Improved Protein Toxin Delivery Based on ATTEMPTS Systems

Current status and prospects of gelatin and its derivatives in oncological applications: Review

Treating cancer remains challenging due to the substantial side effects and unfavourable pharmacokinetic characteristics of antineoplastic medications, despite the progress made in comprehending the properties and actions of tumour cells in recent years. The advancement of biomaterials, such as stents, implants, personalised drug delivery systems, tailored grafts, cell sheets, and other transplantable materials, has brought about a significant transformation in healthcare and medicine in recent years. Gelatin is a very adaptable natural polymer that finds extensive application in healthcare-related industries owing to its favourable characteristics, including biocompatibility, biodegradability, affordability, and the presence of accessible chemical groups. Gelatin is used as a biomaterial in the biomedical sector for the creation of drug delivery systems (DDSs) since it may be applied to various synthetic procedures. Gelatin nanoparticles (NPs) have been extensively employed as carriers for drugs and genes, specifically targeting diseased tissues such as cancer, tuberculosis, and HIV infection, as well as treating vasospasm and restenosis. This is mostly due to their biocompatibility and ability to degrade naturally. Gelatins possess a diverse array of potential applications that require more elucidation. This review focuses on the use of gelatin and its derivatives in the diagnosis and treatment of cancer. The advancement of biomaterials and bioreactors, coupled with the increasing understanding of emerging applications for biomaterials, has enabled progress in enhancing the efficacy of tumour treatment.

Biosynthesized tumor acidity and MMP dual-responsive plant toxin gelonin for robust cancer therapy

Among all kinds of anticancer agents, small molecule drugs produce an unsatisfactory therapeutic effect due to the lack of selectivity, notorious drug resistance and side effects. Therefore, researchers have begun to pay extensive attention to macromolecular drugs with high efficacy and specificity. As a plant toxin, gelonin exerts potent antitumor activity via inhibiting intracellular protein synthesis. However, gelonin lacks a translocation domain, and thus its poor cellular uptake leads to low outcomes of antitumor response. Here, tumor acidity and matrix metalloproteinase (MMP) dual-responsive functional gelonin (Trx-PVGLIG-pHLIP-gelonin, TPpG), composed of a thioredoxin (Trx) tag, a pH low insertion peptide (pHLIP), an MMP-responsive motif PVGLIG hexapeptide and gelonin, was innovatively proposed and biologically synthesized by a gene recombination technique. TPpG exhibited good thermal and serum stability, showed MMP responsiveness and could enter tumor cells under weakly acidic conditions, especially for MMP2-overexpressing HT1080 cells. Compared to low MMP2-expressing MCF-7 cells, TPpG displayed enhanced in vitro antitumor efficacy to HT1080 cells at pH 6.5 as determined by different methods. Likewise, TPpG was much more effective in triggering cell apoptosis and inhibiting protein synthesis in HT1080 cells than in MCF-7 cells. Intriguingly, with enhanced stability and pH/MMP dual responsiveness, TPpG notably inhibited subcutaneous HT1080 xenograft growth in mice and no noticeable off-target side effect was observed. This ingeniously designed strategy aims at providing new perspectives for the development of a smart platform that can intelligently respond to a tumor microenvironment for efficient protein delivery.

Advances on Delivery of Cytotoxic Enzymes as Anticancer Agents

Cancer is one of the most serious human diseases, causing millions of deaths worldwide annually, and, therefore, it is one of the most investigated research disciplines. Developing efficient anticancer tools includes studying the effects of different natural enzymes of plant and microbial origin on tumor cells. The development of various smart delivery systems based on enzyme drugs has been conducted for more than two decades. Some of these delivery systems have been developed to the point that they have reached clinical stages, and a few have even found application in selected cancer treatments. Various biological, chemical, and physical approaches have been utilized to enhance their efficiencies by improving their delivery and targeting. In this paper, we review advanced delivery systems for enzyme drugs for use in cancer therapy. Their structure-based functions, mechanisms of action, fused forms with other peptides in terms of targeting and penetration, and other main results from in vivo and clinical studies of these advanced delivery systems are highlighted.

