B-Cell Receptor Pathobiology and Targeting in NHL

Overcoming Ibrutinib Resistance in Chronic Lymphocytic Leukemia

Ibrutinib is the first Bruton's tyrosine kinase (BTK) inhibitor, which showed significant clinical activity in chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) patients regardless of cytogenetic risk factors. Recent results of phase III clinical trials in treatment-naïve CLL patients shift the importance of the agent to frontline therapy. Nevertheless, beside its clinical efficacy, ibrutinib possesses some off-target activity resulting in ibrutinib-characteristic adverse events including bleeding diathesis and arrhythmias. Furthermore, acquired and primary resistance to the drug have been described. As the use of ibrutinib in clinical practice increases, the problem of resistance is becoming apparent, and new methods of overcoming this clinical problem arise. In this review, we summarize the mechanisms of BTK inhibitors' resistance and discuss the post-ibrutinib treatment options.

Triazol: a privileged scaffold for proteolysis targeting chimeras

Current traditional drugs such as enzyme inhibitors and receptor agonists/antagonists present inherent limitations due to occupancy-driven pharmacology as the mode of action. Proteolysis targeting chimeras (PROTACs) are composed of an E3 ligand, a connecting linker and a target protein ligand, and are an attractive approach to specifically knockdown-targeted proteins utilizing an event-driven mode of action. The length, hydrophilicity and rigidity of connecting linkers play important role in creating a successful PROTAC. Some PROTACs with a triazole linker have displayed promising anticancer activity. This review provides an overview of PROTACs with a triazole scaffold and discusses its structure-activity relationship. Important milestones in the development of PROTACs are addressed and a critical analysis of this drug discovery strategy is also presented.

Novelties in the management of B-cell malignancies: B-cell receptor signaling inhibitors and lenalidomide

B-cell lymphoproliferative disorders comprise 85% of Non-Hodgkin's lymphomas. Despite successful chemoimmunotherapy regimens, responses are not durable and the outcome is fatal in a considerable portion of patients. There is an inevitable need for less toxic and more potent therapeutic agents. Over the recent years, a plethora of agents including monoclonal antibodies, Bcl-2 antagonists, tyrosine kinase inhibitors, cyclin-dependent kinase inhibitors, mTOR inhibitors and immunomodulatory drugs have been developed in B-cell malignancies. The aim of this paper is to focus on B-cell receptor signaling inhibitors and lenalidomide as an immunomodulatory drug and to provide insight on how and when to incorporate these agents into the treatment algorithms.

Mechanisms of ibrutinib resistance in chronic lymphocytic leukaemia and non-Hodgkin lymphoma

Bruton tyrosine kinase (BTK), a mediator of B-cell receptor (BCR) signalling, has been implicated in the pathogenesis of chronic lymphocytic leukaemia (CLL) and other B-cell malignancies. Ibrutinib is an orally bioavailable and highly specific BTK inhibitor that was recently approved for treatment of patients with recurrent CLL and mantle cell lymphoma (MCL). In addition, ibrutinib has shown efficacy in subsets of patients with diffuse large B cell lymphoma (DLBCL) and Waldenstrom macroglobulinaemia (WM). However, despite ibrutinib's activity in multiple B-cell malignancies, cases of primary and secondary resistance have emerged. The overall reported frequency of resistance is low, but follow-up in many trials was short, and we predict that the incidence of observed resistance will increase as clinical use outside clinical trials expands over time. Mutations within BTK have been described and clearly interfere with drug binding; however, there are also emerging alternative mechanisms that bypass BTK entirely and offer new opportunities for other targeted agents. Improved understanding of mechanisms of primary and secondary resistance is essential to developing appropriate therapeutic strategies to both prevent and address resistance. This review provides a comprehensive analysis of ibrutinib resistance in CLL, MCL, DLBCL and WM and considers potential strategies for further study.

Immunohistochemical analysis indicates that the anatomical location of B-cell non-Hodgkin's lymphoma is determined by differentially expressed chemokine receptors, sphingosine-1-phosphate receptors and integrins

Background

The aim of this study was to elucidate the mechanisms responsible for the location of B-cell non-Hodgkin’s lymphoma (B-NHL) at different anatomical sites. We speculated that the malignant B cells in these disorders have the potential for trafficking between blood and secondary lymphoid organs (SLO) or extranodal sites and that their preferential accumulation at different locations is governed by the expression of key molecules that regulate the trafficking of normal lymphocytes.

Methods

Biopsy or blood samples from 91 cases of B-NHL affecting SLO (n = 27), ocular adnexae (n = 51) or blood (n = 13) were analysed by immunohistochemistry or flow cytometry for the expression of the following molecules: CCR7, CCL21 and αL (required for the entry of normal lymphocytes into SLO); CXCR4, CXCL12 and α4 (required for entry into extranodal sites); CXCR5, CXCL13 and S1PR2 (required for tissue retention); S1PR1 and S1PR3 (required for egress into the blood). The expression of each of these molecules was then related to anatomical location and histological subtype.

Results

The expression of motility/adhesion molecules varied widely between individual patient samples and correlated much more strongly with anatomical location than with histological subtype. SLO lymphomas [comprising 10 follicular lymphoma (FL), 8 diffuse large B-cell lymphoma (DLBCL), 4 mantle-cell lymphoma (MCL) and 5 marginal-zone lymphoma (MZL)] were characterised by pronounced over-expression of S1PR2, suggesting that the malignant cells in these lymphomas are actively retained at the site of clonal expansion. In contrast, the malignant B cells in ocular adnexal lymphomas (10 FL, 9 DLBCL, 4 MCL and 28 MZL) expressed a profile of molecules suggesting a dynamic process of trafficking involving not only tissue retention but also egress via S1PR3 and homing back to extranodal sites via CXCR4/CXCL12 and α4. Finally, leukaemic lymphomas (6 FL, 5 MCL and 2 MZL) were characterised by aberrant expression of the egress receptor S1PR1 and low expression of molecules required for tissue entry/retention.

