Dasatinib sensitizes primary chronic lymphocytic leukaemia lymphocytes to chlorambucil and fludarabine in vitro

Lysosome-Disrupting Agents in Combination with Venetoclax Increase Apoptotic Response in Primary Chronic Lymphocytic Leukemia (CLL) Cells Mediated by Lysosomal Cathepsin D Release and Inhibition of Autophagy

Venetoclax and obinutuzumab are becoming frontline therapies for chronic lymphocytic leukemia (CLL) patients. Unfortunately, drug resistance still occurs, and the combination could be immunosuppressive. Lysosomes have previously been identified as a target for obinutuzumab cytotoxicity in CLL cells, but the mechanism remains unclear. In addition, studies have shown that lysosomotropic agents can cause synergistic cell death in vitro when combined with the BTK inhibitor, ibrutinib, in primary CLL cells. This indicates that targeting lysosomes could be a treatment strategy for CLL. In this study, we have shown that obinutuzumab induces lysosome membrane permeabilization (LMP) and cathepsin D release in CLL cells. Inhibition of cathepsins reduced obinutuzumab-induced cell death in CLL cells. We further determined that the lysosomotropic agent siramesine in combination with venetoclax increased cell death in primary CLL cells through an increase in reactive oxygen species (ROS) and cathepsin release. Siramesine treatment also induced synergistic cytotoxicity when combined with venetoclax. Microenvironmental factors IL4 and CD40L or incubation with HS-5 stromal cells failed to significantly protect CLL cells from siramesine- and venetoclax-induced apoptosis. We also found that siramesine treatment inhibited autophagy through reduced autolysosomes. Finally, the autophagy inhibitor chloroquine failed to further increase siramesine-induced cell death. Taken together, lysosome-targeting drugs could be an effective strategy in combination with venetoclax to overcome drug resistance in CLL.

Emerging Therapies in CLL in the Era of Precision Medicine

Over the past decade, the treatment landscape of CLL has vastly changed from the conventional FC (fludarabine and cyclophosphamide) and FCR (FC with rituximab) chemotherapies to targeted therapies, including inhibitors of Bruton tyrosine kinase (BTK) and phosphatidylinositol 3-kinase (PI3K) as well as inhibitors of BCL2. These treatment options dramatically improved clinical outcomes; however, not all patients respond well to these therapies, especially high-risk patients. Clinical trials of immune checkpoint inhibitors (PD-1, CTLA4) and chimeric antigen receptor T (CAR T) or NK (CAR NK) cell treatment have shown some efficacy; still, long-term outcomes and safety issues have yet to be determined. CLL remains an incurable disease. Thus, there are unmet needs to discover new molecular pathways with targeted or combination therapies to cure the disease. Large-scale genome-wide whole-exome and whole-genome sequencing studies have discovered genetic alterations associated with disease progression, refined the prognostic markers in CLL, identified mutations underlying drug resistance, and pointed out critical targets to treat the disease. More recently, transcriptome and proteome landscape characterization further stratified the disease and revealed novel therapeutic targets in CLL. In this review, we briefly summarize the past and present available single or combination therapies, focusing on potential emerging therapies to address the unmet clinical needs in CLL.

Adverse Toxic Effects of Tyrosine Kinase Inhibitors on Non-Target Zebrafish Liver (ZFL) Cells

Over the past 20 years, numerous tyrosine kinase inhibitors (TKIs) have been introduced for targeted therapy of various types of malignancies. Due to frequent and increasing use, leading to eventual excretion with body fluids, their residues have been found in hospital and household wastewaters as well as surface water. However, the effects of TKI residues in the environment on aquatic organisms are poorly described. In the present study, we investigated the cytotoxic and genotoxic effects of five selected TKIs, namely erlotinib (ERL), dasatinib (DAS), nilotinib (NIL), regorafenib (REG), and sorafenib (SOR), using the in vitro zebrafish liver cell (ZFL) model. Cytotoxicity was determined using the MTS assay and propidium iodide (PI) live/dead staining by flow cytometry. DAS, SOR, and REG decreased ZFL cell viability dose- and time-dependently, with DAS being the most cytotoxic TKI studied. ERL and NIL did not affect viability at concentrations up to their maximum solubility; however, NIL was the only TKI that significantly decreased the proportion of PI negative cells as determined by the flow cytometry. Cell cycle progression analyses showed that DAS, ERL, REG, and SOR caused the cell cycle arrest of ZFL cells in the G0/G1 phase, with a concomitant decrease of cells in the S-phase fraction. No data could be obtained for NIL due to severe DNA fragmentation. The genotoxic activity of the investigated TKIs was evaluated using comet and cytokinesis block micronucleus (CBMN) assays. The dose-dependent induction of DNA single strand breaks was induced by NIL (≥2 μM), DAS (≥0.006 μM), and REG (≥0.8 μM), with DAS being the most potent. None of the TKIs studied induced micronuclei formation. These results suggest that normal non-target fish liver cells are sensitive to the TKIs studied in a concentration range similar to those previously reported for human cancer cell lines. Although the TKI concentrations that induced adverse effects in exposed ZFL cells are several orders of magnitude higher than those currently expected in the aquatic environment, the observed DNA damage and cell cycle effects suggest that residues of TKIs in the environment may pose a hazard to non-intentionally exposed organisms living in environments contaminated with TKIs.

Introduction to DOK2 and its potential role in cancer

Cancer is a complex, multifactorial disease that modern medicine ultimately aims to overcome. Downstream of tyrosine kinase 2 (DOK2) is a well-known tumor suppressor gene, and a member of the downstream protein DOK family of tyrosine kinases. Through a search of original literature indexed in PubMed and other databases, the present review aims to extricate the mechanisms by which DOK2 acts on cancer, thereby identifying more reliable and effective therapeutic targets to promote enhanced methods of cancer prevention and treatment. The review focuses on the role of DOK2 in multiple tumor types in the lungs, intestines, liver, and breast. Additionally, we discuss the potential mechanisms of action of DOK2 and the downstream consequences via the Ras/MPAK/ERK or PI3K/AKT/mTOR signaling pathways.

Combined chronic myeloid leukaemia and chronic lymphocytic leukaemia in five patients, including one with 17p deletion

We report a series of five Australian cases of chronic lymphocytic leukaemia (CLL) occurring concurrently with chronic myeloid leukaemia (CML). Patient management including therapies and response together with clinical progress was obtained from medical records and laboratory information systems. Prior to CML diagnosis, all five had a preceding diagnosis of CLL. Three had received prior fludarabine. All received tyrosine kinase inhibitors (TKI). None required subsequent therapy for CLL. One patient had 17p deletion CLL and another patient had normal CLL cytogenetics. All currently have satisfactory blood counts with quantitative polymerase chain reaction for CML showing molecular response. All remain alive. Thus, such cases can be successfully managed by treating each haematological disorder in the usual manner. The control achieved in CML with the TKI enables satisfactory marrow function to recover in patients with concomitant CLL. The role for allograft in patients with dual malignancies is uncertain and needs to be individualised depending on control of each malignancy.

