Primary Human Chronic Lymphocytic Leukemia Research Articles

Live Lymphoma and CLL Cells inside the Bone Marrow Fibroblasts: Implication in Residual Disease Persistence

Bruton tyrosine kinase inhibitors (BTKi) have generated remarkable clinical responses in patients with chronic lymphocytic leukemia (CLL) and other mature B-cell malignancies. However, deep, and durable response to BTK inhibition is uncommon. A significant number of patients with measurable residual disease relapse with resistance to therapies. Although mutational mechanisms responsible for resistance have been well described, it is not known what mechanism led to persistence of the minimal residual disease (MRD) in the first place. The tumor microenvironment (TME) contributes to drug resistance. Various roles for stroma participation have been described, however, none of these include the physical intracellular sheltering of tumor cells. Cell-in-cell (CIC) describes the microscopic observations of the embodiment of an intact cell by another whole cell ( Fig. 1A). Pathologists have reported this phenomenon sporadically in human fixed tissues for over a century. However, its biological, pathological, and clinical significance remains obscure. In the absence of systematic studies, understanding the significance of live CIC remains challenging. In this investigation, we studied primary human CLL samples using an ex vivo co-culture model system which mimics the CLL TME. In the TME system, CLL cells were cocultured with a primary bone marrow fibroblast line (BMF) in the presence of B-cell growth factors. The tumor cells survive for weeks, become larger, downregulate surface CXCR4. Phenotypically, tumor cells proliferate and divide into daughter cells. Collectively, these features recapitulate the behavior of lymph node-resident CLL cells. Using the TME system, we have demonstrated that modeled drug response correlates well with patient clinical response to BTK inhibitor ibrutinib and BCL2 inhibitor venetoclax. Interestingly, with confocal microscopy and 3D reconstruction, we observed that CLL cells placed in the model system were actively internalized by BMF in all 41 CLL cases studied. CLL cells were live and mobile. Moreover, one CLL cell was captured halfway in ( Fig. 1B). The number of internalized CLL cells was quantified and correlated with patients' clinical and pathological features. No correlations were found between CIC and widely used CLL prognostic indicators, including cytogenetic features and IGHV mutational status. However, we have found that patients who were on treatment for CLL at the time of sample collection had higher levels of CIC than those not treated. We hypothesized that live CIC may be an important mechanism contributing to residual disease persistence and drug resistance. To test the hypothesis, we exposed CLL cells in the TME model system to covalent and noncovalent BTKi including ibrutinib, zanubrutinib, and pirtobrutinib at clinically achievable concentrations. Our results showed that drug exposure drove CLL cells into BMF. This happened specifically to the BTK inhibitors as BCL2 inhibitor venetoclax was not observed to cause such an increase in CIC. These laboratory findings are consistent with the clinical observations that the rate of MRD negativity is much higher with venetoclax treatment than with BTKi. Additionally, CIC was observed in both follicular lymphoma (FL) cell line and primary FL cells suggesting the phenomenon is not limited to CLL. Further, we found that CIC was stimulated by several B-cell growth factors. The chemokine CXCL12-CXCR4 axis played a critical role in this process. Specifically, conditioned medium containing CXCL12 ligand promoted cell internalization, while plerixafor, a CXCR4 antagonist, largely prevented CIC from occurring. Furthermore, plerixafor blocks ibrutinib-driven CIC in cell lines as well as in primary CLL cells. Our study represents the first report implicating the CIC phenomenon in residual disease persistence using a cohort of patient-derived CLL cells assessed with 3D imaging and quantitative approach. These findings suggest that live CIC may be an important mechanism tumor cells use to avoid harmful drug insults, survive, persist, and later proliferate, eventually leading to clinical relapse. Targeting the CXCL12-CXCR4 axis may become a potential therapeutic strategy to minimize residual disease and future relapse. Fig.1. A. Images are reconstructed in 3D using Imaris v10.0. BMF cells are visualized as transparent red surfaces and CLL cells as green surfaces. B. One CLL cell was captured halfway in.

