bjh
`
`review
`
`Bruton tyrosine kinase inhibitors: a promising novel targeted
`treatment for B cell lymphomas
`
`Amin Aalipour and Ranjana H. Advani
`
`Stanford University Medical Center, Stanford, CA, USA
`
`Summary
`
`Constitutive or aberrant signalling of the B cell receptor sig-
`nalling cascade has been implicated in the propagation and
`maintenance of a variety of B cell malignancies. Small mole-
`cule inhibitors of Bruton tyrosine kinase (BTK), a protein
`early in this cascade and specifically expressed in B cells, have
`emerged as a new class of targeted agents. There are several
`BTK inhibitors, including ONO-WG-307, LFM-A13, dasati-
`nib, CC-292, and PCI-32765 (ibrutinib), in preclinical and/or
`clinical development of which ibrutinib is currently in phase
`III trials. Recent clinical data suggest significant activity of
`ibrutinib as a first in class oral inhibitor of BTK. This review
`provides an overview of ongoing clinical studies of BTK
`inhibitors.
`
`Keywords: Bruton tyrosine kinase, B cell receptor signalling,
`refractory non-Hodgkin lymphoma, ibrutinib, CC-292.
`
`B cell receptor signalling pathway
`
`The B cell receptor (BCR) signalling pathway plays a funda-
`mental role in determining B cell fate and function by regu-
`lating
`cellular
`selection, maturation, proliferation,
`and
`antibody production (Fig 1) (Dal Porto et al, 2004). The
`receptor consists of a surface transmembrane immunoglobu-
`lin (Ig) associated with the Iga (CD79A) and Igb (CD79B)
`chains (Wiestner, 2012). In normal B cells, antigenic binding
`to the BCR results in receptor aggregation and subsequent
`phosphorylation of the receptor’s cytoplasmic tyrosine-based
`activation motifs (ITAMs) by the recruited SRC-family kinas-
`es LYN and SYK (Wiestner, 2013). SYK propagates the signal
`through activation of phosphoinositide 3-kinase (PI3Kd),
`which in turn mediates the conversion of phosphatidylinosi-
`tol 4,5 bisphosphate (PIP2) to phosphatidylinositol 3,4,5
`triphosphate (PIP3) (Wiestner, 2013). The ensuing recruitment
`
`Correspondence: Ranjana H. Advani, Stanford University Medical
`
`Center, 875 Blake Wilbur Dr, Suite CC-2338, Stanford, CA 94305-
`
`5821, USA.
`
`E-mail: radvani@stanford.edu
`
`First published online 24 September 2013
`doi: 10.1111/bjh.12573
`
`b1 h BRITISH JOURNAL
`
`OF HAEMATOLOGY
`
`transmits and
`further
`of Bruton tyrosine kinase (BTK)
`amplifies the signal via phosphorylation of phospholipase
`C gamma 2 (PLCc2), mobilization of calcium secondary
`messengers, and eventual activation of MAP kinase pathways,
`nuclear factor of activated T cells (NFAT), and nuclear factor
`jB (NFjB). These signals regulate patterns of gene expres-
`sion necessary for B cell survival and proliferation (Brown,
`2012; Wiestner, 2013).
`While the BCR signalling cascade is generally antigen-
`dependent in normal B cells, antigen-independent signalling,
`also known as ‘tonic’ signalling, has been shown to exist (de
`Rooij et al, 2012). An overactive antigen-independent path-
`way is thought to be a contributing factor to B cell malignan-
`cies characterized by constitutively or aberrantly active BCR
`signalling (Monroe, 2006; Rinaldi et al, 2006; Chen et al,
`2008; Davids & Brown, 2012; D€uhren-von Minden et al,
`2012). Specifically, overactive signalling promotes the devel-
`opment of a supportive tumour microenvironment by modu-
`lating chemokine-controlled migration and integrin-mediated
`adhesion, while lack of such support leads to rapid apoptosis
`in B cells (de Rooij et al, 2012; Wiestner, 2012). Consistent
`with this, several
`inhibitors of protein kinases involved in
`BCR signalling have achieved notable clinical results: a LYN
`inhibitor (Bafetinib), a SYK inhibitor (Fostamatinib), and a
`PI3Kd inhibitor (Idelalisib) (Robak & Robak, 2013).
