Ammonium and guanidinium dendron-carbon nanotubes by amidation and click chemistry and their use for siRNA delivery

Eco-friendly synthesis of carbon nanotubes and their cancer theranostic applications

Carbon nanotubes (CNTs) with attractive physicochemical characteristics such as high surface area, mechanical strength, functionality, and electrical/thermal conductivity have been widely studied in different fields of science. However, the preparation of these nanostructures on a large scale is either expensive or sometimes ecologically unfriendly. In this context, plenty of studies have been conducted to discover innovative methods to fabricate CNTs in an eco-friendly and inexpensive manner. CNTs have been synthesized using various natural hydrocarbon precursors, including plant extracts (e.g., tea-tree extract), essential oils (e.g., eucalyptus and sunflower oil), biodiesel, milk, honey, and eggs, among others. Additionally, agricultural bio-wastes have been widely studied for synthesizing CNTs. Researchers should embrace the usage of natural and renewable precursors as well as greener methods to produce various types of CNTs in large quantities with the advantages of cost-effectiveness and environmentally benign features. In addition, multifunctionalized CNTs with improved biocompatibility and targeting features are promising candidates for cancer theranostic applications owing to their attractive optical, chemical, thermal, and electrical properties. This perspective discusses the recent developments in eco-friendly synthesis of CNTs using green chemistry-based techniques, natural renewable resources, and sustainable catalysts, with emphasis on important challenges and future perspectives and highlighting techniques for the functionalization or modification of CNTs. Significant and promising cancer theranostic applications as well as their biocompatibility and cytotoxicity issues are also discussed.

Carbon-based Nanomaterials for delivery of small RNA molecules: a focus on potential cancer treatment applications

BACKGROUND

Nucleic acid-mediated therapy holds immense potential in the treatment of recalcitrant human diseases such as cancer. This is underscored by advances in understanding the mechanisms of gene regulation. In particular, the endogenous protective mechanism of gene silencing known as RNA interference (RNAi) has been extensively exploited.

METHODS

We review here the developments from 2011 to 2021, in the use of nanographene oxide, carbon nanotubes, fullerenes, carbon nanohorns, carbon nanodots and nanodiamonds for the delivery of therapeutic small RNA molecules.

RESULTS

Appropriately designed effector molecules such as small interfering RNA (siRNA), can, in theory, silence the expression of any disease-causing gene. Alternatively, siRNA can be generated in vivo through the introduction of plasmid-based short hairpin RNA (shRNA) expression vectors. Other small RNAs such as micro RNA (miRNA) also function in post-transcriptional gene regulation and are aberrantly expressed under disease conditions. The miRNA-based therapy involves either restoration of miRNA function through the introduction of miRNA mimics; or the inhibition of miRNA function by delivering anti-miRNA oligomers. However, the large size, hydrophilicity, negative charge and nuclease-sensitivity of nucleic acids necessitate an appropriate carrier for their introduction as medicine into cells.

CONCLUSION

While numerous organic and inorganic materials have been investigated for this purpose, the perfect carrier agent remains elusive. In recent years, carbon-based nanomaterials have received widespread attention in biotechnology due to their tunable surface characteristics, mechanical, electrical, optical and chemical properties.

Guanidinoneomycin-maleimide molecular transporter: synthesis, chemistry and cellular uptake

Guanidinoglycosides are a class of non-cytotoxic molecular transporters capable of delivering high molecular weight bioactive cargos into cells at low nanomolar concentrations. Efficient bioconjugation with guanidinoglycosides has been previously demonstrated by utilizing a guanidinoneomycin decorated with a reactive but also unstable N-hydroxysuccinimmide ester-containing linker. Herein we report the synthesis, chemistry, and application of a new, stable guanidinoneomycin derivative armed with a highly specific maleimide moiety which allows for thiol-maleimide click chemistry, a highly popular bioconjugation strategy, widening the field of application of these intriguing and useful delivery vehicles.

Tailoring the Architecture of Cationic Polymer Brush-Modified Carbon Nanotubes for Efficient siRNA Delivery in Cancer Immunotherapy

The facile and controlled fabrication of homogeneously grafted cationic polymers on carbon nanotubes (CNTs) remains poorly investigated, which further hinders the understanding of interactions between functionalized CNTs with different nucleic acids and the rational design of appropriate gene delivery vehicles. Herein, we describe the controlled grafting of cationic poly(2-dimethylaminoethylmethacrylate) brushes on CNTs via surface-initiated atom transfer radical polymerization integrated with mussel-inspired polydopamine chemistry. The binding of nucleic acids with different brush-CNT hybrids discloses the highly architectural-dependent behavior with dense short brush-coated CNTs displaying the highest binding among all the other hybrids, namely, dense long, sparse long, and sparse short brush-coated CNTs. Additionally, different chemistries of the brush coatings were shown to influence the biocompatibility, cellular uptake, and silencing efficiency in vitro. This platform provides great flexibility for the design of polymer brush-CNT hybrids with precise control over their structure-activity relationship for the rational design of nucleic acid delivery systems.

