A Novel Bispecific Antibody for EpCAM-Directed Inhibition of the CD73/Adenosine Immune Checkpoint in Ovarian Cancer

SIMPLE SUMMARY: Blockade of the immunosuppressive CD73/ADO immune checkpoint has been suggested as a promising alternate immunotherapeutic approach for refractory ovarian cancer (OC). Despite promising preclinical results, midterm clinical trial reports indicate that the efficacy of the CD73-blocking antibody oleclumab is modest. The limited efficacy of oleclumab may be related to the fact that it indiscriminately binds to and blocks CD73 that is present in a massive surplus of normal cells. The aim of our study was to achieve a tumor-directed inhibition of the CD73 immune checkpoint on OC cells. To this end, we constructed a novel bispecific antibody, bsAb CD73xEpCAM, that blocks the CD73 immune checkpoint in an EpCAM-directed manner. Moreover, treatment of OC cells with bsAb CD73xEpCAM inhibited various pro-oncogenic features. Taken together, bsAb CD73xEpCAM may be useful as an alternate and more tumor-directed immunotherapeutic approach to overcome the CD73-mediated immunosuppression in OC patients. ABSTRACT: PD-1/PD-L1-inhibiting antibodies have shown disappointing efficacy in patients with refractory ovarian cancer (OC). Apparently, OC cells exploit nonoverlapping immunosuppressive mechanisms to evade the immune system. In this respect, the CD73-adenosine inhibitory immune checkpoint is of particular interest, as it rapidly converts pro-inflammatory ATP released from cancer cells to immunosuppressive adenosine (ADO). Moreover, cancer-cell-produced ADO is known to form a highly immunosuppressive extra-tumoral ‘halo’ that chronically inhibits the anticancer activity of various immune effector cells. Thus far, conventional CD73-blocking antibodies such as oleclumab show limited clinical efficacy, probably due to the fact that it indiscriminately binds to and blocks CD73 on a massive surplus of normal cells. To address this issue, we constructed a novel bispecific antibody (bsAb) CD73xEpCAM that inhibits CD73 expressed on the OC cell surface in an EpCAM-directed manner. Importantly, bsAb CD73xEpCAM showed potent capacity to inhibit the CD73 enzyme activity in an EpCAM-directed manner and restore the cytotoxic activity of ADO-suppressed anticancer T cells. Additionally, treatment with bsAb CD73xEpCAM potently inhibited the proliferative capacity of OC cells and enhanced their sensitivity to cisplatin, doxorubicin, 5FU, and ionizing radiation. BsAb CD73xEpCAM may be useful in the development of tumor-directed immunotherapeutic approaches to overcome the CD73-mediated immunosuppression in patients with refractory OC.