Chronic Lymphocytic Leukemia Resistance Research Articles

PI3K/AKT confers intrinsic and acquired resistance to pirtobrutinib in chronic lymphocytic leukemia

PurposePirtobrutinib, a non-covalent Bruton’s tyrosine kinase (BTK) inhibitor, has been approved as the first agent to overcome resistance to covalent BTK inhibitors (such as ibrutinib, acalabrutinib, and zanubrutinib). However, the mechanisms of pirtobrutinib resistance in chronic lymphocytic leukemia (CLL) remain poorly understood. MethodsTo investigate pirtobrutinib resistance, we established resistant cell models using BTK knock-out via CRISPR-Cas9 or chronic exposure to pirtobrutinib in MEC-1 cells. These models mimicked intrinsic or acquired resistance, respectively. We then analyzed differential protein expression between wild-type (WT) and resistant MEC-1 cells using Revers Phase Protein microArray (RPPA) and confirmed the findings through Western Blot. Additionally, we evaluated potential drugs to overcome pirtobrutinib resistance by conducting cell proliferation assays, apoptosis studies, and animal experiments using both sensitive and resistant cells. ResultsMEC-1 cells developed resistance to pirtobrutinib either through BTK knock-out or prolonged drug exposure over three months. RPPA analysis revealed significant activation of proteins related to the PI3K/AKT pathway, including AKT and S6, in the resistant cells. Western Blot confirmed increased phosphorylation of AKT and S6 in pirtobrutinib-resistant MEC-1 cells. Notably, both the PI3K inhibitor (CAL101) and the AKT inhibitor (MK2206) effectively reduced cell proliferation and induced apoptosis in the resistant cells. The anti-tumor efficacy of these drugs was mediated by inhibiting the PI3K/AKT pathway. In vivo animal studies further supported the potential of targeting PI3K/AKT to overcome both intrinsic and acquired resistance to pirtobrutinib. ConclusionThe PI3K/AKT pathway plays a crucial role in both intrinsic and acquired resistance to pirtobrutinib in CLL. Therapeutically targeting this pathway may offer a promising strategy to overcome pirtobrutinib resistance.

Leveraging genomics, transcriptomics and epigenomics to understand chemoimmunotherapy resistance in chronic lymphocytic leukemia.

Patients with chronic lymphocytic leukemia (CLL) have differing clinical outcomes. Recent advances integrating multi-omic data have uncovered molecular subtypes in CLL with different prognostic implications and may allow better prediction of therapy response. While finite-duration chemoimmunotherapy (CIT) has enabled deep responses and prolonged duration of responses in the past, the advent of novel targeted therapy for the treatment of CLL has dramatically changed the therapeutic landscape. In this review, we discuss the latest genomic, transcriptomic, and epigenetic alterations regarded as major drivers of resistance to CIT in CLL. Further advances in genomic medicine will allow for better prediction of response to therapy and provide the basis for rational selection of therapy for long-term remissions with minimal toxicity.

Overcoming Resistance in Chronic Lymphocytic Leukemia-Maybe Less Is More?

Acquired mutations in BTK, PLCG2, and BCL2 are associated with resistance to continuous targeted agent therapy in chronic lymphocytic leukemia (CLL). Here, we discuss new evidence that limiting the duration of CLL therapy may prevent the evolution of such resistance mutations, potentially facilitating effective retreatment strategies. See related article by Jain et al., p. 498.

NOD2 silencing promotes cell apoptosis and inhibits drug resistance in chronic lymphocytic leukemia by inhibiting the NF-κB signaling pathway.

