Chemical Conjugation of Evans Blue Derivative: A Strategy to Develop Long-Acting Therapeutics through Albumin Binding

Enhanced capillary delivery with nanobubble-mediated blood-brain barrier opening and advanced high resolution vascular segmentation

Overcoming the blood-brain barrier (BBB) is essential to enhance brain therapy. Here, we utilized nanobubbles with focused ultrasound for targeted and improved BBB opening in mice. A microscopy technique method assessed BBB opening at a single blood vessel resolution employing a dual-dye labeling technique using green fluorescent molecules to label blood vessels and Evans blue brain-impermeable dye for quantifying BBB extravasation. A deep learning architecture enabled blood vessels segmentation, delivering comparable accuracy to manual segmentation with a significant time reduction. Segmentation outcomes were applied to the Evans blue channel to quantify extravasation of each blood vessel. Results were compared to microbubble-mediated BBB opening, where reduced extravasation was observed in capillaries with a diameter of 2-6 μm. In comparison, nanobubbles yield an improved opening in these capillaries, and equivalent efficacy to that of microbubbles in larger vessels. These results indicate the potential of nanobubbles to serve as enhanced agents for BBB opening, amplifying bioeffects in capillaries while preserving comparable opening in larger vessels.

HSA-nanobinders crafted from bioresponsive prodrugs for combined cancer chemoimmunotherapy-an in vitro exploration

Introduction

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer still lacking effective treatment options. Chemotherapy in combination with immunotherapy can restrict tumor progression and repolarize the tumor microenvironment towards an anti-tumor milieu, improving clinical outcome in TNBC patients. The chemotherapeutic drug paclitaxel has been shown to induce immunogenic cell death (ICD), whereas inhibitors of the indoleamine 2,3- dioxygenase 1 (IDO1) enzyme, whose expression is shared in immune regulatory and tumor cells, have been revealed to enhance the anti-tumor immune response. However, poor bioavailability and pharmacokinetics, off-target effects and hurdles in achieving therapeutic drug concentrations at the target tissue often limit the effectiveness of combination therapies.

Methods

This work describes the development of novel biomimetic and carrier-free nanobinders (NBs) loaded with both paclitaxel and the IDO1 inhibitor NLG919 in the form of bioresponsive and biomimetic prodrugs. A fine tuning of the preparation conditions allowed to identify NB@5 as the most suitable nanoformulation in terms of reproducibility, stability and in vitro effectiveness.

Results and discussion

Our data show that NB@5 effectively binds to HSA in cell-free experiments, demonstrating its protective role in the controlled release of drugs and suggesting the potential to exploit the protein as the endogenous vehicle for targeted delivery to the tumor site. Our study successfully proves that the drugs encapsulated within the NBs are preferentially released under the altered redox conditions commonly found in the tumor microenvironment, thereby inducing cell death, promoting ICD, and inhibiting IDO1.

Nanofiber matrix formulations for the delivery of Exendin-4 for tendon regeneration: In vitro and in vivo assessment

Tendon and ligament injuries are the most common musculoskeletal injuries, which not only impact the quality of life but result in a massive economic burden. Surgical interventions for tendon/ligament injuries utilize biological and/or engineered grafts to reconstruct damaged tissue, but these have limitations. Engineered matrices confer superior physicochemical properties over biological grafts but lack desirable bioactivity to promote tissue healing. While incorporating drugs can enhance bioactivity, large matrix surface areas and hydrophobicity can lead to uncontrolled burst release and/or incomplete release due to binding. To overcome these limitations, we evaluated the delivery of a peptide growth factor (exendin-4; Ex-4) using an enhanced nanofiber matrix in a tendon injury model. To overcome drug surface binding due to matrix hydrophobicity of poly(caprolactone) (PCL)-which would be expected to enhance cell-material interactions-we blended PCL and cellulose acetate (CA) and electrospun nanofiber matrices with fiber diameters ranging from 600 to 1000 nm. To avoid burst release and protect the drug, we encapsulated Ex-4 in the open lumen of halloysite nanotubes (HNTs), sealed the HNT tube endings with a polymer blend, and mixed Ex-4-loaded HNTs into the polymer mixture before electrospinning. This reduced burst release from ∼75% to ∼40%, but did not alter matrix morphology, fiber diameter, or tensile properties. We evaluated the bioactivity of the Ex-4 nanofiber formulation by culturing human mesenchymal stem cells (hMSCs) on matrix surfaces for 21 days and measuring tenogenic differentiation, compared with nanofiber matrices in basal media alone. Strikingly, we observed that Ex-4 nanofiber matrices accelerated the hMSC proliferation rate and elevated levels of sulfated glycosaminoglycan, tendon-related genes (Scx, Mkx, and Tnmd), and ECM-related genes (Col-I, Col-III, and Dcn), compared to control. We then assessed the safety and efficacy of Ex-4 nanofiber matrices in a full-thickness rat Achilles tendon defect with histology, marker expression, functional walking track analysis, and mechanical testing. Our analysis confirmed that Ex-4 nanofiber matrices enhanced tendon healing and reduced fibrocartilage formation versus nanofiber matrices alone. These findings implicate Ex-4 as a potentially valuable tool for tendon tissue engineering.

The preclinical study of 177Lu-DOTA-LTVSPWY as a potential therapeutic agent against HER2 overexpressed cancer

BACKGROUND

Peptide receptor radionuclide therapy (PRRT) has evolved in cancer therapy and diagnosis. LTVSPWY, as a peptide, can target HER2 receptor; on the other hand, ¹⁷⁷Lu emits β^- which is helpful for cancer therapy. The radiolabeling of LTVSPWY with ¹⁷⁷Lu results in a therapeutic agent (¹⁷⁷Lu-DOTA-LTVSPWY) capable of cancer treatment.

METHODS

¹⁷⁷Lu-DOTA-LTVSPWY was prepared with high radiochemical purity (RCP). The stability was investigated in saline and human serum. The radiotracer affinity toward the SKOV-3 cell line with overexpression of the HER2 receptor was evaluated. Then the impact of the radiotracer on the colony formation of the SKOV-3 cell line was investigated with colony assay. Moreover, the biodistribution of this radiotracer in SKOV-3 xenograft tumor-bearing nude mice were also studied to determine the radiotracer accumulation in the tumor site. The mice were treated with ¹⁷⁷Lu-DOTA-LTVSPWY and subjected to histopathological evaluation.

RESULTS

The RCP of ¹⁷⁷Lu-DOTA-LTVSPWY after radiolabeling and stability tests was more than 97.7%. The radiotracer displayed high affinity toward the SKOV-3 cell line (K_D = 6.6 ± 3.2 nM). Treatment of the SKOV-3 cell line with the radiotracer reduces the SKOV-3 colony survival to less than 3% for 5 MBq of the radiotracer. Tumor-to-muscle (T/M) ratio is the highest at 48 h and 1 h post-injection (2.3 and 4.75, respectively). The histopathological study also confirms the cellular damage to the tumor tissue.

CONCLUSIONS

¹⁷⁷Lu-DOTA-LTVSPWY can recognize HER2 receptors in vivo and in vitro; hence, it can serve as a therapeutic agent.

