Constitutive activation of Akt contributes to the pathogenesis and survival of mantle cell lymphoma

The dual HCK/BTK inhibitor KIN-8194 impairs growth and integrin-mediated adhesion of BTKi-resistant mantle cell lymphoma

Although Bruton's tyrosine kinase (BTK) inhibitors (BTKi) have significantly improved patient prognosis, mantle cell lymphoma (MCL) is still considered incurable due to primary and acquired resistance. We have recently shown that aberrant expression of the Src-family tyrosine kinase hematopoietic cell kinase (HCK) in MCL correlates with poor prognosis, and that genetic HCK perturbation impairs growth and integrin-mediated adhesion of MCL cells. Here, we show that KIN-8194, a dual inhibitor of BTK and HCK with in vivo activity against Myd88-L265P-driven diffuse large B-cell lymphoma and Waldenström Macroglobulinemia, has a potent growth inhibitory effect in MCL cell lines and primary MCL cells, irrespective of their sensitivity to BTKi (ibrutinib and acalabrutinib). In BTKi-resistant cells this is mediated by inhibition of HCK, which results in repression of AKT-S6 signaling. In addition, KIN-8194 inhibits integrin-mediated adhesion of BTKi-sensitive and insensitive MCL cells to fibronectin and stromal cells in an HCK-dependent manner. Finally, we show that MCL cells with acquired BTKi resistance retain their sensitivity to KIN-8194. Taken together, our data demonstrate that KIN-8194 inhibits growth and integrin-mediated adhesion of BTKi-sensitive MCL cells, as well as MCL cells with primary or acquired BTKi resistance. This renders KIN-8194 a promising novel treatment for MCL patients.

Duvelisib plus romidepsin in relapsed/refractory T cell lymphomas: a phase 1b/2a trial

PI3K-δ inhibitors have shown impressive activity in lymphoid malignancies but have been hampered by autoimmune and infectious toxicities, leading to market withdrawals. We previously demonstrated activity of the PI3K-δγ inhibitor duvelisib in T cell lymphomas (TCLs) that was associated with inflammatory adverse events. As reported here, we conducted a phase 1b/2a study of duvelisib in combination with either romidepsin (n = 66) or bortezomib (n = 32) in patients with relapsed/refractory TCL and found that the addition of romidepsin, but not bortezomib, appeared to increase efficacy while attenuating PI3K inhibitor-driven toxicity. The primary endpoint of the study was to determine the safety and maximum tolerated dose of duvelisib, which was 75 mg twice daily when combined with romidepsin versus 25 mg twice daily when combined with bortezomib. The most common adverse events were neutropenia (42%, 25/59) and fatigue (37%, 22/59) in patients treated with duvelisib and romidepsin and diarrhea (48%, 11/23) and neutropenia (30%, 7/23) in patients treated with duvelisib and bortezomib. Duvelisib and romidepsin resulted in less grade 3/4 hepatotoxicity (14%, 8/59) compared to 40% (14/35) in our previous study with duvelisib monotherapy. This was associated with reductions in circulating inflammatory mediators and myeloid cell inflammatory gene expression. Secondary endpoints of overall and complete response rates were 55% (35/64) and 34% (22/64) for patients treated with duvelisib and romidepsin and 34% (11/32) and 13% (4/32) for patients treated with duvelisib and bortezomib. Among patients with peripheral T cell lymphomas (PTCLs), overall and complete response rates of duvelisib and romidepsin were 56% (27/48) and 44% (21/48), respectively, with exploratory analyses showing increased response rates in patients with a follicular helper T cell subtype. These findings support further development of combined PI3K and histone deacetylase (HDAC) inhibition in TCLs and suggest a unique strategy to enable PI3K inhibitor-based combinations for additional patient populations. ClinicalTrials.gov identifier: NCT02783625 .

B-cell receptor signaling activity identifies patients with mantle cell lymphoma at higher risk of progression

Mantle cell lymphoma (MCL) is an incurable B-cell malignancy characterized by a high clinical variability. Therefore, there is a critical need to define parameters that identify high-risk patients for aggressive disease and therapy resistance. B-cell receptor (BCR) signaling is crucial for MCL initiation and progression and is a target for therapeutic intervention. We interrogated BCR signaling proteins (SYK, LCK, BTK, PLCγ2, p38, AKT, NF-κB p65, and STAT5) in 30 primary MCL samples using phospho-specific flow cytometry. Anti-IgM modulation induced heterogeneous BCR signaling responses among samples allowing the identification of two clusters with differential responses. The cluster with higher response was associated with shorter progression free survival (PFS) and overall survival (OS). Moreover, higher constitutive AKT activity was predictive of inferior response to the Bruton's tyrosine kinase inhibitor (BTKi) ibrutinib. Time-to-event analyses showed that MCL international prognostic index (MIPI) high-risk category and higher STAT5 response were predictors of shorter PFS and OS whilst MIPI high-risk category and high SYK response predicted shorter OS. In conclusion, we identified BCR signaling properties associated with poor clinical outcome and resistance to ibrutinib, thus highlighting the prognostic and predictive significance of BCR activity and advancing our understanding of signaling heterogeneity underlying clinical behavior of MCL.

A phase 2 study of the PI3Kδ inhibitor parsaclisib in relapsed and refractory marginal zone lymphoma (CITADEL-204)

ABSTRACT

Parsaclisib, a potent and highly selective PI3Kδ inhibitor, has shown clinical benefit in patients with relapsed or refractory (R/R) B-cell lymphomas. The phase 2 CITADEL-204 study (NCT03144674, EudraCT 2017-000970-12) assessed efficacy and safety of parsaclisib in Bruton tyrosine kinase (BTK) inhibitor-experienced (cohort 1) or BTK inhibitor-naive (cohort 2) patients with R/R marginal zone lymphoma (MZL). Patients aged ≥18 years with histologically confirmed R/R MZL, treated with ≥1 prior systemic therapy (including ≥1 anti-CD20 antibody) received parsaclisib 20 mg once daily for 8 weeks then 20 mg once weekly (weekly dosing group [WG]) or parsaclisib 20 mg once daily for 8 weeks then 2.5 mg once daily (daily dosing group [DG]); DG was selected for further assessment. Primary end point of the study was objective response rate (ORR). Owing to slower than expected recruitment, cohort 1 was closed with 10 patients (WG, n = 4; DG, n = 6) enrolled. Based on a planned interim analysis in cohort 2, the futility boundary was not crossed, and enrollment continued to study completion. At data cutoff (15 January 2021), 100 patients were enrolled and treated in cohort 2 (WG, n = 28; DG, n = 72). In the DG, the ORR was 58.3% (95% confidence interval [CI], 46.1-69.8), with a complete response rate of 4.2% (95% CI, 0.9-11.7); the lower bound of the ORR 95% CI exceeded the protocol-defined threshold of 40%. The median duration of response was 12.2 months (95% CI, 8.1-17.5) and progression-free survival was 16.5 months (95% CI, 11.5-20.6); median overall survival was not reached. The most common treatment-emergent adverse events (TEAEs) among all patients were diarrhea (47.0%), cough (23.0%), and rash (18.0%); the most common grade ≥3 TEAEs included diarrhea (12.0%), neutropenia, and pneumonia (9.0% each). TEAEs led to dose interruptions, reductions, and discontinuations in 56.0%, 16.0%, and 29.0% of all patients, respectively. Durable responses and an overall manageable safety profile were demonstrated in patients with R/R MZL treated with parsaclisib monotherapy.

Inhibition of a new AXL isoform, AXL3, induces apoptosis of mantle cell lymphoma cells

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma having a poor overall survival that is in need for the development of new therapeutics. In this study, we report the identification and expression of a new isoform splice variant of the tyrosine kinase receptor AXL in MCL cells. This new AXL isoform, called AXL3, lacks the ligand-binding domain of the commonly described AXL splice variants and is constitutively activated in MCL cells. Interestingly, functional characterization of AXL3, using CRISPR inhibition, revealed that only the knock down of this isoform leads to apoptosis of MCL cells. Importantly, pharmacological inhibition of AXL activity resulted in a significant decrease in the activation of well-known proproliferative and survival pathways activated in MCL cells (ie, β-catenin, Ak strain transforming, and NF-κB). Therapeutically, preclinical studies using a xenograft mouse model of MCL indicated that bemcentinib is more effective than ibrutinib in reducing the tumor burden and to increase the overall survival. Our study highlights the importance of a previously unidentified AXL splice variant in cancer and the potential of bemcentinib as a targeted therapy for MCL.

