Acid-Triggered Release of Native Gemcitabine Conjugated in Polyketal Nanoparticles for Enhanced Anticancer Therapy

Acid-sensitive prodrugs; a promising approach for site-specific and targeted drug release

Drugs administered through conventional formulations are devoid of targeting and often spread to various undesired sites, leading to sub-lethal concentrations at the site of action and the emergence of undesired effects. Hence, therapeutic agents should be delivered in a controlled manner at target sites. Currently, stimuli-based drug delivery systems have demonstrated a remarkable potential for the site-specific delivery of therapeutic moieties. pH is one of the widely exploited stimuli for drug delivery as several pathogenic conditions such as tumor cells, infectious and inflammatory sites are characterized by a low pH environment. This review article aims to demonstrate various strategies employed in the design of acid-sensitive prodrugs, providing an overview of commercially available acid-sensitive prodrugs. Furthermore, we have compiled the progress made for the development of new acid-sensitive prodrugs currently undergoing clinical trials. These prodrugs include albumin-binding prodrugs (Aldoxorubicin and DK049), polymeric micelle (NC-6300), polymer conjugates (ProLindac™), and an immunoconjugate (IMMU-110). The article encompasses a broad spectrum of studies focused on the development of acid-sensitive prodrugs for anticancer, antibacterial, and anti-inflammatory agents. Finally, the challenges associated with the acid-sensitive prodrug strategy are discussed, along with future directions.

Regulating Drug Release Performance of Acid-Triggered Dimeric Prodrug-Based Drug Self-Delivery System by Altering Its Aggregation Structure

Dimeric prodrugs have been investigated intensely as carrier-free drug self-delivery systems (DSDSs) in recent decades, and their stimuli-responsive drug release has usually been controlled by the conjugations between the drug molecules, including the stimuli (pH or redox) and responsive sensitivity. Here, an acid-triggered dimeric prodrug of doxorubicin (DOX) was synthesized by conjugating two DOX molecules with an acid-labile ketal linker. It possessed high drug content near the pure drug, while the premature drug leakage in blood circulation was efficiently suppressed. Furthermore, its aggregation structures were controlled by fabricating nanomedicines via different approaches, such as fast precipitation and slow self-assembly, to regulate the drug release performance. Such findings are expected to enable better anti-tumor efficacy with the desired drug release rate, beyond the molecular structure of the dimeric prodrug.

Tumor-penetrating iRGD facilitates penetration of poly(floxuridine-ketal)-based nanomedicine for enhanced pancreatic cancer therapy

Efficient intratumoral penetration is essential for nanomedicine to eradicate pancreatic tumors. Although nanomedicine can enter the perivascular space of pancreatic tumors, their access to distal tumor cells, aloof from the vessels, remains a formidable challenge. Here, we synthesized an acid-activatable macromolecular prodrug of floxuridine (FUDR)-poly(FUDR-ketal), engineered a micellar nanomedicine of FUDR, and intravenously co-administered the nanomedicine with the tumor-penetrating peptide iRGD for enhanced treatment of pancreatic tumor. A FUDR-derived mono-isopropenyl ether was synthesized and underwent self-addition polymerization to afford the hydrophobic poly(FUDR-ketal), which was subsequently co-assembled with amphiphilic DSPE-mPEG into the micellar nanomedicine with size of 12 nm and drug content of 56.8 wt% using nanoprecipitation technique. The acetone-based ketal-linked poly(FUDR-ketal) was triggered by acid to release FUDR to inhibit cell proliferation. In an orthotopic pancreatic tumor model derived from KPC (KrasLSL-G12D/+; Trp53LSL-R172H/+; Pdx1-Cre) cells that overexpress neuropilin-1 (NRP-1) receptor, iRGD improved penetration of FUDR nanomedicine into tumor parenchyma and potentiated the therapeutic efficacy. Our nanoplatform, along with iRGD, thus appears to be promising for efficient penetration and activation of acid-responsive nanomedicines for enhanced pancreatic cancer therapy.

Is it still worth renewing nucleoside anticancer drugs nowadays?