Strategies for developing long-lasting therapeutic nucleic acid aptamer targeting circulating protein: The present and the future

Aptamers are short, single-stranded DNA or RNA oligonucleotide sequences that can bind specific targets. The molecular weight of aptamers (<20 kDa) is lower than the renal filtration threshold (30∼50 kDa), resulting in very short half-lives in vivo, which limit their druggability. The development of long-lasting modification approaches for aptamers can help address the druggability bottleneck of aptamers. This review summarized two distinct kinds of long-lasting modification approaches for aptamers, including macromolecular modification and low-molecular-weight modification. Though it is a current approach to extend the half-life of aptamers, the macromolecular modification approach could limit the space for the dosage increases, thus causing potential compliance concerns due to large molecular weight. As for the other modification approach, the low-molecular-weight modification approach, which uses low molecular weight coupling agents (LMWCAs) to modify aptamers, could greatly increase the proportion of aptamer moiety. However, some LMWCAs could bind to other proteins, causing a decrease in the drug amounts in blood circulation. Given these issues, the outlook for the next generation of long-lasting modification approaches was proposed at the end, including improving the administration method to increase dosage for aptamer drugs modified by macromolecule and developing Artificial intelligence (AI)-based strategies for optimization of LMWCAs.

Current trends in the use of human serum albumin for drug delivery in cancer

INTRODUCTION

Human serum albumin is the most abundant transport protein in plasma, which has recently been extensively utilized to form nanoparticles for drug delivery in cancer. The primary reason for selecting albumin protein as drug delivery cargo is its excellent biocompatibility, biodegradability, and non-immunogenicity. Moreover, the albumin structure containing three homologous domains constituted of a single polypeptide (585 amino acid) incorporates various hydrophobic drugs by non-covalent interactions. Albumin shows active tumor targeting via their interaction with gp60 and SPARC proteins abundant in the tumor-associated endothelial cells and the tumor microenvironment.

AREAS COVERED

The review discusses the importance of albumin as a drug-carrier system, general procedures to prepare albumin NPs, and the current trends in using albumin-based nanomedicines to deliver various chemotherapeutic agents. The various applications of albumin in the nanomedicines, such as NPs surface modifier and fabrication of hybrid/active-tumor targeted NPs, are delineated based on current trends.

EXPERT OPINION

Nanomedicines have the potential to revolutionize cancer treatment. However, clinical translation is limited majorly due to the lack of suitable nanomaterials offering systemic stability, optimum drug encapsulation, tumor-targeted delivery, sustained drug release, and biocompatibility. The potential of albumin could be explored in nanomedicines fabrication for superior treatment outcomes in cancer.

Fluorene methoxycarbonyl-PEG-deferoxamine conjugates "hitchhike" with albumin in situ for iron overload therapy

Although deferoxamine (DFO) has been approved for the treatment the iron overloaded diseases, its clinical application is impeded by very short circulation time and its relating toxicity. In this work, the fluorene methoxycarbonyl (FMOC) for "albumin hitchhiking" was used to prolong the plasma circulation time of DFO and reduce toxicity. The designed FMOC-PEG-DFO conjugates were found to reversible bind to albumin and gradually release DFO in vivo. Herein, the FMOC-PEG₁₀₀₀-DFO conjugates could increase 30 times the blood circulation time of DFO with the improvement of the iron elimination efficacy. Meanwhile, the conjugates markedly reduced the cytotoxicity of DFO. Taken together, the result demonstrated the FMOC-PEG₁₀₀₀-DFO conjugates could be a potential therapeutic choice for iron-overload-related diseases.

“Human and Mouse Cross-Reactive” Albumin-Binding Helix–Loop–Helix Peptide Tag for Prolonged Bioactivity of Therapeutic Proteins

The effectiveness of protein and peptide pharmaceuticals depends essentially on their intrinsic pharmacokinetics. Small-sized pharmaceuticals in particular often suffer from short serum half-lives due to rapid renal clearance. To improve the pharmacokinetics by association with serum albumin (SA) in vivo, we generated an SA-binding tag of a helix–loop–helix (HLH) peptide to be linked with protein pharmaceuticals. For use in future preclinical studies, screening of yeast-displayed HLH peptide libraries against human SA (HSA) and mouse SA (MSA) was alternately repeated to give the SA-binding peptide AY-VE, which exhibited cross-binding activities to HSA and MSA with K_D of 65 and 20 nM, respectively. As a proof of concept, we site-specifically conjugated peptide AY-VE with insulin to examine its bioactivity in vivo. In mouse bioassay monitoring the blood glucose level, the AY-VE conjugate was found to have a prolonged hypoglycemic effect for 12 h. The HLH peptide tag is a general platform for extending the bioactivity of therapeutic peptides or proteins.

Conjugates for use in peptide therapeutics: A systematic review and meta-analysis

While peptides can be excellent therapeutics for several conditions, their limited in vivo half-lives have been a major bottleneck in the development of therapeutic peptides. Conjugating the peptide to an inert chemical moiety is a strategy that has repeatedly proven to be successful in extending the half-life of some therapeutics. This systematic review and meta-analysis was conducted to examine the available literature and assess it in an unbiased manner to determine which conjugates, both biological and synthetic, provide the greatest increase in therapeutic peptide half-life. Systematic searches run on PubMed, Scopus and SciFinder databases resulted in 845 studies pertaining to the topic, 16 of these were included in this review after assessment against pre-specified inclusion criteria registered on PROSPERO (#CRD42020222579). The most common reasons for exclusion were non-IV administration and large peptide size. Of the 16 studies that were included, a diverse suite of conjugates that increased half-life from 0.1 h to 33.57 h was identified. Amongst these peptides, the largest increase in half-life was seen when conjugated with glycosaminoglycans. A meta-analysis of studies that contained fatty acid conjugates indicated that acylation contributed to a statistically significant extension of half-life. Additionally, another meta-analysis followed by a sensitivity analysis suggested that conjugation with specifically engineered recombinant peptides might contribute to a more efficient extension of peptide half-life as compared to PEGylation. Moreover, we confirmed that while polyethylene glycol is a good synthetic conjugate, its chain length likely has an impact on its effectiveness in extending half-life. Furthermore, we found that most animal studies do not include as much detail when reporting findings as compared to human studies. Inclusion of additional experimental detail on aspects such as independent assessment and randomization may be an easily accomplished strategy to drive more conjugated peptides towards clinical studies.

A Comparison of Evans Blue and 4-(p-Iodophenyl)butyryl Albumin Binding Moieties on an Integrin αvβ6 Binding Peptide