Beyond Bruton's tyrosine kinase inhibitors in mantle cell lymphoma: bispecific antibodies, antibody-drug conjugates, CAR T-cells, and novel agents

Mantle cell lymphoma is a B cell non-Hodgkin lymphoma (NHL), representing 2-6% of all NHLs and characterized by overexpression of cyclin D1. The last decade has seen the development of many novel treatment approaches in MCL, most notably the class of Bruton's tyrosine kinase inhibitors (BTKi). BTKi has shown excellent outcomes for patients with relapsed or refractory MCL and is now being studied in the first-line setting. However, patients eventually progress on BTKi due to the development of resistance. Additionally, there is an alteration in the tumor microenvironment in these patients with varying biological and therapeutic implications. Hence, it is necessary to explore novel therapeutic strategies that can be effective in those who progressed on BTKi or potentially circumvent resistance. In this review, we provide a brief overview of BTKi, then discuss the various mechanisms of BTK resistance including the role of genetic alteration, cancer stem cells, tumor microenvironment, and adaptive reprogramming bypassing the effect of BTK inhibition, and then provide a comprehensive review of current and emerging therapeutic options beyond BTKi including novel agents, CAR T cells, bispecific antibodies, and antibody-drug conjugates.

Insights on hematopoietic cell kinase: An oncogenic player in human cancer

Hematopoietic cell kinase (Hck) is a member of the Src family and is expressed in hematopoietic cells. By regulating multiple signaling pathways, HCK can interact with multiple receptors to regulate signaling events involved in cell adhesion, proliferation, migration, invasion, apoptosis, and angiogenesis. However, aberrant expression of Hck in various hematopoietic cells and solid tumors plays a crucial role in tumor-related properties, including cell proliferation and epithelial-mesenchymal transition. In addition, Hck signaling regulates the function of immune cells such as macrophages, contributing to an immunosuppressive tumor microenvironment. The clinical success of various kinase inhibitors targeting the Src kinase family has validated the efficacy of targeting Src, and therapies with highly selective Hck kinase inhibitors are in clinical trials. This article reviews Hck inhibition as an emerging cancer treatment strategy, focusing on the expressions and functions of Hck in tumors and its impact on the tumor microenvironment. It also explores preclinical and clinical pharmacological strategies for Hck targeting to shed light on Hck-targeted tumor therapy.

First Report of FARSA in the Regulation of Cell Cycle and Survival in Mantle Cell Lymphoma Cells via PI3K-AKT and FOXO1-RAG1 Axes

Cancer-associated factors have been largely identified in the understanding of tumorigenesis and progression. However, aminoacyl-transfer RNA (tRNA) synthetases (aaRSs) have so far been neglected in cancer research due to their canonical activities in protein translation and synthesis. FARSA, the alpha subunit of the phenylalanyl-tRNA synthetase is elevated across many cancer types, but its function in mantle cell lymphoma (MCL) remains undetermined. Herein, we found the lowest levels of FARSA in patients with MCL compared with other subtypes of lymphomas, and the same lower levels of FARSA were observed in chemoresistant MCL cell lines. Unexpectedly, despite the essential catalytic roles of FARSA, knockdown of FARSA in MCL cells did not lead to cell death but resulted in accelerated cell proliferation and cell cycle, whereas overexpression of FARSA induced remarkable cell-cycle arrest and overwhelming apoptosis. Further RNA sequencing (RNA-seq) analysis and validation experiments confirmed a strong connection between FARSA and cell cycle in MCL cells. Importantly, FARSA leads to the alteration of cell cycle and survival via both PI3K-AKT and FOXO1-RAG1 axes, highlighting a FARSA-mediated regulatory network in MCL cells. Our findings, for the first time, reveal the noncanonical roles of FARSA in MCL cells, and provide novel insights into understanding the pathogenesis and progression of B-cell malignancies.

Rafting on the Plasma Membrane: Lipid Rafts in Signaling and Disease

The plasma membrane is not a uniform phospholipid bilayer; it has specialized membrane nano- or microdomains called lipid rafts. Lipid rafts are small cholesterol and sphingolipid-rich plasma membrane islands. Although their existence was long debated, their presence in the plasma membrane of living cells is now well accepted with the advent of super-resolution imaging techniques. It is interesting to note that lipid rafts function to compartmentalize receptors and their regulators and substantially modulate cellular signaling. In this review, we will examine the role of lipid rafts and caveolae-lipid raft-like microdomains with a distinct 3D morphology-in cellular signaling. Moreover, we will investigate how raft compartmentalized signaling regulates diverse physiological processes such as proliferation, apoptosis, immune signaling, and development. Also, the deregulation of lipid raft-mediated signaling during tumorigenesis and metastasis will be explored.

A ROR1 Small Molecule Inhibitor (KAN0441571C) Induced Significant Apoptosis of Mantle Cell Lymphoma (MCL) Cells

The receptor tyrosine kinase orphan receptor 1 (ROR1) is absent in most normal adult tissues but overexpressed in various malignancies and is of importance for tumor cell survival, proliferation, and metastasis. In this study, we evaluated the apoptotic effects of a novel small molecule inhibitor of ROR1 (KAN0441571C) as well as venetoclax (BCL-2 inhibitor), bendamustine, idelalisib (PI3Kδ inhibitor), everolimus (mTOR inhibitor), and ibrutinib (BTK inhibitor) alone or in combination in human MCL primary cells and cell lines. ROR1 expression was evaluated by flow cytometry and Western blot (WB). Cytotoxicity was analyzed by MTT and apoptosis by Annexin V/PI staining as well as signaling and apoptotic proteins (WB). ROR1 was expressed both in patient-derived MCL cells and human MCL cell lines. KAN0441571C alone induced significant time- and dose-dependent apoptosis of MCL cells. Apoptosis was accompanied by decreased expression of MCL-1 and BCL-2 and cleavage of PARP and caspase 3. ROR1 was dephosphorylated as well as ROR1-associated signaling pathway molecules, including the non-canonical WNT signaling pathway (PI3Kδ/AKT/mTOR). The combination of KAN0441571C and ibrutinib, venetoclax, idelalisib, everolimus, or bendamustine had a synergistic apoptotic effect and significantly prevented phosphorylation of ROR1-associated signaling molecules as compared to KAN0441571C alone. Our results suggest that targeting ROR1 by a small molecule inhibitor, KAN0441571C, should be further evaluated particularly in combination with other targeting drugs as a new therapeutic approach for MCL.

Protein Kinase CK2 represents a new target to boost Ibrutinib and Venetoclax induced cytotoxicity in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an incurable B cell non-Hodgkin lymphoma, characterized by frequent relapses. In the last decade, the pro-survival pathways related to BCR signaling and Bcl-2 have been considered rational therapeutic targets in B cell derived lymphomas. The BTK inhibitor Ibrutinib and the Bcl-2 inhibitor Venetoclax are emerging as effective drugs for MCL. However, primary and acquired resistance also to these agents may occur. Protein Kinase CK2 is a S/T kinase overexpressed in many solid and blood-derived tumours. CK2 promotes cancer cell growth and clonal expansion, sustaining pivotal survival signaling cascades, such as the ones dependent on AKT, NF-κB, STAT3 and others, counteracting apoptosis through a “non-oncogene” addiction mechanism. We previously showed that CK2 is overexpressed in MCL and regulates the levels of activating phosphorylation on S529 of the NF-κB family member p65/RelA. In the present study, we investigated the effects of CK2 inactivation on MCL cell proliferation, survival and apoptosis and this kinase’s involvement in the BCR and Bcl-2 related signaling. By employing CK2 loss of function MCL cell models, we demonstrated that CK2 sustains BCR signaling (such as BTK, NF-κB and AKT) and the Bcl-2-related Mcl-1 expression. CK2 inactivation enhanced Ibrutinib and Venetoclax-induced cytotoxicity. The demonstration of a CK2-dependent upregulation of pathways that may antagonize the effect of these drugs may offer a novel strategy to overcome primary and secondary resistance.

Regulation of B-Cell Receptor Signaling and Its Therapeutic Relevance in Aggressive B-Cell Lymphomas

The proliferation and survival signals emanating from the B-cell receptor (BCR) constitute a crucial aspect of mature lymphocyte's life. Dysregulated BCR signaling is considered a potent contributor to tumor survival in different subtypes of B-cell non-Hodgkin lymphomas (B-NHLs). In the last decade, the emergence of BCR-associated kinases as rational therapeutic targets has led to the development and approval of several small molecule inhibitors targeting either Bruton's tyrosine kinase (BTK), spleen tyrosine kinase (SYK), or phosphatidylinositol 3 kinase (PI3K), offering alternative treatment options to standard chemoimmunotherapy, and making some of these drugs valuable assets in the anti-lymphoma armamentarium. Despite their initial effectiveness, these precision medicine strategies are limited by primary resistance in aggressive B-cell lymphoma such as diffuse large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL), especially in the case of first generation BTK inhibitors. In these patients, BCR-targeting drugs often fail to produce durable responses, and nearly all cases eventually progress with a dismal outcome, due to secondary resistance. This review will discuss our current understanding of the role of antigen-dependent and antigen-independent BCR signaling in DLBCL and MCL and will cover both approved inhibitors and investigational molecules being evaluated in early preclinical studies. We will discuss how the mechanisms of action of these molecules, and their off/on-target effects can influence their effectiveness and lead to toxicity, and how our actual knowledge supports the development of more specific inhibitors and new, rationally based, combination therapies, for the management of MCL and DLBCL patients.

