Stimulation of surface IgM of chronic lymphocytic leukemia cells induces an unfolded protein response dependent on BTK and SYK

Functional consequences of inhibition of Bruton's tyrosine kinase by ibrutinib in chronic lymphocytic leukemia

The leukemic B cells from patients with chronic lymphocytic leukemia (CLL) require interactions with non-malignant cells and matrix in the tissue microenvironment to survive and grow. These interactions are mediated through the B-cell antigen receptor (BCR), C-X-C chemokine receptor type 4 (CXCR4), and a variety of integrins, including VLA-4. Exciting each receptor type leads to activation of Bruton's tyrosine kinase (BTK), which in turn helps initiate trophic signals that prevent cell death and promote cell activation and growth as well as allowing cells to return to anatomic sites for rescue signals. These represent the two major functional actions targeted by inhibitors of Btk. Here we relate some of the therapeutic actions of ibrutinib, a Btk inhibitor that is extremely helpful for patients with CLL, certain Diffuse Large B-cell Lymphomas (ABC type), and other non-Hodgkin's lymphomas, emphasizing that ibrutinib's value results from blocking beneficial signals, not by inducing lethal ones.

Ibrutinib sensitizes CLL cells to venetoclax by interrupting TLR9-induced CD40 upregulation and protein translation

Chronic lymphocytic leukemia (CLL) cells upregulate Bcl-2 proteins within the lymph node (LN) microenvironment. Signaling via B-cell receptor, Toll-like receptors and CD40 collectively reduce sensitivity to the BCL-2 inhibitor venetoclax. Time-limited treatment with venetoclax plus the BTK-inhibitor ibrutinib results in deep remissions, but how this combination affects LN-related signaling is not yet completely clear. Therefore, samples obtained from the HOVON141/VISION phase 2 clinical trial were used to analyze this. Two cycles of lead-in ibrutinib monotherapy resulted in decreased protein expression of Bcl-2 proteins in circulating CLL cells. Strikingly, at this timepoint CD40-induced venetoclax resistance was strongly attenuated, as was expression of CD40. Since CD40 signaling occurs within the CLL LN, we tested various LN-related signals that could affect CD40 signaling. While BCR stimulation had only a minor effect, TLR9 stimulation via CpG led to significantly increased CD40 expression and importantly, reverted the effects of ibrutinib treatment on venetoclax sensitivity by inducing overall protein translation. Together, these findings identify a novel effect of ibrutinib: interruption of TLR9-induced CD40 upregulation and translation of pro-survival proteins. This mechanism may potentially further inhibit priming of CLL cells in the LN microenvironment for venetoclax resistance.

A bispecific T cell engager recruits both type 1 NKT and Vγ9Vδ2-T cells for the treatment of CD1d-expressing hematological malignancies

Bispecific T cell engagers (bsTCEs) hold great promise for cancer treatment but face challenges due to the induction of cytokine release syndrome (CRS), on-target off-tumor toxicity, and the engagement of immunosuppressive regulatory T cells that limit efficacy. The development of Vγ9Vδ2-T cell engagers may overcome these challenges by combining high therapeutic efficacy with limited toxicity. By linking a CD1d-specific single-domain antibody (VHH) to a Vδ2-TCR-specific VHH, we create a bsTCE with trispecific properties, which engages not only Vγ9Vδ2-T cells but also type 1 NKT cells to CD1d+ tumors and triggers robust proinflammatory cytokine production, effector cell expansion, and target cell lysis in vitro. We show that CD1d is expressed by the majority of patient MM, (myelo)monocytic AML, and CLL cells and that the bsTCE triggers type 1 NKT and Vγ9Vδ2-T cell-mediated antitumor activity against these patient tumor cells and improves survival in in vivo AML, MM, and T-ALL mouse models. Evaluation of a surrogate CD1d-γδ bsTCE in NHPs shows Vγ9Vδ2-T cell engagement and excellent tolerability. Based on these results, CD1d-Vδ2 bsTCE (LAVA-051) is now evaluated in a phase 1/2a study in patients with therapy refractory CLL, MM, or AML.

BTK-independent regulation of calcium signalling downstream of the B-cell receptor in malignant B-cells

BTK inhibitors (BTKi) have dramatically improved outcomes for patients with chronic lymphocytic leukaemia (CLL) and some forms of B-cell lymphoma. However, new strategies are needed to enhance responses. Here we have performed a detailed analysis of the effects of BTKi on B-cell receptor (BCR)-induced signalling using primary malignant cells from CLL patients and B-lymphoma cell lines. Although BTK is considered as a key activator of PLCγ2, BTKi (ibrutinib and acalabrutinib) failed to fully inhibit calcium responses in CLL samples with strong BCR signalling capacity. This BTKi-resistant calcium signalling was sufficient to engage downstream calcium-dependent transcription and suppress CLL cell apoptosis and was entirely independent of BTK and not just its kinase activity as similar results were obtained using a BTK-degrading PROTAC. BTK-independent calcium signalling was also observed in two B-lymphoma cell lines where BTKi had little effect on the initial phase of the calcium response but did accelerate the subsequent decline in intracellular calcium. In contrast to BTKi, calcium responses were completely blocked by inhibition of SYK in CLL and lymphoma cells. Engagement of BTK-independent calcium responses was associated with BTK-independent phosphorylation of PLCγ2 on Y753 and Y759 in both CLL and lymphoma cells. Moreover, in CLL samples, inhibition of RAC, which can mediate BTK-independent activation of PLCγ2, cooperated with ibrutinib to suppress calcium responses. BTK-independent calcium signalling may limit the effectiveness of BTKi to suppress BCR signalling responses and our results suggest inhibition of SYK or dual inhibition of BTK and RAC as alternative strategies to strengthen pathway blockade.

