Inhibiting Bruton's Tyrosine Kinase in CLL and Other B-Cell Malignancies

Inhibitors of Bruton's tyrosine kinase (BTK), a major kinase in the B-cell receptor (BCR) signaling pathway, mediating B-cell proliferation and apoptosis, have substantially altered the management, clinical course, and outcome of patients with B-cell malignancies. This is especially true for patients with previously limited treatment options due to disease characteristics or coexisting diseases. Ibrutinib was the first orally available, nonselective and irreversible inhibitor of BTK approved for the treatment of patients with various B-cell malignancies. Newer and more selective BTK inhibitors are currently in clinical development, including acalabrutinib, which is currently US FDA approved for previously treated mantle cell lymphoma. Significant efforts are underway to investigate the optimal combinations, timing, and sequencing of BTK inhibitors with other regimens and targeted agents, and to capitalize on the immunomodulatory modes of action of BTK inhibitors to correct tumor-induced immune defects and to achieve long-lasting tumor control. This review describes the major milestones in the clinical development of BTK inhibitors in chronic lymphocytic leukemia and other B-cell malignancies, highlights the most recent long-term follow-up results, and evaluates the role of BTK inhibitors and their combination with other agents in B-cell malignancies and other indications.

MAP3K11 is a tumor suppressor targeted by the oncomiR miR-125b in early B cells

MicroRNAs (miRNAs) are a class of small, non-coding RNAs that posttranscriptionally regulate gene expression and thereby control most, if not all, biological processes. Aberrant miRNA expression has been linked to a variety of human diseases including cancer, but the underlying molecular mechanism often remains unclear. Here we have screened a miRNA expression library in a growth factor-dependent mouse pre-B-cell system to identify miRNAs with oncogenic activity. We show that miR-125b is sufficient to render pre-B cells growth factor independent and demonstrate that continuous expression of miR-125b is necessary to keep these cells in a transformed state. Mechanistically, we find that the expression of miR-125b protects against apoptosis induced by growth factor withdrawal, and that it blocks the differentiation of pre-B to immature B cells. In consequence, miR-125b-transformed cells maintain expression of their pre-B-cell receptor that provides signals for continuous proliferation and survival even in the absence of growth factor. Employing microarray analysis, we identified numerous targets of miR-125b, but only reconstitution of MAP3K11, a critical regulator of mitogen- and stress-activated kinase signaling, interferes with the cellular fitness of the transformed cells. Together, this indicates that MAP3K11 might function as an important tumor suppressor neutralized by oncomiR-125b in B-cell leukemia.

Targeting Bruton's tyrosine kinase with ibrutinib in B-cell malignancies

The B-cell receptor signaling pathway, which is critical to the development and maturation of normal B-cells, is emerging as an attractive therapeutic target in B-cell malignancies. Ibrutinib is a potent irreversible inhibitor of Bruton's tyrosine kinase (Btk), a key kinase important for signal transduction in the B-cell receptor (BCR) pathway. In preclinical studies, ibrutinib potently bound to Btk, inhibited BCR signaling, and decreased tumor cell proliferation and survival in many B-cell malignancy models. Excellent safety and efficacy data in clinical trials have led to US Food and Drug Administration (FDA) approval of ibrutinib for previously treated mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL), as well as CLL with 17p deletion. Ongoing clinical studies have also demonstrated great potency of ibrutinib in treating other types of non-Hodgkin's lymphoma (NHL), including diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), and Waldenström's macroglobulinemia (WM). Combination of ibrutinib with chemoimmunotherapy and other promising novel agents in B-cell malignancy therapy has also been under clinical investigation.

Bruton's tyrosine kinase: from X-linked agammaglobulinemia toward targeted therapy for B-cell malignancies

Discovery of Bruton's tyrosine kinase (BTK) mutations as the cause for X-linked agammaglobulinemia was a milestone in understanding the genetic basis of primary immunodeficiencies. Since then, studies have highlighted the critical role of this enzyme in B-cell development and function, and particularly in B-cell receptor signaling. Because its deletion affects mostly B cells, BTK has become an attractive therapeutic target in autoimmune disorders and B-cell malignancies. Ibrutinib (PCI-32765) is the most advanced BTK inhibitor in clinical testing, with ongoing phase III clinical trials in patients with chronic lymphocytic leukemia and mantle-cell lymphoma. In this article, we discuss key discoveries related to BTK and clinically relevant aspects of BTK inhibitors, and we provide an outlook into clinical development and open questions regarding BTK inhibitor therapy.

Targeting Bruton's tyrosine kinase in B cell malignancies

Bruton's tyrosine kinase (BTK) is a key component of B cell receptor (BCR) signalling and functions as an important regulator of cell proliferation and cell survival in various B cell malignancies. Small-molecule inhibitors of BTK have shown antitumour activity in animal models and, recently, in clinical studies. High response rates were reported in patients with chronic lymphocytic leukaemia and mantle cell lymphoma. Remarkably, BTK inhibitors have molecular effects that cannot be explained by the classic role of BTK in BCR signalling. In this Review, we highlight the importance of BTK in various signalling pathways in the context of its therapeutic inhibition.