P300/CBP inhibition sensitizes mantle cell lymphoma to PI3Kδ inhibitor idelalisib

Mantle cell lymphoma (MCL) is a lymphoproliferative disorder lacking reliable therapies. PI3K pathway contributes to the pathogenesis of MCL, serving as a potential target. However, idelalisib, an FDA-approved drug targeting PI3Kδ, has shown intrinsic resistance in MCL treatment. Here we report that a p300/CBP inhibitor, A-485, could overcome resistance to idelalisib in MCL cells in vitro and in vivo. A-485 was discovered in a combinational drug screening from an epigenetic compound library containing 45 small molecule modulators. We found that A-485, the highly selective catalytic inhibitor of p300 and CBP, was the most potent compound that enhanced the sensitivity of MCL cell line Z-138 to idelalisib. Combination of A-485 and idelalisib remarkably decreased the viability of three MCL cell lines tested. Co-treatment with A-485 and idelalisib in Maver-1 and Z-138 MCL cell xenograft mice for 3 weeks dramatically suppressed the tumor growth by reversing the unsustained inhibition in PI3K downstream signaling. We further demonstrated that p300/CBP inhibition decreased histone acetylation at RTKs gene promoters and reduced transcriptional upregulation of RTKs, thereby inhibiting the downstream persistent activation of MAPK/ERK signaling, which also contributed to the pathogenesis of MCL. Therefore, additional inhibition of p300/CBP blocked MAPK/ERK signaling, which rendered maintaining activation to PI3K-mTOR downstream signals p-S6 and p-4E-BP1, thus leading to suppression of cell growth and tumor progression and eliminating the intrinsic resistance to idelalisib ultimately. Our results provide a promising combination therapy for MCL and highlight the potential use of epigenetic inhibitors targeting p300/CBP to reverse drug resistance in tumor.

Preclinical Evaluation of the HDAC Inhibitor Chidamide in Transformed Follicular Lymphoma

The key factors leading to transformed follicular lymphoma (t-FL) include the aberrations of epigenetic modifiers as early and driving events, especially mutations in the gene encoding for histone acetyltransferase. Therefore, reversal of this phenomenon by histone deacetylase (HDAC) inhibitors is essential for the development of new treatment strategies in t-FL. Several t-FL cell lines were treated with various doses of chidamide and subjected to cell proliferation, apoptosis and cell cycle analyses with CCK-8 assay, Annexin V/PI assay and flow cytometry, respectively. Chidamide dose-dependently inhibited cell proliferation, caused G0/G1 cycle arrest and triggered apoptosis in t-FL cells. In addition, the effects of chidamide on tumor growth were evaluated in vivo in xenograft models. RNA-seq analysis revealed gene expression alterations involving the PI3K-AKT signaling pathway might account for the mechanism underlying the antitumor activity of chidamide as a single agent in t-FL. These findings provide a basis for further clinical exploration of chidamide as a promising treatment for FL.

DCZ0014, a novel compound in the therapy of diffuse large B-cell lymphoma via the B cell receptor signaling pathway

Diffuse large B cell lymphoma (DLBCL) is a clinical and genetically heterogeneous lymphoid malignancy. Although R-CHOP (rituximab plus cyclophosphamide, vincristine, doxorubicin, and prednisone) treatment can improve the survival rate of patients with DLBCL, more than 30% of patients exhibit treatment failure, relapse, or refractory disease. Therefore, novel drugs or targeted therapies are needed to improve the survival of patients with DLBCL. The compound DCZ0014 is a novel chemical similar to berberine. In this study, we found that DCZ0014 significantly inhibited the proliferation and activity of DLBCL cells, and induced cell apoptosis. Following treatment with DCZ0014, DLBCL cells accumulated in G0/G1-phase of the cell cycle and showed decreased mitochondrial membrane potential. Additionally, DCZ0014 inhibited DNA synthesis, enhanced DNA damage in DLBCL cells, as well as inhibited Lyn/Syk in B cell receptor signaling pathway. Further experiments demonstrated that DCZ0014 did not significantly affect peripheral blood mononuclear cells. Tumor xenograft model showed that DCZ0014 not only inhibited tumor growth but also extended the survival time of mice. Thus, DCZ0014 showed potential for clinical application in the treatment of patients with DLBCL.

Protein Kinase CK1α Sustains B-Cell Receptor Signaling in Mantle Cell Lymphoma

Mantle Cell Lymphoma (MCL) is still an incurable B-cell malignancy characterized by poor prognosis and frequent relapses. B Cell Receptor (BCR) signaling inhibitors, in particular of the kinases BTK and PI3Kγ/δ, have demonstrated clinically meaningful anti-proliferative effects in B cell tumors. However, refractoriness to these drugs may develop, portending a dismal prognosis. Protein kinase CK1α is an emerging pro-growth enzyme in B cell malignancies. In multiple myeloma, this kinase sustains β-catenin and AKT-dependent survival and is involved in the activation of NF-κB in B cells. In this study, we analyzed the role of CK1α on MCL cell survival and proliferation, on the regulation of BCR-related BTK, NF-κB, PI3K/AKT signaling cascades and the effects of CK1α chemical inhibition or gene silencing in association with the BTK inhibitor Ibrutinib or the PI3Kγ/δ inhibitor Duvelisib. CK1α was found highly expressed in MCL cells as compared to normal B cells. The inactivation/loss of CK1α caused MCL cell apoptosis and proliferation arrest. CK1α sustained BCR signaling, in particular the NF-κB, AKT and BTK pathways by modulating the phosphorylation of Ser 652 on CARD11, Ser 536 p65 on NF-κB, Ser 473 on AKT, Tyr 223 on BTK, as well as the protein levels. We also provided evidence that CK1α-mediated regulation of CARD11 and BTK likely implicates a physical interaction. The combination of CK1α inhibition with Ibrutinib or Duvelisib synergistically increased cytotoxicity, leading to a further decrease of the activation of BCR signaling pathways. Therefore, CK1α sustains MCL growth through the regulation of BCR-linked survival signaling cascades and protects from Ibrutinib/Duvelisib-induced apoptosis. Thus, CK1α could be considered as a rational molecular target for the treatment of MCL, in association with novel agents.

Migration and Adhesion of B-Lymphocytes to Specific Microenvironments in Mantle Cell Lymphoma: Interplay between Signaling Pathways and the Epigenetic Landscape

Lymphocyte migration to and sequestration in specific microenvironments plays a crucial role in their differentiation and survival. Lymphocyte trafficking and homing are tightly regulated by signaling pathways and is mediated by cytokines, chemokines, cytokine/chemokine receptors and adhesion molecules. The production of cytokines and chemokines is largely controlled by transcription factors in the context of a specific epigenetic landscape. These regulatory factors are strongly interconnected, and they influence the gene expression pattern in lymphocytes, promoting processes such as cell survival. The epigenetic status of the genome plays a key role in regulating gene expression during many key biological processes, and it is becoming more evident that dysregulation of epigenetic mechanisms contributes to cancer initiation, progression and drug resistance. Here, we review the signaling pathways that regulate lymphoma cell migration and adhesion with a focus on Mantle cell lymphoma and highlight the fundamental role of epigenetic mechanisms in integrating signals at the level of gene expression throughout the genome.

AKT signaling restrains tumor suppressive functions of FOXO transcription factors and GSK3 kinase in multiple myeloma

The phosphatidylinositide-3 kinases and the downstream mediator AKT drive survival and proliferation of multiple myeloma (MM) cells. AKT signaling is active in MM and has pleiotropic effects; however, the key molecular aspects of AKT dependency in MM are not fully clear. Among the various downstream AKT targets are the Forkhead box O (FOXO) transcription factors (TFs) and glycogen synthase kinase 3 (GSK3), which are negatively regulated by AKT signaling. Here we show that abrogation of AKT signaling in MM cells provokes cell death and cell cycle arrest, which crucially depends on both FOXO TFs and GSK3. Based on gene expression profiling, we defined a FOXO-repressed gene set that has prognostic significance in a large cohort of patients with MM, indicating that AKT-mediated gene activation is associated with inferior overall survival. We further show that AKT signaling stabilizes the antiapoptotic myeloid cell leukemia 1 (MCL1) protein by inhibiting FOXO- and GSK3-mediated MCL1 turnover. In concordance, abrogation of AKT signaling greatly sensitized MM cells for an MCL1-targeting BH3-mimetic, which is currently in clinical development. Taken together, our results indicate that AKT activity is required to restrain the tumor-suppressive functions of FOXO and GSK3, thereby stabilizing the antiapoptotic protein MCL1 in MM. These novel insights into the role of AKT in MM pathogenesis and MCL1 regulation provide opportunities to improve targeted therapy for patients with MM.