Serum albumin binding moieties (ABMs) such as the Evans blue (EB) dye fragment and the 4-(p-iodophenyl)butyryl (IP) have been used to improve the pharmacokinetic profile of many radiopharmaceuticals. The goal of this work was to directly compare these two ABMs when conjugated to an integrin αvβ6 binding peptide (αvβ6-BP); a peptide that is currently being used for positron emission tomography (PET) imaging in patients with metastatic cancer. The ABM-modified αvβ6-BP peptides were synthesized with a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracetic acid (DOTA) chelator for radiolabeling with copper-64 to yield [64Cu]Cu DOTA-EB-αvβ6-BP ([64Cu]1) and [64Cu]Cu DOTA-IP-αvβ6-BP ([64Cu]2). Both peptides were evaluated in vitro for serum albumin binding, serum stability, and cell binding and internalization in the paired engineered melanoma cells DX3puroβ6 (αvβ6 +) and DX3puro (αvβ6 −), and pancreatic BxPC-3 (αvβ6 +) cells and in vivo in a BxPC-3 xenograft mouse model. Serum albumin binding for [64Cu]1 and [64Cu]2 was 53−63% and 42−44%, respectively, with good human serum stability (24 h: [64Cu]1 76%, [64Cu]2 90%). Selective αvβ6 cell binding was observed for both [64Cu]1 and [64Cu]2 (αvβ6 (+) cells: 30.3−55.8% and 48.5−60.2%, respectively, vs. αvβ6 (−) cells <3.1% for both). In vivo BxPC-3 tumor uptake for both peptides at 4 h was 5.29 ± 0.59 and 7.60 ± 0.43% ID/g ([64Cu]1 and [64Cu]2, respectively), and remained at 3.32 ± 0.46 and 4.91 ± 1.19% ID/g, respectively, at 72 h, representing a >3-fold improvement over the non-ABM parent peptide and thereby providing improved PET images. Comparing [64Cu]1 and [64Cu]2, the IP-ABM-αvβ6-BP [64Cu]2 displayed higher serum stability, higher tumor accumulation, and lower kidney and liver accumulation, resulting in better tumor-to-organ ratios for high contrast visualization of the αvβ6 (+) tumor by PET imaging.

Review of arginase as a promising biocatalyst: characteristics, preparation, applications and future challenges

As a committed step in the urea cycle, arginase cleaves l-arginine to form l-ornithine and urea. l-Ornithine is essential to: cell proliferation, collagen formation and other physiological functions, while the urea cycle itself converts highly toxic ammonia to urea for excretion. Recently, arginase was exploited as an efficient catalyst for the environmentally friendly synthesis of l-ornithine, an abundant nonprotein amino acid that is widely employed as a food supplement and nutrition product. It was also proposed as an arginine-reducing agent in order to treat arginase deficiency and to be a means of depleting arginine to treat arginine auxotrophic tumors. Targeting arginase inhibitors of the arginase/ornithine pathway offers great promise as a therapy for: cardiovascular, central nervous system diseases and cancers with high arginase expression. In this review, recent advances in the characteristics, structure, catalytic mechanism and preparation of arginase were summarized, with a focus being placed on the biotechnical and medical applications of arginase. In particular, perspectives have been presented on the challenges and opportunities for the environmentally friendly utilization of arginase during l-ornithine production and in therapies.

Thermostable and Long-Circulating Albumin-Conjugated Arthrobacter globiformis Urate Oxidase

Urate oxidase derived from Aspergillus flavus has been investigated as a treatment for tumor lysis syndrome, hyperuricemia, and gout. However, its long-term use is limited owing to potential immunogenicity, low thermostability, and short circulation time in vivo. Recently, urate oxidase isolated from Arthrobacter globiformis (AgUox) has been reported to be thermostable and less immunogenic than the Aspergillus-derived urate oxidase. Conjugation of human serum albumin (HSA) to therapeutic proteins has become a promising strategy to prolong circulation time in vivo. To develop a thermostable and long-circulating urate oxidase, we investigated the site-specific conjugation of HSA to AgUox based on site-specific incorporation of a clickable non-natural amino acid (frTet) and an inverse electron demand Diels-Alder reaction. We selected 14 sites for frTet incorporation using the ROSETTA design, a computational stability prediction program, among which AgUox containing frTet at position 196 (Ag12) exhibited enzymatic activity and thermostability comparable to those of wild-type AgUox. Furthermore, Ag12 exhibited a high HSA conjugation yield without compromising the enzymatic activity, generating well-defined HSA-conjugated AgUox (Ag12-HSA). In mice, the serum half-life of Ag12-HSA was approximately 29 h, which was roughly 17-fold longer than that of wild-type AgUox. Altogether, this novel formulated AgUox may hold enhanced therapeutic efficacy for several diseases.

Synthesis and Application of a Long-Circulating Radiolabeled Peptide for Targeting of Osteosarcoma

PURPOSE

The small peptide TMTP1 (NVVRQ) has been proved to target a series of highly metastatic tumor cells. The aim of this study was to develop a new agent based on TMTP1 conjugated with Evans blue (EB), to increase tumor uptake and modify the pharmacokinetic characteristics of the resulting radiolabeled agent.

PROCEDURES

DOTA-EB-TMTP1 was prepared through conventional solid-phase peptide synthesis chemistry. Then, it was successfully labeled with Cu-64 to obtain [⁶⁴Cu]DOTA-EB-TMTP1. The tumor targeting properties were evaluated in vivo using 143B xenografts.

RESULTS

DOTA-EB-TMTP1 was successfully labeled with Cu-64 in a yield of 87.3 ± 5.2 %. In a small animal positron emission tomography/X-ray computed tomography (PET/CT) study in osteosarcoma 143B xenograft mice, [⁶⁴Cu]DOTA-EB-TMTP1 was found to rapidly accumulate in the tumor tissue. The tumor uptake increased over time and reached a plateau of 6.50 ± 0.88 % ID/g 8 h after tail vein injection. The radioactivity remained in the tumor tissue 48 h postinjection with a negligible decrease.

CONCLUSIONS

Overall, the introduction of the EB motif to TMTP1 significantly changed its pharmacokinetics in vivo, and this strategy fulfills the purpose of prolonging the blood circulation and enhancing the tumor uptake. [⁶⁴Cu]DOTA-EB-TMTP1 is a promising agent for osteosarcoma targeting. Moreover, our study highlights that DOTA-EB-TMTP1 is a good candidate for labeling with different radionuclides for potential theranostic applications.

Human Serum Albumin as Multifunctional Nanocarrier for Cancer Therapy

Human serum albumin or simply called albumin is a flexible protein employed as a carrier in the fabrication of albumin-based nanocarriers (ANCs) for the administration of cancer therapeutics. Albumin can contribute enhanced tumour specificity, reduced drug induced cytotoxicity and retain concentration of the therapeutically active agent such as drug, peptide, protein, and gene for a prolonged time duration. Nevertheless, apart from cancer management, ANCs are also employed in the diagnosis, imaging, and multimodal cancer therapy. This article figures out salient characteristics, design as well as categories of ANCs in the context of their application in cancer management. In addition, this review article discusses the fabrication methods of ANCs, use of ANCs in gene, cancer, and multimodal therapy along with cancer diagnosis and imaging. Lastly, this review also briefly discusses about (ANCs) formulations, commercial products, and those under clinical testing.

Recent Progress in Aptamer Discoveries and Modifications for Therapeutic Applications

Aptamers are oligonucleotide sequences with a length of about 25-80 bases which have abilities to bind to specific target molecules that rival those of monoclonal antibodies. They are attracting great attention in diverse clinical translations on account of their various advantages, including prolonged storage life, little batch-to-batch differences, very low immunogenicity, and feasibility of chemical modifications for enhancing stability, prolonging the half-life in serum, and targeted delivery. In this Review, we demonstrate the emerging aptamer discovery technologies in developing advanced techniques for producing aptamers with high performance consistently and efficiently as well as requiring less cost and resources but offering a great chance of success. Further, the diverse modifications of aptamers for therapeutic applications including therapeutic agents, aptamer-drug conjugates, and targeted delivery materials are comprehensively summarized.

