A region-confined PROTAC nanoplatform for spatiotemporally tunable protein degradation and enhanced cancer therapy

Innovative sarcoma therapy using multifaceted nano-PROTAC-induced EZH2 degradation and immunity enhancement

Sarcomas are highly malignant tumors characterized by their heterogeneity and resistance to conventional therapies, which significantly limit treatment options. EZH2 is highly expressed in sarcomas, but targeting it is difficult. In this study, we uncovered the non-canonical transcriptional mechanisms of EZH2 in sarcoma and highlighted the essential role of EZH2 in regulating YAP1 through non-canonical transcriptional pathways in the progression of sarcoma. Building on this, we developed YM@VBM, a novel and versatile nano-PROTAC (proteolysis-targeting chimera), by integrating a polyphenol-vanadium oxide system with the EZH2 degrader YM281 PROTAC, encapsulated in methoxy polyethylene glycol-NH2 to enhance biocompatibility. To further facilitate targeted drug delivery to tumors, YM@VBM nano-PROTACs were incorporated into microneedle patches. Our engineered YM@VBM exhibited multiple functionalities, including the peroxidase-like activity to generate reactive oxygen species, depletion of glutathione, and photothermal effects, specifically targeting sarcoma characteristics. YM@VBM significantly enhanced targeting efficacy via inducing potent EZH2 degradation. Most importantly, it can also activate anti-tumor immunity via excluding myeloid-derived suppressor cells, maturing dendritic cells, and forming tertiary lymphoid structures. Hence, we reveal that YM@VBM presents a promising treatment strategy for sarcoma, offering a multifaceted approach to combat this challenging malignancy.

Photo-Activated PROTACs for Targeted BRD4 Degradation and Synergistic Photodynamic Therapy in Bladder Cancer

Proteolysis-targeting chimera (PROTAC) drugs rely on the formation of a ternary complex consisting of the target protein, the drug, and a ubiquitin-protein ligase (E3 ubiquitin ligase). However, some cancer patients may not exhibit sufficient expression of both the target protein and the E3 ligase in tumor tissues, leading to potential off-target effects when treated with conventional PROTACs. In this study, we have developed a photoactivated PROTAC strategy that employs the photosensitizer monosubstituted amino phthalocyanine (ZnPc) and the bromine domain protein 4 (BRD4) ligand (JQ1) as core components. A series of highly active compounds were designed and the most effective and safe candidate (ZnPc-O3-JQ1), was identified. Upon activation by light, ZnPc-O3-JQ1 generates reactive oxygen species (ROS) that degrade BRD4. The degradation of BRD4 results in downregulation of hypoxia-inducible factor-1α (HIF-1α), thereby counteracting the treatment resistance induced by tumor hypoxia during photodynamic therapy (PDT). Furthermore, to mitigate oxidative stress caused by ROS, cells upregulate cystine/glutamate antiporter system (Xc- system, SLC7A11) to enhance glutathione (GSH) synthesis. However, downregulation of HIF-1α inhibits GSH synthesis by inhibiting glutamate-cysteine ligase (GCL, the key enzyme in the de novo synthesis of GSH), disrupting the antioxidant defense system. This photo-PROTAC strategy enables a mutually synergistic effect between PDT and PROTAC, providing a new avenue for the design of safer and more efficient PROTAC drugs, photosensitizers, and combination therapies.

Pt(IV)-PROTAC Complexes with Synergistic Antitumor Activity and Enhanced Membrane Permeability

A class of Pt(IV)-PROTAC complexes was designed and synthesized with dual aims of inducing DNA strand damage and inhibiting DNA repair. These complexes showed good antiproliferative activity against a range of cancer cell lines. Enhanced intracellular uptake of platinum and PROTAC was observed. Multiple mechanisms of action were identified, including the induction of DNA damage, disruption of DNA repair, and activation of mitochondrial-dependent apoptosis. One of the Pt(IV)-PROTACs, CW-2, showed excellent antitumor activity in a xenograft mouse model. These results suggest that Pt(IV)-PROTAC represents a promising strategy for the development of novel antitumor therapeutics.

