Chemical Modification of Cytochrome C for Acid-Responsive Intracellular Apoptotic Protein Delivery for Cancer Eradication

Delivering bioactive proteins into cells without carriers presents significant challenges in biomedical applications due to limited cell membrane permeability and the need for targeted delivery. Here, we introduce a novel carrier-free method that addresses these challenges by chemically modifying proteins with an acid-responsive cell-penetrating peptide (CPP) for selective intracellular delivery within tumours. Cytochrome C, a protein known for inducing apoptosis, served as a model for intracellular delivery of therapeutic proteins for cancer treatment. The CPP was protected with 2,3-dimethyl maleic anhydride (DMA) and chemically conjugated onto the protein surface, creating an acid-responsive protein delivery system. In the acidic tumour microenvironment, DMA deprotects and exposes the positively charged CPP, enabling membrane penetration. Both in vitro and in vivo assays validated the pH-dependent shielding mechanism, demonstrating the modified cytochrome C could induce apoptosis in cancer cells in a pH-selective manner. These findings provide a promising new approach for carrier-free and tumour-targeted intracellular delivery of therapeutic proteins for a wide range of potential applications.

Acid-Responsive Aggregation of Gold Nanoparticles for the Photothermal Treatment of Bacterial Infections

Photothermal therapy (PTT) is considered to be one of the promising methods to combat pathogenic bacteria. However, traditional PTT is prone to generate undesired temperature increase to surrounding normal tissues, which limits the application of PTT. Herein, an acid-responsive PTT system (Au nanoparticles system: AuNPs-S) was constructed based on the photothermal feature of spherical gold nanoparticles (AuNPs) and the low pH of the bacterial infected site. AuNPs-S is composed of two kinds of AuNPs: AuNPs modified with Asp-Asp-Asp-Asp-Asp-Cys (peptide A) were denoted as AuNPs-A; AuNPs modified with 2,3-dimethylmaleic anhydride (DA) grafted Lys-Gly-Gly-Lys-Gly-Gly-Lys-Cys (peptide B) were denoted as AuNPs-B/DA. AuNPs-B/DA with an acid-responsive moiety showed a charge-convertible feature. The negatively charged AuNPs-B/DA became positively charged AuNPs-B at low pH, aggregating with the negatively charged AuNPs-A via an electrostatic interaction, reaching the threshold to the interparticle plasmonic coupling effect among AuNPs, thereby killing bacteria precisely under the irradiation of near-infrared (NIR) light through the elevated temperature at the targeted area. This acid-responsive PTT strategy supplies an excellent mode for combating bacterial infections with no vital damage to normal tissues.

Delivery of Small-Molecule Drugs and Protein Drugs by Injectable Acid-Responsive Self-Assembled COF Hydrogels for Combinatorial Lung Cancer Treatment

Covalent organic frameworks (COFs) have revealed enormous application prospects for cancer therapeutics recently, but their assembly systems face considerable challenges, such as the codelivery of hydrophobic and hydrophilic protein drugs with different physicochemical properties for in vivo delivery and release, as well as endosomal/lysosomal escape of protein drugs. To address these issues, we leveraged the high specific surface area, lipotropism, and structural tunability of boronate ester-linked COFs (COF-1) for the construction of advanced drug delivery systems. We first encapsulated the small-molecule drug doxorubicin (DOX) into a lipophilic COF (COF-1@DOX) and immobilized the functional protein drug ribonuclease A (RNase A) on the surface of the COF (RNase A-COF-1@DOX). We then created a novel composite delivery system (RNase A-COF-1@DOX gel) by cross-linking an albumin-oxygenated hydrogel (gel) network into the pores of COFs, allowing targeted codelivery of protein and small-molecule drugs in vivo. Using in-living body and multichannel fluorescence imaging, we analyzed the in vivo codelivery of protein and small-molecule drugs in a Lewis lung carcinoma (LLC) model. Finally, we applied the RNase A-COF-1@DOX gel to treat lung cancer in mice. This study paves an avenue for constructing COF-based drug delivery systems for lung cancer treatment and holds the potential to be extended to other types of cancer for more effective and targeted therapeutic treatments.

