D. Y. Patil School of Biotechnology and Bioinformatics
Cancer is a life-threatening disease and traditional cancer treatments have their own limitations. Bacteriotherapy, the use of bacteria in cancer therapy is found to have a scope in future cancer treatments. Therapeutic bacteria can be used to overcome some of the limitations in cancer therapy. Bacteria alone act as a potent antitumour agent. Bacteria can be genetically engineered and hence they can be altered to synthesize and release specific compounds and adapt their metabolic pathways.
Therapeutic bacteria target the hypoxic areas of tumours and penetrate the tissue and allow different strategies such as the secretion of toxins or enzymes including proteases and lipases to be tested. Bacteria are used as vectors to carry tumoricidal agents and immunotherapeutic agents. As a result, it destroys tumour cells. But, the fight against cancer is not that easy and innovative efforts to control and enhance the power of bacteria for cancer treatment have to still continue.
For the first time, scientists used live bacteria such as Streptococci and Clostridia for cancer treatment. Presently, genetically modified bacteria are mostly used for this purpose. Bacteria can be used in cancer therapy by employing different strategies. These strategies include combination with other therapies, native bacterial toxicity, bacteria that can control expression of anticancer agents, expression of tumour‐specific antigens, gene transfer and RNA interference. The use of whole live, attenuated and/or genetically modified bacteria alone, or in combination with conventional agents has been tested in several experimental models of cancer.
GENETICALLY MODIFIED BACTERIA IN CANCER THERAPY:
Gene therapy is a forward‐looking alternative approach to cancer therapy. Selective targeting and destruction of tumour cells are the major advantages of gene therapy. Genetically modified bacteria may also be able to lower pathogenicity to the host and increase the antitumour efficacy. Recently, a number of studies have developed a new approach for cancer therapy using genetically engineered bacteria designed to express reporter genes, cytotoxic protein and/or anticancer agents, and tumour‐specific antigens. It has been found that genetically modified bacteria can have a more significant multiplication in tumours than in normal tissues. These studies suggested that a combination of bacteriotherapy with radiotherapy, immunotherapy, or chemotherapy could be a novel and useful approach to cancer treatment.
BACTERIAL TOXINS OR ENZYMES IN CANCER THERAPY:
Various pathogenic microorganisms express and release particular protein toxins that suppress the immune response of the infected host. Some of these microorganisms have been tested to some extent for therapeutic treatment of cancer. These bacterial toxins could be combined with anti‐cancer drugs, or with irradiation to strengthen the potency of cancer therapy.
BACTERIAL SPORES AND VECTORS TUMOURICIDAL AGENTS:
Live bacterial vectors can act as valuable tools for the development of new cancer therapies, which can be added to the collection of existing drugs. In this novel methodology, bacteria are modified to deprive cancerous cells of oxygen, hence causing tumour death.
BACTERIOTHERAPY COMBINED WITH RADIOTHERAPY:
The combination of radiotherapy with bacteria is a novel active area of investigation. There have been few investigations using bacteria to promote radiotherapy. However, this field may still become a practical approach in clinical radiation oncology. It has been shown that genetically engineered Salmonella bacteria have the desired properties of an antitumour vector.
The unique pathophysiology of solid tumours causes major difficulties for traditional anticancer therapies. There are still many limitations in the applications of therapeutic bacteria in cancer therapy. Nevertheless, many problems remain for using bacteria in clinical practice as antitumour agents including; bacterial toxicity, DNA instability, limited targeting efficiency, choice of practical and safe bacterial strains, and testing combination with other therapies. In the future, genetically modified bacteria will be made more practical for both diagnostic and therapeutic anticancer applications.