`
`Bruton tyrosine kinase as a unique target of
`inhibition
`
`Among the many kinases involved in BCR signalling, BTK, a
`tyrosine kinase member of the Tec kinase family, is a unique
`therapeutic target. Loss of gene function mutations of BTK
`in humans results in X-linked agammaglobulinaemia (XLA),
`characterized by a complete lack of B cells,
`low levels of
`serum Ig, and recurring infections. This suggests that BTK is
`required for B cell development and immunoglobulin pro-
`duction (Maas & Hendriks, 2001). As with other kinases in
`the BCR pathway, inhibition of BTK has been shown to inhi-
`bit NFjB DNA binding, reduce integrin-mediated cell adhe-
`sion and migration,
`limit cell production of chemokines,
`diminish cellular response to chemotactic factors, and ulti-
`mately induce apoptosis (Herman et al, 2011; Ponader et al,
`2012; de Rooij et al, 2012).
`
`ª 2013 John Wiley & Sons Ltd
`British Journal of Haematology, 2013, 163, 436–443
`
`

`

`The druggability of BTK is supported by the clinical
`phenotype of patients with XLA, where a lack of functioning
`BTK is both nonlethal and selective to only B cells as
`opposed to T cells (Herman et al, 2011). This selectivity for
`B lymphocytes is promising as inhibitors of BTK will hypo-
`thetically take less of a toll on a patient’s naturally occurring
`immune cells. These properties have made inhibition of BTK
`an attractive target in pharmacology with several drugs in
`the development pipeline. Published data are available for at
`
`Fig 1. The BCR signalling cascade. Antigen binding to the B cell
`receptor initiates kinase-mediated signal transduction resulting in
`activation of secondary messengers and, ultimately,
`transcription
`factors that regulate cell fate.
`
`Review
`
`least five BTK inhibitors that vary in specificity and mecha-
`nism of binding: ONO-WG-307, LFM-A13, dasatinib,
`CC-292, and ibrutinib (PCI-32765) (Table I).
`
`ONO-WG-307 (ONO Pharmaceutical Co., Osaka,
`Japan)
`
`ONO-WG-307 is an oral, potent (50% inhibitory concentra-
`tion [IC50] = 2 nmol/l), reversible inhibitor of BTK that acts
`by blocking auto-phosphorylation at
`the Tyr223 position
`(Yasuhiro et al, 2012). ONO-WG-307 displays high specificity
`for BTK given that its IC50 values for related tyrosine kinases
`(LCK, LYN, FYN) are above 1 lmol/l. The drug exhibits sig-
`nificant activity against the activated B cell-like (ABC) subtype
`of diffuse large B-cell lymphoma (DLBCL) in TMD-8 mouse
`xenograft models, with dose-dependent
`tumour volume
`growth inhibition of up to 84% over 24 d (Kozaki et al, 2011).
`ONO-WG-307 demonstrates in vitro anti-proliferative effects
`in follicular lymphoma (FL), mantle cell lymphoma (MCL),
`and chronic lymphocytic leukaemia (CLL) cell lines and its
`combination with the anti-CD20 antibody rituximab shows
`promise as an effective combination therapy (Kozaki et al,
`2011, 2012). To date, no clinical data are available; however,
`ONO-WG-307’s reversible mechanism may result in fewer
`off-target effects in comparison to irreversible inhibitors.
`
`LFM-A13 (University of Southern California)
`
`LFM-A13 is an intraperitoneally injectable reversible inhibi-
`= 7 5 lmol/l) that binds to the rectangular
`tor of BTK (IC50
`catalytic pocket defined by Leu460, Tyr476, Arg525, and
`Asp539 (Mahajan et al, 1999; Uckun et al, 2002). LFM-A13
`does not affect the enzymatic activity of tyrosine kinases
`
`Table I. Preclinical and phase I study data.
`
`Agent
`
`ONO-WG-307
`
`LFM-A13
`
`Dasatinib
`
`CC-292
`
`Ibrutinib
`
`Developer
`
`ONO Pharmaceutical
`
`University of Southern
`California
`
`Bristol-Myers Squibb
`
`Celgene Corporation
`
`Reversible, Tyr223
`= 2 nmol/l
`IC50
`N/A
`
`Reversible, Unknown
`= 7 5 lmol/l
`IC50
`N/A
`
`Mechanism, Target
`Potency
`Clinical Data From
`Phase I Trials in
`Relapsed/Refractory
`B Cell Malignancies
`
`Reversible, Unknown
`= 5 nmol/l
`IC50
`Multiple Histologies
`n = 19
`ORR 32%, CR 11%
`
`Irreversible, Cys481
`<0 5 nmol/l
`IC50
`Multiple Histologies
`n = 17
`SD: 94%, PR: 6%
`CLL
`n = 50
`ORR 34%, CR 0%
`
`Pharmacyclics
`and Janssen
`Pharmaceuticals
`Irreversible, Cys481
`= 0 5 nmol/l
`IC50
`Multiple Histologies
`n = 56
`(% ORR/CR)
`MCL: 78/33
`CLL/SLL: 69/13
`FL: 55/27
`DLBCL: 29/0
`WM: 75/0
`MZL: 25/0
`
`B-NHL, B cell non-Hodgkin lymphoma; CLL, chronic lymphocytic leukaemia; SLL, small lymphocytic lymphoma; DLBCL, diffuse large B cell
`lymphoma; FL, follicular lymphoma; MCL, mantle cell lymphoma; MZL, marginal zone lymphoma; WM, Waldenstr€om macroglobulinaemia;
`ORR, objective response rate; CR, complete response; PR, partial response; PFS, progression-free survival; R/R, relapsed/refractory; N/A: not avail-
`able.
