Modulation of Autophagy by a Thioxanthone Decreases the Viability of Melanoma Cells

Abstract

(1) Background: Our previous studies unveiled the hit thioxanthone TXA1 as an inhibitor of P-glycoprotein (drug efflux pump) and of human tumor cells growth, namely of melanoma cells. Since TXA1 is structurally similar to lucanthone (an autophagy inhibitor and apoptosis inducer) and to N 10 -substituted phenoxazines (isosteres of thioxanthones, and autophagy inducers), this study aimed at further assessing its cytotoxic mechanism and evaluating its potential as an autophagy modulator in A375-C5 melanoma cells; (2) Methods: Flow cytometry with propidium iodide (PI) for cell cycle profile analysis; Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, flow cytometry with Annexin V/PI labeling and Western blot for apoptosis analysis were conducted. A pharmacophore approach was used for mapping TXA1 onto pharmacophores for autophagy induction. Autophagy analyses included transmission electron microscopy for visualization of autophagic structures, fluorescence microscopy for observation of monodansylcadaverine (MDC) staining, pattern of LC3 expression in the cells and acridine orange staining, and Western blot for autophagic proteins expression; (3) Results: TXA1 induced autophagy of melanoma cells at the GI 50 concentration (3.6 µM) and apoptosis at twice that concentration. Following treatment with TXA1, autophagic structures were observed, together with the accumulation of autophagosomes and the formation of autophagolysosomes. An increase in LC3-II levels was also observed, which was reverted by 3-methyladenine (3-MA) (an early stage autophagy-inhibitor) but further increased by E-64d/pepstatin (late-stage autophagy inhibitors). Finally, 3-MA also reverted the effect of TXA1 in cellular viability; (4) Conclusion: TXA1 decreases the viability of melanoma cells by modulation of autophagy and may, therefore, serve as a lead compound for the development of autophagy modulators with antitumor activity.

Clinical significance of miR-138 in patients with malignant melanoma through targeting of PDK1 in the PI3K/AKT autophagy signaling pathway

“…Cell autophagy can not only eliminate the metabolic products of cells and abnormal intracellular proteins, but can also degrade redundant or damaged organelles (11). Autophagy can be induced during early newborn development, hypoxia, infection and hunger, and its degradation products can provide materials and energy for cells, thus maintaining cell homeostasis (22).…”

“…The autophagy-related genes are critical factors that regulate the process of autophagy (10). The primary functions of autophagy are to eliminate biological waste materials within the body and to promote metabolism by degradation of damaged organelles under stress conditions, such as hunger, which aids in the self-protection of cells and promotes cell survival (11). However, excessive autophagy decreases cell survival by promoting autophagic cell death (11).…”

Enantiomeric Resolution and Docking Studies of Chiral Xanthonic Derivatives on Chirobiotic Columns

“…During the last few decades there has been widespread interest in oxygenated heterocyclic compounds such as molecules with a xanthone scaffold [ 1 , 2 , 3 ], mainly in consideration of their important roles as bioactive agents and because xanthone is an attractive core for molecular modifications [ 4 , 5 , 6 , 7 , 8 , 9 ] and the design of new molecular entities [ 10 , 11 ]. Xanthonic derivatives can be isolated from terrestrial [ 12 , 13 ] and marine [ 2 ] sources, or obtained by synthesis using different synthetic methodologies [ 14 , 15 ].…”

The Antitumor Activity of a Lead Thioxanthone is Associated with Alterations in Cholesterol Localization

“…We have previously shown that a synthetic hit thioxanthonic molecule (1-{[2-(diethylamino)ethyl]amino}-4-propoxy-9H-thioxanthen-9-one, TXA1) and its soluble salt (TXA1.HCl), reduced the in vitro growth of a panel of human tumor cell lines, without affecting the growth of non-tumor cells [18,19,20]. Such antitumor effect was shown to involve autophagy modulation in melanoma and breast cancer cells [20]. Nevertheless, the underlying mechanism of action of TXA1.HCl was not fully elucidated, nor was its antitumor potential in vivo verified.…”