When engineers injected nanoparticles of calcium carbonate—the main ingredient in antacid tablets—into mice, they were able to stop tumors from spreading.
The calcium carbonate changed the pH of the tumor environment, from acidic to more alkaline, and kept the cancer from growing. It’s the first time researchers have shown they can modulate pH in solid tumors using intentionally designed nanoparticles. The results appear in the journal Nanoscale.
“Cancer kills because of metastasis,” says Avik Som, who is working on a doctorate in biomedical engineering in addition to a medical degree at Washington University in St. Louis. “The pH of a tumor has been heavily correlated with metastasis. For a cancer cell to get out of the extracellular matrix, or the cells around it, one of the methods it uses is a decreased pH.”
In water, the pH in calcium carbonate increases as high as 9. But when injected into the body, the team found that calcium carbonate only raises the pH to 7.4, the normal pH in the human body. However, working with calcium carbonate presented some challenges.
“Calcium carbonate doesn’t like to be small,” Som says. “Calcium carbonate crystals are normally 10 to 1,000 times bigger than an ideal nanoparticle for cancer therapy. On top of that, calcium carbonate in water will constantly try to grow, like stalactites and stalagmites in a cave.”
To solve this issue, Som worked with other researchers to create several unique solutions. Ultimately they developed a solvent made of albumin to keep the calcium carbonate nanoparticles from growing, making it possible to inject them into the body intravenously.
Commonly, nanoparticles have been made with gold and silver. However, neither are present in the human body, and there are concerns about them accumulating in the body.
“Calcium and carbonate are both found heavily in the body, and they are generally nontoxic,” Som says. “When calcium carbonate dissolves, the carbonate becomes carbon dioxide and is released through the lungs, and calcium is often incorporated into the bones.”
Som and the team injected the calcium carbonate nanoparticles into the mouse fibrosarcoma model daily, which kept the tumor from growing. However, when they stopped injecting the nanoparticles, it started growing again.
Going forward, the researchers plan to determine the optimal dose to prevent metastasis, improve targeting to tumors, and determine if it could be used with chemotherapy drugs.