Carbon-based nanomaterials for targeted cancer nanotherapy: recent trends and future prospects

Carbon-based nanomaterials are becoming attractive materials due to their unique structural dimensions and promising mechanical, electrical, thermal, optical and chemical characteristics. Carbon nanotubes, graphene, graphene oxide, carbon and graphene quantum dots have numerous applications in diverse areas, including biosensing, drug/gene delivery, tissue engineering, imaging, regenerative medicine, diagnosis, and cancer therapy. Cancer remains one of the major health problems all over the world, and several therapeutic approaches are focussed on designing targeted anticancer drug delivery nanosystems by applying benign and less hazardous resources with high biocompatibility, ease of functionalization, remarkable targeted therapy issues, and low adverse effects. This review highlights the recent development on these carbon based-nanomaterials in the field of targeted cancer therapy and discusses their possible and promising diagnostic and therapeutic applications for the treatment of cancers.

Derivatized Carbon Nanotubes for Gene Therapy in Mammalian and Plant Cells

The concept of gene vectors for therapeutic applications has been known for several years, but it is far from revealing its actual potential. With the advent of hollow cylindrical carbon nanomaterials such as carbon nanotubes (CNTs), researchers have invented several new tools to deliver genes at the required site of action in mammalian and plant cells. The ease of diversified functionalization has allowed CNTs to be by far the most adaptable non-viral vector for gene therapy. This Minireview addresses the dexterity with which CNTs undergo surface modifications and their applications as a potent vector in gene therapy of humans and plants. Specifically, we will discuss the new tools that scientific communities have invented to achieve gene therapy using plasmid DNA, RNA silencing, suicide gene therapy, and plant genetic engineering. Additionally, we will shed some light on the mechanism of gene transportation using carbon nanotubes in cancer cells and plants.

Biomedical applications of carbon nanomaterials: Drug and gene delivery potentials

One of the major components in the development of nanomedicines is the choice of the right biomaterial, which notably determines the subsequent biological responses. The popularity of carbon nanomaterials (CNMs) has been on the rise due to their numerous applications in the fields of drug delivery, bioimaging, tissue engineering, and biosensing. Owing to their considerably high surface area, multifunctional surface chemistry, and excellent optical activity, novel functionalized CNMs possess efficient drug-loading capacity, biocompatibility, and lack of immunogenicity. Over the past few decades, several advances have been made on the functionalization of CNMs to minimize their health concerns and enhance their biosafety. Recent evidence has also implied that CNMs can be functionalized with bioactive peptides, proteins, nucleic acids, and drugs to achieve composites with remarkably low toxicity and high pharmaceutical efficiency. This review focuses on the three main classes of CNMs, including fullerenes, graphenes, and carbon nanotubes, and their recent biomedical applications.

Versatile Two-Step Functionalization of Nanocarbons: Grafting of Propargylic Groups and Click Post-Functionalization

Chemical functionalization of nanocarbons is essential for further applications in various fields. We developed a facile, inexpensive, and gram‐scale one‐pot route towards alkynyl‐functionalized nanocarbons. Nucleophilic addition/propargylic capture places alkyne moieties at the surface of carbon nanotubes (CNTs) and graphene. Thermogravimetric analysis coupled with mass spectrometry and Raman analysis confirmed the efficiency of this process. Conductivity measurements demonstrated the maintenance of the CNT electrical properties. The attached alkynyl moieties were reacted with various azide derivatives through the click‐Huisgen [3+2] cycloaddition and characterized with XPS. The efficient addition of those derivatives enables the application of our finding in various fields. This route is a reliable and convenient alternative to the known diazonium functionalization and oxidation‐esterification reactions to graft alkyne groups.

