Abstract 4883: Targeting tumor-amplified ODC1 with difluoromethylornithine (DFMO) inhibits global protein translation and has antitumor activity in neuroblastoma

Abstract

Abstract MYC genes are predominant oncogenic drivers in neuroblastoma, a lethal pediatric tumor, often via amplification of MYCN. MYC genes coordinately deregulate programs that link cell cycle entry with requisite biomass and energy creation. Polyamine synthesis is one such deregulated program that supports protein synthesis. Ornithine decarboxylase (Odc, encoded by ODC1) is the rate-limiting enzyme in polyamine synthesis, a direct MYC target, and a bonafide oncogene. In addition to hyperactivated MYCN driving polyamine signaling, ODC1 itself is co-amplified in a subset of high-risk tumors. We studied 30 neuroblastoma cell lines and 916 primary tumors via SNP-array. ODC1 amplification (confirmed by qPCR) was found exclusively in tumors with MYCN amplification, though amplification peaks were distinct (ODC1 maps 5.5 Mb telomeric to MYCN). ODC1 amplification was identified in 33 of 256 (13%) MYCN amplified primary tumors and 4 of 13 (31%) MYCN-amplified cell lines. Difluoromethylornithine (DFMO) is an FDA-approved irreversible inhibitor of the oncogenic Odc enzyme, and we have shown DFMO inhibits tumor progression and synergizes with chemotherapy in complementary murine models of neuroblastoma. We postulated DFMO inhibits protein translation as its principal mechanism of anti-tumor activity. Polyamines support protein translation via effects on both eIF5A and eIF4F-complex activities, yet their relative contributions remain poorly defined. Using the puromycin-incorporation assay we show a marked decrease in global protein translation following DFMO exposure (up to 95% reduction), with translation inhibition largely correlated with MYCN amplification status in the tumor cells. Studies to define the dose-response and kinetics of DFMO-mediated inhibition in tumors with distinct MYCN and ODC1 genotypes are ongoing, as are studies of eIF5A-hypusination (by IEF) and eIF4F-complex status (polyamine-dependent 4E-BP phosphorylation). Moreover, eIF5A is required to resolve ribosome stalling at polyproline stretches, so we characterized the human proteome for polyproline motifs (PPP of >3) to define an eIF5A-dependent translatome. Candidate genes of diverse polyproline content are being assessed for sensitivity to DFMO to define whether ribosome pausing and selective translation inhibition contributes to DFMO effects. Elucidating mechanisms of DFMO activity and correlating this with genomic status (MYCN and/or ODC1 amplified) will identify opportunities for drug synergy and provide a responder hypothesis to test in pivotal Phase 2 and 3 clinical trial of DFMO for neuroblastoma. Citation Format: Andrea T. Flynn, Annette Vu, Kangning Liu, Elizabeth Scadden, Edward Attiyeh, Murray Norris, Michelle Haber, Michael Hogarty. Targeting tumor-amplified ODC1 with difluoromethylornithine (DFMO) inhibits global protein translation and has antitumor activity in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4883. doi:10.1158/1538-7445.AM2017-4883