Silvestrol

Silvestrol inhibited protein synthesis in MDA-MB-231 breast and PC-3 prostate cancer cell lines with IC50 ~60 nM following a 1 h exposure) [1]. Silvestrol inhibited cell growth with an IC50 of 12.5-86 nM in four different HCC cell lines [3].
Silvestrol, a member of flavagline family of natural products from the genus of Aglaia exhibiting anti-cancer activity in vitro and in vivo and inhibiting translation initiation, was shown to be capable of modulating chemosensitivity in a mechanism-based mouse model.
Preclinical study: A previous study demonstrated that silvestrol showed antileukemia activity at nanomolar concentrations in both FLT3-wt overexpressing (THP-1) and FLT3-ITD (MV4-11) expressing AML cell lines (IC50 = 3.8 and 2.7 nM, respectively) and patients’ primary blasts [IC50 = ~12 nM (FLT3-wt) and ~5 nM (FLT3-ITD)]. Moreover, silvestrol was observed to efficiently inhibite FLT3 translation resulting in a decrese of FLT3 protein expression by 80–90%. Animal study indicated that the median survival of silvestrol-treated mice significantly increased (silvestrol-treated vs vehicle-treated = 63 vs 29 days postengraftment) [2]. Another study showed that silvestrol could increase the activities of apoptosis and caspase 3/7. In vivo, the antitumor effect was found with 0.4 mg/kg silvestrol, and the survival of tumor-bearing mice was improved with a median survival time of 42 and 28 days in the silvestrol and control groups, respectively [3].
Clinical study: Currently, there is no clinical data about the anti-cancer efficacy of silvestrol. A grant application proposeed to pursue a Phase I clinical trial to assess the safety, maximum tolerated dose, pharmacokinetic and pharmacodynamic properties, and preliminary efficacy of silvestrol in patients with relapsed, refractory Chronic lymphocytic leukemia (Pre-Clinical and Clinical Development of Silvestrol in Chronic Lymphocytic).
References:
[1] Cencic R, Carrier M, Galicia-Vázquez G, Bordeleau ME, Sukarieh R, Bourdeau A, Brem B, Teodoro JG, Greger H, Tremblay ML, Porco JA Jr, Pelletier J Antitumor activity and mechanism of action of the cyclopenta[b]benzofuran, silvestrol. PLoS One. 2009;4(4):e5223. doi: 10.1371/journal.pone.0005223.
[2] Alachkar H, Santhanam R, Harb JG, Lucas DM, Oaks JJ, Hickey CJ, Pan L, Kinghorn AD, Caligiuri MA, Perrotti D, Byrd JC, Garzon R, Grever MR, Marcucci G. Silvestrol exhibits significant in vivo and in vitro antileukemic activities and inhibits FLT3 and miR-155 expressions in acute myeloid leukemia. J Hematol Oncol. 2013;6:21. doi: 10.1186/1756-8722-6-21.
[3] Kogure T, Kinghorn AD, Yan I, Bolon B, Lucas DM, Grever MR, Patel T. Therapeutic potential of the translation inhibitor silvestrol in hepatocellular cancer. PLoS One. 2013;8(9):e76136. doi: 10.1371/journal.pone.0076136.

The translation inhibitor silvestrol exhibits direct anti-tumor activity while preserving innate and adaptive immunity against EBV-driven lymphoproliferative disease.[Pubmed:25393910]

Oncotarget. 2015 Feb 20;6(5):2693-708.

Treatment options for patients with Epstein-Barr Virus-driven lymphoproliferative diseases (EBV-LPD) are limited. Chemo-immunotherapeutic approaches often lead to immune suppression, risk of lethal infection and EBV reactivation, thus it is essential to identify agents that can deliver direct anti-tumor activity while preserving innate and adaptive host immune surveillance. Silvestrol possesses direct anti-tumor activity in multiple hematologic malignancies while causing minimal toxicity to normal mononuclear cells. However, the effects of Silvestrol on immune function have not been described. We utilized in vitro and in vivo models of EBV-LPD to simultaneously examine the impact of Silvestrol on both tumor and normal immune function. We show that Silvestrol induces direct anti-tumor activity against EBV-transformed lymphoblastoid cell lines (LCL), with growth inhibition, decreased expression of the EBV oncogene latent membrane protein-1, and inhibition of the downstream AKT, STAT1 and STAT3 signaling pathways. Silvestrol promoted potent indirect anti-tumor effects by preserving expansion of innate and EBV antigen-specific adaptive immune effector subsets capable of effective clearance of LCL tumor targets in autologous co-cultures. In an animal model of spontaneous EBV-LPD, Silvestrol demonstrated significant therapeutic activity dependent on the presence of CD8-positive T-cells. These findings establish a novel immune-sparing activity of Silvestrol, justifying further exploration in patients with EBV-positive malignancies.

The natural compound silvestrol is a potent inhibitor of Ebola virus replication.[Pubmed:27864075]

Antiviral Res. 2017 Jan;137:76-81.

