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Preliminary Data from Phase 3 VISTA Trial in Bladder Cancer to Be Presented in a Plenary Session at American Urological Association Annual Meeting


Eleven Biotherapeutics to Host Conference Call in Conjunction with
Data Presentation in May

Eleven Biotherapeutics, Inc. (NASDAQ:EBIO), a late-stage clinical
company developing next-generation antibody-drug conjugate (ADC)
therapies for the treatment of cancer, today announced that preliminary
efficacy and safety data from its ongoing Phase 3 VISTA trial of
Vicinium™ in patients with non-muscle invasive bladder cancer (NMIBC)
who have been previously treated with bacillus Calmette-Guérin (BCG)
have been selected for presentation during a plenary session currently
scheduled for Monday, May 21, 2018 at 11:00 a.m. PT at the American
Urological Association Annual Meeting taking place in San Francisco.
Vicinium is a fusion protein, designed to be a next-generation ADC, that
targets the epithelial cell adhesion molecule (EpCAM) antigens on the
surface of bladder cancer cells to deliver a potent cytotoxin into those

Data, as reported in the abstract published online today, are from a
subgroup of the first 75 evaluable carcinoma in situ patients. Within
these patients, preliminary findings show that greater than 95 percent
expressed EpCAM on the surface of tumor cells, the target of Vicinium.
Efficacy data as measured by complete response rates at three-months
will be reported during the plenary session. Vicinium has been
well-tolerated. Treatment-related adverse events (AEs) were reported in
46 percent of patients, the majority of which were Grade 1 or 2. The
most common of these were dysuria (12%), UTI or pollakiuria (10%) and
hematuria (7%), which are often associated with catheter-delivered
treatments into the bladder and bladder cancer itself. As of the
December 2017 data cut off, three treatment-related serious AEs were
reported, including renal failure (CTCAE Grade 5) with cholestatic
hepatitis (Grade 4) in one patient and acute kidney injury (Grade 3) in
a second patient who recovered.

In March 2018, recruitment was completed in the VISTA trial, a
single-arm registration study designed in accordance with U.S. Food and
Drug Administration's final guidance for developing treatments for
BCG-unresponsive NMIBC.

"When treatment with today's standard of care, BCG, is no longer an
option, the next treatment option is typically removal of the patient's
bladder, a challenging, life-altering procedure that many patients elect
not to undergo," said Stephen Hurly, president and chief executive
officer of Eleven Biotherapeutics. "Vicinium has demonstrated that it is
a well-tolerated and active agent in patients with BCG unresponsive
NMIBC in studies to-date. We are excited to be presenting the first
preliminary data from our Phase 3 VISTA trial of Vicinium for patients
with NMIBC at this year's AUA meeting. During our plenary presentation,
we will share initial efficacy findings and data supporting the
favorable safety we have observed so far with Vicinium. We believe
Vicinium holds tremendous potential as a treatment for bladder cancer,
and we look forward to sharing these and additional data later in the

The company plans to host a conference call in conjunction with the data
presentation, with details to follow.

About the VISTA Clinical Trial
The VISTA trial is an
open-label, multicenter, single-arm Phase 3 clinical trial evaluating
the efficacy and tolerability of Vicinium™ in patients with high-risk
non-muscle invasive bladder cancer (NMIBC) that is carcinoma in situ
(CIS, cancer found on the inner lining of the bladder that has not
spread into muscle or other tissue) or papillary (cancer that has grown
from the bladder lining out into the bladder but has not spread into
muscle or other tissue), who have been previously treated with bacillus
Calmette-Guérin (BCG). The primary endpoint of the trial is the complete
response rate in patients with CIS with or without papillary disease and
durability of that response. Patients in the study receive locally
administered Vicinium twice a week for six weeks, followed by
once-weekly treatment for another six weeks, then treatment every other
week for up to two years. Topline data assessing responses and
durability of responses at three-months on treatment are expected in
mid-2018, with 12-month data anticipated in mid-2019.

About Vicinium™
Vicinium™, Eleven Biotherapeutics' lead
product candidate, is a next-generation antibody-drug conjugate
developed using the company's proprietary Targeted Protein Therapeutics
platform. Vicinium is comprised of a recombinant fusion protein that
targets epithelial cell adhesion molecule (EpCAM) antigens on the
surface of tumor cells to deliver a potent protein payload, Pseudomonas
Exotoxin A (ETA). Vicinium is constructed with a stable, genetically
engineered linker to ensure the payload remains attached until it is
internalized by the cancer cell, which is believed to decrease the risk
of toxicity to healthy tissues, thereby improving its safety. In prior
clinical studies conducted by Eleven Biotherapeutics, EpCAM has been
shown to be overexpressed in non-muscle invasive bladder cancer (NMIBC)
cells with minimal to no EpCAM expression observed on normal bladder
cells. Eleven Biotherapeutics is currently conducting the Phase 3 VISTA
trial, designed to support the registration of Vicinium for the
treatment of NMIBC in patients who have previously received two courses
of bacillus Calmette-Guérin (BCG) and whose disease is now
BCG-unresponsive. Topline, three-month data from the trial are expected
in mid-2018. Additionally, Eleven Biotherapeutics believes that
Vicinium's cancer cell-killing properties promote an anti-tumor immune
response that may potentially combine well with immuno-oncology drugs,
such as checkpoint inhibitors. The activity of Vicinium in
BCG-unresponsive NMIBC is also being explored at the US National Cancer
Institute in combination with AstraZeneca's immune checkpoint inhibitor

About Eleven Biotherapeutics
Eleven Biotherapeutics, Inc. is
a late-stage clinical company advancing next-generation antibody-drug
conjugate therapies for the treatment of cancer based on the company's
Targeted Protein Therapeutics platform. The company's lead program,
Vicinium™, is currently in a Phase 3 registration trial for the
treatment of non-muscle invasive bladder cancer, with topline data
expected in mid-2018. Vicinium incorporates a tumor-targeting antibody
fragment and a protein cytotoxic payload into a single protein molecule
designed to selectively and effectively kill cancer cells while sparing
healthy cells. For more information, please visit the company's website

Cautionary Note on Forward-Looking Statements
Any statements
in this press release about future expectations, plans and prospects for
the Company, the Company's strategy, future operations, and other
statements containing the words "anticipate," "believe," "estimate,"
"expect," "intend," "may," "plan," "predict," "project," "target,"
"potential," "will," "would," "could," "should," "continue," and similar
expressions, constitute forward-looking statements within the meaning of
The Private Securities Litigation Reform Act of 1995. Actual results may
differ materially from those indicated by such forward-looking
statements as a result of various important factors, including: the
uncertainties inherent in the initiation and conduct of clinical trials,
our ability to successfully develop our product candidates and complete
our planned clinical programs, our ability to obtain marketing approvals
for our product candidates, expectations regarding our ongoing clinical
trials, availability and timing of data from clinical trials, whether
interim results from a clinical trial will be predictive of the final
results of the trial or results of early clinical studies will be
indicative of the results of future studies, the adequacy of any
clinical models, expectations regarding regulatory approvals and other
factors discussed in the "Risk Factors" section of the Company's Annual
Report on Form 10-K, Quarterly Reports on Form 10-Q and other reports
filed with the Securities and Exchange Commission. In addition, the
forward-looking statements included in this press release represent the
Company's views as of the date hereof. The Company anticipates that
subsequent events and developments will cause the Company's views to
change. However, while the Company may elect to update these
forward-looking statements at some point in the future, the Company
specifically disclaims any obligation to do so. These forward-looking
statements should not be relied upon as representing the Company's views
as of any date subsequent to the date hereof.

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