Recent Advances in Microfluidic Platforms Applied in Cancer Metastasis: Circulating Tumor Cells' (CTCs) Isolation and Tumor‐On‐A‐Chip

Cancer remains the leading cause of death worldwide despite the enormous efforts that are made in the development of cancer biology and anticancer therapeutic treatment. Furthermore, recent studies in oncology have focused on the complex cancer metastatic process as metastatic disease contributes to more than 90% of tumor‐related death. In the metastatic process, isolation and analysis of circulating tumor cells (CTCs) play a vital role in diagnosis and prognosis of cancer patients at an early stage. To obtain relevant information on cancer metastasis and progression from CTCs, reliable approaches are required for CTC detection and isolation. Additionally, experimental platforms mimicking the tumor microenvironment in vitro give a better understanding of the metastatic microenvironment and antimetastatic drugs' screening. With the advancement of microfabrication and rapid prototyping, microfluidic techniques are now increasingly being exploited to study cancer metastasis as they allow precise control of fluids in small volume and rapid sample processing at relatively low cost and with high sensitivity. Recent advancements in microfluidic platforms utilized in various methods for CTCs' isolation and tumor models recapitulating the metastatic microenvironment (tumor‐on‐a‐chip) are comprehensively reviewed. Future perspectives on microfluidics for cancer metastasis are proposed.     

Microfluidic Skin‐on‐a‐Chip Models: Toward Biomimetic Artificial Skin

The role of skin in the human body is indispensable, serving as a barrier, moderating homeostatic balance, and representing a pronounced endpoint for cosmetics and pharmaceuticals. Despite the extensive achievements of in vitro skin models, they do not recapitulate the complexity of human skin; thus, there remains a dependence on animal models during preclinical drug trials, resulting in expensive drug development with high failure rates. By imparting a fine control over the microenvironment and inducing relevant mechanical cues, skin‐on‐a‐chip (SoC) models have circumvented the limitations of conventional cell studies. Enhanced barrier properties, vascularization, and improved phenotypic differentiation have been achieved by SoC models; however, the successful inclusion of appendages such as hair follicles and sweat glands and pigmentation relevance have yet to be realized. The present Review collates the progress of SoC platforms with a focus on their fabrication and the incorporation of mechanical cues, sensors, and blood vessels.     

Organ‐on‐a‐Chip Systems: Microengineering to Biomimic Living Systems

“Organ‐on‐a‐chip” systems integrate microengineering, microfluidic technologies, and biomimetic principles to create key aspects of living organs faithfully, including critical microarchitecture, spatiotemporal cell–cell interactions, and extracellular microenvironments. This creative platform and its multiorgan integration recapitulating organ‐level structures and functions can bring unprecedented benefits to a diversity of applications, such as developing human in vitro models for healthy or diseased organs, enabling the investigation of fundamental mechanisms in disease etiology and organogenesis, benefiting drug development in toxicity screening and target discovery, and potentially serving as replacements for animal testing. Recent advances in novel designs and examples for developing organ‐on‐a‐chip platforms are reviewed. The potential for using this emerging technology in understanding human physiology including mechanical, chemical, and electrical signals with precise spatiotemporal controls are discussed. The current challenges and future directions that need to be pursued for these proof‐of‐concept studies are also be highlighted.     

Dual‐Locking Nanoparticles Disrupt the PD‐1/PD‐L1 Pathway for Efficient Cancer Immunotherapy

The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR‐associated (Cas) enzyme, Cas13a, holds great promise in cancer treatment due to its potential for selective destruction of tumor cells via collateral effects after target recognition. However, these collateral effects do not specifically target tumor cells and may cause safety issues when administered systemically. Herein, a dual‐locking nanoparticle (DLNP) that can restrict CRISPR/Cas13a activation to tumor tissues is described. DLNP has a core–shell structure, in which the CRISPR/Cas13a system (plasmid DNA, pDNA) is encapsulated inside the core with a dual‐responsive polymer layer. This polymer layer endows the DLNP with enhanced stability during blood circulation or in normal tissues and facilitates cellular internalization of the CRISPR/Cas13a system and activation of gene editing upon entry into tumor tissue. After carefully screening and optimizing the CRISPR RNA (crRNA) sequence that targets programmed death‐ligand 1 (PD‐L1), DLNP demonstrates the effective activation of T‐cell‐mediated antitumor immunity and the reshaping of immunosuppressive tumor microenvironment (TME) in B16F10‐bearing mice, resulting in significantly enhanced antitumor effect and improved survival rate. Further development by replacing the specific crRNA of target genes can potentially make DLNP a universal platform for the rapid development of safe and efficient cancer immunotherapies.     

