Tumor-Localized Costimulatory T-Cell Engagement by the 4-1BB/HER2 Bispecific Antibody-Anticalin Fusion PRS-343

Abstract

Purpose: 4-1BB (CD137) is a key costimulatory immunoreceptor and promising therapeutic target in cancer. To overcome limitations of current 4-1BB-targeting antibodies, we have developed PRS-343, a 4-1BB/HER2 bispecific molecule. PRS-343 is designed to facilitate T-cell costimulation by tumorlocalized, HER2-dependent 4-1BB clustering and activation. Experimental Design: PRS-343 was generated by the genetic fusion of 4-1BB-specific Anticalin proteins to a variant of trastuzumab with an engineered IgG4 isotype. Its activity was characterized using a panel of in vitro assays and humanized mouse models. The safety was assessed using ex vivo human cell assays and a toxicity study in cynomolgus monkeys. Results: PRS-343 targets 4-1BB and HER2 with high affinity and binds both targets simultaneously. 4-1BB-expressing T cells are efficiently costimulated when incubated with PRS-343 in the presence of cancer cells expressing HER2, as evidenced by increased production of proinflammatory cytokines (IL2, GM-CSF, TNFa, and IFNg). In a humanized mouse model engrafted with HER2-positive SK-OV-3 tumor cells and human peripheral blood mononuclear cells, PRS-343 leads to tumor growth inhibition and a dose-dependent increase of tumor-infiltrating lymphocytes. In IND-enabling studies, PRS-343 was found to be well tolerated, with no overt toxicity and no relevant drug-related toxicologic findings. Conclusions: PRS-343 facilitates tumor-localized targeting of T cells by bispecific engagement of HER2 and 4-1BB. This approach has the potential to provide a more localized activation of the immune system with higher efficacy and reduced peripheral toxicity compared with current monospecific approaches. The reported data led to initiation of a phase I clinical trial with this first-in-class molecule. See related commentary by Su et al., p. 5732

Mechanistic Quantitative Pharmacology Strategies for the Early Clinical Development of Bispecific Antibodies in Oncology

“…For example, the initial clinical development of the agonistic 4‐1BB monospecific antibody urelumab was terminated due to fatal hepatotoxicity, with a maximum tolerated dose of 0.1 mg/kg q3w 18 . A 4‐1BB/HER2 bispecific molecule PRS‐343 is designed to facilitate T‐cell co‐stimulation by tumor‐localized, HER2‐dependent 4‐1BB clustering, and activation ( Figure ) 19 . In a phase I study in patients with HER2‐positive cancer, PRS‐343 demonstrated single‐agent antitumor activity, including partial responses, and was well‐tolerated at doses up to 8 mg/kg q2w 20 …”

Crosstalk between HER2 and PD-1/PD-L1 in Breast Cancer: From Clinical Applications to Mathematical Models

“…Currently, atezolizumab is the only FDA-approved immune checkpoint inhibitor for BC (TNBC) treatment. Out of many new drugs that are under clinical trial, margetuximab (MGA-H22) received FDA approval for fast track investigation on its potency to treat HER2 + metastatic BC [146][147][148]. This is a novel HER2-targeted monoclonal antibody tailored to enhance the binding affinity to multiple sites by mediating activation of Fc-γ receptors.…”

“…Developing mathematical models in terms of the biomarkers related to disease prognosis (e.g., PDL1 expression + high Tregs + less TILs = poor prognosis), and treatment response (e.g., presence of TILs favors response to trastuzumab) can help to identify patient cohorts that will benefit from a certain therapy [146].…”

An engineered 4-1BBL fusion protein with “activity-on-demand”

“…A FAP-targeted immunocytokine with trimeric single-chain 4-1BBL has recently started phase I clinical testing in cancer patients, but the product did not exhibit a conditional activation of the 4-1BBL moiety 84 . A fusion protein of trastuzumab with a 4-1BB-specific anticalin™ has been described 85 , which had shown antigen-dependent modulation of 4-1BB agonistic activity in vitro and which has recently started clinical trials 85 .…”

“…The approach described in this article should be generally applicable to members of the TNF superfamily. Alternative approaches may involve bispecific antibodies 93,94 , the modular use of small protein domains 85,95 or of chemically-modified bicyclic peptides 96 . Members of the TNF receptor superfamily are particularly suited for cooperative activation strategies in view of their homotrimeric structure and clustering-driven activation properties [97][98][99] .…”