Network analysis reveals a major role for 14q32 cluster miRNAs in determining transcriptional differences between IGHV-mutated and unmutated CLL

Chronic lymphocytic leukaemia (CLL) cells can express unmutated (U-CLL) or mutated (M-CLL) immunoglobulin heavy chain (IGHV) genes with differing clinical behaviours, variable B cell receptor (BCR) signalling capacity and distinct transcriptional profiles. As it remains unclear how these differences reflect the tumour cells' innate pre/post germinal centre origin or their BCR signalling competence, we applied mRNA/miRNA sequencing to 38 CLL cases categorised into three subsets by IGHV mutational status and BCR signalling capacity. We identified 492 mRNAs and 38 miRNAs differentially expressed between U-CLL and M-CLL, but only 9 mRNAs and 0 miRNAs associated with BCR competence within M-CLL. Of the IGHV-associated miRNAs, (14/38 (37%)) derived from chr14q32 clusters where all miRNAs were co-expressed with the MEG3 lncRNA from a cancer associated imprinted locus. Integrative analysis of miRNA/mRNA data revealed pronounced regulatory potential for the 14q32 miRNAs, potentially accounting for up to 25% of the IGHV-related transcriptome signature. GAB1, a positive regulator of BCR signalling, was potentially regulated by five 14q32 miRNAs and we confirmed that two of these (miR-409-3p and miR-411-3p) significantly repressed activity of the GAB1 3'UTR. Our analysis demonstrates a potential key role of the 14q32 miRNA locus in the regulation of CLL-related gene regulation.

Characterization of metabolic alterations of chronic lymphocytic leukemia in the lymph node microenvironment

Altered metabolism is a hallmark of both cell division and cancer. Chronic lymphocytic leukemia (CLL) cells circulate between peripheral blood (PB) and lymph nodes (LNs), where they receive proliferative and prosurvival signals from surrounding cells. However, insight into the metabolism of LN CLL and how this may relate to therapeutic response is lacking. To obtain insight into CLL LN metabolism, we applied a 2-tiered strategy. First, we sampled PB from 8 patients at baseline and after 3-month ibrutinib (IBR) treatment, which forces egress of CLL cells from LNs. Second, we applied in vitro B-cell receptor (BCR) or CD40 stimulation to mimic the LN microenvironment and performed metabolomic and transcriptomic analyses. The combined analyses indicated prominent changes in purine, glucose, and glutamate metabolism occurring in the LNs. CD40 signaling mostly regulated amino acid metabolism, tricarboxylic acid cycle (TCA), and energy production. BCR signaling preferably engaged glucose and glycerol metabolism and several biosynthesis routes. Pathway analyses demonstrated opposite effects of in vitro stimulation vs IBR treatment. In agreement, the metabolic regulator MYC and its target genes were induced after BCR/CD40 stimulation and suppressed by IBR. Next, 13C fluxomics performed on CD40/BCR-stimulated cells confirmed a strong contribution of glutamine as fuel for the TCA cycle, whereas glucose was mainly converted into lactate and ribose-5-phosphate. Finally, inhibition of glutamine import with V9302 attenuated CD40/BCR-induced resistance to venetoclax. Together, these data provide insight into crucial metabolic changes driven by the CLL LN microenvironment. The prominent use of amino acids as fuel for the TCA cycle suggests new therapeutic vulnerabilities.

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.

B-cell receptor dependent phagocytosis and presentation of particulate antigen by chronic lymphocytic leukemia cells

Aim

T-helper cells could play an important role in the pathogenesis of chronic lymphocytic leukemia (CLL), a common B-cell neoplasm. Although CLL cells can present soluble antigens targeted from the B-cell receptor to T-helper cells via major histocompatibility complex (MHC) class II, antigens recognized by some CLL cells may be encountered in a particulate form. Here the ability of CLL cells to internalize and present anti-immunoglobulin M (IgM) beads as a model for the interaction of CLL cells with particulate antigens was investigated.

Methods

The effect of anti-IgM beads on antigen presentation pathways was analyzed using RNA-seq and internalization of anti-IgM beads by primary CLL cells was investigated using confocal microscopy and flow cytometry. Antigen presentation was investigated by analyzing activation of a T-cell line expressing a T-cell receptor specific for a peptide derived from mouse κ light chains after incubating CLL cells with a mouse κ light chain-containing anti-IgM monoclonal antibody. Kinase inhibitors were used to characterize the pathways mediating internalization and antigen presentation.

Results

Stimulation of surface IgM of CLL cells increased expression of the antigen presentation machinery and CLL cells were able to phagocytose anti-IgM beads. Internalization of anti-IgM beads was associated with MHC class II-restricted activation of cognate T-helper cells. Antigen presentation by CLL cells was dependent on activity of spleen tyrosine kinase (SYK) and phosphatidylinositol 3-kinase delta (PI3Kδ) but was unaffected by inhibitors of Bruton's tyrosine kinase (BTK).

Conclusions

CLL cells can internalize and present antigen from anti-IgM beads. This capacity of CLL cells may be particularly important for recruitment of T-cell help in vivo in response to particulate antigens.

Insertion of atypical glycans into the tumor antigen-binding site identifies DLBCLs with distinct origin and behavior

Glycosylation of the surface immunoglobulin (Ig) variable region is a remarkable follicular lymphoma-associated feature rarely seen in normal B cells. Here, we define a subset of diffuse large B-cell lymphomas (DLBCLs) that acquire N-glycosylation sites selectively in the Ig complementarity-determining regions (CDRs) of the antigen-binding sites. Mass spectrometry and X-ray crystallography demonstrate how the inserted glycans are stalled at oligomannose-type structures because they are buried in the CDR loops. Acquisition of sites occurs in ∼50% of germinal-center B-cell-like DLBCL (GCB-DLBCL), mainly of the genetic EZB subtype, irrespective of IGHV-D-J use. This markedly contrasts with the activated B-cell-like DLBCL Ig, which rarely has sites in the CDR and does not seem to acquire oligomannose-type structures. Acquisition of CDR-located acceptor sites associates with mutations of epigenetic regulators and BCL2 translocations, indicating an origin shared with follicular lymphoma. Within the EZB subtype, these sites are associated with more rapid disease progression and with significant gene set enrichment of the B-cell receptor, PI3K/AKT/MTORC1 pathway, glucose metabolism, and MYC signaling pathways, particularly in the fraction devoid of MYC translocations. The oligomannose-type glycans on the lymphoma cells interact with the candidate lectin dendritic cell-specific intercellular adhesion molecule 3 grabbing non-integrin (DC-SIGN), mediating low-level signals, and lectin-expressing cells form clusters with lymphoma cells. Both clustering and signaling are inhibited by antibodies specifically targeting the DC-SIGN carbohydrate recognition domain. Oligomannosylation of the tumor Ig is a posttranslational modification that readily identifies a distinct GCB-DLBCL category with more aggressive clinical behavior, and it could be a potential precise therapeutic target via antibody-mediated inhibition of the tumor Ig interaction with DC-SIGN-expressing M2-polarized macrophages.

