Selective cancer targeting with prodrugs activated by histone deacetylases and a tumour-associated protease

Tandem activated caged galactoside prodrugs: advancing beyond single galactosidase dependence

β-Galactoside prodrugs, activated by β-galactosidase (β-gal) highly expressed in some cancer cells, have been explored as anticancer agents for three decades. However, the distribution of β-gal lacks sufficient specificity to ensure precise drug release at cancer sites. By utilizing the highly stringent substrate specificity of β-gal, we chose the naturally occurring hydroxyl group of galactose as a prodrug modification site and developed a new class of tandem activated caged galactoside (TACG) prodrugs that require an additional trigger for more controlled on-demand drug release. We demonstrated that attaching various masking groups to the 6-hydroxyl group of galactose renders the galactosides resistant to β-gal hydrolysis. Focusing on the photosensitive mask 4,5-dimethoxy-2-nitrobenzyl (DMNB), we synthesized O6-DMNB modified galactosides of combretastatin A4 and 8-hydroxyquinoline, showcasing their UV/β-gal-dependent anticancer activities. We further established synthetic routes for O2-, O3-, and O4-DMNB modified TACGs. Comparative intracellular studies highlighted the O2-DMNB modified TACG as the most effective positional isomer, offering superior light-dependent selectivity. This insight led to the discovery of the O2-DMNB modified galactoside of combretastatin A4 as a potent UV-dependent microtubule assembly inhibitor. Our work provides a straightforward, effective, and universally applicable strategy for constructing dual-stimulus responsive galactoside prodrugs, extendable to various glycoside prodrugs, advancing carbohydrate-based drug discovery.

Sequential metabolic probes illuminate nuclear DNA for discrimination of cancerous and normal cells

Elucidating the timing and spatial distribution of DNA synthesis within cancer cells is vital for cancer diagnosis and targeted therapy. However, current probes for staining nucleic acids rely on electrostatic interactions and hydrogen bonds with the nucleic acid, resulting in "static" DNA staining and the inability to distinguish cell types. Here, we present a proof-of-concept study of sequential metabolic probes, for the first time allowing for cancer-cell-specific illumination of DNA. This breakthrough is achieved by the combination of a "dual-locked" nucleoside analog VdU-Lys, and a new tetrazine-based bioorthogonal probe. Specifically, 5-vinyl-2'-deoxyuridine (VdU) release is only conducted in programmatically triggered histone deacetylases (HDACs) and cathepsin L (CTSL) as "sequential keys", enabling the modification of vinyl groups into the nuclear DNA of cancerous cells rather than normal cells. Subsequently, tetrazine-based Et-PT-Tz could in situ light-up DNA containing VdUs with significant fluorescence illumination (120-fold enhancement) through rapid bioorthogonal reaction. We demonstrated the compatibility of our probe in cancer-specific sensing of DNA with a high signal-to-noise ratio ranging from in vitro multiple cell lines to whole-organism scale. This approach would serve as a benchmark for the development of cell-specific metabolic reporters for DNA labelling, to characterize DNA metabolism in various types of cell lines.

Dual-Action-Only PROTACs

Proteolysis targeting chimera (PROTAC)-based degraders are highly potent pseudocatalytic drugs, but on-target off-site homing could yield undesirable consequences. We report here a generalizable AND-logic gated PROTAC, where the concurrent presence of two different disease-relevant endogenous stimuli liberates an active protein degrader. We design Dual-Action-Only PROTAC (DAO-PROTAC) molecules that are dormant and can only be activated in the presence of both hypoxia and cathepsin-L to degrade the protein of interest (POI). We also show that the dormancy of DAO-PROTACs translates to considerable mitigation of cytotoxicity, demonstrating the potential advantages over the corresponding free PROTAC and single-stimulus triggerable pro-PROTACs.

Anti-Tumor Strategies Targeting Nutritional Deprivation: Challenges and Opportunities

Higher and richer nutrient requirements are typical features that distinguish tumor cells from AU: cells, ensuring adequate substrates and energy sources for tumor cell proliferation and migration. Therefore, nutrient deprivation strategies based on targeted technologies can induce impaired cell viability in tumor cells, which are more sensitive than normal cells. In this review, nutrients that are required by tumor cells and related metabolic pathways are introduced, and anti-tumor strategies developed to target nutrient deprivation are described. In addition to tumor cells, the nutritional and metabolic characteristics of other cells in the tumor microenvironment (including macrophages, neutrophils, natural killer cells, T cells, and cancer-associated fibroblasts) and related new anti-tumor strategies are also summarized. In conclusion, recent advances in anti-tumor strategies targeting nutrient blockade are reviewed, and the challenges and prospects of these anti-tumor strategies are discussed, which are of theoretical significance for optimizing the clinical application of tumor nutrition deprivation strategies.

A smart cascade theranostic prodrug system activated by hydrogen peroxide for podophyllotoxin delivery

The construction of selectively activated prodrugs serves as a crucial strategy for reducing the adverse effects associated with disease treatment. Cascade self-assembled visual prodrugs have been applied to the construction of selective activated prodrugs with low background interference and in situ fluorescence. In this work, we rationally designed an anticancer theranostic prodrug (CM-PPT) consisting of an anticancer drug podophyllotoxin, a fluorescent dye precursor, and an H2O2 trigger boronate ester group, which could be activated by H2O2 oxidation, thereby releasing active anticancer molecules and forming fluorescent fragments concurrently. In vitro experiments revealed that the prodrug has potent anticancer efficacy, and the drug release rate could be visualized by the fluorescence intensity. In addition, intraperitoneal administration of the prodrug to mice demonstrated outstanding antitumor activities. Thus, this design of H2O2-responsive prodrug may provide a promising strategy for selective imaging of H2O2 status, real-time tracking of drug release, and personalized tumor treatment.

An enzyme-responsive double-locked amonafide prodrug for the treatment of glioblastoma with minimal side effects

Amonafide (ANF), a topoisomerase II inhibitor and DNA intercalator, has exhibited promise in phase II trials but faces significant limitations due to adverse side effects. Here, we have developed a novel enzyme-triggered fluorogenic prodrug, AcKLP, that incorporates dual-locked enzyme activation, ensuring that the prodrug remains inactive until it confronts the unique enzymatic environment of glioblastoma cells. This approach minimizes premature activation and reduces toxicity to normal cells, with an IC50 > 100 μM for human umbilical vein endothelial cells (HUVEC) and ∼2.3 μM for human glioblastoma cells (U87). Upon activation of AcKLP by two distinct enzymes prevalent in glioblastoma cells, amonafide is released and emits a fluorescence signal response, facilitating treatment and the monitoring of real-time drug distribution. Mechanistic studies indicate that AcKLP mainly induces autophagic cell death in U87 cells. Moreover, three-dimensional multicellular U87 tumor spheroid assays and in vivo experiments confirm the potent antiproliferative activity of AcKLP against glioblastoma cells. This work demonstrates a novel de-caging strategy to improve the selectivity and efficacy of amonafide for cancer therapy.

