Recent Developments in Heteroatom/Metal-Doped Carbon Dot-Based Image-Guided Photodynamic Therapy for Cancer

Carbon nanodots (CNDs) are advanced nanomaterials with a size of 2–10 nm and are considered zero-dimensional carbonaceous materials. CNDs have received great attention in the area of cancer theranostics. The majority of review articles have shown the improvement of CNDs for use in cancer therapy and bioimaging applications. However, there is a minimal number of consolidated studies on the currently developed doped CNDs that are used in various ways in cancer therapies. Hence, in this review, we discuss the current developments in different types of heteroatom elements/metal ion-doped CNDs along with their preparations, physicochemical and biological properties, multimodal-imaging, and emerging applications in image-guided photodynamic therapies for cancer.

Carbon nanomaterials as emerging nanotherapeutic platforms to tackle the rising tide of cancer - A review

Cancer has become one of the main reasons for human death in recent years. Around 18 million new cancer cases and approximately 9.6 million deaths from cancer reported in 2018, and the annual number of cancer cases will have increased to 22 million in the next two decades. These alarming facts have rekindled researchers' attention to develop and apply different approaches for cancer therapy. Unfortunately, most of the applied methods for cancer therapy not only have adverse side effects like toxicity and damage of healthy cells but also have a short lifetime. To this end, introducing innovative and effective methods for cancer therapy is vital and necessary. Among different potential materials, carbon nanomaterials can cope with the rising threats of cancer. Due to unique physicochemical properties of different carbon nanomaterials including carbon, fullerene, carbon dots, graphite, single-walled carbon nanotube and multi-walled carbon nanotubes, they exhibit possibilities to address the drawbacks for cancer therapy. Carbon nanomaterials are prodigious materials due to their ability in drug delivery or remedial of small molecules. Functionalization of carbon nanomaterials can improve the cancer therapy process and decrement the side effects. These exceptional traits make carbon nanomaterials as versatile and prevalent materials for application in cancer therapy. This article spotlights the recent findings in cancer therapy using carbon nanomaterials (2015-till now). Different types of carbon nanomaterials and their utilization in cancer therapy were highlighted. The plausible mechanisms for the action of carbon nanomaterials in cancer therapy were elucidated and the advantages and disadvantages of each material were also illustrated. Finally, the current problems and future challenges for cancer therapy based on carbon nanomaterials were discussed.

Photoinactivation of mycobacteria to combat infection diseases: current state and perspectives

Abstract

The spread of multi-drug-resistant bacterial strains causing serious infectious diseases dictates the development of new approaches to combat these diseases. In addition to drug resistance, the important causative agent of tuberculosis (Mycobacterium tuberculosis (Mtb)) is able to persist asymptomatically in individuals for many years, causing latent forms of tuberculosis. In such a dormant state, Mtb cells are also resistant to known antibiotics. In this regard, photodynamic inactivation (PDI) could be an effective alternative to antibiotics as its action is based on the generation of active forms of oxygen independently on the presence of specific antibiotic targets, thereby inactivating both drug-resistant and dormant bacteria. In this review, we summarise examples of the application of PDI for the elimination of representatives of the genus Mycobacteria, both in vitro and in vivo. According to published results, including photosensitisers in the PDI regime results in a significantly higher lethal effect. Such experiments were mainly performed using chemically synthesised photosensitisers, which need to be transported to the areas of bacterial infections, limiting PDI usage by surface (skin) diseases. In this regard, endogenous photosensitisers (mainly porphyrins) could be used to solve the problem of transportation. In vitro experiments demonstrate the effective application of PDI for mycobacteria, including Mtb, using endogenous porphyrins; the intracellular contents of these substances can be elevated by administration of 5-aminolevulenic acid, a precursor of porphyrin synthesis. Photodynamic inactivation can also be used for dormant mycobacteria, which are characterised by high levels of endogenous porphyrins. Thus, PDI can effectively eliminate drug-resistant mycobacteria. The exploitation of modern light-transmitting techniques opens new possibilities to use PDI in clinical settings.

Key points

•The potential effects of photodynamic inactivation of mycobacteria are critically reviewed.

