Abstract LB406: Synergistic antitumor effect of FRα TOP1i antibody drug conjugate, AZD5335, in combination with the PARP1 inhibitor, saruparib (AZD5305), in preclinical models of ovarian cancer

Abstract Folate receptor alpha (FRα) is a cell surface GPI-anchored protein overexpressed in several solid tumors with highest prevalence in ovarian cancer and lung adenocarcinoma but restricted expression in normal tissues. AZD5335, an FRα-targeting antibody conjugated to AZ’s proprietary topoisomerase 1 inhibitor (TOP1i) payload, AZ14170132, is currently being investigated in the FONTANA Phase 1/2 clinical trial (NCT05797168). Since homologous recombination repair deficiency (HRD) and mutations in genes involved with homologous recombination repair (HRRm+) are associated with sensitivity to DNA damaging agents, we evaluated the efficacy of AZD5335 in ovarian cancer patient-derived xenograft (PDX) models assessed for HRRm, as described1. Sixteen ovarian cancer PDX models were each treated with a single dose of AZD5335 (5 mg/kg IV). Of the HRRm- cohort, 8/11 (73%) cohort responded to treatment with a tumor regression >30% from baseline. In the HRRm+ cohort 4/5 (80%) responded to AZD5335. PARP1 can act as a positive regulator of genomic stability by counteracting TOP1-induced DNA damage (Malanga and Althaus, 2004) that led to the hypothesis that the efficacy of TOP1i drugs can be enhanced by combination with PARP inhibitors. To evaluate for potential synergy of AZD5335 with the PARP1 inhibitor, saruparib (AZD5305): Three FRα-expressing cancer cell lines, KB, IGROV-1 and OVCAR-3, were treated with AZD5335 +/- saruparib, revealing evidence of synergistic cytotoxicity. These results encouraged us to investigate this combination in pre-clinical HRRm+ in vivo xenograft models (OVCAR-3 and OV2022F). In OVCAR-3 xenograft models, single agent activity with saruparib (1 mg/kg PO QD x28) was 37% tumor growth inhibition (TGI) and with AZD5335 (0.625 mg/kg IV x1) was 50% TGI while combined administration at the same doses improved TGI to 86%. Similar combinatorial activity was seen in OV2022F with TGI 61%, 54%, and 97% for saruparib, AZD5335, and saruparib +AZD5335, respectively. In conclusion, AZD5335 exhibits a similar degree of single agent antitumor activity in both HRRm+ and HRRm- preclinical models, and the efficacy can be potentiated by combining with the PARP inhibitor, saruparib. 1. Clarke et al. 2022, NEJM Evid 2022;1(9) DOI: 10.1056/EVIDoa22000432. Malanga and Althaus 2004, JBC 2004; 279(7) DOI: 10.1074/jbc.C3004372003. Citation Format: Marco Gymnopoulos, Ravinder Tammali, Ana De Almeida, Jixin Wang, Claire Myers, Mark Albertella, Paula G. Fraenkel, Puja Sapra. Synergistic antitumor effect of FRα TOP1i antibody drug conjugate, AZD5335, in combination with the PARP1 inhibitor, saruparib (AZD5305), in preclinical models of ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB406.