An unexpected strategy to alleviate hypoxia limitation of photodynamic therapy by biotinylation of photosensitizers

Heavy-atom-free π-twisted photosensitizers for fluorescence bioimaging and photodynamic therapy

As the field of preclinical research on photosensitizers (PSs) for anticancer photodynamic therapy (PDT) continues to expand, a focused effort is underway to develop agents with innovative molecular structures that offer enhanced targeting, selectivity, activation, and imaging capabilities. In this context, we introduce two new heavy-atom-free PSs, DBXI and DBAI, characterized by a twisted π-conjugation framework. This innovative approach enhances the spin-orbit coupling (SOC) between the singlet excited state (S1) and the triplet state (T1), resulting in improved and efficient intersystem crossing (ISC). Both PSs are highly effective in producing reactive oxygen species (ROS), including singlet oxygen and/or superoxide species. Additionally, they also demonstrate remarkably strong fluorescence emission. Indeed, in addition to providing exceptional photocytotoxicity, this emissive feature, generally lacking in other reported structures, allows for the precise monitoring of the PSs' distribution within specific cellular organelles even at nanomolar concentrations. These findings underscore the dual functionality of these PSs, serving as both fluorescent imaging probes and light-activated therapeutic agents, emphasizing their potential as versatile and multifunctional tools in the field of PDT.

Constructing Heavy-Atom-Free Photosensitizers for Hypoxic Tumor Phototherapy Based on Donor-Excited Photoinduced Electron-Transfer-Driven Type-I and Type-II Mechanisms

The spin-orbit charge transfer intersystem crossing (SOCT-ISC) photophysical process has shown great potential for constructing heavy-atom-free photosensitizers (PSs) for photodynamic therapy (PDT) of tumors. However, for almost all such PSs reported to date, the SOCT-ISC is driven by the acceptor-excited photoinduced electron transfer (a-PeT). In this work, for the first time the donor-excited photoinduced electron transfer (d-PeT)-driven SOCT-ISC mechanism is utilized to construct the heavy-atom-free PSs for PDT of tumors by directly installing the electron-deficient N-alkylquinolinium unit (as an electron acceptor) into the meso-position of the near-infrared (NIR) distyryl Bodipy chromophore (as an electron donor). In the less polar environment, the PSs exist as the monomer and promote the production of singlet oxygen (1O2) (Type-II) relying on the d-PeT-driven population of the triplet excited state via SOCT-ISC, whereas in the aqueous environment, they exist as nanoaggregates and induce the generation of superoxides (O2-•) and hydroxyl radicals (HO•) (Type-I) via the d-PeT-driven formation of the delocalized charge-separated state. The PSs could rapidly be internalized into cancer cells and induce the simultaneous production of intracellular 1O2, O2-•, and HO• upon NIR light irradiation, endowing the PSs with superb photocytotoxicity with IC50 values up to submicromolar levels whether under normoxia or under hypoxia. Based on the PSs platform, a tumor-targetable PS is developed, and its abilities in killing cancer cells and in ablating tumors without damage to normal cells/tissues under NIR light irradiation are verified in vitro and in vivo. The study expands the design scope of PSs by introducing the d-PeT conception, thus being highly valuable for achieving novel PSs in the realm of tumor PDT.

Metal-polyphenol self-assembled nanodots for NIR-II fluorescence imaging-guided chemodynamic/photodynamic therapy-amplified ferroptosis

The effectiveness of tumor treatment using reactive oxygen species as the primary therapeutic medium is hindered by limitations of tumor microenvironment (TME), such as intrinsic hypoxia in photodynamic therapy (PDT) and overproduction of reducing glutathione (GSH) in chemodynamic therapy (CDT). Herein, we fabricate metal-polyphenol self-assembled nanodots (Fe@BDP NDs) guided by second near-infrared (NIR-II) fluorescence imaging. The Fe@BDP NDs are designed for synergistic combination of type-I PDT and CDT-amplified ferroptosis. In a mildly acidic TME, Fe@BDP NDs demonstrate great Fenton activity, leading to the generation of highly toxic hydroxyl radicals from overproduced hydrogen peroxide in tumor cells. Furthermore, Fe@BDP NDs show favorable efficacy in type-I PDT, even in tolerating tumor hypoxia, generating active superoxide anion upon exposure to 808 nm laser irradiation. The significant efficiency in reactive oxygen species (ROS) products results in the oxidation of sensitive polyunsaturated fatty acids, accelerating lethal lipid peroxidation (LPO) bioprocess. Additionally, Fe@BDP NDs illustrate an outstanding capability for GSH depletion, causing the inactivation of glutathione peroxidase 4 and further promoting lethal LPO. The synergistic type-I photodynamic and chemodynamic cytotoxicity effectively trigger irreversible ferroptosis by disrupting the intracellular redox homeostasis. Moreover, Fe@BDP NDs demonstrate charming NIR-II fluorescence imaging capability and effectively accumulated at the tumor site, visualizing the distribution of Fe@BDP NDs and the treatment process. The chemo/photo-dynamic-amplified ferroptotic efficacy of Fe@BDP NDs was evidenced both in vitro and in vivo. This study presents a compelling approach to intensify ferroptosis via visualized CDT and PDT. STATEMENT OF SIGNIFICANCE: In this study, we detailed the fabrication of metal-polyphenol self-assembled nanodots (Fe@BDP NDs) guided by second near-infrared (NIR-II) fluorescence imaging, aiming to intensify ferroptosis via the synergistic combination of type-I PDT and CDT. In a mildly acidic TME, Fe@BDP NDs exhibited significant Fenton activity, resulting in the generation of highly toxic •OH from overproduced H2O2 in tumor cells. Fe@BDP NDs possessed a remarkable capability for GSH depletion, resulting in the inactivation of glutathione peroxidase 4 (GPX4) and further accelerating lethal LPO. This study presented a compelling approach to intensify ferroptosis via visualized CDT and PDT.

Efficient hydroxyl radical generation of an activatable phthalocyanine photosensitizer: oligomer higher than monomer and nanoaggregate

It remains a challenge to develop a single-component organic photosensitizer that efficiently produces hydroxyl radicals (˙OH) without oxygen involvement, especially while maintaining tumor-targeting capability. Herein, we propose an intelligent molecular design strategy whereby a tumor-targeted phthalocyanine is initially ˙OH-free and can be activated by overexpressed β-nicotinamide adenine dinucleotide sodium salt hydrate (NAD(P)H) in hypoxic tumors to efficiently produce ˙OH under light irradiation. Furthermore, the oligomer models based on the phthalocyanine molecules were constructed by a supramolecular regulation strategy, which were in an intermediate state between monomer and nanoaggregate, to achieve enhanced ˙OH generation. The level of NAD(P)H in cancer cells can be exhausted through two pathways, including spontaneous redox and the photocatalytic redox of phthalocyanines. As a result, the in vivo and in vitro assays illustrated that the oligomeric phthalocyanine containing N-O units (OligPcNOB) can specifically target cancer cells and tumor tissue with overexpressing biotin receptors. OligPcNOB exhibited significant photocytotoxicity even in an extremely low oxygen environment and successfully inhibited tumor progression.

Lutetium Texaphyrin-Celecoxib Conjugate as a Potential Immuno-Photodynamic Therapy Agent

Immuno-photodynamic therapy (IPDT) has emerged as a new modality for cancer treatment. Novel photosensitizers can help achieve the promise inherent in IPDT, namely, the complete eradication of a tumor without recurrence. We report here a small molecule photosensitizer conjugate, LuCXB. This IPDT agent integrates a celecoxib (cyclooxygenase-2 inhibitor) moiety with a near-infrared absorbing lutetium texaphyrin photocatalytic core. In aqueous environments, the two components of LuCXB are self-associated through inferred donor-acceptor interactions. A consequence of this intramolecular association is that upon photoirradiation with 730 nm light, LuCXB produces superoxide radicals (O2-•) via a type I photodynamic pathway; this provides a first line of defense against the tumor while promoting IPDT. For in vivo therapeutic applications, we prepared a CD133-targeting, aptamer-functionalized exosome-based nanophotosensitizer (Ex-apt@LuCXB) designed to target cancer stem cells. Ex-apt@LuCXB was found to display good photosensitivity, acceptable biocompatibility, and robust tumor targetability. Under conditions of photoirradiation, Ex-apt@LuCXB acts to amplify IPDT while exerting a significant antitumor effect in both liver and breast cancer mouse models. The observed therapeutic effects are attributed to a synergistic mechanism that combines antiangiogenesis and photoinduced cancer immunotherapy.

