BRAF status and mitogen-activated protein/extracellular signal-regulated kinase kinase 1/2 activity indicate sensitivity of melanoma cells to anthrax lethal toxin

Abstract

Anthrax lethal toxin, composed of protective antigen and lethal factor, was tested for cytotoxicity to human melanoma cell lines and normal human cells. Eleven of 18 melanoma cell lines were sensitive to anthrax lethal toxin (IC 50 < 400 pmol/L) and 10 of these 11 sensitive cell lines carried the V599E BRAF mutation. Most normal cell types (10 of 15) were not sensitive to anthrax lethal toxin and only 5 of 15 normal human cell types were sensitive to anthrax lethal toxin (IC 50 < 400 pmol/L). These cells included monocytes and a subset of endothelial cells. In both melanoma cell lines and normal cells, anthrax toxin receptor expression levels did not correlate with anthrax lethal toxin cytotoxicity. Furthermore, an anthrax toxin receptor -deficient cell line (PR230) did not show any enhanced sensitivity to anthrax lethal toxin when transfected with anthrax toxin receptor. Anthrax lethal toxin toxicity correlated with elevated phosphorylation levels of mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) 1/2 in both melanoma cell lines and normal cells. Anthrax lethal toxin -sensitive melanoma cell lines and normal cells had higher phospho-MEK1/2 levels than anthrax lethal toxin -resistant melanoma cell lines and normal tissue types. U0126, a specific MEK1/2 inhibitor, was not toxic to anthrax lethal toxinresistant melanoma cell lines but was toxic to 8 of 11 anthrax lethal toxin -sensitive cell lines. These results show that anthrax lethal toxin toxicity correlates with elevated levels of active MEK1/2 pathway but not with anthrax toxin receptor expression levels in both normal and malignant tissues. Anthrax lethal toxin may be a useful therapeutic for melanoma patients, especially those carrying the V599E BRAF mutation with constitutive activation of the mitogen-activated protein kinase pathway. [Mol Cancer Ther 2005;4(9):1303 -10]

Heterodimeric integrin complexes containing β1-integrin promote internalization and lethality of anthrax toxin

“…Diverse cell lines treated with LF-PA show a wide range of sensitivities to the toxin (9,(20)(21)(22)(23)(24)(25), and cell death occurs only in cells that have impaired MAPK kinase function (21). We hypothesized that such phenotypic differences might enable microarray-based identification of other genes whose differentially elevated or reduced expression correlates with differential toxin lethality.…”

“…GABRIEL software (26) separated cancer cell lines (SK-MEL-5, SK-MEL28, M-14, MALME-3M, MDA-MB-435, MDA-N, SK-MEL-2, HL-60, MCF7, SW-620, EKVX, and A549) into two groups, LF-PA-sensitive and LF-PA-resistant, based on previous reports (9,(20)(21)(22)(23)(24)(25). GABRIEL (27) was used for correlation of steady-state levels of expression with toxin lethality.…”

Systemic Anthrax Lethal Toxin Therapy Produces Regressions of Subcutaneous Human Melanoma Tumors in Athymic Nude Mice

“…Furthermore, we showed that only V599E BRAF mutant melanoma cell lines are sensitive to LeTx whereas Q61K/R N-Ras mutant melanoma cells are not (15). A pilot study of the in vivo potency of LeTx by Koo and colleagues showed that the i.t.…”

Targeting the Raf-MEK-ERK mitogen-activated protein kinase cascade for the treatment of cancer

“…LeTx was shown to block the transformed and tumorigenic growth of Ras-transformed rodent fibroblasts (Duesbery et al, 2001). LeTx also showed preferential inhibition of growth of melanoma cell lines that harbored mutated B-Raf and elevated ERK activity (Abi-Habib et al, 2005). Yersinia outer protein J (YopJ) is another bacterial toxin that inhibits MEK function.…”