Nucleoside has situated the convergence point in the discovery of novel drugs for decades, and a large number of nucleoside derivatives have been constructed for screening novel pharmacological properties at various experimental platforms. Notably, nearly 20 nucleosides are approved to be used in the clinic treatment of various cancers. Nevertheless, the blossom of synthetic nucleoside analogs in comparison with the scarcity of nucleoside anticancer drugs leads to a question: Is it still worth insisting on the screening of novel anticancer drugs from nucleoside derivatives? Hence, this review attempts to emphasize the importance of nucleoside analogs in the discovery of novel anticancer drugs. Firstly, we introduce the metabolic procedures of nucleoside anticancer drug (such as 5-fluorouracil) and summarize the designing of novel nucleoside anticancer candidates based on clinically used nucleoside anticancer drugs (such as gemcitabine). Furthermore, we collect anticancer properties of some recently synthesized nucleoside analogs, aiming at emphasizing the availability of nucleoside analogs in the discovery of anticancer drugs. Finally, a variety of synthetic strategies including the linkage of sugar moiety with nucleobase scaffold, modifications on the sugar moiety, and variations on the nucleobase structure are collected to exhibit the abundant protocols in the achievement of nucleoside analogs. Taken the above discussions collectively, nucleoside still advantages for the finding of novel anticancer drugs because of the clearly metabolic procedures, successfully clinic applications, and abundantly synthetic routines.

Lipid-like gemcitabine diester-loaded liposomes for improved chemotherapy of pancreatic cancer

Gemcitabine (GEM) is a non-selective chemotherapeutic agent used in the treatment of pancreatic cancer. Its antitumor efficacy is limited by a short plasma half-life and severe adverse reactions. To overcome these shortcomings, four novel lipid-like GEM diesters were synthesized and encapsulated into liposomes. Through optimization, dimyristoyl GEM (dmGEM)-loaded liposomes (LipodmGEM) were successfully obtained with an almost complete encapsulation efficiency. Compared to free GEM, LipodmGEM showed enhanced cellular uptake and cell apoptosis, improved inhibition of cell migration on AsPC-1 cells and a greatly extended half-life (7.22 vs. 1.78 h). LipodmGEM succeeded in enriching the drug in the tumor (5.28 vs. 0.03 μmol/g at 8 h), overcoming a major shortcoming of GEM, showed excellent anticancer efficacy in vivo and negligible systemic toxicity, superior to GEM. Attractive as well, suspensions of LipodmGEM remained stable at 2-10 °C away from light for no <2 years. Our results suggest that LipodmGEM might become of high interest for treating pancreatic cancer while the simple strategy we reported might be explored as well for converting other antitumor drugs with high water-solubility and short plasma half-life into attractive nanomedicines.

Fine-tuning the sequential drug release of nano-formulated mutual prodrugs dictates the combination effects

Nanoformulated mutual prodrugs able to release two drugs either in order or simultaneously which significantly affected the combination effects consistently in vitro and in vivo, and links the in vitro–in vivo optimization of therapeutic effects.

pH and its applications in targeted drug delivery

Physiologic pH is vital for the normal functioning of tissues and varies in different parts of the body. The varying pH of the body has been exploited to design pH-sensitive smart oral, transdermal and vaginal drug delivery systems (DDS). The DDS demonstrated promising results in hard-to-treat diseases such as cancer and Helicobacter pylori infection. In some cases, a change in pH of tissues or body fluids has also been employed as a useful diagnostic biomarker. This paper aims to comprehensively review the development and applications of pH-sensitive DDS as well as recent advances in the field.

Emerging Strategies in Stimuli-Responsive Prodrug Nanosystems for Cancer Therapy

Prodrugs are chemically modified drug molecules that are inactive before administration. After administration, they are converted in situ to parent drugs and induce the mechanism of action. The development of prodrugs has upgraded conventional drug treatments in terms of bioavailability, targeting, and reduced side effects. Especially in cancer therapy, the application of prodrugs has achieved substantial therapeutic effects. From serendipitous discovery in the early stage to functional design with pertinence nowadays, the importance of prodrugs in drug design is self-evident. At present, studying stimuli-responsive activation mechanisms, regulating the stimuli intensity in vivo, and designing nanoscale prodrug formulations are the major strategies to promote the development of prodrugs. In this review, we provide an outlook of recent cutting-edge studies on stimuli-responsive prodrug nanosystems from these three aspects. We also discuss prospects and challenges in the future development of such prodrugs.

