Update on Phytochemical and Biological Studies on Rocaglate Derivatives from Aglaia Species

Additional Bioactive Silvestrol Analogs from the Roots of Aglaia perviridis Collected in Vietnam

The tropical plant Aglaia perviridis is known to produce cyclopenta[b]benzofuran and other types of rocaglate derivatives including silvestrol (3) and 5‴-episilvestrol (4) that are of current pharmacological interest. In the present work, further investigation of A. perviridis roots collected in Vietnam has yielded two new rocaglate acetonide derivatives (1 and 2) and a known pentanor-3,4-seco-dammarane triterpenoid (7) found for the first time as a natural product, in addition to four known rocaglates (3-6). The structures of compounds 1 and 2 were confirmed by partial synthesis experiments, and their potential occurrence as extraction artifacts was investigated by targeted selective ion monitoring using UHPLC-MS. All compounds obtained were evaluated against a panel of four human cancer cell lines, in which the six rocaglate derivatives (1-6) tested all showed submicromolar potencies.

In Vitro Discovery of a Therapeutic Lead for HFMD From a Library Screen of Rocaglates/Aglains

The lack of effective antiviral treatments for enteroviruses, including human enterovirus A71 (EV-A71), have resulted in an immense global healthcare burden associated with hand-foot-and-mouth disease (HFMD). Rocaglates and aglains belong to a family of compounds produced by Aglaia genus plants. Since the initial discovery of rocaglates in 1982, various rocaglates and aglains have been synthesized and extensively studied mainly as anticancer agents. Here, we report the discovery of a novel aglain derivative as a potential EV-A71 inhibitor. From an immunofluorescence-based phenotypic screen of a library of 296 rocaglate and aglain derivatives, we identified a lead aglain which effectively suppressed EV-A71 replication by 2.3 log fold at a non-cytotoxic concentration, with a host cell CC50 of 21.78 µM, an EV-A71 infection EC50 of 3.57 µM, and a selectivity index of 6.1. Further validation revealed inhibition of EV-A71 across multiple human cell types and a pan-enterovirus inhibitory spectrum against other enteroviruses. Subsequent mechanistic investigation revealed interference with EV-A71 intracellular post-entry events including viral RNA transcription and translation. Findings from this study have established a strong foundation for development of aglain scaffolds as much needed antiviral agents for HFMD, paving the way for future medicinal chemistry optimization and in vivo studies.

Silvestrol, a potent anticancer agent with unfavourable pharmacokinetics: Current knowledge on its pharmacological properties and future directions for the development of novel drugs

Cancer remains a leading cause of death, with increasing incidence. Conventional treatments offer limited efficacy and cause significant side effects, hence novel drugs with improved pharmacological properties and safety are required. Silvestrol (SLV) is a flavagline derived from some plants of the Aglaia genus that has shown potent anticancer effects, warranting further study. Despite its efficacy in inhibiting the growth of several types of cancer cells, SLV is characterized by an unfavorable pharmacokinetics that hamper its use as a drug. A consistent research over the recent years has led to develop novel SLV derivatives with comparable pharmacodynamics and an ameliorated pharmacokinetic profile, demonstrating potential applications in the clinical management of cancer. This comprehensive review aims to highlight the most recent data available on SLV and its synthetic derivatives, addressing their pharmacological profile and therapeutic potential in cancer treatment. A systematic literature review of both in vitro and in vivo studies focusing on anticancer effects, pharmacodynamics, and pharmacokinetics of these compounds is presented. Overall, literature data highlight that rationale chemical modifications of SLV are critical for the development of novel drugs with high efficacy on a broad variety of cancers and improved bioavailability in vivo. Nevertheless, SLV analogues need to be further studied to better understand their mechanisms of action, which can be partially different to SLV. Furthermore, clinical research is still required to assess their efficacy in humans and their safety.

Undescribed 2,9-deoxyflavonoids and flavonol-diamide [3+2] adduct from the leaves of Aglaia odorata Lour. Inhibit nitric oxide production

Phytochemical study on the methanol extract of Aglaia odorata leaves resulted in the isolation of four previously undescribed compounds, including three 2,9-deoxyflavonoids and one flavonol-diamide [3 + 2] adduct, and 13 known compounds. The chemical structures of the four undescribed compounds were elucidated on the basis of their IR, HR-ESI-MS, 1D and 2D NMR, and ECD spectra. The results revealed an unprecedented 2,9-deoxyflavonoid framework, which was confirmed by TD-DFT, ECD, and GIAO 13C-NMR calculations using sorted training set methods. The 17 compounds were examined for their ability to inhibit NO production activity in cultured lipopolysaccharide-activated RAW264.7 cells with aglaodoratas A-C, odorine, and epi-odorine inhibiting NO production, with IC50 values in the range of 16.2-24.3 μM. The other investigated compounds had either weak or no activity.

