FLX Bio Selects Immuno-Oncology Clinical Candidate

— Phase 1 Clinical Study of CCR4 Antagonist FLX475 to Begin in Late
2017 ––

— Appoints Scott Antonia, M.D., Ph.D., of Moffitt Cancer Center to
Scientific Advisory Board —

SOUTH SAN FRANCISCO, Calif.–(BUSINESS WIRE)–FLX Bio, Inc., a biopharmaceutical company focused on the discovery and
development of oral small-molecule drugs to activate the immune system,
today announced the selection of FLX475 as its first immuno-oncology
clinical candidate for the treatment of cancer. FLX475 is a
best-in-class, oral, small molecule antagonist of CCR4. By blocking
CCR4, a receptor protein that plays a role in the recruitment and
accumulation of regulatory T (Treg) cells in the tumor environment,
FLX475 has the potential to provide a new mechanism to treat cancer. FLX
Bio expects to begin clinical trials of FLX475 in late 2017.

“Tumors surround themselves with a barrier of regulatory T cells,
preventing a normal immune response,” stated Alexander Rudensky,
Chairman of FLX Bio’s Scientific Advisory Board and Chair of the
Immunology Program at the Sloan Kettering Institute, Director of the
Ludwig Center for Cancer Immunotherapy at Memorial Sloan Kettering
Cancer Center and Member, National Academy of Sciences. “CCR4 represents
a key pathway by which tumors recruit regulatory T cells to suppress
tumor immunity. By blocking this pathway with a CCR4 antagonist, it may
be possible to prevent regulatory T cell recruitment to the tumor site,
reduce the number of regulatory T cells in the tumor and importantly,
enable immune activation and tumor killing.”

In April 2017, FLX Bio researchers presented preclinical
efficacy data
on internally-generated CCR4 antagonists at the
American Association of Cancer Research Conference. The data
demonstrated that FLX Bio’s CCR4 antagonists are potent and selective,
reduce regulatory T cells selectively at the tumor site and reverse
tumor growth in mouse models particularly when combined with other
immuno-oncology agents.

Brian R. Wong, M.D., Ph.D., CEO of FLX Bio commented, “Based upon
compelling preclinical data, we look forward to advancing FLX745 into
clinical trials later this year. FLX475 was generated using FLX Bio’s
integrated discovery engine, which the company is leveraging to build a
pipeline of small molecule compounds targeting regulatory T cells or
tumor myeloid cells, both of which work upstream of checkpoint
inhibitors and prevent tumor immunity.”

Appointment of Scott J. Antonia, M.D., Ph.D., to Scientific Advisory
Board

FLX Bio also announced the appointment of Scott J. Antonia, M.D., Ph.D.,
Chair of the department of thoracic surgery for Moffitt Cancer Center,
to its scientific advisory board (SAB).

Dr. Antonia joins Philip Greenberg, M.D., David Goeddel, Ph.D., Drew
Pardoll, M.D., Ph.D., Antoni Ribas, M.D., Ph.D., Alexander Rudensky,
Ph.D. and Robert Zamboni, Ph.D., bringing the total FLX Bio SAB to seven
key opinion leaders in immunotherapy.

“Scott is a highly-respected and experienced investigator and clinician
in the immuno-oncology field, and we are thrilled to add his expertise
to our robust scientific advisory board,” Dr. Wong continued. “With
FLX475 entering the clinic later this year, we look forward to applying
Scott’s deep knowledge as we select specific cancer targets for our
clinical candidates.”

Dr. Antonia serves as the chair of the thoracic oncology department at
the H. Lee Moffitt Cancer Center and Research Institute as well as
professor of Oncologic Sciences at the University of South Florida
College of Medicine. His expertise lies in treating cancer patients
through immunotherapeutic strategies to thwart the immunosuppressive
mechanisms used by tumors to evade T cell-mediated rejection. He has
designed and conducted numerous cutting-edge studies with novel
immunotherapeutic agents. Dr. Antonia has received numerous awards
including Moffitt Physician of the Year, Moffitt Mentor of the Year and
the W. Jackson Pledger Researcher of the Year and was inducted into the
National Academy of Inventors in 2015. He received his M.D. and Ph.D. in
Immunology from the University of Connecticut Health Center in
Farmington, Connecticut. He completed an internal medicine residency and
pursued additional medical oncology and immunobiology training at Yale
University School of Medicine. He is the author of several peer-reviewed
publications and an inventor on two patents.

About C-C Chemokine Receptor 4 (CCR4)

CCR4 is a receptor protein expressed on regulatory T cells. While
regulatory T cells help prevent autoimmune diseases and control
inflammation in a healthy body, cancer cells can co-opt this protective
feature by recruiting large numbers of regulatory T cells to a tumor
site (tumor microenvironment). Within the tumor microenvironment,
regulatory T cells prevent the body from mounting an immune response to
eliminate the cancer cells, allowing tumor growth to proceed unchecked.
To recruit regulatory T cells, cells in tumors send out chemical signals
(CCL17 and CCL22) which bind to CCR4. FLX475 inhibits CCR4 to prevent
the unwanted migration of regulatory T cells to the site of a tumor.

About FLX475

FLX475 is a best-in-class oral, small molecule antagonist of CCR4. CCR4
ligands are elevated in multiple tumor types when compared to normal
tissue. In preclinical studies, FLX475 inhibited tumor growth and
increased tumor regression. In addition, FLX475 enhanced the antitumor
effects of various checkpoint inhibitors including anti-PD-L1 and
anti-CTLA4 antibodies as well as immune agonists such as anti-4-1BB. In
addition, FLX475 has the potential to enhance cell-based immunotherapies
such as CAR-T and cancer vaccines. Unlike antibodies to CCR4, FLX475
selectively blocks the recruitment of regulatory T cells to the tumor
site, and does not deplete regulatory T cells in healthy tissue such as
blood, spleen or skin. FLX Bio intends to initiate clinical trials of
FLX475 alone and in combination with checkpoint inhibitors in late 2017.

About FLX Bio

FLX Bio, Inc. is a cancer immunotherapy company focused on the discovery
and development of orally-available, small molecule drugs to activate
the immune system and eradicate cancer. Using its integrated
immuno-oncology drug discovery platform, FLX Bio’s small molecule
compounds specifically target proteins and pathways that selectively
inhibit regulatory T cells and myeloid cells within the tumor
microenvironment. Its lead candidate, a best-in-class CCR4 inhibitor,
has the potential to be used alone or in combination with checkpoint
inhibitors to treat a variety of cancers, and is expected to enter the
clinic in 2017.

Located in South San Francisco, Calif., and funded by leading investors,
including Kleiner Perkins Caufield & Byers (KPCB), The Column Group
(TCG), Topspin Partners and Celgene, FLX Bio has assembled a leadership
team and advisory group with a proven track record of success and team
of scientists with substantial knowledge and expertise in drug
discovery and translational areas essential to execute on this approach.
For more information, please visit www.flxbio.com.

Contacts

For FLX Bio, Inc.
Angela Bitting, 925-202-6211
media@flxbio.com