Search

In chronic lymphocytic leukemia (CLL), epigenetic alterations are considered to centrally shape the transcriptional signatures that drive disease evolution and that underlie its biological and clinical subsets. Characterizations of epigenetic regulators, particularly histone-modifying enzymes, are very rudimentary in CLL. In efforts to establish effectors of the CLL-associated oncogene T-cell leukemia 1A (TCL1A), we identified here the lysine-specific histone demethylase KDM1A to interact with the TCL1A protein in B-cells in conjunction with an increased catalytic activity of KDM1A. We demonstrate that KDM1A is upregulated in malignant B-cells. Elevated KDM1A and associated gene expression signatures correlated with aggressive disease features and adverse clinical outcomes in a large prospective CLL trial cohort. Genetic Kdm1a knockdown (Kdm1a-KD) in Eμ-TCL1A mice reduced leukemic burden and prolonged animal survival, accompanied by upregulated p53 and pro-apoptotic pathways. Genetic KDM1A depletion also affected milieu components (T-, stromal, monocytic cells), resulting in significant reductions of their capacity to support CLL cell survival and proliferation. Integrated analyses of differential global transcriptomes (RNA-seq) and H3K4me3 marks (ChIP-seq) in Eµ-TCL1A vs. iKdm1aKD;Eµ-TCL1A mice (confirmed in human CLL) implicate KDM1A as an oncogenic transcriptional repressor in CLL by altering histone methylation patterns with pronounced effects on defined cell death and motility pathways. Finally, pharmacologic KDM1A inhibition altered H3K4/9 target methylation and revealed marked anti-B-cell-leukemic synergisms. Overall, we established the pathogenic role and effector networks of KDM1A in CLL, namely via tumor-cell intrinsic mechanisms and impacts in cells of the microenvironment. Our data also provide rationales to further investigate therapeutic KDM1A targeting in CLL.

Covalent Bruton tyrosine kinase (BTK) inhibitors, such as ibrutinib, have proven to be highly beneficial in the treatment of chronic lymphocytic leukemia (CLL). Interestingly, the off-target inhibition of IL-2-inducible T-cell kinase (ITK) by ibrutinib may also play a role in modulating the tumor microenvironment, potentially enhancing the treatment benefit. However, resistance to covalently binding BTK inhibitors can develop as the result of a mutation in cysteine 481 of BTK (C481S), which prevents irreversible binding of the drugs. In the present study we performed preclinical characterization of vecabrutinib, a next-generation noncovalent BTK inhibitor that has ITK-inhibitory properties similar to those of ibrutinib. Unlike ibrutinib and other covalent BTK inhibitors, vecabrutinib showed retention of the inhibitory effect on C481S BTK mutants in vitro, similar to that of wild-type BTK. In the murine Eμ-TCL1 adoptive transfer model, vecabrutinib reduced tumor burden and significantly improved survival. Vecabrutinib treatment led to a decrease in CD8+ effector and memory T-cell populations, whereas the naive populations were increased. Of importance, vecabrutinib treatment significantly reduced the frequency of regulatory CD4+ T cells in vivo. Unlike ibrutinib, vecabrutinib treatment showed minimal adverse impact on the activation and proliferation of isolated T cells. Lastly, combination treatment with vecabrutinib and venetoclax augmented treatment efficacy, significantly improved survival, and led to favorable reprogramming of the microenvironment in the murine Eμ-TCL1 model. Thus, noncovalent BTK/ITK inhibitors, such as vecabrutinib, may be efficacious in C481S BTK mutant CLL while preserving the T-cell immunomodulatory function of ibrutinib.

Background: Genomically instable (GI) chronic lymphocytic leukemia (CLL) is characterized by frequent alterations in DNA-damage response (DDR) genes (e.g. TP53, ATM) and related pathways. Conversely, pathogenic networks in CLL cases which maintain genomic integrity and operate with a functional DDR remain incompletely described. Methods: Molecular profiling was conducted on CD19 sorted samples derived from patients registered on the CLL8 study (1st-line, FC vs. FCR) for gene expression (GEP)(n=337, Exon 1.0 ST arrays, Affymetrix), copy number aberrations (CNAs) (n=309, SNP Arrays 6.0, Affymetrix) and mutation analyses/signature projections (n=171, whole exome sequencing, Illumina). FISH, IGHV and TP53 mutation analysis was conducted at trial enrolment. Results: Unsupervised consensus clustering (k=2-6) on variably expressed genes (SD>0.5) was used for class discovery. Two small, but highly differentiated clusters were identified, characterized through NRIP1 and EBF1/tri12. GSEA also segregated the remaining samples into four major clusters showing signatures of inflammation (I) and without inflammation (NI). These clusters were further segregated into GI-CLL clusters with increased “DNA-repair” or clusters with “epithelial-mesenchymal transition”-like signatures (EMT-L). Variability for del(17p)/TP53 mutation was found across clusters (p

Apoptosis is controlled by the expression levels and interplay of pro- and anti-apoptotic BCL-2 family proteins. The specific BCL-2 inhibitor Venetoclax (VEN) showed high efficiency in BCL-2 dependent cancers like chronic lymphocytic leukemia (CLL) or mantle cell lymphoma (MCL). Despite its high efficiency in CLL and MCL, refractory disease can develop. BCL-2 mutations have been described to mediate resistance in CLL cases, however these mutations are only found in a proportion of VEN resistant cases and in a fraction of cells. In order to design alternative therapeutic strategies to overcome drug resistance, a better understanding of the mechanisms mediating resistance to VEN is necessary. VEN-resistant (VEN-R) MCL cell lines (MINO and MAVER-1) were generated by chronic exposure to increasing amounts of VEN (up to 3µM). A significant and stable upregulation of BCL-XL mRNA and protein was seen in the MINO and MAVER-1 resistant cell lines (2 and 4 fold increase in mRNA and 2.6 and 4.5 fold increase in protein, respectively). We used BH3 profiling in combination with VEN treatment for 4h to investigate the differences in anti- and pro-apoptotic signaling in parental and VEN-R cell lines. Additionally, sensitivity to VEN was restored upon shRNA-mediated knockdown of BCL-XL. These results confirmed the importance of BCL-XL upregulation in mediating resistance. Furthermore, we did not detect mutations in BCL-2 upon resistance to VEN via targeted NGS, which is in contrast to results obtained in VEN-R CLL patients (Blombery et al., Cancer Discovery 2019 and Tausch et al., Hematologica 2019). However, the results obtained by dynamic BH3-profiling (VEN treatment in combination with BH3 Profiling) suggest that increase in BCL-XL is most likely not the only alteration necessary to render cells resistant to VEN. In addition, reduced activation of pro-apoptotic proteins like BAX and BAK might contribute to resistance to VEN. In order, to investigate if VEN resistance can be overcome by drug mediated inhibition of BCL-XL we used different therapeutic approaches. Combinational treatment with the