Abstract 1886: A novel inhibitor of eIF4F protein translation complex sensitizes DLBCL cells to BCL-2 targeted therapy

Abstract

Abstract The purpose of this project is to investigate the feasibility of using small molecules targeting cap-dependent translation to sensitize B cell lymphoma cells to killing by BCL-2 inhibitors (venetoclax/ ABT-199). We hypothesized that diffuse large B-cell lymphoma (DLBCL) cell survival requires cap-dependent translation, which is facilitated by eukaryotic translation initiation factor 4E (eIF4E)-eIF4G interaction and is promoted by mTOR complex 1 (mTORC1). We used the compound SBI-756, a novel inhibitor targeting the scaffolding protein eIF4G (1). SBI-756 is more potent and selective than previously reported compounds targeting the eIF4E cap-binding protein, or compounds targeting eIF4A helicase. By treating DLBCL cells (germinal center B-cell subtype) with SBI-756 (sub μM concentrations), we discovered profound synergistic induction of apoptosis when combined with venetoclax. Cell viability was reduced even more compared to mTOR kinase inhibitor (TOR-KI) treatment combination. Moreover, SBI-756 was found to reduce the viability (IC50 = 653nM) of VAL lymphoma cells lacking 4E-BP1, while VAL were insensitive to TOR-KI treatment. By using Proximity Ligation Assay (PLA) we showed that SBI-756 treatment prevents eIF4E-eIF4G association in intact lymphoma cells. Dual luciferase assays validated this and indicated a dose-dependent reduction in cap-dependent translation following SBI-756 treatment. Also, Western blot analyses confirmed that SBI-756 treatment did not change mTOR substrates' phosphorylation, indicating that the SBI-756 effect is specific to preventing the eIF4E-eIF4G interaction. Furthermore, SBI-756 treatment reduced polysome formation with a corresponding increase in abundance of monosomes. Lastly, induced expression of 4E-BP1 mutant, which irreversibly binds eIF4E, sensitized DLBCL cells to venetoclax treatment to a similar extent as TOR-KI treatment. Ongoing studies will investigate: (1) The molecular mechanism by which translation inhibition by SBI-756 synergizes with venetoclax to prime DLBCL cells toward apoptosis, and (2) pharmacokinetic and pharmacodynamic effects of venetoclax and SBI-756 treatment on DLBCL progression in vivo. Hence, this project highlights a novel combination for treatment of aggressive lymphomas, and establishes its efficacy using preclinical models. Reference: 1. Feng Y., et al. SBI-0640756 attenuates the growth of clinically unresponsive melanomas by disrupting the eIF4F translation initiation complex. Cancer Res 2015;75(24):OF1-8. Citation Format: Lee-or Herzog, Nancy Nguyen, Honyin Chiu, Sharmila Mallya, Ze'ev A. Ronai, David A. Fruman. A novel inhibitor of eIF4F protein translation complex sensitizes DLBCL cells to BCL-2 targeted therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1886.