Repurposing atovaquone as a STAT3 inhibitor for the treatment of platinum resistant ovarian cancer.

Abstract

TPS5631 Background: Despite advances, ovarian cancer (OC) is the most lethal gynecologic cancer with 5-year survival rates for stage III and IV disease 41% and 21%, respectively. After initial treatment with cytoreductive surgery and chemotherapy, 70% of patients (pts) will relapse. Treatment of relapsed OC is dependent on the amount of time between completion of platinum-based therapy and relapse, known as the platinum-free interval (PFI). Pts with PFI of less than six months are deemed platinum-resistant with low response to further chemotherapy and median progression-free survival (PFS) of 3.6 months. Additional treatment options are needed. Oncogenic signal transduction pathways are a critical component of cancer pathogenesis. In a variety of cancer types, including OC, the transcription factor STAT3 (Signal Transducer and Activator of Transcription 3) has emerged as a key promoter of cellular proliferation and resistance to therapeutic drugs. In OC cells, STAT3 is constitutively activated in over 70% of cells, resulting in enhanced cell survival, angiogenesis, and metastasis. STAT3 also controls innate and adaptive immune response by driving myeloid-derived suppressor cells and regulatory T cells, while hampering CD8+ T cell cytotoxicity. Using the Connectivity Map database to identify drugs that induce gene expression changes contrary to the STAT3 signature, the FDA-approved antimicrobial atovaquone (ATO) was identified as the most active. ATO, a well-tolerated, readily available drug inhibits STAT3 tyrosine phosphorylation by downregulating the cell surface expression of glycoprotein 130, which is necessary for signaling of IL-6 and Janus Kinase, and subsequent phosphorylation of STAT3. Given that the STAT3 pathway is constitutively activated in OC, we hypothesize that ATO, a potent inhibitor of STAT3, could be a repurposed therapeutic agent in OC. Methods: A Phase II, single-arm, investigator-initiated clinical trial is in process at our institution where we are evaluating ATO as targeted therapy in pts with platinum resistant OC whose tumors have progressed despite standard therapies. To date, we have currently enrolled 2 of an anticipated 28 pts. The primary endpoint is PFS, with clinical secondary endpoints to include clinical benefit rate and overall survival. In addition, to confirm the STAT inhibitory effect on OC cells, pre and on-treatment tissue sampling is being obtained to assess changes in STAT3 dependent gene expression via RT-PCR and quantitate changes to the immune profile via flow cytometry. We hypothesize targeting inappropriate activation of STAT3 could be a novel and promising treatment approach in OC. This is the first clinical trial evaluating the clinical efficacy of ATO in OC and could have wide implications on treatment options in the future. Clinical trial information: NCT05998135 .