Targeting of B‐cell receptor signalling in B‐cell malignancies

Pharmacological agents that inhibit enzymes of the B‐cell receptor (BCR) pathway are of increasing importance in the treatment of B‐cell malignancies. These include inhibitors of Bruton tyrosine kinase (BTK), phosphatidylinositol 3‐kinase (PI3K), splenic tyrosine kinase and protein kinase Cβ. Two agents are already approved in the USA and Europe: ibrutinib, a BTK inhibitor, for the treatment of chronic lymphatic leukaemia (CLL), mantle cell lymphoma (MCL) and Waldenström's macroglobulinemia; and idelalisib, a PI3Kδ inhibitor, for the treatment of CLL and follicular lymphoma. In addition, the role of these drugs in diffuse large B‐cell lymphoma and marginal zone lymphoma is under investigation, as single agents and in combination with chemotherapy. In CLL, both ibrutinib and idelalisib have an established role as first‐line therapy in patients with del(17p), and in MCL, ibrutinib is a standard option for patients relapsing after chemoimmunotherapy. Unexpected toxicities have been encountered when combining these potent new agents with other drugs, including chemotherapy and lenalidomide, and based on this experience the risks and benefits of novel combinations must be evaluated carefully. In this review, we summarize the efficacy and safety results with these inhibitors and discuss novel combinations that are under study and the future role of BCR inhibitors in these disorders.     

Nature and nurture: a case of transcending haematological pre‐malignancies in a pair of monozygotic twins adding possible clues on the pathogenesis of B‐cell proliferations

We describe a comprehensive molecular analysis of a pair of monozygotic twins, who came to our attention when one experienced amaurosis fugax and was diagnosed with JAK2+ polycythaemia vera. He (Twin A) was also found to have an asymptomatic B‐cell chronic lymphocytic leukaemia (B‐CLL). Although JAK2?, Twin B was subsequently shown to have a benign monoclonal B‐cell lymphocytosis (MBL). Flow cytometric and molecular analyses of the B‐cell compartments revealed different immunoglobulin light and heavy chain usage in each twin. We hypothesized that whole exome sequencing could help delineating the pattern of germline B‐cell disorder susceptibility and reveal somatic mutations potentially contributing to the differential patterns of pre‐malignancy. Comparing bone marrow cells and T cells and employing in‐house engineered integrative analysis, we found aberrations in Twin A consistent with a myeloid neoplasm, i.e. in TET2, RUNX1, PLCB1 and ELF4. Employing the method for detecting high‐ranking variants by extensive annotation and relevance scoring, we also identified shared germline variants in genes of proteins interacting with B‐cell receptor signalling mediators and the WNT‐pathway, including IRF8, PTPRO, BCL9L, SIT1 and SIRPB1, all with possible implications in B‐cell proliferation. Similar patterns of IGHV‐gene usage to those demonstrated here have been observed in inherited acute lymphoblastic leukaemia. Collectively, these findings may help in facilitating identification of putative master gene(s) involved in B‐cell proliferations in general and MBL and B‐CLL in particular.     

Pro‐apoptotic TP53 homolog TAp63 is repressed via epigenetic silencing and B‐cell receptor signalling in chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is an accumulative disorder marked by deficient apoptosis. The TP53 homolog TAp63 promotes apoptosis and chemosensitivity in solid tumours and its deregulation may contribute to CLL cell survival. We found that TAp63α was the most prevalent TP63 isoform in CLL. Compared to healthy B cells, TAp63 mRNA was repressed in 55·7% of CLL samples. TP63 promoter methylation was high in CLL and inversely correlated with TP63 protein expression in B‐cell lymphoma cell lines. siRNA‐mediated knockdown of TP63 resulted in partial protection from spontaneous apoptosis accompanied by reductions in PMAIP1 (NOXA), BBC3 (PUMA), and BAX mRNA in CLL cells and increased proliferation of Raji lymphoma cells. TAp63 mRNA levels were higher in CLL with unmutated IGHV. B‐cell receptor (BCR) engagement led to repression of TP63 mRNA expression in malignant B cells, while pharmacological inhibition of BCR signalling prevented TP63 downregulation. MIR21, known to target TAp63, correlated inversely with TAp63 expression in CLL, and BCR‐mediated downregulation of TP63 was accompanied by MIR21 upregulation in most CLL samples. Our data illustrate the pro‐apoptotic function of TP63, provide insights into the mechanisms of BCR‐targeting agents, and establish a rationale for designing novel approaches to induce TP63 in CLL and B‐cell lymphoma.     

