FeOOH-loaded mesoporous silica nanoparticles as a theranostic platform with pH-responsive MRI contrast enhancement and drug release

Recent development of pH-responsive theranostic nanoplatforms for magnetic resonance imaging-guided cancer therapy

The acidic characteristic of the tumor site is one of the most well-known features and provides a series of opportunities for cancer-specific theranostic strategies. In this regard, pH-responsive theranostic nanoplatforms that integrate diagnostic and therapeutic capabilities are highly developed. The fluidity of the tumor microenvironment (TME), with its temporal and spatial heterogeneities, makes noninvasive molecular magnetic resonance imaging (MRI) technology very desirable for imaging TME constituents and developing MRI-guided theranostic nanoplatforms for tumor-specific treatments. Therefore, various MRI-based theranostic strategies which employ assorted therapeutic modes have been drawn up for more efficient cancer therapy through the raised local concentration of therapeutic agents in pathological tissues. In this review, we summarize the pH-responsive mechanisms of organic components (including polymers, biological molecules, and organosilicas) as well as inorganic components (including metal coordination compounds, metal oxides, and metal salts) of theranostic nanoplatforms. Furthermore, we review the designs and applications of pH-responsive theranostic nanoplatforms for the diagnosis and treatment of cancer. In addition, the challenges and prospects in developing theranostic nanoplatforms with pH-responsiveness for cancer diagnosis and therapy are discussed.

Multifunctional Metal Complex-based Gene Delivery for tumor immune checkpoint blockade combination therapy

Immune checkpoint blocking based on the PD-1/PD-L1 pathway has shown exciting results in various types of cancer. However, due to the off-target effect of PD-1/PD-L1 blocker, low tumor immunogenicity and tumor immunosuppressive microenvironment, a significant proportion of patients do not benefit from this treatment. Here, we constructed a novel multifunctional metal complex Fe/PEI-Tn by the coordination of polyethyleneimine (PEI) with Fe³⁺ and the modification of bifunctional peptides Tn containing the cell penetrating peptide (TAT) and nuclear localization signal peptide (NLS), which was coated with hyaluronic acid (HA) to prolong the circulation time in vivo. Fe/PEI-Tn can condensate PD-L1 trap plasmid (pPD-L1 trap) and mediate PD-L1 trap protein expression in tumor tissues in situ, thus blocking the PD-1/PD-L1 pathway. Besides, Fe/PEI-Tn metal complex itself can act as an immune adjuvant to activate macrophages, reverse the phenotype of pro-tumor M2-type macrophages, and promote anti-tumor immunity. Meanwhile, Fe/PEI-Tn treatment can induce damage in tumor cells and release tumor-specific antigens into tumor microenvironment, thus stimulating anti-tumor immune response. Studies showed that HA/Fe/PEI-Tn/pPD-L1 trap complexes could promote the immune activation of tumor tissues and effectively delay tumor growth. This strategy provides a new direction for tumor combination therapy based on PD-1/PD-L1 blockade.

A pH-Activatable MnCO3 Nanoparticle for Improved Magnetic Resonance Imaging of Tumor Malignancy and Metastasis

Engineered magnetic nanoparticles have been extensively explored for magnetic resonance imaging (MRI) diagnosis of a tumor to improve the visibility. However, most of these nanoparticles display "always-on" signals without tumor specificity, causing insufficient contrast and false positives. Here, we provide a new paradigm of MRI diagnosis using MnCO₃ nanorhombohedras (MnNRs) as an ultrasensitive T₁-weighted MRI contrast agent, which smartly enhances the MR signal in response to the tumor microenvironment. MnNRs would quickly decompose and release Mn²⁺ at mild acidity, one of the pathophysiological parameters associated with cancer malignancy, and then Mn²⁺ binds to surrounding proteins to achieve a remarkable amplification of T₁ relaxivity. In vivo MRI experiments demonstrate that MnNRs can selectively brighten subcutaneous tumors from the edge to the interior may be because of the upregulated vascular permeation at the tumor edge, where cancer cell proliferation and angiogenesis are more active. Specially, benefiting from the T₂ shortening effect in normal liver tissues, MnNRs can detect millimeter-sized liver metastases with an ultrahigh contrast of 294%. The results also indicate an effective hepatic excretion of MnNRs through the gallbladder. As such, this pH-activatable MRI strategy with facility, biocompatibility, and excellent efficiency may open new avenues for tumor malignancy and metastasis diagnosis and holds great promise for precision medicine.