Biodegradable Ruthenium-Rhenium Complexes Containing Nanoamplifiers: Triggering ROS-Induced CO Release for Synergistic Cancer Treatment

The constrained effectiveness of photodynamic therapy (PDT) has impeded its widespread use in clinical practice. Urgent efforts are needed to address the shortcomings faced in photodynamic therapy, such as photosensitizer toxicity, short half-life, and limited action range of reactive oxygen species (ROS). In this study, a biodegradable copolymer nanoamplifier is reported that contains ruthenium complex (Ru-complex) as photosensitizer (PS) and rhenium complex (Re-complex) as carbon monoxide (CO)-release molecule (CORM). The well-designed nanoamplifier brings PS and CORM into close spatial proximity, significantly promotes the utilization of light-stimulated reactive oxygen species (ROS), and cascaded amplifying CO release, thus enabling an enhanced synergistic effect of PDT and gas therapy for cancer treatment. Moreover, owing to its intrinsic photodegradable nature, the nanoamplifier exhibits good tumor accumulation and penetration ability, and excellent biocompatibility in vivo. These findings suggest that the biodegradable cascaded nanoamplifiers pave the way for a synergistic and clinically viable integration of photodynamic and gas therapy.

Modular Prodrug-Engineered Oxygen Nano-Tank With Outstanding Nanoassembly Performance, High Oxygen Loading, and Closed-Loop Tumor Hypoxia Relief

The clinical translation of tumor hypoxia intervention modalities still falls short of expectation, restricted by poor biocompatibility of oxygen-carrying materials, unsatisfactory oxygen loading performance, and abnormally high cellular oxygen consumption-caused insufficient hypoxia relief. Herein, a carrier-free oxygen nano-tank based on modular fluorination prodrug design and co-assembly nanotechnology is elaborately exploited, which is facilely fabricated through the molecular nanoassembly of a fluorinated prodrug (FSSP) of pyropheophorbide a (PPa) and an oxygen consumption inhibitor (atovaquone, ATO). The nano-tank adeptly achieves sufficient oxygen enrichment while simultaneously suppressing oxygen consumption within tumors for complete tumor hypoxia alleviation. Significant, the fluorination module in FSSP not only confers favorable co-assemblage of FSSP and ATO, but also empowers the nanoassembly to readily carry oxygen. As expected, it displays excellent oxygen carrying capacity, favorable pharmacokinetics, on-demand laser-triggerable ATO release, closed-loop tumor hypoxia relief, and significant enhancement to PPa-mediated PDT in vitro and in vivo. This study provides a novel nanotherapeutic paradigm for tumor hypoxia intervention-enhanced cancer therapy.

An Electron Donor-Acceptor Structured Rhenium(I) Complex Photo-Sensitizer Evokes Mutually Reinforcing "Closed-Loop" Ferroptosis and Immunotherapy

The hypoxic microenvironment of solid tumors severely lowers the efficacy of oxygen-dependent photodynamic therapy (PDT). The development of hypoxia-tolerant photosensitizers for PDT is an urgent requirement. In this study, a novel rhenium complex (Re-TTPY) to develop a "closed-loop" therapy based on PDT-induced ferroptosis and immune therapy is reported. Due to its electron donor-acceptor (D-A) structure, Re-TTPY undergoes energy transfer and electron transfer processes under 550 nm light irradiation and displays hypoxia-tolerant type I/II combined PDT capability, which can generate 1O2, O2 -, and ·OH simultaneously. Further, the reactive oxygen species (ROSs) leads to the depletion of 1,4-dihydronicotinamide adenine dinucleotide (NADH), glutathione peroxidase 4 (GPX4), and glutathione (GSH). As a result, ferroptosis occurs in cells, simultaneously triggers immunogenic cell death (ICD), and promotes the maturation of dendritic cells (DCs) and infiltration of T cells. The release of interferon-γ (IFN-γ) by CD8+ T cells downregulates the expression of GPX4, further enhancing the occurrence of ferroptosis, and thereby, forming a mutually reinforcing "closed-loop" therapeutic approach.

Totally Caged Type I Pro-Photosensitizer for Oxygen-Independent Synergistic Phototherapy of Hypoxic Tumors

Activatable type I photosensitizers are an effective way to overcome the insufficiency and imprecision of photodynamic therapy in the treatment of hypoxic tumors, however, the incompletely inhibited photoactivity of pro-photosensitizer and the limited oxidative phototoxicity of post-photosensitizer are major limitations. It is still a great challenge to address these issues using a single and facile design. Herein, a series of totally caged type I pro-photosensitizers (Pro-I-PSs) are rationally developed that are only activated in tumor hypoxic environment and combine two oxygen-independent therapeutic mechanisms under single-pulse laser irradiation to enhance the phototherapeutic efficacy. Specifically, five benzophenothiazine-based dyes modified with different nitroaromatic groups, BPN 1-5, are designed and explored as latent hypoxia-activatable Pro-I-PSs. By comparing their optical responses to nitroreductase (NTR), it is identified that the 2-methoxy-4-nitrophenyl decorated dye (BPN 2) is the optimal Pro-I-PSs, which can achieve NTR-activated background-free fluorescence/photoacoustic dual-modality tumor imaging. Furthermore, upon activation, BPN 2 can simultaneously produce an oxygen-independent photoacoustic cavitation effect and a photodynamic type I process at single-pulse laser irradiation. Detailed studies in vitro and in vivo indicated that BPN 2 can effectively induce cancer cell apoptosis through synergistic effects. This study provides promising potential for overcoming the pitfalls of hypoxic-tumor photodynamic therapy.

Thymoquinone as an electron transfer mediator to convert Type II photosensitizers to Type I photosensitizers

The development of Type I photosensitizers (PSs) is of great importance due to the inherent hypoxic intolerance of photodynamic therapy (PDT) in the hypoxic microenvironment. Compared to Type II PSs, Type I PSs are less reported due to the absence of a general molecular design strategy. Herein, we report that the combination of typical Type II PS and natural substrate carvacrol (CA) can significantly facilitate the Type I pathway to efficiently generate superoxide radical (O2-•). Detailed mechanism study suggests that CA is activated into thymoquinone (TQ) by local singlet oxygen generated from the PS upon light irradiation. With TQ as an efficient electron transfer mediator, it promotes the conversion of O2 to O2-• by PS via electron transfer-based Type I pathway. Notably, three classical Type II PSs are employed to demonstrate the universality of the proposed approach. The Type I PDT against S. aureus has been demonstrated under hypoxic conditions in vitro. Furthermore, this coupled photodynamic agent exhibits significant bactericidal activity with an antibacterial rate of 99.6% for the bacterial-infection female mice in the in vivo experiments. Here, we show a simple, effective, and universal method to endow traditional Type II PSs with hypoxic tolerance.

Microenvironment-Responsive Targeted Nanomedicine for a Collaborative Integration of Tumor Theranostics and Bone Defect Repair

Despite advancements in breast cancer treatment, bone metastases remain a significant concern for advanced breast cancer patients. Current theranostics strategies face challenges in integrating tumor theranostics and bone formation. Herein, this work develops an activatable targeted nanomedicine AuMnCO@BSA-N3 (AMCBN) to enable a novel collaborative integration of second near-infrared (NIR-II) fluorescence imaging guided precise theranostics for breast cancer bone metastases and osteogenic microenvironment remolding. This strategy employs a chemical coordination between noble metal complex and metal carbonyl (MnCO), with surface modification of azide groups to enhance tumor affinity through passive and active targeting. The initiated respondent behavior of AMCBN by tumor microenvironment accelerate the degradation of coordinated MnCO, resulting in a rapid release of multifunctional agents for efficient chemodynamic therapy (CDT)/gas synergistic therapy. Meanwhile, the exceptional bone-binding properties enable the efficient and controlled release of Mn2+ ions and carbon monoxide (CO) in the bone microenvironment, thereby facilitating the expression of osteogenesis-related proteins and establishing a novel synchronous theranostics process for tumor-bone repair.

