Carbon nanotube bottles for incorporation, release and enhanced cytotoxic effect of cisplatin.

Carbon nanotubes (CNTs) have emerged as promising drug delivery systems particularly for cancer therapy, due to their abilities to overcome some of the challenges faced by cancer treatment, namely non-specificity, poor permeability into tumour tissues, and poor stability of anticancer drugs. Encapsulation of anticancer agents inside CNTs provides protection from external deactivating agents. However, the open ends of the CNTs leave the encapsulated drugs exposed to the environment and eventually their uncontrolled release before reaching the desired target. In this study, we report the successful encapsulation of cisplatin, a FDA-approved chemotherapeutic drug, into multi-walled carbon nanotubes and the capping at the ends with functionalised gold nanoparticles to achieve a "carbon nanotube bottle" structure. In this proof-of-concept study, these caps did not prevent the encapsulation of drug in the inner space of CNTs; on the contrary, we achieved higher drug loading inside the nanotubes in comparison with data reported in literature. In addition, we demonstrated that encapsulated cisplatin could be delivered in living cells under physiological conditions to exert its pharmacological action.

Mitochondria-acting hexokinase II peptides carried by short-length carbon nanotubes with increased cellular uptake, endosomal evasion, and enhanced bioactivity against cancer cells.

Type II hexokinase (HKII) has emerged as a viable therapeutic target due to its involvement in metabolic reprogramming and also apoptosis prevention. The peptide derived from the fifteen amino acid sequence in the HKII N-terminal region [HKII(pep)] can compete with endogenous proteins for binding on mitochondria and trigger apoptosis. However, this peptide is not cell-permeable. In this study, multi-walled carbon nanotubes (MWCNTs) were used to effectively deliver HKII(pep) across cellular barriers without compromising their bioactivity. The peptide was conjugated on either oxidized MWCNTs or 2,2'-(ethylenedioxy)bis(ethylamine)-functionalized MWCNTs, yielding MWCNT-HKII(pep) and MWCNT-TEG-HKII(pep), respectively. Both conjugates were shown to be internalized by breast cancer MCF-7 cells using confocal microscopy. Moreover, these nanoconjugates seemed to have escaped from endosomes and be in the vicinity of mitochondria. The WST-1 cytotoxicity assay conducted on MCF-7 and colon carcinoma HCT116 cells revealed that MWCNT-peptide conjugates were significantly more effective in curbing cancer cell growth compared to a commercially available cell permeable HKII fusion peptide. In addition, both nanoconjugates displayed an enhanced ability in eliciting apoptosis and depleting the ATP level in HCT116 cells compared to the mere HKII peptide. Importantly, hexokinase II release from mitochondria was demonstrated in MWCNT-HKII(pep) and MWCNT-TEG-HKII(pep) treated cells, highlighting that the structure and bioactivity of HKII(pep) were not compromised after covalent conjugation to MWCNTs.

In vitro controlled release of cisplatin from gold-carbon nanobottles via cleavable linkages.

Carbon nanotubes' (CNTs) hollow interior space has been explored for biomedical applications, such as drug repository against undesirable inactivation. To further devise CNTs as smart material for controlled release of cargo molecules, we propose the concept of "gold-carbon nanobottles". After encapsulating cis-diammineplatinum(II) dichloride (cisplatin, CDDP) in CNTs, we covalently attached gold nanoparticles (AuNPs) at the open-tips of CNTs via different cleavable linkages, namely hydrazine, ester, and disulfide-containing linkages. Compared with our previous study in which more than 80% of CDDP leaked from CNTs in 2 hours, AuNPs were found to significantly decrease such spontaneous release to <40%. In addition, CDDP release from AuNP-capped CNTs via disulfide linkage was selectively enhanced by twofolds in reducing conditions (namely with 1 mM dithiothreitol [DTT]), which mimic the intracellular environment. We treated human colon adenocarcinoma cells HCT116 with our CDDP-loaded gold-carbon nanobottles and examined the cell viability using lactate dehydrogenase assay. Interestingly, we found that our nanobottles with cleavable disulfide linkage exerted stronger cytotoxic effect in HCT116 compared with normal human fetal lung fibroblast cells IMR-90. Therefore, we infer that our nanobottles strategy with inbuilt disulfide linkage could attain selective release of payload in highly reductive tumor tissues while avoiding collateral damage to normal tissues.

Enhanced cytotoxicity to cancer cells by mitochondria-targeting MWCNTs containing platinum(IV) prodrug of cisplatin.

