Neutrophil elastase as a versatile cleavage enzyme for activation of αvβ3 integrin-targeted small molecule drug conjugates with different payload classes in the tumor microenvironment

Introduction: The development of bioconjugates for the targeted delivery of anticancer agents is gaining momentum after recent success of antibody drug conjugates (ADCs) in the clinic. Smaller format conjugates may have several advantages including better tumor penetration; however, cellular uptake and trafficking may be substantially different from ADCs. To fully leverage the potential of small molecule drug conjugates (SMDCs) with potent binding molecules mediating tumor homing, novel linker chemistries susceptible for efficient extracellular activation and payload release in the tumor microenvironment (TME) need to be explored. Methods: We designed a novel class of SMDCs, which target αvβ3 integrins for tumor homing and are cleaved by neutrophil elastase (NE), a serine protease active in the TME. A peptidomimetic αvβ3 ligand was attached via optimized linkers composed of substrate peptide sequences of NE connected to different functional groups of various payload classes, such as camptothecins, monomethyl auristatin E, kinesin spindle protein inhibitors (KSPi) and cyclin-dependent kinase 9 inhibitors (CDK-9i). Results: NE-mediated cleavage was found compatible with the diverse linker attachments via hindered ester bonds, amide bonds and sulfoximide bonds. Efficient and traceless release of the respective payloads was demonstrated in biochemical assays. The newly designed SMDCs were highly stable in buffer as well as in rat and human plasma. Cytotoxicity of the SMDCs in cancer cell lines was clearly dependent on NE. IC50 values were in the nanomolar or sub-nanomolar range across several cancer cell lines reaching similar potencies as compared to the respective payloads only in the presence of NE. In vivo pharmacokinetics evaluating SMDC and free payload exposures in rat and particularly the robust efficacy with good tolerability in triple negative breast and small cell lung cancer murine models demonstrate the utility of this approach for selective delivery of payloads to the tumor. Discussion: These results highlight the broad scope of potential payloads and suitable conjugation chemistries paving the way for future SMDCs harnessing the safety features of targeted delivery approaches in combination with NE cleavage in the TME.

Enitociclib, a Selective CDK9 Inhibitor, Induces Complete Regression of MYC+ Lymphoma by Downregulation of RNA Polymerase II Mediated Transcription

Double-hit diffuse large B-cell lymphoma (DH-DLBCL) is an aggressive, and often refractory, type of B-cell non-Hodgkin lymphoma (NHL) characterized by rearrangements in MYC and BCL2. Cyclin-dependent kinase 9 (CDK9) regulates transcriptional elongation and activation of transcription factors, including MYC, making it a potential targeted approach for the treatment of MYC+ lymphomas. Enitociclib is a well-tolerated and clinically active CDK9 inhibitor leading to complete metabolic remissions in 2 of 7 patients with DH-DLBCL treated with once weekly 30 mg intravenous administration. Herein, we investigate the pharmacodynamic effect of CDK9 inhibition in preclinical models and in blood samples from patients [DH-DLBCL (n = 10) and MYC+ NHL (n = 5)] treated with 30 mg i.v. once weekly enitociclib. Enitociclib shows significant regulation of RNA polymerase II Ser2 phosphorylation in a MYC-amplified SU-DHL-4 cell line and depletion of MYC and antiapoptosis protein MCL1 in SU-DHL-4 and MYC-overexpressing SU-DHL-10 cell lines in vitro. Tumor growth inhibition reaching 0.5% of control treated SU-DHL-10 xenografts is achieved in vivo and MYC and MCL1 depletion as well as evidence of apoptosis activation after enitociclib treatment is demonstrated. An unbiased analysis of the genes affected by CDK9 inhibition in both cell lines demonstrates that RNA polymerase II and transcription pathways are primarily affected and novel enitociclib targets such as PHF23 and TP53RK are discovered. These findings are recapitulated in blood samples from enitociclib-treated patients; while MYC downregulation is most robust with enitociclib treatment, other CDK9-regulated targets may be MYC independent delivering a transcriptional downregulation via RNA polymerase II.

SIGNIFICANCE

MYC+ lymphomas are refractory to standard of care and novel treatments that downregulate MYC are needed. The utility of enitociclib, a selective CDK9 inhibitor in this patient population, is demonstrated in preclinical models and patients. Enitociclib inhibits RNA polymerase II function conferring a transcriptional shift and depletion of MYC and MCL1. Enitociclib intermittent dosing downregulates transcription factors including MYC, providing a therapeutic window for durable responses in patients with MYC+ lymphoma.

Cusatuzumab plus azacitidine in newly diagnosed acute myeloid leukaemia ineligible for intensive chemotherapy (CULMINATE): part one of a randomised, phase 2, dose optimisation study

BACKGROUND

Cusatuzumab, a high-affinity anti-CD70 antibody, has shown preliminary activity as a treatment for acute myeloid leukaemia when combined with azacitidine. We aimed to determine the optimum dose for future trials of cusatuzumab in combination with azacitidine in patients with previously untreated acute myeloid leukaemia who are not eligible for intensive chemotherapy.

METHODS

In this randomised, phase 2, open-label, dose-optimisation study we enrolled adult patients aged 18 years or older with newly diagnosed acute myeloid leukaemia not eligible for intensive chemotherapy, and with Eastern Cooperative Oncology Group scores of 0-2, from 40 hospitals and centres across seven countries. In part one of the trial, participants were randomly allocated 1:1 to 10 mg/kg or 20 mg/kg intravenous cusatuzumab on days 3 and 17, combined with subcutaneous or intravenous azacitidine 75 mg/m2 on days 1-7 in 28-day cycles. The primary efficacy outcome was the rate of complete remission in the intention-to-treat group. The two dose cohorts were evaluated independently without between-cohort statistical comparison. Safety analyses were performed in all patients who received one dose of study drug. Part two of the trial was planned to be a single-arm expansion to evaluate cusatuzumab plus azacitidine at the cusatuzumab dose level selected in part one (primary hypothesis ≥35% rate of complete remission vs null hypothesis of 20%); however, changes in the acute myeloid leukaemia treatment landscape during this trial made it unlikely that enrolment to part two of the study would be clinically feasible, so the study stopped at the end of part one. The trial was registered at ClinicalTrials.gov, NCT04023526.

FINDINGS

103 patients were enrolled between Aug 30, 2019, and Feb 25, 2020, and randomly assigned to either cusatuzumab 10 mg/kg (n=51) or 20 mg/kg (n=52). Median follow-up was 7·2 months (IQR 10·7 months). 57 of 103 (55%) patients were male and 46 (45%) patients were female, 78 (76%) were White, one (1%) was Asian, and 24 (23%) did not report their race. In the 10 mg/kg group, complete remission rate was 12% (six of 51 patients; 95% CI 6-23) and in the 20 mg/kg group was 27% (14 of 52; 17-40). Grade 3 or worse treatment-emergent adverse events (TEAEs) were similar between the cusatuzumab 10 mg/kg (n=51) and 20 mg/kg (n=51) cohorts and included thrombocytopenia (24 patients [47%] vs 29 [57%]), anaemia (24 [47%] vs 17 [33%]), and neutropenia (20 [39%] in both cohorts). Serious TEAEs were also similar in the two cohorts (44 [86%] vs 40 [78%]). Treatment-related TEAEs leading to death were reported in both groups (three patients [6%] in the 10 mg/kg group vs one patient [2%] in the 20 mg/kg group); the reported causes of death were pneumonia (n=2) and septic shock (n=2).

INTERPRETATION

Although part one of this study was not designed to formally compare the two dose cohorts for efficacy, the totality of clinical data for cusatuzumab studies performed to date indicate that cusatuzumab 20 mg/kg plus azacitidine represents the optimal dose for further studies. A phase 1b study investigating the triple combination of cusatuzumab with venetoclax and azacitidine is underway (NCT04150887).

FUNDING

Janssen Research & Development and argenx.

Discovery of VIP236, an αvβ3-Targeted Small-Molecule-Drug Conjugate with Neutrophil Elastase-Mediated Activation of 7-Ethyl Camptothecin Payload for Treatment of Solid Tumors

The emerging field of small-molecule-drug conjugates (SMDCs) using small-molecule biomarker-targeted compounds for tumor homing may provide new perspectives for targeted delivery. Here, for the first time, we disclose the structure and the synthesis of VIP236, an SMDC designed for the treatment of metastatic solid tumors by targeting αvβ3 integrins and extracellular cleavage of the 7-ethyl camptothecin payload by neutrophil elastase in the tumor microenvironment. Imaging studies in the Lewis lung mouse model using an elastase cleavable quenched substrate showed pronounced elastase activity in the tumor. Pharmacokinetics studies of VIP236 in tumor-bearing mice demonstrated high stability of the SMDC in plasma and high tumor accumulation of the cleaved payload. Studies in bile-duct-cannulated rats showed that biliary excretion of the unmodified conjugate is the primary route of elimination. Treatment- and time-dependent phosphorylation of H2AX, a marker of DNA damage downstream of topoisomerase 1 inhibition, verified the on-target activity of the payload cleaved from VIP236 in vivo. Treatment with VIP236 resulted in long-lasting tumor regression in subcutaneous patient-derived xenograft (PDX) models from patients with non-small-cell lung, colon, and renal cancer as well as in two orthotopic metastatic triple-negative breast cancer PDX models. In these models, a significant reduction of brain and lung metastases also was observed.