Tumor Microenvironment-Responsive Polymer Delivery Platforms for Cancer Therapy

Most chemotherapeutic and bioimaging agents struggle with inadequate bioavailability, primarily due to their limited biocompatibility and lack of specificity in targeting, leading to low or decreased anticancer efficacy and inaccurate imaging. To surmount these obstacles, the development of stimuli-responsive polymer delivery platforms, predominantly leveraging the tumor microenvironment (TME), has emerged as a promising strategy. Therapeutic and diagnostic agents can be released controllably at the tumor site by virtue of the bond cleavage or hydrophobic to hydrophilic transformation of TME-sensitive linkages in TME-responsive systems, thus augmenting cancer treatment and imaging precision, while simultaneously attenuating the damage to healthy tissues and false imaging signals caused by non-specific drug leakage. In this comprehensive review, we scrutinize recent studies of TME-responsive polymer delivery platforms, encompassing pH-, ROS-, GSH-, enzyme-, and hypoxia-responsive vectors, significantly from the perspective of their molecular design and responsive mechanism, and further summarizing their bio-application in drug delivery and diagnostic imaging. Moreover, this review encapsulates the critical challenges and offers an insightful perspective on the future prospects of TME-responsive polymer delivery platforms in terms of molecular and vector design.

PROTAC Delivery Strategies for Overcoming Physicochemical Properties and Physiological Barriers in Targeted Protein Degradation

Proteolysis targeting chimeras (PROTACs), heterobifunctional molecules that hijack the ubiquitin-proteasome system (UPS) to degrade specific proteins, hold great promise in treating diseases driven by traditionally "undruggable" targets. However, their large molecular weight, high hydrophobicity, and other physicochemical hurdles contribute to their limited bioavailability, suboptimal pharmacokinetics, and attenuated therapeutic efficacy. Consequently, diverse formulation innovations have been investigated to optimize PROTAC delivery. This review examines current challenges and advances in specialized drug delivery approaches designed to bolster PROTAC pharmacological performance. We first outline the fundamental limitations of PROTACs-their low aqueous solubility, poor cell permeability, rapid clearance, and concentration-dependent "hook effect". We then discuss how various enabling formulations address these issues, including polymeric micelles, emulsions, amorphous solid dispersions, lipid-based nanoparticles, liposomes, and exosomes. Collectively, these delivery technologies substantially improve the therapeutic outcomes of PROTACs in preclinical cancer models. Future applications may extend beyond oncology to address other complex diseases using newly emerging heterobifunctional molecules. By integrating advanced formulation science with innovative degrader design, the field stands poised to unlock the clinical potential of PROTACs for protein degradation therapies.

Self-Oxygenating PROTAC Microneedle for Spatiotemporally-Confined Protein Degradation and Enhanced Glioblastoma Therapy

Glioblastoma (GBM) is the most aggressive subtype of primary brain tumors, which marginally respond to standard chemotherapy due to the blood-brain barrier (BBB) and the low tumor specificity of the therapeutics. Herein, a double-layered microneedle (MN) patch is rationally engineered by integrating acid and light dual-activatable PROteolysis TArgeting Chimera (PROTAC) nanoparticles and self-oxygenating BSA-MnO2 (BM) nanoparticles for GBM treatment. The MN is administrated at the tumor site to locally deliver the PROTAC prodrug and BM nanoparticles. The PROTAC nanoparticles are rapidly released from the outer layer of the MN and specifically activated in the acidic intracellular environment of tumor cells. Subsequently, near-infrared light activates the photosensitizer to produce singlet oxygen (1O2) through photodynamic therapy (PDT), thereby triggering spatiotemporally-tunable degradation of bromodomain and extraterminal protein 4 (BRD4). The BM nanoparticles, in the inner layer of the MN, serve as an oxygen supply station, and counteracts tumor hypoxia by converting hydrogen peroxide (H2O2) into oxygen (O2), thus promoting PDT and PROTAC activation. This PROTAC prodrug-integrated MN significantly inhibits tumor growth in both subcutaneous and orthotopic GBM tumor models. This study describes the first spatiotemporally-tunable protein degradation strategy for highly efficient GBM therapy, potentially advancing precise therapy of other kinds of refractory brain tumors.

Exploring the clinical trials, regulatory insights, and challenges of PROTACs in oncology

While various targeted therapies exist for cancer, resistance mechanisms remain a significant challenge. Recent advancements in cancer treatment have led to the emergence of proteolysis-targeting chimeras (PROTACs), a promising technology utilizing hetero-bifunctional molecules to target and degrade proteins implicated in cancer progression through the ubiquitin-proteasome system (UPS). PROTACs offer a novel approach, with recent studies and clinical trials demonstrating promising outcomes in degrading endogenous proteins linked to cancer. This work explores classification, regulatory approvals, and ongoing clinical trials of PROTAC technology in cancer management. It emphasizes the importance of regulatory compliance to expedite approvals from relevant authorities. It also highlights challenges and opportunities associated with their implementation. Despite these preliminary efforts, PROTACs show immense potential in effectively addressing cancer. Their ability to target specific proteins for degradation represents a significant advancement in cancer therapeutics, offering new hope for improved outcomes in patient care.