B-cell receptor signaling induces proteasomal degradation of PDCD4 via MEK1/2 and mTORC1 in malignant B cells

B-cell receptor (BCR) signaling plays a major role in the pathogenesis of B-cell malignancies and is an established target for therapy, including in chronic lymphocytic leukemia cells (CLL), the most common B-cell malignancy. We previously demonstrated that activation of BCR signaling in primary CLL cells downregulated expression of PDCD4, an inhibitor of the translational initiation factor eIF4A and a potential tumor suppressor in lymphoma. Regulation of the PDCD4/eIF4A axis appeared to be important for expression of the MYC oncoprotein as MYC mRNA translation was increased following BCR stimulation and MYC protein induction was repressed by pharmacological inhibition of eIF4A. Here we show that MYC expression is also associated with PDCD4 down-regulation in CLL cells in vivo and characterize the signaling pathways that mediate BCR-induced PDCD4 down-regulation in CLL and lymphoma cells. PDCD4 downregulation was mediated by proteasomal degradation as it was inhibited by proteasome inhibitors in both primary CLL cells and B-lymphoma cell lines. In lymphoma cells, PDCD4 degradation was predominantly dependent on signaling via the AKT pathway. By contrast, in CLL cells, both ERK and AKT pathways contributed to PDCD4 down-regulation and dual inhibition using ibrutinib with either MEK1/2 or mTORC1 inhibition was required to fully reverse PDCD4 down-regulation. Consistent with this, dual inhibition of BTK with MEK1/2 or mTORC1 resulted in the strongest inhibition of BCR-induced MYC expression. This study provides important new insight into the regulation of mRNA translation in B-cell malignancies and a rationale for combinations of kinase inhibitors to target translation control and MYC expression.

O-GlcNAcylation in Chronic Lymphocytic Leukemia and Other Blood Cancers

In the past decade, aberrant O-GlcNAcylation has emerged as a new hallmark of cancer. O-GlcNAcylation is a post-translational modification that results when the amino-sugar β-D-N-acetylglucosamine (GlcNAc) is made in the hexosamine biosynthesis pathway (HBP) and covalently attached to serine and threonine residues in intracellular proteins by the glycosyltransferase O-GlcNAc transferase (OGT). O-GlcNAc moieties reflect the metabolic state of a cell and are removed by O-GlcNAcase (OGA). O-GlcNAcylation affects signaling pathways and protein expression by cross-talk with kinases and proteasomes and changes gene expression by altering protein interactions, localization, and complex formation. The HBP and O-GlcNAcylation are also recognized to mediate survival of cells in harsh conditions. Consequently, O-GlcNAcylation can affect many of the cellular processes that are relevant for cancer and is generally thought to promote tumor growth, disease progression, and immune escape. However, recent studies suggest a more nuanced view with O-GlcNAcylation acting as a tumor promoter or suppressor depending on the stage of disease or the genetic abnormalities, proliferative status, and state of the p53 axis in the cancer cell. Clinically relevant HBP and OGA inhibitors are already available and OGT inhibitors are in development to modulate O-GlcNAcylation as a potentially novel cancer treatment. Here recent studies that implicate O-GlcNAcylation in oncogenic properties of blood cancers are reviewed, focusing on chronic lymphocytic leukemia and effects on signal transduction and stress resistance in the cancer microenvironment. Therapeutic strategies for targeting the HBP and O-GlcNAcylation are also discussed.

Targeted inhibition of eIF4A suppresses B-cell receptor-induced translation and expression of MYC and MCL1 in chronic lymphocytic leukemia cells

Signaling via the B-cell receptor (BCR) is a key driver and therapeutic target in chronic lymphocytic leukemia (CLL). BCR stimulation of CLL cells induces expression of eIF4A, an initiation factor important for translation of multiple oncoproteins, and reduces expression of PDCD4, a natural inhibitor of eIF4A, suggesting that eIF4A may be a critical nexus controlling protein expression downstream of the BCR in these cells. We, therefore, investigated the effect of eIF4A inhibitors (eIF4Ai) on BCR-induced responses. We demonstrated that eIF4Ai (silvestrol and rocaglamide A) reduced anti-IgM-induced global mRNA translation in CLL cells and also inhibited accumulation of MYC and MCL1, key drivers of proliferation and survival, respectively, without effects on upstream signaling responses (ERK1/2 and AKT phosphorylation). Analysis of normal naïve and non-switched memory B cells, likely counterparts of the two main subsets of CLL, demonstrated that basal RNA translation was higher in memory B cells, but was similarly increased and susceptible to eIF4Ai-mediated inhibition in both. We probed the fate of MYC mRNA in eIF4Ai-treated CLL cells and found that eIF4Ai caused a profound accumulation of MYC mRNA in anti-IgM treated cells. This was mediated by MYC mRNA stabilization and was not observed for MCL1 mRNA. Following drug wash-out, MYC mRNA levels declined but without substantial MYC protein accumulation, indicating that stabilized MYC mRNA remained blocked from translation. In conclusion, BCR-induced regulation of eIF4A may be a critical signal-dependent nexus for therapeutic attack in CLL and other B-cell malignancies, especially those dependent on MYC and/or MCL1.

