Targeting Protein Translation by Rocaglamide and Didesmethylrocaglamide to Treat MPNST and Other Sarcomas

Aglaia elliptifolia Leaf Extract Inhibits Autophagy-Related 4B Protease and Suppresses Malignancies of Colorectal Cancer Cells

Autophagy is a self-eating pathway for maintaining normal cellular physiology, while dysregulation of autophagy is associated with cancer progression. Autophagy-related 4B gene (ATG4B) is a cysteine protease to regulate autophagosome formation and is positively correlated with poor prognosis of colorectal cancer (CRC) patients. An increasing number of reports have implied that ATG4B might be an attractive drug target for CRC. Natural products are the most important source of drug development for cancer therapy due to their high degree of diversity in chemical structure. However, there are few natural products targeting autophagy regulation, especially targeting ATG4B. We aim to identify effective natural compounds from costal plants against ATG4B as potential CRC therapies. We extracted the whole plants, stem, and leaves from nine coastal plant species of Taiwan using different solvents including acetone, methanol, or chloroform. We then evaluated their effects on ATG4B activity and cancer malignancy in CRC cells (DLD-1, HCT116, and SW620). Among these 26 extracts, we found that the methanol leaf extract of A. elliptifolia significantly inhibited ATG4B proteolytic activity. Moreover, cell viability and colony formation and mobility were decreased in CRC cells treated with the extract. The extract further reduced the number of living cells and induced subG1 proportion of CRC cells. The cytotoxicity of A. elliptifolia leaf extract was also enhanced in CRC cells under starvation, whereas it had no additional effects in ATG4B or autophagy deficient cells. Taken together, the methanol leaf extract of A. elliptifolia might contains bioactive compounds for inhibiting ATG4B and autophagy activity to diminish viability and mobility of CRC cells, indicating its potential as an anti-CRC drug for future development.

Pharmacologic Inhibition of EIF4A Blocks NRF2 Synthesis to Prevent Osteosarcoma Metastasis

PURPOSE

Effective therapies for metastatic osteosarcoma (OS) remain a critical unmet need. Targeting mRNA translation in metastatic OS offers a promising option, as selective translation drives the synthesis of cytoprotective proteins under harsh microenvironmental conditions to facilitate metastatic competence.

EXPERIMENTAL DESIGN

We assessed the expression levels of eukaryotic translation factors in OS, revealing the high expression of the eukaryotic initiation factor 4A1 (EIF4A1). Using a panel of metastatic OS cell lines and patient-derived xenograft (PDX) models, EIF4A1 inhibitors were evaluated for their ability to block proliferation and reduce survival under oxidative stress, mimicking harsh conditions of the lung microenvironment. Inhibitors were also evaluated for their antimetastatic activity using the ex vivo pulmonary metastasis assay and in vivo metastasis models. Proteomics was performed to catalog which cytoprotective proteins or pathways were affected by EIF4A1 inhibition.

RESULTS

CR-1-31B, a rocaglate-based EIF4A1 inhibitor, exhibited nanomolar cytotoxicity against all metastatic OS models tested. CR-1-31B exacerbated oxidative stress and apoptosis when OS cells were co-treated with tert-butylhydroquinone, a chemical oxidative stress inducer. CR-1-31B potently inhibited OS growth in the pulmonary metastasis assay model and in experimental and spontaneous models of OS lung metastasis. Proteomic analysis revealed that tert-butylhydroquinone-mediated upregulation of the NRF2 antioxidant factor was blocked by co-treatment with CR-1-31B. Genetic inactivation of NRF2 phenocopied the antimetastatic activity of CR-1-31B. Finally, the clinical-grade EIF4A1 phase-1-to-2 inhibitor, zotatifin, similarly blocked NRF2 synthesis and the OS metastatic phenotype.

CONCLUSIONS

Collectively, our data reveal that pharmacologic targeting of EIF4A1 is highly effective in blocking OS metastasis by blunting the NRF2 antioxidant response.

Putting a Kink in HIV-1 Particle Infectivity: Rocaglamide Inhibits HIV-1 Replication by Altering Gag-Genomic RNA Interaction

Our examination of RNA helicases for effects on HIV-1 protein production and particle assembly identified Rocaglamide (RocA), a known modulator of eIF4A1 function, as an inhibitor of HIV-1 replication in primary CD4+ T cells and three cell systems. HIV-1 attenuation by low-nM RocA doses was associated with reduced viral particle formation without a marked decrease in Gag production. Rather, the co-localization of Gag and HIV-1 genomic RNA (gRNA) assemblies was impaired by RocA treatment in a reversible fashion. Ribonucleoprotein (RNP) immunoprecipitation studies recapitulated the loss of Gag-gRNA assemblies upon RocA treatment. Parallel biophysical studies determined that neither RocA nor eIF4A1 independently affected the ability of Gag to interact with viral RNA, but together, they distorted the structure of the HIV-1 RNP visualized by electron microscopy. Taken together, several lines of evidence indicate that RocA induces stable binding of eIF4A1 onto the viral RNA genome in a manner that interferes with the ordered assembly of Gag along Gag-gRNA assemblies required to generate infectious virions.

