Nanoparticles in Medicine: Current Status in Cancer Treatment

Cancer is still a leading cause of deaths worldwide, especially due to those cases diagnosed at late stages with metastases that are still considered untreatable and are managed in such a way that a lengthy chronic state is achieved. Nanotechnology has been acknowledged as one possible solution to improve existing cancer treatments, but also as an innovative approach to developing new therapeutic solutions that will lower systemic toxicity and increase targeted action on tumors and metastatic tumor cells. In particular, the nanoparticles studied in the context of cancer treatment include organic and inorganic particles whose role may often be expanded into diagnostic applications. Some of the best studied nanoparticles include metallic gold and silver nanoparticles, quantum dots, polymeric nanoparticles, carbon nanotubes and graphene, with diverse mechanisms of action such as, for example, the increased induction of reactive oxygen species, increased cellular uptake and functionalization properties for improved targeted delivery. Recently, novel nanoparticles for improved cancer cell targeting also include nanobubbles, which have already demonstrated increased localization of anticancer molecules in tumor tissues. In this review, we will accordingly present and discuss state-of-the-art nanoparticles and nano-formulations for cancer treatment and limitations for their application in a clinical setting.

PEG-modified aziridines for stereoselective synthesis of water-soluble fulleropyrrolidines

Diastereoselective synthesis of water-soluble fullerene compounds bearing a pharmacophore pyrrolofullerene-2',5'-dicarboxylate unit is reported. The stereocontrol of the product configuration is achieved through stereospecificity of two consecutive concerted reactions: electrocyclic aziridine ring opening followed by 1,3-dipolar cycloaddition of the resulting azomethyne ylide. The solubility in water (up to 20 μM through direct dissolution) is secured by introducing a polyethylene glycol (PEG) hydrophilic pendant. The structure and molecular-mass distribution of the resulting PEGylated fulleropyrrolidines are exhaustively characterized by 1H, 13C NMR and HRMS. According to absorbance spectroscopy, AFM and DLS studies, the synthesized compound tends to aggregate in aqueous media forming associates of ca. 4-9 nm radius surrounded by a solvation shell resulting in an effective hydrodynamic diameter of ca. 90 nm. In view of notable solubility in water, well-defined chemical structure and resemblance to the compounds with known anti-HIV activity, the synthesized PEGylated diethyl trans-pyrrolofullerene-2',5'-dicarboxylate might be an attractive candidate for biological evaluation.

Carbon-Based Nanomaterials for Cancer Therapy via Targeting Tumor Microenvironment

Cancer remains one of the major health problems all over the world and conventional therapeutic approaches have failed to attain an effective cure. Tumor microenvironments (TME) present a unique challenge in tumor therapy due to their complex structures and multiple components, which also serve as the soil for tumor growth, development, invasion, and migration. The complex TME includes immune cells, fibrous collagen structures, and tortuous blood vessels, in which conventional therapeutic approaches are rendered useless. State-of-the-art nanotechnologies have potential to cope with the threats of malignant tumors. With unique physiochemical properties, carbon nanomaterials (CNMs), including graphene, fullerenes, carbon nanotubes, and carbon quantum dots, offer opportunities to resolve the hurdles, by targeting not only cancer cells but also the TME. This review summarizes the progress about CNM-based cancer therapy strategies, which mainly focuses on both the treatment for cancer cells and TME-targeted modulation. In the last, the challenges for TME-based therapy via CNMs are discussed, which will be important in guiding current basic research to clinical translation in the future.

Visible light-switched cytosol release of siRNA by amphiphilic fullerene derivative to enhance RNAi efficacy in vitro and in vivo