Activation of unfolded protein response overcomes Ibrutinib resistance in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most widespread type of non-Hodgkin lymphoma (NHL). As the most aggressive form of the DLBCL, the activated B-cell-like (ABC) subtype is often resistant to standard chemotherapies. Bruton's tyrosine kinase (BTK) inhibitor ibrutinib provides a potential therapeutic approach for the DLBCL but fails to improve the outcome in the phase III trial. In the current study, we investigated the molecular mechanisms underlying ibrutinib resistance and explored new combination therapy with ibrutinib. We generated an ibrutinib-resistant ABC-DLBCL cell line (OCI-ly10-IR) through continuous exposure to ibrutinib. Transcriptome analysis of the parental and ibrutinib-resistant cell lines revealed that the ibrutinib-resistant cells had significantly lower expression of the unfolded protein response (UPR) marker genes. Overexpression of one UPR branch-XBP1s greatly potentiated ibrutinib-induced apoptosis in both sensitive and resistant cells. The UPR inhibitor tauroursodeoxycholic acid (TUDCA) partially reduced the apoptotic rate induced by the ibrutinib in sensitive cells. The UPR activator 2-deoxy-D-glucose (2-DG) in combination with the ibrutinib triggered even greater cell growth inhibition, apoptosis, and stronger calcium (Ca2+) flux inhibition than either of the agents alone. A combination treatment of ibrutinib (15 mg·kg-1·d-1, po.) and 2-DG (500 mg/kg, po, b.i.d.) synergistically retarded tumor growth in NOD/SCID mice bearing OCI-ly10-IR xenograft. In addition, ibrutinib induced the UPR in the sensitive cell lines but not in the resistant cell lines of the DLBCL. There was also a combined synergistic effect in the primary resistant DLBCL cell lines. Overall, our results suggest that targeting the UPR could be a potential combination strategy to overcome ibrutinib resistance in the DLBCL.

Extracellular vesicles (EVs): What we know of the mesmerizing roles of these tiny vesicles in hematological malignancies?

Cancer is a complex disease in which a bidirectional collaboration between malignant cells and surrounding microenvironment creates an appropriate platform which ultimately facilitates the progression of the disease. The discovery of extracellular vesicles (EVs) was a turning point in the modern era of cancer biology, as their importance in human malignancies has set the stage to widen research interest in the field of cell-to-cell communication. The implication in short- and long-distance interaction via horizontally transfer of cellular components, ranging from non-coding RNAs to functional proteins, as well as stimulating target cells receptors by the means of ligands anchored on their membrane endows these "tiny vesicles with giant impacts" with incredible potential to re-educate normal tissues, and thus, to re-shape the surrounding niche. In this review, we highlight the pathogenic roles of EVs in human cancers, with an extensive focus on the recent advances in hematological malignancies.

The ClpP activator ONC-212 (TR-31) inhibits BCL2 and B-cell receptor signaling in CLL

Despite advances in therapy, a significant proportion of patients with chronic lymphocytic leukemia (CLL) relapse with drug resistant disease. Novel treatment approaches are required, particularly for high risk disease. The imipridones represent a new class of cancer therapy that has been investigated in pre-clinical and clinical trials against a range of different cancers. We investigated the effects of the imipridone, ONC-212, against CLL cells cultured under conditions that mimic aspects of the tumour microenvironment and a TP53ko CLL cell line (OSU-CLL-TP53ko). ONC-212 induced dose-dependent apoptosis, cell cycle arrest and reduced the migration of CLL cells in vitro, including cells from patients with TP53 lesions and OSU-CLL-TP53ko cells. The effects of ONC-212 were associated with protein changes consistent with activation of the mitochondrial protease, CIpP, and the integrated stress response. We also observed inhibition of pathways downstream of the B-cell receptor (BCR) (AKT and MAPK-ERK1/2) and a pro-apoptotic shift in the balance of proteins of the BCL2 family of proteins (BCL2, MCL1, BCLxL, BAX and NOXA). In conclusion, the study suggests ONC-212 may represent an effective treatment for high risk CLL disease by inhibiting multiple facets of the BCR signaling pathway and the pro-survival effects of the BCL2-family proteins.

ER Stress and Unfolded Protein Response in Leukemia: Friend, Foe, or Both?

The unfolded protein response (UPR) is an evolutionarily conserved adaptive signaling pathway triggered by a stress of the endoplasmic reticulum (ER) lumen compartment, which is initiated by the accumulation of unfolded proteins. This response, mediated by three sensors-Inositol Requiring Enzyme 1 (IRE1), Activating Transcription Factor 6 (ATF6), and Protein Kinase RNA-Like Endoplasmic Reticulum Kinase (PERK)—allows restoring protein homeostasis and maintaining cell survival. UPR represents a major cytoprotective signaling network for cancer cells, which frequently experience disturbed proteostasis owing to their rapid proliferation in an usually unfavorable microenvironment. Increased basal UPR also participates in the resistance of tumor cells against chemotherapy. UPR activation also occurs during hematopoiesis, and growing evidence supports the critical cytoprotective role played by ER stress in the emergence and proliferation of leukemic cells. In case of severe or prolonged stress, pro-survival UPR may however evolve into a cell death program called terminal UPR. Interestingly, a large number of studies have revealed that the induction of proapoptotic UPR can also strongly contribute to the sensitization of leukemic cells to chemotherapy. Here, we review the current knowledge on the consequences of the deregulation of UPR signaling in leukemias and their implications for the treatment of these diseases.