Strategies for the discovery of potential anticancer agents from plants collected from Southeast Asian tropical rainforests as a case study

Covering up to early 2023The present review summarizes recent accomplishments made as part of a multidisciplinary, multi-institutional anticancer drug discovery project, wherein samples comprising higher plants were collected primarily from Southeast Asia, and also from Central America, and the West Indies. In the introductory paragraphs, a short perspective is provided on the current importance of plants in the discovery of cancer therapeutic agents, and the contributions of other groups working towards this objective are mentioned. For our own investigations, following their collection, tropical plants have been subjected to solvent extraction and biological evaluation for their antitumor potential. Several examples of purified plant lead bioactive compounds were obtained and characterized, and found to exhibit diverse structures, including those of the alkaloid, cardiac glycoside, coumarin, cucurbitacin, cyclobenzofuran (rocaglate), flavonoid, lignan, and terpenoid types. In order to maximize the efficiency of work on drug discovery from tropical plant species, strategies to optimize various research components have been developed, including those for the plant collections and taxonomic identification, in accordance with the requirements of contemporary international treaties and with a focus on species conservation. A major component of this aspect of the work is the development of collaborative research agreements with representatives of the source countries of tropical rainforest plants. The phytochemical aspects have included the preparation of plant extracts for initial screening and the selection of promising extracts for activity-guided fractionation. In an attempt to facilitate this process, a TOCSY-based NMR procedure has been applied for the determination of bioactive rocaglate derivatives in samples of Aglaia species (Meliaceae) collected for the project. Preliminary in vitro and in vivo mechanistic studies carried out by the authors are described for two tropical plant-derived bioactive lead compounds, corchorusoside C and (+)-betulin, including work conducted with a zebrafish (Danio rerio) model. In the concluding remarks, a number of lessons are summarized that our group has learned as a result of working on anticancer drug discovery using tropical plants, which we hope will be of interest to future workers.

Identification of structurally re-engineered rocaglates as inhibitors against hepatitis E virus replication

Hepatitis E virus (HEV) infections are a leading cause of acute viral hepatitis in humans and pose a considerable threat to public health. Current standard of care treatment is limited to the off-label use of nucleoside-analog ribavirin (RBV) and PEGylated interferon-α, both of which are associated with significant side effects and provide limited efficacy. In the past few years, a promising natural product compound class of eukaryotic initiation factor 4A (eIF4A) inhibitors (translation initiation inhibitors), called rocaglates, were identified as antiviral agents against RNA virus infections. In the present study, we evaluated a total of 205 synthetic rocaglate derivatives from the BU-CMD compound library for their antiviral properties against HEV. At least eleven compounds showed inhibitory activities against the HEV genotype 3 (HEV-3) subgenomic replicon below 30 nM (EC₅₀ value) as determined by Gaussia luciferase assay. Three amidino-rocaglates (ADRs) (CMLD012073, CMLD012118, and CMLD012612) possessed antiviral activity against HEV with EC₅₀ values between 1 and 9 nM. In addition, these three selected compounds inhibited subgenomic replicons of different genotypes (HEV-1 [Sar55], wild boar HEV-3 [83-2] and human HEV-3 [p6]) in a dose-dependent manner and at low nanomolar concentrations. Furthermore, tested ADRs tend to be better tolerated in primary hepatocytes than hepatoma cancer cell lines and combination treatment of CMLD012118 with RBV and interferon-α (IFN-α) showed that CMLD012118 acts additive to RBV and IFN-α treatment. In conclusion, our results indicate that ADRs, especially CMLD012073, CMLD012118, and CMLD012612 may prove to be potential therapeutic candidates for the treatment of HEV infections and may contribute to the discovery of pan-genotypic inhibitors in the future.

Discovery of Anticancer Agents of Diverse Natural Origin

Research progress from mainly over the last five years is described for a multidisciplinary collaborative program project directed toward the discovery of potential anticancer agents from a broad range of taxonomically defined organisms. Selected lead compounds with potential as new antitumor agents that are representative of considerable structural diversity have continued to be obtained from each of tropical plants, terrestrial and aquatic cyanobacteria, and filamentous fungi. Recently, a new focus has been on the investigation of the constituents of U.S. lichens and their fungal mycobionts. A medicinal chemistry and pharmacokinetics component of the project has optimized structurally selected lead natural products, leading to enhanced cytotoxic potencies against selected cancer cell lines. Biological testing has shown several compounds to have in vivo activity, and relevant preliminary structure-activity relationship and mechanism of action studies have been performed. Several promising lead compounds worthy of further investigation have been identified from the most recent collaborative work performed.