Significant and Various Effects of ML329-Induced MITF Suppression in the Melanoma Cell Line

Abstract

To study the inhibitory effects on microphthalmia-associated transcription factor (MITF)-related biological aspects in malignant melanomas (MMs) in the presence or absence of the low-molecular MITF specific inhibitor ML329, cell viability, cellular metabolic functions, and three-dimensional (3D) spheroid formation efficacy were compared among MM cell lines including SK-mel-24, A375, dabrafenib- and trametinib-resistant A375 (A375DT), and WM266-4. Upon exposure to 2 or 10 μM of ML329, cell viability was significantly decreased in WM266-4, SK-mel-24, and A375DT cells, but not A375 cells, in a dose-dependent manner, and these toxic effects of ML329 were most evident in WM266-4 cells. Extracellular flux assays conducted using a Seahorse bioanalyzer revealed that treatment with ML329 increased basal respiration, ATP-linked respiration, proton leakage, and non-mitochondrial respiration in WM266-4 cells and decreased glycolytic function in SK-mel-24 cells, whereas there were no marked effects of ML329 on A375 and A375DT cells. A glycolytic stress assay under conditions of high glucose concentrations also demonstrated that the inhibitory effect of ML329 on the glycolytic function of WM266-4 cells was dose-dependent. In addition, ML329 significantly decreased 3D-spheroid-forming ability, though the effects of ML329 were variable among the MM cell lines. Furthermore, the mRNA expression levels of selected genes, including STAT3 as a possible regulator of 3D spheroid formation, KRAS and SOX2 as oncogenic-signaling-related factors, PCG1a as the main regulator of mitochondrial biogenesis, and HIF1a as a major hypoxia transcriptional regulator, fluctuated among the MM cell lines, possibly supporting the diverse ML329 effects mentioned above. The findings of diverse ML329 effects on various MM cell lines suggest that MITF-associated biological activities are different among various types of MM.

Role of Surgery in Metastatic Melanoma and Review of Melanoma Molecular Characteristics

“…Currently, there are no direct inhibitors of MITF available. However, various investigations have identified possible treatment candidates that target the upstream regulators and downstream effectors of MITF, including the following: HDAC inhibitors decrease MITF expression and inhibit tumor growth in the human cutaneous melanoma xenograft model; The HDAC trichostatin A (TSA) increases miR-137 expression, reducing MITF expression in uveal melanoma cells; A small molecule inhibitor of p300/CBP significantly reduces human cutaneous melanoma cells in vitro; Both the HDAC inhibitor ACY-1215 and a small-molecule inhibitor of the MITF pathway (ML329) decrease the proliferation of the metastatic uveal melanoma (UM) cell line in vitro [ 23 ]. …”

“…Both the HDAC inhibitor ACY-1215 and a small-molecule inhibitor of the MITF pathway (ML329) decrease the proliferation of the metastatic uveal melanoma (UM) cell line in vitro [ 23 ].…”