Sequential activation of anticancer therapy triggered by tumor microenvironment-selective imaging

Tumor microenvironment-responsive degradable silica nanoparticles: design principles and precision theranostic applications

Silica nanoparticles have emerged as promising candidates in the field of nanomedicine due to their remarkable versatility and customizable properties. However, concerns about their potential toxicity in healthy tissues and organs have hindered their widespread clinical translation. To address this challenge, significant attention has been directed toward a specific subset of silica nanoparticles, namely degradable silica nanoparticles, primarily because of their excellent biocompatibility and responsive biodegradability. In this review, we provide a comprehensive understanding of degradable silica nanoparticles, categorizing them into two distinct groups: inorganic species-doped and organic moiety-doped silica nanoparticles based on their framework components. Next, the recent progress of tumor microenvironment (TME)-responsive degradable silica nanoparticles for precision theranostic applications is summarized in detail. Finally, current bottlenecks and future opportunities of theranostic nanomedicines based on degradable silica nanoparticles in clinical applications are also outlined and discussed. The aim of this comprehensive review is to shed light on the potential of degradable silica nanoparticles in addressing current challenges in nanomedicine, offering insights into their design, applications in tumor diagnosis and treatment, and paving the way for future advancements in clinical theranostic nanomedicines.

Enzyme-responsive macrocyclic metal complexes for biomedical imaging

Metal chelator-based contrast agents are used as tumor navigators for cancer diagnosis. Although approved metal chelators show excellent contrast performance in magnetic resonance imaging (MRI), large doses are required for cancer diagnoses due to rapid clearance and nonspecific accumulation throughout the body, which can compromise safety. The present study describes an enzyme-responsive metal delivery system, in which enzyme overexpressed in the tumor microenvironment selectively activates the tumor uptake of gadolinium (Gd). Gd was loaded into enzyme-responsive macrocyclam (ErMC) modified with a PEGylated enzyme-cleavable peptide resulting in Gd@ErMC. The PEGylated shell layer protected Gd@ErMC from nonspecific binding in the blood, increasing the half-life of the contrast agent. Specific cleavage of the PEGylated shell layer by the enzyme selectively liberated Gd from Gd@ErMC at the tumor site. Evaluation of the in vivo distribution of Gd@ErMC in tumor-bearing mice by MRI and positron emission tomography (PET) showed that Gd@ErMC had an extended half-life and was highly specific. Histological and serological analysis of Gd@ErMC-treated mice showed that this agent was safe. This novel enzyme-responsive contrast agent delivery system shows promise as specific theranostic agent for MR-guided radiotherapy.

Optimizing the enzymatic release of MMAE from isoDGR-based small molecule drug conjugate by incorporation of a GPLG-PABC enzymatically cleavable linker

Antibody-Drug Conjugates (ADCs) and Small Molecule-Drug Conjugates (SMDCs) represent successful examples of targeted drug-delivery technologies for overcoming unwanted side effects of conventional chemotherapy in cancer treatment. In both strategies, a cytotoxic payload is connected to the tumor homing moiety through a linker that releases the drug inside or in proximity of the tumor cell, and that represents a key component for the final therapeutic effect of the conjugate. Here, we show that the replacement of the Val-Ala-p-aminobenzyloxycarbamate linker with the Gly-Pro-Leu-Gly-p-aminobenzyloxycarbamate (GPLG-PABC) sequence as enzymatically cleavable linker in the SMDC bearing the cyclo[DKP-isoDGR] α_Vβ₃ integrin ligand as tumor homing moiety and the monomethyl auristatin E (MMAE) as cytotoxic payload led to a 4-fold more potent anti-tumoral effect of the final conjugate on different cancer cell lines. In addition, the synthesized conjugate resulted to be significantly more potent than the free MMAE when tested following the "kiss-and-run" protocol, and the relative potency were clearly consistent with the expression of the α_Vβ₃ integrin receptor in the considered cancer cell lines. In vitro enzymatic cleavage tests showed that the GPLG-PABC linker is cleaved by lysosomal enzymes, and that the released drug is observable already after 15 min of incubation. Although additional data are needed to fully characterize the releasing capacity of GPLG-PABC linker, our findings are of therapeutic significance since we are introducing an alternative to other well-established enzymatically sensitive peptide sequences that might be used in the future for generating more efficient and less toxic drug delivery systems.