Multi-walled carbon nanotubes act as a chemokine and recruit macrophages by activating the PLC/IP3/CRAC channel signaling pathway

The impact of nanomaterials on immune cells is gaining attention but is not well documented. Here, we report a novel stimulating effect of carboxylated multi-walled carbon nanotubes (c-MWCNTs) on the migration of macrophages and uncover the underlying mechanisms, especially the upstream signaling, using a series of techniques including transwell migration assay, patch clamp, ELISA and confocal microscopy. c-MWCNTs dramatically stimulated the migration of RAW264.7 macrophages when endocytosed, and this effect was abolished by inhibiting phospholipase C (PLC) with U-73122, antagonizing the IP3 receptor with 2-APB, and blocking calcium release-activated calcium (CRAC) channels with SK&F96365. c-MWCNTs directly activated PLC and increased the IP3 level and [Ca²⁺]_i level in RAW264.7 cells, promoted the translocation of the ER-resident stromal interaction molecule 1 (STIM1) towards the membranous calcium release-activated calcium channel modulator 1 (Orai1), and increased CRAC current densities in both RAW264.7 cells and HEK293 cells stably expressing the CRAC channel subunits Orai1 and STIM1. c-MWCNTs also induced dramatic spatial polarization of KCa3.1 channels in the RAW264.7 cells. We conclude that c-MWCNT is an activator of PLC and strongly recruits macrophages via the PLC/IP3/CRAC channel signaling cascade. These novel findings may provide a fundamental basis for the impact of MWCNTs on the immune system.

Second Generation Amphiphilic Poly-Lysine Dendrons Inhibit Glioblastoma Cell Proliferation without Toxicity for Neurons or Astrocytes

Glioblastomas are the most common malignant primary brain tumours in adults and one of the most aggressive and difficult-to-treat cancers. No effective treatment exits actually for this tumour and new therapeutic approaches are needed for this disease. One possible innovative approach involves the nanoparticle-mediated specific delivery of drugs and/or genetic material to glioblastoma cells where they can provide therapeutic benefits. In the present work, we have synthesised and characterised several second generation amphiphilic polylysine dendrons to be used as siRNA carriers. We have found that, in addition to their siRNA binding properties, these new compounds inhibit the proliferation of two glioblastoma cell lines while being nontoxic for non-tumoural central nervous system cells like neurons and glia, cell types that share the anatomical space with glioblastoma cells during the course of the disease. The selective toxicity of these nanoparticles to glioblastoma cells, as compared to neurons and glial cells, involves mitochondrial depolarisation and reactive oxygen species production. This selective toxicity, together with the ability to complex and release siRNA, suggests that these new polylysine dendrons might offer a scaffold in the development of future nanoparticles designed to restrict the proliferation of glioblastoma cells.

Recent advances in siRNA delivery

In the 1990s an unexpected gene-silencing phenomena in plants, the later called RNA interference (RNAi), perplexed scientists. Following the proof of activity in mammalian cells, small interfering RNAs (siRNAs) have quickly crept into biomedical research as a new powerful tool for the potential treatment of different human diseases based on altered gene expression. In the past decades, several promising data from ongoing clinical trials have been reported. However, despite surprising successes in many pre-clinical studies, concrete obstacles still need to be overcome to translate therapeutic siRNAs into clinical reality. Here, we provide an update on the recent advances of RNAi-based therapeutics and highlight novel synthetic platforms for the intracellular delivery of siRNAs.

Carbon Nanomaterials Interfacing with Neurons: An In vivo Perspective

Developing new tools that outperform current state of the art technologies for imaging, drug delivery or electrical sensing in neuronal tissues is one of the great challenges in neurosciences. Investigations into the potential use of carbon nanomaterials for such applications started about two decades ago. Since then, numerous in vitro studies have examined interactions between these nanomaterials and neurons, either by evaluating their compatibility, as vectors for drug delivery, or for their potential use in electric activity sensing and manipulation. The results obtained indicate that carbon nanomaterials may be suitable for medical therapies. However, a relatively small number of in vivo studies have been carried out to date. In order to facilitate the transformation of carbon nanomaterial into practical neurobiomedical applications, it is essential to identify and highlight in the existing literature the strengths and weakness that different carbon nanomaterials have displayed when probed in vivo. Unfortunately the current literature is sometimes sparse and confusing. To offer a clearer picture of the in vivo studies on carbon nanomaterials in the central nervous system, we provide a systematic and critical review. Hereby we identify properties and behavior of carbon nanomaterials in vivo inside the neural tissues, and we examine key achievements and potentially problematic toxicological issues.

Photocontrolled reversible morphology conversion of protein nanowires mediated by an azobenzene-cored dendrimer

Photocontrolled protein nanowires with reversible morphology were constructed through photoisomerizable azobenzene-cored dendrimer evoked protein self-assembly.

