Amorphous calcium phosphate nanoparticles could function as a novel cancer therapeutic agent by employing a suitable targeted drug delivery platform

Synthetic amorphous calcium phosphates (ACPs): preparation, structure, properties, and biomedical applications

Amorphous calcium phosphates (ACPs) represent a metastable amorphous state of other calcium orthophosphates (abbreviated as CaPO₄) possessing variable compositional but rather identical glass-like physical properties, in which there are neither translational nor orientational long-range orders of the atomic positions. In nature, ACPs of a biological origin are found in the calcified tissues of mammals, some parts of primitive organisms, as well as in the mammalian milk. Manmade ACPs can be synthesized in a laboratory by various methods including wet-chemical precipitation, in which they are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing dissolved ions of Ca²⁺ and PO₄^3- in sufficient amounts. Due to the amorphous nature, all types of synthetic ACPs appear to be thermodynamically unstable and, unless stored in dry conditions or doped by stabilizers, they tend to transform spontaneously to crystalline CaPO₄, mainly to ones with an apatitic structure. This intrinsic metastability of the ACPs is of a great biological relevance. In particular, the initiating role that metastable ACPs play in matrix vesicle biomineralization raises their importance from a mere laboratory curiosity to that of a reasonable key intermediate in skeletal calcifications. In addition, synthetic ACPs appear to be very promising biomaterials both for manufacturing artificial bone grafts and for dental applications. In this review, the current knowledge on the occurrence, structural design, chemical composition, preparation, properties, and biomedical applications of the synthetic ACPs have been summarized.

Fabrication of Calcium Sulfate Coated Selenium Nanoparticles and Corresponding In-Vitro Cytotoxicity Effects Against 4T1 Breast Cancer Cell Line

BACKGROUND

The inhibitory effect of selenium nanoparticles (SeNPs) on cancer cells has been reported in many studies. In this study, the purpose was to compare the in vitro effects of SeNPs and calcium sulfate coated selenium nanoparticles (CaSO₄@SeNPs) on breast cancer cells.

METHODS

CaSO₄@SeNPs and SeNPs were chemically synthesized and characterized with Field Emission Scanning Electron Microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDX). By applying MTT assay, the cytotoxicity effect of both nanomaterials on the 4T1 cancer cells was investigated.

RESULTS

While LD₅₀ of SeNPs on 4T1 cancer cells was 80 μg, the LD₅₀ of CaSO₄@SeNPs was reported to be only 15 μg. The difference between the inhibition rates obtained for SeNPs and CaSO₄@SeNPs was statistically significant (p=0.05). In addition, at higher concentrations (50 μg) of CaSO₄@SeNPs, the cytotoxicity was 100% more than SeNPs alone.

CONCLUSION

According to the result of the present work, it can be concluded that decoration of SeNPs with calcium sulfate leads to an increase in potency by decreasing the effective dose. This effect can be attributed to activation of intrinsic apoptosis signaling and/or pH regulatory properties of CaSO₄@SeNPs. However, further studies are still needed to determine the exact corresponding mechanisms of this synergistic effect.

Effect of zoledronic acid and graphene oxide on the physical and in vitro properties of injectable bone substitutes

The aim of this work was to develop injectable bone substitutes (IBS) consisting of zoledronic acid (ZOL) and graphene oxide (GO) for the treatment of osteoporosis and metastasis. The powder phase was consisting of tetra calcium phosphate (TTCP), dicalcium phosphate dihyrate (DCPD) and calcium sulfate dihyrate (CSD), while the liquid phase comprised of methylcellulose (MC), gelatin and sodium citrate dihyrate (SC), ZOL and GO. The structural analysis of IBS samples was performed by Fourier Transform Infrared Spectroscopy (FTIR). Injectability, setting time and mechanical strength were investigated. Additionally, in vitro properties of synthesized IBS were analyzed by means of bioactivity, ZOL release, degradation, pH variation, PO₄^3- ion release and cell studies. Overall, all IBS exhibited excellent injectability results with no phase separation. The setting time of the IBS was prolonged with ZOL incorporation while the prolonging effect decreased with GO incorporation. The mechanical properties decreased with ZOL addition and increased with the incorporation of GO. The maximum compressive strength was found as 25.73 MPa for 1.5GO0ZOL incorporated IBS. In vitro results showed that ZOL and GO loaded IBS also revealed clinically suitable properties with controlled release of ZOL, pH value and PO₄^3- ions. In in vitro cell studies, both the inhibitory effect of ZOL and GO loaded IBS on MCF-7 cells and proliferative effect on osteoblast cells were observed. Moreover, the prepared IBS led to proliferation, differentiation and mineralization of osteoblasts. The results are encouraging and support the conclusion that developed IBS have promising physical and in vitro properties which needs to be further validated by gene expression and in vivo studies.

