Nanomaterials-Induced Redox Imbalance: Challenged and Opportunities for Nanomaterials in Cancer Therapy

Cancer cells typically display redox imbalance compared with normal cells due to increased metabolic rate, accumulated mitochondrial dysfunction, elevated cell signaling, and accelerated peroxisomal activities. This redox imbalance may regulate gene expression, alter protein stability, and modulate existing cellular programs, resulting in inefficient treatment modalities. Therapeutic strategies targeting intra- or extracellular redox states of cancer cells at varying state of progression may trigger programmed cell death if exceeded a certain threshold, enabling therapeutic selectivity and overcoming cancer resistance to radiotherapy and chemotherapy. Nanotechnology provides new opportunities for modulating redox state in cancer cells due to their excellent designability and high reactivity. Various nanomaterials are widely researched to enhance highly reactive substances (free radicals) production, disrupt the endogenous antioxidant defense systems, or both. Here, the physiological features of redox imbalance in cancer cells are described and the challenges in modulating redox state in cancer cells are illustrated. Then, nanomaterials that regulate redox imbalance are classified and elaborated upon based on their ability to target redox regulations. Finally, the future perspectives in this field are proposed. It is hoped this review provides guidance for the design of nanomaterials-based approaches involving modulating intra- or extracellular redox states for cancer therapy, especially for cancers resistant to radiotherapy or chemotherapy, etc.

Exploiting Cancer Vulnerabilities by Blocking of the DHODH and GPX4 Pathways: A Multifunctional Bodipy/PROTAC Nanoplatform for the Efficient Synergistic Ferroptosis Therapy

Ferroptosis is a form of programmed cell death and plays an important role in many diseases. Dihydroorotate dehydrogenase (DHODH) and glutathione peroxidase 4 (GPX4) play major roles in cell resistance to ferroptosis. Therefore, inactivation of these proteins provides an excellent opportunity for efficient ferroptosis-based synergistic cancer therapy. In this study, a multifunctional nanoagent (BPNpro ) containing a GPX4 targeting boron dipyrromethene (Bodipy) probe (BP) and a DHODH targeting proteolysis targeting chimera (PROTAC) is reported. BPNpro is prepared using a nanoprecipitation method in the presence of a thermoresponsive liposome, where BP is encapsulated inside and the cathepsin B (CatB)-cleavable PROTAC peptide (DPCP) is modified on the outer surface. In the presence of near-infrared (NIR) photoirradiation, BPNpro is melted and BP is released in tumor cells. Subsequently, BP inhibits the activity of GPX4 by covalently bonding with the selenocysteine at the enzyme active site. In addition, DPCP achieves sustained degradation of DHODH upon activation by CatB overexpressed in the tumor. The synergistic deactivation of GPX4 and DHODH induces extensive ferroptosis and subsequent cell death. In vivo and in vitro studies clearly show that the proposed ferroptosis therapy provides excellent antitumor effect.

Near-infrared photodynamic and photothermal co-therapy based on organic small molecular dyes

Near-infrared (NIR) organic small molecule dyes (OSMDs) are effective photothermal agents for photothermal therapy (PTT) due to their advantages of low cost and toxicity, good biodegradation, and strong NIR absorption over a wide wavelength range. Nevertheless, OSMDs have limited applicability in PTT due to their low photothermal conversion efficiency and inadequate destruction of tumor regions that are nonirradiated by NIR light. However, they can also act as photosensitizers (PSs) to produce reactive oxygen species (ROS), which can be further eradicated by using ROS-related therapies to address the above limitations of PTT. In this review, the synergistic mechanism, composition, and properties of photodynamic therapy (PDT)-PTT nanoplatforms were comprehensively discussed. In addition, some specific strategies for further improving the combined PTT and PDT based on OSMDs for cancer to completely eradicate cancer cells were outlined. These strategies include performing image-guided co-therapy, enhancing tumor infiltration, increasing H2O2 or O2 in the tumor microenvironment, and loading anticancer drugs onto nanoplatforms to enable combined therapy with phototherapy and chemotherapy. Meanwhile, the intriguing prospects and challenges of this treatment modality were also summarized with a focus on the future trends of its clinical application.

