ZIOPHARM Announces Presentation of Updated Results From Ad-RTS-IL-12 Phase I Study in Advanced Melanoma at the 2013 ASCO Annual

ZIOPHARM Announces Presentation of Updated Results From Ad-RTS-IL-12 Phase I
Study in Advanced Melanoma at the 2013 ASCO Annual Meeting

BOSTON, June 1, 2013 (GLOBE NEWSWIRE) -- ZIOPHARM Oncology, Inc. (Nasdaq:ZIOP)
today announced updated results from the Phase 1 study in advanced melanoma
using Ad-RTS-IL-12, a novel DNA-based therapeutic candidate. Findings were
presented in a poster presentation at the 2013 American Society for Clinical
Oncology (ASCO) Annual Meeting being held May 31 – June 4, 2013 at McCormick
Place in Chicago, IL. A presentation of the poster, titled "A phase I
open-label study of Αd-RTS-hIL-12, an adenoviral vector engineered to express
hIL-12 under the control of an oral activator ligand, in subjects with
unresectable stage III/IV melanoma," was delivered by Gerald P. Linette, MD,
PhD, Associate Professor, Medicine and Neurosurgery, Division of Oncology, at
the Washington University School of Medicine.

For the study, Ad-RTS-IL-12, an adenoviral vector engineered to express IL-12
utilizing the RheoSwitch Therapeutic System® (RTS®) technology, was injected
intratumorally in patients with advanced melanoma (n=14). Expression of IL-12
was controlled through the administration of an oral activator ligand
(INXN‑1001), which was administered in four ascending dose cohorts.The
Company previously reported that compelling clinical activity was observed in
five of seven (71 percent) patients dosed at the two highest dose levels
(Nemunaitis et al. ASGCT 2013). The study further demonstrated that treatment
with Ad-RTS-IL-12 + INXN-1001 was shown to increase intratumoral IL-12 mRNA
transcription.The mRNA level was very tightly controlled (on and off) by the
biologic switch and oral activator ligand.Consequent on the increase in IL-12
expression there was a major increase in tumor-infiltrating lymphocytes
(CD8^+, CD45RO^+) in the tumor microenvironment as measured in tumor
biopsies.Subsequently clinical activity was observed in injected and
non-injected lesions, primarily at the higher doses of INXN-1001 (100 and 160
mg), with inflammation, shrinkage, flattening, and depigmentation of lesions
correlated with the highest serum levels of IFN-γ.

ZIOPHARM is currently conducting a Phase 2 multi-center, single-arm,
open-label expansion study in up to 15 patients with unresectable Stage III or
IV melanoma. The Phase 2 study will focus on optimization of the dosing
schedule, guided by pharmacokinetics and tolerability, using every other day
dosing of the oral activator ligand.

"The promise of immune stimulation in cancer treatment is now at the leading
edge of oncology research, with Ad-RTS-IL-12, as a potent and highly
controllable immune stimulator, demonstrating meaningful potential in this
field," said Dr. Linette. "Being able to regulate the expression of IL-12
through a gene therapy strategy provides for the ability to optimize response
and tolerability in ways that cannot be achieved with recombinant proteins or
other drug delivery strategies. We look forward to taking advantage of this
ability and our observations in Phase I to optimize the ongoing Phase 2 study
of Ad-RTS-IL-12 in advanced melanoma."

About ZIOPHARM Oncology, Inc.:

ZIOPHARM Oncology is a biopharmaceutical company focused on the development
and commercialization of new cancer therapies. The Company's clinical programs
include:

Ad-RTS-IL-12 is currently being tested in two Phase 2 studies, the first for
the treatment of advanced melanoma, and the second in combination with
palifosfamide for the treatment of non-resectable recurrent or metastatic
breast cancer. Ad-RTS-IL-12 uses synthetic biology to enable controlled
delivery of therapeutic interleukin-12 (IL-12), a protein important for
enhancing the development of an immune response to cancer. In partnership with
Intrexon Corporation, ZIOPHARM's DNA synthetic biology platform employs an
inducible gene-delivery system that enables controlled delivery of genes that
produce therapeutic proteins to treat cancer. This controlled delivery is
achieved by producing IL-12 under the control of Intrexon's proprietary
biological "switch" (the RheoSwitch Therapeutic System® or RTS® platform) to
turn on/off the therapeutic protein expression at the tumor site.

