Vemurafenib (
PLX4032), an inhibitor of BRAF(V600E), has demonstrated significant clinical anti-
melanoma effects. However, the majority of treated patients develop resistance, due to a variety of molecular mechanisms including MAPK reactivation through
MEK. The induction of a
cancer cell death modality associated with danger-signalling resulting in surface mobilization of crucial damage-associated-molecular-patterns (DAMPs), e.g.
calreticulin (CRT) and heat shock protein-90 (HSP90), from dying cells, is emerging to be crucial for therapeutic success. Both cell death and danger-signalling are modulated by autophagy, a key adaptation mechanism stimulated during
melanoma progression. However, whether
melanoma cell death induced by MAPK inhibition is associated with danger-signalling, and the reliance of these mechanisms on autophagy, has not yet been scrutinized. Using a panel of isogenic PLX4032-sensitive and resistant
melanoma cell lines we show that PLX4032-induced
caspase-dependent cell death and DAMPs exposure in the
drug-sensitive cells, but failed to do so in the
drug-resistant cells, displaying heightened
MEK activation.
MEK inhibitor,
U0126, treatment sensitized PLX4032-resistant cells to death and re-established their danger-signalling capacity. Only
melanoma cells exposing death-induced danger-signals were phagocytosed and induced DC maturation. Although the PLX4032-resistant
melanoma cells displayed higher basal and
drug-induced autophagy, compromising autophagy, pharmacologically or by ATG5 knockdown, was insufficient to re-establish their
PLX4032 sensitivity. Interestingly, autophagy abrogation was particularly efficacious in boosting cell death and ecto-CRT/ecto-HSP90 in PLX4032-resistant cells upon blockage of
MEK hyper-activation by
U0126. Thus combination of
MEK inhibitors with autophagy blockers may represent a novel treatment regime to increase both cell death and danger-signalling in
Vemurafenib-resistant metastatic
melanoma.