In vivo, ex vivo and in vitro dasatinib activity in chronic lymphocytic leukemia

Dasatinib inhibits the breakpoint cluster region-Abelson murine leukemia 1 (BCR-ABL1) gene along with other kinases known to be overexpressed and abnormally active in patients with chronic lymphocytic leukemia (CLL). The current study used primary leukemic cells obtained from 53 patients with CLL that were treated with dasatinib. A 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay and Annexin V staining was performed to assess the cytotoxic effects of dasatinib treatment. The XTT assay revealed that the median cytotoxicity of dasatinib was 8.30% (range, 0.00–77.89%). Due to high dispersion of dasatinib activity, patients were divided into sensitive (n=27; 50.94%; median cytotoxicity, 22.81%) and resistant groups (n=26; 49.06%; median cytotoxicity, 0.00%). A median cytotoxicity of 8.30% was selected as a cut off value. Using Annexin V staining and flow cytometry on exemplary sensitive and resistant CLL samples, it was revealed that 17.71 and 1.84% of cells were apoptotic, respectively. The current study presented a case of a patient with concomitant occurrence of CLL and chronic myeloid leukemia (CML) with a major molecular response after dasatinib treatment. A simultaneous reduction of circulating CLL cells indicated in vivo anti-CLL activity induced by dasatinib. After an in vitro culture of the patient's mononuclear cells with subsequent dasatinib treatment, a higher percentage of CLL cells undergoing apoptosis was obsevered when compared with untreated samples (38.19 vs. 21.99%, respectively). Similarly, the percentage of CLL apoptotic cells (ΔΨm^low) measured by chloromethyl-X-rosamine was higher after incubation with dasatinib (7.28%) than in the negative control (2.86%). In conclusion, dasatinib induced antileukemic effects against CML and CLL cells. The results of the current study indicated that dasatinib may induce apoptosis ex vivo, in vitro and in vivo in CLL.

Transcriptional Modulation by Idelalisib Synergizes with Bendamustine in Chronic Lymphocytic Leukemia

The phosphatidyl-inositol 3 kinase (PI3K) δ inhibitor, idelalisib (IDE), is a potent inhibitor of the B-cell receptor pathway and a novel and highly effective agent for the treatment of chronic lymphocytic leukemia (CLL). We evaluated the activities of IDE in comparison to bendamusine (BEN), a commonly used alkylating agent, in primary CLL cells ex vivo. In contrast to BEN, IDE was cytotoxic to cells from extensively-treated patients, including those with a deletion (del)17p. Cross-resistance was not observed between BEN and IDE, confirming their different modes of cytotoxicity. Marked synergy was seen between BEN and IDE, even in cases that were resistant to BEN or IDE individually, and those with deletion (del) 17p. CD40L/interleukin 4 (IL4) co-treatment mimicking the CLL microenvironment increased resistance to IDE, but synergy was retained. PI3Kδ-deficient murine splenic B cells were more resistant to IDE and showed reduced synergy with BEN, thus confirming the importance of functional PI3Kδ protein. Although IDE was observed to induce γH2AX, IDE did not enhance activation of the DNA damage response nor DNA repair activity. Interestingly, IDE decreased global RNA synthesis and was antagonistic with 5,6-Dichlorobenzimidazole 1-b-D-ribofuranoside (DRB), an inhibitor of transcription. These findings add to the increasingly complex cellular effects of IDE, and B cell receptor (BCR) inhibitors in general, in CLL.

A phase 2 study of ofatumumab (Arzerra®) in combination with a pan-AKT inhibitor (afuresertib) in previously treated patients with chronic lymphocytic leukemia (CLL)

AKT plays a centralized role in tumor proliferation and survival and is aberrantly activated in chronic lymphocytic leukemia (CLL). In this phase 2 trial, 30 relapsed/refractory CLL patients were treated with combination afuresertib, a novel oral AKT inhibitor, and ofatumumab for 6 months, followed by afuresertib maintenance for 12 months. We aimed to achieve deeper and more durable responses, without requiring long-term continuous treatment. Treatment was generally well tolerated but respiratory infections were common, with 18% severe requiring hospitalization. Hematologic toxicities were manageable (grade 3-4 neutropenia 39%). At a median follow-up of 13.4 months, overall responses were 50% (complete responses 3.6%). Median progression-free survival was 8.5 months and overall survival 34.8 months. Combination therapy with ofatumumab and afuresertib is active and well tolerated, but does not appear to lead to durable responses and may not provide additional benefit over single-agent ofatumumab in relapsed/refractory CLL. Novel agent combinations are currently undergoing intense investigation.

Chronic lymphocytic leukemia: 2015 Update on diagnosis, risk stratification, and treatment

DISEASE OVERVIEW

Chronic lymphocytic leukemia (CLL) is the commonest leukemia in western countries. The disease typically occurs in elderly patients and has a highly variable clinical course. Leukemic transformation is initiated by specific genomic alterations that impair apoptosis of clonal B-cells.

DIAGNOSIS

The diagnosis is established by blood counts, blood smears, and immunophenotyping of circulating B-lymphocytes, which identify a clonal B-cell population carrying the CD5 antigen as well as B-cell markers.

PROGNOSIS

Two prognostic staging systems exist, the Rai and Binet staging systems, which are established by physical examination and blood counts. Various biological and genetic markers also have prognostic value. Deletions of the short arm of chromosome 17 (del(17p)) predict resistance to available chemotherapies. Comprehensive prognostic scores are currently being developed.

THERAPY

Patients with active or symptomatic disease or with advanced Binet or Rai stages require therapy. For physical fit patients, chemoimmunotherapy with fludarabine, cyclophosphamide, and rituximab remains the current standard therapy. For unfit patients, treatment with an anti-CD20 antibody (obinutuzumab or rituximab or ofatumumab) plus a milder chemotherapy (Chlorambucil) may be applied. At relapse, the initial treatment may be repeated, if the treatment-free interval exceeds two to three years. If the disease relapses earlier, therapy should be changed using alternative agents such as bendamustine (plus rituximab), alemtuzumab, lenalidomide, ofatumumab, ibrutinib, or idelalisib. Patients with a del(17p) or TP53 mutation can be treated with ibrutinib or a combination of idelalisib and rituximab. An allogeneic SCT may be considered in relapsing patients with TP53 mutations or del(17p) or patients that are refractory to repeated chemoimmunotherapies. Future challenges: Several new agents (e.g., ibrutinib, idelalisib, obinutuzumab) hold the potential to improve the outcome of patients with CLL. However, their optimal use (in terms of combination, sequence, and duration) is unknown. Therefore, CLL patients should be treated in clinical trials whenever possible.

