Thomas Brennan

Abstract 5449: FP-1039/GSK3052230, an FGF ligand trap, enhances VEGF antagonist therapy in preclinical models of RCC and HCC

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA An increasing body of evidence has implicated FGF2 as one of the drivers of resistance to various inhibitors of VEGF-mediated angiogenesis. This resistance may play a role as a key limitation to the efficacy of therapies targeted at VEGF and its receptors. We investigated the potential for FP-1039/GSK3052230, a ligand trap that sequesters FGFs and inhibits their signaling, to enhance the activity of VEGF antagonist therapies in certain preclinical models of renal cell (RCC) and hepatocellular (HCC) carcinomas. First, we examined whether FP-1039/GSK3052230 has single agent efficacy against human RCC and HCC xenografts that express relatively high levels of FGF2, a profile that would mimic FGF2-driven resistance to VEGF therapy. We determined that this expression profile represents 34% of clear cell RCC (ccRCC) and 31% of HCC patients, based on the cancer genome atlas (TCGA) data. Human ccRCC xenografts with high FGF2 expression and low VEGFA expression demonstrated a significant inhibition in tumor growth when treated with FP-1039/GSK3052230 alone (TGI: 39-81%). In addition, we show that the high FGF2 expression profile is similarly predictive for the anti-tumor response of a human HCC model to single-agent FP-1039/GSK3052230 (TGI: 31-55%). In contrast, RCC models with low FGF2 expression, representing 66% of all ccRCC in the TCGA, are relatively insensitive to FP-1039/GSK3052230 as a single-agent. However, combination therapy of FP-1039/GSK3052230 with pazopanib in these tumors is significantly more effective than either agent alone. FP-1039/GSK3052230 not only slows tumor growth, but can induce ∼25% tumor regression when administered to mice bearing ccRCC xenografts that have become resistant to pazopanib. Together, our data demonstrate that FP-1039/GSK3052230 may be an effective therapy against RCC and HCC, both as a single agent in disease driven by FGF2 and in combination with VEGF antagonist therapies that represent the current standards of care for advanced disease. Citation Format: David I. Bellovin, Servando Palencia, Kevin Hestir, Ernestine Lee, M. Phillip DeYoung, Thomas Brennan, Gerrit Los, Kevin Baker. FP-1039/GSK3052230, an FGF ligand trap, enhances VEGF antagonist therapy in preclinical models of RCC and HCC. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5449. doi:10.1158/1538-7445.AM2014-5449

Abstract 5446: FPA144: A therapeutic antibody for treating patients with gastric cancers bearing FGFR2 gene amplification

A subset of patients with gastric cancer have an amplification of the receptor tyrosine kinase fibroblast growth factor receptor 2 (FGFR2) gene. The amplification is most common in the diffuse type of gastric cancer and its presence correlates with poor patient prognosis. Although it has been reported that there is high expression of FGFR2 protein in patients with the amplification, it has been unknown which of the two major FGFR2 isoforms, FGFR2b or 2c, is expressed. In this study, we demonstrate, by both qPCR and immunohistochemistry using FGFR2b-selective antibodies, that it is the FGFR2b isoform, and not FGFR2c, that is overexpressed in gastric cancer tumors that contain the FGFR2 amplification. Five Prime Therapeutics has developed an FGFR2b-specific antibody, FPA144, to treat patients with gastric cancers bearing amplification of the FGFR2 gene. FPA144 is glycoengineered for enhanced antibody-dependent cell cytotoxicity (ADCC). FPA144 causes tumor growth inhibition by 72% to 100% in gastric cancer xenograft models with FGFR2 gene amplification that overexpress the FGFR2b protein isoform. In the SNU-16 model, FPA144 reduces the levels of FGFR2b protein expressed in the tumors by approximately 50%, and decreases both FGFR2b phosphorylation and phosphorylation of the downstream effector, FRS2. The anti-tumor effect of FPA144 is additive with the standard of care chemotherapy regimens of 5-fluoruracil/cisplatin and paclitaxel in the OCUM-2 gastric cancer xenograft model. Since FPA144, unlike small molecule FGFR tyrosine kinase inhibitors, blocks signaling by only the FGFR2b and not the other FGFRs, we expect a favorable toxicology profile, either alone or in combination with chemotherapy. In addition, by engaging immune effector cells for direct tumor cell killing, FPA144 has a second mechanism of action that small molecule FGFR tyrosine kinase inhibitors do not have. We anticipate starting clinical trials of FPA144 in the last quarter of 2014. Citation Format: Abigael T. Gemo, Amit M. Deshpande, Servando Palencia, David I. Bellovin, Thomas J. Brennan, Namrata S. Patil, Carol Huang, Gerrit Los, Kristen L. Pierce. FPA144: A therapeutic antibody for treating patients with gastric cancers bearing FGFR2 gene amplification. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5446. doi:10.1158/1538-7445.AM2014-5446

Abstract 2633: Identification of novel T cell co-inhibitory and co-stimulatory receptors from screening a comprehensive library of extracellular proteins

