Alcaloides indólicos de Tabernaemontana catharinensis: fracionamento, isolamento, síntese e estudos de atividade in vitro e in silico

Abstract

The molecular diversity provided by plants has been used successfully in the field of medicinal chemistry, especially in obtaining substances, since the plant’s secondary metabolites, in many cases, are active in biological systems. As a result, there is a source of new substances as prototypes in the search for new drugs. Alkaloids are the class with the greatest structural diversity in nature. Focusing on biological activity, in vitro and in vivo, these compounds have been applied, mainly, as mitotic inhibitors, as well as the disassembly of microtubules and topoisomerase I inhibitors. Therefore, this work aimed to conduct a bio-guided study of the antitumor activity of the indole alkaloids from the plant Tabernaemontana catharinensis. For this, fractions were obtained and evaluated for cytotoxicity in vitro against two tumor lines A375 (melanoma) and A549 (lung). In addition, the indole alkaloids identified in these fractions were evaluated for their in silico toxicity and binding affinities with the topoisomerase I enzyme. In the preliminary result, it was noticed that the most active fraction was contained the indole alkaloid affinisine. Thus, this substance was carried-out, as well chemically characterized by NMR and HRMS. Subsequently, this compound was tested in vitro with different strains of melanoma (A375, WM1366 and SK-MEL-28), in addition to evaluating the induction of apoptosis and the arrest of the cell cycle to identify the mechanism of action. The result of this second step showed that the affinisine was more active compared to the lines WM1366 and A375, with IC50 varying between 32.86 and 57.62 μg/mL. Furthermore, the induction of apoptosis and the arrest of cells in the G0/G1 phase indicated that the compound might be a potential prototype for the development of new antineoplastic agents. In this context, the last step of this study was the proposal of nine compounds with a structure similar to affinisine and molecular simplification, for in silico evaluation regarding the activity, toxicity and binding affinities with topoisomerase I. Based on the results obtained, the synthesis of a compound and evaluation of cytotoxicity against melanoma cells (WM1366 and A375) were performed. However, the substance showed no activity against these cell lines. In summary, this work indicated that affinisine is the best prototype and can be used in new antitumor studies, as a basic structure model for the search for other active compounds.