Targeted delivery of PROTAC-based prodrug activated by bond-cleavage bioorthogonal chemistry for microneedle-assisted cancer therapy

Bioorthogonal strategy-triggered In situ co-activation of aggregation-induced emission photosensitizers and chemotherapeutic prodrugs for boosting synergistic chemo-photodynamic-immunotherapy

In situ activation of prodrugs or photosensitizers is a promising strategy for specifically killing tumor cells while avoiding toxic side effects. Herein, we originally develop a bioorthogonally activatable prodrug and pro-photosensitizer system to synchronously yield an aggregation-induced emission (AIE) photosensitizer and a chemotherapeutic drug for synergistic chemo-photodynamic-immunotherapy of tumors. By employing molecular engineering strategy, we rationally design a family of tetrazine-functionalized tetraphenylene-based photosensitizers, one of which (named TzPS5) exhibits a high turn-on ratio, a NIR emission, a typical AIE character, and an excellent ROS generation efficiency upon bioorthogonal-activation. With the aid of integrin- or mitochondria-pretargeting, TzPS5 is successfully applied for highly effective PDT ablation of cancer cells both in vitro and in vivo. On this basis, tumor-targeting TzPS5 (TzPS5-cRGD) is constructed and used jointly with a bioorthogonal prodrug, DOX-TCO, and the two are mutually activated to induce cooperative and tumor-specific PDT and chemotherapy, resulting in amplified therapeutic outcomes and improved biosafeties. Moreover, this combination modality elicits robust immunogenic cell death, stimulates systemic antitumor immunity, thereby suppressing both primary and distant tumors, and blocking the pulmonary tumor metastasis. This work is expected to provide a useful guidance for the rational design of activatable phototheranostic agents, and offer a new strategy for co-activation of prodrugs/pro-photosensitizers to boost synergistic antitumor chemo-photodynamic-immunotherapy.

Advancements in delivery Systems for Proteolysis-Targeting Chimeras (PROTACs): Overcoming challenges and expanding biomedical applications

PROTAC (Proteolysis-Targeting Chimera), an emerging drug development strategy based on small molecule technology, has garnered widespread attention due to its high efficiency, broad applicability, low resistance, and dosage advantages. However, PROTAC molecules still exhibit certain limitations that require urgent resolution. Although significant progress has been made in designing PROTACs that target various disease-related proteins, research on drug delivery systems (DDS) for PROTACs remains relatively limited. This review aims to explore the critical role of delivery system design in addressing the inherent challenges associated with PROTAC molecules from a novel perspective. Beginning with five major challenges-insufficient targeting, poor pharmacokinetic properties, low cell permeability, limited accessibility, and the Hook effect-this article introduces formulation strategies to mitigate these deficiencies. It discusses potential solutions through targeted modifications, nano-delivery systems, intelligent response systems, and membrane biomimetic technologies, among others. Furthermore, it elucidates the mechanisms and principles underlying these approaches and analyzes the advantages of various delivery strategies. The insights provided in this review offer insights for designing delivery systems tailored to PROTACs with diverse characteristics for different disease applications.

Targeted Degradation of Bromodomain-Containing Protein 4 Enabled by Reactive Oxygen Species-Activatable NanoPROTACs as an Efficient Strategy to Reverse Liver Fibrosis in Chronic Liver Injury

Liver fibrosis is an inadequate response to tissue stress, with reactive oxygen species (ROS) overproduction in activated hepatic stellate cells (aHSCs). Bromodomain-containing protein 4 (BRD4) was found to be upregulated in aHSCs and has been identified as an effective target for the treatment of liver fibrosis. However, inhibition of BRD4 with traditional kinase inhibitors achieved only limited success because of its low therapeutic efficiency. Furthermore, the exact mechanism by which BRD4 regulates liver fibrosis remains unclear and needs to be elucidated. In this work, we proposed an efficiency strategy, i.e., targeted degradation of BRD4 by ROS-activatable NanoPROTACs, for the treatment of liver fibrosis, both in vitro and in vivo. More importantly, we clarified the mechanism by which BRD4 regulates liver fibrosis. Thus, this strategy may represent an alternative to previously reported strategies and may be extensively applied to the design of ROS-activatable proteolysis-targeting chimeras for the treatment of other organ fibrosis.

