All-natural-molecule, bioluminescent photodynamic therapy results in complete tumor regression and prevents metastasis

Laser-Free Photosensitive Systems in Cancer Therapy: A Comprehensive Review

Photodynamic therapy (PDT) involves the use of photosensitizers (PSs) that, upon activation by specific wavelengths of light, generate reactive oxygen species (ROS), including singlet oxygen (1O2) and hydroxyl radicals (·OH), within the targeted tissue, typically tumor cells. The generated ROS induces cellular damage, disrupts cellular processes, and ultimately leads to apoptosis or necrosis of the tumor cells. However, the clinical application of PDT is significantly hindered by the limited tissue penetration ability of light. To address this limitation, laser-free self-luminescent photosensitive systems have emerged as potential solutions for achieving deep-tissue PDT and imaging. This review provides a comprehensive analysis of various laser-independent photosensitive systems, with a particular emphasis on those based on resonance energy transfer (RET), chemically induced electron exchange luminescence (CIEEL), and Cherenkov radiation energy transfer (CRET). The aim is to offer a theoretical framework for the development of novel photodynamic systems and to reassess the application potential of certain previously overlooked photosensitizers (PSs).

Recent Advances in Strategies to Enhance Photodynamic and Photothermal Therapy Performance of Single-Component Organic Phototherapeutic Agents

Photodynamic therapy (PDT) and photothermal therapy (PTT) have emerged as promising treatment options, showcasing immense potential in addressing both oncologic and nononcologic diseases. Single-component organic phototherapeutic agents (SCOPAs) offer advantages compared to inorganic or multicomponent nanomedicine, including better biosafety, lower toxicity, simpler synthesis, and enhanced reproducibility. Nonetheless, how to further improve the therapeutic effectiveness of SCOPAs remains a challenging research area. This review delves deeply into strategies to improve the performance of PDT or PTT by optimizing the structural design of SCOPAs. These strategies encompass augmenting reactive oxygen species (ROS) generation, mitigating oxygen dependence, elevating light absorption capacity, broadening the absorption region, and enhancing the photothermal conversion efficiency (PCE). Additionally, this review also underscores the ideal strategies for developing SCOPAs with balanced PDT and PTT. Furthermore, the potential synergies are highlighted between PDT and PTT with other treatment modalities such as ferroptosis, gas therapy, chemotherapy, and immunotherapy. By providing a comprehensive analysis of these strategies, this review aspires to serve as a valuable resource for clinicians and researchers, facilitating the wider application and advancement of SCOPAs-mediated PDT and PTT.

Simultaneously Controlling Inflammation and Infection by Smart Nanomedicine Responding to the Inflammatory Microenvironment

The overactivated immune cells in the infectious lesion may lead to irreversible organ damages under severe infections. However, clinically used immunosuppressive anti-inflammatory drugs will usually disturb immune homeostasis and conversely increase the risk of infections. Regulating the balance between anti-inflammation and anti-infection is thus critical in treating certain infectious diseases. Herein, considering that hydrogen peroxide (H2O2), myeloperoxidase (MPO), and neutrophils are upregulated in the inflammatory microenvironment and closely related to the severity of appendectomy patients, an inflammatory-microenvironment-responsive nanomedicine is designed by using poly(lactic-co-glycolic) acid (PLGA) nanoparticles to load chlorine E6 (Ce6), a photosensitizer, and luminal (Lum), a chemiluminescent agent. The obtained Lum/Ce6@PLGA nanoparticles, being non-toxic within normal physiological environment, can generate cytotoxic single oxygen via bioluminescence resonance energy transfer (BRET) in the inflammatory microenvironment with upregulated H2O2 and MPO, simultaneously killing pathogens and excessive inflammatory immune cells in the lesion, without disturbing immune homeostasis. As evidenced in various clinically relevant bacterial infection models and virus-induced pneumonia, Lum/Ce6@PLGA nanoparticles appeared to be rather effective in controlling both infection and inflammation, resulting in significantly improved animal survival. Therefore, the BRET-based nanoparticles by simultaneously controlling infections and inflammation may be promising nano-therapeutics for treatment of severe infectious diseases.