BCL-XL inhibitor A-1331852 and VEN or the single treatment with Navitoclax, a combined inhibitor of BCL-2, BCL-W and BCL-XL for 48h reduced cell viability in VEN-R MINO and MAVER-1 cell lines. Furthermore, BDA-366, a BH4 domain BCL-2 inhibitor effectively reduced the cell viability after 48h of treatment in a dose dependent manner in both parental and VEN-R cell lines. The binding of BDA-366 to the anti-apoptotic BCL-2 protein leads to a conformational change into a pro-apoptotic molecule by the exposure of the BH3 domain of the protein. Despite mediating apoptosis in a TP53-independent manner, VEN treatment in CLL has been associated with inferior outcome in the presence of TP53 aberrations. In order to address the role of TP53 dysfunction in mediating resistance to VEN, we generated p53 knock out cell lines (N=2) by CRISPR/Cas9 gene editing. This significantly decreased the sensitivity to VEN compared to p53 WT cell lines. Additionally, the sensitivity to BDA-366 was significantly reduced upon knockout of p53, suggesting an interference of p53 downstream of BCL-2. Overall, VEN resistance is mediated by a permanent increase in BCL-XL mRNA and protein level in MCL. Importantly, BDA-366, which converts the anti-apoptotic BCL-2 molecule into a BAX-like death molecule, could be a potential alternative treatment strategy for BCL-2 dependent cancers even when resistant to VEN. Despite mediating apoptosis in a p53 independent manner, VEN seems to be less effective in p53 deficient cells, underlining the importance of further investigations of treatment combinations in these groups. Disclosures Tausch: Roche: Consultancy, Honoraria, Speakers Bureau; AbbVie: Consultancy, Honoraria, Other: travel support, Speakers Bureau. Döhner:AbbVie, Agios, Amgen, Astellas, Astex, Celator, Janssen, Jazz, Seattle Genetics: Consultancy, Honoraria; AROG, Bristol Myers Squibb, Pfizer: Research Funding; Celgene, Novartis, Sunesis: Honoraria, Research Funding. Stilgenbauer:Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Gilead: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Hoffmann La-Roche: Consultancy, Honoraria, Research Funding, Speakers Bureau; Pharmacyclics: Other: Travel support; Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; AbbVie: Consultancy, Honoraria, Research Funding, Speakers Bureau; AstraZeneca: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; GSK: Consultancy, Honoraria, Research Funding, Speakers Bureau. Schneider:Celgene: Other: travel grant.

In chronic lymphocytic leukemia (CLL) short telomeres are associated with other adverse prognostic factors and poor survival. We and others have described association of telomere length with genomic complexity and clonal evolution in CLL. To understand if telomere shortening rather than being only a marker of cell proliferation, could also functionally contribute to disease progression, we generated Terc knock out in the Eµ-TCL1 murine CLL model (Eµ-TCL1 mTerc-/- mice). Comparison of the Eµ-TCL1 mTerc-/- mice from the generations G1, G2 and G3 with that of Eµ-TCL1 (TCL1+) did not show a difference in disease initiation, progression as well as survival even though a significant decrease in telomere length of tumor cells was observed with increasing generations. Of interest, the Eµ-TCL1 mTerc-/- G3 tumors (n=8; G3) more frequently showed defective DNA damage response compared to TCL1+ tumors (n=8), as analysed by changes in phosphorylation of gamma-H2AX, ATM and p53 measured by FACS at 1, 3, 6, 16 and 24 hours after gamma irradiation. Despite this predisposition to undergo genomic complexity, the G3 mice showed no difference in disease development compared to TCL1+ mice. Therefore we investigated if cell extrinsic factors in Terc-/- mice could affect tumor development. The Terc-/- microenvironment is known to be restrictive to B and T-lymphopoiesis and could hence inhibit CLL development. To study the impact of Terc-/- microenvironment, splenic tumors from the Eµ-TCL1 mTerc-/- G3 (n=11; G3) mice were transferred into syngeneic Terc+/+ C57Bl6 mice and compared with that of TCL1+ (n=11). No significant difference in disease burden and survival was observed between these 2 cohorts, indicating that there is no adverse influence of the Terc-/- microenvironment on the tumor growth in the Eµ-TCL1 mTerc-/- mice. Further, we hypothesized that the telomere length in the G3 mice may not be short enough to induce genomic instability and enhance disease aggressiveness. The mice were thus crossed to obtain the Eµ-TCL1 mTerc-/- generation G4 (G4). Though the survival of these mice were similar to that of Eµ-TCL1 controls (median survival :49 vs. 51 weeks; P=0.301), the G4 mice showed significantly decreased disease burden as measured by spleen weight, liver weights and tumor cell fraction. The G4 mice showed decreased fertility and hence further crosses to generate G5 were not performed. However, further shortening of telomeres was achieved by serially transplanting the tumors from G3 into syngeneic recipient mice for 2 generations. Telomere length of the tumor cells analysed by Q-PCR showed a significant decrease with increasing transfer rounds, compared to primary TCL1+ tumors. Interestingly, the 2nd round transfer of the G3 tumors led to a less severe disease and significantly longer survival of the recipient mice compared to 2nd round TCL1+ tumors transplants (median survival from date of transplantation: 15 vs. 7 weeks; P=0.030), indicating that cell intrinsic factors in the G3 tumors hamper proliferation of these cells. We finally analyzed if absence of telomerase could mask disease aggressiveness of the G3 tumors by crossing the G3 mice with wildtype Terc+/+ mice. The resulting TCL1+ mTerc+/- G4 mice showed an increased telomerase activity but had significantly shorter telomere length compared to TCL1+ mice. Strikingly, the TCL1+ mTerc+/- G4 mice showed faster disease development and significantly shorter survival (median survival: 42 vs. 51 weeks; p In summary, the TCL1+ mTerc-/- mice crossed through generations G1 to G4 did not show a difference in disease initiation, progression or survival despite significant shortening of telomeres. However, the tumors from G3 had defective DDR, indicating a potential for accumulating genetic aberrations and clonal evolution. But the absence of functional telomerase decreased the growth potential of these genomic instable tumors. Reconstitution of telomerase in G3 mice resulted in aggressive tumors with short telomere length and could therefore be a valuable murine model for genomic instability and aggressive CLL. Disclosures Tausch: Roche: Consultancy, Honoraria, Speakers Bureau; AbbVie: Consultancy, Honoraria, Other: travel support, Speakers Bureau. Schneider:Celgene: Other: travel grant. Döhner:AbbVie, Agios, Amgen, Astellas, Astex, Celator, Janssen, Jazz, Seattle Genetics: Consultancy, Honoraria; AROG, Bristol Myers Squibb, Pfizer: Research Funding; Celgene, Novartis, Sunesis: Honoraria, Research Funding. Stilgenbauer:AbbVie, AstraZeneca, Celgene, Gilead Sciences, Inc., GSK, Hoffmann La-Roche, Janssen, Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau.

