Applications of Nanotechnology-based Approaches to Overcome Multi-drug Resistance in Cancer

Cancer is one of the leading causes of death worldwide. Chemotherapy and radiation therapy are the major treatments used for the management of cancer. Multidrug resistance (MDR) is a major hindrance faced in the treatment of cancer and is also responsible for cancer relapse. To date, several studies have been carried out on strategies to overcome or reverse MDR in cancer. Unfortunately, the MDR reversing agents have been proven to have minimal clinical benefits, and eventually, no improvement has been made in therapeutic efficacy to date. Thus, several investigational studies have also focused on overcoming drug resistance rather than reversing the MDR. In this review, we focus primarily on nanoformulations regarded as a novel approach to overcome or bypass the MDR in cancer. The nanoformulation systems serve as an attractive strategy as these nanosized materials selectively get accumulated in tumor tissues, thereby improving the clinical outcomes of patients suffering from MDR cancer. In the current work, we present an overview of recent trends in the application of various nano-formulations, belonging to different mechanistic classes and functionalization like carbon nanotubes, carbon nanohorns, carbon nanospheres, liposomes, dendrimers, etc., to overcome MDR in cancer. A detailed overview of these techniques will help researchers in exploring the applicability of nanotechnologybased approaches to treat MDR.

PEGylation and folate conjugation effects on the stability of chitosan-tripolyphosphate nanoparticles

Chitosan-based nanoparticles (Ch-NPs) prepared via ionotropic gelation of Ch with sodium tripolyphosphate (TPP) have been widely examined as potential drug carriers. Yet, recent studies have shown these particles to be unstable in model (pH 7.2-7.4) physiological media. To this end, here we explored the possibility of improving TPP-crosslinked Ch-NP stability through chemical Ch modification. Specifically, Ch samples with either 76% or 92% degrees of deacetylation (DD) were grafted with either polyethylene glycol (PEG), a hydrophilic molecule, or folic acid (F), a hydrophobic molecule. Limited variation in dispersion light scattering intensity, particle size and apparent ζ-potential, and lack of macroscopic precipitation were chosen as analytical evidence of dispersion stability. TPP titrations were performed to determine the optimal TPP:glucosamine molar ratio for preparing particles with near 200-nm diameters, which are desirable for systemic administration of drugs, cellular uptake, and enhancing NP blood circulation. Both DD and Ch modification influenced the particle formation process and the evolution in NP size and ζ-potential upon 30-day storage in virtually salt-free water at 25 °C and 37 °C, where the NPs underwent partial aggregation (along with possible dissolution and swelling) but remained colloidally dispersed. Under model physiological (pH 7.2; 163 mM ionic strength) conditions, however (where the chitosan amine groups were largely deprotonated), the particles quickly became destabilized, evidently due to particle dissolution followed by Ch precipitation. Overall, within the degrees of substitution used for this work (~1% for PEG, and 3 and 6% for F), neither PEG nor F qualitatively improved Ch-NP stability at physiological pH 7.2 conditions. Thus, application of TPP-crosslinked Ch-NPs in drug delivery (even when Ch is derivatized with PEG or F) should likely be limited to administration routes with acidic pH (at which these NPs remain stable).

Calcium-based biomaterials for diagnosis, treatment, and theranostics

Calcium-based biomaterials with good biosafety and bio-absorbability are promising for biomedical applications such as diagnosis, treatment, and theranostics.

PEG-chitosan hydrogel with tunable stiffness for study of drug response of breast cancer cells

Mechanical properties of the extracellular matrix have a profound effect on the behavior of anchorage-dependent cells. However, the mechanisms that define the effects of matrix stiffness on cell behavior remains unclear. Therefore, the development and fabrication of synthetic matrices with well-defined stiffness is invaluable for studying the interactions of cells with their biophysical microenvironment in vitro. We demonstrate a methoxypolyethylene glycol (mPEG)-modified chitosan hydrogel network where hydrogel stiffness can be easily modulated under physiological conditions by adjusting the degree of mPEG grafting onto chitosan (PEGylation). We show that the storage modulus of the hydrogel increases as PEGylation decreases and the gels exhibit instant self-recovery after deformation. Breast cancer cells cultured on the stiffest hydrogels adopt a more malignant phenotype with increased resistance to doxorubicin as compared with cells cultured on tissue culture polystyrene or Matrigel. This work demonstrates the utility of mPEG-modified chitosan hydrogel, with tunable mechanical properties, as an improved replacement of conventional culture system for in vitro characterization of breast cancer cell phenotype and evaluation of cancer therapies.

