Self‐Assembling Prodrugs by Precise Programming of Molecular Structures that Contribute Distinct Stability, Pharmacokinetics, and Antitumor Efficacy

Multifunctional delivery strategies and nanoplatforms of SN-38 in cancer therapeutics

SN-38 or 7-ethyl-10-hydroxycamptothecin is the active metabolite of irinotecan, a widely used chemotherapeutic agent for the treatment of colorectal, pancreatic, lung, breast, gastric, esophageal, hepatocellular, ovarian, brain, leukemia, and lymphoma malignancies. SN-38's antitumoral effect is 100 to 1000 times more potent than that of irinotecan. However, its clinical application is hindered by its poor solubility and chemical instability. To circumvent these challenges and avoid systemic toxicities, such as myelosuppression and diarrhea, several SN-38 delivery systems have been explored. In that regard, formulations based on targeted, controlled and tumor-responsive release of SN-38 have demonstrated to enhance its antitumoral effects and reduce the associated systemic toxicities by limiting the pharmacological activity to the desired tumor location. To this end, prodrugs, conjugates, nanoparticles, dendrimers, or lipid-based strategies for SN-38 delivery have been used. Most recently, multifunctional approaches have emerged as an attractive alternative to develop SN-38 delivery systems, combining several strategies in a single formulation, i.e., encapsulating nanocarriers, tumor-targeting ligands, stimuli-responsive elements, optimal linkers, drug combinations or bioimaging agents. Despite their therapeutic advantages, multifunctional delivery systems often face challenges concerning their clinical translation compared to conventional therapies, such as biocompatibility, scalability and cost-effectiveness issues. The aim of this work is to review the most recent progress that has been made in the development and assessment of multifunctional delivery systems for cancer treatment.

A self-assembling cytotoxic nanotherapeutic strategy for high drug loading and synergistic delivery of molecularly targeted therapies

Despite significant advancements in anticancer nanotherapeutics, the efficient encapsulation of multiple therapeutic modalities within single nanocarriers remains challenging due to the complex requirements of supramolecular self-assembly and/or chemical modification. These intricate synthesis procedures often impede the clinical translation of promising nanomedicines. In this study, we introduce a cost-effective and straightforward self-assembling cytotoxic nanotherapeutic strategy that enables the noncovalent incorporation of water-insoluble anticancer molecular inhibitors with high drug loading. This was achieved through the lipid conjugation of camptothecin, enabling nanoassembly in aqueous solutions devoid of excipients. These nanoassemblies were further developed into nanovehicles capable of encapsulating a high capacity of structurally diverse cargos, including molecularly targeted agents. Notably, nanoassemblies composed of linoleic acid-conjugated camptothecin and sorafenib demonstrated stability and sustained release of their payloads. The combination nanoparticles exhibited synergistic effects and effectively overcame ABCG2-mediated drug resistance in hepatocellular carcinoma (HCC). Systemic administration of these nanotherapeutics led to sustained tumor growth inhibition in various HCC xenograft-bearing mouse models, including a chemically induced orthotopic HCC model. This innovative supramolecular assembly strategy, which allows a single vehicle to deliver multimodal therapies, shows promise in overcoming drug resistance in human HCC and could be adapted for the development of other injectable nanomedicines, warranting further investigation. STATEMENT OF SIGNIFICANCE: This study advances anticancer nanotherapy by developing a simple and cost-effective self-assembling strategy that enables high loading of multiple water-insoluble chemotherapeutics. Using lipid-conjugated camptothecin, we created stable nanoassemblies capable of synergistically delivering diverse molecularly targeted agents. This combinatory platform effectively overcame therapeutic resistance and demonstrated sustained tumor inhibition in hepatocellular carcinoma-bearing mouse models. This new self-assembling cytotoxic nanotherapeutic strategy has potential applications for the development of other injectable nanomedicines.

A self-assembled copper-artemisinin nanoprodrug as an efficient reactive oxygen species amplified cascade system for cancer treatment

Chemodynamic therapy (CDT) is a tumor-specific intervention methodology, which is based on the upregulation of reactive oxygen species (ROS) content by triggering the Fenton or Fenton-like reaction within the tumor microenvironment (TME). However, there are still challenges in achieving high-efficiency CDT on account of both the limited intracellular hydrogen peroxide (H2O2) and delivery efficiency of Fenton metal ions. Copper-based nanotherapeutic systems have attracted extensive attention and have been widely applied in the construction of nanotherapeutic systems and multimodal synergistic therapy. Herein, we propose a strategy to synergize chemotherapy drugs that upregulate intracellular ROS content with chemodynamic therapy and construct an artemisinin-copper nanoprodrug for proof-of-concept. With the proposed biomimetic self-assembly strategy, we successfully construct an injectable nanoprodrug with suitable size distribution and high drug loading content (68.1 wt%) through the self-assembly of amphiphilic artemisinin prodrug and copper ions. After reaching the TME, both Cu2+ ions and free AH drugs can be released from AHCu nanoprodrugs. Subsequently, the disassembled Cu2+ ions are converted into Cu+ ions by consuming the intracellular GSH. The generated Cu+ ions serve as a highly efficient Fenton-like reagent for robust ROS generation from both AH and tumor-over-produced H2O2. Results show that the nanoprodrug can realize the cascade amplification of ROS generation via artemisinin delivery and subsequent in situ Fenton-like reaction and a high tumor inhibition rate of 62.48% in vivo. This work provides a promising strategy for the design and development of an efficient nanoprodrug for tumor-specific treatment.

Mitochondrial rewiring with small-molecule drug-free nanoassemblies unleashes anticancer immunity

The immunosuppressive tumor microenvironment (TME) remains a major obstacle to tumor control and causes suboptimal responses to immune checkpoint blockade (ICB) therapy. Thus, developing feasible therapeutic strategies that trigger inflammatory responses in the TME could improve the ICB efficacy. Mitochondria play an essential role in inflammation regulation and tumor immunogenicity induction. Herein, we report the discovery and characterization of a class of small molecules that can recapitulate aqueous self-assembly behavior, specifically target cellular organelles (e.g., mitochondria), and invigorate tumor cell immunogenicity. Mechanistically, this nanoassembly platform dynamically rewires mitochondria, induces endoplasmic reticulum stress, and causes apoptosis/paraptosis-associated immunogenic cell death. After treatment, stressed and dying tumor cells can act as prophylactic or therapeutic cancer vaccines. In preclinical mouse models of cancers with intrinsic or acquired resistance to PD-1 blockade, the local administration of nanoassemblies inflames the immunologically silent TME and synergizes with ICB therapy, generating potent antitumor immunity. This chemically programmed small-molecule immune enhancer acts distinctly from regular cytotoxic therapeutics and offers a promising strategy for synchronous and dynamic tailoring of innate immunity to achieve traceless cancer therapy and overcome immunosuppression in cancers.

Chemically engineered mTOR-nanoparticle blockers enhance antitumour efficacy

BACKGROUND

Hepatocellular carcinoma (HCC) is a highly prevalent and deadly type of cancer, and although pharmacotherapy remains the cornerstone of treatment, therapeutic outcomes are often unsatisfactory. Pharmacological inhibition of mammalian target of rapamycin (mTOR) has been closely associated with HCC regression.

METHODS

Herein, we covalently conjugated AZD8055, a potent mTORC1/2 blocker, with a small panel of unsaturated fatty acids via a dynamically activating linkage to enable aqueous self-assembly of prodrug conjugates to form mTOR nanoblockers. Cell-based experiments were carried out to evaluate the effects of the nanoblocker against hepatocellular carcinoma (HCC) cells. The orthotopic and subcutaneous HCC mouse models were established to examine its antitumour activity.

