Hypoxia-Responsive, Polymeric Nanocarriers for Targeted Drug Delivery to Estrogen Receptor-Positive Breast Cancer Cell Spheroids

Uncontrolled cell growth, division, and lack of enough blood supply causes low oxygen content or hypoxia in cancerous tumor microenvironments. 17β-Estradiol (E 2 ), an estrogen receptor (ER) ligand, can be incorporated on the surface of nanocarriers for targeted drug delivery to breast cancer cells overexpressing ER. In the present study, we synthesized estradiol-conjugated hypoxia-responsive polymeric nanoparticles (polymersomes) encapsulating the anticancer drug doxorubicin (E 2 -Dox-HRPs) for targeted delivery into the hypoxic niches of estrogen-receptor-positive breast cancer microtumors. Estradiol-conjugated polymersomes released over 90% of their encapsulated Dox in a sustained manner within hypoxia (2% oxygen) after 12 h. However, they released about 30% of Dox in normal oxygen partial pressure (21% oxygen, normoxia) during this time. Fluorescence microscopic studies demonstrated higher cytosolic and nuclear internalization of E 2 -Dox-HRPs (targeted polymersomes) compared to those of Dox-HRPs (nontargeted polymersomes). Monolayer cell viability studies on ER-positive MCF7 cells showed higher cytotoxicity of targeted polymersomes in hypoxia compared to in normoxia. Cytotoxicity studies with hypoxic three-dimensional spheroid cultures of MCF7 cells treated with targeted polymersomes indicated significant differences compared to those of normoxic spheroids. The novel estradiol-conjugated hypoxia-responsive polymersomes described here have the potential for targeted drug delivery in estrogen-receptor-positive breast cancer therapy.