An upconversion nanoplatform with extracellular pH-driven tumor-targeting ability for improved photodynamic therapy

Review of NIR-responsive ''Smart'' carriers for photothermal chemotherapy

This review focuses on the versatile applications of near-infrared (NIR)-responsive smart carriers in biomedical applications, particularly drug delivery and photothermal chemotherapy. These carriers demonstrate multi-responsive theranostics capabilities, including pH-dependent drug release, targeted delivery of chemotherapeutics, heat-mediated drug release, and photothermal tumor damage. Biological samples are transparent to NIR light with a suitable wavelength, and therefore, NIR light is advantageous for deep-tissue penetration. It also generates sufficient heat in tissue samples, which is beneficial for on-demand NIR-responsive drug delivery in vivo systems. The development of biocompatible materials with sufficient NIR light absorption properties and drug-carrying functionality has shown tremendous growth in the last five years. Thus, this review offers insights into the current research development of NIR-responsive materials with therapeutic potential and prospects aimed at overcoming challenges to improve the therapeutic efficacy and safety in the dynamic field of NIR-responsive drug delivery.

Prodrug-conjugated tumor-seeking commensals for targeted cancer therapy

Prodrugs have been explored as an alternative to conventional chemotherapy; however, their target specificity remains limited. The tumor microenvironment harbors a range of microorganisms that potentially serve as tumor-targeting vectors for delivering prodrugs. In this study, we harness bacteria-cancer interactions native to the tumor microbiome to achieve high target specificity for prodrug delivery. We identify an oral commensal strain of Lactobacillus plantarum with an intrinsic cancer-binding mechanism and engineer the strain to enable the surface loading of anticancer prodrugs, with nasopharyngeal carcinoma (NPC) as a model cancer. The engineered commensals show specific binding to NPC via OppA-mediated recognition of surface heparan sulfate, and the loaded prodrugs are activated by tumor-associated biosignals to release SN-38, a chemotherapy compound, near NPC. In vitro experiments demonstrate that the prodrug-loaded microbes significantly increase the potency of SN-38 against NPC cell lines, up to 10-fold. In a mouse xenograft model, intravenous injection of the engineered L. plantarum leads to bacterial colonization in NPC tumors and a 67% inhibition in tumor growth, enhancing the efficacy of SN-38 by 54%.

Engineering peptide drug therapeutics through chemical conjugation and implication in clinics

The development of peptide drugs has made tremendous progress in the past few decades because of the advancements in modification chemistry and analytical technologies. The novel-designed peptide drugs have been modified through various biochemical methods with improved diagnostic, therapeutic, and drug-delivery strategies. Researchers found it a helping hand to overcome the inherent limitations of peptides and bring continued advancements in their applications. Furthermore, the emergence of peptide-drug conjugates (PDCs)-utilizes target-oriented peptide moieties as a vehicle for cytotoxic payloads via conjugation with cleavable chemical agents, resulting in the key foundation of the new era of targeted peptide drugs. This review summarizes the various classifications of peptide drugs, suitable chemical modification strategies to improve the ADME (adsorption, distribution, metabolism, and excretion) features of peptide drugs, and recent (2015-early 2024) progress/achievements in peptide-based drug delivery systems as well as their fruitful implication in preclinical and clinical studies. Furthermore, we also summarized the brief description of other types of PDCs, including peptide-MOF conjugates and peptide-UCNP conjugates. The principal aim is to provide scattered and diversified knowledge in one place and to help researchers understand the pinching knots in the science of PDC development and progress toward a bright future of novel peptide drugs.