Background: The MYC proto-oncogene encodes a DNA-binding factor that can induce widespread changes in gene expression profiles (GEP). Activation of MYC is a hallmark of aggressive lymphomas and frequently observed in Richter transformation of CLL. In contrast, the role of MYC-related pathogenic networks is less clearly defined in untransformed CLL. Aims: We hypothesized that MYC activation in CLL could lead to specific GEP associated with aggressive disease. We combined the analysis of genomic copy number alterations (CNA) and GEP involved in MYC pathway activation on specimens from patients registered on the CLL8 trial (front line therapy FC vs. FCR). Methods: GEP were derived from CD19-enriched CLL samples (n=337, Human Exon 1.0 ST, Affymetrix) and analysis of CNA was performed based on availability of DNA (n=309, Human SNP Arrays 6.0, Affymetrix). Sample work-up upon trial registration included FISH and TP53 mutation analysis. Results: Genomic gains involving the MYC locus on 8q24.21 were observed in 4.5% of cases. To test the hypothesis of specific GEP associated with MYC activation, we explored the distribution of cases with MYC gain using an unsupervised approach on GEP. After consensus clustering (k=6 clusters) of variably expressed genes (SD>0.5), cases with MYC gain were non-randomly distributed and showed a characteristic pattern. Preferential enrichment was observed in one cluster ("MYC-CNA" group, comprising 40% of all cases) with 64% of MYC gains. Gene set enrichment analysis (GSEA) confirmed overrepresentation of MYC target genes (gene set: HALLMARK_MYC_TARGETS_V1, FDR Conclusion: MYC pathway alterations were frequently observed in treatment-naive CLL and may involve various mechanism such as CNA affecting MYC and its repressors, TP53 defect or sole transcriptional changes. Cases with MYC activation may be segregated based on cell cycle checkpoint deregulation and consecutive proliferative capacity. Clusters with MYC activation had an inferior clinical course when treated with FC but, when adding rituximab, both MYC-CNA and MYC-EA showed a significant improvement for outcome. Disclosures Bahlo: Roche: Honoraria, Other: Travel Grants. Humphrey:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Wenger:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership, Other: Ownership interests PLC. Tausch:AbbVie: Consultancy, Other: Travel grants; Celgene: Consultancy, Other: Travel grants; Gilead: Consultancy, Other: Travel grants. Bullinger:Bayer Oncology: Research Funding; Pfizer: Speakers Bureau; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Speakers Bureau; Sanofi: Research Funding, Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Fischer:Roche: Other: Travel support. Hallek:Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Mundipharma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Boehringer Ingelheim: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Stilgenbauer:Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Hoffmann La-Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Mundipharma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmcyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genzyme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer-Ingelheim: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

B cell receptor signaling (BCR) in chronic lymphocytic leukemia (CLL) drives tumor cell proliferation and survival. Inhibition of Bruton's tyrosine kinase (BTK), a key enzyme in the BCR pathway, has proved to be efficacious even in poor-risk and chemo-refractory patients. However resistance to the BTK inhibitor ibrutinib has been shown to emerge in a subset of CLL patients. Of importance, the C481S BTK mutation conferred resistance by preventing the covalent binding of ibrutinib to its target cysteine 481 in BTK. Vecabrutinib (formerly known as SNS-062, a succinate salt) is a novel, highly potent, next generation noncovalent BTK inhibitor which demonstrated biochemical and cellular activity against C481S BTK mutant in vitro. However, the efficacy of vecabrutinib and its impact on the T-cell microenvironment has not been studied in in vivo preclinical CLL models. In the present study, the efficacy of vecabrutinib was investigated using the Eµ-TCL1 adoptive transfer model. Mice were randomized to treatment with either 40mg/kg vecabrutinib succinate, twice daily by oral gavage (n=6) or vehicle control (n=6). The mice were sacrificed after 2 weeks of treatment and changes in tumor burden as well as alterations in T-cell microenvironment were analysed in detail. Treatment with vecabrutinib decreased tumor burden as observed by a significant decrease in WBC count (36.5 vs. 17.1 giga/L; P=0.002), spleen weight (median 0.56g vs. 0.31g; P=0.005) and liver weight (median 1.5g vs. 1.2g; P=0.005) compared to vehicle treatment. Correspondingly, the CD5+ CD19+ tumor cells were significantly decreased in blood (P=0.002) and spleen (P=0.002) while no significant difference was observed in bone marrow (P=0.818) upon treatment with vecabrutinib. Since BTK inhibition is known to reshape the tumor microenvironment, we studied the impact of vecabrutinib specifically on T-cell subsets. Firstly, no difference in the proportions of CD4 or CD8 expressing T-cells was observed in mice treated with vehicle or vecabrutinib. However, of interest, the percentage of CD4+ CD25+ FoxP3+ regulatory T cells (Tregs) were significantly decreased upon treatment with vecabrutinib in peripheral blood (P=0.026) and spleen (P=0.009). The decrease in Tregs was due to reduced proliferation of these cells upon exposure to the drug as measured by Ki-67 staining. Also, the Tregs expressing the maturation and activation markers such as CD103 and GITR were significantly decreased in blood and spleen upon drug treatment. Further, we analysed the changes