Designing intelligent bioorthogonal nanozymes: Recent advances of stimuli-responsive catalytic systems for biomedical applications

Bioorthogonal nanozymes have emerged as a potent tool in biomedicine due to their unique ability to perform enzymatic reactions that do not interfere with native biochemical processes. The integration of stimuli-responsive mechanisms into these nanozymes has further expanded their potential, allowing for controlled activation and targeted delivery. As such, intelligent bioorthogonal nanozymes have received more and more attention in developing therapeutic approaches. This review provides a comprehensive overview of the recent advances in the development and application of stimuli-responsive bioorthogonal nanozymes. By summarizing the design outlines for anchoring bioorthogonal nanozymes with stimuli-responsive capability, this review seeks to offer valuable insights and guidance for the rational design of these remarkable materials. This review highlights the significant progress made in this exciting field with different types of stimuli and the various applications. Additionally, it also examines the current challenges and limitations in the design, synthesis, and application of these systems, and proposes potential solutions and research directions. This review aims to stimulate further research toward the development of more efficient and versatile stimuli-responsive bioorthogonal nanozymes for biomedical applications.

Modular Development of Enzyme-Activatable Proteolysis Targeting Chimeras for Selective Protein Degradation and Cancer Targeting

As an emerging therapeutic modality, proteolysis targeting chimeras (PROTACs) indiscriminately degrade proteins in both healthy and diseased cells, posing a risk of on-target off-site toxicity in normal tissues. Herein, we present the modular development of enzyme-activatable PROTACs, which utilize enzyme-recognition moieties to block protein degradation activities and can be specifically activated by elevated enzymes in cancer cells to enable cell-selective protein degradation and cancer targeting. We identified the methylene alkoxy carbamate (MAC) unit as an optimal self-immolative linker, possessing high stability and release efficiency for conjugating enzyme-recognition moieties with PROTACs. Leveraging the MAC linker, we developed a series of enzyme-activatable PROTACs, harnessing distinct enzymes for cancer-cell-selective protein degradation. Significantly, we introduced the first dual-enzyme-activatable PROTAC that requires the presence of two cancer-associated enzymes for activation, demonstrating highly selective protein degradation in cancer cells over nonmalignant cells, potent in vivo antitumor efficacy, and no off-tumor toxicity to normal tissues. The broad applicability of enzyme-activatable PROTACs was further demonstrated by caging other PROTACs via the MAC linker to target different proteins and E3 ligases. Our work underscores the substantial potential of enzyme-activatable PROTACs in overcoming the off-site toxicity associated with conventional PROTACs and offers new opportunities for targeted cancer treatment.

Therapeutic resurgence of 6-diazo-5-oxo-l-norleucine (DON) through tissue-targeted prodrugs

The recognition that rapidly proliferating cancer cells rely heavily on glutamine for their survival and growth has renewed interest in the development of glutamine antagonists for cancer therapy. Glutamine plays a pivotal role as a carbon source for synthesizing lipids and metabolites through the TCA cycle, as well as a nitrogen source for synthesis of amino acid and nucleotides. Numerous studies have explored the significance of glutamine metabolism in cancer, providing a robust rationale for targeting this metabolic pathway in cancer treatment. The glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON) has been explored as an anticancer therapeutic for nearly six decades. Initial investigations revealed remarkable efficacy in preclinical studies and promising outcomes in early clinical trials. However, further advancement of DON was hindered due to dose-limiting gastrointestinal (GI) toxicities as the GI system is highly dependent on glutamine for regulating growth and repair. In an effort to repurpose DON and mitigate gastrointestinal (GI) toxicity concerns, prodrug strategies were utilized. These strategies aimed to enhance the delivery of DON to specific target tissues, such as tumors and the central nervous system (CNS), while sparing DON delivery to normal tissues, particularly the GI tract. When administered at low daily doses, optimized for metabolic inhibition, these prodrugs exhibit remarkable effectiveness without inducing significant toxicity to normal tissues. This approach holds promise for overcoming past challenges associated with DON, offering an avenue for its successful utilization in cancer treatment.

HDAC inhibition regulates oxidative stress in CD4+Thelper cells of chronic obstructive pulmonary disease and non-small cell lung cancer patients via mitochondrial transcription factor a (mtTFA) modulating NF-κB/HIF1α axis

Histone deacetylases (HDACs) play a crucial role in the epigenetic regulation of gene expression by remodelling chromatin. Isoenzymes of the HDAC family exhibit aberrant regulation in a wide variety of cancers as well as several inflammatory lung disorders like chronic obstructive pulmonary disease (COPD). Inhibition of HDACs is a potential therapeutic strategy that could be used to reverse epigenetic modification. Trichostatin A (TSA), a powerful histone deacetylase (HDAC) inhibitor, has anti-cancer effects in numerous cancer types. However, it is not yet apparent how HDAC inhibitors affect human non-small cell lung cancer cells (NSCLC) and COPD. This study aims to investigate TSA's role in restoring mitochondrial dysfunction and its effect on hypoxia and inflammation in CD4+T cells obtained from patients with COPD and lung cancer. As a result of treatment with TSA, there is a reduction in the expression of inflammatory cytokines and a decreased enrichment of transcriptional factors associated with inflammation at VEGFA gene loci. We have seen a substantial decrease in the expression of NF-κB and HIF1α, which are the critical mediators of inflammation and hypoxia, respectively. Following TSA treatment, mtTFA expression was increased, facilitating patients with COPD and NSCLC in the recovery of their dysfunctional mitochondria. Furthermore, we have discovered that TSA treatment in patients with COPD and NSCLC may lead to immunoprotective ness by inducing Th1ness. Our finding gives a new insight into the existing body of knowledge regarding TSA-based therapeutic methods and highlights the necessity of epigenetic therapy for these devastating lung disorders.

Synthesis and anticancer evaluation of acetylated-lysine conjugated gemcitabine prodrugs

Gemcitabine is an antimetabolite drug approved for the treatment of various cancers. However, its use is limited due to several issues such as stability, toxicity and drug resistance. Herein, we present the design and synthesis of a series of gemcitabine prodrugs with modifications on the 4-N-amino group by employing an acetylated l- or d-lysine moiety masked by different substitutions. Prodrugs 1-3 and 6-8 showed up to 2.4 times greater anticancer activity than gemcitabine in A549 lung cells, while they exhibited potent activity against BxPC-3 pancreatic cells with IC50 values in the range of 7-40 nM. Moreover, prodrugs 2-3 and 7-8 were found to be less potent against CTSL low expression Caco-2 cells and at least 69-fold less toxic towards human normal HEK-293T cells compared to gemcitabine, leading to improved selectivity and safety profiles. Further stability studies showed that representative prodrugs 2 and 7 exhibited enhanced metabolic stability in human plasma, human liver microsomes and cytidine deaminase. Prodrug 1 can be cleaved by tumor cell-enriched CTSL to release parent drug gemcitabine. Overall, these results demonstrated that acetylated lysine conjugated gemcitabine prodrugs could serve as promising leads for further evaluation as new anticancer drugs.