Deferasirox induces cyclin D1 degradation and apoptosis in mantle cell lymphoma in a reactive oxygen species- and GSK3β-dependent mechanism

Mantle cell lymphoma (MCL) is a difficult-to-treat B-cell malignancy characterized by cyclin D1 (CD1) overexpression. Targeting CD1 in MCL has been shown to be of therapeutic significance. However, treatment of MCL remains challenging since patients are still subject to early and frequent relapse of the disease. To ensure their high proliferation rate, tumour cells have increased iron needs, making them more susceptible to iron deprivation. Indeed, several iron chelators proved to be effective anti-cancer agents. In this study, we demonstrate that the clinically approved iron chelator deferasirox (DFX) exerts an anti-tumoural effect in MCL cell lines and patient cells. The exposure of MCL cells to clinically feasible concentrations of DFX resulted in growth inhibition, cell cycle arrest and induction of apoptosis. We show that DFX unfolds its cytotoxic effect by a rapid induction of reactive oxygen species (ROS) that leads to oxidative stress and severe DNA damage and by triggering CD1 proteolysis in a mechanism that requires its phosphorylation on T286 by glycogen synthase kinase-3β (GSK3β). Moreover, we demonstrate that DFX mediates CD1 proteolysis by repressing the phosphatidylinositol 3-kinase (PI3K)/AKT/GSK3β pathway via ROS generation. Our data suggest DFX as a potential therapeutic option for MCL and paves the way for more treatment options for these patients.

Targeting Casein Kinase 1 (CK1) in Hematological Cancers

The casein kinase 1 enzymes (CK1) form a family of serine/threonine kinases with seven CK1 isoforms identified in humans. The most important substrates of CK1 kinases are proteins that act in the regulatory nodes essential for tumorigenesis of hematological malignancies. Among those, the most important are the functions of CK1s in the regulation of Wnt pathways, cell proliferation, apoptosis and autophagy. In this review we summarize the recent developments in the understanding of biology and therapeutic potential of the inhibition of CK1 isoforms in the pathogenesis of chronic lymphocytic leukemia (CLL), other non-Hodgkin lymphomas (NHL), myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and multiple myeloma (MM). CK1δ/ε inhibitors block CLL development in preclinical models via inhibition of WNT-5A/ROR1-driven non-canonical Wnt pathway. While no selective CK1 inhibitors have reached clinical stage to date, one dual PI3Kδ and CK1ε inhibitor, umbralisib, is currently in clinical trials for CLL and NHL patients. In MDS, AML and MM, inhibition of CK1α, acting via activation of p53 pathway, showed promising preclinical activities and the first CK1α inhibitor has now entered the clinical trials.

Linking Immunoevasion and Metabolic Reprogramming in B-Cell-Derived Lymphomas

Lymphomas represent a diverse group of malignancies that emerge from lymphocytes. Despite improvements in diagnosis and treatment of lymphomas of B-cell origin, relapsed and refractory disease represents an unmet clinical need. Therefore, it is of utmost importance to better understand the lymphomas’ intrinsic features as well as the interactions with their cellular microenvironment for developing novel therapeutic strategies. In fact, the role of immune-based approaches is steadily increasing and involves amongst others the use of monoclonal antibodies against tumor antigens, inhibitors of immunological checkpoints, and even genetically modified T-cells. Metabolic reprogramming and immune escape both represent well established cancer hallmarks. Tumor metabolism as introduced by Otto Warburg in the early 20th century promotes survival, proliferation, and therapeutic resistance. Simultaneously, malignant cells employ a plethora of mechanisms to evade immune surveillance. Increasing evidence suggests that metabolic reprogramming does not only confer cell intrinsic growth and survival advantages to tumor cells but also impacts local as well as systemic anti-tumor immunity. Tumor and immune cells compete over nutrients such as carbohydrates or amino acids that are critical for the immune cell function. Moreover, skewed metabolic pathways in malignant cells can result in abundant production and release of bioactive metabolites such as lactic acid, kynurenine or reactive oxygen species (ROS) that affect immune cell fitness and function. This “metabolic re-modeling” of the tumor microenvironment shifts anti-tumor immune reactivity toward tolerance. Here, we will review molecular events leading to metabolic alterations in B-cell lymphomas and their impact on anti-tumor immunity.

Can Next-Generation PI3K Inhibitors Unlock the Full Potential of the Class in Patients With B-Cell Lymphoma?

Although outcomes after first-line therapy for patients with indolent or aggressive non-Hodgkin lymphoma (NHL) are continually improving, relapse is still common. Current treatment options for patients with relapsed or refractory disease have limited efficacy, and various targeted therapies are under investigation to help improve outcomes in this patient population. The phosphatidylinositol 3-kinase (PI3K) pathway was identified as being involved in hematologic malignancies, leading to significant research for potential therapeutic agents. This has led to 3 PI3K inhibitors (idelalisib, copanlisib, and duvelisib) being approved for the treatment of patients with relapsed or refractory follicular lymphoma who have received at least 2 prior systemic therapies, with reported response rates of 40% to 59%. With potential class-specific and PI3K isoform-related toxicities that may limit clinical utility, the safety of the approved PI3K inhibitors has been carefully evaluated to weigh the risk/benefit ratio of therapy. Currently, there are no approved PI3K inhibitors for patients with aggressive NHL. A number of newer PI3K inhibitors are in clinical development for the treatment of relapsed or refractory NHL, aiming to improve treatment benefit for patients. We discuss a number of attributes that are important to increase the therapeutic potential of newer PI3K inhibitors. More promising results may come from combination trials with these newer PI3K inhibitors, developed to limit toxicities (including long-term adverse events), and other antitumor agents.

Mantle cell lymphoma: insights into therapeutic targets at the preclinical level

INTRODUCTION

Mantle cell lymphoma (MCL) is a chronically relapsing B-cell non-Hodgkin lymphoma characterized by recurrent molecular-cytogenetic aberrations that lead to deregulation of DNA damage response, cell cycle progression, epigenetics, apoptosis, proliferation, and motility. In the last 10 years, clinical approval of several innovative drugs dramatically changed the landscape of treatment options in the relapsed/refractory (R/R) MCL, which translated into significantly improved survival parameters.

AREAS COVERED

Here, up-to-date knowledge on the biology of MCL together with currently approved and clinically tested frontline and salvage therapies are reviewed. In addition, novel therapeutic targets in MCL based on the scientific reports published in Pubmed are discussed.

EXPERT OPINION

Bruton tyrosine-kinase inhibitors, NFkappaB inhibitors, BCL2 inhibitors, and immunomodulary agents in combination with monoclonal antibodies and genotoxic drugs have the potential to induce long-term remissions in majority of newly diagnosed MCL patients. Several other classes of anti-tumor drugs including phosphoinositole-3-kinase, cyclin-dependent kinase or DNA damage response kinase inhibitors have demonstrated promising anti-lymphoma efficacy in R/R MCL. Most importantly, adoptive immunotherapy with genetically modified T-cells carrying chimeric antigen receptor represents a potentially curative treatment approach even in the patients with chemotherapy and ibrutinib-refractory disease.

Blastoid Mantle Cell Lymphoma

Blastoid and pleomorphic mantle cell lymphoma (MCL) are among the worst prognostic, aggressive histology, high-risk variants of MCL, and, in this article, they are presented as blastoid MCL. Blastoid MCL have not been systematically studied, probably due to their rarity. De novo blastoid MCLs have superior outcomes compared with transformed MCL. Compared with classic MCL, extranodal involvement (mainly skin, central nervous system), frequent relapses, and inferior responses to conventional chemoimmunotherapy, BTK inhibitors and venetoclax are frequent in blastoid MCL. KTE-X19 induces excellent response in blastoid MCL. Combinations with novel agents are actively investigated. This article presents a comprehensive review on blastoid MCL in 2020.