Biocompatible and colloidally stabilized mPEG-PE/calcium phosphate hybrid nanoparticles loaded with siRNAs targeting tumors

Calcium phosphate nanoparticles are safe and effective delivery vehicles for small interfering RNA (siRNA), as a result of their excellent biocompatibility. In this work, mPEG-PE (polyethylene glycol-L-α-phosphatidylethanolamine) was synthesized and used to prepare nanoparticles composed of mPEG-PE and calcium phosphate for siRNA delivery. Calcium phosphate and mPEG-PE formed the stable hybrid nanoparticles through self-assembly resulting from electrostatic interaction in water. The average size of the hybrid nanoparticles was approximately 53.2 nm with a negative charge of approximately -16.7 mV, which was confirmed by dynamic light scattering (DLS) measurements. The nanoparticles exhibited excellent stability in serum and could protect siRNA from ribonuclease (RNase) degradation. The cellular internalization of siRNA-loaded nanoparticles was evaluated in SMMC-7721 cells using a laser scanning confocal microscope (CLSM) and flow cytometry. The hybrid nanoparticles could efficiently deliver siRNA to cells compared with free siRNA. Moreover, the in vivo distribution of Cy5-siRNA-loaded hybrid nanoparticles was observed after being injected into tumor-bearing nude mice. The nanoparticles concentrated in the tumor regions through an enhanced permeability and retention (EPR) effect based on the fluorescence intensities of tissue distribution. A safety evaluation of the nanoparticles was performed both in vitro and in vivo demonstrating that the hybrid nanoparticle delivery system had almost no toxicity. These results indicated that the mPEG-PE/CaP hybrid nanoparticles could be a stable, safe and promising siRNA nanocarrier for anticancer therapy.

Multifunctional Gd,Ce,Tb co-doped β-tricalcium phosphate porous nanospheres for sustained drug release and bioimaging

Uniform Gd,Ce,Tb co-doped β-TCP porous nanospheres are prepared by a solvothermal method using (CH₃O)₃PO as the organic phosphorus source and they demonstrate multifunctional bioapplications.

A novel legumain protease-activated micelle cargo enhances anticancer activity and cellular internalization of doxorubicin

Legumain is the only acidic asparaginly-endopeptidase in mammals that is highly up-regulated in tumor tissue and tumor associated cells. In this study, a novel legumain protease-activated micelle was successfully synthesized and prepared by loading with doxorubicin (DOX). The prepared micelle exhibited a spherical morphology and possessed a low critical micelle concentration of 1.21 × 10^-3 mg mL^-1 with a DOX loading capacity and entrapment efficiency of 4.05% and 60.6% respectively. The release profile of DOX from this micelle formulation was observed to be legumain concentration dependent. The micelle encapsulation of DOX highly enhanced the cellular uptake of DOX by tumor cell lines of DAOY, Y79, MCF-7, and MCF-7/DOX. Furthermore, encapsulation of DOX boosts the cytotoxicity against the tumor cells while reducing cytotoxicity against RPE and HEK293 cells. In addition, blank micelles did not exhibit any biological effects on tumor or RPE or HEK293 cells at the concentration range of 0-300 μg mL^-1, indicating good biocompatibility. The results suggest that this micelle formulation has potential applications in sustained drug delivery for legumain up-regulated tumors.

In situ DOX-calcium phosphate mineralized CPT-amphiphilic gelatin nanoparticle for intracellular controlled sequential release of multiple drugs

A co-delivery strategy has been developed to achieve the synergistic effect of a hydrophobic drug (camptothecin, CPT) and a hydrophilic drug (doxorubicin, DOX) by utilizing the unique structure of amphiphilic gelatin/camptothecin @calcium phosphate-doxorubicin (AG/CPT@CaP-DOX) nanoparticles as a carriers in order to replace double emulsions while preserving the advantages of inorganic materials. The hydrophobic agent (CPT) was encapsulated via emulsion with an amphiphilic gelatin core, and subsequently mineralized by CaP-hydrophilic drug (DOX) through precipitation to form a CaP shell on the CPT-AG amphiphilic gelatin core so that drug molecules with different characteristics (i.e. hydrophobic and hydrophilic) can be encapsulated in different regions to avoid their interaction. The existence of the CaP shell can protect the DOX against free release and cause an increased transfer of DOX across membranes, overcoming multidrug resistance. Release studies from core-shell carriers showed the possibility of achieving sequential release of more than one type of drug by controlling the pH-sensitive CaP shell and degradable AG core. The highly pH-responsive behavior of the carrier can modulate the dual-drug-release of DOX/CPT, specifically in acidic intracellular pH environments. The AG/CPT@CaP-DOX nanoparticles also exhibited higher drug efficiencies against MCF-7/ADR cells than MCF-7 cells, thanks to a synergistic cell cycle arrest/apoptosis-inducing effect between CPT and DOX. As such, this core-shell system can serve as a general platform for the localized, controlled, sequential delivery of multiple drugs to treat several diseases, especially for multidrug-resistant cancer cells.

