# Bacterial Therapy of Cancer: A Way to the Dustbin of History or to the Medicine of the Future?
## 5 Bacteria in Cancer Therapy
### Mechanisms of Antitumor Action
#### 5.2.2 Production of the Cell-Death-Inducing Agents
For instance, nisin, one of the well-studied and widely used bacteriocin produced by _Lactococcus lactis_, has demonstrated antimicrobial activity against the majority of the Gram-negative bacteria and has also demonstrated to be cytotoxic to MCF-7 cells (the human breast adenocarcinoma cell line) [115]. Another well-known class of antimicrobial peptides, colicins, also showed anticancer activity in in vitro studies [47]. _<Biosurfactant_> Biosurfactants are the surface-active substances of different structures produced by microorganisms. In recent years, it was reported that biosurfactants can act as anticancer agents by interfering with cancer-progression processes by inhibiting some crucial signaling pathways. In addition, biosurfactants can stimulate NK cells, inhibit angiogenesis, and induce apoptosis via death receptors in cancer cells [116; 117]. Microbial biosurfactants are considered biodegradable and less toxic than synthetic analogs [118]. One of the examples is surfactin from _Bacillus safensis_, which exhibited pronounced intratumoral efficacy against T47D breast cancer cells and B16F10 mouse melanoma cells [119]. Another example is a cyclic lipopeptide, viscosin from _Pseudomonas libanensis_, which demonstrated extensive antitumor activities. The MTT results indicated that viscosin inhibited the proliferation of MDA-MB-231 in breast cancer. Moreover, viscosin inhibited the migration of the prostate cancer cell line PC-3M [120; 121]. _<Dormant Spores_> In unfavorable conditions, bacteria survive by producing dormant spores. In the hypoxic tumor microenvironment, spores revive and transform into the active state. Thus, it was shown that _Clostridum novyi_ NT spores are an effective therapeutic agent for experimental tumors in mice, and that they do not contain lethal toxins and do not cause any systemic side effects in the injected host [122; 123]. Summing up the section, it is worth noting that, although bacteria produce a wide variety of therapeutics, the timely and effective release of these substances from bacteria into the microenvironment is an ongoing challenge. There have been attempts to solve this problem by expressing specific phage lysis genes [124] or lyse bacteria by means of antimicrobial drugs, and thus releasing plasmids for tumor cell uptake [125]. In addition to releasing therapeutics, instantaneous lysis can provide the release of bacterial adjuvants that may stimulate immune responses, also reducing population growth after completing its task. Other mechanisms unrelated to immune stimulation or the production of tumor-destroying agents have also been considered. Particularly, bacteria are regarded as antitumor agents through the salvation of tumor cells by depleting required nutrients or through the formation of bacterial biofilms, which could play a role in carcinogenesis by inhibiting the growth, metastasis, and diffusion of tumor cells, and accumulating and delivering therapeutics [24; 47; 96]. However, whatever the mechanism of action of bacteria on the tumor affecting the macroorganism, it is worth keeping in mind that the main issue is the safety of such an approach. The principle of \"do no harm\" still remains fundamental in medicine; therefore, the possibility of complications in a patient subjected to \"bacterial cancer therapy\" should be minimized. Various approaches are used to ensure security, such as the weakening of bacteria, depriving them of pathogenic factors, as well as designing genetically engineered bacteria. The possibility to modify a bacterium or even almost create it anew, strengthening the desired properties and minimizing harm to humans, will be the subject of the final section.