pH-Controlled Delivery of Doxorubicin to Cancer Cells, Based on Small Mesoporous Carbon Nanospheres

Mesoporous carbon nanospheres (MCNs) with small diameters of ≈90 nm are developed as an efficient transmembrane delivery vehicle of an anticancer drug, doxorubicin (DOX). MCNs exhibit a high loading capacity toward DOX due to hydrophobic interactions and the supramolecular π stacking between DOX and the carbonaceous structures, on which the pH-dependent drug release are successfully achieved. Specifically, DOX can be loaded onto MCNs in basic solution and in a physiological pH range, while release occurs in acidic solution in its ionized state. By effective passive and active targeting, MCNs can be readily internalized into HeLa cells, where the carried DOX can be efficiently released in the acidic microenvironment of the tumors for further therapy. The endocytosis and cytotoxicity of DOX@MCNs toward HeLa cells are investigated by confocal microscopy and MTT assay. This smart pH-dependent drug loading and release property of DOX@MCNs makes it possible to reduce the cytotoxicity to normal tissues during circulation in the body since the normal physiological pH is ≈7.4.     

A Transformable Chimeric Peptide for Cell Encapsulation to Overcome Multidrug Resistance

Multidrug resistance (MDR) remains one of the biggest obstacles in chemotherapy of tumor mainly due to P‐glycoprotein (P‐gp)‐mediated drug efflux. Here, a transformable chimeric peptide is designed to target and self‐assemble on cell membrane for encapsulating cells and overcoming tumor MDR. This chimeric peptide (C₁₆‐K(TPE)‐GGGH‐GFLGK‐PEG₈, denoted as CTGP) with cathepsin B‐responsive and cell membrane‐targeting abilities can self‐assemble into nanomicelles and further encapsulate the therapeutic agent doxorubicin (termed as CTGP@DOX). After the cleavage of the Gly‐Phe‐Leu‐Gly (GFLG) sequence by pericellular overexpressed cathepsin B, CTGP@DOX is dissociated and transformed from spherical nanoparticles to nanofibers due to the hydrophilic–hydrophobic conversion and hydrogen bonding interactions. Thus obtained nanofibers with cell membrane‐targeting 16‐carbon alkyl chains can adhere firmly to the cell membrane for cell encapsulation and restricting DOX efflux. In comparison to free DOX, 45‐time higher drug retention and 49‐fold greater anti‐MDR ability of CTGP@DOX to drug‐resistant MCF‐7R cells are achieved. This novel strategy to encapsulate cells and reverse tumor MDR via morphology transformation would open a new avenue towards chemotherapy of tumor.     

Magnetoresponsive Virus‐Mimetic Nanocapsules with Dual Heat‐Triggered Sequential‐Infected Multiple Drug‐Delivery Approach for Combinatorial Tumor Therapy

Stimuli‐responsive drug‐delivery systems constitute an appealing approach to direct and restrict drug release spatiotemporally at the specific site of interest. However, it is difficult for most systems to affect every cancer cell in a tumor tissue due to the presence of the natural tumor barrier, leading to potential tumor recurrence. Here, core–shell magnetoresponsive virus‐mimetic nanocapsules (VNs), which can infect cancer cells sequentially and double as a magnetothermal agent fabricated through anchoring iron oxide nanoparticles in a single‐component protein (lactoferrin) shell, are reported. With large payload of hydrophilic/hydrophobic anticancer cargos, doxorubicin and palictaxel, VNs can simultaneously give a rapid drug release and intense heat while applying an external high‐frequency magnetic field (HFMF). Furthermore, after being liberated from dead cells by HFMF manipulation, the constructive VNs can sequentially infect neighboring cancer cells and deliver sufficient therapeutic agents to next targeted sites. With high efficiency for sequential cell infections, VNs have successfully eliminated subcutaneous tumor after a combinatorial treatment. These results demonstrate that the VNs could be used for locally targeted, on‐demand, magnetoresponsive chemotherapy/hyperthermia, combined with repeated cell infections for tumor therapy and other therapeutic applications.     

