Bruton tyrosine kinase represents a promising therapeutic target for treatment of chronic lymphocytic leukemia and is effectively targeted by PCI-32765. Blood. 2011;117:6287-6296. [PMID: 21422473 DOI: 10.1182/blood-2011-01-328484]

Effects of CD20 antibodies and kinase inhibitors on B-cell receptor signalling and survival of chronic lymphocytic leukaemia cells

Recently, clinical trial results have established inhibitors of B-cell receptor (BCR)-associated kinase (BAKi), with or without CD20 moniclonal antibodies (mAbs), as the preferred first-line treatment for most chronic lymphocytic leukaemia (CLL) patients. Using phosphospecific flow cytometry, we showed that in leukaemic cells from CLL patients the CD20 therapeutic antibodies - rituximab, ofatumumab, and obinutuzumab - inhibited BCR signalling pathways targeting preferentially pBTK^Y551 - but not BTK^Y223 - and pAKT. On the contrary, ibrutinib and idelalisib reduced pBTK^Y223 to a higher extent than pBTK^Y551 . The strong reduction of pAKT induced by idelalisib was enhanced by its combination with rituximab or ofatumumab. Moreover, CD20 mAbs and BAKi induced the death of leukaemia cells that was significantly potentiated by their combination. Analysis of the enhancement of cell death in these combinations revealed an approximately additive enhancement induced by rituximab or obinutuzumab combined with ibrutinib or idelalisib. Taken together, our data identified negative regulatory effects of CD20 mAbs and their combinations with BAKi on BCR signalling and cell survival in CLL. In conclusion, this study advances our understanding of mechanisms of action of CD20 mAbs as single agents or in combination with BAKi and could inform on the potential of combined therapies in ongoing and future clinical trials in patients with CLL.

Regulation of p53 by the 14-3-3 protein interaction network: new opportunities for drug discovery in cancer

Most cancers evolve to disable the p53 pathway, a key tumour suppressor mechanism that prevents transformation and malignant cell growth. However, only ~50% exhibit inactivating mutations of p53, while in the rest its activity is suppressed by changes in the proteins that modulate the pathway. Therefore, restoring p53 activity in cells in which it is still wild type is a highly attractive therapeutic strategy that could be effective in many different cancer types. To this end, drugs can be used to stabilise p53 levels by modulating its regulatory pathways. However, despite the emergence of promising strategies, drug development has stalled in clinical trials. The need for alternative approaches has shifted the spotlight to the 14-3-3 family of proteins, which strongly influence p53 stability and transcriptional activity through direct and indirect interactions. Here, we present the first detailed review of how 14-3-3 proteins regulate p53, with special emphasis on the mechanisms involved in their binding to different members of the pathway. This information will be important to design new compounds that can reactivate p53 in cancer cells by influencing protein-protein interactions. The intricate relationship between the 14-3-3 isoforms and the p53 pathway suggests that many potential drug targets for p53 reactivation could be identified and exploited to design novel antineoplastic therapies with a wide range of applications.

Acalabrutinib monotherapy in patients with relapsed/refractory chronic lymphocytic leukemia: updated phase 2 results

