Amorphous Calcium Carbonate Shows Anti-Cancer Properties That are Attributed to Its Buffering Capacity

SIMPLE SUMMARY: Lung cancer is by far the leading cause of cancer death, making up almost 25% of all cancer deaths. Each year, more people die of lung cancer than colon, breast, and prostate cancers combined. Developing safe new treatments is of great importance. A main feature of solid tumors is their evolved acidic microenvironment. Although this phenomenon has been known for almost 100 years (also known as aerobic glycolysis or the Warburg effect), it was seldom evaluated as a therapeutic target. A recent understanding of the tumor’s microenvironment acidity has shown its impact on disease aggressiveness, the lack of immune system response, drug and irradiation resistance, and overall poor patient prognosis. Amorphous calcium carbonate (ACC) is a non-crystalline form of calcium carbonate, and it is composed of nanoparticles with known buffering capacities. This work describes in vivo and in vitro results showing the anti-cancerous effects of ACC, which are associated with its buffering activity, suggesting a promising therapeutic potential of ACC as a safe treatment for cancer. ABSTRACT: Aim: Amorphous calcium carbonate (ACC) is a non-crystalline form of calcium carbonate, and it is composed of aggregated nano-size primary particles. Here, we evaluated its anti-cancer effect postulated relative to its buffering capabilities in lung cancer. Methods: Tumors were evaluated in vivo using the Lewis lung carcinoma (LLC) mouse cell line and A549 human lung cancer carcinoma cell line. LLC and A549 cells were injected subcutaneously into the right hind leg of mice. Treatments (ACC, cisplatin, vehicle, and ACC with cisplatin, all given via daily IP injections) started once tumors reached a measurable size. Treatments were carried out for 14 days in the LLC model and for 22 and 24 days in the xenograft model (two experiments). LLC tumors were resected from ACC at the end of the study, and vehicle groups were evaluated for cathepsin B activity. Differential gene expression was carried out on A549 cells following 8 weeks of in vitro culture in the presence or absence of ACC in a culture medium. Results: The ACC treatment decelerated tumor growth rates in both models. When tumor volumes were compared on the last day of each study, the ACC-treated animal tumor volume was reduced by 44.83% compared to vehicle-treated animals in the LLC model. In the xenograft model, the tumor volume was reduced by 51.6% in ACC-treated animals compared to vehicle-treated animals. A more substantial reduction of 74.75% occurred in the combined treatment of ACC and cisplatin compared to the vehicle (carried out only in the LLC model). Cathepsin B activity was significantly reduced in ACC-treated LLC tumors compared to control tumors. Differential gene expression results showed a shift towards anti-tumorigenic pathways in the ACC-treated A549 cells. Conclusion: This study supports the ACC anti-malignant buffering hypothesis by demonstrating decelerated tumor growth, reduced cathepsin B activity, and altered gene expressions to produce anti-cancerous effects.