A type I and type II chemical biology toolbox to overcome the hypoxic tumour microenvironment for photodynamic therapy

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality employed for the treatment of various types of cancers, localized infections, and other diseases. Upon illumination, the photo-excited photosensitizer generates singlet oxygen and other reactive species, thereby inducing cytotoxicity in the target cells. The hypoxic tumour microenvironment (TME), however, poses a limitation on the supply of oxygen in tumour tissues. Moreover, under such conditions, tumour metastasis and drug resistance frequently occur, further compromising the efficacy of PDT in combating tumours. Traditionally, type I photosensitizers with lower oxygen consumption demonstrate significant potential in overcoming hypoxic environments and play a crucial role in determining the therapeutic efficacy of PDT because type I photosensitizers can generate highly cytotoxic free radicals. In comparison, type II photosensitizers exhibit high oxygen dependence. The rate of reactive oxygen species (ROS) generation in the type II process is significantly higher than that in the type I process. Thus, the efficiency and selectivity of PDT depend on the properties of the photosensitizer. Here, the recent development and application of type I and type II photosensitizers, mainly in the past year, are summarized. The design methods, electronic structures, photophysical properties, lipophilic properties, electric charge, and other molecular characteristics of these photosensitizers are discussed in detail. These modifications alter the microstructure of photosensitizers and directly impact the results of PDT. The main content of this paper will have a positive promoting and inspiring effect on the future development of PDT.

Photochemical and biological dual-effects enhance the inhibition of photosensitizers for tumour growth

Photosensitizers typically rely on a singular photochemical reaction to generate reactive oxygen species, which can then inhibit or eradicate lesions. However, photosensitizers often exhibit limited therapeutic efficiency due to their reliance on a single photochemical effect. Herein, we propose a new strategy that integrates the photochemical effect (type-I photochemical effect) with a biological effect (proton sponge effect). To test our strategy, we designed a series of photosensitizers (ZZ-sers) based on the naphthalimide molecule. ZZ-sers incorporate both a p-toluenesulfonyl moiety and weakly basic groups to activate the proton sponge effect while simultaneously strengthening the type-I photochemical effect, resulting in enhanced apoptosis and programmed cell death. Experiments confirmed near-complete eradication of the tumour burden after 14 days (Wlight/Wcontrol ≈ 0.18, W represents the tumour weight). These findings support the notion that the coupling of a type-I photochemical effect with a proton sponge effect can enhance the tumour inhibition by ZZ-sers, even if the basic molecular backbones of the photosensitizers exhibit nearly zero or minimal tumour inhibition ability. We anticipate that this strategy can be generalized to develop additional new photosensitizers with improved therapeutic efficacy while overcoming limitations associated with systems relying solely on single photochemical effects.

Self-Adaptive Photodynamic-to-Photothermal Switch for Smart Antitumor Photoimmunotherapy

Photodynamic therapy (PDT) and photothermal therapy (PTT) possess different merits in cancer phototherapy, but the tumor microenvironment becomes unfavorable during the phototheranostic progress. Herein, we report a self-adaptive cyanine derivative Cy5-TPA with the PDT-dominated state to PTT-dominated state autoswitch feature for enhanced photoimmunotherapy. The incorporation of rotatable triphenylamine (TPA) moiety renders Cy5-TPA with the temperature or intramolecular-motion regulated photoactivities, which shows preferable reactive oxygen species (ROS) generation at lower temperature while stronger photothermal conversion at higher ones. Such a promising feature permits the in situ switch from PDT-dominated state to PTT-dominated state along with intratumoral temperature increase during laser irradiation, which also works in line with the concurrently reduced intratumoral oxygen level, exhibiting a self-adaptive phototherapeutic behavior to maximize the phototherapeutic antitumor outcome. Most importantly, the self-adaptive PDT-dominated state to PTT-dominated state switch also facilitates the sequential generation and release of damage-associated molecular patterns during immunogenic cell death (ICD). Hence, Cy5-TPA demonstrates excellent photoimmunotherapy performance in ICD induction, dendritic cell maturation, and T cell activation for tumor eradication and metastasis inhibition.

Enhanced Osteosarcoma Immunotherapy via CaCO3 Nanoparticles: Remodeling Tumor Acidic and Immune Microenvironment for Photodynamic Therapy

Osteosarcoma (OS) is a "cold" tumor enriched in noninflammatory M2 phenotype tumor-associated macrophages (TAMs), which limits the efficacy of immunotherapy. The acidic tumor microenvironment (TME), generated by factors such as excess hydrogen (H+) ions and high lactate levels, activates immunosuppressive cells, further promoting a suppressive tumor immune microenvironment (TIME). Therefore, a multitarget synergistic combination strategy that neutralizes the acidic TME and reprograms TAMs can be beneficial for OS therapy. Here, a calcium carbonate (CaCO3)/polydopamine (PDA)-based nanosystem (A-NPs@(SHK+Ce6)) is developed. CaCO3 nanoparticles are used to neutralize H+ ions and alleviate the suppressive TIME, and the loaded SHK not only synergizes with photodynamic therapy (PDT) but also inhibits lactate production, further reversing the acidic TME and repolarizing TAMs to consequently lead to enhanced PDT-induced tumor suppression and comprehensive beneficial effects on antitumor immune responses. Importantly, A-NPs@(SHK+Ce6), in combination with programmed cell death protein 1 (PD-1) checkpoint blockade, shows a remarkable ability to eliminate distant tumors and promote long-term immune memory function to protect against rechallenged tumors. This work presents a novel multiple-component combination strategy that coregulates the acidic TME and TAM polarization to reprogram the TIME.

Programmable Singlet Oxygen Battery for Automated Photodynamic Therapy Enabled by Pyridone-Pyridine Tautomer Engineering

The efficacy of photodynamic therapy is hindered by the hypoxic environment in tumors and limited light penetration depth. The singlet oxygen battery (SOB) has emerged as a promising solution, enabling oxygen- and light-independent 1O2 release. However, conventional SOB systems typically exhibit an "always-ON" 1O2 release, leading to potential 1O2 leakage before and after treatment. This not only compromises therapeutic outcomes but also raises substantial biosafety concerns. In this work, we introduce a programmable singlet oxygen battery, engineered to address all the issues discussed above. The concept is illustrated through the development of a tumor-microenvironment-responsive pyridone-pyridine switch, PyAce, which exists in two tautomeric forms: PyAce-0 (pyridine) and PyAce (pyridone) with different 1O2 storage half-lives. In its native state, PyAce remains in the pyridone form, capable of storing 1O2 (t1/2 = 18.5 h). Upon reaching the tumor microenvironment, PyAce is switched to the pyridine form, facilitating rapid and thorough 1O2 release (t1/2 = 16 min), followed by quenched 1O2 release post-therapy. This mechanism ensures suppressed 1O2 production pre- and post-therapy with selective and rapid 1O2 release at the tumor site, maximizing therapeutic efficacy while minimizing side effects. The achieved "OFF-ON-OFF" 1O2 therapy showed high spatiotemporal selectivity and was independent of the oxygen supply and light illumination.

Molecular engineering to design a bright near-infrared red photosensitizer: cellular bioimaging and phototherapy

Near-infrared red (NIR) fluorescence imaging guide phototherapeutic therapy (PDT) has the advantages of deep tissue penetration, real-time monitoring of drug treatment and disease, little damage to normal tissue, low cytotoxicity and almost no side effects, and thus, it is attracting increasing research attention and is expected to show promising potential for clinical tumor treatment. The photosensitizer (PS), light source and oxygen are the three basic and important factors to construct PDT technology, and highly efficient PSs are still being passionately pursued because they determine the PDT efficiency. Ideal PSs should have properties such as good biocompatibility, deep tissue penetration, and highly efficient reactive oxygen species (ROS) generation despite the hypoxic environment. Therefore, pure organic type I PSs with NIR fluorescence have been receiving increasing attention due to their deep penetration and hypoxia resistance. However, reported NIR-active type I PSs usually require complex synthetic procedures, which presents a challenge for mass production. In this research work, based on the molecular design ideas of introducing the heavy atom effect and intramolecular charge transfer, we prepared three NIR-active type I PSs (TNZ, TNZBr, and TNZCHO) using a very simple method with one or two synthetic steps. Clear characterizations of photophysical properties, ROS performance tests, and fluorescent imaging of human umbilical vein endothelial (HUVE) cells and PDT treatment of HepG2 cells were carried out. The results revealed that the heavy atom and intramolecular charge transfer (ICT) effects could obviously enhance the ROS efficiency, and both PSs produce only type I ROS without any type II ROS (1O2) generation. The good NIR fluorescence brightness and type I ROS efficiency ensure satisfactory bioimaging and PDT outcomes. This research provides the possibility of preparing NIR-active type I PSs via mass production.