Therapeutic targeting of Bruton tyrosine kinase (BTK) has dramatically improved survival outcomes for patients with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). Acalabrutinib is an oral, highly selective BTK inhibitor that allows for twice-daily dosing due to its selectivity. In this phase 1b/2 study, 134 patients with relapsed/refractory CLL or SLL (median age, 66 years [range, 42-85 years]; median prior therapies, 2 [range, 1-13]) received acalabrutinib 100 mg twice daily for a median of 41 months (range, 0.2-58 months). Median trough BTK occupancy at steady state was 97%. Most adverse events (AEs) were mild or moderate, and were most commonly diarrhea (52%) and headache (51%). Grade ≥3 AEs (occurring in ≥5% of patients) were neutropenia (14%), pneumonia (11%), hypertension (7%), anemia (7%), and diarrhea (5%). Atrial fibrillation and major bleeding AEs (all grades) occurred in 7% and 5% of patients, respectively. Most patients (56%) remain on treatment; the primary reasons for discontinuation were progressive disease (21%) and AEs (11%). The overall response rate, including partial response with lymphocytosis, with acalabrutinib was 94%; responses were similar regardless of genomic features (presence of del(11)(q22.3), del(17)(p13.1), complex karyotype, or immunoglobulin variable region heavy chain mutation status). Median duration of response and progression-free survival (PFS) have not been reached; the estimated 45-month PFS was 62% (95% confidence interval, 51% to 71%). BTK mutation was detected in 6 of 9 patients (67%) at relapse. This updated and expanded study confirms the efficacy, durability of response, and long-term safety of acalabrutinib, justifying its further investigation in previously untreated and treated patients with CLL/SLL. This trial was registered at www.clinicaltrials.gov as #NCT02029443.

Combination strategies to overcome resistance to the BCL2 inhibitor venetoclax in hematologic malignancies

Venetoclax has been approved by the United States Food and Drug Administration since 2016 as a monotherapy for treating patients with relapsed/refractory chronic lymphocytic leukemia having 17p deletion. It has led to a breakthrough in the treatment of hematologic malignancies in recent years. However, unfortunately, resistance to venetoclax is inevitable. Multiple studies confirmed that the upregulation of the anti-apoptotic proteins of the B-cell lymphoma 2 (BCL2) family mediated by various mechanisms, such as tumor microenvironment, and the activation of intracellular signaling pathways were the major factors leading to resistance to venetoclax. Therefore, only targeting BCL2 often fails to achieve the expected therapeutic effect. Based on the mechanism of resistance in specific hematologic malignancies, the combination of specific drugs with venetoclax was a clinically optional treatment strategy for overcoming resistance to venetoclax. This study aimed to summarize the possible resistance mechanisms of various hematologic tumors to venetoclax and the corresponding clinical strategies to overcome resistance to venetoclax in hematologic malignancies.

Proliferative Signals in Chronic Lymphocytic Leukemia; What Are We Missing?

Chronic lymphocytic leukemia (CLL) cells cycle between lymphoid tissue sites where they actively proliferate, and the peripheral blood (PB) where they become quiescent. Strong evidence exists for a crucial role of B cell receptor (BCR) triggering, either by (self-)antigen or by receptor auto-engagement in the lymph node (LN) to drive CLL proliferation and provide adhesion. The clinical success of Bruton's tyrosine kinase (BTK) inhibitors is widely accepted to be based on blockade of the BCR signal. Additional signals in the LN that support CLL survival derive from surrounding cells, such as CD40L-presenting T helper cells, myeloid and stromal cells. It is not quite clear if and to what extent these non-BCR signals contribute to proliferation in situ. In vitro BCR triggering, in contrast, leads to low-level activation and does not result in cell division. Various combinations of non-BCR signals delivered via co-stimulatory receptors, Toll-like receptors (TLRs), and/or soluble cytokines are applied, leading to comparatively modest and short-lived CLL proliferation in vitro. Thus, an unresolved gap exists between the condition in the patient as we now understand it and applicable knowledge that can be harnessed in the laboratory for future therapeutic applications. Even in this era of targeted drugs, CLL remains largely incurable with frequent relapses and emergence of resistance. Therefore, we require better insight into all aspects of CLL growth and potential rewiring of signaling pathways. We aim here to provide an overview of in vivo versus in vitro signals involved in CLL proliferation, point out areas of missing knowledge and suggest future directions for research.