In Vivo Half-Life Extension of BMP1/TLL Metalloproteinase Inhibitors Using Small-Molecule Human Serum Albumin Binders

Reducing the required frequence of drug dosing can improve the adherence of patients to chronic treatments. Hence, drugs with longer in vivo half-lives are highly desirable. One of the most promising approaches to extend the in vivo half-life of drugs is conjugation to human serum albumin (HSA). In this work, we describe the use of AlbuBinder 1, a small-molecule noncovalent HSA binder, to extend the in vivo half-life and pharmacology of small-molecule BMP1/TLL inhibitors in humanized mice (HSA KI/KI). A series of conjugates of AlbuBinder 1 with BMP1/TLL inhibitors were prepared. In particular, conjugate c showed good solubility and a half-life extension of >20-fold versus the parent molecule in the HSA KI/KI mice, reaching half-lives of >48 h with maintained maximal inhibition of plasma BMP1/TLL. The same conjugate showed a half-life of only 3 h in the wild-type mice, suggesting that the half-life extension was principally due to specific interactions with HSA. It is envisioned that conjugation to AlbuBinder 1 should be applicable to a wide range of small molecule or peptide drugs with short half-lives. In this context, AlbuBinders represent a viable alternative to existing half-life extension technologies.

Strategies to expand peptide functionality through hybridisation with a small molecule component

Combining different compound classes gives molecular hybrids that can offer access to novel chemical space and unique properties. Peptides provide ideal starting points for such molecular hybrids, which can be easily modified with a variety of molecular entities. The addition of small molecules can improve the potency, stability and cell permeability of therapeutically relevant peptides. Furthermore, they are often applied to create peptide-based tools in chemical biology. In this review, we discuss general methods that allow the discovery of this compound class and highlight key examples of peptide-small molecule hybrids categorised by the application and function of the small molecule entity.

Engineering a protease-based and site-specific PEGylation-based strategy for the controlled release of exenatide

Using the commercially available antidiabetic drug exenatide (exendin-4) as a model peptide, we designed a novel exenatide derivative, termed LEX-1, comprising a 12-mer albumin-binding peptide, a protease-sensitive linker and a native exenatide. In addition, site-specific PEGylation was performed using LEX-1 as a lead sequence to generate four exenatide derivatives (LEX-2 to LEX-5). Moreover, we determined the optimal molecular weight of maleimide-derivatized PEG for the site-specific PEGylation of LEX-1 by an in vitro stability assay and an in vivo hypoglycemic efficacy test. As a result, LEX-3 (PEG10 kDa) exerted enhanced proteolytic stability, rational release rate of free exenatide and the best glucose-stabilizing capability compared with others. In addition, the prolonged hypoglycemic effects of LEX-1 and LEX-3 were demonstrated in type 2 diabetic mice by multiple OGTTs and a hypoglycemic duration test. Furthermore, a pharmacokinetic test was conducted using Sprague Dawley (SD) rats; LEX-3 (PEG10 kDa) showed the best circulating t _1/2 of ∼119.7 h for exenatide release from LEX-3, suggesting that LEX-3 has the potential to be developed into a once-weekly antidiabetic agent. The consecutive 8 week treatment of both LEX-1 and LEX-3 exhibited enhanced beneficial efficacies on body weight gain, cumulative food intake, % fat and hemoglobin A1c (HbA1c) reduction compared with exenatide treatment. Meanwhile, the chronic administration of LEX-1 and LEX-3 also effectively improved the blood biochemical indexes. Our results indicate the enhanced antidiabetic effects of LEX-1 and LEX-3, and our strategy of PEGylation and albumin conjugation can be applied to other bioactive agents.

Drug Delivery Strategies for Enhancing the Therapeutic Efficacy of Toxin-Derived Anti-Diabetic Peptides

Toxin peptides derived from the skin secretions of amphibians possess unique hypoglycemic activities. Many of these peptides share cationic and amphipathic structural similarities and appear to possess cell-penetrating abilities. The mechanism of their insulinotropic action is yet not elucidated, but they have shown great potential in regulating the blood glucose levels in animal models. Therefore, they have emerged as potential drug candidates as therapeutics for type 2 diabetes. Despite their anti-diabetic activity, there remain pharmaceutical challenges to be addressed for their clinical applications. Here, we present an overview of recent studies related to the toxin-derived anti-diabetic peptides derived from the skin secretions of amphibians. In the latter part, we introduce the bottleneck challenges for their delivery in vivo and general drug delivery strategies that may be applicable to extend their blood circulation time. We focus our research on the strategies that have been successfully applied to improve the plasma half-life of exendin-4, a clinically available toxin-derived anti-diabetic peptide drug.

Development of a new class of PSMA radioligands comprising ibuprofen as an albumin-binding entity

Prostate-specific membrane antigen (PSMA)-targeted radioligands have been used for the treatment of metastatic castration-resistant prostate cancer (mCRPC). Recently, albumin-binding PSMA radioligands with enhanced blood circulation were developed to increase the tumor accumulation of activity. The present study aimed at the design, synthesis and preclinical evaluation of a novel class of PSMA-targeting radioligands equipped with ibuprofen as a weak albumin-binding entity in order to improve the pharmacokinetic properties.

Methods: Four novel glutamate-urea-based PSMA ligands were synthesized with ibuprofen, conjugated via variable amino acid-based linker entities. The albumin-binding properties of the ¹⁷⁷Lu-labeled PSMA ligands were tested in vitro using mouse and human plasma. Affinity of the radioligands to PSMA and cellular uptake and internalization was investigated using PSMA-positive PC-3 PIP and PSMA-negative PC-3 flu tumor cells. The tissue distribution profile of the radioligands was assessed in biodistribution and imaging studies using PC-3 PIP/flu tumor-bearing nude mice.

Results: The PSMA ligands were obtained in moderate yields at high purity (>99%). ¹⁷⁷Lu-labeling of the ligands was achieved at up to 100 MBq/nmol with >96% radiochemical purity. In vitro assays confirmed high binding of all radioligands to mouse and human plasma proteins and specific uptake and internalization into PSMA-positive PC-3 PIP tumor cells. Biodistribution studies and SPECT/CT scans revealed high accumulation in PC-3 PIP tumors but negligible uptake in PC-3 flu tumor xenografts as well as rapid clearance of activity from background organs and tissues. ¹⁷⁷Lu-Ibu-DAB-PSMA, in which ibuprofen was conjugated via a positively-charged diaminobutyric acid (DAB) entity, showed distinguished tumor uptake and the most favorable tumor-to-blood and tumor-to-kidney ratios.

Conclusion: The high accumulation of activity in the tumor and fast clearance from background organs was a common favorable characteristic of PSMA radioligands modified with ibuprofen as albumin-binding entity. ¹⁷⁷Lu-Ibu-DAB-PSMA emerged as the most promising candidate; hence, more detailed preclinical investigations with this radioligand are warranted in view of a clinical translation.

Design and evaluation of novel thrombin-based GLP-1 analogs with peptidic albumin binding domain for the controlled release of GLP-1

Currently, the curative effects of polypeptide drugs are often restricted due to the short in vivo duration of action.

