Market Overview

Omeros Corporation Reaches Agreement with FDA on OMS721 Phase 3 Trial Protocol for IgA Nephropathy


-- Also Initiates OMS721 Phase 3 Program in HCT-TMA --

Omeros Corporation (NASDAQ:OMER) today announced that it has reached
agreement with the US Food and Drug Administration (FDA) on Omeros'
protocol for its Phase 3 clinical trial evaluating OMS721 in patients
with IgA nephropathy (IgAN). Patient enrollment is expected to begin
early next month.

The single Phase 3 trial is a randomized, double-blind,
placebo-controlled trial in patients at least 18 years of age with
biopsy-confirmed IgAN and with 24-hour urine protein excretion greater
than 1 g/day at baseline on optimized renin-angiotensin system (RAS)
blockade. Patients will receive an initial 12 weekly intravenous doses
of study drug; additional weekly dosing can be administered for partial
responders and relapsers. The primary endpoint, which could suffice for
full approval, is reduction in proteinuria at 24 weeks after the start
of dosing. The trial will employ an adaptive design that will allow
intra-trial adjustment in sample size. For purposes of safety and
efficacy assessments, the initial sample size for the proteinuria
endpoint is estimated at 140 patients in each of the treatment and
placebo groups. This will include a subset of patients with high levels
of proteinuria (i.e., equal to or greater than 2 g/day) at baseline, and
full approval could also be obtained if a substantial improvement is
seen at 24 weeks in this subset of patients alone. The trial design will
allow assessment for either full or accelerated approval at 24 weeks
based on proteinuria results either (1) across the general population of
study patients or (2) in the high-proteinuria subset of patients. In the
event that the primary endpoint at 24 weeks results in accelerated
approval from FDA, change in estimated glomerular filtration rate (eGFR)
will be assessed at approximately three years after the start of dosing.
The initial sample size estimate for the eGFR endpoint is approximately
160 patients per group and also will be adjustable under the study's
adaptive design.

FDA granted both breakthrough therapy designation and orphan drug
designation for OMS721 in IgAN. Omeros' applications to the European
Medicines Agency (EMA) for orphan drug status and for eligibility to the
Priority Medicines (PRIME) program for OMS721 in IgAN are pending.

Omeros has also initiated its Phase 3 program for OMS721 in
hematopoietic stem cell-associated thrombotic microangiopathy (HCT-TMA)
and intends to amend the ongoing Phase 2 protocol following discussion
with FDA and/or EMA to transition the protocol into a Phase 3/pivotal
trial. In the third quarter of 2017, Omeros submitted a preliminary
breakthrough therapy designation request to FDA for OMS721 in HCT-TMA.
Based on the data in that submission, FDA requested that Omeros submit a
full application for breakthrough therapy designation for OMS721 in
HCT-TMA following collection of additional information on the patients
in the Phase 2 clinical trial. Omeros intends to submit the full
application for breakthrough therapy designation by the end of this
month. Enrollment in the Phase 2 trial has continued pending initiation
of/conversion to the pivotal trial. Omeros also recently applied for
eligibility to EMA's PRIME program for OMS721 in HCT-TMA. FDA has
already granted orphan designation for OMS721 in the prevention
(inhibition) of complement-mediated TMAs, which includes HCT-TMA.

The company's Phase 3 program in aHUS is also ongoing in both the US and
Europe. The single-arm, open label, Phase 3 trial is targeting
approximately 40 patients for EMA approval and US accelerated approval
with 80 patients required for full approval in the US. Dosing consists
of an initial IV loading followed by daily subcutaneous dosing. The FDA
has granted OMS721 fast track designation in aHUS as well as orphan
designation for OMS721 in aHUS and other complement-mediated TMAs.

"We're pleased to have received agreement from FDA for our OMS721 Phase
3 protocol in IgA nephropathy," said Gregory A. Demopulos, M.D.,
chairman and chief executive officer of Omeros. "Final preparations to
begin the trial can now be completed and enrollment is expected to open
in early February. To our OMS721 Phase 3 programs in IgA nephropathy and
aHUS, we have recently added a third Phase 3 program in stem cell
transplant-associated TMA. We look forward to ongoing discussions with
both FDA and EMA regarding the HCT-TMA Phase 3 trial as well as
breakthrough and PRIME designations. In the meantime, enrollment in the
Phase 2 HCT-TMA trial has progressed with patients expected to have a
very high mortality rate doing well on OMS721."

