396P - Evaluation of MUC1-C/CD3 biparatopic-bispecific (BPBS) T cell engager as an immunotherapeutic agent for the treatment of MUC1-expressing metastatic breast cancer (mBC)

Background

MUC1 is a heterodimeric oncoprotein overexpressed in >85% of mBC cell surface and an attractive tumor associated antigen. Biparatopic antibodies have recently emerged as promising class of immunotherapeutic agents that show higher apparent affinity and potent antitumor efficacy. However, identification of non-competing antibodies against the MUC1-C antigen has proven to be challenging because of the small extracellular domain (58 AA). Leveraging novel immunization strategies, we have generated unique biparatopic MAb (3D1-XY017), which was coupled with CD3 to generate an exciting BPBS T-cell engager product (3D1-XY017/CD3).

Methods

Biparatopic MAb from the XY017 and 3D1 antibodies was fused with CD3 MAb to the C-terminal and constructs optimization was done to obtain specific chain combination for the productive format. Biophysical and cellular characterization was performed to ascertain that the BPBS MAb retained binding to the non-competing epitopes on MUC1 antigen and to the CD3 antigen.

Results

The purity of the BPBS protein was more than 98% when analyzed by both SDS-PAGE and SEC-HPLC. Strong binding of BPBS MAb was obtained with its respective antigens. Purified BPBS MAb exhibited binding to MUC1 on the mBC cells and CD3 on the T cells. Functional analysis was determined for cytotoxicity using MUC1⁺ mBC cells as the target cells. The results demonstrate, induction of cytotoxic activity of T cell as measured using a Jurkat T cell line engineered to express luciferase reporter gene under the control of NFAT that is linked to T-cell activation. Preliminary in-vivo data suggest that this novel MUC1-C BPBS drug product exhibits potent antitumor activity against ZR-75-1 mBC xenografts.

Conclusions

These findings demonstrate that MUC1-C-3D1/MUC1-C XY017/CD3 BPBS T-cell engager is capable of inducing a potent mobilization of lymphocyte cytotoxic functions against cancer cells and can be developed as a novel therapeutic for mBC.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

XYone Therapeutics Inc.

Funding

XYone Therapeutics Inc.

Disclosure

R. Jasuja: Financial Interests, Personal, Officer: XYone Therapeutics Inc. D. Raina: Financial Interests, Personal, Other: XYone Therapeutics Inc. R. Ahmad: Financial Interests, Personal, Other: XYone Therapeutics Inc. S. Choudhary: Financial Interests, Personal, Other: XYone Therapeutics Inc. G. Panchamoorthy: Financial Interests, Personal, Other: XYone Therapeutics Inc. S. Kharbanda: Financial Interests, Personal, Officer: XYone Therapeutics Inc. All other authors have declared no conflicts of interest.