Genetic and Non-Genetic Mechanisms of Resistance to BCR Signaling Inhibitors in B Cell Malignancies

The approval of BTK and PI3K inhibitors (ibrutinib, idelalisib) represents a revolution in the therapy of B cell malignancies such as chronic lymphocytic leukemia (CLL), mantle-cell lymphoma (MCL), diffuse large B cell lymphoma (DLBCL), follicular lymphoma (FL), or Waldenström's macroglobulinemia (WM). However, these "BCR inhibitors" function by interfering with B cell pathophysiology in a more complex way than anticipated, and resistance develops through multiple mechanisms. In ibrutinib treated patients, the most commonly described resistance-mechanism is a mutation in BTK itself, which prevents the covalent binding of ibrutinib, or a mutation in PLCG2, which acts to bypass the dependency on BTK at the BCR signalosome. However, additional genetic aberrations leading to resistance are being described (such as mutations in the CARD11, CCND1, BIRC3, TRAF2, TRAF3, TNFAIP3, loss of chromosomal region 6q or 8p, a gain of Toll-like receptor (TLR)/MYD88 signaling or gain of 2p chromosomal region). Furthermore, relative resistance to BTK inhibitors can be caused by non-genetic adaptive mechanisms leading to compensatory pro-survival pathway activation. For instance, PI3K/mTOR/Akt, NFkB and MAPK activation, BCL2, MYC, and XPO1 upregulation or PTEN downregulation lead to B cell survival despite BTK inhibition. Resistance could also arise from activating microenvironmental pathways such as chemokine or integrin signaling via CXCR4 or VLA4 upregulation, respectively. Defining these compensatory pro-survival mechanisms can help to develop novel therapeutic combinations of BTK inhibitors with other inhibitors (such as BH3-mimetic venetoclax, XPO1 inhibitor selinexor, mTOR, or MEK inhibitors). The mechanisms of resistance to PI3K inhibitors remain relatively unclear, but some studies point to MAPK signaling upregulation via both genetic and non-genetic changes, which could be co-targeted therapeutically. Alternatively, drugs mimicking the BTK/PI3K inhibition effect can be used to prevent adhesion and/or malignant B cell migration (chemokine and integrin inhibitors) or to block the pro-proliferative T cell signals in the microenvironment (such as IL4/STAT signaling inhibitors). Here we review the genetic and non-genetic mechanisms of resistance and adaptation to the first generation of BTK and PI3K inhibitors (ibrutinib and idelalisib, respectively), and discuss possible combinatorial therapeutic strategies to overcome resistance or to increase clinical efficacy.

Harrison C, Eswaran J, Soundararajan M. DAP Kinase-Related Apoptosis-Inducing Protein Kinase 2 (DRAK2) Is a Key Regulator and Molecular Marker in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the Western World and it is characterized by a marked degree of clinical heterogeneity. An impaired balance between pro- and anti-apoptotic stimuli determines chemorefractoriness and outcome. The low proliferation rate of CLL cells indicates that one of the primary mechanisms involved in disease development may be an apoptotic failure. Here, we study the clinical and functional significance of DRAK2, a novel stress response kinase that plays a critical role in apoptosis, T-cell biology, and B-cell activation in CLL. We have analyzed CLL patient samples and showed that low expression levels of DRAK2 were significantly associated with unfavorable outcome in our CLL cohort. DRAK2 expression levels showed a positive correlation with the expression of DAPK1, and TGFBR1. Consistent with clinical data, the downregulation of DRAK2 in MEC-1 CLL cells strongly increased cell viability and proliferation. Further, our transcriptome data from MEC-1 cells highlighted MAPK, NF-κB, and Akt and as critical signaling hubs upon DRAK2 knockdown. Taken together, our results indicate DRAK2 as a novel marker of CLL survival that plays key regulatory roles in CLL prognosis.

Toll-like Receptors as a Novel Therapeutic Target for Natural Products Against Chronic Diseases

Toll-like receptors (TLR) are one among the initial responders of the immune system which participate in the activation inflammatory processes. Several different types of TLR such as TLR2, TLR4, TLR7 and TLR9 have been identified in various cell types, each having distinct ligands like lipids, lipoproteins, nucleic acids and proteins. Though its prime concern is xenobiotic defences, TLR signalling has also recognized as an activator of inflammation and associated development of chronic degenerative disorders (CDDs) including obesity, type 2 diabetes mellitus (T2DM), fatty liver disease, cardiovascular and neurodegenerative disorders as well as various types of cancers. Numerous drugs are in use to prevent these disorders, which specifically inhibit different pathways associated with the development of CDDs. Compared to these drug targets, inhibition of TLR, which specifically responsible for the inflammatory insults has proven to be a better drug target. Several natural products have emerged as inhibitors of CDDs, which specifically targets TLR signalling, among these, many are in the clinical trials. This review is intended to summarize the recent progress on TLR association with CDDs and to list possible use of natural products, their combinations and their synthetic derivative in the prevention of TLR-driven CDD development.

Development of PROTACs to address clinical limitations associated with BTK-targeted kinase inhibitors

Chronic lymphocytic leukemia is a common form of leukemia and is dependent on growth-promoting signaling via the B-cell receptor. The Bruton tyrosine kinase (BTK) is an important mediator of B-cell receptor signaling and the irreversible BTK inhibitor ibrutinib can trigger dramatic clinical responses in treated patients. However, emergence of resistance and toxicity are major limitations which lead to treatment discontinuation. There remains, therefore, a clear need for new therapeutic options. In this review, we discuss recent progress in the development of BTK-targeted proteolysis targeting chimeras (PROTACs) describing how such agents may provide advantages over ibrutinib and highlighting features of PROTACs that are important for the development of effective BTK degrading agents. Overall, PROTACs appear to be an exciting new approach to target BTK. However, development is at a very early stage and considerable progress is required to refine these agents and optimize their drug-like properties before progression to clinical testing.