CRISPR-Cas9 Genome Editing of Primary Chronic Lymphocytic Leukemia Cells

Chronic lymphocytic leukemia (CLL) is a common B-cell neoplasia that exhibits a very heterogeneous course. Over the last decade, multiple molecular studies have described the genomic, epigenomic and transcriptional landscape of the disease. These studies have led to the identification of more than 60 recurrently mutated genes as well as a large number of deregulated genes and regulatory elements. While the prognostic significance of some of these alterations is well described, their specific contributions to the pathogenesis of the disease remains largely unknown. Attempts to address this experimentally have employed genetically engineered mouse models and human cell lines. Although mouse models have been helpful to recapitulate disease aspects that can be only properly studied in vivo, significant limitations exist that prevent extrapolation of data from mice to human. Moreover, cell lines are commonly obtained from patients with end-stage, refractory diseases and are frequently EBV-positive, showing great discrepancies with primary cells, including high proliferation rate and absence of spontaneous apoptosis. In addition, they do not faithfully recapitulate the transcriptional and chromatin landscape of CLL primary cases. Thus, there is a need of better cellular models that recapitulate these disease aspects. An attractive solution to this problem would be the use of primary human CLL cells as a platform for ex vivo genetic manipulation, applying CRISPR-Cas9 genome editing technology. However, this is technically challenging, as (i) CLL cells are critically dependent on stimulatory signals coming from the tumor microenvironment, particularly in the lymph nodes (LN), and (ii) primary cells are resistant to most gene transfer methods. In order to overcome these limitations, we took advantage of a cell culture system that is reminiscent of a LN environment and induces vigorous proliferation of CLL primary cells for several weeks, allowing retroviral gene transfer with high efficiency and minimal toxicity (Mangolini, M. et al., 2022, Nat Commun, in press). To avoid undesired off-target effects induced by the constitutive expression of a CRISPR-Cas9 viral plasmid, we used transient expression systems. As an initial proof of concept, we designed sgRNA targeting the CD19 gene, a pan-B cell marker highly expressed in CLL cells, and assessed the transfection efficiency and cell viability when introducing the Cas9-CD19 sgRNA ribonucleoprotein complex using the Neon Transfection System (Thermo Fisher Scientific). Cryopreserved CLL primary cells (from peripheral blood samples) were expanded for 3 days in vitro and were subsequently electroporated with optimized conditions. Cell viability and electroporation efficiency were assessed 24 hours later and demonstrated a remarkable low percentage of apoptotic cells, with only 10% of cell death compared to non-electroporated cells (measured by flow cytometry using the LIVE/DEAD fixable Aqua dead cell stain, n= 6 cases); while high transfection efficiency was accomplished, with over 80% of cells containing the fluorescent Cas9-ATTO550 sgRNA ribonucleoprotein. Finally, 72 hours after electroporation we observed a downregulation greater than 85% of CD19 levels by flow cytometry (n=6 cases). After successful CD19 downregulation, we aimed at targeting the cell cycle regulatory protein Cyclin D2 (CCND2), which is upregulated by CLL cells at proliferation centers and the most upregulated cyclin in our cell culture system. Two independent sgRNAs were electroporated with the Cas9 protein into 3 CLL primary cases, with a minimum effect on cell viability after 24 hours. CCND2 knock-down (KD) efficiency was of 70% and 60% respectively in all cases studied, assessed by qRT-PCR. Interestingly, despite being exposed to cell culture conditions promoting vigorous proliferation, CCND2 KD blocked cell proliferation, and a cell growth reduction of 50-70% was obtained with both sgRNAs compared with non-targeting controls already at 48 hours. Altogether, these results demonstrate the feasibility to genetically modify primary CLL cells using the CRISPR-Cas9 system. This strategy overcomes the current dependency on cell lines or mouse models and represents a powerful tool to unveil the role of candidate genes involved in CLL pathogenesis.

Pharmacological modulation of Kv1.3 potassium channel selectively triggers pathological B lymphocyte apoptosis in vivo in a genetic CLL model

BackgroundIon channels are emerging as promising oncological targets. The potassium channels Kv1.3 and IKCa are highly expressed in the plasma membrane and mitochondria of human chronic lymphocytic leukemia (CLL) cells, compared to healthy lymphocytes. In vitro, inhibition of mitoKv1.3 by PAPTP was shown to kill ex vivo primary human CLL cells, while targeting IKCa with TRAM-34 decreased CLL cell proliferation.MethodsHere we evaluated the effect of the above drugs in CLL cells from ibrutinib-resistant patients and in combination with Venetoclax, two drugs used in the clinical practice. The effects of the drugs were tested also in the Eμ-TCL1 genetic CLL murine model, characterized by a lympho-proliferative disease reminiscent of aggressive human CLL. Eμ-TCL1 mice showing overt disease state were treated with intraperitoneal injections of non-toxic 5 nmol/g PAPTP or 10 nmol/g TRAM-34 once a day and the number and percentage of pathological B cells (CD19+CD5+) in different, pathologically relevant body districts were determined.ResultsWe show that Kv1.3 expression correlates with sensitivity of the human and mouse neoplastic cells to PAPTP. Primary CLL cells from ibrutinib-resistant patients could be killed with PAPTP and this drug enhanced the effect of Venetoclax, by acting on mitoKv1.3 of the inner mitochondrial membrane and triggering rapid mitochondrial changes and cytochrome c release. In vivo, after 2 week- therapy of Eμ-TCL1 mice harboring distinct CLL clones, leukemia burden was reduced by more than 85%: the number and percentage of CLL B cells fall in the spleen and peritoneal cavity and in the peripheral blood, without signs of toxicity. Notably, CLL infiltration into liver and spleen and splenomegaly were also drastically reduced upon PAPTP treatment. In contrast, TRAM-34 did not exert any beneficial effect when administered in vivo to Eμ-TCL1 mice at non-toxic concentration.ConclusionAltogether, by comparing vehicle versus compound effect in different Eμ-TCL1 animals bearing unique clones similarly to CLL patients, we conclude that PAPTP significantly reduced leukemia burden in CLL-relevant districts, even in animals with advanced stage of the disease. Our results thus identify PAPTP as a very promising drug for CLL treatment, even for the chemoresistant forms of the disease.