A kinase-independent function of CDK6 links the cell cycle to tumor angiogenesis

In contrast to its close homolog CDK4, the cell cycle kinase CDK6 is expressed at high levels in lymphoid malignancies. In a model for p185BCR-ABL+ B-acute lymphoid leukemia, we show that CDK6 is part of a transcription complex that induces the expression of the tumor suppressor p16INK4a and the pro-angiogenic factor VEGF-A. This function is independent of CDK6's kinase activity. High CDK6 expression thus suppresses proliferation by upregulating p16INK4a, providing an internal safeguard. However, in the absence of p16INK4a, CDK6 can exert its full tumor-promoting function by enhancing proliferation and stimulating angiogenesis. The finding that CDK6 connects cell-cycle progression to angiogenesis confirms CDK6's central role in hematopoietic malignancies and could underlie the selection pressure to upregulate CDK6 and silence p16INK4a.

The dual kinase inhibitor NVP-BEZ235 in combination with cytotoxic drugs exerts anti-proliferative activity towards acute lymphoblastic leukemia cells

BACKGROUND

Inhibition of signal transduction pathways has been successfully introduced into cancer treatment. The dual phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitor NVP-BEZ235 has antitumor activity in vitro against solid tumors. Here, we examined the activity of NVP-BEZ235 in acute lymphoblastic leukemia (ALL) cells and the best modalities for combination approaches.

MATERIALS AND METHODS

ALL cell lines (SEM, RS4;11, Jurkat and MOLT4) were treated with NVP-BEZ235 alone, or in combination with cytarabine (AraC), doxorubicin (Doxo) or dexamethasone (Dexa).

RESULTS

NVP-BEZ235 potently inhibited the proliferation and metabolic activity of ALL cells. Antiproliferative effects were associated with G(0)/G(1) arrest and reduced levels of cyclin-dependent kinase 4 (CDK4) and cyclin D3. Inhibition of PI3K and mTOR activity was detected at 10 and 100 nM. NVP-BEZ235 combined with AraC, Doxo or Dexa synergistically enhanced the cytotoxicity compared to single-drug treatment, even in glucocorticoid-resistant cells.

CONCLUSION

NVP-BEZ235 displays pronounced antiproliferative effects in ALL cells and might therefore be a useful drug in the treatment of ALL.

Bruton's tyrosine kinase prevents activation of the anti-apoptotic transcription factor STAT3 and promotes apoptosis in neoplastic B-cells and B-cell precursors exposed to oxidative stress

Bruton's tyrosine kinase (BTK) was previously demonstrated to be a mediator of oxidative stress-induced apoptosis in irradiated neoplastic B-cells and B-cell precursors. Defective BTK expression in leukaemic B-cell precursors from infants with t(4;11) acute lymphoblastic leukaemia has been associated with radiation resistance. The present study examined whether BTK mediates apoptosis during oxidative stress by interfering with the anti-apoptotic function of signal transducer and activator of transcription 3 (STAT3). BTK physically associated with and tyrosine phosphorylated STAT3; this association was promoted by pervanadate (PV)-induced oxidative stress. The BTK/STAT3 interaction appeared to prevent STAT3 response to oxidative stress, because PV-induced STAT3 activation was markedly enhanced in DT40 chicken lymphoma B-cells that were rendered BTK-deficient by targeted disruption of the btk gene as well as in BTK-deficient RAMOS-1 human lymphoma B-cells. These BTK-deficient cells were highly resistant to oxidative stress-induced apoptosis triggered by PV treatment. Reconstitution of BTK-deficient DT40 cells with wild-type human BTK gene eliminated the amplification of the STAT3 response and restored the PV-induced apoptotic signal. Similarly, while the BTK-positive NALM-6 human leukaemic B-cell precursor cell line showed no STAT3 activation after PV treatment and was exquisitely sensitive to PV-induced apoptosis, PV failed to induce apoptosis in BTK-deficient RAMOS-1 human lymphoma B-cells that showed a robust STAT3 response. These results provide unprecedented biochemical and genetic evidence for a unique mode of cross-talk that occurs between BTK and STAT3 pathways during oxidative stress, whereby BTK may trigger apoptosis via negative regulation of the anti-apoptotic STAT3 activity.

MMP-9 in B-cell chronic lymphocytic leukemia is up-regulated by alpha4beta1 integrin or CXCR4 engagement via distinct signaling pathways, localizes to podosomes, and is involved in cell invasion and migration