•Approaches to photoinactivation of mycobacteria using exogenous and endogenous photosensitisers are described.

•Prospects for the use of photodynamic inactivation in the treatment of tuberculosis are discussed.

OBP-functionalized/hybrid superparamagnetic nanoparticles for Candida albicans treatment

Infections caused by the opportunistic yeast Candida albicans are one of the major life threats for hospitalized and immunocompromised patients, as a result of antibiotic and long-term antifungal treatment abuse. Odorant binding proteins can be considered interesting candidates to develop systems able to reduce the proliferation and virulence of this yeast, because of their intrinsic antimicrobial properties and complexation capabilities toward farnesol, the major quorum sensing molecule of Candida albicans. In the present study, a hybrid system characterized by a superparamagnetic iron oxide core functionalized with bovine odorant binding protein (bOBP) was successfully developed. The nanoparticles were designed to be suitable for magnetic protein delivery to inflamed areas of the body. The inorganic superparamagnetic core was characterized by an average diameter of 6.5 ± 1.1 nm and a spherical shape. Nanoparticles were functionalized by using 11-phosphonoundecanoic acid as spacer and linked to bOBP via amide bonds, resulting in a concentration level of 26.0 ± 1.2 mg bOBP/g SPIONs. Finally, both the biocompatibility of the developed hybrid system and the fungistatic activity against Candida albicans by submicromolar OBP levels were demonstrated by in vitro experiments.

Recoverable peroxidase-like Fe3O4@MoS2-Ag nanozyme with enhanced antibacterial ability

Antibacterial agents with enzyme-like properties and bacteria-binding ability have provided an alternative method to efficiently disinfect drug-resistance microorganism. Herein, a Fe₃O₄@MoS₂-Ag nanozyme with defect-rich rough surface was constructed by a simple hydrothermal method and in-situ photodeposition of Ag nanoparticles. The nanozyme exhibited good antibacterial performance against E. coli (~69.4%) by the generated ROS and released Ag⁺, while the nanozyme could further achieve an excellent synergistic disinfection (~100%) by combining with the near-infrared photothermal property of Fe₃O₄@MoS₂-Ag. The antibacterial mechanism study showed that the antibacterial process was determined by the collaborative work of peroxidase-like activity, photothermal effect and leakage of Ag⁺. The defect-rich rough surface of MoS₂ layers facilitated the capture of bacteria, which enhanced the accurate and rapid attack of •OH and Ag⁺ to the membrane of E. coli with the assistance of local hyperthermia. This method showed broad-spectrum antibacterial performance against Gram-negative bacteria, Gram-positive bacteria, drug-resistant bacteria and fungal bacteria. Meanwhile, the magnetism of Fe₃O₄ was used to recycle the nanozyme. This work showed great potential of engineered nanozymes for efficient disinfection treatment.

Photodynamic therapy with nanoparticles to combat microbial infection and resistance

Infections caused by drug-resistant pathogens are rapidly increasing in incidence and pose an urgent global health concern. New treatments are needed to address this critical situation while preventing further resistance acquired by the pathogens. One promising approach is antimicrobial photodynamic therapy (PDT), a technique that selectively damages pathogenic cells through reactive oxygen species (ROS) that have been deliberately produced by light-activated chemical reactions via a photosensitiser. There are currently some limitations to its wider deployment, including aggregation, hydrophobicity, and sub-optimal penetration capabilities of the photosensitiser, all of which decrease the production of ROS and lead to reduced therapeutic performance. In combination with nanoparticles, however, these challenges may be overcome. Their small size, functionalisable structure, and large contact surface allow a high degree of internalization by cellular membranes and tissue barriers. In this review, we first summarise the mechanism of PDT action and the interaction between nanoparticles and the cell membrane. We then introduce the categorisation of nanoparticles in PDT, acting as nanocarriers, photosensitising molecules, and transducers, in which we highlight their use against a range of bacterial and fungal pathogens. We also compare the antimicrobial efficiency of nanoparticles to unbound photosensitisers and examine the relevant safety considerations. Finally, we discuss the use of nanoparticulate drug delivery systems in clinical applications of antimicrobial PDT.

