Development of novel tumor-targeted theranostic nanoparticles activated by membrane-type matrix metalloproteinases for combined cancer magnetic resonance imaging and therapy

Preparation and characterization of peptide modified ultrasmall superparamagnetic iron oxides used as tumor targeting MRI contrast agent

As desirable contrast agents for magnetic resonance imaging (MRI), ultrasmall superparamagnetic iron oxides (USPIOs) are required to exhibit both low cytotoxicity and specific targetability besides superparamagnetism to achieve better imaging contrast at lower dose, and cladding with biocompatible polymers and modification with targeting ligands are considered to be the most effective strategies. In this study, novel dextran wrapped and peptide WSGPGVWGASVK (peptide-WSG) grafted USPIOs were meticulously prepared and systematically characterized. Firstly, dextran (Dex) cladded USPIOs (USPIOs@Dex) were synthesized with a well-designed co-precipitation procedure in which the biocompatible dextran played dual roles of grain inhibitor and cladding agent. After that, sodium citrate was applied to carboxylize the hydroxyls of the dextran molecules via an esterification reaction, and then tumor targeting peptide-WSG was grafted to the carboxyl groups by the EDC method. The XRD, TEM, and FTIR results showed that inverse spinel structure Fe₃O₄ crystallites were nucleated and grown in aqueous solution, and the catenulate dextran molecules gradually bound on their surface, meanwhile the growth of grains was inhibited. The size of original crystallite grains was about 7 nm, but the mean size of USPIOs@Dex aggregates was 165.20 nm. After surface modification by sodium citrate and peptide-WSG with ultrasonic agitation, the size of the USPIOs@Dex-WSG aggregates was smaller (66.06 nm) because the hydrophilicity was improved, so USPIOs@Dex-WSG could evade being eliminated by RES more easily, and prolong residence time in blood circulation. The VSM and T₂-weighted MRI results showed that USPIOs@Dex-WSG were superparamagnetic with a saturation magnetization of 44.65 emu g⁻¹, and with high transverse relaxivity as the R₂ relaxivity coefficient value was 229.70 mM⁻¹ s⁻¹. The results of MTT assays and the Prussian blue staining in vitro revealed that USPIOs@Dex-WSG exhibited nontoxicity for normal cells such as L929 and HUVECs, and were specifically targeted to the SKOV-3 cells. Thus, the novel dextran wrapped and WSG-peptide grafted USPIOs have potential to be applied as tumor active targeting contrast agents for MRI.

As desirable contrast agents for magnetic resonance imaging (MRI), ultrasmall superparamagnetic iron oxides (USPIOs) modified with targeting ligands are considered to be the most effective strategies to achieve better imaging contrast at lower dose.

Synthesis of Doxorubicin and miRNA Stimuli-Sensitive Conjugates for Combination Therapy

Recent advances in combination therapy by using chemotherapeutic drugs and small noncoding RNAs have highlighted the need for optimization of such agents to allow their carriage in a single delivery system. This protocol details the synthesis of a doxorubicin prodrug, where a NHS coupling reaction was used to sensitize the drug to the proteolytic activity of tumor microenvironments. The design of a lipid-modified miRNA by an S-S coupling reaction is also described. Modification of both, doxorubicin and miRNA, facilitated their simultaneous incorporation into mixed micelles for use in combination therapy against tumor cells.

Evaluation of pancreatic tumor development in KPC mice using multi-parametric MRI

Background

Pancreatic ductal adenocarcinoma (PDA) is a fatal disease with very poor prognosis. Development of sensitive and noninvasive methods to monitor tumor progression in PDA is a critical and unmet need. Magnetic resonance imaging (MRI) can noninvasively provide information regarding underlying pathophysiological processes such as necrosis, inflammatory changes and fibrotic tissue deposition.

Methods

A genetically engineered KPC mouse model that recapitulates human PDA was used to characterize disease progression. MR measures of T₁ and T₂ relaxation times, magnetization transfer ratio (MTR), diffusion and chemical exchange saturation transfer were compared in two separate phases i.e. slow and rapid growth phase of tumor. Fibrotic tissue accumulation was assessed histologically using Masson’s trichrome staining. Pearson correlation coefficient (r) was computed to assess the relationship between the fibrotic tissue accumulation and different MR parameters.

Results

There was a negative correlation between amide proton transfer signal intensity and tumor volume (r = − 0.63, p = 0.003) in the slow growth phase of the tumor development. In the terminal stage of rapid growth phase of the tumor development MTR was strongly correlated with tumor volume (r = 0.62, p = 0.008). Finally, MTR was significantly correlated with % fibrosis (r = 0.87; p < 0.01), followed by moderate correlation between tumor volume (r = 0.42); T₁ (r = − 0.61), T₂ (r = − 0.61) and accumulation of fibrotic tissue.

Conclusions

Here we demonstrated, using multi-parametric MRI (mp-MRI), that MRI parameters changed with tumor progression in a mouse model of PDA. Use of mp-MRI may have the potential to monitor the dynamic changes of tumor microenvironment with increase in tumor size in the transgenic KPC mouse model of pancreatic tumor.

Electronic supplementary material

The online version of this article (10.1186/s40644-018-0172-6) contains supplementary material, which is available to authorized users.