B Cell-Restricted Depletion of Dnmt3a Activates Notch Signaling and Causes Chronic Lymphocytic Leukemia

B Cell-Restricted Depletion of Dnmt3a Activates Notch Signaling and Causes Chronic Lymphocytic Leukemia

A novel class of oxazepine-based anti-cancer agents induces cell death in primary human CLL cells and efficiently reduces tumor growth in Eμ-TCL1 mice through the JNK/STAT4/p66Shc axis

Survival and expansion of malignant B cells in chronic lymphocytic leukemia (CLL) are highly dependent both on intrinsic defects in the apoptotic machinery and on the interactions with cells and soluble factors in the lymphoid microenvironment. The adaptor protein p66Shc is a negative regulator of antigen receptor signaling, chemotaxis and apoptosis whose loss in CLL B cells contributes to their extended survival and poor prognosis. Hence, the identification of compounds that restore p66Shc expression and function in malignant B cells may pave the way to a new therapeutic approach for CLL. Here we show that a novel oxazepine-based compound (OBC-1) restores p66Shc expression in primary human CLL cells by promoting JNK-dependent STAT4 activation without affecting normal B cells. Moreover, we demonstrate that the potent pro-apoptotic activity of OBC-1 in human leukemic cells directly correlates with p66Shc expression levels and is abrogated when p66Shc is genetically deleted. Preclinical testing of OBC-1 and the novel analogue OBC-2 in Eμ-TCL1 tumor-bearing mice resulted in a significantly longer overall survival and a reduction of the tumor burden in the spleen and peritoneum. Interestingly, OBCs promote leukemic cell mobilization from the spleen to the blood, which correlates with upregulation of sphingosine-1-phosphate receptor expression. In summary, our work identifies OBCs as a promising class of compounds that, by boosting p66Shc expression through the activation of the JNK/STAT4 pathway, display dual therapeutic effects for CLL intervention, namely the ability to mobilize cells from secondary lymphoid organs and a potent pro-apoptotic activity against circulating leukemic cells.

Multifunctional barcoding with ClonMapper enables high-resolution study of clonal dynamics during tumor evolution and treatment.

Lineage-tracing methods have enabled characterization of clonal dynamics in complex populations, but generally lack the ability to integrate genomic, epigenomic and transcriptomic measurements with live-cell manipulation of specific clones of interest. We developed a functionalized lineage-tracing system, ClonMapper, which integrates DNA barcoding with single-cell RNA sequencing and clonal isolation to comprehensively characterize thousands of clones within heterogeneous populations. Using ClonMapper, we identified subpopulations of a chronic lymphocytic leukemia cell line with distinct clonal compositions, transcriptional signatures and chemotherapy survivorship trajectories; patterns that were also observed in primary human chronic lymphocytic leukemia. The ability to retrieve specific clones before, during and after treatment enabled direct measurements of clonal diversification and durable subpopulation transcriptional signatures. ClonMapper is a powerful multifunctional approach to dissect the complex clonal dynamics of tumor progression and therapeutic response.

Musashi 2 influences chronic lymphocytic leukemia cell survival and growth making it a potential therapeutic target

Progression of chronic lymphocytic leukemia (CLL) results from the expansion of a small fraction of proliferating leukemic B cells. When comparing the global gene expression of recently divided CLL cells with that of previously divided cells, we found higher levels of genes involved in regulating gene expression. One of these was the oncogene Musashi 2 (MSI2), an RNA-binding protein that induces or represses translation. While there is an established role for MSI2 in normal and malignant stem cells, much less is known about its expression and role in CLL. Here we report for the first time ex vivo and in vitro experiments that MSI2 protein levels are higher in dividing and recently divided leukemic cells and that downregulating MSI2 expression or blocking its function eliminates primary human and murine CLL and mature myeloid cells. Notably, mature T cells and hematopoietic stem and progenitor cells are not affected. We also confirm that higher MSI2 levels correlate with poor outcome markers, shorter time-to-first-treatment, and overall survival. Thus, our data highlight an important role for MSI2 in CLL-cell survival and proliferation and associate MSI2 with poor prognosis in CLL patients. Collectively, these findings pinpoint MSI2 as a potentially valuable therapeutic target in CLL.

Idelalisib Rescues Natural Killer Cells from Monocyte-Induced Immunosuppression by Inhibiting NOX2-Derived Reactive Oxygen Species.

