Selectively Potentiating Hypoxia Levels by Combretastatin A4 Nanomedicine: Toward Highly Enhanced Hypoxia‐Activated Prodrug Tirapazamine Therapy for Metastatic Tumors

Hypoxia‐activated prodrugs (HAPs) have the potential to selectively kill hypoxic cells and convert tumor hypoxia from a problem to a selective treatment advantage. However, HAPs are unsuccessful in most clinical trials owing to inadequate hypoxia within the treated tumors, as implied by a further substudy of a phase II clinical trial. Here, a novel strategy for the combination of HAPs plus vascular disrupting agent (VDA) nanomedicine for efficacious solid tumor therapy is developed. An effective VDA nanomedicine of poly(l ‐glutamic acid)‐graft‐methoxy poly(ethylene glycol)/combretastatin A4 (CA4‐NPs) is prepared and can selectively enhance tumor hypoxia and boost a typical HAP tirapazamine (TPZ) therapy against metastatic 4T1 breast tumors. After treatment with the combination of TPZ plus CA4‐NPs, complete tumor reduction is observed in 4T1 xenograft mice (initial tumor volume is 180 mm³), and significant tumor shrinkage and antimetastatic effects are observed in challenging large tumors with initial volume of 500 mm³. The report here highlights the potential of using a combination of HAPs plus VDA nanomedicine in solid tumor therapy.     

Protein‐Based Nanomedicine Platforms for Drug Delivery

Protein‐based nanomedicine platforms for drug delivery comprise naturally self‐assembled protein subunits of the same protein or a combination of proteins making up a complete system. They are ideal for drug‐delivery platforms due to their biocompatibility and biodegradability coupled with low toxicity. A variety of proteins have been used and characterized for drug‐delivery systems, including the ferritin/apoferritin protein cage, plant‐derived viral capsids, the small Heat shock protein (sHsp) cage, albumin, soy and whey protein, collagen, and gelatin. There are many different types and shapes that have been prepared to deliver drug molecules using protein‐based platforms, including various protein cages, microspheres, nanoparticles, hydrogels, films, minirods, and minipellets. The protein cage is the most newly developed biomaterial for drug delivery and therapeutic applications. The uniform size, multifunctionality, and biodegradability push it to the frontier of drug delivery. In this Review, the recent strategic development of drug delivery is discussed with emphasis on polymer‐based, especially protein‐based, nanomedicine platforms for drug delivery. The advantages and disadvantages are also discussed for each type of protein‐based drug‐delivery system.

     

Tailoring Nanomaterials for Targeting Tumor‐Associated Macrophages

Advances in the field of nanotechnology together with an increase understanding of tumor immunology have paved the way for the development of more personalized cancer immuno‐nanomedicines. Nanovehicles, due to their specific physicochemical properties, are emerging as key translational moieties in tackling tumor‐promoting, M2‐like tumor‐associated macrophages (TAMs). Cancer immuno‐nanomedicines target TAMs primarily by blocking M2‐like TAM survival or affecting their signaling cascades, restricting macrophage recruitment to tumors and re‐educating tumor‐promoting M2‐like TAMs to the tumoricidal, M1‐like phenotype. Here, the TAM effector mechanisms and strategies for targeting TAMs are summarized, followed by a focus on the mechanistic considerations in the development of novel immuno‐nanomedicines. Furthermore, imaging TAMs with nanoparticles so as to forecast a patient's clinical outcome, describing treatment options, and observing therapy responses is also discussed. At present, strategies that target TAMs are being investigated not only at the basic research level but also in early clinical trials. The significance of TAM‐targeting biomaterials is highlighted, with the goal of facilitating future clinical translation.     

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.     

Combretastatin A4 Nanodrug‐Induced MMP9 Amplification Boosts Tumor‐Selective Release of Doxorubicin Prodrug

Tumor‐associated enzyme‐activated prodrugs can potentially improve the selectivity of chemotherapeutics. However, the paucity of tumor‐associated enzymes which are essential for prodrug activation usually limits the antitumor potency. A cooperative strategy that utilizes combretastatin A4 nanodrug (CA4‐NPs) and matrix metalloproteinase 9 (MMP9)‐activated doxorubicin prodrug (MMP9‐DOX‐NPs) is developed. CA4 is a typical vascular disrupting agent that can selectively disrupt immature tumor blood vessels and exacerbate the tumor hypoxia state. After treatment with CA4‐NPs, MMP9 expression can be significantly enhanced by 5.6‐fold in treated tumors, which further boosts tumor‐selective active drug release of MMP9‐DOX‐NPs by 3.7‐fold in an orthotopic 4T1 mammary adenocarcinoma mouse model. The sequential delivery of CA4‐NPs and MMP9‐DOX‐NPs exhibits enhanced antitumor efficacy with reduced systemic toxicity compared with the noncooperative controls.     