Hypoxia-Activated Theragnostic Prodrugs (HATPs): Current State and Future Perspectives

Hypoxia is a significant feature of solid tumors and frequently poses a challenge to the effectiveness of tumor-targeted chemotherapeutics, thereby limiting their anticancer activity. Hypoxia-activated prodrugs represent a class of bio-reductive agents that can be selectively activated in hypoxic compartments to unleash the toxic warhead and thus, eliminate malignant tumor cells. However, their applicability can be further elevated by installing fluorescent modalities to yield hypoxia-activated theragnostic prodrugs (HATPs), which can be utilized for the simultaneous visualization and treatment of hypoxic tumor cells. The scope of this review is to summarize noteworthy advances in recent HATPs, highlight the challenges and opportunities for their further development, and discuss their potency to serve as personalized medicines in the future.

Rational design of type-I photosensitizer molecules for mitochondrion-targeted photodynamic therapy

Photodynamic therapy (PDT) has emerged as a promising approach for tumor treatment. However, traditional type II PDT faces limitations due to its oxygen-dependent nature. Type-I photosensitizers (PSs) exhibit superiority over conventional type-II PSs owing to their diminished oxygen dependence. Nevertheless, designing effective type-I PSs remains a significant challenge. In this work, we provide a novel strategy to tune the PDT mechanism of an excited photosensitizer through aryl substituent engineering. Using S-rhodamine as the base structure, three PSs were synthesized by incorporating phenyl, furyl, or thienyl groups at the meso position. Interestingly, furyl- or thienyl-substituted S-rhodamine are type-I-dominated PSs that produce O2˙-, while phenyl S-rhodamine results in O2˙- and 1O2 through type-I and type-II mechanisms, respectively. Experimental analyses and theoretical calculations showed that the introduction of a five-membered heterocycle at the meso position promoted intersystem crossing (ISC) and electron transfer, facilitating the production of O2˙-. Furthermore, furyl- or thienyl-substituted S-rhodamine exhibited high phototoxicity at ultralow concentrations. Thienyl-substituted S-rhodamine showed promising PDT efficacy against hypoxic solid tumors. This innovative strategy provides an alternative approach to developing new type-I PSs without the necessity for creating entirely new skeletons.

Deciphering Oxygen-Independent Augmented Photodynamic Oncotherapy by Facilitating the Separation of Electron-Hole Pairs

Developing Type-I photosensitizers provides an attractive approach to solve the dilemma of inadequate efficacy of photodynamic therapy (PDT) caused by the inherent oxygen consumption of traditional Type-II PDT and anoxic tumor microenvironment. The challenge for the exploration of Type-I PSs is to facilitate the electron transfer ability of photosensitization molecules for transforming oxygen or H2O to reactive oxygen species (ROS). Herein, we propose an electronic acceptor-triggered photoinduced electron transfer (a-PET) strategy promoting the separation of electron-hole pairs by marriage of two organic semiconducting molecules of a non-fullerene scaffold-based photosensitizer and a perylene diimide that significantly boost the Type-I PDT pathway to produce plentiful ROS, especially, inducing 3.5-fold and 2.5-fold amplification of hydroxyl (OH⋅) and superoxide (O2 -⋅) generation. Systematic mechanism exploration reveals that intermolecular electron transfer and intramolecular charge separation after photoirradiation generate a competent production of radical ion pairs that promote the Type-I PDT process by theoretical calculation and ultrafast femtosecond transient absorption (fs-TA) spectroscopy. By complementary tumor diagnosis with photoacoustic imaging and second near-infrared fluorescence imaging, this as-prepared nanoplatform exhibits fabulous photocytotoxicity in harsh hypoxic conditions and terrific cancer revoked abilities in living mice. We envision that this work will broaden the insight into high-efficiency Type-I PDT for cancer phototheranostics.

Aggregation-Induced Emission Photosensitizer-Engineered Anticancer Nanomedicine for Synergistic Chemo/Chemodynamic/Photodynamic Therapy

Photodynamic therapy (PDT) with aggregation-induced emission (AIE) photosensitizers (PSs) is a promising therapeutic strategy to achieve better anticancer results. However, eradicating solid tumors completely by PDT alone can be difficult owing to the inherent drawbacks of this treatment, and the combination of PDT with other therapeutic modalities provides opportunities to achieve cooperative enhancement interactions among various treatments. Herein, this work presents the construction of a biocompatible nanocomposite, namely CaO2@DOX@ZIF@ASQ, featuring light-responsive reactive oxygen species (ROS) generation and tumor-targeting oxygen and hydrogen peroxide discharge, as well as controlled doxorubicin (DOX) and copper ion release, thus allowing the combined PDT/CT/CDT effect by AIE PS-enhanced PDT, DOX-based chemotherapy (CT), and copper-involved Fenton-like reaction-driven chemodynamic therapy (CDT). In vitro and in vivo studies verify that the generation of both ROS and O2 by this nanomedicine, stimulated by light, exhibits superior anticancer efficacy, alleviating tumor hypoxia and achieving synergistic PDT/CT/CDT therapeutic effect. This multifunctional nanomedicine remarkably suppresses the tumor growth with minimized systemic toxicity, providing a new strategy for constructing multimodal PDT/CT/CDT therapeutic systems to overcome hypoxia limitations, and potentially increase the antitumor efficacy at lower doses of PSs and chemotherapeutic drugs, thus minimizing potential toxicity to non-malignant tissues.

Theranostics - a sure cure for cancer after 100 years?

Cancer has remained a formidable challenge in medicine and has claimed an enormous number of lives worldwide. Theranostics, combining diagnostic methods with personalized therapeutic approaches, shows huge potential to advance the battle against cancer. This review aims to provide an overview of theranostics in oncology: exploring its history, current advances, challenges, and prospects. We present the fundamental evolution of theranostics from radiotherapeutics, cellular therapeutics, and nanotherapeutics, showcasing critical milestones in the last decade. From the early concept of targeted drug delivery to the emergence of personalized medicine, theranostics has benefited from advances in imaging technologies, molecular biology, and nanomedicine. Furthermore, we emphasize pertinent illustrations showcasing that revolutionary strategies in cancer management enhance diagnostic accuracy and provide targeted therapies customized for individual patients, thereby facilitating the implementation of personalized medicine. Finally, we describe future perspectives on current challenges, emerging topics, and advances in the field.

Oxygen-independent organic photosensitizer with ultralow-power NIR photoexcitation for tumor-specific photodynamic therapy

Photodynamic therapy (PDT) is a promising cancer treatment but has limitations due to its dependence on oxygen and high-power-density photoexcitation. Here, we report polymer-based organic photosensitizers (PSs) through rational PS skeleton design and precise side-chain engineering to generate •O2- and •OH under oxygen-free conditions using ultralow-power 808 nm photoexcitation for tumor-specific photodynamic ablation. The designed organic PS skeletons can generate electron-hole pairs to sensitize H2O into •O2- and •OH under oxygen-free conditions with 808 nm photoexcitation, achieving NIR-photoexcited and oxygen-independent •O2- and •OH production. Further, compared with commonly used alkyl side chains, glycol oligomer as the PS side chain mitigates electron-hole recombination and offers more H2O molecules around the electron-hole pairs generated from the hydrophobic PS skeletons, which can yield 4-fold stronger •O2- and •OH production, thus allowing an ultralow-power photoexcitation to yield high PDT effect. Finally, the feasibility of developing activatable PSs for tumor-specific photodynamic therapy in female mice is further demonstrated under 808 nm irradiation with an ultralow-power of 15 mW cm-2. The study not only provides further insights into the PDT mechanism but also offers a general design guideline to develop an oxygen-independent organic PS using ultralow-power NIR photoexcitation for tumor-specific PDT.

