Significance of Specific Oxidoreductases in the Design of Hypoxia-Activated Prodrugs and Fluorescent Turn Off–On Probes for Hypoxia Imaging

Toxicity, Half-Life and Antitumor Activity of Phenyl 4-(2-Oxo-3-alkylimidazolidin-1-yl)benzenesulfonates as Novel Antimitotic CYP1A1-Targeted Prodrugs in Female Mouse Models

Background/Objectives: Chemoresistance of breast cancers (BCs) is a major impediment to current chemotherapeutics that urges the development of new drugs and new therapeutic approaches. To that end, phenyl 4-(2-oxo-3-alkylimidazolidin-1-yl)benzenesulfonates (PAIB-SOs) were recently prepared to fulfill some of the unmet needs with classic chemotherapeutics. PAIB-SOs are prodrugs bioactivated into potent antimitotics by the cytochrome P450 1A1 (CYP1A1), which is a frequent enzyme in resistant BC cells, but mostly missing in normal cells. Our screening program studies of PAIB-SO chemolibraries selected three prototypical PAIB-SOs as antimitotic prodrugs amenable for studies using BC animal models. Methods: Healthy female CD1® IGS mice were treated with three prototypical PAIB-SOs, namely CEU-835, -934, and -938, for the determination of their toxicity and half-lives. Moreover, MCF7 tumor-bearing CD1-Foxn1nu Nude female mice were treated with the three prototypical PAIB-SOs for the determination of their antitumor activity. Results: Herein, we show that multi-intravenous administrations of CEU-835, -934, and -938 at their maximal solubilities are well tolerated in healthy female CD1® IGS mice, as depicted by the evaluation of distress behaviors, organ necropsy, total blood cell count, and histology. Moreover, the half-life of CEU-835, -934, and -938 administered intravenously in healthy CD1® IGS female mice were 8.1, 23.2, and 21.5 h, respectively. Finally, their intravenous administrations of CEU-934 and -938 decreased MCF7 tumor growth as efficiently as paclitaxel in MCF7 tumor-bearing CD1-Foxn1nu Nude mouse model. Conclusions: overall, our study demonstrated for the first time that pentyl-bearing PAIB-SOs are new CYP1A1-dependent prodrugs efficiently decrease breast cancer tumor growth, and show no side effects at their pharmacological concentration in mouse models.

Nitroaromatic-based triazene prodrugs to target the hypoxic microenvironment in glioblastoma

Hypoxia is a hallmark of the glioblastoma multiforme microenvironment and represents a promising therapeutic target for cancer treatment. Herein, we report nitroaromatic-based triazene prodrugs designed for selective activation by tumoral endogenous reductases and release of the cytotoxic methyldiazonium ion via a self-immolative mechanism. While compounds bearing a 2-nitrofuran bioreductive group were more efficiently activated by nitroreductases, 4-nitrobenzyl prodrugs 1b, 1d and 1e elicited a more pronounced cytotoxic effect against LN-229 and U-87 MG glioblastoma cell lines under hypoxic conditions when compared to temozolomide (TMZ), the golden standard for glioblastoma treatment. This cytotoxic response aligns with the increased apoptosis levels in LN-229 cells and senescence induction in U-87 MG cells, promoted by prodrugs 1d and 1e, under hypoxic conditions. These results highlight the potential of these hypoxia-activated nitroaromatic-based triazene prodrugs for selective delivery of the cytotoxic methyldiazonium ion and support further optimization to provide a safer alternative for glioblastoma treatment.

Gene expression and DNA methylation changes in response to hypoxia in toxicant-adapted Atlantic killifish (Fundulus heteroclitus)

Coastal fish populations are threatened by multiple anthropogenic impacts, including the accumulation of industrial contaminants and the increasing frequency of hypoxia. Some populations of the Atlantic killifish (Fundulus heteroclitus), like those in New Bedford Harbor (NBH), Massachusetts, USA, have evolved a resistance to dioxin-like polychlorinated biphenyls (PCBs) that may influence their ability to cope with secondary stressors. To address this question, we compared hepatic gene expression and DNA methylation patterns in response to mild or severe hypoxia in killifish from NBH and Scorton Creek (SC), a reference population from a relatively pristine environment. We hypothesized that NBH fish would show altered responses to hypoxia due to trade-offs linked to toxicant resistance. Our results revealed substantial differences between populations. SC fish demonstrated dose-dependent changes in gene expression in response to hypoxia, while NBH fish exhibited a muted transcriptional response to severe hypoxia. Interestingly, NBH fish showed significant DNA methylation changes in response to hypoxia, while SC fish did not exhibit notable epigenetic alterations. These findings suggest that toxicant-adapted killifish may face trade-offs in their molecular response to environmental stress, potentially impacting their ability to survive severe hypoxia in coastal habitats. Further research is needed to elucidate the functional implications of these epigenetic modifications and their role in adaptive stress responses.

