Enhancing Accumulation and Penetration of HPMA Copolymer-Doxorubicin Conjugates in 2D and 3D Prostate Cancer Cells via iRGD Conjugation with an MMP-2 Cleavable Spacer

Polymer nanomedicines

Polymer nanomedicines (macromolecular therapeutics, polymer-drug conjugates, drug-free macromolecular therapeutics) are a group of biologically active compounds that are characterized by their large molecular weight. This review focuses on bioconjugates of water-soluble macromolecules with low molecular weight drugs and selected proteins. After analyzing the design principles, different structures of polymer carriers are discussed followed by the examination of the efficacy of the conjugates in animal models and challenges for their translation into the clinic. Two innovative directions in macromolecular therapeutics that depend on receptor crosslinking are highlighted: a) Combination chemotherapy of backbone degradable polymer-drug conjugates with immune checkpoint blockade by multivalent polymer peptide antagonists; and b) Drug-free macromolecular therapeutics, a new paradigm in drug delivery.

Peptide Spiders: Peptide-Polymer Conjugates to Traffic Nucleic Acids

Therapeutic nucleic acids hold great promise for the treatment of genetic diseases, yet the delivery of this highly charged macromolecular drug remains a challenge in the field. Peptides are promising agents to mediate nucleic acid delivery because they can encode a biological function to overcome the trafficking barriers. Electrostatic nanocomplexes of nucleic acid and peptides can achieve effective delivery, but the balance between their stability and biological function must be finely tuned. In this work, we explore two peptide building blocks that have been studied in the literature: targeting ligands and intracellular trafficking peptides. We grafted these peptides on a polyethylene glycol (PEG) backbone with eight sites for substitution to create so-called "peptide spiders". These conjugates achieve stability via the well-known hydrophilic shielding effect of PEG. In addition, the coordination of peptide building blocks into multimers may create new biological properties, such as the well-known phenomena of increased binding avidity with multivalent ligands. In this work, we linked two trafficking peptides to the PEG backbone using either nonreducible or reducible chemistries and investigated the ability of these materials to carry silencing RNAs into mammalian cells. We then investigated these nanomaterials for their pharmacokinetic properties and silencing of undruggable targets in a mouse model of cancer. While reducible linkages were more potent at silencing in vitro, this effect was reversed when applied in the context of living animals. This work offers an insight into peptide-based delivery materials and investigates peptide-polymer linkages.

An iRGD peptide fused superantigen mutant induced tumor-targeting and T lymphocyte infiltrating in cancer immunotherapy

Solid tumors are intrinsically resistant to immunotherapy because of the major challenges including the immunosuppression and poor penetration of drugs and lymphocytes into solid tumors due to the complicated tumor microenvironment (TME). Our previous study has created a novel superantigen mutant ST-4 to efficiently active the T lymphocytes and alleviate immune suppression. In the present study, to accumulate ST-4 into the TME, we constructed a recombinant protein, ST-4-iRGD, by fusing ST-4 to a tumor-homing peptide, iRGD. We hypothesized that ST-4-iRGD could internalize into the TME through iRGD-mediated tumor targeting and tumor tissue penetrating to activate the regional immunoreaction. The results of in vitro studies showed that ST-4-iRGD achieved improved tumor targeting and cytotoxicity in mouse B16F10 melanoma cells. The iRGD-mediated tumor tissue penetration was further confirmed by imaging and immunofluorescence studies in vivo, wherein higher distribution of ST-4-iRGD was observed in the mouse 4T1 breast tumor model. Moreover, ST-4-iRGD exhibited enhanced anti-solid tumor characteristics and induced improved lymphocyte infiltration in the B16F10 and 4T1 models. In conclusion, using iRGD to facilitate better dissemination of the therapeutic agent ST-4 throughout a solid tumor mass is feasible, and ST-4-iRGD may be a potential candidate for efficient cancer immunotherapy in the future.

Supramolecular prodrug hydrogelator as an immune booster for checkpoint blocker-based immunotherapy

Immune checkpoint blockers (ICBs) have shown great promise at harnessing immune system to combat cancer. However, only a fraction of patients can directly benefit from the anti-programmed cell death protein 1 (aPD1) therapy, and the treatment often leads to immune-related adverse effects. In this context, we developed a prodrug hydrogelator for local delivery of ICBs to boost the host's immune system against tumor. We found that this carrier-free therapeutic system can serve as a reservoir for extended tumoral release of camptothecin and aPD1 antibody, resulting in an immune-stimulating tumor microenvironment for boosted PD-1 blockade immune response. Our in vivo results revealed that this combination chemoimmunotherapy elicits robust and durable systemic anticancer immunity, inducing tumor regression and inhibiting tumor recurrence and metastasis. This work sheds important light into the use of small-molecule prodrugs as both chemotherapeutic and carrier to awaken and enhance antitumor immune system for improved ICBs therapy.