Mantle cell lymphoma

MCL is a well-characterized generally aggressive lymphoma with a poor prognosis. However, patients with a more indolent disease have been reported in whom the initiation of therapy can be delayed without any consequence for the survival. In 2017 the World Health Organization updated the classification of MCL describing two main subtypes with specific molecular characteristics and clinical features, classical and indolent leukaemic nonnodal MCL. Recent research results suggested an improving outcome of this neoplasm. The addition of rituximab to conventional chemotherapy has increased overall response rates, but it did not improve overall survival compared to chemotherapy alone. The use of intensive frontline therapies including rituximab and consolidation with autologous stem cell transplantation ameliorated response rate and prolonged progression-free survival in young fit patients, but any impact on survival remains to be proven. Furthermore, the optimal timing, cytoreductive regimen and conditioning regimen, and the clinical implications of achieving a disease remission even at molecular level remain to be elucidated. The development of targeted therapies as the consequence of better understanding of pathogenetic pathways in MCL might improve the outcome of conventional chemotherapy and spare the toxicity of intense therapy in most patients. Cases not eligible for intensive regimens, may be considered for less demanding therapies, such as the combination of rituximab either with CHOP or with purine analogues, or bendamustine. Allogeneic SCT can be an effective option for relapsed disease in patients who are fit enough and have a compatible donor. Maintenance rituximab may be considered after response to immunochemotherapy as the first-line strategy in a wide range of patients. Finally, since the optimal approach to the management of MCL is still evolving, it is critical that these patients are enrolled in clinical trials to identify the better treatment options.

Inhibition of Skp2 Sensitizes Chronic Myeloid Leukemia Cells to Imatinib

Introduction

Skp2 is an E3 ubiquitin ligase that plays an important role in modulating tumor progression. The mechanisms underlying Skp2 in the promotion of proliferation and its function in the primary resistance to tyrosine kinase inhibitors (TKIs) in human CML remain to be determined. This study aimed to investigate the function of Skp2 in CML progression as well as its effects on TKI sensitivity.

Methods

Expression of Skp2 in leukocytes from patients with CML and normal blood samples was analyzed by qRT-PCR. Cell proliferation was analyzed by EdU incorporation and cell counting assays. Luciferase reporter and chromatin immunoprecipitation assays were used for examination of the effects of CREB on Skp2 expression. The apoptosis in vitro of K562 cells was analyzed by MTT and caspase 3/7 activity assays.

Results

The present study demonstrates that Skp2 was expressed at a higher level in patients with CML compared with healthy donors, and the elevated expression of Skp2 is critical for CML cell proliferation. Mechanistically, Skp2 was transcriptionally upregulated by CREB responsive to the PI3K/Akt signaling pathway. Furthermore, inhibition of Skp2 expression by shRNAs or blocking the PI3K/Akt/CREB pathway greatly enhances the sensitivity of CML cells to Imatinib treatment.

Conclusion

We conclude that the PI3K/Akt/CREB axis regulates the sensitivity of K562 cells to Imatinib via mediating Skp2 expression. The present study revealed an unknown role of Skp2 in CML progression and provided new aspects on the Skp2-modulated TKI sensitivity in CML, contributing to the development of potential therapeutic anticancer drugs.

Management of Drug Resistance in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a rare but aggressive B-cell hemopathy characterized by the translocation t(11;14)(q13;q32) that leads to the overexpression of the cell cycle regulatory protein cyclin D1. This translocation is the initial event of the lymphomagenesis, but tumor cells can acquire additional alterations allowing the progression of the disease with a more aggressive phenotype and a tight dependency on microenvironment signaling. To date, the chemotherapeutic-based standard care is largely inefficient and despite the recent advent of different targeted therapies including proteasome inhibitors, immunomodulatory drugs, tyrosine kinase inhibitors, relapses are frequent and are generally related to a dismal prognosis. As a result, MCL remains an incurable disease. In this review, we will present the molecular mechanisms of drug resistance learned from both preclinical and clinical experiences in MCL, detailing the main tumor intrinsic processes and signaling pathways associated to therapeutic drug escape. We will also discuss the possibility to counteract the acquisition of drug refractoriness through the design of more efficient strategies, with an emphasis on the most recent combination approaches.

Lipid rafts as signaling hubs in cancer cell survival/death and invasion: implications in tumor progression and therapy: Thematic Review Series: Biology of Lipid Rafts

Cholesterol/sphingolipid-rich membrane domains, known as lipid rafts or membrane rafts, play a critical role in the compartmentalization of signaling pathways. Physical segregation of proteins in lipid rafts may modulate the accessibility of proteins to regulatory or effector molecules. Thus, lipid rafts serve as sorting platforms and hubs for signal transduction proteins. Cancer cells contain higher levels of intracellular cholesterol and lipid rafts than their normal non-tumorigenic counterparts. Many signal transduction processes involved in cancer development (insulin-like growth factor system and phosphatidylinositol 3-kinase-AKT) and metastasis [cluster of differentiation (CD)44] are dependent on or modulated by lipid rafts. Additional proteins playing an important role in several malignant cancers (e.g., transmembrane glycoprotein mucin 1) are also being detected in association with lipid rafts, suggesting a major role of lipid rafts in tumor progression. Conversely, lipid rafts also serve as scaffolds for the recruitment and clustering of Fas/CD95 death receptors and downstream signaling molecules leading to cell death-promoting raft platforms. The partition of death receptors and downstream signaling molecules in aggregated lipid rafts has led to the formation of the so-called cluster of apoptotic signaling molecule-enriched rafts, or CASMER, which leads to apoptosis amplification and can be pharmacologically modulated. These death-promoting rafts can be viewed as a linchpin from which apoptotic signals are launched. In this review, we discuss the involvement of lipid rafts in major signaling processes in cancer cells, including cell survival, cell death, and metastasis, and we consider the potential of lipid raft modulation as a promising target in cancer therapy.

Parsaclisib Is a Next-Generation Phosphoinositide 3-Kinase δ Inhibitor with Reduced Hepatotoxicity and Potent Antitumor and Immunomodulatory Activities in Models of B-Cell Malignancy

The clinical use of first-generation phosphoinositide 3-kinase (PI3K)δ inhibitors in B-cell malignancies is hampered by hepatotoxicity, requiring dose reduction, treatment interruption, and/or discontinuation of therapy. In addition, potential molecular mechanisms by which resistance to this class of drugs occurs have not been investigated. Parsaclisib (INCB050465) is a potent and selective next-generation PI3Kδ inhibitor that differs in structure from first-generation PI3Kδ inhibitors and has shown encouraging anti-B-cell tumor activity and reduced hepatotoxicity in phase 1/2 clinical studies. Here, we present preclinical data demonstrating parsaclisib as a potent inhibitor of PI3Kδ with over 1000-fold selectivity against other class 1 PI3K isozymes. Parsaclisib directly blocks PI3K signaling-mediated cell proliferation in B-cell lines in vitro and in vivo and indirectly controls tumor growth by lessening immunosuppression through regulatory T-cell inhibition in a syngeneic lymphoma model. Diffuse large B-cell lymphoma cell lines overexpressing MYC were insensitive to proliferation blockade via PI3Kδ signaling inhibition by parsaclisib, but their proliferative activities were reduced by suppression of MYC gene transcription. Molecular structure analysis of the first- and next-generation PI3Kδ inhibitors combined with clinical observation suggests that hepatotoxicity seen with the first-generation inhibitors could result from a structure-related off-target effect. Parsaclisib is currently being evaluated in multiple phase 2 clinical trials as a therapy against various hematologic malignancies of B-cell origin (NCT03126019, NCT02998476, NCT03235544, NCT03144674, and NCT02018861). SIGNIFICANCE STATEMENT: The preclinical properties described here provide the mechanism of action and support clinical investigations of parsaclisib as a therapy for B-cell malignancies. MYC overexpression was identified as a resistance mechanism to parsaclisib in DLBCL cells, which may be useful in guiding further translational studies for the selection of patients with DLBCL who might benefit from PI3Kδ inhibitor treatment in future trials. Hepatotoxicity associated with first-generation PI3Kδ inhibitors may be an off-target effect of that class of compounds.

Extensive investigation of benzylic N-containing substituents on the pyrrolopyrimidine skeleton as Akt inhibitors with potent anticancer activity

Continuous optimization of benzylic substituents on 1-(4-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)piperazin-1-yl)-2-phenylethan-1-one structure as Akt inhibitors was described in this paper. Particularly, compounds 8 and 14g exhibited high enzymatic potency against all Akt isoforms and antiproliferative effects in mantle cell lymphoma cell lines, as well as favorable cytotoxicities in patient primary cancer cells. Low micromolar doses of both 8 and 14g dose-dependently induced cell apoptosis and G₂/M cell cycle arrest, also suppressed the phosphorylation level of Akt downstream targets GSK3β and S6.