'Sharpshooter' in Botanic Garden: the tale of a rare plant-insect interaction

Here we report a unique plant-insect interaction between the leafhopper Aloka depressa (tribe Phlogisini) and the host liana, Diploclisia glaucescens, from a Botanic Garden located at the southern edge of Western Ghats in India. Field observations and SEM micrographs were employed to derive evidences on this rare plant-insect interaction. 20-Hydroxyecdysone (20E), insect moulting hormone, was detected and quantified in the host plant D. glaucescens using HPTLC-densitometry. 20E was isolated and characterized from D. glaucescens using column chromatography, 1H-, 13C-NMR and HR-MS. 20E was also detected in A. depressa excrement using HPTLC-densitometry. The leafhopper A. depressa is functioning as a 'sharpshooter' drawing nutrients from the host liana, D. glaucescens, and flinging the waste fluid as droplets through their tail ends. SEM micrographs of A. depressa revealed its external morphological features, characteristic of a sharpshooter. We quantified 20E (0.44-1.44%, dry wt.) in various parts of D. glaucescens. 20E (1.47%, dry wt.) was also detected in the excrement of A. depressa. This plant (D. glaucescens)-insect (A. depressa) association crucially is not damaging the host liana. Considering the diseases caused by sharpshooting leafhoppers in the Americas, this association and the survival of the host plant (D. glaucescens) is illustrating a unique plant-insect interaction.

VIP152 is a selective CDK9 inhibitor with pre-clinical in vitro and in vivo efficacy in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is effectively treated with targeted therapies including Bruton tyrosine kinase inhibitors and BCL2 antagonists. When these become ineffective, treatment options are limited. Positive transcription elongation factor complex (P-TEFb), a heterodimeric protein complex composed of cyclin dependent kinase 9 (CDK9) and cyclin T1, functions to regulate short half-life transcripts by phosphorylation of RNA Polymerase II (POLII). These transcripts are frequently dysregulated in hematologic malignancies; however, therapies targeting inhibition of P-TEFb have not yet achieved approval for cancer treatment. VIP152 kinome profiling revealed CDK9 as the main enzyme inhibited at 100 nM, with over a 10-fold increase in potency compared with other inhibitors currently in development for this target. VIP152 induced cell death in CLL cell lines and primary patient samples. Transcriptome analysis revealed inhibition of RNA degradation through the AU-Rich Element (ARE) dysregulation. Mechanistically, VIP152 inhibits the assembly of P-TEFb onto the transcription machinery and disturbs binding partners. Finally, immune competent mice engrafted with CLL-like cells of Eµ-MTCP1 over-expressing mice and treated with VIP152 demonstrated reduced disease burden and improvement in overall survival compared to vehicle-treated mice. These data suggest that VIP152 is a highly selective inhibitor of CDK9 that represents an attractive new therapy for CLL.

DNA Origami Nanostructures Elicit Dose-Dependent Immunogenicity and Are Nontoxic up to High Doses In Vivo

DNA origami (DO) nanotechnology enables the construction of precise nanostructures capable of functionalization with small molecule drugs, nucleic acids, and proteins, suggesting a promising platform for biomedical applications. Despite the potential for drug and vaccine delivery, the impact of DO vehicles on immunogenicity in vivo is not well understood. Here, two DO vehicles, a flat triangle and a nanorod, at varying concentrations are evaluated in vitro and with a repeated dosing regimen administered at a high dose in vivo to study early and late immunogenicity. The studies show normal CD11b⁺ myeloid cell populations preferentially internalize DO in vitro. DO structures distribute well systemically in vivo, elicit a modest pro-inflammatory immune response that diminishes over time and are nontoxic as shown by weight, histopathology, lack of cytokine storm, and a complete biochemistry panel at the day 10 end point. The results take critical steps to characterize the biological response to DO and suggest that DO vehicles represent a promising platform for drug delivery and vaccine development where immunogenicity should be a key consideration.

Abstract 1859: VIP152, a selective CDK9 inhibitor, demonstrates sensitivity in gynecologic cell lines that are cisplatin sensitive or resistant and delivers in vivo antitumor efficacy

Background: The Myc transcription factor has a short half-life of 20-30 minutes (Ramsay et al. 1984) and oncogenic activation and transcriptional addiction leads to sustained levels of Myc, (Gabay et al. 2014). Mechanisms of activation include MYC gene amplification, mutation or rearrangement and have been reported to be prevalent in gynecologic malignancies, such as serous ovarian (39.2%), uterine (28.1%) and endometrial (19.5%) (https://www.cancer.gov/tcga). Since CDK9 phosphorylation of RNA polymerase II is required for transcription of Myc mRNA, we evaluate VIP152, a highly selective CDK9 inhibitor (Lücking et al 2021), to deliver antitumor responses in preclinical models of gynecologic malignancies.

Methods: Gynecologic cell lines were treated with 9 dose levels of VIP152 with DMSO and cisplatin as controls. IC50 were calculated using CellTiter-Glo luminescent cell viability assay after 72 hours treatment. A preliminary analysis of 19 cell lines was undertaken to determine whether response to VIP152 is associated with baseline mutation, gene expression, or copy number variation data. Monotherapy efficacy of VIP152 was evaluated in a cisplatin sensitive A2780 in vivo xenograft mouse model.

Results: Screening of gynecologic cell lines demonstrates a 3-log range of sensitivity with VIP152 IC50s ranging from 38-593nM. Simultaneous cisplatin screening identified sensitive and resistant cell lines in the same panel. Low VIP152 IC50s were observed in cell lines sensitive or resistant to cisplatin. Cell lines were assigned as sensitive and resistant based on the VIP152 IC50 values. Preliminary analysis suggests a gene signature could predict response to VIP152 in gynecologic malignancies. VIP152 was evaluated in an ovarian cancer A2780 in vivo xenograft model. Monotherapy treatment with 4 doses of VIP152 across 5 dose levels from 5- to 15-mg/kg weekly regimens provided increasing tumor growth inhibition compared with vehicle control.

Conclusions: VIP152 demonstrates sensitivity in gynecologic cell lines independent of cisplatin sensitivity. An interim gene signature that is associated with VIP152 sensitivity was defined and we plan to optimize this signature with a larger cell line panel. Dose-dependent tumor growth inhibition in an in vivo xenograft model is demonstrated. VIP152 is currently being evaluated in the clinic (ClinicalTrials.gov Identifiers: NCT02635672 and NCT04978779). References: Gabay et al. 2014. Cold Spring Harb Perspect Med. 4(6):a014241. Lücking et al. 2021. J Med Chem. 64(15):11651-11674. Ramsay et al. 1984. PNAS. 81(24):7742-7746.

Citation Format: Melanie M. Frigault, Hermes Garban, Joy M. Greer, Stuart Hwang, Raquel Izumi, Amy J. Johnson, Beatrix Stelte-Ludwig, Ahmed Hamdy. VIP152, a selective CDK9 inhibitor, demonstrates sensitivity in gynecologic cell lines that are cisplatin sensitive or resistant and delivers in vivo antitumor efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1859.

Accelerated Epigenetic Aging Mediates the Association between Vitamin D Levels and Knee Pain in Community-Dwelling Individuals

OBJECTIVES

To examine the relationship between Vitamin D status and pain intensity and disability in individuals with and without knee pain, and to examine the role of epigenetics in this relationship.

DESIGN

Cross-sectional analysis of data from the UPLOAD-2 study (Understanding Pain and Limitations in OsteoArthritic Disease-2).

PARTICIPANTS

189 individuals aged 45-65 years and older.

MEASUREMENTS

Serum Vitamin D levels, pain related interference and characteristic pain intensity measures, and the epigenetic clock GrimAge derived from blood analyses.

RESULTS

Lower Vitamin D was associated with advanced epigenetic aging (AgeAccelGrim), greater pain and disability and that (AgeAccelGrim) mediated the relationship between Vitamin D status and self-reported pain (ab = -0.0799; CI [-0.1492, -0.0237]) and disability (ab = -0.0669; CI [-0.1365, -0.0149]) outcomes.

CONCLUSION

These data support the notion that lifestyle factors such as nutrition status play a key role in aging process, as well as the development and maintenance of age-related diseases such as pain. Modifying nutrition status could help promote healthy aging and reduce pain.

Immune signatures underlying post-acute COVID-19 lung sequelae

[Figure: see text].

Optimizing extracellular vesicles' isolation from chronic lymphocytic leukemia patient plasma and cell line supernatant

In chronic lymphocytic leukemia (CLL) and very likely all cancer types, extracellular vesicles (EVs) are a common mechanism by which intercellular messages are communicated between normal, diseased, and transformed cells. Studies of EVs in CLL and other cancers have great variability and often lack reproducibility. For CLL patient plasma and cell lines, we sought to characterize current approaches used in isolating EV products and understand whether cell culture-conditioned media or complex biological fluids confound results. Utilizing nanoparticle tracking analysis, protein quantification, and electron microscopy, we show that ultracentrifugation with an OptiPrep cushion can effectively minimize contaminants from starting materials including plasma and conditioned media of CLL cell lines grown in EV-depleted complete RPMI media but not grown in the serum-free media AIM V commonly used in CLL experimental work. Moreover, we confirm the benefit of including 25 mM trehalose in PBS during EV isolation steps to reduce EV aggregation, to preserve function for downstream applications and characterization. Furthermore, we report the highest particles/μg EVs were obtained from our CLL cell lines utilizing the CELLine bioreactor flask. Finally, we optimized a proliferation assay that offers a functional evaluation of our EVs with minimal sample requirements.

Cancer-Specific Stress and Trajectories of Psychological and Physical Functioning in Patients With Relapsed/Refractory Chronic Lymphocytic Leukemia

Background

Chronic lymphocytic leukemia is the most prevalent adult leukemia. The disease is incurable with a cycling of treatment and relapse common. Little is known about the psychological and physical functioning of patients with relapsed/refractory chronic lymphocytic leukemia. Cancer-specific stress is an important individual difference variable that predicts psychological and physical outcomes.

Purpose

To examine cancer-specific stress at treatment initiation as a predictor of psychological and physical functioning trajectories in patients with relapsed/refractory chronic lymphocytic leukemia during the first 5 months of treatment.

Methods

Patients with relapsed/refractory chronic lymphocytic leukemia (N = 152) enrolled in a phase II clinical trial completed self-report measures at treatment initiation (baseline), 1, 2, and 5 months of treatment. Cancer-specific stress at baseline was examined as a predictor of psychological (cognitive-affective depressive symptoms, negative mood, mental health quality of life) and physical functioning (fatigue interference, sleep problems, physical health quality of life), controlling for demographic and treatment variables.

