Abstract LB116: Prostaglandin F2 Receptor Negative Regulator (PTGFRN) is a novel target to inhibit tumor growth via antibody drug conjugate

Introduction: Antibody-drug conjugates (ADC) are effective antibody-based therapeutics for a growing number of cancers, particularly hematopoietic and lymphoid tumors. There is need to identify new targets for ADCs, particularly for cancers with unmet needs. Methods: Our strategy has been to develop hybridoma libraries developed against cancer cells surface proteins and select antibody able to bind and internalize in cancer cell lines. Selected antibody can then be used for identification of the cancer cell surface target by immunoprecipitation (IP) and mass spectrometric analysis (Mass-spec), followed by target validation. After target validation, binding and target positivity can be tested by flow cytometry and western blot analysis on several cancer cell lines. The in vitro and in vivo efficacy of the antibody conjugated to a cytotoxic payload as ADC can then be evaluated with the target positive cancer cell lines.Results: Using the strategy described above, we have selected a monoclonal antibody named 33B7 able to bind and internalize in several cancer cell lines. The cell surface target binding 33B7 was identified by IP/Mass-spec as Prostaglandin F2 Receptor Negative Regulator (PTGFRN), a transmembrane protein in the Tetraspanin family. This target was then validated by showing that cells transfected with PTGFRN cDNA bound and internalized the antibody. Screening by Flow bidning and by western blot identified several human cancer cells lines expressing PTGFRN. In vitro treatment of these cell lines with the 33B7-saporin ADC inhibited their proliferation in a dose-dependent fashion. 33B7 conjugated to saporin was also able to block tumor growth in vivo in mouse xenografts when compared to a control ADC. Conclusion: These findings show that screening antibody libraries for internalizing antibodies in cancer cell lines is a good approach to identify new cancer targets for ADC development. These results suggest PTGFRN is a possible therapeutic target via antibody-based approach for certain cancers. The elucidation of PTGFRN role in cancer cells, particularly in possibly mediating metastasis is presently being carried out. Citation Format: Jorge Marquez, Jianping Dong, Chun Dong, Ginette Serrero. Prostaglandin F2 Receptor Negative Regulator (PTGFRN) is a novel target to inhibit tumor growth via antibody drug conjugate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB116.