Glycolipid GD3 and GD3 synthase are key drivers for glioblastoma stem cells and tumorigenicity.

The cancer stem cells (CSCs) of glioblastoma multiforme (GBM), a grade IV astrocytoma, have been enriched by the expressed marker CD133. However, recent studies have shown that CD133(-) cells also possess tumor-initiating potential. By analysis of gangliosides on various cells, we show that ganglioside D3 (GD3) is overexpressed on eight neurospheres and tumor cells; in combination with CD133, the sorted cells exhibit a higher expression of stemness genes and self-renewal potential; and as few as six cells will form neurospheres and 20-30 cells will grow tumor in mice. Furthermore, GD3 synthase (GD3S) is increased in neurospheres and human GBM tissues, but not in normal brain tissues, and suppression of GD3S results in decreased GBM stem cell (GSC)-associated properties. In addition, a GD3 antibody is shown to induce complement-dependent cytotoxicity against cells expressing GD3 and inhibition of GBM tumor growth in vivo. Our results demonstrate that GD3 and GD3S are highly expressed in GSCs, play a key role in glioblastoma tumorigenicity, and are potential therapeutic targets against GBM.

Stage-specific embryonic antigen-4 as a potential therapeutic target in glioblastoma multiforme and other cancers.

Glioblastoma multiforme (GBM), the grade IV astrocytoma, is the most common and aggressive brain tumor in adults. Despite advances in medical management, the survival rate of GBM patients remains poor, suggesting that identification of GBM-specific targets for therapeutic development is urgently needed. Analysis of several glycan antigens on GBM cell lines revealed that eight of 11 GBM cell lines are positive for stage-specific embryonic antigen-4 (SSEA-4), and immunohistochemical staining confirmed that 38/55 (69%) of human GBM specimens, but not normal brain tissue, were SSEA-4(+) and correlated with high-grade astrocytoma. In addition, an SSEA-4-specific mAb was found to induce complement-dependent cytotoxicity against SSEA-4(hi) GBM cell lines in vitro and suppressed GBM tumor growth in mice. Because SSEA-4 is expressed on GBM and many other types of cancers, but not on normal cells, it could be a target for development of therapeutic antibodies and vaccines.

Redox regulation of the protein tyrosine phosphatase PTP1B in cancer cells.

The oxidation and inactivation of protein tyrosine phosphatases is one mechanism by which reactive oxygen species influence tyrosine phosphorylation-dependent signaling events and exert their biological functions. In the present study, we determined the redox status of endogenous protein tyrosine phosphatases in HepG2 and A431 human cancer cells, in which reactive oxygen species are produced constitutively. We used mass spectrometry to assess the state of oxidation of the catalytic cysteine residue of endogenous PTP1B and show that this residue underwent both reversible and irreversible oxidation to high stoichiometry in response to intrinsic reactive oxygen species production. In addition, our data show that the oxidation of PTP1B is specific to the active site Cys, with the other Cys residues in the protein remaining in a reduced state. Treatment of these cells with diphenyleniodonium, an inhibitor of NADPH oxidases, decreased reactive oxygen species levels. This resulted in inhibition of protein tyrosine phosphatase oxidation, concomitant with decreased tyrosine phosphorylation of cellular proteins and inhibition of anchorage-independent cell growth. Therefore, our data also suggest that the high level of intrinsic reactive oxygen species may contribute to the transformed phenotype of HepG2 and A431 cells via constitutive inactivation of cellular protein tyrosine phosphatases.