Promising therapies for the treatment of chronic lymphocytic leukemia

INTRODUCTION

The combination schedule of fludarabine, cyclophosphamide and rituximab is the gold standard of therapy for younger, physically fit chronic lymphocytic leukemia (CLL) patients; it allows achieving high and durable complete response rates. Although treatment outcome has considerably improved with chemo-immunotherapy, most patients eventually relapse and CLL is still incurable. Thus, newer and more rationally developed drugs are needed to improve CLL therapy, particularly in cases of relapsed/refractory disease.

AREAS COVERED

The authors review preclinical and clinical data regarding newer CLL agents, currently undergoing examination, such as: signal transduction and cyclin-dependent kinase inhibitors, immunomodulatory agents, B-cell lymphoma 2 inhibitors, next generation mAbs, heat shock protein 90 and histone deacetylase inhibitors, and chimeric antigen receptor T-cell therapy.

EXPERT OPINION

Newer compounds with different mechanisms of action, such as B-cell receptor signal transduction inhibitors, lenalidomide, next generation mAbs and several pro-apoptotic molecules, have shown efficacy in relapsed or refractory CLL patients. Several studies are under way to investigate the efficacy of combinations of these novel drugs. Hopefully, the combined use of these molecules in risk-adapted treatment strategies will change the therapeutic approach in the near future and will pave the way for a long-term control of CLL.

Src family kinases and their role in hematological malignancies

The Src family protein tyrosine kinases (SFKs) are non-receptor intracellular kinases that have important roles in both hematopoiesis and leukemogenesis. The derangement of their expression or activation has been demonstrated to contribute to hematological malignancies. This review first examines the mechanisms of SFK overexpression and hyperactivation, emphasizing the dysregulation of the upstream modulators. Subsequently, the role of SFK up-regulation in the initiation, progression and therapy resistance of many hematological malignancies is also analyzed. The presented evidence endeavors to highlight the influence of SFK up-regulation on an extensive number of hematological malignancies and the need to consider them as candidates in targeted anticancer therapy.

Resistance to Dasatinib in primary chronic lymphocytic leukemia lymphocytes involves AMPK-mediated energetic re-programming

Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults in the western world. Although promising new therapies for this incurable disease are being tested in clinical trials, the therapeutic relevance of metabolic rewiring in chronic lymphocytic leukemia (CLL) is poorly understood. The aim of this study was to identify targetable metabolic differences in primary CLL lymphocytes by the use of Dasatinib. Dasatinib is a multi-tyrosine kinase inhibitor used to treat chronic myelogenous leukemia (CML) and is being tested in clinical trials for several cancers including CLL. This drug has been shown to be beneficial to CML patients suffering from diabetes by reducing their glucose plasma levels. In keeping with this previous observation, we report that Dasatinib induced glucose use while reducing lactate production, suggesting that this tyrosine kinase inhibitor decreases aerobic glycolysis and shifts glucose use in primary CLL lymphocytes. Our results suggest that primary CLL lymphocytes (independently of traditional prognostic factors) can be stratified in two subsets by their sensitivity to Dasatinib in vitro. Increased glucose use induced by Dasatinib or by inhibition of mitochondrial respiration was not sufficient to sustain survival and ATP levels in CLL samples sensitive to Dasatinib. The two subsets of primary CLL lymphocytes are characterized as well by a differential dependency on mitochondrial respiration and the use of anabolic or catabolic processes to cope with induced metabolic/energetic stress. Differential metabolic reprogramming between subsets is supported by the contrasting effect on the survival of Dasatinib treated CLL lymphocytes with pharmacological inhibition of two master metabolic regulators (mTorc1 and AMPK) as well as induced autophagy. Alternative metabolic organization between subsets is further supported by the differential basal expression (freshly purified lymphocytes) of active AMPK, regulators of glucose metabolism and modulators of AKT signaling. The contrasting metabolic features revealed by our strategy could be used to metabolically target CLL lymphocyte subsets creating new therapeutic windows for this disease for mTORC1 or AMPK inhibitors. Indeed, we report that Metformin, a drug used to treat diabetes was selectively cytotoxic to Dasatinib sensitive samples. Ultimately, we suggest that a similar strategy could be applied to other cancer types by using Dasatinib and/or relevant tyrosine kinase inhibitors.

Dasatinib

Dasatinib is an orally available short-acting dual ABL/SRC tyrosine kinase inhibitor (TKI). It potently inhibits BCR-ABL and SRC family kinases (SRC, LCK, YES, FYN), but also c-KIT, PDGFR-α and PDGFR-β, and ephrin receptor kinase. Dasatinib is an effective treatment for chronic myeloid leukemia (CML) and Philadelphia chromosome positive acute lymphoblastic leukemia (Ph+ ALL). Both diseases are characterized by a constitutively active tyrosine kinase; BCR-ABL. Dasatinib inhibits BCR-ABL with greater potency compared with other BCR-ABL inhibitors and is active in CML resistant or intolerant to imatinib. Dasatinib is approved for the treatment of CML (all phases) and for the treatment of Ph+ ALL, resistant or intolerant to prior imatinib treatment. Randomized trial data in CML show that first-line dasatinib provides superior responses compared with imatinib and enables patients to achieve early, deep responses, correlated with improved longer-term outcomes. A once-daily dose of 100 mg in chronic phase CML results in high hematologic and molecular remission rates and prolongation of survival. In accelerated and blastic phase of CML, as well as in Ph+ ALL, complete hematologic and cytogenetic remissions frequently occur. Remissions however are very short. In these patients, once-daily 140 mg is the recommended dose. The effect of dasatinib in other malignancies including solid tumors is subject of clinical studies. Regardless of many clinical trials in different tumor types and in different combinations of dasatinib with other agents, the role of dasatinib in the treatment of solid tumors has not yet been defined. Side effects of dasatinib are frequent but mostly moderate and manageable and include cytopenias and pleural effusions. The review presents the preclinical and clinical activity of dasatinib with a focus on clinical studies in CML.

BTK inhibition targets in vivo CLL proliferation through its effects on B-cell receptor signaling activity

Bruton agammaglobulinemia tyrosine kinase (BTK), a cytoplasmic protein tyrosine kinase, is a component of the B-cell receptor signaling pathway. Ibrutinib, a BTK inhibitor, has demonstrated a significant clinical activity against chronic lymphocytic leukemia (CLL) in early clinical trials. Understanding the molecular mechanisms of action would shed light on CLL pathophysiology and provide additional opportunities for the development of new therapies. In this study, we have chosen an in vivo approach by employing an ongoing phase 1b trial of ibrutinib. We prospectively collected and analyzed serial samples from the CLL patients before and after the initiation of ibrutinib. We found that the blockage of cell proliferation was one of the primary effects of ibrutinib against leukemic CLL cells in vivo. Using a co-culture system that induces CLL proliferation in vitro, analysis of several parameters, including Ki-67 expression and bromodeoxyuridine (BrdU) incorporation, revealed that the proliferation of CLL cells was directly inhibited by ibrutinib. Furthermore, activities of BTK and phospholipase Cγ2 as well as downstream signaling molecules, AKT and ERK, were all coordinately downregulated over time in ibrutinib-treated patients. Our findings suggest that the cell proliferation is one of the essential properties of CLL. Blocking cell proliferation via inhibition of BTK-mediated signaling may contribute to clinical responses in ibrutinib-treated patients.