Nanostructured Calcium-based Biomaterials and their Application in Drug Delivery

In the past several decades, various types of nanostructured biomaterials have been developed. These nanostructured biomaterials have promising applications in biomedical fields such as bone repair, tissue engineering, drug delivery, gene delivery, antibacterial agents, and bioimaging. Nanostructured biomaterials with high biocompatibility, including calcium phosphate, hydroxyapatite, and calcium silicate, are ideal candidates for drug delivery. This review article is not intended to offer a comprehensive review of the nanostructured biomaterials and their application in drug delivery but rather presents a brief summary of the recent progress in this field. Our recent endeavors in the research of nanostructured biomaterials for drug delivery are also summarized. Special attention is paid to the synthesis and properties of nanostructured biomaterials and their application in drug delivery with the use of typical examples. Finally, we discuss the problems and future perspectives of nanostructured biomaterials in the drug delivery field.

A Novel Contrast Agent Based on Magnetic Nanoparticles for Cholesterol Detection as Alzheimer's Disease Biomarker

BACKGROUND

Considering the high incidence of Alzheimer's disease among the world population over the years, and the costs that the disease poses in sanitary and social terms to countries, it is necessary to develop non-invasive diagnostic tests that allow to detect early biomarkers of the disease. Within the early diagnosis methods, the development of contrast agents for magnetic resonance imaging becomes especially useful. Accumulating evidence suggests that cholesterol may play a role in the pathogenesis of Alzheimer's disease since abnormal deposits of cholesterol surrounding senile plaques have been described in animal transgenic models and patients with Alzheimer's disease. In vivo experiments have also shown that diet-induced hypercholesterolemia enhances intraneuronal accumulation of β-amyloid protein accompanied by microgliosis and accelerates β-amyloid deposition in brains.

PRESENTATION OF THE HYPOTHESIS

In the present study, we propose for the first time the synthesis of a new nanoconjugate composed of magnetic nanoparticles bound to an anti-cholesterol antibody, to detect the abnormal deposits of cholesterol observed in senile plaques in Alzheimer's disease by magnetic resonance imaging. The nanoplatform could also reveal the decrease of cholesterol observed in neuronal plasmatic membranes associated with this pathology.

TESTING THE HYPOTHESIS

Experimental design to test the hypothesis will be done first in vitro and then in ex vivo and in vivo studies in a second stage.

IMPLICATIONS OF THE HYPOTHESIS

The designed nanoplatform could therefore detect cholesterol deposits at the cerebral level. The detection of this biomarker in areas coinciding with senile plaque accumulations could provide early information on the onset and progression of Alzheimer's disease.