One-pot synthesis of AuPd@FexOy nanoagent with the activable Fe species for enhanced Chemodynamic-photothermal synergetic therapy

Facile fabrication of Fe-based nanotheranostic agents with the enhanced Chemodynamic therapy (CDT) effect and multiple functions is important for oncotherapy. In this report, noble-metal@Fe_xO_y core-shell nanoparticles (Au@Fe_xO_y NPs, AuRu@Fe_xO_y NPs, AuPt@Fe_xO_y NPs and AuPd@Fe_xO_y NPs) are one-pot constructed by a simply redox self-assembly strategy. As a typical example, AuPd@Fe_xO_y NPs are applied for oncotherapy. Compared to their crystalline counterparts (e.g., AuPd@c-Fe₂O₃ nanocrystals (NCs)), AuPd@Fe_xO_y NPs with the metastable Fe_xO_y shell can be activated by a small amount of NaBH₄ to obviously enhance the production of ·OH in subsequent Fenton reaction (these activated products are termed as r-AuPd@Fe_xO_y NPs). In addition, a favorable photothermal effect (63.5% photothermal conversion efficiency) of r-AuPd@Fe_xO_y NPs can further promote the ·OH generation. Moreover, r-AuPd@Fe_xO_y NPs also show a pH-responsive T₁-weighted MRI contrast property, CT imaging capacity and the function of regulating tumor microenvironment. This work presents an attractive route to prepare versatile nanotheranostic agents.

In situ embedding dual-Fe nanoparticles in synchronously generated carbon for the synergistic integration of magnetic resonance imaging and drug delivery

In situ incorporating versatile magnetic iron nanoparticles into ordered mesoporous carbon (OMC) by means of synthetic methodology for functional integration is a great challenge. Inspired by the phenomenon of uniovular twins in nature, a homometallic [Fe₉(μ₃-O)₄(O₃PPh)₃(O₂CCMe₃)₁₃] ({Fe₉P₃}) cluster was synthesized and used as the ovulum to in situ produce dual-Fe nanoparticle (γ-Fe₂O₃ and Fe(PO₃)₃)-functionalized OMC (dual-Fe/OMC). In vitro magnetic resonance imaging (MRI) studies showed a longitudinal relaxation (r ₁) and transverse relaxation (r ₂) of 9.74 and 26.59 mM^-1 s^-1 with a r ₂/r ₁ ratio of 2.73 at 0.5 T. The MRI performances were further examined by mouse model with a subcutaneous HeLa tumor. In addition, the low cytotoxicity, considerable loading capacity and delivery of doxorubicin hydrochloride (DOX) were also studied in vitro. These results demonstrate the feasibility of the concept of uniovular twins in the one-pot preparation of dual-Fe/OMC for functional integration.

Moderate cooling coprecipitation for extremely small iron oxide as a pH dependent T1-MRI contrast agent