The Yin and Yang of the protein corona on the delivery journey of nanoparticles

Nanoparticles-based drug delivery systems have attracted significant attention in biomedical fields because they can deliver loaded cargoes to the target site in a controlled manner. However, tremendous challenges must still be overcome to reach the expected targeting and therapeutic efficacy in vivo. These challenges mainly arise because the interaction between nanoparticles and biological systems is complex and dynamic and is influenced by the physicochemical properties of the nanoparticles and the heterogeneity of biological systems. Importantly, once the nanoparticles are injected into the blood, a protein corona will inevitably form on the surface. The protein corona creates a new biological identity which plays a vital role in mediating the bio-nano interaction and determining the ultimate results. Thus, it is essential to understand how the protein corona affects the delivery journey of nanoparticles in vivo and what we can do to exploit the protein corona for better delivery efficiency. In this review, we first summarize the fundamental impact of the protein corona on the delivery journey of nanoparticles. Next, we emphasize the strategies that have been developed for tailoring and exploiting the protein corona to improve the transportation behavior of nanoparticles in vivo. Finally, we highlight what we need to do as a next step towards better understanding and exploitation of the protein corona. We hope these insights into the "Yin and Yang" effect of the protein corona will have profound implications for understanding the role of the protein corona in a wide range of nanoparticles.

Degradable polyprodrugs: design and therapeutic efficiency

Prodrugs are developed to increase the therapeutic properties of drugs and reduce their side effects. Polyprodrugs emerged as highly efficient prodrugs produced by the polymerization of one or several drug monomers. Polyprodrugs can be gradually degraded to release therapeutic agents. The complete degradation of polyprodrugs is an important factor to guarantee the successful disposal of the drug delivery system from the body. The degradation of polyprodrugs and release rate of the drugs can be controlled by the type of covalent bonds linking the monomer drug units in the polymer structure. Therefore, various types of polyprodrugs have been developed based on polyesters, polyanhydrides, polycarbonates, polyurethanes, polyamides, polyketals, polymetallodrugs, polyphosphazenes, and polyimines. Furthermore, the presence of stimuli-responsive groups, such as redox-responsive linkages (disulfide, boronate ester, metal-complex, and oxalate), pH-responsive linkages (ester, imine, hydrazone, acetal, orthoester, P-O and P-N), light-responsive (metal-complex, o-nitrophenyl groups) and enzyme-responsive linkages (ester, peptides) allow for a selective degradation of the polymer backbone in targeted tumors. We envision that new strategies providing a more efficient synergistic therapy will be developed by combining polyprodrugs with gene delivery segments and targeting moieties.

Recent Progress in Bio-Responsive Drug Delivery Systems for Tumor Therapy

Spatially- and/or temporally-controlled drug release has always been the pursuit of drug delivery systems (DDSs) to achieve the ideal therapeutic effect. The abnormal pathophysiological characteristics of the tumor microenvironment, including acidosis, overexpression of special enzymes, hypoxia, and high levels of ROS, GSH, and ATP, offer the possibility for the design of stimulus-responsive DDSs for controlled drug release to realize more efficient drug delivery and anti-tumor activity. With the help of these stimulus signals, responsive DDSs can realize controlled drug release more precisely within the local tumor site and decrease the injected dose and systemic toxicity. This review first describes the major pathophysiological characteristics of the tumor microenvironment, and highlights the recent cutting-edge advances in DDSs responding to the tumor pathophysiological environment for cancer therapy. Finally, the challenges and future directions of bio-responsive DDSs are discussed.