FINDINGS

Among several fatty acids as promoieties, linoleic acid-conjugated self-assembling nanoblocker exhibited optimal size distribution and superior physiochemical properties. Compared with free agents, PEGylated AZD8055 nanoblocker (termed AZD NB) was pharmacokinetically optimized after intravenous administration. In vivo investigations confirmed that AZD NB significantly suppressed tumour outgrowth in subcutaneous HCCLM3 xenograft, Hepatoma-22, and orthotopic Hepa1-6 liver tumour models. Strikingly, treatment with AZD NB, but not free agent, increased intratumour infiltration of IFN-γ+CD8+ T cells and CD8+ memory T cells, suggesting a potential role of the mTOR nanoblocker to remodel the tumour microenvironment. Overall, a single conjugation with fatty acid transformed a hydrophobic mTOR blocker into a systemically injectable nanomedicine, representing a facile and generalizable strategy for improving the therapeutic index of mTOR inhibition-based cancer therapy.

INTERPRETATION

The mTOR inhibition by chemically engineered nanoblocker presented here had enhanced efficacy against tumours compared with the pristine drug and thus has the potential to improve the survival outcomes of patients with HCC. Additionally, this new nanosystem derived from co-assembling of small-molecule prodrug entities can serve as a delivery platform for the synergistic co-administration of distinct pharmaceutical agents.

FUNDING

This work was supported by the National Natural Science Foundation of China (32171368,81721091), the Zhejiang Provincial Natural Science Foundation of China (LZ21H180001), the Jinan Provincial Laboratory Research Project of Microecological Biomedicine (JNL-2022039c and JNL-2022010B), State Key Laboratory for Diagnosis and Treatment of Infectious Diseases (zz202310), and Natural Science Foundation of Shandong Province (ZR2023ZD59).

Oral liposomal delivery of an activatable budesonide prodrug reduces colitis in experimental mice

Inflammatory bowel disease (IBD) is one of the most common intestinal disorders, with increasing global incidence and prevalence. Numerous therapeutic drugs are available but require intravenous administration and are associated with high toxicity and insufficient patient compliance. Here, an oral liposome that entraps the activatable corticosteroid anti-inflammatory budesonide was developed for efficacious and safe IBD therapy. The prodrug was produced via the ligation of budesonide with linoleic acid linked by a hydrolytic ester bond, which was further constrained into lipid constituents to form colloidal stable nanoliposomes (termed budsomes). Chemical modification with linoleic acid augmented the compatibility and miscibility of the resulting prodrug in lipid bilayers to provide protection from the harsh environment of the gastrointestinal tract, while liposomal nanoformulation enables preferential accumulation to inflamed vasculature. Hence, when delivered orally, budsomes exhibited high stability with low drug release in the stomach in the presence of ultra-acidic pH but released active budesonide after accumulation in inflamed intestinal tissues. Notably, oral administration of budsomes demonstrated favorable anti-colitis effect with only ∼7% mouse body weight loss, whereas at least ∼16% weight loss was observed in other treatment groups. Overall, budsomes exhibited higher therapeutic efficiency than free budesonide treatment and potently induced remission of acute colitis without any adverse side effects. These data suggest a new and reliable approach for improving the efficacy of budesonide. Our in vivo preclinical data demonstrate the safety and increased efficacy of the budsome platform for IBD treatment, further supporting clinical evaluation of this orally efficacious budesonide therapeutic.

Advance Progress in Assembly Mechanisms of Carrier-Free Nanodrugs for Cancer Treatment

Nanocarriers have been widely studied and applied in the field of cancer treatment. However, conventional nanocarriers still suffer from complicated preparation processes, low drug loading, and potential toxicity of carriers themselves. To tackle the hindrance, carrier-free nanodrugs with biological activity have received increasing attention in cancer therapy. Extensive efforts have been made to exploit new self-assembly methods and mechanisms to expand the scope of carrier-free nanodrugs with enhanced therapeutic performance. In this review, we summarize the advanced progress and applications of carrier-free nanodrugs based on different types of assembly mechanisms and strategies, which involved noncovalent interactions, a combination of covalent bonds and noncovalent interactions, and metal ions-coordinated self-assembly. These carrier-free nanodrugs are introduced in detail according to their assembly and antitumor applications. Finally, the prospects and existing challenges of carrier-free nanodrugs in future development and clinical application are discussed. We hope that this comprehensive review will provide new insights into the rational design of more effective carrier-free nanodrug systems and advancing clinical cancer and other diseases (e.g., bacterial infections) infection treatment.

Drug Self-Delivery Systems: Molecule Design, Construction Strategy, and Biological Application

Drug self-delivery systems (DSDSs) offer new ways to create novel drug delivery systems (DDSs). In typical DSDSs, therapeutic reagents are not considered passive cargos but active delivery agents of actionable targets. As an advanced drug delivery strategy, DSDSs with positive cooperativity of both free drugs and nanocarriers exhibit the clear merits of unprecedented drug-loading capacity, minimized systemic toxicity, and flexible preparation of nanoscale deliverables for passive targeted therapy. This review highlights the recent advances and future trends in DSDSs on the basis of two differently constructed structures: covalent and noncovalent bond-based DSDSs. Specifically, various chemical and architectural designs, fabrication strategies, and responsive and functional features are comprehensively discussed for these two types of DSDSs. In addition, additional comments on the current development status of DSDSs and the potential applications of their molecular designs are presented in the corresponding discussion. Finally, the promising potential of DSDSs in biological applications is revealed and the relationship between preliminary molecular design of DSDSs and therapeutic effects of subsequent DSDSs biological applications is clarified.

Tailoring carrier-free nanocombo of small-molecule prodrug for combinational cancer therapy

The outcomes of monotherapy could not satisfy clinical cancer treatment owing to the challenges of tumor heterogeneity, multi-drug resistance, tumor metastasis and relapse. In response, the significance of combinational cancer therapy has been highlighted. Traditional combinational schemes usually utilize "free" drug for multi drug administration, independently. The diverse pharmacokinetics and biodistribution greatly hinder the antitumor effects and cause systematic toxicity. To tackle the hinderance, various nanoparticulate drug delivery systems (Nano-DDSs) have been developed. However, conventional Nano-DDSs encapsulate drugs into carrier materials through noncovalent interactions, resulting in low drug loading, fixed multi drug encapsulation ratio, chemical instability and carrier-associated toxicity. Recently, carrier-free nanocombos based on self-assembling small-molecule prodrugs (SPNCs) have emerged as a versatile Nano-DDSs for multiple drug delivery. Benefited by the self-assembly capability, SPNCs could be facilely fabricated with distinct merits of ultra-high drug loading, adjustable drug ratio and negligible carrier-associated toxicity. Herein, we summarize the latest trends of SPNCs. First, a basic review on self-assembling small-molecule prodrugs is presented. Additionally, facile techniques to prepare SPNCs are introduced. Furthermore, advanced combinational therapies based on SPNCs are spotlighted with special emphasis on synergistic mechanisms. Finally, future prospects and challenges are discussed.

Antihypertension Nanoblockers Increase Intratumoral Perfusion of Sequential Cytotoxic Nanoparticles to Enhance Chemotherapy Efficacy against Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), one of the worst prognosis types of tumors, is characterized by dense extracellular matrix, which compresses tumor vessels and forms a physical barrier to inhibit therapeutic drug penetration and efficacy. Herein, losartan, an antihypertension agent, is applied as a tumor stroma modulator and developed into a nanosystem. A series of lipophilic losartan prodrugs are constructed by esterification of the hydroxyl group on losartan to fatty acids. Based on the self-assembly ability and hydrodynamic diameter, the losartan-linoleic acid conjugate is selected for further investigation. To improve the stability in vivo, nanoassemblies are refined with PEGylation to form losartan nanoblocker (Los NB), and administered via intravenous injection for experiments. On murine models of pancreatic cancer, Los NB shows a greater ability to remodel the tumor microenvironment than free losartan, including stromal depletion, vessel perfusion increase, and hypoxia relief. Furthermore, Los NB pretreatment remarkably enhances the accumulation and penetration of 7-ethyl-10-hydroxycamptothecin (SN38)-loaded nanodrugs (SN38 NPs) in tumor tissues. Expectedly, overall therapeutic efficacy of SN38 NPs is significantly enhanced after Los NB pretreatment. Since losartan is one of the most commonly used antihypertension agents, this study may provide a potential for clinical transformation in stroma-rich PDAC treatment.

