Refametinib

Refametinib is a selective and orally available allosteric inhibitor of MEK 1 and MEK 2 with IC50 values of 19nM and 47nM, respectively [1].

Refametinib is a non–ATP-competitive inhibitor of MEK1/2. It inhibits MEK activity in an in vitro assay with IC50 values of 19nM and 47nM for MEK1 and MEK2, respectively. X-ray shows refametinib binds to an allosteric site of MEK. It does not affect ATP binding but precludes binding to the substrate ERK, thus preventing ERK phosphorylation. Refametinib inhibits MEK with EC50 values ranging from 2.5nM to 15.8nM in a variety of human cancer cells including A375, Colo205, HT-29 and MDA-MB-231. In addition, in the cancer cell lines harboring V600E BRAF mutant, refametinib suppresses cell growth with GI50 values ranging from 67nM to 89nM. Furthermore, in the human melanoma A375 tumor xenograft model, treatment of refametinib causes obvious tumor growth delay and regression. Refametinib also shows tumor growth inhibition in the xenograft model of human Colo205 tumor [1].

References:
[1] Iverson C, Larson G, Lai C, et al. RDEA119/BAY 869766: a potent, selective, allosteric inhibitor of MEK1/2 for the treatment of cancer. Cancer research, 2009, 69(17): 6839-6847.

Allosteric MEK1/2 inhibitor refametinib (BAY 86-9766) in combination with sorafenib exhibits antitumor activity in preclinical murine and rat models of hepatocellular carcinoma.[Pubmed:24204195]

Neoplasia. 2013 Oct;15(10):1161-71.

OBJECTIVE: The objectives of the study were to evaluate the allosteric mitogen-activated protein kinase kinase (MEK) inhibitor BAY 86-9766 in monotherapy and in combination with sorafenib in orthotopic and subcutaneous hepatocellular carcinoma (HCC) models with different underlying etiologies in two species. DESIGN: Antiproliferative potential of BAY 86-9766 and synergistic effects with sorafenib were studied in several HCC cell lines. Relevant pathway signaling was studied in MH3924a cells. For in vivo testing, the HCC cells were implanted subcutaneously or orthotopically. Survival and mode of action (MoA) were analyzed. RESULTS: BAY 86-9766 exhibited potent antiproliferative activity in HCC cell lines with half-maximal inhibitory concentration values ranging from 33 to 762 nM. BAY 86-9766 was strongly synergistic with sorafenib in suppressing tumor cell proliferation and inhibiting phosphorylation of the extracellular signal-regulated kinase (ERK). BAY 86-9766 prolonged survival in Hep3B xenografts, murine Hepa129 allografts, and MH3924A rat allografts. Additionally, tumor growth, ascites formation, and serum alpha-fetoprotein levels were reduced. Synergistic effects in combination with sorafenib were shown in Huh-7, Hep3B xenografts, and MH3924A allografts. On the signaling pathway level, the combination of BAY 86-9766 and sorafenib led to inhibition of the upregulatory feedback loop toward MEK phosphorylation observed after BAY 86-9766 monotreatment. With regard to the underlying MoA, inhibition of ERK phosphorylation, tumor cell proliferation, and microvessel density was observed in vivo. CONCLUSION: BAY 86-9766 shows potent single-agent antitumor activity and acts synergistically in combination with sorafenib in preclinical HCC models. These results support the ongoing clinical development of BAY 86-9766 and sorafenib in advanced HCC.

A phase II study of the efficacy and safety of the combination therapy of the MEK inhibitor refametinib (BAY 86-9766) plus sorafenib for Asian patients with unresectable hepatocellular carcinoma.[Pubmed:25294897]

Clin Cancer Res. 2014 Dec 1;20(23):5976-85.

PURPOSE: There is an unmet need for treatment options in hepatocellular carcinoma (HCC). Sorafenib is currently the only approved systemic treatment for HCC. Refametinib, an oral, allosteric MEK inhibitor, has demonstrated antitumor activity in combination with sorafenib in vitro and in vivo. A phase II study evaluated efficacy and safety of Refametinib plus sorafenib in Asian patients with HCC (NCT01204177). EXPERIMENTAL DESIGN: Eligible patients received twice-daily Refametinib 50 mg plus twice-daily sorafenib 200 mg (morning)/400 mg (evening), with dose escalation to sorafenib 400 mg twice daily from cycle 2 if no grade >/= 2 hand-foot skin reaction, fatigue, or gastrointestinal toxicity occurred. Primary efficacy endpoint: disease control rate. Secondary endpoints: time to progression, overall survival, pharmacokinetic assessment, biomarker analysis, safety, and tolerability. RESULTS: Of 95 enrolled patients, 70 received study treatment. Most patients had liver cirrhosis (82.9%) and hepatitis B viral infection (75.7%). Disease control rate was 44.8% (primary efficacy analysis; n = 58). Median time to progression was 122 days, median overall survival was 290 days (n = 70). Best clinical responders had RAS mutations; majority of poor responders had wild-type RAS. Most frequent drug-related adverse events were diarrhea, rash, aspartate aminotransferase elevation, vomiting, and nausea. Dose modifications due to adverse events were necessary in almost all patients. CONCLUSIONS: Refametinib plus sorafenib showed antitumor activity in patients with HCC and was tolerated at reduced doses by most patients. Frequent dose modifications due to grade 3 adverse events may have contributed to limited treatment effect. Patients with RAS mutations appear to benefit from Refametinib/sorafenib combination.

