Acalabrutinib monotherapy in patients with Waldenström macroglobulinemia: a single-arm, multicentre, phase 2 study

BACKGROUND

Chemoimmunotherapy is typically the standard of care for patients with Waldenström macroglobulinemia; however, infectious and hematologic toxic effects are problematic. Acalabrutinib is a selective, potent Bruton tyrosine-kinase inhibitor. The aim of this trial was to evaluate the activity and safety of acalabrutinib in patients with Waldenström macroglobulinemia.

METHODS

This single-arm, multicentre, phase 2 trial was done in 19 European academic centres in France, Italy, Greece, the Netherlands, and the UK, and eight academic centres in the USA. Eligible patients were 18 years or older and had treatment naive (declined or not eligible for chemoimmunotherapy) or relapsed or refractory (at least one previous therapy) Waldenström macroglobulinemia that required treatment, an Eastern Cooperative Oncology Group performance status of 2 or less, and received no previous Bruton tyrosine-kinase inhibitor therapy. Patients received 100 mg oral acalabrutinib twice per day in 28-day cycles until disease progression or unacceptable toxicity. The primary endpoint was investigator-assessed overall response (at least a minor response) according to the 6th International Workshop for Waldenström Macroglobulinemia (IWWM) and the modified 3rd IWWM workshop criteria. The primary outcome and safety were assessed in all patients who received at least one dose of treatment. This study is registered with ClinicalTrials.gov, number NCT02180724, and is ongoing, but no longer enrolling.

FINDINGS

Between Sept 8, 2014, and Dec 24, 2015, 122 patients were assessed for eligibility, of which 106 (87%) patients were given acalabrutinib (14 were treatment naive and 92 had relapsed or refractory disease). With a median follow-up of 27·4 months (IQR 26·0-29·7), 13 (93% [95% CI 66-100]) of 14 treatment naive patients achieved an overall response and 86 (93% [86-98]) of 92 relapsed or refractory patients per both the modified 3rd and 6th IWWM criteria. Seven (50%) of 14 treatment naive patients and 23 (25%) of 92 relapsed or refractory patients discontinued treatment on study. Grade 3-4 adverse events occurring in more than 5% of patients were neutropenia (17 [16%] of 106 patients) and pneumonia (7 [7%]). Grade 3-4 atrial fibrillation occurred in one (1%) patient and grade 3-4 bleeding occurred in three (3%) patients. The most common serious adverse events were lower respiratory tract infection (n=7 [7%]), pneumonia (n=7 [7%]), pyrexia (n=4 [4%]), cellulitis (n=3 [3%]), fall (n=3 [3%]), and sepsis (n=3 [3%]). Pneumonia (n=5 [5%]) and lower respiratory tract infection (n=4 [4%]) were considered treatment related. One treatment-related death was reported (intracranial hematoma).

INTERPRETATION

This study provides evidence that acalabrutinib is active as single-agent therapy with a manageable safety profile in patients with treatment-naive, or relapse or refractory Waldenström macroglobulinemia. Further studies are needed to establish its efficacy against current standard treatments and to investigate whether outcomes can be improved with combination therapies.

FUNDING

Acerta Pharma.

Acalabrutinib (ACP-196): A Covalent Bruton Tyrosine Kinase Inhibitor with a Differentiated Selectivity and In Vivo Potency Profile

