Cancer stem cells (CSCs), a rare population in any type of cancers, including colon cancer, are tumorigenic. It has been thought that CSCs are responsible for cancer recurrence, metastasis, and drug resistance. Isolating CSCs in colon cancers is challenging, and thus the molecular mechanism regulating the self-renewing and differentiation of CSCs remains unknown. We cultured DLD-1 cells, one of types of cells derived from colon cancers, in serum-free medium to obtain spheroid cells. These cells possessed the characteristics of CSCs, with the expression of CD133, CD166, Lgr5, and ALDH1, higher capacities of chemo-resistance, migration, invasion, and tumorigenicity in vitro and in vivo than the adherent DLD-1 cells. Krüppel-like factor 4 (KLF4) is essential factor for maintaining self-renewal of adult and embryonic stem cells. It has been used to induce pluripotent stem cells (iPS) from somatic cells. Since KLF4 is expressed in colon cancer cells, we investigated its role in spheroid cells isolated from DLD-1 cells and found that KLF4 was overexpressed only in spheroid cells and reducing the expression of KLF4 by short-hairpin RNA significantly decreased the capacities of these cells to resist the chemicals, migrate, invade, and generate tumors in vitro and in vivo. The spheroid cells with reduced KLF4 expression also had decreased expression of CSCs markers and mesenchymal markers. Taken together, culturing DLD-1 cells in serum-free medium enriches CSCs and the expression of KLF4 is essential for the characteristics of CSCs in DLD-1; thus KLF4 can be a potential therapeutic target for treating colon cancer.

Gastric cancer is the fourth most common type of cancer and the second cause of cancer-related mortalities worldwide despite the use of multimodal therapy. Cadherins are transmembrane glycoproteins that are involved in tumorigenesis. CDH17 has been found to be over-expressed in gastric cancer and its overexpression was associated with lymph node metastasis and tumor-node-metastasis stage of the patients, yet the exact role and molecular mechanism of CDH17 in gastric cancer have not been determined. Using a lentiviral system as a delivery mediator of RNA interference, we found that inhibition of CDH17 can lead to reduce proliferation and increase apoptosis of gastric cancer cell line MKN28 in vitro and significantly diminish their tumorigenicity in vivo. Our results of the present study suggest that CDH17 may be a promising candidate for the therapeutic targeting of gastric cancer.