Biochemical transformation of calciprotein particles in uraemia

Calciprotein particles (CPP) have emerged as nanoscale mediators of phosphate-induced toxicity in Chronic Kidney Disease (CKD). Uraemia favors ripening of the particle mineral content from the amorphous (CPP-I) to the crystalline state (CPP-II) but the pathophysiological significance of this transformation is uncertain. Clinical studies suggest an association between CPP ripening and inflammation, vascular dysfunction and mortality. Although ripening has been modelled in vitro, it is unknown whether particles synthesised in serum resemble their in vivo counterparts. Here we show that in vitro formation and ripening of CPP in uraemic serum is characterised by extensive physiochemical rearrangements involving the accretion of mineral, loss of surface charge and transformation of the mineral phase from a spherical arrangement of diffuse domains of amorphous calcium phosphate to densely-packed lamellar aggregates of crystalline hydroxyapatite. These physiochemical changes were paralleled by enrichment with small soluble apolipoproteins, complement factors and the binding of fatty acids. In comparison, endogenous CPP represent a highly heterogeneous mixture of particles with characteristics mostly intermediate to synthetic CPP-I and CPP-II, but are also uniquely enriched for carbonate-substituted apatite, DNA fragments, small RNA and microbe-derived components. Pathway analysis of protein enrichment predicted the activation of cell death and pro-inflammatory processes by endogenous CPP and synthetic CPP-II alike. This comprehensive characterisation validates the use of CPP-II generated in uraemic serum as in vitro equivalents of their endogenous counterparts and provides insight into the nature and pathological significance of CPP in CKD, which may act as vehicles for various bioactive ligands.

Tailored design of multifunctional and programmable pH-responsive self-assembling polypeptides as drug delivery nanocarrier for cancer therapy

Breast cancer has become the second leading cause of cancer-related mortality in female wherein more than 90% of breast cancer-related death results from cancer metastasis to distant organs at advanced stage. The purpose of this study is to develop biodegradable nanoparticles composed of natural polypeptides and calcium phosphate (CaP) with sequential pH-responsivity to tumor microenvironments for active targeted drug delivery. Two different amphiphilic copolymers, poly(ethylene glycol)₃₄₀₀-aconityl linkage-poly(l-glutamic acid)₁₅-poly(l-histidine)₁₀-poly(l-leucine)₁₀ and LyP1-poly(ethylene glycol)₁₁₀₀-poly(l-glutamic acid)₁₅-poly(l-histidine)₁₀-poly(l-leucine)₁₀, were exploited to self-assemble into micelles in aqueous phase. The bio-stable nanoparticles provide three distinct functional domains: the anionic PGlu shell for CaP mineralization, the protonation of PHis segment for facilitating anticancer drug release at target site, and the hydrophobic core of PLeu for encapsulation of anticancer drugs. Furthermore, the hydrated PEG outer corona is used for prolonging circulation time, while the active targeting ligand, LyP-1, is served to bind to breast cancer cells and lymphatic endothelial cells in tumor for inhibiting metastasis. Mineralized DOX-loaded nanoparticles (M-DOX NPs) efficiently prevent the drug leakage at physiological pH value and facilitate the encapsulated drug release at acidic condition when compared to DOX-loaded nanoparticles (DOX NPs). M-DOX NPs with LyP-1 targeting ligand effectively accumulated in MDA-MB-231 breast cancer cells. The inhibition effect on cell proliferation also enhances with time, illustrating the prominent anti-tumor efficacy. Moreover, the in vitro metastatic inhibition model shows the profound inhibition effect of inhibitory nanoparticles. In brief, this self-assembling peptide-based drug delivery nanocarrier with multifunctionality and programmable pH-sensitivity is of great promise and potential for anti-cancer therapy.

STATEMENT OF SIGNIFICANCE

This tailored-design polypeptide-based nanoparticles with self-assembling and programmable stimulus-responsive properties enable to 1) have stable pH in physiological value with a low level of drug loss and effectively release the encapsulated drug with pH variations according to the tumor microenvironment, 2) enhance targeting ability to hard-to-treat breast cancer cells and activate endothelial cells (tumor region), 3) significantly inhibit the growth and prevent from malignant metastasis of cancer cells in consonance with promising anti-tumor efficacy, and 4) make tumors stick to localized position so that these confined solid tumors can be more accessible by different treatment modalities. This work contributes to designing a programmable pH-responsive drug delivery system based on the tailor-designed polypeptides.

