Hao, Yansheng

Abstract B-cell receptor (BCR) signaling pathway components represent promising treatment targets in multiple B-cell tumors including diffuse large B-cell lymphoma (DLBCL). BCR signaling activates proximal pathway components such as the spleen tyrosine kinase (SYK) and downstream effectors including PI3K/AKT and NF-κB. In recent studies, we characterized distinct SYK/PI3K/AKT-dependent viability pathways in BCR DLBCL cell lines and primary tumors with high- or low-baseline NF-κB activity and defined additional SYK/PI3K/AKT-dependent processes essential for BCR DLBCLs with low- or high-baseline NF-κB (Chen et al Cancer Cell 2013; 23:826-838). For example, SYK/PI3K/AKT-dependent cholesterol biosynthesis was identified as a feed-forward mechanism of preserving the integrity of BCRs in lipid rafts in all BCR-dependent DLBCLs. In the current study, we sought to identify biomarkers of intact BCR signaling in DLBCLs with low or high baseline NF-κB. We found highly significant transcriptional upregulation of CXCR4 in all BCR-dependent DLBCLs treated with a chemical SYK inhibitor (R406). These results were of particular interest because BCR signaling inhibits stromal cell-derived factor (SDF)-1α chemotaxis and promotes intermobilization of the SDF-1α receptor, CXCR4. To expand on our findings, we analyzed CXCR4 transcript abundance in a large panel of cell lines including BCR-dependent/ low NF-κB (GC type) and BCR-dependent/ high NF-κB (ABC type) and BCR-independent/ OxPhos DLBCLs. CXCR4 transcript abundance was significantly and selectively upregulated in all BCR-dependent DLBCL lines assessed by qRT-PCR following chemical SYK inhibition. Consistent with the qRT-PCR results, SYK blockade also selectively upregulated cell surface CXCR4 expression in all BCR-dependent DLBCLs. Similar results were obtained following SYK knockdown with multiple independent shRNAs; CXCR4 transcript abundance was significantly and selectively upregulated in all BCR-dependent/ low NF-κB (GCB) DLBCLs and BCR-dependent/ high NF-κB (ABC) DLBCLs but was not altered in BCR-independent/ OxPhos tumors. Following SYK blockade, we also observed significant CXCR4 induction (by qRT-PCR) in multiple primary BCR-dependent DLBCLs (NF-κB low and NF-κB high) and unchanged CXCR4 levels in primary BCR-independent tumors. These data confirm that the observations regarding SYK blockade and CXCR4 induction in BCR-dependent DLBCL cell lines translated to primary tumors. Our recent studies indicate that all BCR-dependent DLBCLs exhibit SYK/PI3K/AKT signaling and modulation of FOXO1 regardless of baseline NF-κB levels. Given the recent identification of CXCR4 as a FOXO1 target, we asked whether modulation of CXCR4 in DLBCLs was via a PI3K/AKT pathway. In BCR-dependent DLBCLs with low or high baseline NF-κB, chemical PI3K inhibition (LY294002) phenocopied chemical SYK blockade (R406) with highly significant transcriptional upregulation of CXCR4. Moreover, in BCR-dependent DLBCL cell lines, enforced expression of a constitutively active form of AKT (myrAKT) abrogated CXCR4 upregulation resulting from SYK blockade. These data indicate that in BCR-dependent DLBCLs, CXCR4 is modulated by a SYK/PI3K/AKT-dependent pathway. To assess the functional significance of CXCR4 upregulation in BCR-dependent DLBCLs, we performed a transwell chemotaxis assay and evaluated migration toward a SDF-1α gradient. Following chemical SYK inhibition, all BCR-dependent DLBCLs exhibited significantly increased migration toward the CXCR4 ligand, SDF-1α, whereas the BCR-independent/ OxPhos DLBCLs were unaffected. The enhanced SDF-1α dependent migration was abrogated when the chemotaxis assay was performed in the presence of the specific CXCR4 inhibitor, AMD3100, confirming the specificity of the observed effect. Therefore, in BCR-dependent DLBCLs with low or high baseline NF-kB, SYK/PI3K inhibition is associated with significant and functionally relevant upregulation of CXCR4. For these reasons, CXCR4 may serve as a robust biomarker to assess the integrity of the BCR pathway and evaluate the efficacy of BCR inhibition in DLBCL. Disclosures: Off Label Use: R406 is not get approved, but is being evaluated in DLBCL and CLL.

