Two-Photon Fluorescence Imaging and Bimodal Phototherapy of Epidermal Cancer Cells with Biocompatible Self-Assembled Polymer Nanoparticles

Discrete Macrocyclic Polymer Hosts-Induced Cascade Luminescence Enhancement and Application in Bioimaging

The integration of polymers, supramolecular macrocycles and aggregation-induced emission (AIE) molecules provides numerous possibilities for constructing various functional supramolecular systems. Herein, we constructed supramolecular assembled systems based on discrete macrocyclic polymer hosts via the cooperation of hydra-headed macrocycles containing two or three pillar[5]arene units (defined as P2, P3), the block polymer F127 and AIE molecules (alkyl-cyano modified tetraphenylethene, alkyl-triazole-cyano modified 9,10-distyrylanthracene, defined as TPE-(CN)4 and DSA-(TACN)2). Compared with the binary assembly between hydra-headed hosts or F127 and AIE molecules, cascaded supramolecular assembly-induced emission enhancement (SAIEE) in aqueous solution was achieved in discrete macrocyclic polymer-based supramolecular assembled systems. Considering the cascaded SAIEE performance, we have successfully applied discrete macrocyclic polymer-based supramolecular assembled systems to bioimaging and constructed an artificial light-harvesting system (LHs) to explore more potential applications. The supramolecular assembly form of discrete macrocyclic polymers hosts and AIE molecules proposed in this work provides new inspiration for the construction and application of high-performance supramolecular luminescent systems.

Supramolecular red-light-photosensitized nitric oxide release with fluorescence self-reporting within biocompatible nanocarriers

The strict dependence of the biological effects of nitric oxide (NO) on its concentration and generation site requires this inorganic free radical to be delivered with precise spatiotemporal control. Light-activation by suitable NO photoprecursors represents an ideal approach. Developing strategies to activate NO release using long-wavelength excitation light in the therapeutic window (650-1300 nm) is challenging. In this contribution, we demonstrate that NO release by a blue-light activatable NO photodonor (NOPD) with self-fluorescence reporting can be triggered catalytically by the much more biocompatible red light exploiting a supramolecular photosensitization process. Different red-light absorbing photosensitizers (PSs) are co-entrapped with the NOPD within different biocompatible nanocarriers such as Pluronic® micelles, microemulsions and branched cyclodextrin polymers. The intra-carrier photosensitized NO release, involving the lowest, long-lived triplet state of the PS as the key intermediate and its quenching by the NOPD, is competitive with that by molecular oxygen. This allows NO to be released with good efficacy, even under aerobic conditions. Therefore, the adopted general strategy provides a valuable tool for generating NO from an already available NOPD, otherwise activatable with the poorly biocompatible blue light, without requiring any chemical modification and using sophisticated and expensive irradiation sources.

Mixed β-γ-Cyclodextrin Branched Polymer with Multiple Photo-Chemotherapeutic Cargos

The achievement of biocompatible platforms for multimodal therapies is one of the major challenges in the burgeoning field of nanomedicine. Here, we report on a mixed β- and γ-cyclodextrin-based branched polymeric material (βγCD-NOPD) covalently integrating a nitric oxide (NO) photodonor (NOPD) within its macromolecular scaffold, and its supramolecular ensemble with a singlet oxygen (1O2) photosensitizer (PS) Zn(II) phthalocyanine (ZnPc) and the chemodrug Lenvatinib (LVB). This polymer is highly water-soluble and generates NO under visible blue light stimuli with an efficiency of more than 1 order of magnitude higher than that of the single NOPD. The PS, which in an aqueous solution is aggregated and non-photoresponsive, can be entangled in the polymeric network as a photoresponsive monomeric species. In addition, the poorly water-soluble LVB can be co-encapsulated within the polymeric host, which increases the drug solubility by more than 30-fold compared to the free drug and more than 2-fold compared with a similar branched polymer containing only βCD units. The supramolecular nanoensemble, ca. 15 nm in diameter, retains well the photochemical properties of both the NOPD and PS, which can operate in parallel under light stimuli of different energies. Irradiation with blue and red light results in the photogeneration of NO and 1O2 associated with red fluorescence emission, without inducing any photodegradation of LVB. This result is not trivial and is due to the absence of significant, mutual interactions between the NOPD, the PS and LVB both in the ground and excited states, despite these components are confined in the same host. The proposed polymeric nanoplatform may represent a potential trimodal nanomedicine for biomedical research studies, since it combines the double photodynamic action of NO and 1O2, two species that do not suffer multidrug resistance, with the therapeutic activity of a conventional chemodrug.

