Tumor Abnormality-Oriented Nanomedicine Design.

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Role of Micelle Size in Cell Transcytosis-Based Tumor Extravasation, Infiltration, and Treatment Efficacy.

Transcytosis-based active transport of cancer nanomedicine has shown great promise for enhancing its tumor extravasation and infiltration and antitumor activity, but how the key nanoproperties of nanomedicine, particularly particle size, influence the transcytosis remains unknown. Herein, we used a transcytosis-inducing polymer, poly[2-(N-oxide-N,N-diethylamino)ethyl methacrylate] (OPDEA), and fabricated stable OPDEA-based micelles with different sizes (30, 70, and 140 nm in diameter) from its amphiphilic block copolymer, OPDEA-block-polystyrene (OPDEA-PS). The study of the micelle size effects on cell transcytosis, tumor extravasation, and infiltration showed that the smallest micelles (30 nm) had the fastest transcytosis and, thus, the most efficient tumor extravasation and infiltration. So, the 7-ethyl-10-hydroxyl camptothecin (SN38)-conjugated OPDEA micelles of 30 nm had much enhanced antitumor activity compared with the 140 nm micelles. These results are instructive for the design of active cancer nanomedicine.

Highly Sensitive Imaging of Tumor Metastasis Based on the Targeting and Polarization of M2-like Macrophages.

Tumor-associated macrophages, especially M2-like macrophages, are extensively involved in tumor growth and metastasis, suppressing the innate immunity to help tumor cells escape and reshaping the microenvironment to help metastatic cells grow. However, in vivo, real-time visualized migration of M2-like macrophages has never been explored to monitor the tumor metastasis process. Herein, we prepared an M2-like macrophage-targeting nitric oxide (NO)-responsive nanoprobe (NRP@M-PHCQ) consisting of an amphiphilic block copolymer with mannose and hydroxychloroquine (HCQ) moieties (denoted as M-PHCQ) and a NO-responsive NIR-II probe (denoted as NRP). The mannose moieties provided M2-like macrophage-targeting capacity, and the HCQ moieties polarized M2-like macrophages to M1-like ones with enhanced NO secretion. Consequently, NRP@M-PHCQ was lit up by the secreted NO to visualize the migration and polarization of M2-like macrophages in real time. In vivo metastasis imaging with NRP@M-PHCQ successfully tracked early tumor metastasis in the lymph nodes and the lungs with high sensitivity, even superior to Luci-labeled bioluminescence imaging, suggesting the extensive distribution and critical role of M2-like macrophages in tumor metastasis. In general, this work provided a new strategy to sensitively image metastatic tumors by tracking the polarization of M2-like macrophages and visually disclosed the critical role of M2-like macrophages in early tumor metastasis.

Natural Polyphenols-Platinum Nanocomplexes Stimulate Immune System for Combination Cancer Therapy.

Nanocarriers have been employed extensively to enhance drug delivery efficacy and reduce the side effect. However, carrier materials for drug delivery have challenging aspects, including safety concerns, low drug content, complexity in preparation, and low reproducibility. Herein, we propose a facile, universal, and green preparation way to use natural polyphenols to build platinum nanocomplex with stable structure, proper size, and high Pt content. The nanocomplexes are constructed by metal-polyphenol coordination using natural polyphenols and 1,2-diaminocyclohexane-Pt (II), enabling dual-responsive drug release behavior. For proof of concept, we demonstrate the antitumor activity of the Pt nanocomplex using a representative tannic acid-Pt nanocomplex (denoted as PTI). PTI can induce intensive tumor cell apoptosis, trigger immunogenic cell death (ICD), remarkably promote cytotoxic T lymphocytes (CTLs) infiltration in tumors, and significantly reduce immunosuppression of the tumor microenvironments, thus stimulating potent antitumor immune responses and showing effective antitumor activity by synergizing immune checkpoint blockade (ICB) therapy.

Aminopeptidase N-Responsive Conjugates with Tunable Charge-Reversal Properties for Highly Efficient Tumor Accumulation and Penetration.