Unveiling the photophysical mechanistic mysteries of tetrazine-functionalized fluorogenic labels

Tetrazine-based fluorogenic labels are widely utilized in medical and biological studies, exhibiting substantial fluorescence enhancement (FE) following tetrazine degradation through bio-orthogonal reactions. However, the underlying mechanisms driving this fluorogenic response remain only partially resolved, particularly regarding the diminished FE efficiency in the deep-red and near-infrared (NIR) regions. This knowledge gap has impeded efforts to optimize these labels for extended emission wavelengths and improved FE ratios. This review offers a photophysical perspective, discussing the fluorescence quenching pathways (i.e., energy flows and charge separation) that regulate the fluorogenic properties exhibited in various types of tetrazine labels. Moreover, this work examines the emerging role of intramolecular rotations in certain tetrazine-based structures and the integration of additional quencher units. The proposed alternative quenching channel offers the potential to surpass traditional wavelength constraints while achieving improved FE. By examining these photophysical mechanisms, this review aims to advance the understanding of tetrazine-functionalized fluorogenic labels and provide guiding principles for their future design and practical applications.

In Vivo Self-Assembly of PROTACs by Bioorthogonal Chemistry for Precision Cancer Therapy

Proteolysis targeting chimeras (PROTACs) hold immense promise for targeted protein degradation; however, challenges such as off-target effects, poor drug-likeness properties, and the "hook effect" remain. This study introduces Nano-Click-formed PROTACs (Nano-CLIPTACs) for precise tumor protein degradation in vivo. Traditional PROTACs with high molecular weight were first divided into two smaller druglike precursors capable of self-assembling to form functional PROTACs through a bioorthogonal reaction. Then, optimal CLIPTACs precursors (W4 and Z2) were encapsulated individually into cyclic RGDfC-peptide-modified liposomes to prepare Nano-CLIPTACs, enabling tumor-targeted delivery and subsequent in situ self-assembly to form PROTACs WZ42 within tumor cells. The degradation abilities of Nano-CLIPTACs in vitro and in vivo were further verified using a key oncology target, anaplastic lymphoma kinase (ALK), validating the safety, efficacy and "anti-hook effect" of this strategy. Overall, Nano-CLIPTACs represent a critical step towards the clinical translation of PROTACs technology for precise targeted anti-cancer therapies.

PROTAC delivery in tumor immunotherapy: Where are we and where are we going?

Immunotherapy has emerged as a pioneering therapeutic modality, particularly within the realm of oncology, where Chimeric Antigen Receptor T-cell (CAR-T) therapy has manifested significant efficacy in the treatment of hematological malignancies. Nonetheless, the extension of immunotherapy to solid tumors poses a considerable challenge. This challenge is largely attributed to the intrinsic "cold" characteristics of certain tumors, which are defined by scant T-cell infiltration and a diminished immune response. Additionally, the impediment is exacerbated by the elusive nature of numerous targets within the tumor microenvironment, notably those deemed "undruggable" by small molecule inhibitors. This scenario underscores an acute necessity for the inception of innovative therapeutic strategies aimed at countering the resistance mechanisms underlying immune evasion in cold tumors, thereby amplifying the efficacy of cancer immunotherapy. Among the promising strategies is the deployment of Proteolysis Targeting Chimeras (PROTACs), which facilitate the targeted degradation of proteins. PROTACs present unique advantages and have become indispensable in oncology. However, they concurrently grapple with challenges such as solubility issues, permeability barriers, and the classical Hook effect. Notably, advanced delivery systems have been instrumental in surmounting these obstacles. This review commences with an analysis of the factors contributing to the suboptimal responses to immunotherapy in cold tumors. Subsequently, it delivers a thorough synthesis of immunotherapeutic concepts tailored for these tumors, clarifying the integral role of PROTACs in their management and delineating the trajectory of PROTAC technology from bench-side investigation to clinical utilization, facilitated by drug delivery systems. Ultimately, the review extrapolates the prospective future of this approach, aspiring to present novel insights that could catalyze progress in immunotherapy for the treatment of cold tumors.