Modulating Resonance Energy Transfer with Supramolecular Control in a Layered Hybrid Perovskite and Chromium Photosensitizer Assembly

Recently, the low-dimensional organic-inorganic halide perovskites (OIHP) have been exploited heavily for their favorable exciton dynamics, broad-band emission, remarkable stability, and tunable band-edge excited-state energy compared to their 3D counterparts for potential optoelectronic applications. Low-dimensional perovskites are generally good candidates for utilization as room-temperature photoluminescence (PL) materials. Further, doping divalent transition metals like Mn²⁺ into OIHP is expected to introduce a ⁴T₁-⁶A₁-based low-energy luminescence emission around 600 nm; an optical property that is favorable for biomedical optoelectronics. Doping Mn²⁺ in the perovskite lattice is also expected to induce the generation of cytotoxic singlet oxygen species (¹O₂), a ROS that is being exploited for various therapeutic applications. To integrate these optical and therapeutic properties of a 2D (PEA)₂PbBr₄ (Pb PeV; PEA = phenylethylammonium cation) perovskite alloyed with Mn²⁺ ions (Mn:PbPeV) and the option for a photoinduced energy transfer process involving a Cr(III)-based ¹O₂ generating photosensitizer (CrPS), we designed a unique purpose-built nanoassembly (Mn:PbPeV@PCD) using the encapsulation properties of a water-soluble polymer derived from β-cyclodextrin (PCD). Here the PCD is observed to modulate the classical internal energy transfer of Pb²⁺ exciton to alloyed Mn²⁺ orange emission, resulting in the emergence of a new blue emission. The addition of CrPS into the Mn:PbPeV@PCD to generate the CrPS@Mn:PbPeV@PCD assembly results in restoring perovskite luminescence followed by the external energy transfer to CrPS. We have elucidated the mechanism of these cascade energy transfer processes between multiple components using steady-state and time-resolved luminescence techniques. Efficient ROS generation and its potential to induce an oxidation reaction of a biomolecule are realized using guanine as the target molecule. Further photoinduced cleavage studies with biomolecules confirmed the efficacy of the nanoassembly in inducing the cleavage of guanine-rich DNA. The study opens up a new direction in the field of perovskite for biomedical applications.

A Supramolecular Nanoassembly of Lenvatinib and a Green Light-Activatable NO Releaser for Combined Chemo-Phototherapy

The chemotherapeutic Lenvatinib (LVB) and a nitric oxide (NO) photodonor based on a rhodamine antenna (RD-NO) activatable by the highly compatible green light are supramolecularly assembled by a β-cyclodextrin branched polymer (PolyCD). The poorly water-soluble LVB and RD-NO solubilize very well within the polymeric host leading to a ternary supramolecular nanoassembly with a diameter of ~55 nm. The efficiency of the NO photorelease and the typical red fluorescence of RD-NO significantly enhance within the polymer due to its active role in the photochemical and photophysical deactivation pathways. The co-presence of LVB within the same host does not affect either the nature or the efficiency of the photoinduced processes of RD-NO. Besides, irradiation of RD-NO does not lead to the decomposition of LVB, ruling out any intermolecular photoinduced process between the two guests despite sharing the same host. Ad-hoc devised Förster Resonance Energy Transfer experiments demonstrate this to be the result of the not close proximity of the two guests, which are confined in different compartments of the same polymeric host. The supramolecular complex is stable in a culture medium, and its biological activity has been evaluated against HEP-G2 hepatocarcinoma cell lines in the dark and under irradiation with visible green light, using LVB at a concentration well below the IC₅₀. Comparative experiments performed using the polymeric host encapsulating the individual LVB and RD-NO components under the same experimental conditions show that the moderate cell mortality induced by the ternary complex in the dark increases significantly upon irradiation with visible green light, more likely as the result of synergism between the NO photogenerated and the chemotherapeutic.