Self-deliverable and self-immolative prodrug nanoassemblies as tumor targeted nanomedicine with triple cooperative anticancer actions

Stimulus-responsive self-assembling prodrug-based nanomedicine has emerged as a novel paradigm in controlled drug delivery. All-trans retinoic acid (RA), one of vitamin A metabolites, induces apoptotic cancer cell death, but its clinical applications are limited by weak anticancer efficacy. To fully maximize the therapeutic potential of RA, we exploited the unique chemistry of arylboronic acid which undergoes hydrogen peroxide (H2O2)-triggered degradation to release quinone methide (QM) that alkylates glutathione (GSH) to disrupt redox homeostasis and is also converted into hydroxybenzyl alcohol (HBA) to suppress the expression of vascular endothelial growth factor (VEGF). Here, we report that boronated retinoic acid prodrug (RABA) can be formulated into self-deliverable nanoassemblies which release both RA and QM in a H2O2-triggered self-immolative manner to exert cooperative anticancer activities. RABA nanoassemblies exert anticancer effects by inducing reactive oxygen species (ROS)-mediated apoptosis, eliciting immunogenic cell death (ICD) and suppressing angiogenic VEGF expression. The excellent anticancer efficacy of RABA nanoassemblies can be explained by benefits of self-assembling prodrug-based drug self-delivery and cooperative anticancer actions. The design strategy of RABA would provide a new insight into the rational design of self-deliverable and self-immolative boronated prodrug nanoassemblies for targeted cancer therapy.

Combinatorial nanococktails via self-assembling lipid prodrugs for synergistically overcoming drug resistance and effective cancer therapy

Background

Combinatorial systemic chemotherapy is a powerful treatment paradigm against cancer, but it is fraught with problems due to the emergence of chemoresistance and additive systemic toxicity. In addition, coadministration of individual drugs suffers from uncontrollable pharmacokinetics and biodistribution, resulting in suboptimal combination synergy.

Methods

Toward the goal of addressing these unmet medical issues, we describe a unique strategy to integrate multiple structurally disparate drugs into a self-assembling nanococktail platform. Conjugation of a polyunsaturated fatty acid (e.g., linoleic acid) with two chemotherapies generated prodrug entities that were miscible with tunable drug ratios for aqueous self-assembly. In vitro and in vivo assays were performed to investigate the mechanism of combinatorial nanococktails in mitigating chemoresistance and the efficacy of nanotherapy.

Results

The coassembled nanoparticle cocktails were feasibly fabricated and further refined with an amphiphilic matrix to form a systemically injectable and PEGylated nanomedicine with minimal excipients. The drug ratio incorporated into the nanococktails was optimized and carefully examined in lung cancer cells to maximize therapeutic synergy. Mechanistically, subjugated resistance by nanococktail therapy was achieved through the altered cellular uptake pathway and compromised DNA repair via the ATM/Chk2/p53 cascade. In mice harboring cisplatin-resistant lung tumor xenografts, administration of the nanococktail outperformed free drug combinations in terms of antitumor efficacy and drug tolerability.

Conclusion

Overall, our study provides a facile and cost-effective approach for the generation of cytotoxic nanoparticles to synergistically treat chemoresistant cancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-022-00249-7.

Engineering of small-molecule lipidic prodrugs as novel nanomedicines for enhanced drug delivery

A widely established prodrug strategy can effectively optimize the unappealing properties of therapeutic agents in cancer treatment. Among them, lipidic prodrugs extremely uplift the physicochemical properties, site-specificity, and antitumor activities of therapeutic agents while reducing systemic toxicity. Although great perspectives have been summarized in the progress of prodrug-based nanoplatforms, no attention has been paid to emphasizing the rational design of small-molecule lipidic prodrugs (SLPs). With the aim of outlining the prospect of the SLPs approach, the review will first provide an overview of conjugation strategies that are amenable to SLPs fabrication. Then, the rational design of SLPs in response to the physiological barriers of chemotherapeutic agents is highlighted. Finally, their biomedical applications are also emphasized with special functions, followed by a brief introduction of the promising opportunities and potential challenges of SLPs-based drug delivery systems (DDSs) in clinical application.

Graphical Abstract

Supramolecular grafting of stimuli-responsive, carrier-free, self-deliverable nanoparticles of camptothecin and antisense DNA for combination cancer therapy

A supramolecular approach for the crafting of self-deliverable nanoparticles of antisense DNA and camptothecin for combination cancer therapy is reported.

Prostate-Specific Membrane Antigen and Esterase Dual Responsive Camptothecin-Oligopeptide Self-Assembled Nanoparticles for Efficient Anticancer Drug Delivery

Background

The clinical utility of camptothecin (CPT) is restricted by poor aqueous solubility, high lipophilicity, active lactone ring instability, and off-targeted toxicities. We report here a prostate-specific membrane antigen (PSMA) and esterase dual responsive self-assembled nanoparticles (CPT-WT-H NPs) for highly efficient CPT delivery and effective cancer therapy.

Methods and Results

In this study, smart self-assembled nanoparticles CPT-WT-H NPs were elaborately designed and synthesized by combing hydrophobic CPT with hydrophilic PSMA-responsive penta-peptide via a cleavable ester bond. This dual responsive nanoparticle with negatively charged surface first respond to the extracellular PSMA and then to the intracellular esterase, achieving a programmable release of CPT at the tumor site and producing the byproducts of biocompatible glutamic acid and aspartic acid. Our data demonstrated that CPT-WT-H NPs exhibited greatly improved water solubility and stability. Results from MTT and flow cytometry showed CPT-WT-H NPs exhibited significantly higher cytotoxicity as well as apoptosis-inducing activity against PSMA-expressing LNCaP-FGC cells than the non-PSMA-expressing cancer cells, showing excellent cytotoxic selectivity. Moreover, the unique nanostructure provided the efficient transportation of CPT to tumor site, which resulted in the effective inhibition of tumor growth and low systemic toxicity in vivo.

Conclusion

CPT-WT-H NPs exhibited excellent in vitro PSMA-response ability and in vivo antitumor activity and safety, holding the promise to become a new and potent anticancer drug. The current research presents a promising strategy for efficient drug delivery.

Nanoplatforms for Sepsis Management: Rapid Detection/Warning, Pathogen Elimination and Restoring Immune Homeostasis

Sepsis, a highly life-threatening organ dysfunction caused by uncontrollable immune responses to infection, is a leading contributor to mortality in intensive care units. Sepsis-related deaths have been reported to account for 19.7% of all global deaths. However, no effective and specific therapeutic for clinical sepsis management is available due to the complex pathogenesis. Concurrently eliminating infections and restoring immune homeostasis are regarded as the core strategies to manage sepsis. Sophisticated nanoplatforms guided by supramolecular and medicinal chemistry, targeting infection and/or imbalanced immune responses, have emerged as potent tools to combat sepsis by supporting more accurate diagnosis and precision treatment. Nanoplatforms can overcome the barriers faced by clinical strategies, including delayed diagnosis, drug resistance and incapacity to manage immune disorders. Here, we present a comprehensive review highlighting the pathogenetic characteristics of sepsis and future therapeutic concepts, summarizing the progress of these well-designed nanoplatforms in sepsis management and discussing the ongoing challenges and perspectives regarding future potential therapies. Based on these state-of-the-art studies, this review will advance multidisciplinary collaboration and drive clinical translation to remedy sepsis.

