Abstract 3575: Novel targets and monoclonal antibodies for antibody-drug conjugate therapy

The study focuses on two novel potential therapeutic targets identified by an immune-histochemistry (IHC) screening with a large collection of polyclonal antibodies (approximately 1600) raised against marginally characterized human proteins. Here we describe the molecular characterization of two surface-exposed proteins (EXN91 and EXN36) associated to different cancer types. EXN91 is an adhesion molecule and it acts as a signaling receptor, cell communication and motility. Prevalence studies showed that the protein is mainly detected in colon cancer (CRC)with high frequency (approximately 90%), both in early and advanced colon cancer stages, with a statistical association for early cancer stages. Moreover, the protein is clearly surface exposed in liver metastasis from colon. Experiments are ongoing to assess whether EXN91 is also expressed in precancerous conditions of colon and rectum that have the potential to develop into cancer. Interestingly, EXN91 is over-expressed in KRAS and BRAF mutant CRC with high frequency. Moreover, an expanded IHC analysis revealed that it is also over-expressed and surface exposed in a number of other cancers, including HCC, RCC, bladder and endometrium cancer. Preliminary data showed that EXN91 behaves as an auto-antigen being able to induce specific autoantibodies in CRC patients. EXN36 is mainly over-expressed in ovary and breast cancers (frequency of approximately 30-40%), including triple negative breast cancer. EXN36 prevalence studies in different cancer entities are ongoing. Moreover, EXN36 is involved in cell proliferation, migration and invasiveness. Murine monoclonal antibodies (mAb) able to recognize EXN91 and EXN36 on the surface of cancer cells show potential for specific therapeutic indications. In particular, a murine mAb recognizes EXN91 on the surface of colon cancer cells, including KRAS and BRAF mutant CRC. This antibody inhibits growth of colon cancer in xenograft mouse models. Concerning anti-EXN36 antibodies, they are able to bind the surface of different breast and ovary cancer cells. EXN36 and EXN91 mAbs show a high number of binding sites on the cell surface. The mAb specificity has been confirmed in different immunoassays by gene silencing and peptide competition assays. Moreover, they show limited IHC reactivity in normal tissues. The anti-EXN36 and antiEXN91 antibodies are efficiently internalized by cancer cells, suggesting that they can be exploited for the development of Antibody-Drug-Conjuga