Results

Using multilevel modeling, higher baseline cancer-specific stress was related to worse psychological (cognitive-affective depressive symptoms, negative mood, mental health quality of life) and physical functioning (fatigue interference, sleep problems) at baseline and more rapid improvements during the next 5 months. Despite these improvements, higher baseline cancer-specific stress remained associated with poorer 5-month psychological, though not physical, functioning.

Conclusions

Findings suggest cancer-specific stress at treatment initiation may be a risk factor for poorer psychological functioning during treatment for patients with relapsed/refractory chronic lymphocytic leukemia.

Illness Perceptions in Chronic Lymphocytic Leukemia: Testing Leventhal's Self-regulatory Model

BACKGROUND

Leventhal's Self-regulatory Model proposes that somatic characteristics of a health threat (e.g., symptom severity), and prior experience with the threat (e.g., unsuccessful treatment), are determinants of illness perceptions. Chronic lymphocytic leukemia (CLL) is appropriate for test of these postulates, having three phases differing in symptom severity and prior treatment experiences: indolent disease requiring no treatment (active surveillance; AS), symptomatic disease requiring a first treatment (FT), and highly symptomatic disease in those who have relapsed and/or failed to respond to prior treatments (relapsed/refractory; RR).

PURPOSE

To test symptom severity and prior treatment experiences as determinants of illness perceptions, illness perceptions were characterized and contrasted between CLL groups.

METHODS

Three hundred and thirty CLL patients (AS, n = 100; FT, n = 78; RR, n = 152) provided illness perception data on one occasion during a surveillance visit (AS) or prior to beginning treatment (FT, RR).

RESULTS

Analysis of variance with planned comparisons revealed that consequences, identity, and concern were least favorable among RR patients, followed by FT, then AS (ps < .01). AS patients endorsed the lowest levels of coherence (ps < .01), and the most chronic illness timeline (ps < .01). FT patients endorsed the highest levels of personal and treatment control (ps < .01).

CONCLUSIONS

Data provide preliminary empirical support for Self-regulatory Model postulates that symptom severity and prior disease experiences influence illness perceptions. Unique knowledge needs for AS patients and elevated psychological/physical symptoms for later-stage CLL patients may warrant clinical attention.

Targeting PI3Kδ function for amelioration of murine chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is a leading cause of morbidity and mortality following allotransplant. Activated donor effector T cells can differentiate into pathogenic T helper (Th)-17 cells and germinal center (GC)-promoting T follicular helper (Tfh) cells, resulting in cGVHD. Phosphoinositide-3-kinase-δ (PI3Kδ), a lipid kinase, is critical for activated T cell survival, proliferation, differentiation, and metabolism. We demonstrate PI3Kδ activity in donor T cells that become Tfh cells is required for cGVHD in a nonsclerodermatous multiorgan system disease model that includes bronchiolitis obliterans (BO), dependent upon GC B cells, Tfhs, and counterbalanced by T follicular regulatory cells, each requiring PI3Kδ signaling for function and survival. Although B cells rely on PI3Kδ pathway signaling and GC formation is disrupted resulting in a substantial decrease in Ig production, PI3Kδ kinase-dead mutant donor bone marrow-derived GC B cells still supported BO cGVHD generation. A PI3Kδ-specific inhibitor, compound GS-649443, that has superior potency to idelalisib while maintaining selectivity, reduced cGVHD in mice with active disease. In a Th1-dependent and Th17-associated scleroderma model, GS-649443 effectively treated mice with active cGVHD. These data provide a foundation for clinical trials of US Food and Drug Administration (FDA)-approved PI3Kδ inhibitors for cGVHD therapy in patients.

Use of mean platelet volume in the assessment of intrauterine infection in newborns with combined thrombocytopenia and leukopenia at birth

Objective: Intrauterine stress can be reflected on hematological disturbance at birth. Thrombocytopenia and leukopenia may be a result of exposure to maternal hypertensive disorders but may also indicate fetal inflammatory response to intrauterine infection, prompting empiric antibiotics use during the initial assessment after birth. Emerging data suggest long-term adverse health outcomes associated with antibiotics exposure early in life. In this report, we sought to assess the use of mean platelet volume (MPV) at birth in predicting fetal inflammatory response in newborns with combined thrombocytopenia and leukopenia.Materials and methods: This is a retrospective study from a single academic medical center. Data were collected prospectively on all newborns with thrombocytopenia and leukopenia within the first 24 h of life. The primary outcome was a composite of fetal tachycardia, premature preterm rupture of membrane with preterm labor, and histological evidence of chorioamnionitis/funisitis/villitis on placental pathology reports evaluated using a multiple logistical regression analysis.Results: The prevalence of combined thrombocytopenia and leukopenia was 5.8% (99 out of 1693 newborns) during the study period. The prevalence was highly associated with gestational age (R² = 0.873). Twenty-four (32.4%) had abnormal MPV values at birth, defined as MPV > 9 or < 7 fL. Newborns with abnormal MPV had lower platelet counts and were more likely to have I:T ratio ≥0.2. In a univariate analysis, abnormal MPV (OR: 6.205, 95% CI: 1.923-20.022, p = .002), I:T ratio ≥0.2 (OR: 8.462, 95% CI: 1.396-51.281, p = .02), and platelet counts (OR: 98.4, 95% CI: 96.9%-99.9%, p = .035) were each significantly associated with a positive composite outcome. In a multivariate analysis, only abnormal MPV remained significantly associated with an increased likelihood of having a positive composite outcome, with an OR of 3.922 (95% CI: 1.094-14.06, p = .036).Conclusions: MPV may be a more reliable marker than I:T ratio ≥0.2 for fetal inflammatory response in newborns with combined thrombocytopenia and leukopenia during the initial assessment of intrauterine infection. Future prospective studies are required to confirm findings from this report.

Modulation of immune checkpoint molecule expression in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive B-cell malignancy for which novel therapeutics with improved efficacy are greatly needed. To provide support for clinical immune checkpoint blockade, we comprehensively evaluated the expression of therapeutically targetable immune checkpoint molecules on primary MCL cells. MCL cells showed constitutive expression of Programmed Death 1 (PD-1) and Programmed Death Ligand 1 (PD-L1), variable CD200, absent PD-L2, Lymphocyte Activation Gene 3 (LAG-3), and Cytotoxic T-cell Associated Protein 4 (CTLA-4). Effector cells from MCL patients expressed PD-1. Co-culture of MCL cells with T-cells induced PD-L1 surface expression, a phenomenon regulated by IFNγ and CD40:CD40L interaction. Induction of PD-L1 was attenuated by concurrent treatment with ibrutinib or duvelisib, suggesting BTK and PI3K are important mediators of PD-L1 expression. Overall, our data provide further insight into the expression of checkpoint molecules in MCL and support the use of PD-L1 blocking antibodies in MCL patients.

PI3K p110δ inactivation antagonizes chronic lymphocytic leukemia and reverses T cell immune suppression

Targeted therapy with small molecules directed at essential survival pathways in leukemia represents a major advance, including the phosphatidylinositol-3'-kinase (PI3K) p110δ inhibitor idelalisib. Here, we found that genetic inactivation of p110δ (p110δD910A/D910A) in the Eμ-TCL1 murine chronic lymphocytic leukemia (CLL) model impaired B cell receptor signaling and B cell migration, and significantly delayed leukemia pathogenesis. Regardless of TCL1 expression, p110δ inactivation led to rectal prolapse in mice resembling autoimmune colitis in patients receiving idelalisib. Moreover, we showed that p110δ inactivation in the microenvironment protected against CLL and acute myeloid leukemia. After receiving higher numbers of TCL1 leukemia cells, half of p110δD910A/D910A mice spontaneously recovered from high disease burden and resisted leukemia rechallenge. Despite disease resistance, p110δD910A/D910A mice exhibited compromised CD4+ and CD8+ T cell response, and depletion of CD4+ or CD8+ T cells restored leukemia. Interestingly, p110δD910A/D910A mice showed significantly impaired Treg expansion that associated with disease clearance. Reconstitution of p110δD910A/D910A mice with p110δWT/WT Tregs reversed leukemia resistance. Our findings suggest that p110δ inhibitors may have direct antileukemic and indirect immune-activating effects, further supporting that p110δ blockade may have a broader immune-modulatory role in types of leukemia that are not sensitive to p110δ inhibition.

The BTK Inhibitor ARQ 531 Targets Ibrutinib-Resistant CLL and Richter Transformation

Targeted inhibition of Bruton tyrosine kinase (BTK) with the irreversible inhibitor ibrutinib has improved outcomes for patients with hematologic malignancies, including chronic lymphocytic leukemia (CLL). Here, we describe preclinical investigations of ARQ 531, a potent, reversible inhibitor of BTK with additional activity against Src family kinases and kinases related to ERK signaling. We hypothesized that targeting additional kinases would improve global inhibition of signaling pathways, producing more robust responses. In vitro treatment of patient CLL cells with ARQ 531 decreases BTK-mediated functions including B-cell receptor (BCR) signaling, viability, migration, CD40 and CD86 expression, and NF-κB gene transcription. In vivo, ARQ 531 was found to increase survival over ibrutinib in a murine Eμ-TCL1 engraftment model of CLL and a murine Eμ-MYC/TCL1 engraftment model resembling Richter transformation. Additionally, ARQ 531 inhibits CLL cell survival and suppresses BCR-mediated activation of C481S BTK and PLCγ2 mutants, which facilitate clinical resistance to ibrutinib.Significance: This study characterizes a rationally designed kinase inhibitor with efficacy in models recapitulating the most common mechanisms of acquired resistance to ibrutinib. Reversible BTK inhibition is a promising strategy to combat progressive CLL, and multikinase inhibition demonstrates superior efficacy to targeted ibrutinib therapy in the setting of Richter transformation. Cancer Discov; 8(10); 1300-15. ©2018 AACR. This article is highlighted in the In This Issue feature, p. 1195.