Type-I Photodynamic Therapy Induced by Pt-Coordination of Type-II Photosensitizers into Supramolecular Complexes

Platinum supramolecular complexes based on photosensitizers have garnered great interest in photodynamic therapy (PDT) due to Pt (II) centers as chemotherapeutic agents to eliminate tumor cells completely, which greatly improve the antitumor efficacy of PDT. However, in comparison to precursor photosensitizer ligand, the formed platinum supramolecular complexes typically exhibit inferior outcomes in terms of reactive oxygen species (ROS) generation. How to boost ROS generation in the formed platinum supramolecular complexes for enhanced PDT is an enticing yet highly challenging task. Here we report a Pt-coordination-based dimeric photosensitizer complex (Cz-BTZ-Py)2Pt(OTf)2. It is found that comparing with photosensitizer ligand Cz-BTZ-Py, the formed supramolecular complex exhibit redshifts of absorption wavelength as well as enhanced ROS generation efficiency. Moreover, type-I ROS generation (O2⋅-) is produced in the formed platinum supramolecular complexes mainly due to a reduced energy gap ΔEST resulting from exciton coupling between two photosensitizer ligands. And type-I ROS (O2⋅-) generation significantly amplifies the photodynamic therapy (PDT) outcomes. In vitro evaluation shows excellent photochemotherapy performance of (Cz-BTZ-Py)2Pt(OTf)2 nanoparticles. We anticipate this work would provide a novel approach to design type-I photosensitizers for efficient PDT.

Hypoxia Reversion by Low-Immunogenic Ultra-Acid-Sensitive Comicelles of Protein-Polymer Conjugates Sensitizes Tumors to Photodynamic Therapy

Hypoxia is characteristic of the tumor microenvironment, which is correlated with resistance to photodynamic therapy (PDT), radiotherapy, chemotherapy, and immunotherapy. Catalase is potentially useful to catalyze the conversion of endogenous H2O2 to O2 for hypoxia reversion. However, the efficient delivery of catalase into the hypoxia regions of tumors is a huge challenge. Here, we report the self-assembly of ultra-acid-sensitive polymer conjugates of catalase and albumin into nanomicelles that are responsive to the acidic tumor microenvironment. The immunogenicity of catalase is mitigated by the presence of albumin, which reduces the cross-linking of catalase with B cell receptors, resulting in improved pharmacokinetics. The ultra acid sensitivity of the nanomicelles makes it possible to efficiently escape the lysosomal degradation after endocytosis and permeate into the interior of tumors to reverse hypoxia in vitro and in vivo. In mice bearing triple-negative breast cancer, the nanomicelles loaded with a photosensitizer effectively accumulate and penetrate into the whole tumors to generate a sufficient amount of O2 to reverse hypoxia, leading to enhanced efficacy of PDT without detectable side effects. These findings provide a general strategy of self-assembly to design low-immunogenic ultra-acid-sensitive comicelles of protein-polymer conjugates to reverse tumor hypoxia, which sensitizes tumors to PDT.

Current advances in modulating tumor hypoxia for enhanced therapeutic efficacy

Hypoxia is a common feature of most solid tumors, which promotes the proliferation, invasion, metastasis, and therapeutic resistance of tumors. Researchers have been developing advanced strategies and nanoplatforms to modulate tumor hypoxia to enhance therapeutic effects. A timely review of this rapidly developing research topic is therefore highly desirable. For this purpose, this review first introduces the impact of hypoxia on tumor development and therapeutic resistance in detail. Current developments in the construction of various nanoplatforms to enhance tumor treatment in response to hypoxia are also systematically summarized, including hypoxia-overcoming, hypoxia-exploiting, and hypoxia-disregarding strategies. We provide a detailed discussion of the rationale and research progress of these strategies. Through a review of current trends, it is hoped that this comprehensive overview can provide new prospects for clinical application in tumor treatment. STATEMENT OF SIGNIFICANCE: As a common feature of most solid tumors, hypoxia significantly promotes tumor progression. Advanced nanoplatforms have been developed to modulate tumor hypoxia to enhanced therapeutic effects. In this review, we first introduce the impact of hypoxia on tumor progression. Current developments in the construction of various nanoplatforms to enhance tumor treatment in response to hypoxia are systematically summarized, including hypoxia-overcoming, hypoxia-exploiting, and hypoxia-disregarding strategies. We discuss the rationale and research progress of the above strategies in detail, and finally introduce future challenges for treatment of hypoxic tumors. By reviewing the current trends, this comprehensive overview can provide new prospects for clinical translatable tumor therapy.

An ER-targeted, Viscosity-sensitive Hemicyanine Dye for the Diagnosis of Nonalcoholic Fatty Liver and Photodynamic Cancer Therapy by Activating Pyroptosis Pathway

The concept of molecular design, integrating diagnostic and therapeutic functions, aligns with the general trend of modern medical advancement. Herein, we rationally designed the smart molecule ER-ZS for endoplasmic reticulum (ER)-targeted diagnosis and treatment in cell and animal models by combining hemicyanine dyes with ER-targeted functional groups (p-toluenesulfonamide). Owing to its ability to target the ER with a highly specific response to viscosity, ER-ZS demonstrated substantial fluorescence turn-on only after binding to the ER, independent of other physiological environments. In addition, ER-ZS, being a small molecule, allows for the diagnosis of nonalcoholic fatty liver disease (NAFLD) via liver imaging based on high ER stress. Importantly, ER-ZS is a type I photosensitizer, producing O2 ⋅- and ⋅OH under light irradiation. Thus, after irradiating for a certain period, the photodynamic therapy inflicted severe oxidative damage to the ER of tumor cells in hypoxic (2 % O2 ) conditions and activated the unique pyroptosis pathway, demonstrating excellent antitumor capacity in xenograft tumor models. Hence, the proposed strategy will likely shed new light on integrating molecular optics for NAFLD diagnosis and cancer therapy.

Molecular Nanoarchitectonics of Natural Photosensitizers and Their Derivatives Nanostructures for Improved Photodynamic Therapy

Natural photosensitizers (PSs) and their derivatives have drawn ever-increasing attention in photodynamic therapy (PDT) for their wild range of sources, desirable biocompatibility, and good photosensitivity. Nevertheless, many factors such as poor solubility, high body clearance rate, limited tumor targeting ability, and short excitation wavelengths severely hinder their applications in efficient PDT. In recent years, fabricating nanostructures by utilizing molecular assembly technique is proposed to solve these problems. This technique is easy to put into effect, and the assembled nanostructures could improve the physical properties of the PSs so as to meet the requirement of PDT. In this concept, we focus on the construction of natural PSs and their derivatives nanostructures through molecular assembly technique to enhance PDT efficacy (Figure 1). Furthermore, current challenges and future perspectives of natural PSs and their derivatives for efficient PDT are discussed.

Suppressing ACQ of molecular photosensitizers by distorting the conjugated-plane for enhanced tumor photodynamic therapy

Non-AIE-type molecular photosensitizers (PSs) suffer from the aggregation-caused-quenching (ACQ) effect in an aqueous medium due to the strong hydrophobic and π-π interactions of their conjugated planes, which significantly hinders the enhancement of tumor photodynamic therapy (PDT). So far, some ionic PSs have been reported with good water-solubility, though the ACQ effect can still be induced in a biological environment rich in ions, leading to unsatisfactory in vivo delivery and fluorescence imaging performance. Hence, designing molecular PSs with outstanding anti-ACQ properties in water is highly desirable, but it remains a tough challenge for non-AIE-type fluorophores. Herein, we demonstrated a strategy for the design of porphyrin-type molecular PSs with remarkable solubility and anti-ACQ properties in an aqueous medium, which was assisted by quantum chemical simulations. It was found that cationic branched side chains can induce serious plane distortion in diphenyl porphyrin (DPP), which was not observed for tetraphenyl porphyrin (TPP) with the same side chains. Moreover, the hydrophilicity of the chain spacer is also crucial to the plane distortion for attaining the desired anti-ACQ properties. Compared to ACQ porphyrin, anti-ACQ porphyrin displayed type-I ROS generation in hypoxia and much higher tumor accumulation efficacy by blood circulation, leading to highly efficient in vivo PDT for hypoxic tumors. This study demonstrates the power of sidechain chemistry in tuning the configuration and aggregation behaviors of porphyrins in water, offering a new path to boost the performance of PSs to fulfill the increasing clinical demands on cancer theranostics.