Targeting peripheral immune organs with self-assembling prodrug nanoparticles ameliorates allogeneic heart transplant rejection

Organ transplantation has become a mainstay of therapy for patients with end-stage organ diseases. However, long-term administration of immunosuppressive agents, a scheme for improving the survival of transplant recipients, has been compromised by severe side effects and posttransplant complications. Therapeutic delivery targeting immune organs has the potential to address these unmet medical issues. Here, through screening of a small panel of mammalian target of rapamycin complex kinase inhibitor (TORKinib) compounds, a TORKinib PP242 is identified to be able to inhibit T cell function. Further chemical derivatization of PP242 using polyunsaturated fatty acids (i.e., docosahexaenoic acid) transforms this water-insoluble hydrophobic agent into a self-assembling nanoparticle (DHA-PP242 nanoparticle [DPNP]). Surface PEGylation of DPNP with amphiphilic copolymers renders the nanoparticles aqueously soluble for preclinical studies. Systemically administered DPNP shows tropism for macrophages within peripheral immune organs. Furthermore, DPNP regulates differentiation of adoptively transferred T cells in a macrophage-dependent manner in Rag1-/- mouse model. In an experimental model of heart transplantation, DPNP significantly extends the survival of grafts through inducing immune suppression, thus reducing the inflammatory response of the recipients. These findings suggest that targeted delivery of TORKinibs exploiting prodrug-assembled nanoparticle scaffolds may provide a therapeutic option against organ rejection.

Small-Molecule Prodrug Nanoassemblies: An Emerging Nanoplatform for Anticancer Drug Delivery

The antitumor efficiency and clinical translation of traditional nanomedicines is mainly restricted by low drug loading, complex preparation technology, and potential toxicity caused by the overused carrier materials. In recent decades, small-molecule prodrug nanoassemblies (SMP-NAs), which are formed by the self-assembly of prodrugs themselves, have been widely investigated with distinct advantages of ultrahigh drug-loading and negligible excipients-trigged adverse reaction. Benefited from the simple preparation process, SMP-NAs are widely used for chemotherapy, phototherapy, immunotherapy, and tumor diagnosis. In addition, combination therapy based on the accurate co-delivery behavior of SMP-NAs can effectively address the challenges of tumor heterogeneity and multidrug resistance. Recent trends in SMP-NAs are outlined, and the corresponding self-assembly mechanisms are discussed in detail. Besides, the smart stimuli-responsive SMP-NAs and the combination therapy based on SMP-NAs are summarized, with special emphasis on the structure-function relationships. Finally, the outlooks and potential challenges of SMP-NAs in cancer therapy are highlighted.

Antitumor Activity of α-Linolenic Acid-Paclitaxel Conjugate Nanoparticles: In vitro and in vivo

Purpose

Small molecule modified antitumor drug conjugate nanoparticles have the advantages of high drug loading, simple synthesis and preparation, and better biocompatibility. Due to the large demand for exogenous α-linolenic acid (ALA) by tumor cells, we synthesized α-linolenic acid-paclitaxel conjugate (ALA-PTX) and prepared α-linolenic acid-paclitaxel conjugate nanoparticles (ALA-PTX NPs), in order to obtain better tumor cellular uptake and antitumor activity in vitro and in vivo.

Methods

We synthesized and characterized ALA-PTX, and then prepared and characterized ALA-PTX NPs. The cellular uptake, uptake pathways, intracellular behavior, in vitro and in vivo antitumor activity of ALA-PTX NPs were evaluated.

Results

The size of ALA-PTX NPs was approximately 110.7±1.7 nm. The drug loading was approximately 90% (w/w) with CrEL-free and organic solvent-free characteristics. The cellular uptake of ALA-PTX NPs was significantly higher than that of PTX injection by MCF-7, MCF-7/ADR and HepG2 cells. In these three cell lines, the cellular uptake of ALA-PTX NPs at 6h was approximately 1.5-2.6 times higher than that of PTX injection. ALA-PTX NPs were ingested through clathrin-mediated endocytosis, then transferred to lysosomes, and could dissolve in cells to play an antitumor activity. The in vitro and in vivo antitumor activity of ALA-PTX NPs was confirmed in MCF-7/ADR and HepG2 cell models and tumor-bearing nude mouse models.

Conclusion

ALA-PTX NPs developed in our study could provide a new method for the preparation of nano-delivery systems suitable for antitumor therapy that could increase tumor cellular uptake and enhance antitumor activity.

Self-Assembly Dual-Responsive NO Donor Nanoparticles for Effective Cancer Therapy

Drug resistance and the serious side effects caused by classical chemotherapy drugs necessitate the development of novel targeted drug delivery systems. The high lipophilicity and short half-life of nitric oxide (NO), a gas with strong antitumor activity, make it difficult to reach the tumor site and result in a poor therapeutic effect in vivo. In order to overcome the deficiencies of the existing NO donors and NO delivery vehicles, a novel strategy was proposed to deliver NO for cancer chemotherapy by the prodrug dimer self-assembly nanoparticles of NO donors. Specifically, phenylsulfonylfuroxan (FZ) was chosen as the NO donor to synthesize the prodrug dimer precursor (FZ-SS-FZ) by disulfide linkages and ester bonds. The insertion of disulfide linkages promotes the self-assembly of FZ-SS-FZ in water. After this, the dual-responsive and tumor-targeting NO delivery system (FZ-SS-FZ@FA NPs) will finally be fabricated by further introducing folic acid on the surface of nanoparticles. FZ-SS-FZ can self-assemble to form uniform nanoparticles in water, which can effectively deliver NO to the tumor site and be uptaken by tumor cells, thus resulting in specific NO release in tumor cells and inducing tumor cell apoptosis. FZ-SS-FZ@FA NPs significantly improve the drug loading and delivery efficiencies of NO for chemotherapy, while enhancing its efficacy, providing a novel strategy for the tumor-targeted delivery of NO and at the same time laying a theoretical basis for the clinical translation of NO-based gas chemotherapy, opening up a new approach for cancer chemotherapy.

Amphiphilic small molecular mates match hydrophobic drugs to form nanoassemblies based on drug-mate strategy

Nanomedicine has made great progress in the targeted therapy of cancer. Here, we established a novel drug-mate strategy by studying the formulation of nanodrugs at the molecular level. In the drug-mate combination, the drug is a hydrophobic drug that is poorly soluble in water, and the mate is an amphiphilic small molecule (SMA) that has both hydrophilic and lipophilic properties. We proposed that the hydrophobic drug could co-assemble with a suitable SMA on a nanoscale without additive agents. The proof-of-concept methodology and results were presented to support our hypothesis. We selected five hydrophobic drugs and more than ten amphiphilic small molecules to construct a library. Through molecular dynamic simulation and quantum chemistry computation, we speculated that the formation of nanoassemblies was related to the binding energy of the drug-mate, and the drug-mate interaction must overcome drug-drug interaction. Furthermore, the obtained SF/VECOONa nanoassemblieswas selected as a model, which had an ultra-high drug loading content (46%), improved pharmacokinetics, increased bioavailability, and enhanced therapeutic efficacy. In summary, the drug-mate strategy is an essential resource to design exact SMA for many hydrophobic drugs and provides a reference for the design of a carrier-free drug delivery system.

