Advances in treating chronic lymphocytic leukemia

3D-STED Super-Resolution Microscopy Reveals Distinct Nanoscale Organization of the Hematopoietic Cell-Specific Lyn Substrate-1 (HS1) in Normal and Leukemic B Cells

HS1, the hematopoietic homolog of cortactin, acts as a versatile actin-binding protein in leucocytes. After phosphorylation, it is involved in GTPase and integrin activation, and in BCR, TCR, and CXCR4 downstream signaling. In normal and leukemic B cells, HS1 is a central cytoskeletal interactor and its phosphorylation and expression are prognostic factors in chronic lymphocytic leukemia (CLL) patients. We here introduce for the first time a super-resolution imaging study based on single-cell 3D-STED microscopy optimized for revealing and comparing the nanoscale distribution of endogenous HS1 in healthy B and CLL primary cells. Our study reveals that the endogenous HS1 forms heterogeneous nanoclusters, similar to those of YFP-HS1 overexpressed in the leukemic MEC1 cell line. HS1 nanoclusters in healthy and leukemic B cells form bulky assemblies at the basal sides, suggesting the recruitment of HS1 for cell adhesion. This observation agrees with a phasor-FLIM-FRET and STED colocalization analyses of the endogenous MEC1-HS1, indicating an increased interaction with Vimentin at the cell adhesion sites. In CLL cells isolated from patients with poor prognosis, we observed a larger accumulation of HS1 at the basal region and a higher density of HS1 nanoclusters in the central regions of the cells if compared to good-prognosis CLL and healthy B cells, suggesting a different role for the protein in the cell types analyzed. Our 3D-STED approach lays the ground for revealing tiny differences of HS1 distribution, its functionally active forms, and colocalization with protein partners.

Assessment of microRNA expression in leukemic cells as predictors of sensitivity to purine nucleoside analogs, fludarabine and cladribine, in chronic lymphocytic leukemia patients

Background: Great progress has been achieved lately in the therapy for chronic lymphocytic leukemia (CLL), one of the most frequently diagnosed adult leukemias. New classes of drugs, such as kinase inhibitors and BCL-2 protein antagonists, have been approved for treatment of CLL patients. Despite the abovementioned therapies the disease can still be effectively treated with purine nucleoside analogs (PNA). However, some patients, for example, those with TP53 gene abnormalities, become resistant, and the other factors involved in the therapy resistance are still being investigated. This study was aimed at analyzing the possible role of microRNAs as markers predicting the outcome of chemotherapy based on PNA – fludarabine and cladribine in CLL patients.

Methods: The expression of miR-21, miR-34a, miR-181a and miR-221 in previously separated leukemic cells was assessed with the use of qRQ-PCR technique at the moment of diagnosis in 40 CLL patients. In turn, apoptosis induced by fludarabine and cladribine in 24-hour cell culture was evaluated by determining the increase in the percentage of apoptotic cells of CD5+/CD19+/Cas3+ phenotype, using a flow cytometry method. Nine of the 40 studied subjects were treated with fludarabine-based regimens and were analyzed with regards to in vivo response to PNA.

Results: We detected a significantly higher PNA-induced apoptosis rate in patients with high miR-34a expression in comparison to low expression ones. Interestingly, such differences were detected particularly in standard cytogenetic patients.

Conclusions: These results may prove an important role of miR-34a expression as a predictor of apoptosis, even in cases when other risk factors like cytogenetic abnormalities are absent. An assessment of microRNAs expression seems to be useful as an indicator of sensitivity to PNA and may help to predict PNA-based therapy outcome.

