Antiproliferative and quinone reductase-inducing activities of withanolides derivatives

Covalent binding of withanolides to cysteines of protein targets

Withanolides represent an important category of natural products with a steroidal lactone core. Many of them contain an α,β-unsaturated carbonyl moiety with a high reactivity toward sulfhydryl groups, including protein cysteine thiols. Different withanolides endowed with marked antitumor and anti-inflammatory have been shown to form stable covalent complexes with exposed cysteines present in the active site of oncogenic kinases (BTK, IKKβ, Zap70), metabolism enzymes (Prdx-1/6, Pin1, PHGDH), transcription factors (Nrf2, NFκB, C/EBPβ) and other structural and signaling molecules (GFAP, β-tubulin, p97, Hsp90, vimentin, Mpro, IPO5, NEMO, …). The present review analyzed the covalent complexes formed through Michael addition alkylation reactions between six major withanolides (withaferin A, physalin A, withangulatin A, 4β-hydroxywithanolide E, withanone and tubocapsanolide A) and key cysteine residues of about 20 proteins and the resulting biological effects. The covalent conjugation of the α,β-unsaturated carbonyl system of withanolides with reactive protein thiols can occur with a large set of soluble and membrane proteins. It points to a general mechanism, well described with the leading natural product withaferin A, but likely valid for most withanolides harboring a reactive (electrophilic) enone moiety susceptible to react covalently with cysteinyl residues of proteins. The multiplicity of reactive proteins should be taken into account when studying the mechanism of action of new withanolides. Proteomic and network analyses shall be implemented to capture and compare the cysteine covalent-binding map for the major withanolides, so as to identify the protein targets at the origin of their activity and/or unwanted effects. Screening of the cysteinome will help understanding the mechanism of action and designing cysteine-reactive electrophilic drug candidates.

Expanding Diterpene Complexity and Diversity via Photoinduced Ring Distortions

Natural products and their semi-synthetic derivatives undoubtedly constitute an important source of therapeutic agents. Their importance lies in their own origin and evolution, since they have great chemical diversity, biochemical specificity, and pharmacological properties. Currently, there is a renewed interest in the development of methodologies capable of efficiently modifying the chemical structure of these bioactive platforms. In this work, the photoderivatization of the diterpene solidagenone was performed using a complexity-to-diversity-oriented approach. By exploring [2+2]-photocycloaddition, photoinduced-hydrogen abstraction, and photoxygenation reactions, a set of solidagenone derivatives was obtained, showing different ring fusions, side chain rearrangements, and modifications of the original furan ring's substitution pattern. The derivatives obtained were characterised by NMR methodologies. To evaluate the structural diversity of the labdane-derived compounds, their physicochemical properties, structural similarity, and chemical space were analysed. These results suggest that photochemical reactions are a useful tool for performing ring distortion transformations, generating derivatives of natural compounds with wide diversity, structural complexity, and with potential biological properties.

Natural withanolides, an update

Covering: March 2010 to December 2020. Previous review: Nat. Prod. Rep., 2011, 28, 705This review summarizes the latest progress and perspectives on the structural classification, biological activities and mechanisms, metabolism and pharmacokinetic investigations, biosynthesis, chemical synthesis and structural modifications, as well as future research directions of the promising natural withanolides. The literature from March 2010 to December 2020 is reviewed, and 287 references are cited.

Synthesis and biological evaluation of novel withangulatin A derivatives as potential anticancer agents

Novel withangulatin A (WA) derivatives were synthesized and evaluated for antiproliferative activity against four human cancer cell lines (U2OS, MDA-MB-231, HepG2, and A549). Among these derivatives, 10 exhibited the most potent antiproliferative activity, with an IC₅₀ value of 74.0 nM against the human breast cancer cell line MDA-MB-231 and potency that was 70-fold that of WA (IC₅₀ = 5.22 µM). Moreover, 10 caused G2-phase cell cycle arrest in a concentration-dependent manner and induced the apoptosis of MDA-MB-231 cells by increasing intracellular reactive oxygen species (ROS). Compound 10 showed a high selectivity index (SI = 267.03) for breast cancer MDA-MB-231 cells. These results suggest that 10 is a promising anticancer agent.

Synthesis of Benzothiophene-Fused Oxa[6.6.5]tricyclic Skeletons through a Cinchonidine- or NaOH-Promoted Quadruple Domino Sequence

Two base-promoted quadruple domino reactions between thioaurones and allylic phosphonium salts have been developed to synthesize benzothiophene-fused oxa[6.6.5]tricyclic skeletons in moderate to good yields with excellent stereoselectivity and broad functional-group tolerance. This is a simple and useful protocol for the rapid construction of the umbrella-like oxa[6.6.5]tricyclic skeleton.

Potential Anticancer Properties and Mechanisms of Action of Withanolides

Plant-based Ayurvedic medicine has been practiced in India for thousands of years for the treatment of a variety of disorders. They are rich sources of bioactive compounds potentially useful for prevention and treatment of cancer. Withania somnifera (commonly known as Ashwagandha in Ayurvedic medicine) is a widely used medicinal plant whose anticancer value was recognized after isolation of steroidal compounds withanolides from the leaves of this shrub. Withaferin A is the first member of withanolides to be isolated, and it is the most abundant withanolide present in W. somnifera. Its cancer-protective role has now been established using chemically induced and oncogene-driven rodent cancer models. The present review summarizes the key preclinical studies demonstrating anticancer effects of withaferin along with its molecular targets and mechanisms related to its anticancer effects. Anticancer potential of other withanolides is also discussed.