ALK-positive histiocytosis associated with chronic lymphocytic leukaemia/small lymphocytic lymphoma: a multitarget response under ibrutinib

ALK-positive histiocytosis is a recently described entity with few reported cases in literature. Herein, we report an unusual case of ALK-positive histiocytosis showing an Erdheim-Chester disease (ECD)-like presentation, occurring in a 37-year-old woman with a 2-year history of chronic lymphocytic leukaemia (CLL). Our CLL patient relapsed 6 months after the end of fludarabine, cyclophosphamide and rituximab frontline therapy and complained of lower limb pains. A bone marrow biopsy was performed and showed concomitant CLL/small lymphocytic lymphoma and ALK-positive histiocytosis with an identical immunoglobulin heavy-chain gene rearrangement in both neoplasms, suggesting clonal relationship. After 4 years under ibrutinib therapy, our patient remains free of both diseases. This report extends the spectrum of composite hematolymphoid neoplasms and shows that ALK rearrangement should be considered in all histiocytosis subtypes. Moreover, both tumours eradication under ibrutinib suggests that BTK inhibitors may also be effective in histiocytic neoplasms.

Neutralization of B-Cell Activating Factor (BAFF) by Belimumab Reinforces Small Molecule Inhibitor Treatment in Chronic Lymphocytic Leukemia

Simple Summary

Chronic lymphocytic leukemia (CLL) is the most common form of leukemia in Western countries. Despite the substantial progress achieved by the recent introduction of the novel small molecule inhibitors idelalisib, ibrutinib and venetoclax in CLL treatment, therapy resistance occurs frequently and the disease so far remains incurable. In the present study we report that BAFF, a member of the TNF protein family, protects CLL cells from treatment-induced cell death. In turn, the therapeutic effects of idelalisib, ibrutinib and venetoclax can be reinforced by neutralizing BAFF with belimumab, an antibody which presently is clinically approved for treatment of systemic lupus erythematosus. Based on the data presented in this study, a clinical study to evaluate whether drug repurposing of belimumab for BAFF neutralization can serve to improve response to small molecule inhibitor treatment in CLL is in preparation.

Abstract

The introduction of idelalisib, ibrutinib and venetoclax for treatment of chronic lymphocytic leukemia (CLL) has greatly improved long term survival of patients. However, many patients do not achieve complete remission and suffer from development of resistance upon treatment with these small molecule inhibitors. Here we report that the TNF family member B-cell activating factor (BAFF) mediates resistance of CLL cells to idelalisib, ibrutinib and venetoclax by sustaining survival and preventing apoptosis of the malignant B cells as revealed by analysis of cellular ATP levels and mitochondrial membrane integrity as well as caspase activation, respectively. As BAFF also plays a prominent role in autoimmune diseases, the BAFF-neutralizing antibody belimumab was developed and approved for treatment of systemic lupus erythematosus (SLE). When we employed belimumab in the context of CLL treatment with idelalisib, ibrutinib and venetoclax, BAFF neutralization was found to significantly increase the sensitivity of the leukemic cells to all three small molecule inhibitors. Notably, BAFF neutralization proved to be beneficial independently of clinical stage according to Binet and Rai or IgVH mutational status. Our results identify drug repurposing of belimumab for neutralization of BAFF to complement small molecule inhibitor treatment as a promising therapeutic approach in CLL that is presently undergoing clinical evaluation.

The Emerging Therapeutic Potential of Nitro Fatty Acids and Other Michael Acceptor-Containing Drugs for the Treatment of Inflammation and Cancer

