Abdellatif Amri

Molecular targeting of the oncogene eIF4E in acute myeloid leukemia (AML): a proof-of-principle clinical trial with ribavirin

The eukaryotic translation initiation factor eIF4E is elevated in 30% of malignancies including M4/M5 subtypes of acute myeloid leukemia (AML). The oncogenic potential of eIF4E arises from its ability to bind the 7-methyl guanosine (m(7)G) cap on mRNAs, thereby selectively enhancing eIF4E-dependent nuclear mRNA export and translation. We tested the clinical efficacy of targeting eIF4E in M4/M5 AML patients with a physical mimic of the m(7)G cap, ribavirin. Among 11 evaluable patients there were 1 complete remission (CR), 2 partial remissions (PRs), 2 blast responses (BRs), 4 stable diseases (SDs), and 2 progressive diseases (PDs). Ribavirin-induced relocalization of nuclear eIF4E to the cytoplasm and reduction of eIF4E levels were associated with clinical response. Lack of response or relapse coincided with continued or renewed nuclear localization of eIF4E. This first clinical study to target eIF4E in human malignancy demonstrates clinical activity and associated molecular responses in leukemic blasts. This trial is registered at ClinicalTrials.gov (NCT00559091).

The sonic hedgehog factor GLI1 imparts drug resistance through inducible glucuronidation

Drug resistance is a major hurdle in oncology. Responses of acute myeloid leukaemia (AML) patients to cytarabine (Ara-C)-based therapies are often short lived with a median overall survival of months. Therapies are under development to improve outcomes and include targeting the eukaryotic translation initiation factor (eIF4E) with its inhibitor ribavirin. In a Phase II clinical trial in poor prognosis AML, ribavirin monotherapy yielded promising responses including remissions; however, all patients relapsed. Here we identify a novel form of drug resistance to ribavirin and Ara-C. We observe that the sonic hedgehog transcription factor glioma-associated protein 1 (GLI1) and the UDP glucuronosyltransferase (UGT1A) family of enzymes are elevated in resistant cells. UGT1As add glucuronic acid to many drugs, modifying their activity in diverse tissues. GLI1 alone is sufficient to drive UGT1A-dependent glucuronidation of ribavirin and Ara-C, and thus drug resistance. Resistance is overcome by genetic or pharmacological inhibition of GLI1, revealing a potential strategy to overcome drug resistance in some patients.

The eIF4E RNA regulon promotes the Akt signaling pathway

Eukaryotic initiation factor 4E (eIF4E) promotes cellular proliferation and can rescue cells from apoptotic stimuli such as serum starvation. However, the mechanisms underlying apoptotic rescue are not well understood. In this study, we demonstrate that eIF4E overexpression leads to enhanced survival signaling through Akt and that eIF4E requires Akt1 to rescue serum-deprived fibroblasts. Furthermore, a mutant form of eIF4E (W73A), which is messenger RNA (mRNA) export competent but does not promote translation, rescues cells as readily as wild-type eIF4E. We show that eIF4E mediates Akt activation via up-regulation of Nijmegen breakage syndrome 1 (NBS1), a phosphoinositide-3 kinase–Akt pathway upstream activator. Additionally, eIF4E coordinately up-regulates the expression of downstream effectors of the Akt pathway, thereby amplifying Akt signaling effects. A negative regulator of eIF4E, the promyelocytic leukemia protein (PML), suppresses Akt activation and apoptotic rescue. These PML activities likely arise, at least in part, through its inhibition of eIF4E-mediated NBS1 mRNA export. In summary, eIF4E coordinately regulates gene expression to potentiate Akt activation, an activity required for apoptotic rescue.

The Oncogene eIF4E Reprograms the Nuclear Pore Complex to Promote mRNA Export and Oncogenic Transformation

The eukaryotic translation initiation factor eIF4E is a potent oncogene that promotes the nuclear export and translation of specific transcripts. Here, we have discovered that eIF4E alters the cytoplasmic face of the nuclear pore complex (NPC), which leads to enhanced mRNA export of eIF4E target mRNAs. Specifically, eIF4E substantially reduces the major component of the cytoplasmic fibrils of the NPC, RanBP2, relocalizes an associated nucleoporin, Nup214, and elevates RanBP1 and the RNA export factors, Gle1 and DDX19. Genetic or pharmacological inhibition of eIF4E impedes these effects. RanBP2 overexpression specifically inhibits the eIF4E mRNA export pathway and impairs oncogenic transformation by eIF4E. The RanBP2 cytoplasmic fibrils most likely slow the release and/or recycling of critical export factors to the nucleus. eIF4E overcomes this inhibitory mechanism by indirectly reducing levels of RanBP2. More generally, these results suggest that reprogramming the NPC is a means by which oncogenes can harness the proliferative capacity of the cell.

Abstract 3165: Anti-tumor activity of the eIF4E-targeted drug ribavirin in breast cancer cells

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC In this study, we explored the potential of targeting the eukaryotic translation initiation factor (eIF4E) with ribavirin as a novel anti-tumor agent in breast cancer. eIF4E is an oncogene that facilitates nuclear export and translation of specific, growth-stimulatory mRNAs, including cyclins, c-myc, survivin, VEGF and others, thereby promoting cell survival. Overexpression of eIF4E also leads indirectly to activation of Akt, providing a positive feed-back loop for eIF4E activation and Akt signaling effects. Ribavirin is an antiviral drug that has been shown to inhibit oncogenic transformation mediated by eIF4E and reduce the clonogenic potential of cancer cells with high eIF4E levels. Ribavirin specifically inhibits translation and/or nuclear export of eIF4E targets in cells both in vitro and in patients, as shown in a recent phase I/II proof-of-principle trial in patients with AML. In this trial, dramatic clinical improvements were observed and reductions in eIF4E levels and activity correlated with clinical response. Importantly, ribavirin is largely non-toxic even at high doses, possibly due to an eIF4E oncogene addiction specific to tumor cells. eIF4E is overexpressed in more than 50% of breast cancers, and high levels are associated with increased angiogenesis, clinical progression and poor prognosis. Targeting eIF4E with ribavirin may therefore be an attractive therapeutic strategy for this malignancy. We studied the effects of ribavirin in a panel of breast cancer cells, representing luminal and basal-type tumors with various ER, PR and Her2 status. Western blot analysis showed that eIF4E was overexpressed compared to normal breast tissue and predominantly cytoplasmic in all of the cell lines. In addition, we examined eIF4E levels in metastatic skin lesions of three breast cancer patients and found highly elevated levels compared to normal skin. Ribavirin anti-proliferative activity was assessed using a cell viability assay and clonogenic assays were performed to examine changes in both anchorage dependent and -independent growth. At clinically relevant concentrations, the majority of the cell lines responded to ribavirin, with varying sensitivity. Inhibition of cell growth was associated with decreased protein levels of eIF4E targets such as cyclin D1 and survivin, and a reduction in phosphorylation of Akt as well as eIF4E binding protein 1 (4E-BP1) were observed. Cell cycle analysis showed that ribavirin caused a significant S-phase arrest in sensitive cells, while apoptosis was only observed at elevated concentrations of the drug. This data encourages further study of ribavirin as a breast cancer therapeutic and identification of potential combination regimens. A clinical trial of single agent ribavirin in patients with advanced metastatic breast cancer is planned in the near future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3165.