Tumor enzyme-responsive charge-reversal carriers can induce efficient transcytosis and lead to efficient tumor infiltration and potent anticancer efficacy. However, the correlations of molecular structure with charge-reversal property, tumor penetration, and drug delivery efficiency are unknown. Herein, aminopeptidase N (APN)-responsive conjugates were synthesized to investigate these correlations. We found that the monomeric unit structure and the polymer chain structure determined the enzymatic hydrolysis and charge-reversal rates, and accordingly, the transcytosis and tumor accumulation and penetration of the APN-responsive conjugates. The conjugate with moderate APN responsiveness balanced the in vitro transcytosis and in vivo overall drug delivery process and achieved the best tumor delivery efficiency, giving potent antitumor efficacy. This work provides new insight into the design of tumor enzyme-responsive charge-reversal nanomedicines for efficient cancer drug delivery.

Hydrophobicity Effects of γ-Glutamyl Transpeptidase-Responsive Polymers on the Catalytic Activity and Transcytosis Efficacy.

Active transcytosis has recently sparked great interest in drug delivery as a novel route for tumor extravasation and infiltration. However, the rational design of transcytosis-inducing nanomedicines remains challenging. We recently demonstrated that the γ-glutamyl transpeptidase (GGT)-responsive polymer cationization induced efficient adsorption-mediated transcytosis (AMT). However, it remains unclear how the nanomedicines' physicochemical properties influence the GGT-responsive cationization and induced transcytosis behaviors. Herein, through a combination of experimental techniques and molecular dynamics (MD) simulations, we find that the random copolymers with high hydrophobic monomers tend to form compact structures accessible to the catalytic site of GGT, leading to a fast cationization and thus high transcytosis efficiency, while the homopolymers of the hydrophilic GGT-sensitive monomers have elongated structures unable to enter the active site and thus exhibit poor GGT sensitivity. As a result, the more hydrophobic polymer-drug conjugates with high camptothecin contents exhibit higher GGT-responsive activity, which in turn leads to faster cationization and cellular internalization, enhanced tumor infiltration, and more potent antitumor activity. These findings indicate the hydrophobicity is a main parameter determining the GGT catalytic activity and transcytosis efficiency of the GGT-activatable co(homo)polymers, providing guidelines for the rational design of GGT-induced charge reversal carriers for transcytotic nanomedicines.

Glutathione-Responsive Magnetic Nanoparticles for Highly Sensitive Diagnosis of Liver Metastases.

Liver metastasis (LM) occurs in various cancers, and its early and accurate diagnosis is of great importance. However, the detection of small LMs is still a great challenge because of the subtle differences between normal liver tissue and small metastases. Herein, we prepare glutathione (GSH)-responsive hyaluronic acid-coated iron oxide nanoparticles (HIONPs) for highly sensitive diagnosis of LMs through a facile one-pot method. HIONPs greatly enhance the signal of MRI in tumor metastases as T1 contrast agent (CA), whereas they substantially decrease the signal of liver as T2 CA as they aggregate into clusters upon the high GSH in liver. Consequently, MRI contrasted by HIONPs clearly distinguishes metastatic tumors (bright) from surrounding liver tissues (dark). HIONPs with superior LM contrasting capability and facile synthesis are very promising for clinical translation and indicate a new strategy to develop an ultrasensitive MRI CA for LM diagnosis that exploits high GSH level in the liver.

Molecularly Precise, Bright, Photostable, and Biocompatible Cyanine Nanodots as Alternatives to Quantum Dots for Biomedical Applications.

Fluorescent imaging with fluorophores has become a powerful way to explore complex biological systems and visualize nanoparticles for drug delivery. However, it is challenging to develop fluorophores with ideal physical and optical properties. We report a method to synthesize cyanine nanodots with a single-molecule structure, well-defined particle size, customizable fluorescent spectrum, and bright and stable fluorescence. These cyanine nanodots are acquired by the divergent synthesis of cyanine-dye-cored polylysine (PLL) dendrimers. We demonstrated the feasibility of the method by synthesizing cyanine 3 (Cy3), cyanine 5 (Cy5), or cyanine 7 (Cy7) cored single-molecule nanodots up to eight generations with a size of around 11 nm. We show that these cyanine nanodots are capable of multiple biomedical applications, including multicolor cellular tracing and cancer imaging. These cyanine nanodots possess many merits of organic dots and quantum dots that are promising for future application.

Effect of Cationic Charge Density on Transcytosis of Polyethylenimine.