Polypeptide-based self-healing hydrogels: Design and biomedical applications

Self-healing hydrogels can heal themselves on the damaged sites, which opens up a fascinating way for enhancing lifetimes of materials. Polypeptide/poly(amino acid) is a class of polymers in which natural amino acid monomers or derivatives are linked by amide bonds with a stable and similar secondary structure as natural proteins (α-helix or β-fold). They have the advantages of nontoxicity, biodegradability, and low immunogenicity as well as easy modification. All these properties make polypeptides extremely suitable for the preparation of self-healing hydrogels for biomedical applications. In this review, we mainly focus on the progress in the fabrication strategies of polypeptide-based self-healing hydrogels and their biomedical applications in the recent 5 years. Various crosslinking methods for the preparation of polypeptide-based self-healing hydrogels are first introduced, including host-guest interactions, hydrogen bonding, electrostatic interactions, supramolecular self-assembly of β-sheets, and reversible covalent bonds of imine and hydrazone as well as molecular multi-interactions. Some representative biomedical applications of these self-healing hydrogels such as delivery system, tissue engineering, 3D-bioprinting, antibacterial and wound healing as well as bioadhesion and hemostasis are also summarized. Current challenges and perspectives in future for these "smart" hydrogels are proposed at the end . STATEMENT OF SIGNIFICANCE: Polypeptides with the advantages of nontoxicity, biodegradability, hydrophilicity and low immunogenicity, are extremely suitable for the preparation of self-healing hydrogels in biomedical applications. Recently, the researches of polypeptide-based self-healing hydrogel have drawn the great attentions for scientists and engineers. A review to summarize the recent progress in design and biomedical applications of these polypeptide-based self-healing hydrogels is highly needed. In this review, we mainly focus on the progress in fabrication strategies of polypeptide-based self-healing hydrogels and biomedical applications in recent five years and aim to draw the increased attention to the importance of these "smart" hydrogels, facilitating the advances in biomedical applications. We believe this work would draw interest from readers of Acta Biomaterialia.

Concanavalin A-Rose Bengal bioconjugate for targeted Gram-negative antimicrobial photodynamic therapy

Photodynamic therapy (PDT) is considered a very promising therapeutic modality for antimicrobial therapy. Although several studies have demonstrated that Gram-positive bacteria are very sensitive to PDT, Gram-negative bacteria are more resistant to photodynamic action. This difference is due to a different cell wall structure. Gram-negative bacteria have an outer cell membrane containing lipopolysaccharides (LPS) that hinder the binding of photosensitizer molecules, protecting the bacterial cells from chemical attacks. Combination of the lipopolysaccharides-binding activity of Concanavalin A (ConA) with the photodynamic properties of Rose Bengal (RB) holds the potential of an innovative protein platform for targeted photodynamic therapy against Gram-negative bacteria. A ConA-RB bioconjugate was synthesized and characterized. Approximately 2.4 RB molecules were conjugated per ConA monomer. The conjugation of RB to ConA determines a decrease of the singlet oxygen generation and an increase of superoxide and peroxide production. The photokilling efficacy of the ConA-RB bioconjugate was demonstrated in a planktonic culture of E. coli. Irradiation with white light from a LED lamp produced a dose-dependent photokilling of bacteria. ConA-RB conjugates exhibited a consistent improvement over RB (up to 117-fold). The improved uptake of the photosensitizer explains the enhanced PDT effect accompanying increased membrane damages induced by the ConA-RB conjugate. The approach can be readily generalized (i) using different photo/sonosensitizers, (ii) to target other pathogens characterized by cell membranes containing lipopolysaccharides (LPS).