Several small-molecule Bruton tyrosine kinase (BTK) inhibitors are in development for B cell malignancies and autoimmune disorders, each characterized by distinct potency and selectivity patterns. Herein we describe the pharmacologic characterization of BTK inhibitor acalabrutinib [compound 1, ACP-196 (4-[8-amino-3-[(2S)-1-but-2-ynoylpyrrolidin-2-yl]imidazo[1,5-a]pyrazin-1-yl]-N-(2-pyridyl)benzamide)]. Acalabrutinib possesses a reactive butynamide group that binds covalently to Cys481 in BTK. Relative to the other BTK inhibitors described here, the reduced intrinsic reactivity of acalabrutinib helps to limit inhibition of off-target kinases having cysteine-mediated covalent binding potential. Acalabrutinib demonstrated higher biochemical and cellular selectivity than ibrutinib and spebrutinib (compounds 2 and 3, respectively). Importantly, off-target kinases, such as epidermal growth factor receptor (EGFR) and interleukin 2-inducible T cell kinase (ITK), were not inhibited. Determination of the inhibitory potential of anti-immunoglobulin M-induced CD69 expression in human peripheral blood mononuclear cells and whole blood demonstrated that acalabrutinib is a potent functional BTK inhibitor. In vivo evaluation in mice revealed that acalabrutinib is more potent than ibrutinib and spebrutinib. Preclinical and clinical studies showed that the level and duration of BTK occupancy correlates with in vivo efficacy. Evaluation of the pharmacokinetic properties of acalabrutinib in healthy adult volunteers demonstrated rapid absorption and fast elimination. In these healthy individuals, a single oral dose of 100 mg showed approximately 99% median target coverage at 3 and 12 hours and around 90% at 24 hours in peripheral B cells. In conclusion, acalabrutinib is a BTK inhibitor with key pharmacologic differentiators versus ibrutinib and spebrutinib and is currently being evaluated in clinical trials.

Stored red blood cell susceptibility to in vitro transfusion-associated stress conditions is higher after longer storage and increased by storage in saline-adenine-glucose-mannitol compared to AS-1

BACKGROUND

Biochemical changes induced in red blood cells (RBCs) during storage may impair their function upon transfusion. Transfusion-associated stresses may further amplify storage lesion effects including increased phosphatidylserine (PS) exposure at the RBC membrane, microparticle (MP) release, and adhesion to endothelial cells (ECs). RBC stress susceptibility in vitro was investigated in relation to storage time and additive solution.

STUDY DESIGN AND METHODS

Leukoreduced whole blood donations (n = 18) were paired, mixed, and resplit before separating the RBCs for storage in saline-adenine-glucose-mannitol (SAGM) or AS-1. Samples were taken after 3, 21, or 35 days. For oxidative stress treatment, RBCs were exposed to 0.5 mmol/L tert-butylhydroperoxide. Transfusion-associated stress was simulated by overnight culture at 37 °C with plasma containing inflammatory mediators. PS exposure and MPs were measured by flow cytometry and adhesion to ECs was tested under flow conditions. PS specificity of adhesion was tested by blocking with PS-containing lipid vesicles.

RESULTS

Oxidative stress induced significantly higher PS exposure and adhesion to ECs in RBCs stored for 35 days compared to 3 days (p < 0.04). PS-containing vesicles blocked RBC-EC adhesion. After overnight culture with or without plasma, PS exposure and EC adhesion were significantly increased (p < 0.05). MP numbers increased with longer RBC storage and after RBC culture with plasma. Culture conditions influenced MP numbers from Day 35 RBCs. RBCs stored in SAGM had significantly higher PS exposure after stress treatment than AS-1 RBCs (p < 0.02).

CONCLUSION

Storage for 35 days significantly increased RBC susceptibility to oxidative and in vitro transfusion-associated stresses and was higher for RBCs stored in SAGM compared to AS-1.

Ex-vivo analysis of human natural killer T cells demonstrates heterogeneity between tissues and within established CD4(+) and CD4(-) subsets