The In Vitro Association of Antihemophilic Factor and von Willebrand Factor

Considerable evidence, including results of gel chromatography, indicates that antihemophilic factor (AHF; factor VIII: C) is associated with von Willebrand factor (vWF; factor VIIIR: RC or VTIIR: Ag) in citrated plasma. The present study was undertaken to determine whether these factors are also associated in plasma with a physiologic calcium ion concentration, or in an artificial medium using purified antihemophilic factor and plasma as a source of vWF. When fresh BaS04-treated native normal plasma was passed through a column of Sepharose CL-4B that was equilibrated and eluted with fresh BaS04-treated plasma from a patient with severe von Willebrand’s disease, the AHF and vWF activities were found in the void volume. Thus, AHF remains associated with vWF on gel chromatography in the presence of physiological concentrations of all plasma constituents except the vitamin-K-dependent clotting factors. On the other hand, when to 200,000 X purified “vWF-free” AHF was chromatographed in buffered 4% albumin with 2 mM CaCl2, virtually all of it appeared in the included volume of the column with an apparent molecular weight between that of fibrinogen or factor V (340,000) and gamma globulin (160,000). The combination of the “vWF-free” AHF with the vWF in plasma was studied by adding the AHF to BaS04-treated plasma from normal subjects or patients with severe hemophilia or von Willebrand’s disease and chromatographing the mixture. The AHF activity appeared in the void volume in an amount that was inversely related to the ratio of the AHF to vWF activity. Thus, with 1-12 U of AHF per unit of vWF, virtually all of the AHF eluted in the void volume, with 30 and 500 units of AHF per unit of vWF, only about 50% and 10% of the AHF, respectively, eluted in the void volume, and in the absence of vWF, none of the AHF activity eluted in the void volume.

Abstract 1963: ARQ 531, a potent reversible BTK inhibitor, exhibits potent antitumor activity in ibrutinib-resistant diffuse large B-cell lymphoma

Background: B-cell receptor (BCR)-mediated signaling plays an important role in the pathogenesis of a subset of diffuse large B-cell lymphoma (DLBCL). Despite major advances in the treatment, ~40% of the relapsed/refractory DLBCL patients still experience early treatment failure after initial response to chemotherapy. ARQ 531, a reversible inhibitor of BTK and BTK-C481S mutant, also potently suppresses BCR signaling. Here we demonstrate that ARQ 531 targets additional kinases and suppresses multiple oncogenic pathways, this inhibitory potency is coupled to broad anti-tumor activity in DLBCL subtypes including tumors resistant to BCR targeted therapy.

Methods: Biochemical inhibition and broad kinase profiling were assessed using recombinant proteins. Binding kinetics and the residence time with BTK and BTK-C481S were measured by Surface Plasmon Resonance (SPR) assay. Binding mode of ARQ 531 with BTK was determined by protein crystallography. Pathway inhibition assessments, in vivo efficacy and in vivo target inhibition were performed in DLBCL tumor models derived from TMD8, SUDHL-4 and DOHH-2 cell lines.

Results: ARQ 531 potently inhibited BTK (IC50 = 0.85 nM), the binding potency was accompanied by long residence time (51 min). Crystal structure of BTK/ARQ 531 complex showed that ARQ 531 occupies the ATP-binding pocket. Kinase selectivity profile suggested that ARQ 531 inhibits sub-families of Tec, Src, Trk kinases. Significant anti-proliferative activity (GI50 = &lt; 1µM) was observed in hematological malignant cell lines characterized by addiction to BTK signaling and primarily resistant to ibrutinib. Pathway inhibition analysis suggested that ARQ 531 targets multiple oncogenic signaling pathways in both ABC- and GCB-DLBCL cell lines. Unlike ibrutinib, ARQ 531 suppressed both the upstream activating signals (via inhibition of a select member of Src kinase family) and the downstream signaling pathways (via pAKT and pERK kinases). In GCB-DLBCL cell lines (SUDHL-4 and DOHH-2), ARQ 531 potently suppressed expression of anti-apoptotic c-Myc and BCL6 oncoproteins in a dose dependent fashion, and concomitantly induced apoptotic cleavage of PARP protein. In the ibrutinib-resistant SUDHL-4 mouse xenograft model, ARQ 531 potently suppressed tumor growth (&gt;80% inhibition) compared to the control group when dosed orally at 75 mg/kg. Additionally, preliminary data suggest that ARQ 531 crosses the blood, brain-barrier.

Conclusion: ARQ 531 is a potent reversible inhibitor of BTK, its distinct kinase selectivity profile offers significant advantage for simultaneous inhibition of multiple therapeutically relevant targets. ARQ 531 attenuated the expression of key oncogenic drivers via inhibition of downstream BCR activating kinases. These results highlight the therapeutic potential of inhibition of BCR signaling inhibition by ARQ 531 in the treatment of DLBCL.

Citation Format: Sudharshan Eathiraj, Yi Yu, Ron Savage, Jennifer A. Woyach, Sean D. Reiff, Amy J. Johnson, Brian Schwartz. ARQ 531, a potent reversible BTK inhibitor, exhibits potent antitumor activity in ibrutinib-resistant diffuse large B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1963.

Cells, cytokines, chemokines, and cancer stress: A biobehavioral study of patients with chronic lymphocytic leukemia

BACKGROUND

Chronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia, with profound disease-related cellular, humoral, and innate immune suppression. The objective of this study was to study the correlations between stress and disease-specific, negative prognostic cellular, cytokine, and chemokine markers in patients with CLL.

METHODS

A single-group, observational design was used. Patients with relapsed/refractory CLL (N = 96) who were entering a phase 2 trial of an experimental therapy (ibrutinib) were studied. Before the first dose, a validated self-report measure of stress (the Impact of Event Scale) was completed, and blood was drawn for absolute lymphocyte counts (ALCs) and for cytokine and chemokine enzyme-linked immunosorbent assays. Multiple linear regression models tested stress as a concurrent predictor of ALCs; of cytokines (tumor necrosis factor α [TNFα], a proliferation-inducing ligand [APRIL], B-cell activating factor [BAFF], interleukin 6 [IL-6], IL-10, IL-16, and vascular endothelial growth factor [VEGF]); and of the chemokine (C-C motif) ligand 3 (CCL3).

RESULTS

Controlling for relevant demographic variables, comorbidities, CLL genetic risk (deletion of the short arm of chromosome 17 [del17p]), and correlates of inflammation, stress predicted higher ALCs (P < .05), and higher levels of TNFα (P < .05), IL-16 (P < .01), and CCL3 (P < .05). Stress was not associated with APRIL, BAFF, IL-6, IL-10, or VEGF.

CONCLUSIONS

Novel biobehavioral data from patients with relapsed/refractory CLL demonstrate that stress is related to heightened levels of cellular, cytokine, and chemokine markers associated previously with progressive disease in CLL. The current results indicate that stress is related to immune and inflammatory processes that contribute to cancer cell proliferation and survival. These data provide a first look into these processes. Cancer 2018. © 2018 American Cancer Society.

Single-agent ibrutinib in treatment-naïve and relapsed/refractory chronic lymphocytic leukemia: a 5-year experience

We previously reported durable responses and manageable safety of ibrutinib from a 3-year follow-up of treatment-naïve (TN) older patients (≥65 years of age) and relapsed/refractory (R/R) patients with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). We now report on long-term efficacy and safety with median follow-up of 5 years in this patient population with TN (N = 31) and R/R (N = 101) CLL/SLL. With the current 5-year follow-up, ibrutinib continues to yield a high overall response rate of 89%, with complete response rates increasing over time to 29% in TN patients and 10% in R/R patients. The median progression-free survival (PFS) was not reached in TN patients. The 5-year PFS rate was 92% in TN patients and 44% in R/R patients. Median PFS in R/R patients was 51 months; in those with del(11q), del(17p), and unmutated IGHV, it was 51, 26, and 43 months, respectively, demonstrating long-term efficacy of ibrutinib in some high-risk subgroups. Survival outcomes were less robust for R/R patients with del(17p) and those who received more prior therapies. The onset of grade ≥3 cytopenias, such as neutropenia and thrombocytopenia, decreased over time. Treatment--limiting adverse events were more frequent during the first year compared with subsequent periods. These results demonstrate sustained efficacy and acceptable tolerability of ibrutinib over an extended time, providing the longest experience for Bruton tyrosine kinase inhibitor treatment in patients with CLL/SLL. These trials were registered at www.clinicaltrials.gov as #NCT01105247 and #NCT01109069.

Hsp90 inhibition increases SOCS3 transcript and regulates migration and cell death in chronic lymphocytic leukemia

Epigenetic or transcriptional silencing of important tumor suppressors has been described to contribute to cell survival and tumorigenesis in chronic lymphocytic leukemia (CLL). Using gene expression microarray analysis, we found that thousands of genes are repressed more than 2-fold in CLL compared to normal B cells; however therapeutic approaches to reverse this have been limited in CLL. Following treatment with the Hsp90 inhibitor 17-DMAG, a significant number of these repressed genes were significantly re-expressed. One of the genes significantly repressed in CLL and up-regulated by 17-DMAG was suppressor of cytokine signaling 3, (SOCS3). SOCS3 has been shown to be silenced in solid tumors as well as myeloid leukemia; however little is known about the regulation in CLL. We found that 17-DMAG induces expression of SOCS3 by via the activation of p38 signaling, and subsequently inhibits AKT and STAT3 phosphorylation resulting in downstream effects on cell migration and survival. We therefore suggest that SOCS3 is an important signaling protein in CLL, and Hsp90 inhibitors represent a novel approach to target transcriptional repression in B cell lymphoproliferative disorders which exhibit a substantial degree of gene repression.

Ibrutinib treatment improves T cell number and function in CLL patients

BACKGROUND

Ibrutinib has been shown to have immunomodulatory effects by inhibiting Bruton's tyrosine kinase (BTK) and IL-2-inducible T cell kinase (ITK). The relative importance of inhibiting these 2 kinases has not been examined despite its relevance to immune-based therapies.

METHODS

Peripheral blood mononuclear cells from chronic lymphocytic leukemia (CLL) patients on clinical trials of ibrutinib (BTK/ITK inhibitor; n = 19) or acalabrutinib (selective BTK inhibitor; n = 13) were collected serially. T cell phenotype, immune function, and CLL cell immunosuppressive capacity were evaluated.

