Breast cancer is resistant to conventional treatments due to the specific tumour microenvironment, the associated acidic pH and the overexpression of receptors that enhance cells tumorigenicity. Herein, we optimized the synthesis of acidic resorbable calcium carbonate (CaCO3) nanoparticles and the encapsulation of a low molecular weight model molecule (Rhodamine). The addition of ethylene glycol during the synthetic process resulted in a particle size decrease: we obtained homogeneous CaCO3 particles with an average size of 564 nm. Their negative charge enabled the assembly of layer-by-layer (LbL) coatings with surface-exposed hyaluronic acid (HA), a ligand of tumour-associated receptor CD44. The coating decreased Rhodamine release by two-fold compared to uncoated nanoparticles. We demonstrated the effect of nanoparticles on two breast cancer cell lines with different aggressiveness â SK-BR-3 and the more aggressive MDA-MB-231 â and compared them with the normal breast cell line MCF10A. CaCO3 nanoparticles (coated and uncoated) significantly decreased the metabolic activity of the breast cancer cells. The interactions between LbL-coated nanoparticles and cells depended on HA expression on the cell surface: more particles were observed on the surface of MDA-MB-231 cells, which had the thickest endogenous HA coating. We concluded that CaCO3 nanoparticles are potential candidates to carry low molecular weight chemotherapeutics and deliver them to aggressive breast cancer sites with an HA-abundant pericellular matrix. 

[Excerpt] Introduction: Current radio- and chemotherapies are not efficient and many tumors remain resistant to conventional cancer treatments. Specific properties and signaling molecules from tumor microenvironment (TME) have been explored to increase treatment efficacy. An example is the acidic pH of the TME that has been explored to develop stimuli responsive release systems. Herein, we obtained biocompatible calcium carbonate (CaCO3) nanoparticles that are stable at neutral pH but dissolve at acidic conditions and evaluated their potential as a drug carrier for local cancer treatment. METHODS: CaCO3 nanoparticles were produced by co-precipitation of calcium chloride (CaCl2) and sodium carbonate (Na2CO3) in the presence of ethylene glycol [1]. Rhodamine was encapsulated as a model drug. The morphology and diameter of the nanoparticles were determined by scanning electron microscopy and dynamic laser scattering. The particles were coated by layer-by-layer (LbL) assembly of poly-L-lysine and hyaluronic acid (HA). The release was studied in phosphate buffered saline at pH 6.3 and 7.4. Cultures of two breast cancer cell lines (MDA-MB-231 and SK-BR-3) and a healthy epithelial cell line MCF10A (control) were observed under confocal laser scanning microscopy to assess particles internalization and their effect on cell viability (live/dead staining) and metabolic activity (Alamar Blue). [...]