Redox-responsive self-assembled polymeric nanoprodrug for delivery of gemcitabine in B-cell lymphoma therapy

Gemcitabine, as a standard and classic strategy for B-cell lymphoma in the clinic, is limited by its poor pharmacodynamics. Although stimuli-responsive polymeric nanodelivery systems have been widely investigated in the past decade, issues such as complicated procedures, low loading capacity, and uncontrollable release kinetics still hinder their clinical translation. In view of the above considerations, we attempt to construct hyperbranched polyprodrug micelles with considerable drug loading via simple procedures and make use of the particularity of the tumor microenvironment to ensure that the micelles are "inactivated" in normal tissues and "activated" in the tumor microenvironment. Hence, in this work, a redox-responsive polymeric gemcitabine-prodrug (GEM-S-S-PEG) was one-pot synthesized via facile esterification and acylation. The self-assembled subsize (< 100 nm) GEM-S-S-PEG (GSP NPs) with considerable loading capacity (≈ 24.6%) exhibited on-demand and accurate control of gemcitabine release under a simulated tumor microenvironment and thus significantly induced the apoptosis of B-cell lymphoma in vitro. Moreover, in the A20 tumor xenograft murine model, GSP NPs efficiently decreased the expansion of tumor tissues with minimal systemic toxicity. In summary, these redox-responsive and self-assembling GSP NPs with a facile one-pot synthesis procedure may hold great potency in clinical translation for enhanced chemotherapy of B-cell lymphoma. STATEMENT OF SIGNIFICANCE: A redox-responsive polymeric gemcitabine-prodrug (GEM-S-S-PEG) was one-pot synthesized via facile esterification and acylation. The self-assembled subsize (< 100 nm) GEM-S-S-PEG (GSP NPs) exhibited significant tumor therapeutic effects in vitro and in vivo. The polyprodrug GEM-S-S-PEG prepared in this study shows the great potential of redox-responsive nanodrugs for antitumor activity, which provides a reference value for the optimization of the design of functional polyprodrugs.

Stimulus-responsive self-assembled prodrugs in cancer therapy

Small-molecule prodrugs have become the main toolbox to improve the unfavorable physicochemical properties of potential therapeutic compounds in contemporary anti-cancer drug development. Many approved small-molecule prodrugs, however, still face key challenges in their pharmacokinetic (PK) and pharmacodynamic (PD) properties, thus severely restricting their further clinical applications. Self-assembled prodrugs thus emerged as they could take advantage of key benefits in both prodrug design and nanomedicine, so as to maximize drug loading, reduce premature leakage, and improve PK/PD parameters and targeting ability. Notably, temporally and spatially controlled release of drugs at cancerous sites could be achieved by encoding various activable linkers that are sensitive to chemical or biological stimuli in the tumor microenvironment (TME). In this review, we have comprehensively summarized the recent progress made in the development of single/multiple-stimulus-responsive self-assembled prodrugs for mono- and combinatorial therapy. A special focus was placed on various prodrug conjugation strategies (polymer-drug conjugates, drug-drug conjugates, etc.) that facilitated the engineering of self-assembled prodrugs, and various linker chemistries that enabled selective controlled release of active drugs at tumor sites. Furthermore, some polymeric nano-prodrugs that entered clinical trials have also been elaborated here. Finally, we have discussed the bottlenecks in the field of prodrug nanoassembly and offered potential solutions to overcome them. We believe that this review will provide a comprehensive reference for the rational design of effective prodrug nanoassemblies that have clinic translation potential.

Stimuli-Responsive Delivery Strategies for Controllable Gene Editing in Tumor Therapeutics

CRISPR system has attracted significant interest due to its great potential in tumour therapy. Developing effective, precise and safe delivery vectors is a prerequisite for CRISPR applications. Some disease-related biological...