RESULTS

Ibrutinib markedly increased CD4+ and CD8+ T cell numbers in CLL patients. This effect was more prominent in effector/effector memory subsets and was not observed with acalabrutinib. Ex vivo studies demonstrated that this may be due to diminished activation-induced cell death through ITK inhibition. PD-1 and CTLA-4 expression was significantly markedly reduced in T cells by both agents. While the number of Treg cells remained unchanged, the ratio of these to conventional CD4+ T cells was reduced with ibrutinib, but not acalabrutinib. Both agents reduced expression of the immunosuppressive molecules CD200 and BTLA as well as IL-10 production by CLL cells.

CONCLUSIONS

Ibrutinib treatment increased the in vivo persistence of activated T cells, decreased the Treg/CD4+ T cell ratio, and diminished the immune-suppressive properties of CLL cells through BTK-dependent and -independent mechanisms. These features provide a strong rationale for combination immunotherapy approaches with ibrutinib in CLL and other cancers.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01589302 and NCT02029443. Samples described here were collected per OSU-0025.

FUNDING

The National Cancer Institute.

Abstract 3150: PLCG2 C2-domain mutations co-occur with BTK and PLCG2 resistance mutations in chronic lymphocytic leukemia undergoing treatment with the BTK inhibitor ibrutinib

Background: The Bruton agammaglobulinemia tyrosine kinase (BTK) activates B-cell receptor signaling through activation of phospholipase C gamma 2 (PLCG2). Clinical resistance to the Bruton tyrosine kinase (BTK) inhibitor ibrutinib in chronic lymphocytic leukemia (CLL) is highly associated with emergence of the BTK C481 mutations that prevent ibrutinib covalent binding. PLCG2 mutations also occur in these ibrutinib-resistant samples but the spectrum of mutations and their occurrence with BTK changes have not been fully delineated.

Materials and Methods: All peripheral blood samples with adequate depth of sequencing coverage were included from CLL patients receiving ibrutinib (with or without other therapies) that were submitted from Ohio State University (OSU) to the OSU James Polaris Molecular Laboratory. Genomic DNA was extracted from negatively selected B cells and deep sequencing of the entire coding regions of BTK and PLCG2 performed using a custom Ion Torrent Ampliseq panel. A mean depth of greater than 1000X was obtained with hotspot mutations validated down to 1% variant allele fraction (VAF) in the B cell preparations using orthogonal mutation-specific detection methods.

Results: Among 1063 CLL samples from 380 patients who received ibrutinib, BTK C481 resistance mutations were identified in 79 (20.8%) patients including 20 patients that also had co-occurring PLCG2 mutations. 11 patients (2.9%) had PLCG2 mutations without accompanying BTK C481 alterations for a cumulative incidence of PLCG2 mutations in 8.2% of ibrutinib-treated patients. These included previously described mutations in the SH2 and SH3 domain of PLCG2 (R665W, S707F, A708P and L845F) but also previously uncharacterized mutations in the PLCG2 C2 domain that were seen in 12 patients (3.2%). C2 domain mutations, always seen in association with another PLCG2 and/or BTK resistance mutation, affected codons 1140-1144 that include the highly conserved aspartic acid residues that bind calcium and mediate membrane localization in other C2-domain containing proteins. In sequential samples, PLCG2 C2-domain mutations tracked at similar levels to the co-occurring BTK and PLCG2 resistance mutations indicating their presence in the same population of CLL cells.

Conclusions: Mutations in three different PLCG2 structural domains commonly co-occur with BTK C481 mutations. The identification of PLCG2 mutations in the calcium-regulated C2 domain expands the possible mechanisms that can produce PLCG2 activation following ibrutinib treatment. The diversity of recurrent mutations observed supports the need for complete PLCG2 sequencing for full characterization of ibrutinib-treated CLL samples.

Citation Format: Dan Jones, Jennifer A. Woyach, Weiqiang Zhao, Sean Caruthers, Huolin Tu, Joshua Coleman, John C. Byrd, Amy J. Johnson, Gerard Lozanski. PLCG2 C2-domain mutations co-occur with BTK and PLCG2 resistance mutations in chronic lymphocytic leukemia undergoing treatment with the BTK inhibitor ibrutinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3150. doi:10.1158/1538-7445.AM2017-3150

Abstract 3014: BCL3 over-expression contributes an in vivo growth advantage in a B-cell lymphoma xenograft model and is a risk factor for ibrutinib relapse in CLL

Chronic lymphocytic leukemia (CLL) relies on chronic B-cell receptor (BCR) signaling, and as such is effectively treated with Bruton's tyrosine kinase (BTK) inhibitors. However patients who relapse on BTK inhibitors such as ibrutinib have an extremely poor prognosis without additional intervention. Therefore, identifying and characterizing risk factors that predict relapse to BTK inhibitors is important. A series of 308 CLL patients have been enrolled on various ibrutinib clinical trials at the Ohio State University. Seven of these patients were identified to carry the translocation t(14;19), which leads to over-expression of B-cell leukemia 3 (BCL3), Of these 7, 6 (85%) have relapsed on ibrutinib while only 27% of patients (83/308) overall have progressed. BCL3 is known to regulate NF-κB transcription and influence B-cell function, and we found that overall BCL3 expression is increased in CLL compared to normal B-cells, therefore hypothesized that BCL3 may provide a competitive advantage to promote ibrutinib resistance. In order to test the role of BCL3 in ibrutinib resistance using an in vitro system, we overexpressed BCL3 or an empty vector (EV) control in ibrutinib responsive B-cell lines (BCL3 was at least 2-fold over-expressed relative to endogenous BCL3). Cells were treated with vehicle or 1uM ibrutinib for 1 hour followed by a washout, and proliferation and viability were evaluated at various time points. Ibrutinib inhibited cell proliferation and induced apoptosis, however BCL3 expression did not abrogate these effects. However, while examining BCR signaling proteins we found that BCL3 expression enhanced phosphorylation of BTK, suggesting that BCL3 stabilizes activated BTK to circumvent ibrutinib treatment. We next engrafted these EV or BCL3 over-expressing cells into the left or right flank, respectively, of immune-compromised (NSG) mice. Mice were sacrificed when either tumor reached a volume of 2000cm3, and the tumors were isolated and weighed. Tumors which developed from the BCL3 over-expressing cells at sacrifice were larger than those which developed from the EV cells by an average of 1332g. We also evaluated a disseminated tumor model where HBL-1 EV or BCL3 over-expressing cells were injected via the tail vein. Disease was monitored by weekly peripheral blood flow cytometry for human CD19. We saw that 6 of 11 mice intravenously engrafted with HBL-1 BCL3 present with peripheral disease when the mice meet removal criteria, whereas only 1 of 11 mice engrafted with HBL-1 EV cells developed peripheral disease. We conclude that the presence of t(14;19) indicates a higher risk of relapse in patients undergoing ibrutinib therapy, and these patients should be closely monitored for evidence of progression. Our studies also suggest that BCL3 promotes more aggressive disease in a lymphoma xenograft model, and may be involved in tumor migration in vivo.

Citation Format: Timothy L. Chen, Bonnie K. Harrington, Larry Beaver, Amy S. Ruppert, Nyla A. Heerema, Xiaoli Zhang, Hatice Gulcin Ozer, Amy J. Johnson, Jennifer A. Woyach, Erin Hertlein, John C. Byrd. BCL3 over-expression contributes an in vivo growth advantage in a B-cell lymphoma xenograft model and is a risk factor for ibrutinib relapse in CLL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3014. doi:10.1158/1538-7445.AM2017-3014

Abstract 4471: Novel SF3B1 deletion mutations result in aberrant RNA splicing in CLL patients

Recurrent heterozygous mutations in SF3B1, a component of the U2snRNP complex involved in branchsite recognition during the first step of splicing catalysis, are found in various solid tumors and hematologic cancers including myelodysplastic syndromes (MDS) and chronic lymphocytic leukemia (CLL). To provide broader insight into the effects of SF3B1 mutations on RNA splicing in CLL, RNAseq was performed on 215 CLL patient samples with unknown SF3B1 mutation status. 37 patients (17%) demonstrated cryptic 3’ splice site usage we and others have previously reported in patients with known SF3B1 hotspot mutations. Interestingly, 3 patient samples harbored previously unreported in-frame deletions in SF3B1 around K700, the most common amino acid mutated in hematologic cancers with SF3B1 mutations. In particular, 2 patient sequences contained 6 nucleotide (nt) deletions (c.2186 to c.2191) resulting in replacement of Q698, Q699 and K700 with Q (p.Q698_K700delinsQ: “p.Q698del”) and 1 patient sequence had a 3 nt deletion (c.2192 to c.2194) resulting in replacement of K700 and V701 with N (p.K700_V701delinsN: “p.K700del”) in SF3B1. The variant allele fraction (VAF) of these deletions was 20-40%. Targeted resequencing of DNA confirmed presence of these mutations at similar VAFs. Differential splicing analysis across patients with wild-type SF3B1, mutant SF3B1 and our novel deletions revealed similar alternative 3’ splice site patterns. To study the mechanism of alternative 3’ splice site selection induced by these novel p.Q698del and p.K700del in-frame deletions we used our ZDHHC16 minigene system with modifications in the canonical and cryptic 3’ splice sites and respective branchsites. After confirming expression of these deletion mutants and their incorporation in the SF3b complex by qPCR and co-immunoprecipitation, we demonstrated that recognition of both canonical 3’ splice site and alternate branchsite are important for aberrant splicing. This observation is identical to the intronic features required for aberrant splicing that we previously reported for the p.K700E SF3B1 hotspot mutation in CLL and MDS. By comparing the recent cryo-electron microscopy and X-ray crystal structures of SF3b complexes (PDB: 5GM6 and 5IFE, respectively), it is evident that the K700 present at the edge of heat repeat domain 6 is important for pre-mRNA interactions. Both the in-frame deletions and substitution mutations at K700 perturb SF3B1 charge, likely affecting a side-chain interaction with pre-mRNA, thus altering splice-site recognition through a mechanism that is still not well understood. Together, these data indicate that small in-frame deletions in SF3B1 around K700 offer a novel mechanism to induce aberrant splicing in patients with CLL. The common mechanism of action of these mutations and deletions suggest that they should also be sensitive to splicing modulators.

