Aspartic vinyl sulfones: Inhibitors of a caspase-3-dependent pathway

Modeling Necroptotic and Pyroptotic Signaling in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae is the paradigm of a eukaryotic model organism. In virtue of a substantial degree of functional conservation, it has been extensively exploited to understand multiple aspects of the genetic, molecular, and cellular biology of human disease. Many aspects of cell signaling in cancer, aging, or metabolic diseases have been tackled in yeast. Here, we review the strategies undertaken throughout the years for the development of humanized yeast models to study regulated cell death (RCD) pathways in general, and specifically, those related to innate immunity and inflammation, with an emphasis on pyroptosis and necroptosis. Such pathways involve the assembly of distinct modular signaling complexes such as the inflammasome and the necrosome. Like other supramolecular organizing centers (SMOCs), such intricate molecular arrangements trigger the activity of enzymes, like caspases or protein kinases, culminating in the activation of lytic pore-forming final effectors, respectively, Gasdermin D (GSDMD) in pyroptosis and MLKL in necroptosis. Even though pathways related to those governing innate immunity and inflammation in mammals are missing in fungi, the heterologous expression of their components in the S. cerevisiae model provides a "cellular test tube" to readily study their properties and interactions, thus constituting a valuable tool for finding novel therapies.

Design and testing of selective inactivators against an antifungal enzyme target

Systemic infections from fungal organisms are becoming increasingly difficult to treat as drug resistance continues to emerge. To substantially expand the antifungal drug landscape new compounds must be identified and developed with novel modes of action against previously untested drug targets. Most drugs block the activity of their targets through reversible, noncovalent interactions. However, a significant number of drugs form irreversible, covalent bonds with their selected targets. While more challenging to develop, these irreversible inactivators offer some significant advantages as novel antifungal agents. Vinyl sulfones contain a potentially reactive functional group that could function as a selective enzyme inactivator, and members of this class of compounds are now being developed as inactivators against an antifungal drug target. The enzyme aspartate semialdehyde dehydrogenase (ASADH) catalyzes a key step in an essential microbial pathway and is essential for the survival of every microorganism examined. A series of vinyl sulfones have been designed, guided by molecular modeling and docking studies to enhance their affinity for fungal ASADHs. These newly synthesized compounds have been examined against this target enzyme from the pathogenic fungal organism Candida albicans. Vinyl sulfones containing complementary structural elements inhibit this enzyme with inhibition constants in the low-micromolar range. These inhibitors have also led to the rapid and irreversible inactivation of this enzyme, and show some initial selectivity when compared to the inactivation of a bacterial ASADH. The best inactivators will serve as lead compounds for the development of potent and selective antifungal agents.

Efficient synthesis, biological evaluation, and docking study of isatin based derivatives as caspase inhibitors

In this paper, a new series of isatin-sulphonamide based derivatives were designed, synthesised and evaluated as caspase inhibitors. The compounds containing 1-(pyrrolidinyl)sulphonyl and 2-(phenoxymethyl)pyrrolidin-1-yl)sulphonyl substitution at C5 position of isatin core exhibited better results compared to unsubstituted derivatives. According to the results of caspase inhibitory activity, compound 20d showed moderate inhibitory activity against caspase-3 and −7 in vitro compared to Ac-DEVD-CHO (IC₅₀ = 0.016 ± 0.002 μM). Among the studied compounds, some active inhibitors with IC_50s in the range of 2.33–116.91 μM were identified. The activity of compound 20d was rationalised by the molecular modelling studies exhibiting the additional van der Waals interaction of N-phenylacetamide substitution along with efficacious T-shaped π-π and pi-cation interactions. The introduction of compound 20d with good caspase inhibitory activity will help researchers to find more potent agents.

Synthesis and optimisation of P3 substituted vinyl sulfone-based inhibitors as anti-trypanosomal agents

A series of lysine-based vinyl sulfone peptidomimetics were synthesised and evaluated for anti-trypanosomal activity against bloodstream forms of T. brucei. This focused set of compounds, varying in the P₃ position, were accessed in a divergent manner from a common intermediate (ammonium salt 8). Several P₃ analogues exhibited sub-micromolar EC₅₀ values, with thiourea 14, urea 15 and amide 21 representing the most potent anti-trypanosomal derivatives of the series. In order to establish an in vitro selectivity index the most active anti-trypanosomal compounds were also assessed for their impact on cell viability and cytotoxity effects in mammalian cells. Encouragingly, all compounds only reduced cellular metabolic activity in mammalian cells to a modest level and little, or no cytotoxicity, was observed with the series.

