Preventive effects of <i>Dendrobium</i> hybrid extract on free radical activity and melanoma cell proliferation by inducing apoptotic gene expression

<i>Dendrobium</i> species are used in folk medicines due to their medicinal properties by acting as antioxidants and anticancer agents. Derived from parent plants used in dermatological treatments and cosmetics, <i>Dendrobium</i> Pearl Vera hybrid (DH) was extracted and investigated for its inhibitory effects on free radicals and skin cancer cell proliferation. Based on colorimetric spectrophotometry, the propanolic extract (DH-P) from the whole plant contained flavonoids, phenolics and alkaloids at 80.11±0.69, 50.51±0.44 and 38.75±1.77 µg/g fresh weight, respectively. Using high-resolution mass spectrometry, eight compounds involved in skin protection were annotated: Fuanosine, L-glutamine, threonic acid, quercetagetin, shikimic acid, mannose, <i>p</i>-coumaric acid and L-malic acid. DH-P scavenged free radicals in a concentration-dependent manner and inhibited the activity of collagenase and hyaluronidase, but not in a concentration-dependent manner. Treatment using DH-P for 96 h significantly decreased the proliferation of SK-MEL-28 melanoma cells in a dose-dependent manner, with a half-maximal inhibitory concentration of 20.23±1.04 µg/ml. Thus, DH-P at 20 µg/ml was used in further studies. Cell migration was not inhibited by DH-P. However, DH-P may induce SK-MEL-28 cell death through apoptosis, as nuclear condensation and fragmentation was observed after 48 h DH-P treatment. Gene expression analysis was performed to evaluate key signaling molecules involved in cell apoptosis, such as <i>bax</i>, <i>bcl-2</i>, <i>cytochrome c</i>, caspases (<i>cas)-3</i> and <i>-9</i> and <i>p53</i>. The expression levels of <i>cas-3</i> and <i>cas-9</i>, executors in the apoptosis pathway, were significantly upregulated in the SK-MEL-28 cells treated with DH-P for 48 h, further confirming that cell death may occur through an apoptosis mechanism.