Antitumor effects and mechanisms of 1,25(OH)2D3 in the Pfeiffer diffuse large B lymphoma cell line

Diffuse large B cell lymphoma (DLBCL) represents the most common subtype of non-Hodgkin lymphoma in China. 1,25-Dihydroxyvitamin D₃ [1,25(OH)₂D₃] has been shown to possess significant antitumor potential and is degraded by 25-hydroxyvitamin D-24-hydroxylase (CYP24A1). In the present study, the role of CYP24A1 and autophagy, and their underlying mechanisms in the anticancer effects of 1,25(OH)₂D₃ in DLBCL cells, were investigated. It was found that the levels of CYP24A1 in DLBCL lymph node tissues were higher than in hyperplasia lymphadenitis tissue. Moreover, the expression of CYP24A1 was positively associated with the Ann Arbor stage and the International Prognostic Index in patients with DLBCL, and negatively associated with the clinical response to treatment. Patients >60 years of age were found to have a higher level of CYP24A1. 1,25(OH)₂D₃ inhibited the proliferation of the Pfeiffer DLBCL cell line and increased the G1 phase population of Pfeiffer cells. Rapamycin (RAPA) in combination with 1,25(OH)₂D₃ increased the G1 phase distribution of Pfeiffer cells. Furthermore, RAPA blocked the increase of CYP24A1 and vitamin D receptor (VDR) expression induced by 1,25(OH)₂D₃. 1,25(OH)₂D₃ induced the formation of autophagosomes, increased the expression of autophagy related protein light chain (LC)3II/LC3I and reduced the expression of the ubiquitin binding protein P62. In addition, 1,25(OH)₂D₃ decreased the phosphorylation of AKT and mammalian target of RAPA (mTOR), and downstream targets eukaryotic translation imitation factor 4E-binding protein 1 and ribosomal protein S6 kinase β-1 in Pfeiffer cells. The results from the present study suggested that CYP24A1 may be a novel prognostic indicator for DLBCL. 1,25(OH)₂D₃ inhibited proliferation and induced autophagy of Pfeiffer cells. In addition, 1,25(OH)₂D₃ increased the G1 phase population of Pfeiffer cells. These effects may be mediated by inhibition of the AKT/mTOR/PI3K signaling pathway. RAPA increased the cell cycle arrest induced by 1,25(OH)₂D₃ by blocking the upregulated expression of CYP24A1 and VDR.

Therapeutic potential of PI3K signaling in distinct entities of B-cell lymphoma

Introduction: Aberrant phosphatidylinositide 3-kinase (PI3K) signaling drives survival and proliferation of malignant B-cells of different lymphoma entities. Thus, inhibition of PI3K isoforms represents a novel and promising therapeutic approach for the treatment of patients with B-cell lymphomas.Areas covered: Here the authors provide an overview about the PI3K signaling pathway as well as available preclinical and clinical results of different PI3K inhibitors in both indolent and aggressive lymphoma entities.Expert opinion: PI3K inhibitors have shown to be efficacious in different entities of B-cell lymphoma, at this stage particularly in relapsed/refractory settings. However, responses of PI3K inhibitors widely vary among different lymphomas. Additionally, especially infectious and immune-mediated toxicities limit their use at this stage. Thus, the decision to use PI3K inhibitors needs to be balanced between the potential efficacy and associated toxicities as well as the availability of other therapeutic options. Future research might eventually lead to the stratification of patients according to the specific oncogenic addictions of the underlying lymphoma. Additionally, PI3K inhibitors will need to be combined with other therapeutic agents for more specific and effective treatment regimens.

The Signal Transducer and Activator of Transcription 5B (STAT5B) Gene Promotes Proliferation and Drug Resistance of Human Mantle Cell Lymphoma Cells by Activating the Akt Signaling Pathway

Background

Mantle cell lymphoma (MCL) is a high-grade B-cell lymphoma with poor prognosis. Fludarabine is used alone or in combination for relapsed and advanced-stage MCL. The expression of the signal transducer and activator of transcription 5B (STAT5B) gene is associated with tumorigenesis in solid tumors, but its role in MCL remains unknown. The aims of this study were to investigate the role of STAT5B in GRANTA-519 human mantle cell lymphoma cells and drug resistance.

Material/Methods

GRANTA-519 human mantle cell lymphoma cells were cultured with and without 10 μM fludarabine dephosphorylated 9-β-D-arabinofuranosyl-2-fluoroadenine, (2-F-araA) or 10 μM 4-hydroperoxycyclophosphamide (4-HC). The MTT assay assessed cell proliferation. Flow cytometry was used to investigate the cell cycle in MCL cells treated with the specific inhibitor of the Akt pathway, LY294002, and assessed cell cycle and cell apoptosis. Western blot was used to detect the expression levels of p-Akt/Akt and STAT5B/p-STAT5B. The gene expression profiles of lymph node (LN)-derived MCL cells were compared with peripheral blood (PB)-derived lymphocytes using bioinformatics and hierarchical cluster analysis. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was performed to determine the expression of the marker of proliferation Ki-67 (MKI67) gene.

Results

STAT5B was significantly upregulated in LN-derived MCL cells compared with PB lymphocytes. Increased expression of STAT5B was associated with increased MCL cell proliferation and reduced cell apoptosis and was associated with drug resistance and activation of Akt.

Conclusions

STAT5B promoted cell proliferation and drug resistance in human MCL cells by activating the Akt signaling pathway.

Activation of MYC, a bona fide client of HSP90, contributes to intrinsic ibrutinib resistance in mantle cell lymphoma

The BTK inhibitor ibrutinib has demonstrated a remarkable therapeutic effect in mantle cell lymphoma (MCL). However, approximately one-third of patients do not respond to the drug initially. To identify the mechanisms underlying primary ibrutinib resistance in MCL, we analyzed the transcriptome changes in ibrutinib-sensitive and ibrutinib-resistant cell lines on ibrutinib treatment. We found that MYC gene signature was suppressed by ibrutinib in sensitive but not resistant cell lines. We demonstrated that MYC gene was structurally abnormal and MYC protein was overexpressed in MCL cells. Further, MYC knockdown with RNA interference inhibited cell growth in ibrutinib-sensitive as well as ibrutinib-resistant cells. We explored the possibility of inhibiting MYC through HSP90 inhibition. The chaperon protein is overexpressed in both cell lines and primary MCL cells from the patients. We demonstrated that MYC is a bona fide client of HSP90 in the context of MCL by both immunoprecipitation and chemical precipitation. Furthermore, inhibition of HSP90 using PU-H71 induced apoptosis and caused cell cycle arrest. PU-H71 also demonstrates strong and relatively specific inhibition of the MYC transcriptional program compared with other oncogenic pathways. In a MCL patient-derived xenograft model, the HSP90 inhibitor retards tumor growth and prolongs survival. Last, we showed that PU-H71 induced apoptosis and downregulated MYC protein in MCL cells derived from patients who were clinically resistant to ibrutinib. In conclusion, MYC activity underlies intrinsic resistance to ibrutinib in MCL. As a client protein of HSP90, MYC can be inhibited via PU-H71 to overcome primary ibrutinib resistance.

Reproducibility and Crossplatform Validation of Reverse-Phase Protein Array Data

Reverse-phase protein array (RPPA) technology is a high-throughput antibody- and microarray-based approach for the rapid profiling of levels of proteins and protein posttranslational modifications in biological specimens. The technology consumes small amounts of samples, can sensitively detect low-abundance proteins and posttranslational modifications, enables measurements of multiple signaling pathways in parallel, has the capacity to analyze large sample numbers, and offers robust interexperimental reproducibility. These features of RPPA experiments have motivated and enabled the use of RPPA technology in various biomedical, translational, and clinical applications, including the delineation of molecular mechanisms of disease, profiling of druggable signaling pathway activation, and search for new prognostic markers. Owing to the complexity of many of these applications, such as developing multiplex protein assays for diagnostic laboratories or integrating posttranslational modification-level data using large-scale proteogenomic approaches, robust and well-validated data are essential. There are many distinct components of an RPPA workflow, and numerous possible technical setups and analysis parameter options exist. The differences between RPPA platform setups around the world offer opportunities to assess and minimize interplatform variation. Crossplatform validation may also aid in the evaluation of robust, platform-independent protein markers of disease and response to therapy.

