| has gloss | eng: TH-302 is an experimental anticancer agent that is in clinical development at Threshold Pharmaceuticals, Inc. It is activated only at very low levels of oxygen (hypoxia). Such levels are common in human solid tumors, a phenomenon known as tumor hypoxia. TH-302 exploits the activation of a nitroazole prodrug by a process that involves a one electron reduction mediated by ubiquitous cellular reductases such as the NADPH cytochrome P450 to generate a radical anion prodrug (RP). In the presence of oxygen (normoxia) the radical anion prodrug reacts rapidly with oxygen to generate the original prodrug and superoxide (SO). Under the low oxygen conditions of the hypoxic zones in tumors, however, the radical anion prodrug undergoes further irreversible reductions to the hydroxylamine (HA) followed by elimination, releasing the active drug and an azole derivative (AZ). |