Reactive Reductive Species Participating Photodynamic Therapy for Cancer Treatment

Although the development of oxidative photodynamic therapy (O-PDT) based on reactive oxygen species (ROS) has led to great progress in cancer treatment, tumor hypoxia, cellular adaptation and intrinsic antioxidant defenses are still obstacles at this stage. Fortunately, with the discovery and development of reactive reductive species (RRS) in the PDT process, reductive PDT (R-PDT) is receiving increasing research interest. R-PDT with oxygen-independence is an effective reduction therapy that promises excellent therapeutic efficacy in extremely hypoxic or even anaerobic environments. In the concept, we introduce representative strategies to boost the type-I photosensitizing pathway, and then focus on the most recent R-PDT involving hydrogen radical (H⋅) and the single electron transfer (SET) process.

Metallopolymer strategy to explore hypoxic active narrow-bandgap photosensitizers for effective cancer photodynamic therapy

Practical photodynamic therapy calls for high-performance, less O2-dependent, long-wavelength-light-activated photosensitizers to suit the hypoxic tumor microenvironment. Iridium-based photosensitizers exhibit excellent photocatalytic performance, but the in vivo applications are hindered by conventional O2-dependent Type-II photochemistry and poor absorption. Here we show a general metallopolymerization strategy for engineering iridium complexes exhibiting Type-I photochemistry and enhancing absorption intensity in the blue to near-infrared region. Reactive oxygen species generation of metallopolymer Ir-P1, where the iridium atom is covalently coupled to the polymer backbone, is over 80 times higher than that of its mother polymer without iridium under 680 nm irradiation. This strategy also works effectively when the iridium atom is directly included (Ir-P2) in the polymer backbones, exhibiting wide generality. The metallopolymer nanoparticles exhibiting efficient O2•- generation are conjugated with integrin αvβ3 binding cRGD to achieve targeted photodynamic therapy.

NIR-II Emissive Superoxide Radical Photogenerator for Photothermal/Photodynamic Therapy against Hypoxic Tumor

Due to the "Achilles' heels" of hypoxia, complicated location in solid tumor, small molecular photosensitizers with second near-infrared window (NIR-II) fluorescence, type-I photodynamic therapy (PDT), and photothermal therapy (PTT) have attracted great attention. However, these photosensitizers are still few but yet challenging. Herein, an "all in one" NIR-II acceptor-donor-acceptor fused-ring photosensitizer, Y6-Th, is presented for the in-depth diagnosis and efficient treatment of cancer. Benefiting from the strong intramolecular charge transfer, promoted highly efficient intersystem crossing, largely p-conjugated fused-ring structure, and reduced planarity, the fabricated nanoparticles (Y6-Th nanoparticles) can emit NIR-II fluorescence with the peak located at 1020 nm, exclusively generate O2•- for type-I PDT, and display excellent PTT performance under an 808 nm laser stimulation. These characteristics make Y6-Th a distinguished NIR-wavelength-triggered phototheranostic agent, which can effectively therapy the hypoxic tumor using NIR-II-fluorescence-guided type-I PDT/PTT. This work provides a valuable guideline for fabricating high-performing NIR-II emissive superoxide radical photogenerators.

Synthesis of germanium/germanium phosphide in-plane heterostructure with efficient photothermal and enhanced photodynamic effects in the second near-infrared biowindow

Inspired by the bifunctional phototherapy agents (PTAs), constructing compact PTAs with efficient photothermal therapy (PTT) and photodynamic therapy (PDT) effects in the near-infrared (NIR-II) biowindow is crucial for high therapeutic efficacy. Herein, none-layered germanium (Ge) is transformed to layered Ge/germanium phosphide (Ge/GeP) structure, and a novel two-dimensional sheet-like compact S-scheme Ge/GeP in-plane heterostructure with a large extinction coefficient of 15.66 L/g cm-1 at 1,064 nm is designed and demonstrated. In addition to the outstanding photothermal effects, biocompatibility and degradability, type I and type II PDT effects are activated by a single laser. Furthermore, enhanced reactive oxygen species generation under longer wavelength NIR laser irradiation is achieved, and production of singlet oxygen and superoxide radical upon 1,064 nm laser irradiation is more than double that under 660 nm laser irradiation. The S-scheme charge transfer mechanism between Ge and GeP, is demonstrated by photo-irradiated Kelvin probe force microscopy and electron spin resonance analysis. Thus, the obtained S-scheme Ge/GeP in-plane heterostructure shows synergistic therapeutic effects of PTT/PDT both in vitro and in vivo in the NIR-II biowindow and the novel nanoplatform with excellent properties has large clinical potential.

Exploration of Thermally Activated Delayed Fluorescence (TADF)-Based Photoredox Catalyst To Establish the Mechanisms of Action for Photodynamic Therapy

The mechanisms of action (MoA) have been proposed to further reduce the O2 dependence of photodynamic therapy (PDT) significantly. However, the triplet states of traditional photosensitizers are relatively short and also are easily deactivated by the quenching of H2O or O2. This is not conducive for the electron transfer in the photocatalytic process and poses a great obstacle to establish the MoA. Therefore, we selected and synthesized a zirconium(IV) complex (Zr(MesPDPPh)2) reported by Milsmann to address this issue. The specific symmetric and intact geometry endowed Zr(MesPDPPh)2 NPs with long-lived triplet excited state (τ = 350 μs), desired sensitized ability, and improved anti-interfering performance on O2, which was matched with the requirements of photoredox catalyst significantly. The results showed that while PDT (I) and PDT (II) could be achieved simultaneously by leveraging Zr(MesPDPPh)2 NPs, it also could be served as a rare example of thermally activated delayed fluorescence (TADF)-based photoredox catalyst to implement the MoA of PDT. It involved the oxidation of NADH and the establishment of catalytic cycle collaborating by O2 and cytochrome c (cyt c) in normoxia and hypoxia, respectively. As a result, the oxygen-free PDT and tumor-growth inhibition was realized.

Host-Guest Photosensitizer of a Cationic BODIPY Derivative and Cucurbit[7]uril for High-Efficiency Visible Light-Induced Photooxidation Reactions

In recent years, there has been a notable surge of interest in the fields of organic and pharmaceutical research about photocatalysts (PCs) and photosensitizers (PSs). In this study, a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) molecule adorned with quaternary ammonium (TMB) functionality was meticulously designed and synthesized. This compound has remarkable characteristics such as exceptional water solubility, great optical qualities, and commendable photostability. It can form a 1:1 complex (TMB-CB[7]) with cucurbit[7]uril (CB[7]) through host-guest interactions in the aqueous solution and shows obvious fluorescence enhancement. The reactive oxygen species (ROS) including superoxide anion radical (O2·-) and singlet oxygen (1O2) generation ability of TMB-CB[7] were promoted compared with that of TMB in the aqueous solution. More interestingly, the ROS generated from TMB-CB[7] can be used as PCs for aerobic cross dehydrogenation coupling reactions and photooxidation reactions in water with high yields of 89 and 95%, respectively. Therefore, the utilization of a host-guest PS presents a novel and environmentally friendly approach for conducting photocatalyzed organic processes under ambient conditions using visible light.

Acetylacetonate Ruthenium Nitrosyls: A Gateway to Nitric Oxide Release in Water under Near-Infrared Excitation by Two-Photon Absorption

A fundamental challenge for phototriggered therapies is to obtain robust molecular frameworks that can withstand biological media. Photoactivatable nitric oxide (NO) releasing molecules (photoNORMs) based on ruthenium nitrosyl (RuNO) complexes are among the most studied systems due to several appealing features that make them attractive for therapeutic applications. Nevertheless, the propensity of the NO ligand to be attacked by nucleophiles frequently manifests as significant instability in water for this class of photoNORMs. Our approach to overcome this limitation involved enhancing the Ru-NO π-backbonding to lower the electrophilicity at the NO by replacing the commonly employed 2,2'-bipyridine (bpy) ligand by an anionic, electron-rich, acetylacetonate (acac). A versatile and convenient synthetic route is developed and applied for the preparation of a large library of RuNO photoNORMs with the general formula [RuNO(tpy)(acac)]2+ (tpy = 2,2':6',2″-terpyridine). A combined theoretical and experimental analysis of the Ru-NO bonding in these complexes is presented, supported by extensive single-crystal X-ray diffraction experiments and by topological analyses of the electron charge density by DFT. The enhanced π-back-bonding, systematically evidenced by several techniques, resulted in a remarkable stability in water for these complexes, where significant NO release efficiencies were recorded. We finally demonstrate the possibility of obtaining sophisticated water-stable multipolar NO-delivery platforms that can be activated in the near-IR region by two-photon absorption (TPA), as demonstrated for an octupolar complex with a TPA cross section of 1530 GM at λ = 800 nm and for which NO photorelease was demonstrated under TPA irradiation in aqueous media.