MicroRNA-Triggered Programmable DNA-Encoded Pre-PROTACs for Cell-Selective and Controlled Protein Degradation

Proteolysis-targeting chimeras (PROTACs) have accelerated drug development; however, some challenges still exist owing to their lack of tumor selectivity and on-demand protein degradation. Here, we developed a miRNA-initiated assembled pre-PROTAC (miRiaTAC) platform that enables the on-demand activation and termination of target degradation in a cell type-specific manner. Using miRNA-21 as a model, we engineered DNA hairpins labeled with JQ-1 and pomalidomide and facilitated the modular assembly of DNA-encoded pre-PROTACs through a hybridization chain reaction. This configuration promoted the selective polyubiquitination and degradation of BRD4 upon miR-21 initiation, highlighting significant tumor selectivity and minimal systemic toxicity. Furthermore, the platform incorporates photolabile groups, enabling the precise optical control of pre-PROTACs during DNA assembly/disassembly, mitigating the risk of excessive protein degradation. Additionally, by introducing a secondary ligand targeting CDK6, these pre-PROTACs were used as a modular scaffold for the programmable assembly of active miRiaTACs containing two different warheads in exact stoichiometry, enabling orthogonal multitarget degradation. The integration of near-infrared light-mediated photodynamic therapy through an upconversion nanosystem further enhanced the efficacy of the platform with potent in vivo anticancer activity. We anticipate that miRiaTAC represents a significant intersection between dynamic DNA nanotechnology and PROTAC, potentially expanding the versatility of PROTAC toolkit for cancer therapy.

Precision-engineered PROTACs minimize off-tissue effects in cancer therapy

Proteolysis-targeting chimeras (PROTACs) offer a groundbreaking approach to selectively degrade disease-related proteins by utilizing the ubiquitin-proteasome system. While this strategy shows great potential in preclinical and clinical settings, off-tissue effects remain a major challenge, leading to toxicity in healthy tissues. This review explores recent advancements aimed at improving PROTAC specificity, including tumor-specific ligand-directed PROTACs, pro-PROTACs activated in tumor environments, and E3 ligase overexpression strategies. Innovations such as PEGylation and nanotechnology also play a role in optimizing PROTAC efficacy. These developments hold promise for safer, more effective cancer therapies, though challenges remain for clinical translation.

Dual targeting and bioresponsive nano-PROTAC induced precise and effective lung cancer therapy

Epigenetic regulation has emerged as a promising therapeutic strategy for lung cancer treatment, which can facilitate the antitumor responses by modulating epigenetic dysregulation of target proteins in lung cancer. The proteolysis-targeting chimera (PROTAC) reagent, dBET6 shows effective inhibition of bromodomain-containing protein 4 (BRD4) that exerts antitumor efficacy by degrading BRD4 via the ubiquitin-proteasome system. Nevertheless, the low tissue specificity and bioavailability impede its therapeutic effects and clinical translation on lung cancer treatment. Herein, we developed a type of dual targeting and bioresponsive nano-PROTAC (c R GD/L LC membrane/D S-P LGA/d B ET6, named RLDPB), which was constructed by using the pH and glutathione (GSH)-responsive polymer, disulfide bond-linked poly(lactic-co-glycolic acid) (PLGA-S-S-PLGA, DS-PLGA) to load the PROTAC agent dBET6, and further camouflaged with the homotypic LLC cell membranes, followed by the conjugation with cRGD ligand to the surface of the nanoparticles. Notably, RLDPB showed enhanced celluar uptake by lung cancer cells in vitro and accumulation in the tumors via the dual targeting structure including cRGD and LLC membrane. The pH/GSH responsiveness improved the release of dBET6 from the DS-PLGA-based nanoparticles within the cells. RLDPB was demonstrated to facilitate tumor regression by inducing the apoptosis of lung cancer cells with the degradation of BRD4. Thus, RLDPB can be considered a powerful tool to suppress lung cancer, which opens a new avenue to treat lung cancer by PROTAC.

