A potential estrogen mimetic effect of a bis(ethyl)polyamine analogue on estrogen receptor positive MCF-7 breast cancer cells

BE-3-3-3-3 (1,15-(ethylamino)4,8,12-triazapentadecane) is a bis(ethyl)polyamine analogue under investigation as a therapeutic agent for breast cancer. Since estradiol (E(2)) is a critical regulatory molecule in the growth of 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 E(2). In the presence of E(2), a concentration-dependent decrease in DNA synthesis was observed using [(3)H]-thymidine incorporation assay. In the absence of E(2), low concentrations (2.5-10 μM) of BE-3-3-3-3 increased [(3)H]-thymidine incorporation at 24 and 48 h. BE-3-3-3-3 induced the expression of early response genes, c-myc and c-fos, in the absence of E(2), but not in its presence, as determined by real-time quantitative polymerase chain reaction (qPCR). BE-3-3-3-3 had no significant effect on these genes in an ERα-negative cell line, MDA-MB-231. Chromatin immunoprecipitation assay demonstrated enhanced promoter occupation by either E(2) or BE-3-3-3-3 of an estrogen-responsive gene pS2/Tff1 by ERα and its co-activator, steroid receptor co-activator 3 (SRC-3). Confocal microscopy of BE-3-3-3-3-treated cells revealed membrane localization of ERα, similar to that induced by E(2). The failure of BE-3-3-3-3 to inhibit cell proliferation was associated with autophagic vacuole formation, and the induction of Beclin 1 and MAP LC3 II. These results indicate a differential effect of BE-3-3-3-3 on MCF-7 cells in the absence and presence of E(2), and suggest that pre-clinical and clinical development of polyamine analogues might require special precautions and selection of sensitive subpopulation of patients.

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

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.

Regulation of estrogenic effects by beclin 1 in breast cancer cells

Beclin 1 is an essential mediator of autophagy and a regulator of cell growth and cell death. We examined the effect of Beclin 1 overexpression on the action of estradiol (E(2)) and two antiestrogens, raloxifene and 4-hydroxytamoxifen, in estrogen receptor alpha (ERalpha)-positive MCF-7 breast cancer cells. [(3)H]-thymidine incorporation studies showed that Beclin 1-overexpressing cells (MCF-7 x beclin) had a lower proliferative response to E(2) compared with cells transfected with vector control (MCF-7 x control). There was only a 35% increase in [(3)H]-thymidine incorporation, after 24 hours of E(2) treatment of MCF-7 x beclin cells compared with untreated cells, whereas this increase was 2-fold for MCF-7 x control cells. E(2)-induced changes in the expression of early-response genes were examined by real-time quantitiative PCR. There were significant differences in the pattern of expression of E(2)-induced genes c-myc, c-fos, Erg-1, and Nur77 between MCF-7 x beclin and MCF-7 x control cells two hours after treatment. Although E(2)-induced growth of MCF-7 x control cells was completely inhibited by 500 nmol/L raloxifene or 500 nmol/L 4-hydroxytamoxifen, these concentrations of antiestrogens had no significant effect on the growth of MCF-7 x beclin cells. Confocal microscopic and coimmunoprecipitation studies showed evidence for colocalization and association of Beclin 1 and ERalpha. In addition, E(2) caused a decrease in Akt phosphorylation in MCF-7 x beclin cells, compared with a 3-fold increase in MCF-7 cells, five minutes after treatment. These results indicate that Beclin 1 can down-regulate estrogenic signaling and growth response, and contribute to the development of antiestrogen resistance. This observation might be useful to define and overcome antiestrogen resistance of breast cancer.

Mechanistic differences in DNA nanoparticle formation in the presence of oligolysines and poly-L-lysine

We studied the effectiveness of trilysine (Lys3), tetralysine (Lys4), pentalysine (Lys5), and poly-l-lysine (PLL) (MW 50000) on lambda-DNA nanoparticle formation and characterized the size, shape, and stability of nanoparticles. Light scattering experiments showed EC50 (lysine concentration at 50% DNA compaction) values of approximately 0.0036, 2, and 20 micromol/L, respectively, for PLL, Lys5, and Lys4 at 10 mM [Na+]. Plots of log EC50 versus log [Na+] showed positive slopes of 1.09 and 1.7, respectively, for Lys4 and Lys5 and a negative slope of -0.1 for PLL. Hydrodynamic radii of oligolysine condensed particles increased (48-173 nm) with increasing [Na+], whereas no significant change occurred to nanoparticles formed with PLL. There was an increase in the size of nanoparticles formed with Lys5 at >40 degrees C, whereas no such change occurred with PLL. The DNA melting temperature increased with oligolysine concentration. These results indicate distinct differences in the mechanism(s) by which oligolysines and PLL provoke DNA condensation to nanoparticles.