Unadulterated BODIPY nanoparticles as light driven antibacterial agents for treating bacterial infections and promoting wound healing

Antimicrobial photodynamic therapy (aPDT) is an effective strategy to eliminate bacteria without inducing bacterial resistance. As typical aPDT photosensitizers, most of boron-dipyrromethene (BODIPY) are hydrophobic, and nanometerization is imperative to render them dispersible in physiological media. Recently, carrier-free nanoparticles (NPs) are formed via the self-assembly of BODIPYs without the help of any surfactants or auxiliaries, arousing people's interest. So as to fabricate carrier-free NPs, BODIPYs usually need to be derived into dimers, trimers, or amphiphiles through complex reactions. Few unadulterated NPs were obtained from BODIPYs with precise structures. Herein, BNP1-BNP3 were synthesized by the self-assembly of BODIPY, which showed excellent anti-Staphylococcus aureus ability. Among them, BNP2 could effectively fight bacterial infections and promote wound healing in vivo.

Porphyrin-Based Nanoparticles: A Promising Phototherapy Platform

Phototherapy, including photodynamic therapy and photothermal therapy, is an emerging form of non-invasive treatment. The combination of imaging technology and phototherapy is becoming an attractive development in the treatment of cancer, as it allows for highly effective therapeutic results through image-guided phototherapy. Porphyrins have attracted significant interest in the treatment and diagnosis of cancer due to their excellent phototherapeutic effects in phototherapy and their remarkable imaging capabilities in fluorescence imaging, magnetic resonance imaging and photoacoustic imaging. However, porphyrins suffer from poor water solubility, low near-infrared absorption and insufficient tumor accumulation. The development of nanotechnology provides an effective way to improve the bioavailability, phototherapeutic effect and imaging capability of porphyrins. This review highlights the research results of porphyrin-based small molecule nanoparticles in phototherapy and image-guided phototherapy in the last decade and discusses the challenges and directions for the development of porphyrin-based small molecule nanoparticles in phototherapy.

A carrier-free nanoparticle with dual NIR/acid responsiveness by co-assembly of enediyne and IR820 for combined PTT/chemotherapy

Combined photothermal therapy/chemotherapy by co-delivery of a photosensitizer (PS) and a chemotherapeutic drug has demonstrated great potential for cancer treatment. The intrinsic drawbacks of traditional drug delivery systems (DDSs), such as tedious synthetic procedures, side effects originated from the carrier materials, low loading efficiency, and uncontrolled drug release, however, have impaired their further advancement. On the other hand, enediyne antibiotics are highly cytotoxic toward cancer cells through the generation of lethal carbon radicals via thermal-induced cyclization, endowing them with great potential to achieve enhanced synergistic anticancer performance by incorporation with the photothermal effect of PS. To this end, a carrier-free and NIR/acid dual-responsive DDS was constructed for combined photothermal therapy/chemotherapy. The facile co-assembly of maleimide-based enediyne and PS IR820 was achieved in aqueous solution to give nanoparticles (EICN) with a hydrodynamic diameter of 90 nm and high stability. In vitro study confirmed the acid/NIR dual-responsive degradation and drug release, free radical generation and DNA-cleaving ability of EICN, which was accomplished by the corporation of enediyne and IR820 moieties. Further tests on HeLa cells verified the excellent synergistic anticancer performance of EICN including the improved cellular uptake, NIR-enhanced drug release, DNA damage and histone deacetylase inhibitor capacity. Overall, this carrier-free DDS with dual acid/NIR-responsivity would potentially provide new insights for the development of combined photothermal/chemotherapy.

Leveraging BODIPY nanomaterials for enhanced tumor photothermal therapy

In the past ten years, photothermal therapy (PTT) has attracted widespread attention in tumor treatment due to its non-invasiveness and little side effects. PTT utilizes heat produced by photothermal agents under the irradiation of near-infrared light to kill tumor cells. Boron-dipyrromethene (BODIPY), an organic phototherapy agent, has been widely used in tumor phototherapy due to its higher molar extinction coefficient, robust photostability and good phototherapy effect. However, there are some issues in the application of BODIPY for tumor PTT, such as low photothermal conversion efficiency and short absorption wavelength. In this review, we focus on the latest development of BODIPY nanomaterials for overcoming the above problems and enhancing the PTT effect.

