Antiestrogen fulvestrant enhances the antiproliferative effects of epidermal growth factor receptor inhibitors in human non-small-cell lung cancer.

INTRODUCTION: Estrogen receptor (ER) signaling and its interaction with epidermal growth factor receptor (EGFR) is a potential therapeutic target in non-small-cell lung cancer (NSCLC). To explore cross-communication between ER and EGFR, we have correlated ER pathway gene and protein expression profiles and examined effects of antiestrogens with or without EGFR inhibitors in preclinical models of human NSCLC.

METHODS: We evaluated 54 NSCLC cell lines for growth inhibition with EGFR inhibitors, antiestrogen treatment, or the combination. Each line was evaluated for baseline ER pathway protein expression. The majority were also evaluated for baseline ER pathway gene expression. Human NSCLC xenografts were evaluated for effects of inhibition of each pathway, either individually, or in combination.

RESULTS: The specific antiestrogen fulvestrant has modest single agent activity in vitro, but in many lines, fulvestrant adds to effects of EGFR inhibitors, including synergy in the EGFR-mutant, erlotinib-resistant H1975 line. ERα, ERβ, progesterone receptor-A, progesterone receptor-B, and aromatase proteins are expressed in all lines to varying degrees, with trends toward lower aromatase in more sensitive cell lines. Sensitivity to fulvestrant correlates with greater baseline ERα gene expression. Tumor stability is achieved in human tumor xenografts with either fulvestrant or EGFR inhibitors, but tumors regress significantly when both pathways are inhibited.

CONCLUSIONS: These data provide a rationale for further investigation of the antitumor activity of combined therapy with antiestrogen and anti-EGFR agents in the clinic. Future work should also evaluate dual ER and EGFR inhibition in the setting of secondary resistance to EGFR inhibition.