Cancer Therapy: Preclinical Src Inhibition with Saracatinib Reverses Fulvestrant Resistance in ER-Positive Ovarian Cancer Models In Vitro and In Vivo

Purpose: More effective, less toxic treatments for recurrent ovarian cancer are needed. Although more than 60% of ovarian cancers express the estrogen receptor (ER), ER-targeted drugs have been disappointing due to drug resistance. In other estrogen-sensitive cancers, estrogen activates Src to phosphorylate p27 promoting its degradation and increasing cell-cycle progression. Because Src is activated in most ovarian cancers, we investigated whether combined Src and ER blockade by saracatinib and fulvestrant would circumvent antiestrogen resistance. ExperimentalDesign:ER andSrcwere assayed in 338primary ovarian cancers.Dual ER andSrc blockade effects on cell cycle, ER target gene expression, and survival were assayed in ERaþ ovarian cancer lines, a primary human ovarian cancer culture in vitro, and on xenograft growth. Results: Most primary ovarian cancers express ER. Src activity was greater in ovarian cancer lines than normal epithelial lines. Estrogen activated Src, ER-Src binding, and ER translocation from cytoplasm to nucleus. Estrogen-mediated mitogenesis was via ERa, not ERb. While each alone had little effect, combined saracatinib and fulvestrant increased p27 and inhibited cyclin E-Cdk2 and cell-cycle progression. Saracatinib also impaired induction of ER-target genes c-Myc and FOSL1; this was greatest with dual therapy. Combined therapy induced autophagy andmore effectively inhibited ovarian cancer xenograft growth thanmonotherapy. Conclusions: Saracatinib augments effects of fulvestrant by opposing estrogen-mediated Src activation and target gene expression, increasing cell-cycle arrest, and impairing survival, all of which would oppose antiestrogen resistance in these ERþ ovarian cancermodels. These data support further preclinical and clinical evaluation of combined fulvestrant and saracatinib in ovarian cancer. Clin Cancer Res; 18(21); 5911–23.