Tumor microenvironment-responsive nanoparticles for cancer theragnostic applications

BACKGROUND

Cancer is one of the deadliest threats to human health. Abnormal physiochemical conditions and dysregulated biosynthetic intermediates in the tumor microenvironment (TME) play a significant role in modulating cancer cells to evade or defend conventional anti-cancer therapy such as surgery, chemotherapy and radiotherapy. One of the most important challenges in the development of anti-tumor therapy is the successful delivery of therapeutic and imaging agents specifically to solid tumors.

MAIN BODY

The recent progresses in development of TME responsive nanoparticles offers promising strategies for combating cancer by making use of the common attributes of tumor such as acidic and hypoxic microenvironments. In this review, we discussed the prominent strategies utilized in the development of tumor microenvironment-responsive nanoparticles and mode of release of therapeutic cargo.

CONCLUSION

Tumor microenvironment-responsive nanoparticles offers a universal approach for anti-cancer therapy.

Enzymatically promoted release of organic molecules linked to magnetic nanoparticles

Magnetite-based magnetic nanoparticles have been successfully coupled to an organic system constituted of a fluorescent molecule, a tripeptide specifier and a spacer. The system is able to selectively release the fluorescent molecule upon targeted enzymatic hydrolysis promoted by a lysine/arginine specific protease.

Magnetic iron oxide nanoparticles as drug carriers: preparation, conjugation and delivery

Magnetic nanoparticles (MNPs), particularly made of iron oxides, have been extensively studied as diagnostic imaging agents and therapeutic delivery vehicles. In this review, special emphasis is set on the 'recent advancements of drug-conjugated MNPs used for therapeutic applications'. The most prevalent preparation methods and chemical functionalization strategies required for translational biomedical nanoformulations are outlined. Particular attention is, then, devoted to the tailored conjugation of drugs to the MNP carrier according to either noncovalent or covalent attachments, with advantages and drawbacks of both pathways conferred. Notable examples are presented to demonstrate the advantages of MNPs in respective drug-delivery applications. Understanding of the preparation, conjugation and delivery processes will definitely bring, in the next decades, a novel magneto-nanovehicle for effective theranostics.

Inflammation and Cancer: In Medio Stat Nano

Cancer treatment still remains a challenge due to the several limitations of currently used chemotherapeutics, such as their poor pharmacokinetics, unfavorable chemical properties, as well as inability to discriminate between healthy and diseased tissue. Nanotechnology offered potent tools to overcome these limitations. Drug encapsulation within a delivery system permitted i) to protect the payload from enzymatic degradation/ inactivation in the blood stream, ii) to improve the physicochemical properties of poorly water-soluble drugs, like paclitaxel, and iii) to selectively deliver chemotherapeutics to the cancer lesions, thus reducing the off-target toxicity, and promoting the intracellular internalization. To accomplish this purpose, several strategies have been developed, based on biological and physical changes happening locally and systemically as a consequence of tumorigenesis. Here, we will discuss the role of inflammation in the different steps of tumor development and the strategies based on the use of nanoparticles that exploit the inflammatory pathways in order to selectively target the tumor-associated microenvironment for therapeutic and diagnostic purposes.

Human mesenchymal stem cell-derived iron oxide exosomes allow targeted ablation of tumor cells via magnetic hyperthermia

Magnetic hyperthermia, or the heating of tissues using magnetic materials, is a promising approach for treating cancer. We found that human mesenchymal stem cells (MSCs) isolated from various tissues and MSCs expressing the yeast cytosine deaminase∷uracil phosphoribosyl transferase suicide fusion gene (yCD∷UPRT) can be labeled with Venofer, an iron oxide carbohydrate nanoparticle. Venofer labeling did not affect cell proliferation or the ability to home to tumors. All Venofer-labeled MSCs released exosomes that contained iron oxide. Furthermore, these exosomes were efficiently endocytosed by tumor cells. Exosomes from Venofer-labeled MSCs expressing the yCD∷UPRT gene in the presence of the prodrug 5-fluorocytosine inhibited tumor growth in a dose-dependent fashion. The treated tumor cells were also effectively ablated following induction of hyperthermia using an external alternating magnetic field. Cumulatively, we found that magnetic nanoparticles packaged into MSC exosomes are efficiently endocytosed by tumor cells, facilitating targeted tumor cell ablation via magnetically induced hyperthermia.

GSH-Activated NIR Fluorescent Prodrug for Podophyllotoxin Delivery

Theranostic prodrug therapy enables the targeted delivery of anticancer drugs with minimized adverse effects and real-time in situ monitoring of activation of the prodrugs. In this work, we report the synthesis and biological assessment of the near-infrared (NIR) prodrug DCM-S-PPT and its amphiphilic copolymer (mPEG-DSPE)-encapsulated nanoparticles. DCM-S-PPT is composed of podophyllotoxin (PPT) as the anticancer moiety and a dicyanomethylene-4H-pyran (DCM) derivative as the NIR fluorescent reporter, which are linked by a thiol-specific cleavable disulfide bond. In vitro experiments indicated that DCM-S-PPT has low cytotoxicity and that glutathione (GSH) can activate DCM-S-PPT resulting in PPT release and a concomitant significant enhancement in NIR fluorescence at 665 nm. After being intravenously injected into tumor-bearing nude mice, DCM-S-PPT exhibited excellent tumor-activated performance. Furthermore, we have demonstrated that mPEG-DSPE as a nanocarrier loaded with DCM-S-PPT (mPEG-DSPE/DCM-S-PPT) showed even greater tumor-targeting performance than DCM-S-PPT on account of the enhanced permeability and retention effect. Its tumor-targeting ability and specific drug release in tumors make DCM-S-PPT a promising prodrug that could provide a significant strategy for theranostic drug delivery systems.

