Portuguese Propolis Antitumoral Activity in Melanoma Involves ROS Production and Induction of Apoptosis

Abstract

Melanoma is the most aggressive and life-threatening skin cancer type. The melanoma genome is the most frequently mutated, with the BRAF mutation present in 40–60% of melanoma cases. BRAF-mutated melanomas are characterized by a higher aggressiveness and progression. Adjuvant targeted treatments, such as BRAF and MEK inhibitors, are added to surgical excision in BRAF-mutated metastatic melanomas to maximize treatment effectiveness. However, resistance remains the major therapeutic problem. Interest in natural products, like propolis, for therapeutic applications, has increased in the last years. Propolis healing proprieties offer great potential for the development of novel cancer drugs. As the activity of Portuguese propolis has never been studied in melanoma, we evaluated the antitumoral activity of propolis from Gerês (G18.EE) and its fractions (n-hexane, ethyl acetate (EtOAc), and n-butanol) in A375 and WM9 melanoma cell lines. Results from DPPH•/ABTS• radical scavenging assays indicated that the samples had relevant antioxidant activity, however, this was not confirmed in the cell models. G18.EE and its fractions decreased cell viability (SRB assay) and promoted ROS production (DHE/Mitotracker probes by flow cytometry), leading to activation of apoptotic signaling (expression of apoptosis markers). Our results suggest that the n-BuOH fraction has the potential to be explored in the pharmacological therapy of melanoma.

Selective Cytotoxicity of Portuguese Propolis Ethyl Acetate Fraction towards Renal Cancer Cells

“…Chemical composition of the G18.EE and its fractions was already investigated and published by our research group [26], revealing the presence of compounds such as apigenin, pinobanksin, pinobanksin 3-O-acetate, chrysin, acacetin, CAIE, and pinocembrin. Partitioning of G18.EE-EtOAc fraction led to the isolation of the compound P1 and eleven subfractions (FG2-FG7 and FG8-1-FG8-5) composed of a mixture of compounds (Figure 1).…”

Phenolic Compounds Contribution to Portuguese Propolis Anti-Melanoma Activity

“…Propolis from Gerês, one of the most studied Portuguese propolis [ 40 , 41 , 42 , 43 , 44 , 45 , 46 ], displays high antioxidant and antimicrobial activities, regardless of the harvesting year [ 40 ]. An ethanol extract of propolis from Gerês collected in 2018 (G18.EE) and its three fractions—ethyl acetate (G18.EE-EtOAc), n -hexane (G18.EE- n -hexane), and n -butanol (G18.EE- n -BuOH)—promoted apoptosis mediated by ROS (reactive oxygen species) in melanoma, thus demonstrating to be cytotoxic to BRAF -mutated melanoma cell lines.…”

“…G18.EE- n -BuOH emerged as the fraction with the highest activity among the tested samples. This result suggests that G18.EE- n -BuOH can be an interesting melanoma therapeutic source [ 43 ]. In this way, G18.EE- n -BuOH was fractioned to separate its components in subfractions according to their polarity, and the cytotoxic effect of the obtained subfractions was assessed in A375—a BRAF -mutated melanoma cell line.…”

An Insight on the Biomedical Potential of Portuguese Propolis from Gerês

“…Portuguese propolis is far from being completely characterized but results to date indicate that this natural product exhibits some biological properties, namely antimicrobial, mainly antibacterial, but also antifungal activities [ 35 , 36 , 37 , 38 , 39 ]; antioxidant potential [ 35 , 40 , 41 , 42 ]; as well as genotoxic [ 40 , 41 , 43 ] and antitumor [ 38 , 44 , 45 , 46 ] activities, renewing the interest in researching national propolis. More recently, Portuguese propolis samples from Gerês revealed constancy in biological and chemical profiles over the years [ 35 ], which seems to be a distinctive and particular feature of this kind of propolis.…”