Scaffold-based method for culturing antitumour bacteria

Bacteria-based cancer therapy represents an exciting new treatment option, due to bacteria’s natural ability to penetrate the rigid stromal barrier and target solid tumours — but in order to fully harness this approach, a safe and efficient method for producing natural anticancer bacteria is needed. Now researchers from the Japan Advanced Institute of Science and Technology (JAIST) and the University of Tsukuba have developed a way to culture antitumour bacteria using highly porous scaffolds, which they described in the Chemical Engineering Journal.

Before bacteria can be used in medical treatments or clinical trials, they must be weakened or ‘attenuated’ to ensure their safe use in animals and humans. Additionally, a simple manufacturing procedure is needed to produce safe and effective anticancer bacteria. This called for the development of an optimal culturing method for bacteria.

Previously, the Japanese researchers isolated a group of bacteria, named A-gyo and UN-gyo, from tumours in mice. A-gyo refers to the bacterium Proteus mirabilis, and UN-gyo to the photosynthetic bacterium Rhodopseudomonas palustris. These bacteria inhabit tumour cells, interacting with them and potentially influencing tumour growth and response to treatment. Together, they form the ‘AUN bacterial consortium’, which shows great promise as a powerful tool for cancer detection because of its ability to effectively target tumours and its safety. However, finding the best way to grow these bacteria was challenging.

To address the challenges of culturing AUN, the researchers explored using specially designed scaffolds. They prepared the microporous scaffold using a biocompatible substance called polydimethylsiloxane (PDMS), combined with titanium dioxide (TiO₂). The addition of TiO₂ helped create a balance where the bacteria could effectively target tumours but were controlled enough to avoid overly aggressive bacterial growth leading to unintended infections or immune responses. These porous scaffolds significantly boosted the bacteria’s anticancer properties, making them more effective.

Once the researchers prepared the PDMS-TiO₂ composite, they cultured AUN bacteria along with blocks of the scaffold while exposing the entire set-up to light. They found that when exposed to light, TiO₂ in the scaffold effectively attenuated the bacteria by producing toxic molecules called reactive oxygen species (ROS), helping ensure safety during treatment.

Next, they evaluated the anticancer efficacy of AUN. Surprisingly, the researchers found that AUN cultured with the scaffold exhibited an enhanced ability to kill different types of tumour cells. When tested on mice with breast cancer, treatment with the attenuated AUN bacteria led to improved survival rates. Heightened anticancer activity was observed in mice with drug-resistant breast cancer.

“We discovered that the strong anticancer response was due to the oncolytic (cancer-killing) properties of AUN itself, with the assistance of various activated immune cells such as T cells, NK cells and macrophages in the tumour microenvironment,” said Mikako Miyahara, a doctoral student at JAIST and lead author on the study. The study also confirmed that the AUN cultured with scaffolds could be safely administered not only to mice, but also to dogs.

According to study leader Professor Eijiro Miyako, also from JAIST, “Our discovery of how porous scaffolds influence the bacterial activities of AUN will help in designing artificial scaffold material for effective treatment against drug-resistant cancers.” The study authors expect that their technology will be available for clinical trials within the next 10 years.