Microfluidic assembly of small-molecule prodrug cocktail nanoparticles with high reproducibility for synergistic combination of cancer therapy

Therapeutic nanoparticles (NPs) self-assembled from small molecular (pro)drug entities, opens up novel avenues for the generation of a wide range of drug delivery systems. Particularly, cocktail NPs created by co-assembly of multiple therapeutics often show profound efficacy beyond their individual agents. However, fabrication of synergistic NPs with high reproducibility and capability to deliver multiple therapeutics in a predefined ratio remains a challenge, which deters NP therapeutics from further clinical translation. In this work, a simple but versatile strategy has been developed to combine drug reconstitution and supramolecular nanoassembly to prodrug cocktail nanoparticle fabrication with microfluidics. Prodrugs reconstructed by PUFAylation were self-assembled into hybrid nanoparticles via microfluidic chip to synergistically deliver two chemotherapeutic drugs, 7-ethyl-10-hydroxy camptothecin (SN38) and paclitaxel (PTX), in a single nanoparticle container. In vitro cell-based assays demonstrate that the combinatorial chemotherapy is superior to each prodrug used alone while reduces the dosage of both drugs at the same time. Furthermore, the double-drug combination suppresses colon tumors by 86% at a total dosage of 16.7 mg/kg through synergy, and histological analysis indicates the safety of the hybrid nanoparticles. In general, this work shows that the nanomedicine synthesized by microfluidics provides considerable advantages including better size control and reproducibility, and great potential in effective combination therapy. It is expected to be applied to the fabrication of more chemical agent combination for other cancer types.

Lipophilic Conjugates of Drugs: A Tool to Improve Drug Pharmacokinetic and Therapeutic Profiles

Lipophilic conjugates (LCs) of small molecule drugs have been used widely in clinical and pre-clinical studies to achieve a number of pharmacokinetic and therapeutic benefits. For example, lipophilic derivatives of drugs are employed in several long acting injectable products to provide sustained drug exposure for hormone replacement therapy and to treat conditions such as neuropsychiatric diseases. LCs can also be used to modulate drug metabolism, and to enhance drug permeation across membranes, either by increasing lipophilicity to enhance passive diffusion or by increasing protein-mediated active transport. Furthermore, such conjugation strategies have been employed to promote drug association with endogenous macromolecular carriers (e.g. albumin and lipoproteins), and this in turn results in altered drug distribution and pharmacokinetic profiles, where the changes can be 'general' (e.g. prolonged plasma half-life) or 'specific' (e.g. enhanced delivery to specific tissues in parallel with the macromolecular carriers). Another utility of LCs is to enhance the encapsulation of drugs within engineered nanoscale drug delivery systems, in order to best take advantage of the targeting and pharmacokinetic benefits of nanomedicines. The current review provides a summary of the mechanisms by which lipophilic conjugates, including in combination with delivery vehicles, can be used to control drug delivery, distribution and therapeutic profiles. The article is structured into sections which highlight a specific benefit of LCs and then demonstrate this benefit with case studies. The review attempts to provide a toolbox to assist researchers to design and optimise drug candidates, including consideration of drug-formulation compatibility.

Nanodelivery of a self-assembling prodrug with exceptionally high drug loading potentiates chemotherapy efficacy

Nanomedicines have achieved several successful clinical applications for cancer therapy over the past decades. To date, numerous nanomedicine formats and design rationales have been proposed to improve pharmaceutical delivery and treatment efficacy. Despite these advances, the achievement of high drug loading and loading efficiencies of drug payloads in nanocarriers remains a technical challenge. In addition, study of the correlation between therapeutic potential and drug loading has been ignored. Here, using a self-assembling dimeric cabazitaxel prodrug, we show that the prodrug can be quantitatively entrapped within clinically approved polymer matrices for intravenous injection and that the drug loading in the nanoparticles (NPs) is tunable. The engineered NPs (NPs1-4) with different drug loading values exhibit dissimilar morphologies, release kinetics, in vitro cytotoxic activity, pharmacokinetic properties, tissue distribution, and in vivo anticancer efficacy and safety profiles. Furthermore, the effect of drug loading on the treatment outcomes was explored through detailed in vitro and in vivo studies. Intriguingly, among the constructed NPs, those comprising poly(ethylene glycol)-block-poly(D,L-lactic acid) (PEG-PLA) copolymers showed substantially prolonged pharmacokinetic properties in the blood circulation, which further promoted their intratumoral delivery and accumulation. Furthermore, the PEG-PLA-composed NPs with high drug loading (~50%) demonstrated favorable efficacy and safety profile in animal models. These data provide convincing evidence that the in vivo performance of a given self-assembling drug is not compromised by high drug loading in nanoplatforms, which may potentially reduce concerns over excipient-associated side effects and immunotoxicities. Overall, our study provides new insight into the rationale for designing more effective and less toxic delivery systems.

Effect of XlogP and hansen solubility parameters on the prediction of small molecule modified docetaxel, doxorubicin and irinotecan conjugates forming stable nanoparticles

Small molecule-chemotherapeutic drug conjugate nanoparticles (SMCDC NPs) has a great advantage in improving drug loading. However, the factors which influence these conjugates forming stable nanoparticles (NPs) are currently unclear. In our previous studies, we synthesized a series of fatty acid-paclitaxel conjugates and suggested that the changes in the hydrophobic parameters (XlogP), solubility parameters and crystallinity of these fatty acid-paclitaxel conjugates were the key factors for affecting these small molecule-chemotherapeutic drug conjugates (SMCDCs) forming stable NPs in water. Here, we selected clinically widely used chemotherapeutic drug (docetaxel (DTX), doxorubicin (DOX) and irinotecan (Ir)) as model drug, and chose three straight-chain fatty acids (acetic acid (Ac), hexanoic acid (HA) and stearic acid (SA)) and one branched small molecule (N-(tert-butoxycarbonyl) glycine (B-G)) to synthesize 12 SMCDCs. Our results indicated that our prediction criterions obtained from paclitaxel conjugates were also appropriated for these synthesized SMCDCs. We suggested that the present studies expanded the scope of application of the above-mentioned influencing factors, provided research ideas for the rational design of SMCDC forming NPs and a basis for screening NPs with good anticancer activity.

Bioinspired Microenvironment Responsive Nanoprodrug as an Efficient Hydrophobic Drug Self-Delivery System for Cancer Therapy

Artemisinin compounds have shown satisfactory safety records in anti-malarial clinical practice over decades and have revealed value as inexpensive anti-tumor adjuvant chemotherapeutic drugs. However, the rational design and precise preparation of nanomedicines based on the artemisinin drugs are still limited due to their non-aromatic and fragile chemical structure. Herein, a bioinspired coordination-driven self-assembly strategy was developed to manufacture the artemisinin-based nanoprodrug with a significantly increased drug loading efficacy (∼70 wt %) and decreased preparation complexity compared to conventional nanodrugs. The nanoprodrug has suitable size distribution and robust colloidal stability for cancer targeting in vivo. The nanoprodrug was able to quickly disassemble in the tumor microenvironment with weak acidity and a high glutathione concentration, which guarantees a better tumor inhibitory effect than direct administration and fewer side effects on normal tissues in vivo. This work highlights a new strategy to harness a robust, simplified, organic solvent-free, and highly repeatable route for nanoprodrug manufacturing, which may offer opportunities to develop cost-effective, safe, and clinically available nanomedicines.

Self-stabilized Pt(IV) amphiphiles by precise regulation of branch length for enhanced chemotherapy

A surge of platinum(IV) compounds are utilized or investigated in cancer treatment but their therapeutic outcomes have been greatly compromised by remaining adverse effects and limited antitumor performance, attributable to nonspecific distribution and insufficient activation in tumor site. Herein, we designed a series of disulfide bond introduced Pt(IV)-lipid prodrugs with different branch length, all of which are able to self-stabilize into nanomedicine and be activated by high intracellular glutathione (GSH) level. The impact of precise modification of these prodrugs on their assembly stability, pharmacokinetics and cytotoxicity was probed to establish a connection between chemical structure and antiproliferation efficiency. With optimal assembly manner and delivery efficacy, the longest axial branched Pt(IV) prodrug CSS18 exhibited the most impressive therapeutic outcome, providing a potential path to more efficient nanocarriers for chemotherapeutic agents by chemical modulation and, giving insights into the rational design of reduction responsive platinum delivery system.

