(440e) Engineered Nanoparticles That Mimic Bacterial Pathogens for the Treatment of Breast Cancer

Bacterial pathogens have evolved mechanisms by which they can control the fate of host cells during infection. Some Gram-negative bacteria use needle-like structures, known as the type III secretion system (T3SS), through which they can inject effector proteins directly into the cytoplasm of host cells. These effector proteins have high potential as therapeutic agents because they are capable of efficiently subverting a variety of eukaryotic signaling pathways by regulating protein factors involved in signal transduction. The NF-κB and MAPK pathways are common targets of these proteins and are fundamental in the development and progression of inflammatory diseases and cancer. However, bacterial delivery of effector proteins for therapeutic purposes is not a viable option.

In order to mimic the mechanism used by bacterial pathogens we have selected one of these effector proteins, acetyltransferase-H (ATH), which simultaneously down-regulates the NF-κB and MAPK pathways. We have engineered ATH as a fusion protein with glutathione S-transferase (GST) that assembles into nanoparticles with 100nm average hydrodynamic diameters. In vitro studies with two breast cancer cell-lines show that within 72 hours the ATH-GST fusion protein induces 91% cell death of MCF-7 cells, which are hormone receptor positive and don’t overexpress MAPK or NF-κB. Strikingly, we have observed statistically higher cytotoxicity levels (98% cell death) in SK-BR-3 cells over the same period of time. Because SK-BR-3 cells have overactive MAPK and NF-κB pathways they are more prone to develop chemotherapy-resistance and become metastatic.

We have demonstrated that ATH retains its normal activity as a fusion protein by confirming its ability to down-regulate the MAPK pathway. Consequently, this fusion protein nanosystem is a promising novel delivery alternative for the replacement of the T3SS of bacterial pathogens for efficient delivery of effector proteins for therapeutic purposes.