BACKGROUND Resistance to therapy with BRAF kinase inhibitors is associated with reactivation of the mitogen-activated protein kinase (MAPK) pathway. To address this problem, we conducted a phase 1 and 2 trial of combined treatment with dabrafenib, a selective BRAF inhibitor, and trametinib, a selective MAPK kinase (MEK) inhibitor. METHODS In this open-label study involving 247 patients with metastatic melanoma and BRAF V600 mutations, we evaluated the pharmacokinetic activity and safety of oral dabrafenib (75 or 150 mg twice daily) and trametinib (1, 1.5, or 2 mg daily) in 85 patients and then randomly assigned 162 patients to receive combination therapy with dabrafenib (150 mg) plus trametinib (1 or 2 mg) or dabrafenib monotherapy. The primary end points were the incidence of cutaneous squamous-cell carcinoma, survival free of melanoma progression, and response. Secondary end points were overall survival and pharmacokinetic activity. RESULTS Dose-limiting toxic effects were infrequently observed in patients receiving combination therapy with 150 mg of dabrafenib and 2 mg of trametinib (combination 150/2). Cutaneous squamous-cell carcinoma was seen in 7% of patients receiving combination 150/2 and in 19% receiving monotherapy (P = 0.09), whereas pyrexia was more common in the combination 150/2 group than in the monotherapy group (71% vs. 26%). Median progression-free survival in the combination 150/2 group was 9.4 months, as compared with 5.8 months in the monotherapy group (hazard ratio for progression or death, 0.39; 95% confidence interval, 0.25 to 0.62; P<0.001). The rate of complete or partial response with combination 150/2 therapy was 76%, as compared with 54% with monotherapy (P = 0.03). CONCLUSIONS Dabrafenib and trametinib were safely combined at full monotherapy doses. The rate of pyrexia was increased with combination therapy, whereas the rate of proliferative skin lesions was nonsignificantly reduced. Progression-free survival was significantly improved. (Funded by GlaxoSmithKline; ClinicalTrials.gov number, NCT01072175.)

Background Dabrafenib (GSK2118436) is a potent ATP-competitive inhibitor of BRAF kinase and was highly selective for mutant BRAF in kinase panel screening, cell lines, and xenografts. Methods A Phase I trial of dabrafenib was conducted to evaluate safety and tolerability in patients with incurable solid tumours. Efficacy at the recommended Phase II dose (RP2D) was studied in patients with BRAF-mutant tumours, including those with non-V600E mutations, in three cohorts: (1) metastatic melanoma, (2) melanoma with untreated brain metastases, and (3) non-melanoma solid tumours. Findings 184 patients enrolled, and 150 mg twice daily was chosen as the RP2D, based on safety, pharmacokinetic, and pharmacodynamic data. At the RP2D in patients with V600 BRAF-mutant melanoma, a response rate of 69% (a confirmed response rate of 50%) was observed overall and a 78% response rate (a confirmed response rate of 56%) in V600E BRAF-mutant melanoma. In V600 BRAF-mutant melanoma, responses were durable, with 17 patients (47%) on treatment for more than 6 months and a median progression-free survival (PFS) of 5·5 months. Responses were observed in patients with non-V600E BRAF mutations, including V600K and V600G. In the RP2D expansion of melanoma with untreated brain metastases, nine of ten patients (90%) showed reduction in brain lesion size and the median PFS was 4.2 months. Among BRAF-mutant non-melanoma solid tumours, antitumour activity was observed in gastrointestinal stromal tumour, papillary thyroid, non-small cell lung, ovarian, and colorectal cancer. Interpretation Dabrafenib is a highly active inhibitor of V600-mutant BRAF with a high response rate in V600E melanoma, and is the first drug of its class to demonstrate activity in melanoma brain metastases. Funding This study was funded and sponsored by GlaxoSmithKline