Advancing Proteolysis Targeting Chimera (PROTAC) Nanotechnology in Protein Homeostasis Reprograming for Disease Treatment

Proteolysis targeting chimeras (PROTACs) represent a transformative class of therapeutic agents that leverage the intrinsic protein degradation machinery to modulate the hemostasis of key disease-associated proteins selectively. Although several PROTACs have been approved for clinical application, suboptimal therapeutic efficacy and potential adverse side effects remain challenging. Benefiting from the enhanced targeted delivery, reduced systemic toxicity, and improved bioavailability, nanomedicines can be tailored with precision to integrate with PROTACs which hold significant potential to facilitate PROTAC nanomedicines (nano-PROTACs) for clinical translation with enhanced efficacy and reduced side effects. In this review, we provide an overview of the recent progress in the convergence of nanotechnology with PROTAC design, leveraging the inherent properties of nanomaterials, such as lipids, polymers, inorganic nanoparticles, nanohydrogels, proteins, and nucleic acids, for precise PROTAC delivery. Additionally, we discuss the various categories of PROTAC targets and provide insights into their clinical translational potential, alongside the challenges that need to be addressed.

Microneedle system for tissue engineering and regenerative medicines: a smart and efficient therapeutic approach

The global demand for an enhanced quality of life and extended lifespan has driven significant advancements in tissue engineering and regenerative medicine. These fields utilize a range of interdisciplinary theories and techniques to repair structurally impaired or damaged tissues and organs, as well as restore their normal functions. Nevertheless, the clinical efficacy of medications, materials, and potent cells used at the laboratory level is always constrained by technological limitations. A novel platform known as adaptable microneedles has been developed to address the abovementioned issues. These microneedles offer a solution for the localized distribution of various cargos while minimizing invasiveness. Microneedles provide favorable patient compliance in clinical settings due to their effective administration and ability to provide a painless and convenient process. In this review article, we summarized the most recent development of microneedles, and we started by classifying various microneedle systems, advantages, and fundamental properties. Subsequently, it provides a comprehensive overview of different types of microneedles, the material used to fabricate microneedles, the fundamental properties of ideal microneedles, and their applications in tissue engineering and regenerative medicine, primarily focusing on preserving and restoring impaired tissues and organs. The limitations and perspectives have been discussed by concluding their future therapeutic applications in tissue engineering and regenerative medicines.

Controlled bioorthogonal activation of Bromodomain-containing protein 4 degrader by co-delivery of PROTAC and Pd-catalyst for tumor-specific therapy

The precise and safe treatment of bioorthogonal prodrug system is hindered by separate administration of prodrug and its activator, which often results in poor therapeutic effects and severe side effects. To address above issues, we herein construct a single bioorthogonal-activated co-delivery system for simultaneous PROTAC prodrug (proPROTAC) delivery and controlled, site-specific activation for tumor-specific treatment. In this co-delivery system (termed AuPLs), prodrug (proPROTAC) and water-soluble Pd-catalyst are first encapsulated by gold nanocubes (AuNCs), which are further coated with a layer of phase-change material (lauric acid/stearic acid, LA/SA). Below 39 °C, the solid state of LA/SA prevents the activation of Pd-mediated bioorthogonal reaction due to the solidification of Pd-catalyst and proPROTAC. Nevertheless, once over 42 °C, the phase change of LA/SA into liquid state, enabled by the photothermal effect of AuNCs, triggers the simultaneous release of proPROTAC and Pd-catalyst and initiates the in situ bioorthogonal reaction for proPROTAC activation. In the tumor-bearing mouse models, the systemic administration of AuPLs results in the accumulation in tumor region, where the photothermal effect activates and controls the tumor-specific bioorthogonal reaction to degrade BRD4 protein, leading to anti-tumor effects with minimized side effects. Overall, the co-delivery proPROTAC and Pd-catalyst and controlled activation by photothermal effects provide a precise way for biorthogonal-based anticancer prodrugs.