HPMA-based polymeric conjugates in anticancer therapeutics

Polymer therapeutics has gained prominence due to an attractive structural polymer chemistry and its applications in diseases therapy. In this review, we discussed the development and capabilities of N-(2-hydroxypropyl) methacrylamide (HPMA) and HPMA-drug conjugates in cancer therapy. The design, architecture, and structural properties of HPMA make it a versatile system for the synthesis of polymeric conjugations for biomedical applications. Research suggests that HPMA could be a possible alternative for polymers such polyethylene glycol (PEG) in biomedical applications. Although numerous clinical trials of HPMA-drug conjugates are ongoing, yet no product has been successfully brought to the market. Thus, further research is required to develop HPMA-drug conjugates as successful cancer therapeutics.

Polyamide Backbone Modified Cell Targeting and Penetrating Peptides in Cancer Detection and Treatment

Cell penetrating and targeting peptides (CPPs and CTPs) encompass an important class of biochemically active peptides owning the capabilities of targeting and translocating within selected cell types. As such, they have been widely used in the delivery of imaging and therapeutic agents for the diagnosis and treatment of various diseases, especially in cancer. Despite their potential utility, first generation CTPs and CPPs based on the native peptide sequences are limited by poor biological and pharmacological properties, thereby restricting their efficacy. Therefore, medicinal chemistry approaches have been designed and developed to construct related peptidomimetics. Of specific interest herein, are the design applications which modify the polyamide backbone of lead CTPs and CPPs. These modifications aim to improve the biochemical characteristics of the native peptide sequence in order to enhance its diagnostic and therapeutic capabilities. This review will focus on a selected set of cell penetrating and targeting peptides and their related peptidomimetics whose polyamide backbone has been modified in order to improve their applications in cancer detection and treatment.

Facile Dye-Initiated Polymerization of Lactide-Glycolide Generates Highly Fluorescent Poly(lactic-co-glycolic Acid) for Enhanced Characterization of Cellular Delivery

Poly(lactic-co-glycolic acid) (PLGA) is a versatile synthetic copolymer that is widely used in pharmaceutical applications. This is because it is well-tolerated in the body, and copolymers of varying physicochemical properties are readily available via ring-opening polymerization. However, native PLGA polymers are hard to track as drug delivery carriers when delivered to subcellular spaces, due to the absence of an easily accessible "handle" for fluorescent labeling. Here we show a one-step, scalable, solvent-free, synthetic route to fluorescent blue (2-aminoanthracene), green (5-aminofluorescein), and red (rhodamine-6G) PLGA, in which every polymer chain in the sample is fluorescently labeled. The utility of initiator-labeled PLGA was demonstrated through the preparation of nanoparticles, capable of therapeutic subcellular delivery to T-helper-precursor-1 (THP-1) macrophages, a model cell line for determining in vitro biocompatibility and particle uptake. Super resolution confocal fluorescence microscopy imaging showed that dye-initiated PLGA nanoparticles were internalized to punctate regions and retained bright fluorescence over at least 24 h. In comparison, PLGA nanoparticles with 5-aminofluorescein introduced by conventional nanoprecipitation/encapsulation showed diffuse and much lower fluorescence intensity in the same cells and over the same time periods. The utility of this approach for in vitro drug delivery experiments was demonstrated through the concurrent imaging of the fluorescent drug doxorubicin (λ_ex = 480 nm, λ_em = 590 nm) with carrier 5-aminofluorescein PLGA, also in THP-1 cells, in which the intracellular locations of the drug and the polymer could be clearly visualized. Finally, the dye-labeled particles were evaluated in an in vivo model, via delivery to the nematode Caenorhabditis elegans, with bright fluorescence again apparent in the internal tract after 3 h. The results presented in this manuscript highlight the ease of synthesis of highly fluorescent PLGA, which could be used to augment tracking of future therapeutics and accelerate in vitro and in vivo characterization of delivery systems prior to clinical translation.

Polymeric nanocarriers as stimuli-responsive systems for targeted tumor (cancer) therapy: Recent advances in drug delivery

In the last decade, considerable attention has been devoted to the use of biodegradable polymeric materials as potential drug delivery carriers. However, bioavailability and drug release at the disease site remain uncontrollable even with the use of polymeric nanocarriers. To address this issue, successful methodologies have been developed to synthesize polymeric nanocarriers incorporated with regions exhibiting a response to stimuli such as redox potential, temperature, pH, and light. The resultant stimuli-responsive polymeric nanocarriers have shown tremendous promise in drug delivery applications, owing to their ability to enhance the bioavailability of drugs at the disease site. In such systems, drug release is controlled in response to specific stimuli, either exogenous or endogenous. This review reports recent advances in the design of stimuli-responsive nanocarriers for drug delivery in cancer therapy. In particular, the synthetic methodologies investigated to date to introduce different types of stimuli-responsive elements within the biomaterials are described. The sufficient understanding of these stimuli-responsive nanocarriers will allow the development of a better drug delivery system that will allow us to solve the challenges encountered in targeted cancer therapy.

