availability. Our findings may help to target this compound toward appropriate subsets of breast cancer patients. In addition, our results indicate a novel pathway for the action of bis(ethyl) polyamine analogues in the balance of cell growth and autophagy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4594.