SB590885

SB590885 is a potent and selective inhibitor of B-Raf kinase with Ki value of 0.16nM [1].

SB590885 is a potent inhibitor of oncogenic B-Raf protein kinase with Ki value of 0.16nM. It is more potent to inhibit B-Raf than C-Raf. The Ki value of SB590885 for C-Raf is 1.72nM. SB590885 is a quite selective inhibitor. It shows no activity against 48 other human kinases such as Abl, AMPK, CK1, CK2 and ERK2. It is found that SB590885 binds to B-Raf within the ATP-binding pocket and stabilizes the active conformation of B-Raf. SB590885 decreases the phosphorylation of ERK and shows anti-proliferation only in tumor cells expressing oncogenic B-Raf V600E. The normal cells and tumor cells not expressing mutant B-Raf have no sensitivity towards SB590885 except the normal melanocytes and primary melanoma cells expressing wild-type B-Raf. Moreover, SB590885 is also found to decrease the transformed and tumorigenic properties of malignant cells expressing mutant B-Raf [1].

References:
[1] King A J, Patrick D R, Batorsky R S, et al. Demonstration of a genetic therapeutic index for tumors expressing oncogenic BRAF by the kinase inhibitor SB-590885. Cancer research, 2006, 66(23): 11100-11105.

Synergistic antitumour activity of RAF265 and ZSTK474 on human TT medullary thyroid cancer cells.[Pubmed:26081844]

J Cell Mol Med. 2015 Sep;19(9):2244-52.

Medullary thyroid cancer (MTC) is an aggressive malignancy responsible for up to 14% of all thyroid cancer-related deaths. It is characterized by point mutations in the rearranged during transfection (RET) proto-oncogene. The activated RET kinase is known to signal via extracellular signal regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K), leading to enhanced proliferation and resistance to apoptosis. In the present work, we have investigated the effect of two serine/threonine-protein kinase B-Raf (BRAF) inhibitors (RAF265 and SB590885), and a PI3K inhibitor (ZSTK474), on RET-mediated signalling and proliferation in a MTC cell line (TT cells) harbouring the RETC634W activating mutation. The effects of the inhibitors on VEGFR2, PI3K/Akt and mitogen-activated protein kinases signalling pathways, cell cycle, apoptosis and calcitonin production were also investigated. Only the RAF265+ ZSTK474 combination synergistically reduced the viability of treated cells. We observed a strong decrease in phosphorylated VEGFR2 for RAF265+ ZSTK474 and a signal reduction in activated Akt for ZSTK474. The activated ERK signal also decreased after RAF265 and RAF265+ ZSTK474 treatments. Alone and in combination with ZSTK474, RAF265 induced a sustained increase in necrosis. Only RAF265, alone and combined with ZSTK474, prompted a significant drop in calcitonin production. Combination therapy using RAF265 and ZSTK47 proved effective in MTC, demonstrating a cytotoxic effect. As the two inhibitors have been successfully tested individually in clinical trials on other human cancers, our preclinical data support the feasibility of their combined use in aggressive MTC.

The combination of RAF265, SB590885, ZSTK474 on thyroid cancer cell lines deeply impact on proliferation and MAPK and PI3K/Akt signaling pathways.[Pubmed:24821574]

Invest New Drugs. 2014 Aug;32(4):626-35.

Papillary thyroid cancer (PTC) is the most frequent thyroid cancer entity, accounting for 88 % of cases. It may metastasize and loose iodine uptake capability, preventing any radioiodine or surgical treatment. The main gene altered in PTC is BRAF, which is found altered in over 50 % of cases. Moreover MAPK and PI3K/Akt pathways are greatly implicated in PTC development. Many target therapies for PTC are currently under investigation, unfortunately without the expected results. Aim of this study was to characterized the preclinical effectiveness of novel promising drugs, RAF265, SB590885 and ZSTK474 in 3 thyroid cancer cell lines (BCPAP, K1, 8505C). RAF265 and SB590885 target differentially BRAF, while ZSTK474 acts on PI3K. IC50 demonstrated high drug activities ranging from 0.1 to 6.2 muM, depending on drugs and cell type, while combination index revealed an interesting synergistic effect of combination regimen (RAF265 + ZSTK474 and SB590885 + ZSTK474) in almost all cell lines. Moreover this synergistic effect was particularly evident by Western blot, whereas dual MAPK and PI3K/Akt inhibition was detected. In addition, treating cells with SB590885 induced marked morphological changes, leading to massive vacuolization. This suggests an activation of apoptotic process, as underlined by Annexin V flow cytometry analysis. Also cell cycle was altered in treated cells, without evidence of a common pattern, but rather with a more specific effect relying on single drug or combination regimen used. Since beneficial effects of in vitro combination regimen (RAF265 + ZSTK474 and SB590885 + ZSTK474), it is recommended additional investigation. These data suggest the potential use of combination regimen in in vivo experiment or afterwards in human PTC.