Coordinating bioorthogonal reactions with two tumor-microenvironment-responsive nanovehicles for spatiotemporally controlled prodrug activation

Precise activation of prodrugs in tumor tissues is critical to ensuring specific antitumor efficacy, meanwhile reducing the serious adverse effects. Here, a spatiotemporally controlled prodrug activation strategy was provided by integrating the inverse electron demand Diels-Alder (IEDDA) reaction with two tumor-microenvironment-responsive nanovehicles. The prodrug (Dox-TCO) and [4-(6-methyl-1,2,4,5-tetrazin-3-yl)phenyl]methanamine (Tz) were separately camouflaged into low pH and matrix metalloproteinase 2 (MMP-2) sensitive micellar nanoparticles. After systemic administration, only in the tumor tissues could both the nanovehicles dissociate via responding to two special tumor microenvironments, with Dox-TCO and Tz released and then immediately triggering the prodrug activation through the IEDDA reaction. The hierarchically regulated and locally confined Dox liberation led to dramatically decreased side-effects that were much lower than those of the clinical Doxorubicin Hydrochloride Liposomal Injection (Doxil), while the antitumor therapeutic effect was potent.

Discovering pH triggered charge rebound surface modulated topical nanotherapy against aggressive skin papilloma

A modified facile biomimetic Temozolomide Chitosan nanogel (TCNL) was developed offering pH responsive, charge attracted and microenvironment dependent tumor targeting nanotherapy. USFDA approved chemotherapeutic TMZ (Temozolomide) was encapsulated in a cationic biocompatible chitosan nanogel subsequently surface modified with nonionic Transcutol by inotropic gelation method and evaluated for its combined anti-metastatic and antitumor efficiency. The in-vitro results authenticated that TMZ encapsulated TCNL was effectively uptake and distributed in HaCaT cell line inducing high apoptosis and necrosis of tumor cells prior to the electron microscopic (TEM & SEM) and thermal evaluations (DSC, DTA & TG) suggesting spherical and thermo-stable nanogel system. An accelerated sustained release pattern of TMZ from TCNL was displayed in mildly acidic conditions (pH 6) signifying ultra-sensitivity of TCNL. In-vivo evaluation over 16 week DMBA/croton oil tumor induced mice model showed noteworthy tumor targeting with down regulation of overexpressed COX-2, cytokines and nuclear factors on western blot analysis. Moreover, advanced gamma scintigraphy analysis displayed significant drug accommodation and expressing potent tumor accumulation, suppression and metastasis effect on carcinogenic mice. The TCNL outcomes displayed effective tumor targeting on transdermal delivery for operative nanotherapy against skin cancer.

Targeting delivery of partial VAR2CSA peptide guided N-2-Hydroxypropyl trimethyl ammonium chloride chitosan nanoparticles for multiple cancer types

To developing a multiple cancer types targeting drug delivery carrier system, a 28 amino acids from the VAR2CSA was synthesized as the placental CSA-binding peptide (plCSA-BP). Its specific binding ability to cancer cells was tested on cancer tissue array, and the results showed that plCSA-BP could bind to multiple cancer types. Then, the plCSA-BP was used as a guiding peptide to coat nanoparticles synthesized from N-2-HACC (CSA/HACC-NPs) which were loaded with prodigiosin (CSA/HACC-PNPs) or indocyanine green (CSA/HACC-INPs). The cancer cells specific targeting and efficacy of the CSA/HACC-PNPs were tested by different cancer cells in vitro and various cancer xenograft model in vivo. A scramble peptide (SCR) was used as control and synthesized SCR/HACC-PNPs and SCR/HACC-INPs. The results showed that the CSA/HACC-INPs could specifically uptake by JEG-3, PC3 and A594 cells, and the CSA/HACC-PNPs exhibited better anti-cancer activity and lower toxic effect in subcutaneous choriocarcinoma and prostatic tumor models compared with the free prodigiosin, HACC-PNPs and SCR/HACC-PNPs. So, the CSA/HACC-NPs could be used as a specific delivery carrier for multiple cancer types, and provided an alternate treatment option of various cancers with a single recipe.

