Preclinical study of MEK1/2 inhibitor AZD6244 combined with gemcitabine for treatment of biliary cancer.

Abstract

240 Background: MEK1/2 is an integral component of the Ras/Raf/MEK/ERK signaling pathway, implicated in uncontrolled cell proliferation and cell survival, a key hallmark of cancer. AZD6244, a novel inhibitor of MEK1/2, is currently completing Phase II clinical trials in biliary cancer, with modest antitumor activity observed as monotherapy. Gemcitabine is a cytotoxic drug commonly used in biliary cancer therapy but many patients showed early resistance. In this preclinical study, we investigated the sequence-dependent antitumor effects of AZD6244 combined with gemcitabine in biliary cancer models. Methods: Two biliary cancer cell lines (EGI-1 and TFK-1) were used. In vitro the effects of single drug or three combination protocols(concurrently; AZD6244 followed by GEM or Gem followed by AZD6244) on cell proliferation, DNA synthesis, and cell cycle distribution were evaluated by MTS, clonogenic assay, EdU uptake and flow cytometry. Drug interactions were analyzed by Chou-Talaly method. In vivo, 4 tumor models subcutaneously xenografted in SCID mice from the two cell lines and 2 human patients were set up to compare the therapeutic effects of different sequence-scheduled combinations. Results: AZD6244 caused G1-S cell cycle arrest in biliary cancer cells in vitro and in vivo, and this effect is correlated with the MEK/ERK signaling pathway blocking. Synchronized progression of the population through S phase were observed in 15h after removal of AZD6244 in cell culture or 48h after final dose of acute AZD6244 treatment in vivo. Antagonistic or additive effects was observed in vitro when combination were given as concurrently(CI=2.03~2.46) or Gem followed by AZD6244(CI=1.34~1.78). In contrast, a synergistic antiproliferative activity was obtained when AZD6244 was given first followed by a drug-free interval before Gem treatment (CI=0.53~0.69). In vivo, the best therapeutic effects were obtained with the sequence of AZD6244 followed by Gem, compared with concurrent or reverse sequence. Conclusions: This study provides a sound rationale for a Phase II trial of a potentially synergistic sequence of MEK inhibitor AZD6244 followed by gemcitabine in patients with advanced biliary cancer.