Enantioselective Synthesis of γ-Phenyl-γ-amino Vinyl Phosphonates and Sulfones and Their Application to the Synthesis of Novel Highly Potent Antimalarials

Racemic and enantioselective syntheses of γ-phenyl-γ-amino vinyl phosphonates and sulfones have been achieved using Horner-Wadsworth-Emmons olefination of trityl protected α-phenyl-α-amino aldehydes with tetraethyl methylenediphosphonate and diethyl ((phenylsulfonyl)methyl)phosphonate, respectively, without any racemization. The present strategy has also been successfully applied to the synthesis of peptidyl vinyl phosphonate and peptidyl vinyl sulfone derivatives as potential cysteine protease inhibitors of Chagas disease, K11002, with 100% de. The developed synthetic protocol was further utilized to synthesize hybrid molecules consisting of artemisinin as an inhibitor of major cysteine protease falcipain-2 present in the food vacuole of the malarial parasite. The synthesized artemisinin-dipeptidyl vinyl sulfone hybrid compounds showed effective in vitro inhibition of falcipain-2 and potent parasiticidal efficacies against Plasmodium falciparum in nanomolar ranges. Overall, the developed synthetic protocol could be effectively utilized to design cysteine protease inhibitors not only as novel antimalarial compounds but also to be involved in other life-threatening diseases.

Spinal Cord Injury: Pathophysiology, Multimolecular Interactions, and Underlying Recovery Mechanisms

Spinal cord injury (SCI) is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions. Its pathophysiology comprises acute and chronic phases and incorporates a cascade of destructive events such as ischemia, oxidative stress, inflammatory events, apoptotic pathways and locomotor dysfunctions. Many therapeutic strategies have been proposed to overcome neurodegenerative events and reduce secondary neuronal damage. Efforts have also been devoted in developing neuroprotective and neuro-regenerative therapies that promote neuronal recovery and outcome. Although varying degrees of success have been achieved, curative accomplishment is still elusive probably due to the complex healing and protective mechanisms involved. Thus, current understanding in this area must be assessed to formulate appropriate treatment modalities to improve SCI recovery. This review aims to promote the understanding of SCI pathophysiology, interrelated or interlinked multimolecular interactions and various methods of neuronal recovery i.e., neuroprotective, immunomodulatory and neuro-regenerative pathways and relevant approaches.

Caspase-3 probes for PET imaging of apoptotic tumor response to anticancer therapy

Apoptosis is a highly regulated process involved in the normal organism development and homeostasis. In the context of anticancer therapy, apoptosis is also studied intensively in an attempt to induce cell death in cancer cells. Caspase activation is a known key event in the apoptotic process. In particular, active caspase-3 and -7 are the common effectors in several apoptotic pathways, therefore effector caspase activation may be a promising biomarker for response evaluation to anticancer therapy. Quantitative imaging of apoptosis in vivo could provide early assessment of therapeutic effectiveness and could also be used in drug development to evaluate the efficacy as well as potential toxicity of novel treatments. Positron Emission Tomography (PET) is a highly sensitive molecular imaging modality that allows non-invasive in vivo imaging of biological processes such as apoptosis by using radiolabeled probes. Here we describe the development and evaluation of fluorine-18-labeled caspase-3 activity-based probes (ABPs) for PET imaging of apoptosis. ABPs were selected by screening of a small library of fluorine-19-labeled DEVD peptides containing different electrophilic warhead groups. An acyloxymethyl ketone was identified with low nanomolar affinity for caspase-3 and was radiolabeled with fluorine-18. The resulting radiotracer, [18F]MICA-302, showed good labeling of active caspase-3 in vitro and favorable pharmacokinetic properties. A μPET imaging experiment in colorectal tumor xenografts demonstrated an increased tumor accumulation of [18F]MICA-302 in drug-treated versus control animals. Therefore, our data suggest this radiotracer may be useful for clinical PET imaging of response to anticancer therapy.

Yeast as a model for the identification of novel survival-promoting compounds applicable to treat degenerative diseases

Programmed cell death (PCD) plays an important role in development and normal metabolic functioning of organisms. Excessive cell death is the cause of many degenerative diseases, like neurodegenerative disorders and Wilson's disease, for which current therapies remain insufficient. Current therapies are mainly focused on decreasing the disease symptoms following cell death, rather than blocking the cell death process itself. The latter can be obtained by either decreasing the presence of the toxic trigger (like protein aggregation in case of many commonly known neurodegenerative diseases) or by blocking death-inducing signaling cascade(s). Given the high conservation in PCD processes between yeast and mammalian cells, in this review, we will focus on yeast as a model organism to study PCD-related diseases as well as on its use for drug discovery purposes. More specifically, we will provide a comprehensive overview of new compounds, which were identified in yeast-based drug screens, that either decrease the amount of toxic trigger or inhibit PCD signaling cascades under PCD-inducing conditions.