Synthesis and Characterization of Novel Co(III)/Ru(II) Heterobimetallic Complexes as Hypoxia-Activated Iron-Sequestering Anticancer Prodrugs

Heterobimetallic complexes of an ambidentate deferiprone derivative, 3-hydroxy-2-methyl-1-(3-((pyridin-2-ylmethyl)amino)propyl)pyridin-4(1H)-one (PyPropHpH), incorporating an octahedral [Co(4N)]3+ (4N = tris(2-aminoethyl)amine (tren) or tris(2-pyridylmethyl)amine (tpa)) and a half-sandwich type [(η6-p-cym)Ru]2+ (p-cym = p-cymene) entity have been synthesized and characterized by various analytical techniques. The reaction between PyPropHpH and [Co(4N)Cl]Cl2 resulted in the exclusive (O,O) coordination of the ligand to Co(III) yielding [Co(tren)PyPropHp](PF6)2 (1) and [Co(tpa)PyPropHp](PF6)2 (2). This binding mode was further supported by the molecular structure of [Co(tpa)PyPropHp]2(ClO4)3(OH)·6H2O (5) and [Co(tren)PyPropHpH]Cl(PF6)2·2H2O·C2H5OH (6), respectively, obtained via the slow evaporation of the appropriate reaction mixtures and analyzed using X-ray crystallography. Subsequent treatment of 1 or 2 with [Ru(η6-p-cym)Cl2]2 in a one-pot reaction afforded the corresponding heterobimetallic complexes, [Co(tren)PyPropHp(η6-p-cym)RuCl](PF6)3 (3) and [Co(tpa)PyPropHp(η6-p-cym)RuCl](PF6)3 (4), in which the piano-stool Ru core is coordinated by the (N,N) chelating set of the ligand. Cyclic voltammetric measurements revealed that the tpa complexes can be reduced at less negative potentials, suggesting their capability to be bioreductively activated under hypoxia (1% O2). Hypoxia activation of 2 and 4 was demonstrated by cytotoxicity studies on the MCF-7 human breast cancer cell line. PyPropHpH was shown to be a typical iron-chelating anticancer agent, raising the mRNA levels of TfR1, Ndrg1 and p21. Further qRT-PCR studies provided unambiguous evidence for the bioreduction of 2 after 72 h incubation under hypoxia, in which the characteristic gene induction profile caused by the liberated iron-sequestering PyPropHpH was observed.

Tailoring Drug Release Kinetics by the Design and Optimization of Substituents in Azobenzene Molecules in the Photosensitive Liposomal System

A light-sensitive moiety, e.g., azobenzene, for the light-sensitive liposomal drug carrier has shown advantages as an advanced drug delivery system in site-specific smart therapy due to its reversible photoisomerization characteristics. In this work, a series of 4-position-cholesterol-functionalized azobenzene derivatives with 4'-position substituted pyridine, quinoline, isoquinoline, triethylamine, or ethylenediamine were synthesized, and the relationship between the molecular structure and drug release behaviors was clarified. We found that the charge and electrophilicity of substituents were two important factors (expressed as the characteristic time) that can precisely regulate the isomerization ratio in the liposomal system. There was an approximately linear correlation between the characteristic time of photoisomerization and the fitted first-order constant of photoinduced drug release rate. The photoinduced drug release could be achieved at the desired time and in an appropriate amount by tailoring the substituents at the 4'-position of azobenzene-cholesterol derivatives.

