Preclinical testing of farletuzumab ecteribulin (FZEC [MORAb-202]) and MORAb-109, folate receptor α and mesothelin targeting antibody-drug conjugates (ADCs), in rare gynecologic cancers.

Abstract

e17634 Background: Rare gynecologic cancers, such as ovarian carcinosarcoma (OCS), uterine serous carcinoma (USC) and ovarian clear cell adenocarcinoma (OCCA), have limited treatment options and molecular alterations that drive cell proliferation and drug resistance, resulting in poor overall survival. The anti-microtubule agent (AMA) paclitaxel is used in first-line treatment of most gynecologic cancers; however, the AMA eribulin is known to have additional anticancer properties (Goto et al. Anticancer Res 38:2929, 2018; Ho et al. Cancer Res 82:4457, 2022). Eribulin ADCs have been developed for targeted delivery to limit toxicity and maximize response. FZEC is an anti-folate receptor α (FRA)-eribulin ADC (Shimizu et al. Clin Cancer Res 27:3905, 2021) and MORAb-109 targets eribulin to mesothelin (MSLN; Albone et al. Annals Oncol 31:S491, 2020). Here we provide preclinical data to support clinical trials of FZEC and MORAb-109 in rare gynecologic cancers. Methods: Fresh tumor tissue from patients consented to the WEHI Stafford Fox Rare Cancer Program was used to establish a cohort of patient-derived xenograft (PDX) models of high-grade serous ovarian carcinoma (HGSOC), OCS, USC and OCCA. PDX models were screened for FRA and MSLN expression by IHC and quantified by HALO software, and 15 models were selected for in vivo testing. Tumor-bearing mice were treated with eribulin (1 mg/kg TIW 3 wks), FZEC (12.5 mg/kg Q14Dx3) or MORAb-109 (25 mg/kg Q14Dx3) and compared to standard of care treatments. Results: About 80% of HGSOC PDX models were FRA positive with no difference between models from chemonaïve samples vs multiple lines of prior treatment. FRA expression was frequent in USC and OCCA models, with MSLN seen in a smaller subset. Despite most (80%) models being cisplatin refractory, 11/15 responded to eribulin with the 4 non-responders having high MDR1 expression and being from previously treated patients. Overall, responses to FZEC and MORAb-109 appeared to correlate with FRA and MSLN expression; importantly, some models with moderate to high target antigen expression showed deeper and more durable responses to FZEC and MORAb-109 compared to eribulin. Conclusions: Responses to FZEC and MORAb-109 correlated with FRA and MSLN expression, with equivalent or better activity compared to eribulin in target-positive PDX models of HGSOC, USC and OCCA. [Table: see text]