ROS‐Responsive Polyprodrug Nanoparticles for Triggered Drug Delivery and Effective Cancer Therapy

The application of nanoparticles (NPs) to drug delivery has led to the development of novel nanotherapeutics for the treatment of various diseases including cancer. However, clinical use of NP‐mediated drug delivery has not always translated into improved survival of cancer patients, in part due to the suboptimal properties of NP platforms, such as premature drug leakage during preparation, storage, or blood circulation, lack of active targeting to tumor tissue and cells, and poor tissue penetration. Herein, an innovative reactive oxygen species (ROS)‐responsive polyprodrug is reported that can self‐assemble into stable NPs with high drug loading. This new NP platform is composed of the following key components: (i) polyprodrug inner core that can respond to ROS for triggered release of intact therapeutic molecules, (ii) polyethylene glycol (PEG) outer shell to prolong blood circulation; and (iii) surface‐encoded internalizing RGD (iRGD) to enhance tumor targeting and tissue penetration. These targeted ROS‐responsive polyprodrug NPs show significant inhibition of tumor cell growth both in vitro and in vivo.     

Sequential Targeting TGF‐β Signaling and KRAS Mutation Increases Therapeutic Efficacy in Pancreatic Cancer

Pancreatic cancer is a highly aggressive malignancy that strongly resists extant treatments. The failure of existing therapies is majorly attributed to the tough tumor microenvironment (TME) limiting drug access and the undruggable targets of tumor cells. The formation of suppressive TME is regulated by transforming growth factor beta (TGF‐β) signaling, while the poor response and short survival of almost 90% of pancreatic cancer patients results from the oncogenic KRAS mutation. Hence, simultaneously targeting both the TGF‐β and KRAS pathways might dismantle the obstacles of pancreatic cancer therapy. Here, a novel sequential‐targeting strategy is developed, in which antifibrotic fraxinellone‐loaded CGKRK‐modified nanoparticles (Frax‐NP‐CGKRK) are constructed to regulate TGF‐β signaling and siRNA‐loaded lipid‐coated calcium phosphate (LCP) biomimetic nanoparticles (siKras‐LCP‐ApoE3) are applied to interfere with the oncogenic KRAS. Frax‐NP‐CGKRK successfully targets the tumor sites through the recognition of overexpressed heparan sulfate proteoglycan, reverses the activated cancer‐associated fibroblasts (CAFs), attenuates the dense stroma barrier, and enhances tumor blood perfusion. Afterward, siKras‐LCP‐ApoE3 is efficiently internalized by the tumor cells through macropinocytosis and specifically silencing KRAS mutation. Compared with gemcitabine, this sequential‐targeting strategy significantly elongates the lifespans of pancreatic tumor‐bearing animals, hence providing a promising approach for pancreatic cancer therapy.     

Facile One Step Formation and Screening of Tumor Spheroids Using Droplet‐Microarray Platform

Tumor spheroids or microtumors are important 3D in vitro tumor models that closely resemble a tumor's in vivo “microenvironment” compared to 2D cell culture. Microtumors are widely applied in the fields of fundamental cancer research, drug discovery, and precision medicine. In precision medicine tumor spheroids derived from patient tumor cells represent a promising system for drug sensitivity and resistance testing. Established and commonly used platforms for routine screenings of cell spheroids, based on microtiter plates of 96‐ and 384‐well formats, require relatively large numbers of cells and compounds, and often lead to the formation of multiple spheroids per well. In this study, an application of the Droplet Microarray platform, based on hydrophilic–superhydrophobic patterning, in combination with the method of hanging droplet, is demonstrated for the formation of highly miniaturized single‐spheroid‐microarrays. Formation of spheroids from several commonly used cancer cell lines in 100 nL droplets starting with as few as 150 cells per spheroid within 24–48 h is demonstrated. Established methodology carries a potential to be adopted for routine workflows of high‐throughput compound screening in 3D cancer spheroids or microtumors, which is crucial for the fields of fundamental cancer research, drug discovery, and precision medicine.     