Solvothermal synthesis of β-tricalcium phosphate porous nanospheres by using organic phosphorus source and their biomedical potentials

Uniform β-tricalcium phosphate porous nanospheres with substructures are prepared by a solvothermal method using (CH₃O)₃PO as the organic phosphorus source and they demonstrate excellent biocompatibility.

Core-shell hollow microspheres of magnetic iron oxide@amorphous calcium phosphate: synthesis using adenosine 5'-triphosphate and application in pH-responsive drug delivery

Drug nanocarriers with magnetic targeting and pH-responsive drug-release behavior are promising for applications in controlled drug delivery. Magnetic iron oxides show excellent magnetism, but their application in drug delivery is limited by low drug-loading capacity and poor control over drug release. Herein, core-shell hollow microspheres of magnetic iron oxide@amorphous calcium phosphate (MIO@ACP) were prepared and investigated as magnetic, pH-responsive drug nanocarriers. Hollow microspheres of magnetic iron oxide (HMIOs) were prepared by etching solid MIO microspheres in hydrochloric acid/ethanol solution. After loading a drug into the HMIOs, the drug-loaded HMIOs were coated with a protective layer of ACP by using adenosine 5'-triphosphate (ATP) disodium salt (Na2 ATP) as stabilizer, and drug-loaded core-shell hollow microspheres of MIO@ACP (HMIOs/drug/ACP) were obtained. The as-prepared HMIOs/drug/ACP drug-delivery system exhibits superparamagnetism and pH-responsive drug-release behavior. In a medium with pH 7.4, drug release was slow, but it was significantly accelerated at pH 4.5 due to dissolution of the ACP shell. Docetaxel-loaded core-shell hollow microspheres of MIO@ACP exhibited high anticancer activity.

Preparation and properties of biocompatible PS-PEG/calcium phosphate nanospheres

A facile room-temperature method was used to prepare phosphatidylserine (PS)-poly(ethylene glycol) (PEG)/calcium phosphate (CaP) nanospheres (PS-poly(ethylene glycol) methyl ether/CaP nanospheres). Transmission electron microscopy (TEM) results confirmed that the PS-PEG/CaP porous nanospheres were spherical with a diameter of 8-12 nm. X-ray and thermo-gravimetric analysis (TGA) results also confirmed that the PS-PEG micelle was packed in the CaP shell. PS-PEG/CaP nanospheres exhibited little effect on the hemolysis, coagulation characteristics of blood and inflammatory response, demonstrating a negligible cytotoxicity response in LO2 liver cells. Experiments performed in zebrafish demonstrated that the PS-PEG/CaP nanospheres had a long circulatory residence time and did not induce apoptosis in zebrafish. Taken together, these results suggest that the PS-PEG/CaP nanospheres have great potential to be used as a drug carrier.

F127/Calcium phosphate hybrid nanoparticles: a promising vector for improving siRNA delivery and gene silencing

Calcium phosphate-based transfection method had been used to transfer DNA into living cells. However, it had so far not been studied in detail to what extend siRNA delivery system. In this study, Pluronic F127/calcium phosphate hybrid nanoparticles (F127/CaP) were prepared by a facile room temperature method and employed as carriers to deliver siRNA to silence tumor cell. The morphology of the F127/CaP hybrid nanoparticles was investigated with TEM. In order to determine the ratio of F127 to CaP in the hybrid nanoparticles, TGA (the thermogravimetric analysis) was applied. MTT assays confirmed that the F127/CaP hybrid nanoparticles were quite safe. The hybrid F127/CaP nanoparticles obtained were 120-210 nm in diameter, and they were applied as siRNA carriers for siRNA loading and in vitro transfection. The siRNA encapsulating efficiency was 91.5 wt.% with a loading content of 6.5 wt.%. Compared to traditional CaP transfection method, the siRNA-loaded F127/CaP exhibited higher gene inhibition efficiency, and this was supported by fluorescence microscopy. Quantitative analysis of GFP silencing efficiency of various siRNA formulations was measured by using FACS flow cytometry analysis. Additionally, both custom CaP and F127/CaP are biocompatible and biodegradable, thus the as-prepared F127/CaP hybrid nanoparticles are promising for siRNA delivery.