Hsp70-Targeting and Size-Tunable Nanoparticles Combine with PD-1 Checkpoint Blockade to Treat Glioma

Invasive glioma usually disrupts the integrity of the blood-brain barrier (BBB), making the delivery of nanodrugs across the BBB possible, but sufficient targeting ability is still avidly needed to improve drug accumulation in glioma. Membrane-bound heat shock protein 70 (Hsp70) is expressed on the membrane of glioma cells rather than adjacent normal cells, therefore it can serve as a specific glioma target. Meanwhile, prolonging the retention in tumors is important for active-targeting nanoparticles to overcome receptor-binding barriers. Herein, the Hsp70-targeting and acid-triggered self-assembled gold nanoparticles (D-A-DA/TPP) are proposed to realize selective delivery of doxorubicin (DOX) to glioma. In the weakly acidic glioma matrix, D-A-DA/TPP formed aggregates to prolong retention, improve receptor-binding efficiency and facilitate acid-responsive DOX release. DOX accumulation in glioma induced immunogenic cell death (ICD) to promote antigen presentation. Meanwhile, combination with the PD-1 checkpoint blockade further activate T cells and provokes robust anti-tumor immunity. The results showed that D-A-DA/TPP can induce more glioma apoptosis. Furthermore, in vivo studies indicated D-A-DA/TPP plus PD-1 checkpoint blockade significantly improved median survival time. This study offeres a potential nanocarrier combining size-tunable strategy with active targeting ability to increase drug enrichment in glioma and synergizes with PD-1 checkpoint blockade to achieve chemo-immunotherapy.

Acid-Sensitive Supramolecular Nanoassemblies with Multivalent Interaction: Effective Tumor Retention and Deep Intratumor Infiltration

It remains a conundrum to reconcile the contradiction between effective tumor retention and deep intratumor infiltration for nanotherapeutics due to the sophisticated drug delivery journey. Herein, we reported an acid-sensitive supramolecular nanoassemblies (DCD SNs) based on the multivalent host-gest inclusions of two polymer conjugates for conquering diverse physiological blockages and amplifying therapeutic efficacy. The multiple inclusions of repetitive units on the hydrophilic polymer backbone reinforced the binding affinity and induced robust self-assembly, ameliorating instability of the self-assemblies and facilitating to prolong the drug retention time. By virtue of the acid-sensitive Schiff base linkages, the supramolecular nanoassembly could respond to the unique tumor microenvironment (TME), dissociate, and transform into smaller particles (∼30 nm), thereby efficiently traversing the complicated extracellular matrix and irregular blood vessels to achieve deep intratumor infiltration. The acid-sensitive DCD SNs can absorb a large number of protons in the acidic lysosomal environment, causing the proton sponge effect, which was conducive to their escape from endolysosomes and accelerated lysosomal disruption, so that the active chemotherapeutic doxorubicin (DOX) could enter the nucleus well and exert severe DNA damage to induce apoptosis. This versatile supramolecular nanoplatform is anticipated to be a promising candidate to overcome the limitations of insufficient stability within the circulation and weak intratumor penetration.

Acid-Responsive Adamantane-Cored Amphiphilic Block Polymers as Platforms for Drug Delivery

Four-arm star-shaped (denoted as ‘S’) polymer adamantane-[poly(lactic-co-glycolic acid)-b-poly(N,N’-diethylaminoethyl methacrylate) poly(ethylene glycol) monomethyl ether]₄ (S-PLGA-D-P) and its linear (denoted as ‘L’) counterpart (L-PLGA-D-P) were synthesized, then their self-assembled micelles were further developed to be platforms for anticancer drug delivery. Two types of polymeric micelles exhibited strong pH-responsiveness and good drug loading capacity (21.6% for S-PLGA-D-P and 22.9% for L-PLGA-D-P). Using doxorubicin (DOX) as the model drug, their DOX-loaded micelles displayed well controlled drug release behavior (18.5–19.0% of DOX release at pH 7.4 and 77.6–78.8% of DOX release at pH 5.0 within 80 h), good cytocompatibility against NIH-3T3 cells and effective anticancer efficacy against MCF-7 cells. However, the star-shaped polymeric micelles exhibited preferable stability, which was confirmed by the lower critical micelle concentration (CMC 0.0034 mg/mL) and decrease rate of particle sizes after 7 days incubation (3.5%), compared with the linear polymeric micelle L-PLGA-D-P (CMC 0.0070 mg/mL, decrease rate of particle sizes was 9.6%). Overall, these developed polymeric micelles have promising application as drug delivery system in cancer therapy.