Targeting protein kinase CK2 and CDK4/6 pathways with a multi-kinase inhibitor ON108110 suppresses pro-survival signaling and growth in mantle cell lymphoma and T-acute lymphoblastic leukemia

Overexpression and constitutive activation of CYCLIN D1 and Casein Kinase 2 are common features of many hematologic malignancies, including mantle cell lymphoma (MCL) and leukemias such as T-cell acute lymphoblastic leukemia (T-ALL). Although both CK2 and CDK4 inhibitors have shown promising results against these tumor types, none of these agents have achieved objective responses in the clinic as monotherapies. Because both proteins play key roles in these and other hematological malignancies, we have analyzed the therapeutic potential of ON108110, a novel dual specificity ATP-competitive inhibitor of protein kinase CK2 as well as CDK4/6 in MCL and T-ALL. We show that in cell growth inhibition assays, MCL and T-ALL cell lines exhibited increased sensitivity to ON108110 when compared to other tumor types. Treatment with ON108110 reduced the level of phosphorylated RB-family proteins. In addition, ON108110 treatment resulted in concentration dependent inhibition of PTEN phosphorylation and a concomitant decrease in PI3K-AKT signaling mediated by CK2. Accordingly, cells treated with ON108110 rapidly accumulated in the G₀/G₁ stage of the cell cycle as a function of increasing concentration followed by rapid onset of apoptosis. Together, these results indicate that dual inhibition of CK2 and CDK4/6 may be an efficient treatment of MCL and T-ALLs displaying upregulation of CK2/PI3K and CDK4 signaling pathways.

Metabolic Reprogramming of Non-Hodgkin's B-Cell Lymphomas and Potential Therapeutic Strategies

Metabolism is a wide and general term that refers to any intracellular pathways the cell utilizes in order to satisfy its energetic demand and to support cell viability and/or division. Along with phenotypic changes, all mammalian cells including immune cells modulate their metabolic program in order to reach their effector functions. Exacerbated metabolism and metabolic flexibility are also hallmarks of tumor initiation and of tumor cell progression in a complex tumor microenvironment. Metabolic reprogramming is mainly directed by the serine/threonine kinase mTOR (mammalian target of rapamycin). mTOR exists in two structurally and functionally distinct complexes, mTORC1 and mTORC2 that coordinate environmental signals and metabolic/anabolic pathways to provide macromolecules and energy needed for survival and growth. Activation of mTORC1 is required during development, differentiation and activation of immune cells. Aberrant and persistent activation of mTORC1 is often observed in malignant B cells such as Non-Hodgkin's (NH) B-cell lymphomas. Here, we review recent insights on cell metabolism and on basic mechanisms of mTORC1 regulation and metabolic functions. We highlight the distinct mechanisms driving mTORC1 activation in the three most-common types of NH B-cell lymphomas (Diffuse Large B Cell Lymphomas, Follicular Lymphomas, and Mantle Cell Lymphomas), for which the first generation of mTORC1 inhibitors (rapalogs) have been extensively evaluated in preclinical and clinical settings. Finally, we discuss the reasons for limited clinical success of this therapy and focus on potential therapeutic strategies targeting metabolic pathways, upstream and downstream of mTORC1, that can be combined to rapalogs in order to improve patient's outcome.

Pleiotropic Action of Novel Bruton's Tyrosine Kinase Inhibitor BGB-3111 in Mantle Cell Lymphoma

Bruton's tyrosine kinase (BTK) is a key mediator of BCR-dependent cell growth signaling and a clinically effective therapeutic target in mantle cell lymphoma (MCL). The molecular impact of BTK inhibition remains unclear particularly in hematopoietic malignancies. We analyzed the molecular mechanisms of BTK inhibition with the novel inhibitor BGB-3111 (zanubrutinib) in MCL models. The efficacy of BGB-3111 was investigated using growth proliferation/cell viability and apoptosis assays in MCL cell lines and patient-derived xenograft (PDX) MCL cells. The activity and mechanisms of BGB-3111 were further confirmed using a cell line xenograft model, an MCL PDX mouse model, and a human phosphokinase profiler array and reverse phase protein array. Finally, the mechanisms related to resistance to BTK inhibition were analyzed by creating cell lines with low levels of BTK using CRISPR/Cas 9 genome editing. We found that inhibition of BTK leads to suppression of tumor growth, which was mediated via potent suppression of AKT/mTOR, apoptosis, and metabolic stress. Moreover, targeted disruption of the BTK gene in MCL cells resulted in resistance to BTK inhibition and the emergence of novel survival mechanisms. Our studies suggest a general efficacy of BTK inhibition in MCL and potential drug resistance mechanism via alternative signaling pathways.

New quinoline/chalcone hybrids as anti-cancer agents: Design, synthesis, and evaluations of cytotoxicity and PI3K inhibitory activity

A series of quinoline-chalcone hybrids was designed as potential anti-cancer agents, synthesized and evaluated. Different cytotoxic assays revealed that compounds experienced promising activity. Compounds 9i and 9j were the most potent against all the cell lines tested with IC₅₀ = 1.91-5.29 µM against A549 and K-562 cells. Mechanistically, 9i and 9j induced G₂/M cell cycle arrest and apoptosis in both A549 and K562 cells. Moreover, all PI3K isoforms were inhibited non selectively with IC₅₀s of 52-473 nM when tested against the two mentioned compounds with 9i being most potent against PI3K-γ (IC₅₀ = 52 nM). Docking of 9i and 9j showed a possible formation of H-bonding with essential valine residues in the active site of PI3K-γ isoform. Meanwhile, Western blotting analysis revealed that 9i and 9j inhibited the phosphorylation of PI3K, Akt, mTOR, as well as GSK-3β in both A549 and K562 cells, suggesting the correlation of blocking PI3K/Akt/mTOR pathway with the above antitumor activities. Together, our findings support the antitumor potential of quinoline-chalcone derivatives for NSCLC and CML by inhibiting the PI3K/Akt/mTOR pathway.

Targeting the PI3K/Akt/mTOR signaling pathway by pterostilbene attenuates mantle cell lymphoma progression

Mantle cell lymphoma (MCL) is an aggressive and mostly incurable B-cell malignancy with frequent relapses after an initial response to standard chemotherapy. Therefore, novel therapies are urgently required to improve MCL clinical outcomes. In this study, MCL cell lines were treated with pterostilbene (PTE), a non-toxic natural phenolic compound primarily found in blueberries. The antitumor activity of PTE was examined by using the Cell Counting Kit-8, apoptosis assays, cell cycle analysis, JC-1 mitochondrial membrane potential assay, western blot analysis, and tumor xenograft models. PTE treatment induced a dose-dependent inhibition of cell proliferation, including the induction of cell apoptosis and cell cycle arrest at the G0/G1 phase. Moreover, the PI3K/Akt/mTOR pathway was downregulated after PTE treatment, which might account for the anti-MCL effects of PTE. Synergistic cytotoxicity was also observed, both in MCL cells and in xenograft mouse models, when PTE was administered in combination with bortezomib (BTZ). The antitumor effects of PTE shown in our study provide an innovative option for MCL patients with poor responses to standardized therapy. It is noteworthy that the treatment combining PTE with BTZ warrants clinical investigation, which may offer an alternative and effective MCL treatment in the future.

Targeting the B cell receptor pathway in non-Hodgkin lymphoma

INTRODUCTION

Dysregulated B cell receptor (BCR) signaling has been identified as a potent contributor to tumor survival in B cell non-Hodgkin lymphomas (NHLs). This pathway's emergence as a rational therapeutic target in NHL led to development of BCR-directed agents, including inhibitors of Bruton's tyrosine kinase (BTK), spleen tyrosine kinase (SYK), and phosphatidylinositol 3 kinase (PI3K). Several drugs have become valuable assets in the anti-lymphoma armamentarium.

AREAS COVERED

We provide an overview of the BCR pathway, its dysregulation in B cell NHL, and the drugs developed to target BCR signaling in lymphoma. Mechanisms, pharmacokinetics, pharmacodynamics, efficacy, and toxicity of currently available BTK, SYK, and PI3K inhibitors are described.

EXPERT OPINION

While the excellent response rates and favorable toxicity profile of the BTK inhibitor ibrutinib in certain NHL subtypes have propelled it to consideration as frontline therapy in selected populations, additional data and clinical studies are needed before other agents targeting BCR signaling influence clinical practice similarly. PI3K inhibitors remain an option for some relapsed indolent lymphomas and chronic lymphocytic leukemia, but their widespread use may be limited by adverse effects. Future research should include efforts to overcome resistance to BTK inhibitors, combination therapy using BCR-targeted agents, and exploration of novel agents.