Recent years have witnessed increasing studies on the effect of epigenetic silencing of genes in the progression of chronic lymphocytic leukemia (CLL). This study investigates whether the nucleotide binding oligomerization domain containing 2 (NOD2) participates in the cell apoptosis and drug resistance of CLL cells. Cells were treated with adriamycin (ADR), etoposide, aclacinomycin and daunorubicin. After treatment, drug resistance and cell proliferation were examined to detect the inhibitory effect of ADR on cell proliferation; flow cytometry to identify ADR accumulation, the cell cycle distribution and apoptosis after transfection, and rhodamine 123 accumulation and efflux tests to assess P-glycoprotein (P-gp) function. NOD2 silencing or inhibition of the nuclear factor kappa-B (NF-κB) signaling pathway suppressed the multidrug resistance level in CLL, the inhibition rate, and cell proliferation caused by ADR at concentrations of approximately 0.25-1.5 μmol/L. Greater accumulation of ADR was observed in the CLL-AAT cell line than in the CLL-AAT/A02 cell line, but NOD2 silencing or inhibition of the NF-κB signaling pathway further increased the accumulation of ADR drugs in the CLL-AAT cell line and inhibited the drug efflux pump function of P-gp. Additionally, NOD2 silencing or NF-κB signaling pathway inhibition increased the apoptotic rate. The results of this study indicate that NOD2 promotes cell apoptosis and reduces the drug resistance of CLL by inhibiting the NF-κB signaling pathway.

Electron transport chain and mTOR inhibition synergistically decrease CD40 signaling and counteract venetoclax resistance in chronic lymphocytic leukemia.

CD40 signaling upregulates BCL-XL and MCL-1 expression in the chronic lymphocytic leukemia (CLL) lymph node microenvironment, affording resistance to the BCL-2 inhibitor, venetoclax. Venetoclax resistance in the therapeutic setting and after long-term laboratory selection has been linked to metabolic alterations, but the underlying mechanism(s) are unknown. We aimed here to discover how CD40 stimulation as a model for tumor microenvironment-mediated metabolic changes, affects venetoclax sensitivity/resistance. CD40 stimulation increased oxidative phosphorylation and glycolysis, but only inhibition of oxidative phosphorylation countered venetoclax resistance. Furthermore, blocking mitochondrial import of pyruvate, glutamine or fatty acids affected CLL metabolism, but did not prevent CD40-mediated resistance to venetoclax. In contrast, inhibition of the electron transport chain (ETC) at complex I, III or V attenuated CLL activation and ATP production, and downregulated MCL-1 and BCL-XL, correlating with reduced CD40 surface expression. Moreover, ETC inhibition equaled mTOR1/2 but not mTOR1 inhibition alone for venetoclax resistance, and all three pathways were linked to control of general protein translation. In line with this, ETC plus mTOR inhibition synergistically counteracted venetoclax resistance. These findings link oxidative CLL metabolism to CD40 expression and cellular signaling, and may hold clinical potential.

High expression level of ROR1 and ROR1-signaling associates with venetoclax resistance in chronic lymphocytic leukemia

Although the BH3-mimetic venetoclax is highly cytotoxic for chronic lymphocytic leukemia (CLL) cells, some patients with CLL fail to clear minimal residual disease (MRD). We examined the CLL cells of seven such patients (CLL1-7) and found each had high-level expression of ROR1. By examining the CLL cells from such patients prior to therapy at SC1 and then more than 1 year later (Sample Collection 2 (SC2)), when they had progressive increases in MRD despite continued venetoclax therapy, we found the levels of ROR1 expressed on CLL cells at SC2 were significantly higher than that on CLL cells collected at SC1. At SC2, we also observed upregulation of genes induced by Wnt5a-induced ROR1 signaling, including BCL2L1. Transduction of the CLL-cell-line MEC1 to express ROR1 enhanced expression of target genes induced by ROR1-signaling, increased expression of BCL-XL, and enhanced resistance to venetoclax, even in MEC1 made to express mutant forms of BCL2, which are associated with venetoclax resistance. Treatment of primary CLL cells with Wnt5a also increased their resistance to venetoclax, an effect that could be inhibited by the anti-ROR1 mAb (UC-961, zilovertamab). Collectively, these studies indicate that Wnt5a-induced ROR1-signaling can enhance resistance to venetoclax therapy.

