靶向间皮素膜近端区域并在可溶性间皮素存在下保持高抗癌活性的双特异性抗体

Mesothelin (MSLN) is a cell-surface protein that is expressed in many cancers, which makes it a popular target for Ab-based cancer therapy.

However, MSLN is shed from cancer cells at high levels via proteases that cleave at its membrane-proximal C-terminal region. Shed MSLN accumulates in patients' fluids and tumors and can block Ab-based MSLN-targeting drugs from killing cancer cells. A previously established mAb, 15B6, binds MSLN at its protease-sensitive C-terminal region and does not bind shed MSLN.

Moreover, 15B6 variable fragment (Fv)-derived chimeric antigen receptor T cells are not inhibited by shed MSLN and kill tumors in mice more effectively than mAb SS1 Fv-derived chimeric antigen receptor T cells, which bind an epitope retained in shed MSLN. In this study, we have established 15B6 Fv-derived MSLN × CD3 bispecific antibodies (BsAb) that target MSLN-expressing cancers.

We identified our lead candidate BsAb 5 after screening multiple 15B6-derived BsAb formats in vitro for cytotoxic activity. BsAb 5 activates T cells to kill various cancer cell lines in a MSLN-specific manner. MSLN 296-591 His, a recombinant protein mimicking shed MSLN, does not inhibit 15B6-derived BsAb 5 but completely inhibits humanized SS1-derived BsAb 7.

Furthermore, BsAb 5 inhibits and delays tumor growth and is not inhibited by MSLN 296-585 His in mice.

Our findings indicate that by targeting the protease-sensitive region of MSLN, BsAb 5 has high MSLN-specific anticancer activity that is not inhibited by shed MSLN. BsAb 5 may be a promising immunotherapy candidate for MSLN-expressing cancers.