Anti-tumor effects of the eIF4A inhibitor didesmethylrocaglamide and its derivatives in human and canine osteosarcomas

Inhibition of translation initiation using eIF4A inhibitors like (-)-didesmethylrocaglamide [(-)-DDR] and (-)-rocaglamide [(-)-Roc] is a potential cancer treatment strategy as they simultaneously diminish multiple oncogenic drivers. We showed that human and dog osteosarcoma cells expressed higher levels of eIF4A1/2 compared with mesenchymal stem cells. Genetic depletion of eIF4A1 and/or 2 slowed osteosarcoma cell growth. To advance preclinical development of eIF4A inhibitors, we demonstrated the importance of (-)-chirality in DDR for growth-inhibitory activity. Bromination of DDR at carbon-5 abolished growth-inhibitory activity, while acetylating DDR at carbon-1 was tolerated. Like (-)-DDR, (±)-DDR, and (-)-Roc, (±)-DDR-acetate increased γH2A.X levels and induced G2/M arrest and apoptosis. Consistent with translation inhibition, these rocaglates decreased the levels of several mitogenic kinases, the STAT3 transcription factor, and the stress-activated protein kinase p38. However, phosphorylated p38 was greatly enhanced in treated cells, suggesting activation of stress response pathways. RNA sequencing identified RHOB as a top upregulated gene in both (-)-DDR- and (-)-Roc-treated osteosarcoma cells, but the Rho inhibitor Rhosin did not enhance the growth-inhibitory activity of (-)-DDR or (-)-Roc. Nonetheless, these rocaglates potently suppressed tumor growth in a canine osteosarcoma patient-derived xenograft model. These results suggest that these eIF4A inhibitors can be leveraged to treat both human and dog osteosarcomas.

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.

Anti-tumor Effects of the eIF4A Inhibitor Didesmethylrocaglamide and Its Derivatives in Human and Canine Osteosarcomas

Inhibition of translation initiation using eIF4A inhibitors like (-)-didesmethylrocaglamide [(-)-DDR] and (-)-rocaglamide [(-)-Roc] is a potential cancer treatment strategy as they simultaneously diminish multiple oncogenic drivers. We showed that human and dog osteosarcoma cells expressed high levels of eIF4A1/2, particularly eIF4A2. Genetic depletion of eIF4A1 and/or 2 slowed osteosarcoma cell growth. To advance preclinical development of eIF4A inhibitors, we demonstrated the importance of (-)-chirality in DDR for growth-inhibitory activity. Bromination of DDR at carbon-5 abolished growth-inhibitory activity, while acetylating DDR at carbon-1 was tolerated. Like DDR and Roc, DDR-acetate increased the γH2A.X levels and induced G2/M arrest and apoptosis. Consistent with translation inhibition, these rocaglates decreased the levels of several mitogenic kinases, the STAT3 transcription factor, and the stress-activated protein kinase p38. However, phosphorylated p38 was greatly enhanced in treated cells, suggesting activation of stress response pathways. RNA sequencing identified RHOB as a top upregulated gene in both DDR- and Roc-treated osteosarcoma cells, but the Rho inhibitor Rhosin did not enhance the growth-inhibitory activity of (-)-DDR or (-)-Roc. Nonetheless, these rocaglates potently suppressed tumor growth in a canine osteosarcoma patient-derived xenograft model. These results suggest that these eIF4A inhibitors can be leveraged to treat both human and dog osteosarcomas.

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.

Osteosarcoma

Osteosarcoma is the most common primary malignant tumour of the bone. Osteosarcoma incidence is bimodal, peaking at 18 and 60 years of age, and is slightly more common in males. The key pathophysiological mechanism involves several possible genetic drivers of disease linked to bone formation, causing malignant progression and metastasis. While there have been significant improvements in the outcome of patients with localized disease, with event-free survival outcomes exceeding 60%, in patients with metastatic disease, event-free survival outcomes remain poor at less than 30%. The suspicion of osteosarcoma based on radiographs still requires pathological evaluation of a bone biopsy specimen for definitive diagnosis and CT imaging of the chest should be performed to identify lung nodules. So far, population-based screening and surveillance strategies have not been implemented due to the rarity of osteosarcoma and the lack of reliable markers. Current screening focuses only on groups at high risk such as patients with genetic cancer predisposition syndromes. Management of osteosarcoma requires a multidisciplinary team of paediatric and medical oncologists, orthopaedic and general surgeons, pathologists, radiologists and specialist nurses. Survivors of osteosarcoma require specialized medical follow-up, as curative treatment consisting of chemotherapy and surgery has long-term adverse effects, which also affect the quality of life of patients. The development of osteosarcoma model systems and related research as well as the evaluation of new treatment approaches are ongoing to improve disease outcomes, especially for patients with metastases.

