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

Design and Proof of Programmed 5-Aminolevulinic Acid Prodrug Nanocarriers for Targeted Photodynamic Cancer Therapy

5-Aminolevulinic acid (ALA), the precursor of photosensitizer protoporphyrin IX (PpIX), is a U.S. FDA-approved photodynamic therapeutic agent. However, realizing efficient delivery of ALA is still a big challenge as it is hydrophilic and cannot be recognized and selectively accumulated in tumor cells. In this study, matrix metalloproteinase-2 (MMP-2) and pH dual-sensitive ALA prodrug nanocarriers were constructed as a programmed delivery strategy for the targeted delivery of ALA. The nanocarriers were prepared by the co-modification of gold nanoparticles (AuNPs) with hydrazone-linked ALA and MMP-2-activatable cell-penetrating peptides (CPPs). Cationic CPP RRRRRRRR (R8) was shielded by zwitterionic stealth peptide EKEKEKEKEKEKEKEKEKEK (EK10) via MMP-2 substrate peptide PLGLAG. The zwitterionic stealth peptide EK10 is designed to endow ALA prodrug nanocarriers with strong antifouling ability and prolonged circulation time. Upon arriving at the tumor tissue, the shielded cationic CPP R8 can be activated by tumor-microenvironment-overexpressed MMP-2, which enabled enhanced cellular uptake of ALA. The results of drug loading and release, cellular uptake, PpIX generation and accumulation, photodynamic cytotoxicity, and photodynamic tumor inhibition demonstrated that such tumor-microenvironment-sensitive ALA prodrug nanocarriers could be considered as potential candidates for targeted photodynamic cancer therapy.

Host Materials Transformable in Tumor Microenvironment for Homing Theranostics

A pathology-adaptive nanosystem, in which nest-like hosts are built based on nanofibers that are transformed from i.v. injected nanoparticles under the acidic tumor microenvironment. The solid tumor is artificially modified by nest-like hosts readily and firmly, resulting in highly efficient accumulation and stabilization of guest theranostics. This strategy shows great potential for the theranostics delivery to tumors.

Rational Design of Cancer Nanomedicine: Nanoproperty Integration and Synchronization

Current cancer nanomedicines can only mitigate adverse effects but fail to enhance therapeutic efficacies of anticancer drugs. Rational design of next-generation cancer nanomedicines should aim to enhance their therapeutic efficacies. Taking this into account, this review first analyzes the typical cancer-drug-delivery process of an intravenously administered nanomedicine and concludes that the delivery involves a five-step CAPIR cascade and that high efficiency at every step is critical to guarantee high overall therapeutic efficiency. Further analysis shows that the nanoproperties needed in each step for a nanomedicine to maximize its efficiency are different and even opposing in different steps, particularly what the authors call the PEG, surface-charge, size and stability dilemmas. To resolve those dilemmas in order to integrate all needed nanoproperties into one nanomedicine, stability, surface and size nanoproperty transitions (3S transitions for short) are proposed and the reported strategies to realize these transitions are comprehensively summarized. Examples of nanomedicines capable of the 3S transitions are discussed, as are future research directions to design high-performance cancer nanomedicines and their clinical translations.

Tumor-Penetrating Nanoparticles for Enhanced Anticancer Activity of Combined Photodynamic and Hypoxia-Activated Therapy

Poor tumor penetration is a major challenge for the use of nanoparticles in anticancer therapy. Moreover, the inability to reach hypoxic tumor cells that are distant from blood vessels results in inadequate exposure to antitumor therapeutics and contributes to development of chemoresistance and increased metastasis. In the present study, we developed iRGD-modified nanoparticles for simultaneous tumor delivery of a photosensitizer indocyanine green (ICG) and hypoxia-activated prodrug tirapazamine (TPZ). The iRGD-modified nanoparticles loaded with ICG and TPZ showed significantly improved penetration in both 3D tumor spheroids in vitro and orthotopic breast tumors in vivo. ICG-mediated photodynamic therapy upon irradiation with a near-IR laser induced hypoxia, which activated antitumor activity of the codelivered TPZ for synergistic cell-killing effect. In vivo studies demonstrated that the nanoparticles could efficiently deliver the drug combination in 4T1 orthotopic tumors. Primary tumor growth and metastasis were effectively inhibited by the iRGD-modified combination nanoparticles with minimal side effects. The results also showed the anticancer benefits of codelivering ICG and TPZ in a single nanoparticle formulation in contrast to a mixture of nanoparticles containing individual drugs. The study demonstrates the benefits of combining tumor-penetrating nanoparticles with hypoxia-activated drug treatment and establishes a delivery platform for PDT and hypoxia-activated chemotherapy.

