Background: Per COSMIC database, RAS mutations are uncommon events in hepatocellular carcinoma (HCC). Refametinib (BAY 86-9766) is a potent (IC50=17-60 nM) allosteric dual MEK 1/2 inhibitor, which exhibits high selectivity for MEK as compared to other kinases as well as strong preclinical synergy in combination with sorafenib, suggesting it may have potential utility in treating HCC patients. As part of a phase II study that evaluated the efficacy and safety of refametinib plus sorafenib in Asian patients with HCC, a biomarker analysis was performed using plasma DNA to investigate a possible correlation between mutational status and clinical outcome.

Methods: Refametinib was tested in a kinase panel of 205 enzymes at 10 μM and in a variety of cancer cell lines for antiproliferative effects. In vivo refametinib was tested for tumor growth inhibition in monotherapy or in combination with sorafenib mouse xenograft HCC models. Mutational analysis of clinical plasma specimens was performed by Inostics GmbH (Hamburg, Germany) using BEAMing (Beads, Emulsions, Amplification, and Magnetics) technology on DNA isolated from plasma samples collected at baseline. Mutational status was correlated with clinical outcome using descriptive analyses. Plasma from 69 patients was evaluated for the following mutations: KRAS (G12A, C, D, R, S, V; G13D; Q61H; A146T); NRAS (Q61H, K, L, R) and BRAF (V600E).

Results: Based on it allosteric binding mode refametinib shows more than 100-fold selectivity for MEK. There was strong antiproliferative activity of BAY 86-9766 in HCC cell lines being most active in an NRAS amplified model (HepG2). In the orthotopic HBV-driven human Hep3B xenograft model, BAY 86-9766 (25 mg/kg) monotherapy was more effective than sorafenib at its maximally tolerated dose (30 mg/kg) in prolonging survival and exhibited strong synergism in improving this endpoint when combined with sorafenib. Based on the BEAMing data, the frequency of HCC patients with mutant RAS identified in our study (5.8%) was similar to the frequency of RAS mutations reported in HCC patients (5%) (COSMIC). A RAS mutation was identified in 4 patients, 3 of whom were still receiving study treatment at the cut-off date used for the final data analysis. These 3 patients had achieved confirmed PR, with duration of responses ranging from 128 to 382 days. The fourth patient with a RAS mutation discontinued study treatment after 41 days on therapy due to PD. No mutations in BRAF were identified in these 69 samples.

Conclusions: In this exploratory retrospective study, HCC patients with mutant RAS exhibited a particularly robust clinical response to refametinib plus sorafenib compared to patients with wild-type RAS. Further investigation is required to assess the clinical activity of this drug combination in HCC patients with mutant RAS. Accordingly, we have initiated two single-arm phase 2 studies in patients with prospectively identified, BEAMing-confirmed RAS-mutated HCC; sorafenib and refametinib in first-line (NCT01915602), and refametinib as first- or second-line monotherapy (NCT01915589).

Citation Format: Ho Yeong Lim, Heiko Krissel, Michael Teufel, Florian Puehler, Joachim Reischl, Frank Diehl, Barrett H. Childs, Josep M. Llovet. RAS mutations detected by cell-free plasma DNA (BEAMing) assay may portend a favorable response to refametinib +/- sorafenib in hepatocellular carcinoma. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B42. doi: 10.1158/1557-3125.RASONC14-B42