The adsorption-mediated transcytosis (AMT) induced by the electrostatic interaction between the positively charged surface of carriers and negatively charged cell membrane is a new paradigm enabling nanomedicine's tumor extravasation and infiltration. However, little is known about the correlation between the carrier's charge density and its AMT-induced tumor infiltration efficiency. Herein, we investigate the effect of the cationic polymer's charge on the AMT-induced tumor penetration ability using in vitro multilayer tumor spheroids (MTSs). A cationic polymer, polyethylenimine (PEI), is amidized with acetic anhydride to obtain acetylated PEIs (AcPEIs) with different cationic charge densities. As the amidization ratio increases, the AcPEIs' cytotoxicity, zeta potential, and cell-binding affinity significantly decrease. Notably, not only does the weak cell binding (AcPEIs with high acetylation degrees) lead to slow endocytosis and inefficient transcytosis, so does the strong cell-binding PEI. The PEI with 24% acetylation (AcPEI24%) is found to have the highest transcytosis efficiency because its balanced cell-binding affinity triggers fast adsorption-mediated endocytosis. The subsequent Golgi apparatus/endoplasmic reticulum-mediated exocytosis via extracellular vesicles leads to highly effective transcellular delivery and tumor penetration in MTSs. Therefore, the drug carrier's surface cationic charge density critically influences its AMT-induced tumor penetration efficiency. This study provides mechanistic insights into the design of drug-delivery systems with active transcytosis for improved tumor penetration and enhanced therapeutic efficiency.

Active Transportation of Liposome Enhances Tumor Accumulation, Penetration, and Therapeutic Efficacy.

Liposomes are the first and mostly explored nanocarriers for cancer drug delivery, which have shown great promise in clinical applications, but their limited accumulation and penetration into the tumor interstitial space, significantly reduce the therapeutic efficacy. Here, a γ-glutamyltranspeptidase (GGT)-triggered charge-switchable approach is reported that can trigger the fast endocytosis and transcytosis of the liposome in tumor microenvironments to overcome the harsh biological barriers in tumor tissues. The active transporting liposomal nanocarrier (GCSDL) is prepared by surface modification with a glutathione (GSH) moiety and encapsulated with doxorubicin (DOX). When the GCSDL contacts with tumor vascular endothelial cells, the overexpressed GGT enzyme on cytomembrane catalyzes the hydrolysis of GSH to generate cationic primary amines. The cationic GCSDL triggers fast caveolae-mediated endocytosis and vesicle-mediated transcytosis, resulting in sequential transcytosis to augment its tumor accumulation and penetration. Along with continual intercellular transportation, GCSDL can release DOX throughout the tumor to induce cancer cell apoptosis, resulting in complete eradication of hepatocellular carcinoma and cessation of pancreatic ductal adenocarcinoma's progression. This study develops an efficient strategy to realize high tumor accumulation and deep penetration for the liposomal drug delivery system via active transcytosis.

Drug-binding albumins forming stabilized nanoparticles for efficient anticancer therapy.

Albumin is a serum transport protein, which has been utilized as a carrier for a variety of drugs to improve their delivery efficiency and to obtain favorable pharmacokinetic profiles. However, natural albumin possesses only a few high-affinity binding sites for a limited number of drugs. This results in deficiencies in drug-loading and serum stability, and consequently, in impaired therapeutic efficacy. Herein, BSA was modified with different isothiocyanate conjugates (BSA-ITCs), which self-assembled with paclitaxel (PTX) to produce BSA-ITCs/PTX nanoparticles. Among these BSA-ITCs, phenethyl isothiocyanate (PEITC)-modified BSA (BSA-PEITC35) conjugates effectively loaded PTX and formed highly stable BSA-PEITC35/PTX nanoparticles. Molecular modeling studies suggested that PEITC groups in BSA-PEITC35 can significantly lower the PTX binding free energy. BSA-PEITC35/PTX showed enhanced stability, prolonged blood circulation and increased tumor accumulation than unmodified BSA/PTX, and exerted more potent antitumor activity than both BSA/PTX and Abraxane in subcutaneous mouse tumor models after intravenous administration.

Glycyrrhizin Acid and Glycyrrhetinic Acid Modified Polyethyleneimine for Targeted DNA Delivery to Hepatocellular Carcinoma.

