Targeting the C481S Ibrutinib-Resistance Mutation in Bruton's Tyrosine Kinase Using PROTAC-Mediated Degradation.

Inhibition of Bruton's tyrosine kinase (BTK) with the irreversible inhibitor ibrutinib has emerged as a transformative treatment option for patients with chronic lymphocytic leukemia (CLL) and other B-cell malignancies, yet >80% of CLL patients develop resistance due to a cysteine to serine mutation at the site covalently bound by ibrutinib (C481S). Currently, an effective treatment option for C481S patients exhibiting relapse to ibrutinib does not exist, and these patients have poor outcomes. To address this, we have developed a PROteolysis TArgeting Chimera (PROTAC) that induces degradation of both wild-type and C481S mutant BTK. We selected a lead PROTAC, MT-802, from several candidates on the basis of its potency to induce BTK knockdown. MT-802 recruits BTK to the cereblon E3 ubiquitin ligase complex to trigger BTK ubiquitination and degradation via the proteasome. MT-802 binds fewer off-target kinases than ibrutinib does and retains an equivalent potency (>99% degradation at nanomolar concentrations) against wild-type and C481S BTK. In cells isolated from CLL patients with the C481S mutation, MT-802 is able to reduce the pool of active, phosphorylated BTK whereas ibrutinib cannot. Collectively, these data provide a basis for further preclinical study of BTK PROTACs as a novel strategy for treatment of C481S mutant CLL.

Characterization of CLL exosomes reveals a distinct microRNA signature and enhanced secretion by activation of BCR signaling.

Multiple studies show that chronic lymphocytic leukemia (CLL) cells are heavily dependent on their microenvironment for survival. Communication between CLL cells and the microenvironment is mediated through direct cell contact, soluble factors, and extracellular vesicles. Exosomes are small particles enclosed with lipids, proteins, and small RNAs that can convey biological materials to surrounding cells. Our data herein demonstrate that CLL cells release significant amounts of exosomes in plasma that exhibit abundant CD37, CD9, and CD63 expression. Our work also pinpoints the regulation of B-cell receptor (BCR) signaling in the release of CLL exosomes: BCR activation by α-immunoglobulin (Ig)M induces exosome secretion, whereas BCR inactivation via ibrutinib impedes α-IgM-stimulated exosome release. Moreover, analysis of serial plasma samples collected from CLL patients on an ibrutinib clinical trial revealed that exosome plasma concentration was significantly decreased following ibrutinib therapy. Furthermore, microRNA (miR) profiling of plasma-derived exosomes identified a distinct exosome microRNA signature, including miR-29 family, miR-150, miR-155, and miR-223 that have been associated with CLL disease. Interestingly, expression of exosome miR-150 and miR-155 increases with BCR activation. In all, this study successfully characterized CLL exosomes, demonstrated the control of BCR signaling in the release of CLL exosomes, and uncovered a disease-relevant exosome microRNA profile.

Selinexor is effective in acquired resistance to ibrutinib and synergizes with ibrutinib in chronic lymphocytic leukemia.

Despite the therapeutic efficacy of ibrutinib in chronic lymphocytic leukemia (CLL), complete responses are infrequent, and acquired resistance to Bruton agammaglobulinemia tyrosine kinase (BTK) inhibition is being observed in an increasing number of patients. Combination regimens that increase frequency of complete remissions, accelerate time to remission, and overcome single agent resistance are of considerable interest. We previously showed that the XPO1 inhibitor selinexor is proapoptotic in CLL cells and disrupts B-cell receptor signaling via BTK depletion. Herein we show the combination of selinexor and ibrutinib elicits a synergistic cytotoxic effect in primary CLL cells and increases overall survival compared with ibrutinib alone in a mouse model of CLL. Selinexor is effective in cells isolated from patients with prolonged lymphocytosis following ibrutinib therapy. Finally, selinexor is effective in ibrutinib-refractory mice and in a cell line harboring the BTK C481S mutation. This is the first report describing the combined activity of ibrutinib and selinexor in CLL, which represents a new treatment paradigm and warrants further evaluation in clinical trials of CLL patients including those with acquired ibrutinib resistance.

Ibrutinib is an irreversible molecular inhibitor of ITK driving a Th1-selective pressure in T lymphocytes.