Green Synthesis of Near-Infrared Plasmonic Gold Nanostructures by Pomegranate Extract and Their Supramolecular Assembling with Chemo- and Photo-Therapeutics

Au nanostructures exhibiting a localized surface plasmon resonance in the near-infrared spectral window are obtained in a single, green step at room temperature by pomegranate extract in the presence of a highly biocompatible β-cyclodextrin branched polymer, without the need of preformed seeds, external reducing and sacrificial agents, and conventional surfactants. The polymeric component makes the Au nanostructures dispersible in water, stable for weeks and permits their supramolecular assembling with the chemotherapeutic sorafenib and a nitric oxide (NO) photodonor (NOPD), chosen as representative for chemo- and photo-therapeutics. Irradiation of the plasmonic Au nanostructures in the therapeutic window with 808 nm laser light results in a good photothermal response, which (i) is not affected by the presence of either the chemo- or the phototherapeutic guests and (ii) does not lead to their photoinduced decomposition. Besides, irradiation of the hybrid Au nanoassembly with the highly biocompatible green light results in the NO release from the NOPD with efficiency similar to that observed for the free guest. Preliminary biological experiments against Hep-G2 hepatocarcinoma cell lines are also reported.

Recent Advances in Biomedical Applications of Polymeric Nanoplatform Assisted with Two-Photon Absorption Process

Polymers are well-recognized carriers useful for delivering therapeutic drug and imaging probes to the target specified in the defined pathophysiological site. The functional drug molecules and imaging agents were chemically attached or physically loaded in the carrier polymer matrix via cleavable spacers. Using appropriate targeting moieties, these polymeric carriers (PCs) loaded with functional molecules were designed to realize target-specific delivery at the cellular level. The biodistribution of these carriers can be tracked using imaging agents with suitable imaging techniques. The drug molecules can be released by cleaving the spacers either by endogenous stimuli (e.g., pH, redox species, glucose level and enzymes) at the targeted physiological site or exogenous stimuli (e.g., light, electrical pulses, ultrasound and magnetism). Recently, two-photon absorption (2PA)-mediated drug delivery and imaging has gained significant attention because TPA from near-infrared light (700-950 nm, NIR) renders light energy similar to the one-photon absorption from ultraviolet (UV) light. NIR has been considered biologically safe unlike UV, which is harmful to soft tissues, cells and blood vessels. In addition to the heat and reactive oxygen species generating capability of 2PA molecules, 2PA-functionalized PCs were also found to be useful for treating diseases such as cancer by photothermal and photodynamic therapies. Herein, insights attained towards the design, synthesis and biomedical applications of 2PA-activated PCs are reviewed. In particular, specific focus is provided to the imaging and drug delivery applications with a special emphasis on multi-responsive platforms.

Implementation of Water-Soluble Cyclodextrin-Based Polymers in Biomedical Applications: How Far are we?

Cyclodextrin-based polymers can be prepared starting from the naturally occurring monomers following green and low-cost procedures. They can be selectively derivatized pre- or post-polymerization allowing to fine-tune functionalities of ad hoc customized polymers. Preparation nowadays has reached the 100 g scale thanks also to the interest of industries in these extremely versatile compounds. During the last 15 years these macromolecules have been the object of intense investigations in view of possible biomedical applications as the ultimate goal and large amounts of scientific data are now available. Compared to their monomeric models, already used in the formulation of various therapeutic agents, they display superior behavior in terms of their solubility in water and solubilizing power towards drugs incompatible with biological fluids. Moreover, they allow the combination of more than one type of therapeutic agent in the polymeric system. In this review we provide a complete state-of-the-art on the knowledge and potentialities of water-soluble cyclodextrin-based polymers as therapeutic agents as well as carrier systems for different types of therapeutics to implement combination therapy. Finally, we give a perspective on their assets for innovation in disease treatment as well as their limits that still need to be addressed. This article is protected by copyright. All rights reserved.