The role of cell-penetrating peptides in potential anti-cancer therapy

Due to the complex physiological structure, microenvironment and multiple physiological barriers, traditional anti-cancer drugs are severely restricted from reaching the tumour site. Cell-penetrating peptides (CPPs) are typically made up of 5-30 amino acids, and can be utilised as molecular transporters to facilitate the passage of therapeutic drugs across physiological barriers. Up to now, CPPs have widely been used in many anti-cancer treatment strategies, serving as an excellent potential choice for oncology treatment. However, their drawbacks, such as the lack of cell specificity, short duration of action, poor stability in vivo, compatibility problems (i.e. immunogenicity), poor therapeutic efficacy and formation of unwanted metabolites, have limited their further application in cancer treatment. The cellular uptake mechanisms of CPPs involve mainly endocytosis and direct penetration, but still remain highly controversial in academia. The CPPs-based drug delivery strategy could be improved by clever design or chemical modifications to develop the next-generation CPPs with enhanced cell penetration capability, stability and selectivity. In addition, some recent advances in targeted cell penetration that involve CPPs provide some new ideas to optimise CPPs.

Multi-Arm PEG/Peptidomimetic Conjugate Inhibitors of DR6/APP Interaction Block Hematogenous Tumor Cell Extravasation

The binding of amyloid precursor protein (APP) expressed on tumor cells to death receptor 6 (DR6) could initiate the necroptosis pathway, which leads to necroptotic cell death of vascular endothelial cells (ECs) and results in tumor cells (TCs) extravasation and metastasis. This study reports the first inhibitor of DR6/APP interaction as a novel class of anti-hematogenous metastatic agent. By rationally utilizing three combined strategies including selection based on phage display library, d-retro-inverso modification, and multiple conjugation of screened peptidomimetic with 4-arm PEG, the polymer-peptidomimetic conjugate PEG-tAHP-DRI (tetra-(D-retro-inverso isomer of AHP-12) substitued 4-arm PEG5k ) is obtained as the most promising agent with the strongest binding potency (KD  = 51.12 × 10-9  m) and excellent pharmacokinetic properties. Importantly, PEG-tAHP-DRI provides efficient protection against TC-induced ECs necroptosis both in vitro and in vivo. Moreover, this ligand exhibits prominent anti-hematogenous metastatic activity in serval different metastatic mouse models (B16F10, 4T1, CT26, and spontaneous lung metastasis of 4T1 orthotopic tumor model) and displays no apparent detrimental effects in preliminary safety evaluation. Collectively, this study demonstrates the feasibility of exploiting DR6/APP interaction to regulate hematogenous tumor cells transendothelial migration and provides PEG-tAHP-DRI as a novel and promising inhibitor of DR6/APP interaction for developments of anti-hematogenous metastatic therapies.

Toxic proteins application in cancer therapy

Ribosome inactivating proteins (RIPs) as family of anti-cancer drugs recently received much attention due to their interesting anti-cancer mechanism. In spite of small drugs, RIPs use the large-size effect (LSE) to prevent the efflux process governed by drug resistance transporters (DRTs) which prevents inside of the cells against drug transfection. There are many clinical translation obstacles that severely restrict their applications especially their delivery approach to the tumor cells. As the main goal of this review, we will focus on trichosanthin (TCS) and gelonin (Gel) and other types, especially scorpion venom-derived RIPs to clarify that they are struggling with what types of bio-barriers and these challenges could be solved in cancer therapy science. Then, we will try to highlight recent state-of-the-arts in delivery of RIPs for cancer therapy.

Advances on Tumor-Targeting Delivery of Cytotoxic Proteins

Great attention has been paid to cytotoxic proteins (e.g., ribosome-inactivating proteins, RIPs) possessing high anticancer activities; unlike small drugs, cytotoxic proteins can effectively retain inside the cells and avoid drug efflux mediated by multidrug resistance transporters due to the large-size effect. However, the clinical translation of these proteins is severely limited because of various biobarriers that hamper their effective delivery to tumor cells. Hence, in order to overcome these barriers, many smart drug delivery systems (DDS) have been developed. In this review, we will introduce two representative type I RIPs, trichosanthin (TCS) and gelonin (Gel), and overview the major biobarriers for protein-based cancer therapy. Finally, we outline advances on the development of smart DDS for effective delivery of these cytotoxic proteins for various applications in cancer treatment.