Cooperative miRNA-dependent PTEN regulation drives resistance to BTK inhibition in B-cell lymphoid malignancies

Aberrant microRNA (miR) expression plays an important role in pathogenesis of different types of cancers, including B-cell lymphoid malignancies and in the development of chemo-sensitivity or -resistance in chronic lymphocytic leukemia (CLL) as well as diffuse large B-cell lymphoma (DLBCL). Ibrutinib is a first-in class, oral, covalent Bruton’s tyrosine kinase (BTK) inhibitor (BTKi) that has shown impressive clinical activity, yet many ibrutinib-treated patients relapse or develop resistance over time. We have reported that acquired resistance to ibrutinib is associated with downregulation of tumor suppressor protein PTEN and activation of the PI3K/AKT pathway. Yet how PTEN mediates chemoresistance in B-cell malignancies is not clear. We now show that the BTKi ibrutinib and a second-generation compound, acalabrutinib downregulate miRNAs located in the 14q32 miRNA cluster region, including miR-494, miR-495, and miR-543. BTKi-resistant CLL and DLBCL cells had striking overexpression of miR-494, miR-495, miR-543, and reduced PTEN expression, indicating further regulation of the PI3K/AKT/mTOR pathway in acquired BTKi resistance. Additionally, unlike ibrutinib-sensitive CLL patient samples, those with resistance to ibrutinib treatment, demonstrated upregulation of 14q32 cluster miRNAs, including miR-494, miR-495, and miR-543 and decreased pten mRNA expression. Luciferase reporter gene assay showed that miR-494 directly targeted and suppressed PTEN expression by recognizing two conserved binding sites in the PTEN 3′-UTR, and subsequently activated AKTSer473. Importantly, overexpression of a miR-494 mimic abrogated both PTEN mRNA and protein levels, further indicating regulation of apoptosis by PTEN/AKT/mTOR. Conversely, overexpression of a miR-494 inhibitor in BTKi-resistant cells restored PTEN mRNA and protein levels, thereby sensitizing cells to BTKi-induced apoptosis. Inhibition of miR-494 and miR-495 sensitized cells by cooperative targeting of pten, with additional miRNAs in the 14q32 cluster that target pten able to contribute to its regulation. Therefore, targeting 14q32 cluster miRNAs may have therapeutic value in acquired BTK-resistant patients via regulation of the PTEN/AKT/mTOR signaling axis.