Recent Advances in Imaging Agents Anchored with pH (Low) Insertion Peptides for Cancer Theranostics

The acidic extracellular microenvironment has become an effective target for diagnosing and treating tumors. A pH (low) insertion peptide (pHLIP) is a kind of peptide that can spontaneously fold into a transmembrane helix in an acidic microenvironment, and then insert into and cross the cell membrane for material transfer. The characteristics of the acidic tumor microenvironment provide a new method for pH-targeted molecular imaging and tumor-targeted therapy. As research has increased, the role of pHLIP as an imaging agent carrier in the field of tumor theranostics has become increasingly prominent. In this paper, we describe the current applications of pHLIP-anchored imaging agents for tumor diagnosis and treatment in terms of different molecular imaging methods, including magnetic resonance T1 imaging, magnetic resonance T2 imaging, SPECT/PET, fluorescence imaging, and photoacoustic imaging. Additionally, we discuss relevant challenges and future development prospects.

Recent Advances in Near Infrared Upconverting Nanomaterials for Targeted Photodynamic Therapy of Cancer

Photodynamic therapy (PDT) is a well-established treatment of cancer that uses the toxic reactive oxygen species, including singlet oxygen (1O2), generated by photosensitiser drugs following irradiation of a specific wavelength to destroy the cancerous cells and tumours. Visible light is commonly used as the excitation source in PDT, which is not ideal for cancer treatment due to its reduced tissue penetration, and thus inefficiency to treat deep-lying tumours. Additionally, these wavelengths exhibit elevated autofluorescence background from the biological tissues which hinders optical biomedical imaging. An alternative to UV-Vis irradiation is the use of near infrared (NIR) excitation for PDT. This can be achieved using upconverting nanoparticles (UCNPs) functionalised with photosensitiser (PS) drugs where UCNPs can be used as an indirect excitation source for the activation of PS drugs yielding to the production of singlet 1O2 following NIR excitation. The use of nanoparticles for PDT is also beneficial due to their tumour targeting capability, either passively via the enhanced permeability and retention (EPR) effect or actively via stimuli-responsive targeting and ligand-mediated targeting (ie. using recognition units that can bind specific receptors only present or overexpressed on tumour cells). Here, we review recent advances in NIR upconverting nanomaterials for PDT of cancer with a clear distinction between those reported nanoparticles that could potentially target the tumour due to accumulation via the EPR effect (passive targeting) and nanoparticle-based systems that contain targeting agents with the aim of actively target the tumour via a molecular recognition process.

Roles of key residues and lipid dynamics reveal pHLIP-membrane interactions at intermediate pH

The pH-low insertion peptide (pHLIP) and its analogs sense the microenvironmental pH variations in tumorous cells and serve as useful anticancer drug deliveries. The pHLIP binds peripherally to membranes and adopts random coil conformation at the physiological pH. The peptide switches from random coil to α-helical conformation and inserts unidirectionally into membrane bilayers when pH drops below a critical transition value that has been routinely determined by the Trp fluorescence spectroscopy. Recent high-resolution studies using solid-state NMR spectroscopy revealed the presence of thermodynamically stable intermediate states of membrane-associated pHLIP around the fluorescence-based transition pH-value. However, the molecular structural features and their mechanistic roles of these intermediate states in the pH-driven membrane insertion process of pHLIP remain largely unknown. This work utilizes solid-state NMR spectroscopy to explore 1) the mechanistic roles of key proline and arginine residues within the pHLIP sequence at intermediate pH-values, and 2) the changes in lipid dynamics at intermediate pH-values in multiple types of model bilayers with anionic phospholipid and/or cholesterol. Our results demonstrate several molecular structural and dynamics changes at around the transition pH-values, including the isomerization of proline-threonine backbone configuration, breaking of arginine-aspartic acid salt bridge and the formation of arginine-lipid interactions, and a universal decreasing of dynamics in lipid headgroups and alkyl chains. Overall, the outcomes provide important insights on the molecular interactions between pHLIP and membrane bilayers at intermediate pH-values and, therefore, prompt the understanding of pH-driven membrane insertion process of this anticancer drug-delivering peptide.

