Investigating Overexpressed Cytosolic Phospholipase A2α in a Triple Negative Breast Cancer Model

Abstract

Breast cancer is the type of cancer that affects the most women worldwide and approximately 18% of these incidents belong to the category of triple negative breast cancer (TNBC). TNBC lacks targeted treatments and the diagnosis is associated with a low survival rate and palliative therapy within 5 years. Hence, there is an urgent need to develop better treatment options for this breast cancer subtype.

In this thesis, the overexpressed enzyme, cytosolic phospholipase A2α (cPLA2α), has been investigated as a potential novel therapeutic target for this breast cancer subtype. A patient derived TNBC cell line, MDA-MB-436, has been studied using cPLA2α inhibitors and immunofluorescence imaging of the enzyme. Four inhibitors of cPLA2α (AVX002, Compound 1, Compound 2, Compound 3) developed by Avexxin and one phosphoinositide 3-kinase inhibitor (Buparlisib/BKM120) have been evaluated. The result of this exploration was IC50 values for all the agents except Compound 2. In addition, the MDA-MB-436 cells was more sensitive to cPLA2α inhibition compared to another TNBC cell line with lower expression of the enzyme, previously studied at this laboratory. This finding suggests that expression levels can correlate with sensitivity for cPLA2α inhibition. Furthermore, synergy between Compound 1 and BKM120 was found and a cell death assay suggested that Compound 1 promote apoptosis. The targeted mechanism of action of the four cPLA2α inhibitors was confirmed due to their ability to reduced secreted prostaglandin E2 levels markedly. Finally, an analytic pipeline for the image analyses was generated to detect accumulations of cPLA2 enzymes. This revealed that serum starvation and TNF-α caused enzyme aggregation and possibly activation, in clusters adjacent to the nucleus.

cPLA2α demonstrated itself as a good therapeutic target in this TNBC model system and several inhibitors from Avexxin could serve as both chemopreventive single agents or in combination with established treatments against this target in the future. The inhibitors also show promise as potent therapeutics in personalised medicine for TNBC and other cancer types where cPLA2α is overexpressed.