Mechanisms of Venetoclax Resistance in Chronic Lymphocytic Leukemia

Rationale: Treatment with the small-molecule BCL2-inhibitor venetoclax (ABT-199) has demonstrated substantial efficacy in patients with chronic lymphocytic leukemia (CLL), particularly in cases with relapsed/refractory disease and mutated or deleted TP53 . While resistance to the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib has been associated with the de-novo acquisition of gene mutations in the primary drug target itself and downstream effectors like PLCG2, genetic causes of treatment resistance towards venetoclax have not been identified to date.Methods: To this end, we performed whole exome sequencing and methylation array profiling in a pilot set of 8 patients (7 men, 1 woman) with pre-treated (1-8 pretreatments) and TP53 -deficient CLL, who had progressive disease or relapsed under oral venetoclax therapy. We investigated serial CLL specimen from peripheral blood before treatment initiation and from peripheral blood, lymph node or bone marrow and at 1-2 follow up time points during disease progression/relapse. Detected genetic alterations of interest were confirmed by either dideoxy sequencing or digital droplet PCR. Copy number changes detected by exome sequencing were verified by methylation arrays.Results: On average, we detected a total of 25.5 exonic mutations (including silent, insertions, and deletions) prior to venetoclax therapy. As expected from ongoing genome evolution, copy number changes and the number of point mutations increased during venetoclax therapy. Methylation profiles, however, remained stable under treatment pressure.We reconstructed phylogenetic trees to illustrate the clonal trajectories of cell populations with distinct genetic events across the obtained cancer samples and over time. We observed a wide spectrum of evolutionary dynamics including linear, divergent, and convergent evolution.Recurrent non-synonymous mutations developing under venetoclax treatment were seen in TP53, NOTCH1, and BTG1, whereas BRAF, SF3B1, RB1, BIRC3, and MLL3 were non-synonymously affected in single patients only.Recurrent genomic changes that evolved during venetoclax treatment were homozygous deletions affecting CDKN2A/B (p16Ink4a/p14Arf) in 3 patients and BTG1 missense mutations in 2 cases. Reconstruction of the branching evolution of subclones harboring these alterations strongly suggested that they may confer a survival advantage to CLL cells under venetoclax treatment pressure.Two patients developed genome alterations that would qualify for further therapeutic options after venetoclax therapy: One patient presented a BRAF p.K601E mutation at the time of resistance. We confirmed that mutationally activated BRAF is able to decrease the sensitivity towards venetoclax-mediated cell killing in an in vitro cell line model. Another patient demonstrated a high-level amplification of C D274, which was paralleled by high protein levels of the immune checkpoint ligand CD274/PD-L1 per immunohistochemistry in the progressive lymph node. This alteration may suggest the use of immune checkpoint inhibition in this patient.Conclusion: Whole exome sequencing of CLL specimens from 8 patients before the initiation of venetoclax therapy and at the time of venetoclax resistance revealed diverse patterns of clonal evolution. Mutations in BTG1 and homozygous deletions in CDKN2A/B may play a role in the biology of acquired venetoclax resistance. Furthermore, our genetic analysis identified genome alterations at relapse that might hint to options for salvage therapies. To further pinpoint genetic mechanisms of venetoclax resistance, larger studies with repeated longitudinal sampling of CLL cell material under therapy and at disease progression/relapse are warranted. DisclosuresFrenzel:Gilead: Research Funding; Abbvie: Consultancy; Roche: Research Funding. Cramer:Janssen-Cilag: Consultancy, Honoraria, Other: travel support, Research Funding; F. Hoffmann-LaRoche: Honoraria, Other: travel support, Research Funding; GSK: Research Funding; Novartis: Consultancy, Research Funding; AbbVie: Consultancy; Gilead: Other: travel support, Research Funding; AstraZeneca: Consultancy. Wendtner:Hoffmann La Roche: Other: Grant, Personal Fees; Mundipharma: Other: Grant, Personal Fees; Celgene: Consultancy, Research Funding; Janssen-Cilag: Other: Personal Fees; Abbvie: Other: Personal Fees; Morphosys: Other: Personal Fees; Servier: Other: Grant, Personal Fees; Gilead: Other: Personal Fees; Novartis: Other: Personal Fees. Eichhorst:Gilead: Consultancy, Honoraria, Other: travel support, Research Funding; Janssen-Cilag: Consultancy, Honoraria, Other: travel support, Research Funding; Abbvie: Consultancy, Honoraria, Other: trav, Research Funding; Mundipharma: Consultancy, Honoraria, Other: travel support, Research Funding; F. Hoffmann-LaRoche: Consultancy, Honoraria, Other: tra, Research Funding; Celgene: Consultancy, Honoraria, Other: travel support, Research Funding; GlaxoSmithKline: Consultancy, Honoraria, Other: travel support, Research Funding. Kreuzer:Janssen-Cilag: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Other: Personal Fees, Research Funding; F. Hoffmann-LaRoche: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Honoraria, Research Funding; Mundipharma: Consultancy, Honoraria, Research Funding. Reinhardt:Gilead: Research Funding. Hallek:AbbVie: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; F. Hoffmann-LaRoche: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Honoraria, Research Funding; Janssen-Cilag: Consultancy, Honoraria, Research Funding; Mundipharma: Consultancy, Honoraria, Research Funding.

Single-Cell RNA-Seq Reveals LGALS1 and LAG3 as Novel Drivers of Ibrutinib Resistance in Chronic Lymphocytic Leukemia