The Hexosamine Biosynthesis Pathway: Regulation and Function

The hexosamine biosynthesis pathway (HBP) produces uridine diphosphate-N-acetyl glucosamine, UDP-GlcNAc, which is a key metabolite that is used for N- or O-linked glycosylation, a co- or post-translational modification, respectively, that modulates protein activity and expression. The production of hexosamines can occur via de novo or salvage mechanisms that are catalyzed by metabolic enzymes. Nutrients including glutamine, glucose, acetyl-CoA, and UTP are utilized by the HBP. Together with availability of these nutrients, signaling molecules that respond to environmental signals, such as mTOR, AMPK, and stress-regulated transcription factors, modulate the HBP. This review discusses the regulation of GFAT, the key enzyme of the de novo HBP, as well as other metabolic enzymes that catalyze the reactions to produce UDP-GlcNAc. We also examine the contribution of the salvage mechanisms in the HBP and how dietary supplementation of the salvage metabolites glucosamine and N-acetylglucosamine could reprogram metabolism and have therapeutic potential. We elaborate on how UDP-GlcNAc is utilized for N-glycosylation of membrane and secretory proteins and how the HBP is reprogrammed during nutrient fluctuations to maintain proteostasis. We also consider how O-GlcNAcylation is coupled to nutrient availability and how this modification modulates cell signaling. We summarize how deregulation of protein N-glycosylation and O-GlcNAcylation can lead to diseases including cancer, diabetes, immunodeficiencies, and congenital disorders of glycosylation. We review the current pharmacological strategies to inhibit GFAT and other enzymes involved in the HBP or glycosylation and how engineered prodrugs could have better therapeutic efficacy for the treatment of diseases related to HBP deregulation.

Puromycin Prodrug Activation by Thioredoxin Reductase Overcomes Its Promiscuous Cytotoxicity

Overexpression of the selenoprotein thioredoxin reductase (TrxR) has been documented in malignant tissues and is of pathological significance for many types of tumors. The antibiotic puromycin (Puro) is a protein synthesis inhibitor causing premature polypeptide chain termination during translation. The well-defined action mechanism of Puro makes it a useful tool in biomedical studies. However, the nonselective cytotoxicity of Puro limits its therapeutic applications. We report herein the construction and evaluation of two Puro prodrugs, that is, S1-Puro with a five-membered cyclic disulfide trigger and S2-Puro with a linear disulfide trigger. S1-Puro is selectively activated by TrxR and shows the TrxR-dependent cytotoxicity to cancer cells, while S2-Puro is readily activated by thiols. Furthermore, S1-Puro displays higher stability in plasma than S2-Puro. We expect that this prodrug strategy may promote the further development of Puro as a therapeutic agent.

Discovery of DRP-104, a tumor-targeted metabolic inhibitor prodrug

6-Diazo-5-oxo-l-norleucine (DON) is a glutamine antagonist that suppresses cancer cell metabolism but concurrently enhances the metabolic fitness of tumor CD8+ T cells. DON showed promising efficacy in clinical trials; however, its development was halted by dose-limiting gastrointestinal (GI) toxicities. Given its clinical potential, we designed DON peptide prodrugs and found DRP-104 [isopropyl(S)-2-((S)-2-acetamido-3-(1H-indol-3-yl)-propanamido)-6-diazo-5-oxo-hexanoate] that was preferentially bioactivated to DON in tumor while bioinactivated to an inert metabolite in GI tissues. In drug distribution studies, DRP-104 delivered a prodigious 11-fold greater exposure of DON to tumor versus GI tissues. DRP-104 affected multiple metabolic pathways in tumor, including decreased glutamine flux into the TCA cycle. In efficacy studies, both DRP-104 and DON caused complete tumor regression; however, DRP-104 had a markedly improved tolerability profile. DRP-104's effect was CD8+ T cell dependent and resulted in robust immunologic memory. DRP-104 represents a first-in-class prodrug with differential metabolism in target versus toxicity tissue. DRP-104 is now in clinical trials under the FDA Fast Track designation.

Targeting Glutamine Metabolism to Enhance Immunoprevention of EGFR-Driven Lung Cancer

Lung cancer is the leading cause of cancer death worldwide. Vaccination against EGFR can be one of the venues to prevent lung cancer. Blocking glutamine metabolism has been shown to improve anticancer immunity. Here, the authors report that JHU083, an orally active glutamine antagonist prodrug designed to be preferentially activated in the tumor microenvironment, has potent anticancer effects on EGFR-driven mouse lung tumorigenesis. Lung tumor development is significantly suppressed when treatment with JHU083 is combined with an EGFR peptide vaccine (EVax) than either single treatment. Flow cytometry and single-cell RNA sequencing of the lung tumors reveal that JHU083 increases CD8+ T cell and CD4+ Th1 cell infiltration, while EVax elicits robust Th1 cell-mediated immune responses and protects mice against EGFRL858R mutation-driven lung tumorigenesis. JHU083 treatment decreases immune suppressive cells, including both monocytic- and granulocytic-myeloid-derived suppressor cells, regulatory T cells, and pro-tumor CD4+ Th17 cells in mouse models. Interestingly, Th1 cells are found to robustly upregulate oxidative metabolism and adopt a highly activated and memory-like phenotype upon glutamine inhibition. These results suggest that JHU083 is highly effective against EGFR-driven lung tumorigenesis and promotes an adaptive T cell-mediated tumor-specific immune response that enhances the efficacy of EVax.

Rational Control of Protein-Protein Interactions with Protein-ATRP-Generated Protease-Sensitive Polymer Cages

Protease-protease interactions lie at the heart of the biological cascades that provide rapid molecular responses to living systems. Blood clotting cascades, apoptosis signaling networks, bacterial infection, and virus trafficking have all evolved to be activated and sustained by protease-protease interactions. Biomimetic strategies designed to target drugs to specific locations have generated proprotein drugs that can be activated by proteolytic cleavage to release native protein. We have previously demonstrated that the modification of enzymes with a custom-designed comb-shaped polymer nanoarmor can shield the enzyme surface and eliminate almost all protein-protein interactions. We now describe the synthesis and characterization of protease-sensitive comb-shaped nanoarmor cages using poly(ethylene glycol) [Sundy, J. S. Arthritis Rheum. 2008, 58(9), 2882-2891]methacrylate macromonomers where the PEG tines of the comb are connected to the backbone of the growing polymer chain by peptide linkers. Protease-induced cleavage of the tines of the comb releases a polymer-modified protein that can once again participate in protein-protein interactions. Atom transfer radical polymerization (ATRP) was used to copolymerize the macromonomer and carboxybetaine methacrylate from initiator-labeled chymotrypsin and trypsin enzymes, yielding proprotease conjugates that retained activity toward small peptide substrates but prevented activity against proteins. Native proteases triggered the release of the PEG side chains from the polymer backbone within 20 min, thereby increasing the activity of the conjugate toward larger protein substrates by 100%. Biomimetic cascade initiation of nanoarmored protease-sensitive protein-polymer conjugates may open the door to a new class of responsive targeted therapies.