Nitro fatty acids (NFAs) are endogenously generated lipid mediators deriving from reactions of unsaturated electrophilic fatty acids with reactive nitrogen species. Furthermore, Mediterranean diets can be a source of NFA. These highly electrophilic fatty acids can undergo Michael addition reaction with cysteine residues, leading to post-translational modifications (PTM) of selected regulatory proteins. Such modifications are capable of changing target protein function during cell signaling or in biosynthetic pathways. NFA target proteins include the peroxisome proliferator-activated receptor γ (PPAR-γ), the pro-inflammatory and tumorigenic nuclear factor-κB (NF-κB) signaling pathway, the pro-inflammatory 5-lipoxygenases (5-LO) biosynthesis pathway as well as soluble epoxide hydrolase (sEH), which is essentially involved in the regulation of vascular tone. In several animal models of inflammation and cancer, the therapeutic efficacy of well-tolerated NFA has been demonstrated. This has already led to clinical phase II studies investigating possible therapeutic effects of NFA in subjects with pulmonary arterial hypertension. Albeit Michael acceptors feature a broad spectrum of bioactivity, they have for a rather long time been avoided as drug candidates owing to their presumed unselective reactivity and toxicity. However, targeted covalent modification of regulatory proteins by Michael acceptors became recognized as a promising approach to drug discovery with the recent FDA approvals of the cancer therapeutics, afatanib (2013), ibrutinib (2013), and osimertinib (2015). Furthermore, the Michael acceptor, neratinib, a dual inhibitor of the human epidermal growth factor receptor 2 and epidermal growth factor receptor, was recently approved by the FDA (2017) and by the EMA (2018) for the treatment of breast cancer. Finally, a number of further Michael acceptor drug candidates are currently under clinical investigation for pharmacotherapy of inflammation and cancer. In this review, we focus on the pharmacology of NFA and other Michael acceptor drugs, summarizing their potential as an emerging class of future antiphlogistics and adjuvant in tumor therapeutics.

Innovative Therapeutic Approaches in Primary Cutaneous B Cell Lymphoma

Background: Primary cutaneous B-cell lymphomas (pCBCL) include an infrequent group of non-Hodgkin lymphomas that are limited to skin sites at the time of diagnosis. They comprise roughly 20–25% of all cutaneous lymphomas and are subdivided into primary cutaneous marginal zone lymphoma (PCMZL), primary cutaneous follicle center lymphoma (PCFCL), and primary cutaneous diffuse large cell B cell lymphoma, leg type (PCDLCBCL, LT). The first two show a rather indolent course while PCDLCBCL, LT carries a worse prognosis. Intravascular large cell B-cell lymphoma is the most infrequent subtype, and its therapy is not covered in this review.

Topical Therapy: For solitary, single-site PCMZL and PCFCL, several topical treatment options exist. They include, but are not limited to, excision, radiotherapy, and intralesional therapies, discussed in this review. However, in selected cases, even “watchful waiting” is reasonable.

Systemic Therapy: Indolent types of pCBCL rarely require systemic treatment. However, in extended cases and more importantly DLCBCL, LT, systemic treatment is the first choice. Monoclonal anti-CD20-antibody rituximab is often used as monotherapy in PCMZL and PCFCL or combined with chemotherapy in PCDLBCL, LT. Newer options are monoclonal anti-CD40 antibody dacetuzumab, anti-PD-1 and anti-PD-L1 checkpoint inhibitors, and Bruton tyrosine kinase inhibitors.

Conclusion: Indolent pCBCL are treated with a risk-adapted strategy using intralesional steroids, RT, and interferon-α as first-line treatments. Relapsing cases may profit from rituximab. In aggressive PCDLCBCL, LT, rituximab with polychemotherapy is recommended. Innovative therapies include intralesional oncolytic virotherapy, systemic monoclonal antibodies, and small molecules.

BTK Inhibition Impairs the Innate Response Against Fungal Infection in Patients With Chronic Lymphocytic Leukemia

