Five Prime Therapeutics Announces Preliminary FPA008 Phase 1 Data in Rheumatoid Arthritis Patients Presented at the 2015 ACR Annual Meeting

SOUTH SAN FRANCISCO, Calif., Nov. 10, 2015 (GLOBE NEWSWIRE) -- Five Prime Therapeutics, Inc. (Nasdaq:FPRX), a clinical-stage biotechnology company focused on discovering and developing novel protein therapeutics for cancer and inflammatory diseases, announced that preliminary data from part 3 of Five Prime's ongoing Phase 1 trial of FPA008 in rheumatoid arthritis (RA) patients were presented today at the 2015 American College of Rheumatology (ACR)/Association of Rheumatology Health Professionals Annual Meeting in San Francisco. FPA008 is Five Prime's anti-CSF1R antibody that blocks the binding of CSF1 and IL-34 ligands to CSF1R, resulting in inhibition of the activation and survival of inflammatory macrophages and osteoclasts.

The Phase 1 clinical trial of FPA008 is being conducted in three parts. Parts 1 and 2 involved dose administration and escalation in healthy volunteers and data on safety, pharmacokinetics (PK), and biomarkers from this portion of the study were presented during the 2014 ACR Annual Meeting. Part 3 of the trial consists of an open-label evaluation of 2 or 3 doses of FPA008 at 3 dose levels in RA patients on a stable dose of methotrexate who have not responded adequately to disease modifying anti-rheumatic drugs. The primary endpoint of the trial is safety, with secondary endpoints including PK, pharmacodynamics (PD) and disease activity as measured by ACR scores and joint MRI.

The poster entitled, "A Phase 1 Study of FPA008, an Anti-Colony Stimulating Factor 1 Receptor (anti-CSF1R) Antibody in Patients with Rheumatoid Arthritis (RA): Preliminary Results," included data as of October 16, 2015, from 12 RA patients in Part 3 of the trial. FPA008 was well tolerated up to 6 mg/kg x 2 doses, the highest dose level at the time of data cutoff. The most common FPA008 treatment-related adverse event was eyelid/periorbital edema, which is a class effect for compounds targeting the CSF1R pathway. The events were Grade 1 or 2, and were reversible. Compared to healthy volunteers, FPA008 appears to clear faster in RA patients and significant inter-patient variabilities were noted. Modulation of CD14+CD16++ non-classical monocytes and bone turnover markers and dose-dependent increases in serum CSF1 and IL-34 levels with FPA008 treatment observed in the trial demonstrate the anti-CSF1R effect. With limited doses administered, there was no preliminary evidence of a dose response in RA patients, as measured by ACR scores and MRI imaging. The trial continues to assess tolerability and PK in a final cohort of 6 mg/kg x 3 doses of FPA008.

"We were pleased that results to date further support FPA008's ability to inhibit CSF1R and modulate key biomarkers, and confirm its safety profile," said Julie Hambleton, MD, Chief Medical Officer of Five Prime. "While we aren't planning to proceed to the randomized portion of this trial or other trials in RA after completing the open-label portion of this study, the data we are gathering on safety, dosing and biomarker responses in RA patients are very important to the ongoing development of FPA008 in PVNS, a CSF1R-driven tumor affecting the joints, and in immuno-oncology."

The poster will be made available at http://www.fiveprime.com/news-media/publications-presentations.

About FPA008

FPA008 is an investigational antibody that inhibits CSF1R and has been shown in preclinical models to block the activation and survival of monocytes and macrophages. Early data have shown that inhibition of CSF1R in inflamed RA joints blocks the production of inflammatory cytokines by macrophages and inhibits osteoclasts, monocyte-lineage cells that can cause bone erosions and joint destruction. Inhibition of CSF1R in preclinical models of several cancers reduces the number of immunosuppressive tumor-associated macrophages (TAMs) in the tumor microenvironment, thereby facilitating an immune response against tumors. FPA008 is currently in phase 1 clinical trials in several immunology and oncology indications.

About Five Prime

Five Prime Therapeutics, Inc. discovers and develops innovative therapeutics to improve the lives of patients with serious diseases. Five Prime's comprehensive discovery platform, which encompasses virtually every medically relevant extracellular protein, positions it to explore pathways in cancer, inflammation and their intersection in immuno-oncology, an area with significant therapeutic potential and a growing focus of the company's R&D activities. Five Prime has entered into strategic collaborations with leading global pharmaceutical companies and has promising product candidates in clinical and late preclinical development. For more information, please visit www.fiveprime.com.

Cautionary Note on Forward-looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate," "estimate," "intend" and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements. These forward-looking statements are based on Five Prime's expectations and assumptions as of the date of this press release. Each of these forward-looking statements involves risks and uncertainties. Actual results may differ materially from these forward-looking statements. Factors that may cause actual results to differ from those expressed or implied in the forward-looking statements in this press release are discussed in Five Prime's filings with the U.S. Securities and Exchange Commission, including the "Risk Factors" contained therein. Except as required by law, Five Prime assumes no obligation to update any forward-looking statements contained herein to reflect any change in expectations, even as new information becomes available.

CONTACT: Amy Kendall,
         Corporate Communications
         415-365-5776
         amy.kendall@fiveprime.com

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