Conclusions

In summary, our study strongly suggests that anatomical location in B-NHL is governed by the differential expression of specific adhesion/motility molecules. This novel observation has important implications for therapeutic strategies that aim to disrupt protective micro-environmental interactions.

Electronic supplementary material

The online version of this article (doi:10.1186/s40164-015-0004-3) contains supplementary material, which is available to authorized users.

Functional interleukin-21 polymorphism is a protective factor of diffuse large B-cell lymphoma

Interleukin-21 (IL-21) is a recently discovered cytokine and plays critical roles in antitumor immune responses. Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. In this study, we investigated the association between IL-21 genetic polymorphisms and the susceptibility to DLBCL, and the possible functions of these polymorphisms. Two IL-21 polymorphisms, rs907715G/A and rs2221903A/G, were examined in 212 DLBCL patients and 232 healthy controls. Data showed that percentages of rs907715GA and AA genotypes were significantly lower in patients than in controls (odds ratio [OR]=0.60, 95% confidence interval [CI]: 0.40-0.90, p=0.014; OR=0.31, 95% CI: 0.17-0.56, p<0.001, respectively). Frequency of the rs2221903A/G polymorphism did not reveal any significant differences between patients and healthy donors. Further analyses demonstrated a significantly decreased number of rs907715AA genotype in patients with advanced Ann Arbor stages (III+IV). Moreover, we investigated the correlation between IL-21 polymorphisms and serum level of IL-21. Results showed that subjects carrying rs907715AA had significantly increased level of IL-21 than those with GG genotype or GA genotype. These data suggest that rs907715G/A polymorphism may act as a protective factor of DLBCL and might affect the serum level of IL-21.

Characterization of ibrutinib-sensitive and -resistant mantle lymphoma cells

Ibrutinib inhibits Bruton tyrosine kinase (BTK), a key component of early B-cell receptor (BCR) signalling pathways. A multicentre phase 2 trial of ibrutinib in patients with relapsed/refractory mantle cell lymphoma (MCL) demonstrated a remarkable response rate. However, approximately one-third of patients have primary resistance to the drug while other patients appear to lose response and develop secondary resistance. Understanding the molecular mechanisms underlying ibrutinib sensitivity is of paramount importance. In this study, we investigated cell lines and primary MCL cells that display differential sensitivity to ibrutinib. We found that the primary cells display a higher BTK activity than normal B cells and MCL cells show differential sensitivity to BTK inhibition. Genetic knockdown of BTK inhibits the growth, survival and proliferation of ibrutinib-sensitive but not resistant MCL cell lines, suggesting that ibrutinib acts through BTK to produce its anti-tumour activities. Interestingly, inhibition of ERK1/2 and AKT, but not BTK phosphorylation per se, correlates well with cellular response to BTK inhibition in cell lines as well as in primary tumours. Our study suggests that, to prevent primary resistance or to overcome secondary resistance to BTK inhibition, a combinatory strategy that targets multiple components or multiple pathways may represent the most effective approach.

Fibroblast growth factor receptor 4 polymorphism is associated with increased risk and poor prognosis of non-Hodgkin's lymphoma

Fibroblast growth factor receptor 4 (FGFR4) is expressed in various cell types and plays important roles in regulating immune responses. Evidence has shown that FGFR4 rs351855 (Gly388Arg) polymorphism may act as a risk factor for many diseases. In the current study, we investigated the association between FGFR4 polymorphisms and the susceptibility to non-Hodgkin's lymphoma (NHL) in the Chinese population. Two polymorphisms in the FGFR4 gene (rs351855G/A and rs147603016G/A) were detected by polymerase chain reaction-restriction fragment length polymorphism in 421 NHL cases and 486 healthy controls. Results showed that prevalence of rs351855AA genotype was significantly increased in patients than in controls (odds ratio [OR] = 2.02, 95% confidence interval [CI] 1.91-3.23, P < 0.001). Similarly, rs351855A allele presented significantly higher numbers in cases compared to healthy donors (49.8 versus 40.1%, P < 0.001). Further study revealed that the frequency of the rs351855G/A polymorphism was clearly elevated in cases with B cell subtype than those with T cell subtypes. When analyzing the survival time of NHL patients with FGFR4 rs351855G/A polymorphism, cases with AA genotype had significantly shorter survival time compared to the patients with GG genotype (P < 0.001) or GA genotype (P < 0.001). These results suggest that FGFR4 rs351855G/A polymorphism is associated with increased susceptibility to NHL and could be used as a marker for predicting the prognosis of the malignancy.

Treatment challenges in the management of relapsed or refractory non-Hodgkin's lymphoma - novel and emerging therapies

Over the last few decades, advances in immunochemotherapy have led to dramatic improvement in the prognosis of non-Hodgkin's lymphoma (NHL). Despite these advances, relapsed and refractory disease represents a major treatment challenge. For both aggressive and indolent subtypes of NHL, there is no standard of care for salvage regimens, with prognosis after relapse remaining relatively poor. Nevertheless, there are multiple emerging classes of targeted therapies for relapsed/refractory disease, including monoclonal antibodies, antibody- drug conjugates, radioimmunotherapy, small-molecule inhibitors of cell-growth pathways, and novel chemotherapy agents. This review will discuss treatment challenges of NHL, current available salvage regimens for relapsed/refractory NHL, and the safety and efficacy of novel emerging therapies.