Given its critical role in T-cell signaling, interleukin-2-inducible kinase (ITK) is an appealing therapeutic target that can contribute to the pathogenesis of certain infectious, autoimmune, and neoplastic diseases. Ablation of ITK subverts Th2 immunity, thereby potentiating Th1-based immune responses. While small-molecule ITK inhibitors have been identified, none have demonstrated clinical utility. Ibrutinib is a confirmed irreversible inhibitor of Bruton tyrosine kinase (BTK) with outstanding clinical activity and tolerability in B-cell malignancies. Significant homology between BTK and ITK alongside in silico docking studies support ibrutinib as an immunomodulatory inhibitor of both ITK and BTK. Our comprehensive molecular and phenotypic analysis confirms ITK as an irreversible T-cell target of ibrutinib. Using ibrutinib clinical trial samples along with well-characterized neoplastic (chronic lymphocytic leukemia), parasitic infection (Leishmania major), and infectious disease (Listeria monocytogenes) models, we establish ibrutinib as a clinically relevant and physiologically potent ITK inhibitor with broad therapeutic utility. This trial was registered at www.clinicaltrials.gov as #NCT01105247 and #NCT01217749.

A contemporary analysis of induction immunosuppression in pediatric lung transplant recipients.

There is an increasing trend in the use of induction immunosuppression in children undergoing lung transplantation (LTx). To evaluate the effect of this practice on survival, the United Network for Organ Sharing (UNOS) was queried from 1987 to 2012, restricting analysis to transplant patients 6-17 years old from 2001 to 2012, who received no induction (NONE) or induction (INDUCED) with the contemporary agents of basiliximab, alemtuzumab, thymoglobulin, antilymphocyte globulin (ALG), or antithymocyte globulin (ATG). Of 23 951 lung transplants, 330 met inclusion criteria with 177 (54%) being INDUCED. Of the INDUCED agents, 121 (68%) were basiliximab, 3 (2%) alemtuzumab, and 53 (30%) ALG/ATG/thymoglobulin. The mean patient age was 13.6 (SD = 3.2) and 14 (SD = 3.0) years for the INDUCED and NONE groups, respectively. The median survival in the INDUCED group was 77.4 months (95% CI: 46.1, 125.6) compared with 50.8 months (95% CI: 42.9, 61.3) for the NONE (log-rank P-value = 0.3601). The most common cause of death was due to allograft failure or pulmonary complications with only one patient dying from post-transplant lymphoproliferative disorder. The estimated hazard ratio for INDUCED versus NONE was 0.859 (95% CI: 0.620, 1.191; P = 0.3618); there were no significant confounders or effect modifiers among the demographic and clinical variables. In conclusion, antibody-based induction immunosuppression with contemporary agents had a trend toward a protective, but not statistically significant, effect in 6- to 17-year-old patients.

The 17-Gene Genomic Prostate Score Assay Is Prognostic for Biochemical Failure in Men With Localized Prostate Cancer After Radiation Therapy at a Community Cancer Center.

Purpose: The objective of this study was to assess the association between the Oncotype DX Genomic Prostate Score (GPS) assay and long-term outcomes in men with localized prostate cancer (PCa) after radiation therapy (RT). We hypothesized that the GPS assay is prognostic for biochemical failure (BCF), along with distant metastasis (DM) and PCa-specific mortality in patients with PCa receiving RT. Methods and Materials: We retrospectively studied men with localized PCa treated with definitive RT at Georgia Urology from 2010 to 2016. The primary objective was to assess the association between GPS results and time to BCF per the Phoenix criteria; we also assessed time to DM and PCa-specific mortality. We used Cox proportional hazards regression models for all analyses, with clinicopathologic covariates determined a priori for multivariable modeling. Results: A total of 450 patients (median age, 65 years; 35% Black) met eligibility criteria. There was a strong univariable association between GPS result and time to BCF (hazard ratio [HR] per 20-unit increase = 3.08; 95% confidence interval [CI], 2.11-4.46; P < .001), which persisted after adjusting for clinicopathologic characteristics in multivariable analyses. We also observed this association for time to DM (HR = 5.19; 95% CI, 3.06-8.77; P < .001) and PCa-specific mortality (HR = 13.07; 95% CI, 4.42-49.39; P < .001). Race was not a predictor of time to BCF or DM, and the GPS assay was strongly prognostic for all endpoints in Black and White patients. Conclusions: In a community-based cohort, the GPS assay was strongly prognostic for time to BCF as well as long-term outcomes in men treated with RT for localized PCa.

Dysregulation of PRMT5 in chronic lymphocytic leukemia promotes progression with high risk of Richter's transformation.