Next-generation superparamagnetic iron oxide nanoparticles for cancer theranostics

Superparamagnetic iron oxide (SPIO) nanoparticles have been intensively studied for the development of contrast agents in MRI. First-generation SPIO nanoparticles had diagnostic capabilities only, whereas a new generation of SPIO nanoparticle has multifunctional characteristics for combined therapeutic and diagnostic applications. These theranostic nanoparticles hold great potential for image-guided cancer therapies. In particular, polymer-coated theranostic SPIO nanoparticles have enjoyed increasing attention as a result of good biocompatibility, biodegradability and versatile functionality endowed by polymeric matrices. This review provides an overview of recently developed polymer-coated multifunctional SPIO nanoparticles for cancer theranostics and discusses current challenges and future perspectives.

A Novel Theranostic Strategy for MMP-14-Expressing Glioblastomas Impacts Survival

Glioblastoma (GBM) has a dismal prognosis. Evidence from preclinical tumor models and human trials indicates the role of GBM-initiating cells (GIC) in GBM drug resistance. Here, we propose a new treatment option with tumor enzyme-activatable, combined therapeutic and diagnostic (theranostic) nanoparticles, which caused specific toxicity against GBM tumor cells and GICs. The theranostic cross-linked iron oxide nanoparticles (CLIO) were conjugated to a highly potent vascular disrupting agent (ICT) and secured with a matrix-metalloproteinase (MMP-14) cleavable peptide. Treatment with CLIO-ICT disrupted tumor vasculature of MMP-14-expressing GBM, induced GIC apoptosis, and significantly impaired tumor growth. In addition, the iron core of CLIO-ICT enabled in vivo drug tracking with MR imaging. Treatment with CLIO-ICT plus temozolomide achieved tumor remission and significantly increased survival of human GBM-bearing mice by more than 2-fold compared with treatment with temozolomide alone. Thus, we present a novel therapeutic strategy with significant impact on survival and great potential for clinical translation. Mol Cancer Ther; 16(9); 1909-21. ©2017 AACR.

Nanoparticle design strategies for enhanced anticancer therapy by exploiting the tumour microenvironment

Nanovehicles can efficiently carry and deliver anticancer agents to tumour sites. Compared with normal tissue, the tumour microenvironment has some unique properties, such as vascular abnormalities, hypoxia and acidic pH. There are many types of cells, including tumour cells, macrophages, immune and fibroblast cells, fed by defective blood vessels in the solid tumour. Exploiting the tumour microenvironment can benefit the design of nanoparticles for enhanced therapeutic effectiveness. In this review article, we summarized the recent progress in various nanoformulations for cancer therapy, with a special emphasis on tumour microenvironment stimuli-responsive ones. Numerous tumour microenvironment modulation strategies with promising cancer therapeutic efficacy have also been highlighted. Future challenges and opportunities of design consideration are also discussed in detail. We believe that these tumour microenvironment modulation strategies offer a good chance for the practical translation of nanoparticle formulas into clinic.

A self-immolative prodrug nanosystem capable of releasing a drug and a NIR reporter for in vivo imaging and therapy

In vivo monitoring of the biodistribution and activation of prodrugs is highly attractive, and the self-immolative dendritic architecture is deemed as a promising approach for constructing theranostic prodrug in which the release/activation of different payloads is needed. Herein, A GSH-triggered and self-immolative dendritic platform comprising an anticancer drug camptothecin (CPT), a cleavable linker and a two-photon NIR fluorophore (dicyanomethylene-4H-pyran, DCM) has been developed for in situ tracking of drug release and antitumour therapy. In vitro experiments demonstrate that, the presence of glutathione (GSH) induces the cleavage of the self-immolative linker, resulting in comitant release of the drug and the dye. Upon cell internalization and under one- or two-photon excitation, prominent intracellular fluorescence can be observed, indicating the release of the payloads in live cells. Upon loaded in phospholipid vesicles, the prodrug has also been successfully utilized for in vivo and in situ tracking of drug release and cancer therapy in a mouse model. Several hours post injection, the prodrug generates strong fluorescence on tumour sites, demonstrating the prodrug's capability of monitoring the on-site drug release. Moreover, the prodrug shows considerable high activity and exerts obvious inhibition towards tumour growth. This work suggests that the prodrug with self-immolative dendritic structure can work well in vivo and this strategy may provide an alternative approach for designing theranostic drug delivery systems.

Protease-Sensitive Nanomaterials for Cancer Therapeutics and Imaging

Many diseases can be characterized by the abnormal activity exhibited by various biomolecules, the targeting of which can provide therapeutic and diagnostic utility. Recent trends in medicine and nanotechnology have prompted the development of protease-sensitive nanomaterials systems for therapeutic, diagnostic, and theranostic applications. These systems can act specifically in response to the target enzyme and its associated disease conditions, thus enabling personalized treatment and improved prognosis. In this Review, we discuss recent advancements in the development of protease-responsive materials for imaging and drug delivery and analyze several representative systems to illustrate their key design principles.

