FS222, a CD137/PD-L1 Tetravalent Bispecific Antibody, Exhibits Low Toxicity and Antitumor Activity in Colorectal Cancer Models

Abstract

Purpose: With the increased prevalence in checkpoint therapy resistance, there remains a significant unmet need for additional therapies for patients with relapsing or refractory cancer. We have developed FS222, a bispecific tetravalent antibody targeting CD137 and PD-L1, to induce T-cell activation to eradicate tumors without the current toxicity and efficacy limitations seen in the clinic. Experimental Design: A bispecific antibody (FS222) was developed by engineering CD137 antigen-binding sites into the Fc region of a PD-L1 IgG1 mAb. T-cell activation by FS222 was investigated using multiple in vitro assays. The antitumor efficacy, survival benefit, pharmacodynamics, and liver pharmacology of a murine surrogate molecule were assessed in syngeneic mouse tumor models. Toxicology and the pharmacokinetic/pharmacodynamic profile of FS222 were investigated in a non-human primate dose-range finding study. Results: We demonstrated simultaneous binding of CD137 and PD-L1 and showed potent T-cell activation across CD8 þ T-cell activation assays in a PD-L1-dependent manner with a CD137/PD-L1 bispecific antibody, FS222. FS222 also activated T cells in a human primary mixed lymphocyte reaction assay, with greater potency than the monospecific mAb combination. FS222 showed no signs of liver toxicity up to 30 mg/kg in a non-human primate dose-range finding study. A surrogate molecule caused significant tumor growth inhibition and survival benefit, concomitant with CD8 þ T-cell activation, in CT26 and MC38 syngeneic mouse tumor models. Conclusions: By targeting CD137 agonism to areas of PD-L1 expression, predominantly found in the tumor microenvironment, FS222 has the potential to leverage a focused, potent, and safe immune response augmenting the PD-(L)1 axis blockade.

Systematic analysis of CD39, CD103, CD137 and PD-1 as biomarkers for naturally occurring tumor antigen-specific TILs

“…The response rate to anti-PD-1 antibody treatment in ovarian cancer nearly triples when a CTLA-4 blocking antibody is added to the treatment regimen 37 . Furthermore, agonizing CD137 may aid in promoting antitumor responses in patients, and although CD137 agonism in the clinic has had toxicities 33,34 , dual bispecific antibodies that agonize CD137 are being developed in order to enhance T cell proliferation and antitumor activity in human cancer without the safety limitations observed in the clinic 35,36 . The recently developed CD137/OX40 bispecific antibody 35 may be promising to test in an ovarian cancer model, as we observed that effector molecule expressing CD137 + TILs also co-expressed OX40 ( Figure 2A ).…”

“…The recently developed CD137/OX40 bispecific antibody 35 may be promising to test in an ovarian cancer model, as we observed that effector molecule expressing CD137 + TILs also co-expressed OX40 ( Figure 2A ). Future studies are needed to determine if CD137 + TILs are reinvigorated by anti-PD-1 therapy, whether they require CD28 signaling, and how they contribute to successful immune checkpoint blockade monotherapy or combinatorial immunotherapy strategies 35,36 .…”

Intratumoural administration and tumour tissue targeting of cancer immunotherapies

“…Hence, co-targeting with natural co-stimulatory ligands or mAb agonists of co-stimulatory receptors is of interest because of its potential to provide signal 2 for full T cell activation. In this regard, interesting bispecific agents have been developed that integrate anti-fibroblast activated protein (FAP) 221 or anti-PD-L1 antibodies 222 (for tumour targeting) with the receptor-binding regions of CD137 ligand (for co-stimulation of T cells via binding to CD137). One such agent has already entered clinical testing in combination with the anti-PD-L1 antibody atezolizumab (NCT03869190); however, combination with CD3-targeted BiTEs is perhaps a more relevant approach following the observation of potent synergy in preclinical xenograft models 221 .…”

Generation of a safe and efficacious llama single-domain antibody fragment (vHH) targeting the membrane-proximal region of 4-1BB for engineering therapeutic bispecific antibodies for cancer

“…One strategy to reduce their liver-related on-target effects has been to optimize FcγR binding to FcγRs that are normally enriched in tumors, 16 but next-generation bispecific antibodies have an advantage through crosslinking 4-1BB receptors only in the presence of tumor-associated antigens (TAAs) through cross-bridging, and various programs are currently entering the clinic targeting TAAs such as epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2). [19][20][21][22] PD-L1 (CD274, B7-H1), one of the ligands for PD-1, is a checkpoint regulator that restrains T cell activation during antigen presentation and effector function. PD-L1 expression has been identified in a wide variety of solid tumors, which makes it a potential TAA for PD-L1/4-1BB bispecific antibody development.…”

“…PD-L1/4-1BB bispecific antibodies could therefore combine PD-L1 blockade and 4-1BB agonism to provide a substantial survival benefit in multiple mouse tumor models with low/ no toxicity. 22 Here, we report the discovery and development of a bispecific antibody towards PD-L1 and 4-1BB (PM1003). PM1003 potently blocks the interaction between PD-1 and PD-L1 and binds to 4-1BB at the CRD4 domain allowing for effective dose-dependent activation of 4-1BB in the presence of PD-L1, with minimal toxicity.…”