Richter's Transformation (RT) is a poorly understood and fatal progression of chronic lymphocytic leukemia (CLL) manifesting histologically as diffuse large B-cell lymphoma. Protein arginine methyltransferase 5 (PRMT5) is implicated in lymphomagenesis, but its role in CLL or RT progression is unknown. We demonstrate herein that tumors uniformly overexpress PRMT5 in patients with progression to RT. Furthermore, mice with B-specific overexpression of hPRMT5 develop a B-lymphoid expansion with increased risk of death, and Eµ-PRMT5/TCL1 double transgenic mice develop a highly aggressive disease with transformation that histologically resembles RT; where large-scale transcriptional profiling identifies oncogenic pathways mediating PRMT5-driven disease progression. Lastly, we report the development of a SAM-competitive PRMT5 inhibitor, PRT382, with exclusive selectivity and optimal in vitro and in vivo activity compared to available PRMT5 inhibitors. Taken together, the discovery that PRMT5 drives oncogenic pathways promoting RT provides a compelling rationale for clinical investigation of PRMT5 inhibitors such as PRT382 in aggressive CLL/RT cases.

The long-term effects of semiconductor diode laser transscleral cyclophotocoagulation on the normal equine eye and intraocular pressure(a).

OBJECTIVE: To describe the long-term histologic and intraocular pressure (IOP) lowering effects of diode laser transscleral cyclophotocoagulation (TSCP) on the normal equine eye. ANIMALS: Eight normal adult horses. PROCEDURES: TSCP was performed in one randomly assigned eye. Sixty spots were treated at settings of 1500 ms and 1500 mW. Two horses were randomly selected for euthanasia at 2, 4, 12, or 24 weeks post-TSCP. Both eyes were enucleated and histologically evaluated. Intraocular pressure was measured by applanation tonometry prior to TSCP, immediately post-TSCP, twice daily for 7 days post-TSCP and then monthly until study conclusion. A longitudinal model estimated the average IOP values for the treated and untreated eyes at 1 week, 1, 3, and 6 months post-TSCP. RESULTS: All treated eyes at all time periods exhibited four characteristic histologic lesions: scleral collagen hyalinization, ciliary body pigment dispersion and clumping, focal disruption of the ciliary body epithelium, and focal ciliary process atrophy. After TSCP, there were no significant changes in IOP from baseline for the control eyes, while the IOP in treated eyes was significantly decreased from baseline (P < 0.05) at all time periods. The estimated decrease in IOP in the treated eyes compared to baseline IOP at 6 months was -3.76 mmHg for an average decrease in IOP of 20% from baseline. CONCLUSION: Diode laser TSCP produces histologic lesions in the equine ciliary body that result in a significant and sustained decrease in IOP. TSCP may be an effective management for equine glaucoma.

Preclinical evaluation of the Hsp90 inhibitor SNX-5422 in ibrutinib resistant CLL.

B-cell receptor (BCR) antagonists such as the BTK inhibitor ibrutinib have proven to effectively target chronic lymphocytic leukemia (CLL) tumor cells, leading to impressive response rates in these patients. However patients do still relapse on ibrutinib, and the progressive disease is often quite aggressive requiring immediate treatment. Several strategies are being pursued to treat patients who relapse on ibrutinib therapy. As the most common form of relapse is the development of a mutant form of BTK which limits ibrutinib binding, agents which lead to degradation of the BTK protein are a promising strategy. Our study explores the efficacy of the Hsp90 inhibitor, SNX-5422, in CLL. The SNX Hsp90 inhibitor was effective in primary CLL cells, as well as B-cell lines expressing either BTK wild type or C481 mutant BTK, which has been identified as the primary resistance mechanism to ibrutinib in CLL patients. Furthermore the combination of SNX-5422 and ibrutinib provided a remarkable in vivo survival benefit in the Eµ-TCL1 mouse model of CLL compared to the vehicle or single agent groups (51 day median survival in the vehicle and ibrutinib groups versus 100 day median survival in the combination). We report here preclinical data suggesting that the Hsp90 inhibitor SNX-5422, which has been pursued in clinical trials in both solid tumor and hematological malignancies, is a potential therapy for ibrutinib resistant CLL.

Targeting DNA Damage Repair Functions of Two Histone Deacetylases, HDAC8 and SIRT6, Sensitizes Acute Myeloid Leukemia to NAMPT Inhibition.