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.

Targeted intervention of eIF4A1 inhibits EMT and metastasis of pancreatic cancer cells via c-MYC/miR-9 signaling

Background

Owing to the lack of effective treatment options, early metastasis remains the major cause of pancreatic ductal adenocarcinoma (PDAC) recurrence and mortality. However, the molecular mechanism of early metastasis is largely unknown. We characterized the function of eukaryotic translation initiation factors (eIFs) in epithelial-mesenchymal-transition (EMT) and metastasis in pancreatic cancer cells to investigate whether eIFs and downstream c-MYC affect EMT and metastasis by joint interference.

Methods

We used The Cancer Genome Atlas (TCGA) and Genome Tissue Expression (GTEx) databases to analyze eIF4A1 expression in PDAC tissues and further validated the findings with a microarray containing 53 PDAC samples. Expression regulation and pharmacological inhibition of eIF4A1 and c-MYC were performed to determine their role in migration, invasion, and metastasis in pancreatic cancer cells in vitro and in vivo.

Results

Elevated eIF4A1 expression was positively correlated with lymph node infiltration, tumor size, and indicated a poor prognosis. eIF4A1 decreased E-cadherin expression through the c-MYC/miR-9 axis. Loss of eIF4A1 and c-MYC decreased the EMT and metastasis capabilities of pancreatic cancer cells, whereas upregulation of eIF4A1 attenuated the inhibition of EMT and metastasis induced by c-MYC downregulation. Treatment with the eIF4A1 inhibitor rocaglamide (RocA) or the c-MYC inhibitor Mycro3 either alone or in combination significantly decreased the expression level of EMT markers in pancreatic cancer cells in vitro. However, the efficiency and safety of RocA alone were not inferior to those of the combination treatment in vivo.

Conclusion

Overexpression of eIF4A1 downregulated E-cadherin expression through the c-MYC/miR-9 axis, which promoted EMT and metastasis of pancreatic cancer cells. Despite the potential feedback loop between eIF4A1 and c-MYC, RocA monotherapy is a promising treatment inhibiting eIF4A1-induced PDAC metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02390-0.

Neurofibromatosis: Molecular Pathogenesis and Natural Compounds as Potential Treatments

The neurofibromatosis syndromes, including NF1, NF2, and schwannomatosis, are tumor suppressor syndromes characterized by multiple nervous system tumors, particularly Schwann cell neoplasms. NF-related tumors are mainly treated by surgery, and some of them have been treated by but are refractory to conventional chemotherapy. Recent advances in molecular genetics and genomics alongside the development of multiple animal models have provided a better understanding of NF tumor biology and facilitated target identification and therapeutic evaluation. Many targeted therapies have been evaluated in preclinical models and patients with limited success. One major advance is the FDA approval of the MEK inhibitor selumetinib for the treatment of NF1-associated plexiform neurofibroma. Due to their anti-neoplastic, antioxidant, and anti-inflammatory properties, selected natural compounds could be useful as a primary therapy or as an adjuvant therapy prior to or following surgery and/or radiation for patients with tumor predisposition syndromes, as patients often take them as dietary supplements and for health enhancement purposes. Here we review the natural compounds that have been evaluated in NF models. Some have demonstrated potent anti-tumor effects and may become viable treatments in the future.

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

With about 120 species, Aglaia is one of the largest genera of the plant family Meliaceae (the mahogany plants). It is native to the tropical rainforests of the Indo-Australian region, ranging from India and Sri Lanka eastward to Polynesia and Micronesia. Various Aglaia species have been investigated since the 1960s for their phytochemical constituents and biological properties, with the cyclopenta[b]benzofurans (rocaglates or flavaglines) being of particular interest. Phytochemists, medicinal chemists, and biologists have conducted extensive research in establishing these secondary metabolites as potential lead compounds with antineoplastic and antiviral effects, among others. The varied biological properties of rocaglates can be attributed to their unusual structures and their ability to act as inhibitors of the eukaryotic translation initiation factor 4A (eIF4A), affecting protein translation. The present review provides an update on the recently reported phytochemical constituents of Aglaia species, focusing on rocaglate derivatives. Furthermore, laboratory work performed on investigating the biological activities of these chemical constituents is also covered.