Antimicrobial Hydroxyapatite-Gelatin-Silica Composite Pastes with Tunable Setting Properties

Bone grafting is one of the commonest surgical procedures, yet all bone substitutes developed so far suffer from specific weaknesses and the search for a bone graft material with ideal physical and biological properties is still ongoing. Calcium phosphate pastes are the most frequently used synthetic bone grafts, yet they (a) often take an impractically long time to set, (b) release the drug content too fast, and (c) do not form pores large enough to accommodate host cells and foster osseointegration. To make up for these deficiencies, we introduced gelatin and silica to pastes composed of 5-15 nm sized hydroxyapatite nanoparticles and yielded a bioresorbable composite that is compact, yet flowing upon injection; that prevents setting at room temperature, but sets promptly, in minutes, at 37 °C; that displays an increase in surface porosity following immersion in physiological fluids; that allows for sustained release of antibiotics; and that sets in a tunable manner and in clinically relevant time windows: 1-3 minutes at its fastest. Timelapse, in situ X-ray diffraction analysis demonstrated that the setting process is accompanied by an increase in crystallinity of the initially amorphous hydroxyapatite, involving no polymorphic phase transitions in its course. Setting time can be tuned by controlling the weight content of gelatin or powder-to-liquid ratio. The release of vancomycin was slow, ~ 8 % after 2 weeks, and unaffected by the gelatin content. While vancomycin-loaded pastes were effective in reducing the concentration of all bacterial species analyzed, the bacteriostatic effects of the antibiotic-free pastes were pronounced against S. liquefaciens and E. coli. S. liquefaciens bacilli underwent beading and filamentation during the treatment, suggesting that the antimicrobial effects are attributable to cell wall disruption by hydroxyapatite nanoparticles. Vancomycin-loaded pastes augmented the activity of the antibiotic against P. aeruginosa and S. liquefaciens, while exhibiting no negative effects against human mesenchymal stem cells. They were also uptaken three times more abundantly than pure hydroxyapatite, indicating the theoretical favorability of their use for intracellular delivery of therapeutics. This selectivity, toxic for bacteria and harmless for primary stem cells, is promising for application as bone grafts for osteomyelitis.

Synthetic mimetics of the endogenous gastrointestinal nanomineral: Silent constructs that trap macromolecules for intracellular delivery

Amorphous magnesium-substituted calcium phosphate (AMCP) nanoparticles (75-150nm) form constitutively in large numbers in the mammalian gut. Collective evidence indicates that they trap and deliver luminal macromolecules to mucosal antigen presenting cells (APCs) and facilitate gut immune homeostasis. Here, we report on a synthetic mimetic of the endogenous AMCP and show that it has marked capacity to trap macromolecules during formation. Macromolecular capture into AMCP involved incorporation as shown by STEM tomography of the synthetic AMCP particle with 5nm ultra-fine iron (III) oxohydroxide. In vitro, organic cargo-loaded synthetic AMCP was taken up by APCs and tracked to lysosomal compartments. The AMCP itself did not regulate any gene, or modify any gene regulation by its cargo, based upon whole genome transcriptomic analyses. We conclude that synthetic AMCP can efficiently trap macromolecules and deliver them to APCs in a silent fashion, and may thus represent a new platform for antigen delivery.

An insight into functionalized calcium based inorganic nanomaterials in biomedicine: Trends and transitions

Over the recent years the use of biocompatible and biodegradable nanoparticles in biomedicine has become a significant priority. Calcium based ceramic nanoparticles like calcium phosphate (CaP) and calcium carbonate (CaCO3) are therefore considered as attractive carriers as they are naturally present in human body with nanosize range. Their application in tissue engineering and localized controlled delivery of bioactives for bones and teeth is well established now, but recently their use has increased significantly as carrier of bioactives through other routes also. These delivery systems have become most potential alternatives to other commonly used delivery system because of their cost effectiveness, biodegradability, chemical stability, controlled and stimuli responsive behaviour. This review comprehensively covers their characteristic features, method of preparation and applications but the thrust is to focus their recent development, functionalization and use in systemic delivery. On the same platform mineralization of other nanoparticulate delivery system which has widened their application drug delivery will be discussed. The emphasis has been given on their pH dependent properties which make them excellent carriers for tumour targeting and intracellular delivery. Finally this review also attempts to discuss their drawback which limits their clinical utility.