Enzyme responsive drug delivery systems in cancer treatment

Recent technological approaches in drug delivery have attracted scientist interest for improving therapeutic index of medicines and drug compliance. One of the powerful strategies to control the transportation of drugs is implementation of intelligent stimuli-responsive drug delivery system (DDS). In this regard, tumor tissues with unique characteristics including leaky vasculature and diverse enzyme expression profiles facilitate the development of efficient enzyme-responsive nanoscale delivery systems. Based on the stimuli nature (physical, chemical and biological), these systems can be categorized into three groups according to the nature of trigger initiating the drug release. Enzymes are substantial constituents of the biotechnology toolbox offering promising capabilities and ideal characteristics to accelerate chemical reactions. Nanoparticles which have the ability to trigger their cargo release in the presence of specific enzymes are fabricated implementing fascinating physico-chemical properties of different materials in a nanoscale dimension. In order to reduce the adverse effects of the therapeutic agents, nanocarriers can be utilized and modified with enzyme-labile linkages to provide on-demand enzyme-responsive drug release. In the current review, we give an overview of drug delivery systems which can deliver drugs to the tumor microenvironment and initiate the drug release in response to specific enzymes highly expressed in particular tumor tissues. This strategy offers a versatile platform for intelligent drug release at the site of action.

iRGD: A Promising Peptide for Cancer Imaging and a Potential Therapeutic Agent for Various Cancers

Poor penetration into the tumor parenchyma and the reduced therapeutic efficacy of anticancer drugs and other medications are the major problems in tumor treatment. A new tumor-homing and penetrating peptide, iRGD (CRGDK/RGPD/EC), can be effectively used to combine and deliver imaging agents or anticancer drugs into tumors. The different “vascular zip codes” expressed in different tissues can serve as targets for docking-based (synaptic) delivery of diagnostic and therapeutic molecules. αv-Integrins are abundantly expressed in the tumor vasculature, where they are recognized by peptides containing the RGD integrin recognition motif. The iRGD peptide follows a multistep tumor-targeting process: First, it is proteolytically cleaved to generate the CRGDK fragment by binding to the surface of cells expressing αv integrins (αvβ3 and αvβ5). Then, the fragment binds to neuropilin-1 and penetrates the tumor parenchyma more deeply. Compared with conventional RGD peptides, the affinity of iRGD for αv integrins is in the mid to low nanomolar range, and the CRGDK fragment has a stronger affinity for neuropilin-1 than that for αv integrins because of the C-terminal exposure of a conditional C-end Rule (CendR) motif (R/KXXR/K), whose receptor proved to be neuropilin-1. Consequently, these advantages facilitate the transfer of CRGDK fragments from integrins to neuropilin-1 and consequently deeper penetration into the tumor. Due to its specific binding and strong affinity, the iRGD peptide can deliver imaging agents and anticancer drugs into tumors effectively and deeply, which is useful in detecting the tumor, blocking tumor growth, and inhibiting tumor metastasis. This review aims to focus on the role of iRGD in the imaging and treatment of various cancers.

Matrix metallopeptidase 2 targeted delivery of gold nanostars decorated with IR-780 iodide for dual-modal imaging and enhanced photothermal/photodynamic therapy

Nanotheranostics has gained increasing interest, as it offers a great potential to realize personalized diagnostics and therapy. In this work, we report a facile approach of the fabrication of gold nanostars (GNS) attached with matrix metalloproteinases (MMP2) polypeptides (Ac-GPLGIAGQ) and IR-780 iodide through bovine serum albumin (BSA) for targeted dual-modal photoacoustic (PA)/near-infrared (NIR) fluorescence imaging and enhanced photothermal therapy (PTT)/photodynamic therapy (PDT) for lung cancer. MMP2 polypeptides served as the targeting ligand, IR-780 iodide functioned as the NIR fluorescence imaging agent as well as PTT/PDT agent, and GNS acted as the carrier of IR-780 molecules and performed PA imaging and PTT. DLS and CCK-8 assay demonstrated that the nanoprobes (GNS@BSA/I-MMP2) exhibited excellent stability and biocompatibility under physiological conditions. Subsequent in vitro studies verified that GNS@BSA/I-MMP2 nanoparticles (NPs) were effectively internalized by A549 cancer cells and exhibited remarkable antitumor efficacy. Furthermore, GNS@BSA/I-MMP2 NPs could specifically target the tumor and significantly suppress the tumor growth, and their antitumor effects were mainly through the synergistic effects of PDT and PTT based on IR-780 and GNS. These findings imply the potential of GNS@BSA/I-MMP2 NPs as a targeting PA/NIR probe in tumor diagnosis and combined therapy with a single light source. STATEMENT OF SIGNIFICANCE: We reported a convenient and facile approach to load IR-780 iodides in gold nanostars (GNS). This material could simultaneously perform near-infrared imaging/photoacoustic imaging and thermotherapy/photodynamic therapy. MMP2 coating on the surface of GNS@BSA/IR-780 promoted the prepared nanoparticles (GNS@BSA/I-MMP2) to target the tumor region. The heat generated by the synergistic effect of the GNS and IR-780 molecules resulted in the high temperature of the GNS@BSA/I-MMP2 NPs, which efficiently suppressed the growth of tumor, and the tumor volume decreased by 93% compared with that in the PBS groups with laser irradiation.

