Previously, we have succeeded in converting induced pluripotent stem cells (iPSCs) into cancer stem cells (CSCs) by treating the iPSCs with conditioned medium of Lewis lung carcinoma (LLC) cells. The converted CSCs, named miPS-LLCcm cells, exhibited the self-renewal, differentiation potential, and potential to form malignant tumors with metastasis. In this study, we further characterized miPS-LLCcm cells both in vivo and in vitro. The tumors formed by subcutaneous injection showed the structures with pathophysiological features consisting of undifferentiated and malignant phenotypes generally found in adenocarcinoma. Metastasis in the lung was also observed as nodule structures. Excising from the tumors, primary cultured cells from the tumor and the nodule showed self-renewal, differentiation potential as well as tumor forming ability, which are the essential characters of CSCs. We then characterized the epigenetic regulation occurring in the CSCs. By comparing the DNA methylation level of CG rich regions, the differentially methylated regions (DMRs) were evaluated in all stages of CSCs when compared with the parental iPSCs. In DMRs, hypomethylation was found superior to hypermethylation in the miPS-LLCcm cells and its derivatives. The hypo- and hypermethylated genes were used to nominate KEGG pathways related with CSC. As a result, several categories were defined in the KEGG pathways from which most related with cancers, significant and high expression of components was PI3K-AKT signaling pathway. Simultaneously, the AKT activation was also confirmed in the CSCs. The PI3K-Akt signaling pathway should be an important pathway for the CSCs established by the treatment with conditioned medium of LLC cells.

Paclitaxel (PTX) is one of the front-line drugs approved for the treatment of ovarian cancer. However, the application of PTX is limited due to the significant hydrophobicity and poor pharmacokinetics. We previously reported target-directed liposomes carrying tumor-selective conjugated antibody and encapsulated glycosylated PTX (gPTX-L) which successfully overcome the PTX limitation. The tubulin stabilizing activity of gPTX was equivalent to that of PTX while the cytotoxic activity of gPTX was reduced. In human ovarian cancer cell lines, SK-OV-3 and OVK18, the concentration at which cell growth was inhibited by 50% (IC50) for gPTX range from 15–20 nM, which was sensitive enough to address gPTX-L with tumor-selective antibody coupling for ovarian cancer therapy. The cell membrane receptor CD44 is associated with cancer progression and has been recognized as a cancer stem cell marker including ovarian cancer, becoming a suitable candidate to be targeted by gPTX-L therapy. In this study, gPTX-loading liposomes conjugated with anti-CD44 antibody (gPTX-IL) were assessed for the efficacy of targeting CD44-positive ovarian cancer cells. We successfully encapsulated gPTX into liposomes with the loading efficiency (LE) more than 80% in both of gPTX-L and gPTX-IL with a diameter of approximately 100 nm with efficacy of enhanced cytotoxicity in vitro and of convenient treatment in vivo. As the result, gPTX-IL efficiently suppressed tumor growth in vivo. Therefore gPTX-IL could be a promising formulation for effective ovarian cancer therapies.

The surface reactivity of gold nanoparticles (AuNPs) is receiving attention as a radiosensitizer of cancer cells for radiation therapy and/or as a drug carrier to target cells. This study demonstrates the potential of DNA-AuNPs (prepared by mixing calf thymus DNA with HAuCl4 solution) as a radiosensitizer of human glioma cells that have cancer stem cell (CSC)-like properties, to reduce their survival. CSC-like U251MG-P1 cells and their parental glioblastoma U251MG cells are treated with a prepared DNA-AuNP colloid. The radiosensitivity of the resultant AuNP-associated cells are significantly enhanced. To reveal the mechanism by which survival is reduced, the generation of reactive oxygen species (ROS), apoptosis induction, or DNA damage in the cells is assayed using the fluorescent dye DCFDA, annexin V-FITC/PI, and foci formation of γ-H2AX, respectively. X-ray irradiation with administration of AuNPs overcomes the radioresistance of U251MG-P1 cells. It does not induce ROS generation or apoptosis in the cells but enhances the number of abnormal nuclei with abundant γ-H2AX foci, which is judged as cell death by mitotic catastrophe. The AuNP association with the cells effectively induces mitotic catastrophe in x-ray-irradiated CSC-like cells, implicating that DNA-AuNPs might be a promising tool to develop an efficient radiosensitizer against CSC.