`
`ª 2013 John Wiley & Sons Ltd
`British Journal of Haematology, 2013, 163, 436–443
`
`437
`
`

`

`Review
`
`JAK1, JAK3, HCK, epidermal growth factor receptor kinase,
`and insulin receptor kinase and was shown to increase sensi-
`tivity of B-lineage leukaemic cells to ceramide- and vincris-
`tine-induced apoptosis in vitro (Mahajan et al, 1999). In
`leukaemic mouse models, LFM-A13 was non-toxic when
`administered at dose levels ranging from 10 to 80 mg/kg and
`significantly prolonged survival when delivered in combina-
`tion with vincristine, methylprednisolone, and L-asparaginase
`(VPL) compared to only VPL therapy (Uckun et al, 2002).
`Preliminary data suggest that chemoresistance in relapsed B
`cell precursor acute lymphoblastic leukaemia can be over-
`come with LFM-A13 in combination with chemotherapy
`(Uckun et al, 2011). No clinical data are available to date.
`
`Dasatinib (Bristol-Myers Squibb, New York, NY, USA)
`
`Dasatinib is an orally available, reversible tyrosine kinase
`inhibitor
`currently
`approved for
`treatment of
`chronic
`myeloid leukaemia (CML) and Philadelphia chromosome-
`positive acute lymphoblastic leukaemia (ALL) (Steinberg,
`2007). At the time of approval, only BCR-ABL and SRC
`kinases had been considered as relevant targets, but dasatinib
`was later discovered to also be a potent inhibitor of BTK
`= 5 nmol/l) in vitro with selective activity over ITK
`(IC50
`(Hantschel et al, 2007). Mutation of the gatekeeper residue
`Thr474 to Ile in BTK confers complete resistance to dasatinib
`and is suggestive of
`its mode of
`interaction with BTK
`(Hantschel et al, 2007).
`Preliminary phase I/II data has been reported on 27
`patients with relapsed/refractory (R/R) non-Hodgkin lym-
`phoma (NHL) (William et al, 2010). Patients received dasati-
`nib at doses of 100, 150, or 200 mg once daily for 28-day
`cycles. The median age was 58 years (range: 34–87), and
`patients had received a median of 4 (range: 1–20) prior ther-
`apies. The maximum tolerable dose (MTD) was determined
`to be 150 mg. At a median follow up of 24 months, of the
`19 evaluable patients the objective response rate (ORR) was
`32%: 2 complete responses (CRs), 4 partial responses (PRs),
`and 8 with stable disease (SD) (Table I). Progression-free
`
`Table II. Clinical data from phase II studies with BTK inhibitors.
`
`survival (PFS) was 17% at 1 year and 13% at 2 years. Grade 3
`and 4 adverse events (AEs) included pleural effusion (22%),
`thrombocytopenia (19%), neutropenia (11%), anaemia (7%),
`diarrhoea (7%), leucopenia (4%), rash (4%), weakness/ortho-
`stasis (4%), prolonged QTc interval (4%), flash pulmonary
`oedema (4%), and skin graft failure (4%).
`Dasatinib has also been evaluated in a phase II study of
`R/R CLL (Amrein et al, 2011). 15 patients, median age
`59 years (range: 40–78) and median 3 prior therapies, were
`enrolled with a median time on study of 14 weeks. Seventy
`three percent had either del(11q) or del(17p). 3 patients
`achieved a PR for an ORR of 20% (Table II). Of the remain-
`ing 12 patients, 6 had nodal responses. Grade 3 and 4
`haematological toxicities were frequent including neutropenia
`(67%) and thrombocytopenia (40%). Two patients developed
`grade 3 pneumonia and four developed pleural effusions.
`33% of patients were removed from the study within
`4 months due to severe myelosuppression. 73% patients had
`treatment interrupted at some point in the study due to
`toxicity.
