Threshold Pharmaceuticals, Inc. is a biotechnology company focused on discovering and developing therapeutic agents that selectively target tumor cells for the treatment of cancer patients. The Company�s lead investigational small molecule, TH-302, is being evaluated in two pivotal Phase III clinical trials and multiple earlier-stage clinical trials. The Company has a global license and co-development agreement for TH-302 with Merck KGaA, with an option to co-commercialize in the United States. As a prodrug, TH-302 is designed to remain essentially inactive in normal tissues, but to activate under conditions of tumor hypoxia. Upon activation, TH-302 releases bromo isophosphoramide mustard (Br-IPM), a potent cytotoxin that kills cells by causing DNA to crosslink. In March 2013, Threshold announced the acquisition of [18F]-HX4 from Siemens Healthcare, to develop [18F]-HX4 to determine a patient�s tumor hypoxia profile.