Recent Advances in the Application of Nitro(het)aromatic Compounds for Treating and/or Fluorescent Imaging of Tumor Hypoxia

This review delves into recent advancements in the field of nitro(het)aromatic bioreductive agents tailored for hypoxic environments. These compounds are designed to exploit the low-oxygen conditions typically found in solid tumors, making them promising candidates for targeted cancer therapies. Initially, this review focused on their role as gene-directed enzyme prodrugs, which are inert until activated by specific enzymes within tumor cells. Upon activation, these prodrugs undergo chemical transformations that convert them into potent cytotoxic agents, selectively targeting cancerous tissue while sparing healthy cells. Additionally, this review discusses recent developments in prodrug conjugates containing nitro(het)aromatic moieties, designed to activate under low-oxygen conditions within tumors. This approach enhances their efficacy and specificity in cancer treatment. Furthermore, this review covers innovative research on using nitro(het)aromatic compounds as fluorescent probes for imaging hypoxic tumors. These probes enable non-invasive visualization of low-oxygen regions within tumors, providing valuable insights for the diagnosis, treatment planning, and monitoring of therapeutic responses. We hope this review will inspire researchers to design and synthesize improved compounds for selective cancer treatment and early diagnostics.

Nitroreductase-Triggered Fluorophore Labeling of Cells and Tissues under Hypoxia

Several reductases, including nitroreductase, are upregulated under hypoxic conditions characterized by an oxygen-deficient microenvironment. Given that hypoxia is a prominent feature of solid tumors, our investigation focused on developing a bioconjugative probe designed for staining tissue under hypoxic conditions, particularly activated by nitroreductase. This probe, developed using our trigger-release-bioconjugation system rooted in the ortho-quinone methide chemistry, exhibited selective activation by nitroreductase and fluorophore labeling within mitochondria and endoplasmic reticulum. As a result, it displayed sustained fluorescence that persisted even after washing steps in cells and tissues. We applied this innovative probe to stain mouse kidney tissue in an acute kidney injury model induced by inadequate oxygen supply. Among various organ tissues examined, only kidney tissue showed significantly higher fluorescence in the injury model compared with the control tissue, as revealed by two-photon microscopic imaging. This research presents a promising avenue for the development of practical staining agents for image-guided tumor surgery.

Liposome encapsulated polydopamine nanoparticles: Enhancing ferroptosis and activating hypoxia prodrug activity

The short lifespan of active oxygen species and depressed O2 level during ferroptosis treatment in tumor cells weaken ferroptosis therapy. How to improve the utilization efficiency of active oxygen species generated in real time is pivotal for anticancer treatment. Herein, the tirapazamine (TPZ) loaded polydopamine-Fe nanoparticles (PDA-Fe-TPZ) was modified with unsaturated liposome (Lip), which was constructed to overcome the drawbacks of traditional ferroptosis therapy. The Lip@PDA-Fe-TPZ nanoliposomes can react with H2O2 to produce •OH by Fenton reaction, which then attacks Lip and transforms into radical intermediate (L•) and phospholipid peroxide radical (LOO•) to avoid the annihilation of •OH. The introduced Lip enhances lipid peroxidation and promotes oxygen consumption, resulting in increased hypoxia at tumor site. The introduced TPZ can be triggered by reductase in tumor cells under hypoxia, which can reduce to transient oxidative free radicals by reductase enzymes and destroy the structure of the surrounding biomacromolecules, thus achieving the synergistic treatment of ferroptosis and chemotherapy. In this work, we organically combined enhanced ferrroptosis with hypoxic activated chemotherapy to achieve efficient and specific tumor killing effect, which can sever as a promising treatment of cancer in the future.

Ratiometric near-infrared fluorescent probe for nitroreductase activity enables 3D imaging of hypoxic cells within intact tumor spheroids

Fluorescent molecular probes that report nitroreductase activity have promise as imaging tools to elucidate the biology of hypoxic cells and report the past hypoxic history of biomedical tissue. This study describes the synthesis and validation of a "first-in-class" ratiometric, hydrophilic near-infrared fluorescent molecular probe for imaging hypoxia-induced nitroreductase activity in 2D cell culture monolayers and 3D multicellular tumor spheroids. The probe's molecular structure is charge-balanced and the change in ratiometric signal is based on Förster Resonance Energy Transfer (FRET) from a deep-red, pentamethine cyanine donor dye (Cy5, emits ∼660 nm) to a linked near-infrared, heptamethine cyanine acceptor dye (Cy7, emits ∼780 nm). Enzymatic reduction of a 4-nitrobenzyl group on the Cy7 component induces a large increase in Cy7/Cy5 fluorescence ratio. The deep penetration of near-infrared light enables 3D optical sectioning of intact tumor spheroids, and visualization of individual hypoxic cells (i.e., cells with raised Cy7/Cy5 ratio) as a new way to study tumor spheroids. Beyond preclinical imaging, the near-infrared fluorescent molecular probe has high potential for ratiometric imaging of hypoxic tissue in living subjects.