B-cell chronic lymphocytic leukemia (B-CLL) progression is determined by malignant cell extravasation and lymphoid tissue infiltration. We have studied the role and regulation of matrix metalloproteinase-9 (MMP-9) in B-CLL cell migration and invasion. Adhesion of B-CLL cells to the fibronectin fragment FN-H89, VCAM-1, or TNF-alpha-activated human umbilical vein endothelial cells (HUVECs) up-regulated MMP-9 production, measured by gelatin zymography. This effect was mediated by alpha4beta1 integrin and required PI3-K/Akt signaling. The chemokine CXCL12 also up-regulated MMP-9, independently of alpha4beta1 and involving ERK1/2 but not Akt activity. Accordingly, alpha4beta1 engagement activated the PI3-K/Akt/NF-kappaB pathway, while CXCL12/CXCR4 interaction activated ERK1/2/c-Fos signaling. Anti-MMP-9 antibodies, the MMP-9 inhibitor TIMP-1, or transfection with 3 different MMP-9 siRNAs significantly blocked migration through Matrigel or HUVECs. Cell-associated MMP-9 was mainly at the membrane and contained the proactive and mature forms. Moreover, B-CLL cells formed podosomes upon adhesion to FN-H89, VCAM-1, or fibronectin; MMP-9 localized to podosomes in a PI3-K-dependent manner and degraded a fibronectin/gelatin matrix. Our results are the first to show that MMP-9 is physiologically regulated by alpha4beta1 integrin and CXCL12 and plays a key role in cell invasion and transendothelial migration, thus contributing to B-CLL progression. MMP-9 could therefore constitute a target for treatment of this malignancy.

ZAP-70 in B cell malignancies

ZAP-70 has emerged as a protein of potential prognostic importance in chronic lymphocytic leukemia (CLL) following gene expression profiling which compared the 2 well established prognostic sub-sets, those with unmutated and mutated IgVH genes. This protein tyrosine kinase (PTK), known to be of importance in T and NK cell signaling but absent in normal peripheral B cells, is expressed in the majority of the poorer prognosis unmutated CLL and absent in most cases with mutated IgVH genes. ZAP-70 has been shown to be functionally important in the CLL cases in which it is expressed; it is also important in B cell development in mice and there is preliminary evidence for its expression in human B cell progenitors and activated B cells. Whether its expression in a sub-set of CLL cases is a result of a more activated cell type or a reflection of the stage of maturation of the transforming event(s) in CLL is open to debate. ZAP-70 is expressed in a minority of other B cell tumors but correlation with IgVH gene mutational status is lacking. The problems with ZAP-70 measurement, which has yet to be standardized, are reviewed together with its current status as a prognostic marker in CLL.

Subversion of protein kinase C alpha signaling in hematopoietic progenitor cells results in the generation of a B-cell chronic lymphocytic leukemia-like population in vivo

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of long-lived mature B cells with the distinctive phenotype CD19(hi) CD5+ CD23+ IgM(lo), which are refractory to apoptosis. An increased level of apoptosis has been observed on treatment of human B-CLL cells with protein kinase C (PKC) inhibitors, suggesting that this family of protein kinases mediate survival signals within B-CLL cells. Therefore, to investigate the ability of individual PKC isoforms to transform developing B cells, we stably expressed plasmids encoding PKC mutants in fetal liver-derived hematopoietic progenitor cells (HPC) from wild-type mice and then cultured them in B-cell generation systems in vitro and in vivo. Surprisingly, we noted that expression of a plasmid-encoding dominant-negative PKC alpha (PKC alpha-KR) in HPCs and subsequent culture both in vitro and in vivo resulted in the generation of a population of cells that displayed an enhanced proliferative capacity over untransfected cells and phenotypically resemble human B-CLL cells. In the absence of growth factors and stroma, these B-CLL-like cells undergo cell cycle arrest and, consistent with their ability to escape growth factor withdrawal-induced apoptosis, exhibited elevated levels of Bcl-2 expression. These studies therefore identify a unique oncogenic trigger for the development of a B-CLL-like disease resulting from the subversion of PKC alpha signaling. Our findings uncover novel avenues not only for the study of the induction of leukemic B cells but also for the development of therapeutic drugs to combat PKC alpha-regulated transformation events.

Hyperforin inhibits MMP-9 secretion by B-CLL cells and microtubule formation by endothelial cells

We previously reported that hyperforin (HF), a natural phloroglucinol purified from Saint John's wort, can induce the apoptosis of leukemic cells from patients with B-cell lymphocytic leukemia (B-CLL) ex vivo. We show here that treatment of cultured B-CLL patients' cells with HF results in a marked inhibition of their capacity to secrete matrix metalloproteinase-9, an essential component in neo-angiogenesis through degradation of the extracellular matrix process. The phloroglucinol acts by decreasing the production of the latent 92 kDa pro-enzyme. The inhibitory effect of HF is associated with a decrease in VEGF release by the leukemic cells. Moreover, HF is found to prevent the formation of microtubules by human bone marrow endothelial cells cultured on Matrigel, evidencing its capacity to inhibit vessel formation. Our results show the antiangiogenesis activity of HF and strengthen its potential interest in the therapy of B-CLL.

Interference of BCR-ABL1 kinase activity with antigen receptor signaling in B cell precursor leukemia cells

The chromosomal translocation t,(9;22) resulting in the fusion of the BCR and ABL1 genes, represents a recurrent aberration in B cell precursor leukemia cells. Their normal counterparts, B cell precursor cells, are positively selected for survival signals through the antigen receptor, whose expression requires a functional immunoglobulin heavy chain (IGH) gene rearrangement. Unexpectedly, B cell precursor leukemia cells harboring a BCR-ABL1 gene rearrangement do not depend on antigen receptor mediated survival signals. Genes involved in the signaling cascade of the antigen receptor are silenced and in most cases, the dominant tumor clone does not carry a functional IGH gene rearrangement. However, upon inhibition of the BCR-ABL1 kinase activity by STI571, only leukemia cells expressing an antigen receptor are able to survive. Since resistance to STI571 is frequent in the therapy of BCR-ABL1(+) B cell precursor leukemia, antigen receptor signaling may represent a mechanism through which these cells can temporarily evade STI571-induced apoptosis. This may open a time frame, during which leukemia cells acquire secondary transforming events that confer definitive resistance to STI571.