Integrin αvβ3-targeted radionuclide therapy combined with immune checkpoint blockade immunotherapy synergistically enhances anti-tumor efficacy

Rationale: Radiotherapy combined with immunotherapy has revealed promising outcomes in both preclinical studies and ongoing clinical trials. Targeted radionuclide therapy (TRT) is a branch of radiotherapy concerned with the use of radioisotopes, radiolabeled molecules or nanoparticles that deliver particulate radiation to cancer cells. TRT is a promising approach in cases of metastatic disease where conventional treatments are no longer effective. The increasing use of TRT raises the question of how to best integrate TRT with immunotherapy. In this study, we proposed a novel therapeutic regimen that combined programmed death ligand 1 (PD-L1)-based immunotherapy with peptide-based TRT (¹⁷⁷Lu as the radionuclide) in the murine colon cancer model.

Methods: To explore the most appropriate timing of immunotherapy after radionuclide therapy, the anti-PD-L1 antibody (αPD-L1 mAb) was delivered in a concurrent or sequential manner when ¹⁷⁷Lu TRT was given.

Results: The results demonstrated that TRT led to an acute increase in PD-L1 expression on T cells, and TRT in combination with αPD-L1 mAb stimulated the infiltration of CD8⁺ T cells, which improved local tumor control, overall survival and protection against tumor rechallenge. Moreover, our data revealed that the time window for this combination therapy may be critical to outcome.

Conclusions: This therapeutic combination may be a promising approach to treating metastatic tumors in which TRT can be used. Clinical translation of the result would suggest that concurrent rather than sequential blockade of the PD-1/PD-L1 axis combined with TRT improves overall survival and long-term tumor control.

Engineering an enhanced thrombin-based GLP-1 analog with long-lasting glucose-lowering and efficient weight reduction

Peptides are considered as potent therapeutic drugs primarily due to the exquisite potency and selectivity to targets. However, the development and clinical application of peptide drugs were severely limited by the poor in vivo lifespans. Here, we designed an improved small albumin-binding polypeptide that can associate with human serum albumin (HSA) and liberate the bioactive peptide. Using glucagon-like peptide-1 (GLP-1) as a model, two new long-lasting GLP-1 analogs (termed XTS1 and XTS2) containing an albumin-binding domain, a protease-cleavable linker and a mutated GLP-1(A8Aib) were designed to demonstrate the sustained release of GLP-1 due to the plasma thrombin (TBN) digestion. Two XTS peptides were prepared of high purity (>99%) and accurate molecular weight determined by reversed high-performance liquid chromatography and mass spectrometry, respectively. In vitro measurements of surface plasmon resonance indicated that XTS1 associate with serum albumins of all species with higher affinity compared with XTS2. Metabolic stability of XTS1 in vitro in human plasma was also better than that of XTS2. Protease cleavage assay results of XTS peptides demonstrated the controlled-release of transient GLP-1 from the XTS1 and XTS2 mixture after thrombin-catalyzed hydrolysis. Then the intraperitoneal glucose tolerance test (IPGTT) showed that the glucose-lowering efficacies of XTS1 were in a dosage-dependent manner within the range of 0.1–0.9 mg kg⁻¹. In addition, XTS1 showed similar hypoglycemic intensity and significantly longer action duration compared to Liraglutide in both multiple IPGTTs and hypoglycemic duration test. Apparently extended plasma half-lives of ∼2.3 and ∼3.5 days were observed after a single subcutaneous administration of XTS1 (0.9 mg kg⁻¹) in rats and cynomolgus monkeys, respectively. Furthermore, twice-weekly subcutaneously dosed XTS1 in db/db mice achieved long-term beneficial effects on body weight, hemoglobin A1C (HbA1C) lowering and the function of pancreatic beta cells. These studies support that XTS1 exerts potential as a therapeutic drug for the treatment of T2DM.

Peptides are considered as potent therapeutic drugs primarily due to the exquisite potency and selectivity to targets.

Non-covalent albumin-binding ligands for extending the circulating half-life of small biotherapeutics

Peptides and small protein scaffolds are gaining increasing interest as therapeutics. Similarly to full-length antibodies, they can bind a target with a high binding affinity and specificity while remaining small enough to diffuse into tissues. However, despite their numerous advantages, small biotherapeutics often suffer from a relatively short circulating half-life, thus requiring frequent applications that ultimately restrict their ease of use and user compliance. To overcome this limitation, a large variety of half-life extension strategies have been developed in the last decades. Linkage to ligands that non-covalently bind to albumin, the most abundant serum protein with a circulating half-life of ∼19 days in humans, represents one of the most successful approaches for the generation of long-lasting biotherapeutics with improved pharmacokinetic properties and superior efficacy in the clinic.

An Albumin Sandwich Enhances in Vivo Circulation and Stability of Metabolically Labile Peptides

The effectiveness of numerous molecular drugs is hampered by their poor pharmacokinetics. Different from previous approaches with limited effectiveness, most recently, emerging high-affinity albumin binding moieties (ABMs) for in vivo hitchhiking of endogenous albumin opens up an avenue to chaperone small molecules for long-acting therapeutics. Although several FDA-approved fatty acids have shown prolonged residence and therapeutic effect, an easily synthesized, water-soluble, and high-efficiency ABM with versatile drug loading ability is urgently needed to improve the therapeutic efficacy of short-lived constructs. We herein identified an ideal bivalent Evans blue derivative, denoted as N(tEB)₂, as a smart ABM-delivery platform to chaperone short-lived molecules, through both computational modeling screening and efficient synthetic schemes. The optimal N(tEB)₂ could reversibly link two molecules of albumin through its two binding heads with a preferable spacer, resulting in significantly extended circulation half-life of a preloaded cargo and water-soluble. Notably, this in situ dimerization of albumin was able to sandwich peptide therapeutics to protect them from proteolysis. As an application, we conjugated N(tEB)₂ with exendin-4 for long-acting glucose control in a diabetic mouse model, and it was superior to both previously tested NtEB-exendin-4 (Abextide) and the newly FDA-approved semaglutide, which has been arguably the best commercial weekly formula so far. Hence, this novel albumin binder has excellent clinical potential for next-generation biomimetic drug delivery systems.

Albumin Nanovectors in Cancer Therapy and Imaging

Albumin nanovectors represent one of the most promising carriers recently generated because of the cost-effectiveness of their fabrication, biocompatibility, safety, and versatility in delivering hydrophilic and hydrophobic therapeutics and diagnostic agents. In this review, we describe and discuss the recent advances in how this technology has been harnessed for drug delivery in cancer, evaluating the commonly used synthesis protocols and considering the key factors that determine the biological transport and the effectiveness of such technology. With this in mind, we highlight how clinical and experimental albumin-based delivery nanoplatforms may be designed for tackling tumor progression or improving the currently established diagnostic procedures.

Antidiabetic Effect of Abextide, a Long-Acting Exendin-4 Analogue in Cynomolgus Monkeys

Abextide, synthesized by conjugating an albumin-binding moiety-truncated Evans blue-to glucagon-like peptide 1 receptor (GLP-1R) agonist exendin-4, shows extended drug release and enhanced hypoglycemic effect in diabetic mice. The aim of this study is to evaluate the pharmacodynamics of Abextide in nonhuman primates. Two batches of elderly cynomolgus monkeys with naturally occurring diabetes are used for this study. During the whole experiment period, no abnormalities such as swelling at the injection site, lethargy, or hypoglycemia are observed in all animals. The monkeys in the Abextide group lose appetite after drug administration and then recover over time. In the single dose treatment, at day 1 and day 3 after treatment, decreased plasma glucose level is observed in the Abextide-treated group but not in placebo or Albiglutide-treated group. For monkeys that receive two doses of drug, the blood glucose level in all subjects in Abextide group decreases rapidly upon drug administration and return to a plateau by day 3. A similar pattern of response is seen after the second dose administration. The delayed drug release and hypoglycemic effect of Abextide make it potentially useful as an antidiabetic drug for weekly subcutaneous administration.