Use of parvovirus B19-like particles in self-illuminated photodynamic therapy for solid tumors

Bioluminescence resonance energy transfer photodynamic therapy, which uses light generated by bioluminescent proteins to activate photosensitizers and produce reactive oxygen species without the need for external irradiation, has shown promising results in cancer models. However, the characterization of delivery systems that can incorporate the components of this therapy for preferential delivery to the tumor remains necessary. In this work, we have characterized parvovirus B19-like particles (B19V-VLPs) as a platform for a photosensitizer and a bioluminescent protein. By chemical and biorthogonal conjugation, we conjugated rose Bengal photosensitizer and firefly luciferase to B19V-VLPs and a protein for added specificity. The results showed that B19V-VLPs can withstand decoration with all three components without affecting its structure or stability. The conjugated luciferase showed activity and was able to activate rose Bengal to produce singlet oxygen without the need for external light. The photodynamic reaction generated by the functionalized VLPs-B19 can decrease the viability of tumor cells in vitro and affect tumor growth and metastasis in the 4 T1 model. Treatment with functionalized VLPs-B19 also increased the percentage of CD4 and CD8 cell populations in the spleen and in inguinal lymph nodes compared to vehicle-treated mice. Our results support B19V-VLPs as a delivery platform for bioluminescent photodynamic therapy components to solid tumors.

Development of a Self-Luminescent Living Bioreactor for Enhancing Photodynamic Therapy in Breast Cancer

The penetration ability of visible light (<2 mm) and near-infrared (NIR) light (∼1 cm) remarkably impairs the therapeutic efficacy and clinical applications of photodynamic therapy (PDT). To address the limitation of light penetration depth, a novel self-luminescent bacterium, teLuc.FP-EcN, has been engineered through transfection of a fusion expression plasmid containing the luciferase gene teLuc and bright red fluorescent protein mScarlet-I into Escherichia coli Nissle 1917 (EcN). The engineered teLuc.FP-EcN can specifically target and colonize tumors without significant toxicity to the host. Acting as a continuous internal light source, teLuc.FP-EcN can activate the photosensitizer chlorin e6 (Ce6) to generate reactive oxygen species (ROS) and then effectively destroy tumor tissue from the inside. As a result, a significant reduction in tumor proliferation and extension of the overall survival in mouse tumor models has been observed. Furthermore, teLuc.FP-EcN-boosted PDT amplified its therapeutic effect by activating antitumor immune response, including the conversion of M2 macrophages into pro-inflammatory M1 macrophages, as well as an increase in the proportion of CD3+ T cells and a decrease in T-cell exhaustion. In conclusion, teLuc.FP-EcN can be used as an implantable light source for tumor phototherapy, which simultaneously possesses ROS generation and immune regulation.

Injectable nano-in situ-thermosensitive-hydrogels based on halofuginone and silver for postoperative treatment against triple-negative breast cancer

Postoperative distant metastasis and high recurrence rate causes a dilemma in treating triple-negative breast cancer (TNBC) owing to its unforeseeable invasion into various organs or tissues. The wealth of nutrition provided by vascular may facilitate the proliferation and angiogenesis of cancer cells, which further enhance the rates of postoperative metastasis and recurrence. Chemotherapy, as a systemic postoperative adjuvant therapy, is generally applied to diminish recurrence and metastasis of TNBC. Herein, an halofuginone-silver nano thermosensitive hydrogel (HTPM&AgNPs-gel) was prepared via a physical swelling method. The in vitro anticancer efficacy of HTPM&AgNPs-gel was analyzed by investigating cell proliferation, migration, invasion, and angiogenesis capacity. Furthermore, the in vivo anti-cancer activity of HTPM&AgNPs-gel was further appraised through the tumor suppression, anti-metastatic, anti-angiogenic, and anti-inflammatory ability. The optimized HTPM&AgNPs-gel, a thermosensitive hydrogel, showed excellent properties, including syringeability, swelling behavior, and a sustained release effect without hemolysis. In addition, HTPM&AgNPs-gel was confirmed to effectively inhibit the proliferation, migration, invasion, and angiogenesis of MDA-MB-231 cells. An evaluation of the in vivo anti-tumor efficacy demonstrated that HTPM&AgNPs-gel showed a stronger tumor inhibition rate (68.17%) than did HTPM-gel or AgNPs-gel used alone and exhibited outstanding biocompatibility. Notably, HTPM&AgNPs-gel also inhibited lung metastasis induced by residual tumor tissue after surgery and further blocked angiogenesis-related inflammatory responses. Taken together, the suppression of inflammation by interdicting the blood vessels adjoining the tumor and inhibiting angiogenesis is a potential strategy to attenuate the recurrence and metastasis of TNBC. HTPM&AgNPs-gel is a promising anticancer agent for TNBC as a local postoperative treatment.