Antibody blockade of immune checkpoint regulators such as PD-1 and CTLA-4 has been shown to be an effective cancer treatment strategy; however, a large percentage of patients still do not respond to existing therapies. Discovery of additional immune checkpoints and co-stimulatory receptors and development of antibody therapeutics against them are likely critical to address this unmet patient need. We generated a comprehensive library of essentially all human extracellular proteins and have used this library to screen for new agents that modulate the function of various immune cell subsets both in vitro and in vivo. Using primary T effector and regulatory T cells, we have identified new targets that modulate the activities of these T cell populations in vitro and are currently evaluating these proteins as possible targets for cancer immunotherapy. In addition, we have expressed a subset of the library in three different models of tumor-bearing mice and have identified several proteins that modulate anti-tumor immunity in vivo. Several of the proteins identified in these screens have activity across multiple primary cell and in vivo tumor model screens and we are rapidly evaluating them as possible targets for novel immuno-oncology therapeutics. Taken together, we believe that we have developed robust in vitro and in vivo platforms that will allow us to discover novel cancer immuno-therapeutics that will help address the needs of cancer patients that fail to respond to current immunomodulatory therapies. Citation Format: Arthur Brace, Nathan Sallee, Justin Chou, Lindsay Garrenton, Diana Chen, Ryan Liang, Greg Kemper, David Yang, Marina Jaquez, Janine Powers, Mikayel Mkrtichyan, Thomas Brennan, Luis Borges. Identification of novel T cell co-inhibitory and co-stimulatory receptors from screening a comprehensive library of extracellular proteins [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2633. doi:10.1158/1538-7445.AM2017-2633

cmFPA008, an anti-mouse CSF-1R antibody, combines with multiple immunotherapies to reduce tumor growth in nonclinical models

The colony stimulating factor 1 receptor (CSF1R) signaling pathway drives the recruitment, differentiation, and survival of tumor-associated macrophages (TAMs) in the neoplastic microenvironment, promoting tumor progression and modulation of the immune response. As such, CSF1R represents an intriguing therapeutic target for immuno-oncology. FivePrime has developed FPA008, an IgG4 antibody with high affinity (KD = 0.35 nM) for CSF1R and the ability to block binding of both CSF1 and IL-34 to this receptor. In order to interrogate the impact of CSF1R signaling inhibition on tumor growth and the immune environment, we generated a surrogate antibody, cmFPA008, which targets mouse CSF1R and demonstrates equivalent affinity and ligand-blocking ability as FPA008. Consistent with other reports on molecules targeting this pathway, cmFPA008 as monotherapy results in statistically significant but modest growth inhibition in multiple preclinical tumor models, including MC38 colon adenocarcinoma and B16 melanoma. Utilizing a combination of flow cytometric, immunohistochemical, and gene expression analyses, we show that CSF1R inhibition induces dramatic reduction of TAMs and an increase in the CD8+ T cell to regulatory T cell ratio in syngeneic tumor models. Given that the regulation an anti-tumor immune response is complex, effective cancer therapy may require combining multiple immunotherapy agents. We sought to determine whether inhibition of CSF1R when combined with other immuno-oncology therapeutics enhanced the anti-tumor impact. We observed increased PD-L1 (CD274) expression in the tumor after treatment with cmFPA008 monotherapy, thereby providing a rationale for a combination of FPA008 with a compound targeting the PD-1 pathway. Our results show that cmFPA008 significantly enhances anti-tumor efficacy when combined with an anti-PD1 therapeutic in multiple syngeneic tumor models. In addition, we show that co-administration of cmFPA008 with an agonist anti-CD40 significantly enhances tumor suppression compared to either therapy alone. Changes in tumor-infiltrating lymphocyte (TIL) populations upon treatment provide important insight into the mechanism of action of cmFPA008 monotherapy and in combination with other immunotherapies. These results provide support for ongoing clinical efforts to evaluate FPA008 as an anti-cancer immunotherapy, particularly in combination with other immuno-oncology therapeutics. FivePrime has planned a clinical trial in collaboration with Bristol-Myers Squibb (BMS) to investigate the efficacy of FPA008 in combination with the anti-PD1 therapeutic Opdivo® (nivolumab) in six tumor types.

Identification of a novel immune checkpoint regulator and potential therapeutic antibody target in oncology

Antibody blockade of immune checkpoint regulators such as PD-1 and CTLA4 has been shown to be an effective cancer treatment strategy; however, a large percentage of patients still do not respond to existing therapies. Discovery of additional immune checkpoints and development of antibody therapeutics against them are likely critical to address this unmet patient need. We generated a comprehensive library of essentially all human extracellular proteins and screened proteins in this library in vitro and in vivo for the ability to modulate immune responses or tumor growth. As a result of these screens, we identified a number of novel immune checkpoints1. One such protein, referred to herein as Novel Checkpoint 1, was originally identified through its inhibitory activity on anti-CD3-stimulated human T cell proliferation. To confirm its activity as an immune checkpoint, we demonstrated that the native protein expressed on an antigen-presenting cell line could inhibit antigen-stimulated CD8+ T cell activation. Furthermore, blocking antibodies against this protein relieved the inhibition. This inhibitory activity translated to a murine system, as the mouse ortholog and blocking antibodies behaved similarly in murine T cell activation assays. Overexpression of the protein in mouse syngeneic tumor models resulted in increased tumor growth, consistent with inhibition of anti-tumor immune responses. Novel Checkpoint 1 is expressed primarily on activated and regulatory T cells in humans and mice – an expression profile similar to those of PD-1 and CTLA4. Additionally, it is expressed on 40-70% of tumor-infiltrating T cells while only on 10-15% of circulating T cells from those tumor-bearing mice. We are currently evaluating the anti-tumor activity of blocking antibodies in mouse tumor models, either alone or in combination with other checkpoint blocking antibodies. Taken together, we believe that these data demonstrate that this newly discovered protein may act as a checkpoint regulator in tumors and that blocking antibodies against it have potential as a novel cancer immunotherapeutic.