B-RAF and its novel negative regulator reticulocalbin 1 (RCN1) modulates cardiomyocyte hypertrophy.[Pubmed:24492844]

Cardiovasc Res. 2014 Apr 1;102(1):88-96.

AIM: Activation of the kinase RAF and its downstream targets leads to cardiomyocyte hypertrophy. It has been hypothesized that B-RAF might be the main activator of MEK in various cell types. Therefore, the aim of this study was to investigate the role of B-RAF and its modulating factors in cardiomyocyte hypertrophy. METHODS AND RESULTS: Neonatal rat cardiomyocytes were pre-treated with and without the specific B-RAF inhibitor SB590885 and then stimulated with phenylephrine to induce hypertrophy. Inhibition of B-RAF completely impeded the hypertrophic response and led to a significant reduction of MEK1/2 phosphorylation. By applying a eukaryotic cDNA expression screen, based on a dual-luciferase reporter assay for B-RAF activity measurement, we identified RCN1 as a new negative modulator of B-RAF activity. Adenovirus-mediated overexpression of reticulocalbin 1 (RCN1) completely impeded phenylephrine-induced hypertrophy and led to significantly reduced MEK1/2 phosphorylation. Conversely, adenoviral knockdown of RCN1 with a specific synthetic miRNA induced cardiomyocyte hypertrophy and significantly increased MEK1/2 phosphorylation. CONCLUSIONS: In summary, our results show that the inhibition of B-RAF abolishes cardiomyocyte hypertrophy and we identified RCN1 as novel negative modulator of cardiomyocyte hypertrophy by inhibition of the mitogen-activated protein kinase signalling cascade. Our results show that B-RAF kinase activity is essential for cardiac hypertrophy and RCN1, its newly identified negative regulator, abolishes hypertrophic response of cardiomyocytes in vitro.

Demonstration of a genetic therapeutic index for tumors expressing oncogenic BRAF by the kinase inhibitor SB-590885.[Pubmed:17145850]

Cancer Res. 2006 Dec 1;66(23):11100-5.

Oncogenic BRAF alleles are both necessary and sufficient for cellular transformation, suggesting that chemical inhibition of the activated mutant protein kinase may reverse the tumor phenotype. Here, we report the characterization of SB-590885, a novel triarylimidazole that selectively inhibits Raf kinases with more potency towards B-Raf than c-Raf. Crystallographic analysis revealed that SB-590885 stabilizes the oncogenic B-Raf kinase domain in an active configuration, which is distinct from the previously reported mechanism of action of the multi-kinase inhibitor, BAY43-9006. Malignant cells expressing oncogenic B-Raf show selective inhibition of mitogen-activated protein kinase activation, proliferation, transformation, and tumorigenicity when exposed to SB-590885, whereas other cancer cell lines and normal cells display variable sensitivities or resistance to similar treatment. These studies support the validation of oncogenic B-Raf as a target for cancer therapy and provide the first evidence of a correlation between the expression of oncogenic BRAF alleles and a positive response to a selective B-Raf inhibitor.

The identification of potent and selective imidazole-based inhibitors of B-Raf kinase.[Pubmed:16260133]

Bioorg Med Chem Lett. 2006 Jan 15;16(2):378-81.

A novel triarylimidazole derivative, SB-590885 (33), bearing a 2,3-dihydro-1H-inden-1-one oxime substituent has been identified as a potent and extremely selective inhibitor of B-Raf kinase.

SB-590885 is a potent B-Raf inhibitor with Ki of 0.16 nM, and has 11-fold greater selectivity for B-Raf over c-Raf, without inhibition to other human kinases.

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