A Biomimetic Tumor Model of Heterogeneous Invasion in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a complex, heterogeneous, and genetically unstable disease. Its tumor microenvironment (TME) is complicated by heterogeneous cancer cell populations and strong desmoplastic stroma. This complex and heterogeneous environment makes it challenging to discover and validate unique therapeutic targets. Reliable and relevant in vitro PDAC tumor models can significantly advance the understanding of the PDAC TME and may enable the discovery and validation of novel drug targets. In this study, an engineered tumor model is developed to mimic the PDAC TME. This biomimetic model, named ductal tumor‐microenvironment‐on‐chip (dT‐MOC), permits analysis and experimentation on the epithelial–mesenchymal transition (EMT) and local invasion with intratumoral heterogeneity. This dT‐MOC is a microfluidic platform where a duct of murine genetically engineered pancreatic cancer cells is embedded within a collagen matrix. The cancer cells used carry two of the three mutations of KRAS, CDKN2A, and TP53, which are key driver mutations of human PDAC. The intratumoral heterogeneity is mimicked by co‐culturing these cancer cells. Using the dT‐MOC model, heterogeneous invasion characteristics, and response to transforming growth factor‐beta1 are studied. A mechanism of EMT and local invasion caused by the interaction between heterogeneous cancer cell populations is proposed.     

Cryo‐EM‐On‐a‐Chip: Custom‐Designed Substrates for the 3D Analysis of Macromolecules

The fight against human disease requires a multidisciplinary scientific approach. Applying tools from seemingly unrelated areas, such as materials science and molecular biology, researchers can overcome long‐standing challenges to improve knowledge of molecular pathologies. Here, custom‐designed substrates composed of silicon nitride (SiN) are used to study the 3D attributes of tumor suppressor proteins that function in DNA repair events. New on‐chip preparation strategies enable the isolation of native protein complexes from human cancer cells. Combined techniques of cryo‐electron microscopy (EM) and molecular modeling reveal a new modified form of the p53 tumor suppressor present in aggressive glioblastoma multiforme cancer cells. Taken together, the findings provide a radical new design for cryo‐EM substrates to evaluate the structures of disease‐related macromolecules.     

Optical Imaging Approaches to Monitor Static and Dynamic Cell‐on‐Chip Platforms: A Tutorial Review

Miniaturized laboratories on chip platforms play an important role in handling life sciences studies. The platforms may contain static or dynamic biological cells. Examples are a fixed medium of an organ‐on‐a‐chip and individual cells moving in a microfluidic channel, respectively. Due to feasibility of control or investigation and ethical implications of live targets, both static and dynamic cell‐on‐chip platforms promise various applications in biology. To extract necessary information from the experiments, the demand for direct monitoring is rapidly increasing. Among different microscopy methods, optical imaging is a straightforward choice. Considering light interaction with biological agents, imaging signals may be generated as a result of scattering or emission effects from a sample. Thus, optical imaging techniques could be categorized into scattering‐based and emission‐based techniques. In this review, various optical imaging approaches used in monitoring static and dynamic platforms are introduced along with their optical systems, advantages, challenges, and applications. This review may help biologists to find a suitable imaging technique for different cell‐on‐chip studies and might also be useful for the people who are going to develop optical imaging systems in life sciences studies.     

A Spontaneous 3D Bone‐On‐a‐Chip for Bone Metastasis Study of Breast Cancer Cells

Bone metastasis occurs at ≈70% frequency in metastatic breast cancer. The mechanisms used by tumors to hijack the skeleton, promote bone metastases, and confer therapeutic resistance are poorly understood. This has led to the development of various bone models to investigate the interactions between cancer cells and host bone marrow cells and related physiological changes. However, it is challenging to perform bone studies due to the difficulty in periodic sampling. Herein, a bone‐on‐a‐chip (BC) is reported for spontaneous growth of a 3D, mineralized, collagenous bone tissue. Mature osteoblastic tissue of up to 85 µm thickness containing heavily mineralized collagen fibers naturally formed in 720 h without the aid of differentiation agents. Moreover, co‐culture of metastatic breast cancer cells is examined with osteoblastic tissues. The new bone‐on‐a‐chip design not only increases experimental throughput by miniaturization, but also maximizes the chances of cancer cell interaction with bone matrix of a concentrated surface area and facilitates easy, frequent observation. As a result, unique hallmarks of breast cancer bone colonization, previously confirmed only in vivo, are observed. The spontaneous 3D BC keeps the promise as a physiologically relevant model for the in vitro study of breast cancer bone metastasis.     