Rationalized Computer-Aided Design of Matrix-Metalloprotease-Selective Prodrugs

Matrix metalloproteinases (MMPs) are central to cancer development and metastasis. They are highly active in the tumor environment and absent or inactive in normal tissues; therefore they represent viable targets for cancer drug discovery. In this study we evaluated in silico docking to develop MMP-subtype-selective tumor-activated prodrugs. Proof of principle for this therapeutic approach was demonstrated in vitro against an aggressive human glioma model, with involvement of MMPs confirmed using pharmacological inhibition.

Light/magnetic hyperthermia triggered drug released from multi-functional thermo-sensitive magnetoliposomes for precise cancer synergetic theranostics

Precise delivery of antineoplastic drugs to specific tumor region has drawn much attention in recent years. Herein, a light/magnetic hyperthermia triggered drug delivery with multiple functionality is designed based on methotrexate (MTX) modified thermo-sensitive magnetoliposomes (MTX-MagTSLs). In this system, MTX and oleic acid modified magnetic nanoparticles (MNPs) can be applied in biological and magnetic targeting. Meanwhile, lipophilic fluorescent dye Cy5.5 and MNPs are encapsulated into the bilayer of liposomes, which can not only achieve dual-imaging effect to verify the MTX-MagTSLs accumulation in tumor region, but also provide an appropriate laser irradiation region to release Doxorubicin (Dox) under alternating magnetic field (AMF). Both in vitro and in vivo results revealed that MTX-MagTSLs possessed an excellent targeting ability towards HeLa cells and HeLa tumor-bearing mice. Furthermore, the heating effect of MTX-MagTSLs was amplified 4.2-fold upon combination with AMF and local precise near-infrared laser irradiation (808nm) (DUAL-mode) to rapidly reach the phase change temperature (Tm) of MTX-MagTSLs in 5min compared with either AMF or laser stimulation alone, resulting in a significantly enhanced release of Dox at tumor region and precise cancer synergetic theranostics.

Activatable probes for diagnosis and biomarker detection by MRI

Magnetic resonance imaging (MRI) is a non-invasive imaging technique with widespread use in diagnosis. Frequently, contrast in MRI is enhanced with the aid of a contrast agent, among which smart, responsive, OFF/ON or activatable probes are of particular interest. These kinds of probes elicit a response to selective stimuli, evidencing the presence of enzymes or acidic pH, for instance. In this review, we will focus on smart probes that are detectable by both ¹H and ¹⁹F MRI, frequently based on nanomaterials. We will discuss the triggering factors and the strategies employed thus far to activate each probe.

The Current State of Nanoparticle-Induced Macrophage Polarization and Reprogramming Research

Macrophages are vital regulators of the host defense in organisms. In response to different local microenvironments, resting macrophages (M0) can be polarized into different phenotypes, pro-inflammatory (M1) or anti-inflammatory (M2), and perform different roles in different physiological or pathological conditions. Polarized macrophages can also be further reprogrammed by reversing their phenotype according to the changed milieu. Macrophage polarization and reprogramming play essential roles in maintaining the steady state of the immune system and are involved in the processes of many diseases. As foreign substances, nanoparticles (NPs) mainly target macrophages after entering the body. NPs can perturb the polarization and reprogramming of macrophages, affect their immunological function and, therefore, affect the pathological process of disease. Optimally-designed NPs for the modulation of macrophage polarization and reprogramming might provide new solutions for treating diseases. Systematically investigating how NPs affect macrophage polarization is crucial for understanding the regulatory effects of NPs on immune cells in vivo. In this review, macrophage polarization by NPs is summarized and discussed.

Matrix-metalloproteinases as targets for controlled delivery in cancer: An analysis of upregulation and expression

While commonly known for degradation of the extracellular matrix, matrix metalloproteinases (MMPs) exhibit broad potential for use in targeting of bioactive and imaging agents in cancer treatment. MMPs are upregulated at all stages of expression in cancers. A comprehensive analysis of published literature on expression of all MMP subtypes at the genetic, protein, and activity levels in normal and diseased tissues indicate targeting applicability in a variety of cancers. This expression significantly increases at advanced cancer stages, providing an improved opportunity for controlled release in higher-stage patients. Since MMPs are integral at every stage of metastasis, MMP roles in cancer are discussed with a focus on MMP distribution and mobility within cells and tumors for cancer targeting applications. Several strategies for MMP utilization in targeting - such as matrix degradation, MMP cleavage, MMP binding, and MMP-induced environmental changes - are addressed.