Four-year follow-up of a single arm, phase II clinical trial of ibrutinib with rituximab (IR) in patients with relapsed/refractory mantle cell lymphoma (MCL)

Ibrutinib has shown significant activity in patients with relapsed or refractory mantle cell lymphoma (RR-MCL). We report the long-term outcome and safety profile of a single-centre, single arm, open-label, phase 2 study of RR-MCL treated with IR. Overall, the median follow-up time was 47 months (range 1-52 months), median duration on treatment was 16 months (range 1-53 months) and median number of treatment cycles was 17 (range 1-56). Twenty-nine patients (58%) achieved complete remission and of these, 12 patients continue on study. Thirty-eight patients discontinued treatment, 14 due to disease progression (2 transformed). Patients with blastoid morphology, high risk MCL International Prognostic Index score and high Ki67% had inferior survival. The commonest grade 1-2 toxicities were fatigue, diarrhoea, nausea, arthralgias and myalgias. None had long term toxicities. Median progression-free survival was 43 months. Eighteen patients (36%) died (14 deaths were MCL-related). The median overall survival has not been reached. Treatment with IR can provide durable remissions in a subset of patients with RR-MCL, especially those with low Ki67%. The possible benefit of adding other therapies in combination with IR in RR-MCL is under exploration.

Regulation of Hematopoietic Cell Development and Function Through Phosphoinositides

One of the most paramount receptor-induced signal transduction mechanisms in hematopoietic cells is production of the lipid second messenger phosphatidylinositol(3,4,5)trisphosphate (PIP₃) by class I phosphoinositide 3 kinases (PI3K). Defective PIP₃ signaling impairs almost every aspect of hematopoiesis, including T cell development and function. Limiting PIP₃ signaling is particularly important, because excessive PIP₃ function in lymphocytes can transform them and cause blood cancers. Here, we review the key functions of PIP₃ and related phosphoinositides in hematopoietic cells, with a special focus on those mechanisms dampening PIP₃ production, turnover, or function. Recent studies have shown that beyond “canonical” turnover by the PIP₃ phosphatases and tumor suppressors phosphatase and tensin homolog (PTEN) and SH2 domain-containing inositol-5-phosphatase-1 (SHIP-1/2), PIP₃ function in hematopoietic cells can also be dampened through antagonism with the soluble PIP₃ analogs inositol(1,3,4,5)tetrakisphosphate (IP₄) and inositol-heptakisphosphate (IP₇). Other evidence suggests that IP₄ can promote PIP₃ function in thymocytes. Moreover, IP₄ or the kinases producing it limit store-operated Ca²⁺ entry through Orai channels in B cells, T cells, and neutrophils to control cell survival and function. We discuss current models for how soluble inositol phosphates can have such diverse functions and can govern as distinct processes as hematopoietic stem cell homeostasis, neutrophil macrophage and NK cell function, and development and function of B cells and T cells. Finally, we will review the pathological consequences of dysregulated IP₄ activity in immune cells and highlight contributions of impaired inositol phosphate functions in disorders such as Kawasaki disease, common variable immunodeficiency, or blood cancer.

SNORD126 promotes HCC and CRC cell growth by activating the PI3K-AKT pathway through FGFR2

Small nucleolar RNA (snoRNA) dysfunctions have been associated with cancer development. SNORD126 is an orphan C/D box snoRNA that is encoded within introns 5-6 of its host gene, cyclin B1-interacting protein 1 (CCNB1IP1). The cancer-associated molecular mechanisms triggered by SNORD126 are not fully understood. Here, we demonstrate that SNORD126 is highly expressed in hepatocellular carcinoma (HCC) and colorectal cancer (CRC) patient samples. SNORD126 increased Huh-7 and SW480 cell growth and tumorigenicity in nude mice. Knockdown of SNORD126 inhibited HepG2 and LS174T cell growth. We verified that SNORD126 was not processed into small RNAs with miRNA activity. Moreover, SNORD126 did not show a significant expression correlation with CCNB1IP1 in HCC samples or regulate CCNB1IP1 expression. Our gene expression profile analysis indicated that SNORD126-upregulated genes frequently mapped to the PI3K-AKT pathway. SNORD126 overexpression increased the levels of phosphorylated AKT, GSK-3β, and p70S6K and elevated fibroblast growth factor receptor 2 (FGFR2) expression. siRNA-mediated knockdown or AZD4547-mediated inactivation of FGFR2 in SNORD126-overexpressing Huh-7 cells inhibited AKT phosphorylation and suppressed cell growth. These findings indicate an oncogenic role for SNORD126 in cancer and suggest its potential as a therapeutic target.

The proto-oncogene Mer tyrosine kinase is a novel therapeutic target in mantle cell lymphoma

BACKGROUND

Mantle cell lymphoma (MCL) is an incurable B cell-derived malignant tumor with a median overall survival of 4-5 years. Mer tyrosine kinase (MerTK) has been reported to be aberrantly expressed in leukemia, melanoma, and gastric cancer, and plays a pivotal role in the process of oncogenesis. This study assessed the role of MerTK in MCL for the first time.

METHODS

Immunohistochemistry and western blot were performed to figure out expression of MerTK in MCL. MerTK inhibition by either shRNA or treatment with UNC2250 (a MerTK-selective small molecular inhibitor) was conducted in MCL cell lines. MCL-cell-derived xenograft models were established to evaluate the anti-tumor effects of UNC2250 in vivo.

RESULTS

MerTK was ectopically expressed in four of six MCL cell lines. Sixty-five of 132 (48.9%) MCL patients showed positive expression of MerTK. MerTK inhibition by either shRNA or treatment with UNC2250 decreased activation of downstream AKT and p38, inhibited proliferation and invasion in MCL cells, and sensitized MCL cells to treatment with vincristine in vitro and doxorubicin in vitro and in vivo. UNC2250 induced G2/M phase arrest and prompted apoptosis in MCL cells, accompanied by increased expression of Bax, cleaved caspase 3 and poly (ADP-ribose) polymerase, and decreased expression of Bcl-2, Mcl-1 and Bcl-xL. Moreover, UNC2250 delayed disease progression in MCL-cell-derived xenograft models.

CONCLUSIONS

Our data prove that ectopic MerTK may be a novel therapeutic target in MCL, and further pre-clinical or even clinical studies of UNC2250 or new MerTK inhibitors are essential and of great significance.

Critically dysregulated signaling pathways and clinical utility of the pathway biomarkers in lymphoid malignancies

Accumulating evidence confirmed that many dysregulated signaling pathways and aberrant genetic alterations contribute to the oncogenesis and heterogeneity of lymphoid malignancies. Therapeutically targeting dysregulating signaling pathways and their hidden oncogenic biomarkers are becoming available, but did not show desired therapeutic effect in current clinical practice. It is meaningful to further understand the underlying mechanisms of the dysregulated signaling pathways and to address the potential utility of pathway-related biomarkers. To precisely identify the dysregulation of signaling pathways and the “driver” oncogenic biomarkers, as well as to develop reliable and reproducible risk-stratification based on biomarkers will be challenging. Nevertheless, pathway-based targeted therapy will raise the hope to improve the outcomes of the patients with lymphoid malignancies, especially with aggressive types, and the efficient utility of pathway-related biomarkers in diagnosis, prognosis, prediction of lymphoid malignancies may also be able to power precision medicine.

DEPTOR promotes survival of cervical squamous cell carcinoma cells and its silencing induces apoptosis through downregulating PI3K/AKT and by up-regulating p38 MAP kinase

DEPTOR is an endogenous inhibitor of mTOR complexes, de-regulated in cancers. The present study reveals a vital role for DEPTOR in survival of cervical squamous cell carcinoma (SCC). DEPTOR was found to be overexpressed in both cervical SCC cells and tissues and it's silencing in cervical SCC cells induced apoptosis, mainly by up-regulation of p38 MAPK and by inhibiting PI3K/AKT pathway via a feed-back inhibition from mTORC1-S6K. DEPTOR silencing resulted in reduced expression of the nitric oxide synthases iNOS and eNOS, as well as increased activation of ERK1/2 and p38 MAP kinases. Activation of AKT signaling by overexpression of constitutively active-AKT (CA-AKT) failed to overcome the apoptosis caused by DEPTOR silencing. Similarly pharmacological inhibition of ERK also failed to control apoptosis. However pharmacological inhibition of p38 MAPK rescued the cells from apoptosis, indicating the major role of p38 MAPK in cell death induced by DEPTOR silencing. DEPTOR was also found to regulate ERK1/2 in an AKT dependent manner. DEPTOR knockdown induced cell death in SiHa cells overexpressing the anti-apoptotic Bcl-2 and Bcl-xL, indicating strong survival role of DEPTOR in these cells. DEPTOR overexpression activated PI3K/AKT by relieving the negative feed-back inhibition from mTORC1-S6K. DEPTOR regulation was also observed to be independent of HPV E6/E7 oncoproteins, but it might be a molecular co-factor contributing to cervical carcinogenesis. In summary, DEPTOR is found to promote survival of cervical SCC cells and its reduction induced apoptosis via differential effects on PI3K/AKT and p38 MAPK and can be a potential target in cervical SCC.