Unfolded Protein Response in Leukemia: From Basic Understanding to Therapeutic Opportunities

Understanding genetic and epigenetic changes that underlie abnormal proliferation of hematopoietic stem and progenitor cells is critical for development of new approaches to monitor and treat leukemia. The unfolded protein response (UPR) is a conserved adaptive signaling pathway that governs protein folding, secretion, and energy production and serves to maintain protein homeostasis in various cellular compartments. Deregulated UPR signaling, which often occurs in hematopoietic stem cells and leukemia, defines the degree of cellular toxicity and perturbs protein homeostasis, and at the same time, offers a novel therapeutic target. Here, we review current knowledge related to altered UPR signaling in leukemia and highlight possible strategies for exploiting the UPR as treatment for this disease.

Preclinical Evaluation of a Novel SHIP1 Phosphatase Activator for Inhibition of PI3K Signaling in Malignant B Cells

PURPOSE

PI3K signaling is a common feature of B-cell neoplasms, including chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL), and PI3K inhibitors have been introduced into the clinic. However, there remains a clear need to develop new strategies to target PI3K signaling. PI3K activity is countered by Src homology domain 2-containing inositol-5'-phosphatase 1 (SHIP1) and, here, we have characterized the activity of a novel SHIP1 activator, AQX-435, in preclinical models of B-cell malignancies.

EXPERIMENTAL DESIGN

In vitro activity of AQX-435 was evaluated using primary CLL cells and DLBCL-derived cell lines. In vivo activity of AQX-435, alone or in combination with the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, was assessed using DLBCL cell line and patient-derived xenograft models.

RESULTS

Pharmacologic activation of SHIP1 using AQX-435 was sufficient to inhibit anti-IgM-induced PI3K-mediated signaling, including induction of AKT phosphorylation and MYC expression, without effects on upstream SYK phosphorylation. AQX-435 also cooperated with the BTK inhibitor ibrutinib to enhance inhibition of anti-IgM-induced AKT phosphorylation. AQX-435 induced caspase-dependent apoptosis of CLL cells preferentially as compared with normal B cells, and overcame in vitro survival-promoting effects of microenvironmental stimuli. Finally, AQX-435 reduced AKT phosphorylation and growth of DLBCL in vivo and cooperated with ibrutinib for tumor growth inhibition.

CONCLUSIONS

Our results using AQX-435 demonstrate that SHIP1 activation may be an effective novel therapeutic strategy for treatment of B-cell neoplasms, alone or in combination with ibrutinib.

Pharmacologic inhibition of the ubiquitin-activating enzyme induces ER stress and apoptosis in chronic lymphocytic leukemia and ibrutinib-resistant mantle cell lymphoma cells

With the advent of proteasome inhibitors (bortezomib) and pleiotropic pathway modulators which target cereblon E3 ligase (lenalidomide), the ubiquitin-proteasome system has emerged as a tractable target in non-Hodgkin lymphoma and multiple myeloma. Here we report that TAK-243, a small molecule inhibitor of the ubiquitin-activating enzyme (UAE), induced ER stress and the unfolded protein response in primary chronic lymphocytic leukemia cells, facilitating cell death. Moreover, targeting UAE was effective in ibrutinib-resistant mantle cell lymphoma cell lines and primary cells in vitro. Thus, UAE is a promising target in lymphoid malignancies, including ibrutinib-resistant lymphomas, an area of unmet medical need.

Targeting the unfolded protein response in head and neck and oral cavity cancers

Many FDA-approved anti-cancer therapies, targeted toward a wide array of molecular targets and signaling networks, have been demonstrated to activate the unfolded protein response (UPR). Despite a critical role for UPR signaling in the apoptotic execution of cancer cells by many of these compounds, the authors are currently unaware of any instance whereby a cancer drug was developed with the UPR as the intended target. With the essential role of the UPR as a driving force in the genesis and maintenance of the malignant phenotype, a great number of pre-clinical studies have surged into the medical literature describing the ability of dozens of compounds to induce UPR signaling in a myriad of cancer models. The focus of the current work is to review the literature and explore the role of the UPR as a mediator of chemotherapy-induced cell death in squamous cell carcinomas of the head and neck (HNSCC) and oral cavity (OCSCC), with an emphasis on preclinical studies.

Targeting protein disulfide isomerase with the flavonoid isoquercetin to improve hypercoagulability in advanced cancer

BACKGROUND

Protein disulfide isomerase (PDI) is a thiol isomerase secreted by vascular cells that is required for thrombus formation. Quercetin flavonoids inhibit PDI activity and block platelet accumulation and fibrin generation at the site of a vascular injury in mouse models, but the clinical effect of targeting extracellular PDI in humans has not been studied.

METHODS

We conducted a multicenter phase II trial of sequential dosing cohorts to evaluate the efficacy of targeting PDI with isoquercetin to reduce hypercoagulability in cancer patients at high risk for thrombosis. Patients received isoquercetin at 500 mg (cohort A, n = 28) or 1000 mg (cohort B, n = 29) daily for 56 days, with laboratory assays performed at baseline and the end of the study, along with bilateral lower extremity compression ultrasound. The primary efficacy endpoint was a reduction in D-dimer, and the primary clinical endpoint included pulmonary embolism or proximal deep vein thrombosis.

RESULTS

The administration of 1000 mg isoquercetin decreased D-dimer plasma concentrations by a median of -21.9% (P = 0.0002). There were no primary VTE events or major hemorrhages observed in either cohort. Isoquercetin increased PDI inhibitory activity in plasma (37.0% in cohort A, n = 25, P < 0.001; 73.3% in cohort B, n = 22, P < 0.001, respectively). Corroborating the antithrombotic efficacy, we also observed a significant decrease in platelet-dependent thrombin generation (cohort A median decrease -31.1%, P = 0.007; cohort B median decrease -57.2%, P = 0.004) and circulating soluble P selectin at the 1000 mg isoquercetin dose (median decrease -57.9%, P < 0.0001).

