Antitumor Activity of Whole-Plant Extracts from In Vitro Cultured and Wild-Growing _Clinopodium vulgare_ Plants on a Panel of Human Tumor Cell Lines  
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4 Clime of Thoracic Surgery, Military Medical Academy, Georgi Solviski Str., 3, 1606 Sofia, Bulgaria; [EMAIL_ADDRESS] (S.A.); nrandecowsk@ict  
been discovered and used clinically, but they have failed to meet expectations for effective treatment. Thus, researchers' efforts continue to be strongly focused on the search for new effective and affordable anticancer drugs [2]. The use of natural products to support the therapy of malignant diseases has been applied for decades. Plants, in particular, are a continuous source of biologically active compounds and are used to treat a range of diseases, including cancer [3]. Between 50,000 and 80,000 species are medicinal plants that are applied in medicine and pharmacy worldwide [4]. Over 3000 species are known plants with anticancer properties, and they account for over 60% of the anticancer agents used today [5]. In addition to their therapeutic efficacy, herbal medicines also attract attention due to their accessibility, low cost and little or no side effects. Due to its geological characteristics and soil, as well as its specific microclimate conditions, Bulgaria has a significant diversity of plant species, including medicinal plants with valuable properties [6]. One such plant is _Clinopodium vulgare_ L (wild basil) of the Lamiaceae family, which in Bulgaria is officially recognized as a herb with medicinal properties under the Medicinal Plants Act, Bulgaria [7], and which in traditional Bulgarian medicine is used to treat warts, skin irritations, wounds, mastitis, diabetes, prostatitis and stomach ulcers [8; 9; 10]. In recent years, an increasing number of scientific studies focused on the elucidation of the phytochemical composition and assessment of the biological and pharmacological activities of plant species belonging to the Lamiaceae family, especially the _C. vulgare_ species, have been published [11]. _Clinopodium vulgare_ L is rich in flavonoids, monoterpenoids, phenolic acids, diet-penoid quinines, triterpenoid glycosides, triterpen saponins and essential oils, including rosmarinic acid, chlorogenic acid, caffeic acid, rutin, kaempfer, quercetin, betulinic and ursolic acids [12; 13] known for their anticancer properties [14]. Numerous studies have confirmed the valuable properties of _C. vulgare_ plant extracts, including their antioxidant [10; 13; 15], DNA-protective [16], anti-inflammatory [17; 18; 19], anti-bacterial [20; 21; 22], antihypertensive [23] and enzyme-inhibiting [10; 18] effects. In recent years, its antitumor effect and anticancer activities have also been investigated [8; 24; 25; 26]. The various methods for the extraction, separation and identification of _C. vulgare_ phytoconstituents, as well as the numerous valuable pharmacological activities established in different studies, have been summarized in a recently published review article [11]. Based on analysis of the currently available data, the toxicity assessment of _C. vulgare_ has been established as one of the main research priorities for the determination of its safety profile and ensuring the suitability of the plant for therapeutic applications [11]. The phytochemical composition and biological activity of plants of the same species collected from wild populations can vary significantly depending on the conditions of the specific habitat. With the help of in vitro techniques, it is possible to achieve both a constant quality and a change in the content of metabolites in the plant culture [27]. In a previous study [26], we compared the antioxidant and antitumor effects of the extracts of the stems, leaves and flowers of in vitro cultivated _C. vulgare_ plants with corresponding extracts of the wild-growing plants.