Enhancing the Anticancer Activity of Sorafenib through Its Combination with a Nitric Oxide Photodelivering β-Cyclodextrin Polymer

In this contribution, we report a strategy to enhance the therapeutic action of the chemotherapeutic Sorafenib (SRB) through its combination with a multifunctional β-cyclodextrin-based polymer able to deliver nitric oxide (NO) and emit green fluorescence upon visible light excitation (PolyCDNO). The basically water-insoluble SRB is effectively encapsulated in the polymeric host (1 mg mL⁻¹) up to a concentration of 18 μg mL⁻¹. The resulting host-guest supramolecular complex is able to release SRB in sink conditions and to preserve very well the photophysical and photochemical properties of the free PolyCDNO, as demonstrated by the similar values of the NO release and fluorescence emission quantum efficiencies found. The complex PolyCDNO/SRB internalizes in HEP-G2 hepatocarcinoma, MCF-7 breast cancer and ACHN kidney adenocarcinoma cells, localizing in all cases mainly at the cytoplasmic level. Biological experiments have been performed at SRB concentrations below the IC₅₀ and with light doses producing NO at nontoxic concentrations. The results demonstrate exceptional mortality levels for PolyCDNO/SRB upon visible light irradiation in all the different cell lines tested, indicating a clear synergistic action between the chemotherapeutic drug and the NO. These findings can open up exciting avenues to potentiate the anticancer action of SRB and, in principle, to reduce its side effects through its use at low dosages when in combination with the photo-regulated release of NO.

Macrophage Reprogramming and Cancer Therapeutics: Role of iNOS-Derived NO

Nitric oxide and its production by iNOS is an established mechanism critical to tumor promotion or suppression. Macrophages have important roles in immunity, development, and progression of cancer and have a controversial role in pro- and antitumoral effects. The tumor microenvironment consists of tumor-associated macrophages (TAM), among other cell types that influence the fate of the growing tumor. Depending on the microenvironment and various cues, macrophages polarize into a continuum represented by the M1-like pro-inflammatory phenotype or the anti-inflammatory M2-like phenotype; these two are predominant, while there are subsets and intermediates. Manipulating their plasticity through programming or reprogramming of M2-like to M1-like phenotypes presents the opportunity to maximize tumoricidal defenses. The dual role of iNOS-derived NO also influences TAM activity by repolarization to tumoricidal M1-type phenotype. Regulatory pathways and immunomodulation achieve this through miRNA that may inhibit the immunosuppressive tumor microenvironment. This review summarizes the classical physiology of macrophages and polarization, iNOS activities, and evidence towards TAM reprogramming with current information in glioblastoma and melanoma models, and the immunomodulatory and therapeutic options using iNOS or NO-dependent strategies.

More than skin deep: using polymers to facilitate topical delivery of nitric oxide

Skin, the largest organ in the human body, provides several important functions, including providing protection from mechanical impacts, micro-organisms, radiation and chemicals; regulation of body temperature; the sensations of touch and temperature; and the synthesis of several substances including vitamin D, melanin, and keratin. Common dermatological disorders (CDDs) include inflammatory or immune-mediated skin diseases, skin infection, skin cancer, and wounds. In the treatment of skin disorders, topical administration has advantages over other routes of administration, and polymers are widely used as vehicles to facilitate the delivery of topical therapeutic agents, serving as matrices to keep therapeutic agents in contact with the skin. Nitric oxide (NO), a cellular signalling molecule, has attracted significant interest in treating a broad spectrum of diseases, including various skin disorders. However, there are a number of challenges in effectively delivering NO. It must be delivered in a controlled manner at sufficient concentrations to be efficacious and the delivery system must be stable during storage. The use of polymer-based systems to deliver NO topically can be an effective strategy to overcome these challenges. There are three main approaches for incorporating NO with polymers in topical delivery systems: (i) physical incorporation of NO donors into polymer bases; (ii) covalent attachment of NO donors to polymers; and (iii) encapsulation of NO donors in polymer-based particles. The latter two approaches provide the greatest control over NO release and have been used by numerous researchers in treating CDDs, including chronic wounds and skin cancer.