Beyond Photo: Xdynamic Therapies in Fighting Cancer

Reactive oxygen species (ROS)-related therapeutic approaches are developed as a promising modality for cancer treatment because the aberrant increase of intracellular ROS level can cause cell death due to nonspecific oxidation damage to key cellular biomolecules. However, the most widely considered strategy, photodynamic therapy (PDT), suffers from critical limitations such as limited tissue-penetration depth, high oxygen dependence, and phototoxicity. Non-photo-induced ROS generation strategies, which are defined as Xdynamic therapies (X = sono, radio, microwave, chemo, thermo, and electro), show good potential to overcome the drawbacks of PDT. Herein, recent advances in the development of Xdynamic therapies, including the design of systems, the working mechanisms, and examples of cancer therapy application, are introduced. Furthermore, the approaches to enhance treatment efficiency of Xdynamic therapy are highlighted. Finally, the perspectives and challenges of these strategies are also discussed.

Recent Progress of Alkyl Radicals Generation-Based Agents for Biomedical Applications

Photodynamic therapy (PDT) is extensively explored for anticancer and antibacterial applications. It typically relies on oxygen-dependent generation of reactive oxygen species (ROS) to realize its killing effect. This type of therapy modality shows compromised therapeutic results for treating hypoxic tumors or bacteria-infected wounds. Recently, alkyl radicals attracted much attention as they can be generated from some azo-based initiators only under mild heat stimulus without oxygen participation. Many nanocarriers or hydrogel systems have been developed to load and deliver these radical initiators to lesion sites for theranostics. These systems show good anticancer or antimicrobial effect in hypoxic environment and some of them possess specific imaging abilities providing precise guidance for treatment. This review summarizes the developed materials that aim at treating hypoxic cancer and bacteria-infected wound by using this kind of oxygen-irrelevant alkyl radicals. Based on the carrier components, these agents are divided into three groups: inorganic, organic, as well as inorganic and organic hybrid carrier-based therapeutic systems. The construction of these agents and their specific advantages in biomedical field are highlighted. Finally, the existing problems and future promising development directions are discussed.

Inhibiting Radiative Transition-Mediated Multifunctional Polymeric Nanoplatforms for Highly Efficient Tumor Phototherapeutics

It is highly desired to explore ideal phototherapeutic nanoplatforms, especially containing satisfactory phototherapeutic agents (PTAs), for potential cancer therapies. Herein, we proposed an effective strategy for designing a highly efficient PTA through inhibiting radiative transition (IRT). Specifically, we developed an ultralow radiative BODIPY derivative (TPA-IBDP) by simply conjugating two triphenylamine units to iodine-substituted BODIPY, which could simultaneously facilitate the nonradiative decay channels of singlet-to-triplet intersystem crossing and intramolecular charge transfer. In comparison to the normal BODIPY compound, TPA-IBDP exhibited an outstanding singlet oxygen yield (31.8-fold) and a higher photothermal conversion efficiency (PCE; over 3-fold), respectively, benefiting from the extended π-conjugated donor-to-accepter (D-A) structure and the heavy atom effect. For tumor phototherapy using TPA-IBDP, TPA-IBDP was conjugated with a H₂O₂-responsive amphiphilic copolymer POEGMA₁₀-b-[PBMA₅-co-(PS-N₃)₂] to construct a multifunctional phototherapeutic BODIPY-based nanoplatform (PB). PB produced abundant singlet oxygen (¹O₂) and heat along with negligible fluorescence emission under near-infrared laser irradiation. Additionally, PB could generate a GSH-depletion scavenger (quinone methide, QM) after reacting with the abundant intracellular H₂O₂ in tumor for the cooperative enhancement of IRT-mediated phototherapy. We envision that this highly efficient multifunctional phototherapeutic nanoplatform cooperated by GSH-depletion could be a valuable paradigm for tumor treatments.