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.

Exploiting Endogenous Enzymes for Cancer-Cell Selective Metabolic Labeling of RNA in Vivo

Tissues and organs are composed of many diverse cell types, making cell-specific gene expression profiling a major challenge. Herein we report that endogenous enzymes, unique to a cell of interest, can be utilized to enable cell-specific metabolic labeling of RNA. We demonstrate that appropriately designed "caged" nucleosides can be rendered active by serving as a substrate for cancer-cell specific enzymes to enable RNA metabolic labeling, only in cancer cells. We envision that the ease and high stringency of our approach will enable expression analysis of tumor cells in complex environments.

ABCB1 can actively pump-out the background-free tame fluorescent probe CO-1 from live cells

Cell labelling using a small fluorescent probe is an important technique in biomedical sciences. We previously developed a biocompatible and membrane-permeable probe, CO-1, which has low nonspecific binding affinity towards nontarget molecules. Although this background-free tame probe has been utilized for labelling of various intracellular biomolecules in live cells, the probes'  backgroung-free staining mechanism was not fully understood. Here, we propose that Gating-Oriented Live-cell Distinction (GOLD) mechanism occurs when ABCB1 transporter removes unbound CO-1 molecules from mammalian cells and, in a minor role, DIRC2 pumps CO-1 out from lysosomes. We also showed that solute carrier transporters were not involved in carrying CO-1 inside of cells. The role of reporters in assisting the probes' influx-efflux was analyzed by the combination of CRISPR library sceenings and inhibitors test. In summary, tame probe CO-1 cellular staining occurs in a dual mechanism where the probe moves freely through the cells membrane, but its washable property can be directly related to the action of ABCB1 transporter.

Enzyme-activated Prodrugs and Their Release Mechanisms for Treatment of Cancer

Enzyme-activated prodrugs have received a lot of attention in recent years. These prodrugs have low toxicity to cells before they are activated, and when they interact with specific enzymes, they...

A fluorogenic probe targeting two spatially separated enzymes for selective imaging of cancer cells

We describe a fluorogenic probe BocLys(Ac)-AB-FC targeting both histone deacetylases (HDACs) and cathepsin L, which are overexpressed in spatially separated subcellular organelles of cancer cells. The results show that the...

MicroRNA-Mediated Drug Repurposing Unveiled Potential Candidate Drugs for Prolactinoma Treatment

INTRODUCTION

Prolactinomas, also called lactotroph adenomas, are the most encountered type of hormone-secreting pituitary neuroendocrine tumors in the clinic. The preferred first-line therapy is a medical treatment with dopamine agonists (DAs), mainly cabergoline, to reduce serum prolactin levels, tumor volume, and mass effect. However, in some cases, patients have displayed DA resistance with aggressive tumor behavior or are faced with recurrence after drug withdrawal. Also, currently used therapeutics have notorious side effects and impair the life quality of the patients.

METHODS

Since the amalgamation of clinical and laboratory data besides tumor histopathogenesis and transcriptional regulatory features of the tumor emerges to exhibit essential roles in the behavior and progression of prolactinomas; in this work, we integrated mRNA- and microRNA (miRNA)-level transcriptome data that exploit disease-specific signatures in addition to biological and pharmacological data to elucidate a rational prioritization of pathways and drugs in prolactinoma.

RESULTS

We identified 8 drug candidates through drug repurposing based on mRNA-miRNA-level data integration and evaluated their potential through in vitro assays in the MMQ cell line. Seven repurposed drugs including 5-fluorocytosine, nortriptyline, neratinib, puromycin, taxifolin, vorinostat, and zileuton were proposed as potential drug candidates for the treatment of prolactinoma. We further hypothesized possible mechanisms of drug action on MMQ cell viability through analyzing the PI3K/Akt signaling pathway and cell cycle arrest via flow cytometry and Western blotting.

DISCUSSION

We presented the transcriptomic landscape of prolactinoma through miRNA and mRNA-level data integration and proposed repurposed drug candidates based on this integration. We validated our findings through testing cell viability, cell cycle phases, and PI3K/Akt protein expressions. Effects of the drugs on cell cycle phases and inhibition of the PI3K/Akt pathway by all drugs gave us promising output for further studies using these drugs in the treatment of prolactinoma. This is the first study that reports miRNA-mediated repurposed drugs for prolactinoma treatment via in vitro experiments.

X-rays Actuate Anticancer Drugs: Opening New Vistas in Prodrug Therapy

Chemotherapy is the primary treatment modality employed in the clinic for the treatment of cancer. Despite proven clinical success, adverse side effects are one of the drawbacks of this approach. The prodrug strategy has emerged as an alternative approach with the aim of alleviating these drawbacks. Prodrug activation is typically achieved by either endogenous or exogenous triggers. Exogenous triggers like light are appealing as they are independent of inherent patient and/or cancer-type variations. However, tissue penetration depth remains the Achilles' heel of this approach. In this context, usage of X-rays as the external trigger with infinite tissue penetration depth opens up exciting prospects in prodrug activation strategies.

Sequential enzyme-activated macrotheranostic probe for selective tumor mitochondria targeting

Subcellular organelle targeted imaging and therapy are of enormous interest in cancer theranostics. However, the lack of tumor-selective organelle targeting has compromised their efficacy and safety. In this work, we found that the near-infrared (NIR) fluorophore hemicyanine (CyNH₂) can selectively target mitochondria with strong cytotoxicity through decreasing the mitochondrial membrane potential and increasing the intracellular reactive oxygen species (ROS) levels. A macrotheranostic probe (denoted as PLCy) based on conjugating CyNH₂ with an acetylated lysine group was developed with masked fluorescence and cytotoxicity, which could both be unmasked through sequential activation by cancer cells overexpressing histone deacetylases (HDACs) and cathepsin L (CTSL) enzymes for selective cancer cell mitochondria-targeted imaging and therapy. In vitro and in vivo studies confirmed that the specific fluorescence turn-on and toxicity were restored in cancer cells and efficiently inhibited tumor growth. This macrotheranostic probe with sequential enzyme activation and mitochondrial targeting is expected to have promising applications in imaging-guided cancer therapy with high specificity and efficiency. STATEMENT OF SIGNIFICANCE: To improve the targeting efficiency and enhance the anti-cancer activities of macrotheranostic probe. We designed macrotheranostic probe PLCy that can be activated via sequential enzymes for selective tumor mitochondria targeting. More importantly, the activated CyNH₂ can decrease the mitochondrial membrane potential and elevate the reactive oxygen species level in cancer cells without light irradiation, which can further induce apoptosis of tumor cells for chemotherapy. Therefore, the use of sequential enzyme activation and mitochondria targeting strategies in the context of enzymatic activation may provide a general strategy for organelle-targeted imaging and therapy with high specificity and efficiency.

