Threshold Announces Acquisition of Investigational Hypoxia PET Imaging Agent [18F]HX4 From Siemens

Threshold Announces Acquisition of Investigational Hypoxia PET Imaging Agent 
[18F]HX4 From Siemens 
Threshold to Develop PET Tracer [18F]HX4 as a Potential Companion
Diagnostic for Its Hypoxia-Targeted Therapeutics 
SOUTH SAN FRANCISCO, CA -- (Marketwire) -- 03/21/13 --  Threshold
Pharmaceuticals, Inc. (NASDAQ: THLD) today announced 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 tumor 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, Ph.D., 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
"The further development of our hypoxia-targeted PET tracer with
d'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." 
About [18F]HX4
 [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 tumors 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 centers globally. [18F]HX4
has a 2-nitroimidazole "trigger" that is designed to be activated
under the extreme hypoxic conditions generally found in tumors but
not typically in normal healthy tissue.(1) Clinical data has
demonstrated the potential of [18F]HX4 to quantify the degree of
hypoxia within different tumors.(2-4)  
Hypoxia-Targeted Therapeutics for the Treatment of Cancer
or abnormally low oxygen concentration, is a common feature of the
tumor microenvironment in most solid tumors and in the bone marrow of
patients with some hematological malignancies (for example, leukemia
and multiple myeloma). Tumor 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
tumors. With such relatively selective activation, Threshold's
hypoxia-targeted therapeutics are designed to target tumor hypoxia
while minimally impacting healthy cells and tissues.  
About Threshold Pharmaceuticals, Inc.
 Threshold Pharmaceuticals,
Inc., is a biotechnology company focused on the discovery and
development of drugs targeting tumor hypoxia, the low oxygen
condition found in the microenvironments of most solid tumors as well
as the bone marrows of some patients with hematologic malignancies.
This approach offers broad potential to treat a variety of cancers.
By selectively targeting tumor cells, we are building a pipeline of
drugs that hold promise to be more effective and less toxic to
healthy tissues than conventional anticancer drugs. For additional
information, please visit our website ( 
Forward-Looking Statements
 Except for statements of historical fact,
the statements in this press release are forward-looking statements,
including statements regarding the potential uses and benefits of
[18F]HX4 to identify patients with tumor hypoxia and contribute to
therapy for such patients, and development plans for [18F]HX4 as a
companion diagnostic. These statements involve risks and
uncertainties that can cause actual results to differ materially from
those in such forward-looking statements. Potential risks and
uncertainties include, but are not limited to, Threshold's ability to
conduct or manage clinical trials of [18F]HX4, Threshold's ability to
obtain regulatory approval for [18F]HX4 as a diagnostic, and
Threshold's ability to continue development of [18F]HX4. Further
information regarding risks faced by Threshold is included under the
heading "Risk Factors" in Threshold's Annual Report on Form 10-K,
which has been filed with the Securities and Exchange Commission on
March 7, 2013 and is available from the SEC's website (
and on our website ( under the heading
"Investors." We undertake no duty to update any forward-looking
statement made in this news release. 
1. Dubois, L.J. et al. Preclinical evaluation and validation of
[18F]HX4, a promising hypoxia marker for PET imaging. Proc Natl Acad
Sci USA 108: 14620-14625, 2011. 
 2. van Loon, J. et al. PET imaging
of hypoxia using [18F]HX4: a phase I trial. Eur J Nucl Med Mol
Imaging 37: 1663-1668, 2010. 
 3. Doss, M. et al. Biodistribution and
radiation dosimetry of the hypoxia marker 18F-HX4 in monkeys and
humans determined by using whole-body PET/CT. Nucl Med Commun 31:
1016-1024, 2010. 
 4. Chen, L. et al. [18F]-HX4 hypoxia imaging with
PET/CT in head and neck cancer: a comparison with [18F]-FMISO. Nucl
Med Commun 33: 1096-1102, 2012.  
Laura Hansen, Ph.D.
Senior Director, Corporate Communications 
Phone: 650-474-8206
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