Cytotoxic isoflavones from the stem bark of <i>Protea gaguedi</i>

Abstract

<i>Protea gaguedi</i> is widely used in Ethiopia for the treatments of diarrhea, tumor, urological diseases, and menorrhagia. Despite its extensive use by traditional healers, the pharmacological properties and chemical composition of this medicinal plant remain largely unexplored. Anticipated by these claims, the chromatographic separation of CH₂Cl₂/CH₃OH (1:1) stem bark extract of <i>P. gaguedi</i> led to the isolation of a new isoflavone (<b>1</b>) together with five known compounds: jamaicin (<b>2</b>), 5-methoxydurmillone (<b>3</b>), dipteryxine (<b>4</b>), 4'-<i>O</i>-geranylisoliquiritigenin (<b>5</b>), and stigmasterol (<b>6</b>), whose structures were determined using IR, UV, MS, and NMR and comparison with literature data. The cytotoxic effects of the isolated compounds were evaluated using human cervical carcinoma cell line, KB-3-1. Compounds <b>1</b>, <b>2</b>, and <b>3</b> demonstrated remarkable cytotoxicity with IC₅₀ values of 24.6 nM, 3.09 µM, and 21.70 µM, respectively, while the other compounds demonstrated negligible or no inhibitory activities against the tested strain. Following the high cytotoxicity of compound <b>1</b> against KB-3-1, its activity against the multidrug-resistant subclone KB-V1 was also evaluated and revealing an IC₅₀ of 17.5 nM. <i>In silico</i> molecular docking analyses were performed for these active compounds and revealed relative binding energies (-10.0, -9.4, -9.5 kJ/mol for compounds <b>1</b>, <b>2</b> and <b>3</b>, respectively) against the ternary target protein complex HPV16 E6/E6AP/p53 (PDB ID: 4XR8). ADME analysis also revealed good cytotoxicity candidacy of these compounds, provided that <i>in vivo</i> activities have been performed for further confirmation.