Drugtamer-PROTAC Conjugation Strategy for Targeted PROTAC Delivery and Synergistic Antitumor Therapy

Proteolysis-targeting chimeras (PROTACs) have emerged as a promising strategy for targeted protein degradation and drug discovery. To overcome the inherent limitations of conventional PROTACs, an innovative drugtamer-PROTAC conjugation approach is developed to enhance tumor targeting and antitumor potency. Specifically, a smart prodrug is designed by conjugating "drugtamer" to a nicotinamide phosphoribosyltransferase (NAMPT) PROTAC using a tumor microenvironment responsible linker. The "drugtamer" consists of fluorouridine nucleotide and DNA-like oligomer. Compared to NAMPT PROTAC and the combination of PROTAC + fluorouracil, the designed prodrug AS-2F-NP demonstrates superior tumor targeting, efficient cellular uptake, improved in vivo potency and reduced side effects. This study provides a promising strategy for the precise delivery of PROTAC and synergistic antitumor agents.

Bromodomain and Extraterminal Domain Protein 2 in Multiple Human Diseases

Bromodomain and extraterminal domain protein 2 (BRD2), a member of the bromodomain and extraterminal domain (BET) protein family, is a crucial epigenetic regulator with significant function in various diseases and cellular processes. The central function of BRD2 is modulating gene transcription by binding to acetylated lysine residues on histones and transcription factors. This review highlights key findings on BRD2 in recent years, emphasizing its roles in maintaining genomic stability, influencing chromatin spatial organization, and participating in transcriptional regulation. BRD2's diverse functions are underscored by its involvement in diseases such as malignant tumors, neurologic disorders, inflammatory conditions, metabolic diseases, and virus infection. Notably, the potential role of BRD2 as a diagnostic marker and therapeutic target is discussed in the context of various diseases. Although pan inhibitors targeting the BET family have shown promise in preclinical studies, a critical need exists for the development of highly selective BRD2 inhibitors. In conclusion, this review offers insights into the multifaceted nature of BRD2 and calls for continued research to unravel its intricate mechanisms and harness its therapeutic potential. SIGNIFICANCE STATEMENT: BRD2 is involved in the occurrence and development of diseases through maintaining genomic stability, influencing chromatin spatial organization, and participating in transcriptional regulation. Targeting BRD2 through protein degradation-targeting complexes technology is emerging as a promising therapeutic approach for malignant cancer and inflammatory diseases.

New-generation advanced PROTACs as potential therapeutic agents in cancer therapy

Proteolysis-targeting chimeras (PROTACs) technology has garnered significant attention over the last 10 years, representing a burgeoning therapeutic approach with the potential to address pathogenic proteins that have historically posed challenges for traditional small-molecule inhibitors. PROTACs exploit the endogenous E3 ubiquitin ligases to facilitate degradation of the proteins of interest (POIs) through the ubiquitin-proteasome system (UPS) in a cyclic catalytic manner. Despite recent endeavors to advance the utilization of PROTACs in clinical settings, the majority of PROTACs fail to progress beyond the preclinical phase of drug development. There are multiple factors impeding the market entry of PROTACs, with the insufficiently precise degradation of favorable POIs standing out as one of the most formidable obstacles. Recently, there has been exploration of new-generation advanced PROTACs, including small-molecule PROTAC prodrugs, biomacromolecule-PROTAC conjugates, and nano-PROTACs, to improve the in vivo efficacy of PROTACs. These improved PROTACs possess the capability to mitigate undesirable physicochemical characteristics inherent in traditional PROTACs, thereby enhancing their targetability and reducing off-target side effects. The new-generation of advanced PROTACs will mark a pivotal turning point in the realm of targeted protein degradation. In this comprehensive review, we have meticulously summarized the state-of-the-art advancements achieved by these cutting-edge PROTACs, elucidated their underlying design principles, deliberated upon the prevailing challenges encountered, and provided an insightful outlook on future prospects within this burgeoning field.