`
`CC-292 (Celgene Corporation, Summit, NJ, USA)
`
`CC-292, formerly known as AVL-292, is an orally available,
`
`potent (IC50 apparent = 0 5 nmol/l, half maximal effective con-
`centration [EC50] = 8 nmol/l),
`irreversible small molecule
`inhibitor of BTK that forms a covalent bond with Cys481
`(Evans et al, 2013). CC-292 displays high levels of specificity
`for BTK in comparison to other SRC family kinases. The
`inhibitory activity of CC-292 has been demonstrated in both
`immunoblot analysis, which revealed that CC-292 strongly
`inhibits auto-phosphorylation in human na€ıve primary B
`cells, and flow cytometry tracking of CD69 upregulation
`(a surrogate for B cell activation) which exhibited a dose-
`dependent reduction in CD69 expression with increasing
`concentrations of CC-292 in vitro. Covalent probe analysis of
`human B cells coupled with enzyme linked immunosorbent
`assay (ELISA) quantification methods demonstrated 42%
`BTK occupancy in a 1-h incubation with 10 nmol/l CC-292.
`
`Regimen
`
`Ibrutinib
`
`Ibrutinib + Ofatumumab
`Ibrutinib + Bendamustine-Rituximab
`Dasatinib
`
`Disease
`
`CLL, TN
`CLL, R/R
`MCL, R/R
`GCB DLBCL, R/R
`ABC DLBCL, R/R
`CLL, R/R
`CLL, R/R
`CLL, R/R
`
`n
`
`31
`85
`111
`20
`29
`27
`30
`15
`
`%ORR (CR)
`
`Outcome
`
`67 (2)
`71 (3)
`68 (21)
`5 3 (0)
`40 (8)
`100 (4)
`93 (13)
`20 (0)
`
`26-month PFS: 96%
`26-month PFS: 75%
`13 9 months
`Median OS: 3 35 months
`Median OS: 9 76 months
`89% remain on study
`8 1-month PFS: 90%
`N/A
`
`TN, treatment na€ıve; R/R, relapsed/refractory; CLL, chronic lymphocytic leukaemia; MCL, mantle cell lymphoma; DLBCL, Diffuse large B cell
`lymphoma; GCB, Germinal centre B cell, ABC, activated B cell; ORR, objective response rate; CR, complete response; PFS, progression-free
`survival; OS, overall survival; N/A, not available.
`
`438
`
`ª 2013 John Wiley & Sons Ltd
`British Journal of Haematology, 2013, 163, 436–443
`
`

`

`In mice models, % BTK occupancy was positively correlated
`with reduced signs of arthritic disease.
`CC-292 was evaluated in healthy adult subjects and was
`found to be safe and well tolerated following oral administra-
`tion at dose levels ranging from 0 5 mg/kg to 7 0 mg/kg.
`(Evans et al, 2011). PK data was reported for the 2 0 mg/kg
`single oral dose (Evans et al, 2013). CC-292 was rapidly
`absorbed (Tmax c. 30–120 min), achieving >84% BTK occu-
`pancy and mean peak plasma levels (Cmax = 542 ng/ml)
`this dose. The T1/2 = 1 9 h, and BTK occupancy was
`at
`sustained over a 24-h period.
`Preliminary phase Ib data with CC-292 was reported on
`12 patients with R/R B cell NHL (B-NHL) (8 CLL, 1 DLBCL,
`1 FL, 1 marginal zone lymphoma (MZL)) (Brown et al,
`2012a). Escalating cohorts of 125, 250, and 400 mg/d for 28-
`day cycles were evaluated. Full BTK occupancy was reached
`at 250 mg/d and the MTD was >400 mg/d. The median age
`of patients was 68 years (range: 45–79), median number of
`prior therapies 2 5 (range: 1–10), and reported median time
`on treatment was 65 d. While the duration of response
`(DOR) was not available at the time of the report, 10 of the
`12 patients were continuing on treatment. All 8 CLL patients
`had SD with a median 28% decrease from baseline lymph
`node measurement. The MZL patient also had SD. The
`DLBCL patient had progressive disease (PD) and the FL
`patient was not evaluable due to dose limiting toxicity
`(DLT). The drug was generally well tolerated with no grade
`4 AEs reported and only a single grade 3 AE of a low abso-
`lute neutrophil count, probably treatment-related.
`Updated results were recently presented on 86 patients (23
`B-NHL, 6 Waldenstr€om macroglobulinaemia (WM), 57 CLL/
`small lymphocytic lymphoma (SLL)) treated with CC-292 at
`doses of 125, 250, 400, 625, 750, and 1000 mg QD or 375
`and 500 mg BID (Table I) (Brown et al, 2013). An expan-
`sion cohort of CLL patients at 750 mg QD was also tested.