Imaging the Tumor Microenvironment

The tumor microenvironment consists of tumor, stromal, and immune cells, as well as extracellular milieu. Changes in numbers of these cell types and their environments have an impact on cancer growth and metastasis. Non-invasive imaging of aspects of the tumor microenvironment can provide important information on the aggressiveness of the cancer, whether or not it is metastatic, and can also help to determine early response to treatment. This chapter provides an overview on non-invasive in vivo imaging in humans and mouse models of various cell types and physiological parameters that are unique to the tumor microenvironment. Current clinical imaging and research investigation are in the areas of nuclear imaging (positron emission tomography (PET) and single photon emission computed tomography (SPECT)), magnetic resonance imaging (MRI) and optical (near infrared (NIR) fluorescence) imaging. Aspects of the tumor microenvironment that have been imaged by PET, MRI and/or optical imaging are tumor associated inflammation (primarily macrophages and T cells), hypoxia, pH changes, as well as enzymes and integrins that are highly prevalent in tumors, stroma and immune cells. Many imaging agents and strategies are currently available for cancer patients; however, the investigation of novel avenues for targeting aspects of the tumor microenvironment in pre-clinical models of cancer provides the cancer researcher with a means to monitor changes and evaluate novel treatments that can be translated into the clinic.

Rethinking Brain Cancer Therapy: Tumor Enzyme Activatable Theranostic Nanoparticles

This invited commentary discusses a recent article by Mohanty et al in Molecular Cancer Therapeutics about significant therapeutic efficacies of novel theranostic nanoparticles (TNPs) for the treatment of human brain cancers in mouse models. The TNPs were cleaved by enzymes in the tumor tissue, matrix metalloproteinase (MMP-14), which lead to release of a highly potent therapeutic drug, azademethylcolchicine. Data showed that the TNPs caused selective toxic effects in MMP-14-expressing glioblastoma and not normal brain. In addition, the iron oxide nanoparticle backbone enabled in vivo drug tracking with magnetic resonance imaging (MRI). This commentary discusses previous efforts of MMP-targeted therapeutics as well as opportunities for further refinements of tumor enzyme-activatable TNPs. If successfully translated to clinical applications, the TNPs might hold substantial potential to improving cytotoxic indexes and long-term outcomes of patients with brain cancer compared to standard therapy.

Iron oxide nanoparticles inhibit tumour growth by inducing pro-inflammatory macrophage polarization in tumour tissues

Until now, the Food and Drug Administration (FDA)-approved iron supplement ferumoxytol and other iron oxide nanoparticles have been used for treating iron deficiency, as contrast agents for magnetic resonance imaging and as drug carriers. Here, we show an intrinsic therapeutic effect of ferumoxytol on the growth of early mammary cancers, and lung cancer metastases in liver and lungs. In vitro, adenocarcinoma cells co-incubated with ferumoxytol and macrophages showed increased caspase-3 activity. Macrophages exposed to ferumoxytol displayed increased mRNA associated with pro-inflammatory Th1-type responses. In vivo, ferumoxytol significantly inhibited growth of subcutaneous adenocarcinomas in mice. In addition, intravenous ferumoxytol treatment before intravenous tumour cell challenge prevented development of liver metastasis. Fluorescence-activated cell sorting (FACS) and histopathology studies showed that the observed tumour growth inhibition was accompanied by increased presence of pro-inflammatory M1 macrophages in the tumour tissues. Our results suggest that ferumoxytol could be applied 'off label' to protect the liver from metastatic seeds and potentiate macrophage-modulating cancer immunotherapies.

Remote Actuation of Magnetic Nanoparticles For Cancer Cell Selective Treatment Through Cytoskeletal Disruption

Motion of micron and sub-micron size magnetic particles in alternating magnetic fields can activate mechanosensitive cellular functions or physically destruct cancer cells. However, such effects are usually observed with relatively large magnetic particles (>250 nm) that would be difficult if at all possible to deliver to remote sites in the body to treat disease. Here we show a completely new mechanism of selective toxicity of superparamagnetic nanoparticles (SMNP) of 7 to 8 nm in diameter to cancer cells. These particles are coated by block copolymers, which facilitates their entry into the cells and clustering in the lysosomes, where they are then magneto-mechanically actuated by remotely applied alternating current (AC) magnetic fields of very low frequency (50 Hz). Such fields and treatments are safe for surrounding tissues but produce cytoskeletal disruption and subsequent death of cancer cells while leaving healthy cells intact.

Nanoparticle-based probes to enable noninvasive imaging of proteolytic activity for cancer diagnosis

Proteases play a key role in tumor biology, with high expression levels often correlating with poor prognosis for cancer patients - making them excellent disease markers for tumor diagnosis. Despite their significance, quantifying proteolytic activity in vivo remains a challenge. Nanoparticles, with their ability to serve as scaffolds having unique chemical, optical and magnetic properties, offer the promise of merging diagnostic medicine with material engineering. Such nanoparticles can interact preferentially with proteases enriched in tumors, providing the ability to assess disease state in a noninvasive and spatiotemporal manner. We review recent advances in the development of nanoparticles for imaging and quantification of proteolytic activity in tumor models, and prognosticate future advancements.

White Paper on P4 Concepts for Pediatric Imaging

Over the past decade, innovations in the field of pediatric imaging have been based largely on single-center and retrospective studies, which provided limited advances for the benefit of pediatric patients. To identify opportunities for potential "quantum-leap" progress in the field of pediatric imaging, the ACR-Pediatric Imaging Research (PIR) Committee has identified high-impact research directions related to the P4 concept of predictive, preventive, personalized, and participatory diagnosis and intervention. Input from 237 members of the Society for Pediatric Radiology was clustered around 10 priority areas, which are discussed in this article. Needs within each priority area have been analyzed in detail by ACR-PIR experts on these topics. By facilitating work in these priority areas, we hope to revolutionize the care of children by shifting our efforts from unilateral reaction to clinical symptoms, to interactive maintenance of child health.