Dasatinib in combination with fludarabine in patients with refractory chronic lymphocytic leukemia: a multicenter phase 2 study

Resistance to chemotherapy-induced apoptosis in CLL is associated with overexpression of antiapoptotic proteins induced by signals from the microenvironment. In vitro, dasatinib effectively inhibits expression of anti-apoptotic regulators and restores fludarabine sensitivity in activated CLL. The aim of this study was to evaluate efficacy of one cycle of dasatinib monotherapy (100mg/day, days 1-28) followed by combination of dasatinib with fludarabine (40mg/m²/day, days 1-3 every 28 day) for a total of 6 cycles in fludarabine-refractory CLL. The primary endpoint was overall response rate according to the IWCLL'08 criteria. 20 patients were enrolled: 18 completed at least one cycle of treatment of which 67% finished at least 2 cycles of combination treatment. 3 of these 18 patients reached a formal PR (16.7%). Majority of patients obtained some reduction in lymph node (LN) size. Most frequent toxicity was related to myelosuppression. NF-κB RNA expression levels of circulating CLL cells decreased whereas the levels of pro-apoptotic NOXA increased during treatment. In conclusion, dasatinib/fludarabine combination has modest clinical efficacy in fludarabine-refractory patients.

Biology of chronic lymphocytic leukemia in different microenvironments: clinical and therapeutic implications

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature monoclonal B cells in peripheral blood, bone marrow, spleen, and lymph nodes. The trafficking, survival, and proliferation of CLL cells is tightly regulated by the surrounding tissue microenvironment and is mediated by antigenic stimulation, close interaction with various accessory cells and exposure to different cytokines, chemokines, and extracellular matrix components. In the last decade there have been major advances in the understanding of the reciprocal interactions between CLL cells and the various microenvironmental compartments. This article discusses the role of the microenvironment in the context of efforts to develop novel therapeutics that target the biology of CLL.

Src kinases in chondrosarcoma chemoresistance and migration: dasatinib sensitises to doxorubicin in TP53 mutant cells

BACKGROUND

Chondrosarcomas are malignant cartilage-forming tumours of bone. Because of their resistance to conventional chemotherapy and radiotherapy, currently no treatment strategies exist for unresectable and metastatic chondrosarcoma. Previously, PI3K/AKT/GSK3β and Src kinase pathways were shown to be activated in chondrosarcoma cell lines. Our aim was to investigate the role of these kinases in chemoresistance and migration in chondrosarcoma in relation to TP53 mutation status.

METHODS

We used five conventional and three dedifferentiated chondrosarcoma cell lines and investigated the effect of PI3K/AKT/GSK3β pathway inhibition (enzastaurin) and Src pathway inhibition (dasatinib) in chemoresistance using WST assay and live cell imaging with AnnexinV staining. Immunohistochemistry on tissue microarrays (TMAs) containing 157 cartilaginous tumours was performed for Src family members. Migration assays were performed with the RTCA xCelligence System.

RESULTS

Src inhibition was found to overcome chemoresistance, to induce apoptosis and to inhibit migration. Cell lines with TP53 mutations responded better to combination therapy than wild-type cell lines (P=0.002). Tissue microarray immunohistochemistry confirmed active Src (pSrc) signalling, with Fyn being most abundantly expressed (76.1%).

CONCLUSION

These results strongly indicate Src family kinases, in particular Fyn, as a potential target for the treatment of inoperable and metastatic chondrosarcomas, and to sensitise for doxorubicin especially in the presence of TP53 mutations.

Chronic lymphocytic leukemia: 2013 update on diagnosis, risk stratification and treatment

DISEASE OVERVIEW

Chronic lymphocytic leukemia (CLL) is the commonest leukemia in western countries. The disease typically occurs in elderly patients and has a highly variable clinical course. Leukemic transformation is initiated by specific genomic alterations that impair apoptosis of clonal B-cells.

DIAGNOSIS

The diagnosis is established by blood counts, blood smears, and immunophenotyping of circulating B-lymphocytes, which identify a clonal B-cell population carrying the CD5 antigen as well as B-cell markers.

PROGNOSIS

Two prognostic staging systems exist, the Rai and Binet staging systems, which are established by physical examination and blood counts. Various biological and genetic markers also have prognostic value. Deletions of the short arm of chromosome 17 (del(17p)) predict resistance to most available therapies.

THERAPY

Patients with active or symptomatic disease or with advanced Binet or Rai stages require therapy. For physical fit patients, chemoimmunotherapy with fludarabine, cyclophosphamide and rituximab represents the current standard therapy. For unfit patients, treatment with an anti-CD20 antibody plus a milder chemotherapy (chlorambucil) is currently established as standard treatment. At relapse, the initial treatment may be repeated, if the treatment-free interval exceeds two years. If the disease relapses earlier, alternative therapies such as bendamustine alone or with rituximab, alemtuzumab, lenalidomide, or ofatumumab should be used. Patients with a del(17p) or TP53 should be considered for an allogeneic SCT.

FUTURE CHALLENGES

Several new agents (e.g., ibrutinib, obinutuzumab) hold the potential to change standard of CLL treatment in the next 6-12 months. Therefore, CLL patients should be included into current clinical trials whenever possible.

Telomerase contributes to fludarabine resistance in primary human leukemic lymphocytes

We report that Imetelstat, a telomerase inhibitor that binds to the RNA component of telomerase (hTR), can sensitize primary CLL lymphocytes to fludarabine in vitro. This effect was observed in lymphocytes from clinically resistant cases and with cytogenetic abnormalities associated with bad prognosis. Imetelstat mediated-sensitization to fludarabine was not associated with telomerase activity, but with the basal expression of Ku80. Since both Imetelstat and Ku80 bind hTR, we assessed 1) if Ku80 and Imetelstat alter each other's binding to hTR in vitro and 2) the effect of an oligonucleotide complementary to the Ku binding site in hTR (Ku oligo) on the survival of primary CLL lymphocytes exposed to fludarabine. We show that Imetelstat interferes with the binding of Ku70/80 (Ku) to hTR and that the Ku oligo can sensitize CLL lymphocytes to FLU. Our results suggest that Ku binding to hTR may contribute to fludarabine resistance in CLL lmphocytes. This is the first report highlighting the potentially broad effectiveness of Imetelstat in CLL, and the potential biological and clinical implications of a functional interaction between Ku and hTR in primary human cancer cells.

