Bioreactor-based production of eumelanin nanoparticles by Streptomyces glaucescens NEAE-H: physicochemical characterization, anticancer and anti-inflammatory activities, and in silico analysis

Abstract

Microbial eumelanin nanoparticles (EuM-NPs) have attracted increasing attention as biocompatible and biodegradable nanomaterials with promising biomedical applications. In the present study, the production of EuM-NPs by Streptomyces glaucescens NEAE-H was optimized in a 7-L stirred-tank bioreactor under controlled fermentation conditions. The study investigated the physicochemical characteristics and the in vivo, in vitro, and in silico anticancer and anti-inflammatory activities of EuM-NPs. The maximum EuM-NPs yield reached 367.51 μg/mL after 22 h of cultivation at an agitation rate of 200 rpm. Physicochemical characterization revealed the formation of nearly spherical nanoparticles with particle sizes ranging from 1.23 to 26 nm and a mean diameter of 15.64 ± 4.576 nm. ζ-potential measurements demonstrated good colloidal stability with a surface charge of − 32.6 ± 4.65 mV. Thermogravimetric analysis confirmed high thermal stability, whereas X-ray diffraction analysis verified the characteristic amorphous structure of the produced EuM-NPs. LC–MS/MS analysis detected the oxidative degradation products pyrrole-2,3-dicarboxylic acid (PDCA) [m/z 156.9] and pyrrole-2,3,5-tricarboxylic acid (PTCA) [m/z 199.9], supporting the presence of eumelanin-derived structural components. In vivo investigations demonstrated significant anticancer activity against Ehrlich ascites carcinoma and solid tumors, reducing tumor volume by up to 78% and tumor weight by up to 83%. Furthermore, EuM-NPs exhibited potent anti-inflammatory activity, achieving 62.62% inhibition of carrageenan-induced paw edema. In vitro cyclooxygenase inhibition assays revealed selective inhibition of COX-2 (IC50 5.61µg/mL , selectivity ratio > 8.91) compared with COX-1 (IC50 > 50 µg/mL ) In silico drug-likeness, pharmacokinetics and molecular docking analyses of seven potential eumelanin 5,6-dihydroxyindole (DHI)-precursors highlighted 2,4′-DHI-dimer as the most promising, showing binding affinities of − 5.93 kcal/mol (COX-1) and − 5.27 kcal/mol (COX-2). These findings demonstrate that controlled bioreactor cultivation significantly reduced the production time required to obtain EuM-NPs by Streptomyces glaucescens NEAE-H while maintaining comparable production levels and highlighted their potential as multifunctional nanomaterials for anticancer therapy, inflammation management, and future nanomedicine applications.