The Peptide Functionalized Inorganic Nanoparticles for Cancer-Related Bioanalytical and Biomedical Applications

In order to improve their bioapplications, inorganic nanoparticles (NPs) are usually functionalized with specific biomolecules. Peptides with short amino acid sequences have attracted great attention in the NP functionalization since they are easy to be synthesized on a large scale by the automatic synthesizer and can integrate various functionalities including specific biorecognition and therapeutic function into one sequence. Conjugation of peptides with NPs can generate novel theranostic/drug delivery nanosystems with active tumor targeting ability and efficient nanosensing platforms for sensitive detection of various analytes, such as heavy metallic ions and biomarkers. Massive studies demonstrate that applications of the peptide-NP bioconjugates can help to achieve the precise diagnosis and therapy of diseases. In particular, the peptide-NP bioconjugates show tremendous potential for development of effective anti-tumor nanomedicines. This review provides an overview of the effects of properties of peptide functionalized NPs on precise diagnostics and therapy of cancers through summarizing the recent publications on the applications of peptide-NP bioconjugates for biomarkers (antigens and enzymes) and carcinogens (e.g., heavy metallic ions) detection, drug delivery, and imaging-guided therapy. The current challenges and future prospects of the subject are also discussed.

Multi-Smart and Scalable Bioligands-Free Nanomedical Platform for Intratumorally Targeted Tambjamine Delivery, a Difficult to Administrate Highly Cytotoxic Drug

Cancer is one of the leading causes of mortality worldwide due, in part, to limited success of some current therapeutic approaches. The clinical potential of many promising drugs is restricted by their systemic toxicity and lack of selectivity towards cancer cells, leading to insufficient drug concentration at the tumor site. To overcome these hurdles, we developed a novel drug delivery system based on polyurea/polyurethane nanocapsules (NCs) showing pH-synchronized amphoteric properties that facilitate their accumulation and selectivity into acidic tissues, such as tumor microenvironment. We have demonstrated that the anticancer drug used in this study, a hydrophobic anionophore named T21, increases its cytotoxic activity in acidic conditions when nanoencapsulated, which correlates with a more efficient cellular internalization. A biodistribution assay performed in mice has shown that the NCs are able to reach the tumor and the observed systemic toxicity of the free drug is significantly reduced in vivo when nanoencapsulated. Additionally, T21 antitumor activity is preserved, accompanied by tumor mass reduction compared to control mice. Altogether, this work shows these NCs as a potential drug delivery system able to reach the tumor microenvironment, reducing the undesired systemic toxic effects. Moreover, these nanosystems are prepared under scalable methodologies and straightforward process, and provide tumor selectivity through a smart mechanism independent of targeting ligands.

Optimal fluorescence and photosensitivity properties of dual-functional NaYb1−xF4:Tmx3+ nanoparticles for applications in imaging guided photodynamic therapy

The fluorescence and photosensitivity properties of NaYb_1−xF₄:Tm_x³⁺ nanoparticles were optimized to develop noninvasive near-infrared fluorescence imaging-guided photodynamic therapy. The emission at 800 nm from Tm³⁺ presented an exponential increase with an increase in the Tm³⁺ doping concentration from 0 to 2%. The photosensitivity properties of NaYb_1−xF₄:Tm_x³⁺ nanoparticles were also studied via the chemoprobe method, which used a reactive oxygen quencher, 1,3-diphenylisobenzofuran (DPBF). With the increase in the doping concentration of Tm³⁺, the generation rate of reactive oxygen species in NaYb_1−xF₄:Tm_x³⁺ nanoparticles decreased linearly at a rate of 0.3. The doping concentration of Tm³⁺ had two opposite effects on the 800 nm emission and generation rates of reactive oxygen species. The competitive relationship was discussed and an optimal value for the Tm³⁺ doping concentration of approximately 1% was determined. At this concentration, the energy of the Yb³⁺ excited state can be fully utilized, and the fluorescence and photosensitivity properties are an effective combination.

An optimal Tm³⁺ concentration of approximately 1% was determined for the most efficient energy distribution to balance imaging and PDT.