Dual-locking nanoprobe based on hemicyanine for orthogonal stimuli-triggered precise cancer imaging and therapy

Currently, stimulus-responsive nanomedicines are usually activated by a single cancer-associated biomarker and utilize different image/therapeutic agents for cancer imaging/therapy, which restricts the specificity of nanomedicine and complicates their design. Herein, we report a novel dual-locking theranostic nanoprobe (DL-P) based on near-infrared (NIR) hemicyanine CyNH₂ with two orthogonal stimuli of cancer cell lysosomal pH (first "lock")- and lysosome-overexpressed cathepsin B (CTB, second "lock")-triggered NIR fluorescence turn-on and drug activation to improve the specificity of cancer imaging and therapy. The fluorescence of CyNH₂ was initially quenched due to intramolecular charge transfer (ICT) but could be selectively activated under the dual-key stimulation of lysosomal pH and CTB to liberate CyNH₂, resulting in strong NIR fluorescence turn-on for cancer imaging. Moreover, CyNH₂ caused mitochondrial dysfunction to inhibit cancer cell proliferation in the absence of laser irradiation, which can be used in cancer therapy. Compared with previously reported probes that respond to a single stimulus, this dual-locking nanoprobe that is responsive to two orthogonal stimuli triggers with integrated imaging and therapy function in a single agent exhibits increased selectivity and specificity, which provides a prospective strategy for precise cancer imaging and therapy.

Rational design of thioamide peptides as selective inhibitors of cysteine protease cathepsin L

Aberrant levels of cathepsin L (Cts L), a ubiquitously expressed endosomal cysteine protease, have been implicated in many diseases such as cancer and diabetes. Significantly, Cts L has been identified as a potential target for the treatment of COVID-19 due to its recently unveiled critical role in SARS-CoV-2 entry into the host cells. However, there are currently no clinically approved specific inhibitors of Cts L, as it is often challenging to obtain specificity against the many highly homologous cathepsin family cysteine proteases. Peptide-based agents are often promising protease inhibitors as they offer high selectivity and potency, but unfortunately are subject to degradation in vivo. Thioamide substitution, a single-atom O-to-S modification in the peptide backbone, has been shown to improve the proteolytic stability of peptides addressing this issue. Utilizing this approach, we demonstrate herein that good peptidyl substrates can be converted into sub-micromolar inhibitors of Cts L by a single thioamide substitution in the peptide backbone. We have designed and scanned several thioamide stabilized peptide scaffolds, in which one peptide, RS 1A, was stabilized against proteolysis by all five cathepsins (Cts L, Cts V, Cts K, Cts S, and Cts B) while inhibiting Cts L with >25-fold specificity against the other cathepsins. We further showed that this stabilized RS 1A peptide could inhibit Cts L in human liver carcinoma lysates (IC50 = 19 μM). Our study demonstrates that one can rationally design a stabilized, specific peptidyl protease inhibitor by strategic placement of a thioamide and reaffirms the place of this single-atom modification in the toolbox of peptide-based rational drug design.

Novel Non-Congeneric Derivatives of the Choline Kinase Alpha Inhibitor ICL-CCIC-0019

Choline kinase alpha (CHKA) is a promising target for the development of cancer therapeutics. We have previously reported ICL-CCIC-0019, a potent CHKA inhibitor with high cellular activity but with some unfavorable pharmacological properties. In this work, we present an active analogue of ICL-CCIC-0019 bearing a piperazine handle (CK146) to facilitate further structural elaboration of the pharmacophore and thus improve the biological profile. Two different strategies were evaluated in this study: (1) a prodrug approach whereby selective CHKA inhibition could be achieved through modulating the activity of CK146, via the incorporation of an ε-(Ac) Lys motif, cleavable by elevated levels of histone deacetylase (HDAC) and cathepsin L (CTSL) in tumour cells; (2) a prostate-specific membrane antigen (PSMA) receptor targeted delivery strategy. Prodrug (CK145) and PSMA-targeted (CK147) derivatives were successfully synthesized and evaluated in vitro. While the exploitation of CK146 in those two strategies did not deliver the expected results, important and informative structure-activity relationships were observed and have been reported.

Inhibitory Effect of a Glutamine Antagonist on Proliferation and Migration of VSMCs via Simultaneous Attenuation of Glycolysis and Oxidative Phosphorylation

Excessive proliferation and migration of vascular smooth muscle cells (VSMCs) contribute to the development of atherosclerosis and restenosis. Glycolysis and glutaminolysis are increased in rapidly proliferating VSMCs to support their increased energy requirements and biomass production. Thus, it is essential to develop new pharmacological tools that regulate metabolic reprogramming in VSMCs for treatment of atherosclerosis. The effects of 6-diazo-5-oxo-L-norleucine (DON), a glutamine antagonist, have been broadly investigated in highly proliferative cells; however, it is unclear whether DON inhibits proliferation of VSMCs and neointima formation. Here, we investigated the effects of DON on neointima formation in vivo as well as proliferation and migration of VSMCs in vitro. DON simultaneously inhibited FBS- or PDGF-stimulated glycolysis and glutaminolysis as well as mammalian target of rapamycin complex I activity in growth factor-stimulated VSMCs, and thereby suppressed their proliferation and migration. Furthermore, a DON-derived prodrug, named JHU-083, significantly attenuated carotid artery ligation-induced neointima formation in mice. Our results suggest that treatment with a glutamine antagonist is a promising approach to prevent progression of atherosclerosis and restenosis.

Strategies for Dodging the Obstacles in CAR T Cell Therapy

Chimeric antigen receptor (CAR) T cell therapy has offered cancer patients a new alternative therapeutic choice in recent years. This novel type of therapy holds tremendous promise for the treatment of various hematologic malignancies including B-cell acute lymphoblastic leukemia (B-ALL) and lymphoma. However, CAR T cell therapy has experienced its ups and downs in terms of toxicities and efficacy shortcomings. Adverse events such as cytokine release syndrome (CRS), neurotoxicity, graft rejection, on-target off-tumor toxicities, and tumor relapse have tied the rescuing hands of CAR T cell therapies. Moreover, in the case of solid tumor treatment, CAR T cell therapies have not yielded encouraging results mainly due to challenges such as the formidable network of the tumor microenvironments (TME) that operates in a suppressive fashion resulting in CAR T cell dysfunction. In this review, we tend to shine a light on emerging strategies and solutions for addressing the mentioned barriers. These solutions might dramatically help shorten the gap between a successful clinical outcome and the hope for it.

