COBRA™: a highly potent conditionally active T cell engager engineered for the treatment of solid tumors

Abstract

Conditionally active COBRA™ (COnditional Bispecific Redirected Activation) T cell engagers are engineered to overcome the limitations of inherently active first-generation T cell engagers, which are unable to discern between tumor and healthy tissues. Designed to be administered as prodrugs, COBRAs target cell surface antigens upon administration, but engage T cells only after they are activated within the tumor microenvironment (TME). This allows COBRAs to be preferentially turned on in tumors while safely remaining inactive in healthy tissue. Here, we describe the development of the COBRA design and the characterization of these conditionally active T cell engagers. Upon administration COBRAs are engineered to bind to tumor-associated antigens (TAAs) and serum albumin (to extend their half-life in circulation), but are inhibited from interacting with the T cell receptor complex signaling molecule CD3. In the TME, a matrix metalloproteinase (MMP)-mediated linker cleavage event occurs within the COBRA construct, which rearranges the molecule, allowing it to co-engage TAAs and CD3, thereby activating T cells against the tumor. COBRAs are conditionally activated through cleavage with MMP9, and once active are highly potent, displaying sub-pM EC 50 s in T cell killing assays. Studies in tumor-bearing mice demonstrate COBRA administration completely regresses established solid tumor xenografts. These results strongly support the further characterization of the novel COBRA design in preclinical development studies.

Overcoming Challenges for CD3-Bispecific Antibody Therapy in Solid Tumors

“…Additionally, the masked variant greatly prolonged plasma concentrations at higher dosing concentrations. Very recently, Panchal et al described the development of conditional bispecific-redirected activation (COBRA) T-cell engagers [ 115 ]. This format separates the α-CD3 V H and V L via a matrix metallopeptidase 9 (MMP9)-degradable linker, thereby only allowing CD3 binding after linker cleavage, while constantly allowing EGFR and serum albumin binding (to increase half-life).…”

The Masking Game: Design of Activatable Antibodies and Mimetics for Selective Therapeutics and Cell Control

“… 62 − 65 (C) Approaches relying on the interaction with more conserved regions in the Fv could enable transferability to other antibody specificities and formats. 66 , 67 (D) Several strategies generally applicable to certain antibody formats have been developed relying on steric hindrance with variable degrees of inactivation efficiency. 68 − 72 (E) Masking via N-terminal coiled-coil domains is efficient and suggests high transferability to other antigen specificities.…”

“…Conditional T-cell engagers named COBRAs (Maverick Therapeutics) rely on the cleavage of an inactivating domain and subsequent dimerization of the active domains of an scFv to allow binding to CD3. 67 To the best of our knowledge, this is the only protease-sensitive strategy that involves allosteric disruption of the binding conformation rather than masking of the paratope. Despite its complexity, this system is functional in vivo as proven by its capacity to target T-cell-dependent cytotoxicity to HT-29 xenograft murine models, inducing complete tumor remission at modest doses.…”

Engineered Multifunctional Nano‐ and Biological Materials for Cancer Immunotherapy

“…All portions a–h show the different form factors that these antibodies can take on which allow for a variety of methods and strategies to be utilized in targeting receptors or ligands on both immune cells and cancer cells. The references for each of the following multispecific antibody forms are as follows: a [ 144 ] , b [ 147 ] , c [ 142 ] , d [ 149 ] , e [ 152 ] , f [ 135 ] , g [ 137 ] , and h [ 139 ] .…”

“…A hemi‐COBRA and full‐length COBRA structure have been synthesized that allows for an inactive version of the bispecific to only become active in the presence of specific proteolytic stimuli. [ 139 ] MMP2/9 is highly expressed in solid tumors and is regulated in healthy tissues, allowing for the active prodrug to target these areas. Hemi‐COBRAs were designed with two domains of scFvs for CD3 ε and EGFR.…”