Gadolinium Metallofullerene‐Based Activatable Contrast Agent for Tumor Signal Amplification and Monitoring of Drug Release

Activatable imaging probes are promising to achieve increased signal‐to‐noise ratio for accurate tumor diagnosis and treatment monitoring. Magnetic resonance imaging (MRI) is a noninvasive imaging technique with excellent anatomic spatial resolution and unlimited tissue penetration depth. However, most of the activatable MRI contrast agents suffer from metal ion‐associated potential long‐term toxicity, which may limit their bioapplications and clinical translation. Herein, an activatable MRI agent with efficient MRI performance and high safety is developed for drug (doxorubicin) loading and tumor signal amplification. The agent is based on pH‐responsive polymer and gadolinium metallofullerene (GMF). This GMF‐based contrast agent shows high relaxivity and low risk of gadolinium ion release. At physiological pH, both GMF and drug molecules are encapsulated into the hydrophobic core of nanoparticles formed by the pH‐responsive polymer and shielded from the aqueous environment, resulting in relatively low longitudinal relativity and slow drug release. However, in acidic tumor microenvironment, the hydrophobic‐to‐hydrophilic conversion of the pH‐responsive polymer leads to amplified MR signal and rapid drug release simultaneously. These results suggest that the prepared activatable MRI contrast agent holds great promise for tumor detection and monitoring of drug release.     

Synthesis of pH-responsive triazine skeleton nano-polymer composite containing AIE group for drug delivery

We exploited a unique porous structure of the nano-covalent triazinepolymer(NCTP)containing aggregation-induced emission(AlE)group to achievecontrolled release and drug tracking in tumor acidic microenvironment.NCTP wassynthesized by the Friedel-Crafts alkylation and the McMurry coupling reaction.It notonly had strong doxorubicin(DOX)-loading capacity due to its high specific surface areaand large pore volume,but also showed the significant cumulative drug release as aresult of the pH response of triazine polymers.NCTP was induced luminescence aftermass accumulation near tumor cells.Besides,it had excellent biocompatibility andobvious antineoplastic toxicity.The results demonstrate that NCTP as a utility-type drugcarrier provides a new route for designing the multi-functional drug delivery platform.     

Gold Nanoparticle–Protein Agglomerates as Versatile Nanocarriers for Drug Delivery

The fabrication of a versatile nanocarrier based on agglomerated structures of gold nanoparticle (Au NP)–lysozyme (Lyz) in aqueous medium is reported. The carriers exhibit efficient loading capacities for both hydrophilic (doxorubicin) and hydrophobic (pyrene) molecules. The nanocarriers are finally coated with an albumin layer to render them stable and also facilitate their uptake by cancer cells. The interaction between agglomerated structures and the payloads is non‐covalent. Cell viability assay in vitro showed that the nanocarriers by themselves are non‐cytotoxic, whereas the doxorubicin‐loaded ones are cytotoxic, with efficiencies higher than that of the free drug. Transmission electron microscopy and fluorescence microscopy along with flow cytometry analysis confirm the uptake of the drug‐loaded nanocarriers by a human cervical cancer HeLa cell line. Field‐emission scanning electron microscopy reveals the formation of apoptotic bodies leading to cell death, confirming the release of the payloads from the nanocarriers into the cell. Overall, the findings suggest the fabrication of novel Au NP–protein agglomerate‐based nanocarriers with efficient drug‐loading and ‐releasing capabilities, enabling them to act as multimodal drug‐delivery vehicles.     

Regulation of particle morphology of pH-dependent poly(epsilon-caprolactone)-poly(gamma-glutamic acid) micellar nanoparticles to combat breast cancer cells

The advantage of polymeric drug carriers lies in the uptake of the polymer nanoparticles by cancer cells before they release the drug, thereby reducing its toxic effects on healthy cells. A poly(gamma-glutamic acid)-b-poly(epsilon-caprolactone)-b-poly(gamma-glutamic acid) block copolymer was synthesized to encapsulate the anti-cancer drug doxorubicin in the treatment of wild type human breast cancer cells (MCF-7/WT). This pH-controllable carrier is negatively-charged in the presence of healthy tissues leading to lower cellular uptake. On the other hand, it becomes more hydrophobic in the acidic environment of cancer tissues, increasing its cellular uptake through the lipid bilayer. The block copolymer was characterized using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry and dynamic light scattering. The micelles formed at a critical concentration range of 62-130 microg/mL depending on the composition of poly(gamma-glutamic acid) and poly(epsilon-caprolactone) chains. The nano-sized micelles were found to have pH-dependent sizes in the range of 90-200 nm. The role of poly(gamma-glutamic acid) was to increase the hydrophilicity and decrease the particle size of the copolymer. The structures of micelles that were more compact and less anionic showed better stability in plasma. It was found that the drug loading content and drug loading efficiency were 12.14% and 97.22% respectively. The copolymer showed shrinking and aggregation at low pH which led to a slower drug release. These nano-sized micelles showed potential as effective drug delivery carriers for doxorubicin because of its accumulation and slow release inside the MCF-7/WT cells.     