Transporters at the Interface between Cytosolic and Mitochondrial Amino Acid Metabolism

Mitochondria are central organelles that coordinate a vast array of metabolic and biologic functions important for cellular health. Amino acids are intricately linked to the bioenergetic, biosynthetic, and homeostatic function of the mitochondrion and require specific transporters to facilitate their import, export, and exchange across the inner mitochondrial membrane. Here we review key cellular metabolic outputs of eukaryotic mitochondrial amino acid metabolism and discuss both known and unknown transporters involved. Furthermore, we discuss how utilization of compartmentalized amino acid metabolism functions in disease and physiological contexts. We examine how improved methods to study mitochondrial metabolism, define organelle metabolite composition, and visualize cellular gradients allow for a more comprehensive understanding of how transporters facilitate compartmentalized metabolism.

Autophagy and salivary gland cancer: A putative target for salivary gland tumors

Salivary gland carcinomas are a group of heterogeneous tumors of different histological subtypes, presenting relatively low incidence but the entire variable of types. Although novel treatment options for salivary gland carcinomas patients' outcomes have improved, the treatment of this type of cancer is still not standardized. In addition, a significant number of patients, with a lack of optimal treatment strategies, have reduced survival. In the last two decades, a plethora of evidence pointed to the importance of autophagy, an essential catabolic process of cytoplasmatic component digestion, in cancer. In vitro and in vivo studies highlight the importance of autophagy in salivary gland carcinomas development as a tumor suppressor or promoter mechanism. Despite the potential of autophagy in salivary gland carcinomas development, no therapies are currently available that specifically focus on autophagy modulation in salivary gland carcinomas. In this review, we summarize current knowledge and clinical trials in regard to the interplay between autophagy and the development of salivary gland carcinomas. Autophagy manipulation may be a putative therapeutic strategy for salivary gland carcinomas patients.

Protease-activated prodrugs: strategies, challenges, and future directions

Proteases play critical roles in virtually all biological processes, including proliferation, cell death and survival, protein turnover, and migration. However, when dysregulated, these enzymes contribute to the progression of multiple diseases, with cancer, neurodegenerative disorders, inflammation, and blood disorders being the most prominent examples. For a long time, disease-associated proteases have been used for the activation of various prodrugs due to their well-characterized catalytic activity and ability to selectively cleave only those substrates that strictly correspond with their active site architecture. To date, versatile peptide sequences that are cleaved by proteases in a site-specific manner have been utilized as bioactive linkers for the targeted delivery of multiple types of cargo, including fluorescent dyes, photosensitizers, cytotoxic drugs, antibiotics, and pro-antibodies. This platform is highly adaptive, as multiple protease-labile conjugates have already been developed, some of which are currently in clinical use for cancer treatment. In this review, recent advancements in the development of novel protease-cleavable linkers for selective drug delivery are described. Moreover, the current limitations regarding the selectivity of linkers are discussed, and the future perspectives that rely on the application of unnatural amino acids for the development of highly selective peptide linkers are also presented.

The science of puromycin: From studies of ribosome function to applications in biotechnology

Puromycin is a naturally occurring aminonucleoside antibiotic that inhibits protein synthesis by ribosome-catalyzed incorporation into the C-terminus of elongating nascent chains, blocking further extension and resulting in premature termination of translation. It is most commonly known as a selection marker for cell lines genetically engineered to express a resistance transgene, but its additional uses as a probe for protein synthesis have proven invaluable across a wide variety of model systems, ranging from purified ribosomes and cell-free translation to intact cultured cells and whole animals. Puromycin is comprised of a nucleoside covalently bound to an amino acid, mimicking the 3′ end of aminoacylated tRNAs that participate in delivery of amino acids to elongating ribosomes. Both moieties can tolerate some chemical substitutions and modifications without significant loss of activity, generating a diverse toolbox of puromycin-based reagents with added functionality, such as biotin for affinity purification or fluorophores for fluorescent microscopy detection. These reagents, as well as anti-puromycin antibodies, have played a pivotal role in advancing our understanding of the regulation and dysregulation of protein synthesis in normal and pathological processes, including immune response and neurological function. This manuscript reviews the current state of puromycin-based research, including structure and mechanism of action, relevant derivatives, use in advanced methodologies and some of the major insights generated using such techniques both in the lab and the clinic.

Semiconducting Polymer Nanomaterials as Near-Infrared Photoactivatable Protherapeutics for Cancer

Cancer therapy is routinely performed in the clinic to cure cancer and control its progression, wherein therapeutic agents are generally used. To reduce side effects, protherapeutic agents that can be activated by overexpressed cancer biomarkers are under development. However, these agents still face certain extent of off-target activation in normal tissues, stimulating the interest to design external-stimuli activatable protherapeutics. In this regard, photoactivatable protherapeutic agents have been utilized for cancer treatments. However, because of the intrinsic features of photolabile moieties, most photoactivatable protherapeutic agents only respond to ultraviolet-visible light, limiting their in vivo applications. Thus, protherapeutic agents that can be activated by near-infrared (NIR) light with minimal phototoxicity and increased tissue penetration are highly desired.In this Account, we summarize our semiconducting polymer nanomaterials (SPNs) as NIR photoactivatable protherapeutic agents for cancer treatment. SPNs are transformed from π-conjugated polymers that efficiently convert NIR light into heat or singlet oxygen (¹O₂). With photothermal and photodynamic properties, SPNs can be directly used as photomedicine or serve as light transducers to activate heat or ¹O₂-responsive protherapeutic agents.The heat-activatable SPN-based protherapeutic agents are developed by loading or conjugating of SPNs with therapeutic agents (e.g., agonist, gene, and enzyme). For instance, photothermally triggered release of agonists specifically activates certain protein ion channels on the cellular membrane, leading to ion overinflux induced mitochondria dysfunction and consequently apoptosis of cancer cells. Moreover, photothermal activation of temperature-sensitive bromelain can promote the in situ degradation of collagens (the major components of extracellular matrix), resulting in an improved accumulation of agents in tumor tissues and thus amplified therapeutic outcome.The ¹O₂-activatable SPN-based protherapeutic agents are constructed through covalent conjugation of SPNs with caged therapeutic agents via hypoxia- or ¹O₂-cleavable linkers. Upon NIR photoirradiation, SPNs consume oxygen to generate ¹O₂, which leads to photodynamic therapy (PDT), and meanwhile breaks hypoxia- or ¹O₂-cleavable linkers for on-demand release and in situ activation of caged protherapeutic molecules (e.g., chemodrug, enzyme, and inhibitor). Such remote activation of SPN-based protherapeutic agents can be applied to induce DNA damage, ribonucleic acid degradation, inhibition of protein biosynthesis, or immune system activation in tumors of living animals. By synergizing PDT with NIR photoactivation of those biological actions, these protherapeutic agents effectively eliminate tumors and even fully inhibit tumor metastasis.This Account highlights the potential of SPNs for construction of versatile NIR photoactivatable protherapeutics to treat cancer at designated times and locations with high therapeutic outcome and precision.