In the last 2-3 decades, gene therapy represented a promising option for hepatocellular carcinoma (HCC) treatment. However, the design of safe and efficient gene delivery systems is still one of the major challenges that require solutions. In this study, we demonstrate a versatile method for covalent conjugation of glycyrrhizin acid (GL) or glycyrrhetinic acid (GA) to increase the transfection efficiency of Polyethyleneimine (PEI, Mw 1.8K) and improve their targeting abilities of hepatoma carcinoma cells. GA and GL targeting ligands were grafted to PEI via N-acylation, and we systematically investigated their biophysical properties, cytotoxicity, liver targeting and transfection efficiency, and endocytosis pathway trafficking. PEI-GA0.75, PEI-GL10.62 and PEI-GL20.65 conjugates caused significant increases in gene transfection efficiency and superior selectivity for HepG2 cells, with all three conjugates showing specific recognition of HepG2 cells by the free GA competition assay. The endocytosis inhibition and intracellular trafficking results indicated that PEI-GA0.75 and GL10.62 conjugates behaved similarly to SV40 virus, by proceeding via the caveolae- and clathrin-independent mediated endocytosis pathway and bypassing entry into lysosomes, with an energy independent manner, achieving their high transfection efficiencies. In the HepG2 intraperitoneal tumor model, PEI-GA0.75 and PEI-GL10.62 carrying the luciferase reporter gene gained high gene expression, suggesting potential use for in vivo application.

Magnetic resonance molecular imaging of metastatic breast cancer by targeting extradomain-B fibronectin in the tumor microenvironment.

PURPOSE: Non-invasive early accurate detection of malignant breast cancer is paramount to the clinical management of the life-threatening disease. Here, we aim to test a small peptide targeted MRI contrast agent, ZD2-Gd(HP-DO3A), specific to an oncoprotein, extradomain-B fibronectin (EDB-FN), in the tumor microenvironment for MR molecular imaging of breast cancer. METHOD: EDB-FN expression in 4T1 and MDA-MB-231 cancers was analyzed with quantitative real-time PCR and western blot. Primary and metastatic triple negative breast cancer mouse models were developed using 4T1 and MDA-MB-231 cells. Contrast-enhanced MRI was carried out to evaluate the use of ZD2-Gd(HP-DO3A) in detecting 4T1 and MDA-MB-231 primary and metastatic tumors. RESULTS: EDB-FN was abundantly expressed in the extracellular matrix (ECM) of both the primary and metastatic TNBC tumors. In T1 -weighted MRI, ZD2-Gd(HP-DO3A) generated superior contrast enhancement in primary TNBC tumors than a nonspecific clinical agent Gd(HP-DO3A), during 30 min after contrast injection. ZD2-Gd(HP-DO3A) also produced a significant increase in contrast-to-noise ratio (CNR) of TNBC metastases, enabling sensitive localization and delineation of metastases that occulted in non-contrast-enhanced or Gd(HP-DO3A)-enhanced MRI. CONCLUSIONS: These findings potentiate the use of ZD2-Gd(HP-DO3A) for MR molecular imaging of malignant breast cancers to improve the healthcare of breast cancer patients. Magn Reson Med 79:3135-3143, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Targeted Contrast Agent Specific to an Oncoprotein in Tumor Microenvironment with the Potential for Detection and Risk Stratification of Prostate Cancer with MRI.

Accurate detection and risk stratification are paramount to the clinical management of prostate cancer. Current diagnostic methods, including prostate specific antigen (PSA) screening, are unable to differentiate high-risk tumors from low-risk tumors, resulting in overdiagnosis and overtreatment. A peptide targeted contrast agent, ZD2-Gd(HP-DO3A), specific to an oncoprotein in tumor microenvironment, EDB-FN, was synthesized for noninvasive detection and characterization of aggressive prostate cancer. EDB-FN, one of the subtypes of oncofetal fibronectin, is involved in tumor epithelial-to-mesenchymal transition (EMT), which is implicated in drug resistance and metastasis. The EDB-FN mRNA level in the metastatic PC3 cells was at least three times higher than that in non-metastatic LNCaP cells. In tumors, EDB-FN protein was highly expressed in PC3 tumor xenografts, but not in LNCaP tumors, as revealed by Western blot analysis. ZD2-Gd(HP-DO3A) produced over two times higher contrast-to-noise ratio in the PC3 tumors than in the LNCaP tumors in contrast-enhanced MRI during 30 min after injection. ZD2-Gd(HP-DO3A) possessed high chelate stability against transmetalation and minimal tissue accumulation. Our results demonstrate that molecular MRI of EDB-FN with ZD2-Gd(HP-DO3A) can potentially be used for noninvasive detection and risk stratification of human prostate cancer. Incorporation of this targeted contrast agent in the existing clinical contrast enhanced MRI procedures has the potential to improve diagnostic accuracy of prostate cancer.