Treatment resistance analysis reveals GLUT-1-mediated glucose uptake as a major target of synthetic rocaglates in cancer cells

Rocaglates are natural compounds that have been extensively studied for their ability to inhibit translation initiation. Rocaglates represent promising drug candidates for tumor treatment due to their growth‐inhibitory effects on neoplastic cells. In contrast to natural rocaglates, synthetic analogues of rocaglates have been less comprehensively characterized, but were also shown to have similar effects on the process of protein translation. Here, we demonstrate an enhanced growth‐inhibitory effect of synthetic rocaglates when combined with glucose anti‐metabolite 2‐deoxy‐D‐glucose (2DG) in different cancer cell lines. Moreover, we unravel a new aspect in the mechanism of action of synthetic rocaglates involving reduction of glucose uptake mediated by downregulation or abrogation of glucose transporter GLUT‐1 expression. Importantly, cells with genetically induced resistance to synthetic rocaglates showed substantially less pronounced treatment effect on glucose metabolism and did not demonstrate GLUT‐1 downregulation, pointing at the crucial role of this mechanism for the anti‐tumor activity of the synthetic rocaglates. Transcriptome profiling revealed glycolysis as one of the major pathways differentially regulated in sensitive and resistant cells. Analysis of synthetic rocaglate efficacy in a 3D tissue context with a co‐culture of tumor and normal cells demonstrated a selective effect on tumor cells and substantiated the mechanistic observations obtained in cancer cell lines. Increased glucose uptake and metabolism is a universal feature across different tumor types. Therefore, targeting this feature by synthetic rocaglates could represent a promising direction for exploitation of rocaglates in novel anti‐tumor therapies.

Natural products as drugs and tools for influencing core processes of eukaryotic mRNA translation

Eukaryotic protein synthesis is the highly conserved, complex mechanism of translating genetic information into proteins. Although this process is essential for cellular homoeostasis, dysregulations are associated with cellular malfunctions and diseases including cancer and diabetes. In the challenging and ongoing search for adequate treatment possibilities, natural products represent excellent research tools and drug leads for new interactions with the translational machinery and for influencing mRNA translation. In this review, bacterial-, marine- and plant-derived natural compounds that interact with different steps of mRNA translation, comprising ribosomal assembly, translation initiation and elongation, are highlighted. Thereby, the exact binding and interacting partners are unveiled in order to accurately understand the mode of action of each natural product. The pharmacological relevance of these compounds is furthermore assessed by evaluating the observed biological activities in the light of translational inhibition and by enlightening potential obstacles and undesired side-effects, e.g. in clinical trials. As many of the natural products presented here possess the potential to serve as drug leads for synthetic derivatives, structural motifs, which are indispensable for both mode of action and biological activities, are discussed. Evaluating the natural products emphasises the strong diversity of their points of attack. Especially the fact that selected binding partners can be set in direct relation to different diseases emphasises the indispensability of natural products in the field of drug development. Discovery of new, unique and unusual interacting partners again renders them promising tools for future research in the field of eukaryotic mRNA translation.

The translational repressor 4E-BP1 regulates RRM2 levels and functions as a tumor suppressor in Ewing sarcoma tumors

Ribonucleotide reductase (RNR), which is a heterodimeric tetramer composed of RRM1 and RRM2 subunits, is the rate-limiting enzyme in the synthesis of deoxyribonucleoside triphosphates (dNTPs) and essential for both DNA replication and the repair of DNA damage. The activity of RNR is coordinated with the cell cycle and regulated by fluctuations in the level of the RRM2 subunit. Multiple cancer types, including Ewing sarcoma tumors, are sensitive to inhibitors of RNR or a reduction in the levels of either the RRM1 or RRM2 subunits of RNR. Here, we show that the expression of the RRM2 protein is dependent on active protein synthesis and that 4E-BP1, a repressor of cap-dependent protein translation, specifically regulates the level of the RRM2 protein. Furthermore, inhibition of mTORC1/2, but not mTORC1, activates 4E-BP1, inhibits protein synthesis, and reduces the level of the RRM2 protein in multiple sarcoma cell lines. This effect of mTORC1/2 inhibitors on protein synthesis and RRM2 levels was rescued in cell lines with the CRISPR/Cas9-mediated knockout of 4E-BP1. In addition, the inducible expression of a mutant 4E-BP1 protein that cannot be phosphorylated by mTOR blocked protein synthesis and inhibited the growth of Ewing sarcoma cells in vitro and in vivo in a xenograft. Overall, these results provide insight into the multifaceted regulation of RRM2 protein levels and identify a regulatory link between protein translation and DNA replication.