Among the arsenal of nano-materials, carbon nanotubes (CNTs) are becoming more prominent due to favorable attributes including their unique shape, which promotes cellular-uptake, and large aspect-ratio that facilitates functionalization of bioactive molecules on their surface. In this study, multi-walled carbon nanotubes (MWCNTs) were functionalized with either mitochondrial-targeting fluorescent rhodamine-110 (MWCNT-Rho) or non-targeting fluorescein (MWCNT-Fluo). Despite structural similarities, MWCNT-Rho associated well with mitochondria (ca. 80% co-localization) in contrast to MWCNT-Fluo, which was poorly localized (ca. 21% co-localization). Additionally, MWCNT-Rho entrapping platinum(IV) pro-drug of cisplatin (PtBz) displayed enhanced potency (IC50 = 0.34 ± 0.07 µM) compared to a construct based on MWCNT-Fluo (IC50 ≥ 2.64 µM). Concurrently, preliminary in vitro toxicity evaluation revealed that empty MWCNT-Rho neither decreased cell viability significantly nor interfered with mitochondrial membrane-potential, while seemingly being partially expelled from cells. Due to its targeting capability and apparent lack of cytotoxicity, MWCNT-Rho complex was used to co-encapsulate PtBz and a chemo-potentiator, 3-bromopyruvate (BP), and the resulting MWCNT-Rho(PtBz+BP) construct demonstrated superior efficacy over PtBz free drug in several cancer cell lines tested. Importantly, a 2-fold decrease in mitochondrial potential was observed, implying that mitochondrial targeting of compounds indeed incurred additional intended damage to mitochondria.

Carbon nanotubes for delivery of small molecule drugs.

In the realm of drug delivery, carbon nanotubes (CNTs) have gained tremendous attention as promising nanocarriers, owing to their distinct characteristics, such as high surface area, enhanced cellular uptake and the possibility to be easily conjugated with many therapeutics, including both small molecules and biologics, displaying superior efficacy, enhanced specificity and diminished side effects. While most CNT-based drug delivery system (DDS) had been engineered to combat cancers, there are also emerging reports that employ CNTs as either the main carrier or adjunct material for the delivery of various non-anticancer drugs. In this review, the delivery of small molecule drugs is expounded, with special attention paid to the current progress of in vitro and in vivo research involving CNT-based DDSs, before finally concluding with some consideration on inevitable complications that hamper successful disease intervention with CNTs.

Iron oxide filled magnetic carbon nanotube-enzyme conjugates for recycling of amyloglucosidase: toward useful applications in biofuel production process.

Biofuels are fast advancing as a new research area to provide alternative sources of sustainable and clean energy. Recent advances in nanotechnology have sought to improve the efficiency of biofuel production, enhancing energy security. In this study, we have incorporated iron oxide nanoparticles into single-walled carbon nanotubes (SWCNTs) to produce magnetic single-walled carbon nanotubes (mSWCNTs). Our objective is to bridge both nanotechnology and biofuel production by immobilizing the enzyme, Amyloglucosidase (AMG), onto mSWCNTs using physical adsorption and covalent immobilization, with the aim of recycling the immobilized enzyme, toward useful applications in biofuel production processes. We have demonstrated that the enzyme retains a certain percentage of its catalytic efficiency (up to 40%) in starch prototype biomass hydrolysis when used repeatedly (up to ten cycles) after immobilization on mSWCNTs, since the nanotubes can be easily separated from the reaction mixture using a simple magnet. The enzyme loading, activity, and structural changes after immobilization onto mSWCNTs were also studied. In addition, we have demonstrated that the immobilized enzyme retains its activity when stored at 4 °C for at least one month. These results, combined with the unique intrinsic properties of the nanotubes, pave the way for greater efficiency in carbon nanotube-enzyme bioreactors and reduced capital costs in industrial enzyme systems.

Secreted M-ficolin anchors onto monocyte transmembrane G protein-coupled receptor 43 and cross talks with plasma C-reactive protein to mediate immune signaling and regulate host defense.

Although transmembrane C-type lectins (CLs) are known to initiate immune signaling, the participation and mechanism of action of soluble CLs have remained enigmatic. In this study, we found that M-ficolin, a conserved soluble CL of monocyte origin, overcomes its lack of membrane-anchor domain by docking constitutively onto a monocyte transmembrane receptor, G protein-coupled receptor 43 (GPCR43), to form a pathogen sensor-cum-signal transducer. On encountering microbial invaders, the M-ficolin-GPCR43 complex activates the NF-κB cascade to upregulate IL-8 production. We showed that mild acidosis at the local site of infection induces conformational changes in the M-ficolin molecule, which provokes a strong interaction between the C-reactive protein (CRP) and the M-ficolin-GPCR43 complex. The collaboration among CRP-M-ficolin-GPCR43 under acidosis curtails IL-8 production thus preventing immune overactivation. Therefore, we propose that a soluble CL may become membrane-associated through interaction with a transmembrane protein, whereupon infection collaborates with other plasma protein to transduce the infection signal and regulate host defense. Our finding implies a possible mechanism whereby the host might expand its repertoire of immune recognition-cum-regulation tactics by promiscuous protein networking. Furthermore, our identification of the pH-sensitive interfaces of M-ficolin-CRP provides a powerful template for future design of potential immunomodulators.