Hypoxia-inducible factor 1 (HIF-1) is the central mediator of cellular responses to low oxygen and has recently become an important therapeutic target for solid tumor therapy. Inhibition of HIF-1 is expected to result in the attenuation of hypoxia-inducible genes, which are vital to many aspects of tumor biology, including adaptative responses for survival under anaerobic conditions. To identify small molecules inhibiting the HIF-1 pathway, we did a biological screen on a 10,000-membered natural product-like combinatorial library. The compounds of the library, which share a 2,2-dimethylbenzopyran structural motif, were tested for their ability to inhibit the hypoxic activation of an alkaline phosphatase reporter gene under the control of hypoxia-responsive elements in human glioma cells. This effort led to the discovery of 103D5R, a novel small-molecule inhibitor of HIF-1α. 103D5R markedly decreased HIF-1α protein levels induced by hypoxia or cobaltous ions in a dose- and time-dependent manner, whereas minimally affecting global cellular protein expression levels, including that of control proteins such as HIF-1β, IκBα, and β-actin. The inhibitory activity of 103D5R against HIF-1α was clearly shown under normoxia and hypoxia in cells derived from different cancer types, including glioma, prostate, and breast cancers. This inhibition prevented the activation of HIF-1 target genes under hypoxia such as vascular endothelial growth factor (VEGF) and glucose transporter-1 (Glut-1). Investigations into the molecular mechanism showed that 103D5R strongly reduced HIF-1α protein synthesis, whereas HIF-1α mRNA levels and HIF-1α degradation were not affected. 103D5R inhibited the phosphorylation of Akt, Erk1/2, and stress-activated protein kinase/c-jun-NH2-kinase, without changing the total levels of these proteins. Further studies on the mechanism of action of 103D5R will likely provide new insights into its validity/applicability for the pharmacologic targeting of HIF-1α for therapeutic purposes.

AP-1 transcription factor known to playa role in cell proliferation and neuronal activation, it is also involved in apoptosis of cells in response to stress, DNA damaging agents or lack of survival signals. AP-l DNA binding complex is not a single transcritpion factor but a dimer consisting of members of Fos and Jun families. In this review, we discuss evidence that composition of the AP-1 complex is different under various physiological and pathophysiological conditions. Furthermore, we describe biochemical properties of Fos and Jun proteins that may explain the ability of this transcription factor to activate different sets of genes in response to different stimuli. We propose a hypothesis that AP-1 might contribute to distinct biological processes because an activation of specific signaling pathways results in changes of AP-1 composition and/or phosphorylation status and modulates its transactivating potential towards different promoters.

Malignant gliomas are the most common and the most lethal primary brain tumors in adults. Among malignant gliomas, 60%–80% show loss of P14ARF tumor suppressor activity due to somatic alterations of the INK4A/ARF genetic locus. The tumor suppressor activity of P14ARF is in part a result of its ability to prevent the degradation of P53 by binding to and sequestering HDM2. However, the subsequent finding of P14ARF loss in conjunction with TP53 gene loss in some tumors suggests the protein may have other P53-independent tumor suppressor functions. Here, we report what we believe to be a novel tumor suppressor function for P14ARF as an inhibitor of tumor-induced angiogenesis. We found that P14ARF mediates antiangiogenic effects by upregulating expression of tissue inhibitor of metalloproteinase–3 (TIMP3) in a P53-independent fashion. Mechanistically, this regulation occurred at the gene transcription level and was controlled by HDM2-SP1 interplay, where P14ARF relieved a dominant negative interaction of HDM2 with SP1. P14ARF-induced expression of TIMP3 inhibited endothelial cell migration and vessel formation in response to angiogenic stimuli produced by cancer cells. The discovery of this angiogenesis regulatory pathway may provide new insights into P53-independent P14ARF tumor-suppressive mechanisms that have implications for the development of novel therapies directed at tumors and other diseases characterized by vascular pathology.