The endogenous, immunologically active peptide apelin inhibits lymphocytic cholinergic activity during immunological responses

We investigated the effects of apelin, an immunologically active peptide ligand for orphan receptor APJ, on acetylcholine (ACh) synthesis in MOLT-3 human leukemic T cells. We initially confirmed expression of APJ mRNA in several human T- and B-cell lines by reverse transcription-polymerase chain reaction (RT-PCR). We also found that in phytohemagglutinin (PHA)-stimulated MOLT-3 cells, an active apelin fragment, apelin-13, down-regulates expression of choline acetyltransferase (ChAT) mRNA and significantly reduces ChAT activity and cellular ACh content and release. It thus appears that apelin inhibits lymphocytic cholinergic activity via APJ during immunological responses.

Activated proliferation of B-cell lymphomas/leukemias with the SHP1 gene silencing by aberrant CpG methylation

Previously we showed reduced protein and mRNA expression of the SHP1 gene in lymphoma/leukemia cell lines and patient specimens by Northern blot, RT-PCR, Western blot, and immunohistochemical analyses. In this study, aberrant methylation in the SHP1 gene promoter was detected in many B-cell leukemia/lymphoma cell lines as well as in patient specimens, including diffuse large B-cell lymphoma (methylation frequency 93%), MALT lymphoma (82%), mantle cell lymphoma (75%), plasmacytoma (100%) and follicular lymphoma (96%) by methylation-specific PCR, bisulfite sequencing, and restriction enzyme-mediated PCR analyses. The methylation frequency was significantly higher in high-grade MALT lymphoma cases (100%) than in low-grade MALT lymphoma cases (70%), which correlated well with the frequency of no expression of SHP1 protein in high-grade (80%) and low-grade MALT lymphoma (54%). It suggests that the SHP1 gene silencing with aberrant CpG methylation relates to the lymphoma progression. SHP1 protein expression was recovered in B-cell lines after the treatment of the demethylating reagent: 5-aza-2'-deoxycytidine. Transfection of the intact SHP1 gene to the hematopoietic cultured cells, which show no expression of the SHP1 gene, induced growth inhibition, indicating that gene silencing of the SHP1 gene by aberrant methylation plays an important role to get the growth advantage of the malignant lymphoma/leukemia cells. The extraordinarily high frequency (75 to 100%) of CpG methylation of the SHP1 gene in B-cell lymphoma/leukemia patient specimens indicates that the SHP1 gene silencing is one of the critical events to the onset of malignant lymphomas/leukemias as well as important implications for the diagnostic or prognostic markers and the target of gene therapy. These data support the possibility that the SHP1 gene is one of the tumor suppressor genes.

Heat- and 4-hydroperoxy-ifosfamide-induced apoptosis in B cell precursor leukaemias

In the group of high risk childhood acute lymphoblastic leukaemia (ALL), very early and early relapses have a very poor prognosis with conventional chemotherapy alone. Remission induction in these patients is often hindered by drug resistance. Thus, intensifying chemotherapy strategies are required. Application of hyperthermia enhances efficacy of certain anti-neoplastic drugs such as ifosfamide. In this study, effects and molecular mechanisms of ifosfamide - and hyperthermia-induced apoptosis are investigated in a B cell precursor leukaemia cell line (REH) and in primary patient-derived B cell progenitor leukaemic blasts. Both 4OOH-IFA and hyperthermia are able to induce cell death in leukaemic cells, mainly by induction of caspase-dependent apoptosis. However, completely different kinetics of caspase-3, -8 and -9 activation are found for both stimuli. In addition, activation of caspase-1 is only observed following stimulation with hyperthermia. Combined application of ifosfamide and hyperthermia reveals increased cytotoxicity in both the leukaemia cell line and in 5/8 of the patient-derived leukaemic blast samples. In conclusion, hyperthermia and ifosfamide mediate cytotoxicity in B precursor leukaemic blasts by different kinetics of caspase activation. This might explain the additive effects of 4OOH-IFA and heat on leukaemic cell death. Therefore, whole body thermochemotherapy could be considered as a treatment option in relapsed leukaemic patients.