Mercury-containing supramolecular micelles with highly sensitive pH-responsiveness for selective cancer therapy

Construction and manipulation of metal-based supramolecular polymers-which are based on a combination of nucleobase hydrogen bonding interactions and functional metal ions-to obtain the desired physicochemical properties and achieve the efficacy and safety required for biomedical applications remain extremely challenging. We successfully designed and synthesized a new mercury-based supramolecular polymer, Hg-BU-PPG, containing an oligomeric polypropylene glycol backbone and pH-sensitive uracil-mercury-uracil (U-Hg-U) linkages. This multifunctional metallo-supramolecular material spontaneously self-organizes into nanosized spherical micelles in aqueous solution. The micelles possess several attractive properties, including desired long-term structural stability in serum-rich conditions, unique fluorescence behavior and highly sensitive, well-controlled pH-responsiveness. Interestingly, Hg-BU-PPG micelles exhibited strong, selective cytotoxic effects towards cancer cells in vitro, without harming normal cells. The highly selective cytotoxicity can be attributed to rapid dissociation of the U-Hg-U complexes within the micelles in the mildly acidic intracellular pH of cancer cells, followed by release of inherently toxic mercury ions. Importantly, fluorescence microscopy and flow cytometry clearly demonstrated that Hg-BU-PPG selectively entered the cancer cells via endocytosis and rapidly promoted massive apoptotic cell death. In contrast, internalization of Hg-BU-PPG by normal cells was limited, resulting in high biocompatibility and no cytotoxic effects. Thus, this newly discovered 'cytotoxicity-concealing' supramolecular system could represent a viable route to enhance the safety and efficacy of cancer therapy and bioimaging via a strategy that does not require incorporation of anticancer drugs and fluorescent probes. STATEMENT OF SIGNIFICANCE: We report a significant breakthrough in the construction of mercury-containing supramolecular polymers, namely the creation of multifunctional micelles with unique chemical and physical properties conferred by pH-sensitive uracil-mercury-uracil (U-Hg-U) linkages and tunable structural and dynamical features due to the presence of hydrogen-bonded uracil moieties. Importantly, in vitro experiments clearly demonstrated that introduction of the U-Hg-U complexes into the micelles not only improved the efficiency of selective uptake via endocytosis into cancer cells, but also accelerated the induction of massive apoptotic cell death. Thus, this work provides crucial new insight for the development of metallo-supramolecular polymeric micelles that may substantially enhance the safety and efficacy of cancer therapy and bioimaging without requiring incorporation of anticancer drugs or fluorescent probes.

Interface-sensitized prodrug nanoaggregate as an effective in situ antitumor vaccine

In situ antitumor vaccines have been widely explored as an effective strategy to inhibit tumor growth by stimulating antitumor immune responses. Herein, we reported a simple and effective in situ antitumor vaccine, which was prepared by co-assembling cationic lipids (DOTAP) with the disulfide bond-linked lipid-drug conjugates of camptothecin and resiquimod. The resulting vaccine had a rod-sharped morphology with nanoscale sizes (average hydrodynamic diameter of ∼163.7 nm) and positively-charged interfaces (zeta potential ∼ +36.2 mV). The interfacial cationization of nanoaggregate resulted in 1000 folds faster redox-responsive drug release than that of unmodified ones, which induced a much more potent in vivo antitumor immune by accelerating the glutathione-responsive drug release at the tumor site. Such cationic lipid-drug nanoaggregates displayed many benefits, such as high co-loading capacity, simple preparation process, and wide applicability, which would serve as a promising new approach to design effective in situ antitumor vaccines.

Drug Release from Disulfide-Linked Prodrugs: Role of Thiol Agents

The disulfide bond (SS) has been widely used in prodrugs for the redox-responsive drug release, but its drug release mechanism and rate were seldom compared in different thiol agents. Herein, self-assembling nanoaggregates (NAs) formed by camptothecin (CPT)-oleic acid (OA) prodrugs linked by two frequently used SS linkers (ETCSS and ACSS) were used for such comparative investigation. It is found that the cleavage of ETCSS was directly coupled with CPT release, whereas the breakage of ACSS resulted in the generation of CPT intermediates, the chemical stability of which determined CPT release. In both cases, the redox-responsive drug release was highly dependent on the reactivity between SS and thiol agents, with an order of dithiothreitol > cysteine ≈ glutathione. Moreover, the presence of SS significantly accelerated the extracellular CPT release, which was around 3-4 fold higher than intracellular CPT release. Therefore, the in vitro cytotoxicity of SS-linked CPT-OA NAs could not be ascribed to the glutathione-trigged intracellular drug release but rather to the SS-accelerated extracellular CPT release. The above results would effectively guide the rational design and evaluation of SS-linked prodrug NAs for efficient drug delivery.

Recent trends in bioresponsive linker technologies of Prodrug-Based Self-Assembling nanomaterials

Prodrugs are designed to improve pharmaceutical properties of potent compounds and represent a central approach in drug development. The success of the prodrug strategy relies on incorporation of a reversible linkage facilitating controlled release of the parent drug. While prodrug approaches enhance pharmacokinetic properties over their parent drug, they still face challenges in absorption, distribution, metabolism, elimination, and toxicity (ADMET). Conjugating a drug to a carrier molecule such as a polymer can create an amphiphile that self-assembles into nanoparticles. These nanoparticles display prolonged blood circulation and passive targeting ability. Furthermore, the drug release can be tailored using a variety of linkers between the parent drug and the carrier molecule. In this review, we introduce the concept of self-assembling prodrugs and summarize different approaches for controlling the drug release with a focus on the linker technology. We also summarize recent clinical trials, discuss the emerging challenges, and provide our perspective on the utility and future potential of this technology.

Novel multi-stimuli responsive functionalized PEG-based co-delivery nanovehicles toward sustainable treatments of multidrug resistant tumor

The efficacy of ongoing anticancer treatment is often compromised by some barriers, such as low drug content, nonspecific release of drug delivery system, and multidrug resistance (MDR) effect of tumors. Herein, in the research a novel functionalized PEG-based polymer cystine-(polyethylene glycol)2-b-(poly(2-methacryloyloxyethyl ferrocenecarboxylate)2) (Cys-(PEG45)2-b-(PMAOEFC)2) with multi-stimuli sensitive mechanism was constructed, in which doxorubicin (DOX) was chemical bonded through Schiff base structure to provide acid labile DOX prodrug (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2. Afterwards, paclitaxel (PTX) and its diselenide bond linked PTX dimer were encapsulated into the prodrug through physical loading, to achieve pH and triple redox responsive (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2@PTX and (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2@PTX dimer with ultrahigh drugs content. The obtained nanovehicles could self-assemble into globular micelles with good stability based on fluorescence spectra and TEM observation. Moreover, there was a remarkable "reassembly-disassembly" behavior caused by phase transition of micelles under the mimic cancerous physiological environment. DOX and PTX could be on-demand released in acid and redox stress mode, respectively. Meanwhile, in vivo anticancer studies revealed the significant tumor inhibition of nanoformulas. This work offered facile strategies to fabricate drug nanaovehicles with tunable drug content and types, it has a profound significance in overcoming MDR effect, which provided more options for sustainable cancer treatment according to the desired drug dosage and the stage of tumor growth.