Selective Elimination of Senescent Cancer Cells by Galacto-Modified PROTACs

Although the selective and effective clearance of senescent cancer cells can improve cancer treatment, their development is confronted by many challenges. As part of efforts designed to overcome these problems, prodrugs, whose design is based on senescence-associated β-galactosidase (SA-β-gal), have been developed to selectively eliminate senescent cells. However, chemotherapies relying on targeted molecular inhibitors as senolytic drugs can induce drug resistance. In the current investigation, we devised a new strategy for selective degradation of target proteins in senescent cancer cells that utilizes a prodrug composed of the SA-β-gal substrate galactose (galacto) and the proteolysis-targeting chimeras (PROTACs) as senolytic agents. Prodrugs Gal-ARV-771 and Gal-MS99 were found to display senolytic indexes higher than those of ARV-771 and MS99. Significantly, results of in vivo studies utilizing a human lung A549 xenograft mouse model demonstrated that concomitant treatment with etoposide and Gal-ARV-771 leads to a significant inhibition of tumor growth without eliciting significant toxicity.

Targeted Protein Degraders- The Druggability Perspective

Targeted Protein degraders (TPDs) show promise in harnessing cellular machinery to eliminate disease-causing proteins, even those previously considered undruggable. Especially if protein turnover is low, targeted protein removal bestows lasting therapeutic effect over typical inhibition. The demonstrated safety and efficacy profile of clinical candidates has fueled the surge in the number of potential candidates across different therapeutic areas. As TPDs often do not comply with Lipinski's rule of five, developing novel TPDs and unlocking their full potential requires overcoming solubility, permeability and oral bioavailability challenges. Tailored in-vitro assays are key to precise profiling and optimization, propelling breakthroughs in targeted protein degradation.

Nano-PROTACs: state of the art and perspectives

PROteolysis TArgeting Chimeras (PROTACs), as a recently identified technique in the field of new drug development, provide new concepts for disease treatment and are expected to revolutionize drug discovery. With high specificity and flexibility, PROTACs serve as an innovative research tool to target and degrade disease-relevant proteins that are not currently pharmaceutically vulnerable to eliminating their functions by hijacking the ubiquitin-proteasome system. To date, PROTACs still face the challenges of low solubility, poor permeability, off-target effects, and metabolic instability. The combination of nanotechnology and PROTACs has been explored to enhance the in vivo performance of PROTACs regarding overcoming these challenging hurdles. In this review, we summarize the latest advancements in the building-block design of PROTAC prodrug nanoparticles and provide an overview of existing/potential delivery systems and loading approaches for PROTAC drugs. Furthermore, we discuss the current status and prospects of the split-and-mix approach for PROTAC drug optimization. Additionally, the advantages and translational potentials of carrier-free nano-PROTACs and their combinational therapeutic effects are highlighted. This review aims to foster a deeper understanding of this rapidly evolving field and facilitate the progress of nano-PROTACs that will continue to push the boundaries of achieving selectivity and controlled release of PROTAC drugs.

Aggregation-induced emission photosensitizer microneedles for enhanced melanoma photodynamic therapy

The incidence and mortality rates of skin melanoma have been increasing annually. Photodynamic therapy (PDT) enables effective destruction of tumor cells while minimizing harm to normal cells. However, traditional photosensitizers (PSs) suffer from photobleaching, photodegradation and the aggregation-caused quenching (ACQ) effect, and it is challenging for light to reach the deep layers of the skin to maximize the efficacy of PSs. Herein, we developed dissolving microneedles (MNs) loaded with PSs of TPE-EPy@CB[7] through supramolecular assembly. The PSs effectively enhanced the type-I reactive oxygen species (ROS) generation capacity, with a concentration of 2 μM possessing nearly half of the tumor cell-killing ability under 10 min white light irradiation. The MNs were successfully pierced into the targeted site for precise drug delivery. Additionally, the conical structure of the MNs, as well as the lens-like structure after dissolution, facilitated the transmission of light in the subcutaneous tissue, achieving significant inhibition of tumor growth with a tumor suppression rate of 97.8% and no systemic toxicity or side effects in melanoma mice. The results demonstrated the potent melanoma inhibition and biosafety of this treatment approach, exhibiting a new and promising strategy to conquer malignant melanoma.