Applications of Photoinduced Phenomena in Supramolecularly Arranged Phthalocyanine Derivatives: A Perspective

This review focuses on the description of several examples of supramolecular assemblies of phthalocyanine derivatives differently functionalized and interfaced with diverse kinds of chemical species for photo-induced phenomena applications. In fact, the role of different substituents was investigated in order to tune peculiar aggregates formation as well as, with the same aim, the possibility to interface these derivatives with other molecular species, as electron donor and acceptor, carbon allotropes, cyclodextrins, protein cages, drugs. Phthalocyanine photo-physical features are indeed really interesting and appealing but need to be preserved and optimized. Here, we highlight that the supramolecular approach is a versatile method to build up very complex and functional architectures. Further, the possibility to minimize the organization energy and to facilitate the spontaneous assembly of the molecules, in numerous examples, has been demonstrated to be more useful and performing than the covalent approach.

Host-guest complexes - Boosting the performance of photosensitizers

In this review, we will show the diversity of supramolecular host-guest complexes of cyclodextrins, cucurbit[n]urils, calix[n]- and pillar[n]arenes with photosensitizers, like porphyrins and phthalocyanines. Host-guest complexes are one of the main building blocks in supramolecular chemistry. For example, they have been widely used to encapsulate hydrophobic drug molecules to enhance the bioavailability in the human body. In these days of multiresistant bacteria and difficulties in cancer therapy, supramolecular host-guest systems with photosensitizers for the photodynamic therapy(PDT) gain more and more interest. In general, photosensitizers with a (large) conjugated aromatic π-system are used, which tend to π-πstacking in aqueous media suppressing the cell toxicity by singletoxygen production quenching. This can be overcome by the formation of host-guest complexes. Besides that, encapsulation of the photosensitizers in host molecules can enhance the solubility, increase cellular uptake, lead to hydrogels, rotaxanes, and switchable systems.

Porphyrinoid-Cyclodextrin Assemblies in Biomedical Research: An Update

Porphyrinoids, well-known cofactors in fundamental processes of life, have stimulated interest as synthetic models of natural systems and integral components of photodynamic therapy, but their utilization is compromised by self-aggregation in aqueous media. The capacity of cyclodextrins to include hydrophobic molecules in their cavity provides porphyrinoids with a protective environment against oxidation and the ability to disperse efficiently in biological fluids. Moreover, engineered cyclodextrin-porphyrinoid assemblies enhance the photodynamic abilities of porphyrinoids, can carry chemotherapeutics for synergistic modalities, and can be enriched with functions including cell recognition, tissue penetration, and imaging. This Perspective includes synthetic porphyrinoid-cyclodextrin models of proteins participating in fundamental processes, such as enzymatic catalysis, respiration, and electron transfer. In addition, since porphyrinoid-cyclodextrin systems comprise third generation photosensitizers, recent developments for their utilization in photomedicine, that is, multimodal therapy for cancer (e.g., PDT, PTT) and antimicrobial treatment, and eventually in biocompatible therapeutic or diagnostic platforms for next-generation nanomedicine and theranostics are discussed.

Nitric Oxide (NO)-Releasing Macromolecules: Rational Design and Biomedical Applications

Nitric oxide (NO) has been recognized as a ubiquitous gaseous transmitter and the therapeutic potential has nowadays received increasing interest. However, NO cannot be easily directly administered due to its high reactivity in air and high concentration-dependent physiological roles. As such, a plethora of NO donors have been developed that can reversibly store and release NO under specific conditions. To enhance the stability and modulate the NO release profiles, small molecule-based NO donors were covalently linked to polymeric scaffolds, rendering them with multifunctional integration, prolonged release durations, and optimized therapeutic outcomes. In this minireview, we highlight the recent achievements of NO-releasing macromolecules in terms of chemical design and biomedical applications. We hope that more efforts could be devoted to this emerging yet promising field.