Kinobead Profiling Reveals Reprogramming of BCR Signaling in Response to Therapy within Primary CLL Cells

PURPOSE

B-cell receptor (BCR) signaling is critical for the pathogenesis of chronic lymphocytic leukemia (CLL), promoting both malignant cell survival and disease progression. Although vital, understanding of the wider signaling network associated with malignant BCR stimulation is poor. This is relevant with respect to potential changes in response to therapy, particularly involving kinase inhibitors. In the current study, we describe a novel high-resolution approach to investigate BCR signaling in primary CLL cells and track the influence of therapy on signaling response.

EXPERIMENTAL DESIGN

A kinobead/mass spectrometry-based protocol was used to study BCR signaling in primary CLL cells. Longitudinal analysis of samples donated by clinical trial patients was used to investigate the impact of chemoimmunotherapy and ibrutinib on signaling following surface IgM engagement. Complementary Nanostring and immunoblotting analysis was used to verify our findings.

RESULTS

Our protocol isolated a unique, patient-specific signature of over 30 kinases from BCR-stimulated CLL cells. This signature was associated with 13 distinct Kyoto Encyclopedia of Genes and Genomes pathways and showed significant change in cells from treatment-naïve patients compared with those from patients who had previously undergone therapy. This change was validated by longitudinal analysis of clinical trials samples where BCR-induced kinome responses in CLL cells altered between baseline and disease progression in patients failing chemoimmunotherapy and between baseline and treatment in patients taking ibrutinib.

CONCLUSIONS

These data comprise the first comprehensive proteomic investigation of the BCR signaling response within CLL cells and reveal unique evidence that these cells undergo adaptive reprogramming of this signaling in response to therapy.

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.

KDM5 inhibition offers a novel therapeutic strategy for the treatment of KMT2D mutant lymphomas

Loss-of-function mutations in KMT2D are a striking feature of germinal center (GC) lymphomas, resulting in decreased histone 3 lysine 4 (H3K4) methylation and altered gene expression. We hypothesized that inhibition of the KDM5 family, which demethylates H3K4me3/me2, would reestablish H3K4 methylation and restore the expression of genes repressed on loss of KMT2D. KDM5 inhibition increased H3K4me3 levels and caused an antiproliferative response in vitro, which was markedly greater in both endogenous and gene-edited KMT2D mutant diffuse large B-cell lymphoma cell lines, whereas tumor growth was inhibited in KMT2D mutant xenografts in vivo. KDM5 inhibition reactivated both KMT2D-dependent and -independent genes, resulting in diminished B-cell signaling and altered expression of B-cell lymphoma 2 (BCL2) family members, including BCL2 itself. KDM5 inhibition may offer an effective therapeutic strategy for ameliorating KMT2D loss-of-function mutations in GC lymphomas.

DC-SIGN binding to mannosylated B-cell receptors in follicular lymphoma down-modulates receptor signaling capacity

In follicular lymphoma (FL), surface immunoglobulin (sIg) carries mandatory N-glycosylation sites in the variable regions, inserted during somatic hypermutation. These glycosylation sites are tumor-specific, indicating a critical function in FL. Added glycan unexpectedly terminates at high mannose (Mann) and confers capability for sIg-mediated interaction with local macrophage-expressed DC-SIGN lectin resulting in low-level activation of upstream B-cell receptor signaling responses. Here we show that despite being of low-level, DC-SIGN induces a similar downstream transcriptional response to anti-IgM in primary FL cells, characterized by activation of pathways associated with B-cell survival, proliferation and cell-cell communication. Lectin binding was also able to engage post-transcriptional receptor cross-talk pathways since, like anti-IgM, DC-SIGN down-modulated cell surface expression of CXCR4. Importantly, pre-exposure of a FL-derived cell line expressing sIgM-Mann or primary FL cells to DC-SIGN, which does not block anti-IgM binding, reversibly paralyzed the subsequent Ca2+ response to anti-IgM. These novel findings indicate that modulation of sIg function occurs in FL via lectin binding to acquired mannoses. The B-cell receptor alternative engagement described here provides two advantages to lymphoma cells: (i) activation of signaling, which, albeit of low-level, is sufficient to trigger canonical lymphoma-promoting responses, and (ii) protection from exogenous antigen by paralyzing anti-IgM-induced signaling. Blockade of this alternative engagement could offer a new therapeutic strategy.

Synthesis of Carboxamide-Containing Tranylcypromine Analogues as LSD1 (KDM1A) Inhibitors Targeting Acute Myeloid Leukemia

Lysine-specific demethylase 1 (LSD1/KDM1A) oxidatively removes methyl groups from histone proteins, and its aberrant activity has been correlated with cancers including acute myeloid leukemia (AML). We report a novel series of tranylcypromine analogues with a carboxamide at the 4-position of the aryl ring. These compounds, such as 5 a and 5 b with benzyl and phenethylamide substituents, respectively, had potent sub-micromolar IC50 values for the inhibition of LSD1 as well as cell proliferation in a panel of AML cell lines. The dose-dependent increase in cellular expression levels of H3K4me2, CD86, CD11b and CD14 supported a mechanism involving LSD1 inhibition. The tert-butyl and ethyl carbamate derivatives of these tranylcypromines, although inactive in LSD1 inhibition, were of similar potency in cell-based assays with a more rapid onset of action. This suggests that carbamates can act as metabolically labile tranylcypromine prodrugs with superior pharmacokinetics.

V-ATPase Inhibition Decreases Mutant Androgen Receptor Activity in Castrate-resistant Prostate Cancer

Prostate cancer is critically dependent on androgen receptor (AR) signaling. Despite initial responsiveness to androgen deprivation, most patients with advanced prostate cancer subsequently progress to a clinically aggressive castrate-resistant prostate cancer (CRPC) phenotype, typically associated with expression of splice-variant or mutant AR forms. Although current evidence suggests that the vacuolar-ATPase (V-ATPase), a multiprotein complex that catalyzes proton transport across intracellular and plasma membranes, influences wild-type AR function, the effect of V-ATPase inhibition on variant AR function is unknown.Inhibition of V-ATPase reduced AR function in wild-type and mutant AR luciferase reporter models. In hormone-sensitive prostate cancer cell lines (LNCaP, DuCaP) and mutant AR CRPC cell lines (22Rv1, LNCaP-F877L/T878A), V-ATPase inhibition using bafilomycin-A1 and concanamycin-A reduced AR expression, and expression of AR target genes, at mRNA and protein levels. Furthermore, combining chemical V-ATPase inhibition with the AR antagonist enzalutamide resulted in a greater reduction in AR downstream target expression than enzalutamide alone in LNCaP cells. To investigate the role of individual subunit isoforms, siRNA and CRISPR-Cas9 were used to target the V1C1 subunit in 22Rv1 cells. Whereas transfection with ATP6V1C1-targeted siRNA significantly reduced AR protein levels and function, CRISPR-Cas9-mediated V1C1 knockout showed no substantial change in AR expression, but a compensatory increase in protein levels of the alternate V1C2 isoform.Overall, these results indicate that V-ATPase dysregulation is directly linked to both hormone-responsive prostate cancer and CRPC via impact on AR function. In particular, V-ATPase inhibition can reduce AR signaling regardless of mutant AR expression.