`All patients received continuous dosing in 28-day cycles until
`PD or intolerable toxicity. The median age was 65 years
`(range: 29–89) and median number of prior therapies 3
`(range: 1–12). Of the 57 CLL patients, 39 (68 4%) had at
`least 1 high risk factor, including 30 (52 6%) with unmutat-
`ed IGHV, and 26 (45 6%) with del11q22 (n = 12), del17p
`(n = 14), or both (n = 2). The median time on therapy was
`144 d (range: 13–515). Three DLTs were reported, including
`thrombocytopenia (400 mg), pneumonitis (1000 mg), and
`altered mental status (500 mg BID). The MTD has not been
`reached. The most frequent treatment emergent AEs (≥10%
`of patients regardless of causality) were grade 1–2.
`All 17 efficacy-evaluable B-NHL patients had SD except
`for a single PR in a patient with MZL who started at 250 mg
`and escalated sequentially up to 750 mg QD, achieving a PR
`at cycle 16. Of 50 efficacy-evaluable CLL patients, 17 (34%)
`achieved a PR and 24 (45%) showed lymph node reduction.
`Lymphocytosis, a class effect of these agents (discussed under
`the ibrutinib section) was noted in 10 patients and resolved
`in 5 patients. At the time of reporting, the median duration
`
`ª 2013 John Wiley & Sons Ltd
`British Journal of Haematology, 2013, 163, 436–443
`
`Review
`
`of treatment was 176 d (range: 16–473), and 2 CLL patients
`had been on treatment for over 15 cycles, both initiating
`treatment at 400 mg QD and experiencing nodal reductions
`of 32% and 27%.
`The ORR was 31% at 750 mg QD, 50% at 1000 mg QD
`and 66 7% at 375 mg BID, suggesting that BID dosing
`maybe more efficacious. Most patients at 500 mg BID were
`not eligible for response evaluation at the time of publica-
`tion. Among the responding patients, poor
`risk factors
`included unmutated IGHV (n = 8), del11q (n = 3), and/or
`del17p (n = 2) suggesting efficacy in these subgroups.
`Currently there is an ongoing phase Ib study of CC-292 in
`combination with lenalidomide in patients with R/R B cell
`lymphoma, but no data has been reported to date.
`
`Ibrutinib (PCI-32765) (Pharmacyclics, Inc., Sunnyvale,
`CA, USA and Janssen Pharmaceuticals, Inc., Titusville,
`NJ, USA)
`
`Ibrutinib is the most advanced of the BTK inhibitors in clini-
`cal development (Burger & Buggy, 2013). It is an orally avail-
`= 0 5 nmol/l),
`irreversible inhibitor of
`able, potent
`(IC50
`BTK that forms a covalent bond with Cys481 (Honigberg
`et al, 2010). In vitro, treatment of DOHH2 cells with ibruti-
`nib prevents phosphorylation of BTK’s immediate substrate
`PLCc2 and the further downstream kinase ERK, while not
`affecting upstream kinases like SYK. Specificity for BTK was
`confirmed by showing a lack of significant activity against a
`sample of 19 other related kinases, including seven kinases
`that share the cysteine residue targeted by ibrutinib. BTK
`occupancy can be measured with a fluorescently tagged affin-
`ity probe, PCI-33380, which consists of the core inhibitor
`molecule linked with a Bodipy FL fluorophore via a pipera-
`zine linker. Levels of irreversible probe binding to BTK can
`be detected by denaturing gel electrophoresis and fluorescent
`gel staining of BTK-transfected cell lysates treated with PCI-
`33380 such that increased target occupancy by drug results
`in lower probe signalling (Honigberg et al, 2010). Continu-
`ous exposure to ibrutinib inhibits upregulation of CD69
`while maintaining over 1000-fold selectivity for B cells over
`T cells (Honigberg et al, 2010).
`In vivo data confirmed the therapeutic potential of the
`drug (Honigberg et al, 2010). In mice models, reduction in
`signs of arthritic disease correlated with levels of inhibition
`of BTK by ibrutinib and was marked by reductions in pro-
`duction of anticollagen autoantibodies and total IgG levels.
`Similarly, in canine models with both na€ıve and previously
`treated
`naturally
`occurring B-NHL,
`objective
`clinical
`responses were achieved with full BTK occupancy at dosages
`of 2 5–20 mg/kg/d.