PURPOSE: Nicotinamide phosphoribosyltransferase (NAMPT) inhibitors (NAMPTi) are currently in development, but may be limited as single-agent therapy due to compound-specific toxicity and cancer metabolic plasticity allowing resistance development. To potentially lower the doses of NAMPTis required for therapeutic benefit against acute myeloid leukemia (AML), we performed a genome-wide CRISPRi screen to identify rational disease-specific partners for a novel NAMPTi, KPT-9274. EXPERIMENTAL DESIGN: Cell lines and primary cells were analyzed for cell viability, self-renewal, and responses at RNA and protein levels with loss-of-function approaches and pharmacologic treatments. In vivo efficacy of combination therapy was evaluated with a xenograft model. RESULTS: We identified two histone deacetylases (HDAC), HDAC8 and SIRT6, whose knockout conferred synthetic lethality with KPT-9274 in AML. Furthermore, HDAC8-specific inhibitor, PCI-34051, or clinical class I HDAC inhibitor, AR-42, in combination with KPT-9274, synergistically decreased the survival of AML cells in a dose-dependent manner. AR-42/KPT-9274 cotreatment attenuated colony-forming potentials of patient cells while sparing healthy hematopoietic cells. Importantly, combined therapy demonstrated promising in vivo efficacy compared with KPT-9274 or AR-42 monotherapy. Mechanistically, genetic inhibition of SIRT6 potentiated the effect of KPT-9274 on PARP-1 suppression by abolishing mono-ADP ribosylation. AR-42/KPT-9274 cotreatment resulted in synergistic attenuation of homologous recombination and nonhomologous end joining pathways in cell lines and leukemia-initiating cells. CONCLUSIONS: Our findings provide evidence that HDAC8 inhibition- or shSIRT6-induced DNA repair deficiencies are potently synergistic with NAMPT targeting, with minimal toxicity toward normal cells, providing a rationale for a novel-novel combination-based treatment for AML.

Psychosocial predictors of adherence to risk-appropriate cervical cancer screening guidelines: a cross sectional study of women in Ohio Appalachia participating in the Community Awareness Resources and Education (CARE) project.

OBJECTIVE: We describe factors, in the context of the Social Determinants of Health model, associated with receiving Pap smears within risk-appropriate guidelines (i.e., guidelines that specify screening intervals based upon a woman's individual risk of developing cervical cancer). METHODS: Completed in June 2006, we conducted a cross-sectional survey of women from 14 health clinics in Ohio Appalachia pertaining to psychosocial, demographic, biological, and health-related factors. A logistic regression model was constructed to predict whether or not a woman was within risk-appropriate cervical cancer screening guidelines. RESULTS: Of 562 women with a date of last Pap smear, 380 (68%) were within risk-appropriate guidelines. Logistic regression showed that, compared to women with low-level SES, women with middle- and high-level SES had 3.39 [1.85, 6.21] and 3.86 [2.03, 7.34] times the odds, respectively, of being within risk-appropriate guidelines. Odds of being within guidelines increased 1.09 [1.04, 1.15] fold for each decrease of one major life event. Additionally, women that were financially better off or financially worse off than their parents at the same age had lower odds (0.41 [0.23, 0.73] and 0.49 [0.24, 0.98], respectively) of being within guidelines than women who reported their finances were the same as their parents. Results also showed an interaction between marital status and age at first intercourse (p=0.001). CONCLUSION: The results suggest an impact of psychosocial factors on Pap smear testing behaviors, and illustrate the need to examine risk-appropriate interventions to improve screening.

IFN-alpha-2b-induced signal transduction and gene regulation in patient peripheral blood mononuclear cells is not enhanced by a dose increase from 5 to 10 megaunits/m2.

PURPOSE: The precise molecular targets of IFN-alpha therapy of melanoma are unknown but likely involve signal transducer and activator of transcription (STAT) 1 signal transduction within host immune effector cells. We hypothesized that intermediate and high doses of IFN-alpha would be equally effective in activating patient immune cells. EXPERIMENTAL DESIGN: Eleven metastatic melanoma patients who were enrolled in a clinical trial of bevacizumab in combination with escalating doses of IFN-alpha-2b (5 megaunits/m(2) and then 10 megaunits/m(2)) were included in the study. Peripheral blood mononuclear cells (PBMC) were procured from patient blood just before therapy and again 1 h after each dose of IFN-alpha-2b and analyzed for the presence of phosphorylated STAT1, phosphorylated STAT2, and the induction of IFN-stimulated gene (ISG) transcripts. RESULTS: Phosphorylated STAT1 was significantly greater at the 5 megaunits/m(2) dose compared with the 10 megaunits/m(2) dose of IFN-alpha-2b (P = 0.02). In contrast, no significant difference in phosphorylated STAT2 was observed at a dose of 5 megaunits/m(2) compared with 10 megaunits/m(2) (P = 0.20). There were also no significant differences in the induction of ISGs within PBMCs between the two doses (P > 0.4 for all ISGs). Suppressor of cytokine signaling 1 and 3 (two inhibitors of IFN-alpha signaling) transcripts were significantly higher among patient PBMCs following the 10 megaunits/m(2) dose of IFN-alpha (P < 0.001). CONCLUSION: These results suggest that lower doses of IFN-alpha-2b are as effective as higher doses with respect to the induction of Janus-activated kinase-STAT signal transduction and the transcription of ISGs within immune effector cells.

