Mefloquine induces ER stress and apoptosis in BRAFi-resistant A375-BRAFV600E/NRASQ61K malignant melanoma cells targeting intracranial tumors in a bioluminescent murine model

Molecularly targeted therapeutics have revolutionized the treatment of BRAF(V600E)-driven malignant melanoma, but the rapid development of resistance to BRAF kinase inhibitors (BRAFi) presents a significant obstacle. The use of clinical antimalarials for the investigational treatment of malignant melanoma has shown only moderate promise, attributed mostly to inhibition of lysosomal-autophagic adaptations of cancer cells, but identification of specific antimalarials displaying single-agent antimelanoma activity has remained elusive. Here, we have screened a focused library of clinically used artemisinin-combination therapeutic (ACT) antimalarials for the apoptotic elimination of cultured malignant melanoma cell lines, also examining feasibility of overcoming BRAFi-resistance comparing isogenic melanoma cells that differ only by NRAS mutational status (BRAFi-sensitive A375-BRAF(V600E)/NRAS(Q61) vs. BRAFi-resistant A375-BRAF(V600E)/NRAS(Q61K)). Among ACT antimalarials tested, mefloquine (MQ) was the only apoptogenic agent causing melanoma cell death at low micromolar concentrations. Comparative gene expression-array analysis (A375-BRAF(V600E)/NRAS(Q61) vs. A375-BRAF(V600E)/NRAS(Q61K)) revealed that MQ is a dual inducer of endoplasmic reticulum (ER) and redox stress responses that precede MQ-induced loss of viability. ER-tracker(TM) DPX fluorescence imaging and electron microscopy indicated ER swelling, accompanied by rapid induction of ER stress signaling (phospho-eIF2 alpha, XBP-1s, ATF4). Fluo-4 AM-fluorescence indicated the occurrence of cytosolic calcium overload observable within seconds of MQ exposure. In a bioluminescent murine model employing intracranial injection of A375-Luc2 (BRAF(V600E)/NRAS(Q61K)) cells, an oral MQ regimen efficiently antagonized brain tumor growth. Taken together, these data suggest that the clinical antimalarial MQ may be a valid candidate for drug repurposing aiming at chemotherapeutic elimination of malignant melanoma cells, even if metastasized to the brain and BRAFi-resistant.

Automated summary

The study suggests that the clinical antimalarial drug mefloquine may be an effective candidate for drug repurposing to eliminate malignant melanoma cells, even when metastasized to the brain and resistant to BRAF kinase inhibitors.