in CD8 T-cell subsets following treatment with vecabrutinib. Treatment with the drug resulted in expansion of the CD127+ CD44- naïve CD8 T-cells in blood, bone marrow and spleen (all P values 0.002) while the CD127+ CD44+ memory CD8 T-cells were significantly decreased in bone marrow and spleen (all P values 0.009). Also, the CD127low CD44int-hi effector CD8 T-cells were decreased in blood (P=0.004), bone marrow (P=0.004) and spleen (P=0.002) upon vecabrutinib treatment. Therefore, vecabrutinib treatment did not alter the percentage of CD4+ and CD8+ T cells in mice however, significant changes in the subset composition of the CD4 and CD8 T cells were observed. Lastly, to analyse the impact of vecabrutinib on survival, a cohort of mice (n=12) were transplanted with 5 million splenic tumor cells isolated from Eµ-TCL1 transgenic mice. After allowing for engraftment, the mice were randomized to treatment with the drug (n=6) or vehicle (n=6). Of note, the mice treated with the drug showed a significant increase in survival (median 35 days from transplant; P In summary, vecabrutinib was efficacious in vivo in a preclinical CLL adoptive transfer model, decreasing tumor burden in different organs and significantly improving survival. Treatment with the drug altered the T-cell architecture in vivo. Of interest, the immunosuppressive Tregs, which protect the tumor from immune surveillance were decreased in various tissue compartments; however, a decrease in the effector CD8 T cells might impact anti-tumor immunity if there is a consistent effect upon drug treatment. Vecabrutinib antitumor activity and effects on T-cell populations in vivo in this preclinical CLL model are intriguing, merits further investigation and supports the ongoing phase 1b/2 study in patients with previously treated B-lymphoid malignancies (NCT03037645). Disclosures Tausch: AbbVie: Consultancy, Other: Travel grants; Celgene: Consultancy, Other: Travel grants; Gilead: Consultancy, Other: Travel grants. Fox:Sunesis Pharmaceuticals: Employment; Amphivena Therapeutics: Employment. Taverna:Sunesis Pharmaceuticals: Employment. Stilgenbauer:Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer-Ingelheim: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Hoffmann La-Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genzyme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmcyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Mundipharma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

In many cancers the equilibrium of pro- versus anti-apoptotic BCL-2 proteins is deregulated. BCL-2 inhibitors like Venetoclax (VEN) have been shown to be highly active drugs in BCL-2 dependent cancers like chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). Despite being highly efficient in cell killing, resistance to VEN can be acquired over time. In addition to understanding the underlying mechanisms of resistance to VEN it is important to identify additional treatment options. BDA-366 is a BCL-2 inhibitor with a different mode of action than the BH3 mimetic VEN. BDA-366 acts by inhibiting the BH4 domain and thereby inducing a conversion of anti-apoptotic BCL-2 into a pro-apoptotic protein. BDA-366 showed high effectivity in inducing apoptosis in CLL cells, in primary as well as in cell lines, while all of the CLL cell lines (n=7) tested were resistant to VEN. Furthermore all of the MCL cell lines (n=5) tested were sensitive to the treatment with BDA-366 while only a subset (3 out of 5) responded to treatment with VEN. In order to investigate whether BDA-366 would be a treatment option for VEN-resistant patients, we generated VEN-resistant MCL cell lines (MINO and MAVER-1) by chronic exposure to the drug. In the resistant cell lines, BCL-2 protein levels were not deregulated. In variance to previous reports in diffuse large B cell lymphoma (DLBCL) (Choudhary et al, Cell Death Dis 2015), resistance in MCL cell lines was not mediated by MCL-1 upregulation. In VEN-resistant MINO cells, MCL-1 expression was similar to the parental cells, while MCL-1 was significantly downregulated in VEN-resistant MAVER-1 cells. In contrast, VEN-resistant MCL cell lines showed BCL-XL upregulation as compared to parental cells, which is in line with results obtained in DLBCL (Choudhary et al, Cell Death Dis 2015). Furthermore, dynamic BH3 profiling validated a dependency on BCL-XL in resistant cells and confirmed that resistance was not mediated by MCL-1. The significance of BCL-XL in mediating resistance to VEN was underlined by additional experiments using navitoclax. In contrast to VEN, navitoclax inhibits BCL-2, BCL-XL and BCL-W and was sufficient to induce apoptosis in both parental and resistant cells. In contrast to the BH3 domain inhibitor VEN, the BCL-2 inhibitor BDA-366 acts by converting BCL-2 into a pro-apoptotic molecule. BDA-366 efficiently induced dose dependent apoptosis in VEN-resistant cells. MINO as well as MINO VEN-resistant cells showed the same sensitivity to BDA-366 while VEN-resistant MAVER-1 cells showed reduced sensitivity to BDA-366 as compared to the parental cells. However, with increased BDA-366 concentrations efficient cell killing was achieved in the VEN-resistant cell lines Overall, these results suggest that VEN-resistance is mostly mediated by permanent upregulation of BCL-XL. BCL-2 levels are not deregulated upon development of resistance to VEN. The inhibition of the BH4 domain and thereby converting BCL-2 into a pro-apoptotic protein proved to be a promising therapeutic option even in cancers with acquired resistance to VEN. Disclosures Döhner: Pfizer: Research Funding; Amgen: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Seattle Genetics: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Agios: Consultancy, Honoraria; Pfizer: Research