Fibroblast Growth Factor-1 Inhibition Enhances FAS-Induced Apoptosis in Mantle Cell Lymphoma Cells By Accelerated BIRC2/3 Degradation
Authors: Sehgal Lalit , Jain Neeraj , Tamer Khashab , Willingham Natalie , Samaniego Felipe 
Published: October 2019

Abstract
Fibroblast growth factor-1 Inhibition Enhances FAS-Induced Apoptosis in Mantle Cell Lymphoma Cells by Accelerated BIRC2/3 Degradation.
Neeraj Jain1, Tamer Khashab1, Natalie Willingham2, Felipe Samaniego1 and Lalit Sehgal2
1 Department of Lymphoma/Myeloma, UT MD Anderson Cancer center, Houston, TX 77054
2 Division of Hematology, Comprehensive Cancer Center, The Ohio State University, Columbus, OH, USA
Introduction Mantle cell lymphoma (MCL) is an aggressive form of non-Hodgkin lymphoma that is characterized by the t(11:14)(q13:p32) translocation. MCL cells have altered cyclinD1 levels, impaired cell cycle regulation, DNA damage response, and likely defects in apoptosis signaling. Furthermore, up-regulated anti-apoptotic mediators such as the target of NF-κB BIRC2 and BIRC3 were correlated with decreased apoptosis signaling. Also many cancer cells and malignant tumors show a prevalent resistance to apoptosis induction by FAS. Thus, by understanding the underpinnings of apoptosis resistance, we will be in a better position to develop strategies that improve Fas-induced killing of lymphoma cells.
Methods More detailed insight into MCL pathogenesis has been delayed until the recent development of a tissue culture system, using human mesenchymal stromal cells (hMSC), suitable for propagating primary MCL cells. Isolates of primary MCL cells were co-cultured with human mesenchymal stem cells (hMSCs) and the content of MCL-ICs was analyzed by flow-cytometry based on marker expression profile; CD34-CD3-CD45+CD19-. Cytokine array was used to identify the soluble factors enriched in the co-cultures and the expression of these factors was confirmed by RT-PCR analysis. The signaling pathways employed by the newly-identified factors were blocked in 3 MCL cell lines (JVM2, Mino, Z138) to confirm their essential role in survival of MCL cells and, more importantly, for MCL-ICs.
Results Co-cultures of primary MCL isolates with hMSCs supported the growth of MCL cells for over 4 weeks with continued presence of MCL-ICs (CD34-CD3-CD45+CD19-) representing about 1% of MCL cells. We found that IL-6 produced by hMSCs triggered an FGF/FGFR autocrine loop in MCL-ICs. The extent of FGFR expression correlated tightly with expression of SOX11, a pathology related negative prognostic marker in MCL. MCL cell survival and growth was regulated via the FGFR-1 mediated BIRC2/3 axis. Blocking of this signaling pathway with FGFR-1 inhibitors consistently induced early degradation in BIRC2/3 levels and subsequently MCL cell death.
Conclusion We established that propagation of primary MCL in co-cultures with hMSCs depends on activation of FGF/FGFR-1 autocrine loop that enhances BIRC2/3 protein expression and thus, supports survival of MCL cells. We identified the factors essential for survival of MCL and MCL-ICs that present new targets for improved MCL treatment strategies. This study reveals that inhibition of FGFR-1 signaling by specific inhibitor has a profound positive impact on extrinsic cell death signaling; it enhances FAS sensitivity by promoting processing of caspases through enhanced BIRC2/3 degradation. The capacity of FGFR-1 inhibition to target stability of BIRC2/3, underscores its potential for enhancing efficacy of conventional cancer therapies.

Disclosures
Samaniego: ADC Therapeutics: Research Funding.