The phosphatidylinositol 3‐kinases (PI3K) inhibitor GS‐1101 synergistically potentiates histone deacetylase inhibitor‐induced proliferation inhibition and apoptosis through the inactivation of PI3K and extracellular signal‐regulated kinase pathways

Previously, we showed that inhibition of the protein kinase C β (PKCβ)/AKT pathway augments engagement of the histone deacetylase inhibitor (HDI)‐induced apoptosis in lymphoma cells. In the present study, we investigated the cytotoxicity and mechanisms of cell death induced by the delta isoform‐specific phosphatidylinositide 3‐kinase (PI3K) inhibitor, GS‐1101, in combination with the HDI, panobinostat (LBH589) and suberoylanilide hydroxamic acid (SAHA). Lymphoma cell lines, primary non‐Hodgkin Lymphoma (NHL) and chronic lymphocytic leukaemia (CLL) cells were simultaneously treated with the HDI, LBH589 and GS‐1101. An interaction of the LBH589/GS‐1101 combination was formally examined by using various concentrations of LBH589 and GS‐1101. Combined treatment resulted in a synergistic inhibition of proliferation and showed synergistic effect on apoptotic induction in all tested cell lines and primary NHL and CLL cells. This study indicates that interference with PI3K signalling dramatically increases HDI‐mediated apoptosis in malignant haematopoietic cells, possibly through both AKT‐dependent or AKT‐ independent mechanisms. Moreover, the increase in HDI‐related apoptosis observed in PI3K inhibitor‐treated cells appears to be related to the disruption of the extracellular signal‐regulated kinase (ERK) signalling pathway. This study provides a strong rational for testing the combination of PI3K inhibitors and HDI in the clinic.     

Targeting SYK kinase‐dependent anti‐apoptotic resistance pathway in B‐lineage acute lymphoblastic leukaemia (ALL) cells with a potent SYK inhibitory pentapeptide mimic

The present study found that the pentapeptide mimic C‐61, targeting the substrate binding P‐site of SYK tyrosine kinase acted as a potent inducer of apoptosis in chemotherapy‐resistant SYK‐expressing primary leukemic B‐cell precursors taken directly from relapsed B‐precursor leukaemia (BPL) patients (but not SYK‐deficient infant pro‐B leukaemia cells), exhibited favourable pharmacokinetics in mice and non‐human primates, and eradicated in vivo clonogenic leukaemia cells in severe combined immunodeficient mouse xenograft models of chemotherapy‐resistant human BPL at dose levels non‐toxic to mice and non‐human primates. These in vitro and in vivo findings provide proof of principle for effective treatment of chemotherapy‐resistant BPL by targeting SYK‐dependent anti‐apoptotic blast cell survival machinery with a SYK P‐Site inhibitor. Further development of C‐61 may provide the foundation for therapeutic innovation against chemotherapy‐resistant BPL.     

Fludarabine, as well as 2-chlorodeoxyadenosine, can induce eosinophilia during treatment of lymphoid malignancies

We treated 25 patients suffering from low-grade lymphoid malignancies with nucleoside analogues. In 11 patients undergoing treatment with fludarabine, two patients with follicular lymphoma developed a marked absolute peripheral blood eosinophilia devoid of clinical symptoms which resolved without medical intervention. Of 15 patients treated with 2-chlorodeoxyadenosine, one patient with B-cell chronic lymphocytic leukaemia (CLL) experienced repeated episodes of eosinophilia that required steroid treatment. Eosinophilia in these three patients was not coupled to tumour lysis, and we found no correlation between the occurrence of eosinophilia and clinical response to treatment. Thus, for the first time, we can report eosinophilia as a side-effect of fludarabine treatment, and these are also the first published cases of this complication occurring in patients treated with nucleoside analogues for follicular lymphoma and CLL.     