Funding; AROG Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding; Astex Pharmaceuticals: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; AROG Pharmaceuticals: Research Funding; Astellas: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Astex Pharmaceuticals: Consultancy, Honoraria; Celator: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Celator: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Research Funding; Janssen: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding. Stilgenbauer:Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer-Ingelheim: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Hoffmann La-Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genzyme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Mundipharma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmcyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Inhibitors of B-cell receptor (BCR) signaling have proven effective in the treatment of chronic lymphocytic leukemia (CLL). An important downstream mediator of BCR signaling is phosphoinositide 3-kinase delta (PI3Kd), which through activation of AKT, controls cell survival, growth and proliferation. Since it is expressed predominantly in cells of hematopoietic origin, PI3Kd is a promising target in CLL, and the novel PI3Kd inhibitor idelalisib is effective in treating relapsed/refractory CLL. However, a subset of patients relapse under therapy, and the mechanisms leading to resistance are not understood. To generate and study resistance mechanisms in vivo, a tool compound GS-649443 with favorable murine pharmacokinetic properties in vivo as compared to Idelalisib was used. GS-649443 is a highly specific and potent small molecule inhibitor of the PI3K isoform d, with an IC50 of 0.3nM and 86/420/4120 fold selectivity over PI3K isoforms g/b/a respectively. We performed an in vivo serial transfer and treatment scheme to generate specific resistance against GS-649443 using the transferable murine CLL clone TCL1-192(Chen SS et al., 2013). 5 million TCL1-192 cells were transferred by intravenous injection into the tail vein of CB17.SCID mice, followed by treatment with vehicle (N=12) or 5mg/kg GS-649443 (N=12) twice daily by oral gavage, starting from day 10. Analysis of the animals (N=6 vs. 6) at the death of the vehicle treated mice (11 days) showed a drastic reduction in spleen weight (median 0.650g vs. 0.345g, P=0.005), liver weight (median2.025g vs. 1.145g, P=0.0022) and WBC count (median220.4 cells/nl vs. 1.7 cells/nl, P=0.0078) as compared to vehicle treated mice. Also, GS-649443 treatment almost doubled the survival of the mice in comparison to vehicle treatment (Fig. 1, P=0.0011). To generate resistance against GS-649443 in vivo, TCL1-192 cells were kept under selection pressure using serial transfers and subsequent treatment. After three rounds of transfer and treatment, the mice treated with GS-649443 failed to respond and showed a survival identical to vehicle controls (Fig.1). Mutations acquired over time during the serial transfers in TCL1-192 cells from resistant mice were identified using whole exome sequencing. 64 treatment specific mutations were identified with a tumor variant allele frequency of ≥10%. Intriguingly, no single recurrent mutation that would likely contribute to drug resistance was identified. This is similar to the observation in patients refractory to idelalisib (abstract Ghia et al., submitted to ASH 2016). However, a subset of the genes such as Grb2, Mylk, Srfbp1, Ptk2, Cd44 and Prkd1 harboring mutations could be functionally grouped into integrin and extracellular matrix signaling. Consistent with this, all the resistant tumors showed a significant upregulation of genes involved in the integrin receptor complex such as talin 1 (P=0.004), talin 2 (P=0.004) and vinculin (P=0.009). RNAseq analysis for detecting changes in gene expression identified an upregulation of Igf1r expression in the resistant samples compared to vehicle treated samples (P The synergy between the receptor tyrosine kinases such as IGF1R and integrin mediated signaling is established in different cancers and a similar mechanism may play a role in compensating for the inhibition of BCR mediated PI3K/AKT signaling. In conclusion, resistance to a tool PI3Kd inhibitor is not mediated by unique recurrent mutations but by alterations in survival signaling with mutations playing a probable cooperative role. Treatment scheme for generation of resistance in vivo. Treatment scheme for generation of resistance in vivo. Disclosures Tausch: Celgene: Other: Travel support; Amgen: Other: Travel support; Gilead: Other: Travel support, Speakers Bureau. Yahiaoui:Gilead Sciences: Employment. Munugalavadla:Gilead Sciences: Employment, Equity Ownership. Tannheimer:Gilead Sciences: Employment. Stilgenbauer:Pharmacyclics: Consultancy, Honoraria, Other: Travel grants , Research Funding; GSK: Consultancy, Honoraria, Other: Travel grants , Research Funding; Novartis: Consultancy, Honoraria, Other: Travel grants , Research Funding; Amgen: Consultancy, Honoraria, Other: Travel grants, Research Funding; Sanofi: Consultancy, Honoraria, Other: Travel grants , Research Funding; Boehringer Ingelheim: Consultancy, Honoraria, Other: Travel grants , Research Funding; Gilead: Consultancy, Honoraria, Other: Travel grants , Research Funding; Janssen: Consultancy, Honoraria, Other: Travel grants , Research Funding; Hoffmann-La Roche: Consultancy, Honoraria, Other: Travel grants , Research Funding; AbbVie: Consultancy, Honoraria, Other: Travel grants, Research Funding; Mundipharma: Consultancy, Honoraria, Other: Travel grants , Research Funding; Genzyme: Consultancy, Honoraria, Other: Travel grants , Research Funding; Genentech: Consultancy, Honoraria, Other: Travel grants , Research Funding; Celgene: Consultancy, Honoraria, Other: Travel grants , Research Funding.