Background: Chronic lymphocytic leukemia (CLL) is a highly heterogeneous malignant lymphoproliferative B-cell disorder that can be treated using ibrutinib, a Bruton’s tyrosine kinase inhibitor. However, the ibrutinib resistance of CLL patients has caused widespread concerns, necessitating the development of novel treatment strategies. Methods: Here, we identified lectin galactoside-binding soluble 1 (LGALS1) and lymphocyte-activating gene 3 (LAG3) as potential markers for ibrutinib-resistant CLL using single-cell RNA sequencing (scRNA-seq), and the results were validated in an ibrutinib-resistant CLL cell line (MEC1-IR) and primary cells from CLL patients. Marker-gene expression was detected while functional analyses were conducted with or without OTX008, a selective Galectin-1 inhibitor. ScRNA-seq revealed that the biological features, gene expression profiles, and clonal signatures of peripheral blood mononuclear cells (PBMCs) from patients with ibrutinib-resistant CLL were distinct from those displayed by PBMCs from ibrutinib-sensitive patients. Findings: A close correlation between LGALS1 and LAG3 expression was observed and these factors were found to be highly expressed in ibrutinib-resistant CLL, with diagnostic and prognostic stratification, indicating that they may serve as drivers of ibrutinib-resistant CLL. Concordantly, LGALS1 and LAG3 expression was higher in ibrutinib-resistant CLL cells and primary cells, and OTX008 suppressed proliferation and induced apoptosis in both cells. Interpretation: LGALS1 and LAG3 gene panel is promising indicator of ibrutinib-sensitivity and prognosis marker of CLL. LGALS1 inhibitor OTX008 is effective in CLL patients, both those naive to and those resistant to ibrutinib. This work highlights the pathogenic mechanism and represents a novel therapeutic target for CLL. Funding Statement: This work was supported by grants from National Natural Science Foundation of China (Grant #81720108002, 81970146, 81770166, 81972358 and 91959113), Key Research & Development Program of Jiangsu Province (Grant #BE2017733), Basic Research Program of Jiangsu Province (Grant #BK20180036), Jiangsu Province’s Medical Elite Programme (Grant #ZDRCA2016022), Project of National Key Clinical Specialty, Jiangsu Provincial Special Program of Medical Science (Grant #BE2017751), Six Top Talent Project of Jiangsu Province (Grant #WSN-001). Declaration of Interests: The authors declare that they have no competing interests. Ethics Approval Statement: Human sample study was approved by the Medical Ethics Committee of First Affiliated Hospital of Nanjing Medical University. Written informed consent was obtained from all participants.

Detection of somatic TP53 mutations and 17p deletions in patients with chronic lymphocytic leukemia: a review of the current methods.

Chronic lymphocytic leukemia is the most common hematologic malignancy among adults in Western countries. Several studies show that somatic mutations in the TP53 gene are present in up to 50% of patients with relapsed or refractory chronic lymphocytic leukemia. This study aims to review and compare the methods used to detect somatic TP53 mutations and/or 17p deletions and analyze their importance in the chronic lymphocytic leukemia diagnosis and follow-up. In chronic lymphocytic leukemia patients with refractory or recurrent disease, the probability of clonal expansion of cells with the TP53 mutation and/or 17p deletion is very high. The studies assessed showed several methodologies able to detect these changes. For the 17p deletion, the chromosome G-banding (karyotype) and interphase fluorescence in situ hybridization are the most sensitive. For somatic mutations involving the TP53 gene, moderate or high-coverage read next-generation sequencing and Sanger sequencing are the most recommended ones. The TP53 gene mutations represent a strong adverse prognostic factor for patient survival and treatment resistance in chronic lymphocytic leukemia. Patients carrying low-proportion TP53 mutation (less than 20–25% of all alleles) remain a challenge to these tests. Thus, for any of the methods employed, it is essential that the laboratory conduct its analytical validation, documenting its accuracy, precision and sensitivity/limit of detection.

In Chronic Lymphocytic Leukemia the JAK2/STAT3 Pathway Is Constitutively Activated and Its Inhibition Leads to CLL Cell Death Unaffected by the Protective Bone Marrow Microenvironment

The bone marrow microenvironment promotes proliferation and drug resistance in chronic lymphocytic leukemia (CLL). Although ibrutinib is active in CLL, it is rarely able to clear leukemic cells protected by bone marrow mesenchymal stromal cells (BMSCs) within the marrow niche. We investigated the modulation of JAK2/STAT3 pathway in CLL by BMSCs and its targeting with AG490 (JAK2 inhibitor) or Stattic (STAT3 inhibitor). B cells collected from controls and CLL patients, were treated with medium alone, ibrutinib, JAK/Signal Transducer and Activator of Transcription (STAT) inhibitors, or both drugs, in the presence of absence of BMSCs. JAK2/STAT3 axis was evaluated by western blotting, flow cytometry, and confocal microscopy. We demonstrated that STAT3 was phosphorylated in Tyr705 in the majority of CLL patients at basal condition, and increased following co-cultures with BMSCs or IL-6. Treatment with AG490, but not Stattic, caused STAT3 and Lyn dephosphorylation, through re-activation of SHP-1, and triggered CLL apoptosis even when leukemic cells were cultured on BMSC layers. Moreover, while BMSCs hamper ibrutinib activity, the combination of ibrutinib+JAK/STAT inhibitors increase ibrutinib-mediated leukemic cell death, bypassing the pro-survival stimuli derived from BMSCs. We herein provide evidence that JAK2/STAT3 signaling might play a key role in the regulation of CLL-BMSC interactions and its inhibition enhances ibrutinib, counteracting the bone marrow niche.