Cationic macromolecules are attractive for use as small interfering RNA (siRNA) carriers due to their performance in non-immunological reactions, customization during synthesis, and low costs compared to viral carriers. However, their low transfection efficiency substantially hinders their application in both clinical practices and academic research, which is mostly attributable to the low capacity of siRNA/cationic macromolecule complexes to escape lysosomes. To address this challenge, we designed an amphiphilic fullerene derivative (C₆₀-Dex-NH₂) for efficient and controllable siRNA delivery. To synthesize C₆₀-Dex-NH₂, terminally aminated dextran was conjugated to C₆₀. The conjugate was further cationized by covalently introducing ethylenediamine to the dextran. The physicochemical characteristics of C₆₀-Dex-NH₂ was examined with elemental analyses, gel permeation chromatography, solid-state nuclear magnetic resonance (¹³C, HPDEC), agarose gel electrophoresis, and dynamic light scattering. The cytotoxicity, cellular uptake, intracellular distribution, and in vitro RNA interference (RNAi) of siRNA/C₆₀-Dex-NH₂ complex was evaluated in the human breast cancer cell line MDA-MB-231. The RNAi efficiencies mediated by C₆₀-Dex-NH₂in vivo was evaluated in subcutaneous tumor-bearing mice. The results showed that C₆₀-Dex-NH₂ has a specific amphiphilic skeleton and could form micelle-like aggregate structures in water, which could prevent siRNA from destroying by reactive oxygen species (ROS). When exposed to visible light, C₆₀-Dex-NH₂ could trigger controllable ROS generation which could destroy the lysosome membrane, promote the lysosomal escape, and enhance the gene silencing efficiency of siRNA in vitro and in vivo. The gene silencing efficiency could reach a maximum of 53% in the MDA-MB-231-EGFP cells and 69% in the 4T1-GFP-Luc2 tumor-bearing mice.

STATEMENT OF SIGNIFICANCE

We designed a novel photosensitive amphiphilic carrier (C₆₀-Dex-NH₂) for efficient and controllable siRNA delivery, which can be used in gene therapy. We showed that C₆₀-Dex-NH₂ could destroy lysosome membrane via controllable generation of ROS when exposed to light, which can help siRNA to escape from lysosome before degradation. This can enhance the gene silencing efficiency significantly and provides a useful way to regulate RNAi efficiency by light. One advantage for C₆₀-Dex-NH₂ system is C₆₀ has broad absorbance spectrum and can be activated by weak visible light; Furthermore, C₆₀-Dex-NH₂ has a specific amphiphilic structure, which may prevent siRNA from degrading and allows C₆₀-Dex-NH₂ to embed into the lipid membrane of lysosome to improve the ROS induced lysosomal disturbance after internalization.

Polyhydroxylated metallofullerenols stimulate IL-1β secretion of macrophage through TLRs/MyD88/NF-κB pathway and NLRP₃ inflammasome activation

Polyhydroxylated fullerenols especially gadolinium endohedral metallofullerenols (Gd@C82(OH)22) are shown as a promising agent for antitumor chemotherapeutics and good immunoregulatory effects with low toxicity. However, their underlying mechanism remains largely unclear. We found for the first time the persistent uptake and subcellular distribution of metallofullerenols in macrophages by taking advantages of synchrotron-based scanning transmission X-ray microscopy (STXM) with high spatial resolution of 30 nm. Gd@C82(OH)22 can significantly activate primary mouse macrophages to produce pro-inflammatory cytokines like IL-1β. Small interfering RNA (siRNA) knockdown shows that NLRP3 inflammasomes, but not NLRC4, participate in fullerenol-induced IL-1β production. Potassium efflux, activation of P2X7 receptor and intracellular reactive oxygen speciesare also important factors required for fullerenols-induced IL-1β release. Stronger NF-κB signal triggered by Gd@C82(OH)22 is in agreement with higher pro-IL-1β expression than C60(OH)22. Interestingly, TLR4/MyD88 pathway but not TLR2 mediates IL-1β secretion in Gd@C82(OH)22 exposure confirmed by macrophages from MyD88(-/-)/TLR4(-/-)/TLR2(-/-) knockout mice, which is different from C60(OH)22. Our work demonstrated that fullerenols can greatly activate macrophage and promote IL-1β production via both TLRs/MyD88/NF-κB pathway and NLRP3 inflammasome activation, while Gd@C82(OH)22 had stronger ability C60(OH)22 due to the different electron affinity on the surface of carbon cage induced by the encaged gadolinium ion.

Applications of functionalized fullerenes in tumor theranostics

Functionalized fullerenes with specific physicochemical properties have been developed for cancer diagnosis and therapy. Notably, metallofullerene is a new class of magnetic resonance imaging (MRI) contrast-enhancing agent, and may have promising applications for clinical diagnosis. Polyhydroxylated and carboxyl fullerenes have been applied to photoacoustic imaging. Moreover, in recent years, functionalized fullerenes have shown potential in tumor therapies, such as photodynamic therapy, photothermal treatment, radiotherapy and chemotherapeutics. Their antitumor effects may be associated with the modulation of oxidative stress, anti-angiogenesis, and immunostimulatory activity. While various types of novel nanoparticle agents have been exploited in tumor theranostics, their distribution, metabolism and toxicity in organisms have also been a source of concern among researchers. The present review summarizes the potential of fullerenes as tumor theranostics agents and their possible underlying mechanisms are discussed.