Eighteen‐month lamivudine prophylaxis on preventing occult hepatitis B virus infection reactivation in patients with haematological malignancies receiving immunosuppression therapy

This study evaluated the long‐term efficacy and safety of an 18‐month lamivudine prophylaxis in 68 HBsAg‐negative/anti–HBc‐positive patients with oncohaematological disease. All 68 consecutive HBsAg‐negative/anti–HBc‐positive patients with an oncohaematological disease and naïve for chemotherapy observed from April 2008 to December 2012 at 2 Hematology Units in Naples were treated with lamivudine for 18 months after stopping chemotherapy and monitored for HBsAg at months 1 and 3 during chemotherapy and then every 3 months after its discontinuation. During follow‐up, 13 (19.1%) of the 68 patients died of complications related to their oncohaematological disease, and 3 (4%) showed a virological HBV reactivation (retroconversion to HBsAg positivity) 1‐7 months after the discontinuation of lamivudine prophylaxis (2 treated for chronic lymphocytic leukaemia and one for Waldenstrom's disease); of these, 2 showed a biochemical reactivation. Comparing the demographic and clinical characteristics of the 3 patients with a virological HBV reactivation to the 65 without, the former were older (median age and range: 67 years [75‐78] vs. 61 [24‐88]; P = .05) and were less frequently treated for B‐cell non‐Hodgkin lymphoma (B‐NHL) (0 vs. 70.7%, P = .03). In conclusion, a 18 months of lamivudine prophylaxis was effective in preventing HBV reactivation in HBsAg‐negative/anti–HBc‐positive patients treated for B‐NHL. However, in patients with chronic and severe immunodepression, such as those with chronic lymphocytic leukaemia and Waldenstrom's disease, prophylaxis should be continued for an indefinite period.     

A new hope: novel therapeutic approaches to treatment of chronic lymphocytic leukaemia with defects in TP53

Chronic lymphocytic leukaemia (CLL) is an indolent B‐cell malignancy with heterogeneous outcomes. Chromosomal abnormalities in CLL are predictive of the natural disease course; del(11q) and del(17p) are recognized as high risk genetic lesions. Del(17p) is associated with an impaired function of TP53, a key tumour suppressor, and is particularly problematic. Such patients respond poorly to chemo‐immunotherapy and have significantly shorter survival compared to patients with standard and low‐risk cytogenetics. While TP53 pathway defects are rare at initial diagnosis, their frequency increases in relapsed CLL. Until very recently, this group of patients represented an unmet clinical need with few therapeutic options. However, the advent of targeted therapies has expanded the drug armamentarium and introduced new hope for these highly refractory patients. Agents that target B‐cell receptor signalling, BH3‐mimetics and others induce apoptosis of the neoplastic B‐cells in a TP53‐independent manner. Their use in the clinic is associated with remarkable activity in patients with del(17p). In this review we discuss the frequency and clinical significance of del(17p) and genetic mutations leading to disrupted TP53, the putative role of other TP53 homologues, and the results of key clinical trials involving both conventional chemotherapy and novel agents.     

Evolution to plasmablastic lymphoma evades CD19‐directed chimeric antigen receptor T cells

A patient with relapsed and refractory chronic lymphocytic leukaemia with Richter transformation was treated with chimeric antigen receptor (CAR)‐modified T cells targeted for CD19 but later relapsed with a clonally related plasmablastic lymphoma. The loss of most routine markers of pre‐plasma cell or B lymphoid differentiation (including CD19) highlights the ability of such mature lymphomas to evade lineage‐specific targeted immunotherapy by differentiating along pathways comparable to their normal cellular counterparts. Molecular genetic evaluation demonstrated multiple independent lines of CD19‐negative disease that eventually evolved in this single patient. Such plasticity represents potential challenges for antigen‐directed CAR‐T cell therapy, while serving as a testament to the selective pressure exerted by these engineered T cells over time.     

In leukaemic CD5+ B cells the expression of BCL-2 gene family is shifted toward protection from apoptosis