Plasma and ear tissue concentrations of enrofloxacin and its metabolite ciprofloxacin in dogs with chronic end-stage otitis externa after intravenous administration of enrofloxacin.

The purpose of this study was to measure the concentrations of enrofloxacin and its metabolite ciprofloxacin following intravenous administration of enrofloxacin in the plasma and ear tissue of dogs with chronic end-stage otitis undergoing a total ear canal ablation and lateral bulla osteotomy. The goals were to determine the relationship between the dose of enrofloxacin and the concentrations of enrofloxacin and ciprofloxacin, and determine appropriate doses of enrofloxacin for treatment of chronic otitis externa and media. Thirty dogs were randomized to an enrofloxacin-treatment group (5, 10, 15 or 20 mg kg(-1)) or control group (no enrofloxacin). After surgical removal, ear tissue samples (skin, vertical ear canal, horizontal ear canal, middle ear) and a blood sample were collected. Concentrations of enrofloxacin and ciprofloxacin in the plasma and ear tissue were measured by high performance liquid chromatography. Repeated measures models were applied to log-transformed data to assess dosing trends and Pearson correlations were calculated to assess concentration associations. Ear tissue concentrations of enrofloxacin and ciprofloxacin were significantly (P < 0.05) higher than plasma concentrations. Each 5 mg kg(-1 )increase in the dose of enrofloxacin resulted in a 72% and 37% increase in enrofloxacin and ciprofloxacin concentrations, respectively. For bacteria with an minimal inhibitory concentration of 0.12-0.15 or less, 0.19-0.24, 0.31-0.39 and 0.51-0.64 microg mL(-1), enrofloxacin should be dosed at 5, 10, 15 and 20 mg kg(-1), respectively. Treatment with enrofloxacin would not be recommended for a bacterial organism intermediate or resistant in susceptibility to enrofloxacin since appropriate levels of enrofloxacin would not be attained.

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.

Peritubular capillary C4d staining in late acute renal allograft rejection--is it relevant?

BACKGROUND: In the early post-transplant period, renal allograft rejection with diffuse peritubular capillary (PTC) C4d deposition predicts poor graft survival. In the late post-transplant setting, that is, one or more yr after transplantation, the implication of diffuse PTC C4d deposition is still a topic of debate. The purpose of our study was to see if diffuse PTC C4d deposition, in late acute rejection (LAR), occurring more than one yr post-transplant, has any impact on graft survival and function. METHODS: We selected cases, both cadaveric as well as living donor renal transplant recipients, in whom acute rejection with PTC C4d deposition was first detected after the first year post-transplant. Recipients with multiple acute rejection episodes during the first year post-transplant were excluded from the study. The first biopsy diagnosed with LAR was considered the index biopsy (n = 40). We formed two groups: group 1, C4d-positive LAR (n = 20), and group 2, C4d-negative LAR (n = 20). Groups were matched for maintenance and post-rejection immunosuppressive therapy, baseline serum creatinine levels before the time of the index biopsy, time from transplant to index biopsy, as well as chronic allograft damage index (CADI) score in the index biopsies. We compared the rate of graft loss, and the graft function of the surviving grafts at the end of the study period, as well as histologic parameters in the index biopsy specimens between the two groups. The mean follow-up period was 20 months. RESULTS: No significant differences in the rate of graft loss or graft function were found between groups 1 and 2 at the end of the follow-up period. Histologically, PTC margination and transplant glomerulopathy were more common in the C4d-positive group, and this difference was statistically significant. There was no statistically significant difference in the degree of plasma cell infiltrates. CONCLUSIONS: Unlike in the acute setting, the presence or absence of PTC C4d staining in renal allografts with LAR may not have a predictive value regarding graft outcome.

