Mantle cell lymphoma (MCL) is a heterogeneous disease with most patients following an aggressive clinical course, whereas others having an indolent behavior. We conducted an integrative and multidisciplinary analysis of 177 MCL to determine whether the immunogenetic features of the clonotypic B-cell receptors (BcR) may identify different subsets of tumors. Truly unmutated (100% identity) IGHV genes were found in 24% cases, 40% were minimally/borderline mutated (99.9%–97%), 19% significantly mutated (96.9%–95%), and 17% hypermutated (<95%). Tumors with high or low mutational load used different IGHV genes, and their gene expression profiles were also different for several gene pathways. A gene set enrichment analysis showed that MCL with high and low IGHV mutations were enriched in memory and naive B-cell signatures, respectively. Furthermore, the highly mutated tumors had less genomic complexity, were preferentially SOX11-negative, and showed more frequent nonnodal disease. The best cut-off of germline identity of IGHV genes to predict survival was 97%. Patients with high and low mutational load had significant different outcome with 5-year overall survival (OS) of 59% and 40%, respectively (P = 0.004). Nodal presentation and SOX11 expression also predicted for poor OS. In a multivariate analysis, IGHV gene status and SOX11 expression were independent risk factors. In conclusion, these observations suggest the idea that MCL with mutated IGHV, SOX11-negativity, and nonnodal presentation correspond to a subtype of the disease with more indolent behavior. Cancer Res; 72(20); 5307–16. ©2012 AACR.

In summary, SKLB1028 is a novel multikinase inhibitor that displays exceptional activity in models of FLT3-driven AML and considerable potency in CML that harbors Abl mutations. SKLB1028 has the convenience of oral administration, favorable pharmacokinetic properties and low toxicity. Collectively, preclinical assessment of the pharmacodynamics, pharmacokinetics and initial toxicity of SKLB1028 supports the use of SKLB1028 as a promising candidate for clinical studies in patients with leukemia. Finally, we must mention that SKLB1028 differs from other known FLT3 inhibitors in that it is also a typical EGFR inhibitor. This characteristic of SKLB1028 is noteworthy because of the recent unexpected findings that EGFR inhibitors, such as 4,5-dianilinophthalimide (DAPH1), gefitinib and erlotinib, are able to promote differentiation and induce apoptosis in AML blasts in vitro. 14,15 Because AML cells do not express EGFR, the observed activity of EGFR inhibitors on AML cells cannot be due to inhibition of EGFR, but must have resulted from inhibition of an off-target kinase that is as yet uncharacterized. Whether SKLB1028 has the same effect on AML or acts on the same off-target kinases as other EGFR inhibitors remains to be determined.

Mantle cell lymphoma (MCL) is one of the most aggressive lymphoid neoplasms whose pathogenesis is not fully understood. The neural transcription factor SOX11 is overexpressed in most MCL but is not detected in other mature B-cell lymphomas or normal lymphoid cells. The specific expression of SOX11 in MCL suggests that it may be an important element in the development of this tumor, but its potential function is not known. Here, we show that SOX11 promotes tumor growth in a MCL-xenotransplant mouse model. Using chromatin immunoprecipitation microarray analysis combined with gene expression profiling upon SOX11 knockdown, we identify target genes and transcriptional programs regulated by SOX11 including the block of mature B-cell differentiation, modulation of cell cycle, apoptosis, and stem cell development. PAX5 emerges as one of the major SOX11 direct targets. SOX11 silencing downregulates PAX5, induces BLIMP1 expression, and promotes the shift from a mature B cell into the initial plasmacytic differentiation phenotype in both primary tumor cells and an in vitro model. Our results suggest that SOX11 contributes to tumor development by altering the terminal B-cell differentiation program of MCL and provide perspectives that may have clinical implications in the diagnosis and design of new therapeutic strategies.

SOX11 overexpression in Mantle Cell Lymphoma (MCL) has been associated with more aggresive behavior and worse outcome. However, SOX11 oncogenic pathways driving MCL tumor progression are poorly known. Here, we demonstrate that SOX11 binds to regulatory regions of two important genes for microenvironment-signals in cancer, (C-X-C motif) chemokine receptor 4 (CXCR4) and PTK2 (encoding for focal adhesion kinase (FAK)). Moreover, SOX11-positive xenograft and human primary MCL tumors overexpress cell migration and stromal stimulation gene signatures compared to their SOX11-negative counterparts. We show that SOX11 directly up-regulates CXCR4 and FAK expression, activating PI3K/AKT and ERK1/2 FAK-downstream pathways in MCL. Concordantly, SOX11-positive MCL cells have higher cell migration, transmigration through endothelial cells, adhesion to stromal cells and cell proliferation; and display an increased resistance to conventional drug therapies, compared to SOX11-negative MCL cells. Specific FAK inhibition blocks downstream PI3K/AKT- and ERK1/2-mediated phosphorylation. Additionally, specific FAK- and PI3K-inhibitors reduce SOX11-enhanced MCL cell migration and stromal-interactions, and revert cell adhesion mediated-drug resistance (CAM-DR), to the same levels as SOX11-negative MCL cells. In intravenous MCL xenograft models, SOX11-positive MCL cells display higher cell migration, invasion and growth compared to SOX11-knockdown cells, and specific FAK- and CXCR4-inhibitors impair SOX11-enhanced MCL engraftment in bone marrow. Overall, our results suggest that SOX11 promotes MCL homing and invasion, and increases CAM-DR through the direct regulation of CXCR4 and FAK expression and FAK/PI3K/AKT pathway activation, contributing to a more aggressive phenotype. Inhibition of this pathway may represent an efficient strategy to overcome stromal-mediated chemo-refractoriness in aggressive MCL. Key points SOX11 regulates MCL homing and invasion via direct regulation of CXCR4 and FAK expression, and PI3K/AKT and ERK1/2 signaling activation. SOX11 expression increases cell adhesion mediated-drug resistance (CAM-DR) contributing to a more aggressive MCL phenotype.

SOX11 is overexpressed in several solid tumors and in the vast majority of aggressive mantle cell lymphomas (MCLs). We have recently proven that SOX11 silencing reduces tumor growth in a MCL xenograft model, consistent with the indolent clinical course of the human SOX11-negative mantle cell lymphoma (MCL). However, the direct oncogenic mechanisms and downstream effector pathways implicated in SOX11-driven transformation remain poorly understood. Here, we observed that SOX11-positive xenograft and human primary MCL tumors overexpressed angiogenic gene signatures and had a higher microvascular density compared with their SOX11-negative counterparts. Conditioned media of SOX11-positive MCL cell lines induced in vitro endothelial cell proliferation, migration, tube formation, and activation of downstream angiogenic pathways. We identified PDGFA as a SOX11 direct target gene upregulated in MCL cells whose inhibition impaired SOX11-enhanced in vitro angiogenic effects on endothelial cells. In addition, platelet-derived growth factor A (PDGFA) was overexpressed in SOX11-positive but not in SOX11-negative MCL. In vivo, imatinib impaired tumor angiogenesis and lymphoma growth in SOX11-positive MCL xenograft tumors. Overall, our results demonstrate a prominent role for SOX11 as a driver of proangiogenic signals in MCL, and highlight the SOX11-PDGFA axis as a potential therapeutic target for the treatment of this aggressive disease.