BET inhibitors synergize with venetoclax to induce apoptosis in MYC-driven lymphomas with high BCL-2 expression

Although the MYC oncogenic network represents an attractive therapeutic target for lymphoma, MYC inhibitors have been difficult to develop. Alternatively, inhibitors of epigenetic/ transcriptional regulators, particularly the bromodomain and extraterminal (BET) family, have been used to modulate MYC. However, current benzodiazepine-derivative BET inhibitors (BETi) elicit disappointing responses and dose-limiting toxicity in relapsed/refractory lymphoma, potentially because of enrichment of high-risk molecular features and chemical backbone-associated toxicities. Consequently, novel nonbenzodiazepine BETi and improved mechanistic understanding are required. Here we characterize the responses of aggressive MYC-driven lymphomas to 2 nonbenzodiazepine BETi: PLX51107 and PLX2853. Both invoked BIM-dependent apoptosis and in vivo therapy, associated with miR-17∼92 repression, in murine Eµ-myc lymphomas, with PLX2853 exhibiting enhanced potency. Accordingly, exogenous BCL-2 expression abrogated these effects. Because high BCL-2 expression is common in diffuse large B-cell lymphoma (DLBCL), BETi were ineffective in driving apoptosis and in vivo therapy of DLBCL cell lines, mirroring clinical results. However, BETi-mediated BIM upregulation and miR-17∼92 repression remained intact. Consequently, coadministration of BETi and ABT199/venetoclax restored cell death and in vivo therapy. Collectively, these data identify BIM-dependent apoptosis as a critical mechanism of action for this class of BETi that, via coadministration of BH3 mimetics, can deliver effective tumor control in DLBCL.

Upregulation of epithelial metallothioneins by metal-rich ultrafine particulate matter from an underground railway

Airborne particulate matter (PM) is a leading cause of mortality and morbidity. However, understanding of the range and mechanisms of effects of PM components is poor. PM generated in underground railways is rich in metals, especially iron. In the ultrafine (UFPM; <0.1 μm diameter) fraction, the combination of small size and metal enrichment poses an unknown health risk. This study aimed to analyse transcriptomic responses to underground UFPM in primary bronchial epithelial cells (PBECs), a key site of PM deposition. The oxidation state of iron in UFPM from an underground station was determined by X-ray absorption near edge structure (XANES) spectroscopy. Antioxidant response was assayed using a reporter cell line transfected with an antioxidant response element (ARE)-luciferase construct. Differentiated PBECs were exposed to UFPM for 6 h or 24 h for RNA-Seq and RT-qPCR analysis. XANES showed predominance of redox-active Fe3O4, with ROS generation confirmed by induction of ARE-luciferase expression. 6 h exposure of PBECs to UFPM identified 52 differentially expressed genes (DEGs), especially associated with epithelial maintenance, whereas 24 h exposure yielded 23 DEGs, particularly involved with redox homeostasis and metal binding. At both timepoints, there was upregulation of members of the metallothionein family, low molecular weight proteins with antioxidant activity whose main function is binding and homeostasis of zinc and copper ions, but not iron ions. This upregulation was partially inhibited by metal chelation or ROS scavenging. These data suggest differential regulation of responses to metal-rich UFPM depending on exposure period, and highlight novel pathways and markers of PM exposure, with the role of metallothioneins warranting further investigation.

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.

Correction: Bidirectional linkage between the B-cell receptor and NOTCH1 in chronic lymphocytic leukemia and in Richter's syndrome: therapeutic implications

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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.

Targeted inhibition of mRNA translation initiation factors as a novel therapeutic strategy for mature B-cell neoplasms

Cancer development is frequently associated with dysregulation of mRNA translation to enhance both increased global protein synthesis and translation of specific mRNAs encoding oncoproteins. Thus, targeted inhibition of mRNA translation is viewed as a promising new approach for cancer therapy. In this article we review current progress in investigating dysregulation of mRNA translation initiation in mature B-cell neoplasms, focusing on chronic lymphocytic leukemia, follicular lymphoma and diffuse large B-cell lymphoma. We discuss mechanisms and regulation of mRNA translation, potential pathways by which genetic alterations and the tumor microenvironment alters mRNA translation in malignant B cells, preclinical evaluation of drugs targeted against specific eukaryotic initiation factors and current progress towards clinical development. Overall, inhibition of mRNA translation initiation factors is an exciting and promising area for development of novel targeted anti-tumor drugs.

Bidirectional linkage between the B-cell receptor and NOTCH1 in chronic lymphocytic leukemia and in Richter's syndrome: therapeutic implications

NOTCH1 mutations in chronic lymphocytic leukemia (CLL) lead to accumulation of NOTCH1 intracellular domain (NICD) and prolong signaling. These mutations associate with a more aggressive disease compared to wild-type (WT) CLL. In this work we demonstrate a bidirectional functional relationship between NOTCH1 and the B cell receptor (BCR) pathways. By using highly homogeneous cohorts of primary CLL cells, activation of NOTCH1 is shown to increase expression of surface IgM, as well as LYN, BTK, and BLNK, ultimately enhancing BCR signaling responses, including global mRNA translation. Upon BCR cross-linking, NOTCH1 itself is actively translated and increased on cell surface. Furthermore, BCR ligation induces calcium mobilization that can facilitate ligand-independent NOTCH1 activation. These data suggest that the two pathways are functionally linked, providing a rationale for dual inhibition strategies. Consistently, addition of the γ-secretase inhibitor DAPT to ibrutinib significantly potentiates its effects, both in vitro and in a short-term patient-derived xenograft model. While this observation may find limited applications in the CLL field, it is more relevant for Richter's Syndrome (RS) management, where very few successful therapeutic options exist. Treatment of RS-patient-derived xenografts (RS-PDX) with the combination of ibrutinib and DAPT decreases disease burden and increases overall survival.