Morphological transformation enhances Tumor Retention by Regulating the Self-assembly of Doxorubicin-peptide Conjugates

Rationale: Both spatial accuracy and temporal persistence are crucial in drug delivery, especially for anti-tumor intravenous nanomedicines, which have limited persistence due to their small particle sizes and easy removal from tumors. The present study takes advantage of morphological transformation strategy to regulate intravenous nanomedicines to display different sizes in different areas, achieving high efficient enrichment and long retention in lesions. Methods: We designed and synthesized functional doxorubicin-peptide conjugate nanoparticles (FDPC-NPs) consisting of self-assembled doxorubicin-peptide conjugates (DPCs) and an acidic-responsive shielding layer named the functional polylysine graft (FPG), which can regulate the assembly morphology of the DPCs from spherical DPC nanoparticles (DPC-NPs) to DPC-nanofibers (DPC-NFs) by preventing the assembly force from π-π stacking and hydrogen bond between the DPC-NPs. The morphology transformation and particle changes of FDPC-NPs in different environments were determined with DLS, TEM and SEM. We used FRET to explore the enhanced retention effect of FDPC-NPs in tumor site in vivo. HPLC-MS/MS analytical method was established to analyze the biodistribution of FDPC-NPs in H22 hepatoma xenograft mouse model. Finally, the antitumor effect and safety of FDPC-NPs was evaluated. Results: The FDPC-NPs were stable in blood circulation and responsively self-assembled into DPC-NFs when the FDPC-NPs underwent the acid-sensitive separation of the shielding layer in a mildly acidic microenvironment. The FDPC-NPs maintained a uniform spherical size of 80 nm and exhibited good morphological stability in neutral aqueous solution (pH 7.4) but aggregated into a long necklace-like chain structure or a crosslinked fiber structure over time in a weakly acidic solution (pH 6.5). These acidity-triggered transformable FDPC-NPs prolonged the accumulation in tumor tissue for more than 5 days after a single injection and improved the relative uptake rate of doxorubicin in tumors 31-fold. As a result, FDPC-NPs exhibited a preferable anti-tumor efficacy and a reduced side effect in vivo compared with free DOX solution and DOX liposomes. Conclusions: Morphology-transformable FDPC-NPs represent a promising therapeutic approach for prolonging the residence time of drugs at the target site to reduce side effect and enhance therapeutic efficacy. Our studies provide a new and simple idea for the design of long-term delivery systems for intravenous chemotherapeutic drugs.

Smart pH-Sensitive Nanogels for Enhancing Synergistic Anticancer Effects of Integrin αvβ3 Specific Apoptotic Peptide and Therapeutic Nitric Oxide

Apoptotic peptide (kla), which can trigger the mitochondria-mediated apoptotic programmed cell death, has been widely recognized as a potential anticancer agent. However, its therapeutic potential has been significantly impaired by its poor biostability, lack of tumor specificity, and particularly low cellular uptake. Herein, a linear peptide Arg-Trp-d-Arg-Asn-Arg (RWrNR) was identified as an integrin α_vβ₃ specific ligand with a nanomolar dissociation constant (K_d = 0.95 nM), which can greatly improve kla antitumor activity (IC₅₀ = 8.81 μM) by improving its cellular uptake, compared to the classic integrin-recognition motif c-RGDyK (IC₅₀ = 37.96 μM). Particularly, the RWrNR-kla conjugate can be entrapped in acidic sensitive nanogels (RK/Parg/CMCS-NGs), composed of poly-l-arginine (Parg) and carboxymethyl chitosan (CMCS, pI = 6.8), which can not only carry out controlled release of RWrNR-kla in response to the tumor acidic microenvironment, and consequently enhance its tumor specificity and cell internalization, but also trigger tumor-associated macrophages to generate nitric oxide, leading to enhanced synergistic anticancer efficacy. Importantly, RK/Parg/CMCS-NGs have been proven to effectively activate the apoptosis signaling pathway in vivo and significantly inhibit tumor growth with minimal adverse effects. To summarize, RK/Parg/CMCS-NGs are a promising apoptotic peptide-based therapeutics with enhanced tumor accumulation, cytosolic delivery, and synergistic anticancer effects, thereby holding great potential for the treatment of malignant tumors.

Silk Fibroin-Coated Nanoagents for Acidic Lysosome Targeting by a Functional Preservation Strategy in Cancer Chemotherapy

Background: Premature drug leakage and inefficient cellular uptake are stand out as considerable hurdles for low drug delivery efficiency in tumor chemotherapy. Thus, we established a novel drug delivery and transportation strategy mediated by biocompatible silk fibroin (SF)-coated nanoparticles to overcome these therapeutic hurdles.