Tailoring nanoparticles based on boron dipyrromethene for cancer imaging and therapy

Boron dipyrromethene (BODIPY), as a traditional fluorescent dye, has drawn increasing attention because of its excellent photophysical properties like adjustable spectra and outstanding photostability. BODIPY dyes could be assembled into nanoparticles for cancer imaging and therapy via rational design. In this review, the bio-applications of BODIPY-containing nanoparticles are introduced in detail, such as cellular imaging, near-infrared fluorescence imaging, computed tomography imaging, photoacoustic imaging, phototherapy, and theranostics. The construction strategies of BODIPY-containing nanoparticles are emphasized so the review has three sections-self-assembly of small molecules, chemical conjugation with hydrophilic compounds, and physical encapsulation. This review not only summarizes various and colorific bio-applications of BODIPY-containing nanoparticles, but also provides reasonable design methods of BODIPY-containing nanoparticles for cancer theranostics. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Red fluorescent pyrazoline-BODIPY nanoparticles for ultrafast and long-term bioimaging

Fluorescence bioimaging is very significant in studying biological processes. Fluorescent nanoparticles (NPs) manufactured from aggregation-induced emission (AIE) materials, as promising candidates, have attracted more attention. However, it is still a challenge to explore suitable AIE NPs for bioimaging. Herein, we synthesized pyrazoline-BODIPY (PZL-BDP) with a donor and acceptor (D-A) structure by a condensation reaction, cultured its single crystal, and studied its twisted intramolecular charge transfer (TICT) and AIE effects. PZL-BDP could self-assemble to form red fluorescent nanoparticles (PZL-BDP NPs) which showed a good fluorescence quantum yield of 15.8% in water. PZL-BDP NPs with excellent stability and biocompatibility exhibited a large Stokes shift (Δλ = 111 nm) which resulted in the reduction of external interference and enhancement of the fluorescence contrast. Furthermore, these nanoparticles could be readily internalized by HeLa cells and they stain the cells in just five seconds, indicating an ultrafast bioimaging protocol. Moreover, long-term tracking fluorescence signals in vivo for about 12 days were obtained. The bright red fluorescence, ultrafast cell staining ability, and long-term in vivo tracking competence outline the great potential of rational design nanomaterials with AIE characteristics for monitoring biological processes.

Tetraphenylporphine-Modified Polymeric Nanoparticles Containing NIR Photosensitizer for Mitochondria-Targeting and Imaging-Guided Photodynamic Therapy

Near-infrared (NIR) photodynamic therapy (PDT) is a promising antitumor strategy under NIR light irradiation to kill cancer cells. Mitochondria has a critical function in sustaining cellular viability and death, which is the ideal organelle for PDT. Here, we reported a tetraphenylporphine (TPP)-conjugated amphiphilic copolymer and an iodinated boron dipyrromethene photosensitizer (BDPI) with high singlet oxygen yield to form nanoparticles (PBDPI-TPP), which could realize mitochondria-targeting and improve the NIR imaging-guided PDT. The as-prepared mitochondria-targeting nanoplatform could show effective subcellular localization and bring about significant irreversible mitochondrial injury for enhanced PDT. Both in vitro and in vivo experiments revealed that the mitochondria-targeting PDT system could achieve a remarkable therapeutic effect, indicating that it is a promising nanoplatform for NIR imaging-guided PDT in cancer therapeutics.

Mitochondria-Targeting Thermosensitive Initiator with Enhanced Anticancer Efficiency

As one of the most important organelles in cells, the mitochondrion has been reported to exhibit higher temperatures and is vulnerable to free radicals, especially in cancer cells. Here, we report on the use of a mitochondria-targeted thermosensitive radical initiator for cancer cell killing. The thermal-sensitive radical initiator, V044 (2,2'-azobis [2-(2-imidazolin-2-yl)propane]dihydrochloride), was applied as a radical source, which was linked with a mitochondrial targeting moiety, triphenylphosphine (TPP), to construct the mitochondria-targeting radical initiator (TPPV). Mitochondria were applied as the endogenous thermal source of cells, which accelerated the free radical generation of TPPV. Results showed that TPPV could effectively generate free radicals in the mitochondrial area, and the released free radicals effectively damaged mitochondria, exhibiting an enhanced anticancer efficiency. This therapy based on endogenous mitochondrial heat avoids tissue penetration limits and offers a target for mitochondria-targeting systems.