Infections represent a cause of morbidity and mortality in patients affected by chronic lymphocytic leukemia (CLL). Introduction of new drugs in CLL clinical practice has showed impressive efficacy, in particular those targeting BTK. Among the consistent clinical data, an increasing number of reports describing the occurrence of unexpected opportunistic fungal infections has been reported during treatment with ibrutinib in the first 6 months of treatment. The reason underlying manifestations of invasive fungal infections in patients treated with ibrutinib is still under investigation. Our study aimed to understand the impact of BTK inhibition on immune response to fungal infection mediated by macrophages and CD14+ monocytic population obtained from CLL patients. Exposure to ibrutinib and acalabrutinib reduced signaling pathways activated by Aspergillus fumigatus determining an exacerbation of an immunosuppressive signature, a reduction of phagocytosis and a significant deficit in the secretion of inflammatory cytokines either in macrophages and monocytes isolated from CLL patients and healthy donors. These effects lead to a failure in completely counteracting conidia germination. In addition we investigated the biological effects of ibrutinib on monocyte counterpart in patients who were undergoing therapy. A significant impairment in cytokine secretion and a deficit of phagocytosis in circulating monocytes were detected after 3 months of treatment. Thus, our results uncover modifications in the innate response in CLL patients induced by ibrutinib that may impair the immunological response to fungal infection.

KEYPOINTS

•BTK inhibition affects a productive immune response of CLL-associated macrophages (NLC) during Aspergillus fumigatus infection.•Reduction of TNF-α secretion and phagocytosis are detected in monocytes isolated from CLL patients during ibrutinib therapy.

Importance of Crosstalk Between Chronic Lymphocytic Leukemia Cells and the Stromal Microenvironment: Direct Contact, Soluble Factors, and Extracellular Vesicles

Chronic lymphocytic leukemia (CLL) is caused by the accumulation of malignant B cells due to a defect in apoptosis and the presence of small population of proliferating cells principally in the lymph nodes. The abnormal survival of CLL B cells is explained by a plethora of supportive stimuli produced by the surrounding cells of the microenvironment, including follicular dendritic cells (FDCs), and mesenchymal stromal cells (MSCs). This crosstalk between malignant cells and normal cells can take place directly by cell-to-cell contact (assisted by adhesion molecules such as VLA-4 or CD100), indirectly by soluble factors (chemokines such as CXCL12, CXCL13, or CCL2) interacting with their receptors or by the exchange of material (protein, microRNAs or long non-coding RNAs) via extracellular vesicles. These different communication methods lead to different activation pathways (including BCR and NFκB pathways), gene expression modifications (chemokines, antiapoptotic protein increase, prognostic biomarkers), chemotaxis, homing in lymphoid tissues and survival of leukemic cells. In addition, these interactions are bidirectional, and CLL cells can manipulate the normal surrounding stromal cells in different ways to establish a supportive microenvironment. Here, we review this complex crosstalk between CLL cells and stromal cells, focusing on the different types of interactions, activated pathways, treatment strategies to disrupt this bidirectional communication, and the prognostic impact of these induced modifications.

Resistance Mechanisms to Targeted Agents in Chronic Lymphocytic Leukemia

Agents that specifically target pathologic mechanisms of survival have now been approved for the treatment of chronic lymphocytic leukemia in both the treatment-naive and relapsed/refractory settings. These 4 agents include the Bruton tyrosine kinase inhibitor ibrutinib, the B-cell leukemia/lymphoma-2 inhibitor venetoclax, and the phosphatidylinositol-3 kinase inhibitors idelalisib and duvelisib. Although clinical outcomes are improved with all of these inhibitors, acquired resistance does occur and leads to progression of disease. Resistance to targeted therapy can occur through direct mutations of the target or through the overexpression of alternative cell survival pathways not affected by the specific inhibitor. Determining which patients will develop resistance, why resistance occurs, how to overcome resistance, and when to test for resistance are all subjects of ongoing research. In this review, we describe the current data relative to the development of resistance to targeted therapies in CLL.