Our understanding of human type 1 natural killer T (NKT) cells has been heavily dependent on studies of cells from peripheral blood. These have identified two functionally distinct subsets defined by expression of CD4, although it is widely believed that this underestimates the true number of subsets. Two recent studies supporting this view have provided more detail about diversity of the human NKT cells, but relied on analysis of NKT cells from human blood that had been expanded in vitro prior to analysis. In this study we extend those findings by assessing the heterogeneity of CD4(+) and CD4(-) human NKT cell subsets from peripheral blood, cord blood, thymus and spleen without prior expansion ex vivo, and identifying for the first time cytokines expressed by human NKT cells from spleen and thymus. Our comparative analysis reveals highly heterogeneous expression of surface antigens by CD4(+) and CD4(-) NKT cell subsets and identifies several antigens whose differential expression correlates with the cytokine response. Collectively, our findings reveal that the common classification of NKT cells into CD4(+) and CD4(-) subsets fails to reflect the diversity of this lineage, and that more studies are needed to establish the functional significance of the antigen expression patterns and tissue residency of human NKT cells.

The effector T cell response to ryegrass pollen is counterregulated by simultaneous induction of regulatory T cells

Allergy is associated with pathological Th2 responses to otherwise harmless environmental Ags. In contrast, nonallergic individuals mount nonpathological immune responses to allergens, partly attributed to regulatory T cell (Treg) activity. Although thymus-derived natural Tregs have been shown to maintain tolerance to self-Ags and prevent autoimmunity, the generation of Tregs specific to non-self-Ags is less well understood. We investigated the potential for induction of Tregs from PBMCs of ryegrass pollen-allergic or healthy subjects by stimulation in vitro with ryegrass pollen extract in the absence of additional exogenous stimuli. We found that two subsets of proliferating CD4(+) T cells were induced, one expressing intermediate levels of Foxp3 (and IFN-gamma, IL-4, IL-17, or IL-2) and the other expressing high levels of Foxp3 (and no effector cytokines). After enrichment based on CD39 expression, the Foxp3(hi) subset suppressed CD4(+) T cell proliferation and IFN-gamma production. The Foxp3(hi) Treg originated from both conversion of dividing non-Tregs (CD4(+)CD25(-)CD127(hi)) and expansion of natural Tregs (CD4(+)CD25(+)CD127(lo)). Stable functional Tregs expressing high levels of Foxp3 were induced simultaneously with effector T cells by allergen stimulation. Induction of Foxp3(hi) Tregs was reduced in allergic subjects. These results indicate that the cogeneration of Foxp3(hi) Tregs in response to allergen may be a mechanism for controlling allergic reactions in healthy individuals, which is impaired in those with allergies.

Molecular cloning, expression and immunological characterisation of Pas n 1, the major allergen of Bahia grass Paspalum notatum pollen

Bahia grass, Paspalum notatum, is a clinically important subtropical grass with a prolonged pollination season from spring to autumn. We aimed to clone and characterise the major Bahia grass pollen allergen, Pas n 1. Grass pollen-allergic patients presenting to a tertiary hospital allergy clinic were tested for IgE reactivity with Bahia grass pollen extract by skin prick testing, ImmunoCAP, ELISA and immunoblotting. Using primers deduced from the N-terminal peptide sequence of a group 1 allergen of Bahia grass pollen extract separated by two-dimensional gel electrophoresis, the complete Pas n 1 cDNA was obtained by rapid amplification of cDNA ends and cloned. Biological relevance of recombinant Pas n 1 expressed in Escherichia coli was assessed by serum IgE reactivity and basophil activation. Twenty-nine of 34 (85%) consecutive patients presenting with grass pollen allergy were skin prick test positive to Bahia grass pollen. The Pas n 1 cDNA has sequence homology with the beta-expansin 1 glycoprotein family and is more closely related to the maize pollen group 1 allergen (85% identity) than to ryegrass Lol p 1 or Timothy grass Phl p 1 (64 and 66% identity, respectively). rPas n 1 reacted with serum IgE in 47 of 55 (85%) Bahia grass pollen-allergic patients, activated basophils and inhibited serum IgE reactivity with the 29 kDa band of Bahia grass pollen extract. In conclusion the cDNA for the major group 1 allergen of the subtropical Bahia grass pollen, Pas n 1, was identified and cloned. rPas n 1 is immunologically active and is a valuable reagent for diagnosis and specific immunotherapy of grass pollen allergy.

