## 1 Introduction  
Scientists want to use natural herbal sources in the treatment of many diseases, especially cancer, diabetes, and obesity. Synthetic chemotherapeutic and radiotherapeutic agents are used in cancer treatment, but these treatment options have many side effects. An antioxidant binds to a free radical and neutralizes it, thereby eliminating the negative effects. Previous studies have recommended that natural antioxidants are more efficient in neutralizing free radicals than synthetic antioxidants [1; 2; 3; 4].  
Active substances obtained from plants are used as chemotherapeutic agents [5; 6], as they are less harmful to humans [7; 8]. In recent years, more importance has been given to herbal medicines that contain natural active substances compared to synthetic medicines [9]. While the synthetic anticancer drugs currently in use destroy cancer cells, they also kill normal cells in large amounts. In addition, if resistance develops against antineoplastic drugs, they will not affect cancer cells [10; 11]. Therefore, the idea that natural anticancer drugs should be developed has emerged.  
Plants have played an important role in protecting human health for many years. Plants are used to make spices, beverages, cosmetics, dyes, and medicines [12], and current research on finding new active substances in plants to fight cancer has gained momentum [13; 14]. The success of herbal antineoplastic drugs obtained from plants, such as etoposide, vinblastine, teniposide, vincristine, etc., has accelerated on these studies. Therefore, studies have been conducted to investigate the antioxidant and anticancer properties of active substances extracted from plants for the purposes of treating different diseases, especially cancer [15].  
_H. salsolifolium_ is a herbaceous, perennial, endemic plant from the family Clusiaceae that grows on the calcareous hills and steppes of the Southeastern Anatolia Region of Turkey [16]. It is commonly known as Urfa centaury in Turkey.  
Hypericum species contain numerous secondary metabolites, including phenolic acids, flavonoids, organic acids, carnitines, essential oils, amino acids, and other water-soluble components. Hypericum species are known to have many different medicinal effects because they contain secondary metabolites, and they are used in medicine and pharmacy for their antidepressant [17], antiviral [18], wound-healing, anti-inflammatory [19], antimicrobial [20], and anticancer [21] effects.  
We hypothesized that these properties might be related to the bioavailability of major functional compounds in _H. salsolifolium_, especially syringic acid and vanillic acid. It is important that phenolic compounds are well absorbed from the intestine in terms of their activities and bioavailability in the body. Some studies have shown that high dietary phenolic content is associated with _Lactobacillus_ and _Bifidobacterium_ spp. It has been determined that beneficial bacteria in the intestinal microbiota positively affect the variability of the intestinal microbiota. In addition, the gut microbiota plays an important role in converting polyphenols into bioactive and bioavailable compounds [22].  
Our aim was to evaluate the potential of the _H. salsolifolium_ plant, which is endemic and grows in Sanluirfa, for use in treatment by investigating its antioxidant and anticancer effects in cells. This study is of scientific value as the plant is endemic in Turkey and there is no previous research on this plant in the literature.