Methods: we first synthesised a TME-responsive biocompatible nanoplatform constructed of amorphous calcium carbonate (ACC) cores and SF shells for enhanced chemotherapy by concurrently inhibiting premature drug release, achieving lysosome-targeted explosion and locally sprayed DOX, and monitoring via PAI, which was verified both in vitro and in vivo.

Results: The natural SF polymer first served as a “gatekeeper” to inhibit a drug from prematurely leaking into the circulation was demonstrated both in vitro and in vivo. Upon encountering TMEs and targeting to the acidic pH environments of lysosomes, the sensitive ACC nanoparticles were gradually degraded, eventually generating a large amount of Ca²⁺ and CO₂, resulting in lysosomal collapse, thus preventing both the efflux of DOX from cancer cells and the protonation of DOX within the lysosome, releasing multiple hydrolytic enzyme to cytoplasm, exhibiting the optimal therapeutic dose and remarkable synergetic therapeutic performance. In particular, CO₂ gas generated by the pH response of ACC nanocarriers demonstrated their imaging capability for PAI, providing the potential for quantifying and guiding drug release in targets.

Conclusion: In this work, we constructed TME-responsive biocompatible NPs by coating DOX-preloaded ACC-DOX clusters with SF via a bioinspired mineralization method for efficient therapeutics. This functional lysosome-targeted preservation-strategy-based therapeutic system could provid novel insights into cancer chemotherapy.

Inflammation-Responsive Drug-Conjugated Dextran Nanoparticles Enhance Anti-Inflammatory Drug Efficacy

Stimuli-responsive nanoparticles (NPs) are especially interesting to enhance the drug delivery specificity for biomedical applications. With the aim to achieve a highly stable and inflammation-specific drug release, we designed a reactive oxygen species (ROS)-responsive dextran-drug conjugate (Nap-Dex). By blending Nap-Dex with the acid-sensitive acetalated dextran polymer, we achieved a dual-responsive NP with high specificity toward the inflammatory environment. The inflammatory environment not only has elevated ROS levels but also has a lower pH than healthy tissues, making pH and ROS highly suitable triggers to target inflammatory diseases. The anti-inflammatory cyclooxygenase inhibitor naproxen was modified with an ROS-responsive phenylboronic acid (PBA) and conjugated onto dextran. The dextran units were functionalized with up to 87% modified naproxen. This resulted in a complete drug release from the polymer within 20 min at 10 mM H2O2. The dual-responsive NPs reduced the levels of the proinflammatory cytokine IL-6 120 times more efficiently and TNFα 6 times more efficiently than free naproxen from lipopolysaccharide (LPS)-activated macrophages. These additional anti-inflammatory effects were found to be mainly attributed to ROS-scavenging effects. In addition, the model cargo fluorescein diacetate was released in an LPS-induced inflammatory response in vitro. We believe that drug conjugation using PBA can be applied to various drugs and dextran-based materials for enhanced drug efficacy, where this work demonstrates the significance of functionalized carbohydrates polymer-drug conjugates.

Acidity-Triggered Ligand-Presenting Nanoparticles To Overcome Sequential Drug Delivery Barriers to Tumors

The success of cancer chemotherapy is impeded by poor drug delivery efficiency due to the existence of a series of pathophysiological barriers in the tumor. In this study, we reported a tumor acidity-triggered ligand-presenting (ATLP) nanoparticle for cancer therapy. The ATLP nanoparticles were composed of an acid-responsive diblock copolymer as a sheddable matrix and an iRGD-modified polymeric prodrug of doxorubicin (iPDOX) as an amphiphilic core. A PEG corona of the polymer matrix protected the iRGD ligand from serum degradation and nonspecific interactions with the normal tissues while circulating in the blood. The ATLP nanoparticles specifically accumulated at the tumor site through the enhanced permeability and retention (EPR) effect, followed by acid-triggered dissociation of the polymer matrix within the tumoral acidic microenvironment (pH ∼ 6.8) and subsequently exposing the iRGD ligand for facilitating tumor penetration and cellular uptake of the PDOX prodrug. Additionally, the acid-triggered dissociation of the polymer matrix induced a 4.5-fold increase of the fluorescent signal for monitoring nanoparticle activation in vivo. Upon near-infrared (NIR) laser irradiation, activation of Ce6-induced significant reactive oxygen species (ROS) generation, promoted drug diffusion inside the tumor mass and circumvented the acquired drug resistance by altering the gene expression profile of the tumor cells. The ATLP strategy might provide a novel insight for cancer nanomedicine.