Metabolic targets of watercress and PEITC in MCF-7 and MCF-10A cells explain differential sensitisation responses to ionising radiation

PURPOSE

Watercress is a rich source of phytochemicals with anticancer potential, including phenethyl isothiocyanate (PEITC). We examined the potential for watercress extracts and PEITC to increase the DNA damage caused by ionising radiation (IR) in breast cancer cells and to be protective against radiation-induced collateral damage in healthy breast cells. The metabolic events that mediate such responses were explored using metabolic profiling.

METHODS

1H nuclear magnetic resonance spectroscopy-based metabolic profiling was coupled with DNA damage-related assays (cell cycle, Comet assay, viability assays) to profile the comparative effects of watercress and PEITC in MCF-7 breast cancer cells and MCF-10A non-tumorigenic breast cells with and without exposure to IR.

RESULTS

Both the watercress extract and PEITC-modulated biosynthetic pathways of lipid and protein synthesis and resulted in changes in cellular bioenergetics. Disruptions to the redox balance occurred with both treatments in the two cell lines, characterised by shifts in the abundance of glutathione. PEITC enhanced the sensitivity of the breast cancer cells to IR increasing the effectiveness of the cancer-killing process. In contrast, watercress-protected non-tumorigenic breast cells from radiation-induced damage. These effects were driven by changes in the cellular content of the antioxidant glutathione following exposure to PEITC and other phytochemicals in watercress.

CONCLUSION

These findings support the potential prophylactic impact of watercress during radiotherapy. Extracted compounds from watercress and PEITC differentially modulate cellular metabolism collectively enhancing the therapeutic outcomes of radiotherapy.

Ibrutinib Therapy Releases Leukemic Surface IgM from Antigen Drive in Chronic Lymphocytic Leukemia Patients

PURPOSE

In chronic lymphocytic leukemia (CLL), disease progression associates with surface IgM (sIgM) levels and signaling capacity. These are variably downmodulated in vivo and recover in vitro, suggesting a reversible influence of tissue-located antigen. Therapeutic targeting of sIgM function via ibrutinib, an inhibitor of Bruton tyrosine kinase (BTK), causes inhibition and tumor cell redistribution into the blood, with significant clinical benefit. Circulating CLL cells persist in an inhibited state, offering a tool to investigate the effects of drug on BTK-inhibited sIgM.

EXPERIMENTAL DESIGN

We investigated the consequences of ibrutinib therapy on levels and function of sIgM in circulating leukemic cells of patients with CLL.

RESULTS

At week 1, there was a significant increase of sIgM expression (64% increase from pretherapy) on CLL cells either recently released from tissue or persisting in blood. In contrast, surface IgD (sIgD) and a range of other receptors did not change. SIgM levels remained higher than pretherapy in the following 3 months despite gradual cell size reduction and ongoing autophagy and apoptotic activity. Conversely, IgD and other receptors did not increase and gradually declined. Recovered sIgM was fully N-glycosylated, another feature of escape from antigen, and expression did not increase further during culture in vitro. The sIgM was fully capable of mediating phosphorylation of SYK, which lies upstream of BTK in the B-cell receptor pathway.

CONCLUSIONS

This specific IgM increase in patients underpins the key role of tissue-based engagement with antigen in CLL, confirms the inhibitory action of ibrutinib, and reveals dynamic adaptability of CLL cells to precision monotherapy.See related commentary by Burger, p. 2372.

Target-Based Screening against eIF4A1 Reveals the Marine Natural Product Elatol as a Novel Inhibitor of Translation Initiation with In Vivo Antitumor Activity

Purpose: The DEAD-box RNA helicase eIF4A1 carries out the key enzymatic step of cap-dependent translation initiation and is a well-established target for cancer therapy, but no drug against it has entered evaluation in patients. We identified and characterized a natural compound with broad antitumor activities that emerged from the first target-based screen to identify novel eIF4A1 inhibitors.Experimental Design: We tested potency and specificity of the marine compound elatol versus eIF4A1 ATPase activity. We also assessed eIF4A1 helicase inhibition, binding between the compound and the target including binding site mutagenesis, and extensive mechanistic studies in cells. Finally, we determined maximum tolerated dosing in vivo and assessed activity against xenografted tumors.Results: We found elatol is a specific inhibitor of ATP hydrolysis by eIF4A1 in vitro with broad activity against multiple tumor types. The compound inhibits eIF4A1 helicase activity and binds the target with unexpected 2:1 stoichiometry at key sites in its helicase core. Sensitive tumor cells suffer acute loss of translationally regulated proteins, leading to growth arrest and apoptosis. In contrast to other eIF4A1 inhibitors, elatol induces markers of an integrated stress response, likely an off-target effect, but these effects do not mediate its cytotoxic activities. Elatol is less potent in vitro than the well-studied eIF4A1 inhibitor silvestrol but is tolerated in vivo at approximately 100× relative dosing, leading to significant activity against lymphoma xenografts.Conclusions: Elatol's identification as an eIF4A1 inhibitor with in vivo antitumor activities provides proof of principle for target-based screening against this highly promising target for cancer therapy. Clin Cancer Res; 24(17); 4256-70. ©2018 AACR.

CD40L/IL-4-stimulated CLL demonstrates variation in translational regulation of DNA damage response genes including ATM

CD40L/interleukin-4 (IL-4) stimulation occurs in vivo in the tumor microenvironment and induces global translation to varying degrees in individuals with chronic lymphocytic leukemia (CLL) in vitro. However, the implications of CD40L/IL-4 for the translation of specific genes is not known. To determine the most highly translationally regulated genes in response to CD40L/IL-4, we carried out ribosome profiling, a next-generation sequencing method. Significant differences in the translational efficiency of DNA damage response genes, specifically ataxia-telangiectasia-mutated kinase (ATM) and the MRE11/RAD50/NBN (MRN) complex, were observed between patients, suggesting different patterns of translational regulation. We confirmed associations between CD40L/IL-4 response and baseline ATM levels, induction of ATM, and phosphorylation of the ATM targets, p53 and H2AX. X-irradiation was used to demonstrate that CD40L/IL-4 stimulation tended to improve DNA damage repair. Baseline ATM levels, independent of the presence of 11q deletion, correlated with overall survival (OS). Overall, we suggest that there are individual differences in translation of specific genes, including ATM, in response to CD40L/IL-4 and that these interpatient differences might be clinically important.

Vacuolar ATPase as a potential therapeutic target and mediator of treatment resistance in cancer

Vacuolar ATPase (V-ATPase) is an ATP-dependent H+ -transporter that pumps protons across intracellular and plasma membranes. It consists of a large multi-subunit protein complex and influences a wide range of cellular processes. This review focuses on emerging evidence for the roles for V-ATPase in cancer. This includes how V-ATPase dysregulation contributes to cancer growth, metastasis, invasion and proliferation, and the potential link between V-ATPase and the development of drug resistance.