A phototherapeutic fluorescent β-cyclodextrin branched polymer delivering nitric oxide

A water soluble b-CD-branched polymer covalently binds a fluorescein moiety for imaging and a NO photodonor for therapy that can be operated in parallel upon visible light excitation.

Combination of PDT photosensitizers with NO photodononors

Combination of photodynamic therapy (PDT) with other treatment modalities is emerging as one of the most suitable strategies to increase the effectiveness of therapeutic action on cancer and bacterial diseases and to minimize side effects. This approach aims at exploiting the additive/synergistic effects arising from multiple therapeutic species acting on different mechanistic pathways. The coupling of PDT with photocontrolled release of nitric oxide (NO) through the appropriate assembly of PDT photosensitizers (PSs) and NO photodonors (NOPDs) may open up intriguing avenues towards new and still underexplored multimodal therapies not based on "conventional" drugs but entirely controlled by light stimuli. In this contribution, we present an overview of the most recent advances in this field, illustrating several strategies to assemble PSs and NOPDs allowing them to operate independently without reciprocal interferences and describing the potential applications with particular emphasis on their impact in anticancer and antibacterial research.

Use of Cyclodextrins in Anticancer Photodynamic Therapy Treatment

Photodynamic therapy (PDT) is mainly used to destroy cancerous cells; it combines the action of three components: a photoactivatable molecule or photosensitizer (PS), the light of an appropriate wavelength, and naturally occurring molecular oxygen. After light excitation of the PS, the excited PS then reacts with molecular oxygen to produce reactive oxygen species (ROS), leading to cellular damage. One of the drawbacks of PSs is their lack of solubility in water and body tissue fluids, thereby causing low bioavailability, drug-delivery efficiency, therapeutic efficacy, and ROS production. To improve the water-solubility and/or drug delivery of PSs, using cyclodextrins (CDs) is an interesting strategy. This review describes the in vitro or/and in vivo use of natural and derived CDs to improve antitumoral PDT efficiency in aqueous media. To achieve these goals, three types of binding modes of PSs with CDs are developed: non-covalent CD⁻PS inclusion complexes, covalent CD⁻PS conjugates, and CD⁻PS nanoassemblies. This review is divided into three parts: (1) non-covalent CD-PS inclusion complexes, covalent CD⁻PS conjugates, and CD⁻PS nanoassemblies, (2) incorporating CD⁻PS systems into hybrid nanoparticles (NPs) using up-converting or other types of NPs, and (3) CDs with fullerenes as PSs.

NIR fluorescent organic nanoparticles for photoinduced nitric oxide delivery with self monitoring and real time reporting abilities

Nitric oxide photodonor (NOD) conjugated perylene tetracarboxylate ester (TPT) based fluorescent organic TPT(NOD)₄ nanoparticles (NPs) with aggregation induced NIR emission have shown photoinduced nitric oxide delivery along with a red to green emission transition.

Self-assembled nanomaterials for synergistic antitumour therapy

Recent progress on self-assembled nanodrugs for anticancer treatment was discussed.

Self-assemble nanoparticles based on polypeptides containing C-terminal luminescent Pt-cysteine complex

The growing attention to the luminescent nanocarriers is strongly stimulated by their potential application as drug delivery systems and by the necessity to monitor their distribution in cells and tissues. In this communication we report on the synthesis of amphiphilic polypeptides bearing C-terminal phosphorescent label together with preparation of nanoparticles using the polypeptides obtained. The approach suggested is based on a unique and highly technological process where the new phosphorescent Pt-cysteine complex serves as initiator of the ring-opening polymerization of α-amino acid N-carboxyanhydrides to obtain the polypeptides bearing intact the platinum chromophore covalently bound to the polymer chain. It was established that the luminescent label retains unchanged its emission characteristics not only in the polypeptides but also in more complicated nanoaggregates such as the polymer derived amphiphilic block-copolymers and self-assembled nanoparticles. The phosphorescent nanoparticles display no cytotoxicity and hemolytic activity in the tested range of concentrations and easily internalize into living cells that makes possible in vivo cell visualization, including prospective application in time resolved imaging and drug delivery monitoring.