Palifosfamide (ZIO-201) is a potent, bi-functional DNA alkylating agent that
has activity in multiple tumors by evading typical resistance pathways.
Palifosfamide is in the same class as bendamustine, cyclophosphamide, and
ifosfamide. It is currently being studied in an adaptive Phase 3 study in
small cell lung cancer. Enrollment in this study was suspended with 188
subjects randomized, and being followed for overall survival. Data is expected
in the first half of 2014.

Indibulin (ZIO-301) is a novel, tubulin binding agent that is expected to have
several potential benefits, including oral dosing, application in multi-drug
resistant tumors, no neuropathy and a tolerable toxicity profile. It is
currently being studied in a Phase 1/2 trial in metastatic breast cancer.

Darinaparsin (ZIO-101) is a novel mitochondrial-and hedgehog-targeted agent
(organic arsenic) currently in ongoing studies with Solasia Pharma K.K.

ZIOPHARM's operations are located in Boston, MA. Further information about
ZIOPHARM may be found at www.ziopharm.com.

Forward-Looking Safe Harbor Statement:

This press release contains certain forward-looking information about ZIOPHARM
Oncology, Inc. that is intended to be covered by the safe harbor for
"forward-looking statements" provided by the Private Securities Litigation
Reform Act of 1995, as amended. Forward-looking statements are statements that
are not historical facts. Words such as "expect(s)," "feel(s)," "believe(s),"
"will," "may," "anticipate(s)" and similar expressions are intended to
identify forward-looking statements. These statements include, but are not
limited to, statements regarding our ability to successfully develop and
commercialize our therapeutic products; our ability to expand our long-term
business opportunities; financial projections and estimates and their
underlying assumptions; and future performance. All of such statements are
subject to certain risks and uncertainties, many of which are difficult to
predict and generally beyond the control of the Company, that could cause
actual results to differ materially from those expressed in, or implied or
projected by, the forward-looking information and statements. These risks and
uncertainties include, but are not limited to: whether palifosfamide,
Ad-RTS-IL-12, darinaparsin, indibulin, or any of our other therapeutic
products will advance further in the clinical trials process and whether and
when, if at all, they will receive final approval from the U.S. Food and Drug
Administration or equivalent foreign regulatory agencies and for which
indications; whether palifosfamide, Ad-RTS-IL-12, darinaparsin, indibulin, and
our other therapeutic products will be successfully marketed if approved;
whether any of our other therapeutic product discovery and development efforts
will be successful; our ability to achieve the results contemplated by our
collaboration agreements; the strength and enforceability of our intellectual
property rights; competition from other pharmaceutical and biotechnology
companies; the development of, and our ability to take advantage of, the
market for our therapeutic products; our ability to raise additional capital
to fund our operations on terms acceptable to us; general economic conditions;
and the other risk factors contained in our periodic and interim SEC reports
filed from time to time with the Securities and Exchange Commission, including
but not limited to, our Annual Report on Form 10-K for the fiscal year ended
December 31, 2012, and our Quarterly Report on Form 10-Q for the quarter ended
March 31, 2013. Readers are cautioned not to place undue reliance on these
forward-looking statements that speak only as of the date hereof, and we do
not undertake any obligation to revise and disseminate forward-looking
statements to reflect events or circumstances after the date hereof, or to
reflect the occurrence of or non-occurrence of any events.

Trademarks

RheoSwitch Therapeutic System^® (RTS^®) is a registered trademark of Intrexon
Corporation.

CONTACT: For ZIOPHARM Investor Relations:
         David Pitts
         Argot Partners
         212-600-1902
         david@argotpartners.com
        
         Media Contacts:
         David Schull or Lena Evans
         Russo Partners, LLC
         858-717-2310
         212-845-4262
         david.schull@russopartnersllc.com
         lena.evans@russopartnersllc.com

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