Tumors typically deplete the oxygen in the surrounding non-cancerous tissues as they grow, resulting in the tumors’ cells becoming oxygen-free, or hypoxic. Hypoxia-activated prodrugs (HAPs), a type of drug, aim to take advantage of this feature by only targeting hypoxic cells, minimizing damage to healthy cells, and reducing side effects. However, the effectiveness of HAPs has not been well established, and none are currently approved for clinical use. Now, a new study has found that implanting an oxygen-consuming battery while simultaneously administering the experimental class of cancer drugs in mice with cancer caused the tumors to shrink or disappear within two weeks.

A team of researchers at Fudan University (Shanghai, China) has developed a self-charging battery that can be implanted and is powered by salt water injected into its surrounding area. The battery generates very low-voltage electricity and consumes oxygen, creating a hypoxic environment that can enhance the efficacy of hypoxia-activated prodrugs (HAPs). To test their innovation, the researchers implanted the battery into the armpits of 25 mice with breast cancer. Five of the mice received both the working battery and HAP treatment. The remaining mice were divided into groups that received no treatment, HAP drugs only, a non-functional implanted battery, or just the working battery, which can operate for up to 500 hours within mouse tissue.

After 14 days, the tumors in the five mice that received both the working battery and HAP treatment had decreased by an average of 90%, with four of these mice experiencing complete tumor disappearance. Conversely, the tumors in the other mice groups either remained the same size or increased. While the implanted battery did not pose any safety issues in mice, the team noted that human safety standards are higher, and further research is required to ensure the compatibility of the battery with human tissue before testing it in humans. Inducing hypoxia in tumors may have drawbacks, such as increasing the likelihood of cancer spreading to other parts of the body. Although this did not occur in the mice, the benefits and drawbacks of utilizing the battery in human treatment would need to be evaluated before any human trials are conducted.

“The battery can cover the tumor and persistently consume the oxygen within it for more than 14 days, which is much longer than previous agents [that worked for] usually not more than two days,” said Fan Zhang at Fudan University who led the research team. 

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