Amonafide-based H2O2-responsive theranostic prodrugs: Exploring the correlation between H2O2 level and anticancer efficacy

Leveraging the elevated hydrogen peroxide (H2O2) levels in cancer cells, H2O2-activated prodrugs have emerged as promising candidates for anticancer therapy. Notably, the efficacy of these prodrugs is influenced by the varying H2O2 levels across different cancer cell types. In this context, we have developed a novel H2O2-activated prodrug, PBE-AMF, which incorporates a phenylboronic ester (PBE) motif. Upon H2O2 exposure, PBE-AMF liberates the fluorescent and cytotoxic molecule amonafide (AMF), functioning as a theranostic agent. Our studies with PBE-AMF have demonstrated a positive correlation between intracellular H2O2 concentration and anticancer activity. The breast cancer cell line MDA-MB-231, characterized by high H2O2 content, showed the greatest susceptibility to this prodrug. Subsequently, we replaced the PBE structure with phenylboronic acid (PBA) to obtain the prodrug PBA-AMF, which exhibited enhanced stability, aqueous solubility, and tumor cell selectivity. This selectivity is attributed to its affinity for sialic acid, which is overexpressed on the surfaces of cancer cells. In vitro assays confirmed that PBA-AMF potently and selectively inhibited the proliferation of MDA-MB-231 cells, while sparing non-cancerous MCF-10A cells. Mechanistic investigations indicated that PBA-AMF impedes tumor proliferation by inhibiting DNA synthesis, reducing ATP levels, inducing apoptosis, and arresting the cell cycle. Our work broadens the range of small molecule H2O2-activated anticancer theranostic prodrugs, which are currently limited in number. We anticipate that the applications of PBA-AMF will extend to a wider spectrum of tumors and other diseases associated with increased H2O2 levels, thereby offering new horizons in cancer diagnostics and treatment.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Functional Upgrading of an Organo-Ir(III) Complex to an Organo-Ir(III) Prodrug as a DNA Damage-Responsive Autophagic Inducer for Hypoxic Lung Cancer Therapy

The efficiency of nitrogen mustards (NMs), among the first chemotherapeutic agents against cancer, is limited by their monotonous mechanism of action (MoA). And tumor hypoxia is a significant obstacle in the attenuation of the chemotherapeutic efficacy. To repurpose the drug and combat hypoxia, herein, we constructed an organo-Ir(III) prodrug, IrCpNM, with the composition of a reactive oxygen species (ROS)-inducing moiety (Ir-arene fragment)-a hypoxic responsive moiety (azo linker)-a DNA-alkylating moiety (nitrogen mustard), and realized DNA damage response (DDR)-mediated autophagy for hypoxic lung cancer therapy for the first time. Prodrug IrCpNM could upregulate the level of catalase (CAT) to catalyze the decomposition of excessive H2O2 to O2 and downregulate the expression of the hypoxia-inducible factor (HIF-1α) to relieve hypoxia. Subsequently, IrCpNM initiates the quadruple synergetic actions under hypoxia, as simultaneous ROS promotion and glutathione (GSH) depletion to enhance the redox disbalance and severe oxidative and cross-linking DNA damages to trigger the occurrence of DDR-mediated autophagy via the ATM/Chk2 cascade and the PIK3CA/PI3K-AKT1-mTOR-RPS6KB1 signaling pathway. In vitro and in vivo experiments have confirmed the greatly antiproliferative capacity of IrCpNM against the hypoxic solid tumor. This work demonstrated the effectiveness of the DNA damage-responsive organometallic prodrug strategy with the microenvironment targeting system and the rebirth of traditional chemotherapeutic agents with a new anticancer mechanism.

Dual-Stimuli-Activatable Hybrid Prodrug for the Self-Immolative Delivery of an Anticancer Agent and Hydrogen Sulfide with Turn-On Fluorescence