Tumor-Specific Multiple Stimuli-Activated Dendrimeric Nanoassemblies with Metabolic Blockade Surmount Chemotherapy Resistance

Chemotherapy resistance remains a serious impediment to successful antitumor therapy around the world. However, existing chemotherapeutic approaches are difficult to cope with the notorious multidrug resistance in clinical treatment. Herein, we developed tumor-specific multiple stimuli-activated dendrimeric nanoassemblies with a metabolic blockade to completely combat both physiological barriers and cellular factors of multidrug resistance. With a sophisticated molecular and supramolecular engineering, this type of tumor-specific multiple stimuli-activated nanoassembly based on dendrimeric prodrugs can hierarchically break through the sequential physiological barriers of drug resistance, including stealthy dendritic PEGylated corona to optimize blood transportation, robust nanostructures for efficient tumor passive targeting and accumulation, enzyme-activated tumor microenvironment targeted to deepen tumor penetration and facilitate cellular uptake, cytoplasmic redox-sensitive disintegration for sufficient release of encapsulated agents, and lysosome acid-triggered nucleus delivery of antitumor drugs. In the meantime, we proposed a versatile tactic of a tumor-specific metabolism blockade for provoking several pathways (ATP restriction, apoptotic activation, and anti-apoptotic inhibition) to restrain multiple cellular factors of drug resistance. The highly efficient antitumor activity to drug-resistant MCF-7R tumor in vitro and in vivo supports this design and strongly defeats both physiological barriers and cellular factors of chemotherapy resistance. This work sets up an innovative dendrimeric nanosystem to surmount multidrug resistance, contributing to the development of a comprehensive nanoparticulate strategy for future clinical applications.

Replication Study: Coadministration of a tumor-penetrating peptide enhances the efficacy of cancer drugs

In 2015, as part of the Reproducibility Project: Cancer Biology, we published a Registered Report (Kandela et al., 2015) that described how we intended to replicate selected experiments from the paper "Coadministration of a tumor-penetrating peptide enhances the efficacy of cancer drugs" (Sugahara et al., 2010). Here we report the results of those experiments. We found that coadministration with iRGD peptide did not have an impact on permeability of the chemotherapeutic agent doxorubicin (DOX) in a xenograft model of prostate cancer, whereas the original study reported that it increased the penetrance of this cancer drug (Figure 2B; Sugahara et al., 2010). Further, in mice bearing orthotopic 22Rv1 human prostate tumors, we did not find a statistically significant difference in tumor weight for mice treated with DOX and iRGD compared to DOX alone, whereas the original study reported a decrease in tumor weight when DOX was coadministered with iRGD (Figure 2C; Sugahara et al., 2010). In addition, we did not find a statistically significant difference in TUNEL staining in tumor tissue between mice treated with DOX and iRGD compared to DOX alone, while the original study reported an increase in TUNEL positive staining with iRGD coadministration (Figure 2D; Sugahara et al., 2010). Similar to the original study (Supplemental Figure 9A; Sugahara et al., 2010), we did not observe an impact on mouse body weight with DOX and iRGD treatment. Finally, we report meta-analyses for each result.

Multifunctional "core-shell" nanoparticles-based gene delivery for treatment of aggressive melanoma

Gene therapy may be a promising and powerful strategy for cancer treatment, but efficient targeted gene delivery in vivo has so far remained challenging. Here, we developed a well-tailored and versatile "core-shell" ternary system (RRPHC) of systemic gene delivery for treatment of aggressive melanoma. The capsid-like "shell" of this system was engineered to mediate depth penetration to tissues, simultaneously target the CD44 receptors and integrin α_vβ₃ receptors overexpressed on neovasculature and most malignant tumor cells, while the "core" was responsible for nucleus-targeting and effective transfection. The RRPHC ternary complexes enhanced cellular uptake via dual receptor-mediated endocytosis, improved the endosomal escape and significantly promoted the plasmid penetration into the nucleus. Notably, RRPHC ternary complexes exhibited ultra-high gene transfection efficiency (∼100% in B16F10 cells), which surpassed that of commercial transfection agents, PEI 25K, Lipofectamine 2000 and even Lipofectamine 3000. Especially, RRPHC ternary complexes showed excellent serum resistance and remained high gene transfection efficacy (∼100%) even in medium containing 30% serum. In vivo biodistribution imaging demonstrated RRPHC ternary complexes possessed much more accumulation and extensive distribution throughout tumor regions while minimal location in other organs. Furthermore, systemic delivery of the pro-apoptotic mTRAIL gene to tumor xenografts by RRPHC ternary complexes resulted in remarkable inhibition of melanoma, with no systemic toxicity. These results demonstrated that the designed novel RRPHC ternary complexes might be a promising gene delivery system for targeted cancer therapy in vivo.