High-Level ROR1 and BCL2, Cancer-Stemness, and BCL2 Mutations Associate with Venetoclax Resistance in Chronic Lymphocytic Leukemia

High-Level ROR1 and BCL2, Cancer-Stemness, and BCL2 Mutations Associate with Venetoclax Resistance in Chronic Lymphocytic Leukemia

Systematic Investigation of Microenvironmental Drug Resistance Mechanisms in Chronic Lymphocytic Leukemia

Introduction and Methods To investigate the mechanisms by which microenvironmental signals induce treatment resistance in chronic lymphocytic leukemia (CLL) we conducted a high-throughput perturbation assay combining pairwise 15 clinically relevant drugs with 18 stimulations mimicking the tumor microenvironment. We combined this with multi-layer omics data using whole exome sequencing, genome-wide DNA-methylation profiles and RNA sequencing to investigate molecular determinants of microenvironmental drug resistance. In parallel we assessed the in-vivo relevance of investigated pathways in 100 CLL infiltrated- and 100 healthy lymph node (LN) biopsies by staining for stimulus specific downstream pathway components using immunohistochemistry (IHC). Results We initially clustered drugs and microenvironmental stimuli separately based on the similarity of their response profiles across all CLL samples. We found drug response profiles to be correlated closely for drugs targeting the same signaling-pathway, e.g. the B-cell receptor inhibitors Ibrutinib (BTK) and PRT062607 (Syk) (Pearson correlation coefficient: r=0.78, 95% CI: 0.72 - 0.83). In contrast, responses to microenvironmental stimuli were less correlated, indicating diverse effects are caused by the tumor microenvironment (e.g. Interleukin 4 (IL-4) vs. Interleukin 2, Pearson correlation coefficient: r=0.17, 95% CI: 0.03 - 0.31). Twelve of the 18 tested stimulations enhanced survival of CLL cells, whereas two reduced the viability of CLL cells in-vitro (comparisons yielded BH adjusted t-test p-values <0.0001). The strongest pro-survival effects were mediated by IL-4 and Toll-like receptor (TLR) 7/8/9 stimulation, whereas transforming growth factor β1 (TGF-β1) and Interleukin-6 reduced the viability of CLL cells in-vitro. Ten of the 18 stimulation effects were modulated by genetic alterations in CLL cells, for 6 stimuli two or more response modulating genetic alterations were identified (FDR 10%). IGHV mutation status for instance modulated the effects of TLR 7/8/9 agonists as well as Interleukine-1β, CD40 ligand and TGF-β1. We will present a detailed analysis of how microenvironmental stimuli depend on specific genetic alterations in CLL. To understand how soluble stimuli interfere with drug response we searched for specific interactions between stimulations and drugs with the following linear model: Viability ~ drug-effect + stimulation-effect + drug-effect:stimulation-effect and tested for significance of the interaction term. This approach allowed us to dissect interactions independently of the individual effects. We discovered different types of drug-effect:stimulation-effect interactions: 1) The microenvironmental stimulus had a strong pro-survival effect on the baseline viability and interfered with the response to drugs (e.g. IL-4:Ibrutinib, p-value< 0.0001). 2) The microenvironmental stimulus had no major effect on baseline viability but significantly interfered with response to drugs (e.g. Interferon-γ:Ibrutinib, p-value: 0.014). 3) The microenvironmental stimulus and the drug exhibited no major individual effect on CLL cell survival, but together significantly increased CLL cell viability (e.g. Interferon-γ:Ralimetinib, p-value: < 0.0001). We will present a detailed analysis of microenvironmental stimuli and their influence on drug response. In the final step we investigated the biological relevance of selected microenvironmental stimuli in patient LN- and bone marrow biopsies by IHC. CLL infiltrated LN exhibited a higher signaling activity of the IL-4 and TLR pathway than non-neoplastic LN (t-test, p-values <0.0001). A high signaling activity of IL-4 was associated with shorter time to treatment, indicating that CLL progresses faster with strong microenvironmental support. Conclusion We present a systematic investigation on the tumor microenvironment in CLL, the underlying molecular determinants as well its interference with drug response which will serve as a scientific resource and starting point for further mechanistical investigations. Figure Disclosures Kriegsmann: Celgene: Research Funding; Bristol-Myers Squibb: Research Funding; Sanofi: Research Funding; Morphosys: Research Funding. Müller-Tidow:MSD: Membership on an entity's Board of Directors or advisory committees.