Deep Tumor Penetrating Bioparticulates Inspired Burst Intracellular Drug Release for Precision Chemo‐Phototherapy

The relevance of personalized medicine has inspired research for individually concerted diagnosis and therapy. Numerous efforts are devoted to designing drug particulates with capabilities of tumor penetrating and subcellular trafficking to concurrently discharge theranostics in response to multistimulations. In this study, a bioinspired particulate, formulated with whole components of native high‐density lipoproteins (HDLs) and decorated with the tumor‐penetrating peptide iRGD, is proposed to promote tumor penetration of HDLs (pHDLs) together with payloads. Specifically, paclitaxel (PTX), and the NIR fluorescent probe indocyanine green (ICG) are integrated into pHDLs (pHDL/PTX‐ICG) for synergetic chemo‐phototherapy. Inspired by lipoproteins, pHDLs are not only restored from naturally occurring materials but also possessed artificially endowed functions, leading to an enhanced cellular uptake, higher accumulation, and deep penetration into tumors without causing appreciable adverse effects, compared to reconstituted HDLs or lipid‐based nanoparticles. After intravenous administration, pHDL/PTX‐ICG performs a burst of intracellular drug release and imaging‐guided precision chemo‐phototherapy upon NIR irradiation that completely eradicates xenograft tumors. Neither recurrence nor significant toxicity is observed due to maneuvered regional photodynamic and photothermal therapy. Taken together, pHDL/PTX‐ICG is proven to be a promising platform to achieve deep tumor penetration and imaging‐guided chemo‐phototherapy.     

Silicene: Wet‐Chemical Exfoliation Synthesis and Biodegradable Tumor Nanomedicine

Silicon‐based biomaterials play an indispensable role in biomedical engineering; however, due to the lack of intrinsic functionalities of silicon, the applications of silicon‐based nanomaterials are largely limited to only serving as carriers for drug delivery systems. Meanwhile, the intrinsically poor biodegradation nature for silicon‐based biomaterials as typical inorganic materials also impedes their further in vivo biomedical use and clinical translation. Herein, by the rational design and wet chemical exfoliation synthesis of the 2D silicene nanosheets, traditional 0D nanoparticulate nanosystems are transformed into 2D material systems, silicene nanosheets (SNSs), which feature an intriguing physiochemical nature for photo‐triggered therapeutics and diagnostic imaging and greatly favorable biological effects of biocompatibility and biodegradation. In combination with DFT‐based molecular dynamics (MD) calculations, the underlying mechanism of silicene interactions with bio‐milieu and its degradation behavior are probed under specific simulated physiological conditions. This work introduces a new form of silicon‐based biomaterials with 2D structure featuring biodegradability, biocompatibility, and multifunctionality for theranostic nanomedicine, which is expected to promise high clinical potentials.     

Acid Active Receptor‐Specific Peptide Ligand for In Vivo Tumor‐Targeted Delivery

Targeting therapy of tumors in their early stages is crucial to increase the survival rate of cancer patients. Currently most drug‐delivery systems target the neoplasia through the tumor‐associated receptors overexpressed on the cancer cell membrane. However, the expression of these receptors on normal cells and tissues is inevitable, which leads to unwanted accumulation and side effects. Characteristics of the tumor microenvironment, such as acidosis, are pervasive in almost all solid tumors and can be easily accessed. It is shown that the different extracellular pH value can be used to activate/inactivate the receptor‐mediated endocytosis on tumor/normal cells. This idea is implemented by conjugating a shielding molecule at the terminus of a receptor‐specific ligand via a pH‐sensitive hydrazone bond. The acid‐activated detachment of the shielding molecule and enhanced tumor/background accumulation ratio are demonstrated. These results suggest that acid active receptor‐specific peptide ligand‐modified tumor‐targeting delivery systems have potential use in the treatment of tumors.     

A Sequential Target‐Responsive Nanocarrier with Enhanced Tumor Penetration and Neighboring Effect In Vivo

Nanodrug‐based cancer therapy is impeded by poor penetration into deep tumor tissues mainly due to the overexpression of hyaluronic acid (HA) in the tumor extracellular matrix (ECM). Although modification of nanoparticles (NPs) with hyaluronidase (HAase) is a potent strategy, it remains challenging to get a uniform distribution of drug at the tumor site because of the internalization of NPs by the cells in the tumor and HA regeneration. Herein, an intelligent nanocarrier, which can release HAase in response to the acidic tumor microenvironment (pH 6.5) and perform a strong neighboring effect with size reduction to overcome the above two problems and accomplish drug deep tumor penetration in vivo, is reported. In this design, HAase is encapsulated on the surfaces of doxorubicin (DOX) preloaded ZnO‐DOX NPs using a charge convertible polymer PEG‐PAH‐DMMA (ZDHD). The polymer can release HAase to degrade HA in the tumor ECM (pH 6.5). ZnO‐DOX NPs can release DOX in lysosomes (pH 4.5) to induce cell apoptosis, and exert a neighboring effect with size reduction to infect neighboring cells. The hierarchical targeted release of HAase and drugs is demonstrated to enhance tumor penetration and decrease side effects in vivo. This work shows promise for further application of ZDHD NPs in cancer therapy.     