A Phase I Study of the Safety, Pharmacokinetics, and Pharmacodynamics of Combination Therapy with Refametinib plus Sorafenib in Patients with Advanced Cancer.[Pubmed:26644411]

Clin Cancer Res. 2016 May 15;22(10):2368-76.

PURPOSE: To assess the safety and tolerability of the small-molecule allosteric MEK inhibitor Refametinib combined with sorafenib, in patients with advanced solid malignancies. EXPERIMENTAL DESIGN: This phase I dose-escalation study included an expansion phase at the maximum tolerated dose (MTD). Patients received Refametinib/sorafenib twice daily for 28 days, from a dose of Refametinib 5 mg plus sorafenib 200 mg to a dose of Refametinib 50 mg plus sorafenib 400 mg. Plasma levels of Refametinib, Refametinib metabolite M17, and sorafenib were measured for pharmacokinetic assessments. Tumors were biopsied at the MTD for analysis of MEK pathway mutations and ERK phosphorylation. RESULTS: Thirty-two patients were enrolled in the dose-escalation cohort. The MTD was Refametinib 50 mg twice daily plus sorafenib 400 mg twice daily. The most common treatment-related toxicities were diarrhea and fatigue. Refametinib was readily absorbed following oral administration (plasma half-life of approximately 16 hours at the MTD), and pharmacokinetic parameters displayed near-dose proportionality, with less than 2-fold accumulation after multiple dosing. Another 30 patients were enrolled in the MTD cohort; 19 had hepatocellular carcinoma. The combination was associated with significantly reduced ERK phosphorylation in 5 out of 6 patients biopsied, with the greatest reductions in those with KRAS or BRAF mutations. Disease was stabilized in approximately half of patients, and 1 patient with colorectal cancer achieved a partial response at the MTD lasting approximately 1 year. CONCLUSIONS: In this phase I study, Refametinib plus sorafenib was well tolerated, with good oral absorption, near-dose proportionality, and target inhibition in a range of tumor types. Clin Cancer Res; 22(10); 2368-76. (c)2015 AACR.

Phase I/II Study of Refametinib (BAY 86-9766) in Combination with Gemcitabine in Advanced Pancreatic cancer.[Pubmed:27975152]

Target Oncol. 2017 Feb;12(1):97-109.

BACKGROUND: Activating KRAS mutations are reported in up to 90% of pancreatic cancers. Refametinib potently inhibits MEK1/2, part of the MAPK signaling pathway. This phase I/II study evaluated the safety and efficacy of Refametinib plus gemcitabine in patients with advanced pancreatic cancer. METHODS: Phase I comprised dose escalation, followed by phase II expansion. Refametinib and gemcitabine plasma levels were analyzed for pharmacokinetics. KRAS mutational status was determined from circulating tumor DNA. RESULTS: Ninety patients overall received treatment. The maximum tolerated dose was Refametinib 50 mg twice daily plus standard gemcitabine (1000 mg/m(2) weekly). The combination was well tolerated, with no pharmacokinetic interaction. Treatment-emergent toxicities included thrombocytopenia, fatigue, anemia, and edema. The objective response rate was 23% and the disease control rate was 73%. Overall response rate, disease control rate, progression-free survival, and overall survival were higher in patients without detectable KRAS mutations (48% vs. 28%, 81% vs. 69%, 8.8 vs. 5.3 months, and 18.2 vs. 6.6 months, respectively). CONCLUSION: Refametinib plus gemcitabine was well tolerated, with a promising objective response rate, and had an acceptable safety profile and no pharmacokinetic interaction. There was a trend towards improved outcomes in patients without detectable KRAS mutations that deserves future investigation.

Refametinib (BAY 869766; RDEA119) is an orally available, potent, non-ATP-competitive, selective, allosteric MEK1/MEK2 inhibitor with IC50s of 19 nM and 47 nM, respectively.

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