The phosphatidylinositol-4,5-bisphosphate-3 kinase-δ (PI3Kδ) inhibitor idelalisib, used alone or in combination with anti-CD20, is clinically efficacious in B-cell lymphoma and chronic lymphocytic leukemia (CLL) by promoting apoptosis of malignant B cells. PI3K regulates the formation of reactive oxygen species (ROS) by the myeloid NADPH oxidase NOX2, but the role of PI3Kδ in myeloid cell-induced immunosuppression is unexplored. We assessed the effects of idelalisib on the spontaneous and IgG antibody-induced ROS production by human monocytes, on ROS-induced cell death of human natural killer (NK) cells, and on tumor cell clearance in an NK cell-dependent mouse model of metastasis. Idelalisib potently and efficiently inhibited the formation of NOX2-derived ROS from monocytes and rescued NK cells from ROS-induced cell death. Idelalisib also promoted NK cell cytotoxicity against anti-CD20-coated primary human CLL cells and cultured malignant B cells. Experiments using multiple PI3K inhibitors implicated the PI3Kδ isoform in regulating NOX2-induced ROS formation and immunosuppression. In B6 mice, systemic treatment with idelalisib significantly reduced the formation of lung metastases from intravenously injected melanoma cells but did not affect metastasis in B6.129S6-Cybbtm1Din (Nox2 -/-) mice or in NK cell-deficient mice. Our results imply that idelalisib rescues NK cells from NOX2/ROS-dependent immunosuppression and thus exerts antineoplastic efficacy beyond B-cell inhibition.

Identification of Genotype-Specific Therapeutic Vulnerabilities By Comparative Dynamic BH3 Profiling Analysis of Human and Murine CLL

Identification of Genotype-Specific Therapeutic Vulnerabilities By Comparative Dynamic BH3 Profiling Analysis of Human and Murine CLL

Leukemic B Cell CTLA-4 Suppresses Costimulation of T Cells.

The clinical benefit of CTLA-4 blockade on T cells is known, yet the impact of its expression on cancer cells remains unaddressed. We define an immunosuppressive role for tumor-expressed CTLA-4 using chronic lymphocytic leukemia (CLL) as a disease model. CLL cells, among other cancer cells, are CTLA-4+ Coculture with activated human T cells induced surface CTLA-4 on primary human CLL B cells. CTLA-4 on CLL-derived human cell lines decreased CD80 expression on cocultured CD80+ cells, with restoration upon CTLA-4 blockade. Coculture of CTLA-4+ CLL cells with CD80-GFP+ cell lines revealed transfer of CD80-GFP into CLL tumor cells, similar to CTLA-4+ T cells able to trans-endocytose CD80. Coculture of T cells with CTLA-4+ CLL cells decreased IL-2 production. Using a human CTLA-4 knock-in mouse lacking FcγR function, antitumor efficacy was observed by blocking murine CTLA-4 on tumor cells in isolation of the T cell effect and Fc-mediated depletion. These data implicate tumor CTLA-4 in cancer cell-mediated immunosuppression in vitro and as having a functional role in tumor cells in vivo.

B-Cell Receptor Signaling Drives Glycolysis in Chronic Lymphocytic Leukemia Cells

B-Cell Receptor Signaling Drives Glycolysis in Chronic Lymphocytic Leukemia Cells

Dual-Mode Dark Field and Surface-Enhanced Raman Scattering Liposomes for Lymphoma and Leukemia Cell Imaging.

Multifunctional probes are needed to characterize individual cells simultaneously by different techniques to provide complementary information. A preparative method and an in vitro demonstration of function are presented for a dual-function dark field microscopy/surface-enhanced Raman scattering (SERS) liposome probe for cancer. Liposomes composed of zwitterionic lipids are valuable both to limit biofouling and to serve as a modular matrix to incorporate a variety of functional molecules and hence are used here as vehicles for SERS-active materials. Dark field microscopy and SERS represent new combined functionalities for targeted liposomal probes. Two methods of antibody conjugation to SERS liposomes are demonstrated: (i) direct conjugation to functional groups on the SERS liposome surface and (ii) postinsertion of lipid-functionalized antibody fragments (Fabs) into preformed SERS liposomes. In vitro experiments targeting both lymphoma cell line LY10 and primary human chronic lymphocytic leukemia (CLL) cells demonstrate the usefulness of these probes as optical contrast agents in both dark field and Raman microscopy.

Splicing modulation sensitizes chronic lymphocytic leukemia cells to venetoclax by remodeling mitochondrial apoptotic dependencies.