`In a phase Ia dose escalation trial, 56 patients with R/R
`B-NHL of variable histologies (16 FL, 16 CLL/SLL, 9 MCL,
`7 DLBCL, 4 MZL, and 4 WM) were enrolled to determine
`MTD, safety, PK/pharmacodynamics and tumour response
`(Advani et al, 2013). MTD was defined as a dose three levels
`
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`
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`

`Review
`
`above the dose level with full BTK occupancy, as measured
`by a fluorescent affinity probe. Two dosing schedules were
`evaluated: 35-day cycles with 28 d on and 7 d off and a once
`daily continuous dosing. The median age of patients was
`65 years (range: 41–82), median number of prior therapies
`was 3 (range: 1–10), and median treatment time was 5 cycles.
`Ibrutinib was tolerable at doses of 1 0–12 5 mg/kg/d with no
`DLTs. Pharmacodynamic studies using the competitive bind-
`ing assay with a fluorescent probe showed that 1 25 mg/kg/d
`of ibrutinib achieved sustained BTK engagement over 24 h
`and 2 5 mg/kg/d achieved near complete BTK engagement at
`4 and 24 h post-dosing. PK data suggested that at dose levels
`of 1 25 mg/kg/d,
`the Cmax = 82 ng/ml, Tmax median =
`= 4 92 h (Pollyea et al, 2009). Ibrutinib was
`1 14 h, and T1/2
`well tolerated with the majority of AEs being mainly grade 1
`or 2 with limited occurrences of grade 3 and 4 toxicities
`including neutropenia (12 5%),
`thrombocytopenia (7 2%),
`and anaemia (7 1%). Only two DLTs were reported, a grade
`3 allergic reaction in a patient with a history of similar
`reactions and a dose interruption for more than 7 d due
`to transient grade 2 neutropenia. Continuous dosing was just
`as effective as the interrupted dosing schedule in terms of
`PK/pharmacodynamics
`and a fixed dose of 560 mg/d
`was identified as the dose to move forward with in phase II
`trials.
`Efficacy data was reported on 50 evaluable patients with
`an ORR of 60% (CR 16%) (Advani et al, 2013). Responses
`were noted across histologies: MCL (7 of 9 patients, 3 CRs),
`CLL/SLL (11 of 16 patients, 2 CRs), FL (6 of 16 patients, 3
`CRs), DLBCL (2 of 7 patients), WM (3 of 4 patients), and
`MZL (1 of 4 patients) (Table I). The median PFS was
`13 6 months and 20 patients remained on treatment at the
`time of the report.
`Consistent with observations of other agents that affect
`BCR signalling inhibition in patients with CLL and MCL,
`along with nodal shrinkage there was a simultaneous dra-
`matic spike in plasma lymphocyte levels occurring in cycles 1
`and 2 of treatment with ibrutinib which slowly declined and
`stabilized over time (Herman et al, 2011; Brown, 2012). The
`apparent increase in lymphocyte counts was a result of the
`egress of CLL cells from the lymph nodes and recirculation
`in the blood (Brown, 2012). BCR signalling is implicated in
`integrin-mediated adhesion of cells to fibronectin and, there-
`fore, inhibition reduces cellular retention within the tumour
`microenvironment (Herman et al, 2011).
`An update of the 16 patients with FL treated in the phase
`I study has also been reported (Fowler et al, 2012). The med-
`ian age was 60 years (range: 41–71) with a median of 3 prior
`therapies (range: 1–5). The Follicular Lymphoma Interna-
`tional Prognostic Index (FLIPI) scores were high in 44% of
`patients and intermediate in 38%. Of the 11 patients that
`received treatment with a dose of 2 5 mg/kg or higher (the
`minimum dose necessary for full BTK occupancy), 3 patients
`achieved a CR and 3 a PR for an ORR of 54 5%. The DOR
`was 12 3 months with a median PFS of 13 4 months. The 9
`
`440
`
`patients treated at doses of at least 5 mg/kg had a median
`PFS of 19 6 months with 2 patients remaining on the study
`at 25 and 29 months.
`Collectively, these phase I results suggest that ibrutinib is
`well tolerated and has significant activity in a variety of his-
`tologies (Brown, 2013). These data have led to several phase
`II studies evaluating its efficacy in specific B cell histologies
`(Table II).