Different chemical strategies to aminate oxidised multi-walled carbon nanotubes for siRNA complexation and delivery

In this work, we have investigated the preparation of amino-functionalised multi-walled carbon nanotubes (MWCNTs) as potential carriers for the delivery of siRNA. Several studies have shown promising results exploiting functionalised CNTs for the delivery of genetic material in vitro and in vivo. Our groups have previously observed that the type of surface functionalisation used to modify oxidised MWCNTs (oxMWCNTs) can lead to significant differences in nanotube cellular uptake and delivery capability. In those studies, amino-functionalised CNTs were obtained by cycloaddition reactions. Here, we focused on the direct conversion of the carboxylic groups present on oxMWCNTs into amines, and we attempted different synthetic strategies in order to directly tether the amines onto the CNTs, without extending the lateral chain. The functionalised material was characterised by X-ray photoelectron spectroscopy, Fourier transform infra-red spectroscopy and transmission electron microscopy, and the most water-dispersible CNTs were selected for siRNA complexation and cellular uptake studies. The aminated conjugates are demonstrated to be promising vectors to achieve intracellular transport of genetic information.

DOTAP functionalizing single-walled carbon nanotubes as non-viral vectors for efficient intracellular siRNA delivery

CONTEXT

Functionalized single-walled carbon nanotubes (SWNT) with 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) were used as novel and more convenient carriers of small interfering RNA (siRNA).

OBJECTIVE

To utilize the unique capability of SWNT to be easily modified by functional groups and readily internalized by mammalian cells to bind, condense, stabilize siRNA and enhance its transfection efficiency.

METHODS

After SWNT were non-covalently functionalized by cationic DOTAP (SWNT-DOTAP), siRNA interacted with SWNT-DOTAP via static electricity (SWNT-DOTAP/siRNA). Subsequently, the size, zeta potential and morphology of SWNT-DOTAP/siRNA were analyzed. The optimal compression ratio and stability of siRNA were assessed by agarose gel electrophoresis. Furthermore, in prostate carcinoma PC-3 cells, RT-PCR, flow cytometry and sulforhodamine B assays were used to evaluate the silencing activity, transfection efficiency and cell proliferation, respectively.

RESULTS AND DISCUSSION

The characteristics of SWNT-DOTAP, i.e. an average size of 194.49 nm, a zeta potential of 45.16 mV and lower cytotoxicity than Lipofectamine 2000, indicated that this vector was suitable for siRNA delivery. Moreover, after interaction with SWNT-DOTAP, siRNA of human telomerase reverse transcriptase was bound, condensed and stabilized. In PC-3 cells, SWNT-DOTAP/siRNA exhibited 82.6% silencing activity and 92% transfection efficiency. Furthermore, the complexes inhibited cell proliferation by 42.1%.

CONCLUSION

SWNT-DOTAP may be a promising siRNA delivery vector for gene-based therapeutic applications in cancer.

Design of Cationic Multiwalled Carbon Nanotubes as Efficient siRNA Vectors for Lung Cancer Xenograft Eradication

Polo-Like Kinase (PLK1) has been identified as a potential target in cancer gene therapy via chemical or genetic inhibitory approaches. The biomedical applications of chemically functionalized carbon nanotubes (f-CNTs) in cancer therapy have been studied due to their ability to efficiently deliver siRNA intracellularly. In this study, we established the capacity of cationic MWNT-NH3(+) to deliver the apoptotic siRNA against PLK1 (siPLK1) in Calu6 tumor xenografts by direct intratumoral injections. A direct comparison with cationic liposomes was made. This study validates the PLK1 gene as a potential target in cancer gene therapy including lung cancer, as demonstrated by the therapeutic efficacy of siPLK1:MWNT-NH3(+) complexes and their ability to significantly improve animal survival. Biological analysis of the siPLK1:MWNT-NH3(+) treated tumors by qRT-PCR and Western blot, in addition to TUNEL staining confirmed the biological functionality of the siRNA intratumorally, suggesting that tumor eradication was due to PLK1 knockdown. Furthermore, by using a fluorescently labeled, noncoding siRNA sequence complexed with MWNT-NH3(+), we established for the first time that the improved therapeutic efficacy observed in f-CNT-based siRNA delivery is directly proportional to the enhanced siRNA retention in the solid tumor and subsequent uptake by tumor cells after local administration in vivo.

Cationic Liposome- Multi-Walled Carbon Nanotubes Hybrids for Dual siPLK1 and Doxorubicin Delivery In Vitro

Purpose

To formulate f-MWNTs-cationic liposome hybrids for the simultaneous delivery of siPLK1 and doxorubicin to cancer cells.