Activatable iRGD-based peptide monolith: Targeting, internalization, and fluorescence activation for precise tumor imaging

A disulfide-bridged cyclic RGD peptide, named iRGD (internalizing RGD, c(CRGDK/RGPD/EC)), is known to facilitate tumor targeting as well as tissue penetration. After the RGD motif-induced targeting on αv integrins expressed near tumor tissue, iRGD encounters proteolytic cleavage to expose the CendR motif that promotes penetration into cancer cells via the interaction with neuropilin-1. Based on these proteolytic cleavage and internalization mechanism, we designed an iRGD-based monolithic imaging probe that integrates multiple functions (cancer-specific targeting, internalization and fluorescence activation) within a small peptide framework. To provide the capability of activatable fluorescence signaling, we conjugated a fluorescent dye to the N-terminal of iRGD, which was linked to the internalizing sequence (CendR motif), and a quencher to the opposite C-terminal. It turned out that fluorescence activation of the dye/quencher-conjugated monolithic peptide probe requires dual (reductive and proteolytic) cleavages on both disulfide and amide bond of iRGD peptide. Furthermore, the cleavage of the iRGD peptide leading to fluorescence recovery was indeed operative depending on the tumor-related angiogenic receptors (αvβ3 integrin and neuropilin-1) in vitro as well as in vivo. Compared to an 'always fluorescent' iRGD control probe without quencher conjugation, the dye/quencher-conjugated activatable monolithic peptide probe visualized tumor regions more precisely with lower background noise after intravenous injection, owing to the multifunctional responses specific to tumor microenvironment. All these results, along with minimal in vitro and in vivo toxicity profiles, suggest potential of the iRGD-based activatable monolithic peptide probe as a promising imaging agent for precise tumor diagnosis.

MMP-9 triggered self-assembly of doxorubicin nanofiber depots halts tumor growth

A central challenge in cancer care is to ensure that therapeutic compounds reach their targets. One approach is to use enzyme-responsive biomaterials, which reconfigure in response to endogenous enzymes that are overexpressed in diseased tissues, as potential site-specific anti-tumoral therapies. Here we report peptide micelles that upon MMP-9 catalyzed hydrolysis reconfigure to form fibrillar nanostructures. These structures slowly release a doxorubicin payload at the site of action. Using both in vitro and in vivo models, we demonstrate that the fibrillar depots are formed at the sites of MMP-9 overexpression giving rise to enhanced efficacy of doxorubicin, resulting in inhibition of tumor growth in an animal model.

Intracellularly Acid-Switchable Multifunctional Micelles for Combinational Photo/Chemotherapy of the Drug-Resistant Tumor

The intrinsic or acquired drug resistance is the main challenge for cancer chemotherapy today. So far, many nanosized drug delivery systems (NDDS) have been exploited to combat cancer drug resistance. However, the therapy efficacy of current NDDS is severely impaired by the limited tumor penetration of the nanoparticles due to the existence of physiological and pathological barriers in the solid tumor. In this study, we report on the design and fabrication of intracellularly acid-switchable multifunctional micelles for combinational photo- and chemotherapy of the drug-resistant tumor. The micelles were composed of a pH-responsive diblock copolymer, a photosensitizer, and a polymeric prodrug of doxorubicin. The micelle displayed silenced fluorescence and photoactivity during the blood circulation and switched to an active state in weakly acid conditions (i.e., pH ≤ 6.2) in the endocytic vesicles to dramatically induce a 7.5-fold increase of the fluorescence signal for fluorescence imaging. Upon near-infrared (NIR) laser irradiation, the micelle induced notable reactive oxygen species generation to trigger cytosol release of the chemotherapeutics and perform photodynamic therapy (PDT). Moreover, the micelle efficiently converted the NIR light to local heat for enhancing tumor penetration of the anticancer drug, tumor specific photothermal therapy, and photoacoustic (PA) imaging. Furthermore, the micelles could generate amplified magnetic resonance (MR) signal in an acidic microenvironment to perform MR imaging. Collectively, this study presents a robust nanoplatform for multimodal imaging and combinational therapy of the drug-resistant tumor, which might provide an insight for developing polymer-based NDDS for cancer therapy.