Introduction: Idelalisib (IDELA) is an ATP-competitive, reversible, and selective small molecule inhibitor of the delta isoform of phosphatidylinositol 3-kinase (PI3Kδ) approved for the treatment, in combination with rituximab, of patients with relapsed chronic lymphocytic leukemia (CLL). In the relapsed CLL randomized, controlled trials, IDELA + rituximab showed high response rates with improved progression-free and overall survival as compared with placebo + rituximab. While IDELA therapy has significant efficacy, disease progression after response occurs, indicating that escape mechanisms may develop. However, the molecular basis for relapse or progressive disease (PD) in CLL patients treated with IDELA has not yet been characterized. Methods: Peripheral blood mononuclear cells (PBMCs) were collected from 13 CLL patients enrolled in the phase 3 studies; NCT01539512 (study 116; IDELA + rituximab vs placebo + rituximab), 116 extension study NCT01539291 (study 117) and NCT01659021 (study 119; IDELA + ofatumumab). Sample selection criteria included treatment period of at least 180 days (range: 243-703 days), achieving at least partial nodal response followed by PD, PD did not occur within a drug interruption window, PD was not associated with Richter's transformation, and PBMC samples were available from both baseline and time of PD. Whole-exome sequencing (WES) was conducted on the matched samples from 13 subjects fitting the above criteria. In 6/13 cases, DNA was available from CD19+/CD5+ enriched tumor cells, and neutrophils or T-lymphocytes served as a source of germline DNA. These 6 patients were considered as a discovery set for mutational analysis. Established bioinformatics tools were used for detection of somatic mutations and for the comparison of baseline and PD samples. Results: Baseline clinical patient profiles indicated that 12 of 13 patients with PD had unmutated IGHV genes and 8 patients carried TP53 aberrations (ie, 17p deletion and/or TP53 mutation). WES resulted in a mean read depth of 106X within the targeted coding region across samples. In the discovery set, on average 25 somatic mutations (range: 4-44) at baseline and 32 mutations (range: 15-81) at progression were identified. By comparing baseline and PD samples, we identified 88 PD-associated mutations. These specific mutations were tested for in a complete set of 13 patient samples; however, no recurrent progression-associated mutations were identified in more than 1 patient. In particular, no progression-associated mutations were identified in the PI3K signaling pathway or in any other related pathway. Conclusion: Across 3 phase 3 studies in relapsed CLL, WES on 13 samples from patients with PD while on IDELA treatment were evaluated. This analysis detected no relapse-associated mutations in common across this patient set; in particular, no mutations were identified in the drug-binding site (ie, "gateway mutation") or in any other related signaling pathway. Based on these results, we conclude there is no common mutational mechanism of IDELA resistance in this patient group. Disclosures Ghia: Gilead: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Roche: Honoraria, Research Funding; Adaptive: Consultancy; Abbvie: Consultancy, Honoraria. Tausch:Gilead: Other: Travel support, Speakers Bureau; Celgene: Other: Travel support; Amgen: Other: Travel support. Owen:Roche: Honoraria, Research Funding; Pharmacyclics: Research Funding; Celgene: Honoraria, Research Funding; Abbvie: Honoraria; Lundbeck: Honoraria, Research Funding; Novartis: Honoraria; Janssen: Honoraria; Gilead: Honoraria, Research Funding. Barrientos:Gilead: Consultancy, Research Funding; Janssen: Consultancy; AbbVie: Consultancy, Research Funding. Munugalavadla:Gilead Sciences: Employment, Equity Ownership. Degenhardt:Gilead Sciences: Employment, Equity Ownership. Kim:Gilead Sciences: Employment, Equity Ownership. Dubowy:Gilead Sciences: Employment, Equity Ownership. Dreiling:Gilead Sciences: Employment, Equity Ownership. Rosenquist:Gilead Sciences: Speakers Bureau. Stilgenbauer:Hoffmann-La Roche: Consultancy, Honoraria, Other: Travel grants , Research Funding; AbbVie: Consultancy, Honoraria, Other: Travel grants, Research Funding; GSK: Consultancy, Honoraria, Other: Travel grants , Research Funding; Pharmacyclics: Consultancy, Honoraria, Other: Travel grants , Research Funding; Janssen: Consultancy, Honoraria, Other: Travel grants , Research Funding; Mundipharma: Consultancy, Honoraria, Other: Travel grants , Research Funding; Celgene: Consultancy, Honoraria, Other: Travel grants , Research Funding; Amgen: Consultancy, Honoraria, Other: Travel grants, Research Funding; Novartis: Consultancy, Honoraria, Other: Travel grants , Research Funding; Sanofi: Consultancy, Honoraria, Other: Travel grants , Research Funding; Genzyme: Consultancy, Honoraria, Other: Travel grants , Research Funding; Genentech: Consultancy, Honoraria, Other: Travel grants , Research Funding; Gilead: Consultancy, Honoraria, Other: Travel grants , Research Funding; Boehringer Ingelheim: Consultancy, Honoraria, Other: Travel grants , Research Funding.

Telomere shortening is of pathogenic and prognostic importance in cancers. In the present study, we analyzed telomere length in 73 mantle cell lymphoma (MCL), 55 chronic lymphocytic leukemia (CLL), and 20 normal B-cell samples using quantitative PCR (Q-PCR) to study its association with disease characteristics and outcome. Telomere length was found to be highly variable in MCL (range, 2.2-13.8 kb; median, 4.3 kb). Telomere dysfunction in MCL was evident from comparison with normal B cells (median, 7.5 kb), but had no significant association with any biologic or clinical feature. This was in contrast to CLL, in which a significant correlation of short telomeres with poor prognostic subgroups was confirmed. There was a trend toward an increased number of genomic aberrations with shortening of telomeres in MCL. No difference in survival was observed between the groups with short and long telomeres, indicating that, as opposed to CLL, telomere length is not of prognostic relevance in MCL.

