A photosensitizer with conformational restriction for enhanced photodynamic therapy

A dual-functional photosensitizer for mitochondria-targeting photodynamic therapy and synchronous polarity monitoring

Mitochondria-targeting photodynamic therapy (PDT) has been validated as an effective strategy for inducing cell death through the disruption of mitochondrial function. The mitochondrial microenvironment, such as viscosity, polarity, pH and proteins, undergoes dynamic changes during PDT treatment, and investigating these parameters is crucial for comprehending the intrinsic mechanisms at the cellular level. In this context, disclosure of mitochondrial microenvironment alterations holds significant importance. Nevertheless, a probe capable of visualizing mitochondrial polarity fluctuations during PDT treatment has not been reported. Importantly, a dual-functional photosensitizer (PS) with polarity detection capability is highly advantageous as it can mitigate potential metabolic and localization disparities between the PS and the polarity probe, thus improving the accuracy of detection. In this contribution, a series of potential PSs were prepared by integrating the 2,1,3-benzoxadiazole (BD) scaffold with various heteroatom-incorporated electron-withdrawing groups. Among them, BDI exhibited potent phototoxicity against cancer cells and remarkable sensitivity to polarity changes, establishing it as a dual-functional PS for both photodynamic therapy and polarity detection. Leveraging its polarity detection capability, BDI successfully discriminated mitochondrial polarity discrepancy between cancer cells and normal cells, and indicated mitochondrial polarity fluctuations during drug-induced mitophagy. Crucially, BDI was employed to unveil mitochondrial polarity variations during PDT treatment, underscoring its dual function. Altogether, the meticulous design of the dual-functional PS BDI offers valuable insights into intracellular microenvironment variations during the PDT process, thereby enhancing our understanding and guiding the optimization of PDT treatment.

Rational design of an ultrabright quinolinium-fused rhodamine turn-on fluorescent probe for highly sensitive detection of SO2 derivatives: Applications in food safety and bioimaging

Sulfur dioxide (SO2) is an essential signaling molecule involved in various physiological processes within living organisms. Bisulfite (HSO3-) possesses antioxidant, antimicrobial, and preservative properties, making it a common food additive. However, elevated levels of SO2 or excessive HSO3- intake can lead to a range of diseases, highlighting the importance of detecting SO2 and its derivatives (HSO3-/SO32-). This study presents a quinolinium-fused rhodamine fluorogenic probe (RQB-R) for ultrafast, highly selective, and sensitive detection of HSO3-. The probe operates via a dual-response mechanism, exhibiting a visible color change and a transition from nonemissive to intense red fluorescence upon interaction with HSO3-. The detection mechanism involves a 1,4-nucleophilic addition reaction of HSO3- at the 4-position of the quinolinium unit, which bypasses the photoinduced electron-transfer fluorescence quenching pathway and activates the intramolecular charge transfer mechanism, thereby enhancing fluorescence emission. Practical applications of the RQB-R probe include rapid quantification of HSO3- levels in sugar samples and integration into smartphone-assisted detection platforms. This method demonstrates excellent biocompatibility and enables visualization of both exogenous and endogenous HSO3- within MCF-7 cells, with a specific focus on targeting mitochondria.

A PROTAC Augmenter for Photo-Driven Pyroptosis in Breast Cancer

Proteolysis targeting chimera (PROTAC) has recently emerged as a promising strategy for inducing post-translational knockdown of target proteins in disease treatment. The degradation of bromodomain-containing protein 4 (BRD4), an essential nuclear protein for gene transcription, induced by PROTAC is proposed as an epigenetic approach to treat breast cancer. However, the poor membrane permeability and indiscriminate distribution of PROTAC in vivo results in low bioavailability, limiting its development and application. Herein, a nano "targeting chimera" (abbreviated as L@NBMZ) consisting of BRD4-PROTAC combined with a photosensitizer, to serve as the first augmenter for photo-driven pyroptosis in breast cancer, is developed. With excellent BRD4 degradation ability, high biosafety, and biocompatibility, L@NBMZ blocks gene transcription by degrading BRD4 through proteasomes in vivo, and surprisingly, induces the cleavage of caspase-3. This type of caspase-3 cleavage is synergistically amplified by light irradiation in the presence of photosensitizers, leading to efficient photo-driven pyroptosis. Both in vitro and in vivo outcomes demonstrate the remarkable anti-cancer efficacy of this augmenter, which significantly inhibits the lung metastasis of breast cancer in vivo. Thus, the photo-PROTAC "targeting chimera" augmenter construction strategy may pave a new way for expanding PROTAC applications within anti-cancer paradigms.

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.

A novel furo[3,2-c]pyridine-based AIE photosensitizer for specific imaging and photodynamic ablation of Gram-positive bacteria

An Rh-catalyzed tandem reaction was performed to construct an AIE-active furo[2,3-c]pyridine-based photosensitizer, named LIQ-TF. LIQ-TF showed near-infrared emission with high quantum yield, and high ¹O₂ and ˙OH generation efficiency, and could be used for specific imaging and photodynamic ablation of Gram-positive bacteria in vitro and in vivo, showing great potential for combating multiple drug-resistant bacteria.

Targeted cancer phototherapy using phthalocyanine-anticancer drug conjugates

Phototherapy, the use of light to selectively ablate cancerous tissue, is a compelling prospect. Phototherapy is divided into two major domains: photodynamic and photothermal, whereby photosensitizer irradiation generates reactive oxygen species or heat, respectively, to disrupt the cancer microenvironment. Phthalocyanines (Pcs) are prominent phototherapeutics due to their desirable optical properties and structural versatility. Targeting of Pc photosensitizers historically relied on the enhanced permeation and retention effect, but the weak specificity engendered by this approach has hindered bench-to-clinic translation. To improve specificity, antibody and peptide active-targeting groups have been employed to some effect. An alternative targeting method exploits the binding of anticancer drugs to direct the photosensitizer close to essential cellular components, allowing for precise, synergistic phototherapy. This Perspective explores the use of Pc-drug conjugates as targeted anticancer phototherapeutic systems with examples of Pc-platin, Pc-kinase, and Pc-anthracycline conjugates discussed in detail.

A NIR molecular rotor photosensitizer for efficient PDT and synchronous mitochondrial viscosity imaging

Herein, two mitochondria-targeting photosensitizers (PSs, CCVJ-Mito-1 and CCVJ-Mito-2) that exhibit a turn-on fluorescence response towards increasing viscosity are reported. Notably, CCVJ-Mito-2 exhibits absorption in the near-infrared (NIR) region, and can be employed as a NIR PS targeting mitochondria and a fluorescent probe for tracking mitochondrial viscosity changes during photodynamic therapy (PDT). This dual functional PS can help to shed light on the dynamic changes of the cellular microenvironment during PDT and further guide the PDT process.