Glioblastoma multiforme (GBM) is one of the most aggressive human tumors with a poor prognosis. Current standard treatment includes chemotherapy with the DNA-alkylating agent temozolomide concomitant with surgical resection and/or irradiation. However, a number of cases are resistant to temozolomide-induced DNA damage due to elevated expression of the DNA repair enzyme O 6 -methylguanine-DNA methyltransferase (MGMT). Here, we show that upregulation of both MGMT and STAT3 was accompanied with acquisition of temozolomide resistance in the GBM cell line U87. Inactivation of STAT3 by inhibitor or short hairpin RNA (shRNA) downregulated MGMT expression in GBM cell lines. MGMT upregulation was not observed by the treatment of interleukin (IL)-6 which is a strong activator of STAT3. Contrarily, forced expressed MGMT could be downregulated by STAT3 inhibitor which was partially rescued by the proteasome inhibitor, MG132, suggesting the STAT3-mediated posttranscriptional regulation of the protein levels of MGMT. Immunohistochemical analysis of 44 malignant glioma specimens showed significant positive correlation between expression levels of MGMT and phosphorylated STAT3 (p-STAT3; P < 0.001, r ¼ 0.58). Importantly, the levels of both MGMT and p-STAT3 were increased in the recurrence compared with the primary lesion in paired identical tumors of 12 cases. Finally, we showed that STAT3 inhibitor or STAT3 knockdown potentiated temozolomide efficacy in temozolomide-resistant GBM cell lines. Therefore, STAT3 inhibitor might be one of the candidate reagents for combination therapy with temozolomide for patients with temozolomide-resistant GBM.

Purpose: Hypoxia inducible factor-1 (HIF-1), the central mediator of the cellular response to low oxygen, functions as a transcription factor for a broad range of genes that provide adaptive responses to oxygen deprivation. HIF-1 is overexpressed in cancer and has become an important therapeutic target in solid tumors. In this study, a novel HIF-1α inhibitor was identified and its molecular mechanism was investigated. Experimental Design: Using a HIF-responsive reporter cell-based assay, a 10,000-member natural product-like chemical compound library was screened to identify novel HIF-1 inhibitors. This led us to discover KC7F2, a lead compound with a central structure of cystamine. The effects of KC7F2 on HIF-1 transcription, translation, and protein degradation processes were analyzed. Results: KC7F2 markedly inhibited HIF-mediated transcription in cells derived from different tumor types, including glioma, breast, and prostate cancers, and exhibited enhanced cytotoxicity under hypoxia. KC7F2 prevented the activation of HIF-target genes such as carbonic anhydrase IX, matrix metalloproteinase 2 (MMP2), endothelin 1, and enolase 1. An investigation into the mechanism of action of KC7F2 showed that it worked through the down-regulation of HIF-1α protein synthesis, an effect accompanied by the suppression of the phosphorylation of eukaryotic translation initiation factor 4E binding protein 1 and p70 S6 kinase, key regulators of HIF-1α protein synthesis. Conclusion: These results show that KC7F2 is a potent HIF-1 pathway inhibitor and its potential as a cancer therapy agent warrants further study. (Clin Cancer Res 2009;15 (19):6128-36) Hypoxia, a reduction in partial oxygen pressure, is a major hindrance to effective solid tumor therapy. The microenvironment of rapidly growing solid tumors shows increased energy demand and diminished vascular supply, resulting in focal areas of prominent hypoxia (1). The hypoxic fraction of tumors is resistant to traditional therapies. Radiotherapy is compromised because of the reduced reaction of oxygen with radiationinduced DNA free radicals (2). Chemotherapy is hampered by the diffusion-limited drug delivery to hypoxic regions from distant vasculature. Moreover, many anticancer drugs are most effective against rapidly proliferating cells, and hypoxia (and deficiencies in other nutrients such as glucose) can cause a reduction in cell proliferation rate (3). This is compounded by the induction of the multidrug resistance (MDR1) gene product P-glycoprotein in hypoxic tissue (4), further reducing drug efficacy. Hypoxic tumor regions also impede immune responses, and may promote the growth of cancer stem cells (5,6).Hypoxia drives malignant tumor progression. Tumor hypoxia increases malignant progression and metastasis by promoting angiogenesis through the induction of proangiogenic proteins such as vascular endothelial growth factor (VEGF) and metabolic adaptation through elevation of glycolytic enzymes (7,8). Hypoxia also generates selective pressure for cells to acquir...

Sonodynamic therapy is expected to be a novel therapeutic strategy for malignant gliomas. The titanium dioxide (TiO 2 ) nanoparticle, a photosensitizer, can be activated by ultrasound. In this study, by using water-dispersed TiO 2 nanoparticles, an in vitro comparison was made between the photodynamic and sonodynamic damages on U251human glioblastoma cell lines. Water-dispersed TiO 2 nanoparticles were constructed by the adsorption of chemically modified polyethylene glycole (PEG) on the TiO 2 surface (TiO 2 /PEG). To evaluate cytotoxicity, U251 monolayer cells were incubated in culture medium including 100 μg/ml of TiO 2 /PEG for three hours and subsequently irradiated by