Double‐Targeting Explosible Nanofirework for Tumor Ignition to Guide Tumor‐Depth Photothermal Therapy

This study reports a double‐targeting “nanofirework” for tumor‐ignited imaging to guide effective tumor‐depth photothermal therapy (PTT). Typically, ≈30 nm upconversion nanoparticles (UCNP) are enveloped with a hybrid corona composed of ≈4 nm CuS tethered hyaluronic acid (CuS‐HA). The HA corona provides active tumor‐targeted functionality together with excellent stability and improved biocompatibility. The dimension of UCNP@CuS‐HA is specifically set within the optimal size window for passive tumor‐targeting effect, demonstrating significant contributions to both the in vivo prolonged circulation duration and the enhanced size‐dependent tumor accumulation compared with ultrasmall CuS nanoparticles. The tumors featuring hyaluronidase (HAase) overexpression could induce the escape of CuS away from UCNP@CuS‐HA due to HAase‐catalyzed HA degradation, in turn activating the recovery of initially CuS‐quenched luminescence of UCNP and also driving the tumor‐depth infiltration of ultrasmall CuS for effective PTT. This in vivo transition has proven to be highly dependent on tumor occurrence like a tumor‐ignited explosible firework. Together with the double‐targeting functionality, the pathology‐selective tumor ignition permits precise tumor detection and imaging‐guided spatiotemporal control over PTT operation, leading to complete tumor ablation under near infrared (NIR) irradiation. This study offers a new paradigm of utilizing pathological characteristics to design nanotheranostics for precise detection and personalized therapy of tumors.     

Hierarchical Tumor Microenvironment‐Responsive Nanomedicine for Programmed Delivery of Chemotherapeutics

Nanomedicines have been demonstrated to have passive or active tumor targeting behaviors, which are promising for cancer chemotherapy. However, most nanomedicines still suffer from a suboptimal targeting effect and drug leakage, resulting in unsatisfactory treatment outcome. Herein, a hierarchical responsive nanomedicine (HRNM) is developed for programmed delivery of chemotherapeutics. The HRNMs are prepared via the self‐assembly of cyclic Arg‐Gly‐Asp (RGD) peptide conjugated triblock copolymer, poly(2‐(hexamethyleneimino)ethyl methacrylate)‐poly(oligo‐(ethylene glycol) monomethyl ether methacrylate)‐poly[reduction‐responsive camptothecin] (PC7A‐POEG‐PssCPT). In blood circulation, the RGD peptides are shielded by the POEG coating; therefore, the nanosized HRNMs can achieve effective tumor accumulation through passive targeting. Once the HRNMs reach a tumor site, due to the hydrophobic‐to‐hydrophilic conversion of PC7A chains induced by the acidic tumor microenvironment, the RGD peptides will be exposed for enhanced tumor retention and cellular internalization. Moreover, in response to the glutathione inside cells, active CPT drugs will be released rapidly for chemotherapy. The in vitro and in vivo results confirm effective tumor targeting, potent antitumor effect, and reduced systemic toxicity of the HRNMs. This HRNM is promising for enhanced chemotherapeutic delivery.     

Self‐Assembled Aptamer‐Nanomedicine for Targeted Chemotherapy and Gene Therapy

Chemotherapy is the mainstream treatment of anaplastic large cell lymphoma (ALCL). However, chemotherapy can cause severe adverse effects in patients because it is not ALCL‐specific. In this study, a multifunctional aptamer‐nanomedicine (Apt‐NMed) achieving targeted chemotherapy and gene therapy of ALCL is developed. Apt‐NMed is formulated by self‐assembly of synthetic oligonucleotides containing CD30‐specific aptamer and anaplastic lymphoma kinase (ALK)‐specific siRNA followed by self‐loading of the chemotherapeutic drug doxorubicin (DOX). Apt‐NMed exhibits a well‐defined nanostructure (diameter 59 mm) and stability in human serum. Under aptamer guidance, Apt‐NMed specifically binds and internalizes targeted ALCL cells. Intracellular delivery of Apt‐NMed triggers rapid DOX release for targeted ALCL chemotherapy and intracellular delivery of the ALK‐specific siRNA induced ALK oncogene silencing, resulting in combined therapeutic effects. Animal model studies reveal that upon systemic administration, Apt‐NMed specifically targets and selectively accumulates in ALCL tumor site, but does not react with off‐target tumors in the same xenograft mouse. Importantly, Apt‐NMed not only induces significantly higher inhibition in ALCL tumor growth, but also causes fewer or no side effects in treated mice compared to free DOX. Moreover, Apt‐NMed treatment markedly improves the survival rate of treated mice, opening a new avenue for precision treatment of ALCL.     

