Molecular aspects of antiestrogen resistance and autophagy in breast cancer cells

Abstract

The major objective of this thesis was to examine the molecular aspects of estrogenic growth and autophagy in estrogen receptor α (ERα)-positive breast cancer cells. We first examined the role of autophagy mediator, Beclin 1, in estrogenic signaling and antiestrogen resistance in Beclin 1-overexpressing MCF-7 cells. We found that a potential interaction between ERα and Beclin 1 rendered Beclin 1-transfected cells less sensitive to estradiol (E2)-induced growth stimulation, and to antiestrogen-mediated growth inhibition. Thus, a novel function for Beclin 1 might involve down-regulation of the action of ERα, contributing to resistance of breast cancer cells to antiestrogens. In an attempt to develop novel therapeutic agents for breast cancer, we explored the effect of the polyamine analogue, 1,15-bis(ethylamino)-4,8,12-triazapentadecane (BE-3-3-3-3), on MCF-7 cell growth in the presence and absence of E2. BE-3-3-3-3 caused growth inhibition in the presence of E2. However, it mimicked estradiol and stimulated cell growth in the absence of E2, and induced growth response genes, such as c-fos, c-jun, and c-myc. This also induced autophagy, and increased levels of autophagy-related proteins, Beclin 1 and MAP LC3-II. In another approach to introduce gene therapy for breast cancer treatment, we explored the physico-chemical aspects of DNA nanoparticle formation. In an effort to optimize gene delivery systems, we investigated DNA condensation to nanoparticles in the presence of α,α'-methylated spermine analogues, and characterized the size, shape and stability of the resultant nanoparticles. Although some analogues proved more efficacious DNA condensing agents than spermine, hydrodynamic radii of nanoparticles produced by analogues were comparable to those produced by spermine. We also compared the DNA condensing abilities of poly-L-lysine (PLL) and oligolysines, and characterized the physico-chemical properties of their condensates. PLL was a more effective condensing agent than oligolysines, and produced more stable nanoparticles. We conclude that PLL and oligolysines bind and condense DNA through different mechanisms. In summary, our research provides new insights into the mechanism of antiestrogen resistance and autophagy in breast cancer. We also provide mechanistic insight into DNA nanoparticle formation in the presence of polyamine analogues and lysines.%%%%