Abstract B134: Inhibition of the fibroblast growth factor system by a new FGF trap induces oxidative stress and mitochondrial apoptosis in multiple myeloma cells

Abstract

Abstract Despite advances in systemic and supportive therapies, multiple myeloma (MM) remains incurable because of chemotherapeutic resistance. Fibroblast growth factor-2 (FGF2) plays a pivotal role in MM by acting as an autocrine/paracrine mitogen on plasma cells, bone marrow-derived endothelial cells, and fibroblasts. In keeping with the pivotal role of the FGF system in MM, a recurrent chromosomal translocation t(4;14) is associated with upregulation of FGF receptor-3 (FGFR3) in MM patients. Agents able to hamper FGF signaling are therefore of interest as a novel approach for the treatment of MM. The soluble pattern recognition receptor long pentraxin-3 (PTX3) owns a unique FGF-binding N-terminal domain. Structural/functional characterization of this domain led to the characterization of the pentapeptide ARPCA as a potent FGF antagonist in vitro and in vivo. Subsequently, molecular modeling based on ARPCA structure and small-molecule library fishing have allowed the identification of a novel, orally active 480 Da FGF trap (NSC12) able to hamper tumor growth and vascularization in FGF-driven human lung and prostate tumor models. Here, the therapeutic potential of NSC12 for MM treatment was 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. NSC12 blocked the proliferation of all human MM cell lines with an IC50 ≅ 3 µM. Western blot analysis showed that NSC12 inhibited the activation of FGFR3 signaling and strongly downregulated the antiapoptotic protein mcl-1, leading to the activation of caspase 3. Cytofluorimetric analysis revealed a significant increase of annexin-V+ apoptotic cells as early as 6 hrs after NSC12 treatment, with 100% of cell death after 24 hrs of treatment. Interestingly, apoptosis was observed even when MM cells were cocultured with patient-derived bone marrow stromal cells. In vivo, oral delivery of NSC12 significantly blocked the growth of KMS-11 (286.9 ± 22.4 vs 459.8 ± 27.4 mm3, p<0.001) and RPMI8226 (141.5 ± 17.7 vs 245.9 ± 46.4 mm3, p<0.001) xenografts injected subcutaneously in immune-compromised NOD/SCID mice. Analysis of tumor xenografts from NSC12-treated mice showed a strong increase of TUNEL-positive apoptotic cells and a significant reduction of CD31-positive tumor vascularization compared to xenografts from vehicle-treated mice. In an attempt to get further insights into the proapoptotic mechanism of action of NSC12 in MM cells, we found that NSC12 treatment rapidly induces a significant and progressive increase of mitochondrial depolarization paralleled by massive mitochondrial ROS production, suggesting a key role of mitochondria dysfunction in NSC12-induced MM cell death. In addition, as observed for MM cell lines, NSC12 treatment of patient-derived MM cells (N. of patients=14) strongly reduced FGFR3 phosphorylation and mcl-1 levels and induced the upregulation of oxidative stress-induced genes accompanied by apoptosis. Altogether, these data suggest that NSC12 affects MM tumor growth through a direct cytotoxic activity on MM cells and by inhibiting FGF-mediated paracrine/autocrine crosstalk in the tumor stroma/microenvironment. Thus, NSC12 may represent a novel “two compartment” inhibitor in MM by hampering FGF-dependent angiogenic/oncogenic signaling. Citation Format: Arianna Giacomini, Gaia Cristina Ghedini, Federica Maccarinelli, Silvia Laura Locatelli, Antonio Sacco, Riccardo Castelli, Vanessa Desantis, Aldo Maria Roccaro, Marco Mor, Carmelo Carlo-Stella, Roberto Ronca, Marco Presta. Inhibition of the fibroblast growth factor system by a new FGF trap induces oxidative stress and mitochondrial apoptosis in multiple myeloma cells [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 B134.