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Clinical efficacy of a RAF inhibitor needs broad target blockade in BRAF-mutant melanoma.

ABSTRACT: B-RAF is the most frequently mutated protein kinase in human cancers. The finding that oncogenic mutations in BRAF are common in melanoma, followed by the demonstration that these tumours are dependent on the RAF/MEK/ERK pathway, offered hope that inhibition of B-RAF kinase activity could benefit melanoma patients. Herein, we describe the structure-guided discovery of PLX4032 (RG7204), a potent inhibitor of oncogenic B-RAF kinase activity. Preclinical experiments demonstrated that PLX4032 selectively blocked the RAF/MEK/ERK pathway in BRAF mutant cells and caused regression of BRAF mutant xenografts. Toxicology studies confirmed a wide safety margin consistent with the high degree of selectivity, enabling Phase 1 clinical trials using a crystalline formulation of PLX4032 (ref. 5). In a subset of melanoma patients, pathway inhibition was monitored in paired biopsy specimens collected before treatment initiation and following two weeks of treatment. This analysis revealed substantial inhibition of ERK phosphorylation, yet clinical evaluation did not show tumour regressions. At higher drug exposures afforded by a new amorphous drug formulation, greater than 80% inhibition of ERK phosphorylation in the tumours of patients correlated with clinical response. Indeed, the Phase 1 clinical data revealed a remarkably high 81% response rate in metastatic melanoma patients treated at an oral dose of 960?mg twice daily. These data demonstrate that BRAF-mutant melanomas are highly dependent on B-RAF kinase activity.

SUBMITTER: Bollag G

PROVIDER: S-EPMC2948082 | biostudies-literature | 2010 Sep

REPOSITORIES: biostudies-literature

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Clinical efficacy of a RAF inhibitor needs broad target blockade in BRAF-mutant melanoma.

Bollag Gideon G Hirth Peter P Tsai James J Zhang Jiazhong J Ibrahim Prabha N PN Cho Hanna H Spevak Wayne W Zhang Chao C Zhang Ying Y Habets Gaston G Burton Elizabeth A EA Wong Bernice B Tsang Garson G West Brian L BL Powell Ben B Shellooe Rafe R Marimuthu Adhirai A Nguyen Hoa H Zhang Kam Y J KY Artis Dean R DR Schlessinger Joseph J Su Fei F Higgins Brian B Iyer Raman R D'Andrea Kurt K Koehler Astrid A Stumm Michael M Lin Paul S PS Lee Richard J RJ Grippo Joseph J Puzanov Igor I Kim Kevin B KB Ribas Antoni A McArthur Grant A GA Sosman Jeffrey A JA Chapman Paul B PB Flaherty Keith T KT Xu Xiaowei X Nathanson Katherine L KL Nolop Keith K

Nature 20100901 7315

B-RAF is the most frequently mutated protein kinase in human cancers. The finding that oncogenic mutations in BRAF are common in melanoma, followed by the demonstration that these tumours are dependent on the RAF/MEK/ERK pathway, offered hope that inhibition of B-RAF kinase activity could benefit melanoma patients. Herein, we describe the structure-guided discovery of PLX4032 (RG7204), a potent inhibitor of oncogenic B-RAF kinase activity. Preclinical experiments demonstrated that PLX4032 select ...[more]

PMID: 20823850

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Project description:BackgroundBRAF(V600E)-mediated MAPK pathway activation is associated in melanoma cells with IFNAR1 downregulation. IFNAR1 regulates melanoma cell sensitivity to IFNα, a cytokine used for the adjuvant treatment of melanoma. These findings and the limited therapeutic efficacy of BRAF-I prompted us to examine whether the efficacy of IFNα therapy of BRAF(V600E) melanoma can be increased by its combination with BRAF-I.MethodsBRAF/NRAS genotype, ERK activation, IFNAR1, and HLA class I expression were tested in 60 primary melanoma tumors from treatment-naive patients. The effect of BRAF-I on IFNAR1 expression was assessed in three melanoma cell lines and in four biopsies of BRAF(V600E) metastases. The antiproliferative, pro-apoptotic and immunomodulatory activity of BRAF-I and IFNα combination was tested in vitro and in vivo utilizing three melanoma cell lines, HLA class I-MA peptide complex-specific T-cells and immunodeficient mice (5 per group for survival and 10 per group for tumor growth inhibition). All statistical tests were two-sided. Differences were considered statistically significant when the P value was less than .05.ResultsThe IFNAR1 level was statistically significantly (P < .001) lower in BRAF(V600E) primary melanoma tumors than in BRAF wild-type tumors. IFNAR1 downregulation was reversed by BRAF-I treatment in the three melanoma cell lines (P ≤ .02) and in three out of four metastases. The IFNAR1 level in the melanoma tumors analyzed was increased as early as 10 to 14 days following the beginning of the treatment. These changes were associated with: 1) an increased susceptibility in vitro of melanoma cells to the antiproliferative (P ≤ .04), pro-apoptotic (P ≤ .009) and immunomodulatory activity, including upregulation of HLA class I antigen APM component (P ≤ .04) and MA expression as well as recognition by cognate T-cells (P < .001), of BRAF-I and IFNα combination and 2) an increased survival (P < .001) and inhibition of tumor growth of melanoma cells (P < .001) in vivo by BRAF-I and IFNα combination.ConclusionsThe described results provide a strong rationale for the clinical trials implemented in BRAF(V600E) melanoma patients with BRAF-I and IFNα combination.

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Clinical efficacy of a RAF inhibitor needs broad target blockade in BRAF-mutant melanoma.

Publications

Clinical efficacy of a RAF inhibitor needs broad target blockade in BRAF-mutant melanoma.

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