Virion‐Like Membrane‐Breaking Nanoparticles with Tumor‐Activated Cell‐and‐Tissue Dual‐Penetration Conquer Impermeable Cancer

Poor drug penetration into tumor cells and tissues is a worldwide difficulty in cancer therapy. A strategy is developed for virion‐like membrane‐breaking nanoparticles (MBNs) to smoothly accomplish tumor‐activated cell‐and‐tissue dual‐penetration for surmounting impermeable drug‐resistant cancer. Tailor‐made dendritic arginine‐rich peptide prodrugs are designed to mimic viral protein transduction domains and globular protein architectures. Attractively, these protein mimics self‐assemble into virion‐like nanoparticles in aqueous solution, having highly ordered secondary structure. Tumor‐specific acidity conditions would activate the membrane‐breaking ability of these virion‐like nanoparticles to perforate artificial and natural membrane systems. As expected, MBNs achieve highly efficient drug penetration into drug‐resistant human ovarian (SKOV3/R) cancer cells. Most importantly, the well‐organized MBNs can pass through endothelial/tumor cells and spread from one cell to another one. Intravenous injection of MBNs into nude mice bearing impermeable SKOV3/R tumors suggests that the MBNs can recognize the tumor tissue after prolonged blood circulation, evoke the membrane‐breaking function for robust transvascular extravasation, and penetrate into the deep tumor tissue. This work provides the first demonstration of sophisticated molecular and supramolecular engineering of virion‐like MBNs to realize the long‐awaited cell‐and‐tissue dual‐penetration, contributing to the development of a brand‐new avenue for dealing with incurable cancers.     

An Acidic‐Microenvironment‐Driven DNA Nanomachine Enables Specific ATP Imaging in the Extracellular Milieu of Tumor

Extracellular ATP is an emerging target for cancer treatment because it is a key messenger for shaping the tumor microenvironment (TME) and regulating tumor progression. However, it remains a great challenge to design biochemical probes for targeted imaging of extracellular ATP in the TME. A TME‐driven DNA nanomachine (Apt‐LIP) that permits spatially controlled imaging of ATP in the extracellular milieu of tumors with ultrahigh signal‐to‐background ratio is reported. It operates in response to the mild acidity in the TME with the pH (low) insertion peptide (pHLIP) module, thus allowing the specific anchoring of the structure‐switching signaling aptamer unit to the membrane of tumor cells for “off–on” fluorescence imaging of the extracellular ATP. Apt‐LIP allows for acidity driven visualization of different extracellular concentrations of exogenous ATP, as well as the monitoring of endogenous ATP release from cells. Furthermore, it is demonstrated that Apt‐LIP represents a promising platform for the specific imaging of the extracellular ATP in both primary and metastatic tumors. Ultimately, since diverse aptamers are obtained through in vitro selection, this design strategy can be further applied for precise detection of various extracellular targets in the TME.     

Manganese Dioxide Coated WS2@Fe3O4/sSiO2 Nanocomposites for pH‐Responsive MR Imaging and Oxygen‐Elevated Synergetic Therapy

Recently, the development of multifunctional theranostic nanoplatforms to realize tumor‐specific imaging and enhanced cancer therapy via responding or modulating the tumor microenvironment (TME) has attracted tremendous interests in the field of nanomedicine. Herein, tungsten disulfide (WS₂) nanoflakes with their surface adsorbed with iron oxide nanoparticles (IONPs) via self‐assembly are coated with silica and then subsequently with manganese dioxide (MnO₂), on to which polyethylene glycol (PEG) is attached. The obtained WS₂‐IO/S@MO‐PEG appears to be highly sensitive to pH, enabling tumor pH‐responsive magnetic resonance imaging with IONPs as the pH‐inert T2 contrast probe and MnO₂ as the pH‐sensitive T1 contrast probe. Meanwhile, synergistic combination tumor therapy is realized with such WS₂‐IO/S@MO‐PEG, by utilizing the strong near‐infrared light and X‐ray absorbance of WS₂ for photothermal therapy (PTT) and enhanced cancer radiotherapy (RT), respectively, as well as the ability of MnO₂ to decompose tumor endogenous H₂O₂ and relieve tumor hypoxia to further overcome hypoxia‐associated radiotherapy resistance. The combination of PTT and RT with WS₂‐IO/S@MO‐PEG results in a remarkable synergistic effect to destruct tumors. This work highlights the promise of developing multifunction nanocomposites for TME‐specific imaging and TME modulation, aiming at precision cancer synergistic treatment.     