Repurposing of camptothecin: An esterase-activatable prodrug delivered by a self-emulsifying formulation that improves efficacy in colorectal cancer

The global burden of colorectal cancer (CRC), the third most commonly diagnosed malignancy, continues to rise. Therefore, more effective and less toxic therapies are needed for CRC. CPT-11 (also called irinotecan), the standard-of-care treatment for CRC, has only had limited effects on survival outcomes. In vivo, CPT-11 must be converted to an active metabolite, SN38, to exert antitumor activity in the presence of carboxylesterases, but the conversion rate is extremely low (usually less than 8%). To fully harness the active SN38 compound, we showed here that esterification of SN38 using α-linolenic acid (LNA) generated a prodrug (termed LSN38), which can be formulated in pharmaceutically acceptable surfactants, such as polysorbate 80. Upon blending with an aqueous ethanolic solution, the mixture of LSN38/polysorbate 80 formed self-emulsifying nanomicelles (termed LSN38 NMs), enabling systemic injection. Unlike the insufficient release of active SN38 from CPT-11, drug activation from the LSN38 prodrug was quantitative and relied on esterase, which is abundant in cancerous cells. Pharmacokinetics studies revealed that polysorbate 80-based nanomicelles stably constrained the prodrug in the reservoir and prolonged blood circulation compared to CPT-11. Furthermore, LSN38 NMs showed superior therapeutic efficacy against a colorectal xenograft-bearing mouse model that failed to be treated with clinically approved CPT-11. Overall, these studies highlight the feasibility of converting a chemotherapeutic agent that is not miscible or compatible with pharmaceutical surfactants into an injectable self-emulsifying formulation. This approach could be applied to rescue other drugs or drug candidates that are abandoned in the preclinical stages due to pharmaceutical challenges.

Kinetically-stable small-molecule prodrug nanoassemblies for cancer chemotherapy

Self-delivering nanocarrier based on the small-molecule prodrug nanoassemblies (NAs) have been widely used for the efficient delivery of chemotherapeutics, but the effect of kinetic stability of NAs on their delivery performance has not been illuminated. In this study, two camptothecin (CPT)-oleic acid (OA) prodrugs were used to fabricate self-assembling nanorods with similar size distribution, zeta potential and morphology but having sharply different kinetic stability, which provided an ideal platform to investigate the effects of kinetic stability. It is found that the nanorods with high kinetic stability showed a lower in vitro cytotoxicity, but were more effective to inhibit the tumor growth probably by decreasing the premature CPT release and subsequent generation of the inactive carboxylate CPT. However, such kinetically stable nanorods also resulted in the increased toxicity, probably due to the high prodrug accumulation in tissues after multiple injections. These results outlined the pivotal role of kinetic stability in determining antitumor efficacy of prodrug NAs, which provided a new insight into the delivery mechanism for the small-molecule prodrug self-delivering nanosystems.

Self-assembling a natural small molecular inhibitor that shows aggregation-induced emission and potentiates antitumor efficacy

Targeted therapy using small molecular inhibitors has been developed to rewire key signaling pathways in tumor cells, but these inhibitors have had mixed success in the clinic due to their poor pharmaceutical properties and suboptimal intratumoral concentrations. Here, we developed a "self-assembling natural molecular inhibitor" strategy to test the efficacy and feasibility of the water-insoluble agent dasatinib (DAS), a tyrosine kinase inhibitor, for cancer therapy. By exploiting a facile reprecipitation protocol, the DAS inhibitor self-assembled into soluble supramolecular nanoparticles (termed sDNPs) in aqueous solution, without an exogenous excipient. This strategy is applicable for generating systemically injectable and colloid-stable therapeutic nanoparticles of hydrophobic small-molecule inhibitors. Concurrently, during this process, we observed aggregation-induced emission (AIE) of fluorescence for this self-assembled DAS, which makes sDNPs suitable for bioimaging and tracing of cellular trafficking. Notably, in an orthotopic model of breast cancer, administration of sDNPs induced a durable inhibition of primary tumors and reduced the metastatic tumor burden, significantly surpassing the effects of the free DAS inhibitor after oral delivery. In addition, low toxicity was observed for this platform, with effective avoidance of immunotoxicity. To the best of our knowledge, our studies provide the first successful demonstration of self-assembling natural molecular inhibitors with AIE and highlight the feasibility of this approach for the preparation of therapeutic nanoparticles for highly lethal human cancers and many other diseases.

Emerging insights on drug delivery by fatty acid mediated synthesis of lipophilic prodrugs as novel nanomedicines

Many drug molecules that are currently in the market suffer from short half-life, poor absorption, low specificity, rapid degradation, and resistance development. The design and development of lipophilic prodrugs can provide numerous benefits to overcome these challenges. Fatty acids (FAs), which are lipophilic biomolecules constituted of essential components of the living cells, carry out many necessary functions required for the development of efficient prodrugs. Chemical conjugation of FAs to drug molecules may change their pharmacodynamics/pharmacokinetics in vivo and even their toxicity profile. Well-designed FA-based prodrugs can also present other benefits, such as improved oral bioavailability, promoted tumor targeting efficiency, controlled drug release, and enhanced cellular penetration, leading to improved therapeutic efficacy. In this review, we discuss diverse drug molecules conjugated to various unsaturated FAs. Furthermore, various drug-FA conjugates loaded into various nanostructure delivery systems, including liposomes, solid lipid nanoparticles, emulsions, nano-assemblies, micelles, and polymeric nanoparticles, are reviewed. The present review aims to inspire readers to explore new avenues in prodrug design based on the various FAs with or without nanostructured delivery systems.

Salinomycin-Loaded Small-Molecule Nanoprodrugs Enhance Anticancer Activity in Hepatocellular Carcinoma

Background

There is currently no effective treatment for advanced hepatocellular carcinoma (HCC), and chemotherapy has little effect on long-term survival of HCC patients, largely due to the cancer stem cell (CSC) chemoresistance of HCC.

Methods

We constructed a small-molecule nanometer-sized prodrug (nanoprodrug) loaded with salinomycin (SAL) for the treatment of HCC. SAL was encapsulated by the prodrug LA-SN38 (linoleic acid modified 7-ethyl-10-hydroxycamptothecin) to construct a self-assembled nanoprodrug further PEGylated with DSPE-PEG₂₀₀₀. We characterized this codelivered nanoprodrug and its antitumor activity both in vitro in human HCC cell lines and in vivo in mice.

Results

Delivery of the SAL- and LA-SN38-based nanoprodrugs effectively promoted apoptosis of HCC cells, exerted inhibition of HCC tumor-sphere formation as well as HCC cell motility and invasion, and reduced the proportion of CD133+ HCC-CSC cells. In nude mice, the nanoprodrug suppressed growth of tumor xenografts derived from human cell lines and patient.

Conclusion

Our results show that SAL-based nanoprodrugs are a promising platform for treating patients with HCC and a novel strategy for combination therapy of cancers.