Free‐Blockage Mesoporous Anticancer Nanoparticles Based on ROS‐Responsive Wetting Behavior of Nanopores

To achieve an excellent delivery effect of drug, stimuli‐responsive nano “gate” with physical blockage units is usually constructed on the surface of the mesoporous silica nanocarriers (MSNs). In nature, the aquaporins in cell membrane can control the transport of water molecules by regulating the channel wettability, which is resulted from the conformational change of amino acids in the channel. Inspired by this phonomenon, herein a new concept of free‐blockage controlled release system is proposed, which is achieved by controlling the wettability of the internal surface of nanopores on MSNs. Such a new system is different from the physical‐blockage controlled release system, which bypasses the use of nano “gate” and overcomes the limitations of traditional physical blockage system. Moreover, further studies have shown that the system can selectively release the entrapped doxorubicin in human breast adenocarcinoma (MCF‐7) cells triggered by intracellular reactive oxygen species (ROS) but not in normalhuman umbilical vein endothelial cells (HUVECs) containing ROS with low levels. The wettability‐determined free‐blockage controlled release system is simple and effective, and it can also be triggered by intracellular biological stimuli, which provides a new approach for the future practical application of drug delivery and cancer therapy.     

TPGS‐Functionalized Polydopamine‐Modified Mesoporous Silica as Drug Nanocarriers for Enhanced Lung Cancer Chemotherapy against Multidrug Resistance

A nanocarrier system of d ‐a‐tocopheryl polyethylene glycol 1000 succinate (TPGS)‐functionalized polydopamine‐coated mesoporous silica nanoparticles (NPs) is developed for sustainable and pH‐responsive delivery of doxorubicin (DOX) as a model drug for the treatment of drug‐resistant nonsmall cell lung cancer. Such nanoparticles are of desired particle size, drug loading, and drug release profile. The surface morphology, surface charge, and surface chemical properties are also successfully characterized by a series of techniques such as transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), Brunauer‐Emmett‐Teller (BET) method, thermal gravimetric analysis (TGA), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). The normal A549 cells and drug‐resistant A549 cells are employed to access the cytotoxicity and cellular uptake of the NPs. The therapeutic effects of TPGS‐conjugated nanoparticles are evaluated in vitro and in vivo. Compared with free DOX and DOX‐loaded NPs without TPGS ligand modification, MSNs‐DOX@PDA‐TPGS exhibits outstanding capacity to overcome multidrug resistance and shows better in vivo therapeutic efficacy. This splendid drug delivery platform can also be sued to deliver other hydrophilic and hydrophobic drugs.     

Bioinspired Nano‐Prodrug with Enhanced Tumor Targeting and Increased Therapeutic Efficiency

Nanotechnology‐based drug delivery has a great potential to revolutionize cancer treatment by enhancing anticancer drug efficacy and reducing drug toxicity. Here, a bioinspired nano‐prodrug (BiNp) assembled by an antineoplastic peptidic derivative (FA‐KLA‐Hy‐DOX), a folate acid (FA)‐incorporated proapoptotic peptide (KLAKLAK)₂ (KLA) to doxorubicin (DOX) via an acid‐labile hydrozone bond (Hy) is constructed. The hydrophobic antineoplastic agent DOX is efficiently shielded in the core of nano‐prodrug. With FA targeting moieties on the surface, the obtained BiNp shows significant tumor‐targeting ability and enhances the specific uptake of cancer cells. Upon the trigger by the intracellular acidic microenvironment of endosomes, the antineoplastic agent DOX is released on‐demand and promotes the apoptosis of cancer cells. Simultaneously, the liberated FA‐KLA can induce the dysfunction of mitochondria and evoke mitochondria‐dependent apoptosis. In vitro and in vivo results show that the nano‐prodrug BiNp with integrated programmed functions exhibits remarkable inhibition of tumor and achieves a maximized therapeutic efficiency with a minimized side effect.     