Summary Purpose The mitogen-activated extracellular signal-related kinase kinase (MEK) is a member of the RAS/RAF/MEK/ERK signalling cascade, which is commonly activated in melanoma. Direct inhibition of MEK inhibits ERK signalling. Methods We conducted a multicentre, first-in-human, three-part study (dose escalation, cohort expansion, and pharmacodynamic evaluation) to evaluate the oral small-molecule MEK inhibitor trametininb (GSK1120212) in advanced cancer. Intermittent and continuous dosing regimens were evaluated. Safety and efficacy data in patients with melanoma are presented here, with exploratory analyses of available tumour tissues performed on an Illumina genotyping platform. This completed study is registered with ClinicalTrials.gov, number NCT00687622. Findings Ninety-seven melanoma patients, including 81 with cutaneous or unknown primary melanoma (36 BRAF-mutant, 39 BRAF wild-type, six BRAF status unknown) and 16 uveal melanoma patients were enrolled. The most common treatment-related adverse events were rash/dermatitis acneiform (80 out of 97; 82%) and diarrhoea (n=44; 45%), most of which were grade 2 or lower. No cutaneous squamous cell carcinomas were observed. Among the 36 BRAF-mutant patients, 30 were BRAF-inhibitor naïve. Among these 30 patients, 2 complete responses (CRs) and 10 partial responses (PRs) were observed (unconfirmed response rate=40%) including 2 confirmed CRs and 8 confirmed PRs (confirmed response rate=33%); the median progression-free survival was 5·7 months (95% CI, 4·0–7·4). Among the 6 BRAF-mutant patients who received prior BRAF inhibitor therapy, 1 unconfirmed PR was observed. Among 39 patients with BRAF wild-type melanoma, 4 PRs (all confirmed) were observed (confirmed response rate=10%). Conclusions To our knowledge, this is the first demonstration of substantial clinical activity by a MEK inhibitor in melanoma. These data suggest that MEK is a valid therapeutic target.

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Small-molecule inhibitors of the housekeeping enzyme farnesyltransferase (FT) suppress the malignant growth of Ras-transformed cells. Previous work suggested that the activity of these compounds reflected effects on actin stress fiber regulation rather than Ras inhibition. Rho proteins regulate stress fiber formation, and one member of this family, RhoB, is farnesylated in vivo. Therefore, we tested the hypothesis that interference with RhoB was the principal basis by which the peptidomimetic FT inhibitor L-739,749 suppressed Ras transformation. The half-life of RhoB was found to be ϳ2 h, supporting the possibility that it could be functionally depleted Isoprenylated proteins, which constitute ϳ0.5% of the proteins in the cell, fall into two classes that are characterized by the presence of either farnesyl (C 15 ) or geranylgeranyl (C 20 ) isoprenoids (for reviews, see references 18 and 32). Isoprenylation is required for the biological function and efficient membrane association of these proteins, possibly because of a role of the isoprenyl groups in protein-protein interactions (33). The signal for isoprenyl modification is located in the C terminus of the polypeptide and dictates not only the specificity of the isoprenoid but also further modifications which occur.The housekeeping enzyme farnesyltransferase (FT) is one of at least three isoprenyl-protein transferase activities that have been identified (for reviews, see references 5, 10, 35, and 48). FT recognizes on its substrates a C-terminal CAAX motif (where C is cysteine, A is typically an aliphatic amino acid, and X is any amino acid) and catalyzes transfer of the C 15 isoprenoid from farnesyl PP i to the CAAX cysteine. The farnesylated product is a substrate for additional modification by enzymes which proteolyze the terminal three amino acids and carboxymethylate the new C terminus. Some farnesylated proteins (e.g., H-Ras) are further modified by the addition of palmitate to an additional cysteine(s) that is proximal to the CAAX motif. In these cases, palmitylation appears to increase the avidity of membrane association (20) but is dispensable for biological activity (26).Since FT is responsible for farnesylating oncogenic Ras (8), small-molecule inhibitors of FT were sought as possible cancer therapeutics (16,17). Recently, FT inhibitors have been demonstrated to revert the malignant phenotype of Ras-transformed cells in vitro and in vivo without toxic or anti-proliferative effects on normal cells (15, 24, 28, 28a, 29, 32a). These results present some question as to the biological mechanism of action, since Ras and other farnesylated proteins (e.g., lamin B [14]) are critical for normal cell growth and function. Our previous work revealed that the kinetics of reversion induced by one FT inhibitor, L-739,749, were too rapid to be explained easily by suppression of Ras activity. Instead, the inhibitory effects of L-739,749 correlated with effects on the regulation of actin stress fiber formation (39).We tested the hypothesis that a putative stress fibe...