Stimuli-responsive fluorogenic prodrugs are advantageous for the targeted drug delivery enabling real-time non-invasive monitoring with turn-on fluorescence. We report herein the dual-stimuli (ROS and CA)-responsive thiocarbamate-based prodrug (AM-TCB) for the turn-on fluorogenic delivery of the naphthalimide-based anticancer agent amonafide along with the gasotransmitter hydrogen sulfide (H2 S). A carbamate-based prodrug AM-CB was also designed, capable of releasing the anticancer agent amonafide without any H2 S. The prodrugs were synthesized using multi-step organic synthesis. UV-Vis and fluorescence spectroscopic studies revealed selective reactivity of the boronate ester group of prodrugs towards ROS (primarily H2 O2 ) with the release of amonafide and COS/CO2 via self-immolative processes. Hydrolysis of the generated COS by carbonic anhydrase (CA) produces H2 S. While the prodrug AM-TCB retained the anticancer activity of free amonafide in cancer cells (MDA-MB-231 and HeLa), unlike amonafide, it enhanced the cellular viability of the non-malignant cells (HEK-293). Fluorescence imaging in HeLa cells revealed the simultaneous delivery of the anticancer agent and H2 S from AM-TCB with turn-on fluorescence. Western blot studies further revealed the cytoprotective effects of the released H2 S from AM-TCB. The present adjuvant strategy therefore would be helpful in future for ameliorating the anticancer drug-induced side-effects.

Novel 1,8-Naphthalimide Derivatives As Antitumor Agents and Potent Demethylase Inhibitors

Functional 1,8-naphthalimide derivatives are rapidly developing in the field of anticancer research. Herein, we designed and synthesized a series of naphthalimide derivatives with different substituents. Interestingly, 1,8-naphthalimide derivatives 1 and 7 inhibited a human demethylase FTO (the fat mass and obesity-associated protein). Computer simulation studies further indicated that 1 and 7 entered the FTO's structural domain II binding pocket through hydrophobic and hydrogen bonding interactions. Anticancer mechanism studies showed that 1 and 7 induced DNA damage and autophagic cell death in A549 cells. The high antiproliferative activity of 1 and 7 was further confirmed by 3D multicellular A549 tumor spheroid assays. This study focuses on the cytotoxicity and mode of action of naphthalimide derivatives, which not only have potential anticancer activity but also are potent demethylase inhibitors.

Nano-assemblies from J-aggregated dyes to improve the selectivity of a H2S-activatable photosensitizer

We report J-aggregates of a boron dipyrromethene derivative (BDP-Nit) as an H₂S-activatable nano-photosensitizer. The closely packed BDP-Nit in J-aggregates exhibits high selectivity to H₂S over biothiols to produce an active photosensitizer.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

A Rational Designed Bioorthogonal Surface-Enhanced Raman Scattering Nanoprobe for Quantitatively Visualizing Endogenous Hydrogen Sulfide in Single Living Cells

Understanding the biology of gasotransmitters in living cells is of significance but remains challenging due to largely a lack of robust molecular probes. Here, we present the facile design and synthesis of a bioorthogonal Raman probe, 4-azidobenzenethiol (4-ABT), for endogenous hydrogen sulfide (H₂S) imaging in single live cells by surface-enhanced Raman scattering (SERS). 4-ABT bears a thiol group and an azido group in the benzene ring, thus affording a bifunction to firmly bind to the gold nanoparticle surface and specifically respond to H₂S. Moreover, the 4-ABT-based SERS nanoprobe shows a dose-dependent spectral change in the cellular Raman-silent region upon reacting with H₂S, allowing ratiometric quantitative detection and visualization of intracellular H₂S status without bio-interference. The ease of fabrication and superior performance of the novel SERS nanoprobe demonstrate its promising application in studies of H₂S-related signaling networks.

Biotinylated curcumin as a novel chemosensitizer enhances naphthalimide-induced autophagic cell death in breast cancer cells

Achieving selective release of chemical anticancer agents and improving therapeutic efficacy has always been a hot spot in the field of cancer research, yet how to achieve this remains a great challenge. In this work, we constructed a novel chemical anticancer agent (named MCLOP) by introducing naphthalimide into the skeleton of methylene blue (MB). Under the stimulation by cellular hypochlorous acid (HClO) and visible light, selective release of active naphthalimide can be achieved within breast cancer cell lines, the release process of which can be tracked visually using near-infrared fluorescence of MB (685 nm). More importantly, we developed biotinylated curcumin (Cur-Bio) as a new chemosensitizer, which significantly enhanced the ability of MCLOP to induce autophagic cell death of breast cancer cells. This synergistic treatment strategy exhibited an excellent anti-proliferation effect on breast cancer cells in vitro, three-dimensional (3D) cell sphere model, and mouse tumor model in vivo. This work provides a new strategy for the treatment of breast cancer and also opens new opportunities for the efficient treatment of cancer with curcumin-based chemosensitizer.

