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Ovarian cancer (OC) is the most lethal gynecologic malignancy, and melatonin has shown various antitumor properties. Herein, we investigated the influence of melatonin therapy on energy metabolism and mitochondrial integrity in SKOV-3 cells and tested whether its effects depended on MT1 receptor activation. SKOV-3 cells were exposed to different melatonin concentrations, and experimental groups were divided as to the presence of MT1 receptors (melatonin groups) or receptor absence by RNAi silencing (siRNA MT1+melatonin). Intracellular melatonin levels increased after treatment with melatonin independent of the MT1. The mitochondrial membrane potential of SKOV-3 cells decreased in the group treated with the highest melatonin concentration. Melatonin reduced cellular glucose consumption, while MT1 knockdown increased its consumption. Interconversion of lactate to pyruvate increased after treatment with melatonin and was remarkable in siRNA MT1 groups. Moreover, lactate dehydrogenase activity decreased with melatonin and increased after MT1 silencing at all concentrations. The UCSC XenaBrowser tool showed a positive correlation between the human ASMTL gene and the ATP synthase genes, succinate dehydrogenase gene (SDHD), and pyruvate dehydrogenase genes (PDHA and PDHB). We conclude that melatonin changes the glycolytic phenotype and mitochondrial integrity of SKOV-3 cells independent of the MT1 receptor, thus decreasing the survival advantage of OC cells.

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Ovarian cancer (OC) has a high mortality rate. Although most patients respond to the conventional chemotherapy [e.g., paclitaxel (PTX)], some also develop drug resistance to make the treatment less effective. Since melatonin exhibits antioxidant, antitumor, and immunomodulatory functions in a variety of solid tumors, in this study the effects of a combination of PTX and melatonin on SKOV-3 human ovarian carcinoma cells were investigated and the focus was given to the Toll-like receptor (TLR)-mediated inflammatory pathway and cell signaling-related molecules. Flow cytometry showed that this combination significantly boosted the apoptosis/necrosis responses of the cancer cells. Cell migration was attenuated by melatonin alone, and the combination led to a reduced number of migrating and invasive cells. Melatonin alone and its combination also reduced the levels of TLR4, MyD88, TRIF, and PD-L1, but not TLR2. In addition, the combination significantly lowered the levels of NF-kB p65, PI3K, p-AKT, p38, ERK 1/2, JNK, CREB, p70s6K, and STAT5. The results suggested that this combination was effective in reducing the viability and the invasive capacity of SKOV-3 cells while increasing their apoptosis and necrosis rates. The potential mechanism of this combination is to attenuate the downstream molecules of the TLR4-mediated inflammatory pathway and cell signaling-related proteins in the cancer cells. Thus, melatonin improved the chemosensitivity of the cancer cells to PTX, serving as an effective adjuvant therapy against OC.

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