Two‐Dimensional Antimonene‐Based Photonic Nanomedicine for Cancer Theranostics

Antimonene (AM) is a recently described two‐dimensional (2D) elemental layered material. In this study, a novel photonic drug‐delivery platform based on 2D PEGylated AM nanosheets (NSs) is developed. The platform's multiple advantages include: i) excellent photothermal properties, ii) high drug‐loading capacity, iii) spatiotemporally controlled drug release triggered by near‐infrared (NIR) light and moderate acidic pH, iv) superior accumulation at tumor sites, v) deep tumor penetration by both extrinsic stimuli (i.e., NIR light) and intrinsic stimuli (i.e., pH), vi) excellent multimodal‐imaging properties, and vii) significant inhibition of tumor growth with no observable side effects and potential degradability, thus addressing several key limitations of cancer nanomedicines. The intracellular fate of the prepared NSs is also revealed for the first time, providing deep insights that improve cellular‐level understanding of the nano–bio interactions of AM‐based NSs and other emerging 2D nanomaterials. To the best of knowledge, this is the first report on 2D AM‐based photonic drug‐delivery platforms, possibly marking an exciting jumping‐off point for research into the application of 2D AM nanomaterials in cancer theranostics.     

Antiferromagnetic Pyrite as the Tumor Microenvironment‐Mediated Nanoplatform for Self‐Enhanced Tumor Imaging and Therapy

Several decades of research have identified the specific tumor microenvironment (TME) to develop promising nanotheranostics, such as pH‐sensitive imaging, acidity‐sensitive starving therapy, and hydrogen peroxide‐activated chemotherapy, etc. Herein, a novel TME‐mediated nanoplatform employing antiferromagnetic pyrite nanocubes is presented, exploiting the intratumoral, overproduced peroxide for self‐enhanced magnetic resonance imaging (MRI) and photothermal therapy (PTT)/chemodynamic therapy (CDT). Through the activation of excessive peroxide in the tumor microenvironment, pyrite can lead to in situ surface oxidation and generate hydroxyl radicals to kill tumor cells (i.e., CDT). The increase of the valence state of surface Fe significantly promotes the performance of MRI accompanied by CDT. Furthermore, the localized heat by photothermal treatment can accelerate the intratumoral Fenton process, enabling a synergetic PTT/CDT. To our best knowledge, this is the first study to use the TME‐response valence‐variable strategy based on pyrite for developing a synergetic nanotheranostic, which will open up a new dimension for the design of other TME‐based anticancer strategies.     

Biomechanical Strain Exacerbates Inflammation on a Progeria‐on‐a‐Chip Model

Organ‐on‐a‐chip platforms seek to recapitulate the complex microenvironment of human organs using miniaturized microfluidic devices. Besides modeling healthy organs, these devices have been used to model diseases, yielding new insights into pathophysiology. Hutchinson‐Gilford progeria syndrome (HGPS) is a premature aging disease showing accelerated vascular aging, leading to the death of patients due to cardiovascular diseases. HGPS targets primarily vascular cells, which reside in mechanically active tissues. Here, a progeria‐on‐a‐chip model is developed and the effects of biomechanical strain are examined in the context of vascular aging and disease. Physiological strain induces a contractile phenotype in primary smooth muscle cells (SMCs), while a pathological strain induces a hypertensive phenotype similar to that of angiotensin II treatment. Interestingly, SMCs derived from human induced pluripotent stem cells of HGPS donors (HGPS iPS‐SMCs), but not from healthy donors, show an exacerbated inflammatory response to strain. In particular, increased levels of inflammation markers as well as DNA damage are observed. Pharmacological intervention reverses the strain‐induced damage by shifting gene expression profile away from inflammation. The progeria‐on‐a‐chip is a relevant platform to study biomechanics in vascular biology, particularly in the setting of vascular disease and aging, while simultaneously facilitating the discovery of new drugs and/or therapeutic targets.     