This study further investigated the mechanisms that control apoptosis in leukaemic CD5⁺ B cells, and focused on the Bcl-2 gene family. The pattern of expression of Bcl-2, Bcl-xL, Bcl-xS and Bax genes, selected because of their interrelated role in the control of apoptosis, was analysed in a series of CD5⁺ B-cell chronic lymphoid leukaemias.
Cells from 34 patients with chronic lymphoid leukaemia of B-cell type (23 B-chronic lymphocytic leukaemia (B-CLL) and 11 mantle cell lymphoma (MCL) in leukaemic phase) were investigated. High levels of Bcl-2 mRNA were observed by Northern blot and high levels of Bcl-2 protein were detected by cytofluorograph analysis with a specific monoclonal antibody (MAb) in all cases. Strong Bax expression was detected by RT-PCR in 20/23 B-CLL cases; Bax was also observed in 8/11 MCL in leukaemic phase with variable degree of intensity. In both B-CLL and MCL samples the presence of Bax protein was confirmed by cytofluorograph analysis. RT-PCR detected high levels of Bcl-xL in 16/23 B-CLL and in 8/11 MCL in leukaemic phase, whereas Bcl-xS was detectable in low to trace amounts respectively in 13/23 B-CLL and in 6/11 MCL in leukaemic phase.
According to the functional role of Bcl-2, Bcl-xL, Bcl-xS and Bax, these data indicate that the pattern of Bcl-2 family genes expression in leukaemic CD5⁺ B cells is skewed toward prevention of apoptosis and may thus favour the relentless accumulation of CD5⁺ leukaemic B cells.     

Phase Ib trial of the PI3K/mTOR inhibitor voxtalisib (SAR245409) in combination with chemoimmunotherapy in patients with relapsed or refractory B‐cell malignancies

This phase Ib, dose‐escalation study investigated the maximum tolerated dose (MTD), recommended phase II dose (RP2D), safety, pharmacokinetics (PK) and preliminary efficacy of the pan‐class I phosphoinositide 3‐kinase (PI3K) and mechanistic target of rapamycin (mTOR) inhibitor voxtalisib [30 or 50 mg twice daily (BID)], in combination with rituximab (voxtalisib+rituximab) or rituximab plus bendamustine (voxtalisib+rituximab+bendamustine), in relapsed or refractory indolent B‐cell non‐Hodgkin lymphoma (NHL), mantle cell lymphoma and chronic lymphocytic leukaemia (CLL). MTD and RP2D of voxtalisib were determined using a 3 + 3 dose‐escalation design. Adverse events (AEs), plasma PK and disease response were recorded. Thirty‐seven patients were enrolled. The RP2D of voxtalisib in combination with rituximab or rituximab+bendamustine was 50 mg BID. Four patients experienced a total of five dose‐limiting toxicities. The most frequent AEs were nausea (45·9%), fatigue (37·8%) headache (32·4%) and pyrexia (32·4%). The most frequent grade ≥3 AEs were neutropenia (27·0%), thrombocytopenia (24·3%), anaemia (16·2%) and febrile neutropenia (10·8%). Voxtalisib PK parameters were not affected by co‐administration with rituximab or rituximab+bendamustine. Of 35 efficacy‐evaluable patients, four (11·4%) achieved complete response and 13 (37·1%) achieved partial response. Voxtalisib, in combination with rituximab or rituximab+bendamustine, demonstrated an acceptable safety profile and encouraging anti‐tumour activity in relapsed or refractory B‐cell malignancies.     

Targeting oncogenic interleukin‐7 receptor signalling with N‐acetylcysteine in T cell acute lymphoblastic leukaemia

Activating mutations of the interleukin‐7 receptor (IL7R) occur in approximately 10% of patients with T cell acute lymphoblastic leukaemia (T‐ALL). Most mutations generate a cysteine at the transmembrane domain leading to receptor homodimerization through disulfide bond formation and ligand‐independent activation of STAT5. We hypothesized that the reducing agent N‐acetylcysteine (NAC), a well‐tolerated drug used widely in clinical practice to treat acetaminophen overdose, would reduce disulfide bond formation, and inhibit mutant IL7R‐mediated oncogenic signalling. We found that treatment with NAC disrupted IL7R homodimerization in IL7R‐mutant DND‐41 cells as assessed by non‐reducing Western blot, as well as in a luciferase complementation assay. NAC led to STAT5 dephosphorylation and cell apoptosis at clinically achievable concentrations in DND‐41 cells, and Ba/F3 cells transformed by an IL7R‐mutant construct containing a cysteine insertion. The apoptotic effects of NAC could be rescued in part by a constitutively active allele of STAT5. Despite using doses lower than those tolerated in humans, NAC treatment significantly inhibited the progression of human DND‐41 cells engrafted in immunodeficient mice. Thus, targeting leukaemogenic IL7R homodimerization with NAC offers a potentially effective and feasible therapeutic strategy that warrants testing in patients with T‐ALL.