Application of hyaluronic acid-based nanoparticles for cancer combination therapy

Cancer is a significant public health problem in the world. The treatment methods include surgery, chemotherapy, phototherapy, and immunotherapy. Due to their respective limitations, the treatment effect is often unsatisfactory, laying hidden dangers for metastasis and recurrence. Since their exceptional biocompatibility and excellent targeting capabilities, hyaluronic acid-based biomaterials have generated great interest as drug delivery methods for tumor therapy. Moreover, modified HA can self-assemble into hydrogels or nanoparticles (NPs) for precise drug administration. This article summarizes the application of HA-based NPs in combination therapy. Ultimately, it is anticipated that this research will offer guidance for creating various HA-based NPs utilized in numerous cancer therapies.

A Photochemical Study of Photo-Induced Electron Transfer from DNAs to a Cationic Phthalocyanine Derivative

Water-soluble cationic gallium(III)-Pc complex (GaPc) is capable of photogenerating ROSs but does not exhibit photocytotoxicity in vivo. GaPc binds selectively, through a π-π stacking interaction, to the 5'-terminal G-quartet of a G-quadruplex DNA. The photo-excited state of GaPc of the complex is effectively quenched through electron transfer (ET) from the ground state of DNA guanine (G) bases to the photo-excited state of GaPc (ET(G-GaPc)). Hence the loss of the photocytotoxicity of GaPc in vivo is most likely to be due to the effective quenching of its photo-excited state through ET(G-GaPc). In this study, we investigated the photochemical properties of GaPc in the presence of duplex DNAs formed from a series of sequences to elucidate the nature of ET(G-GaPc). We found that ET(G-GaPc) is allowed in electrostatic complexes between GaPc and G-containing duplex DNAs and that the rate of ET(G-GaPc) (kET(G-GaPc)) can be reasonably interpreted in terms of the distance between Pc moiety of GaPc and DNA G base in the complex. We also found that the quantum yields of singlet oxygen (1O2) generation (ΦΔs) determined for the GaPc-duplex DNA complexes were similar to the value reported for free GaPc (Fujishiro R, Sonoyama H, Ide Y, et al (2019) J Inorg Biochem 192:7-16), indicating that ET(G-GaPc) in the complex is rather limited. These results clearly demonstrated that photocytotoxicity of GaPc is crucially affected by ET(G-GaPc). Thus elucidation of interaction of a photosensitizer with biomolecules, i.e., an initial process in PDT, would be helpful to understand its subsequent photochemical processes.

Unleashing the power of porphyrin photosensitizers: Illuminating breakthroughs in photodynamic therapy

This comprehensive review provides the current trends and recent developments of porphyrin-based photosensitizers. We discuss their evolution from first-generation to third-generation compounds, including cutting-edge nanoparticle-integrated derivatives, and explores their pivotal role in advancing photodynamic therapy (PDT) for enhanced cancer treatment. Integrating porphyrins with nanoparticles represents a promising avenue, offering improved selectivity, reduced toxicity, and heightened biocompatibility. By elucidating recent breakthroughs, innovative methodologies, and emerging applications, this review provides a panoramic snapshot of the dynamic field, addressing challenges and charting prospects. With a focus on harnessing reactive oxygen species (ROS) through light activation, PDT serves as a minimally invasive therapeutic approach. This article offers a valuable resource for researchers, clinicians, and PDT enthusiasts, highlighting the potential of porphyrin photosensitizers to improve the future of cancer therapy.

Biological function, regulatory mechanism, and clinical application of mannose in cancer

Studies examining the regulatory roles and clinical applications of monosaccharides other than glucose in cancer have been neglected. Mannose, a common type of monosaccharide found in human body fluids and tissues, primarily functions in protein glycosylation rather than carbohydrate metabolism. Recent research has demonstrated direct anticancer effects of mannose in vitro and in vivo. Simply supplementing cell culture medium or drinking water with mannose achieved these effects. Moreover, mannose enhances the effectiveness of current cancer treatments including chemotherapy, radiotherapy, targeted therapy, and immune therapy. Besides the advancements in basic research on the anticancer effects of mannose, recent studies have reported its application as a biomarker for cancer or in the delivery of anticancer drugs using mannose-modified drug delivery systems. This review discusses the progress made in understanding the regulatory roles of mannose in cancer progression, the mechanisms underlying its anticancer effects, and its current application in cancer diagnosis and treatment.

Water-soluble phthalocyanine photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is based on a photochemical reaction that is started when a photosensitizing process is activated by the light and results in the death of tumor cells. Solubility is crucial in PDT applications to investigate the physical and chemical characteristics of phthalocyanines, but, unfortunately, most phthalocyanines show limited solubility especially in water. To increase the solubility of phthalocyanines in polar solvents and water, ionic groups such as -SO3-, -NR3+, -COO-, and nonionic groups such as polyoxy chains are frequently added to the peripheral or nonperipheral positions of the phthalocyanine framework. Since water-solubility and NIR-absorbing properties are essential for efficient PDT activation, studies have been focused on the synthesis of these types of phthalocyanine derivatives. This review focuses on the photophysical, photochemical, and some in vitro or in vivo studies of the recently published ionic and nonionic phthalocyanine-mediated photosensitizers carried out in the last five years. This review will have positive contributions to future studies on phthalocyanine chemistry and their PDT applications as well as photochemistry.

Biomimetic biomineralization nanoplatform-mediated differentiation therapy and phototherapy for cancer stem cell inhibition and antitumor immunity activation

Growing evidence suggests that the presence of cancer stem cells (CSCs) is a major challenge in current tumor treatments, especially the transition from non-CSCs to differentiation of CSCs for evading conventional therapies and driving metastasis. Here we propose a therapeutic strategy of synergistic differentiation therapy and phototherapy to induce differentiation of CSCs into mature tumor cells by differentiation inducers and synergistic elimination of them and normal cancer cells through phototherapy. In this work, we synthesized a biomimetic nanoplatform loaded with IR-780 and all-trans retinoic acid (ATRA) via biomineralization. This method can integrate aluminum ions into small-sized protein carriers to form nanoclusters, which undergo responsive degradation under acidic conditions and facilitate deep tumor penetration. With the help of CSC differentiation induced by ATRA, IR-780 inhibited the self-renewal of CSCs and cancer progression by generating hyperthermia and reactive oxygen species in a synergistic manner. Furthermore, ATRA can boost immunogenic cell death induced by phototherapy, thereby strongly causing a systemic anti-tumor immune response and efficiently eliminating CSCs and tumor cells. Taken together, this dual strategy represents a new paradigm of targeted eradication of CSCs and tumors by inducing CSC differentiation, improving photothermal therapy/photodynamic therapy and enhancing antitumor immunity.