Novel nanomedicines to overcome cancer multidrug resistance

Chemotherapy remains a powerful tool to eliminate malignant cells. However, the efficacy of chemotherapy is compromised by the frequent emergence of intrinsic and acquired multidrug resistance (MDR). These chemoresistance modalities are based on a multiplicity of molecular mechanisms of drug resistance, including : 1) Impaired drug uptake into cancer cells; 2) Increased expression of ATP-binding cassette efflux transporters; 3) Loss of function of pro-apoptotic factors; 4) Enhanced DNA repair capacity; 5) Qualitative or quantitative alterations of specific cellular targets; 6) Alterations that allow cancer cells to tolerate adverse or stressful conditions; 7) Increased biotransformation or metabolism of anticancer drugs to less active or completely inactive metabolites; and 8) Intracellular and intercellular drug sequestration in well-defined organelles away from the cellular target. Hence, one of the major aims of cancer research is to develop novel strategies to overcome cancer drug resistance. Over the last decades, nanomedicine, which focuses on targeted delivery of therapeutic drugs into tumor tissues using nano-sized formulations, has emerged as a promising tool for cancer treatment. Therefore, nanomedicine has been introduced as a reliable approach to improve treatment efficacy and minimize detrimental adverse effects as well as overcome cancer drug resistance. With rationally designed strategies including passively targeted delivery, actively targeted delivery, delivery of multidrug combinations, as well as multimodal combination therapy, nanomedicine paves the way towards efficacious cancer treatment and hold great promise in overcoming cancer drug resistance. Herein, we review the recent progress of nanomaterials used in medicine, including liposomal nanoparticles, polymeric nanoparticles, inorganic nanoparticles and hybrid nanoparticles, to surmount cancer multidrug resistance. Finally, the future perspectives of the application of nanomedicine to reverse cancer drug resistance will be addressed.

Targeted Delivery of Drugs and Genes Using Polymer Nanocarriers for Cancer Therapy

Cancer is one of the primary causes of worldwide human deaths. Most cancer patients receive chemotherapy and radiotherapy, but these treatments are usually only partially efficacious and lead to a variety of serious side effects. Therefore, it is necessary to develop new therapeutic strategies. The emergence of nanotechnology has had a profound impact on general clinical treatment. The application of nanotechnology has facilitated the development of nano-drug delivery systems (NDDSs) that are highly tumor selective and allow for the slow release of active anticancer drugs. In recent years, vehicles such as liposomes, dendrimers and polymer nanomaterials have been considered promising carriers for tumor-specific drug delivery, reducing toxicity and improving biocompatibility. Among them, polymer nanoparticles (NPs) are one of the most innovative methods of non-invasive drug delivery. Here, we review the application of polymer NPs in drug delivery, gene therapy, and early diagnostics for cancer therapy.

Recent advances in prodrug-based nanoparticle therapeutics

Extensive research into prodrug modification of active pharmaceutical ingredients and nanoparticle drug delivery systems has led to unprecedented levels of control over the pharmacological properties of drugs and resulted in the approval of many prodrug or nanoparticle-based therapies. In recent years, the combination of these two strategies into prodrug-based nanoparticle drug delivery systems (PNDDS) has been explored as a way to further advance nanomedicine and identify novel therapies for difficult-to-treat indications. Many of the PNDDS currently in the clinical development pipeline are expected to enter the market in the coming years, making the rapidly evolving field of PNDDS highly relevant to pharmaceutical scientists. This review paper is intended to introduce PNDDS to the novice reader while also updating those working in the field with a comprehensive summary of recent efforts. To that end, first, an overview of FDA-approved prodrugs is provided to familiarize the reader with their advantages over traditional small molecule drugs and to describe the chemistries that can be used to create them. Because this article is part of a themed issue on nanoparticles, only a brief introduction to nanoparticle-based drug delivery systems is provided summarizing their successful application and unfulfilled opportunities. Finally, the review's centerpiece is a detailed discussion of rationally designed PNDDS formulations in development that successfully leverage the strengths of prodrug and nanoparticle approaches to yield highly effective therapeutic options for the treatment of many diseases.