Abstract 1871: Development of pelorol analogues to activate the SHIP1 lipid phosphatase; a novel paradigm to suppress B-cell receptor signaling in human B-cell cancers

Signaling via the B-cell receptor (BCR) is a major driver of malignant B-cell proliferation and survival in B-cell malignancies including chronic lymphocytic leukemia (CLL). The role of kinases in BCR signalling is well understood and kinase inhibitors are effective therapies for B-cell cancers. However, resistance is increasingly common and new drugs are required. In this study we investigated an alternate strategy to block BCR signaling via small molecule activation of SHIP1, an inositol lipid phosphatase which suppresses PI3 kinase (PI3K)-mediated signaling by catalysing the conversion of the PI3K product PI(3,4,5)P3 (PIP3) to PI(3,4)P2. We focused on the exemplar compound, AQX-C5, which is structurally related to the natural product pelorol. AQX-C5 interfered with the ability of anti-IgM to activate PIP3-dependent signaling, including downstream phosphorylation of AKT, ERK1/2 and p70-S6K, and induction of MYC, in primary CLL cells. AQX-C5 also induced CLL cell apoptosis and overcame the survival-promoting effects of anti-IgM or CD40-ligand/interleukin-4. CLL cells were more sensitive to pro-apoptotic effects of AQX-C5 compared to non-malignant B cells. The AQX-C5-induced apoptosis in CLL cells was associated with down-modulation of the BCL2-related survival protein MCL1 in anti-IgM-stimulated cells, and induction of the pro-apoptotic protein NOXA. In addition to effects on PIP3-dependent signaling, AQX-C5 triggered down-modulation of CXCR4, a chemokine receptor important for homing of malignant cells to supportive tissue microenvironments. CXCR4 downmodulation was selective, since AQX-C5 did not alter surface expression of other receptors, including IgM and the transferrin receptor. In contrast to AQX-C5, the PI3Kδ inhibitor idelalisib failed to alter CXCR4 expression, indicating that these effects of AQX-C5 may be mediated via PI(3,4)P2 accumulation rather than PIP3 depletion. We evaluated the in vivo anti-lymphoma activity of AQX-C5 in a xenograft model using the TMD8 cell line, derived from a diffuse large B-cell lymphoma. Similar to the BTK inhibitor ibrutinib, AQX-C5 substantially reduced the rate of tumor growth and tumor mass at the end of the experiment, without evidence for gross toxicity. These findings suggest that SHIP1 activators, such as AQX-C5, may be interesting therapeutic agents for various B-cell cancers.

Citation Format: Graham Packham, Elizabeth Lemm, Beatriz Valle-Argos, Lindsay Smith, Nichola Weston-Bell, Freda Stevenson, Matthew J. Carter, Mark S. Cragg, Francesco Forconi, Andrew J. Steele, Jennifer Cross, Curtis Harwig, Georg Lenz, Lloyd Mackenzie, Pavel Klener. Development of pelorol analogues to activate the SHIP1 lipid phosphatase; a novel paradigm to suppress B-cell receptor signaling in human B-cell cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1871.

LSD1 inhibition attenuates androgen receptor V7 splice variant activation in castration resistant prostate cancer models

BACKGROUND

Castrate resistant prostate cancer (CRPC) is often driven by constitutively active forms of the androgen receptor such as the V7 splice variant (AR-V7) and commonly becomes resistant to established hormonal therapy strategies such as enzalutamide as a result. The lysine demethylase LSD1 is a co-activator of the wild type androgen receptor and a potential therapeutic target in hormone sensitive prostate cancer. We evaluated whether LSD1 could also be therapeutically targeted in CRPC models driven by AR-V7.

METHODS

We utilised cell line models of castrate resistant prostate cancer through over expression of AR-V7 to test the impact of chemical LSD1 inhibition on AR activation. We validated findings through depletion of LSD1 expression and in prostate cancer cell lines that express AR-V7.

RESULTS

Chemical inhibition of LSD1 resulted in reduced activation of the androgen receptor through both the wild type and its AR-V7 splice variant forms. This was confirmed and validated in luciferase reporter assays, in LNCaP and 22Rv1 prostate cancer cell lines and in LSD1 depletion experiments.

CONCLUSION

LSD1 contributes to activation of both the wild type and V7 splice variant forms of the androgen receptor and can be therapeutically targeted in models of CRPC. Further development of this approach is warranted.

Long non-coding RNAs within the tumour microenvironment and their role in tumour-stroma cross-talk

Long non-coding RNAs (lncRNAs) are a diverse class of RNA transcripts which have limited protein coding potential. They perform a variety of cellular functions in health, but have also been implicated during malignant transformation. A further theme in recent years is the critical role of the tumour microenvironment and the dynamic interactions between cancer and stromal cells in promoting invasion and disease progression. Whereas the contribution of deregulated lncRNAs within cancer cells has received considerable attention, their significance within the tumour microenvironment is less well understood. The tumour microenvironment consists of cancer-associated stromal cells and structural extracellular components which interact with one another and with the transformed epithelium via complex extracellular signalling pathways. LncRNAs are directly and indirectly involved in tumour/stroma cross-talk and help stimulate a permissive tumour microenvironment which is more conducive for invasive tumour growth. Furthermore, lncRNAs play key roles in determining the phenotype of cancer associated stromal cells and contribute to angiogenesis and immune evasion pathways, extracellular-matrix (ECM) turnover and the response to hypoxic stress. Here we explore the multifaceted roles of lncRNAs within the tumour microenvironment and their putative pathophysiological effects.

The histone deacetylase inhibitor, romidepsin, as a potential treatment for pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive disease that usually affects elderly people. It has a poor prognosis and there are limited therapies. Since epigenetic alterations are associated with IPF, histone deacetylase (HDAC) inhibitors offer a novel therapeutic strategy to address the unmet medical need. This study investigated the potential of romidepsin, an FDA-approved HDAC inhibitor, as an anti-fibrotic treatment and evaluated biomarkers of target engagement that may have utility in future clinical trials. The anti-fibrotic effects of romidepsin were evaluated both in vitro and in vivo together with any harmful effect on alveolar type II cells (ATII). Bronchoalveolar lavage fluid (BALF) from IPF or control donors was analyzed for the presence of lysyl oxidase (LOX). In parallel with an increase in histone acetylation, romidepsin potently inhibited fibroblast proliferation, myofibroblast differentiation and LOX expression. ATII cell numbers and their lamellar bodies were unaffected. In vivo, romidepsin inhibited bleomycin-induced pulmonary fibrosis in association with suppression of LOX expression. LOX was significantly elevated in BALF of IPF patients compared to controls. These data show the anti-fibrotic effects of romidepsin, supporting its potential use as novel treatment for IPF with LOX as a companion biomarker for evaluation of early on-target effects.