Telomeres are nucleo-protein complexes at the ends of the chromosomes that play a key role in protection of the ends from being recognized as DNA damage and to prevent fusion of the chromosomes. The telomeric DNA shortens with each cell division in the absence of telomerase, due to end replication problem. In chronic lymphocytic leukemia (CLL), short telomeres were found to be associated with poor prognostic factors and poor survival in various univariable and multivariable analyses. Short telomeres in CLL are known to be frequently associated with increased DNA damage response and to undergo fusion events, conferring genomic instability. But the contribution of telomere dysfunction to CLL pathogenesis and disease progression has never been studied in vivo using mouse models. Here, we hypothesized that genomic instability resulting from telomere dysfunction could drive acquisition of genetic lesions, contributing to CLL pathogenesis, progression and disease evolution. Thus, the CLL mouse model with telomere dysfunction was generated by crossing the Eµ-TCL1 (TCL1+) mouse with mTerc-/- mouse. The first generation TCL1+ mTerc-/- (G1) mice were inter-crossed to obtain generations G2 and G3, as telomeres are known to shorten with subsequent generations. The TCL1+ mTerc-/- mice from the generations G1 (N=14), G2 (N=33) and G3 (N=26), including TCL1+ (N=34), wildtype (WT, N=18) and mTerc-/- G1 (N=4), G2 (N=5) and G3 (N=13) as controls were initially analyzed for disease burden in peripheral blood (PB) by bleeding at an interval of 4 weeks, starting from 12 weeks and the percentage of CD19+ CD5+ cells was estimated by FACS. No difference in disease onset or progression was observed between the TCL1+ mTerc-/- G1, G2 and G3 in comparison toTCL1+ mice (Fig. 1a). Similarly, analysis of survival showed no significant difference between the TCL1+ mTerc-/- G1 (N=14), G2 (N=33) and G3 (N=26) mice, compared to TCL1+ (N=34) (median: 53, 55, 52 weeks vs. 50.5 weeks, Fig. 1b). Spleen and liver weights in the TCL1+ mTerc-/- G1 (N=12), G2 (N=33) and G3 (N=26) mice were highly variable (spleen: 0.1g to 3.5g, liver: 0.1g to 8.0g) as in the TCL1+ (N=27, spleen: 0.3g to 5.0g, liver: 1.7g to 7.4g) mice but no significant difference in spleen (Fig. 1d) and liver weights was observed between the subgroups. Interestingly, spleen weights were associated with survival only in the TCL1+ mice, with larger spleens associated with worse survival (48.5 vs. 57.5 weeks, P=0.091). Since no difference in disease characteristics was observed, it was verified using Q-PCR, if telomere lengths vary in the tumors from the different subgroups. Telomere lengths of CLL cells from the spleen were significantly shorter (Fig. 1c) in the G1 (median: 20.5kb, P=0.0002), G2 (median: 18.5kb, P=0.0016) and G3 (median: 13.2kb, P Additionally, the G3 mTerc-/- microenvironment is known to restrict B and T lymphopoiesis and thus might influence CLL cell proliferation, masking disease aggressiveness in the TCL1+ mTerc-/- G3 mice. To overcome the influence of mTerc-/- microenvironment, CLL cells obtained from spleens of TCL1+ and TCL1+ mTerc-/- G3 mice were transferred into syngeneic C57Bl6 mice. Briefly, 20 million cells were intravenously injected into the tail vein and disease was monitored by analysis of CD19+ CD5+ cells in PB, once every 4 weeks. Early follow up of 8 weeks clearly show a trend towards increase in CLL cells in PB of mice transferred with TCL1+ mTerc-/- G3 tumors compared to those with TCL1+ tumors (median tumor load: 15.75% vs. 6.1%, P=0.0553). Longer follow up of the experiment is ongoing. In summary, the TCL1+ mTerc-/- mice across the generations G1, G2 and G3 showed no difference in disease onset, progression, disease burden and survival in comparison to TCL1+ mice. The absence of increased disease manifestation in the TCL1+ mTerc-/- may be attributed to the microenvironmental influence on lymphopoiesis, as syngeneic transfer of CLL from TCL1+ mTerc-/- G3 mice showed an increase in tumor load compared to that of TCL1+ tumors, indicating a contribution of telomere shortening to disease aggressiveness in CLL. Figure 1. Figure 1. Disclosures No relevant conflicts of interest to declare.

BACKGROUND: Short telomere length has been described in CLL as independent adverse prognostic factor in multivariate analyses of several single centre series and clinical trial cohorts. However, the clinical impact of short telomeres has not been studied in the context of allogeneic stem cell transplantation (allo-SCT) in CLL. METHODS: Here, we studied telomere length, its associations and impact on outcome in the multicentre CLL3X trial evaluating efficacy of allo-SCT after reduced intensity conditioning in patients with poor-risk CLL (Table 1). Telomere length was analyzed using quantitative PCR on DNA from peripheral blood mononuclear cells (PBMCs) of 69 patients and this cohort was representative of the full trial population. The technique was validated using terminal restriction fragment length analysis (TRF) (R2=0.859, P RESULTS: Telomere length in the CLL3X cohort was found to be highly variable (1.9 kb – 21 kb). Correlation of telomere length with disease characteristics was performed by defining short and long telomere subgroups, based on median telomere length (median=5.35kb). In contrast to several reports on untreated CLL cohorts, telomere length showed no significant associations with age (P=0.400), sex (P=0.306), presence of high leukocyte count (P=0.765), ECOG status (P=1.000), and prior resistance to fludarabine-based therapy (P=0.955) or other clinical characteristics. Analysis of telomere length association with genetic characteristics showed a trend towards association with del(17p) (P=0.088) while no association was observed with del(11q) (P=0.834), 12q trisomy (P=0.650), normal karyotype (P=0.450) and del(13q) (P=0.792). Also, no association of telomere length with mutations of TP53 (P=0.280), NOTCH1 (P=0.2470) and SF3B1 (P=0.819) was observed. With a median observation time of 6 years, analysis of the impact of telomere length below the median on outcome showed no significant association with non-relapse mortality (HR 2.11, P=0.199), event-free survival (EFS) (HR=1.22, P=0.53, Fig.1a) and time to relapse (HR=0.92, P=0.82). Nevertheless, patients with short telomere length tended to have inferior overall survival (OS) (HR=2.04, 95%CI 0.92 - 4.5, P=0.079, Fig. 1b). The OS benefit associated with long telomeres could be largely explained by superior survival after relapse in this subset (HR=3.04, 95%CI 0.96 - 9.57, P=0.058) indicative of better efficacy of salvage treatment. CONCLUSION: In contrast to several reports