DNA Tetrahedron-Driven Multivalent Proteolysis-Targeting Chimeras: Enhancing Protein Degradation Efficiency and Tumor Targeting

Proteolysis-targeting chimeras (PROTACs) are dual-functional molecules composed of a protein of interest (POI) ligand and an E3 ligase ligand connected by a linker, which can recruit POI and E3 ligases simultaneously, thereby inducing the degradation of POI and showing great potential in disease treatment. A challenge in developing PROTACs is the design of linkers and the modification of ligands to establish a multifunctional platform that enhances degradation efficiency and antitumor activity. As a programmable and modifiable nanomaterial, DNA tetrahedron can precisely assemble and selectively recognize molecules and flexibly adjust the distance between molecules, making them ideal linkers. Herein, we developed a multivalent PROTAC based on a DNA tetrahedron, named AS-TD2-PRO. Using DNA tetrahedron as a linker, we combined modules targeting tumor cells, recognizing E3 ligases, and multiple POI together. We took the undruggable target protein signal transducer and activator of transcription 3 (STAT3), associated with the etiology and progression in a variety of malignant tumors, as an example in this study. AS-TD2-PRO with two STAT3 recognition modules demonstrated good potential in enhancing tumor-specific targeting and degradation efficiency compared to traditional bivalent PROTACs. Furthermore, in a mouse tumor model, the superior therapeutic activity of AS-TD2-PRO was observed. Overall, DNA tetrahedron-driven multivalent PROTACs both serve as a proof of principle for multifunctional PROTAC design and introduce a promising avenue for cancer treatment strategies.

H2O2-activated mitochondria-targeting photosensitizer for fluorescence imaging-guided combination photodynamic and radiotherapy

Radiotherapy is a primary modality in cancer treatment but is accompanied by severe side effects to healthy tissues and radiation resistance to some extent. To overcome these limitations, we developed a H2O2-responsive photosensitizer, CyBT, which could be activated by the upregulated H2O2 induced by radiotherapy, enabling near-infrared fluorescence imaging-guided combination photodynamic and radiotherapy. The synthesis of CyBT began with the covalent linkage of hemicyanine and a free radical TEMPO through the click reaction, which demonstrated superior photodynamic properties. Shielding of fluorescence and photodynamic activity was achieved by incorporating phenylboronic acid pinacol ester. In X-ray irradiated tumor cells, the upregulation of H2O2 activated CyBT, thereby restoring its fluorescence and photodynamic activity. Additionally, the positive charge of CyBT facilitated its targeting to the mitochondria within tumor cells for more efficiently triggering cell apoptosis. CyBT was co-assembled with a polymer PEG-b-PDPA to form acid-responsive nanoparticles (NPs-CyBT). This formulation enhanced tumor targeting, improved water solubility of CyBT, and extended in vivo circulation time. Utilizing fluorescence imaging to guide photodynamic and radiotherapy, NPs-CyBT can accurately target solid tumors in mice, and lead to tumor elimination, suggesting that it is a potential strategy for the effective treatment of malignant tumors.

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.

A Self-Immobilizing Photosensitizer with Long-Term Retention for Hypoxia Imaging and Enhanced Photodynamic Therapy

The precise theranostic strategy of fluorescence imaging-guided photodynamic therapy (PDT) can effectively mitigate the adverse effect of photosensitizers in normal cells and tissues. However, low tumor enrichment and high diffusivity of photosensitizers significantly compromise the imaging accuracy and PDT effect. In this study, we have developed a nitroreductase (NTR)-activated and self-immobilizing photosensitizer CyNT-F, which showed enhanced enrichment in tumor tissues and facilitated precise and sustained imaging as well as PDT for hypoxia tumors. mPEG-b-PDPA nanomicelles encapsulating photosensitizers underwent dissociation and released CyNT-F in tumor cells. CyNT-F and NTR enzymatically reacted in situ to generate highly reactive quinone methide, subsequently covalently binding to adjacent proteins for fluorescence and PDT activation. CyNT-F exhibited longer intracellular retention (7 days) and effectively inhibited the tumor growth of solid hypoxia tumor. We believe the activatable and self-immobilizing strategy of PDT presents a novel methodology for minimizing the adverse effect and enabling spatiotemporally accurate ablation of diseased cells and tissues.