Abstract 1515: GCN2 eIF2 kinase promotes polyamine metabolism and progression of prostate cancer

The Integrated Stress Response (ISR) features multiple protein kinases that each sense distinct cellular stresses, phosphorylating eIF2 to direct gene expression that serves to mitigate cell damage and restore homeostasis. Previously, we reported that the eIF2 kinase GCN2 and the ISR are constitutively active in prostate cancer (PCa) and required to maintain amino acid (AA) homeostasis to sustain tumor growth (Cordova et al., 2022, eLife, 11:e81083). GCN2 is induced by nutrient limitation, and basal GCN2 activation in PCa enhances the expression of transporters that ensure sufficient AAs are available for PCa proliferation. However, while genetic or pharmacological inhibition of GCN2 sharply reduces AAs and growth of PCa cells in culture and mouse models, there is minimal cell death. We hypothesized that signaling pathways function to support cell survival in GCN2-deficient PCa cells and can be targeted to promote cell death in combination therapies. Indeed, we discovered that loss of GCN2 leads to compensatory activation of p53 signaling that blocks cell growth and lowers nutrient expenditure (Cordova & Sommers et al., 2024, Science Signaling, 10.1126/scisignal.adp1375). In this recent report, we also carried out a targeted CRISPR-interference screen in castration-resistant 22Rv1 PCa cells with functional wild type (WT) GCN2 or in cells deleted for GCN2 (GCN2 KO). We discovered that reduced expression of ornithine decarboxylase, the rate-limiting enzyme for polyamine (PA) biosynthesis, was synthetically lethal with loss of GCN2. PAs are polycationic metabolites derived from AAs that are ubiquitous among tissues, but especially abundant in prostate tissue. Given that PA biosynthesis requires AAs and GCN2 maintains AA homeostasis in PCa, we propose that GCN2 regulates PA levels in PCa. Indeed, intracellular levels of both AAs and PAs were decreased in GCN2-inhibited LNCaP cells compared to cells treated with vehicle alone. We sought to determine whether defects in PA metabolism also contribute to the growth defect of GCN2-deficient cells. One of the best characterized functions of PAs involves PA-derived hypusination of the translation factor eIF5A, a post-translational modification of eIF5A that is required for efficient translation of mRNAs encoding polyproline tracts. Interestingly, we found that GCN2 promoted eIF5A hypusination and enhanced the expression of several genes associated with PA metabolism in 22Rv1 cells. To investigate whether GCN2-deficient cells are sensitive to defects in eIF5A hypusination, we cultured WT or GCN2 KO 22Rv1 organoids and treated them with a small molecule inhibitor of eIF5A hypusination. While inhibition of eIF5A hypusination resulted in minimal death of WT cells, there was induced death in GCN2 KO cells. Our study suggests that GCN2 maintains PAs in PCa cells and combined therapies targeting GCN2 and PA processes are an effective strategy for the treatment of PCa. Citation Format: Noah R. Sommers, Ricardo A. Cordova, Ronald C. Wek, Kirk A. Staschke. GCN2 eIF2 kinase promotes polyamine metabolism and progression of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1515.