Threshold Pharmaceuticals, Inc.,  a biotechnology company, has entered into a global agreement with Siemens Healthcare to acquire its investigational agent [18F]HX4 [flortanidazole (18F)], a radiolabeled hypoxia Positron Emission Tomography (PET) tracer. [18F]HX4 could potentially be used as a companion diagnostic to hypoxia-targeted therapeutics based on Threshold's drug discovery platform. Threshold initially intends to develop [18F]HX4 to determine a patient's tumour hypoxia profile, which may identify patients who will best respond to Threshold's hypoxia-targeted therapeutics.

Under the terms of the agreement, Siemens will transfer ownership and existing preclinical, clinical and manufacturing data related to [18F]HX4 to Threshold. Threshold will be responsible for the development and commercialization of [18F]HX4. Siemens' PET radiopharmaceutical manufacturer, PETNET Solutions, a wholly-owned subsidiary of Siemens Medical Solutions, will provide technical expertise and manufacturing capability to support clinical and commercial supply of the tracer [18F]HX4 through its extensive global network of integrated PET radiopharmaceutical drug manufacturing facilities and dispensing nuclear pharmacies. Financial terms of the agreement were not disclosed. Threshold does not expect the acquisition of, or development activities related to, [18F]HX4 to have a material impact on its operating expenses in 2013.

"We believe this acquisition of [18F]HX4 strengthens Threshold's position as a leader in the field of hypoxia-targeted therapies for cancer," said Barry Selick, chief executive officer of Threshold. "Siemens is a leader in PET imaging hardware and software technology as well as PET radiopharmaceutical manufacturing and supply reach, and we look forward to collaborating with them on developing this promising new tool with the goal of identifying patients who may be most likely to benefit from hypoxia-targeted therapeutics."

"The further development of our hypoxia-targeted PET tracer with Threshold's hypoxia-targeted therapeutics carries potential to improve patient care," said Britta Fuenfstueck, chief executive officer, Siemens Healthcare Molecular Imaging. "Siemens' PETNET Solutions will continue to provide technical expertise and resources to support Threshold development and potentially commercialize this tracer through its worldwide network of best-in-class radiopharmaceutical manufacturing and distribution facilities."

[18F]HX4 [flortanidazole (18F)] is a novel investigational tumor hypoxia tracer developed by Siemens Healthcare Molecular Imaging to potentially identify and quantify the degree of hypoxia in tumours in vivo. Positron emission tomography (PET) is a nuclear medical imaging technique that non-invasively produces a three-dimensional image of functional processes in the entire body. PET is routinely used to inform physicians on diagnosis and treatment of cancer and is used in cancer treatment centres globally. [18F]HX4 has a 2-nitroimidazole "trigger" that is designed to be activated under the extreme hypoxic conditions generally found in tumours but not typically in normal healthy tissue. Clinical data has demonstrated the potential of [18F]HX4 to quantify the degree of hypoxia within different tumours.

Hypoxia, or abnormally low oxygen concentration, is a common feature of the tumour microenvironment in most solid tumours and in the bone marrow of patients with some haematological malignancies (for example, leukaemia and multiple myeloma). Tumour hypoxia is associated with the development of resistance to traditional anticancer treatments, including chemotherapy and radiotherapy, enhanced metastatic potential, and ultimately treatment failure. Normal healthy tissues, in contrast, are well oxygenated and typically are not hypoxic. Threshold seeks to design prodrugs of known chemotherapeutic agents or related analogs that remain essentially inactive in normal tissues but are activated under conditions of extreme hypoxia found within tumours. With such relatively selective activation, Threshold's hypoxia-targeted therapeutics are designed to target tumor hypoxia while minimally impacting healthy cells and tissues.

Threshold Pharmaceuticals, Inc., is a biotechnology company focused on the discovery and development of drugs targeting tumour hypoxia, the low oxygen condition found in the microenvironments of most solid tumours as well as the bone marrows of some patients with haematologic malignancies.