XenoPort Announces Preliminary Results of Phase 1 Studies Supporting Further Development of XP23829

  XenoPort Announces Preliminary Results of Phase 1 Studies Supporting Further
  Development of XP23829

Business Wire

SANTA CLARA, Calif. -- September 9, 2013

XenoPort, Inc. (Nasdaq:XNPT) announced today the preliminary results from two
Phase 1 studies with XP23829, a novel fumaric acid ester compound that is a
prodrug of monomethyl fumarate (MMF). Based on the favorable preliminary
results from these studies, XenoPort intends to continue to advance the
development of XP23829 as a potential treatment for patients with
relapsing-remitting multiple sclerosis (RRMS) and/or psoriasis.

Ronald W. Barrett, Ph.D., chief executive officer of XenoPort, Inc., stated,
“The results of these recent studies affirm our belief in the potential of
XP23829 to be a next generation fumaric acid ester-based medicine. We now
intend to finalize dose and formulation selection as well as other aspects of
our development plans over the next few months.”

The first Phase 1 study was a randomized, double-blind, placebo-controlled,
multiple ascending dose-escalation study of the pharmacokinetics, safety and
tolerability of two formulations of XP23829 in healthy adult subjects. Five
separate cohorts (12 active and three placebo subjects per cohort) were
enrolled sequentially and received one of two formulations of XP23829 dosed
with or without food. Following up-titration of up to five days, dosing for
each cohort ranged from 400 to 1,000 mg XP23829 per day, administered either
once a day (QD) or twice a day (BID), with dosing for an additional six days.
On the seventh day of target dose administration, pharmacokinetic (PK)
evaluations were conducted following the morning dose. Similarly, a sixth
cohort of healthy subjects received 240 mg BID TECFIDERA^® (dimethyl
fumarate), which is also a prodrug of MMF. As a consequence of its higher
molecular weight, 400 mg of XP23829 is approximately equimolar to 240 mg of
dimethyl fumarate (DMF), i.e., these amounts of each compound can potentially
be enzymatically converted to approximately the same amount of MMF.

The preliminary results of the first Phase 1 study showed that both
formulations of XP23829 produced MMF in the plasma but with different PK
profiles. The 400 mg BID XP23829 Formulation 1 dosed without food provided an
MMF PK profile that was nearly identical to that of 240 mg BID TECFIDERA dosed
without food. As expected, XP23829 Formulation 2, administered as 800 mg QD
and 500 mg BID dosed with food, provided more extended exposure to MMF. These
cohorts had a lower mean maximal plasma concentration (Cmax) of MMF, while
providing a mean daily area under the concentration versus time curve (AUC) of
MMF that was approximately 25% less than that seen after dosing 240 mg BID
TECFIDERA. XP23829 was generally well tolerated in the study. The most common
adverse events were flushing and gastrointestinal-related events, which were
generally mild to moderate in severity.

The second Phase 1 study was an open-label, pharmacokinetic and mass balance
study in healthy male subjects. One group of six subjects received a single
dose of XP23829 that incorporated a radiolabel in the fumarate portion of the
molecule and a separate group of six subjects received XP23829 with the
radiolabel in the promoiety portion of the molecule. As expected, the
metabolism and disposition of radioactivity from the fumarate-labeled version
of XP23829 was similar to what has been publicly reported for dosing healthy
subjects with DMF labeled in the same position. For the promoiety-labeled
version of XP23829, 98% of the recovered radioactivity was in urine. The major
metabolites of the promoiety found in humans were the same as those observed
in animal studies.

XenoPort also announced today that it has completed 13-week toxicology studies
of XP23829 in three species. Each study included a dose of DMF chosen to
provide a similar MMF exposure to that of the highest dose of XP23829. The
adverse effects of XP23829 were similar to those of DMF, except for fewer and
less severe adverse effects in the stomach after dosing XP23829. The target
organs for XP23829 were identical to DMF, and there was no increase in
severity of any adverse effects for XP23829 compared with DMF. These
preliminary results support a conclusion that all observed adverse effects of
XP23829 were attributable to exposure to MMF, the common active metabolite of
DMF and XP23829.

