Abstract #3687: In vivo anticancer activity of E6201, a novel MEK1 inhibitor, against BRAF-mutated human cancer xenografts
Authors: Jiayi Wu, Kenichi Nomoto, John Wang, Galina Kuznetsov, Sergei Agoulnik, Edgar Shuck, Nancy Wong, Murray Towle, Matthew Schnaderbeck, Sara Wu, Bruce Littlefield
Journal: Cancer Research (2009)

AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

The RAS/RAF/MEK/ERK signaling pathway has long been viewed as a crucial pathway for developing novel anticancer therapies, based on its central role in regulating the growth and survival of cells in a broad spectrum of human cancers. Importantly, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1 (MEK1) is downstream of RAS and RAF proteins, which are often mutated and abnormally active in tumors. E6201, a totally synthetic analog of LL-Z1640-2 (in the zearalenone natural product family), is a potent inhibitor of MEK1 and other kinases. Results of in vitro pharmacology studies supported the use of E6201 for treating cancers that are associated with elevation of MEK1 kinase activity such as those with BRAF mutations. Therefore, efficacy of E6201 was tested in vivo against 3 V600E BRAF-mutated human cancer xenograft models (LOX melanoma, COLO 205 colon cancer, DBTRG-05MG glioblastoma), using a Q4D×3 iv administration schedule. Administration of E6201 at doses of 5, 10, 20, and 40 mg/kg resulted in statistically significant anticancer activity in these 3 models. Single iv administration of 40 mg/kg E6201 resulted in time-dependent inhibition of phosphorylation of extracellular-signal-related kinase (ERK) and retinoblastoma proteins (pRb) in LOX tumors by Western blot and immunohistochemistry. Staining for Ki-67, a marker for proliferating cells, also showed inhibition of LOX tumor proliferation. In addition to these proteins, E6201 decreased plasma IL-8 protein levels in UACC-62 V600E BRAF-mutated human melanoma bearing mice. In view of these results, IL-8, phospho-ERK, and phospho-pRb are being further assessed as PD biomarkers to measure response to E6201 in clinical trials. E6201 penetrates the intact blood brain barrier (BBB), with high drug concentrations seen in brain tissue using 20 mg/kg iv dosing in mice and rats. The drug concentration of E6201 in brain was about 4.8-6.4 times higher than in plasma in both species. These data suggest that penetration of E6201 into brain would be adequate for treating tumor metastases in brain. To assess the effect of E6201 in vivo, metastases in brain were established by intra-cardiac injection of G464V BRAF-mutated MDA-MB-231 human breast cancer cells into nude mice. Successive rounds of culture of isolated brain metastases and reinjection into nude mice produced sublines with enhanced brain metastatic potential and/or increased selectivity for brain compared to other metastatic sites. E6201 showed a survival benefit in this brain metastatic model, suggesting that E6201 can be effective for treating tumor metastases in brain. Overall, these data suggest that BRAF mutation status could be an important patient stratification tool for human clinical trials. E6201 is currently in Phase I clinical trials.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 3687.