Advancement in integrin facilitated drug delivery

The research of integrin-targeted anticancer agents has recorded important advancements in ingenious design of delivery systems, based either on the prodrug approach, or on nanoparticle carriers, but for now, none of these has reached a clinical stage of development. Past work in this area has been extensively reviewed by us and others. Thus, the purpose and scope of the present review is to survey the advancement reported in the last 3years, with focus on innovative delivery systems that appear to afford openings for future developments. These systems exploit the labelling with conventional and novel integrin ligands for targeting the interface of cancer cells and of endothelial cells involved in cancer angiogenesis, with the proteins of the extracellular matrix, in the circulation, in tissues, and in tumour stroma, as the site of progression and metastatic evolution of the disease. Furthermore, these systems implement the expertise in the development of nanomedicines to the purpose of achieving preferential biodistribution and uptake in cancer tissues, internalisation in cancer cells, and release of the transported drugs at intracellular sites. The assessment of the value of controlling these factors, and their combination, for future developments requires support of biological testing in appropriate mechanistic models, but also imperatively demand confirmation in therapeutically relevant in vivo models for biodistribution, efficacy, and lack of off-target effects. Thus, among many studies, we have tried to point out the results supported by relevant in vivo studies, and we have emphasised in specific sections those addressing the medical needs of drug delivery to brain tumours, as well as the delivery of oligonucleotides modulating gene-dependent pathological mechanism. The latter could constitute the basis of a promising third branch in the therapeutic armamentarium against cancer, in addition to antibody-based agents and to cytotoxic agents.

A stimuli-responsive Janus peptide dendron–drug conjugate as a safe and nanoscale drug delivery vehicle for breast cancer therapy

A Janus mPEGylated dendron–PVGLIG–DOX conjugate self-assembled into nanoparticles was employed as a matrix metalloproteinase-2/9 enzyme-sensitive and safe nanoscale drug delivery system for breast cancer therapy.

Hyperbranched poly(N-(2-hydroxypropyl) methacrylamide) via RAFT self-condensing vinyl polymerization

We report the first synthesis of hyperbranched poly(N-(2-hydroxypropyl) methacrylamide) (HB-PHPMA) using reversible addition–fragmentation chain transfer (RAFT) self-condensing vinyl polymerization (SCVP).

Self-assembled nanoparticles covalently consisting of doxorubicin and EDB fibronectin specific peptide for solid tumour treatment

We developed a facile modality to prepare nanoparticles consisting of doxorubicin and ZD2 motif for treating solid tumours. The nanoparticles showed great preferential cellular uptake in PC3 cells, high cell suppression, and strong anti-tumour ability.

Chemotherapeutic copolymers prepared via the RAFT polymerization of prodrug monomers

Reversible addition–fragmentation chain transfer (RAFT) polymerization was employed to prepare prodrug polymer carrier systems with the chemotherapeutic agent camptothecin (Cam) and the kinase inhibitor dasatinib (Dt).

Tumor-penetrating peptide modified and pH-sensitive polyplexes for tumor targeted siRNA delivery

The pH-sensitive copolymer enhanced the lysosome escape of polyplexes and modification of iRGD endowed the polyplexes with effective intratumoral delivery and high transfection efficiency.

Polymer-Based Prodrugs: Improving Tumor Targeting and the Solubility of Small Molecule Drugs in Cancer Therapy

The majority of anticancer drugs have poor aqueous solubility, produce adverse effects in healthy tissue, and thus impose major limitations on both clinical efficacy and therapeutic safety of cancer chemotherapy. To help circumvent problems associated with solubility, most cancer drugs are now formulated with co-solubilizers. However, these agents often also introduce severe side effects, thereby restricting effective treatment and patient quality of life. A promising approach to addressing problems in anticancer drug solubility and selectivity is their conjugation with polymeric carriers to form polymer-based prodrugs. These polymer-based prodrugs are macromolecular carriers, designed to increase the aqueous solubility of antitumor drugs, can enhance bioavailability. Additionally, polymer-based prodrugs approach exploits unique features of tumor physiology to passively facilitate intratumoral accumulation, and so improve chemodrug pharmacokinetics and pharmacological properties. This review introduces basic concepts of polymer-based prodrugs, provides an overview of currently emerging synthetic, natural, and genetically engineered polymers that now deliver anticancer drugs in preclinical or clinical trials, and highlights their major anticipated applications in anticancer therapies.

Targeted polymer-drug conjugates: Current progress and future perspective

The combination of polymer technology and targeted drug delivery may pave the way for more effective yet safer therapeutic options for cancer therapy. Polymer-drug conjugates belonging to polymer therapeutics represent an emerging approach for drug delivery. The development of smart targeted polymer-drug conjugates that can specifically deliver drugs at a sustained rate to tumor cells may substantially improve the therapeutic index of anticancer agents. In this update, we provide an overview of the most important targeting molecules, and systemically summarize the recent advances in the development of tumor-targeted polymer-drug conjugates. Additionally, several promising approaches for the future will also be presented.