Combination therapy with anti-CTL antigen-4 and anti-4-1BB antibodies enhances cancer immunity and reduces autoimmunity.

The majority of cancer antigens identified thus far have limited expression in normal tissues. It has been suggested that autoimmune disease is a necessary price for cancer immunity. This notion is supported by a recent clinical trial involving an anti-CTL antigen-4 (CTLA-4) antibody that showed significant clinical responses but severe autoimmune diseases in melanoma patients. To selectively modulate cancer immunity and autoimmunity, we used anti-CTLA-4 and anti-4-1BB antibodies to treat mice with a preexisting cancer, MC38. The combination of the two antibodies led to CD8 T-cell-mediated rejection of large established MC38 tumors and long-lasting immunity to the same tumor cells, although the same regimen was not effective for B16 melanoma. More importantly, whereas individual antibodies induced inflammation and autoimmune manifestations, combination therapy increased cancer immunity while reducing autoimmunity. The reduction of autoimmune effects correlates with an increased function of regulatory T cells. Our results suggest a novel approach to simultaneously enhance cancer immunity and reduce autoimmunity.

Expression Patterns, Prognostic Value, and Intratumoral Heterogeneity of PD-L1 and PD-1 in Thymoma and Thymic Carcinoma.

INTRODUCTION: Thymic epithelial tumors (TETs) including thymoma and thymic carcinoma are rare tumors with little data available to guide treatment. Immunotherapy with checkpoint blockade has shown promising activity, but data regarding the expression patterns and prognostic implications of programmed death 1 (PD-1) and its ligand (PD-L1) in TETs have yielded conflicting results. Intratumoral heterogeneity of PD-1/L1 expression has been shown in other cancers, but has not been described in the TET literature. METHODS: We performed a retrospective single-center review of 35 patients with resected TET. PD-1/L1 expression was assessed by immunohistochemistry using PD-1 clone: NAT105 and PD-L1 clone: 22C3. Tumor samples from 35 patients were evaluated including 32 patients with thymoma and 3 patients with thymic carcinoma. RESULTS: PD-L1 expression was detected in 83% (29 of 35) tumor samples, including 100% (3 of 3) of thymic carcinoma patients and 81% (26 of 32) of thymoma patients. PD-1 expression was detected in 77% (27 of 35), including 33% (1 of 3) of thymic carcinoma patients and 81% (26 of 32) thymoma patients. High PD-1 expression was associated with lower grade tumors. Unlike prior studies, PD-L1 expression was not associated with higher grade tumors or higher stage. Neither PD-L1 nor PD-1 expression was significantly associated with survival. Three patients with thymoma had multiple tumor sections evaluated for expression of PD-1/L1, with differing expression patterns of both PD-L1 and PD-1 observed in two patients. CONCLUSIONS: This study confirms high expression of PD-L1 and PD-1 in TET and shows for the first time intratumoral heterogeneity of PD-L1 and PD-1 in thymoma patients.

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.

BRD4 Profiling Identifies Critical Chronic Lymphocytic Leukemia Oncogenic Circuits and Reveals Sensitivity to PLX51107, a Novel Structurally Distinct BET Inhibitor.

Bromodomain and extra-terminal (BET) family proteins are key regulators of gene expression in cancer. Herein, we utilize BRD4 profiling to identify critical pathways involved in pathogenesis of chronic lymphocytic leukemia (CLL). BRD4 is overexpressed in CLL and is enriched proximal to genes upregulated or de novo expressed in CLL with known functions in disease pathogenesis and progression. These genes, including key members of the B-cell receptor (BCR) signaling pathway, provide a rationale for this therapeutic approach to identify new targets in alternative types of cancer. Additionally, we describe PLX51107, a structurally distinct BET inhibitor with novel in vitro and in vivo pharmacologic properties that emulates or exceeds the efficacy of BCR signaling agents in preclinical models of CLL. Herein, the discovery of the involvement of BRD4 in the core CLL transcriptional program provides a compelling rationale for clinical investigation of PLX51107 as epigenetic therapy in CLL and application of BRD4 profiling in other cancers.Significance: To date, functional studies of BRD4 in CLL are lacking. Through integrated genomic, functional, and pharmacologic analyses, we uncover the existence of BRD4-regulated core CLL transcriptional programs and present preclinical proof-of-concept studies validating BET inhibition as an epigenetic approach to target BCR signaling in CLL. Cancer Discov; 8(4); 458-77. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 371.