Differential alteration of IL-8 in liver cancer stem cell enrichment in response to PI3K/Akt/mTOR inhibitors and sorafenib

Abstract

AbstractLiver cancer stem cells (LCSCs) are derived from damaged and transformed Hepatic progenitor cells (HPCs) during precancerous cirrhosis stage. Ras/Raf/MAPK and PI3K/AKT/mTOR signaling pathways are significantly deregulated in liver cancer. The activation of PI3K/AKT/mTOR pathway in LCSC population is one of the reasons for acquired resistance to Sorafenib in advanced Hepatocellular carcinoma (HCC) patients. Therefore, identifying novel inhibitors targeting this pathway acting on LCSCs is highly essential. We therefore elucidated the bioactivities of small molecule kinase inhibitors on LCSCs acting through PI3K/Akt/mTOR pathway in comparison with DAPT (CSC inhibitor), DNA intercalators and Sorafenib. For this purpose, CD133+/EpCAM+ cells originated from HCC cells were analyzed by flow cytometry and effective inhibitors on LCSCs were further tested for their potential combinatorial effects. Treatment of cells with Sorafenib, and DNA intercalators resulted in enrichment of CD133+/EpCAM+ cells. Yet, mTOR inhibitor Rapamycin, and Notch pathway inhibitor DAPT significantly reduced CD133/EpCAM positivity. Combination studies revealed that sequential treatment strategy, which involves treatment of cells with Rapamycin prior to Sorafenib treatment, decreased the ratio of LCSCs as opposed to Sorafenib treatment alone or Sorafenib treatment prior to Rapamycin. The effect of the inhibitors were also demonstrated with LCSC sphere formation. Additionaly, a large panel of genes involved in cancer pathways were analyzed using Nanostring®nCounter®Technology to identify the differentially expressed genes in Rapamycin, Sorafenib or DAPT treated cells. Pathways involved in stemness (Wnt and Notch pathways) were differentially regulated between Rapamycin or DAPT treated cells and Sorafenib treated cells. Interleukin 8 (IL-8), FLNC, FLNA expressions were down-regulated upon treatment with DAPT or Rapamycin, yet up-regulated upon Sorafenib treatment. Following IL-8 inhibition CD133/EpCAM positivity of cells decreased significantly, indicating that IL-8 signaling is crucial for the conservation of stemness features of cancer cells.ConclusionPI3K/Akt/mTOR pathway inhibitors alter hepatic CSC composition and gene expression in favor or to the detriment of cancer stem cell survival. Blockade of IL-8 signaling provides a promising therapeutic approach for prevention of LCSC enrichment.