Citation Format: Anant A. Agrawal, Michael Seiler, Lindsey Brinton, Rose Mantel, Rosa Lapalombella, Jennifer A. Woyach, Amy J. Johnson, Lihua Yu, John C. Byrd, Peter G. Smith, James S. Blachly*, Silvia Buonamici*. Novel SF3B1 deletion mutations result in aberrant RNA splicing in CLL patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4471. doi:10.1158/1538-7445.AM2017-4471

Ultrafast probing of magnetic field growth inside a laser-driven solenoid

We report on the detection of the time-dependent B-field amplitude and topology in a laser-driven solenoid. The B-field inferred from both proton deflectometry and Faraday rotation ramps up linearly in time reaching 210 ± 35 T at the end of a 0.75-ns laser drive with 1 TW at 351 nm. A lumped-element circuit model agrees well with the linear rise and suggests that the blow-off plasma screens the field between the plates leading to an increased plate capacitance that converts the laser-generated hot-electron current into a voltage source that drives current through the solenoid. ALE3D modeling shows that target disassembly and current diffusion may limit the B-field increase for longer laser drive. Scaling of these experimental results to a National Ignition Facility (NIF) hohlraum target size (∼0.2cm^{3}) indicates that it is possible to achieve several tens of Tesla.

The regulation of tumor-suppressive microRNA, miR-126, in chronic lymphocytic leukemia

The introduction of miR profiling of chronic lymphocytic leukemia (CLL) patients with different cytogenetic profiles and responses to therapy has allowed incorporation of important miR‐mRNA interactions into the understanding of disease biology. In this study, we performed miR expression analysis using NanoString nCounter to discover differentially regulated miRs after therapy with the Bruton tyrosine kinase inhibitor ibrutinib. Of the differentially regulated miRs in the discovery set, miR‐29c and miR‐126 were confirmed using real‐time PCR to be upregulated in CLL patient cells with ibrutinib therapy. In the validation set, an inverse correlation was observed between miR‐126 levels and expression of its putative target p85β, an isoform of the phosphoinositide 3‐kinase p85 regulatory subunit. We found that mRNA for the host gene EGFL7, primary unprocessed miR‐126, and mature miR‐126 are all downregulated in CLL cells compared to normal B cells. Patients in later stages of disease have a greater decrease in miR‐126 expression compared to treatment‐naive patients, indicating that lower miR‐126 levels may associate with disease progression. Overexpression of miR‐126 in leukemia cell lines significantly downregulates p85β expression and decreases activation of prosurvival mitogen‐activated protein kinase (MAPK) signaling. These results implicate miR‐126 in the pathology of CLL.

BTKC481S-Mediated Resistance to Ibrutinib in Chronic Lymphocytic Leukemia

Purpose Therapeutic targeting of Bruton tyrosine kinase (BTK) with ibrutinib in chronic lymphocytic leukemia has led to a paradigm shift in therapy, and relapse has been uncommon with current follow-up. Acquired mutations in BTK and PLCG2 can cause relapse, but data regarding the prevalence and natural history of these mutations are limited. Patients and Methods Patients accrued to four sequential studies of ibrutinib were included in these analyses. Deep sequencing for BTK and PLCG2 was performed retrospectively on patients who experienced relapse and prospectively on a screening population. Results With a median follow-up time of 3.4 years, the estimated cumulative incidence of progression at 4 years is 19% (95% CI, 14% to 24%). Baseline karyotypic complexity, presence of del(17)(p13.1), and age less than 65 years were risk factors for progression. Among patients who experienced relapse, acquired mutations of BTK or PLCG2 were found in 85% (95% CI, 71% to 94%), and these mutations were detected an estimated median of 9.3 months (95% CI, 7.6 to 11.7 months) before relapse. Of a group of 112 patients examined prospectively, eight patients have experienced relapse, and all of these patients had acquired resistance mutations before relapse. A resistance mutation was detected in an additional eight patients who have not yet met criteria for clinical relapse. Conclusion Relapse of chronic lymphocytic leukemia after ibrutinib is an issue of increasing clinical significance. We show that mutations in BTK and PLCG2 appear early and have the potential to be used as a biomarker for future relapse, suggesting an opportunity for intervention.

Extended Treatment with Single-Agent Ibrutinib at the 420 mg Dose Leads to Durable Responses in Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma

Purpose: Ibrutinib, a first-in-class, once-daily, oral inhibitor of Bruton tyrosine kinase, promotes apoptosis, and inhibits B-cell proliferation, adhesion, and migration. Ibrutinib has demonstrated single-agent efficacy and acceptable tolerability at doses of 420 and 840 mg in patients with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) who were treatment-naïve (TN) or had relapsed/refractory (R/R) CLL after ≥1 prior therapy in a phase Ib/II study (PCYC-1102). Subsequently, the ibrutinib 420 mg dose was approved in CLL.Experimental Design: We report data with 44 months of follow-up on 94 patients with TN and R/R CLL/SLL receiving ibrutinib 420 mg once-daily in PCYC-1102 and the long-term extension study PCYC-1103.Results: Ninety-four CLL/SLL patients (27 TN, 67 R/R) were treated with ibrutinib (420 mg/day). Patients with R/R disease had received a median of four prior therapies (range, 1-12). Responses were rapid and durable and median duration of response was not reached. Best overall response was 91% [85% TN (complete response, CR 26%) and 94% R/R (9% CR)]. Median progression-free survival (PFS) was not reached in either group. The 30-month PFS rate was 96% and 76% for TN and R/R patients, respectively. Ibrutinib was well tolerated with extended follow-up; rates of grade ≥3 cytopenias and fatigue, as well as discontinuations due to toxicities decreased over time.Conclusions: Single-agent ibrutinib at 420 mg once-daily resulted in durable responses and was well tolerated with up to 44 months follow-up in patients with TN and R/R CLL/SLL. Currently, 66% of patients continue on ibrutinib. Clin Cancer Res; 23(5); 1149-55. ©2017 AACR.

The Bruton Tyrosine Kinase (BTK) Inhibitor Acalabrutinib Demonstrates Potent On-Target Effects and Efficacy in Two Mouse Models of Chronic Lymphocytic Leukemia

Purpose: Acalabrutinib (ACP-196) is a novel, potent, and highly selective Bruton tyrosine kinase (BTK) inhibitor, which binds covalently to Cys481 in the ATP-binding pocket of BTK. We sought to evaluate the antitumor effects of acalabrutinib treatment in two established mouse models of chronic lymphocytic leukemia (CLL).Experimental Design: Two distinct mouse models were used, the TCL1 adoptive transfer model where leukemic cells from Eμ-TCL1 transgenic mice are transplanted into C57BL/6 mice, and the human NSG primary CLL xenograft model. Mice received either vehicle or acalabrutinib formulated into the drinking water.Results: Utilizing biochemical assays, we demonstrate that acalabrutinib is a highly selective BTK inhibitor as compared with ibrutinib. In the human CLL NSG xenograft model, treatment with acalabrutinib demonstrated on-target effects, including decreased phosphorylation of PLCγ2, ERK, and significant inhibition of CLL cell proliferation. Furthermore, tumor burden in the spleen of the mice treated with acalabrutinib was significantly decreased compared with vehicle-treated mice. Similarly, in the TCL1 adoptive transfer model, decreased phosphorylation of BTK, PLCγ2, and S6 was observed. Most notably, treatment with acalabrutinib resulted in a significant increase in survival compared with mice receiving vehicle.Conclusions: Treatment with acalabrutinib potently inhibits BTK in vivo, leading to on-target decreases in the activation of key signaling molecules (including BTK, PLCγ2, S6, and ERK). In two complementary mouse models of CLL, acalabrutinib significantly reduced tumor burden and increased survival compared with vehicle treatment. Overall, acalabrutinib showed increased BTK selectivity compared with ibrutinib while demonstrating significant antitumor efficacy in vivo on par with ibrutinib. Clin Cancer Res; 23(11); 2831-41. ©2016 AACR.

Motorcyclist's thumb: carpometacarpal injuries of the thumb sustained in motorcycle crashes

The purpose of this study was to investigate motorcycle crash thumb injury patterns. We hypothesized that ulnar collateral ligament injuries at the thumb metacarpophalangeal joint would be most common and there would be a side predilection due to the clutch and brake positions. Motorcyclist admissions following injury between 2002 and 2013 were reviewed, and phalangeal and metacarpal injuries treated acutely identified. Demographics, injury, and treatment characteristics were recorded. Association between laterality and injury type was assessed. Of 128 patients, 59 underwent acute treatment for thumb injuries. Eleven patients sustained thumb ulnar collateral ligament injuries; 27 sustained thumb carpometacarpal injuries. Most carpometacarpal injuries were fracture-dislocations (19/27). Thumb carpometacarpal injuries had no overall side predilection; ulnar collateral ligament injuries occurred more on the right. Carpometacarpal fractures and dislocations are the most frequent motorcycle crash thumb injury, probably due to the mechanics of gripping handlebars and the high-energy force directed into the palm and against the metacarpal base.

LEVEL OF EVIDENCE

Level IV.