Iron based nanomedicine (IBNM) has been one powerful diagnostic tool as a magnetic resonance imaging (MRI) contrast agent (CA) in the clinic for years. Conventional IBNMs are generally employed as T₂-MRI CAs, but most of them are constrained in clinical indication expansion by magnetic susceptibility artifacts. In comparison, extremely small iron oxide (ESIO) with a core size less than 5 nm has demonstrated the T₁-MRI effect, which provides prospects for a Gd-based agent alternative. Nevertheless, currently developed ESIOs for T₁-MRI CAs always require harsh conditions such as a high temperature and high boiling point reagent. Moreover, very few of the currently developed ESIOs meet the stringent pharmaceutical standard. Herein, on the basis of a crystal nuclear precipitation-dissolution equilibrium mechanism and outer/inner sphere T₁-MRI theory, monodisperse ESIOs with an average size of 3.43 nm (polydispersity index of 0.104) are fabricated using a moderate cooling procedure with mild coprecipitation reaction conditions. The as-synthesized ESIOs display around 3-fold higher T₁ MRI signal intensity than that of commercial Ferumoxytol (FMT), comparable to that of Gd-based CAs in vitro. Additionally, the T₁-MRI performance of the ESIOs is pH dependent and delivers bright signal augmentation. Eventually, the internalization into mesenchymal stem cells of the ESIO is realized in the absence of a transferring agent. Considering the identical structure and composition of the ESIOs as compared to that of FMT, they could meet the pharmaceutical criteria, thus providing great potential as T₁-MRI Cas, for instance as stem cell tracers.

Tale of Two Magnets: An Advanced Magnetic Targeting System

Magnetic targeting strategies employ external magnet fields to manipulate magnetic nanoparticles (MNPs) remotely, aiming to enhance their accumulation and penetration in vivo, which have received increasing attention in drug-delivery systems over the past decades. However, this approach has not yet been successful in translational clinical studies, largely due to the low efficacy and uncontrollable distribution of MNPs. The standard magnetic targeting strategy uses a single magnet and, thus, suffers from rapid drop-off of the magnetic field and field gradient with increasing distance away from the magnet surface. As a result, magnetic targeting of MNPs is often limited to superficial regions of interest. As reported in this issue of ACS Nano, Andrew Tsourkas and his colleagues showed that a two-magnet configuration can solve this dilemma by introducing a constant field gradient between the magnets for advanced magnetic targeting. The custom-built two-magnet device evidenced greatly enhanced accumulation and penetration of MNPs in a solid tumor model, shedding new light on future design considerations of magnetic targeting systems.

A glutathione-depleting chemodynamic therapy agent with photothermal and photoacoustic properties for tumor theranostics

Nowadays, Fenton reaction-based chemodynamic therapy (CDT) strategies have drawn extensive attention as tumor-specific nanomedicine-based therapy. Nevertheless, current existing CDTs normally suffer from therapeutic bottlenecks such as the scavenging of hydroxyl radical (˙OH) by intracellular antioxidants and unideal therapeutic outcome of single treatment modality. Herein, we constructed novel all-in-one AFP nanoparticles (NPs) as CDT agents through a one-pot process for multifunctional nanotheranostics. The as-constructed AFP NPs could simultaneously produce ˙OH through the Fenton reaction and scavenge intracellular glutathione, functioning as self-reinforced CDT agents to achieve tumor-triggered enhanced CDT (ECDT). In addition, the AFP NPs possessed the capability of H2O2 and acid-boosted photoacoustic imaging and photothermal therapy, enabling a precise and effective tumor therapeutic outcome with minimal nonspecific damage in combination with ECDT. Our novel nanoplatform would open new perspectives on multi-functional CDT agents for accurate and non-invasive tumor theranostics.

Intra/Extracellular Lactic Acid Exhaustion for Synergistic Metabolic Therapy and Immunotherapy of Tumors

Regulating the tumor microenvironment (TME) has been a promising strategy to improve antitumor therapy. Here, a red blood cell membrane (mRBC)-camouflaged hollow MnO₂ (HMnO₂ ) catalytic nanosystem embedded with lactate oxidase (LOX) and a glycolysis inhibitor (denoted as PMLR) is constructed for intra/extracellular lactic acid exhaustion as well as synergistic metabolic therapy and immunotherapy of tumor. Benefiting from the long-circulation property of the mRBC, the nanosystem can gradually accumulate in a tumor site through the enhanced permeability and retention (EPR) effect. The extracellular nanosystem consumes lactic acid in the TME by catalyzing its oxidation reaction via LOX. Meanwhile, the intracellular nanosystem releases the glycolysis inhibitor to cut off the source of lactic acid, as well as achieve antitumor metabolic therapy through the blockade of the adenosine triphosphate (ATP) supply. Both the extracellular and intracellular processes can be sensitized by O₂ , which can be produced during the decomposition of endogenous H₂ O₂ catalyzed by the PMLR nanosystem. The results show that the PMLR nanosystem can ceaselessly remove lactic acid, and then lead to an immunocompetent TME. Moreover, this TME regulation strategy can effectively improve the antitumor effect of anti-PDL1 therapy without the employment of any immune agonists to avoid the autoimmunity.