Enhanced In Vivo Tumor Detection by Active Tumor Cell Targeting Using Multiple Tumor Receptor‐Binding Peptides Presented on Genetically Engineered Human Ferritin Nanoparticles

Human ferritin heavy‐chain nanoparticle (hFTH) is genetically engineered to present tumor receptor‐binding peptides (affibody and/or RGD‐derived cyclic peptides, named 4CRGD here) on its surface. The affibody and 4CRGD specifically and strongly binds to human epidermal growth factor receptor I (EGFR) and human integrin αvβ3, respectively, which are overexpressed on various tumor cells. Through in vitro culture of EGFR‐overexpressing adenocarcinoma (MDA‐MB‐468) and integrin‐overexpressing glioblastoma cells (U87MG), it is clarified that specific interactions between receptors on tumor cells and receptor‐binding peptides on engineered hFTH is critical in active tumor cell targeting. After labeling with the near‐infrared fluorescence dye (Cy5.5) and intravenouse injection into MDA‐MB‐468 or U87MG tumor‐bearing mice, the recombinant hFTHs presenting either peptide or both of affibody and 4CRGD are successfully delivered to and retained in the tumor for a prolonged period of time. In particular, the recombinant hFTH presenting both affibody and 4CRGD notably enhances in vivo detection of U87MG tumors that express heterogeneous receptors, integrin and EGFR, compared to the other recombinant hFTHs presenting either affibody or 4CRGD only. Like affibody and 4CRGD used in this study, other multiple tumor receptor‐binding peptides can be also genetically introduced to the hFTH surface for actively targeting of in vivo tumors with heterogenous receptors.     

Multitriggered Tumor‐Responsive Drug Delivery Vehicles Based on Protein and Polypeptide Coassembly for Enhanced Photodynamic Tumor Ablation

Tumor‐responsive nanocarriers are highly valuable and demanded for smart drug delivery particularly in the field of photodynamic therapy (PDT), where a quick release of photosensitizers in tumors is preferred. Herein, it is demonstrated that protein‐based nanospheres, prepared by the electrostatic assembly of proteins and polypeptides with intermolecular disulfide cross‐linking and surface polyethylene glycol coupling, can be used as versatile tumor‐responsive drug delivery vehicles for effective PDT. These nanospheres are capable of encapsulation of various photosensitizers including Chlorin e6 (Ce6), protoporphyrin IX, and verteporfin. The Chlorin e6‐encapsulated nanospheres (Ce6‐Ns) are responsive to changes in pH, redox potential, and proteinase concentration, resulting in multitriggered rapid release of Ce6 in an environment mimicking tumor tissues. In vivo fluorescence imaging results indicate that Ce6‐Ns selectively accumulate near tumors and the quick release of Ce6 from Ce6‐Ns can be triggered by tumors. In tumors the fluorescence of released Ce6 from Ce6‐Ns is observed at 0.5 h postinjection, while in normal tissues the fluorescence appeared at 12 h postinjection. Tumor ablation is demonstrated by in vivo PDT using Ce6‐Ns and the biocompatibility of Ce6‐Ns is evident from the histopathology imaging, confirming the enhanced in vivo PDT efficacy and the biocompatibility of the assembled drug delivery vehicles.     

Enhancing Prostate‐Cancer‐Specific MRI by Genetic Amplified Nanoparticle Tumor Homing

Precise localization and visualization of early‐stage prostate cancer (PCa) is critical to improve the success of focal ablation and reduce cancer mortality. However, it remains challenging under the current imaging techniques due to the heterogeneous nature of PCa and the suboptimal sensitivity of the techniques themselves. Herein, a novel genetic amplified nanoparticle tumor‐homing strategy to enhance the MRI accuracy of ultrasmall PCa lesions is reported. This strategy could specifically drive TfR expressions in PCa under PCa‐specific DD3 promoter, and thus remarkably increase Tf‐USPIONs concentrations in a highly accurate manner while minimizing their non‐specific off‐target effects on normal tissues. Consequently, this strategy can pinpoint an ultrasmall PCa lesion, which is otherwise blurred in the current MRI, and thereby addresses the unmet key need in MRI imaging for focal therapy. With this proof‐of‐concept experiment, the synergistic gene–nano strategy holds great promise to boost the MRI effects of a wide variety of commonly used nanoscale and molecular probes that are otherwise limited. In addition, such a strategy may also be translated and applied to MR‐specific imaging of other types of cancers by using their respective tumor‐specific promoters.