CONCLUSIONS

Isoquercetin targets extracellular PDI and improves markers of coagulation in advanced cancer patients.

TRIAL REGISTRATION

Clinicaltrials.gov NCT02195232.

FUNDING

Quercegen Pharmaceuticals; National Heart, Lung, and Blood Institute (NHLBI; U54HL112302, R35HL135775, and T32HL007917); and NHLBI Consortium Linking Oncology and Thrombosis (U01HL143365).

Regulation of gammaherpesvirus lytic replication by endoplasmic reticulum stress-induced transcription factors ATF4 and CHOP

The stress-induced unfolded protein response (UPR) in the endoplasmic reticulum (ER) involves various signaling cross-talks and controls cell fate. B-cell receptor (BCR) signaling, which can trigger UPR, induces gammaherpesvirus lytic replication and serves as a physiological mechanism for gammaherpesvirus reactivation in vivo However, how the UPR regulates BCR-mediated gammaherpesvirus infection is unknown. Here, we demonstrate that the ER stressors tunicamycin and thapsigargin inhibit BCR-mediated murine gammaherpesvirus 68 (MHV68) lytic replication by inducing expression of the UPR mediator Bip and blocking activation of Akt, ERK, and JNK. Both Bip and the downstream transcription factor ATF4 inhibited BCR-mediated MHV68 lytic gene expression, whereas UPR-induced C/EBP homologous protein (CHOP) was required for and promoted BCR-mediated MHV68 lytic replication by suppressing upstream Bip and ATF4 expression. Bip knockout was sufficient to rescue BCR-mediated MHV68 lytic gene expression in CHOP knockout cells, and this rescue was blocked by ectopic ATF4 expression. Furthermore, ATF4 directly inhibited promoter activity of the MHV68 lytic switch transactivator RTA. Altogether, we show that ER stress-induced CHOP inhibits Bip and ATF4 expression and that ATF4, in turn, plays a critical role in CHOP-mediated regulation of BCR-controlled MHV68 lytic replication. We conclude that ER stress-mediated UPR and BCR signaling pathways are interconnected and form a complex network to regulate the gammaherpesvirus infection cycle.

Diffuse large B-cell lymphoma: can genomics improve treatment options for a curable cancer?

Gene-expression profiling and next-generation sequencing have defined diffuse large B-cell lymphoma (DLBCL), the most common lymphoma diagnosis, as a heterogeneous group of subentities. Despite ongoing explosions of data illuminating disparate pathogenic mechanisms, however, the five-drug chemoimmunotherapy combination R-CHOP remains the frontline standard treatment. This has not changed in 15 years, since the anti-CD20 monoclonal antibody rituximab was added to the CHOP backbone, which first entered use in the 1970s. At least a third of patients are not cured by R-CHOP, and relapsed or refractory DLBCL is fatal in ∼90%. Targeted small-molecule inhibitors against distinct molecular pathways activated in different subgroups of DLBCL have so far translated poorly into the clinic, justifying the ongoing reliance on R-CHOP and other long-established chemotherapy-driven combinations. New drugs and improved identification of biomarkers in real time, however, show potential to change the situation eventually, despite some recent setbacks. Here, we review established and putative molecular drivers of DLBCL identified through large-scale genomics, highlighting among other things the care that must be taken when differentiating drivers from passengers, which is influenced by the promiscuity of activation-induced cytidine deaminase. Furthermore, we discuss why, despite having so much genomic data available, it has been difficult to move toward personalized medicine for this umbrella disorder and some steps that may be taken to hasten the process.

Duvelisib treatment is associated with altered expression of apoptotic regulators that helps in sensitization of chronic lymphocytic leukemia cells to venetoclax (ABT-199)

Duvelisib, an oral dual inhibitor of PI3K-δ and PI3K-γ, is in phase III trials for the treatment of chronic lymphocytic leukemia (CLL) and indolent non-Hodgkin's lymphoma. In CLL, duvelisib monotherapy is associated with high iwCLL (International Workshop on Chronic Lymphocytic Leukemia) and nodal response rates, but complete remissions are rare. To characterize the molecular effect of duvelisib, we obtained samples from CLL patients on the duvelisib phase I trial. Gene expression studies (RNAseq, Nanostring, Affymetrix array and real-time RT-PCR) demonstrated increased expression of BCL2 along with several BH3-only pro-apoptotic genes. In concert with induction of transcript levels, reverse phase protein arrays and immunoblots confirmed increase at the protein level. The BCL2 inhibitor venetoclax induced greater apoptosis in ex vivo-cultured CLL cells obtained from patients on duvelisib compared with pre-treatment CLL cells from the same patients. In vitro combination of duvelisib and venetoclax resulted in enhanced apoptosis even in CLL cells cultured under conditions that simulate the tumor microenvironment. These data provide a mechanistic rationale for testing the combination of duvelisib and venetoclax in the clinic. Such combination regimen (NCT02640833) is being evaluated for patients with B-cell malignancies including CLL.

Physiological/pathological ramifications of transcription factors in the unfolded protein response

Numerous environmental, physiological, and pathological insults disrupt protein-folding homeostasis in the endoplasmic reticulum (ER), referred to as ER stress. Eukaryotic cells evolved a set of intracellular signaling pathways, collectively termed the unfolded protein response (UPR), to maintain a productive ER protein-folding environment through reprogramming gene transcription and mRNA translation. The UPR is largely dependent on transcription factors (TFs) that modulate expression of genes involved in many physiological and pathological conditions, including development, metabolism, inflammation, neurodegenerative diseases, and cancer. Here we summarize the current knowledge about these mechanisms, their impact on physiological/pathological processes, and potential therapeutic applications.