Cutaneous adverse-events in patients treated with Ibrutinib

Ibrutinib is a Burton tyrosine kinase inhibitor (BTKi) approved for the treatment of several hematologic malignancies. Analyze skin adverse events (SAE). All the patients treated with Ibrutinib featuring cutaneous adverse events were selected. Twenty five patients were retrieved with a median interval between Ibrutinib start and SAE time of onset of 120 days. Most common SAE observed involved hairs and nails. Eczematous reaction and leucocytoclastic vasculitis were also detected. One patient had a long-history Ibrutinib treatment and experienced numerous cutaneous adverse events. Infective disease such as superficial mycosis and impetigo were rarely present in our series. Despite the development of cutaneous SAE, all the patients continued their concomitant drugs without the onset of any further SAE. Our data suggest Ibrutinib-associated rash should be distinguished in early and late events and a careful dermatologic management of patients should be scheduled.

Recent advances in chronic lymphocytic leukemia therapy

Chronic lymphocytic leukemia is a genetically heterogeneous disease, and a complex set of genetic alterations is associated with its pathogenesis. CLL is the most common leukemia in the western countries, whereas it is rare in Asia, including Korea. The prognostic models integrate the traditional staging systems developed by Rai et al. and Binet et al. with biochemical and genetic markers. With the advent of molecular biology, a variety of targeted agents, including anti-CD20 antibodies, inhibitors of BCR signaling pathway, and BCL-2 inhibitors, have been introduced, which has changed the landscape of CLL treatment greatly. This review will focus on the risk stratification and the management of CLL in the era of novel small molecules.

F10, a new camptothecin derivative, was identified as a new orally-bioavailable, potent antitumor agent

Topoisomerases are interesting targets for drug discovery. In the present study, we attached saturated carbon atoms to the 10-position of camptothecin and synthesized 10 new camptothecin derivatives from 10-HCPT or SN-38. The activities of new compounds were evaluated both in vitro and in vivo. The most promising compound F10, 7-ethyl-10-(2-oxo-2-(piperidin-1-yl)ethoxy)camptothecin, inhibited cancer cells growth with the IC₅₀ of 0.002, 0.003, 0.011 and 0.081 μM on Raji, HCT116, A549 and Lovo cells, respectively. Meanwhile, oral administration of F10 remarkably suppressed the HCT116-xenograft tumor growth in the nude-mice model at the dosage of 0.5, 2.0 and 8.0 mg/kg in vivo. Intraperitoneal administration of F10 can completely inhibit Raji-xenograft tumor growth in established NPG mouse model at 2.0 and 4.0 mg/kg. In addition, the minimum lethal doses of F10 and SN-38 in mice by intravenous administration were 80 and 40 mg/kg (or 0.155, 0.102 mmol/kg), respectively. The solubility of F10 reached 9.86 μg/mL in a buffer solution of pH 4.5. The oral bioavailability of F10 achieved 22.4% in mice. The molecular docking model revealed that F10 can interact with topoisomerase I-DNA complex. Our findings indicate that F10 is a new orally-oavailable antitumor agent with potent anticancer effect. Furthermore, attaching a ring hydrophobic moiety to the 10-position of camptothecin provides a favorable approach in the optimization of camptothecin.

Targeting BTK in CLL: Beyond Ibrutinib

PURPOSE OF REVIEW

While the Bruton's tyrosine kinase inhibitor (BTKi) ibrutinib has revolutionized the treatment of chronic lymphocytic leukemia (CLL), current limitations include off-target toxicities and the development of resistance. In this review, we summarize the emerging data for alternative BTKi.

RECENT FINDINGS

Second-generation BTKi include acalabrutinib, zanubrutinib, and tirabrutinib which offer greater BTK selectivity. While these agents may limit off-target toxicity, they do not overcome common mechanisms of ibrutinib resistance. Reversible BTKi including vecabrutinib and LOXO-305 inhibit BTK in the presence of C481S mutation, and non-selective reversible BTKi, including ARQ-531, may retain activity despite mutations within PLCG2. Early-phase studies are underway to establish the clinical efficacy and toxicity of these agents. A randomized trial of ibrutinib versus acalabrutinib is ongoing, and acalabrutinib may be an option for ibrutinib-intolerant patients. Results from ongoing trials of alternate BTKi will help to define their role in CLL therapy as single agents or in combination therapy.

