DOI: 10.6084/m9.figshare.27075183.v1
title: Biodegradable hafnium-doped CaCO<sub>3</sub> nanoparticles as a dual-modality radiosensitizer for cancer radiotherapy

description: <b>Aim:</b> Radiotherapy employs high-energy ionizing radiation to inflict DNA damage on cancer cells, thereby causing their demise. However, this procedure can inadvertently harm healthy tissue. Thus, this study aimed to develop biodegradable radiosensitizers that counteract these adverse effects by enhancing the radiation sensitivity of tumor cells and safeguarding normal cells. <b>Materials & methods:</b> A biodegradable radiosensitizer was engineered by incorporating hafnium ions (Hf) into calcium carbonate (CaCO<sub>3</sub>) nanoparticles via a chemical precipitation technique, resulting in the formation of Hf:CaCO<sub>3</sub> nanoparticles. <b>Results & conclusion:</b> Our findings demonstrate that Hf:CaCO<sub>3</sub> nanoparticles exhibit pH-dependent solubility and can augment the efficacy of radiotherapy in treating cancer cells. This research underscores the potential of Hf:CaCO<sub>3</sub> nanoparticles as a dual-modality radiosensitizer in radiotherapy. Radiotherapy is a common cancer treatment that uses high-energy rays to kill cancer cells. However, it can also harm healthy cells. To protect healthy cells and make the treatment more effective, we use something called radiosensitizers. In our study, we made a new kind of radiosensitizer using hafnium ions (Hf) and CaCO<sub>3</sub> nanoparticles. We made these nanoparticles using a method called chemical precipitation. Our tests showed that these nanoparticles are safe for the body and can make radiotherapy more effective against cancer cells, which could be a useful tool in cancer treatment. The research focuses on creating a biodegradable radiosensitizer for cancer radiotherapy by incorporating hafnium ions into calcium carbonate nanoparticles (Hf:CaCO<sub>3</sub>). Radiotherapy, a prevalent cancer treatment, uses high-energy ionizing radiation to damage cancer cell DNA. However, it can also negatively affect healthy tissue and cause side effects. Radiosensitizers are substances that enhance tumor cell sensitivity to radiation while minimizing the radiation dose. Hf:CaCO<sub>3</sub> nanoparticles are produced using a chemical precipitation technique. These nanoparticles have an average size of approximately 150 nm, a hexagonal crystal structure of CaCO<sub>3</sub> (vaterite), and high radiopacity due to the presence of Hf. The molecular weight of ethylene glycol significantly influences the size and shape of CaCO<sub>3</sub> particle formation. Hf:CaCO<sub>3</sub> nanoparticles, when engineered at the nanoscale, can serve as a vehicle to enhance the pharmacological and therapeutic properties of drug delivery through the enhanced permeation and retention effect at tumor sites. Hf:CaCO<sub>3</sub> nanoparticles exhibit high biocompatibility and can degrade in acidic environments like the tumor microenvironment. This degradation can help balance the pH of the tumor microenvironment, thereby inhibiting tumor growth and spread. Hf:CaCO<sub>3</sub> nanoparticles can also boost the efficacy of radiotherapy on cancer cells, particularly when the Hf doping level is high (15 mol %). This is because Hf ions can generate high-energy electrons under x-ray irradiation, leading to the production of reactive oxygen species that can damage biological molecules and cause cell death. The research concludes that Hf:CaCO<sub>3</sub> nanoparticles, as dual-functional radiosensitizers for radiotherapy, can regulate the pH value of the tumor microenvironment and enhance radiotherapy. This makes them a promising instrument in cancer treatment.