We established a cancer stem (CS) cell line, U87CS, by means of spheroid culture of U87MG cells derived from glioblastoma (GBM) in neuronal stem cell medium. U87CS cells presented positive immunohistochemical staining for multidrug resistance (MDR)1 and CD133, a marker for a subset of leukemia and GBM CS cells. The gene expression of MDR1 and CD133 on U87CS cells increased by an average of 8.51 and 47.18 times, respectively, compared to the levels on U87MG cells by real-time quantitative RT-PCR. U87CS cells possessed stronger drug-resistance to conventional anti-cancer drugs, such as doxorubicin (Dox), etoposide (VP-16), carboplastin, and BCNU than U87MG cells. Double immunofluoresence staining showed co-expression of MDR1 and CD133 on U87CS cells transplanted into nude mice brains. In addition, we identified the crossreactivity of CD133 and MDR1 in a surgical specimen of GBM. Our results suggest that CS cells may be resistant to current chemotherapy and represent a novel target for GBM therapeutics.

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Based on the X-ray structure of the complex of Ac-Tyr-Val-Ala-Asp-H (L-709049) and interleukin-1 beta converting enzyme (ICE), we synthesized compounds which were derived from 2-NapCO-Val-Pro-Asp-CH2OPh (1) to obtain a potent inhibitor in the cell assay. Among these compounds, (3S)-N-methanesulfonyl-3-[[1-[N-(2-naphthoyl)-L-valyl]-L-prolyl]amino]- 4-oxobutanamide (27c) showed high potency not only in the enzyme assay but also cell assay with IC50 values of 38 nM and 0.23 microM, respectively. Compound 27c, with a c log P value of 1.76, had a more hydrophilic character compared with 1. Compound 27c also dose dependently inhibited LPS-primed ATP-induced IL-1 beta release in mice. The crystal structure of the complex of compound 27c and ICE revealed that compound 27c had further interactions with ICE in the naphthoyl group at the P4 position and in the methyl group of the methanesulfonamidecarbonyl group at the P1 position, compared with L-709049. To our knowledge, compound 27c is the first example that shows a strong inhibitory activity without the carboxyl group at the P1 position.

Cancer stem cells are an important target for effective therapy, since they show tumorigenicity, chemoresistance, and radioresistance. We isolated cancer stem cells from glioma cell lines and tissues and examined the expression of cancer testis antigen (CTA) genes as potential target molecules for cancer vaccine therapy. CTA genes were highly and frequently expressed in cancer stem cells compared with differentiated cells. In addition, histone acetylation levels in the promoter regions of CTA genes were high in cancer stem cells and low in differentiated cells, while DNA methylation analysis of the promoter regions revealed hypomethylation in cancer stem cells. This epigenetic difference between cells leads to heterogeneous expression of CTA genes in the tumor mass, which consists of cells at various levels of differentiation. Moreover, the expression level of HLA class I antigens was not affected by the differentiation status, suggesting that CTA genes may present as surface antigens in cancer stem cells. Taken together, these findings suggest that CTA genes may be attractive candidates for targeted vaccine therapy against cancer stem cells in glioma patients.