Designing Stimuli-Responsive Upconversion Nanoparticles that Exploit the Tumor Microenvironment

Tailoring personalized cancer nanomedicines demands detailed understanding of the tumor microenvironment. In recent years, smart upconversion nanoparticles with the ability to exploit the unique characteristics of the tumor microenvironment for precise targeting have been designed. To activate upconversion nanoparticles, various bio-physicochemical characteristics of the tumor microenvironment, namely, acidic pH, redox reactants, and hypoxia, are exploited. Stimuli-responsive upconversion nanoparticles also utilize the excessive presence of adenosine triphosphate (ATP), riboflavin, and Zn²⁺ in tumors. An overview of the design of stimulus-responsive upconversion nanoparticles that precisely target and respond to tumors via targeting the tumor microenvironment and intracellular signals is provided. Detailed understanding of the tumor microenvironment and the personalized design of upconversion nanoparticles will result in more effective clinical translation.

Activatable Photodynamic Therapy with Therapeutic Effect Prediction Based on a Self-correction Upconversion Nanoprobe

Though emerging as a promising therapeutic approach for cancers, the crucial challenge for photodynamic therapy (PDT) is activatable phototoxicity for selective cancer cell destruction with low "off-target" damage and simultaneous therapeutic effect prediction. Here, we design an upconversion nanoprobe for intracellular cathepsin B (CaB)-responsive PDT with in situ self-corrected therapeutic effect prediction. The upconversion nanoprobe is composed of multishelled upconversion nanoparticles (UCNPs) NaYF₄:Gd@NaYF₄:Er,Yb@NaYF₄:Nd,Yb, which covalently modified with an antenna molecule 800CW for UCNPs luminance enhancement under NIR irradiation, photosensitizer Rose Bengal (RB) for PDT, Cy3 for therapeutic effect prediction, and CaB substrate peptide labeled with a QSY7 quencher. The energy of UCNPs emission at 540 nm is transferred to Cy3/RB and eventually quenched by QSY7 via two continuous luminance resonance energy transfer processes from interior UCNPs to its surface-extended QSY7. The intracellular CaB specifically cleaves peptide to release QSY7, which correspondingly activates RB with reactive oxygen species (ROS) generation for PDT and recovers Cy3 luminance for CaB imaging. UCNPs emission at 540 nm remains unchanged during the peptide cleavage process, which is served as an internal standard for Cy3 luminance correction, and the fluorescence intensity ratio of Cy3 over UCNPs (FI583/FI540) is measured for self-corrected therapeutic effect prediction. The proposed self-corrected upconversion nanoprobe implies significant potential in precise tumor therapy.

Recent progress in the augmentation of reactive species with nanoplatforms for cancer therapy

Reactive species (RS), mainly including reactive oxygen species (ROS) and reactive nitrogen species (RNS), are indispensable in a wide variety of biological processes. RS often have elevated levels in cancer cells and tumor microenvironments. They also have a dual effect on cancer: on the one hand, they promote pro-tumorigenic signaling to facilitate tumor survival and on the other hand, they promote antitumorigenic pathways to induce cell death. Excessive RS would disrupt the cellular redox homeostasis balance and show partiality as oxidants, which would cause irreversible damage to the adjacent biomolecules such as lipids, proteins and nucleic acids. The altered redox environment and the corresponding increased antioxidant capacity in cancer cells render the cells susceptible to RS-manipulated therapies, especially the augmentation of RS. With the rapid development of nanotechnology and nanomedicine, a large number of cancer therapeutic nanoplatforms have been developed to trigger RS overproduction by exogenous and/or endogenous stimulation. In this review, we highlighted the latest progress in the nanoplatforms designed for the augmentation of RS in cancer therapy. Nanoplatforms based on strategies including disabling the antioxidant defense system, photodynamic therapy (PDT), sonodynamic therapy (SDT), and chemodynamic therapy (CDT) were introduced. The crucial obstacles involved in these strategies, such as the light penetration limitation of PDT, relatively low RS release by SDT, and strict conditions of Fenton reaction-mediated CDT, were also discussed, and feasible solutions for improvement were proposed. Furthermore, synergistic therapies among individual therapeutic modalities such as chemotherapy, photothermal therapy, and RS-based dynamic therapies were overviewed, which contributed to achieving more optimal anticancer efficacy than linear addition. This review sheds light on the development of non-invasive cancer therapy based on RS manipulation and provides guidance for establishing promising cancer therapeutic platforms in clinical settings.

