Inhibition of the Translation Initiation Factor eIF4A Enhances Tumor Cell Radiosensitivity

Abstract

A fundamental component of cellular radioresponse is the translational control of gene expression. As a critical regulator of translational control is the eIF4F cap binding complex, we investigated whether eIF4A, the RNA helicase component of eIF4F, can serve as a target for radiosensitization. Knockdown of eIF4A using siRNA reduced translational efficiency, as determined from polysome profiles, and enhanced tumor cell radiosensitivity as determined by clonogenic survival. The increased radiosensitivity was accompanied by a delayed dispersion of radiation-induced γH2AX foci, suggestive of an inhibition of DNA double strand break repair. Studies were then extended to (-)-SDS-1-021, a pharmacological inhibitor of eIF4A. Treatment of cells with the rocaglate (-)-SDS-1-021 resulted in a decrease in translational efficiency as well as protein synthesis. (-)-SDS-1-021 treatment also enhanced the radiosensitivity of tumor cell lines. This (-)-SDS-1-021-induced radiosensitization was accompanied by a delay in radiation-induced γH2AX foci dispersal, consistent with a causative role for the inhibition of double strand break repair. In contrast, while (-)-SDS-1-021 inhibited translation and protein synthesis in a normal fibroblast cell line, it had no effect on radiosensitivity of normal cells. Subcutaneous xenografts were then used to evaluate the in vivo response to (-)-SDS-1-021 and radiation. Treatment of mice bearing subcutaneous xenografts with (-)-SDS-1-021 decreased tumor translational efficiency as determined by polysome profiles. While (-)-SDS-1-021 treatment alone had no effect on tumor growth, it significantly enhanced the radiation-induced growth delay. These results suggest that eIF4A is a tumor selective target for radiosensitization.

Discovery of RNA-Protein Molecular Clamps Using Proteome-Wide Stability Assays

“…Having gained an understanding of optimal TSAR assay parameters, we forged ahead and evaluated a diverse set of representative rocaglates with varied core functionality. Our panel consisted of rocaglaol, RocA, silvestrol, CR-1-31-B , SDS-1-021 (64, 65), and the clinical candidate Zotatifin ( eFT226 ) ( Figure 1 ). Each compound was tested at a concentration of 10 µ M in A549 cell lysate pre-loaded with AMP-PNP (1 mM) and (AG) 8 RNA or (CU) 8 RNA (1 µ M), totaling four separate experiments with each rocaglate-RNA pair tested in quadruplicate.…”

Single Cell Profiling Distinguishes Leukemia-Selective Chemotypes

“…Only the vehicles and three RRs did not trigger significant DNA damage in either cell type. Nearly all ADRs and one RR (SDS-1-021 [61][62][63][64][65] , represented twice in the set as both racemic (CMLD011880) and enantioenriched (CMLD010508) stocks) triggered significant DNA damage in PBMC alone. Distinctly, two ADRs induced significant DNA damage in both cell types.…”

A second-generation eIF4A RNA helicase inhibitor exploits translational reprogramming as a vulnerability in triple-negative breast cancer

“…Our results highlight the value of eIF4A as a therapeutic target in vivo and offer a strategy to directly inhibit mRNA translation by targeting eIF4A activity. Studies testing other rocaglates have shown that eIF4A inhibition increases the radiosensitivity of tumors ( 69 ) and also improves the response to targeted therapies, including MEK ( 70 ) and CDK4/6 inhibitors ( 71 ).…”