on treatment naïve CLL cohorts, telomere length in the poor-risk patient selection of the CLL3X trial was not significantly associated with any known clinical and genetic baseline disease characteristics. While EFS was unaffected by telomere length, short telomeres were associated with poor OS, largely due to inferior survival after CLL relapse, suggesting that rescue treatment after post-transplant disease recurrence was less effective in the presence of short telomeres. Table 1: Patient Characteristics N % Unmutated IGHV 60/65 92.3 Presence of 11q or 17p- 38/64 59.4 Fludarabine refractory 30/45 66.7 Early relapse 26/63 41.3 Previous regimens >1 (Mean = 4 regimens/patient) 57/63 90.5 Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Telomeres are sequences at the ends of each chromosome that confer genomic stability. The presence of dysfunctional telomeres is associated with increased genomic abnormalities and tumorigenesis. In CLL, telomere length has been described as an independent prognostic factor (e.g. Roos et al., Blood 2008) but these analyses have been performed on heterogeneous patient cohorts and have not yet been confirmed within clinical trials. Here, we studied the impact of telomere length on outcome in the international CLL8 trial of the GCLLSG evaluating first-line treatment with fludarabine and cyclophosphamide (FC) versus FC with rituximab (Anti-CD20). Telomere length was analyzed using quantitative PCR of DNA (in triplicates) from baseline samples of 620 patients enrolled on CLL8, and this cohort was representative of the full trial population. The technique was validated using terminal restriction fragment length analysis (TRF) (R2=0.859, P Telomere length was found to be highly variable in CLL (1.94 kb – 33.56 kb), whereas normal B-cells from age matched healthy probands (n=20) showed limited variability (5.39 – 9.60 kb; median 7.54 kb). Analysis of paired CD19+ (malignant) and CD19- (non-malignant) fractions (n=48) showed that telomere shortening in CLL was restricted to the malignant cell population (median: CD19+ 3.37 kb vs. CD19- 5.42 kb; P5cm; P=0.048). Also, unmutated IGHV (P After a median follow up time of 69.97 months, there were 423 events for progression free survival (PFS) and 209 for overall survival (OS). Short telomeres were significantly associated in both treatment arms with poor PFS (FC: median 27.4 vs. 44.0 months, P 0 (HR 1.256; P=0.037), thymidine kinase > 10 (HR 1.312; P=0.042), del(11q) (HR 1.378; P=0.012), del(17p) (HR 3.225; P 0 (HR 1.617; P=0.003), thymidine kinase > 10 (HR 1.850; P=0.007), beta2 microglobulin (HR 1.486; P=0.016), del(17p) (HR 2.716; P In conclusion, the characterization of telomere length in the CLL8 trial revealed significant associations with other biological high-risk features and an independent prognostic impact on outcome after FC or FCR treatment. This points to a role of telomere dysfunction in CLL pathogenesis, progression and response to therapy. Further study of telomere dysfunction in the evolution of CLL and in the context of novel non-genotoxic treatments is warranted. Disclosures: Wenger: F. Hoffmann-La Roche: Employment, Ownership interests (including stock options) in a start-up company, the stock of which is not publicly traded Other. Fingerle-Rowson:F. Hoffmann-La Roche : Employment. Wendtner:Hoffmann-La Roche: Consultancy, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Fischer:Roche: Travel grants Other; Mundipharma: Travel grants, Travel grants Other. Hallek:Roche: Consultancy, Honoraria, Research Funding. Stilgenbauer:Roche: Consultancy, Honoraria, Research Funding.

Abstract 2509 Mantle cell lymphoma (MCL) is a specific subtype of non-Hodgkin lymphoma with a median overall survival of approximately 4–5 years with significant heterogeneity. MCL shows a relatively high number of genomic alterations per case and one of the known causes of genomic instability in somatic cells is telomere dysfunction. Short, dysfunctional telomeres lead to an increase in chromosomal end-to-end fusions which predispose the cells to chromosomal aberrations, genomic complexity and malignant transformation. Here we investigated telomere length in MCL to evaluate associations with biological and clinical disease characteristics as well as outcome. We included a CLL cohort as a control group and for comparison with MCL. A well characterized cohort of 73 MCL and 55 CLL patients treated at the Universities of Ulm, Würzburg and Heidelberg was used for the study. Telomere length was measured using a Q-PCR-based technique with 25ng of DNA used per reaction in triplicates. Three telomere length controls were included in every plate to control for plate to plate variations. The technique was validated by terminal restriction fragment length (TRF) analysis (R2=0.8516). The TRF value of telomere length for each sample was calculated from the linear regression of Q-PCR vs. TRF. Samples were selected for tumor loads of >70% and were analyzed for correlation with biological and clinical factors. Telomere length in MCL had no significant association with IGHV (P=0.4966) and TP53(P=0.4225) mutation status which was in marked contrast to CLL where a significant correlation of short telomeres with unmutated IGHV(Pmedian). No correlation of telomere length with the proliferation index (Ki67) was observed in the MCL samples, which might be due to variable telomerase activity among the different MCL subsets. Telomere length in MCL also did not correlate with blastoid subtype, age, LDH levels, WBC or with MIPI groups. We studied the impact of telomere length on outcome in MCL and no significant difference in overall survival (median 48 vs. 50 months, p=0.7997) (Figure 2) or progression-free survival (median 26.4 vs. 21.7, p=0.9178) was observed between the long (>median) and short ( In conclusion, telomere length in MCL was not associated with any of the established clinical or biological factors relevant for pathogenesis or prognostication and there was no correlation with disease outcome. This is in stark contrast to CLL where telomere length has been significantly associated with biological disease characteristics, pathogenic mechanisms and survival. Figure 1: Telomere length distribution in MCL and CLL samples with mutated/unmutated IGHV and mutant/wildtype TP53. Figure 1:. Telomere length distribution in MCL and CLL samples with mutated/unmutated IGHV and mutant/wildtype TP53. Figure 2: Overall survival in the short (median) subgroups (median 48 vs. 50 months, P=0.7997). Figure 2:. Overall survival in the short (median) subgroups (median 48 vs. 50 months, P=0.7997). Disclosures: No relevant conflicts of interest to declare.