Molecular determinants of melanoma malignancy: Selecting targets for improved efficacy of chemotherapy

Abstract

The BRAFV600E mutation is common in human melanoma. This mutation enhances IκB kinase (IKK)/nuclear factor-κB (NF-κB) and extracellular signal-regulated kinase/activator protein signaling cascades. In this study, we evaluated the efficacy of targeting either B-Raf or IKKβ in combination with the DNA alkylating agent temozolomide for treatment of advanced metastatic melanoma. Xenografts of Hs294T human metastatic melanoma cells exhibiting the BRAFV600E mutation were treated with inhibitors of IKKβ (BMS-345541), B-Raf (BAY 54-9085), and/or temozolomide. Drug response was mechanistically analyzed in vitro and in vivo. In this study, we determined that the antitumor activity of all three drugs depends on inhibition of NF-κB. BMS-345541 inhibits IKKβ-mediated phosphorylation of IκBα and thus blocks the nuclear localization of NF-κB, whereas BAY 54-9085 inhibits activation of NF-κB through a mechanism that does not involve stabilization of IκBα. Moreover, BMS-345541, but not BAY 54-9085, activates the death pathways of p53 and c-Jun-NH 2-kinase, contributing to the killing of melanoma cells. Temozolomide inhibits both NF-κB and extracellular signal-regulated kinase activity, conferring effective in vivo antitumor activity. Thus, temozolomide, but not BAY 54-9085, has a synergistic in vivo antitumor effect with BMS-345541. We conclude that the efficacy of antimelanoma therapy depends on inhibition of expression of antiapoptotic genes transcriptionally regulated by NF-κB. In contrast, drug targeting of the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway alone in melanoma cells is ineffective for melanoma therapy in cases where NF-κB is not also targeted. Copyright © 2009 American Association for Cancer Research.