Redox and pH Dual Responsive Polymer Based Nanoparticles for In Vivo Drug Delivery

Responsive nanomaterials have emerged as promising candidates as drug delivery vehicles in order to address biomedical diseases such as cancer. In this work, polymer‐based responsive nanoparticles prepared by a supramolecular approach are loaded with doxorubicin (DOX) for the cancer therapy. The nanoparticles contain disulfide bonds within the polymer network, allowing the release of the DOX payload in a reducing environment within the endoplasm of cancer cells. In addition, the loaded drug can also be released under acidic environment. In vitro anticancer studies using redox and pH dual responsive nanoparticles show excellent performance in inducing cell death and apoptosis. Zebrafish larvae treated with DOX‐loaded nanoparticles exhibit an improved viability as compared with the cases treated with free DOX by the end of a 3 d treatment. Confocal imaging is utilized to provide the daily assessment of tumor size on zebrafish larva models treated with DOX‐loaded nanoparticles, presenting sustainable reduction of tumor. This work demonstrates the development of functional nanoparticles with dual responsive properties for both in vitro and in vivo drug delivery in the cancer therapy.     

Reduction‐Sensitive,Robust Vesicles with a Non‐covalently Modifiable Surface as a Multifunctional Drug‐Delivery Platform

The design and synthesis of a novel reduction‐sensitive, robust, and biocompatible vesicle (SSCB[6]VC) are reported, which is self‐assembled from an amphiphilic cucurbit[6]uril (CB[6]) derivative that contains disulfide bonds between hexaethylene glycol units and a CB[6] core. The remarkable features of SSCB[6]VC include: 1) facile, non‐destructive, non‐covalent, and modular surface modification using exceptionally strong host–guest chemistry; 2) high structural stability; 3) facile internalization into targeted cells by receptor‐mediated endocytosis, and 4) efficient triggered release of entrapped drugs in a reducing environment such as cytoplasm. Furthermore, a significantly increased cytotoxicity of the anticancer drug doxorubicin to cancer cells is demonstrated using doxorubicin‐loaded SSCB[6]VC, the surface of which is decorated with functional moieties such as a folate–spermidine conjugate and fluorescein isothiocyanate–spermidine conjugate as targeting ligand and fluorescence imaging probe, respectively. SSCB[6]VC with such unique features can be used as a highly versatile multifunctional platform for targeted drug delivery, which may find useful applications in cancer therapy. This novel strategy based on supramolecular chemistry and the unique properties of CB[6] can be extended to design smart multifunctional materials for biomedical applications including gene delivery.     

Ultrasound‐Propelled Nanoporous Gold Wire for Efficient Drug Loading and Release

Ultrasound (US)‐powered nanowire motors based on nanoporous gold segment are developed for increasing the drug loading capacity. The new highly porous nanomotors are characterized with a tunable pore size, high surface area, and high capacity for the drug payload. These nanowire motors are prepared by template membrane deposition of a silver‐gold alloy segment followed by dealloying the silver component. The drug doxorubicin (DOX) is loaded within the nanopores via electrostatic interactions with an anionic polymeric coating. The nanoporous gold structure also facilitates the near‐infrared (NIR) light controlled release of the drug through photothermal effects. Ultrasound‐driven transport of the loaded drug toward cancer cells followed by NIR‐light triggered release is illustrated. The incorporation of the nanoporous gold segment leads to a nearly 20‐fold increase in the active surface area compared to common gold nanowire motors. It is envisioned that such US‐powered nanomotors could provide a new approach to rapidly and efficiently deliver large therapeutic payloads in a target‐specific manner.     

M13 bacteriophage-polymer nanoassemblies as drug delivery vehicles

Poly(caprolactone-b-2-vinylpyridine) (PCL-P2VP) coated with folate-conjugated M13 (FA-M13) provides a nanosized delivery system which is capable of encapsulating hydrophobic antitumor drugs such as doxorubicin (DOX). The DOX-loaded FA-M13-PCL-P2VP assemblies had an average diameter of approximately 200 nm and their structure was characterized using transmission electron microscopy, scanning electron microscopy, and dynamic light scattering. The particles were stable at physiological pH but could be degraded at a lower pH. The release of DOX from the nanoassemblies under acidic conditions was shown to be significantly faster than that observed at physiological pH. In addition, the DOX-loaded FA-M13-PCL-P2VP particles showed a distinctly greater cellular uptake and cytotoxicity against folate-receptor-positive cancer cells than folate-receptor-negative cells, indicating that the receptor facilitates folate uptake via receptor-mediated endocytosis. Furthermore, the DOX-loaded particles also had a significantly higher tumor uptake and selectivity compared to free DOX. This study therefore offers a new way to fabricate nanosized drug delivery vehicles.     

