# Anticancer Efficacy of Antibacterial Quinobenzothiazazines
## 1 Introduction  
The cancerous growth of various tissues has become one of the most frequent causes of illness and death. According to the statistics of the World Health Organization, breast, lung, colon, rectal and prostate cancers are in the first place. It can be stated that, in total, cancer caused almost 10 million deaths in 2020: i.e., every sixth patient died of cancer [1]. For example, in 2008, cancer was the cause of 7.5 million deaths, which was approximately 13% of all deaths [2]. These data show a trend of cancer incidence growth in spite of better diagnostics and treatment. It is important to mention that these diagnoses and their occurrence are highly correlated with the income of the population in different regions of the world. Areas with high incomes also have higher rates of cancer than areas with low incomes. On the one hand, about one-third of cancer deaths are due to high body weight,the heavy consumption of alcohol and tobacco products, a diet low in fruit and vegetables, little physical activity and high levels of stress [1; 2]. On the other hand, infections causing cancer, e.g., hepatitis and human papillomavirus, cause about 30% of cancer cases in low- and middle-income regions. Another group, which is more or less unaffected by income, represents the hereditary burden, such as in the case of breast cancer [1; 2]. Worldwide, great attention is paid to the discovery and development of various anticancer drugs. A wide variety of compounds with different antiproliferative mechanisms of action are currently in use. In general, antineoplastics can be classified into alkylating agents, antimetabolites, cytotoxic antibiotics, alkaloids and plant medicines, complexing compounds from the group of platinum cytostatics, protein kinase inhibitors and monoclonal antibodies [3; 4; 5; 6; 7; 8]. A different drug is suitable for each type of tumor growth. It can be stated that the resistance of tumor cells represents a major problem that combined therapy tries to overcome. Currently, the eyes of the professional and lay public are focused on the therapeutic use of nanoparticles/nanoformulated antineoplastics and a wide range of drug delivery nanosystems [5; 9; 10; 11]. Apoptosis, as programmed, self-automated cell death, is critical for body homeostasis and cellular integrity. Moreover, the impairment of apoptotic process execution can lead to the appearance of various diseases, including breast cancer [12]. Hence, targeting apoptosis regulators and/or inducers in cancer cells is an appealing strategy for the treatment of hormone-sensitive breast cancer. According to the apoptogenic hypothesis, the suppression of estrogen biosynthesis by aromatase inhibition can induce and stimulate apoptotic signaling pathways, reducing the risk of hormone-dependent breast cancer progression [13]. As a matter of fact, aromatase can be competitively inhibited by a diverse range of steroidal and nonsteroidal agents (e.g., phenothiazazine derivatives carrying a benzenesulfonamide moiety); however, novel aromatase inhibitors (AIs) are urgently needed due to side-effect issues (e.g., drug resistance) [14]. Due to their structures, heterocyclic compounds have the ability to interact with a wide variety of biological targets [15; 16; 17; 18] and undoubtedly play an essential role in the design of antineoplastics [19; 20; 21; 22; 23; 24]. Notable heterocyclic structures are phenothiazazine and quinoline scaffolds, which are included in many drugs. Phenothiazazines are used as antipsychotics/neuroleptics, antihistamines, antiemetics, antiprurititics, analgesics and anthelmintics [3; 25; 26; 27]. Quinolines can be found in anti-invasive, analgesic, anticonvulsant, anti-Alzheimer, and antioxidant drugs or in drugs affecting the cardiovascular system and smooth muscles [3; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43]. The fusion of the two scaffolds results in a tetracyclic platform of quinobenzothiazazines showing primarily anticancer and antibacterial activities [44; 45; 46; 47; 48; 49].