Epidermal Growth Factor Receptor Family Inhibition Identifies P38 Mitogen-activated Protein Kinase as a Potential Therapeutic Target in Bladder Cancer

OBJECTIVE

To investigate perturbations in downstream signaling pathway activation and potential resistance mechanisms to epidermal growth factor receptor (EGFR) or human epidermal growth factor receptor 2 (HER2) inhibition in cell line models of bladder cancer.

METHODS

We undertook a structured screening approach by phosphokinase array, followed by validation steps, to detect activated downstream signaling pathway nodes after therapeutic inhibition of EGFR or HER2 in bladder cancer cell lines.

RESULTS

Erlotinib treatment of RT112 cells induced phosphorylation of 9 activated phosphoprotein targets (p38 mitogen-activated protein kinase [MAPK] [Thr180/Tyr182], GSK-3α/β [Ser21/9], MEK1/2 [Ser218/222, Ser222/226], Akt (protein kinase B) [Ser473], TOR [target of rapamycin] [Ser2448], Src [Tyr419], p27 [Thr198], p27 [Thr157], and PLCγ-1 [Tyr783]), whereas STAT4 (signal transducer and activator of transcription 4) (Tyr693) phosphorylation was reduced. Of these, p38 MAPK phosphorylation was confirmed to occur in response to inhibition of either EGFR or HER2 signaling through multiple validation steps, including differing bladder cancer cell lines (RT112, UM-UC-3, and T24) and methods of receptor pathway inhibition (erlotinib, lapatinib, and siRNA depletion of EGFR or HER2). Chemical inhibition of p38 MAPK with SB203580 led to inhibition of proliferation in RT112, UM-UC-3, and T24 cell lines (IC₅₀ 20.85, 76.78, and 79.12 µM, respectively). Fractional effect analyses indicated a synergistic interaction for inhibition of cell proliferation when combining SB203580 with lapatinib.

CONCLUSION

p38 MAPK is a potential therapeutic target in bladder cancer and this strategy warrants further development in this disease. It may also allow combination therapy strategies to be developed in conjunction with EGFR or HER2 inhibition.

IL-10 production by CLL cells is enhanced in the anergic IGHV mutated subset and associates with reduced DNA methylation of the IL10 locus

Chronic lymphocytic leukemias (CLLs) with unmutated (U-CLL) or mutated (M-CLL) IGHV have variable features of immunosuppression, possibly influenced by those CLL cells activated to produce interleukin 10 (IL-10). The two subsets differ in their levels of anergy, defined by low surface immunoglobulin M levels/signaling capacity, and in their DNA methylation profile, particularly variable in M-CLL. We have now found that levels of IL-10 produced by activated CLL cells were highly variable. Levels were higher in M-CLL than in U-CLL and correlated with anergy. DNA methylation analysis of IL10 locus revealed two previously uncharacterized 'variably methylated regions' (CLL-VMRs1/2) in the gene body, but similarly low methylation in the promoter of both U-CLL and M-CLL. CLL-VMR1/2 methylation was lower in M-CLL than in U-CLL and inversely correlated with IL-10 induction. A functional signal transducer and activator of transcription 3 (STAT3) binding site in CLL-VMR2 was confirmed by proximity ligation and luciferase assays, whereas inhibition of SYK-mediated STAT3 activation resulted in suppression of IL10. The data suggest epigenetic control of IL-10 production. Higher tumor load may compensate the reduced IL-10 production in U-CLL, accounting for clinical immunosuppression in both subsets. The observation that SYK inhibition also suppresses IL-10 provides a potential new rationale for therapeutic targeting and immunological rescue by SYK inhibitors in CLL.

BAG-1 as a biomarker in early breast cancer prognosis: a systematic review with meta-analyses

BACKGROUND

The co-chaperone protein Bcl-2-associated athanogene-1 (BAG-1) is overexpressed in breast cancer and has been incorporated in the oncotype DX and PAM50 breast cancer prognostic assays. Bcl-2-associated athanogene-1 exists as multiple protein isoforms that interact with diverse partners, including chaperones Hsc70/Hsp70, Ser/Thr kinase Raf-1 and Bcl-2, to promote cancer cell survival. The BAG-1L isoform specifically binds to and increases the transcriptional activity of oestrogen receptor in cells, and in some, but not all studies, BAG-1 expression is predictive of clinical outcome in breast cancer.

METHODS

A systematic review of published studies reporting BAG-1 (mRNA and/or protein) expression and clinical outcome in early breast cancer. The REporting Recommendations for Tumour MARKer and Prognostic Studies (REMARK) criteria were used as a template against which data were assessed. Meta-analyses were performed for studies that provided a hazard ratio and 95% confidence intervals for clinical outcomes including disease-free survival or breast cancer-specific survival from univariate analysis.

RESULTS

Eighteen studies used differing methodologies and reported on differing outcomes. Meta-analyses were only possible on results from a subset of reported studies. Meta-analyses suggested improved outcome with high BAG-1 mRNA and high BAG-1 nuclear expression by immunohistochemisty.

CONCLUSIONS

Increased levels of BAG-1 are associated with better breast cancer outcomes.

PI3Kδ inhibition elicits anti-leukemic effects through Bim-dependent apoptosis

PI3Kδ plays pivotal roles in the maintenance, proliferation and survival of malignant B-lymphocytes. Although not curative, PI3Kδ inhibitors (PI3Kδi) demonstrate impressive clinical efficacy and, alongside other signaling inhibitors, are revolutionizing the treatment of hematological malignancies. However, only limited in vivo data are available regarding their mechanism of action. With the rising number of novel treatments, the challenge is to identify combinations that deliver curative regimes. A deeper understanding of the molecular mechanism is required to guide these selections. Currently, immunomodulation, inhibition of B-cell receptor signaling, chemokine/cytokine signaling and apoptosis represent potential therapeutic mechanisms for PI3Kδi. Here we characterize the molecular mechanisms responsible for PI3Kδi-induced apoptosis in an in vivo model of chronic lymphocytic leukemia (CLL). In vitro, PI3Kδi-induced substantive apoptosis and disrupted microenvironment-derived signaling in murine (Eμ-Tcl1) and human (CLL) leukemia cells. Furthermore, PI3Kδi imparted significant therapeutic responses in Eμ-Tcl1-bearing animals and enhanced anti-CD20 monoclonal antibody therapy. Responses correlated with upregulation of the pro-apoptotic BH3-only protein Bim. Accordingly, Bim-/- Eμ-Tcl1 Tg leukemias demonstrated resistance to PI3Kδi-induced apoptosis were refractory to PI3Kδi in vivo and failed to display combination efficacy with anti-CD20 monoclonal antibody therapy. Therefore, Bim-dependent apoptosis represents a key in vivo therapeutic mechanism for PI3Kδi, both alone and in combination therapy regimes.