Experimental Transmission and Induction of Ranaviral Disease in Western Ornate Box Turtles (Terrapene ornata ornata) and Red-Eared Sliders (Trachemys scripta elegans)

An experimental transmission study was designed to determine whether a causal relationship exists between a Ranavirus (BSTRV) isolated from a Burmese star tortoise that died and the lesions observed in that tortoise. A pilot study was performed with 3 box turtles ( Terrapene ornata ornata) and 3 red-eared sliders (RESs; Trachemys scripta elegans) to assess their suitability in a larger study. Based on the outcome of this study, RESs were selected, and 2 groups of 4 RESs received either an oral (PO) or intramuscular (IM) inoculum containing105 50% Tissue Culture Infecting Dose (TCID50) of a BSTRV-infected cell lysate. One turtle each was mock inoculated PO or IM with the same volume of uninfected cell lysate. Three of four IM-inoculated RESs developed clinical signs (nasal and ocular discharge [3 of 3], oral plaques [1 of 3], conjunctivitis and hyphema [1 of 3] and extreme lethargy [3 of 3]). A Ranavirus was isolated from kidney homogenates of 3 euthanatized turtles; DNA sequences of a portion of the major capsid protein gene were amplified by polymerase chain reaction. Consistent histologic lesions were observed only in IM-inoculated turtles and included fibrinoid vasculitis centered on splenic ellipsoids, multifocal hepatic necrosis, and multicentric fibrin thrombi in a variety of locations, including hepatic sinusoids, glomerular capillary loops, and pulmonary capillaries. Virions compatible with Ranavirus were observed within necrotic cells of the spleen of 1 IM-inoculated turtle using transmission electron microscopy. This study fulfills Koch's postulates, confirming a causal relationship between BSTRV and the clinical and histologic changes in chelonians infected with this virus.

Intranuclear Coccidiosis in Tortoises: Nine Cases

Chelonian intranuclear coccidiosis has been reported once, in two radiated tortoises ( Geochelone radiata), and is apparently rare. We describe intranuclear coccidiosis diagnosed histologically in two radiated tortoises, three Travancore tortoises ( Indotestudo forstenii), two leopard tortoises ( Geochelone pardalis), one bowsprit tortoise ( Chersina angulata), and one impressed tortoise ( Manouria impressa). Infection was systemic and involved alimentary, urogenital, respiratory, lymphoid, endocrine, and integumentary systems. Trophozoites, meronts, merozoites, macrogametocytes, microgametocytes, and nonsporulated oocysts were seen histologically or by electron microscopy. intracytoplasmic and extracellular stages of parasite development also were identified histologically. Sequencing of a coccidial 18S rRNA consensus polymerase chain reaction (PCR) product revealed a novel sequence that provided phylogenetic information and may be useful for further diagnostic test design. intranuclear coccidiosis was associated with variable degrees of inflammation in all cases, was considered the cause of death in six tortoises, and was a substantial contributing factor to the cause of death in two tortoises.

Carbon dioxide emission from bamboo culms

Bamboos are one of the fastest growing plants on Earth, and are widely considered to have high ability to capture and sequester atmospheric carbon, and consequently to mitigate climate change. We tested this hypothesis by measuring carbon dioxide (CO2 ) emissions from bamboo culms and comparing them with their biomass sequestration potential. We analysed diurnal effluxes from Bambusa vulgaris culm surface and gas mixtures inside hollow sections of various bamboos using gas chromatography. Corresponding variations in gas pressure inside the bamboo section and culm surface temperature were measured. SEM micrographs of rhizome and bud portions of bamboo culms were also recorded. We found very high CO2 effluxes from culm surface, nodes and buds of bamboos. Positive gas pressure and very high concentrations of CO2 were observed inside hollow sections of bamboos. The CO2 effluxes observed from bamboos were very high compared to their carbon sequestration potential. Our measurements suggest that bamboos are net emitters of CO2 during their lifespan.

Emergence of community-associated methicillin-resistant Staphylococcus aureus strains in the neonatal intensive care unit: an infection prevention and patient safety challenge

Methicillin-resistant Staphylococcus aureus (MRSA) infections cause significant morbidity and mortality in neonatal intensive care units (NICUs). We characterized the clinical and molecular epidemiology of MRSA strains colonizing NICU patients. Nasal MRSA isolates (n = 250, from 96 NICU patients) recovered through active surveillance from 2009 to 2014 were characterized with staphylococcal cassette chromosome mec (SCCmec) typing and detection of mupA (marker of high-level mupirocin resistance) and qacA/B (marker associated with chlorhexidine resistance). Factors associated with community-associated (CA-) or healthcare-associated (HA-) MRSA were evaluated. The overall prevalence of MRSA nasal colonization was 3.9%. Of 96 neonates in our retrospective cohort, 60 (63%) were colonized with CA-MRSA strains and 35 (36%) were colonized with HA-MRSA strains. Patients colonized with HA-MRSA were more likely to develop MRSA infections than patients colonized with CA-MRSA (13/35, 37% versus 8/60, 13%; p 0.007), although the interval from colonization to infection was shorter in CA-MRSA-colonized infants (median 0 days, range -1 to 4 versus HA-MRSA-colonized infants, 7 days, -1 to 43; p 0.005). Maternal peripartum antibiotics were associated with CA-MRSA colonization (adjusted odds ratio (aOR) 8.7; 95% CI 1.7-45.0); intubation and surgical procedures were associated with HA-MRSA colonization (aOR 7.8; 95% CI 1.3-47.6 and aOR 6.0; 95% CI 1.4-24.4, respectively). Mupirocin- and chlorhexidine-resistant MRSA was isolated from four and eight patients, respectively; carriage of a mupirocin-resistant strain precluded decolonization. CA-MRSA strains are prominent in the NICU and associated with distinct risk factors. Given community reservoirs for MRSA acquisition and transmission, novel infection prevention strategies are needed.

Translating PI3K-Delta Inhibitors to the Clinic in Chronic Lymphocytic Leukemia: The Story of CAL-101 (GS1101)

Targeted therapy with imatinib has transformed the treatment of chronic myeloid leukemia (CML). Unlike CML, chronic lymphocytic leukemia (CLL) lacks a common genetic aberration but does demonstrate constitutive activation of PI3-kinase (PI3K) as compared to normal B cells. This constitutively active PI3K in CLL likely relates to tonic B-cell receptor signaling that is present across a wide variety of B-cell malignancies. Although PI3K is quite proximal and represents an ideal target to pharmacologically modulate, the complexity of this pathway on which many normal functions are dependent had for many years been problematic. The p110 delta isoform of PI3K is relatively specific to hematopoietic cells, and elegant mouse studies where p110 delta was genetically inactivated demonstrated only a selective B-cell defect. Subsequent development of a potent, selective p110 delta inhibitor prompted translation into the clinic for the treatment of CLL and low-grade non-Hodgkin lymphoma (NHL). From the first patient treated where a dramatic early nodal response was noted, considerable excitement has developed for this class of drugs in CLL and NHL. We will summarize the development process of CAL-101 (now GS1101) in the treatment of chronic lymphoid malignancies such as CLL.

Etiology of Ibrutinib Therapy Discontinuation and Outcomes in Patients With Chronic Lymphocytic Leukemia

IMPORTANCE

The Bruton tyrosine kinase (BTK) inhibitor ibrutinib is effective in patients with chronic lymphocytic leukemia (CLL). Reasons for discontinuing therapy with this drug and outcomes following discontinuation have not been evaluated outside of clinical trials with relatively short follow-up.

OBJECTIVE

To determine features associated with discontinuation of ibrutinib therapy and outcomes.

DESIGN, SETTING, AND PARTICIPANTS

A total of 308 patients participating in 4 sequential trials of ibrutinib at The Ohio State University Comprehensive Cancer Center were included. These clinical trials accrued patients included in this analysis from May 2010 until April 2014, and data were locked in June 2014.

MAIN OUTCOMES AND MEASURES

Patients were evaluated for time to therapy discontinuation, reasons for discontinuation, and survival following discontinuation. For patients who discontinued therapy because of disease progression, targeted deep sequencing was performed in samples at baseline and time of relapse.

RESULTS

With a median follow-up of 20 months, 232 patients remained on therapy, 31 had discontinued because of disease progression, and 45 had discontinued for other reasons. Disease progression includes Richter's transformation (RT) or progressive CLL. Richter's transformation appeared to occur early and CLL progressions later (cumulative incidence at 12 months, 4.5% [95% CI, 2.0%-7.0%] and 0.3% [95% CI, 0%-1.0%], respectively). Median survival following RT was 3.5 months (95% CI, 0.3-6.0 months) and 17.6 months (95% CI, 4.7 months-"not reached") following CLL progression. Sequencing on peripheral blood from 8 patients with RT revealed 2 with mutations in BTK, and a lymph node sample showed no mutations in BTK or PLCG2. Deep sequencing on 11 patients with CLL progression revealed BTK or PLCG2 mutations in all. These mutations were not identified before treatment in any patient.

CONCLUSIONS AND RELEVANCE

This single-institution experience with ibrutinib confirms it to be an effective therapy and identifies, for the first time, baseline factors associated with ibrutinib therapy discontinuation. Outcomes data show poor prognosis after discontinuation, especially for those patients with RT. Finally, sequencing data confirm initial reports associating mutations in BTK and PLCG2 with progression and clearly show that CLL progressions are associated with these mutations, while RT is likely not.

TRIAL REGISTRATIONS

clinicaltrials.gov Identifiers:NCT01105247, NCT01217749, NCT01589302, and NCT01578707.

Acalabrutinib (ACP-196) in Relapsed Chronic Lymphocytic Leukemia

BACKGROUND

Irreversible inhibition of Bruton's tyrosine kinase (BTK) by ibrutinib represents an important therapeutic advance for the treatment of chronic lymphocytic leukemia (CLL). However, ibrutinib also irreversibly inhibits alternative kinase targets, which potentially compromises its therapeutic index. Acalabrutinib (ACP-196) is a more selective, irreversible BTK inhibitor that is specifically designed to improve on the safety and efficacy of first-generation BTK inhibitors.

METHODS

In this uncontrolled, phase 1-2, multicenter study, we administered oral acalabrutinib to 61 patients who had relapsed CLL to assess the safety, efficacy, pharmacokinetics, and pharmacodynamics of acalabrutinib. Patients were treated with acalabrutinib at a dose of 100 to 400 mg once daily in the dose-escalation (phase 1) portion of the study and 100 mg twice daily in the expansion (phase 2) portion.