Pulmonary Codelivery of Doxorubicin and siRNA by pH‐Sensitive Nanoparticles for Therapy of Metastatic Lung Cancer

A pulmonary codelivery system that can simultaneously deliver doxorubicin (DOX) and Bcl2 siRNA to the lungs provides a promising local treatment strategy for lung cancers. In this study, DOX is conjugated onto polyethylenimine (PEI) by using cis‐aconitic anhydride (CA, a pH‐sensitive linker) to obtain PEI‐CA‐DOX conjugates. The PEI‐CA‐DOX/siRNA complex nanoparticles are formed spontaneously via electrostatic interaction between cationic PEI‐CA‐DOX and anionic siRNA. The drug release experiment shows that DOX releases faster at acidic pH than at pH 7.4. Moreover, PEI‐CA‐DOX/Bcl2 siRNA complex nanoparticles show higher cytotoxicity and apoptosis induction in B16F10 cells than those treated with either DOX or Bcl2 siRNA alone. When the codelivery systems are directly sprayed into the lungs of B16F10 melanoma‐bearing mice, the PEI‐CA‐DOX/Bcl2 siRNA complex nanoparticles exhibit enhanced antitumor efficacy compared with the single delivery of DOX or Bcl2 siRNA. Compared with systemic delivery, most drug and siRNA show a long‐term retention in the lungs via pulmonary delivery, and a considerable number of the drug and siRNA accumulate in tumor tissues of lungs, but rarely in normal lung tissues. The PEI‐CA‐DOX/Bcl2 siRNA complex nanoparticles are promising for the treatment of metastatic lung cancer by pulmonary delivery with low side effects on the normal tissues.     

NIR Photoresponsive Crosslinked Upconverting Nanocarriers Toward Selective Intracellular Drug Release

An NIR‐responsive mesoporous silica coated upconverting nanoparticle (UCNP) conjugate is developed for controllable drug delivery and fluorescence imaging in living cells. In this work, antitumor drug doxorubicin (Dox) molecules are encapsulated within cross‐linked photocaged mesoporous silica coated UCNPs. Upon 980 nm light irradiation, Dox could be selectively released through the photocleavage of theo‐nitrobenzyl (NB) caged linker by the converted UV emission from UCNPs. This NIR light‐responsive nanoparticle conjugate demonstrates high efficiency for the controlled release of the drug in cancer cells. Upon functionalization of the nanocarrier with folic acid (FA), this photocaged FA‐conjugated silica‐UCNP nanocarrier will also allow targeted intracellular drug delivery and selective fluorescence imaging towards the cell lines with high level expression of folate receptor (FR).     

Hybrid nanostructured drug carrier with tunable and controlled drug release

We describe here a transformative approach to synthesize a hybrid nanostructured drug carrier that exhibits the characteristics of controlled drug release. The synthesis of the nanohybrid architecture involved two steps. The first step involved direct crystallization of biocompatible copolymer along the long axis of the carbon nanotubes (CNTs), followed by the second step of attachment of drug molecule to the polymer via hydrogen bonding. The extraordinary inorganic–organic hybrid architecture exhibited high drug loading ability and is physically stable even under extreme conditions of acidic media and ultrasonic irradiation. The temperature and pH sensitive characteristics of the hybrid drug carrier and high drug loading ability merit its consideration as a promising carrier and utilization of the fundamental aspects used for synthesis of other promising drug carriers. The higher drug release response during the application of ultrasonic frequency is ascribed to a cavitation-type process in which the acoustic bubbles nucleate and collapse releasing the drug. Furthermore, the study underscores the potential of uniquely combining CNTs and biopolymers for drug delivery.     