Drug resistance to chlorambucil in murine B-cell leukemic cells is overcome by its conjugation to a targeting peptide

Targeting drugs through small-molecule carriers with a high affinity to receptors on cancer cells can overcome the lack of target cell specificity of most anticancer drugs. These targeted carrier-drug conjugates are also capable of reversing drug resistance in cancer cells. Although many targeted drug delivery approaches are being tested, the linkage of several and different drugs to a single carrier molecule might further enhance their therapeutic efficacy, particularly if the drugs are engineered for variable time release. This report shows that murine B-cell leukemic cells previously resistant to a chemotherapeutic drug can be made sensitive to that drug as long as it is conjugated to a targeting peptide and, in particular, when the conjugate contains multiple copies of the drug. Using a 13mer peptide (VHFFKNIVTPRTP) derived from the myelin basic protein (p-MBP), dendrimer-based peptide conjugates containing one, two, or four molecules of chlorambucil were synthesized. Although murine hybridomas expressing antibodies to either p-MBP (MBP cells) or a nonrelevant antigen (BCL-1 cells) were both resistant to free chlorambucil, exposure of the cells to the p-MBP-chlorambucil conjugate completely reversed the drug resistance in MBP, but not BCL-1 cells or normal spleen cells. Moreover, at equivalent drug doses, there was significant enhancement in the cytotoxic activity of multidrug versus single-drug copy conjugates. On the basis of these results, the use of multifunctional dendrone linkers bearing several covalently bound cytotoxic agents allows the development of more effective targeted drug systems and enhances the efficacy of currently approved drugs for B-cell leukemia.

Novel agents for chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a heterogeneous group of B-cell neoplasm. CLL is typically sensitive to a variety of cytotoxic agents, but relapse frequently occurs with conventional approaches. The treatment of CLL is evolving rapidly with the introduction of novel drugs, such as bendamustine, ofatumumab, lenalidomide, ibrutinib, idelalisib, veltuzumab, XmAb5574, navitoclax, dasatinib, alvespimycin, and TRU-016. This review summarizes the most current clinical experiences with these agents in the treatment of CLL.

BCR signaling in chronic lymphocytic leukemia and related inhibitors currently in clinical studies

Normal B lymphocytes receive signals from B-cell antigen receptor (BCR) that are triggered by binding of the BCR to an external antigen. Tonic signaling through the BCR provides growth and signals to chronic lymphocytic leukemia (CLL) cells, and plays an important role in the pathogenesis and progression of the disease. Antigen engagement of BCR is followed by intracellular recruitment and activation of BCR-associated kinases including spleen tyrosine kinase (Syk), Bruton's tyrosine kinase (Btk) and phosphatidylinositol 3-kinases (PI3K). Inhibition of signaling pathways downstream of the BCR induces disruption of chemokine-mediated CLL cell migration and cell killing. BCR signal transduction inhibitors represent a promising new strategy for targeted CLL treatment. A number of therapeutic agents have recently been developed with significant activity in CLL. The compounds that are currently investigated in patients with CLL include ibrutinib -inhibitor of Btk, fostamatinib-inhibitor of Syk and idelalisib (GS-1101) -a specific isoform of the PI3K (PI3K) inhibitor. The clinical activity of ibrutinib, GS-1101 and fostamatinib in patients with CLL is associated with marked lymphocytosis due to release of tumor cells from the lymph nodes into the peripheral blood. Further studies are ongoing with single agents and their combinations with other targeted and conventional therapies. This article will review the preclinical rationale of BCR signaling inhibitors in the treatment of CLL, and the clinical evidence supporting the use of these agents in CLL patients.

Targeting the LYN/HS1 signaling axis in chronic lymphocytic leukemia

HS1 protein activation is differentially regulated by LYN kinase in CLL subsets. Dasatinib targets cytoskeletal activity, BCR signaling and survival of a sizable portion of patients with activated LYN/HS1.

Dasatinib-responsive chronic lymphocytic leukemia in a patient treated for coexisting chronic myeloid leukemia

We herein present a case of concurrent chronic myeloid leukemia (CML) and chronic lymphocytic leukemia (CLL). Two different clones, a Philadelphia (Ph) clone and a CLL clone with a 13q deletion, were identified using fluorescent in situ hybridization. Dasatinib was administered to inhibit Bcr-Abl and Lyn kinase. The patient exhibited a molecular response for CML and a partial response for CLL. To our knowledge, this is the first report to describe the occurrence of a gradual increase in the Bcr-Abl transcript level prior to the diagnosis of Ph-positive CML in an individual with CLL who was successfully treated with dasatinib as the first-line therapy.

Tyrosine kinase inhibitors as potential drugs for B-cell lymphoid malignancies and autoimmune disorders

INTRODUCTION

In the last few years, several tyrosine kinase inhibitors (TKIs) have been synthesized and become available for preclinical studies and clinical trials. This article summarizes recent achievements in the mechanism of action, pharmacological properties, and clinical activity and toxicity, as well as the emerging role of TKIs in lymphoid malignancies, allergic diseases, and autoimmune disorders.

AREAS COVERED

A literature review was conducted of the MEDLINE database PubMed for articles in English. Publications from 2000 through January 2012 were scrutinized. The search terms used were Bruton's tyrosine kinase (Btk) inhibitors, PCI-32765, GDC-0834, LFM-A13, AVL-101, AVL-292, spleen tyrosine kinase (Syk) inhibitors, R343, R406, R112, R788, fostamatinib, BAY-61-3606, C-61, piceatannol, Lyn, imatinib, nilotinib, bafetinib, dasatinib, GDC-0834, PP2, SU6656 in conjunction with lymphoid malignancy, NHL, CLL, autoimmune disease, allergic disease, asthma, and rheumatoid arthritis. Conference proceedings from the previous 5 years of the American Society of Hematology, European Hematology Association, American Society of Clinical Oncology, and ACR/ARHP Annual Scientific Meetings were searched manually. Additional relevant publications were obtained by reviewing the references from the chosen articles.

EXPERT OPINION

The use of TKIs, especially inhibitors of Btk, Syk, and Lyn, is a promising new strategy for targeted treatment of B-cell lymphoid malignancies, autoimmune disorders and allergic diseases. However, definitive data from ongoing and future clinical trials will aid in better defining the status of TKIs in the treatment of these disorders.

