Company: ERAS
Filing Date: 2025-03-20
Form Type: 10-K
Source: 0000950170-25-042682
Chunk: 37

Company: Erasca, Inc.
Filing Date: 2025-03-20
Form: 10-K
Item: Item 1
Chunk 37
---
 efficacious. 

Biparatopic antibodies are a subset of bispecific antibodies that have specificity for unique, non-overlapping epitopes found on the same molecular target. We are developing a bpAb that targets these two distinct domains on the EGFR receptor, which allows the antibody to inhibit both the ligand binding and dimerization functionality of the receptor.

Diagram (A) visualizes the EGFR antibody ER-2a binding to the extracellular domain II of EGFR wildtype (purple), which is accessible when EGFR is in the active state. EGFR assumes an active state conformation when its ligand is bound (the bound ligand is shown in blue). Diagram (B) visualizes the EGFR antibody ER-3a binding to the extracellular domain III of EGFR wildtype (purple), which is accessible when EGFR is in the inactive state. In the rectangle, the portion of ER-2b that recognizes domain II of EGFR and the portion of ER-3b that recognizes domain III of EGFR are combined into a bispecific antibody that binds EGFR in both states.

This dual inhibition can potentially achieve differentiated and potentially more effective EGFR inhibition than currently approved EGFR antibodies. Overall, we anticipate this strategy will result in better control of tumor growth and delay the emergence of resistance mechanisms. 

ERAS-12 is also designed with enhanced Fc-effector functions, including complement dependent cytotoxicity, antibody dependent cellular cytotoxicity, and antibody dependent cellular phagocytosis. The Fc region of IgG1 contains several binding sites for immune effector cells (i.e., Fcγ) and the classical complement protein C1q.  As noted, this antibody is biparatopic, binding to both D2 and D3 of EGFR. This potentially can produce oligomerized EGFR-antibody structures on the cell surface. Complexes of this type can amplify Fc-effector functions creating multiple mechanisms to induce tumor cell death.

The biparatopic antibody ER-3a/ER-2a and EGFR active state-binding antibody ER-2a inhibited cell growth in FaDu, an HNSCC cell line, and HCT-8, a CRC cell line, and the NSCLC cell line H1975. FaDu and HCT-8 expressed wildtype EGFR and H1975 expressed EGFR with two kinase domain mutations, L858R and T790M. EGFR’s ligand, EGF, was added to