Ce6-Modified Carbon Dots for Multimodal-Imaging-Guided and Single-NIR-Laser-Triggered Photothermal/Photodynamic Synergistic Cancer Therapy by Reduced Irradiation Power

Photomediated cancer therapy, mainly including photothermal (PT) therapy (PTT) and photodynamic therapy (PDT), has attracted tremendous attention in recent years thanks to its noninvasive and stimuli-responsive features. The single mode of PTT or PDT, however, has obvious drawbacks, either requiring high-power laser irradiation to generate enough heat or only providing limited efficacy due to the hypoxia nature inside tumors. In addition, the reported synergistic PTT/PDT generally utilized two excitation sources to separately activate PTT and PDT, and the problem of high-power laser irradiation for PTT was still not well solved. Herein, a new concept, loading a small amount of photosensitizers onto a PTT agent (both of them can be triggered by a single-near-infrared (NIR) laser), was proposed to evade the shortcomings of PTT and PDT. To validate this idea, minute quantities of photosensitizer chlorin e6 (Ce6) (0.56% of mass) were anchored onto amino-rich red emissive carbon dots (RCDs) that possess superior photothermal (PT) character under 671 nm NIR laser (PT conversion efficiency to be 46%), and meanwhile the PDT of Ce6 can be activated by this laser irradiation as well. The findings demonstrate that Ce6-modified RCDs (named Ce6-RCDs) offer much higher cancer therapy efficacy under a reduced laser power density (i.e., 0.50 W cm^-2 at 671 nm) in vitro and in vivo than the equivalent RCDs or Ce6 under the same irradiation conditions. Besides, the Ce6-RCDs also exhibit multimodal imaging capabilities (i.e., fluorescence (FL), photoacoustic (PA), and PT), which can be employed for guidance of the phototherapy process. This study suggests not only a strategy to enhance cancer phototherapy efficacy but also a promising candidate (i.e., Ce6-RCDs) for multimodal FL/PA/PT imaging-guided and single-NIR-laser-triggered synergistic PTT/PDT for cancers by a reduced irradiation power.

Self-Assembled Antimicrobial Nanomaterials

Nanotechnology came to stay improving the quality of human life by reducing environmental contamination of earth and water with pathogens. This review discusses how self-assembled antimicrobial nanomaterials can contribute to maintain humans, their water and their environment inside safe boundaries to human life even though some of these nanomaterials display an overt toxicity. At the core of their strategic use, the self-assembled antimicrobial nanomaterials exhibit optimal and biomimetic organization leading to activity at low doses of their toxic components. Antimicrobial bilayer fragments, bilayer-covered or multilayered nanoparticles, functionalized inorganic or organic polymeric materials, coatings and hydrogels disclose their potential for environmental and public health applications in this review.

Modulation of the cooperativity in the assembly of multistranded supramolecular polymers

It is highly desirable that supramolecular polymers self-assemble following small changes in the environment. The degree of responsiveness depends on the degree of cooperativity at play during the assembly. Understanding how to modulate and quantify cooperativity is therefore highly desirable for the study and design of responsive polymers. Here we show that the cooperative assembly of a porphyrin-based, double-stranded polymer is triggered by changes in building blocks and in salt concentration. We develop a model that accounts for this responsiveness by assuming the binding of the salt countercations to the double-stranded polymer. Using our assembly model we generate plots that show the increase in concentration of polymer versus the normalized concentration of monomer. These plots are ideally suited to appreciate changes in cooperativity, and show that, for our system, these changes are consistent with the increase in polymer length observed experimentally. Unexpectedly, we find that polymer stability increases when cooperativity decreases. We attribute this behaviour to the fact that increasing salt concentration stabilizes the overall polymer more than the nucleus. In other words, the cooperativity factor α, defined as the ratio between the growth constant K_g and the nucleation constant K_n decreases as the overall stability of the polymer increases. Using our model to simulate the data, we generate cooperativity plots to explore changes in cooperativity for multistranded polymers. We find that, for the same pairwise association constants, the cooperativity sharply increases with the number of strands in the polymer. We attribute this dependence to the fact that the larger the number of strands, the larger is the nucleus necessary to trigger polymer growth. We show therefore that the cooperativity factor α does not properly account for the cooperativity behaviour of multistranded polymers, or any supramolecular polymer with a nucleus composed of more than 2 building blocks, and propose the use of the corrected cooperativity factor α_m. Finally, we show that multistranded polymers display highly cooperative polymerisation with pairwise association constants as low as 10 M^-1 between the building blocks, which should simplify the design of responsive supramolecular polymers.