Effect of miR-214 on Fludarabine Resistance in Chronic Lymphocytic Leukemia

To investigate effect and mechanism of miR-214 in fludarabine resistance of chronic lympho-cytic leukemia (CLL). A total of 10 patients with CLL resistante to fludarabine (Flu) and 10 healthy persons admitted to Hematology Department of our hospital in August 2014 - July 2018 were selected. Expression level of miR-214 in mononuclear cells in patients with CLL and healthy persons were determined by RT-PCR. Primary CLL cells from patients with CLL were divided into normal control group (control group), negative control group (miR-214-NC group) and viral transinfection group (miR-214-ASO group). After 24 h-transfection, CLL cells were cultured with different con-centration of Flu for 48 h, then the cell proliferation and apoptosis were detected, and the levels of down-stream genes and proteins releted with PTEN and PI3K/AKT signialing pathway were determined. The expression level of miR-214 in mononuclear cells of CLL patients significantly increased in comparison with healthy persons(P<0.05); the expression level of miR-214 in miR-214-ASO group significantly decreased (P<0.05); Absorbance in control group at Flu concentration of 3, 10 and 30 μmol/L was significantly decreased (P<0.05). Apoptosis rate in miR-214-ASO group at Flu concentration of 10 mmol/L significantly increased (P<0.05). At Flu concentration of 10 mmol/L, mRNA levels PTEN and BAD in miR-214-ASO group significantly increased (P<0.05), but mRNA levels of MDM2 and NF-κB significantly decreased (P<0.05). At Flu concentration of 10 mmol/L, protein levels of PTEN and p-BAD in miR-214-ASO group significantly increased (P<0.05), but protein levels of MDM2 and NF-κB significantly decreased (P<0.05). Inhibition of miR-214 can enhance the sensitivity of drug-resistant CLL cells to fludarabine, which may be raleted with the promotion of cell apotosis and regulation of down-stream molecules expression of PTEN/AKT signaling pathway.

Mitochondrial Reprogramming Underlies Resistance to BCL-2 Inhibition in Lymphoid Malignancies

Mitochondrial apoptosis can be effectively targeted in lymphoid malignancies with the FDA-approved Bcell lymphoma 2 (BCL-2) inhibitor venetoclax, but resistance to this agent is emerging. We show that venetoclax resistance in chronic lymphocytic leukemia is associated with complex clonal shifts. To identify determinants of resistance, we conducted parallel genome-scale screens of the BCL-2-driven OCI-Ly1 lymphoma cell line after venetoclax exposure along with integrated expression profiling and functional characterization of drug-resistant and engineered cell lines. We identified regulators of lymphoid transcription and cellular energy metabolism as drivers of venetoclax resistance in addition to the known involvement by BCL-2 family members, which were confirmed in patient samples. Our data support the implementation of combinatorial therapywith metabolic modulators to address venetoclax resistance.

Exome sequencing of the TCL1 mouse model for CLL reveals genetic heterogeneity and dynamics during disease development

The TCL1 mouse model is widely used to study pathophysiology, clonal evolution, and drug sensitivity or resistance of chronic lymphocytic leukemia (CLL). By performing whole exome sequencing, we present the genetic landscape of primary tumors from TCL1 mice and of TCL1 tumors serially transplanted into wild-type recipients to mimic clonal evolution. We show that similar to CLL patients, mutations in mice are frequently subclonal and heterogenous among different primary TCL1 mice. We further describe that this molecular heterogeneity mirrors heterogenous disease characteristics such as organ infiltration or CLL dependent T cell skewing. Similar to human CLL, we further observed the occurrence of novel mutations and structural variations during clonal evolution and found plasticity in the expansion of B cell receptor specific subclones. Thus, our results uncover that the genetic complexity, pathway dependence and clonal dynamics in mouse CLL are in relevant agreement to human CLL, and they are important to consider in future research using the TCL1 mouse for studying CLL.

