Applied sciences  
Cytotoxic Effect of L-Methioninase from _Brevibacterium lines_ BL2 in Combination with Etoposide against Glioblastoma Cells  
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L-methionineinase (E.C.4.4.1.11), also known as methionine-gamma-lyase, methioninease, methionine lyase, and methionine demethylase, has gained attention as a potential therapeutic agent against various cancer types. By degrading the amino acid methionine, which is essential for cancer cell growth and survival, it exhibits selective cytotoxicity toward methionine-dependent cancer cells while potentially sparing healthy cells [8; 9; 10]. Additionally, L-methioninease can enhance the antiproliferative effects of chemotherapeutic drugs, potentially leading to shorter treatment periods for patients [11]. The anticancer effect of L-methioninease was first observed in 1973 when the enzyme derived from Clostridium sporogenes was found to effectively inhibit the growth of Walker carcinosarcoma cells in mice [12]. L-methioninease enzymes are found in numerous bacteria, fungi, and yeast. One of the known sources of L-methionineine is the _Brevibacterium lineens_ BL2 strain. It is a Gram-positive bacterium commonly found on limburger cheeses, contributing to cheese flavor by producing sulfur compounds such as methanethiol [13; 14; 15; 16; 17]. _Brevibacterium lineens_ BL2, also known as _Brevibacterium aurantiaccum_ ATCC(r) 9175, is commercially sold as a SWING BL-2 by Chr. Hansen Company (Hoersholm, Denmark) was used for cheese ripening. A study investigated the anticancer properties of recombinant L-methioninease from _Brevibacterium lineens_ BL2 on HT29, SKOV3, JURKAT, and REH human cancer cell lines, revealing induced cytotoxicity in these cancer cells [18]. Glioblastoma is a highly malignant brain tumor that originates from glial cells and is characterized by aggressive growth and poor prognosis. Glioblastoma tumors, which are composed of various glial cell types, can create their own blood supply, thereby facilitating invasive growth. With limited treatment options, the survival rate of patients with glioblastoma is typically low, highlighting the need for new therapeutic strategies. Glioma cells often exhibit increased methionine consumption and dependency, making methionine a potential therapeutic target [19; 20; 21]. DNA topoisomerases are vital enzymes that are responsible for regulating the structure of genetic material by inducing temporary breaks in DNA molecules. They play crucial roles in essential biological processes, such as DNA replication, transcription, repair, and chromatin remodeling. Topoisomerases are categorized as type I or type II. Topoisomerase type II (TopoII) is involved in the formation of double-strand breaks. In the field of cancer treatment, etoposide is a widely utilized chemotherapeutic agent that targets TopoII activities, inhibits the rejoining of DNA, and thereby affects various aspects of cell metabolism. Beyond its impact on TopoII, Etoposide also displays a strong affinity for chromatin and histones, suggesting that these components could potentially serve as additional drug targets [22]. However, etoposide has limitations that inhibit its use. One limitation of etoposide is the development of drug resistance in cancer cells. In addition, etoposide is known to have toxic side effects. It can affect healthy cells and tissues, leading to various adverse effects such as bone marrow suppression, gastrointestinal issues, and increased susceptibility to infections [23; 24]. To overcome these limitations, researchers and clinicians are exploring different strategies, such as combination therapies.