Leukemia Journal Publishes Results from Darinaparsin Study

Mon Aug 4, 2008 7:30am EDT

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Study Suggests Potentially Broader Therapeutic Spectrum for
                  Darinaparsin than Inorganic Arsenic
NEW YORK--(Business Wire)--
ZIOPHARM Oncology, Inc. (NASDAQ:ZIOP) announced today the
publication of results from a pre-clinical study of darinaparsin
(ZIO-101) in the July 17, 2008 on line advance publication issue of
Leukemia, a Nature publication. The article, titled "A novel arsenical
has antitumor activity toward As(2)O(3)-resistant and MRP(1)/ABCC(1)-
overexpressing cell lines," was led by Wilson Miller, M.D., Ph.D.,
Professor, Medicine and Oncology, McGill University-Jewish General
Hospital in Montreal, Canada.

   The study showed that darinaparsin is highly active in vitro
against certain leukemia cells that are resistant to inorganic arsenic
(arsenic trioxide--ATO) because they express a drug resistance protein
(MRP1/ABCC1). This greater antitumor activity was demonstrated through
the more potent induction of oxidative stress and programmed cell
death (apoptosis). It also correlated with substantially greater
accumulation of arsenic in darinaparsin-treated leukemia cells than
those treated with inorganic arsenic, possibly because inorganic
arsenic is more efficiently exported by the drug resistance proteins.

   The study also demonstrated that darinaparsin triggers apoptosis
by inducing signaling pathways that do not completely overlap with
ATO. Whereas both darinaparsin and ATO act via the Jun kinase (JNK)
pathway, darinaparsin did not depend on mechanisms normally associated
with ATO's therapeutic activity, including the degradation of the
promyelocytic leukemia/retinoic acid receptor (alpha) (PML/RAR(alpha))
oncoprotein and rearrangement of PML nuclear bodies.

   "This study suggests that darinaparsin may have a broader
therapeutic spectrum than inorganic arsenic, as it is less affected by
the resistance mechanisms of certain cancer cells," stated Dr. Miller.
"The successful application of a treatment that offers inorganic
arsenic's efficacy in acute promyelocytic leukemia, to other more
common malignancies, would be significant. I look forward to seeing
more data from ongoing clinical and pre-clinical studies."

   About Darinaparsin

   Darinaparsin is a proprietary small molecule organic arsenic
licensed from The University of Texas M. D. Anderson Cancer Center and
Texas A&M University. Darinaparsin induces cell cycle arrest and cell
death by targeting several cellular pathways essential for cell
survival. Exposure to darinaparsin has a direct as well as indirect
effect on mitochondrial functions, resulting in depletion of energy
supply to the cell and induction of apoptosis (programmed cell death).
Increase in intra-cellular Reactive Oxygen Species enhances this
effect on mitochondrial functions and consequently the activation of
the signal transduction pathway leading to apoptosis. In addition,
darinaparsin interrupts the cell cycle at the G2/M phase of tumor
cells inducing cell death through this pathway.

   About ZIOPHARM Oncology, Inc.

   ZIOPHARM Oncology, Inc. is a biopharmaceutical company engaged in
the development and commercialization of a diverse, risk-sensitive
portfolio of in-licensed cancer drugs to address unmet medical needs.
The Company applies new insights from molecular and cancer biology to
understand the efficacy and safety limitations of approved and
developmental cancer therapies and identifies proprietary and related
molecules for better patient treatment. For more information, visit
www.ziopharm.com.

   Forward-Looking Safe Harbor Statement:

   This press release contains forward-looking statements for
ZIOPHARM Oncology, Inc. that involve risks and uncertainties that
could cause the Company's actual results to differ materially from the
anticipated results and expectations expressed in these
forward-looking statements. These statements are based on current
expectations, forecasts and assumptions that are subject to risks and
uncertainties, which could cause actual outcomes and results to differ
materially from these statements. Among other things, there can be no
assurance that any of the Company's development efforts relating to
its product candidates will be successful, or such product candidates
will be successfully commercialized. Other risks that affect
forward-looking information contained in this press release include
the possibility of being unable to obtain regulatory approval of the
Company's product candidates, the risk that the results of clinical
trials may not support the Company's claims, and risks related to the
Company's ability to protect its intellectual property and its
reliance on third parties to develop its product candidates. The
Company assumes no obligation to update these forward-looking
statements, except as required by law.

   ZIOP-G

ZIOPHARM Oncology, Inc.
Suzanne McKenna, 646-214-0703
smckenna@ziopharm.com
or
Argot Partners
Andrea Rabney, 212-600-1902
andrea@argotpartners.com

Copyright Business Wire 2008
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