Ligand Receives $1.4 Million Milestone Payment from Retrophin, Inc.

  Ligand Receives $1.4 Million Milestone Payment from Retrophin, Inc.

       Ligand’s Partner Preparing to Initiate a Phase 2 trial for FSGS

Business Wire

SAN DIEGO -- February 25, 2013

Ligand Pharmaceuticals Incorporated (NASDAQ: LGND) announces receipt of a $1.4
million milestone payment from Retrophin, Inc. (OTCQB: RTRX) under the terms
of a license agreement signed in February 2012 for the development and
commercialization of Retrophin’s lead clinical candidate RE-021. Ligand will
remit $210,000 to Bristol-Myers Squibb under the terms of a previous license
agreement for RE-021. Ligand is entitled to milestones and royalties on the
successful future development and commercialization of RE-021 under this
agreement.

RE-021 is in development for the treatment of focal segmental
glomerulosclerosis (FSGS), a rare disease that attacks the kidney’s filtering
system (glomeruli), causing serious scarring, kidney degeneration and
ultimately loss in kidney function. An estimated 50,000 patients in the United
States suffer from FSGS, with most patients diagnosed as children or young
adults. Retrophin has announced that it expects to begin enrollment in a Phase
2 clinical trial known as “FONT-3” during the first half of 2013.

“We are impressed with Retrophin’s continued business successes and look
forward to the initiation of the Phase 2 trial of RE-021,” commented John
Higgins, President and Chief Executive Officer of Ligand. “FSGS is an orphan
disease with significant, unmet medical need and no currently approved
therapies. We believe that RE-021 has a very compelling therapeutic profile
and that under Retrophin’s stewardship, it has the potential to become an
important treatment.”

Ligand acquired RE-021 in its acquisition of Pharmacopeia in December 2008.
RE-021 was formerly known as DARA (a Dual Acting Receptor Antagonist of
Angiotensin and Endothelin) and possesses two clinically validated mechanisms
of action that selectively block two potent vasoconstrictor and mitogenic
agents, angiotensin II and endothelin 1, at their respective receptors.

About Retrophin

Retrophin is a biotechnology company focused on the discovery and development
of orphan drugs for the treatment of rare and life-threatening diseases for
which there are currently no viable options. The company is currently focused
on several catastrophic diseases that primarily affect children, including
FSGS, Pantothenate Kinase-Associated Neurodegeneration (PKAN), Duchenne
Muscular Dystrophy and others. Retrophin’s lead compound, RE-021, is scheduled
to begin enrollment in a potentially pivotal Phase 2 clinical trial for FSGS
during the first half of 2013.

About Ligand Pharmaceuticals

Ligand is a biopharmaceutical company that develops and acquires assets it
believes will generate royalty revenues and, under its lean corporate cost
structure, produce sustainable profitability. Ligand has a diverse asset
portfolio addressing the unmet medical needs of patients for a broad spectrum
of diseases including thrombocytopenia, multiple myeloma, diabetes, hepatitis,
muscle wasting, dyslipidemia, anemia and osteoporosis. Ligand’s Captisol
platform technology is a patent-protected, chemically modified cyclodextrin
with a structure designed to optimize the solubility and stability of drugs.
Ligand has established multiple alliances with the world’s leading
pharmaceutical companies including GlaxoSmithKline, Merck, Pfizer, Eli Lilly &
Company, Baxter International, Bristol-Myers Squibb, Celgene, Onyx
Pharmaceuticals, Lundbeck Inc. and The Medicines Company, among others. Please
visit www.captisol.com for more information on Captisol or www.ligand.com for
more information on Ligand.

Follow Ligand on Twitter @Ligand_LGND.

Forward-Looking Statements

This news release contains certain forward-looking statements by Ligand that
involve risks and uncertainties and reflect Ligand’s judgment as of the date
of this release. These statements include those related to continued
development of RE-021. Actual events or results may differ from our
expectations. There can be no assurance Retrophin will continue clinical
development of RE-021; that future clinical trial data will be favorable or
that such trials will confirm any improvements over other products or lack of
negative impacts; that RE-021 will receive required regulatory approvals or
that it will be a commercially successful therapy or be successfully marketed;
or that any future milestone or royalty payments will be received. The failure
to meet expectations with respect to any of the foregoing matters may have a
negative effect on Ligand’s stock price. Additional information concerning
these and other risk factors affecting Ligand’s business can be found in prior
press releases available via www.ligand.com as well as in Ligand’s public
periodic filings with the Securities and Exchange Commission at www.sec.gov.
Ligand disclaims any intent or obligation to update these forward-looking
statements beyond the date of this release. This caution is made under the
safe harbor provisions of the Private Securities Litigation Reform Act of
1995.

Contact:

Ligand Pharmaceuticals Incorporated
John L. Higgins, President and CEO
Jennifer Capuzelo, Investor Relations
jcapuzelo@ligand.com
858-550-7584
or
LHA
Don Markley
dmarkley@lhai.com
310-691-7100