Method

f-MWNTs-cationic liposome hybrids were prepared by the thin film hydration method where the lipid film was hydrated with 100 μg/ml or 1 mg/ml of ox-MWNTs-NH₃⁺ or MWNTs-NH₃⁺ in 5% dextrose. siRNA complexation and protection ability was determined by agarose gel electrophoresis. f-MWNTs and liposome interaction was evaluated using Nile Red (NR) fluorescence spectroscopy. Cellular uptake in A549 cells was assessed by flow cytometry. Silencing of target proteins was determined by Luciferase and MTT assays. Sub-G1 analysis was performed to evaluate apoptosis following co-delivery of siPLK1 and Doxorubicin (Dox).

Results

Zeta potential and siRNA complexation profile obtained for all hybrids were comparable to those achieved with cationic liposomes. ox-MWNTs-NH₃⁺ showed greater extent of interaction with cationic liposomes compared to MWNTs-NH₃⁺. ox-MWNTs-NH₃⁺ was able to protect siRNA from nuclease-mediated degradation. Enhanced cellular uptake of both the carrier and loaded siRNA in A549 cell, were observed for this hybrid compared to the liposomal carrier. A synergistic pro-apoptotic effect was obtained when siPLK1 silencing was combined with doxorubicin treatment for the hybrid:siRNA complexes compared to the lipoplexes, in A549 cells in vitro.

Conclusions

f-MWNTs-cationic liposome hybrid designed in this study can serve as a potential vehicle for the co-delivery of siRNA and cytotoxic drugs to cancer cells in vitro.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-015-1707-1) contains supplementary material, which is available to authorized users.

Advances in the biomedical application of polymer-functionalized carbon nanotubes

Water soluble carbon nanotubes as multivalent nanomaterials for biomedical applications have been discussed.

In vivo detection of magnetic labeled oxidized multi-walled carbon nanotubes by magnetic resonance imaging

Functionalized carbon nanotubes (f-CNTs) have been widely used in bio-medicine as drug carriers, bio-sensors, imaging agents and tissue engineering additives, which demands better understanding of their in vivo behavior because of the increasing exposure potential to humans. However, there are limited studies to investigate the in vivo biodistribution and elimination of f-CNTs. In this study, superparamagnetic iron oxides (SPIOs) were used to label oxidized multiwalled carbon nanotubes (o-MWCNTs) for in vivo distribution study of o-MWCNTs by magnetic resonance imaging (MRI). SPIO labeled o-MWCNTs (((SPIO))o-MWCNTs) were prepared by a hydrothermal reaction process, and characterized by TEM, XRD and magnetometer. ((SPIO))o-MWCNTs exhibited superparamagnetic property, excellent biocompatibility and stability. The intravenously injected ((SPIO))o-MWCNTs were observed in liver, kidney and spleen, while the subcutaneously injected ((SPIO))o-MWCNTs could be only detected in sub mucosa. Most of the intravenously injected ((SPIO))o-MWCNTs could be eliminated from liver, spleen, kidney and sub mucosa on 4 d post injection (P.I.). However, the residual o-MWCNTs could induce 30-40% MRI signal-to-noise ratio changes in these tissues even on 30 d P.I. This in vivo biodistribution and elimination information of o-MWCNTs will greatly facilitate the application of f-CNT based nanoproducts in biomedicine. In addition, the magnetic labeling method provides an approach to investigate the in vivo biodistribution and clearance of other nanomaterials.

Nucleotide sensing with a perylene-based molecular receptor via amplified fluorescence quenching

A competitive fluorescence assay of perylene-based molecular receptors has been established, and selective detection of UTP is achieved through improved aggregation arising from the specific interaction of perylene-tethered guanidinium with uridine and phosphate groups in UTP.

On guanidinium and cellular uptake

Guanidinium-rich scaffolds facilitate cellular translocation and delivery of bioactive cargos through biological barriers. Although impressive uptake has been demonstrated for nonoligomeric and nonpept(o)idic guanidinylated scaffolds in cell cultures and animal models, the fundamental understanding of these processes is lacking. Charge pairing and hydrogen bonding with cell surface counterparts have been proposed, but their exact role remains putative. The impact of the number and spatial relationships of the guanidinium groups on delivery and organelle/organ localization is yet to be established.

A hydrazide-anchored dendron scaffold for chemoselective ligation strategies

We report the design and synthesis of a dendron scaffold, enabling the chemoselective decoration of target molecules with multiple copies of functional species, such as peptides, via a hydrazone bond.