Ovarian cancer (OC) is the deadliest gynecologic malignancy, with the highest mortality among cancers of the female reproductive system. Because of the close interaction between the OC cells and tumor microenvironment (TME), development of approaches which not only target tumor cells but also can maintain their anti-tumor function in this TME is of high importance. Uniquely, Follicle stimulating hormone receptor (FSHR) represents such an important target with specificity for OC and ovarian granulosa cells. We have recently developed monoclonal antibodies (mAbs) that specifically recognize human FSHR on the surface of multiple OC. We characterized them, selected potent anti-FSHR mAb: D2AP11 for detailed investigation and immune engineering in the form of a bispecific T cell engager (D2AP11-TCE) (Bordoloi et al., JCI Insight, 2022). Since most OCs are extremely aggressive and have restricted treatment choices, engaging additional immune effector components may further help. We have developed mAbs against PAN NK marker; Siglec 7 in humanized mice. We identified several Siglec-7 mAbs through high throughput screening and down-selected the pertinent clones. By using a highly potent anti-Siglec-7 clone DB7.2, we have developed a novel NK cell engager (NKCE): DB7.2xD2AP11 NKCE, by linking two antibody binding fragments (scFVs) arranged to bind FSHR, the OC antigen and hman Siglec-7, the NK marker. The NKCE was efficiently expressed in vitro and showed potent binding to both FSHR overexpressing K562 cells as well as Siglec-7 overexpressed HEK293T cells. This novel NKCE resulted in robust and specific killing of multiple OC targets in vitro in the presence of human PBMCs or NK cells, from multiple donors. The OC targets evaluated for killing by the NKCE include high grade serous adenocarcinoma, ovarian clear cell adenocarcinoma and ovarian cystadenocarcinoma lines which carry different mutations; BRCA1&2, AKT, TP53, PIK3CA, BRAF etc. and exhibit resistance against a wide array of cancer drug targets; PARP, HSP90, HDAC, MTORC, DNA alkylating agents, EGFR, PI3K, and WEE1, among others. DB7.2xD2AP11 NKCE displayed killing with EC50-142.87 pM and 236.6 pM against target OVISE-FSHR and OVCAR3 cells respectively, indicating its potency. Further, DNA encoded DB7.2xD2AP11 NKCE significantly attenuated the tumor burden in OVCAR3-FSHR and OVISE challenged humanized mice model. Additionally, this novel NKCE significantly enhanced the median survival of OVCAR3-FSHR challenged mice, suggesting in vivo potency. These data support further research on this novel NKCE as crucial tools for treating OC as well as targeted therapies for other malignancies. Of note, it is the first study of the development of Siglec-7 or any Siglec family member as a bispecific immune engager for targeted immunotherapy.

Citation Format: Devivasha Bordoloi, Abhijeet J. Kulkarni, Opeyemi S. Adeniji, Pratik S. Bhojnagarwala, Shushu Zhao, Candice Ionescu, Mohamed bdel-Mohsen, David B. Weiner. A novel bispecific NK cell engager targeting FSHR and Siglec-7 displays potent anti-tumor immunity against ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr PR-006.