Abstract C052: FGF trapping impairs multiple myeloma growth through c-Myc degradation-induced mitochondrial oxidative stress
Authors: Ronca Roberto , Ghedini Gaia Cristina , Maccarinelli Federica , Sacco Antonio , Locatelli Silvia Laura , Foglio Eleonora , Taranto Sara , Grillo Elisabetta , Matarazzo Sara , Castelli Riccardo , Desantis Vanessa , Cattane Nadia , Cattaneo Annamaria , Mor Marco , Carlo-Stella Carmelo , Roccaro Aldo Maria , Presta Marco , Giacomini Arianna 
Published: March 2020

Multiple myeloma (MM) remains incurable because of chemotherapeutic resistance. Fibroblast growth factors (FGF) play a pivotal role in MM by acting as an autocrine/paracrine mitogen on plasma cells, bone marrow-derived endothelial cells and fibroblasts. Also, a recurrent chromosomal translocation t(4;14) is associated with FGFR3 upregulation in MM patients. Thus, agents able to hamper FGF signaling may represent a novel approach for MM treatment. Recently we have identified the PTX3-derived small molecule NSC12 as the first orally active antitumor pan-FGF trap. Here, the role of FGF/FGFR system in MM cell survival and the therapeutic potential of NSC12 were investigated. In vitro effects of NSC12 were tested on four human MM cell lines harboring (KMS-11 and OPM-2 cells) or not (U-266 and RPMI8226 cells) the t(4:14) translocation and on patient-derived MM cells (N = 26). In vivo effects of FGF blockade were investigated using subcutaneous (KMS-11 and RPMI8226 cells) and systemic (MM-1S cells) xenografts grown in NOD/SCID mice. In addition, gene expression profiling (GEP) and gene set enrichment analyses (GSEA) were performed in NSC12-treated MM cells. NSC12 blocked the proliferation of all human MM cell lines tested, causing inhibition of FGFR signaling, downregulation of the anti-apoptotic protein mcl-1 and caspase 3 activation. Cytofluorimetric analysis revealed a significant increase of apoptotic cells as early as 6 hrs after NSC12 treatment, with 100% of cell death after 24 hrs even when MM cells were co-cultured with patient-derived bone marrow stromal cells. In vivo, NSC12 blocked FGFR activation and reduced the growth of subcutaneous xenografts and MM cell dissemination in the BM. GEP and GSEA analyses of NSC12-treated cells revealed the upregulation of oxidative stress-induced genes and the downmodulation of c-Myc targets. Accordingly, NSC12 caused the rapid proteasomal degradation of c-Myc paralleled by GSH depletion, mitochondrial ROS production and depolarization, DNA damage and finally apoptosis in KMS-11 cells but not in KMS-11 cells expressing the undegradable mutated (T58A) form of c-Myc. Interestingly, these findings were confirmed on Bortezomib-resistant MM cells as well as on bone marrow-derived primary MM cells from newly diagnosed and relapsed/refractory patients, including plasma cells bearing the t(4;14) translocation obtained from high-risk MM patients. Our data reveal that FGF blockade triggers MM mitochondrial oxidative stress, DNA damage and apoptotic cell death via the proteasomal degradation of the c-Myc oncoprotein. Altogether, our findings dissect for the first time the mechanism by which the FGF/FGFR system plays a non-redundant role in MM cell survival and disease progression, and indicate that FGF targeting may represent a therapeutic approach for MM patients with poor prognosis and advanced disease stage.

Citation Format: Roberto Ronca, Gaia Cristina Ghedini, Federica Maccarinelli, Antonio Sacco, Silvia Laura Locatelli, Eleonora Foglio, Sara Taranto, Elisabetta Grillo, Sara Matarazzo, Riccardo Castelli, Vanessa Desantis, Nadia Cattane, Annamaria Cattaneo, Marco Mor, Carmelo Carlo-Stella, Aldo Maria Roccaro, Marco Presta, Arianna Giacomini. FGF trapping impairs multiple myeloma growth through c-Myc degradation-induced mitochondrial oxidative stress [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C052. doi:10.1158/1535-7163.TARG-19-C052