Proteases in cancer drug delivery

Whereas protease inhibitors have been developed successfully against hypertension and viral infections, they have failed thus far as cancer drugs. With advances in cancer profiling we now better understand that the tumor "degradome" (i.e. the repertoire of proteases and their natural inhibitors and interaction partners) forms a complex network in which specific nodes determine the global outcome of manipulation of the protease web. However, knowing which proteases are active in the tumor micro-environment, we may tackle cancers with the use of Protease-Activated Prodrugs (PAPs). Here we exemplify this concept for metallo-, cysteine and serine proteases. PAPs not only exist as small molecular adducts, containing a cleavable substrate sequence and a latent prodrug, they are presently also manufactured as various types of nanoparticles. Although the emphasis of this review is on PAPs for treatment, it is clear that protease activatable probes and nanoparticles are also powerful tools for imaging purposes, including tumor diagnosis and staging, as well as visualization of tumor imaging during microsurgical resections.

In vivo mapping and assay of matrix metalloproteases for liver tumor diagnosis

A fluorescent probe constructed by simultaneous modification of FITC-grafted peptide and thiolated mPEG on the surface of gold nanoparticles forin vivomapping and assay of matrix metalloproteases.

Imaging Tumor Necrosis with Ferumoxytol

OBJECTIVE

Ultra-small superparamagnetic iron oxide nanoparticles (USPIO) are promising contrast agents for magnetic resonance imaging (MRI). USPIO mediated proton relaxation rate enhancement is strongly dependent on compartmentalization of the agent and can vary depending on their intracellular or extracellular location in the tumor microenvironment. We compared the T1- and T2-enhancement pattern of intracellular and extracellular USPIO in mouse models of cancer and pilot data from patients. A better understanding of these MR signal effects will enable non-invasive characterizations of the composition of the tumor microenvironment.

MATERIALS AND METHODS

Six 4T1 and six MMTV-PyMT mammary tumors were grown in mice and imaged with ferumoxytol-enhanced MRI. R1 relaxation rates were calculated for different tumor types and different tumor areas and compared with histology. The transendothelial leakage rate of ferumoxytol was obtained by our measured relaxivity of ferumoxytol and compared between different tumor types, using a t-test. Additionally, 3 patients with malignant sarcomas were imaged with ferumoxytol-enhanced MRI. T1- and T2-enhancement patterns were compared with histopathology in a descriptive manner as a proof of concept for clinical translation of our observations.

RESULTS

4T1 tumors showed central areas of high signal on T1 and low signal on T2 weighted MR images, which corresponded to extracellular nanoparticles in a necrotic core on histopathology. MMTV-PyMT tumors showed little change on T1 but decreased signal on T2 weighted images, which correlated to compartmentalized nanoparticles in tumor associated macrophages. Only 4T1 tumors demonstrated significantly increased R1 relaxation rates of the tumor core compared to the tumor periphery (p<0.001). Transendothelial USPIO leakage was significantly higher for 4T1 tumors (3.4±0.9x10-3 mL/min/100cm3) compared to MMTV-PyMT tumors (1.0±0.9x10-3 mL/min/100 cm3). Likewise, ferumoxytol imaging in patients showed similar findings with high T1 signal in areas of tumor necrosis and low signal in areas of intracellularly compartmentalized iron.

CONCLUSION

Differential T1- and T2-enhancement patterns of USPIO in tumors enable conclusions about their intracellular and extracellular location. This information can be used to characterize the composition of the tumor microenvironment.

Histochemical changes in neonatal liver caused by vaginal instillation of magnetic nanoparticles in pregnant mice

Drug delivery through the vagina is a novel and effective approach for treating embryonic diseases. Magnetic nanoparticles (MNPs) currently are used as drug delivery systems. The safety of MNPs for use with embryonic tissues remains unclear. We used pregnant mice to investigate the possible toxicity of MNPs toward neonatal liver at three embryonic ages using histochemical and immunohistochemical techniques. MNPs were instilled through the vaginas of pregnant mice at days 12 (E12), 15 (E15) and 17 (E17) after fertilization. We found MNPs in the neonatal liver parenchyma after delivery of the pups on day 20. We observed that MNPs caused mild apoptosis of hepatocytes, cytoplasmic vacuolation and lymphocytic infiltration in the neonatal liver after treatment at E15 compared to instillation at E12 and E17. We observed also that MNPs increased the production of caspase proteins and tumor necrosis factor receptor 2 proteins, which are indicators of apoptosis, in the neonatal liver after instillation of MNPs at E15 compared to instillation at E12 and E17. MNPs also increased the number of collagen fibers and the amounts of connective tissue growth factors in the neonatal liver parenchyma after instillation at E15 compared to instillation at E12 and E17. The general carbohydrates in the neonatal liver were decreased in a time-dependent manner after instillation at E17, E15 and E12 owing to the presence of MNPs in the parenchyma. Overall, we determined that MNPs were mildly toxic to neonatal liver.