Clinical characteristics of soybean allergy in Europe: a double-blind, placebo-controlled food challenge study

BACKGROUND

Soybean is a relevant allergenic food, but little is known about individual threshold doses in soy allergy.

OBJECTIVE

We sought to determine the clinical characteristics of soy allergy in Europe, including a dose-response curve.

METHODS

Patients with a history of soy allergy underwent a titrated, double-blind, placebo-controlled food challenge. A statistical model was used to calculate the risk of allergic consumers to experience an allergic reaction to soy. Sera were analyzed for specific IgE to soy, peanut, Bet v 1, and Gly m 4.

RESULTS

All patients but one responded primarily with subjective symptoms to the challenge followed by objective symptoms in 11 subjects, ranging from rhinitis up to a decrease in blood pressure. Cumulative threshold doses for allergic reactions ranged from 10 mg to 50 g for subjective symptoms and from 454 mg to 50 g for objective symptoms. The pattern of IgE reactivity against proteins with molecular weights of between approximately 10 and 70 kd was highly individual among the patients and did not correlate with the severity of symptoms.

CONCLUSIONS

When data are fitted by using a normal distribution statistical model, they predict that 1% of patients with soy allergy would react subjectively and objectively with 0.21 and 37.2 mg of soy protein, respectively.

CLINICAL IMPLICATIONS

Both the clinical and immunologic basis of soy allergy in Europe are highly complex, which affects the diagnosis of soy allergy and the advice given to patients with soy allergy in regard to risk management.

A novel approach for investigation of specific and cross-reactive IgE epitopes on Bet v 1 and homologous food allergens in individual patients

BACKGROUND

A clinically relevant allergic reaction requires recognition of at least two different epitopes on the surface of the allergen by IgE. These epitopes may be specific or cross-reactive. Moreover, patterns of IgE reactivity may be patient-specific. The aim of our study was to compare specific and cross-reactive IgE epitopes and epitope patterns between individual patients. We used Bet v 1-related food allergy as a model.

METHODS

Five patients were investigated by cross-competitive ELISA for specific and cross-reacting IgE to Bet v 1, and its homologues Gly m 4 (soybean), Ara h 8 (peanut), and Pru av 1 (cherry). Allergen-specific as well as cross-reactive IgE epitopes were assessed by competitive immunoscreening of a phage-displayed random 7-mer peptide library using polyclonal purified IgE from individual sera. The resulting peptide mimics were mapped on the surface of the 3D-structure of the allergens using a computer-based algorithm.

RESULTS

Competitive immunoscreening and epitope mapping identified patient-specific IgE epitope patterns. However, one IgE-binding surface area that was recognized by all patients and two recognized by three patients were identified on all four proteins. These results are consistent with the determination of IgE cross-reactivity of the individual patients' sera against the four recombinant allergens by cross-competitive ELISA.

CONCLUSIONS

Selection of phage-displayed peptide mimics with serum IgE from allergic patients in combination with computer-based mapping of the peptide mimics onto the surface of the three-dimensional allergen structure is a promising novel tool to investigate IgE epitope specificity in individual patients. Such basic information on epitope structure may be used for prediction of cross-reactivity and potential allergenicity of novel foods.

Birch pollen-related food allergy to legumes: identification and characterization of the Bet v 1 homologue in mungbean (Vigna radiata), Vig r 1

BACKGROUND

Recently allergic reactions to legumes mediated by Bet v 1-homologous food allergens were described for soy and peanut. In this study we assessed allergic reactions to another legume, to mungbean seedlings, and identified its Bet v 1-homologous allergen Vig r 1.