Fe2+/Fe3+ Ions Chelated with Ultrasmall Polydopamine Nanoparticles Induce Ferroptosis for Cancer Therapy

Ferroptosis, a promising mechanism of killing cancer cells, has become a research hotspot in cancer therapy. Besides, advantages of polymeric nanomaterials in improving anticancer efficacy and reducing side effect are widely accepted. In this work, based on the property of polypodamine to chelate metal ions, ultrasmall poly(ethylene glycol)-modified polydopamine nanoparticles, (UPDA-PEG)@Fe^2+/3+ nanoparticles, a novel ferroptosis agent, was rationally designed by chelating iron ions on ultrasmall polydopamine nanoparticles modified by PEG. This treatment led to a bigger specific surface area, which could support more reactive sites to chelate large number of iron ions, which is beneficial for exploring the detailed mechanism of ferroptosis-induced tumor cell death by iron ions. Also, the pH-dependent release of iron ions can reach approximately 70% at pH 5.0, providing the advantage of application in tumor microenvironment. The in vitro tests showed that the as-prepared NPs exhibit an effective anticancer effect on tumor cells including 4T1 and U87MG cells, yet ferric ions show a stronger ability of killing cancer cells than ferrous ions. Differences between ferrous ions and ferric ions in the ferroptosis pathway were monitored by the change of marker, including reactive oxygen species (ROS), glutathione peroxidase 4, and lipid peroxide (LPO), as well as the promoter and inhibitor of ferroptosis pathway. UPDA-PEG@Fe²⁺ nanoparticles induce ferroptosis that depends more on ROS; however, a more LPO-dependent ferroptosis is induced by UPDA-PEG@Fe³⁺ nanoparticles. Additionally, the in vivo studies using tumor-bearing Balb/c mice demonstrated that the as-prepared NPs could significantly inhibit tumor progression. UPDA-PEG@Fe^2+/3+ nanoparticles reported herein represent the nanoparticles related to iron ions for chemotherapy against cancer through the ferroptosis pathway.

Functional Mesoporous Silica Nanocomposites: Biomedical applications and Biosafety

The rise and development of nanotechnology has enabled the creation of a wide number of systems with new and advantageous features to treat cancer. However, in many cases, the lone application of these new nanotherapeutics has proven not to be enough to achieve acceptable therapeutic efficacies. Hence, to avoid these limitations, the scientific community has embarked on the development of single formulations capable of combining functionalities. Among all possible components, silica-either solid or mesoporous-has become of importance as connecting and coating material for these new-generation therapeutic nanodevices. In the present review, the most recent examples of fully inorganic silica-based functional composites are visited, paying particular attention to those with potential biomedical applicability. Additionally, some highlights will be given with respect to their possible biosafety issues based on their chemical composition.

Iron phosphide nanoparticles as a pH-responsive T1 contrast agent for magnetic resonance tumor imaging

In this work, the potential of FeP nanoparticles as a pH-responsive T₁ contrast agent was investigated. The FeP nanoparticles have good biocompatibility and can significantly amplify T₁ magnetic resonance signals in response to the acidic microenvironment of solid tumors, holding great promise in serving as an acid-activatable T₁ contrast agent for tumor imaging.

In this work, the potential of FeP nanoparticles as a pH-responsive T₁ contrast agent was investigated.