Polymer-drug conjugate therapeutics: advances, insights and prospects

Polymer-drug conjugates have long been a mainstay of the drug delivery field, with several conjugates successfully translated into clinical practice. The conjugation of therapeutic agents to polymeric carriers, such as polyethylene glycol, offers several advantages, including improved drug solubilization, prolonged circulation, reduced immunogenicity, controlled release and enhanced safety. In this Review, we discuss the rational design, physicochemical characteristics and recent advances in the development of different classes of polymer-drug conjugates, including polymer-protein and polymer-small-molecule drug conjugates, dendrimers, polymer nanoparticles and multifunctional systems. Current obstacles hampering the clinical translation of polymer-drug conjugate therapeutics and future prospects are also presented.

Dual-Responsive Size-Shrinking Nanocluster with Hierarchical Disassembly Capability for Improved Tumor Penetration and Therapeutic Efficacy

It is generally known that, for nanoparticles in cancer therapy, sufficient tumor penetration needs a minor particle size, while long in vivo circulation time needs a larger particle size. It is hard to balance them because they are standing on either side of a seesaw. To address these two different requirements, a dual-responsive size-shrinking nanocluster can self-adaptively respond to a complicated tumor microenvironment and transform its particulate property to overcome sequential in vivo barriers and reach a preferable antitumor activity. The nanocluster (RPSPT@SNCs) could preferentially accumulate into tumor tissue and dissociate under extracellular matrix metalloproteinase-2 (MMP-2) to release small-sized micelle formulations (RPSPTs). RPSPT possesses favorable tumor penetration and tumor targeting capability to deliver the antitumor agent paclitaxel (PTX) into deep regions of solid tumor. The intracellular redox microenvironment can also accelerate drug accumulation. The prepared RPSPT@SNCs possesses enhanced cell cytotoxicity and tumor penetration capability on MCF-7 cells and a favorable antitumor activity on the xenograft tumor mouse model.

Engineering Nanoparticles for Targeted Delivery of Nucleic Acid Therapeutics in Tumor

In the past 10 years, with the increase of investment in clinical nano-gene therapy, there are many trials that have been discontinued due to poor efficacy and serious side effects. Therefore, it is particularly important to design a suitable gene delivery system. In this paper, we introduce the application of liposomes, polymers, and inorganics in gene delivery; also, different modifications with some stimuli-responsive systems can effectively improve the efficiency of gene delivery and reduce cytotoxicity and other side effects. Besides, the co-delivery of chemotherapy drugs with a drug tolerance-related gene or oncogene provides a better theoretical basis for clinical cancer gene therapy.

A perspective on magnetic core-shell carriers for responsive and targeted drug delivery systems

Magnetic core-shell nanocarriers have been attracting growing interest owing to their physicochemical and structural properties. The main principles of magnetic nanoparticles (MNPs) are localized treatment and stability under the effect of external magnetic fields. Furthermore, these MNPs can be coated or functionalized to gain a responsive property to a specific trigger, such as pH, heat, or even enzymes. Current investigations have been focused on the employment of this concept in cancer therapies. The evaluation of magnetic core-shell materials includes their magnetization properties, toxicity, and efficacy in drug uptake and release. This review discusses some categories of magnetic core-shell drug carriers based on Fe2O3 and Fe3O4 as the core, and different shells such as poly(lactic-co-glycolic acid), poly(vinylpyrrolidone), chitosan, silica, calcium silicate, metal, and lipids. In addition, the review addresses their recent potential applications for cancer treatment.

An Oxygen Self-sufficient Fluorinated Nanoplatform for Relieved Tumor Hypoxia and Enhanced Photodynamic Therapy of Cancers

The efficacy of photodynamic therapy (PDT) in the solid tumor is hampered by many challenges, including its oxygen self-consuming nature, insufficient oxygen levels within the hypoxic tumor microenvironment, and limited penetration of photosensitizers within tumors. Herein, we develop the IR780@O₂-SFNs/iRGD as an oxygen self-sufficient and tumor-penetrating nanoplatform, which consists of IR780-loaded pH-sensitive fluorocarbon-functionalized nanoparticles (SFNs) and iRGD as a tumor targeting peptide that can penetrate deeper within the tumor. Because of the high oxygen affinity and outstanding permeability of the obtained nanoplatform, oxygen and IR780 which are encapsulated in the same core can play their roles to the utmost, resulting in remarkably accelerated singlet oxygen production, as demonstrated in vitro by the 3D multicellular spheroids and in vivo by tumor tissues. More interestingly, a single-dose intravenous administration of IR780@O₂-SFNs/iRGD into mice bearing orthotopic breast cancer could selectively accumulate at the tumor site, highly alleviate the tumor hypoxia, significantly inhibit the primary tumor growth, and reduce the lung and liver metastasis, enabling the improved photodynamic therapeutic performance. Thus, this work paves an effective way to improve PDT efficacy through increasing tumor oxygenation and selective delivery of photosensitizers to the deep and hypoxic tumor.

