Abstract B051: Exploiting translation inhibition: antitumor efficacy of SVC112 in preclinical models of colorectal cancer

Abstract

Abstract Background: Colorectal cancer (CRC) ranks third in new cases and cancer deaths in the U.S. annually. The current front-line treatments for metastatic CRC (mCRC) are ineffective for an appreciable proportion of patients and induce significant toxicities. Thus, there is an urgent need for the development of new therapeutic strategies. Translation is a novel, underutilized target for cancer therapeutics. Eukaryotic elongation factor 2 (eEF2) is often overexpressed in CRC, causing upregulation of translation, upon which CRC may be dependent. Therefore, it may be possible to differentially target CRC cells by inhibiting translation. SVC112 is a novel inhibitor of translation and the parent molecule of SVC112 has been shown to lock eEF2 onto the ribosome. As such, this agent may be effective against mCRC by blocking translation of key oncogenes such as c-myc, which is overexpressed in mCRC. Methods: Forty-four CRC cell lines were exposed to SVC112 in vitro and CellTiter Glo ATP quantification was used to determine sensitivity or resistance based on IC50 values. Select sensitive and resistant cell lines were further validated with clonogenic assays to evaluate for sustained response. Immunoblotting was performed to assess levels of c-myc, survivin, and cyclin D1 in response to treatment with SVC112. Amino acid incorporation was measured using the Click-IT AHA kit protocol. eEF2 mRNA levels were ascertained from RNA seq data while cell cycle effects were determined by flow cytometry. Two cell line xenografts deemed to be sensitive based on IC50 values were treated in vivo with SVC112. Results: A subset of CRC cell lines were found to be sensitive to SVC112 in vitro, and notably, there was a trend towards increased eEF2 expression and greater responsiveness to SVC112. In sensitive cell lines, c-myc was downregulated by SVC112 in a dose-dependent manner whereas in resistant cell lines c-myc levels were not affected. Moreover, SVC112 caused a reduction of amino acid incorporation in sensitive cell lines compared to resistant cell lines. Likewise, the sensitive cell lines exhibited dose-dependent effects on the cell cycle with SVC112 whereas resistant cell lines did not. SVC112 demonstrates synergy with 5-FU in sensitive cell lines, while in the models and dosing conditions tested thus far, SVC112 has not demonstrated single agent efficacy in vivo. Conclusions: SVC112 demonstrates anticancer effects in a subset of CRC cell lines, indicating that translation machinery may be an effective druggable target in CRC. There is an apparent correlation between EF2 levels and sensitivity, which could be used as a selection strategy for sensitive tumors moving forward. SVC112’s ability to decrease amino acid incorporation and deplete c-myc in sensitive cell lines substantiates the proposed mechanism of action. Further experiments are needed to investigate the mechanism of resistance and whether this is related to anti-eEF2 exposure or a mechanism unrelated to eEF2 escape. Further analysis of SVC112 ribosomal engagement is ongoing. SVC112 has demonstrated synergistic effects with 5-FU, a standard chemotherapeutic for CRC, indicating its potential efficacy in combination therapy. Currently, PK analysis is under way and alternative dosing regimens in vivo may be warranted. Citation Format: Kelli M. Robertson, Annika L. Gustafson, John J. Tentler, Stacey M. Bagby, Capasso Anna, Peter J. Klauck, Todd M. Pitts, Jihye Kim, Aik Choon Tan, Tin Tin Su, S. Gail Eckhardt. Exploiting translation inhibition: antitumor efficacy of SVC112 in preclinical models of colorectal cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B051.