`
`Phase II studies with ibrutinib
`
`Relapsed/refractory chronic lymphocytic leukaemia and
`small lymphocytic lymphoma
`
`In a phase Ib/II study, 85 patients (median age 64 years) with
`R/R disease were enrolled in three cohorts, with 51 patients
`receiving 420 mg/d and 34 patients receiving 840 mg/d in
`28-day cycles (Byrd et al, 2013). Median number of prior
`treatments was 4 (range: 1–12). Of note, 52% of patients had
`bulky adenopathy (>5 cm), 33% had 17p deletion, and 81%
`unmutated IGHV. The ORR was 71% (4% CR) in the
`420 mg cohorts and 71% (0% CR) in the 820 mg cohort. A
`nodal PR (defined as a >50% reduction in total lymph node
`size) with lymphocytosis was seen in 20% and 15% of
`patients in the 420 mg and 840 mg cohorts respectively. The
`lymphocytosis resolved over time. 13% of patients had PD
`while taking ibrutinib. The estimated 26 months PFS was
`75%. The best response was very similar across the two doses
`and therefore 420 mg was selected as the dose for future eval-
`uation. Ibrutinib was well
`tolerated and the majority of
`reported AEs were grade 2. The most common grade ≥3 AEs
`were pneumonia (12%) and dehydration (6%). Grade ≥3
`haematological toxicities were limited: anaemia (6%), neutro-
`penia (15%), and thrombocytopenia (6%).
`
`Therapy na€ıve chronic lymphocytic leukaemia
`
`A phase Ib/II study evaluated treatment of na€ıve elderly CLL
`patients (≥65 years) (Byrd et al, 2012a). 31 patients were
`enrolled in two cohorts with 26 patients receiving 420 mg/d
`and 5 receiving 840 mg/d in 28 d cycles. The 840 mg cohort
`was eventually discontinued due to improved safety of the
`420 mg dose and comparable efficacy (Byrd et al, 2012b).
`The median age was 71 years (range: 65–84) and 55% of
`patients had unmutated IGHV. In the 420 mg cohort at a
`median 16 6 months follow-up, the ORR was 71% (10%
`CR), with an additional 10% of patients achieving PR with
`lymphocytosis. The 22-month estimated PFS was 96%. The
`majority of AEs were grade 2, easily managed, and included
`diarrhoea,
`fatigue, upper respiratory tract
`infection, rash,
`nausea and arthralgias. Grade ≥3 haematological AEs were
`infrequent.
`The very promising single agent activity and tolerability of
`ibrutinib in CLL have paved the way for trials in combina-
`tion with chemoimmunotherapy or obviating the need for
`
`ª 2013 John Wiley & Sons Ltd
`British Journal of Haematology, 2013, 163, 436–443
`
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`

`Review
`
`Table III. Ongoing phase III trials with ibrutinib.
`
`Disease
`
`Trial
`
`Eligibility
`
`Regimen
`
`MCL
`
`CLL
`
`SHINE NCT01776840
`RAY NCT01646021
`RESONATE
`NCT01578707
`RESONATE 2
`NCT01722487
`HELIOS NCT01611090
`US Intergroup Alliance A041202
`NCT01886872
`US Intergroup ECOG E1912
`(Protocol in development)
`UK NCRI CLL10 (Protocol in
`development)
`
`Untreated elderly
`R/R, ≥1 prior therapy
`R/R not eligible for
`purine analogues
`Untreated elderly
`
`R/R, ≥1 prior therapy
`Untreated elderly
`
`Untreated fit patients
`
`BR + Ibrutinib vs. BR + Placebo
`Ibrutinib vs. Temsirolimus
`Ibrutinib vs. Ofatumumab
`
`Ibrutinib vs. Chlorambucil
`
`BR + Ibrutinib vs. BR + placebo
`BR vs. Ibrutinib vs. Ibrutinib + Rituximab
`Ibrutinibbased Therapy vs. Fludarabine + Cyclophosphamide + Rituximab
`
`Untreated fit patients
`
`Ibrutinib + Rituximab vs. Fludarabine + Cyclophosphamide + Rituximab
`
`BR, bendamustine-rituximab; CLL, chronic lymphocytic leukaemia; MCL, mantle cell lymphoma; R/R, relapsed/refractory.
`
`chemoimmunotherapy, especially in elderly patients. Early
`results of ibrutinib and ofatumumab on 27 patients reported
`an ORR of 100% (4% CR) (Jaglowski et al, 2012). Ibrutinib
`in combination with bendamustine-rituximab (n = 30) had
`an ORR of 93% (13% CR) at a median follow up of
`8 1 months with an estimated PFS at 8 1 months of 90%
`(Brown et al, 2012b). Several phase III studies are ongoing
`including the RESONATE trial that evaluates ibrutinib versus
`ofatumumab in R/R patients ineligible for purine analogue-
`based therapy (Table III).