Tumour-associated macrophages act as a slow-release reservoir of nano-therapeutic Pt(IV) pro-drug

Therapeutic nanoparticles (TNPs) aim to deliver drugs more safely and effectively to cancers, yet clinical results have been unpredictable owing to limited in vivo understanding. Here we use single-cell imaging of intratumoral TNP pharmacokinetics and pharmacodynamics to better comprehend their heterogeneous behaviour. Model TNPs comprising a fluorescent platinum(IV) pro-drug and a clinically tested polymer platform (PLGA-b-PEG) promote long drug circulation and alter accumulation by directing cellular uptake toward tumour-associated macrophages (TAMs). Simultaneous imaging of TNP vehicle, its drug payload and single-cell DNA damage response reveals that TAMs serve as a local drug depot that accumulates significant vehicle from which DNA-damaging Pt payload gradually releases to neighbouring tumour cells. Correspondingly, TAM depletion reduces intratumoral TNP accumulation and efficacy. Thus, nanotherapeutics co-opt TAMs for drug delivery, which has implications for TNP design and for selecting patients into trials.

New approaches to selectively target cancer-associated matrix metalloproteinase activity

Heightened matrix metalloproteinase (MMP) activity has been noted in the context of the tumor microenvironment for many years, and causal roles for MMPs have been defined across the spectrum of cancer progression. This is primarily due to the ability of the MMPs to process extracellular matrix (ECM) components and to regulate the bioavailability/activity of a large repertoire of cytokines and growth factors. These characteristics made MMPs an attractive target for therapeutic intervention but notably clinical trials performed in the 1990s did not fulfill the promise of preclinical studies. The reason for the failure of early MMP inhibitor (MMPI) clinical trials that are multifold but arguably principal among them was the inability of early MMP-based inhibitors to selectively target individual MMPs and to distinguish between MMPs and other members of the metzincin family. In the decades that have followed the MMP inhibitor trials, innovations in chemical design, antibody-based strategies, and nanotechnologies have greatly enhanced our ability to specifically target and measure the activity of MMPs. These advances provide us with the opportunity to generate new lines of highly selective MMPIs that will not only extend the overall survival of cancer patients, but will also afford us the ability to utilize heightened MMP activity in the tumor microenvironment as a means by which to deliver MMPIs or MMP activatable prodrugs.

Tumor-activated prodrug (TAP)-conjugated nanoparticles with cleavable domains for safe doxorubicin delivery

A major issue in chemotherapy is the lack of specificity of many antitumor drugs, which cause severe side effects and an impaired therapeutic response. Here we report on the design and characterization of model tumor activated prodrug-conjugated polystyrene (PS) nanoparticles (TAP-NPs) for the release of doxorubicin (Dox) triggered by matrix metalloprotease-2 (MMP2) enzyme, which is overexpressed in the extracellular matrix of tumors. In particular, TAP-NPs were produced by attaching Dox to poly(ethylene glycol) (PEG) through two MMP2-cleavable enzymes. The resulting adduct was then tethered to PS NPs. Results showed that Dox release was actually triggered by MMP2 cleavage and was dependent on enzyme concentration, with a plateau around 20 nM. Furthermore, significant cell cytotoxicity was observed towards three cell lines only in the presence of MMP2, but not in cells without enzyme pre-treatment, even after NP internalization by cells. These findings indicate the potential of TAP-NPs as suitable nanocarriers for an on demand, tumor--specific delivery of antitumor drugs after the response to an endogenous stimulus. Further advancements will focus on the translation of this production technology to biodegradable systems for the safe transport of cytotoxic drug to tumor tissues.

Novel 19F activatable probe for the detection of matrix metalloprotease-2 activity by MRI/MRS

Matrix metalloproteases (MMPs) have been found to be highly expressed in a variety of malignant tumor tissues. Noninvasive visualization of MMP activity may play an important role in the diagnosis of MMP associated diseases. Here we report the design and synthesis of a set of fluorine-19 dendron-based magnetic resonance imaging (MRI) probes for real-time imaging of MMP-2 activity. The probes have the following features: (a) symmetrical fluorine atoms; (b) the number of fluorine atoms can be increased through facile chemical modification; (c) readily accessible peptide sequence as the MMP-2 substrate; (d) activatable ¹⁹F signal (off/on mode) via paramagnetic metal ion incorporation. Following optimization for water solubility, one of the probes was selected to evaluate MMP-2 activity by ¹⁹F magnetic resonance spectroscopy (MRS). Our results showed that the fluorine signal increased by 8.5-fold in the presence of MMP-2. The specific cleavage site was verified by mass spectrometry. The selected probe was further applied to detect secreted MMP-2 activity of living SCC7 squamous cell carcinoma cells. The fluorine signal was increased by 4.8-fold by MRS analysis after 24 h incubation with SCC7 cells. This type of fluorine probe can be applied to evaluate other enzyme activities by simply tuning the substrate structures. This symmetrical fluorine dendron-based probe design extends the scope of the existing ¹⁹F MRI agents and provides a simple but robust method for real-time ¹⁹F MRI application.