A naphthalimide-based peptide conjugate for concurrent imaging and apoptosis induction in cancer cells by utilizing endogenous hydrogen sulfide

The excessive production of endogenous hydrogen sulfide (H2S) in cancer cells leads to enhanced tumor growth and metastasis. On the other hand, decreased endogenous H2S suppresses tumor growth. The reported approaches for inhibiting tumor growth are selective silencing of the tumor-promoting genes and pharmacological inhibition of these proteins. To enhance the antitumor efficacy of frontline chemotherapeutic agents, herein, we synthesized a highly sensitive endogenous H2S responsive fluorescent probe, i.e., a hydrogen sulfide-sensing naphthalimide-based peptide conjugate (HSNPc), which showed selective inhibition of proliferation of cancer cells due to apoptosis induction. Furthermore, HSNPc suppressed the glycolytic reserve, a critical energy source for the proliferation of cancer cells. HSNPc also decreased the Young's modulus of HeLa cells compared to the control cells, which demonstrated a direct relation between cell apoptosis and cell stiffness. Taken together, we demonstrated the dual function of detection and killing of cancer cells by HSNPc that can be likened to a theranostic role.

A phenothiazine-based turn-on fluorescent probe for the selective detection of hydrogen sulfide in food, live cells and animals

In this work, a phenothiazine-based fluorescent probe (PR) has been developed for the selective detection of hydrogen sulfide (H₂S) in biosystems and monitoring H₂S produced in the food spoilage process. The nucleophilic attack of H₂S on the CC double bond of PRvia a Michael addition interdicted the ICT process to trigger 34-fold enhancement of the fluorescence emission. PR featured high selectivity and sensitivity (1.8 μM), low cytotoxicity and reliability at physiological pH. "Naked-eye" monitoring of H₂S produced in the food spoilage process using PR was successfully accomplished. The preliminary fluorescence imaging studies showed that PR is suitable for the visualization of exogenous and endogenous H₂S in living cells and live animals. Moreover, PR has been successfully applied to the visualization of H₂S generation in an inflammation model. The results indicated that PR is an effective tool to monitor H₂S production in the fields of biomedicine and food safety.

Mitochondria-targeted Pt(IV) prodrugs conjugated with an aggregation-induced emission luminogen against breast cancer cells by dual modulation of apoptosis and autophagy inhibition

Theranostic anticancer agents with dual functions of diagnosis and therapy are in highly demand for breast cancer. Herein, a triphenylphosphonium (TPP)-decorated aggregation-induced emission (AIE)-based Pt(IV) prodrug ACPt was developed, which exhibited superior anticancer performance with novel anticancer mechanism of dual modulation of apoptosis and autophagy inhibition. The experimental data showed that ACPt induced increased reactive oxygen species (ROS), and decreased mitochondrial membrane potential (MMP). The morphology and function of mitochondria were also severely damaged and ACPt showed strong inhibition to both mitochondrial and glycolytic bioenergetics. Moreover, DNA damage and cell cycle arrest in the S-phase were also observed after the ACPt treatment, eventually leading to the apoptosis and autophagy inhibition of cancer cells. Furthermore, ACPt also indicated excellent anti-proliferation activity in 3D multicellular tumor spheroids (MCTSs), suggesting the potential to inhibit solid tumors in vivo. Our observation demonstrated that ACPt could serve as a promising anticancer theranostic agent toward breast cancers for prodrug activation monitoring and image-guided chemotherapy.

A self-immolated fluorogenic agent triggered by H2S exhibiting potential anti-glioblastoma activity

Glioblastoma is the most common and aggressive type of malignant brain tumor with poor survival and limited therapeutic options. Theranostic anticancer agents with dual functions of diagnosis and therapy are highly attractive. Self-immolation reaction is a promising approach for theranostic prodrugs triggered by the tumor microenvironment. Overexpression of hydrogen sulfide (H₂S) in glioma cells becomes a potential stimulus for activating prodrugs. Herein, a novel H₂S responsive agent (SNF) containing amonafide (ANF), a self-immolative linker and a trigger group has been developed for imaging and chemotherapy in living cells. SNF exhibited high selectivity and sensitivity towards H₂S and also showed excellent lysosome-targeted capability. The activated SNF could translocate to the nucleus, causing DNA damage and blocking the cell cycle. More mechanistic studies indicated that SNF altered the mitochondrial membrane potential and induced autophagy in human glioblastoma-astrocytoma (U87MG). In addition, 3D multicellular U87MG tumor spheroids were used to further confirm the active drug release and high anti-proliferative activity of SNF. This approach may provide a general strategy for developing H₂S-triggered prodrugs for synergic cancer therapy.