EDB Fibronectin Specific Peptide for Prostate Cancer Targeting.

Extradomain-B fibronectin (EDB-FN), one of the oncofetal fibronectin (onfFN) isoforms, is a high-molecular-weight glycoprotein that mediates cell adhesion and migration. The expression of EDB-FN is associated with a number of cancer-related biological processes such as tumorigenesis, angiogenesis, and epithelial-to-mesenchymal transition (EMT). Here, we report the development of a small peptide specific to EDB-FN for targeting prostate cancer. A cyclic nonapeptide, CTVRTSADC (ZD2), was identified using peptide phage display. A ZD2-Cy5 conjugate was synthesized to accomplish molecular imaging of prostate cancer in vitro and in vivo. ZD2-Cy5 demonstrated effective binding to up-regulated EDB-FN secreted by TGF-ß-induced PC3 cancer cells following EMT. Following intravenous injections, the targeted fluorescent probe specifically bound to and delineated PC3-GFP prostate tumors in nude mice bearing the tumor xenografts. ZD2-Cy5 also showed stronger binding to human prostate tumor specimens with a higher Gleason score (GS9) compared to those with a lower score (GS 7), with no binding in benign prostatic hyperplasia (BPH). Thus, the ZD2 peptide is a promising strategy for molecular imaging and targeted therapy of prostate cancer.

Molecularly precise dendrimer-drug conjugates with tunable drug release for cancer therapy.

The structural preciseness of dendrimers makes them perfect drug delivery carriers, particularly in the form of dendrimer-drug conjugates. Current dendrimer-drug conjugates are synthesized by anchoring drug and functional moieties onto the dendrimer peripheral surface. However, functional groups exhibiting the same reactivity make it impossible to precisely control the number and the position of the functional groups and drug molecules anchored to the dendrimer surface. This structural heterogeneity causes variable pharmacokinetics, preventing such conjugates to be translational. Furthermore, the highly hydrophobic drug molecules anchored on the dendrimer periphery can interact with blood components and alter the pharmacokinetic behavior. To address these problems, we herein report molecularly precise dendrimer-drug conjugates with drug moieties buried inside the dendrimers. Surprisingly, the drug release rates of these conjugates were tailorable by the dendrimer generation, surface chemistry, and acidity.

High-Throughput Screening of Surface Engineered Cyanine Nanodots for Active Transport of Therapeutic Antibodies into Solid Tumor.

The successful delivery of therapeutic biomacromolecules into solid tumor holds great challenge due to their high resistance to penetrate through the complex tumor microenvironments. Here, active-transporting nanoparticles are harnessed to efficiently deliver biomacromolecular drugs into solid tumors through cell transcytosis. A series of molecularly precise cyanine 5-cored polylysine G5 dendrimers (Cy5 nanodots) with different peripheral amino acids (G5-AA) is prepared. The capability of these positively charged nanodots to induce cell endocytosis, exocytosis, and transcytosis is evaluated via fluorescence-based high-throughput screen. The optimized nanodots (G5-R) are conjugated with αPD-L1 (a therapeutic monoclonal antibody binding to programmed-death ligand 1) (αPD-L1-G5-R) to demonstrate the nanoparticle-mediated tumor active transport. The αPD-L1-G5-R can greatly enhance the tumor-penetration capability through adsorption-mediated transcytosis (AMT). The effectiveness of αPD-L1-G5-R is tested in treating mice bearing partially resected CT26 tumors, mimicking the local immunotherapy of residual tumors post-surgery in clinic. The αPD-L1-G5-R embedded in fibrin gel can efficiently mediate tumor cell transcytosis, and deliver αPD-L1 throughout the tumor, thereby enhancing immune checkpoint blockade, reducing tumor recurrence, and significantly prolonging the survival time. The active-transporting nanodots are promising platforms for efficient tumor delivery of therapeutic biomacromolecules.