The identification of targetable vulnerabilities in the context of therapeutic resistance is a key challenge in cancer treatment. We detected pervasive aberrant splicing as a characteristic feature of chronic lymphocytic leukemia (CLL), irrespective of splicing factor mutation status, which was associated with sensitivity to the spliceosome modulator, E7107. Splicing modulation affected CLL survival pathways, including members of the B cell lymphoma-2 (BCL2) family of proteins, remodeling antiapoptotic dependencies of human and murine CLL cells. E7107 treatment decreased myeloid cell leukemia-1 (MCL1) dependence and increased BCL2 dependence, sensitizing primary human CLL cells and venetoclax-resistant CLL-like cells from an Eμ-TCL1-based adoptive transfer murine model to treatment with the BCL2 inhibitor venetoclax. Our data provide preclinical rationale to support the combination of venetoclax with splicing modulators to reprogram apoptotic dependencies in CLL for treating venetoclax-resistant CLL cases.

Potent anti-leukemic activity of a specific cyclin-dependent kinase 9 inhibitor in mouse models of chronic lymphocytic leukemia.

Onset of progression even during therapy with novel drugs remains an issue in chronic lymphocytic leukemia (CLL). Thus, there is ongoing demand for novel agents. Approaches targeting cyclin-dependent kinases (CDK) have reached the clinical trial stage. CDK9 mediating RNA transcriptional elongation is the evolving pivotal CLL CDK inhibitor target. However, more CDK9 selective compounds are desirable. Here, we describe the CDK9 inhibitor LDC526 displaying a low nanomolar biochemical activity against CDK9 and an at least 50-fold selectivity against other CDKs. After demonstrating in vitro MEC-1 cell line and primary human CLL cell cytotoxicity we evaluated the LDC526 in vivo effect on human CLL cells transplanted into NOD/scid/γcnull (NSG) mice. LDC526 administration (75 mg/kg) for 5 days resulted in a 77% reduction of human CLL cells in NSG spleens compared to carrier control treatment. Next, we longitudinally studied the LDC526 impact on circulating CLL cells in the TCL1 transgenic mouse model. LDC526 (50 mg/kg) administration for two days led to a 16-fold reduction of blood CLL cell numbers. Remarkably, residual CLL cells exhibited significantly increased intracellular BCL-2 levels. However, the LDC526 cytotoxic effect was not restricted to CLL cells as also declining numbers of normal B and T lymphocytes were observed in LDC526 treated TCL1 mice. Taken together, our in vivo data provide a strong rational for continued LDC526 development in CLL therapy and argue for the combination with BCL-2 inhibitors.

BI 836826, a Novel Fc-Engineered Antibody in Combination with Phosphoinositide-3-Kinase Inhibitor for Treatment of High Risk Chronic Lymphocytic Leukemia and Lymphoma

BackgroundTargeting new antigens in chronic lymphocytic leukemia (CLL) and lymphoma may increase flexibility in the clinic and help circumvent resistance. The tetraspanin CD37 domain mediates transduction of survival and apoptotic signals (Lapalombella et al.,Cancer Cell, 2014), and has been clinically validated by recent trials of otlertuzumab (TRU-016) in CLL and Non-Hodgkin Lymphoma . Ligation of CD37 by this reagent simultaneously induced pro-apoptotic signaling and inhibited pro-survival signaling of phosphoinositide 3-kinase δ (PI3Kδ), which introduces a unique opportunity to use combination strategies employing activation of CD37 and inhibition of PI3Kδ. A new agent BI 836826 is an Fc-engineered anti-CD37 IgG1 that displays improved effector activities as well as crosslinker-independent direct cytotoxicity. We have evaluated the efficacy of BI 836826 combined with the PI3Kδ-selective inhibitor idelalisib in diffuse large B-cell lymphoma (DLBCL) cell lines and primary human CLL B-cells in the University and then by industry to validate the synergistic finding initially reported.Methods Cell viability assays usedCellTiterGlo to measure inhibition of antibody, isotype control, idelalisib or a combination of antibody and compound over 72h in culture. The cell viability of vehicle is measured at the time of dosing (T0) and after seventy-two hours (T72). A GI reading of 0% represents no growth inhibition, GI 100% represents complete growth inhibition, and a GI 200% represents complete death of all cells in the culture well. Annexin V-FITC and propidium iodide measure by flow cytometry was used to assess enhanced killing of primary CLL cells, with incubation of BI 836826 (0.1 µg/mL) and/or idelalisib (1 µM) at 37°C for 24 hours. Trastuzumab included as a non-specific IgG1 control. Data was reported as percentage of viable cells (Annexin V negative, PI negative) normalized to untreated control.ResultsDLBCL cell lines were variably sensitive to single agent BI 836826. In most of the cell lines tested, the cell viability was inhibited by 40%-50% with BI 836826 in the concentration range of 1-1000 ng/mL (Figure 1A). A synergistic effect was noted in several DLBCL cell lines when BI 836826 was combined with idelalisib. When the maximal effect of BI 836826 was greater than isotype control (GI% > 12, dotted line) and the effect of idelalisib showed a GI50 < 1uM, 3/5 cell lines showed synergy in combination (red dot, Figure 1B). A shift in the EC50of idelalisib can be seen with the addition of increasing amounts of BI 836826 (Figure 1C). In primary CLL B-cell cultures, 1 µM idelalisib displayed weak single agent activity following 24-hour incubation. The cytotoxicity of BI 836826 at 0.1 µg/mL was more variable, although treatment of samples from most CLL patients resulted in 20-50% B-cell death. The combination of these 2 agents resulted in enhanced cytotoxic activity (Figure 2A), and this effect was not attenuated by the presence of del(17)(p13.1), as there was no significant difference in cytotoxicity against these cells compared to those with lower risk cytogenetics (Figure 2B,C). Additionally, the combination was beneficial in CLL B-cells isolated from patients who were refractory to ibrutinib (Figure 2D).ConclusionsThis collaborative industry and academic endeavor with cross validation of initial mechanistic studies of synergy between CD37 and idelalisib demonstrates that addition of idelalisib to BI 836826 augments cytotoxicity against DLBCL cell lines and primary human CLL B-cells in an additive-to-synergistic manner. In addition, it maintains efficacy against CLL B-cells with del(17)(p13.1) and those from ibrutinib-refractory patients. Further exploration of this therapeutic strategy in clinical trials is strongly warranted. [Display omitted] [Display omitted] DisclosuresJones:AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics, LLC, an AbbVie Company: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Awan:Innate Pharma: Research Funding; Pharmacyclics: Consultancy; Novartis Oncology: Consultancy. Grosmaire:Gilead: Employment. Jones:Gilead: Employment. DiPaolo:Gilead: Employment. Tannheimer:Gilead Sciences: Employment. Heider:4Boehringer Ingelheim RCV: Employment.