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.

Chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is a malignancy of CD5+ B cells that is characterized by the accumulation of small, mature-appearing lymphocytes in the blood, marrow and lymphoid tissues. Signalling via surface immunoglobulin, which constitutes the major part of the B cell receptor, and several genetic alterations play a part in CLL pathogenesis, in addition to interactions between CLL cells and other cell types, such as stromal cells, T cells and nurse-like cells in the lymph nodes. The clinical progression of CLL is heterogeneous and ranges from patients who require treatment soon after diagnosis to others who do not require therapy for many years, if at all. Several factors, including the immunoglobulin heavy-chain variable region gene (IGHV) mutational status, genomic changes, patient age and the presence of comorbidities, should be considered when defining the optimal management strategies, which include chemotherapy, chemoimmunotherapy and/or drugs targeting B cell receptor signalling or inhibitors of apoptosis, such as BCL-2. Research on the biology of CLL has profoundly enhanced our ability to identify patients who are at higher risk for disease progression and our capacity to treat patients with drugs that selectively target distinctive phenotypic or physiological features of CLL. How these and other advances have shaped our current understanding and treatment of patients with CLL is the subject of this Primer.

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.

Epigenetic modulators as therapeutic targets in prostate cancer

Prostate cancer is one of the most common non-cutaneous malignancies among men worldwide. Epigenetic aberrations, including changes in DNA methylation patterns and/or histone modifications, are key drivers of prostate carcinogenesis. These epigenetic defects might be due to deregulated function and/or expression of the epigenetic machinery, affecting the expression of several important genes. Remarkably, epigenetic modifications are reversible and numerous compounds that target the epigenetic enzymes and regulatory proteins were reported to be effective in cancer growth control. In fact, some of these drugs are already being tested in clinical trials. This review discusses the most important epigenetic alterations in prostate cancer, highlighting the role of epigenetic modulating compounds in pre-clinical and clinical trials as potential therapeutic agents for prostate cancer management.

Annexin A3 is a mammary marker and a potential neoplastic breast cell therapeutic target

Breast cancers are the most common cancer-affecting women; critically the identification of novel biomarkers for improving early detection, stratification and differentiation from benign tumours is important for the reduction of morbidity and mortality.

To identify and functionally characterise potential biomarkers, we used mass spectrometry (MS) to analyse serum samples representing control, benign breast disease (BBD) and invasive breast cancer (IDC) patients. Complementary and multidimensional proteomic approaches were used to identify and validate novel serum markers.

Annexin A3 (ANX A3) was found to be differentially expressed amongst different breast pathologies. The diagnostic value of serum ANX A3 was subsequently validated by ELISA in an independent serum set representing the three groups. Here, ANX A3 was significantly upregulated in the benign disease group sera compared with other groups (P < 0.0005).

In addition, paired breast tissue immunostaining confirmed that ANX A3 was abundantly expressed in benign and to a lesser extent malignant neoplastic epithelium. Finally, we illustrated ANX A3 expression in cell culture lysates and conditioned media from neoplastic breast cell lines, and its role in neoplastic breast cell migration in vitro.

This study confirms the novel role of ANX A3 as a mammary biomarker, regulator and therapeutic target.

A ribosome-related signature in peripheral blood CLL B cells is linked to reduced survival following treatment

We have used polysome profiling coupled to microarray analysis to examine the translatome of a panel of peripheral blood (PB) B cells isolated from 34 chronic lymphocytic leukaemia (CLL) patients. We have identified a ‘ribosome-related' signature in CLL patients with mRNAs encoding for ribosomal proteins and factors that modify ribosomal RNA, e.g. DKC1 (which encodes dyskerin, a pseudouridine synthase), showing reduced polysomal association and decreased expression of the corresponding proteins. Our data suggest a general impact of dyskerin dysregulation on the translational apparatus in CLL and importantly patients with low dyskerin levels have a significantly shorter period of overall survival following treatment. Thus, translational dysregulation of dyskerin could constitute a mechanism by which the CLL PB B cells acquire an aggressive phenotype and thus have a major role in oncogenesis.

The clinical and biological significance of MIR-224 expression in colorectal cancer metastasis

OBJECTIVE

MicroRNA (miRNA) expression profile can be used as prognostic marker for human cancers. We aim to explore the significance of miRNAs in colorectal cancer (CRC) metastasis.

DESIGN

We performed miRNA microarrays using primary CRC tissues from patients with and without metastasis, and validated selected candidates in 85 CRC samples by quantitative real-time PCR (qRT-PCR). We tested metastatic activity of selected miRNAs and identified miRNA targets by prediction algorithms, qRT-PCR, western blot and luciferase assays. Clinical outcomes were analysed in six sets of CRC cases (n=449), including The Cancer Genome Atlas (TCGA) consortium and correlated with miR-224 status. We used the Kaplan-Meier method and log-rank test to assess the difference in survival between patients with low or high levels of miR-224 expression.

RESULTS

MiR-224 expression increases consistently with tumour burden and microsatellite stable status, and miR-224 enhances CRC metastasis in vitro and in vivo. We identified SMAD4 as a miR-224 target and observed negative correlation (Spearman Rs=-0.44, p<0.0001) between SMAD4 and miR-224 expression in clinical samples. Patients with high miR-224 levels display shorter overall survival in multiple CRC cohorts (p=0.0259, 0.0137, 0.0207, 0.0181, 0.0331 and 0.0037, respectively), and shorter metastasis-free survival (HR 6.51, 95% CI 1.97 to 21.51, p=0.0008). In the TCGA set, combined analysis of miR-224 with SMAD4 expression enhanced correlation with survival (HR 4.12, 95% CI 1.1 to 15.41, p=0.0175).

CONCLUSIONS

MiR-224 promotes CRC metastasis, at least in part, through the regulation of SMAD4. MiR-224 expression in primary CRC, alone or combined with its targets, may have prognostic value for survival of patients with CRC.

