Abstract A237: Elevated Mnk kinase activity is associated with malignant progression and reduced patient survival in human prostate cancer and can be therapeutically inhibited in human prostate cancer cells by the novel, orally bioavailable Mnk inhibitor cercosporamide

In a wide variety of malignancies, progressive disease and reduced patient survival have been linked to increased function of eukaryotic translation initiation factor 4E (eIF4E), which selectively enhances the translation of potent growth and survival factors and oncoproteins (e.g. c-myc, VEGF, cyclin D1, Mcl-1, MMP-9, etc.). Recent published reports have shown that the oncogenic activity of eIF4E is critically dependent on the activity of the MNK kinases (Map kinase interacting kinase 1 and 2), which phosphorylate eIF4E at S209 (p4ES209). Increased p4ES209 has been linked to a variety of advanced cancers, notably head and neck and non-small cell lung cancers. Herein, we report that p4ES209 is significantly elevated in human prostate cancer (CaP) tissues (n=133) and associated with reduced patient survival. p4ES209 is elevated In both low grade (Gleason score ≤ 6) and high grade (Gleason score ≥ 7) CaP vs. adjacent normal prostate tissue (BPH) (p < 0.02 and p < 0.0001, respectively). Elevated p4ES209 in invasive CaP is related to significantly reduced patient survival (p = 0.0216) and increased risk of death from CaP (hazard ratio = 2.729). Moreover, p4ES209 is evident in the LNCaP, LNAI, CWR22Rv1 CaP cell lines, with levels being highest in the castrate-resistant cells (LNAI and CWR22Rv1). shRNA-mediated knock-down of MNK 1 and 2 reduced p4ES209 levels and specifically triggered apoptosis. Similarly, treatment of these cell lines with the novel, orally-bioavailable MNK inhibitor, cercosporamide, reduced p4ES209 in a dose-dependent manner and induced apoptosis coincident with reduced expression of key translationally controlled proteins (e.g. Mcl-1). Further, oral administration of this inhibitor can suppress p4ES209 in normal mouse tissues and in xenografted human cancers within 30 minutes, lasting at least 4 hours in tumor tissue. These data demonstrate the utility of cercosporamide in probing MNK function in vitro and in vivo and highlight the potential utility of targeting MNK for prostate cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A237.