Table 3.

Recently studied calcium phosphate drug delivery systems.

Synthesis Method	Particle Size	Active Drug	In Vitro/In Vivo Results	Ref.
Water-in-oil micro-emulsion method CaCl2 (in Cyclohexane/Igepal) + Na2HPO4 (pH = 9.0) in oil Mix for 20 min	40 nm	siRNA	A 40-fold improved silence activity compared to the previous analogous formulations. Reported nanoparticle vehicles effectively delivered siRNA to a solid tumor in a xenograft model in vitro and in vivo.	[182]
CaCl2 + Na3Cit + Na2HPO4 at pH 8.5 Mix for 5, 10, 20, 60 min at 37 °C	20–50 nm	miRNA	Calcium phosphate nanoparticles efficiently internalized into cardiomyocytes. Dose-response graphs are given. The nanoparticles did not show promoting toxicity or interfering with any functional properties. Nanoparticles successfully encapsulated synthetic miRNAs, which were efficiently delivered into cardiac cells in vitro and in vivo.	[183]
CaCl2 (in Cyclohexane/Igepal) + Na2HPO4 (pH = 9.0) in CHCl3	52–56 nm	DNA	Resulted calcium phosphate carriers showed multifunctional features. PEGylation of these carriers enabled delivery to hepatocytes in vivo. Co-delivery of cationic peptides CR8C supported extensive nuclear translocation of DNA in post-mitotic cells. Monocyclic CR8C significantly enhanced in vivo gene expression over 10-fold more than linear CR8C. Carriers had improved stability and protecte DNA from degradation, though 100-fold lower in gene expression was detected, the developed system presents a greatly decreased invasiveness in its application.	[184]
CaCl2 in bis (2-ethylhexyl) sulphosuccinate (in hexane) + Na2HPO4 in bis (2-ethylhexyl) sulphosuccinate Mix overnight at 4 °C	100–120 nm	DNA	Resulted carriers showed the transfection efficiency of 3% higher than that from the commercial transfecting reagent Polyfect.	[197]
Ca(NO3)2 + (NH4)3PO4 precipitated using a Harvard 22 syringe pump	20–150 nm	DNA	Effective transfection with calcium phosphate particles in different cell types was demonstrated.	[186]
CaCl2 (in Cyclohexane/Igepal) + Na2HPO4 (in Tris-HCl/Cyclohexane/Igepal) Mix for 10 min at 4 °C	20–50 nm	DNA	Resulted DNA carriers showed 5.7% lower cytotoxicity than commercial reagent Lipofectamine 2000. It has been demonstrated that calcium phosphate nanoparticles can be developed into an effective alternative as a non-viral gene delivery system.	[188]
CaCl2 + H24Na3O16P (in NaCl/KCl/dextrose/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) Syringe pump	30–50 nm	DNA and growth factors	Synthesized calcium phosphate particles showed higher levels of biocompatibility (between 84% and 95% of mouse embryo (NIH-3T3) fibroblasts viability) and transfection efficiency into fibroblasts in vitro. Enzyme-linked Immunosorbent Assay (ELISA) test showed 3-fold higher platelet-derived (PDGF-B) growth factor expression in NIH-3T3 fibroblast cell line upon administration of nanocarriers than that of other applied substances.	[187]
CaCl2 + Alendronate-hyaluronic acid conjugate (in HEPES)	170 nm	siRNA	Resulted calcium phosphate carriers showed effectively delivered siRNA in the A549 cells and contributed to the gene silencing (with the efficiency of about 40%) in vivo and in vitro.	[189]
C6H12CaO6 + (NH4)2HPO4	150 nm	siRNA	Particles exhibited rapid cellular uptake, almost no toxicity, and reduced gene expression of approximately 50% compared to the controls. A specific knockdown of target genes at the site of inflammation was achieved.	[190]
CaCl2 (in Igepal/Cyclohexane) + Na2HPO4 (in Igepal/Cyclohexane/DOPA in chloroform)	100 nm	Paclitaxel and miRNA-221/222 inhibitors	Carriers loaded with multiple drugs simultaneously delivered paclitaxel and miRNA-221/222 inhibitors to their intracellular targets, leading to inhibit proliferative mechanisms of mRNA-221/222 with further enhancing the therapeutic efficacy of paclitaxel. It was demonstrated that the co-delivery nanocarrier system had 80% efficiency of tumor cell suppression when compared to free paclitaxel or delivering nanocarrier with a single drug (i.e., miRi only or paclitaxel only).	[191]
Ca(NO3)2 + K2HPO4 Stir for 1 h	129 nm	Cisplatin	Synthesized calcium phosphate nanoparticles were non-toxic. Drug-loaded nanoparticles showed comparable cytotoxicity to free drug in an in vitro cell proliferation assay using the cisplatin-resistant human ovarian carcinoma (A2780cis) cell line. Negatively charged drug nanoconjugates are unable to overcome drug resistance and had the 4-fold increase in IC50 value as compared to the free drug.	[193]
C6H10CaO6 + (NH4)2HPO4 Stir for 20 min	200 nm	Temoporfin, cyclic Arginine-Glycine-Aspartic acid-Phenylalanine-Lysine (RGDfK) peptide, fluorescent dye	Efficient drug delivery resulted in 2 times decrease in tumor vascularization in 1 week of treatment in vivo. Synthesized carriers combined diagnostic imaging, tumor targeting and drug delivery properties.	[194]