The DEAD-box RNA helicase eIF4A, which is part of the heterotrimeric translation initiation complex in eukaryotes, is an important novel drug target in cancer research because its helicase activity is required to unwind extended and highly structured 5'-UTRs of several proto-oncogenes. Silvestrol, a natural compound isolated from the plant Aglaia foveolata, is a highly efficient, non-toxic and specific inhibitor of eIF4A. Importantly, 5'-capped viral mRNAs often contain structured 5'-UTRs as well, which may suggest a dependence on eIF4A for their translation by the host protein synthesis machinery. In view of the recent Ebola virus (EBOV) outbreak in West Africa, the identification of potent antiviral compounds is urgently required. Since Ebola mRNAs are 5'-capped and harbor RNA secondary structures in their extended 5'-UTRs, we initiated a BSL4 study to analyze Silvestrol in EBOV-infected Huh-7 cells and in primary human macrophages for its antiviral activity. We observed that Silvestrol inhibits EBOV infection at low nanomolar concentrations, as inferred from large reductions of viral titers. This correlated with an almost complete disappearance of EBOV proteins, comparable in effect to the translational shutdown of expression of the proto-oncoprotein PIM1, a cellular kinase known to be affected by Silvestrol. Effective Silvestrol concentrations were non-toxic in the tested cell systems. Thus, Silvestrol appears to be a promising first-line drug for the treatment of acute EBOV and possibly other viral infections.

Silvestrol induces early autophagy and apoptosis in human melanoma cells.[Pubmed:26762417]

BMC Cancer. 2016 Jan 13;16:17.

BACKGROUND: Silvestrol is a cyclopenta[b]benzofuran that was isolated from the fruits and twigs of Aglaia foveolata, a plant indigenous to Borneo in Southeast Asia. The purpose of the current study was to determine if inhibition of protein synthesis caused by Silvestrol triggers autophagy and apoptosis in cultured human cancer cells derived from solid tumors. METHODS: In vitro cell viability, flow cytometry, fluorescence microscopy, qPCR and immunoblot was used to study the mechanism of action of Silvestrol in MDA-MB-435 melanoma cells. RESULTS: By 24 h, a decrease in cyclin B and cyclin D expression was observed in Silvestrol-treated cells relative to control. In addition, Silvestrol blocked progression through the cell cycle at the G2-phase. In Silvestrol-treated cells, DAPI staining of nuclear chromatin displayed nucleosomal fragments. Annexin V staining demonstrated an increase in apoptotic cells after Silvestrol treatment. Silvestrol induced caspase-3 activation and apoptotic cell death in a time- and dose-dependent manner. Furthermore, both Silvestrol and SAHA enhanced autophagosome formation in MDA-MB-435 cells. MDA-MB-435 cells responded to Silvestrol treatment with accumulation of LC3-II and time-dependent p62 degradation. Bafilomycin A, an autophagy inhibitor, resulted in the accumulation of LC3 in cells treated with Silvestrol. Silvestrol-mediated cell death was attenuated in ATG7-null mouse embryonic fibroblasts (MEFs) lacking a functional autophagy protein. CONCLUSIONS: Silvestrol potently inhibits cell growth and induces cell death in human melanoma cells through induction of early autophagy and caspase-mediated apoptosis. Silvestrol represents a natural product scaffold that exhibits potent cytotoxic activity and could be used for the further study of autophagy and its relationship to apoptosis in cancer cells.

Inhibition of nasopharyngeal carcinoma cell proliferation and synergism of cisplatin with silvestrol and episilvestrol isolated from Aglaia stellatopilosa.[Pubmed:27284293]

Exp Ther Med. 2016 Jun;11(6):2117-2126.

Nasopharyngeal carcinoma (NPC) is a type of tumour that arises from the epithelial cells that line the surface of the nasopharynx. NPC is treated with radiotherapy and cytotoxic chemotherapeutic drugs such as cisplatin and 5-fluorouracil. However, current strategies are often associated with potential toxicities. This has prompted efforts to identify alternative methods of treatment. The present study aimed to investigate Silvestrol and epiSilvestrol-mediated inhibition of cell proliferation in human NPC cells. The growth kinetics of NPC cells treated with Silvestrol or epiSilvestrol were monitored dynamically using a real-time, impedance-based cell analyzer, and dose-response profiles were generated using a colorimetric cell viability assay. Furthermore, apoptosis was evaluated using flow cytometry and high content analysis. In addition, flow cytometry was performed to determine cell cycle distribution. Finally, the effects of combining Silvestrol or epiSilvestrol with cisplatin on NPC cells was examined. Apoptosis was not observed in Silvestrol and epiSilvestrol-treated NPC cells, although cell cycle perturbation was evident. Treatment with both compounds induced a significant increase in the percentage of cells in the G2/M phase, as compared with the control. In vitro cultures combining Silvestrol or epiSilvestrol with cisplatin showed synergistic effects against NPC cells. The results of the present study suggested that Silvestrol and epiSilvestrol had an anti-tumour activity in NPC cells. Silvestrol and epiSilvestrol, particularly in combination with cisplatin, merit further investigation, so as to determine the cellular mechanisms underlying their action(s) as anti-NPC agents.

Silvestrol is a eukaryotic translation initiation factor 4A (eIF4A) inhibitor isolated from the fruits and twigs of Aglaia foveolata. Silvestrol induces autophagy and caspase-mediated apoptosis.

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