Chimera Research subscribers can read a preview of the important clinical data from ARRY, and in particular in MEK inhibitors, that will be presented at ASCO in June 2012.
Keep reading for a couple of interesting AACR abstracts related to one of Array's MEK inhibitors - selumetinib aka AZD6244.
Abstract Number: LB-362
The MEK inhibitor selumetinib (AZD6244 - ARRY-142886) prevents lung metastasis in a triple-negative breast cancer (TNBC) xenograft model
Patients with TNBC are negative for estrogen receptor, progesterone receptor, and HER2 expression, and have a very poor prognoses because tumors often metastasize, leading to death. Preventing metastasis as well as inhibiting the tumor growth, is crucial to improving the prognosis of TNBC. We previously showed that patients with ERK2-overexpressing TNBC were at higher risk of death than those with low-ERK2-expressing tumors. Interestingly, when we treated the TNBC cells lines MDA-MB-231 and SUM-149 with the MEK1/2 ATP uncompetitive kinase inhibitor (selumetinib) at concentrations of 0.1 and 1.0 μM, it did not reduce cell viability in a two-dimensional (2D) cell culture. However, in a three-dimensional (3D) cell culture model, selumetinib changed the mesenchymal phenotype of TNBC to an epithelial phenotype. Cells undergoing epithelial-mesenchymal transition are well known to potentially contribute to the metastatic process and have increased ability to form mammospheres. Thus, we hypothesized that targeted inhibition of the MEK-ERK pathway by selumetinib may prevent lung metastasis in TNBC.
In the present study, we observed that SUM-149 cells treated with selumetinib (0.1, 1.0 μM) exhibited cell-cycle arrest at G1 but did not exhibit apoptosis indicated by an increased proportion of cells at sub-G1 phase. Both SUM-149 and MDA-MB-231 cells treated with selumetinib exhibited significant inhibition of anchorage-independent growth, an indicator of in vivo tumorigenicity (P<0.005). In addition, in SUM-149 cells and MDA-MB-231, treatment with selumetinib (0.01, 0.1,1.0 and 10μM) suppressed formation of mammospheres in a dose-dependent manner. Next, to determine the role of the MEK-ERK pathway in the prevention of TNBC metastasis, we used a metastatic TNBC animal model established with MDA-MB-231-LM2-4175 (lung metastatic subpopulation) cells transfected with a luciferase gene that were injected intravenously into the tail vein of mice. We observed that mice treated with selumetinib had significantly fewer lung metastases than did control mice injected with a vehicle (P<0.05, 2-sided t test.) These findings support a crucial role for the MAPK pathway in metastasis and suggest that ERK pathway might provide clinical benefit by preventing metastasis. Targeted inhibition of the MEK-ERK pathway with selumetinib may be a novel approach to treatment of TNBC metastasis
Abstract Number: LB-347
Identify signaling responses to MEK inhibitor AZD6244 in lung cancer cells with proteomics reverse phase protein array
AZD6244 is small-molecule inhibitor that targets the MAPK pathway, and is currently in phase I/II clinical evaluation. While some efficacy of these agents has been observed in phase I/II clinical trials, one of the hurdles of targeted therapy is the intrinsic and acquired resistance mediated by complex feedback pathways. Identifying downstream effectors required for cellular response to MEK inhibitors will help us understand the mechanism of resistance, possibly leading to the development of direct therapeutic targets. Explore the signaling responses after treatment with MEK inhibitors will also allow us to identify signaling feedback loops and cross talks. We used reverse phase protein array (RPPA) technology to determine which downstream effectors of MEK/ERK pathways critical for cell growth inhibition or apoptosis induced by MEK inhibitors, and to identify which signaling pathways are inhibited or activated when the pathways is blocked. RPPA is a antibody-based quantitative assay used to analyze nanoliter amounts of sample for 200 proteins to determine expression levels and protein modifications such as phosphorylation or cleavage. Experiments were carried out in 5 resistant and 5 sensitive cell lines with the MEK inhibitor, AZD6244. Cells were treated at different time points (0, 6, 12, 24, 48, and 72 hours) and with various dosages (0, 0.3, 1, 3 and 10 µM). Cell lysates were collected and quantified for RPPA assays. The data was analyzed for the presence of clusters based on differential protein expression by using available methods with a statistical software package (StatSoft, Tulsa, OK). Significantly changed proteins were analyzed with Ingenuity Pathway Analysis (IPA). Proteins Data from RPPA was further validated by using Western blotting with the same antibody used in the RPPA assay. The results showed that inhibition of MEK/ERK could activate multiple signaling pathways including AKT, SRC, STAT3 and IGF1R. Activation of those signaling pathway through signaling cross talk and feedbacks may involved in the intrinsic and acquitted resistance to MEK inhibitor. We also indentified a penal of molecules, such as BIM, P27, p53 and JNK were specifically induced only in the sensitive cells. Those molecules might be the mediators of MEK inhibitor induced cell apoptosis. The results will be helpful in understanding of the signaling cross talks and feedbacks and in the exploration of mechanisms of sensitivity and resistance to the treatment with MEK inhibitors in lung cancer.