Constitutive activation of extracellular signal-regulated kinase and p38 mitogen-activated protein kinase in B-cell lymphoproliferative disorders

Signaling molecules such as p21(ras) (Ras), mitogen-activated protein kinase (MAPK), and Akt kinase play pivotal roles in the proliferation and survival of lymphoid cells in response to many kinds of stimulation. It is not fully understood, however, how these molecules participate in the growth of malignant lymphoid cells. We determined whether Ras, MAPKs such as extracellular signal-regulated kinase (ERK), c-Jun amino-terminal kinase (JNK), and p38 MAPK, and Akt kinase are activated in B-cell tumors, including acute lymphoblastic leukemia, chronic lymphocytic leukemia, Burkitt-like lymphoma, diffuse large B-cell lymphoma, and plasma cell leukemia. We found that Lyn protein tyrosine kinase was constitutively phosphorylated on tyrosine, and that ERK and p38 MAPK were constitutively active in all cases of the B-cell tumor. In contrast, activation of Ras and Akt kinase was found in limited cases, and JNK kinase activity was not observed in any case. These results suggest that ERK and p38 play roles in the oncogenesis of B-cell tumors.

Proteasome inhibitors in the treatment of B-cell malignancies

The proteasome, which plays a pivotal role in the control of many cell cycle-regulatory processes, has become the focus of new approaches to the treatment of cancer, including B-cell malignancies, and the first proteasome inhibitor, bortezomib (VELCADE; formerly PS-341), has entered clinical trials. The proteasome controls the stability of numerous proteins that regulate progression through the cell cycle and apoptosis, such as cyclins, cyclin-dependent kinases, tumor suppressors, and the nuclear factor-kB. By altering the stability or activity of these proteins, proteasome inhibitors sensitize malignant cells to apoptosis. Bortezomib is a dipeptidyl boronic acid proteasome inhibitor that effectively and specifically inhibits proteasome activity. In preclinical studies, bortezomib and other proteasome inhibitors have shown activity against a variety of B-cell malignancies, including multiple myeloma, diffuse large B-cell lymphoma, mantle cell lymphoma, and Hodgkin's lymphoma. These agents can induce apoptosis and sensitize tumor cells to radiation or chemotherapy. Based on these findings, phase I clinical trials were conducted with bortezomib in various solid and hematologic malignancies. In these studies, bortezomib was generally well tolerated with manageable toxicities. Phase II trials have been initiated for relapsed and refractory multiple myeloma, refractory chronic lymphocytic leukemia, and non-Hodgkin's lymphoma. Preliminary data from the multiple myeloma phase II study indicate that a significant number of patients responded to therapy or exhibited stable disease and that the drug had manageable toxicities. These findings, along with extensive preclinical data, suggest that bortezomib and other proteasome inhibitors may have far-reaching potential in the treatment of various cancers, including B-cell malignancies.

Altered regulation of SHP-2 and PTP 1B tyrosine phosphatases in cystic kidneys from bcl-2 -/- mice

Protein tyrosine phosphorylation is a dynamic reversible process in which the level of phosphorylation, at any time, is the result of phosphatase and/or kinase activity. This balance is critical for control of growth and differentiation. The role of tyrosine phosphatases during nephrogenesis and in kidney disease requires delineation. Appropriate regulation of focal adhesion proteins such as focal adhesion kinase (FAK) and paxillin are important in cell adhesion, migration, and differentiation. We have previously shown that B cell lymphoma/leukemia-2 (bcl-2) -/- mice develop cystic kidneys and exhibit sustained phosphorylation of FAK and paxillin. We have examined the expression and activity of focal adhesion tyrosine phosphatases [Src homology-2 domain phosphatase (SHP-2), protein tyrosine phosphatase (PTP 1B), and PTP-proline, glutamate, serine, and threonine sequences (PEST)] during normal nephrogenesis and in cystic kidneys from bcl-2 -/- mice. Cystic kidneys from postnatal day 20 bcl-2 -/- mice demonstrate a reduced expression, sixfold decrease in activity, and altered distribution of SHP-2 and PTP 1B. PTP-PEST expression and distribution were similar in both bcl-2 +/+ and bcl-2 -/- mice. The altered regulation of PTP 1B and SHP-2 in kidneys from bcl-2 -/- mice correlates with sustained phosphorylation of FAK and paxillin. Thus renal cyst formation in the bcl-2 -/- mice may be the result of an inability of complete differentiation due to continued activation of growth processes, including activation of FAK and paxillin.

CpG island methylation of the hTERT promoter is associated with lower telomerase activity in B-cell lymphocytic leukemia

OBJECTIVE

Expression of the catalytic subunit of the telomerase enzyme hTERT is essential for prolonging the replicative lifespan and is the rate-limiting step in cellular immortalization and carcinogenesis. Because hTERT expression is positively correlated with telomerase activity, its regulation is suggested as the major determinant of enzymatic activity. The hTERT promoter region contains two CpG islands, which are known to be target sites for de novo DNA methylation. To elucidate the impact of this epigenetic mechanism on telomerase activity, we analyzed the degree of hTERT promoter methylation in 30 patients with B-cell chronic lymphocytic leukemia.

MATERIALS AND METHODS

hTERT promoter methylation was assessed using a methylation-specific competitive polymerase chain reaction assay. The assay is based on digestion of genomic DNA with a methylation-sensitive restriction enzyme before amplification with an internal standard.

RESULTS

Patients exhibiting high telomerase activity showed significantly less methylation of the hTERT promoter core domain than patients with low enzyme activity. In addition, telomerase activity was significantly associated with telomere length and overall survival.