Depletion of PD-1-positive cells ameliorates autoimmune disease

Targeted suppression of autoimmune diseases without collateral suppression of normal immunity remains an elusive yet clinically important goal. Targeted blockade of programmed-cell-death-protein-1 (PD-1)-an immune checkpoint factor expressed by activated T cells and B cells-is an efficacious therapy for potentiating immune activation against tumours. Here we show that an immunotoxin consisting of an anti-PD-1 single-chain variable fragment, an albumin-binding domain and Pseudomonas exotoxin targeting PD-1-expressing cells, selectively recognizes and induces the killing of the cells. Administration of the immunotoxin to mouse models of autoimmune diabetes delays disease onset, and its administration in mice paralysed by experimental autoimmune encephalomyelitis ameliorates symptoms. In all mouse models, the immunotoxin reduced the numbers of PD-1-expressing cells, of total T cells and of cells of an autoreactive T-cell clone found in inflamed organs, while maintaining active adaptive immunity, as evidenced by full-strength immune responses to vaccinations. The targeted depletion of PD-1-expressing cells contingent to the preservation of adaptive immunity might be effective in the treatment of a wide range of autoimmune diseases.

In vivo monitoring blood-brain barrier permeability using spectral imaging through optical clearing skull window

The blood-brain barrier (BBB) plays a key role in the health of the central nervous system. Opening the BBB is very important for drug delivery to brain tissues to enhance the therapeutic effect on brain diseases. It is necessary to in vivo monitor the BBB permeability for assessing drug release with high resolution; however, an effective method is lacking. In this work, we developed a new method that combined spectral imaging with an optical clearing skull window to in vivo dynamically monitor BBB opening caused by 5-aminolevulinic acid (5-ALA)-mediated photodynamic therapy (PDT), in which the Evans blue dye (EBd) acted as an indicator of the BBB permeability. Using this method, we effectively monitored the cerebrovascular EBd leakage process. Moreover, the analysis of changes in the vascular and extravascular EBd concentrations demonstrated that the PDT-induced BBB opening exhibited spatiotemporal differences in the cortex. This spectral imaging method based on the optical clearing skull window provides a low-cost and simply operated tool for in vivo monitoring BBB opening process. This has a high potential for the visualization of drug delivery to the central nervous system. Thus, it is of tremendous significance in brain disease therapy. Monitoring the changes in PDT-induced BBB permeability by evaluating the EBd concentration using an optical clearing skull window. (A) Entire brains and coronal sections following treatment of PDT with/without an optical clearing skull window after injection of EBd. (B) Typical EBd distribution maps before and after laser irradiation captured by the spectral imaging method. (Colorbar represents the EBd concentration).

Mini-review: Targeted radiopharmaceuticals incorporating reversible, low molecular weight albumin binders

The combination of low molecular weight, reversible human serum albumin (HSA) binders with targeted radiopharmaceuticals in dual-targeted radioconjugates holds great promise, in particular for endoradiotherapy. Attachment of HSA-binders to radiopharmaceuticals extends their blood circulation time and results in an enhanced tumour uptake as well as often in an improved pharmacokinetic profile. In this mini-review, an overview of currently pursued approaches of this novel strategy is provided.

Radioiodinated Portable Albumin Binder as a Versatile Agent for in Vivo Imaging with Single-Photon Emission Computed Tomography

In this study, radioiodinated 4-( p-iodophenyl)butyric acid ([¹³¹I]IBA) was synthesized and evaluated as a portable albumin-binder for potential applications in single photon emission computed tomography imaging of blood pool, tumor, and lymph node with significantly improved pharmacokinetic properties. The [¹³¹I]IBA was prepared under the catalyst of Cu₂O/1,10-phenanthroline. After that, the albumin-binding capability of [¹³¹I]IBA was tested in vitro, ex vivo, and in vivo, respectively. [¹³¹I]IBA was obtained with very high radiolabeling yield (>99%) and good radiochemical purity (>98%) within 10 min. It binds to albumin effectively with high affinity (IC₅₀= 46.5 μM) and has good stability. The results of biodistribution indicated that the [¹³¹I]IBA was mainly accumulated in blood with good retention (10.51 ± 2.58%ID/g at 30 min p.i. and 4.63 ± 0.17%ID/g at 4 h p.i.). In the SPECT imaging of mice models with [¹³¹I]IBA, blood pool, lymph node, and tumors could be imaged clearly with high target-to-background ratio. Overall, the radioiodinated albumin binder of [¹³¹I]IBA with long blood half-life and excellent stability could be used to decorate diversified albumin-binding radioligands and developed as a versatile theranostic agent.

pH-sensitive radiolabeled and superfluorinated ultra-small palladium nanosheet as a high-performance multimodal platform for tumor theranostics

Radiolabeled nanomaterials, especially those with ultra-small structures, have been the research focus in recent years, and thus may open up new prospects for clinical diseases theranostics. Herein, fluorinated Pd nanosheets labeled with Gd or radionuclides are developed as multimodal platforms for tumor theranostics. These nanomaterials decorated by functional polyethylene glycol demonstrate ultrahigh ¹⁹F MRI signal, ultrasmall size and good dispersibility. These ultrasmall materials exhibit good biocompatibility and easily to be modified for multimodal imaging (SPECT/MRI/PAI) by assembling the functional groups like building blocks. Furthermore, with high accumulation in tumor sites, under the guidance of multimodal imaging, combined photothermal therapy and radiotherapy are performed and synergistic effects are obtained. By comparing the in vivo behaviors of nanostructures labeled by different nuclides, the present study suggests the pH-sensitive radioiodinated Pd nanosheet which has unexpected T/NT ratio (>4-fold tumor-to-muscle ratio) in SPECT imaging and solves the critical high background issue of nanoprobes, could improve diagnostic accuracy and guide combination therapy. In summary, this functionalized nanoplatform with promising imaging and therapeutic efficacy has great potential for precision theranostic nanomedicines.

Evans Blue Derivative-Functionalized Gold Nanorods for Photothermal Therapy-Enhanced Tumor Chemotherapy

Chemotherapy is a standard care for cancer management, but the lack of tumor targeting and high dose-induced side effects still limit its utility in patients. Here, we report a chemotherapy combined with photothermal therapy (PTT) for enhanced cancer ablation by functionalization of gold nanorods (GNRs) with a novel small molecule named truncated Evans blue (tEB). On the basis of the high binding affinity of tEB with albumin, an Abraxane-like nanodrug, human serum albumin/hydroxycamptothecin (HSA/HCPT), was further complexed with GNR-tEB. This formed an HCPT/HSA/tEB-GNR (HHEG) with excellent biostability and biocompatibility. With photoacoustic and fluorescence imaging, we observed HHEG tumor targeting, which is mediated by enhanced permeability retention effect. The accumulation of HHEG peaked in tumor at 12 h postinjection. Moreover, HHEG can effectively ablate tumor growth with laser illumination via chemo/thermal therapy after intravenous administration into SCC7 tumor. This combination is much better than chemotherapy or PTT alone. Collectively, we constructed a chemo/thermal therapy nanostructure based on a tEB-modified GNR for better tumor treatment effect. The use of tEB in gold nanoparticles can facilitate many new approaches to design hybrid nanoparticles.