Polymeric Nanoparticles for Cancer Photodynamic Therapy

In chemotherapy a fine balance between therapeutic and toxic effects needs to be found for each patient, adapting standard combination protocols each time. Nanotherapeutics has been introduced into clinical practice for treating tumors with the aim of improving the therapeutic outcome of conventional therapies and of alleviating their toxicity and overcoming multidrug resistance. Photodynamic therapy (PDT) is a clinically approved, minimally invasive procedure emerging in cancer treatment. It involves the administration of a photosensitizer (PS) which, under light irradiation and in the presence of molecular oxygen, produces cytotoxic species. Unfortunately, most PSs lack specificity for tumor cells and are poorly soluble in aqueous media, where they can form aggregates with low photoactivity. Nanotechnological approaches in PDT (nanoPDT) can offer a valid option to deliver PSs in the body and to solve at least some of these issues. Currently, polymeric nanoparticles (NPs) are emerging as nanoPDT system because their features (size, surface properties, and release rate) can be readily manipulated by selecting appropriate materials in a vast range of possible candidates commercially available and by synthesizing novel tailor-made materials. Delivery of PSs through NPs offers a great opportunity to overcome PDT drawbacks based on the concept that a nanocarrier can drive therapeutic concentrations of PS to the tumor cells without generating any harmful effect in non-target tissues. Furthermore, carriers for nanoPDT can surmount solubility issues and the tendency of PS to aggregate, which can severely affect photophysical, chemical, and biological properties. Finally, multimodal NPs carrying different drugs/bioactive species with complementary mechanisms of cancer cell killing and incorporating an imaging agent can be developed. In the following, we describe the principles of PDT use in cancer and the pillars of rational design of nanoPDT carriers dictated by tumor and PS features. Then we illustrate the main nanoPDT systems demonstrating potential in preclinical models together with emerging concepts for their advanced design.

Light-Tunable Generation of Singlet Oxygen and Nitric Oxide with a Bichromophoric Molecular Hybrid: a Bimodal Approach to Killing Cancer Cells

The design, synthesis, photochemical properties, and biological evaluation of a novel photoactivatable bichromophoric conjugate are reported. The compound 1, [4-(4,4-difluoro-2,6-diiodo-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacen-8-yl)-N-(3-((4-nitro-3-(trifluoromethyl)phenyl)amino)propyl)butanamide] combines a 2,6-diiodo-1,3,5,7-tetramethyl BODIPY derivative as singlet oxygen ((1) O2 ) photosensitizer and 4-nitro-3-(trifluoromethyl)aniline (NOPD) as nitric oxide (NO) photodonor, joined by an alkyl spacer. These two chromogenic units absorb in distinct regions of the visible spectrum, and their individual photochemical properties are conserved in the molecular conjugate. Irradiation of the bichromophoric conjugate with green light afforded (1) O2 in high quantum yields, whereas (1) O2 production was negligible with the use of blue light; under this latter condition, NO was released. Photogeneration of NO and cytotoxic (1) O2 can therefore be regulated by appropriately tuning the excitation light wavelength and intensity. Tested on melanoma cancer cells, this resulted in amplified photomortality relative to that of a structurally correlated model compound 2 [4-(4,4-difluoro-2,6-diiodo-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacen-8-yl)-N-(3-(p-tolylamino)propyl)butanamide] deprived of the NO-release capacity. The cellular uptake of 1, evaluated by confocal fluorescence microscopy, showed that the product is localized in the cytoplasm.