Gemcitabine Lipid Prodrugs: The Key Role of the Lipid Moiety on the Self-Assembly into Nanoparticles

A small library of amphiphilic prodrugs has been synthesized by conjugation of gemcitabine (Gem) (a hydrophilic nucleoside analogue) to a series of lipid moieties and investigated for their capacity to spontaneously self-assemble into nanosized objects by simple nanoprecipitation. Four of these conjugates formed stable nanoparticles (NPs), while with the others, immediate aggregation occurred, whatever the tested experimental conditions. Whether such capacity could have been predicted based on the prodrug physicochemical features was a matter of question. Among various parameters, the hydrophilic-lipophilic balance (HLB) value seemed to hold a predictive character. Indeed, we identified a threshold value which well correlated with the tendency (or not) of the synthesized prodrugs to form stable nanoparticles. Such a hypothesis was further confirmed by broadening the analysis to Gem and other nucleoside prodrugs already described in the literature. We also observed that, in the case of Gem prodrugs, the lipid moiety affected not only the colloidal properties but also the in vitro anticancer efficacy of the resulting nanoparticles. Overall, this study provides a useful demonstration of the predictive potential of the HLB value for lipid prodrug NP formulation and highlights the need of their opportune in vitro screening, as optimal drug loading does not always translate in an efficient biological activity.

Evaluation of the Anticancer Activity of pH-Sensitive Polyketal Nanoparticles for Acute Myeloid Leukemia

Polyketals are a class of acid-responsive polymers that have been relatively less explored for drug delivery applications compared to polyesters. The degradation of these polymers is accelerated in an acidic medium and does not result in acidic byproducts. Their biocompatibility depends on the diol used for the synthesis. The present work aims to synthesize, characterize, and fabricate nanospheres of an aliphatic polyketal for delivery of the nucleotide analogue cytarabine toward the treatment of acute myeloid leukemia (AML). The internalization mechanism of the nanospheres was probed, and its implication on the nuclear localization and escape from the endo-lysosomal compartments were studied. The drug-loaded polyketal nanoparticles reduced the cell viability to a greater extent compared with the free drug. The effect of the drug-loaded polyketal nanoparticles on the differential gene expression of leukemic cells was investigated for the first time to understand their therapeutic implications. It was found that treatment with drug-loaded polyketal nanoparticles downregulated AML-specific genes involved in cell proliferation and recurrence compared to the free drug. The protein expression studies were performed for selected genes obtained from gene expression analysis. Biodistribution studies showed that the poly(cyclohexane-1,4-diyl acetone dimethylene ketal) (PCADK) nanoparticles exhibit prolonged circulation time. Overall, our results suggest that polyketal-based delivery of cytarabine represents a more effective alternative strategy for AML therapy.

Stimulus-cleavable chemistry in the field of controlled drug delivery

This review comprehensively summarises stimulus-cleavable linkers from various research areas and their cleavage mechanisms, thus provides an insightful guideline to extend their potential applications to controlled drug release from nanomaterials.

Synergistic Combination Chemotherapy of Lung Cancer: Cisplatin and Doxorubicin Conjugated Prodrug Loaded, Glutathione and pH Sensitive Nanocarriers

Purpose

Prodrug technology-based combination drug therapy has been exploited as a promising treatment strategy to achieve synergistic lung cancer therapy, reduce drug dose, and decrease side effects. In the present study, we synthesized a pH and glutathione (GSH) sensitive prodrug, cisplatin (CIS) and doxorubicin (DOX) conjugates (CIS-DOXp). CIS-DOXp was loaded by nanocarriers and delivered into the tumor site.

Methods

pH and GSH sensitive CIS-DOX prodrug (CIS-DOXp) was synthesized by conjugating GSH responsive CIS prodrug with pH sensitive DOX prodrug. CIS-DOXp-loaded nanocarriers (CIS-DOXp NC) were prepared using emulsification and solvent evaporation method. The morphology, particle size, polydispersity index (PDI) and zeta potential of nanocarriers were measured. In vitro cytotoxicity of nanocarriers and the corresponding free drugs was examined using the MTT assay. In vivo anti-tumor efficiency and biodistribution behaviors were evaluated on lung cancer mice models.