Subarachnoid hemorrhage - Induced block of cerebrospinal fluid flow: Role of brain coagulation factor III (tissue factor)

Subarachnoid hemorrhage (SAH) in 95% of cases results in long-term disabilities due to brain damage, pathogenesis of which remains uncertain. Hindrance of cerebrospinal fluid (CSF) circulation along glymphatic pathways is a possible mechanism interrupting drainage of damaging substances from subarachnoid space and parenchyma. We explored changes in CSF circulation at different time following SAH and possible role of brain tissue factor (TF). Fluorescent solute and fluorescent microspheres injected into cisterna magna were used to track CSF flow in mice. SAH induced by perforation of circle of Willis interrupted CSF flow for up to 30 days. Block of CSF flow did not correlate with the size of hemorrhage. Following SAH, fibrin deposits were observed on the brain surface including areas without visible blood. Block of astroglia-associated TF by intracerebroventricular administration of specific antibodies increased size of hemorrhage, decreased fibrin deposition and facilitated spread of fluorophores in sham/naïve animals. We conclude that brain TF plays an important role in localization of hemorrhage and also regulates CSF flow under normal conditions. Targeting of the TF system will allow developing of new therapeutic approaches to the treatment of SAH and pathologies related to CSF flow such as hydrocephalus.

Harnessing albumin as a carrier for cancer therapies

Serum albumin, a natural ligand carrier that is highly concentrated and long-circulating in the blood, has shown remarkable promise as a carrier for anti-cancer agents. Albumin is able to prolong the circulation half-life of otherwise rapidly cleared drugs and, importantly, promote their accumulation within tumors. The applications for using albumin as a cancer drug carrier are broad and include both traditional cancer chemotherapeutics and new classes of biologics. Strategies for leveraging albumin for drug delivery can be classified broadly into exogenous and in situ binding formulations that utilize covalent attachment, non-covalent association, or encapsulation in albumin-based nanoparticles. These methods have shown remarkable preclinical and clinical successes that are examined in this review.

Evans Blue Dye: A Revisit of Its Applications in Biomedicine

Evans blue (EB) dye has owned a long history as a biological dye and diagnostic agent since its first staining application by Herbert McLean Evans in 1914. Due to its high water solubility and slow excretion, as well as its tight binding to serum albumin, EB has been widely used in biomedicine, including its use in estimating blood volume and vascular permeability, detecting lymph nodes, and localizing the tumor lesions. Recently, a series of EB derivatives have been labeled with PET isotopes and can be used as theranostics with a broad potential due to their improved half-life in the blood and reduced release. Some of EB derivatives have even been used in translational applications in clinics. In addition, a novel necrosis-avid feature of EB has recently been reported in some preclinical animal studies. Given all these interesting and important advances in EB study, a comprehensive revisiting of EB has been made in its biomedical applications in the review.

Engineering a novel protease-based Exendin-4 derivative for type 2 antidiabetic therapeutics

To develop an effective long-acting antidiabetic agent, we designed a novel Exendin-4 derivative (termed LEx4) containing an albumin-binding domain (ABD), a protease-cleavable linker and a native Exendin-4. Here, we present the LEx4 with balanced glucoregulatory activity and prolonged in vivo activity. As a first step, the LEx4 with purity more than 99% was prepared. Microscale thermophoresis (MST) results demonstrated that LEx4 associates with rat and monkey serum albumin with high-affinity (K_a = 1.26 × 10⁶ M^-1 and 1.52 × 10⁶ M^-1, respectively). Then the stability test in vitro showed the enhanced antiproteolytic ability of LEx4 in rat and human plasma compared to native Exendin-4. Oral glucose tolerance test (OGTT) in type 2 diabetic mice showed the glucose-lowering efficacy of LEx4 was clearly dosage-dependent within 25-250 nmol/kg. In addition, the protracted antidiabetic effects of LEx4 were further confirmed by both multiple OGTTs and hypoglycemic efficacies test in type 2 diabetic mice. In Sprague Dawley (SD) rats, LEx4 also showed 3.3-fold longer elimination half-life (t_1/2) than native Exendin-4. Furthermore, once daily injection of LEx4 to db/db mice achieved long-term beneficial effects on body weight, blood biochemical values, glucose tolerance and pancreatic tissue. We believe LEx4 has superior pharmaceutical potential as a therapeutic drug to against type-2 diabetes mellitus (T2DM) based on these results. This strategy of albumin binding is also applicable to other bioactive peptides for development of long-acting therapeutic drugs.

Development of a novel albumin-based and maleimidopropionic acid-conjugated peptide with prolonged half-life and increased in vivo anti-tumor efficacy

Angiogenesis plays a critical role in tumor aggressiveness, and a lot of anti-angiogenic agents have been used in clinical therapy. The therapeutic efficacy of peptides are generally restricted by the short in vivo life-time, thus, we were interested in developing a novel albumin-based and maleimidopropionic acid-conjugated peptide to prolong the half-life and improve the anti-tumor effect.

Methods: We developed a peptide F56 with a maleimidopropionic acid (MPA) at the C-terminal (denoted as F56-CM), which allows immediate and irreversible conjugation with serum albumin. Biological property and anti-tumor activity of F56-CM were evaluated in vitro and in vivo.

Results: We showed that F56-CM reduced migration and tube formation of endothelial cells in vitro and inhibited the generation of subintestinal vessels (SIV) in zebrafish embryos in vivo. F56-CM inhibited vascular endothelial growth factor (VEGF) induced phosphorylation of VEGFR1 and activation of the PI3K-AKT axis. Furthermore, F56-CM rapidly conjugated with albumin upon intravenous injection and extended the biological half-life of F56 from 0.4249 h to 6.967 h in rats. Compared with F56, F56-CM exhibited stronger anti-tumor activity on both BGC-823 gastric cancer and HT-29 colon cancer xenografts in nude mice, and the statistical difference was remarkable. More significantly, the efficacy of F56-CM inhibiting lung metastasis of BGC-823 cells was also better than that of F56. The inhibition rates were 62.1% and 78.9% for F56 and F56-CM respectively when administrated every day, and 43.8% and 63.1% when administrated every four days at equal dose.

Conclusions: Taken together, our results demonstrated that F56-CM has considerable potential for cancer therapy.

Improving long-term subcutaneous drug delivery by regulating material-bioenvironment interaction

Subcutaneous long-acting release (LAR) formulations have been extensively developed in the clinic to increase patient compliance and reduce treatment cost. Despite preliminary success for some LAR systems, a major obstacle limiting the therapeutic effect remains on their interaction with surrounding tissues. In this review, we summarize how living bodies respond to injected or implanted materials, and highlight some typical strategies based on smart material design, which may significantly improve long-term subcutaneous drug delivery. Moreover, possible strategies to achieve ultra-long (months, years) subcutaneous drug delivery systems are proposed. Based on these discussions, we believe the well-designed subcutaneous long-acting formulations will hold great promise to improve patient quality of life in the clinic.