Recurrent mTORC1-activating RRAGC mutations in follicular lymphoma

Follicular lymphoma is an incurable B cell malignancy characterized by the t(14;18) translocation and mutations affecting the epigenome. Although frequent gene mutations in key signaling pathways, including JAK-STAT, NOTCH and NF-κB, have also been defined, the spectrum of these mutations typically overlaps with that in the closely related diffuse large B cell lymphoma (DLBCL). Using a combination of discovery exome and extended targeted sequencing, we identified recurrent somatic mutations in RRAGC uniquely enriched in patients with follicular lymphoma (17%). More than half of the mutations preferentially co-occurred with mutations in ATP6V1B2 and ATP6AP1, which encode components of the vacuolar H(+)-ATP ATPase (V-ATPase) known to be necessary for amino acid-induced activation of mTORC1. The RagC variants increased raptor binding while rendering mTORC1 signaling resistant to amino acid deprivation. The activating nature of the RRAGC mutations, their existence in the dominant clone and their stability during disease progression support their potential as an excellent candidate for therapeutic targeting.

T-cell number and subtype influence the disease course of primary chronic lymphocytic leukaemia xenografts in alymphoid mice

Chronic lymphocytic leukaemia (CLL) cells require microenvironmental support for their proliferation. This can be recapitulated in highly immunocompromised hosts in the presence of T cells and other supporting cells. Current primary CLL xenograft models suffer from limited duration of tumour cell engraftment coupled with gradual T-cell outgrowth. Thus, a greater understanding of the interaction between CLL and T cells could improve their utility. In this study, using two distinct mouse xenograft models, we investigated whether xenografts recapitulate CLL biology, including natural environmental interactions with B-cell receptors and T cells, and whether manipulation of autologous T cells can expand the duration of CLL engraftment. We observed that primary CLL xenografts recapitulated both the tumour phenotype and T-cell repertoire observed in patients and that engraftment was significantly shorter for progressive tumours. A reduction in the number of patient T cells that were injected into the mice to 2-5% of the initial number or specific depletion of CD8(+) cells extended the limited xenograft duration of progressive cases to that characteristic of indolent disease. We conclude that manipulation of T cells can enhance current CLL xenograft models and thus expand their utility for investigation of tumour biology and pre-clinical drug assessment.

High throughput imaging cytometer with acoustic focussing

We demonstrate an imaging flow cytometer that uses acoustic levitation to assemble cells and other particles into a sheet structure. This technique enables a high resolution, low noise CMOS camera to capture images of thousands of cells with each frame. While ultrasonic focussing has previously been demonstrated for 1D cytometry systems, extending the technology to a planar, much higher throughput format and integrating imaging is non-trivial, and represents a significant jump forward in capability, leading to diagnostic possibilities not achievable with current systems. A galvo mirror is used to track the images of the moving cells permitting exposure times of 10 ms at frame rates of 50 fps with motion blur of only a few pixels. At 80 fps, we demonstrate a throughput of 208 000 beads per second. We investigate the factors affecting motion blur and throughput, and demonstrate the system with fluorescent beads, leukaemia cells and a chondrocyte cell line. Cells require more time to reach the acoustic focus than beads, resulting in lower throughputs; however a longer device would remove this constraint.

Abstract 3584: Lysine specific demethylase 1 inhibition attenuates enzalutamide resistant androgen receptor V7 splice variant activation

Prostate cancer remains one of the leading causes of cancer death in men worldwide. The majority of prostate cancer is initially hormone dependent highlighting the central role of the androgen receptor (AR) pathway in this disease. However, in a significant number of the cases, patients relapse and develop castration resistant prostate cancer (CRPC) through a variety of molecular mechanisms, many of which include AR modifications. One common resistant mechanism is through an AR-V7 splice variant lacking the C-terminal ligand-binding domain (LBD) but retaining the transactivating N-terminal domain. AR-V7 is constitutively active. Emerging data imply that hormonal therapy with the AR antagonist enzalutamide, which is highly effective in some CRPC patients, becomes ineffective in the face of AR-V7 consistent with the loss of its LBD binding site.

Lysine-specific demethylase 1 (LSD1) is a co-activator of the AR pathway which interacts with the AR to promote androgen-dependent transcription of target genes by ligand-induced demethylation of mono- and dimethylated histone 3 at Lys 9. In this work we identified LSD1 as new potential target for treatment of CRPC resistant to enzalutamide treatment through AR-V7 expression.

We used reporter assay experiments in human embryonic kidney 293 cells, deficient for androgen receptor, to investigate the transactivation control of the putative androgen receptor responsive element (ARE) in the presence of the wild type (WT) form and the constitutively active V7 variant of the AR. Using this approach we show that enzalutamide effectively inhibits the activation of the ARE by the AR-WT but not the AR-V7 variant upon stimulation with dihydrotestosterone (DHT). However, treatment with a LSD1 inhibitor shows reduced transcription of the ARE promoter with the AR-wt with DHT stimulation and AR-V7 with and without DHT stimulation.

Treatment of an androgen-sensitive human prostate adenocarcinoma cell line (LNCaP) with DHT shows an increase in the expression of prostate specific antigen (PSA) gene, an AR transcriptional target. However when treated with LSD1 inhibitors this activation was impaired or completely blocked as PSA levels were similar to those in non DHT treated sample. Moreover we show that treatment of LNCaP cells with LSD1 inhibitors trigger apoptosis as indicated by PARP cleavage.

Together this results show that by targeting LSD1, a co-activator of the AR, we can inhibit the expression of AR target genes in a clinically relevant model of enzalutamide resistant AR-V7 expressing CRPC. LSD1 holds potential as a target for cancer therapy in castration resistant prostate cancer.

This work was supported by Prostate Cancer UK.

Citation Format: Sergio Regufe da Mota, Sarah Bailey, Rosemary A. Strivens, Annette L. Hayden, Graham Packham, Simon J. Crabb. Lysine specific demethylase 1 inhibition attenuates enzalutamide resistant androgen receptor V7 splice variant activation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3584. doi:10.1158/1538-7445.AM2015-3584

Investigational epigenetically targeted drugs in early phase trials for the treatment of haematological malignancies

INTRODUCTION

For decades, cancer research has focussed on the genetic defects that drive tumourigenesis. However, recent high-resolution sequencing studies have uncovered mounting evidence for the complementary role of epigenetic deregulation as a hallmark of haematological malignancies. The reversibility of epigenetic changes makes them suitable candidates for pharmacological manipulation and therapeutic targeting.

AREAS COVERED

This review summarises the mechanisms of normal epigenetic regulation and how these are perturbed in haematological malignancies as a result of genetic alterations. The article concludes with how these can be reversed and appraises the investigational epigenetically targeted therapies in preclinical and clinical use.

EXPERT OPINION

The identification of recurring alterations in components of the epigenome of leukaemia and lymphoma has driven the rapid development of highly potent epigenetically targeted therapies. This rapid development has alluded to the possibility of a personalised therapeutic approach in selected patient populations. An enhanced understanding of the biological effects of these epigenetic alterations in initiation and progression of haematological malignancies, together with a clear mechanistic insight into how the drugs reverse the phenotypes, will define their translation into routine clinical use.