Overcoming the Supportive Stroma-Induced Proliferation in Waldenstrom's Macroglobulinemia By Selective Inhibition of the FGF/FGF-Receptor Axis

The human fibroblast growth factor receptor (FGF-R) family plays an essential role in a wide range of cellular processes, such as cell growth, proliferation, differentiation, migration and survival. It has been reported that FGF-Rs are expressed in hematopoietic cells; and FGF/FGFR signaling deregulation is largely involved in hematologic malignancies, including Waldenström macroglobulinemia (WM). WM is still an incurable disease, and patients succumb due to disease progression. Therefore, novel therapeutics designed to specifically target deregulated signaling pathways in WM are required. We aimed to investigate the role of FGF/FGF-R system in FGF-dependent WM cell lines by using an anti-pan FGF trap molecule (NSC12), responsible for FGF/FGF-R blocking. We first interrogated the GSE9656 dataset in order to confirm the expression of FGFs and FGF-Rs in WM cells, demonstrating an enrichment of several FGF- and FGF-R-isoforms in primary WM patients' derived tumor cells compared to the normal cellular counterpart (P<0.05); and demonstrated the ability of NSC12 to inhibit FGF-secretion within the conditioned media of NCS12-treated WM cells, as shown by ELISA. Wide-transcriptome profiling of NSC12-treated WM cells (BCWM.1; MWCL1) revealed a significant inhibition of Myc-target related genes, coupled with silencing of genes involved in cell cycle progression, cell proliferation, PI3K-AKT-mTOR signaling, oxidative phosphorylation (Hallmark; FDR<0.25; P<0.05). This prompted us to evaluate the anti-tumor functional sequelae exerted by NSC12 in WM cells: NSC12 induced significant inhibition of WM cell growth (BCWM1 and WMCL1) in a dose-dependent fashion (0.1-10μM; IC50 ~3μM), even in the presence of bone marrow microenvironment. In addition, a significant effect was also observed in primary tumor cells from WM patients; while no effect was observed on healthy donor-derived peripheral blood mononuclear cells. The growth inhibitory effect was associated with induction of apoptotic cell death, caspase activation and PARP cleavage, as demonstrated by flow cytometry and western blot, respectively. Moreover, we also observed a NSC12 dose-dependent increase of mitochondrial reactive oxigen species (ROS), at protein level. Cell cycle analysis revealed a reduction of the S-phase and increase of G0/G1 phase. Mechanistically, NSC12 targeted WM cells by inhibiting MAPK, JAK/STAT3 and PI3K-Akt pathways known to be FGFRs-activated signaling cascades. Importantly, the same effect was maintained in WM cells even in the presence of the supporting BM microenvironment. Functional studies demonstrated the ability of NSC12 to impair the adhesion of both cell lines to the supportive primary bone marrow stromal cells, in vitro. NCS12-dependnet anti-WM activity was also tested in combination with bortezomib, carfilzomib, everolimus and ibrutinib: the combinatory treatment (48h) resulted in a more significant dose-dependent inhibition of WM cell survival and proliferation (P<0.05), thus suggesting the rational for combining FGF-blockade with proteasome-, mTOR-, or BTK-inhibitors. In vivo studies are being performed, in order to further corroborate the anti-WM activity of NSC12 using WM animal models.