Suppression of B-Raf(V600E) cancers by MAPK hyper-activation

Abstract

B-Raf(V600E) activates MEK/MAPK signalling and acts as oncogenic driver of a variety of cancers, including melanoma, colorectal and papillary thyroid carcinoma. Specific B-Raf(V600E) kinase inhibitors (e.g., Vemurafenib) prove initial efficacy in melanoma followed shortly by acquired resistance, while failing in most other B-Raf(V600E) cancers due to primary resistance. Resistance is due to acquired mutations in the Ras/Raf/MEK/MAPK pathway and/or other oncogenic drivers that bypass B-Raf(V600E). Surprisingly, hyper-activation of MAPK by inhibiting its protein phosphatase 2A by a synthetic long-chain fatty acid analogue (MEDICA), results in oncogene-induced growth arrest and apoptosis of B-Raf(V600E) cancer cells. Growth arrest is accompanied by MAPK-mediated serine/threonine phosphorylation and suppression of a variety of oncogenic drivers that resist treatment by B-Raf(V600E) kinase inhibitors, including ErbB members, c-Met, IGFR, IRS, STAT3 and Akt. The combined activities of mutated B-Raf and MEDICA are required for generating hyper-activated MAPK, growth arrest and apoptosis, implying strict specificity for mutated B-Raf cancer cells.

Treatment of ErbB2 breast cancer by mitochondrial targeting

“…Cells were treated as indicated and rinsed on ice three times with PBSCM (PBSx1 pH 8.0, 0.5 mM CaCl, 1 mM MgCl 2 ), followed by adding non-permeable Sulfo-NHS-SS-Biotin (Thermo Scientific) in PBSCM (0.5 mg/ml) for 15 min. Cells were then rinsed with PBSCM, quenched for 10 min at 4 °C with glycine buffer (PBSx1 pH 8.0, 0.1 M Tris pH 8.0, 192 mM glycine), and rinsed twice with PBSx1 pH 8.0, followed by lysing the cells in lysis buffer [ 24 ]. Cells were then centrifuged at 12,000 g for 15 min at 4 °C, supernatant aliquot was kept at − 70 °C for further Western analysis, and the rest incubated overnight at 4 °C with 25 μl of streptavidin beads (Streptavidin Agarose Resin, Thermo Scientific).…”

“…Cells were then centrifuged at 12,000 g for 15 min at 4 °C, supernatant aliquot was kept at − 70 °C for further Western analysis, and the rest incubated overnight at 4 °C with 25 μl of streptavidin beads (Streptavidin Agarose Resin, Thermo Scientific). Beads were rinsed three times with lysis buffer and subjected to Western analysis [ 24 ].…”

“…Protein concentration was determined by BCA (Thermo Scientific). Western blots were analyzed as previously described [ 24 ].…”

Refractory thyroid carcinoma: which systemic treatment to use?

“…In 45–59% of cases, DTCs express a mutation of the gene coding the BRAF protein, 18 , 19 more often in papillary carcinoma than in follicular carcinoma. This mutation activates the MAPK signaling pathway and is associated with a certain degree of tumor aggressiveness, 17 , 19 resulting in a higher incidence in patients with a recurrence or metastasis of a papillary carcinoma. 20 In 40–50% of follicular carcinomas, there is also a RAS mutation leading to constitutive activation of the two MAPK and PI3K/AKT/mTOR signaling pathways.…”

Acquired resistance mechanisms to immunotherapy

“…Finally, several groups are currently investigating combination of targeted and immunotherapy (16)(17)(18)(19). The potential acquired resistance mechanisms described by Zaretsky et al should be taken in consideration when knew therapeutic combinations are tested, particularly because cross-resistance is possible.…”