Tumor targeting DVDMS-nanoliposomes for an enhanced sonodynamic therapy of gliomas

UTMD-assisted intelligent DVDMS encapsulate iRGD-Liposomes mediate SDT with deep tumor penetration and specific targeting ability enhanced anti-glioma efficacy.

KLF2 Inhibits the Migration and Invasion of Prostate Cancer Cells by Downregulating MMP2

KLF2, a member of the Kruppel-like factor (KLF) family, is thought to be a tumor suppressor in many kinds of malignant tumors. Its functions in prostate cancer (PCa) are unknown. This study aimed to explore the role of KLF2 in the migration and invasion of PCa cells. The expression of KLF2 was measured by immunohistochemistry in PCa tissues and in paired non-tumor tissues. KLF2 and MMP2 expression in cells was measured by Western blot and RT-qPCR. Adenoviruses and siRNAs were used in cell function tests to investigate the role of KLF2 in regulating MMP2. Interactions between KLF2 and MMP2 were analyzed by a luciferase activity assay. The present study, for the first time, identified that KLF2 was downregulated both in PCa clinical tissue samples and in cancer cell lines. The overexpression of KLF2 inhibited the migration and invasion of PCa cells via the suppression of MMP2.This study demonstrates that KLF2 might act as a tumor suppressor gene in PCa and that the pharmaceutical upregulation of KLF2 may be a potential approach for treatment.

Synthesis of a Block Copolymer Exhibiting Cell-Responsive Phytochemical Release for Cancer Therapy

Phytochemicals constitute a promising class of therapeutics for the treatment of various diseases, but their delivery poses significant challenges. In this work, a nanoscale polyactive emulsion was designed for smart, cell-responsive delivery of a curcumin prodrug (curcumin dicarboxylate, CDA) that was chemically conjugated to enzymatically labile oligo-peptides with polycaprolactone (PCL) as the carrier. Matrix metalloproteinase (MMP)-sensitive (PLGLYAL) or nonsensitive (GPYYPLG) peptides were used as spacers for conjugating CDA and PCL. This CDA nanoemulsion incorporating the MMP-sensitive sequence exhibited markedly higher anti-cancer activity, cell internalization, and generation of reactive oxygen species in cancer cells in vitro than the control with the nonsensitive oligopeptide. Moreover, the nanopolyactives induced minimal cytotoxicity in noncancerous cell line. This work presents a unique strategy to engineer smart nano-polyactives for efficient and targeted delivery of phytochemicals.

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.

LMTK3 confers chemo-resistance in breast cancer

Lemur tyrosine kinase 3 (LMTK3) is an oncogenic kinase that is involved in different types of cancer (breast, lung, gastric, colorectal) and biological processes including proliferation, invasion, migration, chromatin remodeling as well as innate and acquired endocrine resistance. However, the role of LMTK3 in response to cytotoxic chemotherapy has not been investigated thus far. Using both 2D and 3D tissue culture models, we found that overexpression of LMTK3 decreased the sensitivity of breast cancer cell lines to cytotoxic (doxorubicin) treatment. In a mouse model we showed that ectopic overexpression of LMTK3 decreases the efficacy of doxorubicin in reducing tumor growth. Interestingly, breast cancer cells overexpressing LMTK3 delayed the generation of double strand breaks (DSBs) after exposure to doxorubicin, as measured by the formation of γH2AX foci. This effect was at least partly mediated by decreased activity of ataxia-telangiectasia mutated kinase (ATM) as indicated by its reduced phosphorylation levels. In addition, our RNA-seq analyses showed that doxorubicin differentially regulated the expression of over 700 genes depending on LMTK3 protein expression levels. Furthermore, these genes were found to promote DNA repair, cell viability and tumorigenesis processes / pathways in LMTK3-overexpressing MCF7 cells. In human cancers, immunohistochemistry staining of LMTK3 in pre- and post-chemotherapy breast tumor pairs from four separate clinical cohorts revealed a significant increase of LMTK3 following both doxorubicin and docetaxel based chemotherapy. In aggregate, our findings show for the first time a contribution of LMTK3 in cytotoxic drug resistance in breast cancer.

