ZIOPHARM Announces Oral Presentation Highlighting Ad-RTS-IL-12 Results Correlated With Reducing Cancer Stem Cells in the Brain

ZIOPHARM Announces Oral Presentation Highlighting Ad-RTS-IL-12 Results
Correlated With Reducing Cancer Stem Cells in the Brain at ASGCT 17th Annual
Meeting

BOSTON, May 22, 2014 (GLOBE NEWSWIRE) -- ZIOPHARM Oncology, Inc.
(Nasdaq:ZIOP), a biopharmaceutical company focused on the development and
commercialization of new cancer therapies, announced today results
demonstrating the potent anti-tumor and anti-cancer stem cell (CTC) effects of
Ad-RTS-IL-12 in a glioma (brain cancer) model, and in other preclinical and
clinical settings. Ad-RTS-IL-12 is a novel DNA-based therapeutic candidate for
the controlled expression of IL-12, an important protein for stimulating an
anti-cancer T cell immune response. The presentation, titled "Intratumoral
Regulated Expression of IL-12 as a Gene Therapy Approach to Immunotherapy,"
was presented in an oral session at the 17th Annual Meeting of the American
Society of Gene and Cell Therapy (ASGCT), held May 21-24 in Washington, DC.

Results from human and laboratory studies of Ad-RTS-IL-12 demonstrate that
precise control of IL-12 gene expression levels can be achieved using Intrexon
Corporation's (NYSE:XON) RheoSwitch Therapeutic System® (RTS®). Rapid, tight
modulation of in vivo expression of IL-12 using the activator ligand veledimex
was demonstrated across these studies. When IL-12 expression is "switched on"
it rapidly leads to expression and an immune response. This immune response is
characterized by an increase in tumor infiltrating lymphocytes with system
wide immune activation. This modulated immune response has resulted in
anti-tumor effects in both injected and systemic non-injected legions in Phase
1 and Phase 2 studies of Ad-RTS-IL-12 in subjects with melanoma and breast
cancer.

The data presented today further demonstrate that Ad-RTS-IL-12 has potent
anti-cancer effects in a glioma model, showing both a reduction in tumor mass
and prolonged survival when compared to existing treatment standards. The data
also show a significant reduction in brain cancer stem cells, as measured by
dramatically reduced nestin levels. Brain cancer stem cells are thought to
play a critical role in recurrence and metastasis.

"Ad-RTS-IL-12 seems to offer precise control over a potent immuno-oncology
weapon, the IL-12 cytokine," said Antonio Chiocca, MD, PhD, Prof. and Chairman
of Neurosurgery at Brigham and Women's Hospital and Harvard Medical School.
"With malignant glioma in particular, delivery of IL-12 is one of several
promising experimental approaches being tested, but unlike other therapies the
ability to control IL-12 expression in vivo may prove to be ground breaking.
This is increasingly being demonstrated both in preclinical models, as well as
in the clinic, where patients are showing reversal of immuno-toxicity,
including cytokine storm, and then resume therapy."He continued: "IL-12's
role in reducing cancer stem cells is also very encouraging, as the role of
these cells in recurrence and metastasis is increasingly well understood.I
look forward to further data from these clinical and preclinical programs, as
well as to the initiation of a Phase 1 study of Ad-RTS-IL-12 in brain cancer."

About ZIOPHARM Oncology, Inc.:

ZIOPHARM Oncology is a Boston, Massachusetts-based biotechnology company
employing novel gene expression and control technology to deliver DNA for the
treatment of cancer. ZIOPHARM's technology platform employs Intrexon
Corporation's RheoSwitch Therapeutic System® technology to turn on and off,
and precisely modulate, gene expression at the cancer site in order to improve
the therapeutic index. This technology is currently being evaluated in Phase 2
clinical studies of the immune system cytokine interleukin-12 for the
treatment of breast cancer and advanced melanoma. Multiple new Investigational
New Drug Applications for new targets using synthetic biology technology are
expected through 2015. ZIOPHARM is also developing novel small molecules as
potential cancer therapeutics.

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 Ad-RTS-IL-12,
palifosfamide, 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 Ad-RTS-IL-12, palifosfamide, 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, 2013 and our Quarterly Report on Form 10-Q for the quarter ended
March 31, 2014. 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.

CONTACT: Lori Ann Occhiogrosso
         Director of Corporate Communication
         ZIOPHARM Oncology, Inc.
         617-259-1987
         locchiogrosso@ziopharm.com

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