A paclitaxel prodrug with bifunctional folate and albumin binding moieties for both passive and active targeted cancer therapy

Folate receptor (FR) has proven to be a valuable target for chemotherapy using folic acid (FA) conjugates. However, FA-conjugated chemotherapeutics still have low therapeutic efficacy accompanied with side effects, resulting from complications such as short circulation half-life, limited tumor delivery, as well as high kidney accumulation. Herein, we present a novel FA-conjugated paclitaxel (PTX) prodrug which was additionally conjugated with an Evans blue (EB) derivative for albumin binding. The resulting bifunctional prodrug prolonged blood circulation, enhanced tumor accumulation, and consequently improved tumor therapeutic efficacy. Methods: Fmoc-Cys(Trt)-OH was coupled onto PTX at the 7'-OH position for further synthesis of ester prodrug FA-PTX-EB. The targeting ability was investigated using confocal microscopy and flow cytometry. The pharmacokinetics of this bifunctional compound was also studied. Meanwhile, cell viability was evaluated in normal cells and three cancer cell lines by MTT assay. In vivo therapeutic effect was tested on FR-α overexpressing MDA-MB-231 tumor model. Results: Compared with free PTX, the FA-PTX, PTX-EB and FA-PTX-EB prodrugs increased circulation half-life in mice from 2.19 to 3.82, 4.41, and 7.51 h, respectively. Pharmacokinetics studies showed that the FA-PTX-EB delivered more PTX to tumors than FA-PTX and free PTX. In vitro and in vivo studies demonstrated that FA-EB-conjugated PTX induced potent antitumor activity. Conclusion: FA-PTX-EB showed prolonged blood circulation, enhanced drug accumulation in tumors, higher therapeutic index, and lower side effects than either free PTX or monofunctional FA-PTX and EB-PTX. The results support the potential of using EB for the development of long-acting therapeutics.

"Albumin Hitchhiking" with an Evans Blue Analog for Cancer Theranostics

Although ¹⁷⁷Lu-DOTA-TATE was recently approved in Europe for the treatment of certain neuroendocrine tumors, continued development and optimization has been ongoing to further improve the therapeutic efficacy of somatostatin receptor 2 targeted peptide receptor radionuclide therapy, as well as reducing the renal toxicity. In this work, the use of an Evans blue analog for “albumin hitchhiking” resulted in significant improvement in both the imaging performance and therapeutic efficacy of radiolabeled octreotate, as well as reducing the toxicity since much less radioactivity was used for therapy. Upon clinical translation, such “albumin hitchhiking” could make significant impact in the near future for cancer patient management.

Microneedle-array patches loaded with dual mineralized protein/peptide particles for type 2 diabetes therapy

The delivery of therapeutic peptides for diabetes therapy is compromised by short half-lives of drugs with the consequent need for multiple daily injections that reduce patient compliance and increase treatment cost. In this study, we demonstrate a smart exendin-4 (Ex4) delivery device based on microneedle (MN)-array patches integrated with dual mineralized particles separately containing Ex4 and glucose oxidase (GOx). The dual mineralized particle-based system can specifically release Ex4 while immobilizing GOx as a result of the differential response to the microenvironment induced by biological stimuli. In this manner, the system enables glucose-responsive and closed-loop release to significantly improve Ex4 therapeutic performance. Moreover, integration of mineralized particles can enhance the mechanical strength of alginate-based MN by crosslinking to facilitate skin penetration, thus supporting painless and non-invasive transdermal administration. We believe this smart glucose-responsive Ex4 delivery holds great promise for type 2 diabetes therapy by providing safe, long-term, and on-demand Ex4 therapy.

Diabetes treatments often rely on frequent and scheduled drug administration, which reduces patient compliance and increases treatment cost. Here, the authors develop a microneedle-array patch that separately loads drug-releasing module and glucose-sensing element for on-demand, long-term diabetes therapy.

Strategies for Preparing Albumin-based Nanoparticles for Multifunctional Bioimaging and Drug Delivery

Biosafety is the primary concern in clinical translation of nanomedicine. As an intrinsic ingredient of human blood without immunogenicity and encouraged by its successful clinical application in Abraxane, albumin has been regarded as a promising material to produce nanoparticles for bioimaging and drug delivery. The strategies for synthesizing albumin-based nanoparticles could be generally categorized into five classes: template, nanocarrier, scaffold, stabilizer and albumin-polymer conjugate. This review introduces approaches utilizing albumin in the preparation of nanoparticles and thereby provides scientists with knowledge of goal-driven design on albumin-based nanomedicine.

Lipophilic siRNA targets albumin in situ and promotes bioavailability, tumor penetration, and carrier-free gene silencing

Clinical translation of therapies based on small interfering RNA (siRNA) is hampered by siRNA's comprehensively poor pharmacokinetic properties, which necessitate molecule modifications and complex delivery strategies. We sought an alternative approach to commonly used nanoparticle carriers by leveraging the long-lived endogenous serum protein albumin as an siRNA carrier. We synthesized siRNA conjugated to a diacyl lipid moiety (siRNA-L₂), which rapidly binds albumin in situ. siRNA-L₂, in comparison with unmodified siRNA, exhibited a 5.7-fold increase in circulation half-life, an 8.6-fold increase in bioavailability, and reduced renal accumulation. Benchmarked against leading commercial siRNA nanocarrier in vivo jetPEI, siRNA-L₂ achieved 19-fold greater tumor accumulation and 46-fold increase in per-tumor-cell uptake in a mouse orthotopic model of human triple-negative breast cancer. siRNA-L₂ penetrated tumor tissue rapidly and homogeneously; 30 min after i.v. injection, siRNA-L₂ achieved uptake in 99% of tumor cells, compared with 60% for jetPEI. Remarkably, siRNA-L₂ achieved a tumor:liver accumulation ratio >40:1 vs. <3:1 for jetPEI. The improved pharmacokinetic properties of siRNA-L₂ facilitated significant tumor gene silencing for 7 d after two i.v. doses. Proof-of-concept was extended to a patient-derived xenograft model, in which jetPEI tumor accumulation was reduced fourfold relative to the same formulation in the orthotopic model. The siRNA-L₂ tumor accumulation diminished only twofold, suggesting that the superior tumor distribution of the conjugate over nanoparticles will be accentuated in clinical situations. These data reveal the immense promise of in situ albumin targeting for development of translational, carrier-free RNAi-based cancer therapies.

Long-Acting Release Formulation of Exendin-4 Based on Biomimetic Mineralization for Type 2 Diabetes Therapy

Exendin-4 has been clinically exploited for treating type 2 diabetes, but the short circulation half-life and multiple daily injections limit its widespread application with respect to poor patient compliance, low efficacy, and high treatment cost. In this study, a potent long-acting release system based on biomimetic mineralization was constructed for biocompatible and sustained exendin-4 delivery. Similar to natural biomineralization, exendin-4 can be mineralized to form nanosized mineral solids by means of the reaction between acidic amino acid residues and calcium ions in a supersaturated environment with negligible influence on peptide bioactivity. Mineralized exendin-4 particles may be spontaneously absorbed by a living body under physiologically supersaturated conditions, resulting in gradual dissociation and sustained drug release. In such a way, the glucose level of diabetic mice may be effectively controlled for a long period of time by mineralized exendin-4 without obvious side effects. We believe this biomimetic formulation can serve as a promising candidate for future clinical applications for type 2 diabetes therapies.