Dimerization-induced self-assembly of a redox-responsive prodrug into nanoparticles for improved therapeutic index

Although some formats of nanomedicines are now available for clinical use, the translation of new nanoparticles to the clinic remains a considerable challenge. Here, we describe a simple yet cost-effective strategy that converts a toxic drug, cabazitaxel, into a safe and effective nanomedicine. The strategy involves the ligation of drug molecules via a self-immolating spacer, followed by dimerization-induced self-assembly to assemble stable nanoparticles. Self-assembled cabazitaxel dimers could be further refined by PEGylation with amphiphilic polymers suitable for preclinical studies. This protocol enables the formation of systemically injectable nanoparticles (termed SNPs) with nearly quantitative entrapment efficiencies and exceptionally high drug loading (> 86%). In healthy mice, PEGylated SNPs show a favorable safety profile, with reduced systemic toxicity and negligible immunotoxicity. In two separate mouse xenograft models of cancer, administration of SNPs produces efficient antitumor activity with durable tumor suppression during therapeutic studies. Overall, this methodology opens up a practical and expedient route for the fabrication of clinically useful nanomedicines, transforming a hydrophobic and highly toxic drug into a systemic self-deliverable nanotherapy. STATEMENT OF SIGNIFICANCE: Despite the great progress in cancer nanomedicines, clinical translation of nanomedicines still remains a considerable challenge. In this study, we designed a self-assembling nanoplatform based on cabazitaxel dimer reversibly ligated via a bioactivatable linker. This approach enabled the generation of systemically injectable nanomedicines with quantitative entrapment efficiencies and exceptionally high drug loading (> 86%), which greatly obviates concerns about excipient-associated side effects. Self-assembled dimeric cabazitaxel exhibited a higher safety profile than free cabazitaxel and negligible immunotoxicity in animals. This is a practical and expedient example how the chemical ligation of a hydrophobic and highly toxic anticancer drug can be leveraged to create a self-assembling delivery nanotherapy which preserves inherent pharmacologic efficacy while reduces in vivo systemic and immune toxicity.

Photosensitizer-stabilized self-assembling nanoparticles potentiate chemo/photodynamic efficacy of patient-derived melanoma

Development of injectable nanoparticles for delivery of active anticancer compounds often requires complicated schemes that involve tedious synthetic protocols and nanoformulations. In particular, clinical translation of synergistic nanoparticles that can facilitate multimodal therapies remains a considerable challenge. Herein, we describe a self-assembling, small-molecule nanosystem with unique properties, including near-infrared (NIR) light-responsive drug activation, size transformability, combinatorial synergy, and substantially reduced toxicity. Ligation of anticancer cabazitaxel (CTX) drugs via a reactive oxygen species-activatable thioketal linkage generates a dimeric TKdC prodrug, and subsequent coassembly with a photosensitizer, chlorin e6 (Ce6), forms colloidal-stable nanoassemblies (termed psTKdC NAs). Upon NIR laser irradiation, psTKdC NAs are transformed into smaller size particles and facilitate production of pharmacologically active CTX. Importantly, reactive oxygen species yielded by coassembled Ce6 can synergize with chemotherapy to achieve potent combinatorial effects. In a preclinical orthotopic model of an aggressive, human melanoma patient-derived xenograft (PDX), we show that administration of psTKdC NAs followed by laser irradiation produced durable tumor regression, with the tumors being completely eradicated in three of six PDXs. Furthermore, low systemic toxicity of this smart, photo-activatable nanotherapy was observed in animals. The new self-deliverable combinatorial system addresses essential requirements for high efficacy, safety, and translational capacity and deserves further investigation.

Kinetic stability-driven cytotoxicity of small-molecule prodrug nanoassemblies

Nanoassemblies (NAs) of small-molecule lipophilic prodrugs have been widely investigated for efficient drug delivery in cancer therapy, but their kinetic stability has not attracted sufficient attention in the past studies. Herein, we reported that kinetic stability has a great influence on the drug release from the NAs of lipophilic prodrugs in physiologically relevant media. Based on the co-assembled FRET nanosystems of two lipophilic fluorescent prodrugs, we demonstrated that NAs constructed by lipophilic prodrugs containing shorter alkyl chains or those with higher unsaturated degrees displayed poorer kinetic stability, which further resulted in remarkably faster drug release in mouse plasma and various tissue homogenates. More importantly, these kinetically unstable NAs also induced rapid intracellular drug release, resulting in much more potent cytotoxicity. These findings highlight the crucial role of kinetic stability in determining the drug release from the NAs of lipophilic prodrugs, which would effectively guide their rational designs for cancer therapy.

Transforming a toxic drug into an efficacious nanomedicine using a lipoprodrug strategy for the treatment of patient-derived melanoma xenografts

Despite the progress made with the recent clinical use of the anticancer compound cabazitaxel, the efficacy in patients remains unsatisfactory, largely due to the high in vivo toxicity of the agent. Therefore, strategies that achieve favorable outcomes and good safety profiles will greatly expand the repertoire of this potent agent. Here, we propose a combinatorial strategy to reform the cabazitaxel agent and the use of sequential supramolecular nanoassembly with liposomal compositions to assemble a prodrug-formulated liposome, termed lipoprodrug, for safe and effective drug delivery. Reconstructing cabazitaxel with a polyunsaturated fatty acid (i.e., docosahexaenoic acid) via a hydrolyzable ester bond confers the generated prodrug with the ability to be readily integrated into the lipid bilayer of liposomes for systemic administration. The resulting lipoprodrug scaffold showed significantly sustained drug release profiles and improved pharmacokinetics in rats as well as a reduction in systemic toxicity in vivo. Notably, the lipoprodrug outperformed free cabazitaxel in terms of in vivo therapeutic efficacy in multiple separate tumor xenograft-bearing mouse models, one of which was a patient-derived xenograft model. Surprisingly, the lipoprodrug was able to reduce tumor invasiveness and reprogram the tumor immunosuppressive microenvironment by proinflammatory macrophage polarization. Our findings validate this lipoprodrug approach as a simple yet effective strategy for transforming the highly toxic cabazitaxel agent into an efficacious nanomedicine with excellent in vivo tolerability. This approach could also be applied to rescue other drugs or drug candidates that have failed in clinical trials due to poor pharmacokinetic properties or unacceptable toxicity in patients.

Insulin‐Sensitizing Activity of Sub‐Nanoscaled Polyalkoxyvanadate Clusters

Sub‐nanoscaled polyalkoxyvanadates (PAOVs) functionalized with various aliphatic acids are evaluated for their insulin‐sensitizing activity in lowering the blood glucose levels of diabetic mice in typical glucose tolerance tests. All the PAOVs can restore the blood glucose to normal levels after a single oral administration of PAOVs. Among them, the myristic acid‐modified PAOVs enable the response of insulin to the repeated glucose challenges, lasting for up to 13 h. The combined administration of PAOVs exerts better glucose control over insulin alone, while the capric acid‐ and myristic acid‐modified ones can enhance the responsiveness of insulin to glucose challenge and is comparable to a clinical‐used derivative of insulin. Interestingly, continuous glucose monitoring shows that myristic acid‐modified PAOV derivatives sensitize the responsiveness of insulin, almost matching with that of a healthy pancreas. These discoveries open up new opportunities for the application of PAOVs to promote glucose‐responsive and long‐lasting activity of insulin, which are expected to aid the accurate blood glucose control in insulin therapy while reducing the number of insulin administrations.

Self-assembling nanoparticles of dually hydrophobic prodrugs constructed from camptothecin analogue for cancer therapy

Nanomedicines have shown success in cancer therapy in recent years because of their excellent solubility in aqueous solution and drug accumulation through controlled release in tumor tissues, but the preparation of most nanomedicines still requires ionic materials, surfactants or the amphiphilic structure to maintain nanoparticle stability and function. In this study, we developed a couple of novel dually hydrophobic prodrugs (DHPs) by combining two hydrophobic compounds through different linkers and elaborated their self-assembly mechanisms by virtue of computational simulation. Importantly, without using any excipients, FL-2 NPs exhibited significantly prolonged retention in blood circulation and displayed a remarkable anti-tumor effect at very low concentration in vivo. Both DHPs consisted of camptothecin structural analogue(FL118) and a marine natural product (ES-285). Comparative experiments proved that these compounds could quickly form nanoparticles by way of simple preparation and remained relatively stable for long periods in PBS. FL-2 NPs linked with a disulphide bond could rapidly release bioactive FL118 after being triggered by endogenous reductive stimulus to exert anti-cancer effects. Overall, this study provides a new strategy for design of therapeutic nanomedicines consisting of dually hydrophobic molecules for cancer therapy.