Induction of apoptosis and autophagy in human glioblastoma cells by N-methylflindersine: insights into regulatory role of ERK pathway

Abstract

AIM: Mangrove-associated plants are known for producing natural compounds with antitumor activity. Despite the potential therapeutic value of these compounds, the molecular mechanisms underlying their antitumor effects remain unclear. This study aimed to investigate the antitumor properties of N-methylflindersine, an alkaloid derived from the mangrove-associated plant, Micromelum falcatum (Lour.) Tan., and its effects on U87 human glioblastoma cells. METHODS: We identified and isolated 15 compounds from the stem bark of Micromelum falcatum. Among these, we screened N-methylflindersine for its potential inhibitory effects on U87 cell growth. Various assays, including wound healing, Hoechst 33342/PI staining, and protein expression analysis, were conducted to investigate the compound's impact on cell migration, apoptosis, and autophagy-related proteins. RESULTS: Within 24 h, N-methylflindersine demonstrated the ability to reduce U87 cell migration and increase the apoptotic U87 cell population. Furthermore, it downregulated the anti-apoptosis protein Bcl-2 expression, upregulated the pro-apoptosis protein Bax expression, and elevated the ratio of autophagy-related protein LC3-II/LC3-I in U87 cells. Additionally, the ERK signaling pathway was found to be down-regulated following N-methylflindersine treatment. CONCLUSION: N-methylflindersine appears to induce both apoptosis and autophagic cell death in U87 cells, resulting in reduced cell growth. This effect seems to be associated with the downregulation of the ERK signaling pathway.

1. Introduction

Oceans are abundant repositories of natural compounds. Mangroves are unique marine ecosystems distributed along the coasts of tropical and subtropical regions [1-2]. In addition to widely researched true mangroves and mangrove-associated fungi, mangrove-associated plants growing in the intertidal zone have shown great bioactivity and beneficial application [3-4]. For instance, the aqueous seed extract of Derris trifoliata Lour (a common mangrove liana) has a significantly high 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, multiple antibacterial activities, and a moderate inhibitory effect on A549 cells [5]. The leaf water extract of Barringtonia racemosa (another mangrove-associated plant) modifies the cell cycle and triggers apoptosis in Caco-2 cells [6]. Some mangrove-associated plants were formerly classified as true mangroves; however, they have received more precise descriptions in recent years, including distinctions in leaf features and salt tolerance [7-8]. Some mangrove-associated plant extracts from different genera exhibit antitumor activity [9-11]. This indicates that these plants may be attractive sources of antitumor medicines.

Glioblastomas are the most aggressive brain tumors owing to their frequent occurrence and invasive characteristics within the central nervous system (CNS) [12]. This rapidly developing malignancy has a World Health Organization (WHO) grade 4 CNS tumor, with a poor prognosis that affects the elderly and children [13]. Although surgery, high-dose radiation, and chemotherapy help alleviate patient symptoms, complete glioblastoma control remains a serious problem that must be conquered globally [12]. Therefore, more innovative antineoplastic medicines are urgently required. Xyloketal B is a constituent of the mangrove fungus Xylaria sp. (No. 2508) that inhibits U251 cells by attenuating the MEK/ERK and PI3K/Akt pathways [14]. Mangrove-associated compounds may serve as weapons against glioblastomas.

In this study, 15 compounds were extracted from the stem bark of Micromelum falcatum (a mangrove-associated plant), including ten coumarins 1-10, four alkaloids 11-15, and a new compound (compound 13). Compound 13 (N-methylflindersine) was the focus [15] and exhibited an inhibitory effect against U87 cells. This study explored its antitumor properties and potential mechanisms.