CONCLUSIONS

Our data show that the degree of CpG island methylation of the hTERT promoter exhibits an impact on telomerase activity in a subgroup of patients with B-cell chronic lymphocytic leukemia and therefore is assumed to play a role in regulating hTERT gene expression in these patients.

Determination, activity and biological role of adenylosuccinate lyase in blood cells

Adenylosuccinate lyase deficiency, which is associated with severe mental retardation and autistic features, was discovered in 1984. Since then this enzyme has been analyzed in many human tissues and it is now generally agreed that screening for this enzyme defect should be performed in all unexplained neurological diseases. The aim of the present study was to analyze adenylosuccinate lyase activity in blood cells by a fast simple method adaptable to screening purposes. The activity was also analyzed in B-lymphocytes from patients with B-cell chronic lymphocytic leukemia. The biological role of adenylosuccinate lyase and its importance in regulating cellular levels of AMP is discussed.

Proteasomes modulate balance among proapoptotic and antiapoptotic Bcl-2 family members and compromise functioning of the electron transport chain in leukemic cells

The mechanism underlying apoptosis induced by proteasome inhibition in leukemic Jurkat and Namalwa cells was investigated in this study. The proteasome inhibitor lactacystin differentially regulated the protein levels of proapoptotic Bcl-2 family members and Bik was accumulated at the mitochondria. Bik overexpression sufficed to induce apoptosis in these cells. Detailed examination along the respiration chain showed that lactacystin compromised a step after complex III, and exogenous cytochrome c could overcome this compromise. Probably as a result, the succinate-stimulated generation of mitochondrial membrane potential was significantly diminished. Bcl-x(L) interacted with Bik in the cells, and Bcl-x(L) overexpression prevented cytochrome c leakage out of the mitochondria, corrected the mitochondrial membrane potential defect, and protected the cells from apoptosis. These results show that proteasomes can modulate apoptosis of lymphocytes by affecting the half-life of Bcl-2 family members, Bik being one of them.

Stimulation of Bruton's tyrosine kinase (BTK) and inositol 1,4,5-trisphosphate production in leukemia and lymphoma cells exposed to low energy electromagnetic fields

We examined the effects of low energy electromagnetic field (EMF) exposure on the BTK kinase activity in B18-2 ([Btk-, rBTK(wt)] DT40) chicken lymphoma B cells and NALM-6 leukemic pre-B cells. Exposure of B 18-2 cells to EMF resulted in activation of BTK within 1 to 15 minutes in 8 of 8 independent experiments with stimulation indexes ranging from 1.2 to 13.3. While in some experiments the BTK stimulation was transient, in others the BTK activity continued to be significantly elevated for up to 4 hours. Similarly, exposure of NALM-6 cells to EMF resulted in activation of BTK within 30 minutes in 7 of 7 experiments with stimulation indexes ranging from 1.2 to 7.4. Stimulation of BTK activity in EMF exposed cells was associated with enhanced phosphoinositide turnover and increased inositol-1,4,5-trisphosphate (IP3) production in 7 of 13 experiments with DT40 cells and 7 of 13 experiments with NALM-6 cells. The likelihood and magnitude of an IP3 response after EMF exposure were similar to those after BCR ligation on DT40 cells and CD19 ligation on NALM-6 cells. These results confirm and extend our previous studies regarding EMF-induced biochemical signaling events in B-lineage lymphoid cells.

Apoptotic cytotoxic effects of a histone deacetylase inhibitor, FK228, on malignant lymphoid cells

Histone deacetylases are promising targets for cancer treatment. Here we studied the in vitro effects of a potent histone deacetylase inhibitor, FK228 (formerly FR901228), on human leukemia / lymphoma cells and cell lines compared with normal hematopoietic cells. In a lymphoma cell line, Raji, a nanomolar concentration of FK228 induced G1 arrest and / or apoptotic cell death, depending on the concentration and exposure time. Growth of lymphoid cell lines including Raji (N = 13) was inhibited by 50% (IC(50)) after 2-day treatment at concentrations of 0.83 to 1.87 ng / ml. Viability of clinical samples from patients with acute lymphoblastic leukemia was decreased by 50% at 0.78 +/- 0.46 ng / ml, whereas the IC(50) values for normal mononuclear cells from peripheral blood and bone marrow were 2.3 +/- 0.96 and 7.8 +/- 1.0 ng / ml, respectively. The IC(50) values for normal progenitor cells were 3.1, 4.4 and 7.8 ng / ml for BFU-E, CFU-GM and CFU-Mix, respectively. Expression levels of HDAC-1 and HDAC-3 proteins, which varied among cell lines, but were stable during the treatment with FK228, did not correlate with the sensitivity to FK288. This novel agent might be useful in the treatment of lymphoid malignancies, because the above concentrations are clinically achievable in vivo according to a recent clinical study.