Synthesis and evaluation of Nα,Nε-diacetyl-l-lysine-inositol conjugates as cancer-selective probes for metabolic engineering of GPIs and GPI-anchored proteins

Two myo-inositol derivatives having an Nα,Nε-diacetyl-l-lysine (Ac2Lys) moiety linked to the inositol 1-O-position through a self-cleavable linker and a metabolically stable 2-azidoethyl group linked to the inositol 3-O- and 4-O-positions, respectively, were designed and synthesized. The Ac2Lys moiety blocking the inositol 1-O-position required for GPI biosynthesis was expected to be removable by a combination of two enzymes, histone deacetylase (HDAC) and cathepsin L (CTSL), abundantly expressed in cancer cells, but not in normal cells, to transform these inositol derivatives into biosynthetically useful products with a free 1-O-position. As a result, it was found that these inositol derivatives could be incorporated into the glycosylphosphatidylinositol (GPI) biosynthetic pathway by cancer cells, but not by normal cells, to express azide-labeled GPIs and GPI-anchored proteins on cell surfaces. Consequently, this study has established a novel strategy and new molecular tools for selective metabolic labeling of cancer cells, which should be useful for various biological studies and applications.

Nanotherapeutics for Immuno-Oncology: A Crossroad for New Paradigms

With the rapid increase in the use of nanotechnology and immunotherapy for cancer management in the recent past, there are great implications for using nanotechnology in immuno-oncology. However, to deliver clinical success, the scientific and clinical rationale must be critically evaluated when applying nanotechnology to immuno-oncology challenges. This opinion article distinguishes between designing nanotherapeutics for immunotherapy and the past focus on the placement of chemotherapy agents in nanoparticles. We believe the integration of nanotechnology with cancer immunotherapy for nano-immunotherapeutics provides unique opportunities for both fields, paving the way for entirely new therapeutic paradigms. As a particular focus in our article, we envision the necessities and challenges of nanotechnology in the development of in situ cancer vaccines, immune checkpoint inhibitors, adoptive cell transfer, and bispecific antibody therapy.

A Review of Small Molecule Inhibitors and Functional Probes of Human Cathepsin L

Human cathepsin L belongs to the cathepsin family of proteolytic enzymes with primarily an endopeptidase activity. Although its primary functions were originally thought to be only of a housekeeping enzyme that degraded intracellular and endocytosed proteins in lysosome, numerous recent studies suggest that it plays many critical and specific roles in diverse cellular settings. Not surprisingly, the dysregulated function of cathepsin L has manifested itself in several human diseases, making it an attractive target for drug development. Unfortunately, several redundant and isoform-specific functions have recently emerged, adding complexities to the drug discovery process. To address this, a series of chemical biology tools have been developed that helped define cathepsin L biology with exquisite precision in specific cellular contexts. This review elaborates on the recently developed small molecule inhibitors and probes of human cathepsin L, outlining their mechanisms of action, and describing their potential utilities in dissecting unknown function.

The Deubiquitinase USP38 Promotes NHEJ Repair through Regulation of HDAC1 Activity and Regulates Cancer Cell Response to Genotoxic Insults

The DNA damage response (DDR) is essential for maintaining genome integrity. Mounting evidence reveals that protein modifications play vital roles in the DDR. Here, we show that USP38 is involved in the DDR by regulating the activity of HDAC1. In response to DNA damage, USP38 interacted with HDAC1 and specifically removed the K63-linked ubiquitin chain promoting the deacetylase activity of HDAC1. As a result, HDAC1 was able to deacetylate H3K56. USP38 deletion resulted in persistent focal accumulation of nonhomologous end joining (NHEJ) factors at DNA damage sites and impaired NHEJ efficiency, causing genome instability and sensitizing cancer cells to genotoxic insults. Knockout of USP38 rendered mice hypersensitive to irradiation and shortened survival. In addition, USP38 was expressed at low levels in certain types of cancers including renal cell carcinoma, indicating dysregulation of USP38 expression contributes to genomic instability and may lead to tumorigenesis. In summary, this study identifies a critical role of USP38 in modulating genome integrity and cancer cell resistance to genotoxic insults by deubiquitinating HDAC1 and regulating its deacetylation activity. SIGNIFICANCE: This study demonstrates that USP38 regulates genome stability and mediates cancer cell resistance to DNA-damaging therapy, providing insight into tumorigenesis and implicating USP38 as a potential target for cancer diagnosis.

Cysteine Cathepsins: Potential Applications in Diagnostics and Therapy of Malignant Tumors

Cysteine cathepsins are proteolytic enzymes involved in protein degradation in lysosomes and endosomes. Cysteine cathepsins have been also found in the tumor microenvironment during carcinogenesis, where they are implicated in proliferation, invasion and metastasis of tumor cells through the degradation of extracellular matrix, suppression of cell-cell interactions, and promotion of angiogenesis. In this regard, cathepsins can have a diagnostic value and represent promising targets for antitumor drugs aimed at inhibition of these proteases. Moreover, cysteine cathepsins can be used as activators of novel targeted therapeutic agents. This review summarizes recent discovered roles of cysteine cathepsins in carcinogenesis and discusses new trends in cancer therapy and diagnostics using cysteine cathepsins as markers, targets, or activators.

Multilayered Activatable Nanoprobe for Ultra-Bright Tumor Imaging

The development of tumor targeted probes with strong signal and high contrast is always challenging in cancer imaging. Here, a unique multilayered activatable nanoprobe (MAN) is prepared to fulfill this long-standing goal. MAN adopts a versatile layer-by-layer fabrication technique that sequentially assembles multifunctional polyelectrolytes onto nanoparticles via charge-charge interaction. Unlike the common one-probe-one-fluorochrome construct, MAN offers a dramatic fluorescence enhancement by transporting a large quantity of quenched fluorochromes for maximal signal and contrast. Excellent signal amplification and retention with negligible cytotoxicity is observed in cell study. Upon systemic injection into mice, MAN quickly accumulates in tumor and its fluorescent signal is turned on by proteases overexpressed in tumors, resulting in >700% tumor-to-normal-tissue contrast. This multilayered fabrication provides a simple and powerful universal platform to design sensitive tumor imaging probes.

Near-Infrared Photoactivatable Semiconducting Polymer Nanoblockaders for Metastasis-Inhibited Combination Cancer Therapy

Inhibition of protein biosynthesis is a promising strategy to develop new therapeutic modalities for cancers; however, noninvasive precise regulation of this cellular event in living systems has been rarely reported. In this study, a semiconducting polymer nanoblockader (SPN_B ) is developed that can inhibit intracellular protein synthesis upon near-infrared (NIR) photoactivation to synergize with photodynamic therapy (PDT) for metastasis-inhibited cancer therapy. SPN_B is self-assembled from an amphiphilic semiconducting polymer which is grafted with poly(ethylene glycol) conjugated with a protein biosynthesis blockader through a singlet oxygen (¹ O₂ ) cleavable linker. Such a designed molecular structure not only enables generation of ¹ O₂ under NIR photoirradiation for PDT, but also permits photoactivation of blockaders to terminate protein translation. Thereby, SPN_B exerts a synergistic action to afford an enhanced therapeutic efficacy in tumor ablation. More importantly, SPN_B -mediated photoactivation of protein synthesis inhibition precisely and remotely downregulates the expression levels of metastasis-related proteins in tumor tissues, eventually contributing to the complete inhibition of lung metastasis. This study thus proposes a photoactivatable protherapeutic design for metastasis-inhibited cancer therapy.