A coumarin-labeled vinyl sulfone as tripeptidomimetic activity-based probe for cysteine cathepsins

A coumarin-tetrahydroquinoline hydride 8 was synthesized as a chemical tool for fluorescent labeling. The rigidified tricyclic coumarin structure was chosen for its suitable fluorescence properties. The connection of 8 with a vinyl sulfone building block was accomplished by convergent synthesis thereby leading to the coumarin-based, tripeptidomimetic activity-based probe 10, containing a Gly-Phe-Gly motif. Probe 10 was evaluated as inactivator of the therapeutically relevant human cysteine cathepsins S, L, K, and B: it showed particularly strong inactivation of cathepsin S. The detection of recombinant and native cathepsin S was demonstrated by applying 10 to in-gel fluorescence imaging.

Potential small-molecule activators of caspase-7 identified using yeast-based caspase-3 and -7 screening assays

Caspases-3 and -7 are at the core of the execution phase of apoptosis. The search for activators of these proteases has therefore deserved particular attention in the field of anticancer drug discovery. Here, a simplified yeast-based screening approach was developed and used to search for activators of caspases-3 and -7, followed by evaluation of the activity of the selected compounds in the human tumor cell lines HL-60 (acute promyelocytic leukemia) and MCF-7 (breast adenocarcinoma). By using the yeast approach, two potential activators of caspase-7, 5,6-dihydroxy-7-prenyloxyflavone (1a) and 3-hydroxy-7-geranyloxyflavone (2a), were identified. Unlike the known caspases-3 and -7 activator, the procaspase activating compound-1 (PAC-1), these flavonoids did not interfere with the caspase-3 activity in yeast. Moreover, flavonoids 1a and 2a processed procaspase-7 to the active caspase-7 both in yeast and in vitro processing assays, and inhibited the growth of HL-60 and MCF-7 human tumor cells with higher potencies than PAC-1, particularly in the absence of caspase-3 (MCF-7 cells). In MCF-7 cells, the flavonoids processed procaspase-7, increased its activity and sensitized these cells to the effects of the cytotoxic drug, etoposide. In conclusion, the developed yeast target-based screening assays led to the identification of potential caspase-7 activators. A proof of concept is therefore provided for the effectiveness of the yeast assays in the discovery of caspase activators. Additionally, the identified compounds may pave the way for a new class of caspase activators with improved anticancer properties.

A novel class of small-molecule caspase-3 inhibitors prepared by multicomponent reactions

A series of tetra- and pentasubstituted polyfunctional dihydropyrroles 5 and 6 were synthesized via practical multicomponent reactions (MCRs) for research on their structure-activity relationship as caspase-3 inhibitors. Among 39 compounds evaluated, 14 of them exhibited inhibition against caspase-3 with IC(50) ranging from 5 to 20 μM. The inhibitory activities of 5 and 6 depend on the nature of substituents on different positions. 5 and 6 possess a different scaffold from those previously reported and are the first caspase-3 inhibitors prepared via MCRs. The most active compounds 5k (IC(50) = 5.27 μM) could therefore be used as a lead for the development of highly potent caspase-3 inhibitors as drug candidates for therapeutic agents by taking advantage of MCRs.

New insights into cancer-related proteins provided by the yeast model

Cancer is a devastating disease with a profound impact on society. In recent years, yeast has provided a valuable contribution with respect to uncovering the molecular mechanisms underlying this disease, allowing the identification of new targets and novel therapeutic opportunities. Indeed, several attributes make yeast an ideal model system for the study of human diseases. It combines a high level of conservation between its cellular processes and those of mammalian cells, with advantages such as a short generation time, ease of genetic manipulation and a wealth of experimental tools for genome- and proteome-wide analyses. Additionally, the heterologous expression of disease-causing proteins in yeast has been successfully used to gain an understanding of the functions of these proteins and also to provide clues about the mechanisms of disease progression. Yeast research performed in recent years has demonstrated the tremendous potential of this model system, especially with the validation of findings obtained with yeast in more physiologically relevant models. The present review covers the major aspects of the most recent developments in the yeast research area with respect to cancer. It summarizes our current knowledge on yeast as a cellular model for investigating the molecular mechanisms of action of the major cancer-related proteins that, even without yeast orthologues, still recapitulate in yeast some of the key aspects of this cellular pathology. Moreover, the most recent contributions of yeast genetics and high-throughput screening technologies that aim to identify some of the potential causes underpinning this disorder, as well as discover new therapeutic agents, are discussed.