The Dual Syk/JAK Inhibitor Cerdulatinib Antagonizes B-cell Receptor and Microenvironmental Signaling in Chronic Lymphocytic Leukemia

Purpose: B-cell receptor (BCR)-associated kinase inhibitors, such as ibrutinib, have revolutionized the treatment of chronic lymphocytic leukemia (CLL). However, these agents are not curative, and resistance is already emerging in a proportion of patients. IL4, expressed in CLL lymph nodes, can augment BCR signaling and reduce the effectiveness of BCR kinase inhibitors. Therefore, simultaneous targeting of the IL4- and BCR signaling pathways by cerdulatinib, a novel dual Syk/JAK inhibitor currently in clinical trials (NCT01994382), may improve treatment responses in patients.Experimental Design: PBMCs from patients with CLL were treated in vitro with cerdulatinib alone or in combination with venetoclax. Cell death, chemokine, and cell signaling assay were performed and analyzed by flow cytometry, immunoblotting, q-PCR, and ELISA as indicated.Results: At concentrations achievable in patients, cerdulatinib inhibited BCR- and IL4-induced downstream signaling in CLL cells using multiple readouts and prevented anti-IgM- and nurse-like cell (NLC)-mediated CCL3/CCL4 production. Cerdulatinib induced apoptosis of CLL cells, in a time- and concentration-dependent manner, and particularly in IGHV-unmutated samples with greater BCR signaling capacity and response to IL4, or samples expressing higher levels of sIgM, CD49d+, or ZAP70+ Cerdulatinib overcame anti-IgM, IL4/CD40L, or NLC-mediated protection by preventing upregulation of MCL-1 and BCL-XL; however, BCL-2 expression was unaffected. Furthermore, in samples treated with IL4/CD40L, cerdulatinib synergized with venetoclax in vitro to induce greater apoptosis than either drug alone.Conclusions: Cerdulatinib is a promising therapeutic for the treatment of CLL either alone or in combination with venetoclax, with the potential to target critical survival pathways in this currently incurable disease. Clin Cancer Res; 23(9); 2313-24. ©2016 AACR.

PEITC-mediated inhibition of mRNA translation is associated with both inhibition of mTORC1 and increased eIF2α phosphorylation in established cell lines and primary human leukemia cells

Increased mRNA translation drives carcinogenesis and is an attractive target for the development of new anti-cancer drugs. In this work, we investigated effects of phenethylisothiocyanate (PEITC), a phytochemical with chemopreventive and anti-cancer activity, on mRNA translation. PEITC rapidly inhibited global mRNA translation in human breast cancer-derived MCF7 cells and mouse embryonic fibroblasts (MEFs). In addition to the known inhibitory effects of PEITC on mTORC1 activity, we demonstrate that PEITC increased eIF2α phosphorylation. PEITC also increased formation of stress granules which are typically associated with eIF2α phosphorylation and accumulation of translationally stalled mRNAs. Analysis of genetically modified MEFs demonstrated that optimal inhibition of global mRNA translation by PEITC was dependent on eIF2α phosphorylation, but not mTORC1 inhibition. We extended this study into primary leukemic B cells derived from patients with chronic lymphocytic leukaemia (CLL). CLL cells were stimulated in vitro with anti-IgM to mimic binding of antigen, a major driver of this leukemia. In CLL cells, PEITC increased eIF2α phosphorylation, inhibited anti-IgM-induced mTORC1 activation and decreased both basal and anti-IgM-induced global mRNA translation. PEITC also inhibited transcription and translation of MYC mRNA and accumulation of the MYC oncoprotein, in anti-IgM-stimulated cells. Moreover, treatment of CLL cells with PEITC and the BTK kinase inhibitor ibrutinib decreased anti-IgM-induced translation and induced cell death to a greater extent than either agent alone. Therefore, PEITC can inhibit both global and mRNA specific translation (including MYC) via effects on multiple regulatory pathways. Inhibition of mRNA translation may contribute to the chemopreventive and anti-cancer effects of PEITC.

Dynamics of microvesicle generation in B-cell chronic lymphocytic leukemia: implication in disease progression

Previously, we reported that B-cell chronic lymphocytic leukemia (CLL) patients contained elevated levels of microvesicles (MVs). However, given the quiescent nature of CLL B-cells and the relative indolence of the disease, the dynamics of MV generation and their unique phenotypes are not clearly defined. In this study, we find that CLL B-cells generate MVs spontaneously and can be further induced by B-cell receptor-ligation. Most interestingly, CLL B-cells predominantly generate CD52⁺ MVs, but not CD19⁺ MVs in vitro, suggesting preferential usage of CD52 into leukemic-MVs and that the CLL plasma MV phenotypes corroborate well with the in vitro findings. Importantly, we detected increased accumulation of CD52⁺ MVs in previously untreated CLL patients with progressive disease. Finally, sequential studies on MVs in pre- and post-therapy CLL patients demonstrate that while the plasma CD52⁺ MV levels drop significantly after therapy in most and remain at low levels in some patients, a trend of increased accumulation of CD52⁺ MVs was detected in majority of post-therapy CLL patients (25 of 33). In total this study emphasizes that dynamic accumulation of CD52⁺ MVs in plasma can be used to study CLL progression and may be a useful biomarker for patients as they progress and require therapy.

