The GRP78/BiP inhibitor HA15 synergizes with mitotane action against adrenocortical carcinoma cells through convergent activation of ER stress pathways

Many types of cancer cells present constitutively activated ER stress pathways because of their significant burden of misfolded proteins coded by mutated and rearranged genes. Further increase of ER stress by pharmacological intervention may shift the balance towards cell death and can be exploited therapeutically. Recent studies have shown that an important component in the mechanism of action of mitotane, the only approved drug for the medical treatment of adrenocortical carcinoma (ACC), is represented by activation of ER stress through inhibition of the SOAT1 enzyme and accumulation of toxic lipids. Here we show that HA15, a novel inhibitor of the essential ER chaperone GRP78/BiP, inhibits ACC H295R cell proliferation and steroidogenesis and is able to synergize with mitotane action. These results suggest that convergent activation of ER stress pathways by drugs acting via different mechanisms represents a valuable therapeutic option for ACC.