We recently have established a successful xenograft model of human glioblastoma cells by enriching hyaluronic acid-dependent spheroid-forming populations termed U251MG-P1 cells from U251MG cells. Since U251MG-P1 cells have been confirmed to express CD44 along with principal stemness marker genes, OCT3/4, SOX2, KLF4 and Nanog, this CD44 expressing population appeared to majorly consist of undifferentiated cells. Evaluating the sensitivity to anti-cancer agents, we found U251MG-P1 cells were sensitive to doxorubicin with IC50 at 200 nM. Although doxorubicin has serious side-effects, establishment of an efficient therapy targeting undifferentiated glioblastoma cell population is necessary. We previously designed a chlorotoxin peptide fused to human IgG Fc region without hinge sequence (M-CTX-Fc), which exhibited a stronger growth inhibitory effect on the glioblastoma cell line A172 than an original chlorotoxin peptide. Combining these results together, we designed M-CTX-Fc conjugated liposomes encapsulating doxorubicin and used U251MG-P1 cells as the target model in this study. The liposome modified with M-CTX-Fc was designed with a diameter of approximately 100–150 nm and showed high encapsulation efficiency, adequate loading capacity of anticancer drug, enhanced antitumor effects demonstrating increasing uptake into the cells in vitro; M-CTX-Fc-L-Dox shows great promise in its ability to suppress tumor growth in vivo and it could serve as a template for targeted delivery of other therapeutics.

Cancer stem cells (CSCs) are a class of cancer cells characterized by self-renewal, differentiation and tumorigenic potential. We previously established a model of cScs by culturing mouse induced pluripotent stem cells (miPSCs) for four weeks in the presence of a conditioned medium (CM) of cancer cell lines, which functioned as the tumor microenvironment. Based on this methodology of developing CSCs from miPSCs, we assessed the risk of 110 non-mutagenic chemical compounds, most of which are known as inhibitors of cytoplasmic signaling pathways, as potential carcinogens. We treated miPSCs with each compound for one week in the presence of a CM of Lewis lung carcinoma (LLC) cells. However, one-week period was too short for the CM to convert miPSCs into CSCs. Consequently, PDO325901 (MEK inhibitor), CHIR99021 (GSK-3β inhibitor) and Dasatinib (Abl, Src and c-Kit inhibitor) were found to confer miPSCs with the CSC phenotype in one week. The tumor cells that survived exhibited stemness markers, spheroid formation and tumorigenesis in Balb/c nude mice. Hence, we concluded that the three signal inhibitors accelerated the conversion of mipScs into cScs. Similarly to our previous study, we found that the PI3K-Akt signaling pathway was upregulated in the CSCs. Herein, we focused on the expression of relative genes after the treatment with these three inhibitors. Our results demonstrated an increased expression of pik3ca, pik3cb, pik3r5 and pik3r1 genes indicating class IA PI3K as the responsible signaling pathway. Hence, AKT phosphorylation was found to be up-regulated in the obtained CSCs. Inhibition of Erk1/2, tyrosine kinase, and/or GSK-3β was implied to be involved in the enhancement of the PI3K-AKT signaling pathway in the undifferentiated cells, resulting in the sustained stemness, and subsequent conversion of miPSCs into CSCs in the tumor microenvironment. Alexander A. Maximow, a Russian cell biologist, was the first who proposed the concept of stem cells in 1909 1. In 1961, the two basic features defining stem cells, namely abilities of self-renewal and differentiation into mature cells, were uncovered by Till and McCulloch 2. CSCs were first identified in the granulocytes of acute myeloid leukemia in 1994 3. Since 1997 when Bonnet and Dick identified the CSCs by the ability of self-renewal from