Asparagine synthetase activity in paediatric acute leukaemias: AML-M5 subtype shows lowest activity

Lack of sufficient cellular activity of asparagine synthetase (AS) in blast cells compared with normal tissue is thought to be the basis of the antileukaemic effect of L-asparaginase in acute lymphoblastic leukaemia (ALL). Although L-asparaginase is routinely used in ALL, its role and value in the treatment of acute myelogenous leukaemia (AML) is still being discussed. To evaluate the pharmacological basis for L-asparaginase treatment, we established pretreatment monitoring of the intracellular AS activity in blast cells of patients with AML and ALL. There was no general difference in AS activity between ALL and AML samples. Significantly lower AS activity, however, was found in the B-lineage ALL subgroups as well as AML-M5.

Proteolytic activity of human lymphoid tumor cells. Correlation with tumor progression

Matrix metalloproteinase (MMP) expression and production are associated with advanced-stage tumor and contribute to tumor progression, invasion and metastases. The current study was designed to determine the expression and production of MMP-2 (gelatinase A) and MMP-9 (gelatinase B) by human lymphoid tumor cells. Changes in expression and production were also investigated during tumor progression of multiple myeloma and mycosis fungoides. In situ hybridization analysis revealed that lymphoblastic leukemia B cells (SB cell line), multiple myeloma (MM) cells (U266 cell line) and lymphoblastic leukemia T cells (CEM and Jurkat cell lines) express constitutively the mRNA for MMP-2 and/or MMP-9. We demonstrated by gelatin-zymography of cell culture medium that both enzymes were secreted in their cleaved (activated) form. In situ hybridization of bone marrow plasma cells and gelatin-zymography of the medium showed that patients with active MM (diagnosis, relapse, leukemic progression) express higher levels of MMP-2 mRNA and protein than patients with non-active MM (complete/objective response, plateau) and with monoclonal gammopathies of undetermined significance (MGUS). MMP-9 expression and secretion was similar in all patient groups. In patients with mycosis fungoides (MF), the expression of MMP-2 and MMP-9 mRNAs was significantly upregulated with advancing stage, in terms of lesions both positive for one of two mRNAs and with the greatest intensity of expression. Besides MF cells, the MMP-2 and/or MMP-9 mRNAs were expressed by some stromal cell populations (microvascular endothelial cells, fibroblasts, macrophages), suggesting that these cells cooperate in the process of tumor invasion. Our studies identify MMPs as an important class of proteinases involved in the extracellular matrix (ECM) degradation by human lymphoid tumors, and suggest that MMPs inhibitors may lead to important new treatment for their control.

Establishment of a leukemia cell line with i(12p) from a patient with a mediastinal germ cell tumor and acute lymphoblastic leukemia

We report the establishment of a leukemia cell line (UoC-B10) from a patient who developed leukemia several months after the diagnosis of a mediastinal yolk sac tumor. The patient's yolk sac tumor responded to combination chemotherapy, and a mature teratoma with focal areas of hematopoiesis was subsequently resected. However, 5 months after the initial diagnosis, the patient developed an acute lymphoblastic leukemia with a precursor B-cell phenotype. Cytogenetic analysis showed an i(12p) abnormality in the patient's leukemia cells and in the UoC-B10 cell line. The i(12p) was also identified retrospectively in the mediastinal tumor cells by fluorescent in situ hybridization analysis. The UoC-B10 cell line, which has been growing continuously for > 24 months in culture, was Epstein-Barr virus negative and was generally concordant with the patient's leukemia cells by analysis of immunophenotype, karyotype, and genotype. The UoC-B10 cell line possesses receptors for granulocyte-colony-stimulating factor, a cytokine which the patient received as part of his treatment protocol. This cell line may be useful in studying the relationship between i(12p) and hematological differentiation of human mediastinal germ cell tumors.

[A comparative study of aspartyl and cysteine proteinases and their inhibitors in human B- and T-cell leukemias]

A procedure was developed for simultaneous isolation of aspartyl and cysteine proteinases as well as of the cysteine-proteinase inhibitors. Affinity chromatography using pepstatin-Sepharose enabled one to isolate aspartyl proteinases, while inhibitors of cysteine-proteinases were isolated by affinity chromatography on CM-papain-Sepharose; further purification of the enzymes was carried out using ion exchange chromatography and gel filtration. Partially purified preparations of cathepsin D as well as of cysteine-proteinases and their inhibitors were obtained. Some physicochemical and enzymatic properties of the enzymes and inhibitors obtained were studied.

Human T and B lymphocytes express a structurally conserved focal adhesion kinase, pp125FAK

Clustering of beta 1-integrins on adherent cells with antibodies or ligands results in increased tyrosine phosphorylation and activation of a novel focal adhesion tyrosine kinase, pp125FAK. The genes encoding pp125FAK have been cloned previously from both chicken and mouse cDNA libraries, and the deduced amino acid sequences are nearly identical (94%). Two synthetic peptides derived from sequences at the carboxyl terminus of chicken pp125FAK were conjugated to ovalbumin to generate rabbit heteroantisera. Human pp125FAK was immunodetected in both T and B lymphocytes with these antisera. A basal state of pp125FAK tyrosine phosphorylation was observed in T and B lymphocytes, and its expression level was in general augmented among human T- and B-cell leukemia/lymphoma lines. Additionally, the full-length sequence of human T-cell pp125FAK (huT-FAK) was derived from a Jurkat T-cell cDNA library. huT-FAK is structurally identical with both mouse and chicken FAK, and shares 95% amino acid identity with chicken pp125FAK and has 97% homology with the mouse sequence. This high degree of evolutionary conservation between species suggests that pp125FAK is likely to have a crucial function in the cell. Expression of the full-length huT-FAK gene in COS cells showed an immunologically indistinct human pp125FAK protein compared with the endogenous primate pp125FAK. Taken together, the data indicate that this structurally conserved human T-cell pp125FAK likely functions in T- and B-cell lineages, and its altered expression in human lymphocyte tumor cell lines may contribute to their transformed phenotype.

