In Vitro Shoot Cultures of <i>Micromeria graeca</i>: Micropropagation and Evaluation of Methanolic Extracts for Anticancer and Antimicrobial Activity

<i>Micromeria graeca</i> (L.) Benth. ex Rchb. (Lamiaceae) is a promising medicinal plant valued for its antioxidant, anti-hyperglycemic, anti-hypertensive, antimicrobial, and anti-aflatoxigenic properties. It is rich in phenolic and flavonoid compounds, supporting its traditional use for digestive, respiratory, cardiovascular, and dermatological conditions. Plant tissue culture facilitates controlled in vitro propagation to study plant growth and bioactive properties. The effects of activated charcoal and varying subculture intervals on multiplication and biomass production in <i>M. graeca</i> shoot cultures were investigated. The phenolic composition of methanolic extracts from in vitro-grown plants was characterized using high-performance liquid chromatography (HPLC), identifying rosmarinic, caffeic, and syringic acids as the primary phenolic compounds. Antimicrobial activity against selected microbial strains was evaluated using a micro-well dilution assay. Anticancer activity of selected extracts was assessed in human hepatocellular carcinoma cell line HepG2, with flow cytometry (Annexin-V/PI staining) used to analyze cell death mechanisms, and compared to pure rosmarinic acid (RA). Activated charcoal showed no beneficial effects on multiplication or biomass production, but significantly increased phenolic acid content (up to 4-fold). RA dominated the phenolic profiles, with other phenolic acids present in lower amounts. Methanolic extracts exhibited negligible antimicrobial activity compared to reference antibiotics and fungicide. Extracts from 4-week-old shoot cultures displayed modest anti-hepatoma activity (IC50 values of CV assay ranging from 193 to 274 µg mL⁻¹), inducing HepG2 cell apoptosis via oxidative stress, independent of RA. Our results suggest that the metabolic output of <i>M. graeca</i> shoot cultures and consequently their biological activity can be modulated by varying in vitro culture conditions. These findings underscore the potential of their methanolic extracts for biotechnological production and therapeutic applications.