Effect of combinatorial drug therapy on the progression of breast cancer

Abstract

Resistance to therapies targeting estrogen receptor alpha in breast cancer cells is a major problem in the recurrence and metastasis of breast cancer. Multiple factors contribute to the development of resistance mechanisms of which various growth factor receptors and the pathways they regulate downstream are a key contributor. The current study concentrates on mainly two key aspects. One is to determine Single Nucleotide Polymorphisms (SNPs) in Linkage Disequilibrium (LD) and their impact on different proteins. Second to explore the potential of combinatorial therapy comprising of DpC - a semi thiocarbazone and Tamoxifen - an estrogen receptor modulator on the protein(s) affected by SNPs found to be in LD. To achieve this genome wide association studies were analyzed using SNAP, Regulome DB, Ensembl and PC Viz software. Furthermore, MTT assays, protein expression analysis and confocal microscopy was carried out in both 2D and 3D cell cultures of Tamoxifen sensitive and resistant, estrogen receptor positive cell lines.Results obtained demonstrated that AKT, a vital protein whose aberrant expression has been frequently associated with breast cancer resistance and metastasis was one of the proteins impacted by SNPs found to be in LD. Targeting the PI3K/AKT/mTOR pathway using the aforementioned drug combination we found that DpC alone or in combination with Tamoxifen could potently inhibit AKT activation which may also be responsible for reduced levels of Cyclin D1 and c-Myc. Interestingly, a the marked increase in p27 protein was observed in Tamoxifen resistant cell lines indicative of decreased cell cycle progression, a fact which was confirmed by the reduced expression of the cell proliferative marker Ki67 in 3D models.