Relation of 5'-nucleotidase and phosphatase activities with immunophenotype, drug resistance and clinical prognosis in childhood leukemia

Ecto-5'-nucleotidase (ecto-5'NT) catalyzes the extracellular dephosphorylation of nucleotides like IMP. Cytoplasmic 5'NT (cyto-5'NT) and non-specific (e.g. acid- and alkaline) phosphatases (AP) regulate the intracellular degradation of nucleotides. High NT and AP activities might cause a resistance to the thiopurines 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG). We studied the relation between these enzymes and immunophenotype, drug resistance and prognosis in 77 children with acute lymphoblastic leukemia (ALL). Enzyme activities were assessed radiochemically; in vitro drug resistance was measured with the MTT assay. AP activities were higher in T-ALL and B-ALL than in precursor B-ALL. Cyto-5'NT activity was very low in all phenotypes and accounted for a significant proportion of total IMPase activity only in the very immature CD10- c mu- precursor B-ALL. CD10+ ALL cases with high ecto-5'NT activities showed a trend (p = 0.065) for a lower probability of continuous complete remission than those with a low activity. Ecto-5'NT activity was not related to in vitro drug resistance to 6-TG. A weak correlation was found between in vitro 6-TG resistance and cyto-5'NT and AP activities. We conclude that high ecto-5'NT activities do not cause a resistance to 6-thiopurines in childhood ALL. Some patients have high cyto-5'NT and AP activities associated with 6-thiopurine resistance.

Identification of high affinity receptors for vasoactive intestinal peptide on human lymphocytes of B cell lineage

Specific, high affinity receptors for vasoactive intestinal peptide (VIP) have been identified on a human pre-B cell line, Nalm 6, and on a human plasma cell line, Dakiki. The single class of high affinity sites exhibited a KD of 12.6 +/- 2.9 nM for VIP in Nalm 6 cells and 9.1 +/- 2.7 nM in Dakiki plasma cells. The homologous peptides, peptide histidine methionine (PHM), growth hormone releasing factor (GHRF), and secretin were all less effective than VIP in competitively inhibiting binding of 125I-VIP to Nalm 6 and Dakiki plasma membranes. The putative receptor was characterized as a 47-kDa protein using covalent cross-linking techniques and VIP stimulated adenylate cyclase in pre-B cells. Human lymphocytes of B cell lineage thus appear to express functional VIP receptors homologous to the receptor identified in T lymphoblasts, brain, pituitary, and intestine.

dATP-mediated inhibition of DNA ligase by 2'-deoxycoformycin in T and B cell leukemia

2'-Deoxycoformycin (dCF), a potent adenosine deaminase inhibitor, has been reported to display greater toxicity for T than for B lymphoblasts. Since this compound can block DNA replication and since this effect is mediated by the intracellular ATP/dATP balance, its possible effect on DNA ligase was investigated. dCF at relatively low concentrations (1 microM), in association with dATP (100 microM), is a strong inhibitor of DNA ligase in T blasts, whereas it has no significant effect in B blasts at this concentration. The AMP-ligase complex is the target of the observed inhibition because the combined presence of the inhibitor and dATP results in a more stable dAMP-ligase complex. Because of this observation and of the greater adenosine deaminase activity observed in T cells, the dATP mediated dCF inhibition of ligase might be the crucial replication target of T cell toxicity. These observations are discussed in terms of T immunodeficiencies including Graft Versus Host Disease and related syndromes.

Combined effects of interferon and steroid hormones on 2',5'-oligoadenylate synthetase activity in chronic lymphocytic leukemia cells

2',5'-oligoadenylate synthetase (OAS) has been implicated in the effects of interferons (INF) and steroid hormones on cell growth and differentiation. We studied the combined effects in vitro of hormones and INF on OAS activity in cells from 10 patients with chronic lymphocytic leukemia. IFN enhanced OAS activity in all cells studied and also induced morphologic transformation. Diethylstilbestrol was also found to induce OAS activity, but not morphologic transformation. Progesterone, tamoxifen and dihydrotestosterone had no effect on enzyme activity nor on morphology. In five samples, all with estrogen receptor activity, DES and INF were synergistic in inducing OAS activity. TAM-INF synergism was observed in one sample. DES and TAM did not, however, significantly enhance IFN-induced morphologic transformations. Hydrocortisone reduced OAS activity, and antagonized INF-induced enzyme activity and morphologic transformations. We conclude that hormones can modulate OAS activity in CLL cells. These findings may be of importance in the design of INF-based therapies of CLL.