From Biology to Therapy: The CLL Success Story

Chemoimmunotherapy has been the standard of care for patients with chronic lymphocytic leukemia (CLL) over the last decade. Advances in monoclonal antibody technology have resulted in the development of newer generations of anti-CD20 antibodies with improved therapeutic effectiveness. In parallel, our knowledge about the distinctive biological characteristics of CLL has progressively deepened and has revealed the importance of B-cell receptor (BCR) signaling and upregulated antiapoptotic proteins for survival and expansion of malignant cell clones. This knowledge provided the basis for development of novel targeted agents that revolutionized treatment of CLL. Ibrutinib and idelalisib inhibit the Bruton tyrosine kinase (BTK) and phosphoinositide 3-kinase (PI3K) delta, respectively, thus interfering with supportive signals coming from the microenvironment via the BCR. These drugs induce egress of CLL cells from secondary lymphoid organs and remarkably improve clinical outcomes, especially for patients with unmutated immunoglobulin heavy-chain genes or with p53 abnormalities that do not benefit from classical treatment schemes. Latest clinical trial results have established ibrutinib with or without anti-CD20 antibodies as the preferred first-line treatment for most CLL patients, which will reduce the use of chemoimmunotherapy in the imminent future. Further advances are achieved with venetoclax, a BH3-mimetic that specifically inhibits the antiapoptotic B-cell lymphoma 2 protein and thus causes rapid apoptosis of CLL cells, which translates into deep and prolonged clinical responses including high rates of minimal residual disease negativity. This review summarizes recent advances in the development of targeted CLL therapies, including new combination schemes, novel BTK and PI3K inhibitors, spleen tyrosine kinase inhibitors, immunomodulatory drugs, and cellular immunotherapy.

Assessment of micro RNAs expression in leukemic cells as prognostic markers in chronic lymphocytic leukemia: micro RNAs can predict survival in a course of the disease

Numerous genetic alterations predicting prognosis and clinical outcome are revealed recently in chronic lymphocytic leukemia (CLL). Among them the deregulated expression of micro RNAs that can induce tumor growth, or act as tumor suppressors seem to be of great importance. This study aimed to analyze the possible role of chosen micro RNAs as markers of prognosis in patients with CLL. We assessed the expression of miR-21, miR-34a, miR-181a, miR-199a/b and miR-221 in previously separated leukemic cells with the use of qRQ-PCR technique at the moment of diagnosis. The results were then analyzed in regards to presence of prognostic factors, clinical data and the end points like progression free survival (PFS), time to progression (TP) and overall survival time (OS).

We detected significant correlations between expression of the analyzed micro RNAs and CLL prognostic markers particularly as far as miR-221 and miR-181a were concerned. The subsequent analysis revealed that high expression of miR-34a and miR-181a as well as low miR-21 expression indicated longer TTP, while miR-221 was predictor of OS.

The obtained results prove the role of micro RNAs as CLL prognostic markers, particularly as factors predicting survival in a course of the disease.

Recent therapeutic advances in chronic lymphocytic leukemia

The last several years have witnessed a paradigm shift in the management of patients with chronic lymphocytic leukemia (CLL). The course of this very heterogeneous disease, traditionally treated with chemotherapeutic agents usually in combination with rituximab, typically has been characterized by remissions and relapses, and survival times vary greatly, depending on intrinsic biological attributes of the leukemia. The developments of the last few years have been transformative, ushering in an era of novel, molecularly targeted therapies, made possible by extensive efforts to elucidate the biology of the disease that predated the new targeted drugs. Thus, successful therapeutic targeting of the B-cell receptor signaling pathway and of the Bcl-2 anti-apoptotic protein with small molecules has now made chemotherapy-free approaches possible, hopefully mitigating the risk of development of therapy-related myeloid neoplasms and making eventual cure of CLL with the use of optimal drug combinations a realistic goal. Most importantly, these therapies have demonstrated unprecedented efficacy in patients with deletion 17p/TP53 mutation, a subset that historically has been very difficult to treat. However, as we gain more experience with the newer agents, unique safety concerns and resistance mechanisms have emerged, as has the issue of cost, as these expensive drugs are currently administered indefinitely. Accordingly, novel laboratory-based strategies and clinical trial designs are being explored to address these issues. The availability of whole exome/genome sequencing has given us profound insights into the mutational landscape of CLL. In this article, we highlight some of the most impactful advances since this topic was last reviewed in this journal.