We're Not "DON" Yet: Optimal Dosing and Prodrug Delivery of 6-Diazo-5-oxo-L-norleucine

The broadly active glutamine antagonist 6-diazo-5-oxo-L-norleucine (DON) has been studied for 60 years as a potential anticancer therapeutic. Clinical studies of DON in the 1950s using low daily doses suggested antitumor activity, but later phase I and II trials of DON given intermittently at high doses were hampered by dose-limiting nausea and vomiting. Further clinical development of DON was abandoned. Recently, the recognition that multiple tumor types are glutamine-dependent has renewed interest in metabolic inhibitors such as DON. Here, we describe the prior experience with DON in humans. Evaluation of past studies suggests that the major impediments to successful clinical use included unacceptable gastrointestinal (GI) toxicities, inappropriate dosing schedules for a metabolic inhibitor, and lack of targeted patient selection. To circumvent GI toxicity, prodrug strategies for DON have been developed to enhance delivery of active compound to tumor tissues, including the CNS. When these prodrugs are administered in a low daily dosing regimen, appropriate for metabolic inhibition, they are robustly effective without significant toxicity. Patients whose tumors have genetic, metabolic, or imaging biomarker evidence of glutamine dependence should be prioritized as candidates for future clinical evaluations of novel DON prodrugs, given either as monotherapy or in rationally directed pharmacologic combinations. Mol Cancer Ther; 17(9); 1824-32. ©2018 AACR.

Smart Hybrid Nanocomposite for Photodynamic Inactivation of Cancer Cells with Selectivity

Photodynamic therapy has been efficiently applied for cancer therapy. Here, we have fabricated the folic acid (FA)- and pheophorbide A (PA)-conjugated FA/PA@Fe₃O₄ nanoparticle (smart hybrid nanocomposite, SHN) to enhance the photodynamic inactivation (PDI) of specific cancer cells. SHN coated with the PDI agent is designed to have selectivity for the folate receptor (FR) expressed on cancer cells. Structural characteristics and morphology of the fabricated MNPs were studied with X-ray diffraction and scanning electron microscopy. The photophysical properties of SHN were investigated with absorption, emission spectroscopies, and Fourier transform infrared spectroscopy. In addition, the magnetic property of Fe₃O₄ nanoparticle (MNP) can be utilized for the collection of SHNs by an external magnetic field. The photofunctionality was given by the photosensitizer, PA, which generates reactive oxygen species by irradiation of visible light. Generation of singlet oxygen was directly evaluated with time-resolved phosphorescence spectroscopy. Biocompatibility and cellular interaction of SHN were also analyzed by using various cancer cells, such as KB, HeLa, and MCF-7 cells which express different levels of FR on the surface. Cellular adsorption and the PDI effect of SHN on the various cancer cells in vitro were correlated well with the surface expression levels of FR, suggesting potential applicability of SHN on specific targeting and PDI of FR-positive cancers.

The multifaceted roles of tumor-associated proteases and harnessing their activity for prodrug activation

The role of proteases in cancer was originally thought to be limited to the breakdown of basement membranes and extracellular matrix (ECM), thereby promoting cancer cell invasion into surrounding normal tissues. It is now well understood that proteases play a much more complicated role in all stages of cancer progression and that not only tumor cells, but also stromal cells are an important source of proteases in the tumor microenvironment. Among all the proteolytic enzymes potentially associated with cancer, some proteases have taken on heightened importance due to their significant up-regulation and ability to participate at multiple stages of cancer progression and metastasis. In this review, we discuss some of the advances in understanding of the roles of several key proteases from different classes in the development and progression of cancer and the potential to leverage their upregulated activity for the development of novel targeted treatment strategies.

Introduction of the α-ketoamide structure: en route to develop hydrogen peroxide responsive prodrugs

New light on H₂O₂-activated prodrugs: the first α-ketoamide based prodrug opens up new alternatives for designing non-boron based H₂O₂-responsive promoieties.

Leveraging the elevated levels of hydrogen peroxide (H₂O₂) in cancer, inflammatory diseases and cardiovascular disorders, H₂O₂-activated promoieties have been widely used in drugs and biomaterials design. However, the overwhelming majority of the promoieties only share the common structure of a H₂O₂-responsive arylboronic acid/ester moiety with low diversity. We report here an unprecedented strategy to construct novel H₂O₂-responsive prodrugs based on an α-ketoamide structure. As a proof of concept, we designed and synthesized a panel of α-ketoamide based nitrogen mustard prodrugs, among which KAM-2 showed potent growth inhibitory activity and high selectivity toward cancer cells. The H₂O₂-trigged decomposition of KAM-2 was validated, and the DNA damaging and apoptosis promoting activity attributed to the released nitrogen mustard were demonstrated. Our work unveils α-ketoamide as a new scaffold for prodrug design and may quickly inspire future developments.

Tumor-Targeted Delivery of 6-Diazo-5-oxo-l-norleucine (DON) Using Substituted Acetylated Lysine Prodrugs

6-Diazo-5-oxo-l-norleucine (DON) is a glutamine antagonist with robust anticancer efficacy; however, its therapeutic potential was hampered by its biodistribution and toxicity to normal tissues, specifically gastrointestinal (GI) tissues. To circumvent DON's toxicity, we synthesized a series of tumor-targeted DON prodrugs designed to circulate inert in plasma and preferentially activate over DON in tumor. Our best prodrug 6 (isopropyl 2-(6-acetamido-2-(adamantane-1-carboxamido)hexanamido)-6-diazo-5-oxohexanoate) showed stability in plasma, liver, and intestinal homogenates yet was readily cleaved to DON in P493B lymphoma cells, exhibiting a 55-fold enhanced tumor cell-to-plasma ratio versus that of DON and resulting in a dose-dependent inhibition of cell proliferation. Using carboxylesterase 1 knockout mice that were shown to mimic human prodrug metabolism, systemic administration of 6 delivered 11-fold higher DON exposure to tumor (target tissue; AUC_{0- t} = 5.1 nmol h/g) versus GI tissues (toxicity tissue; AUC_{0- t} = 0.45 nmol h/g). In summary, these studies describe the discovery of a glutamine antagonist prodrug that provides selective tumor exposure.

Azo-based near-infrared fluorescent theranostic probe for tracking hypoxia-activated cancer chemotherapy in vivo

A novel azo-based near-infrared fluorescent therabostic probe activated by hypoxia is applied to real-time visualization of drug delivery in vivo.