Sharp pH-responsive mannose prodrug polypeptide nanoparticles encapsulating a photosensitizer for enhanced near infrared imaging-guided photodynamic therapy

Mannose has been reported as a novel drug to kill cancer cells. The prodrug of mannose will promote its targeted delivery and enrichment at the tumor site and cancer cells. Here, a pH-sensitive polypeptide copolymer with a tertiary amine group has been prepared and a mannose molecule was conjugated to the polymer through the formation of a Schiff base. At the same time, an iodinated boron dipyrromethene (BDPI) photosensitizer with high singlet oxygen generation efficacy and near infrared (NIR) fluorescence was encapsulated by the nanoparticles, which makes it a potential pH-sensitive NIR imaging-guided chemotherapy/PDT agent. In vitro and in vivo studies reveal that in a tumor acidic environment, the protonation of the tertiary amine group destroyed the nanostructure of the nanoparticles, resulting in increased BDPI release. Meanwhile, the bond cleavage of the Schiff base led to the release of conjugated mannose and synergistic inhibition of tumor cell growth with the PDT effect was realized. The combination of these two kinds of tumor suppression effects and photodynamic therapy made this pH-sensitive polypeptide delivery system show great potential for further cancer therapy.

Tumor self-responsive upconversion nanomedicines for theranostic applications

To date, malignant tumors continue to be the most lethal disease, causing more than 8.2 million deaths worldwide each year. In recent years, nanostructures based on rare-earth upconversion luminescent nanoparticles have shown significant advantages in the integration of multimodal imaging and therapy. Compared with normal tissues, the tumor microenvironment (TME) exhibits unique characteristics including high interstitial fluid pressure, abnormal blood vessels, a hypoxic and slightly acidic environment, and high levels of glutathione (GSH) and hydrogen peroxide (H2O2). According to these characteristics, increasing attention in the antitumor field has been given to designing nanomedicines with specific responses to the TME based on rare-earth upconversion nanoparticles (UCNPs) and to achieving efficient tumor diagnosis and treatment under the premise of reducing side effects. Nevertheless, a review that systematically summarizes TME-responsive upconversion nanomedicines (UCNMs) for realizing tumor self-enhanced theranostics has not been published to date. In this review, we summarize the recent progress made in UCNP-based nanotherapeutics by highlighting the increasingly developing trend of TME-responsive UCNMs. The general characteristics of the TME are introduced in detail and their utilization in designing TME-responsive UCNMs is systematically discussed. Based on NIR light-excited optical imaging, we discuss the superiority of UCNMs when applied in tumor theranostics with an emphasis on how to use them to realize TME-mediated multimodal imaging-guided therapy.

Triplet Tellurophene-Based Semiconducting Polymer Nanoparticles for Near-Infrared-Mediated Cancer Theranostics

Semiconducting polymer (SP) nanoparticles (NPs) have recently emerged as one of the most promising agents for photoacoustic imaging (PAI)-guided photothermal/photodynamic therapy (PTT/PDT). Herein, a triplet tellurophene-based SP (PNDI-2T) was synthesized with efficient tin-free direct heteroarylation polycondensation. The PNDI-2T NPs display remarkable near-infrared absorption and low cytotoxicity. In addition, PNDI-2T NPs can generate abundant reactive oxygen species (ROS) since tellurophene facilitates the intersystem crossing to generate triplet excited states. Remarkably, PNDI-2T NPs present a high photothermal conversion efficiency (η = 45%) and a high ROS yield (ΦΔ = 38.7%) under 808 nm laser irradiation. Furthermore, we showed that PNDI-2T NPs could be excellent PAI-guided PTT/PDT agents for cancer theranostics. This study provides a new route to developing highly efficient and low cytotoxic agents for PAI-guided PTT/PDT.