ROS‐Responsive Polymeric siRNA Nanomedicine Stabilized by Triple Interactions for the Robust Glioblastoma Combinational RNAi Therapy

Small interfering RNA (siRNA) holds inherent advantages and great potential for treating refractory diseases. However, lack of suitable siRNA delivery systems that demonstrate excellent circulation stability and effective at‐site delivery ability is currently impeding siRNA therapeutic performance. Here, a polymeric siRNA nanomedicine (3I‐NM@siRNA) stabilized by triple interactions (electrostatic, hydrogen bond, and hydrophobic) is constructed. Incorporating extra hydrogen and hydrophobic interactions significantly improves the physiological stability compared to an siRNA nanomedicine analog that solely relies on the electrostatic interaction for stability. The developed 3I‐NM@siRNA nanomedicine demonstrates effective at‐site siRNA release resulting from tumoral reactive oxygen species (ROS)‐triggered sequential destabilization. Furthermore, the utility of 3I‐NM@siRNA for treating glioblastoma (GBM) by functionalizing 3I‐NM@siRNA nanomedicine with angiopep‐2 peptide is enhanced. The targeted Ang‐3I‐NM@siRNA exhibits superb blood–brain barrier penetration and potent tumor accumulation. Moreover, by cotargeting polo‐like kinase 1 and vascular endothelial growth factor receptor‐2, Ang‐3I‐NM@siRNA shows effective suppression of tumor growth and significantly improved survival time of nude mice bearing orthotopic GBM brain tumors. New siRNA nanomedicines featuring triple‐interaction stabilization together with inbuilt self‐destruct delivery ability provide a robust and potent platform for targeted GBM siRNA therapy, which may have utility for RNA interference therapy of other tumors or brain diseases.     

Inhibition of 3‐D Tumor Spheroids by Timed‐Released Hydrophilic and Hydrophobic Drugs from Multilayered Polymeric Microparticles

First‐line cancer chemotherapy necessitates high parenteral dosage and repeated dosing of a combination of drugs over a prolonged period. Current commercially available chemotherapeutic agents, such as Doxil and Taxol, are only capable of delivering single drug in a bolus dose. The aim of this study is to develop dual‐drug‐loaded, multilayered microparticles and to investigate their antitumor efficacy compared with single‐drug‐loaded particles. Results show hydrophilic doxorubicin HCl (DOX) and hydrophobic paclitaxel (PTX) localized in the poly(dl ‐lactic‐co‐glycolic acid, 50:50) (PLGA) shell and in the poly(l ‐lactic acid) (PLLA) core, respectively. The introduction of poly[(1,6‐bis‐carboxyphenoxy) hexane] (PCPH) into PLGA/PLLA microparticles causes PTX to be localized in the PLLA and PCPH mid‐layers, whereas DOX is found in both the PLGA shell and core. PLGA/PLLA/PCPH microparticles with denser shells allow better control of DOX release. A delayed release of PTX is observed with the addition of PCPH. Three‐dimensional MCF‐7 spheroid studies demonstrate that controlled co‐delivery of DOX and PTX from multilayered microparticles produces a greater reduction in spheroid growth rate compared with single‐drug‐loaded particles. This study provides mechanistic insights into how distinctive structure of multilayered microparticles can be designed to modulate the release profiles of anticancer drugs, and how co‐delivery can potentially provide better antitumor response.     

Subcellular tracking of drug release from carbon nanotube vehicles in living cells

The direct observation of drug release from carbon nanotube vehicles in living cells is realized through a unique two-dye labeling approach. Single-walled carbon nanotubes (SWNTs) are firstly marked with fluorescein isothiocyanate (FITC) to track their location and movement inside the cell. Then a fluorescent anticancer drug doxorubicin (DOX) is attached by means of π-stacking onto SWNTs. Delivered by SWNTs into cells, DOX will detach from the vehicle in an acidic environment due to the pH-dependent π-π stacking interaction between DOX and SWNTs. From observation of the two different kinds of fluorescence (green and red) that respectively represent the carrier SWNTs and drug DOX, the process of drug release inside the living cell can be monitored under a confocal microscope. Results show that the drug DOX detaches from SWNTs inside the lysosomes to yield free molecules and escape into the cytoplasm and finally into the nucleus, while the vehicle SWNTs are trapped inside the lysosomes, without entering the nucleus. The current observations confirm previously proposed mechanisms for drug/DOX release inside cells. The experimental establishment of drug-release mechanisms in living cells here might provide important insights for future design of new drug-delivery and release systems.