IL-4 enhances expression and function of surface IgM in CLL cells

Kinase inhibitors targeting the B-cell receptor (BCR) are now prominent in the treatment of chronic lymphocytic leukemia (CLL). We have focused here on interleukin 4 (IL-4), a cytokine that protects normal and malignant B cells from apoptosis and increases surface immunoglobulin M (sIgM) expression on murine splenic B cells. First, we have demonstrated that IL-4 treatment increased sIgM expression in vitro on peripheral blood B cells obtained from healthy individuals. In CLL, IL-4 target genes are overexpressed in cells purified from the lymph nodes of patients compared with cells derived from matched blood and bone marrow samples. As for normal B cells, IL-4 increased sIgM expression on CLL cells in vitro, especially in samples expressing unmutated V-genes. IL-4-induced sIgM expression was associated with increased receptor signalling activity, measured by anti-IgM-induced calcium mobilization, and with increased expression of CD79B messenger RNA and protein, and the "mature" glycoform of sIgM. Importantly, the ability of the BCR-associated kinase inhibitors idelalisib and ibrutinib, approved for treatment of CLL and other B-cell malignancies, to inhibit anti-IgM-induced signalling was reduced following IL-4 pretreatment in samples from the majority of patients. In contrast to stimulatory effects on sIgM, IL-4 decreased CXCR4 and CXCR5 expression; therefore, CLL cells, particularly within the progressive unmutated V-gene subset, may harness the ability of IL-4 to promote BCR signalling and B-cell retention within lymph nodes. Effects of IL-4 were mediated via JAK3/STAT6 and we propose a potential role for JAK inhibitors in combination with BCR kinase inhibitors for the treatment of CLL.

Cyclin-Dependent Kinase Inhibitor P1446A Induces Apoptosis in a JNK/p38 MAPK-Dependent Manner in Chronic Lymphocytic Leukemia B-Cells

CDK (cyclin-dependent kinase) inhibitors have shown remarkable activity in CLL, where its efficacy has been linked to inhibition of the transcriptional CDKs (7 and 9) and deregulation of RNA polymerase and short-lived pro-survival proteins such as MCL1. Furthermore, ER (endoplasmic reticulum) stress has been implicated in CDK inhibition in CLL. Here we conducted a pre-clinical study of a novel orally active kinase inhibitor P1446A in CLL B-cells. P1446A inhibited CDKs at nanomolar concentrations and induced rapid apoptosis of CLL cells in vitro, irrespective of chromosomal abnormalities or IGHV mutational status. Apoptosis preceded inactivation of RNA polymerase, and was accompanied by phosphorylation of stress kinases JNK (c-Jun N-terminal kinase) and p38 MAPK (mitogen-activated protein kinase). Pharmacologic inhibitors of JNK/p38 MAPK conferred protection from P1446A-mediated apoptosis. Treatment with P1446A led to a dramatic induction of NOXA in a JNK-dependent manner, and sensitized CLL cells to ABT-737, a BH3-mimetic. We observed concurrent activation of apoptosis stress-inducing kinase 1 (ASK1) and its interaction with inositol-requiring enzyme 1 (IRE1) and tumor necrosis factor receptor-associated factor 2 (TRAF2) in CLL cells treated with P1446A, providing insights into upstream regulation of JNK in this setting. Consistent with previous reports on limited functionality of ER stress mechanism in CLL cells, treatment with P1446A failed to induce an extensive unfolded protein response. This study provides rationale for additional investigations of P1446A in CLL.

Engagement of the B-cell receptor of chronic lymphocytic leukemia cells drives global and MYC-specific mRNA translation

Antigenic stimulation via the B-cell receptor (BCR) is a major driver of the proliferation and survival of chronic lymphocytic leukemia (CLL) cells. However, the precise mechanisms by which BCR stimulation leads to accumulation of malignant cells remain incompletely understood. Here, we investigated the ability of BCR stimulation to increase messenger RNA (mRNA) translation, which can promote carcinogenesis by effects on both global mRNA translation and upregulated expression of specific oncoproteins. Re-analysis of gene expression profiles revealed striking upregulation of pathways linked to mRNA translation both in CLL cells derived from lymph nodes, the major site of antigen stimulation in vivo, and after BCR stimulation in vitro. Anti-IgM significantly increased mRNA translation in primary CLL cells, measured using bulk metabolic labeling and a novel flow cytometry assay to quantify responses at a single-cell level. These translational responses were suppressed by inhibitors of BTK (ibrutinib) and SYK (tamatinib). Anti-IgM-induced mRNA translation was associated with increased expression of translation initiation factors eIF4A and eIF4GI, and reduced expression of the eIF4A inhibitor, PDCD4. Anti-IgM also increased mRNA translation in normal blood B cells, but without clear modulatory effects on these factors. In addition, anti-IgM increased translation of mRNA-encoding MYC, a major driver of disease progression. mRNA translation is likely to be an important mediator of the growth-promoting effects of antigen stimulation acting, at least in part, via translational induction of MYC. Differences in mechanisms of translational regulation in CLL and normal B cells may provide opportunities for selective therapeutic attack.

The PI3K/mTOR inhibitor PF-04691502 induces apoptosis and inhibits microenvironmental signaling in CLL and the Eµ-TCL1 mouse model

PF-04691502 induces potent apoptosis in CLL cells and suppresses prosurvival anti–immunoglobulin M signaling and CXCL12-induced migration. PF-04691502 displays powerful antitumor effects in vivo in the Eμ-TCL1 mouse model.

Stress equips CLL cells to survive

In this issue of Blood, Krysov et al demonstrate that B-cell receptor (BCR) signaling in chronic lymphocytic leukemia (CLL) results in partial activation of the unfolded protein response (UPR).