Facile Supramolecular Approach to Nucleic-Acid-Driven Activatable Nanotheranostics That Overcome Drawbacks of Photodynamic Therapy

Supramolecular chemistry provides a "bottom-up" method to fabricate nanostructures for biomedical applications. Herein, we report a facile strategy to directly assemble a phthalocyanine photosensitizer (PcS) with an anticancer drug mitoxantrone (MA) to form uniform nanostructures (PcS-MA), which not only display nanoscale optical properties but also have the capability of undergoing nucleic-acid-responsive disassembly. These supramolecular assemblies possess activatable fluorescence emission and singlet oxygen generation associated with the formation of free PcS, mild photothermal heating, and a concomitant chemotherapeutic effect associated with the formation of free MA. In vivo evaluations indicate that PcS-MA nanostructures have a high level of accumulation in tumor tissues, are capable of being used for cancer imaging, and have significantly improved anticancer effect compared to that of PcS. This study demonstrates an attractive strategy for overcoming the limitations of photodynamic cancer therapy.

Light-triggered release of drug conjugates for an efficient combination of chemotherapy and photodynamic therapy

Herein, we present a series of light-triggered porphyrin-based polymeric drug conjugates PSDTD-m for combined chemo-photodynamic therapy of cancer.

Nanomaterials engineering for drug delivery: a hybridization approach

The last twenty years have witnessed great advances in biology, medicine, and materials science, leading to the development of various nanoparticle (NP)-mediated drug delivery systems. Innovation in materials science has led the generation of biodegradable, biocompatible, stimuli-responsive, and targeted delivery systems. However, currently available nanotherapeutic technologies are not efficient, which has culminated in the failure of their clinical trials. Despite huge efforts devoted to drug delivery nanotherapeutics, only a small amount of the injected material could reach the desired target. One promising strategy to enhance the efficiency of NP drug delivery is to hybridize multiple materials, where each component could play a critical role in an efficient multipurpose delivery system. This review aims to comprehensively cover different techniques, materials, advantages, and drawbacks of various systems to develop hybrid nano-vesicles for drug delivery. Attention is finally given to the hybridization benefits in overcoming the biological barriers for drug delivery. It is believed that the advent of modern nano-formulations for multifunctional hybrid carriers paves the way for future advances to achieve more efficient drug delivery systems.

Multivalence cooperativity leading to "all-or-nothing" assembly: the case of nucleation-growth in supramolecular polymers

All-or-nothing molecular assembly events, essential for the efficient regulation of living systems at the molecular level, are emerging properties of complex chemical systems that are largely attributed to the cooperativity of weak interactions. The link between the self-assembly and the interactions responsible for the assembly is however often poorly defined. In this work we demonstrate how the chelate effect (multivalence cooperativity) can play a central role in the regulation of the all-or-nothing assembly of structures (supramolecular polymers here), even if the building blocks are not multivalent. We have studied the formation of double-stranded supramolecular polymers formed from Co-metalloporphyrin and bi-pyridine building blocks. Their cooperative nucleation-elongation assembly can be summarized as a thermodynamic cycle, where the monomer weakly oligomerizes linearly or weakly dimerizes laterally. But thanks to the chelate effect, the lateral dimer readily oligomerizes linearly and the oligomer readily dimerizes laterally, leading to long double stranded polymers. A model based on this simple thermodynamic cycle can be applied to the assembly of polymers with any number of strands, and allows for the determination of the length of the polymer and the all-or-nothing switching concentration from the pairwise binding constants. The model, which is consistent with the behaviour of supramolecular polymers such as microtubules and gelators, clearly shows that all-or-nothing assembly is triggered by a change in the mode of assembly, from non-multivalent to multivalent, when a critical concentration is reached. We believe this model is applicable to many molecular assembly processes, ranging from the formation of cell-cell focal adhesion points to crystallization.