DNA-cloaked nanoparticles for tumor microenvironment-responsive activation

Although progress has been made in developing tumor microenvironment-responsive delivery systems, the list of cargo-releasing stimuli remains limited. In this study, we report DNA nanothread-cloaked nanoparticles for reactive oxygen species (ROS)-rich tumor microenvironment-responsive delivery systems. ROS is well known to strongly induce DNA fragmentation via oxidative stress. As a model anticancer drug, hydrophobic omacetaxine was entrapped in branched cyclam ligand-modified nanoparticles (BNP). DNA nanothreads were prepared by rolling-circle amplification and complexed to BNP, yielding DNA nanothread-cloaked BNP (DBNP). DBNP was unmasked by DNA nanothread-degrading ROS and culture supernatants of LNCaP cells. The size and zeta potential of DBNP were changed by ROS. In ROS^high LNCaP cells, but not in ROS^low fibroblast cells, the uptake of DBNP was higher than that of other nanoparticles. Molecular imaging revealed that DBNP exhibited greater distribution to tumor tissues, compared to other nanoparticles. Ex vivo mass spectrometry-based imaging showed that omacetaxine metabolites were distributed in tumor tissues of mice treated with DBNP. Intravenous administration of DBNP reduced the tumor volume by 80% compared to untreated tumors. Profiling showed that omacetaxine treatment altered the transcriptional profile. These results collectively support the feasibility of using polymerized DNA-masked nanoparticles for selective activation in the ROS-rich tumor microenvironment.

NIR-I Dye-Based Probe: A New Window for Bimodal Tumor Theranostics

Near-infrared (NIR, 650–1700 nm) bioimaging has emerged as a powerful strategy in tumor diagnosis. In particular, NIR-I fluorescence imaging (650–950 nm) has drawn more attention, benefiting from the high quantum yield and good biocompatibility. Since their biomedical applications are slightly limited by their relatively low penetration depth, NIR-I fluorescence imaging probes have been under extensive development in recent years. This review summarizes the particular application of the NIR-I fluorescent dye-contained bimodal probes, with emphasis on related nanoprobes. These probes have enabled us to overcome the drawbacks of individual imaging modalities as well as achieve synergistic imaging. Meanwhile, the application of these NIR-I fluorescence-based bimodal probes for cancer theranostics is highlighted.

Fibroblast activation protein activated antifibrotic peptide delivery attenuates fibrosis in mouse models of liver fibrosis

In liver fibrosis, activated hepatic stellate cells are known to overexpress fibroblast activation protein. Here we report a targeted antifibrotic peptide-delivery system in which fibroblast activation protein, which is overexpressed in fibrotic regions of the liver, liberates the antifibrotic peptide melittin by cleaving a fibroblast activation protein-specific site in the peptide. The promelittin peptide is linked to pegylated and maleimide-functionalized liposomes, resulting in promelittin-modified liposomes. The promelittin-modified liposomes were effective in reducing the viability of activated hepatic stellate cells but not that of control cells. In three types of liver fibrosis mouse models, intravenously administered promelittin-modified liposomes significantly reduces fibrotic regions. In addition, in the bile duct ligation mouse model promelittin-modified liposome-treatment increases overall survival. Although this peptide-delivery concept was tested for liver fibrosis, it can potentially be adapted to other fibrotic diseases.

Activated hepatic stellate cells contribute towards the pathogenesis of liver fibrosis, and overexpress fibroblast activation protein. Here the authors report a targeted peptide-delivery system in which fibroblast activation protein liberates the antifibrotic peptide melittin, and demonstrate the approach attenuates fibrosis in mouse models of liver fibrosis.