Critical Issues in the Development of Immunotoxins for Anticancer Therapy

Immunotoxins (ITs) are attractive anticancer modalities aimed at cancer-specific delivery of highly potent cytotoxic protein toxins. An IT consists of a targeting domain (an antibody, cytokine, or another cell-binding protein) chemically conjugated or recombinantly fused to a highly cytotoxic payload (a bacterial and plant toxin or human cytotoxic protein). The mode of action of ITs is killing designated cancer cells through the effector function of toxins in the cytosol after cellular internalization via the targeted cell-specific receptor-mediated endocytosis. Although numerous ITs of diverse structures have been tested in the past decades, only 3 ITs-denileukin diftitox, tagraxofusp, and moxetumomab pasudotox-have been clinically approved for treating hematological cancers. No ITs against solid tumors have been approved for clinical use. In this review, we discuss critical research and development issues associated with ITs that limit their clinical success as well as strategies to overcome these obstacles. The issues include off-target and on-target toxicities, immunogenicity, human cytotoxic proteins, antigen target selection, cytosolic delivery efficacy, solid-tumor targeting, and developability. To realize the therapeutic promise of ITs, novel strategies for safe and effective cytosolic delivery into designated tumors, including solid tumors, are urgently needed.

Genetically-engineered protein prodrug-like nanoconjugates for tumor-targeting biomimetic delivery via a SHEATH strategy

The delivery issue is a major hurdle against drug development and the clinical application of the cytoplasmic active proteins (e.g., ribosome-inactivating proteins, RIPs). As a case in point, trichosanthin (TCS) has a very high cytoplasmic activity of killing cancer cells, but the translation is hampered by its unfavorable nature, such as the short half-life, poor tumor targeting and cell permeation. To address this issue, a novel delivery method called a smart hitchhike via endogenous albumin-trichosanthin hinge (SHEATH) system was developed by the genetic fusion of an albumin-binding domain (ABD) and a legumain-substrate peptide to TCS. The SHEATH system is characterized by the feature of smart hitchhike by binding to serum albumin via its ABD domain, and the two proteins (i.e., TCS and albumin) thus form a prodrug-like noncovalent nanoconjugate. The TCS could detach from the albumin carrier by responding to the protease legumain cleavage of the substrate peptide at the tumor site. Such a system can take advantage of the albumin-mediated biomimetic delivery to the tumor via the nutrient transporter pathway of albumin-binding proteins (e.g., SPARC). The antitumor effects were evaluated in orthotopic breast cancer animal models and showed remarkably improved antitumor effects. Our work provides a useful protocol for improving the druggability of such a class of protein toxins for targeted cancer therapy by an endogenous albumin-hitchhike strategy.

Protein Nanotherapeutics as an Emerging Modality for Cancer Therapy

Protein drugs are a unique and versatile class of biotherapeutics that have not only high biological activity but also superb specificity. This rapidly evolving biotechnology has rendered it possible to produce various proteins in a large scale and reproducible way. Many proteins have demonstrated striking anticancer activities and have emerged as advanced alternatives to cytotoxic chemotherapeutic agents for cancer therapy. The clinical translation of anticancer proteins with intracellular targets is, nevertheless, severely hindered by their fast degradation in vivo, poor cell penetration, and inefficient intracellular transportation. The past few years have witnessed tremendous effort and progress in developing polymeric protein delivery nanosystems, ranging from nanoparticles, nanocapsules, nanogels, micelles, to polymersomes, for the treatment of different tumors such as lung tumors, breast tumors, ovarian cancers, and glioblastoma. These proof-of-concept studies point out that protein nanotherapeutics, with rationally designed nanovehicles, are able to overcome the extracellular barriers, cell membrane barriers, and intracellular barriers, and systemically deliver proteins into targeted cancer cells, resulting in effective cancer protein therapy. Protein nanotherapeutics appear to be a novel modality for safe and efficient cancer treatment.