Multifunctional Magnetic Mesoporous Silica Nanoagents for in vivo Enzyme-Responsive Drug Delivery and MR Imaging

In this study, we report novel multifunctional nanoagents for in vivo enzyme-responsive anticancer drug delivery and magnetic resonance imaging (MRI), based on mesoporous silica coated iron oxide nanoparticles (Fe3O4@MSNs). The anticancer drug, DOX, was encapsulated in the porous cavities with a MMP-2 enzyme responsive peptide being covalently linked to the nanoparticles surface. The in vitro experiment results indicated that the enzyme responsive nanoagents own high specificity for controlled drug release in the cell line with high MMP-2 expression. Furthermore, the targeted delivery of the nanoagents to the tumor site purpose has been successfully achieved through magnet-guided nanocarrier accumulation by utilizing the magnetic properties of the Fe3O4 nanocores, which resulted in efficient inhibition of the tumor growth. Additionally, these novel nanoagents can also be used as MRI agent for the real-time diagnosis the tumor treatment process of living animals. Taking the advantages of high specificity, controllable drug release and real-time MRI imaging, we believe these multifunctional nanoagents could also be used as a general platform for the design of stimulus-responsive multifunctional nanomaterials for the aim of accurate diagnosis and efficient treatment of other diseases.

MRI tracing non-invasive TiO2-based nanoparticles activated by ultrasound for multi-mechanism therapy of prostatic cancer

To reduce the side effects of chemotherapy and achieve effective and safe therapy for prostate cancer, herein a simple but multi-functional TiO₂:Gd@DOX/FA system activated by ultrasound was developed for the MRI-guided multi-mechanism therapy of prostate cancer. TiO₂ nanoparticles served as a sonosensitizer as well as a nanocarrier with the pH-responsive release of DOX. The doping of Gd was not only able to endow the TiO₂ with magnetic resonance imaging (MRI) ability, but also further improve the sonodynamic ability of the TiO₂. The characterization of the as-prepared TiO₂:Gd@DOX/FA showed sensitive pH-responsive drug release, high reactive oxygen species (ROS) production, T ₁-MRI contrast performance and excellent biocompatibility. The cytotoxicity assay in vitro showed cell death up to 91.68% after 48 h incubation induced by the TiO₂:Gd@DOX + ultrasound group. Meanwhile, in the in vivo synergistic therapy studies, the tumor sizes of all the nanomedicine groups were smaller than for the free DOX (V:V ₀ = 4.2). More importantly, the body showed nearly no weight loss. This safety was also confirmed by the H&E staining, biodistribution experiment and serum biochemistry results. Altogether, TiO₂:Gd@DOX/FA significantly reduced the side effects of DOX, augmented the levels of ROS and achieved effective and safe therapy, indicating its potential for the multi-mechanism therapy of prostate cancer.

Size shrinkable drug delivery nanosystems and priming the tumor microenvironment for deep intratumoral penetration of nanoparticles

The penetration of nanomedicine into solid tumor still constitutes a great challenge for cancer therapy, which lead to the failure of thorough clearance of tumor cells. Aiming at solving this issue, lots of encouraging progress has been made in the development of multistage nanoparticles triggered by various stimuli in the past few years. Besides, the therapeutical effects of nanoagents are also greatly impacted by the complex tumor microenvironment, and remodeling tumor microenvironment has become another important approach for promoting nanoparticles penetration. In this review, we summarize and analyze recent research progress and challenges in promoting nanoparticle penetration based on two kinds of different strategies, which include size shrinkable nanoparticles and priming tumor microenvironments. Especially, many recent reported multi-strategy approaches based on particle size reduction in conjugated with other therapeutic strategies are discussed. And we expect to provide some useful enlightenments and proposals on nanotechnology-based drug delivery systems for more effective therapy of solid tumors.

Stimuli-Responsive Nanomedicines for Overcoming Cancer Multidrug Resistance

Chemotherapy is still a main option for cancer therapy, but its efficacy is often unsatisfying due to multidrug resistance (MDR). The tumor microenvironment is considered a dominant factor causing MDR. Stimuli-responsive nanomedicines exhibit many superiorities for reversal of MDR. As smart systems, stimuli-responsive nanomedicines are desirable for achieving site-specific accumulation and triggered drug release in response to slight changes in physicochemical properties in pathological conditions or to exogenous stimuli. In this review, we highlight the current progress of various nanomedicines with different stimuli-responsive capabilities for overcoming MDR. The materials, design, construction as well as efficacy in overcoming MDR of these nanomedicines are discussed. Eventually, we look forward to forthcoming intelligent nanoparticle systems with new mechanisms to deliver drugs for practical applications in conquering cancer MDR.

Enzyme-sensitive cytotoxic peptide–dendrimer conjugates enhance cell apoptosis and deep tumor penetration

Cytotoxic peptide conjugated PAMAM dendrimers with MMP2-sensitive PEG for efficient tumor penetration, cellular internalization and mitochondria disruption.