Treatment of chronic lymphocytic leukemia requires targeting of the protective lymph node environment with novel therapeutic approaches

Chronic lymphocytic leukemia (CLL) remains associated with low complete response rates and high relapse rates. This is in part due to poor understanding of CLL biology and thus inadequate targeting of therapy. For years CLL has been proposed as bi-compartmental: the quiescent tumor in the periphery and the proliferating cells within specific microenvironments. Historically the bone marrow was considered the major tissue of the CLL microenvironment. However, many recent innovative studies have categorically shown that peripheral CLL cells are derived from the lymph nodes (LN). Proliferation here is largely driven by helper T cells via CD40-CD40L engagement. Critically, in vitro studies have shown that such engagement additionally protects LN CLLs from apoptosis. Agents inducing apoptosis in non-CD40 engaged CLL cells are frequently ineffective against those continually engaged with CD40L. This emphasizes that, in order to improve responses and prevent relapse, novel therapies must be assessed against CD40L engaged CLL cells to show effective targeting against the LN. This review discusses the evidence supporting the superior involvement of the LN in CLL, how CD40L engaged CLL studies should be conducted, and the novel therapies studied in vitro and in vivo that have been proposed to be effective in this setting.

Refractory chronic lymphocytic leukemia--new therapeutic strategies

Treatment outcome of chronic lymphocytic leukemia (CLL) has considerably improved since the introduction of fludarabine (F) as part of the standard therapy. Nevertheless, refractoriness to fludarabine occurs in a significant number of patients and is associated with an unfavorable prognosis. Important risk factors are 17p deletion and/or mutation of TP53. For this subgroup the CD52 antibody alemtuzumab (A) presents a new treatment approach and has already been approved. Meanwhile we have to face also refractoriness to alemtuzumab. Importantly, the monoclonal CD20 antibody ofatumumab has now shown efficacy in F and A double-refractory CLL. The next generation CD20 antibody GA-101 is currently compared to rituximab (R) and will possibly be its more potent successor. Further B-cell antigens are targeted by lumiliximab (CD23), TRU-016 (CD37) and blinatumomab (CD19). Apart from monoclonal antibody therapies, a great number of small molecules are examined for the treatment of refractory and relapsed CLL. Most of these agents aim to overcome apoptosis resistance in CLL cells or influence the microenvironment. Typical targets are regulators of the cell cycle and antiapoptotic molecules like the members of the Bcl-2 family. Up to now the most promising agents appear to be flavopiridol and lenalidomide among others.

Phase II study of dasatinib in relapsed or refractory chronic lymphocytic leukemia

PURPOSE

Chronic lymphocytic leukemia (CLL) cells treated with dasatinib in vitro undergo apoptosis via inhibition of Lyn kinase. Thus, in this study we tested the activity of dasatinib in patients with relapsed CLL.

EXPERIMENTAL DESIGN

Patients were eligible for this phase II trial if they had documented CLL/SLL and had failed at least 1 prior therapy with a fludarabine-containing regimen and if they required therapy according to NCI-WG criteria. The starting dose of dasatinib was 140 mg daily.

RESULTS

Fifteen patients were enrolled, with a median age of 59 and a median of 3 prior regimens. All patients had received fludarabine, and 5 were fludarabine-refractory. Eleven of the 15 (73%) had high risk del(11q) or del(17p) cytogenetics. The primary toxicity was myelosuppression, with grade 3 or 4 neutropenia and thrombocytopenia in 10 and 6 patients, respectively. Partial responses by NCI-WG criteria were achieved in 3 of the 15 patients (20%; 90% CI: 6-44). Among the remaining 12 patients, 5 had nodal responses by physical exam, and 1 patient had a nodal and lymphocyte response but with severe myelosuppression. Pharmacodynamic studies indicated apoptosis in peripheral blood CLL cells within 3 to 6 hours after dasatinib administration, associated with downregulation of Syk (spleen tyrosine kinase) mRNA.

CONCLUSIONS

Dasatinib as a single agent has activity in relapsed and refractory CLL.

The potential for dasatinib in treating chronic lymphocytic leukemia, acute myeloid leukemia, and myeloproliferative neoplasms

Dasatinib is a kinase inhibitor that inhibits BCR-ABL, Src family kinases, c-Kit, and platelet-derived growth factor receptor kinase. It is licensed for the first- and second-line treatment of chronic myeloid leukemia and second-line treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia on the basis of BCR-ABL inhibition, but the activity of dasatinib against additional molecular targets may enable treatment of other hematologic disorders. Potential targets for dasatinib in chronic lymphocytic leukemia (CLL) include Lyn (a Src family kinase), ABL, and the associated CD40 pathway. Although dasatinib monotherapy has modest clinical activity in CLL, ongoing studies are evaluating combination treatment. In acute myeloid leukemia (AML), FLT3, Lyn, c-Kit, and BCR-ABL are expressed in a subpopulation of patients. To date, clinical responses to dasatinib in patients with unselected AML have been mixed and larger studies are needed, particularly correlating clinical response to molecular markers. Imatinib has been used successfully to treat patients with chronic eosinophilic disorders with the FIP1L1-PDGFRA fusion kinase; limited clinical data indicate that dasatinib could be active in imatinib-resistant disease. Ongoing clinical studies should further define the value of dasatinib in these disorders.

c-Abl regulates Mcl-1 gene expression in chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (CLL) is a malignancy characterized by clonal expansion of mature B cells that are resistant to apoptosis. This resistance to apoptosis partly results from Mcl-1 expression because high levels of this protein in CLL cells correlate with poor disease prognosis and resistance to chemotherapy. Thus, understanding the mechanism(s) regulating Mcl-1 expression in CLL cells may be useful in the development of new therapies for this incurable disease. In the present study, we show a strong relationship between c-Abl and Mcl-1 expression in CLL cells. We show that treatment of CLL cells with Abl-specific siRNA or with imatinib, to inhibit c-Abl activity, results in the down-regulation of Mcl-1 protein and mRNA. A major regulator of Mcl-1 gene expression is STAT3. Our data show that CLL cells expressing high levels of c-Abl also show elevated levels of phospho-STAT3, and that STAT3 phosphorylation in CLL cells is dependent on c-Abl activity. However, STAT3 phosphorylation by c-Abl requires activation of nuclear factor-κB, secretion of autocrine interleukin-6, and active protein kinase C. Taken together, our data demonstrate the mechanism involved in c-Abl regulation of Mcl-1 expression in CLL cells, and suggest that c-Abl inhibition has therapeutic application in the treatment of this disease.

Single-agent lenalidomide in the treatment of previously untreated chronic lymphocytic leukemia

PURPOSE

Lenalidomide is an oral immunomodulatory drug with multiple effects on the immune system and tumor cell microenvironment leading to inhibition of malignant cell growth. Based on encouraging reports of lenalidomide in relapsed and refractory chronic lymphocytic leukemia (CLL), we investigated the first-line use of single-agent lenalidomide in CLL.

PATIENTS AND METHODS

Using a starting dose of lenalidomide 10 mg/d for 21 days of a 28-day cycle and weekly 5-mg dose escalations to a target of 25 mg, we encountered severe toxicities (tumor lysis, fatal sepsis) in the first two patients enrolled. The study was halted and the protocol amended to a more conservative regimen: starting dose of lenalidomide 2.5 mg with monthly escalations to a target dose of 10 mg, and extended tumor lysis prophylaxis and monitoring. Gene expression profiles from patient samples before and after 7 days of lenalidomide were performed.