“In addition to advancing XP23829 development, we believe these new studies
have generated important new intellectual property,” stated Dr. Barrett. “Over
the last five years, XenoPort scientists have generated immense knowledge and
experience concerning prodrugs of MMF. This has resulted in the broad filing
of 15 patent applications that cover composition of matter, methods of
synthesis, crystalline forms, improved formulations, methods to achieve
desired PK profiles and methods to improve tolerability, that in some cases
are applicable to MMF prodrugs in general. We believe we are in a leadership
position with regard to development of patent-protected, next-generation
fumaric-acid ester medicines.”

Conference Call

XenoPort will host a conference call at 5:00 p.m. Eastern Time today to
discuss its XP23829 study results. To access the conference call via the
Internet, go to www.XenoPort.com. To access the live conference call via
phone, dial 1-888-275-3514. International callers may access the live call by
dialing 706-679-1417. The reference number to enter the call is 58004727.

The replay of the conference call will be available for one week and may be
accessed after 8:00 p.m. Eastern Time today via the Internet, at
www.XenoPort.com, or via phone at 1-855-859-2056 for domestic callers, or
404-537-3406 for international callers. The reference number to enter the
replay of the call is 58004727.

About XenoPort

XenoPort, Inc. is a biopharmaceutical company focused on developing and
commercializing a portfolio of internally discovered product candidates for
the potential treatment of neurological disorders. XenoPort is currently
commercializing HORIZANT^® (gabapentin enacarbil) Extended-Release Tablets in
the United States and developing its novel fumaric acid ester product
candidate, XP23829, as a potential treatment for RRMS and/or psoriasis.
REGNITE^® (gabapentin enacarbil) Extended-Release Tablets is being marketed in
Japan by Astellas Pharma Inc. XenoPort's pipeline of product candidates also
includes potential treatments for patients with spasticity related to spinal
cord injury and Parkinson's disease. To learn more about XenoPort, please
visit the company Website at www.XenoPort.com.

Forward-Looking Statements

This press release contains “forward-looking” statements, including, without
limitation, all statements related to advancing the development of XP23829;
the suitability of XP23829 as a potential treatment of RRMS and/or psoriasis;
the therapeutic and commercial potential of XP23829; the anticipated
intellectual property position of XP23829 and the importance thereof; and
further development plans of XenoPort and the timing for finalization thereof.
Any statements contained in this press release that are not statements of
historical fact may be deemed to be forward-looking statements. Words such as
“believe,” “expected,” “intends,” “potential,” “will” and similar expressions
are intended to identify forward-looking statements. These forward-looking
statements are based upon XenoPort's current expectations. Forward-looking
statements involve risks and uncertainties. XenoPort's actual results and the
timing of events could differ materially from those anticipated in such
forward-looking statements as a result of these risks and uncertainties, which
include, without limitation, the difficulty and uncertainty of pharmaceutical
product development and the uncertain results and timing of clinical trials
and other studies, including the risk that success in preclinical testing and
early clinical trials do not ensure that later clinical trials will be
successful, and that the results of clinical trials by other parties may not
be indicative of the results in trials that XenoPort may conduct; XenoPort’s
ability to successfully advance product development and to conduct clinical
trials in the anticipated timeframes, or at all; the uncertainty of the FDA’s
review process and other regulatory requirements; the uncertainty of
protecting and expanding XenoPort’s intellectual property rights, including
the risk that patent rights may not provide XenoPort with sufficient
protection against competitive products or otherwise cover commercially
valuable products or processes; XenoPort’s dependence on potential future
collaborative partners; the availability of resources to develop XenoPort’s
product candidates and to support XenoPort’s operations; and the uncertain
therapeutic and commercial value of XenoPort’s product candidates. These and
other risk factors are discussed under the heading “Risk Factors” in
XenoPort’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2013,
filed with the Securities and Exchange Commission on August 7, 2013. XenoPort
expressly disclaims any obligation or undertaking to release publicly any
updates or revisions to any forward-looking statements contained herein to
reflect any change in the company's expectations with regard thereto or any
change in events, conditions or circumstances on which any such statements are

HORIZANT, REGNITE and XENOPORT are trademarks of XenoPort, Inc.



XenoPort, Inc.
Jackie Cossmon, 408-616-7220
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