Abstract 2968: Trim25 and KLF5 expression predict AFPep-mediated inhibition of estrogen-dependent growth

Introduction: Alpha-fetoprotein (AFP) functions in utero to inhibit estrogen-mediated growth in fetal tissue. AFPep is a 9-amino acid cyclized form of the active site in AFP that impedes phosphorylation and activation of ERα. Recent studies demonstrate that AFPep inhibits estrogen-dependent growth in MCF-7 and T47D xenografts and decreases mammary tumor burden in estrogen-exposed ACI rats. It is important to identify biomarkers that predict the efficacy of AFPep. Dimerized, phosphorylated ERα (pERα) transcribes TRIM25, which is associated with breast cancer metastasis and decreased survival. KLF5 is a transcription factor downstream of pERα and is associated with breast and cervical cancer proliferation, invasiveness, and migration. We hypothesize that treatment with AFPep inhibits expression of TRIM25 and KLF5 and that these are predictive biomarkers for AFPep-mediated inhibition of estrogen-dependent growth. Methods: Expression of ERα, pERα, TRIM25, and KLF5 were assessed in three estrogen-sensitive models: immature mouse uterus, MCF7 xenografts, and canine breast tumors. Immature mice were treated with saline only, AFPep (100 μg) only, estrogen, or estrogen plus AFPep (100 μg). Twenty-four hours post treatment, uteri were removed, weighed, and blotted for biomarkers. Mice bearing MCF7 xenografts were treated with estrogen or estrogen with AFPep and biopsied after 14 days. Finally, two dogs, one with a simple tubular mammary adenoma and the other with a grade II mixed mammary carcinoma, were treated with AFPep for seven days. Results: Immature mice treated with estrogen had greater uterine-to-body weight ratio, increased ratio of pERα to total ERα, and increased KLF5 and TRIM25 expression compared to mice treated with saline alone or AFPep alone. Uteri from mice treated with estrogen and AFPep showed decreased uterine-to-body weight ratio, decreased ratio of pERα to total ERα, and decreased KLF5 and TRIM25 expression compared to uteri treated with estrogen alone. MCF7 xenografts from mice treated with estrogen and AFPep showed decreased ratio of pERα to total ERα compared to mice treated with estrogen alone. AFPep treatment of xenograft-bearing mice decreased expression of TRIM25 and KLF5 in the tumor. In the clinical canine mammary tumor study, a mixed carcinoma expressed pERα and treatment of that dog with AFPep decreased the expression of both KLF5 and TRIM25 in that tumor. A dog with a simple tubular adenoma did not express pERα, and treatment of that dog with AFPep had little impact on the expression of TRIM25 and KLF5 in the tumor. Conclusion: We conclude that AFPep inhibits estrogen-mediated growth and the ratio of pERα to total ERα. KLF5 and TRIM25 also serve as predictive markers for the efficacy of AFPep in uterus and breast tissue respectively. Citation Format: Kanthi J. Bommareddy, Anusri Kadakuntla, Michael Kuna, Priya Shivraj, Roman Ginnan, Ann Hohenhaus, James Bennett, Thomas Andersen. Trim25 and KLF5 expression predict AFPep-mediated inhibition of estrogen-dependent growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2968.