Water-soluble benzylidene cyclopentanone based photosensitizers for in vitro and in vivo antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy (aPDT) has been proposed to cope with the increasing antibiotic resistance among pathogens. As versatile pharmacophores, benzylidene cyclopentanone based photosensitizers (PSs) have been used in various bioactive materials. However, their reports as aPDT agents are very limited, and relationships between their chemical structures and antibacterial abilities have not been systematically discussed. Here, nine water-soluble benzylidene cyclopentanone PSs modified by polyethylene glycol (PEG), carboxylate anionic or pyridyl cationic agents are studied for aPDT. It is found that the binding/uptake abilities and aPDT effects of these PSs toward bacterial cells vary significantly when adjusting the number and position of their terminal charged groups. Though the comparable (also best) binding/uptake amounts are achieved by both cationic PS P3 and anionic PS Y1, only Y1 exhibits much more excellent aPDT activities than other PSs. Antibacterial mechanisms reveal that, relative to the favorable cell wall-binding of cationic PS P3, the anionic PS Y1 can accumulate more in the spheroplast/protoplast of methicillin-resistant Staphylococcus aureus (MRSA), which ensures its high efficient aPDT abilities both in vitro and in vivo. This study suggests the great clinical application potential of Y1 in inactivation of MRSA.

A nuclear targeted dual-photosensitizer for drug-resistant cancer therapy with NIR activated multiple ROS

A nuclear targeted dual-photosensitizer was developed for photodynamic therapy against multidrug resistant cancer. Multiple reactive oxygen species (ROS) could be generated in the nucleus to directly break DNA double strands with a single 980 nm NIR laser irradiation, regardless of drug resistance.

Photodynamic therapy against cancer, especially multidrug resistant cancer, is limited seriously due to the efflux of photosensitizer molecules by P-glycoprotein, which leads to insufficient production of reactive oxygen species (ROS). For the purpose of abundant ROS generation and effective therapeutic response, herein, we firstly design and fabricate a nuclear targeted dual-photosensitizer for photodynamic therapy against multidrug resistant cancer. Molecule-photosensitizer Ce6 was selected and modified on the surface of core/shell structure nano-photosensitizer upconversion@TiO₂ and then nuclear targeted peptides TAT were anchored for nuclear targeting. Through selective doping of rare earth elements Er and Tm, multiple ROS (˙OH, O₂˙^–, and ¹O₂) can be generated for the dual-photosensitizer and realize their functions synergistically using a single 980 nm NIR excitation. The nano-sized photosensitizer accompanied with nuclear targeting can effectively generate multiple ROS in the nucleus regardless of P-glycoprotein and directly break DNA double strands, which is considered as the most direct and serious lesion type for cytotoxic effects. Therefore, enhanced photodynamic therapy can be achieved against multidrug resistant cancer. In vitro and in vivo studies confirmed the excellent therapeutic effect of the dual-photosensitizer against cancer cells and drug-resistant cancer cells, as well as xenograft tumor models.

Incorporation of fluorophore-cholesterol conjugates into liposomal and mycobacterial membranes

Fluorescently-labeled steroids that emit intense blue light in nonpolar solvent (λem (CH2Cl2)≈440nm, ΦF=0.70) were prepared by treating cholesteryl chloroformate with 4-amino-1,8-naphthalimides. The lipid portion of the conjugates embeds into liposomal membrane bilayers in minutes, leaving the fluorophore exposed to the external aqueous environment. This causes a 40-nm red-shift in λem and significant quenching. DFT optimizations predict the conjugates to be about 30Å long when fully extended, but rotation about the linker group can bring the compounds into an 'L'-shape. Such a conformation would allow the cholesteryl anchor to remain parallel to the acyl chains of a membrane while the fluorescent group resides in the interfacial region, instead of extending beyond it. When incubated with Mycobacterium smegmatis mc2 155, a bacterial species known to use natural cholesterol, the labeled steroids support growth and can be found localized in the membrane fraction of the cells using HPLC. These findings demonstrate stable integration of fluorescent cholesterols into bacterial membranes in vivo, indicating that these compounds may be useful for evaluating cholesterol uptake in prokaryotic organisms.

A bivalent cationic dye enabling selective photo-inactivation against Gram-negative bacteria

Selective photoinactivation against Gram-negative bacteria over Gram-positive bacteria was successfully realized by a bivalent triarylmethane dye.