Dynamic nano-assemblies based on two-dimensional inorganic nanoparticles: Construction and preclinical demonstration

Dynamic drug delivery systems (DDSs) have the ability of transforming their morphology and functionality in response to the biological microenvironments at the disease site and/or external stimuli, show spatio-temporally controllable drug delivery, and enhance the treatment efficacy. Due to the large surface area and modification flexibility, two-dimensional (2D) inorganic nanomaterials are being increasingly exploited for developing intelligent DDSs for biomedical applications. In this review, we summarize the engineering methodologies used to construct transformable 2D DDSs, including changing compositions, creating defects, and surface dot-coating with polymers, biomolecules, or nanodots. Then we present and discuss dynamic inorganic 2D DDSs whose transformation is driven by the diseased characteristics, such as pH gradient, redox, hypoxia, and enzyme in the tumor microenvironment as well as the external stimuli including light, magnetism, and ultrasound. Finally, the limitations and challenges of current transformable inorganic DDSs for clinical translation and their in vivo safety assessment are discussed.

Genome-Editing-Mediated Restructuring of Tumor Immune Microenvironment for Prevention of Metastasis

Modulating the tumor immune microenvironment to activate immune cells has been investigated to convert cold to hot tumors. Here, we report that metal-lipid hybrid nanoparticle (MLN)-mediated gene editing of transforming growth factor-β (TGF-β) can restructure the tumor microenvironment to an "immune activated" state for subsequent immunotherapy. MLNs with cationic lipids and elemental metallic Au inside were designed to deliver plasmid DNA encoding TGF-β single guide RNA and Cas9 protein (pC9sTgf) and to convert near-infrared light (NIR) to heat. Upon NIR irradiation, MLNs induced photothermal anticancer effects and calreticulin exposure on B16F10 cancer cells. Lipoplexes of pC9sTgf and MLN (pC9sTgf@MLN) provided gene editing of B16F10 cells and in vivo tumor tissues. In mice treated with pC9sTgf@MLNs and NIR irradiation, the tumor microenvironment showed increases in mature dendritic cells, cytotoxic T cells, and interferon-γ expression. In B16F10 tumor-bearing mice, intratumoral injection of pC9sTgf@MLNs and NIR irradiation resulted in ablation of primary tumors. Application of pC9sTgf@MLNs and NIR irradiation prevented the growth of secondarily challenged B16F10 cells at distant sites and B16F10 lung metastasis. Combined TGF-β gene editing and phototherapy is herein supported as a modality for restructuring the tumor immune microenvironment and preventing tumor recurrence.

Recent advances in graphene-family nanomaterials for effective drug delivery and phototherapy

INTRODUCTION

Owing to the unique properties of graphene, including large specific surface area, excellent thermal conductivity, and optical absorption, graphene-family nanomaterials (GFNs) have attracted extensive attention in biomedical applications, particularly in drug delivery and phototherapy.

AREAS COVERED

In this review, we point out several challenges involved in the clinical application of GFNs. Then, we provide an overview of the most recent publications about GFNs in biomedical applications, including diverse strategies for improving the biocompatibility, specific targeting and stimuli-responsiveness of GFNs for drug delivery, codelivery of drug and gene, photothermal therapy, photodynamic therapy, and multimodal combination therapy.

EXPERT OPINION

Although the application of GFNs is still in the preclinical stage, rational modification of GFNs with functional elements or making full use of GFNs-based multimodal combination therapy might show great potential in biomedicine for clinical application.