Polystyrene Nanofiber Materials for Visible-Light-Driven Dual Antibacterial Action via Simultaneous Photogeneration of NO and O2((1)Δg)

This contribution reports on the preparation, characterization, and biological evaluation of electrospun polystyrene nanofiber materials engineered with a covalently grafted NO photodonor and ionically entangled tetracationic porphyrin and phthalocyanine photosensitizers. These photofunctional materials exhibit an effective and simultaneous photogeneration of two antibacterial species such as nitric oxide (NO) and singlet oxygen, O2((1)Δg) under illumination with visible light, as demonstrated by their direct detection using amperometric and time-resolved spectroscopic techniques. Dual-mode photoantibacterial action is demonstrated by antibacterial tests carried out on Escherichia coli.

Photoactivable platforms for nitric oxide delivery with fluorescence imaging

The multifaceted role nitric oxide (NO) plays in human physiology and pathophysiology has stimulated a massive interest on NO-releasing compounds for therapeutic purposes. A main issue associated with use of NO donors is the precise spatiotemporal control of the NO release, as its effects are strictly site- and dose-dependent. NO photochemical precursors permit surmounting this difficulty since triggering with light offers an exquisite control of location and timing of NO delivery. On the other hand, the combination of NO photodonors with fluorescent components remains an urgent need for image-guided phototherapeutic treatments based on the use of NO. Fluorescence techniques permit not only an easy tracking of the photoprecursor in a biological environment but also the real-time quantification of the NO photoreleased therein in a non-invasive fashion. In this Focus Review we seek to provide an overview of recent advances in photoactivable platforms developed in our and other laboratories which combine the photoregulated release of NO with fluorescent functionalities. We shall focus attention on NO photoreleasing systems exhibiting 1) persistent fluorescence and 2) photoactivable fluorescence signals, highlighting their logical design and potential developments for phototheranostics.

State of the art, challenges and perspectives in the design of nitric oxide-releasing polymeric nanomaterials for biomedical applications

Recently, an increasing number of publications have demonstrated the importance of the small molecule nitric oxide (NO) in several physiological and pathophysiological processes. NO acts as a key modulator in cardiovascular, immunological, neurological, and respiratory systems, and deficiencies in the production of NO or its inactivation has been associated with several pathologic conditions, ranging from hypertension to sexual dysfunction. Although the clinical administration of NO is still a challenge owing to its transient chemical nature, the combination of NO and nanocarriers based on biocompatible polymeric scaffolds has emerged as an efficient approach to overcome the difficulties associated with the biomedical administration of NO. Indeed, significant progress has been achieved by designing NO-releasing polymeric nanomaterials able to promote the spatiotemporal generation of physiologically relevant amounts of NO in diverse pharmacological applications. In this review, we summarize the recent advances in the preparation of versatile NO-releasing nanocarriers based on polymeric nanoparticles, dendrimers and micelles. Despite the significant innovative progress achieved using nanomaterials to tailor NO release, certain drawbacks still need to be overcome to successfully translate these research innovations into clinical applications. In this regard, this review discusses the state of the art regarding the preparation of innovative NO-releasing polymeric nanomaterials, their impact in the biological field and the challenges that need to be overcome. We hope to inspire new research in this exciting area based on NO and nanotechnology.

Carbon quantum dot–NO photoreleaser nanohybrids for two-photon phototherapy of hypoxic tumors

Carbon quantum dots conjugated with a NO photodonor reduce tumor volume in mice bearing human xenograft BXPc-3 pancreatic tumors upon two-photon excitation with NIR light.

Polymer nanoparticles with electrostatically loaded multicargo for combined cancer phototherapy

Fluorescent biocompatible polymeric nanoparticles entangling two photoactive chromophores induce amplified cancer cell death due to the simultaneous photogeneration of¹O₂and NO.

A multi-photoresponsive molecular-hybrid for dual-modal photoinactivation of cancer cells

A bichromophoric molecular conjugate combines red fluorescence with the simultaneous photogeneration of singlet oxygen and nitric oxide, inducing amplified photomortality on melanoma cancer cells.