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

Abstract

Purpose More effective, less toxic treatments for recurrent ovarian cancer (OVCA) are needed. Although >60% of OVCAs 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. Since Src is activated in most OVCAs, we investigated whether combined Src and ER blockade by saracatinib and fulvestrant would circumvent antiestrogen resistance. Experimental Design ER and Src were assayed in 338 primary OVCAs. Dual ER and Src blockade effects on cell cycle, ER target gene expression, and survival were assayed in ERα+ OVCA lines, a primary human OVCA culture in vitro, and on xenograft growth. Results Most primary OVCAs express ER. Src activity was greater in OVCA lines than normal epithelial lines. Estrogen activated Src, ER-Src binding and ER translocation from cytoplasm to nucleus. Estrogen mediated mitogenesis was via ERα, not ERβ. While each alone had little effect, combined saracatinib and fulvestrant increased p27, inhibited cyclin E-Cdk2 and cell cycle progression. Saracatinib also impaired induction of ER-target genes Myc and FOSL1; this was greatest with dual therapy. Combined therapy induced autophagy and more effectively inhibited OVCA xenograft growth than monotherapy. 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 ER+ OVCA models. These data support further pre-clinical and clinical evaluation of combined fulvestrant and saracatinib in OVCA.

Lapatinib induces p27Kip1-dependent G₁ arrest through both transcriptional and post-translational mechanisms

“…28 Recently, it was shown that ERα blockade effectively arrested breast cancer cells at G 1 cell cycle by stabilizing p27. 30,31 However, the roles of ERβ1 and ERβ2 in this process have not yet been clearly established.…”

Estrogen receptor α inhibitor activates the unfolded protein response, blocks protein synthesis, and induces tumor regression

“…Endocrine therapy using aromatase inhibitors to block estrogen production, or tamoxifen and other competitor antiestrogens, often results in selection and outgrowth of resistant tumors. Although 30-70% of epithelial ovarian tumors are ERα-positive (1), endocrine therapy is largely ineffective (5)(6)(7). After several cycles of chemotherapy, tumors recur as resistant ovarian cancer (5), and most patients die within 5 years (8).…”

Treating gynecologic malignancies with selective estrogen receptor downregulators (SERDs): promise and challenges

“…Increased pSrc was also observed in cell line M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT models of fulvestrant resistance (83,84). In two studies, researchers noted that with increased number of passages, PEO1 and Skov3 ovarian cancer cells developed de novo resistance to growth inhibition by treatment with fulvestrant (83,84). Dual treatment with fulvestrant and saracatinib, a Src inhibitor, overcame this resistance in vitro and in vivo; the combination led to increased autophagy and apoptosis.…”

“…Models of fulvestrant resistance have also been developed in ovarian cancer.Fulvestrant resistance that has recently emerged is via activation of c-Src, a non-receptor tyrosine kinase (83,84). Elevated pSrc in ER positive ovarian tumors correlated with poor worse clinical outcome after estrogen antagonist treatment (84).…”

“…Elevated pSrc in ER positive ovarian tumors correlated with poor worse clinical outcome after estrogen antagonist treatment (84). Increased pSrc was also observed in cell line M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT models of fulvestrant resistance (83,84). In two studies, researchers noted that with increased number of passages, PEO1 and Skov3 ovarian cancer cells developed de novo resistance to growth inhibition by treatment with fulvestrant (83,84).…”