`
`Relapsed/refractory mantle cell lymphoma
`
`A phase II trial evaluated 111 patients with median age of
`68 years (range: 40–84) and a median of 3 prior therapies
`(range: 1–5) (Wang et al, 2013). 45% of patients had refrac-
`tory disease. 63 patients were bortezomib-na€ıve. Patients
`received 560 mg/d as a continuous dose in 28-day cycles.
`Similar to the experience with other trials of ibrutinib, most
`AEs were grade 1 or 2. Grade ≥3 AEs included neutropenia
`(16%), thrombocytopenia (11%), anaemia (10%) and pneu-
`monia (6%). At a median treatment time of 15 3 months, 63
`evaluable bortezomib-na€ıve patients achieved an ORR of
`68% (19% CR)
`and 48 evaluable bortezomib-exposed
`patients achieved a comparable ORR of 67% (23% CR). The
`median PFS across all patients was 13 9 months.
`
`Relapsed/refractory diffuse large B cell lymphoma
`
`Interim results of a phase II trial reported responses in ger-
`minal centre B cell-like (GCB) and ABC subtypes of DLBCL
`(Wilson et al, 2012). Unlike GCB-DLBCL, the ABC subtype
`is sustained by chronically active BCR signalling (Davis et al,
`2010). Gain-of-function mutations in the CD79B BCR sub-
`unit, as well as a constitutively active MYD88 (an adapter for
`Toll-like receptors) mutation are common in the ABC but
`not the GCB subtype, leading to the hypothesis that ibrutinib
`might be more active in ABC-subtype patients (Ngo et al,
`
`ª 2013 John Wiley & Sons Ltd
`British Journal of Haematology, 2013, 163, 436–443
`
`2011; Wilson et al, 2012). A total of 70 patients were
`enrolled with a median age of 63 years (range: 28–92) and a
`median of 3 prior therapies (range: 1–7). 54% had refractory
`disease and 23% a prior stem cell transplant. All patients
`received a fixed 560 mg/d dose of ibrutinib. The evaluable
`patients with the GCB subtype did not respond well to treat-
`ment with an ORR of only 5 3% and a median overall
`survival (OS) of 3 35 months. In contrast, the ORR in the
`ABC subtype patients was 40% (8% CR) with a median OS
`of 9 76 months. Responses were also correlated with specific
`molecular subtypes. Five of 7 patients with mutated CD79B
`responded as well as 10 of 29 patients without the mutation,
`suggesting alternative mechanisms of BCR signalling. Patients
`with CARD11 and MYD88 mutations without CD79B muta-
`tions did not respond to treatment suggesting that perhaps
`CD79B-driven activation of the BCR pathway is more domi-
`nant compared to the Toll-like receptor pathway. Future
`studies targeting the ABC subtype are planned including a
`frontline trial in combination with rituximab, cyclophospha-
`mide, doxorubicin, vincristine, and prednisone (R-CHOP)
`(Trial Number: NCT01855750).
`
`Conclusion
`
`The BCR signalling pathway plays a major role in the devel-
`opment of B cell malignancies. Several active agents that tar-
`get this pathway are being evaluated. The impressive clinical
`efficacy and tolerability of ibrutinib to date across multiple B
`cell lymphomas has paved the path for small molecule BTK
`inhibitors as novel agents in the management of B cell lym-
`phomas and CLL. Several other BTK inhibitors have variable
`activity, however, they are relatively early in development.
`Earlier this year,
`the US Food and Drug Administration
`granted ibrutinib a “breakthrough therapy designation” in
`MCL, WM, and CLL with 17p deletion. It is likely that this
`agent has the potential to replace traditional chemoimmuno-
`therapy treatments in elderly patients. Studies are also ongo-
`ing to evaluate the combination of ibrutinib with rituximab
`
`441
`
`

`

`Review
`
`and/or chemotherapy in multiple lymphoma subtypes. A bet-
`ter understanding of the mechanism of resistance to ibrutinib
`will allow for the development of rational combinations with
`other inhibitors of BCR signalling. The considerable progress
`in understanding the link between BCR signalling and B cell
`malignancies will probably result in further expansion of the
`current therapeutic options targeting this pathway. Future
`challenges include how to best combine or sequence the
`various inhibitors of the BCR signalling pathway with each
`other or with chemoimmunotherapy.
`
`Author contributions
`
`Amin Aalipour and Ranjana H. Advani wrote, reviewed, and
`edited the manuscript.
`
`Disclosures
`
`Amin Aalipour declares no conflict of interests. Ranjana H.
`Advani has received research funding from Pharmacyclics,
`Inc. and Janssen Pharmaceuticals, Inc.
`
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