METHODS

Ten patients were selected who had a history of allergic reactions to mungbean seedlings and a respiratory allergy to birch pollen. The Bet v 1 homologue in mungbean seedlings, Vig r 1, was cloned by a PCR strategy, expressed in Escherichia coli, and purified by preparative SDS-PAGE. In all sera, specific IgE against birch pollen, Bet v 1, Bet v 2, Vig r 1, and the Bet v 1 homologues in soy (Gly m 4) and cherry (Pru av 1) was determined by CAP-FEIA. Cross-reactivity of specific IgE with Vig r 1, Bet v 1, Gly m 4, and Pru av 1 was assessed by immunoblot inhibition. Expression of Vig r 1 during development of mungbean seedlings and under wounding stress was analysed by immunoblotting. The Vig r 1 double band was analysed by matrix-assisted laser desorption/ionization time-of-flight and liquid chromatography/tandem mass spectrometry (LC/MS/MS).

RESULTS

All patients were sensitized to birch pollen and Bet v 1, 20% to Bet v 2, and 90% to Gly m 4. Seventy percent of the patients showed IgE binding to a double band at 15 kDa in mungbean extract that was inhibited after pre-incubation of sera with rBet v 1. PCR cloning revealed that the mungbean homologue of Bet v 1 had a molecular weight of 16.2 kDa, a calculated pI of 4.6% and 42.8% amino acid sequence identity with Bet v 1. MS analysis confirmed similarity of the double band with the deduced Vig r 1 sequence, but also indicated the existence of other Vig r 1 isoforms. ImmunoCAP analysis detected IgE against Vig r 1 in 80% of the sera. IgE binding to Vig r 1 was inhibited with Gly m 4 in six of six and with rPru av 1 in four of six patients. Vig r 1 expression occurred during development of seedlings and was increased by wounding stress.

CONCLUSIONS

Food allergy to mungbean seedlings can be caused by primary sensitization to birch pollen and is mediated by Vig r 1 in the majority of the patients with birch pollen-related allergy to mungbean seedlings.

Immunoglobulin E-reactivity of wheat-allergic subjects (baker's asthma, food allergy, wheat-dependent, exercise-induced anaphylaxis) to wheat protein fractions with different solubility and digestibility

Baker's asthma, food allergy to wheat, and wheat-dependent, exercise-induced anaphylaxis (WDEIA) are different clinical forms of wheat allergy. We investigated the correlation of solubility and digestion stability of wheat allergens with the IgE-reactivity patterns of different patient groups. Three wheat protein fractions were extracted according to their solubility: salt-soluble albumins and globulins, ethanol-soluble gliadins, and glutenins soluble only after treatment with detergents and reducing reagents. Sera from subjects with history of each variant of wheat allergy were characterized by CAP FEIA and immunoblotting. There was a high degree of heterogeneity of recognized allergens between the different subject groups as well as within these groups. However, subjects with WDEIA showed similar immunoglobulin E (IgE)-reactivity patterns to gliadins and especially to a 65 kDa protein. Subjects with baker's asthma as well as the food-allergic subjects had the most intense IgE-reactivity to the albumin/globulin fraction. The latter group additionally showed IgE-reactivity to the other fractions. Divergent results of immunoblotting and CAP-FEIA demonstrated that the detection of wheat-specific IgE highly depends on the applied method, thus the diagnostic tool must be carefully chosen. Most wheat allergens were rapidly digested as analyzed by determination of IgE-reactivity on immunoblots to wheat extracts after simulation of gastric and duodenal digestion. However, ethanol-soluble gliadins were stable to gastric enzymes and exhibit low solubility in gastric and duodenal fluids. Therefore, they are likely to be important in food allergy to wheat.

Ara h 8, a Bet v 1–homologous allergen from peanut, is a major allergen in patients with combined birch pollen and peanut allergy

BACKGROUND

We recently described patients with soybean allergy mainly mediated by cross-reactivity to birch pollen allergens. A majority of those patients were reported to have peanut allergy.

OBJECTIVE

We sought to study the occurrence of peanut allergy in patients allergic to birch pollen and characterized the Bet v 1-homologous peanut allergen Ara h 8.