Integrin-Targeted Theranostic Nanoparticles for Clinical MRI-Traceable Treatment of Liver Fibrosis.

Liver fibrosis is the critical stage in the development of chronic liver disease (CLD), from simple injury to irreversible cirrhosis. Timely detection and intervention of liver fibrosis are crucial for preventing CLD from progressing into a fatal condition. Herein, we developed iron oxide (Fe3O4) nanoparticles (IONPs) and ferulic acid (FA) coencapsulated poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs), followed by surface modification with cRGD peptides (cRGD-PLGA/IOFA) for integrin-targeted clinical magnetic resonance imaging (MRI)-traceable treatment of liver fibrosis. The cRGD peptide linked on the surface of the PLGA/IOFA NPs could specifically bind to the overexpressed integrin αvß3 on activated hepatic stellate cells (HSCs) in the fibrotic liver, enabling the high-sensitive clinical MR imaging (3 T) and precise staging of liver fibrosis. The FA encapsulated in cRGD-PLGA/IOFA showed excellent efficacy in reducing oxidative stress and inhibiting the activation of HSCs through the transforming growth factor-ß (TGF-ß)/Smad pathway. Notably, the IONPs encapsulated in cRGD-PLGA/IOFA NPs could alleviate liver fibrosis by regulating hepatic macrophages through the NF-κB pathway, lowering the proportion of Ly6Chigh/CD86+, and degrading collagen fibers. The FA and IONPs in the cRGD-PLGA/IOFA produced a synergistic enhancement effect on collagen degradation, which was more effective than the IONPs treatment alone. This study demonstrates that cRGD-PLGA/IOFA NPs could effectively relieve liver fibrosis by acting on macrophages and HSCs and provide a new strategy for the clinical MRI-traceable treatment of liver fibrosis.

Modulating Intracellular Dynamics for Optimized Intracellular Release and Transcytosis Equilibrium.

Active transcytosis-mediated nanomedicine transport presents considerable potential in overcoming diverse delivery barriers, thereby facilitating tumor accumulation and penetration. Nevertheless, the persistent challenge lies in achieving a nuanced equilibrium between intracellular interception for drug release and transcytosis for tumor penetration. In this study, a comprehensive exploration is conducted involving a series of polyglutamine-paclitaxel conjugates featuring distinct hydrophilic/hydrophobic ratios (HHR) and tertiary amine-oxide proportions (TP) (OPGA-PTX). The screening process, meticulously focused on delineating their subcellular distribution, transcytosis capability, and tumor penetration, unveils a particularly promising candidate denoted as OPPX, characterized by an HHR of 10:1 and a TP of 100%. OPPX, distinguished by its rapid cellular internalization through multiple endocytic pathways, selectively engages in trafficking to the Golgi apparatus for transcytosis to facilitate accumulation within and penetration throughout tumor tissues and simultaneously sorted to lysosomes for cathepsin B-activated drug release. This study not only identifies OPPX as an exemplary nanomedicine but also underscores the feasibility of modulating subcellular distribution to optimize the active transport capabilities and intracellular release mechanisms of nanomedicines, providing an alternative approach to designing efficient anticancer nanomedicines.

Acid-active cell-penetrating peptides for in vivo tumor-targeted drug delivery.

Cell-penetrating peptides (CPPs) such as transactivator of transcription (TAT) peptide have long been explored for promoting in vitro cell penetration and nuclear targeting of various cargos, but their positive charges cause strong nonspecific interactions, making them inapplicable for many in vivo applications. In this work, we used TAT to demonstrate a molecular modification approach for inhibiting nonspecific interactions of CPPs in the bloodstream while reactivating their functions in the targeted tissues or cells. The TAT lysine residues' amines were amidized to succinyl amides ((a)TAT), completely inhibiting TAT's nonspecific interactions in the blood compartment; once in the acidic tumor interstitium or internalized into cell endo/lysosomes, the succinyl amides in the (a)TAT were quickly hydrolyzed, fully restoring TAT's functions. Thus, (a)TAT-functionalized poly(ethylene glycol)-block-poly(ε-caprolactone) micelles achieved long circulation in the blood compartment and efficiently accumulated and delivered doxorubicin to tumor tissues, giving rise to high antitumor activity and low cardiotoxicity. This amidization strategy effectively and easily enables in vivo applications of CPPs.