About Omeros' MASP Programs
Omeros controls the worldwide
rights to MASP-2 and all therapeutics targeting MASP-2, a novel
pro-inflammatory protein target involved in activation of the complement
system, which is an important component of the immune system. The
complement system plays a role in the inflammatory response and becomes
activated as a result of tissue damage or microbial infection. MASP-2 is
the effector enzyme of the lectin pathway, one of the principal
complement activation pathways. Importantly, inhibition of MASP-2 does
not appear to interfere with the antibody-dependent classical complement
activation pathway, which is a critical component of the acquired immune
response to infection, and its abnormal function is associated with a
wide range of autoimmune disorders. MASP-2 is generated by the liver and
is then released into circulation. Adult humans who are genetically
deficient in one of the proteins that activate MASP-2 do not appear to
be detrimentally affected by the deficiency. OMS721 is Omeros' lead
human MASP-2 antibody.

Phase 3 clinical programs are in progress for OMS721 in atypical
hemolytic uremic syndrome (aHUS), in immunoglobulin A (IgA) nephropathy
and in hematopoietic stem cell transplant-associated thrombotic
microangiopathy (HCT-TMA). Also, two Phase 2 trials are ongoing. One is
continuing to enroll IgA nephropathy patients and has already generated
positive data in patients with IgA nephropathy and with lupus nephritis;
the other is enrolling and has reported positive data in patients with
HCT-TMA and in patients with aHUS. OMS721 can be administered both
intravenously and subcutaneously, and Omeros expects to commercialize
each formulation of OMS721 for different therapeutic indications. In
parallel, Omeros is developing small-molecule inhibitors of MASP-2.
Based on requests from treating physicians, Omeros has established a
compassionate-use program for OMS721, which is active in both the U.S.
and Europe. The FDA has granted OMS721 breakthrough therapy designation
for IgA nephropathy, orphan drug status for the prevention (inhibition)
of complement-mediated thrombotic microangiopathies and for the
treatment of IgA nephropathy, and fast track designation for the
treatment of patients with aHUS.

Omeros also has identified MASP-3 as responsible for the conversion of
pro-factor D to factor D and as a critical activator of the human
complement system's alternative pathway. The alternative pathway is
linked to a wide range of immune-related disorders. In addition to its
lectin pathway inhibitors, the company is advancing its development of
antibodies and small-molecule inhibitors against MASP-3 to block
activation of the alternative pathway. Omeros has initiated the
manufacturing scale-up process of its MASP-3 antibodies in preparation
for clinical trials.

About Omeros Corporation
Omeros is a commercial-stage
biopharmaceutical company committed to discovering, developing and
commercializing small-molecule and protein therapeutics for large-market
as well as orphan indications targeting inflammation,
complement-mediated diseases and disorders of the central nervous
system. The company's drug product OMIDRIA® (phenylephrine
and ketorolac intraocular solution) 1% / 0.3% is marketed for use during
cataract surgery or intraocular lens (IOL) replacement to maintain pupil
size by preventing intraoperative miosis (pupil constriction) and to
reduce postoperative ocular pain. In the European Union, the European
Commission has approved OMIDRIA for use in cataract surgery and other
IOL replacement procedures to maintain mydriasis (pupil dilation),
prevent miosis (pupil constriction), and to reduce postoperative eye
pain. Omeros has multiple Phase 3 and Phase 2 clinical-stage development
programs focused on: complement-associated thrombotic microangiopathies;
complement-mediated glomerulonephropathies; Huntington's disease and
cognitive impairment; and addictive and compulsive disorders. In
addition, Omeros has a diverse group of preclinical programs and a
proprietary G protein-coupled receptor (GPCR) platform through which it
controls 54 new GPCR drug targets and corresponding compounds, a number
of which are in preclinical development. The company also exclusively
possesses a novel antibody-generating platform.

Forward-Looking Statements
This press release contains
forward-looking statements within the meaning of Section 27A of the
Securities Act of 1933 and Section 21E of the Securities Exchange Act of
1934, which are subject to the "safe harbor" created by those sections
for such statements. All statements other than statements of historical
fact are forward-looking statements, which are often indicated by terms
such as "anticipate," "believe," "could," "estimate," "expect," "goal,"
"intend," "likely," "look forward to," "may," "plan," "potential,"
"predict," "project," "should," "will," "would" and similar expressions
and variations thereof. Forward-looking statements are based on
management's beliefs and assumptions and on information available to
management only as of the date of this press release. Omeros' actual
results could differ materially from those anticipated in these
forward-looking statements for many reasons, including, without
limitation, risks associated with product commercialization and
commercial operations, unproven preclinical and clinical development
activities, regulatory oversight, intellectual property claims,
competitive developments, litigation, and the risks, uncertainties and
other factors described under the heading "Risk Factors" in the
company's Quarterly Report on Form 10-Q filed with the Securities and
Exchange Commission on November 9, 2017. Given these risks,
uncertainties and other factors, you should not place undue reliance on
these forward-looking statements, and the company assumes no obligation
to update these forward-looking statements, even if new information
becomes available in the future.

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