RESULTS

Twenty-five patients were enrolled on the amended protocol. No further tumor lysis events were reported. Tumor flare was common (88%) but mild. Grade 3 to 4 neutropenia occurred in 72% of patients, with only five episodes of febrile neutropenia. The overall response rate was 56% (no complete responses). Although rapid peripheral lymphocyte reductions were observed, rebound lymphocytoses during the week off-therapy were common. Lenalidomide-induced molecular changes enriched for cytoskeletal and immune-related genes were identified.

CONCLUSION

Lenalidomide is clinically active as first-line CLL therapy and is well-tolerated if a conservative approach with slow dose escalation is used. A lenalidomide-induced molecular signature provides insights into its immunomodulatory mechanisms of action in CLL.

Dasatinib plus Nutlin-3 shows synergistic antileukemic activity in both p53 wild-type and p53 mutated B chronic lymphocytic leukemias by inhibiting the Akt pathway

PURPOSE

To analyze the effect of the combination of Dasatinib, a multikinase inhibitor, plus Nutlin-3, a nongenotoxic activator of the p53 pathway, in primary B chronic lymphocytic leukemia (B-CLL) patient samples and B leukemic cell line models.

EXPERIMENTAL DESIGN

The induction of cytotoxicity was evaluated in both primary B-CLL cell samples (n = 20) and in p53(wild-type) (EHEB, JVM-2) and p53(deleted/mutated) (MEC-2, BJAB) B leukemic cell lines. The role of Akt in modulating leukemic cell survival/apoptosis in response to Dasatinib or Dasatinib + Nutlin-3 was documented by functional experiments carried out using specific pharmacological inhibitors and by overexpression of membrane-targeted constitutively active form of Akt.

RESULTS

The combination of Dasatinib + Nutlin-3 exhibited a synergistic cytotoxicity in the majority (19 out of 20) of B-CLL samples, including patients carrying 17p- (n = 4), and in both p53(wild-type) and p53(deleted/mutated) B leukemic cell lines. At the molecular level, Dasatinib significantly counteracted the Nutlin-3-mediated induction of the p53 transcriptional targets MDM2 and p21 observed in p53(wild-type) leukemic cells. Conversely, Nutlin-3 did not interfere with the ability of Dasatinib to decrease the phosphorylation levels of ERK1/2, p38/MAPK, and Akt in both p53(wild-type) and p53(deleted/mutated) B leukemic cell lines. A critical role of Akt downregulation in mediating the antileukemic activity of Dasatinib and Dasatinib + Nutlin-3 was demonstrated in experiments carried out by specifically modulating the Akt pathway.

CONCLUSIONS

These findings suggest that Dasatinib + Nutlin-3 might represent an innovative therapeutic combination for both p53(wild-type) and p53(deleted/mutated) B-CLL.

Refractory chronic lymphocytic leukemia--new therapeutic strategies

Treatment outcome of chronic lymphocytic leukemia (CLL) has considerably improved since the introduction of fludarabine (F) as part of the standard therapy. Nevertheless, refractoriness to fludarabine occurs in a significant number of patients and is associated with an unfavorable prognosis. Important risk factors are 17p deletion and/or mutation of TP53. For this subgroup the CD52 antibody alemtuzumab (A) presents a new treatment approach and has already been approved. Meanwhile we have to face also refractoriness to alemtuzumab. Importantly, the monoclonal CD20 antibody ofatumumab has now shown efficacy in F and A double-refractory CLL. The next generation CD20 antibody GA-101 is currently compared to rituximab (R) and will possibly be its more potent successor. Further B-cell antigens are targeted by lumiliximab (CD23), TRU-016 (CD37) and blinatumomab (CD19). Apart from monoclonal antibody therapies, a great number of small molecules are examined for the treatment of refractory and relapsed CLL. Most of these agents aim to overcome apoptosis resistance in CLL cells or influence the microenvironment. Typical targets are regulators of the cell cycle and antiapoptotic molecules like the members of the Bcl-2 family. Up to now the most promising agents appear to be flavopiridol and lenalidomide among others.

Anti-leukemic activity of dasatinib in both p53(wild-type) and p53(mutated) B malignant cells

The multi-kinase inhibitor dasatinib induced a variable but significant decrease of viability in both p53(wild-type) (EHEB, JVM-2, JVM-3) and p53(mutated) (MEC-1, MEC-2, BJAB) prolymphocytic B leukemic cells, due to a combination of cell cycle block in G1 and apoptosis. Antibody phospho-kinase array analysis revealed that dasatinib inhibited the phosphorylation of various kinases, including ERK1/2 and p38/MAPK as well as of STAT3 transcription factors, in both p53(wild-type) and p53(mutated) cells. Therefore, dasatinib might offer a novel therapeutic strategy not only for p53(wild-type), but also for p53(mutated) B malignancies that have the worst prognosis and urgently need innovative therapeutic approaches.

Lycorine sensitizes CD40 ligand-protected chronic lymphocytic leukemia cells to bezafibrate- and medroxyprogesterone acetate-induced apoptosis but dasatanib does not overcome reported CD40-mediated drug resistance

BACKGROUND

Tumor cells in chronic lymphocytic leukemia accumulate in the periphery through the proliferation of a minority of cells in lymph nodes. The proliferative and survival signals in these proliferation centers include interactions with T lymphocytes expressing CD40 ligand. We have demonstrated that the low toxicity combination of bezafibrate and medroxyprogesterone acetate induces mitochondrial superoxide-mediated apoptosis of non-CD40-liganded cells but not of cells exposed to CD40 ligand. Here, we assessed the ability of dasatinib and lycorine to restore bezafibrate- and medroxyprogesterone acetate- induced apoptosis in cells exposed to CD40 ligand. In parallel experiments we compared the ability of dasatinib to induce apoptosis of cells co-treated with fludarabine.

DESIGN AND METHODS

Primary chronic lymphocytic leukemia and peripheral blood mononuclear cells were exposed to drug combinations for 72 hours on control and CD40 ligand-expressing fibroblast monolayers. Cells were harvested and analyzed for apoptosis and levels of mitochondrial superoxide using flow cytometry. In some experiments cells were removed from CD40 ligand at 48 hours, retreated and analyzed after a further 24 hours. The effect of CD40 ligand and drug treatments on mitochondrial superoxide levels were assessed.

RESULTS

As previously described, dasatinib rendered cells sensitive to fludarabine but only when CD40 ligand was removed for the last 24 hours of culture. In contrast, lycorine restored the bezafibrate- and medroxyprogesterone acetate-induced apoptosis associated with mitochondrial superoxide even during continuous exposure to CD40 ligand. Furthermore, combined bezafibrate, medroxyprogesterone acetate and lycorine had little effect against normal peripheral blood mononuclear cells, whereas dasatinib with fludarabine induced high levels of apoptosis.

