Microregional antitumor activity of a small-molecule hypoxia-inducible factor 1 inhibitor.

Hypoxia-inducible factor 1 (HIF-1) activates the transcription of genes that play crucial roles in the adaptation of cancer cells to hypoxia. HIF-1α overexpression has been associated with poor prognosis in patients with various types of cancer. Here, we describe ER-400583-00 as a novel HIF-1 inhibitor. ER-400583-00 suppressed the production of HIF-1α protein in response to hypoxia, with a half-maximal inhibitory concentration value of 3.7 nM in human U251 glioma cells. The oral administration of 100 mg/kg ER-400583-00 to mice bearing U251 tumor xenografts resulted in a rapid suppression of HIF-1α that persisted for 24 h. Immunohistochemical analysis revealed that ER-400583-00 suppressed the proliferation of cancer cells most prominently in areas distal to the region of blood perfusion, where HIF-1α-expressing hypoxic cancer cells were located. These hypoxic cancer cells were resistant to radiation therapy. ER-400583-00 showed a synergistic interaction with radiation therapy in terms of antitumor activity. These data suggest that HIF-1 blockade by small compounds may have therapeutic value in cancer, especially in combination with radiation therapy.

Anti-angiogenesis effects of borrelidin are mediated through distinct pathways: threonyl-tRNA synthetase and caspases are independently involved in suppression of proliferation and induction of apoptosis in endothelial cells.

Borrelidin, an antibiotic with anti-angiogenic activity, not only suppresses new capillary tube formation, but also collapses formed capillary tubes in a rat aorta culture model. Since it selectively inhibits threonyl-tRNA synthetase, we examined the effect of threonine on its anti-angiogenic activity. We found that a high concentration of threonine (1 mM) attenuated the ability of borrelidin to inhibit both capillary tube formation in the rat aorta culture model and human umbilical vein endothelial cells (HUVEC) proliferation, yet did not affect the ability of borrelidin to collapse formed capillary tubes or to induce apoptosis in HUVEC. Borrelidin activated caspase-3 and -8, and inhibitors of both caspase-3 and -8 suppressed borrelidin-induced apoptosis in HUVEC. Taken together, these data suggest that the anti-angiogenic effects of borrelidin are mediated through at least two mechanisms, i.e. one threonine-dependent and the other threonine-independent, and borrelidin induces apoptosis in endothelial cells via the caspase-8/-3 pathway.