Bioluminescent Systems for Theranostic Applications

Bioluminescence, the light produced by biochemical reactions involving luciferases in living organisms, has been extensively investigated for various applications. It has attracted particular interest as an internal light source for theranostic applications due to its safe and efficient characteristics that overcome the limited penetration of conventional external light sources. Recent advancements in protein engineering technologies and protein delivery platforms have expanded the application of bioluminescence to a wide range of theranostic areas, including bioimaging, biosensing, photodynamic therapy, and optogenetics. This comprehensive review presents the fundamental concepts of bioluminescence and explores its recent applications across diverse fields. Moreover, it discusses future research directions based on the current status of bioluminescent systems for further expansion of their potential.

Deepened Photodynamic Therapy through Skin Optical Clearing Technology in the Visible Light Window

The trade-off that shorter wavelength light facilitates the efficient generation of reactive oxygen species (ROS) from photosensitizer (PS) while facing the drawback of limited penetration depth through skin tissue restricts the further development of photodynamic therapy (PDT). Here, we address this contradiction and achieve visible-light-tailored deep PDT combined with the skin optical clearing technology. With the help of the prepared skin optical clearing gel, the refractive index inhomogeneity between skin tissue components is greatly attenuated, and the light scattering effect within the skin tissue is remarkably reduced. As a consequence, the transmittance of visible light at 600 nm through in vitro porcine skin and in vivo mouse skin after treatment increases from approximately 10 and 40 to 70 and 70%, respectively. Furthermore, in the tumor cell eradication experiment, the local ROS generation efficiency in the experimental group is several times higher than that in the control group owing to improved visible transmittance, which is thus responsible for the complete eradication of tumor cells, even when shaded by skin tissue. The results suggest that this strategy may serve as a valuable supplement to the current deep PDT strategies.

Internal Light Sources-Mediated Photodynamic Therapy Nanoplatforms: Hope for the Resolution of the Traditional Penetration Problem

Photodynamic therapy (PDT) is an alternative cancer treatment technique with a noninvasive nature, high selectivity, and minimal adverse effects. The indispensable light source used in PDT is a critical factor in determining the energy conversion of photosensitizers (PSs). Traditional light sources are primarily concentrated in the visible light region, severely limiting their penetration depth and making them prone to scattering and absorption when applied to biological tissues. For that reason, its efficacy in treating deep-seated lesions is often inadequate. Self-exciting PDT, also known as auto-PDT (APDT), is an attractive option for circumventing the limited penetration depth of traditional PDT and has acquired significant attention. APDT employs depth-independent internal light sources to excite PSs through resonance or radiative energy transfer. APDT has considerable potential for treating deep-tissue malignancies. To facilitate many researchers' comprehension of the latest research progress in this field and inspire the emergence of more novel research results. This review introduces internal light generation mechanisms and characteristics and provides an overview of current research progress based on the recently reported APDT nanoplatforms. The current challenges and possible solutions of APDT nanoplatforms are also presented and provide insights for future research in the final section of this article.

HER2-specific liposomes loaded with proteinaceous BRET pair as a promising tool for targeted self-excited photodynamic therapy

Photodynamic therapy (PDT) for deep-seated tumors is still challenging due to the limited penetration of visible light through tissues. To resolve this limitation, systems based on bioluminescence resonance energy transfer (BRET), that do not require an external light source are proposed. Herein, for BRET-activated PDT we developed proteinaceous BRET-pair consisting of luciferase NanoLuc, which acts as energy donor upon addition of luciferase specific substrate furimazine, and phototoxic protein SOPP3 as a photosensitizer. We have shown that hybrid protein NanoLuc-SOPP3 is an excellent BRET pair with BRET ratio of 1.12. Targeted delivery of NanoLuc-SOPP3 BRET pair via tumor-specific small liposomes (∼100 nm) to tumors overexpressing the HER2-receptor (human epidermal growth factor receptor 2) was demonstrated in vitro and in vivo. The proposed BRET-activated system has been shown to significantly suppress tumor growth in a model of subcutaneous and, more importantly, deep-seated tumor model. Taking into account the in vivo efficiency of proposed BRET-activated system, we believe that it has great potential for depth-independent PDT and can significantly broaden the application of PDT in the clinic.