Transcriptomic Characterization of SF3B1 Mutation Reveals Its Pleiotropic Effects in Chronic Lymphocytic Leukemia

Mutations in SF3B1, which encodes a spliceosome component, are associated with poor outcome in chronic lymphocytic leukemia (CLL), but how these contribute to CLL progression remains poorly understood. We undertook a transcriptomic characterization of primary human CLL cells to identify transcripts and pathways affected by SF3B1 mutation. Splicing alterations, identified in the analysis of bulk cells, were confirmed in single SF3B1-mutated CLL cells and also found in cell lines ectopically expressing mutant SF3B1. SF3B1 mutation was found to dysregulate multiple cellular functions including DNA damage response, telomere maintenance, and Notch signaling (mediated through KLF8 upregulation, increased TERC and TERT expression, or altered splicing of DVL2 transcript, respectively). SF3B1 mutation leads to diverse changes in CLL-related pathways.

Synergistic Activity of Deguelin and Fludarabine in Cells from Chronic Lymphocytic Leukemia Patients and in the New Zealand Black Murine Model.

B-cell chronic lymphocytic leukemia (CLL) remains an incurable disease, and despite the improvement achieved by therapeutic regimes developed over the last years still a subset of patients face a rather poor prognosis and will eventually relapse and become refractory to therapy. The natural rotenoid deguelin has been shown to induce apoptosis in several cancer cells and cell lines, including primary human CLL cells, and to act as a chemopreventive agent in animal models of induced carcinogenesis. In this work, we show that deguelin induces apoptosis in vitro in primary human CLL cells and in CLL-like cells from the New Zealand Black (NZB) mouse strain. In both of them, deguelin dowregulates AKT, NFκB and several downstream antiapoptotic proteins (XIAP, cIAP, BCL2, BCL-XL and survivin), activating the mitochondrial pathway of apoptosis. Moreover, deguelin inhibits stromal cell-mediated c-Myc upregulation and resistance to fludarabine, increasing fludarabine induced DNA damage. We further show that deguelin has activity in vivo against NZB CLL-like cells in an experimental model of CLL in young NZB mice transplanted with spleen cells from aged NZB mice with lymphoproliferation. Moreover, the combination of deguelin and fludarabine in this model prolonged the survival of transplanted mice at doses of both compounds that were ineffective when administered individually. These results suggest deguelin could have potential for the treatment of human CLL.

Derivatization of agelastatin A leading to bioactive analogs and a trifunctional probe

(−)-Agelastatin A (AglA, 1), a member of the pyrrole-aminoimidazole marine alkaloid (PAI) family, possesses a unique tetracyclic structure and is one of the most potent anticancer PAIs isolated to date. In efforts to expand the SAR of these agents and delineate sites that tolerate modification while retaining activity, we synthesized several derivatives and tested their anticancer activity. The cytotoxic effects of these derivatives were measured against several cancer cell lines including cervical cancer (HeLa), epidermoid carcinoma (A431), ovarian (Igrov and Ovcar3), osteosarcoma (SJSA1), acute T cell leukemia (A3), epidermoid carcinoma (A431) in addition to primary human chronic lymphocytic leukemia (CLL) cells. New positions for modification of AglA and new substitutions were explored leading to novel derivatives, 14-chloro AglA (3) and 14-methyl AglA (12), that retained activity toward various cancer cell lines with decreased toxicity toward B- and T-cells. The SAR data informed the synthesis of a trifunctional probe bearing an alkyne and a diazirine potentially useful for cellular target identification.