The first MCL-1-selective BH3 mimetics have therapeutic potential for chronic lymphocytic leukemia

Small-molecule BH3 mimetics are designed to mimic the BH3 domain of BH3-only BCL-2 family members which are antagonists of the prosurvival members (such as BCL-2, BCL-XL and MCL-1). The BH3 mimetics are intended to bind with high affinity to prosurvival proteins, in order to inhibit their functional activity and hence to induce apoptosis in cancer cells. Both navitoclax (BCL-2/BCL-XL antagonist) and ABT-199/venetoclax (BCL-2-selective inhibitor) have demonstrated therapeutic efficacy especially in chronic lymphocytic leukemia (CLL). However, these BH3 mimetics cannot antagonize the prosurvival protein MCL-1 that is overexpressed and involved in therapeutic resistance in CLL. Furthermore, until now, none of the reported small-molecule MCL-1 inhibitors bound to their target with high affinity. The first MCL-1-selective BH3 mimetics capable of high-affinity binding and inducing apoptosis in cancer cells through an on-target mechanism have just been identified. This discovery should advance the translational research to implement novel drugs in treating CLL.

The skewed balance between Tregs and Th17 in chronic lymphocytic leukemia

While Tregs maintain self-tolerance and inhibit antitumor responses, T helper (Th)17 cells may enhance inflammatory and antitumor responses. The balance between these two important T-cell subsets has been skewed in many immunopathologic conditions such as autoimmune and cancer diseases. B-cell chronic lymphocytic leukemia (CLL) is the most common form of leukemia in the western world and is characterized with monoclonal expansion of B lymphocytes. There is evidence which implies that the progression of CLL is associated with expansion of Treg and downregulation of Th17 cells. In this review, we will discuss about immunobiology of Treg and Th17 cells and their role in immunopathogenesis of CLL as well as their reciprocal changes during disease progression.

Danazol induces apoptosis and cytotoxicity of leukemic cells alone and in combination with purine nucleoside analogs in chronic lymphocytic leukemia

Recently, great progress has been achieved in the treatment of chronic lymphocytic leukemia (CLL). However, some patients, particularly older patients with comorbidities or with relapsed/refractory leukemia, still have limited therapeutic options. There is an urgent need to discover less toxic and more effective drugs for CLL patients. Applying new modalities or substances that are widely used for the treatment of other diseases has been reported to improve results in CLL treatment. This study aimed to assess the non-chemotherapeutic drug danazol for its potential to destroy leukemic cells. Leukemic cells, obtained from the peripheral blood and bone marrow of 23 CLL patients, were cultured in the presence of danazol and its combination with the purine nucleoside analogs fludarabine and cladribine and bendamustine. After 24 h of incubation, the rate of apoptosis indicated by active caspase-3 expression, and cytotoxicity indicated by forward light scatter and light scatter analysis, was assessed by flow cytometry. We also measured expression of apoptosis-regulating proteins of BCL family and active caspase 9 and active caspase 8 expressions in leukemic cells. Danazol had a caspase-dependent pro-apoptotic and cytotoxic effect on leukemic cells in a tumor-specific manner. The mechanisms of its action appear to be complex and should be precisely established; however, induction of apoptosis involving both mitochondrial and receptor cascades appears to be most probable. Danazol showed a synergic effect with cladribine, an additive effect with fludarabine, and an infra-additive effect with bendamustine. The rate of danazol-induced apoptosis and cytotoxicity did not differ between patients with better and worse prognostic markers. Our results indicate that danazol may be a potential therapeutic agent for CLL patients alone and in combination with purine analogs.

The rate of in vitro fludarabine-induced peripheral blood and bone marrow cell apoptosis may predict the chemotherapy outcome in patients with chronic lymphocytic leukemia

Purpose

The problem of drug sensitivity and predicting the outcome of chemotherapy seems to be of great importance in hemato-oncological disorders. There are some factors that can help to predict effects of chemotherapy in chronic lymphocytic leukemia (CLL), such as presence of del17p, del11q, or TP53 gene mutations, which result in resistance to purine analogues and alkylating drugs. Despite the new therapeutic options introduced recently, purine analogues in combination with cyclophosphamide and the monoclonal antibody rituximab is still the gold standard for the first-line treatment of fit patients with CLL. The aim of this study was to assess whether the rate of apoptosis caused by one of purine analogues—fludarabine in cell cultures differs between patients who clinically respond to fludarabine-based chemotherapy and those who do not respond.