In Vitro Inhibition of Xanthine Oxidase Purified from Arthritis Serum Patients by Nanocurcumin and Artemisinin Active Compounds

Curcumin and artemisinin are commonly used in traditional East Asian medicine. In this study, we investigated the inhibitory effects of these active compounds on xanthine oxidase (XO) using allopurinol as a control. XO was purified from the serum of arthritis patients through ammonium sulfate precipitation (65%) and ion exchange chromatography on diethylaminoethyl (DEAE)-cellulose. The specific activity of the purified enzyme was 32.5 U/mg protein, resulting in a 7-fold purification with a yield of 66.8%. Molecular docking analysis revealed that curcumin had the strongest interaction energy with XO, with a binding energy of -9.28 kcal/mol. The amino acid residues Thr1077, Gln762, Phe914, Ala1078, Val1011, Glu1194, and Ala1079 were located closer to the binding site of curcumin than artemisinin, which had a binding energy of -7.2 kcal/mol. In vitro inhibition assays were performed using nanocurcumin and artemisinin at concentrations of 5, 10, 15, 20, and 25 µg/mL. Curcumin inhibited enzyme activity by 67-91%, while artemisinin had a lower inhibition ratio, which ranged from 40-70% compared to allopurinol as a control.

Hypoxia and Cancer: From Bench to Bedside

This Special Issue of Cancers (two original articles, five reviews), presented by international experts in tumor hypoxia, focuses on the role of hypoxia, or low oxygen levels, in the development and progression of cancer [...].

smProdrugs: A repository of small molecule prodrugs

In modern drug discovery and development, the prodrug approach has become a crucial strategy for enhancing the pharmacokinetic profiles of drugs. A prodrug is a chemical compound, which gets metabolized into a pharmacologically active form (drug) inside the body after its administration. In the current work, we report 'smProdrugs' (http://cheminfolab.in/databases/prodrug/), which is one of the first exclusive databases on small molecule prodrugs. It stores the structures, physicochemical properties and experimental ADMET data manually curated from literature. SmProdrugs lists 626 small molecule prodrugs and their active compounds with the above mentioned experimental data from 1808 research articles and 61 patents have been stored. The information page of each record gives the structures and properties of the prodrug and the active drug side by side which makes it easy for the user to instantly compare them. The structural modifications in the prodrug/active drugs are highlighted in a different colour for easy comparison. Experimental data has been curated from the downloaded PubMed and patent articles and were catalogued in a tabular form with more than 25 fields under sub-sections i) name and structures of the prodrugs and their active compounds, ii) mode of activation of the prodrug and enzyme/biocatalyst involved in the conversion, iii) indications/disease, iv) pharmacological target, v) experimental pharmacokinetic properties such as solubility, absorption, volume of distribution, half-life, clearance etc. and vi) information on the purpose/gain from the prodrug strategies. Considering the ever expanding utility of the prodrug approach smProdrugs will be of great use to the scientific community working on rational design of small molecule prodrugs.

Nanomedicines with high drug availability and drug sensitivity overcome hypoxia-associated drug resistance

Tumor hypoxia heterogeneity, a hallmark of the tumor microenvironment, confers resistance to conventional chemotherapy due to insufficient drug availability and drug sensitivity in hypoxic regions. To overcome these challenges, we develope a nanomedicine, NP_HPaPN, constructed with hyaluronic acid (HA) grafted with cisplatin prodrug and PEG-azobenzene for hypoxia-responsive PEG shell deshielding and loaded with a DNA damage repair inhibitor (NERi). After arriving at the tumor site, NP_HPaPN deshields the PEG shell in response to hypoxia due to the enzymolysis of azobenzene and thus exposes HA. The exposed HA binds to the highly expressed CD44 on cisplatin-resistant tumor cells and mediates drug internalization, thus increasing drug availability to hypoxic tumor cells. After intracellular hyaluronidase-mediated cleavage, the HA NPs release the cisplatin prodrug and NERi, and cause enhanced DNA damage and consequent cell death, thus enhancing the drug sensitivity of hypoxic tumor cells. Eventually, NP_HPaPN achieves distinct tumor growth suppression with an ∼84.4% inhibition rate.