Synthetic High-Density Lipoprotein-like Nanoparticles (HDL NP) Cause Apoptosis and Enhance Killing By B-Cell Receptor and BCL-2 Inhibitors in Chronic Lymphocytic Leukemia (CLL)

Introduction:Chronic lymphocytic leukemia is the most frequent adult leukemia that remains incurable, despite the use of innovative compounds targeting crucial signaling pathways of the disease. Additional non-toxic, targeted therapies are urgently needed in order to improve the curability of CLL as well as to increase the therapeutic index of existing drugs through rational combinations. Biomimetic high-density lipoprotein-like nanoparticles (HDL NP) have comparable size, shape, and surface chemistry as natural, spherical HDLs. HDL NPs modulate cellular cholesterol homeostasis, and potently induce apoptotic cell death in B cell lymphoma cell lines after tightly binding to the high-affinity HDL receptor, scavenger receptor type B-1 (SR-B1). Based on these data, we investigated SR-B1 expression and tested the nanoparticles' effect on primary human CLL with the hypothesis that HDL NP binding to SR-B1 and modulation of cellular cholesterol homeostasis in the leukemic cells would produce a therapeutic response. In addition, we explored the possibility of enhancing its therapeutic effect through the combination of the HDL NP with BCL2-inhibitor ABT-199 and the BTK-inhibitor, ibrutinib, in a series of fresh leukemia cells from patients with CLL.Methods:Fresh human CLL cells from peripheral blood were obtained from patients with CLL (N = 20) after signing an informed consent as part of a investigational study approved by the IRB. Samples were also obtained from healthy volunteers. Normal and leukemic B cells were negatively purified using a B-lymphocyte enrichment kit (RosetteSep; StemCell Technologies) and cell lysate was utilized to evaluate SR-B1 expression by Western blotting utilizing a monoclonal antibody (AbCam). HDL NPs were added to the samples at a concentration of 30nM and 100nM and allowed to incubate for 72 hours in vitro. In parallel experiments, ABT-199 (0.003µM) and Ibrutinib (1µM) were added either alone or in the presence of the HDL NP to the cell culture. Flow cytometry was performed using Annexin/PI staining to measure cell death.Results:Among the 11 CLL patients' samples tested, 8 (72%) expressed the SR-B1 receptor as detected by WB. In this series, SR-B1 expression was independent of any known biological features, including IGHV gene mutational status. When purified leukemic cells (n=9) were incubated for 72 hours in the presence of HDL NPs, a dose response pro-apoptotic effect was evident with a higher percentage of Annexin V positive cells compared to untreated controls at a concentration of 30nM (52.6% ± 6.7% range vs 28.6% ± 2.6%), peaking at 100nM (74.2% ± 4.6%) (p<0.01). Interestingly, when total mononuclear cells from CLL patients were cultured in the presence of the particles, the pro-apoptotic effect at 30nM was abrogated (19.8% ± 5.0% vs 17.3% ± 3.5% while it remained significant (p<0.05) at the higher concentration of 100nM (41.7% ± 7.7%). This might be explained either by a protective effect by the microenvironment, as shown also with other drugs, or by a dilution effect due to the uptake of HDL NPs by other by-stander cells. Viability of neither B nor T lymphocytes from healthy donors was affected by the highest concentration of the particles. The combination of HDL NP with ABT-199 and Ibrutinib significantly enhanced the killing of CLL cells by the nanoparticles in particular when utilized at low concentrations (30nM) on unpurified mononuclear cells.Conclusions:Human primary CLL cells express the SR-B1 receptor. HDL NPs are a potential non-toxic therapy for human CLL. A protective effect of the microenvironment is also apparent that can be overcome by increasing the concentration of the particles, without increasing toxicity on normal lymphocytes. In addition, an enhanced response was achieved upon co-treatment of human CLL cells with HDL NPs and ABT-199, improving the efficacy of low doses of the particles, achievable in vivo. Taken together, these data argue for the continued development of the HDL NP platform as a treatment for B cell malignancies. DisclosuresGordon:Dr Leo I. Gordon: Patents & Royalties: Patent for gold nanoparticles pending; Northwestern University: Employment. Giles:Novartis: Consultancy, Honoraria, Research Funding. Thaxton:AuraSense, LLC: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: AuraSense, LLC licensed the high-density lipoprotein nanoparticle technology from Northwestern University. Ghia:AbbVie: Consultancy; Adaptive: Consultancy; Roche: Consultancy, Research Funding; Janssen: Consultancy; GSK: Research Funding; Pharmacyclics: Consultancy; Acerta Pharma BV: Research Funding; Gilead: Consultancy, Research Funding, Speakers Bureau.