Abstract Abstract 1534 + equal contributions Diffuse large B-cell lymphoma (DLBCL) is a clinically and biologically heterogeneous disease with a high proliferation rate and infrequent somatic mutations of TP53 and genes encoding cell cycle pathway components. Despite recent advances in the molecular understanding of DLBCL pathogenesis, clinical models such as the International Prognostic Index (IPI) are still used to identify high-risk patients. By integrating high-resolution high-density SNP array data with transcriptional profiles and performing pathway analysis in 180 primary DLBCLs, we identified a comprehensive set of copy number alterations (CNAs) that decreased p53 activity and perturbed cell cycle regulation. Primary DLBCLs with single copy loss of 17p13.1 (TP53/RPL26/KDM6B) often had CNAs of an additional p53 modifier – 9p21.3 (CDKN2A/ARF), 19q13.42 (BCL2L12), 12q15 (MDM2) or 1q23.3 (MDM4/RFWD2). CNAs of the respective p53 modifiers, CDKN2A (ARF, 9p21.3), MDM2 (12q15) and MDM4/RFWD2 (1q23.3), occurred in largely separate groups of tumors. DLBCLs with CNAs of p53 pathway members frequently exhibited concurrent alterations of additional cell cycle components such as CCND3 (6p21.32), CDK6 (7q22.1), CDK2/CDK4 (12q15) and/or RB1 (13q14.2) or RBL2 (16q12.2). When the primary DLBCLs were clustered in the space of CNAs that perturb p53 pathway and cell cycle components, 66% of tumors had multiple alterations (“complex” pattern) whereas the remaining 34% of tumors lacked these lesions (“clean” signature). Tumors with “complex” alterations of p53 pathway and cell cycle components also had more total CNAs and more frequent TP53 mutations, highlighting the association between p53 deficiency, cell cycle deregulation and increased genomic instability in DLBCL. The patterns of “complex” vs. “clean” CNAs of p53 pathway and cell cycle components and the association between the “complex” signature and total CNAs were confirmed in an independent series of primary DLBCLs. To further characterize DLBCLs with “complex” vs. “clean” CNA patterns, we performed gene set enrichment analyses with publicly available series of p53 target genes and a RB-deficiency gene set which included multiple E2F targets. The p53 target transcripts were significantly less abundant in “complex” DLBCLs, directly linking their genetic signature of p53 deficiency with decreased p53 activity. Furthermore, the RB-deficiency gene set was significantly enriched in “complex” DLBCLs suggesting that these tumors had increased E2F-mediated cell cycle progression. Consistent with these observations, DLBCLs with “complex” CNA patterns also had significantly higher proliferation indices as determined by Ki67 immunostaining. We next assessed the prognostic significance of the “complex” CNA pattern in the subset of patients who were treated with R-CHOP (rituxan, cyclophosphamide, adriamycin, oncovin, prednisone) and had long-term follow-up. R-CHOP treated patients with “complex” CNA patterns had a 5-year overall survival of only 62%; in contrast, those with “clean” CNA signatures had an 100% overall survival (p =.001). The association between CN complexity and outcome was independent of transcriptionally defined categories and additive to the clinical IPI risk model. Taken together, these data provide a structural basis for deregulated cell cycle, increased cellular proliferation and unfavorable outcome in DLBCL and suggest targeted treatment strategies. Disclosures: No relevant conflicts of interest to declare.