Application of 3D cultured multicellular spheroid tumor models in tumor-targeted drug delivery system research

Tumor-targeted drug delivery systems are promising for their advantages in enhanced tumor accumulation and reduced toxicity towards normal organs. However, few nanomedicines have been successfully translated into clinical application. One reason is the gap between current pre-clinical and clinical studies. The prevalent in vitro models utilized in pre-clinical phase are mainly based on the two-dimensional (2D) cell culture and are limited by the difficulty of simulating three-dimensional physiological conditions in human body, such as three-dimensional (3D) architecture, cell heterogeneity, nutrient gradients and the interaction between cells and the extracellular matrix (ECM). In addition, traditional animal models have drawbacks such as high-cost, long periods and physiological differences between animal and human. On the other hand, the employment of 3D tumor cell culture models, especially multicellular tumor spheroids (MCTS), has increased significantly in recent decades. These models have been shown to simulate 3D structures of tumors in vitro with relatively low cost and simple protocols. Currently, MCTS have also been widely exploited in drug delivery system research for comprehensive study of drug efficacy, drug penetration, receptor targeting, and cell recruitment abilities. This review summarizes the delivery barriers for nano-carriers presented in tumor microenvironment, the characteristics and formation methods for applicable multicellular tumor spheroid culture models and recent studies related to their applications in tumor-targeted drug delivery system research.

Acidity-Triggered Ligand-Presenting Nanoparticles To Overcome Sequential Drug Delivery Barriers to Tumors

The success of cancer chemotherapy is impeded by poor drug delivery efficiency due to the existence of a series of pathophysiological barriers in the tumor. In this study, we reported a tumor acidity-triggered ligand-presenting (ATLP) nanoparticle for cancer therapy. The ATLP nanoparticles were composed of an acid-responsive diblock copolymer as a sheddable matrix and an iRGD-modified polymeric prodrug of doxorubicin (iPDOX) as an amphiphilic core. A PEG corona of the polymer matrix protected the iRGD ligand from serum degradation and nonspecific interactions with the normal tissues while circulating in the blood. The ATLP nanoparticles specifically accumulated at the tumor site through the enhanced permeability and retention (EPR) effect, followed by acid-triggered dissociation of the polymer matrix within the tumoral acidic microenvironment (pH ∼ 6.8) and subsequently exposing the iRGD ligand for facilitating tumor penetration and cellular uptake of the PDOX prodrug. Additionally, the acid-triggered dissociation of the polymer matrix induced a 4.5-fold increase of the fluorescent signal for monitoring nanoparticle activation in vivo. Upon near-infrared (NIR) laser irradiation, activation of Ce6-induced significant reactive oxygen species (ROS) generation, promoted drug diffusion inside the tumor mass and circumvented the acquired drug resistance by altering the gene expression profile of the tumor cells. The ATLP strategy might provide a novel insight for cancer nanomedicine.

Multivalency Increases the Binding Strength of RGD Peptidomimetic-Paclitaxel Conjugates to Integrin αV β3

This work reports the synthesis of three multimeric RGD peptidomimetic‐paclitaxel conjugates featuring a number of α_Vβ₃ integrin ligands ranging from 2 to 4. These constructs were assembled by conjugation of the integrin α_Vβ₃ ligand cyclo[DKP‐RGD]‐CH₂NH₂ with paclitaxel via a 2′‐carbamate with a self‐immolative spacer, the lysosomally cleavable Val‐Ala dipeptide linker, a multimeric scaffold, a triazole linkage, and finally a PEG spacer. Two monomeric conjugates were also synthesized as reference compounds. Remarkably, the new multimeric conjugates showed a binding affinity for the purified integrin α_Vβ₃ receptor that increased with the number of integrin ligands (reaching a minimum IC₅₀ value of 1.2 nm for the trimeric), thus demonstrating that multivalency is an effective strategy to strengthen the ligand–target interactions.

Two-step polymer- and liposome-enzyme prodrug therapies for cancer: PDEPT and PELT concepts and future perspectives

Polymer-directed enzyme prodrug therapy (PDEPT) and polymer enzyme liposome therapy (PELT) are two-step therapies developed to provide anticancer drugs site-selective intratumoral accumulation and release. Nanomedicines, such as polymer-drug conjugates and liposomal drugs, accumulate in the tumor site due to extravasation-dependent mechanism (enhanced permeability and retention - EPR - effect), and further need to cross the cellular membrane and release their payload in the intracellular compartment. The subsequent administration of a polymer-enzyme conjugate able to accumulate in the tumor tissue and to trigger the extracellular release of the active drug showed promising preclinical results. The development of polymer-enzyme, polymer-drug conjugates and liposomal drugs had undergone a vast advancement over the past decades. Several examples of enzyme mimics for in vivo therapy can be found in the literature. Moreover, polymer therapeutics often present an enzyme-sensitive mechanism of drug release. These nanomedicines can thus be optimal substrates for PDEPT and this review aims to provide new insights and stimuli toward the future perspectives of this promising combination.