Melanin-loaded CpG DNA hydrogel for modulation of tumor immune microenvironment

Photothermal immunotherapy has emerged as one of the most potent approaches for cancer treatment, but this strategy has suffered from the lack of biodegradability of the photoresponsive materials. In this study, we aimed to develop biodegradable materials for photothermal immunotherapy. To this end, we designed a DNA CpG hydrogel (DH, generated by rolling-circle amplification), loaded it with bis-(3'-5')-cyclic dimeric guanosine monophosphate (G/DH), and coated the formulation with melanin (Mel/G/DH). Mel/G/DH exhibited a temperature increase upon near infrared (NIR) illumination. In vitro, Mel/G/DH plus NIR (808 nm) irradiation, induced the exposure of calreticulin on CT26 cancer cells, and significantly activated the maturation of dendritic cells (DC). In vivo, local administration of Mel/G/DH (+NIR) exerted photothermal killing of primary tumors and induced maturation of DC in lymph nodes. Treatment of primary tumors with Mel/G/DH(+NIR) prevented the growth of rechallenged tumors at a distant site. Survival was 100% in mice treated with Mel/G/DH(+NIR), 5-fold higher than the group treated with Mel/G(+NIR). Mel/G/DH(+NIR) treatment remodeled the immune microenvironment of distant tumors, increasing cytotoxic T cells and decreasing Treg cells. Taken together, the results of this study suggest the potential of Mel/G/DH as a platform for modulating tumor immune microenvironment aimed at preventing the recurrence of distant tumors.

Photosensitizer-Trapped Gold Nanocluster for Dual Light-Responsive Phototherapy

Photoresponsive nanomaterials have recently received great attention in the field of cancer therapy. Here, we report a photosensitizer-trapped gold nanocluster that can facilitate dual light-responsive cancer therapy. We utilized methylene blue (MB) as a model photosensitizer, gold nanocluster as a model photothermal agent, and a polymerized DNA as the backbone of the nanocluster. We synthesized MB-intercalated gold DNA nanocluster (GMDN) via reduction and clustering of gold ions on a template consisting of MB-intercalated long DNA. Upon GMDN treatment, cancer cells revealed clear cellular uptake of MB and gold clusters; following dual light irradiation (660 nm/808 nm), the cells showed reactive oxygen species generation and increased temperature. Significantly higher cancer cell death was observed in cells treated with GMDN and dual irradiation compared with non-irradiated or single light-irradiated cells. Mice systemically injected with GMDN showed enhanced tumor accumulation compared to that of free MB and exhibited increased temperature upon near infrared irradiation of the tumor site. Tumor growth was almost completely inhibited in GMDN-treated tumor-bearing mice after dual light irradiation, and the survival rate of this group was 100% over more than 60 days. These findings suggest that GMDN could potentially function as an effective phototherapeutic for the treatment of cancer disease.

Tannic acid-functionalized boron nitride nanosheets for theranostics

Here, we report a tannic acid-Fe³⁺ coordination complex coating that confers magnetic resonance imaging (MRI) theranostic properties to inert nanomaterials. Boron nitride nanosheets (BNS), which lack magnetic field and light responsiveness, were used as a model nonfunctional nanomaterial. Among various catechol derivatives tested (i.e., dopamine, 3,4-dihydroxyphenylacetic acid, gallic acid, and tannic acid), a coating of tannic acid-Fe³⁺ coordination complex provided the highest magnetic field relaxivity and near infrared (NIR) laser light responsiveness. An in vitro study showed that KB tumor cells treated with tannic acid-Fe³⁺ coordination complex adsorbed on BNS (TA-Fe/BNS) exhibited higher T1-weighted magnetic resonance contrast compared with plain BNS, and BNS coated with tannic acid or Fe alone. NIR irradiation at 808 nm caused a significant increase in KB tumor cell death after treatment with TA-Fe/BNS compared with other treatments. In vivo MRI imaging revealed tumor accumulation of intravenously administered TA-Fe/BNS. Guided by MRI information, application of focused laser irradiation onto tumor tissues resulted in complete tumor ablation. These results support the potential of TA-Fe/BNS for MRI theranostics. Moreover, this study suggests the wide applicability of TA-Fe noncovalent coating as biocompatible and facile tool for converting nonfunctional early-generation nanomaterials into functional new nanomaterials, opening new opportunities for their use in translational biomedical applications such as MRI theranostics.