METHODS

Recombinant Ara h 8 was cloned with degenerated primers and expressed in Escherichia coli. Nine Swiss and 11 Dutch patients with peanut and birch pollen allergy and a positive double-blind, placebo-controlled food challenge result to peanut were investigated for IgE reactivity to birch pollen and purified peanut allergens and cross-reactivity between birch and peanut. Ara h 8 stability against digestion and roasting was assessed by means of RAST inhibition. The IgE cross-linking potency of Ara h 8 was tested on the basis of basophil histamine release.

RESULTS

During double-blind, placebo-controlled food challenge, all patients experienced symptoms in the oral cavity, progressing to more severe symptoms in 40% of patients. CAP-FEIA detected recombinant (r) Ara h 8-specific IgE in 85%. IgE binding to Ara h 8 was inhibited by Bet v 1 in peanut extract immunoblotting and in RAST inhibition. In EAST inhibition recombinant rAra h 8 inhibited IgE binding to peanut in 4 of 7 tested patient sera. Antipeanut response was dominated by Ara h 8 in 12 of 17 tested patients. Furthermore, our results demonstrate a low stability of Ara h 8 to roasting and no stability to gastric digestion. Basophil histamine release with rAra h 8 was more than 20% in 5 of 7 tested sera.

CONCLUSIONS

Peanut allergy might be mediated in a subgroup of our patients by means of cross-reaction of Bet v 1 with the homologous peanut allergen Ara h 8.

Soybean allergy in patients allergic to birch pollen: clinical investigation and molecular characterization of allergens

BACKGROUND

Allergic reactions to legumes are generally thought to be acquired by means of primary sensitization through the gastrointestinal tract. Recently, Gly m 4 (starvation-associated message 22), a Bet v 1-related pathogenesis-related protein 10 from soy, was suggested to be an allergen in patients with allergic reactions to a dietary product containing a soy protein isolate.

OBJECTIVE

We sought to evaluate the clinical relevance of Gly m 4 in subjects allergic to birch pollen with soy allergy and to assess the risk for subjects allergic to birch pollen to acquire soy allergy.

METHODS

Twenty-two patients allergic to birch pollen with soy allergy confirmed by means of positive double-blind, placebo-controlled food challenge results (n = 16) or a convincing history (n = 6) were investigated for IgE reactivity to birch pollen and soy allergens by using the Pharmacia CAP system and immunoblot analysis. Cross-reactivity was assessed by means of enzyme allergosorbent test inhibition. Ninety-four patients with birch pollen allergy were interviewed to assess soy tolerance and screened for IgE reactivity to Gly m 4 by means of immunoblotting. The Gly m 4 content in soy foods and soybean varieties was investigated by means of quantitative evaluation of immunoblots.

RESULTS

During double-blind, placebo-controlled food challenge, 10 patients experienced symptoms localized to the oral cavity, and 6 patients had a more severe reaction. CAP analysis revealed Gly m 4-specific IgE in 96% (21/22) of the patients. All patients had Bet v 1-specific IgE antibodies, and 23% (5/22) had positive Bet v 2 results. In IgE immunoblotting 25% (6/22) of the patients recognized soy profilin (Gly m 3), and 64% (14/22) recognized other soy proteins. IgE binding to soy was at least 80% inhibited by birch pollen and 60% inhibited by rGly m 4 in 9 of 11 sera tested. Seventy-one percent (67/94) of highly Bet v 1-sensitized patients with birch pollen allergy were sensitized to Gly m 4, and 9 (9.6%) of those patients reported soy allergy. The Gly m 4 content in soy products ranged between 0 and 70 ppm (milligrams per kilogram).

CONCLUSIONS

Our results confirm that soybean is another birch pollen-related allergenic food. Gly m 4 is the major soy allergen for patients allergic to birch pollen with soy allergy. The content of Gly m 4 in soy food products strongly depends on the degree of food processing.