Dual Inhibition of PI3K-Delta and Gamma By Duvelisib (IPI-145) Impairs CLL B- and T-Cell Migration, Survival and Proliferation in a Murine Xenograft Model Using Primary Chronic Lymphocytic Leukemia Cells

Duvelisib (IPI-145), a dual inhibitor of phosphoinositide 3-kinase (PI3K)-δ and -γ, has shown clinical activity in treatment-naïve and relapsed/refractory chronic lymphocytic leukemia (CLL) patients. Clinically, duvelisib results in a redistribution of malignant B cells and concomitant reduction in nodal enlargement. These effects are believed to be due to important roles of PI3K- δ and -γ in CXCL12-mediated CLL cell migration (Peluso 2014), cytokine-induced CLL B-cell proliferation, and BCR-stimulated B-cell survival (Balakrishnan 2015). Additional data suggest an effect of duvelisib on the tumor supporting cells of the CLL microenvironment. This includes preclinical studies demonstrating that PI3K-γ inhibition blocks normal T cell migration toward tumor chemokines and prevents murine bone marrow-derived M2 macrophage polarization (Peluso 2014), as well as clinical data in CLL patients receiving duvelisib showing reduced serum levels of myeloid and T cell-secreted cytokines and chemokines (Douglas 2015).To further characterize duvelisib's effect on CLL cells and the tumor microenvironment (TME), a murine xenograft model using primary human CLL cells was employed. We first studied duvelisib's effect on CLL B- and T-cell migration in vivo. CLL PBMCs (n=2; 1 IGHV unmutated (U)-CLL, 1 IGHV mutated (M)-CLL) pre-treated with duvelisib for 48 hours were injected retro-orbitally into NOD-scid IL2Rgammanull (NSG) mice. B- and T-cell localization in tissues and circulation was studied 1 and 24 hours post-injection. Duvelisib treatment (1000 nM) prevented the egress of CLL B and T cells from the circulation into the spleen, indicating impaired homing of CLL B and T cells. To better define the effect of duvelisib on T-cell migration, T cells from CLL patients (n=3; 2 U-CLL, 1 M-CLL) treated ex vivo with duvelisib at 1, 10, 100 and 1000 nM were injected into mice and analyzed for their trafficking 24 hours later. Inhibition of T-cell homing to spleen was dose dependent, with only 100 and 1000 nM having significant effects. Given duvelisib's cellular IC50s for PI3K isoforms, these results suggest that impaired T-cell migration is due to PI3K-γ inhibition, and studies with isoform-selective PI3K-δ and PI3K-γ inhibitors are currently underway to examine this possibility.The effect of duvelisib on CLL T-cell proliferation was evaluated after in vitro activation with anti-CD3/28 Dynabeads plus IL2 (n=6; 3 U-CLL, 3M-CLL). In duvelisib treated cells, CD4+, but not CD8+, T-cell proliferation was inhibited at doses of 100 and 1000 nM, suggesting a role for PI3K-γ. The effects of duvelisib on CLL B- and T-cell growth in vivo (n=4; 2 U-CLL, 2 M-CLL) were then studied. Autologous CLL T cells were stimulated as above and injected with CLL PBMCs into NSG mice. Animals treated orally with duvelisib for 3 weeks at 100 mg/kg/day had preferentially reduced CD4+ T-cell recovery from spleens, thereby decreasing the CD4 to CD8 ratio. In each case, duvelisib treatment reduced the number of splenic CLL B cells. This reduction reflected inhibition of both CLL cell proliferation and survival, since duvelisib treatment decreased the percentage of cycling CLL cells and increased the percentage of apoptotic B cells. Thus, duvelisib may target CLL B-cell growth directly, or indirectly by inhibiting the support of CD4+ T cells in the TME.The potential effect of duvelisib on the tumor-supporting myeloid compartment was also tested. Because of limited human myeloid-cell engraftment in our NSG model, we studied the effect of duvelisib on murine macrophages. Mice receiving duvelisib had reduced numbers of splenic CD11b+ GR-1low LY-6Clow LY-6Gneg macrophages compared to controls, suggesting duvelisib altered macrophage development.Prior in vitro studies demonstrated inhibition of CLL B-cell survival and proliferation by duvelisib, as well as blockade of T-cell migration and M2 macrophage polarization (Balakrishnan 2015; Peluso 2014). Our current in vivo studies further support duvelisib's effect on CLL B-cell growth and survival through inhibition of cellular homing to supportive tissue niches and alterations in the TME. The latter, in part, is through suppression of T-cell support and alterations in the macrophage compartment. Overall, these preclinical results suggest that inhibition of PI3K-δ and PI3K-γ by duvelisib affects CLL cell survival through direct and indirect mechanisms. DisclosuresMcGovern:Infinity Pharmaceuticals, Inc.: Employment. Kutok:Infinity Pharmaceuticals, Inc.: Employment.