Five Prime Therapeutics Announces New Pre-Clinical Data on FPA144 Presented at the 2016 AACR Annual Meeting

  • Engineering of FPA144 for ADCC drives both innate and adaptive responses 
  • Recruitment of Natural Killer (NK) and T cells into the tumor and regression of tumor growth in vivo 
  • FPA144 may have additional anti-tumor activity when combined with PD-1 blockade
  • FPA144 findings to date suggest opportunity to explore combination therapy approaches and additional tumor types beyond gastric cancer

SOUTH SAN FRANCISCO, Calif., April 18, 2016 (GLOBE NEWSWIRE) -- Five Prime Therapeutics, Inc. (Nasdaq:FPRX), a clinical-stage biotechnology company focused on discovering and developing innovative immuno-oncology protein therapeutics, announced that new preclinical data on FPA144 were featured today in a poster presentation from 8 AM to 12 PM (CDT) during the 2016 American Association for Cancer Research (AACR) Annual Meeting, being held April 16-20, in New Orleans.

The poster titled "FPA144, a Therapeutic Monoclonal Antibody Targeting the FGFR2b Receptor, Promotes Antibody Dependent Cell-Mediated Cytotoxicity and Stimulates Sensitivity to PD-1 in the 4T1 Breast Tumor Model in Mice" will be made available on the publications page of the Five Prime website.

"The ability of FPA144 to both recruit and drive an innate response with NK cells followed by an adaptive response with T cells is new and striking biology," said Drew Pardoll, M.D., Ph.D., Seraph Professor of Oncology, Medicine, Pathology and Molecular Biology and Genetics at the Johns Hopkins University of Medicine. "Driving this immune cascade in a patient's tumor could provide a new therapeutic mechanism for treating solid tumors."

FPA144 is an FGFR2b-specific humanized monoclonal antibody designed to treat patients with cancers that overexpress FGFR2b. FPA144 is a targeted immunotherapy that Five Prime engineered to recruit NK cells into the tumor microenvironment and kill cancer cells by antibody-dependent cell-mediated cytotoxicity (ADCC).

"We are excited by the results we've seen in this model. Surprisingly, they suggest that FPA144 can drive an anti-tumor response that involves multiple immune cell types. The upregulation of PD-L1 suggests that combination with an anti-PD-1 agent could yield even more activity," said Robert Sikorski, M.D., Ph.D., Senior Vice President of Global Clinical Development at Five Prime. "Based on these results and the preliminary clinical data we reported in January, we are considering opportunities to evaluate FPA144 in immuno-oncology combination therapies and in tumors types beyond gastric cancer, including those with moderate levels of FGFR2b expression."

Five Prime evaluated the immune cell recruitment and anti-tumor effects of FPA144 in the orthotopic 4T1 model of breast cancer.  In this model, the FGFR2 gene is not amplified and tumor cells express only moderate levels of FGFR2b. Doses of FPA144 or FPA144 N297Q (a modified antibody lacking Fc effector function) were administered at Day 0 and Day 3 and tumor histology and FACS were conducted at Day 1 and Day 4. The following was observed with FPA144 treatment:

24 Hours Post 1st Dose 24 Hours Post 2nd Dose
NK cell infiltration within the tumor Persistence of NK cells
Increase in PD-L1-positive cells within the tumor   Persistence of PD-L1-positive cells  
No change in T cells Increase in T cells within the tumor

Furthermore, therapeutic treatment with FPA144 in this model resulted in a reduction in tumor burden (33%, P<0.001), while FPA144 N297Q neither inhibited tumor growth nor led to the recruitment of NK cells. These data provide further evidence of the ability of FPA144 to increase NK and T cell numbers within a tumor and suggest that its enhanced ADCC activity may play an important mechanistic role in anti-tumor efficacy in cancers with modest FGFR2b expression.

Additionally, the 4T1 model was used to evaluate the anti-tumor effect of FPA144 alone and in combination with an anti-PD-1 antibody (RMP1-14). Following biweekly dosing, tumor volume was assessed at day 19. Although anti-PD-1 treatment alone did not inhibit tumor growth, treatment with anti-PD-1 in combination with FPA144 inhibited tumor growth by 49% (P<0.001). Collectively, these results suggest that FPA144 alters the immune cell composition of the tumor microenvironment in a way that primes the tumor to respond to anti-PD-1 therapy, and an additive anti-tumor effect is observed when FPA144 is combined with PD-1 blockade.

Dose expansion is ongoing in the Phase 1 monotherapy trial of FPA144 in patients with gastric cancer, a disease in which FGFR2b protein overexpression and FGFR2 gene amplification have been associated with poor prognosis. Preliminary data showing anti-cancer activity during the dose escalation portion of the trial were presented at the American Society of Clinical Oncology (ASCO) Gastrointestinal Cancers Symposium in January 2016.  Updated data from the trial have been accepted for oral presentation during the ASCO Annual Meeting in June 2016.

About FPA144
FPA144 is an anti-FGF receptor 2b (FGFR2b) humanized monoclonal antibody in clinical development as a targeted immune therapy for tumors that over-express FGFR2b, as determined by a proprietary immunohistochemistry (IHC) diagnostic assay. FPA144 is designed to block tumor growth through two distinct mechanisms. First, it binds specifically to FGFR2b and prevents the binding of certain fibroblast growth factors that promote tumor growth. Second, it has been engineered to drive immune-based killing of tumor cells by antibody-dependent cell-mediated cytotoxicity (ADCC) and the recruitment of natural killer (NK) cells. FGFR2 gene amplification (as identified by FISH) is found in a number of tumors, including in approximately 5% of gastric cancer patients, and is associated with poor prognosis. 

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 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.

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