Targeted inhibitors elicit heterogeneous clinical responses in genetically stratified groups of patients.,While most studies focus on tumor intrinsic properties, factors in the tumor microenvironment were recently found to modulate the response to inhibitors.,Here, we show that in cutaneous BRAF V600E melanoma, the cytokine TNFα blocks RAF-inhibitor-induced apoptosis via activation of nuclear factor κB (NFκB).,Several NFκB-dependent factors are up-regulated following TNFα and RAF inhibitor treatment.,Of these factors, we show that death receptor inhibitor cellular caspase 8 (FLICE)-like inhibitory protein (c-FLIP) is required for TNFα-induced protection against RAF inhibitor.,Overexpression of c-FLIP_S or c-FLIP_L isoform decreased RAF inhibitor-induced apoptosis in the absence of TNFα.,Importantly, targeting NFκB enhances response to RAF inhibitor in vitro and in vivo.,Together, our results show mechanistic evidence for cytokine-mediated resistance to RAF inhibitor and provide a preclinical rationale for the strategy of co-targeting the RAF-MEK-ERK1/2 pathway and the TNFα/NFκB axis to treat mutant BRAF melanomas.
Molecular chaperone heat shock protein 90 (Hsp90) inhibitors are promising targeted cancer therapeutic drugs, with the advantage that they deplete multiple oncogenic client proteins and modulate all the classical hallmarks of cancer.,They are now in clinical trial and show potential for activity in melanoma and other malignancies.,Here we explore the metabolic response to Hsp90 inhibition in human melanoma cells using magnetic resonance spectroscopy.,We show that, concomitant with growth inhibition and re-differentiation, Hsp90 inhibition in human melanoma cells is associated with increased glycerophosphocholine content.,This was seen with both the clinical geldanamycin-based Hsp90 drug 17-AAG and the structurally dissimilar Hsp90 inhibitor CCT018159.,The effect was noted in both BRAF mutant SKMEL28 and BRAF wildtype CHL-1 melanoma cells.,Elevated content of the -CH2+CH3 fatty acyl chains and cytoplasmic mobile lipid droplets was also observed in 17-AAG-treated SKMEL28 cells.,Importantly, the phospholipase A2 inhibitor bromoenol lactone prevented the rise in glycerophosphocholine seen with 17-AAG, suggesting a role for phospholipase A2 activation in the Hsp90 inhibitor-induced metabolic response.,Our findings provide a basis for using metabolic changes as non-invasive indicators of Hsp90 inhibition and potentially as biomarkers of anticancer activity with Hsp90 drugs in malignant melanoma and possibly in other cancers.