DNA polymerase ν gene expression influences fludarabine resistance in chronic lymphocytic leukemia independently of p53 status.

Alteration in the DNA replication, repair or recombination processes is a highly relevant mechanism of genomic instability. Despite genomic aberrations manifested in hematologic malignancies, such a defect as a source of biomarkers has been underexplored. Here, we investigated the prognostic value of expression of 82 genes involved in DNA replication-repair-recombination in a series of 99 patients with chronic lymphocytic leukemia without detectable 17p deletion or TP53 mutation. We found that expression of the POLN gene, encoding the specialized DNA polymerase ν (Pol ν) correlates with time to relapse after first-line therapy with fludarabine. Moreover, we found that POLN was the only gene up-regulated in primary patients’ lymphocytes when exposed in vitro to proliferative and pro-survival stimuli. By using two cell lines that were sequentially established from the same patient during the course of the disease and Pol ν knockout mouse embryonic fibroblasts, we reveal that high relative POLN expression is important for DNA synthesis and cell survival upon fludarabine treatment. These findings suggest that Pol ν could influence therapeutic resistance in chronic lymphocytic leukemia. (Patients’ samples were obtained from the CLL 2007 FMP clinical trial registered at: clinicaltrials.gov identifer: 00564512).

Clonal dynamics towards the development of venetoclax resistance in chronic lymphocytic leukemia

Deciphering the evolution of cancer cells under therapeutic pressure is a crucial step to understand the mechanisms that lead to treatment resistance. To this end, we analyzed whole-exome sequencing data of eight chronic lymphocytic leukemia (CLL) patients that developed resistance upon BCL2-inhibition by venetoclax. Here, we report recurrent mutations in BTG1 (2 patients) and homozygous deletions affecting CDKN2A/B (3 patients) that developed during treatment, as well as a mutation in BRAF and a high-level focal amplification of CD274 (PD-L1) that might pinpoint molecular aberrations offering structures for further therapeutic interventions.

Clonal evolution leading to ibrutinib resistance in chronic lymphocytic leukemia

AbstractDisease progression in patients with chronic lymphocytic leukemia (CLL) treated with ibrutinib has been attributed to histologic transformation or acquired mutations in BTK and PLCG2. The rate of resistance and clonal composition of PD are incompletely characterized. We report on CLL patients treated with single-agent ibrutinib on an investigator-initiated phase 2 trial. With median follow-up of 34 months, 15 of 84 evaluable patients (17.9%) progressed. Relapsed/refractory disease at study entry, TP53 aberration, advanced Rai stage, and high β-2 microglobulin were independently associated with inferior progression-free survival (P < .05 for all tests). Histologic transformation occurred in 5 patients (6.0%) and was limited to the first 15 months on ibrutinib. In contrast, progression due to CLL in 10 patients (11.9%) occurred later, diagnosed at a median 38 months on study. At progression, mutations in BTK (Cys481) and/or PLCG2 (within the autoinhibitory domain) were found in 9 patients (10.7%), in 8 of 10 patients with progressive CLL, and in 1 patient with prolymphocytic transformation. Applying high-sensitivity testing (detection limit ∼1 in 1000 cells) to stored samples, we detected mutations up to 15 months before manifestation of clinical progression (range, 2.9-15.4 months). In 5 patients (6.0%), multiple subclones carrying different mutations arose independently, leading to subclonal heterogeneity of resistant disease. For a seamless transition to alternative targeted agents, patients progressing with CLL were continued on ibrutinib for up to 3 months, with 19.8 months median survival from the time of progression. This trial was registered at www.clinicaltrials.gov as #NCT01500733.

Deciphering Ibrutinib Resistance in Chronic Lymphocytic Leukemia.

Deciphering Ibrutinib Resistance in Chronic Lymphocytic Leukemia.