Beyond External Light: On-Spot Light Generation or Light Delivery for Highly Penetrated Photodynamic Therapy

External light sources, such as lasers, light emitting diodes (LEDs) and lamps, are widely applied in photodynamic therapy (PDT); however, their use is severely limited by the nature of shallow tissue penetration depth. The recent exploration of light delivery or local generation on tumor sites has attracted much attention, owing to the fact that these systems are significantly endowed with high tissue penetration. In this review, we briefly introduced the principle of "on-spot light generation or delivery systems" in PDT. These systems are divided into different categories: (1) implantable luminescence, (2) mechanoluminescence, (3) electrochemiluminescence, (4) Cerenkov luminescence, (5) chemiluminescence, and (6) bioluminescence. Finally, their applications, advantages, and disadvantages in PDT will be appropriately summarized and further discussed in detail. We believe that this review will provide general guidance for the further design of light generation or delivery systems and clinical studies for PDT-mediated cancer treatments with unparalleled merits.

System for Self-excited Targeted Photodynamic Therapy Based on the Multimodal Protein DARP-NanoLuc-SOPP3

Despite the significant potential of photodynamic therapy (PDT) as a minimally invasive treatment modality, the use of this method in oncology has remained limited due to two serious problems: 1) limited penetration of the excitation light in tissues, which makes it impossible to affect deep-seated tumors and 2) use of chemical photosensitizers that slowly degrade in the body and cause photodermatoses and hyperthermia in patients. To solve these problems, we propose a fully biocompatible targeted system for PDT that does not require an external light source. The proposed system is based on bioluminescent resonance energy transfer (BRET) from the oxidized form of the luciferase substrate to the photosensitizing protein SOPP3. The BRET-activated system is composed of the multimodal protein DARP-NanoLuc-SOPP3, which contains a BRET pair NanoLuc-SOPP3 and a targeting module DARPin. The latter provides the interaction of the multimodal protein with tumors overexpressing tumor-associated antigen HER2 (human epidermal growth factor receptor type II). In vitro experiments in a 2D monolayer cell culture and a 3D spheroid model have confirmed HER2-specific photo-induced cytotoxicity of the system without the use of an external light source; in addition, experiments in animals with subcutaneous HER2-positive tumors have shown selective accumulation of DARP-NanoLuc-SOPP3 on the tumor site. The fully biocompatible system for targeted BRET-induced therapy proposed in this work makes it possible to overcome the following limitations: 1) the need to use an external light source and 2) the side phototoxic effect from aberrant accumulation of chemical photosensitizers. The obtained results demonstrate that the fully protein-based self-excited BRET system has a high potential for targeted PDT.

Escherichia coli-Based In Situ Triggerable Probe as an Amplifier for Sensitive Diagnosis and Penetrated Therapy of Cancer

Escherichia coli (E. coli) was used for cancer therapy due to the tumor-targeting, catalytic, and surface-reducing properties. Effective diagnosis combined with treatment of cancer based on E. coli, however, was rarely demonstrated. In this study, E. coli was used to surface reduce HAuCl4 and as a carrier to modify riboflavin (Rf) and luminol (E-Au@Rf@Lum). After targeted delivery to tumor, the E-Au@Rf@Lum probe could actively emit 425 nm blue-violet chemiluminescence (CL) to achieve cell imaging for cancer diagnosis. Furthermore, this light could in situ trigger the photosensitizer (Rf) through CL resonance energy transfer, which produces reactive oxygen species (ROS) for accurate photodynamic therapy. In return, the excessive ROS enhanced the blue-violet light which was further absorbed by Rf, and ROS production was cyclically amplified. Abundant ROS broke down the dense extracellular matrix network and penetrated deep into tumors. Besides, E. coli with excellent catalytic property could decompose H2O2 to O2 to relieve tumor hypoxia for a long time and enhance the photosensitized process of Rf. By self-illumination, effective penetration, and tumor hypoxia relief, this work opens a self-amplified therapy modality to tumor.

The Molecular Basis of Organic Chemiluminescence

Bioluminescence (BL) and chemiluminescence (CL) are interesting and intriguing phenomena that involve the emission of visible light as a consequence of chemical reactions. The mechanistic basis of BL and CL has been investigated in detail since the 1960s, when the synthesis of several models of cyclic peroxides enabled mechanistic studies on the CL transformations, which led to the formulation of general chemiexcitation mechanisms operating in BL and CL. This review describes these general chemiexcitation mechanisms-the unimolecular decomposition of cyclic peroxides and peroxide decomposition catalyzed by electron/charge transfer from an external (intermolecular) or an internal (intramolecular) electron donor-and discusses recent insights from experimental and theoretical investigation. Additionally, some recent representative examples of chemiluminescence assays are given.