Cytokine chemokine network in tumor microenvironment: Impact on CSC properties and therapeutic applications

A subpopulation of cells in many cancers has stem cell traits, mediates metastasis, and contributes to treatment resistance. These cells are considered as cancer stem cells (CSCs). CSC properties of tumor cells are immensely regulated by close interactions with tumor microenvironment components such as mesenchymal stem cells, tumor related fibroblasts, adipocytes, endothelial cells, and immune cells via the intricate network of cytokines, chemokines, and growth factors. Inflammatory cytokines including interleukin (IL)-1, IL-6, and IL-8 play a major role in these interactions via the activation of signal transduction pathways like Stat3/NF-kappa B etc. in stromal and tumor cells. The activation of these pathways increases the release of more cytokines, resulting in positive feedback loops which help in CSC self-renewal. The pathways controlled by these cytokine loops are similar to those that are active during chronic inflammation and wound healing, suggesting that they might have critical role in establishing relationship between inflammation and cancer. Anti-inflammatory drugs have been identified to inhibit these cytokines and their receptor mediated pathways. These agents have the potential to target CSCs by inhibiting signals from the tumor microenvironment and considered to be a potential candidate for future therapeutics. The significance of cytokines released from the tumor microenvironment in different phases of cancer, as well as their potential application in cancer therapeutics is discussed in this article.