Effect of photodynamic therapy with (17R,18R)-2-(1-hexyloxyethyl)-2-devinyl chlorine E6 trisodium salt on pancreatic cancer cells in vitro and in vivo

AIM

To investigate the antitumor effects and underlying mechanisms of (17R,18R)-2-(1-hexyloxyethyl)-2-devinyl chlorine E6 trisodium salt (YLG-1)-induced photodynamic therapy (PDT) on pancreatic cancer in vitro and in vivo.

METHODS

YLG-1 is a novel photosensitizer extracted from spirulina. Its phototoxicity, cellular uptake and localization, as well as its effect on reactive oxygen species (ROS) production, apoptosis, and expression of apoptosis-associated proteins were detected in vitro. An in vivo imaging system (IVIS), the Lumina K imaging system, and mouse models of subcutaneous Panc-1-bearing tumors were exploited to evaluate the drug delivery pathway and pancreatic cancer growth in vivo.

RESULTS

YLG-1 was localized to the mitochondria, and the appropriate incubation time was 6 h. Under 650 nm light irradiation, YLG-1-PDT exerted a potent cytotoxic effect on pancreatic cancer cells in vitro, which could be abolished by the ROS scavenger N-acetyl-L-cysteine (NAC). The death mode caused by YLG-1-PDT was apoptosis, accompanied by upregulated Bax and cleaved Caspase-3 and decreased Bcl-2 expression. The results from the IVIS images suggested that the optimal administration route was intratumoral (IT) injection and that the best time to conduct YLG-1-PDT was 2 h post-IT injection. Consistent with the results in vitro, YLG-1-PDT showed great growth inhibition effects on pancreatic cancer cells in a mouse model.

CONCLUSION

YLG-1 is a potential photosensitizer for pancreatic cancer PDT via IT injection, the mechanisms of which are associated with inducing ROS and promoting apoptosis.

Y1-receptor-ligand-functionalized ultrasmall upconversion nanoparticles for tumor-targeted trimodality imaging and photodynamic therapy with low toxicity

Achieving efficient photodynamic therapy (PDT) in deeper biological tissue is still the biggest bottleneck that limits its widespread application in clinic. Although deeper biological tissue PDT could be realized through a combination of upconversion nanoparticles with a photosensitizer, issues with particle-size-induced upconversion fluorescence (UF) reduction and the related in vivo toxicity still cannot be solved properly. In this study, we synthesized Y1Rs-ligand [Pro30, Nle31, Bpa32, Leu34]NPY(28-36) (NPY)-modified and photosensitizer MC540-loaded LiLuF4:Yb,Er@nLiGdF4@mSiO2 multifunctional nanocomposites (MNPs) with a core-multishell structure and ultrasmall size. Their in vitro and in vivo breast tumor targeting, trimodality imaging performance, PDT therapeutic efficacy, and acute toxicity were evaluated. Our results demonstrated that the core-multishell MNPs(MC540) could achieve excellent UF imaging, and that doping with Gd3+ and Lu3+ rare earth ions could enhance the MR and CT imaging performance. In addition, the mSiO2 shell provided a higher loading rate for the photosensitizer MC540, and the DSPE-PEG thin layer coating outside the MNPs(MC540) further improved the water solubility and biocompatibility, reducing the acute toxicity of the nanocomposites. Finally, the NPY modification enhanced the targetability of MNPs(MC540)/DSPE-PEG-NPY to breast tumors, improving the trimodality UF, CT, and MR imaging performance and PDT efficacy for Y1-receptor-overexpressed breast cancer. In general, our developed multifunctional nanocomposites can serve as a theranostic agent with low toxicity, providing great potential for their use in clinical breast cancer diagnosis and therapy.