Abstract 1114: Role of the FGFR1-KDM2B-EZH2 signaling axis in bone-marrow microenvironment mediated tumor survival & drug resistance in Mantle cell lymphoma
Authors: Sircar Anuvrat , Singh Satishkumar , Laliotis Georgios , Chavdoula Evangelia , Hart Amber , Tsichlis Philip N. , Sehgal Lalit 
Published: July 2021

Abstract
Mantle Cell Lymphoma (MCL) is a rare but aggressive form of Non-Hodgkin's lymphoma, with high rates of progression & extensive bone marrow (BM) involvement. There is a high propensity towards development of drug resistance against treatment options presently available such as ibrutinib, a Bruton's Tyrosine Kinase (BTK) inhibitor. The BM provides a secure niche for MCL cells to thrive. Unbiased transcriptome analysis revealed Fibroblast Growth Factor Receptor-1 (FGFR1) as a major upregulated candidate in ibrutinib-resistant (IR) patients & MCL cells cultured under the influence of BM stroma. FGFR1 knockdown downregulates expression of EZH2 (a catalytic subunit of PRC2 complex involved in epigenetic regulation), which has a high expression in BM stroma cultured MCL cells & linked to poor patient survival. A putative protein linking these two is KDM2B (Lysine demethylase 2B) shown in other cancer types. We found KDM2B to be higher in BM stroma cultured MCL. However, there is no known information regarding presence/functioning of the FGFR1-KDM2B-EZH2 axis, along with if/how this axis may confer stroma-mediated proliferative or drug resistance benefits in MCL. In this study, we performed variety of proliferation, ibrutinib sensitivity & cell survival tests on MCL grown under BM stromal influence. Cytokine arrays were performed to identify specific cytokine upregulation in stromal milieu, followed by subsequent stromal knockdown & reevaluation of MCL growth kinetics. FGFR1 & KDM2B were individually knocked down (KD) in IR-MCL cells & above-mentioned assays repeated. ChIP-qPCR studies for binding to promoter of miR-101, a previously identified negative regulator of EZH2, were also performed. Our results show that ibrutinib-sensitive MCL patient derived cells have greater proliferation & decreased ibrutinib sensitivity when grown under BM stromal influence, & higher expression of FGFR1, KDM2B & EZH2. The stroma-induced growth advantage is reversed when FGFR1 inhibitor is supplemented in the stromal milieu. Cytokine array identified IL-6 as a major upregulated cytokine in BM stroma-conditioned media, with IL-6 seen to enhance FGFR1 expression & IL-6 KD in stroma reversing the MCL growth advantage. KD of FGFR1 & KDM2B individually in MCL-IR cells reduced proliferation & increased sensitivity to ibrutinib. KDM2B & EZH2 expression were lowered in FGFR1KD cells & expression of miR-101 was increased, along with decreased fold enrichment of KDM2B at the miR-101 promoter locus, indicating a decreased KDM2B-mediated repression of this negative regulator of EZH2, a possible reason for EZH2 down-regulation. These results indicate the vitality of FGFR1-KDM2B-EZH2 signaling axis in tumor progression & drug resistance, shedding light on mechanisms for BM microenvironment mediated tumor survival, paving way for identification of new druggable targets.
Citation Format: Anuvrat Sircar, Satishkumar Singh, Georgios Laliotis, Evangelia Chavdoula, Amber Hart, Philip N. Tsichlis, Lalit Sehgal. Role of the FGFR1-KDM2B-EZH2 signaling axis in bone-marrow microenvironment mediated tumor survival & drug resistance in Mantle cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1114.