Photobacterium angustum has been found to be an effective vector for bacterial cancer immunotherapy in a preclinical study.
Researchers at the Japan Advanced Institute of Science and Technology (Ishikawa Prefecture) have completed initial bacterial immunotherapy studies using Photobacterium angustum (P. angustum). This bacterium, with antitumor properties, was tested in mouse models of colorectal cancer as an alternative to existing immunotherapies. This innovative study demonstrated the bacterium’s ability to selectively target tumor cells, offering hope for more effective cancer treatments.
While new cancer treatments are constantly being developed, many face significant challenges in not solely targeting the tumor cells, thereby running the risk of inducing toxicity to surrounding healthy tissues and vital organs. Immunotherapies have shown promising outcomes but are often hindered by high costs, adverse effects and limited efficacy in some cancer types. These limitations underscore the need for innovative, cost-effective and highly selective treatment options.
The use of bacteria as a vector for immunotherapy has been explored in relation to genetically engineered strains . The research team led by Eijiro Miyako screened multiple marine bacterial strains in colorectal mouse models to appraise their ability to directly kill tumor cells, whilst activating the immune system. The bacterial strains were not genetically modified and were cultured at room temperature, making the approach both practical and scalable.
Out of the several strains analyzed, one stood out from the rest. P. angustum demonstrated outstanding tumor-inhibiting actions with high selectivity and little colony formation in healthy tissue and organs. Biocompatibility tests in the mice treated with P. angustum showed prolonged survival. It was determined that the potency was driven by direct tumor lysis and  strong immune system activation in the tumor via T cells, B cells, neutrophils and proinflammatory cytokines such as TNF-α and IFN-γ.
P. angustum also exhibited an excellent safety profile and a durable response, with all tumor-free mice completely rejecting secondary tumor growth when rechallenged with cancer cells 120 days after initial treatment. The team also noted that the bacterial strain showed antitumor effects in drug-resistant triple-negative breast cancer models, suggesting it may have wider applications.
The result of this research serves as proof-of-concept for bacterial immunotherapy for solid cancer therapy using non-engineered bacterial strains. More research can now be conducted on the mechanisms by which immune activation occurs and expand upon the cancer models tested. Additionally, researchers can now aim to assess the long-term immunological memory induced by P. angustum. With further development, the team hope that P. angustum could pave the way for a new therapeutic paradigm whereby biocompatible bacterial therapy that does not require on genetically modified organisms.