CANCER STEM CELLS AND THE HEDGEHOG SIGNALING PATHWAY IN BREAST CANCER Sk-Br-3 CELLS

Abstract

Many cancers treated with chemotherapy or anti-cancer drugs respond to treatment for a short period only to relapse once again. This relapse could be explained by small numbers of cancer stem cells (approximately 1%) in a tumor population (99%) as determined by fluorescence flow cytometry and confocal microscopy. These stem cells remain resistant to anti-cancer treatments themselves but proliferate to give rise to differentiated tumor cells. A common cell signaling pathway called the Hedgehog (HH) signaling pathway is important for stem cell fate and is deregulated in many cancerous tumor cells. Inhibition of this pathway could help advance cancer therapy in ascertaining the mechanism these cells use to remain resistant to drugs and radiation. Treatment of Sk- Br-3 breast adenocarcinoma cells with a steroidal compound, cyclopamine, specifically antagonizes the HH signaling pathway through direct interaction with smoothened (SMO), a distant relative of G-protein-coupled receptors. The use of small peptide fragments that disrupt the regular functioning of membrane proteins such as SMO is an alternative approach to inhibit the HH pathway. In addition, vitamin D3 (VD3) is structurally similar to cyclopamine and shows a dose dependent decrease in proliferation in Sk-Br-3 cells subsequent to treatment. It was demonstrated that the cells undergo apoptosis when treated with cyclopamine, VD3, and SMO peptides by the TIJNEL Assay. Thus cyclopamine, VD3, and SMO peptides are valuable tools for studying the involvement of HH signaling in the development of tumors and for the inhibition of cancer stem cell proliferation. This model could lead to further research and improved tools to aid in therapies relating to various types of cancers.