Accurate Determination of the Photosensitizer Stern-Volmer Constant by the Oxygen-Dependent Consumption of 1,3-Diphenylisobenzofuran

Because of the absence of phosphorescence, the Stern-Volmer constant (KSV) of the photosensitizer is hard to determine accurately. Although the delayed fluorescence and correlated fluorescence methods have been proposed to determine KSV, the weak signal detection and non-uniform excitation enlarged the measurement error. In this work, a method was proposed to accurately determine KSV by oxygen-dependent consumption of 1,3-diphenylisobenzofuran. The consumption time (δ), as a measurable quantity, is introduced and could be obtained by the absorption spectrum with a high signal-to-noise ratio. Analytically, δ is linearly related to the inverse of oxygen content, and the ratio of the intercept to the slope equals KSV. Experimentally, rose Bengal was selected to perform this determination; the KSV is measured to be 43(1) kPa-1, and the error is reduced by 1 order of magnitude. In addition, metalloporphyrin was used to verify this method.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

A Highly Water-Soluble Aggregation-Induced Emission Luminogen with Anion-π+ Interactions for Targeted NIR Imaging of Cancer Cells and Type I Photodynamic Therapy

The low oxygen dependence of type I photosensitizers (PSs) has made them a popular choice for treating solid tumors. However, the drawbacks of poor water solubility, short emission wavelength, poor stability, and inability to distinguish cancer cells from normal cells limit the application of most type I PSs in clinical therapy. Thereby, developing novel type I PSs for overcoming these problems is an urgent but challenging task. Herein, by utilizing the distinctive structural characteristics of anion-π+ interactions, a highly water-soluble type I PS (DPBC-Br) with aggregation-induced emission (AIE) characteristic and near-infrared (NIR) emission is fabricated for the first time. DPBC-Br displays remarkable water solubility (7.3 mM) and outstanding photobleaching resistance, enabling efficient and precise differentiation between tumor cells and normal cells in a wash-free and long-term tracking manner via NIR-I imaging. Additionally, the superior type I reactive oxygen species (ROS) produced by DPBC-Br provide both specific killing of cancer cells in vitro and inhibition of tumor growth in vivo, with negligible systemic toxicity. This study rationally constructs a highly water-soluble type I PS, which has higher reliability and controllability compared with conventional nanoparticle formulating procedures, offering great potential for clinical cancer treatment.

Formylation as a Chemical Tool to Modulate the Performance of Photosensitizers Based on Boron Dipyrromethene Dimers

Heavy-atom-free photosensitizers are envisioned as the next generation of photoactive molecules for photo-theragnosis. In this approach, and after suitable irradiation, a single molecular scaffold is able to visualize and kill tumour cells by fluorescence signalling and photodynamic therapy (PDT), respectively, with minimal side effects. In this regard, BODIPY-based orthogonal dimers have irrupted as suitable candidates for this aim. Herein, we analyse the photophysical properties of a set of formyl-functionalized BODIPY dimers to ascertain their suitability as fluorescent photosensitizers. The conducted computationally aided spectroscopic study determined that the fluorescence/singlet oxygen generation dual performance of these valuable BODIPY dimers not only depends on the BODIPY-BODIPY linkage and the steric hindrance around it, but also can be modulated by proper formyl functionalization at specific chromophoric positions. Thus, we propose regioselective formylation as an effective tool to modulate such a delicate photonic balance in BODIPY-based dimeric photosensitizers. The taming of the excited-state dynamics, in particular intramolecular charge transfer as the key underlying process mediating fluorescence deactivation vs. intersystem crossing increasing, could serve to increase fluorescence for brighter bioimaging, enhance the generation of singlet oxygen for killing activity, or balance both for photo-theragnosis.

Nanoparticle-mediated synergistic anticancer effect of ferroptosis and photodynamic therapy: Novel insights and perspectives

Current antitumor monotherapy has many limitations, highlighting the need for novel synergistic anticancer strategies. Ferroptosis is an iron-dependent form of nonapoptotic cell death that plays a pivotal regulatory role in tumorigenesis and treatment. Photodynamic therapy (PDT) causes irreversible chemical damage to target lesions and is widely used in antitumor therapy. However, PDT's effectiveness is usually hindered by several obstacles, such as hypoxia, excess glutathione (GSH), and tumor resistance. Ferroptosis improves the anticancer efficacy of PDT by increasing oxygen and reactive oxygen species (ROS) or reducing GSH levels, and PDT also enhances ferroptosis induction due to the ROS effect in the tumor microenvironment (TME). Strategies based on nanoparticles (NPs) can subtly exploit the potential synergy of ferroptosis and PDT. This review explores recent advances and current challenges in the landscape of the underlying mechanisms regulating ferroptosis and PDT, as well as nano delivery system-mediated synergistic anticancer activity. These include polymers, biomimetic materials, metal organic frameworks (MOFs), inorganics, and carrier-free NPs. Finally, we highlight future perspectives of this novel emerging paradigm in targeted cancer therapies.

A New Insight into the Singlet Oxygen Mechanism for Photodynamic Therapy

Modern photodynamic therapy has been built on the mechanism of the interaction between the photosensitizer (porphyrin derivatives) and oxygen to produce singlet oxygen, which relies on energy transfer from the triplet excited state (T₁) of porphyrin to the excited state of oxygen. In this process, the energy transfer from the singlet excited state (S₁) of porphyrin to oxygen is believed to be not pronounced as the rapid decay of S₁ and the large energy mismatch. Here, we have evidenced the existence of an energy transfer between S₁ and oxygen, which can contribute to the production of singlet oxygen. For hematoporphyrin monomethyl ether (HMME), the Stern-Volmer constant of S₁ (K_SV') is 0.023 kPa^-1, according to the oxygen concentration-dependent steady fluorescence intensities. In addition, fluorescence dynamic curves of S₁ under various oxygen concentrations have also been measured through ultrafast pump probe experiments to further verify our results.

Recent advances in type I organic photosensitizers for efficient photodynamic therapy for overcoming tumor hypoxia

Photodynamic therapy (PDT) with an oxygen-dependent character is a noninvasive therapeutic method for cancer treatment. However, its clinical therapeutic effect is greatly restricted by tumor hypoxia. What's more, both PDT-mediated oxygen consumption and microvascular damage aggravate tumor hypoxia, thus, further impeding therapeutic outcomes. Compared to type II PDT with high oxygen dependence and high oxygen consumption, type I PDT with less oxygen consumption exhibits great potential to overcome the vicious hypoxic plight in solid tumors. Type I photosensitizers (PSs) are significantly important for determining the therapeutic efficacy of PDT, which performs an electron transfer photochemical reaction with the surrounding oxygen/substrates to generate highly cytotoxic free radicals such as superoxide radicals (˙O₂^-) as type I ROS. In particular, the primary precursor (˙O₂^-) would progressively undergo a superoxide dismutase (SOD)-mediated disproportionation reaction and a Haber-Weiss/Fenton reaction, yielding higher cytotoxic species (˙OH) with better anticancer effects. As a result, developing high-performance type I PSs to treat hypoxic tumors has become more and more important and urgent. Herein, the latest progress of organic type I PSs (such as AIE-active cationic/neutral PSs, cationic/neutral PSs, polymer-based PSs and supramolecular self-assembled PSs) for monotherapy or synergistic therapeutic modalities is summarized. The molecular design principles and strategies (donor-acceptor system, anion-π⁺ incorporation, polymerization and cationization) are highlighted. Furthermore, the future challenges and prospects of type I PSs in hypoxia-overcoming PDT are proposed.

Efficient NIR-II Type-I AIE Photosensitizer for Mitochondria-Targeted Photodynamic Therapy through Synergistic Apoptosis-Ferroptosis

Hypoxia, the hallmark of malignant tumors, has been recognized as a major obstacle for photodynamic therapy (PDT). Precisely targeting cancer cells in intricate biological scenarios by a hypoxia-resistant photosensitizer (PS) is the cornerstone to conquer the inevitable tumor recurrence and metastasis. Herein, we describe an organic NIR-II PS (TPEQM-DMA) possessing potent type-I phototherapeutic efficacy to overcome the intrinsic pitfalls of PDT in combating hypoxic tumors. TPEQM-DMA exhibited prominent NIR-II emission (>1000 nm) with an aggregation-induced emission feature and efficiently produced superoxide anion and hydroxyl radical in the aggregate state under white light irradiation exclusively through a low-O₂-dependent type-I photochemical process. The suitable cationic nature assisted TPEQM-DMA to accumulate in cancerous mitochondria. Meanwhile, the PDT of TPEQM-DMA impaired the cellular redox homeostasis, led to the mitochondrial dysfunction, and raised the level of lethal peroxidized lipids, which induced cellular apoptosis and ferroptosis. This synergistic cell death modality enabled TPEQM-DMA to suppress the growth of cancer cells, multicellular tumor spheroids, and tumors. To improve the pharmacological properties of TPEQM-DMA, TPEQM-DMA nanoparticles were prepared by encapsulation of polymer. In vivo experiments proved the appealing NIR-II fluorescence imaging-guided PDT effect of TPEQM-DMA nanoparticles for tumors.