Doxycycline and carbonated Hydroxyapatite: A synergistic approach to target cancer cells − An in vitro evaluation of the drug loaded nanoparticles and their incorporation into PLA/PEG fibres

Cancer remains as one of the most common causes of mortality worldwide. To develop future treatment strategies, antibiotics are being repurposed to target cancer cells. Among the antibacterials tested, it has been proposed that doxycycline (DOX) hinders the expansion and survival of tumoral cells. To guarantee its successful delivery, new nanoplatforms that can simultaneously potentiate the effect of DOX must be developed. Calcium phosphates fulfil these requirements due to their good biological activity, tuneable crystallinity, and their capacity to hamper the mitochondrial activity of cancer cells. Therefore, the aims of this study were to first determine the chemical changes produced by DOX on the tumoral HeLa cells via SR-FTIRM, followed by the synthesis, characterization and assessment of the antitumoral effect of DOX-loaded carbonated hydroxyapatite nanoparticles (DOX-CHAp NPs). TEM was used to visualize the morphological hallmarks of the cell death triggered by the nanosystems. Finally, the NPs were encapsulated into electrospun PLA/PEG fibres to facilitate the drug release in the tumour microenvironment. The results indicated that the calcium phosphate constituent ions prime the cancer cells to the DOX effect, leading to a mitochondrial dysfunction that, together with the antibiotic effect, alters the lipids, DNA, and proteins profiles. Altogether, the cell death threshold was reduced, and a higher cytotoxicity was reached with lower DOX concentrations. The NPs encapsulation into PLA/PEG fibres did not affect the bioactivity of the antibiotic but prevented the DOX-Ca²⁺ synergistic effect only observed after the NPs internalization and degradation. These results bring light to the role of the CHAp constituent Ca²⁺ to prime cancer cells for DOX cytotoxicity.