NIH workshop on clinical translation of molecular imaging probes and technology--meeting report

A workshop on "Clinical Translation of Molecular Imaging Probes and Technology" was held August 2, 2013 in Bethesda, Maryland, organized and supported by the National Institute of Biomedical Imaging and Bioengineering (NIBIB). This workshop brought together researchers, clinicians, representatives from pharmaceutical companies, molecular probe developers, and regulatory science experts. Attendees met to talk over current challenges in the discovery, validation, and translation of molecular imaging (MI) probes for key clinical applications. Participants also discussed potential strategies to address these challenges. The workshop consisted of 4 sessions, with 14 presentations and 2 panel discussions. Topics of discussion included (1) challenges and opportunities for clinical research and patient care, (2) advances in molecular probe design, (3) current approaches used by industry and pharmaceutical companies, and (4) clinical translation of MI probes. In the presentations and discussions, there were general agreement that while the barriers for validation and translation of MI probes remain high, there are pressing clinical needs and development opportunities for targets in cardiovascular, cancer, endocrine, neurological, and inflammatory diseases. The strengths of different imaging modalities, and the synergy of multimodality imaging, were highlighted. Participants also underscored the continuing need for close interactions and collaborations between academic and industrial partners, and federal agencies in the imaging probe development process.

Ultrasound-mediated gene and drug delivery using a microbubble-liposome particle system

Theranostic agents present a promising clinical approach for cancer detection and treatment. We herein introduce a microbubble and liposome complex (MB-Lipo) developed for ultrasound (US) imaging and activation. The MB-Lipo particles have a hybrid structure consisting of a MB complexed with multiple Lipos. The MB components are used to generate high echo signals in US imaging, while the Lipos serve as a versatile carrier of therapeutic materials. MB-Lipo allows high contrast US imaging of tumor sites. More importantly, the application of high acoustic pressure bursts MBs, which releases therapeutic Lipos and further enhances their intracellular delivery through sonoporation effect. Both imaging and drug release could thus be achieved by a single US modality, enabling in situ treatment guided by real-time imaging. The MB-Lipo system was applied to specifically deliver anti-cancer drug and genes to tumor cells, which showed enhanced therapeutic effect. We also demonstrate the clinical potential of MB-Lipo by imaging and treating tumor in vivo.

The effect of two novel amino acid-coated magnetic nanoparticles on survival in vascular endothelial cells, bone marrow stromal cells, and macrophages

Magnetic nanoparticles (MNPs) have been popularly used in many fields. Recently, many kinds of MNPs are modified as new absorbents, which have attracted considerable attention and are promising to be applied in waste water. In our previous study, we synthesized two novel MNPs surface-coated with glycine or lysine, which could efficiently remove many anionic and cationic dyes under severe conditions. It should be considered that MNP residues in water may exert some side effects on human health. In the present study, we evaluated the potential nanotoxicity of MNPs in human endothelial cells, macrophages, and rat bone marrow stromal cells. The results showed that the two kinds of nanoparticles were consistently absorbed into the cell cytoplasm. The concentration of MNPs@Gly that could distinctly decrease survival was 15 μg/ml in human umbilical vascular endothelial cells (HUVECs) or bone marrow stromal cells (BMSCs) and 10 μg/ml in macrophages. While the concentration of MNPs@Lys that obviously reduced viability was 15 μg/ml in HUVECs or macrophages and 50 μg/ml in BMSCs. Furthermore, cell nucleus staining and cell integrity assay indicated that the nanoparticles induced cell apoptosis, but not necrosis even at a high concentration. Altogether, these data suggest that the amino acid-coated magnetic nanoparticles exert relatively high cytotoxicity. By contrast, lysine-coated magnetic nanoparticles are more secure than glycine-coated magnetic nanoparticles.

Selective targeting of tumor and stromal cells by a nanocarrier system displaying lipidated cathepsin B inhibitor

Cathepsin B (CtsB) is a lysosomal cysteine proteinase that is specifically translocated to the extracellular milieu during cancer progression. The development of a lipidated CtsB inhibitor incorporated into the envelope of a liposomal nanocarrier (LNC-NS-629) is described. Ex vivo and in vivo studies confirmed selective targeting and internalization of LNC-NS-629 by tumor and stromal cells, thus validating CtsB targeting as a highly promising approach to cancer diagnosis and treatment.

Tumor-targeted prodrug ICT2588 demonstrates therapeutic activity against solid tumors and reduced potential for cardiovascular toxicity

Development of therapeutic strategies for tumor-selective delivery of therapeutics through exploitation of the proteolytic tumor phenotype has significant scope for improvement of cancer treatment. ICT2588 is a peptide-conjugated prodrug of the vascular disrupting agent (VDA) azademethylcolchicine developed to be selectively hydrolyzed by matrix metalloproteinase-14 (MMP-14) within the tumor. In this report, we extend our previous proof-of-concept studies and demonstrate the therapeutic potential of this agent against models of human colorectal, lung, breast, and prostate cancer. In all tumor types, ICT2588 was superior to azademethylcolchicine and was greater or comparable to standard clinically used agents for the respective tumor type. Prodrug activation in clinical human lung tumor homogenates relative to stability in human plasma and liver was observed, supporting clinical translation potential. A major limiting factor to the clinical value of VDAs is their inherent cardiovascular toxicity. No increase in plasma von Willebrand factor (vWF) levels, an indicator of systemic vascular dysfunction and acute cardiovascular toxicity, was detected with ICT2588, thereby supporting the tumor-selective activation and reduced potential of ICT2588 to cause cardiovascular toxicity. Our findings reinforce the improved therapeutic index and tumor-selective approach offered by ICT2588 and this nanotherapeutic approach.