Methods

CLL leukemic cells, obtained from peripheral blood and bone marrow of 23 patients, were cultured in the presence of fludarabine. After 24 h of incubation, the rate of apoptosis, indicated by the expression of active caspase-3, was assessed with flow cytometry and then analyzed regarding clinical response to fludarabine-based regimens.

Results

The percentage of apoptotic cells induced by fludarabine was significantly higher in the group of patients who achieved remission in comparison to the group with no response to purine analogues therapy. Interestingly, we observed that among the patients who did not respond to chemotherapy, the presence of del17p and del11q was detected only once. Other non-responders had no detectable genetic abnormalities.

Conclusions

Based on these results, it can be presumed that in vitro drug sensitivity test, which is easy to perform, may predict the outcome of fludarabine-based chemotherapy in CLL patients.

Electronic supplementary material

The online version of this article (doi:10.1007/s00228-015-1893-0) contains supplementary material, which is available to authorized users.

Molecular basis of chronic lymphocytic leukemia diagnosis and prognosis

BACKGROUNDS

Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in adults and is characterized by a clonal accumulation of mature apoptosis-resistant neoplastic cells. It is also a heterogeneous disease with a variable clinical outcome. Here, we present a review of currently known (epi)genetic alterations that are related to the etiology, progression and chemo-refractoriness of CLL. Relevant literature was identified through a PubMed search (1994-2014) of English-language papers using the terms CLL, signaling pathway, cytogenetic abnormality, somatic mutation, epigenetic alteration and micro-RNA.

RESULTS

CLL is characterized by the presence of gross chromosomal abnormalities, epigenetic alterations, micro-RNA expression alterations, immunoglobulin heavy chain gene mutations and other genetic lesions. The expression of unmutated immunoglobulin heavy chain variable region (IGHV) genes, ZAP-70 and CD38 proteins, the occurrence of chromosomal abnormalities such as 17p and 11q deletions and mutations of the NOTCH1, SF3B1 and BIRC3 genes have been associated with a poor prognosis. In addition, mutations in tumor suppressor genes, such as TP53 and ATM, have been associated with refractoriness to conventional chemotherapeutic agents. Micro-RNA expression alterations and aberrant methylation patterns in genes that are specifically deregulated in CLL, including the BCL-2, TCL1 and ZAP-70 genes, have also been encountered and linked to distinct clinical parameters.

CONCLUSIONS

Specific chromosomal abnormalities and gene mutations may serve as diagnostic and prognostic indicators for disease progression and survival. The identification of these anomalies by state-of-the-art molecular (cyto)genetic techniques such as fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), single nucleotide polymorphism (SNP) microarray-based genomic profiling and next-generation sequencing (NGS) can be of paramount help for the clinical management of these patients, including optimal treatment design. The efficacy of novel therapeutics should to be tested according to the presence of these molecular lesions in CLL patients.

[Chronic lymphocytic leukemia: current standards and novel approaches]

Chronic lymphocytic leukemia (CLL) is the most common leukemia in the western world and affects mainly elderly patients. In current phase III trials, standard treatment options were established that differ mainly based on the fitness and age of the patient. The combination of fludarabine, cyclophosphamide, and the CD20 antibody rituximab (FCR) is recommended for young patients without relevant comorbidity, while bendamustine and rituximab (BR) should be favored for elderly (ca. >65 years) fit individuals. Bendamustine plus ofatumumab is another option in this situation. Patients with major comorbidities should receive chlorambucil combined with CD20 antibody (obinutuzumab or ofatumumab). In 2014, several new compounds were approved for patients with ultrahigh risk genetic factors (17p-, TP53mut) and for relapsed/refractory CLL: both idelalisib and ibrutinib are orally bioavailable kinase inhibitors that block key regulators of central pathways. For both agents, very impressive data are available with regard to tolerability and efficacy that will change the treatment paradigm in CLL. With ABT-199, a direct apoptosis inducer is being developed that in early clinical trials produced high remission rates combined with good tolerability. Combinations and sequences of the "novel" compounds obinutuzumab, ofatumumab, idelalisib, ibrutinib, and ABT-199 will be studied in coming years in clinical trials in order to prolong remission duration and reduce side effects with the eventual aim of curing CLL.