Nanoengineered Immune Niches for Reprogramming the Immunosuppressive Tumor Microenvironment and Enhancing Cancer Immunotherapy

Cancer immunotherapies that harness the body's immune system to combat tumors have received extensive attention and become mainstream strategies for treating cancer. Despite promising results, some problems remain, such as the limited patient response rate and the emergence of severe immune‐related adverse effects. For most patients, the therapeutic efficacy of cancer immunotherapy is mainly limited by the immunosuppressive tumor microenvironment (TME). To overcome such obstacles in the TME, the immunomodulation of immunosuppressive factors and therapeutic immune cells (e.g., T cells and antigen‐presenting cells) should be carefully designed and evaluated. Nanoengineered synthetic immune niches have emerged as highly customizable platforms with a potent capability for reprogramming the immunosuppressive TME. Here, recent developments in nano‐biomaterials that are rationally designed to modulate the immunosuppressive TME in a spatiotemporal manner for enhanced cancer immunotherapy which are rationally designed to modulate the immunosuppressive TME in a spatiotemporal manner for enhanced cancer immunotherapy are highlighted.     

Dual pH/ROS‐Responsive Nanoplatform with Deep Tumor Penetration and Self‐Amplified Drug Release for Enhancing Tumor Chemotherapeutic Efficacy

Poor deep tumor penetration and incomplete intracellular drug release remain challenges for antitumor nanomedicine application in clinical settings. Herein, a nanomedicine (RLPA‐NPs) is developed that can achieve prolonged blood circulation, deep tumor penetration, active‐targeting of cancer cells, endosome/lysosome escape, and intracellular selectivity self‐amplified drug release for effective drug delivery. The RLPA‐NPs are constructed by encapsulation of a pH‐sensitive polymer octadecylamine‐poly(aspartate‐1‐(3‐aminopropyl) imidazole) (OA‐P(Asp‐API)) and a ROS‐generation agent, β‐Lapachone (Lap), in micelles assembled by the tumor‐penetration peptide internalizing RGD (iRGD)‐modified ROS‐responsive paclitaxel (PTX)‐prodrug. iRGD could promote RLPA‐NPs penetration into deep tumor tissue, and specific targeting to cancer cells. After internalization by cancer cells through receptor‐mediated endocytosis, OA‐P(Asp‐API) can rapidly protonate in the endosome's acidic environment, resulting in RLPA‐NPs escape from the endosome through the “proton sponge effect”. At the same time, the RLPA‐NPs micelle disassembles, releasing Lap and PTX‐prodrug. Subsequently, the released Lap could generate ROS, consequently amplifying and accelerating PTX release to kill tumor cells. The in vitro and in vivo studies demonstrated that RLPA‐NPs can significantly improve the therapeutic effect compared to control groups. Therefore, RLPA‐NPs are a promising nanoplatform for overcoming multiple physiological and pathological barriers to enhance drug delivery.     

A Dual‐Responsive Mesoporous Silica Nanoparticle for Tumor‐Triggered Targeting Drug Delivery

A novel pH‐ and redox‐ dual‐responsive tumor‐triggered targeting mesoporous silica nanoparticle (TTTMSN) is designed as a drug carrier. The peptide RGDFFFFC is anchored on the surface of mesoporous silica nanoparticles via disulfide bonds, which are redox‐responsive, as a gatekeeper as well as a tumor‐targeting ligand. PEGylated technology is employed to protect the anchored peptide ligands. The peptide and monomethoxypolyethylene glycol (MPEG) with benzoic‐imine bond, which is pH‐sensitive, are then connected via “click” chemistry to obtain TTTMSN. In vitro cell research demonstrates that the targeting property of TTTMSN is switched off in normal tissues with neutral pH condition, and switched on in tumor tissues with acidic pH condition after removing the MPEG segment by hydrolysis of benzoic‐imine bond under acidic conditions. After deshielding of the MPEG segment, the drug‐loaded nanoparticles are easily taken up by tumor cells due to the exposed peptide targeting ligand, and subsequently the redox signal glutathione in tumor cells induces rapid drug release intracellularly after the cleavage of disulfide bond. This novel intelligent TTTMSN drug delivery system has great potential for cancer therapy.