CONCLUSIONS

Our data indicate the potential of bezafibrate, medroxyprogesterone acetate and lycorine as novel therapy in chronic lymphocytic leukemia and have important implications for the reported potential of c-abl kinase inhibitors in this disease.

p53 and autophagy contribute to dasatinib resistance in primary CLL lymphocytes

B-cell chronic lymphocytic leukemia (CLL) is the most common leukemia in adults and there is no cure for the disease. Although dasatinib is cytotoxic to primary CLL lymphocytes in vitro, the drug has been shown to be active in a small percent of CLL patients. Our previous results suggest that dasatinib targets del17 CLL lymphocytes which are the CLL patients with the worst prognosis. Here we present mechanistic evidence that dasatinib induces endoplasmic reticulum stress and autophagy in CLL lymphocytes. Furthermore we provide evidence suggesting that autophagy mediates resistance to the drugs, process that is modulated by p53.

Current and emerging treatments for chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common adult leukaemia in Europe and North America. The disease is characterized by proliferation and accumulation of small CD5+ B cells in blood, lymph nodes, spleen, liver and bone marrow. The natural clinical course of CLL is highly variable, and chemotherapy is usually not indicated in early and stable disease. However, patients with progressive and more advanced CLL require treatment. For many years, chlorambucil with or without corticosteroids was used in previously untreated patients with CLL. More recently, purine nucleoside analogues (PNAs) [fludarabine, cladribine and pentostatin] have been included in treatment approaches for this disease, and chlorambucil is no longer the leading standard everywhere. Currently, this drug is rather recommended for the treatment of older, unfit patients with co-morbidities, especially in European countries. Significantly higher overall response (OR) and complete response (CR) rates in patients treated initially with PNAs than in those treated with chlorambucil or cyclophosphamide-based combination regimens have been confirmed in randomized, prospective, multicentre trials. Moreover, PNAs administered in combination with cyclophosphamide produce higher response rates, including CR and molecular CR, compared with PNA as monotherapy. Recent reports suggest that the administration of monoclonal antibodies (mAbs) can significantly improve the course of CLL. At present, two mAbs have the most important clinical value in patients with CLL. The first is rituximab, a human mouse antibody that targets CD20 antigens, and the second is alemtuzumab, a humanized form of a rat antibody active against CD52. Several recent reports suggest that in patients with CLL, rituximab combined with a PNA can increase the OR and CR rates compared with PNA or rituximab alone, with acceptable toxicity. In randomized trials, the combination of rituximab with fludarabine and cyclophosphamide (FC-R regimen) demonstrated higher rates of OR, CR and progression-free survival in patients with previously untreated and relapsed or refractory CLL than fludarabine plus cyclophosphamide (FC regimen). Several reports have confirmed significant activity with alemtuzumab in relapsed or refractory CLL, as well as in previously untreated patients. Recently, several new agents have been investigated and have shown promise in treating patients with CLL. These treatments include new mAbs, agents targeting the antiapoptotic bcl-2 family of proteins and receptors involved in mediating survival signals from the microenvironment, antisense oligonucleotides and other agents. The most promising are new mAbs directed against the CD20 molecule, lumiliximab and anti-CD40 mAbs. Oblimersen, alvocidib (flavopiridol) and lenalidomide are also being evaluated both in preclinical studies and in early clinical trials. In recent years, a significant improvement in haematopoietic stem cell transplantation (HSCT) procedures in patients with high-risk CLL has been observed. However, the exact role of HSCT, autologous or allogeneic, in the standard management of CLL patients is still undefined.

Inhibition of Lck enhances glucocorticoid sensitivity and apoptosis in lymphoid cell lines and in chronic lymphocytic leukemia

Glucocorticoids are used as part of front-line therapy to treat lymphoid malignancy because of their remarkable ability to induce apoptosis. Yet, in T cells, glucocorticoid-induced apoptosis is readily inhibited by lymphocyte activation and signaling. We have previously shown that the Src family kinase, Lck (lymphocyte cell-specific tyrosine kinase), which is predominantly expressed in T cells, interacts with IP3 receptors to facilitate calcium signaling. Here, we discovered that dexamethasone downregulates Lck, which, in turn, suppresses lymphocyte activation by inhibiting pro-survival calcium oscillations. Moreover, stable expression of shRNAs that selectively targeted Lck or treatment with the Src inhibitor dasatinib (BMS-354825) enhanced apoptosis induction by dexamethasone. To investigate the effect of Lck inhibition in a primary leukemia model, we employed chronic lymphocytic leukemia (CLL) cells that aberrantly expressed Lck and were relatively insensitive to dexamethasone. Lck expression was correlated with resistance to dexamethasone in CLL cells, and its inhibition by dasatinib or other inhibitors markedly enhanced glucocorticoid sensitivity. Collectively, these data indicate that Lck protects cells from glucocorticoid-induced apoptosis and its inhibition enhances sensitivity to dexamethasone. Small-molecule inhibitors of Lck, such as dasatinib, may function to reverse glucocorticoid resistance in some lymphoid malignancies.

Activities of SYK and PLCgamma2 predict apoptotic response of CLL cells to SRC tyrosine kinase inhibitor dasatinib

PURPOSE

B-cell receptor signaling plays an important role in the pathogenesis of chronic lymphocytic leukemia (CLL). However, blocking B-cell receptor signaling with dasatinib, an inhibitor of SRC kinase, produced variable results in preclinical and clinical studies. We aim to define the molecular mechanisms underlying the differential dasatinib sensitivity and to uncover more effective therapeutic targets in CLL.

EXPERIMENTAL DESIGN

Fresh CLL B cells were treated with dasatinib, and cell viability was followed. The CLL cases were then divided into good and poor responders. The cellular response was correlated with the activities of B-cell receptor signaling molecules, as well as with molecular and cytogenetic prognostic factors.

RESULTS

Among 50 CLL cases, dasatinib treatment reduced cell viability by 2% to 90%, with an average reduction of 47% on day 4 of culture. The drug induced CLL cell death through the intrinsic apoptotic pathway mediated by reactive oxygen species. Unexpectedly, phosphorylation of SRC family kinases was inhibited by dasatinib in good, as well as poor, responders. As opposed to SRC family kinases, activities of two downstream molecules, SYK and phospholipase Cgamma2, correlate well with the apoptotic response of CLL cells to dasatinib.

CONCLUSIONS

Thus, SYK inhibition predicts cellular response to dasatinib. SYK, together with phospholipase Cgamma2, may serve as potential biomarkers to predict dasatinib therapeutic response in patients. From the pathogenic perspective, our study suggests the existence of alternative mechanisms or pathways that activate SYK, independent of SRC kinase activities. The study further implicates that SYK might serve as a more effective therapeutic target in CLL treatment.