Results

The size, PDI, zeta potential, CIS loading efficiency, and DOX loading efficiency of CIS-DOXp NC were 128.6 ± 3.2 nm, 0.196 ± 0.021, 15.7 ± 1.7 mV, 92.1 ± 2.1%, and 90.4 ± 1.8%, respectively. The best cell killing ability (the lowest combination index of 0.57) was found at the combination ratio of 1:3 (CIS:DOX, w/w) in the drugs co-loaded formulations, indicating the strongest synergism effect. CIS-DOXp NC showed the best tumor inhibition efficiency (79.9%) in mice with negligible body weight lost.

Conclusion

CIS-DOXp NC could be applied as a promising system for the synergistic chemotherapy of lung cancer.

Nanotechnology for COVID-19: Therapeutics and Vaccine Research

The current global health threat by the novel coronavirus disease 2019 (COVID-19) requires an urgent deployment of advanced therapeutic options available. The role of nanotechnology is highly relevant to counter this "virus" nano enemy. Nano intervention is discussed in terms of designing effective nanocarriers to counter the conventional limitations of antiviral and biological therapeutics. This strategy directs the safe and effective delivery of available therapeutic options using engineered nanocarriers, blocking the initial interactions of viral spike glycoprotein with host cell surface receptors, and disruption of virion construction. Controlling and eliminating the spread and reoccurrence of this pandemic demands a safe and effective vaccine strategy. Nanocarriers have potential to design risk-free and effective immunization strategies for severe acute respiratory syndrome coronavirus 2 vaccine candidates such as protein constructs and nucleic acids. We discuss recent as well as ongoing nanotechnology-based therapeutic and prophylactic strategies to fight against this pandemic, outlining the key areas for nanoscientists to step in.

Acid-sensitive PEGylated paclitaxel prodrug nanoparticles for cancer therapy: Effect of PEG length on antitumor efficacy

Paclitaxel is one of the most widely used anticancer agents, but strong side effects and low bioavailability limit its clinical efficacy. The use of tumor microenvironment-responsive prodrugs is promising to solve these problems, and a smart linkage is crucial to achieve the efficient release of paclitaxel from such prodrugs in tumor. Herein, an acid-responsive acetone-based acyclic ketal linkage is used to construct paclitaxel prodrugs with different length of poly(ethylene glycol) (PEG). The PEGylated acetone-based acyclic-ketal-linked prodrugs of paclitaxel (PKPs) self-assembled into nanoparticles that were stable in normal physiological environment but released paclitaxel rapidly in mildly acidic environment in tumor. The length of PEG had considerable impact on size and critical micelle concentration of PKP nanoparticles, thereby affecting prodrug hydrolysis kinetics, pharmacokinetics, biodistribution, and antitumor activity for PKP nanoparticles. In an A2780 xenograft mouse model, PKP nanoparticles displayed improved pharmacokinetics and superior antitumor efficacy against Taxol. Our results demonstrate that acyclic-ketal-based prodrugs are useful for the development of acid-responsive anticancer nanomedicines.

Dually Enzyme- and Acid-Triggered Self-Immolative Ketal Glycoside Nanoparticles for Effective Cancer Prodrug Monotherapy

The use of glycoside prodrugs is a promising strategy for developing new targeted medicines for chemotherapy. However, the in vivo utility of such prodrugs is hindered by insufficient activation and the lack of convenient synthetic methods. We have developed an innovative strategy for synthesizing ketal glycoside prodrugs that are unique in being activated by a dual enzyme- and acid-triggered self-immolative mechanism. Amphiphilic glucosyl acetone-based ketal-linked etoposide glycoside prodrug isomers were synthesized and fabricated into excipient-free nanoparticles for effective cancer prodrug monotherapy. Hydrolysis of the glycosidic linkage or the ketal linkage triggered hydrolysis of the other linkage, which resulted in spontaneous self-immolative hydrolysis of the prodrugs. Nanoparticles of the prodrug isomer that was the most labile in a lysosome-mimicking environment displayed high intratumoral accumulation and strong antitumor activity in an A549 xenograft mouse model. Our strategy may be useful for the development of stimulus-responsive self-immolative prodrugs and their nanomedicines.