RESULTS

The median age of the patients was 62 years, and patients had received a median of three previous therapies for CLL; 31% had chromosome 17p13.1 deletion, and 75% had unmutated immunoglobulin heavy-chain variable genes. No dose-limiting toxic effects occurred during the dose-escalation portion of the study. The most common adverse events observed were headache (in 43% of the patients), diarrhea (in 39%), and increased weight (in 26%). Most adverse events were of grade 1 or 2. At a median follow-up of 14.3 months, the overall response rate was 95%, including 85% with a partial response and 10% with a partial response with lymphocytosis; the remaining 5% of patients had stable disease. Among patients with chromosome 17p13.1 deletion, the overall response rate was 100%. No cases of Richter's transformation (CLL that has evolved into large-cell lymphoma) and only one case of CLL progression have occurred.

CONCLUSIONS

In this study, the selective BTK inhibitor acalabrutinib had promising safety and efficacy profiles in patients with relapsed CLL, including those with chromosome 17p13.1 deletion. (Funded by the Acerta Pharma and others; ClinicalTrials.gov number, NCT02029443.).

Up-regulation of CDK9 kinase activity and Mcl-1 stability contributes to the acquired resistance to cyclin-dependent kinase inhibitors in leukemia

Flavopiridol is a small molecule inhibitor of cyclin-dependent kinases (CDK) known to impair global transcription via inactivation of positive transcription elongation factor b. It has been demonstrated to have significant activity predominantly in chronic lymphocytic leukemia and acute myeloid leukemia in phase I/II clinical trials while other similar CDK inhibitors are vigorously being pursued in pre-clinical and clinical studies. Although flavopiridol is a potent therapeutic agent against blood diseases, some patients still have primary or acquired resistance throughout their clinical course. Considering the limited knowledge of resistance mechanisms of flavopiridol, we investigated the potential mechanisms of resistance to flavopiridol in a cell line system, which gradually acquired resistance to flavopiridol in vitro, and then confirmed the mechanism in patient samples. Herein, we present that this resistant cell line developed resistance through up-regulation of phosphorylation of RNA polymerase II C-terminal domain, activation of CDK9 kinase activity, and prolonged Mcl-1 stability to counter flavopiridol's drug actions. Further analyses suggest MAPK/ERK activation-mediated Mcl-1 stabilization contributes to the resistance and knockdown of Mcl-1 in part restores sensitivity to flavopiridol-induced cytotoxicity. Altogether, these findings demonstrate that CDK9 is the most relevant target of flavopiridol and provide avenues to improve the therapeutic strategies in blood malignancies.

Abstract 3985: Characterization of plasma-derived exosomes in CLL reveals a distinct microRNA signature and the BCR regulation in exosome secretion

Chronic lymphocytic leukemia (CLL) is the most diagnosed adult leukemia and has a very heterogeneous clinical course attributed to its defective apoptosis and sustained nurture of the microenvironment. In vivo, CLL resides in close contact with T lymphocytes, stromal cells, monocyte-derived nurse-like cells, follicular dendritic cells, and macrophages, collectively referred to as the “microenvironment.” Interactions between these components result in CLL cell trafficking, survival, proliferation, and anti-apoptosis, which may be partly dependent on direct cell-to-cell contact or mediated through the soluble factors, including the secreted extracellular vesicles (EVs) as an alternative means for intercellular communications. These EVs have distinct biochemical properties and contain cellular components, such as proteins, lipids, mRNAs and microRNAs (miRs). Exosomes are EVs with 40 - 100nm in diameter and considered to initiate from the late endosomal membrane, giving rise to intracellular multivesicular bodies that later fuse with the plasma membrane and release the exosomes to the exterior. The secretion of exosomes has been reported to be regulated by intracellular calcium levels, activation of the cell surface receptor or stress responses. Emerging evidence suggests that cancer releases large amount of exosomes and exosome functions in recipient cells are associated with tumor immune response, metastasis, tumorigenesis, angiogenesis, drug resistance, and changes in signaling transduction. With increasing evidence implicating the importance of these EVs, it prompts us to elucidate the exosome biochemical property and to investigate the relevance of exosome in CLL.

Our data demonstrate that CLL releases high levels of exosomes in plasma than healthy donor and its concentration is not associated with the absolute lymphocyte count. These CLL plasma-derived exosomes express abundant CD63, CD9 and CD37 but not CD41, CD3 or CD56. Activation of BCR by α-IgM stimulation induces CLL to release more exosomes while inhibition of BCR via ibrutinib, a BTK inhibitor, abrogates α-IgM induced exosome secretion. Moreover, analyzing plasma samples collected on an ibrutinib phase 2 clinical trial (OSU-11133, NCT01589302), the exosome concentration decreases in post ibrutinib treatment. In addition, profiling the exosome miR isolated from 69 CLL and 15 healthy donors reveals a distinct miR signature, including up-regulation of miR-29 family, miR-155, miR-150 and down-regulation of miR-223 that have been shown to be associated with the CLL disease. In all, we have successfully characterized the composition of CLL exosome with the optimal methods and demonstrated the control of BCR signaling in the CLL exosome release. Furthermore, the identified CLL exosome miR profile can be explored further to uncover the exosome function and its relevance to the CLL disease.

Citation Format: Yuh-Ying Yeh, Hatice Gulcin Ozer, Amy M. Lehman, Lianbo Yu, Amy J. Johnson, John C. Byrd. Characterization of plasma-derived exosomes in CLL reveals a distinct microRNA signature and the BCR regulation in exosome secretion. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3985. doi:10.1158/1538-7445.AM2015-3985

Targeted therapies in CLL: mechanisms of resistance and strategies for management

The therapy of relapsed chronic lymphocytic leukemia (CLL) has changed dramatically in the past year with the regulatory approval of idelalisib and ibrutinib, with other therapeutic small molecules likely to become widely available in the next few years. Although durable remissions are being seen in many patients with these agents, it is becoming apparent that some patients with high genomic risk disease will relapse. Next-generation sequencing in patients as well as in vitro models is affording us the opportunity to understand the biology behind these relapses, which is the first step to designing rational therapies to prevent and treat targeted therapy-resistant CLL. These strategies are critical, as these relapses can be very difficult to manage, and a coordinated effort to put these patients on clinical trials will be required to efficiently determine the optimal therapies for these patients. In this review, we will describe mechanisms of resistance, both proven and hypothesized, for idelalisib, ibrutinib, and venetoclax, describe patterns of resistance that have been described with ibrutinib, and discuss potential strategies for management of disease resistant to these drugs as well as potential strategies to prevent resistance.

Abstract B44: Pharmacologic inhibition with IPI-145 and genetic inhibition of PI3K p110δ antagonizes intrinsic and extrinsic survival signals in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL), the most common adult leukemia in the western world, remains an incurable B-cell malignancy. It is characterized by the accumulation of malignant mature B cells in the blood, lymph nodes, spleen and bone marrow. CLL cells display up-regulated B cell receptor (BCR) activation, which maintains B cell survival and proliferation through transmitting microenvironmental stimuli. Due to aberrant regulation of the BCR, CLL cells display constitutively activated survival and proliferation pathways, such as phosphoinositide-3 kinase (PI3K) and Bruton's tyrosine kinase (BTK) pathways. Small molecules that target such kinases in the BCR pathway have shown significant clinical activity in CLL patients. The PI3K p110δ inhibitor, idelalisib, was granted a breakthrough therapy designation by the FDA in relapsed CLL and the BTK inhibitor, ibrutinib, has received approval by FDA for treatment of relapsed CLL. However, patients still relapse on these therapies.

Here we use pharmacologic and genetic approaches to further characterize the role of PI3K signaling in the leukemia pathogenesis in the CLL cell and in the microenvironment. We describe that a PI3K p110δ and p110γ inhibitor, IPI-145, which is in late stage clinical development, attenuates pro-survival signals in the OSU-CLL cell line and primary human and murine CLL cells and promotes apoptosis and downstream pathway inactivation in primary human and murine CLL cells in a dose- and time-dependent fashion. To examine the cytotoxicity of IPI-145 in normal immune cells, we incubated whole blood from CLL patients with 0.25-5 μM IPI-145 for 48 hours and analyzed by flow cytometry for absolute count of live CD3+ T cells, CD56+ NK cells and CD19+ B cells. T cells and NK cells were sensitive to IPI-145, displaying about 20% decrease in viability at concentrations greater than 0.5μM, however the B cell population showed about 50% decrease in viability. To specifically examine normal B cells, we isolated CD19+ B cells from healthy volunteer blood and incubated with 1 μM IPI-145 for 48 hours and observed no cytotoxicity, despite observing a significant decrease in CLL cells viability under the same conditions. Additionally, IPI-145 is highly effective at reducing downstream PI3K signaling in a B cell line with the ibrutinib resistance conferring BTK C481S mutation. Genetically we show that the PI3K p110δ-inactivating and the TCL1 leukemia murine models can be utilized to further explore the differential role of PI3K p110δ in leukemic cell and microenvironment. Our study indicates that systemic disruption of PI3K p110δ function in the TCL1 mouse significantly prevents spontaneous leukemia development, indicating that PI3K p110δ is a critical kinase for CLL disease initiation and expansion. Moreover, inactivation of PI3K p110δ in the microenvironment showed a dose dependent effect in delaying leukemia engraftment. This suggests that PI3K p110δ activity is also critical in the non-B cell compartment for leukemia progression. While our group has focused on the role of PI3K p110δ, we continue to examine the role of PI3K p110γ using the PI3K p110δ and p110γ inhibitor, IPI-145.

This study provides solid rationale for ongoing clinical development of IPI-145 in CLL patients. Additionally, as IPI-145 can continue to inhibit the PI3K/AKT pathway in the setting of a C481S BTK mutation, it provides justification for clinical studies of this agent in this subset of patients.

Citation Format: Amy J. Johnson, Shuai Dong, Daphne Guinn, Jason A. Dubovsky, Yiming Zhong, Amy Lehman, Jeff Kutok, Jennifer A. Woyach, John C. Byrd. Pharmacologic inhibition with IPI-145 and genetic inhibition of PI3K p110δ antagonizes intrinsic and extrinsic survival signals in chronic lymphocytic leukemia. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B44.