A Cancer Cell’s Toolbox for Conquering Other Organs: Discovering and Combating the Secretome of a Metastasis Capable Cancer Cell

Abstract

Background and Hypothesis: Previous studies have recognized that abnormal signaling by RAS oncogenes is predominantly observed in metastatic breast cancer. A hypothesis was developed: the cancer cells with abnormal RAS genes release protein factors into the blood stream which can reorganize the signaling of non-breast tissue in a way that mimics breast tissue therefore making this organ prone to metastasis. These RAS-dependent factors can be targeted therapeutically to decrease metastasis.

Experimental Design: Three cell lines were plated for the experiment: KTB-hTERT immortalized cell line as the control line, KTB-hTERT transformed derivatives TKTB RAS + SV40, which forms metastatic adenocarcinomas in NSG mice, and TKTB PIK3CA + SV40, which forms non-metastatic adenocarcinoma in NSG mice. Three Western Blots were conducted with protein readings for phospho-PAK4, PAK4, phospho-PIK3CD, and PIK3CD. These experiments were done to begin to test the hypothesis that phospho-proteome unique to RAS transformed cells regulate secretome with an effect on distant organs. These cell lines were examined for sensitivity to PIK3CD inhibitor Idelalisib and MEK1/MEK2 inhibitor Trametinib, which mediates signals downstream of RAS that regulate PIK3CD, using BrdU-incorporation ELISA proliferation assay.

Results: Through the western blot analysis, it was consistently shown that there is a significant increase in the production of phospho-PIK3CD and PIK3CD in RAS over PIK3CA which shows that PIK3CD could be a protein that leads to metastasis of RAS transformed cells. Idelalisib did not display activity in any cell lines. Trametinib showed decreased growth of all cell lines and RAS transformed cells were less sensitive to the drugs suggesting hyperactivation of this pathway in RAS-transformed cells

Conclusion and Impact: This study brings breast cancer research closer to pinpointing which proteins, in this case PIK3CD, can be targeted to decrease metastasis. The development of a drug that is specific to PIK3CD should be pursued to discover a treatment that decreases breast cancer metastasis.