Progress toward a Glycoprotein VI Modulator for the Treatment of Thrombosis

Pathogenic thrombus formation accounts for the etiology of many serious conditions including myocardial infarction, stroke, deep vein thrombosis, and pulmonary embolism. Despite the development of numerous anticoagulants and antiplatelet agents, the mortality rate associated with these diseases remains high. In recent years, however, significant epidemiological evidence and clinical models have emerged to suggest that modulation of the glycoprotein VI (GPVI) platelet receptor could be harnessed as a novel antiplatelet strategy. As such, many peptidic agents have been described in the past decade, while more recent efforts have focused on the development of small molecule modulators. Herein the rationale for targeting GPVI is summarized and the published GPVI modulators are reviewed, with particular focus on small molecules. A qualitative pharmacophore hypothesis for small molecule ligands at GPVI is also presented.

Development of PROTACs to address clinical limitations associated with BTK-targeted kinase inhibitors

Chronic lymphocytic leukemia is a common form of leukemia and is dependent on growth-promoting signaling via the B-cell receptor. The Bruton tyrosine kinase (BTK) is an important mediator of B-cell receptor signaling and the irreversible BTK inhibitor ibrutinib can trigger dramatic clinical responses in treated patients. However, emergence of resistance and toxicity are major limitations which lead to treatment discontinuation. There remains, therefore, a clear need for new therapeutic options. In this review, we discuss recent progress in the development of BTK-targeted proteolysis targeting chimeras (PROTACs) describing how such agents may provide advantages over ibrutinib and highlighting features of PROTACs that are important for the development of effective BTK degrading agents. Overall, PROTACs appear to be an exciting new approach to target BTK. However, development is at a very early stage and considerable progress is required to refine these agents and optimize their drug-like properties before progression to clinical testing.

In Human Visualization of Ibrutinib-Induced CLL Compartment Shift

Bruton tyrosine kinase inhibitor ibrutinib is effective in treating chronic lymphocytic leukemia (CLL). However, after ibrutinib treatment initiation, patients frequently experience an increase of CLL blood cell count. This phenomenon in clinical practice is thought to reflect a "compartment shift" of CLL cells from lymph nodes to the peripheral blood, but the actual shifting has not yet been demonstrated. Using [⁶⁸Ga]Pentixafor-PET/MRI for in vivo CXCR4 visualization, we here provide images of topical changes of CLL cells upon ibrutinib treatment. Within the first month of ibrutinib treatment, mean standardized [⁶⁸Ga]Pentixafor uptake decreased in the bone marrow and lymph nodes, whereas [⁶⁸Ga]Pentixafor uptake increased in the spleen. Leukocytosis rose, as did numbers of CXCR4^high (tissue-resident) CLL cells. Volumes of lymph nodes and spleen decreased. Upon longer ibrutinib treatment, leukocytosis decreased, followed by a decrease of [⁶⁸Ga]Pentixafor uptake in the spleen. These results support the preexisting clinical hypothesis of a "compartment shift" of CLL cells from the lymph nodes to the peripheral blood, but also refine the mechanistic model by describing early clearing of the bone marrow and redistribution of CLL cells to the orthotopic splenic cavernous system in response to ibrutinib treatment.

LC-FACSeq is a method for detecting rare clones in leukemia

Detecting, characterizing, and monitoring rare populations of cells can increase testing sensitivity, give insight into disease mechanism, and inform clinical decision making. One area that can benefit from increased resolution is management of cancers in clinical remission but with measurable residual disease (MRD) by multicolor FACS. Detecting and monitoring genomic clonal resistance to treatment in the setting of MRD is technically difficult and resource intensive due to the limited amounts of disease cells. Here, we describe limited-cell FACS sequencing (LC-FACSeq), a reproducible, highly sensitive method of characterizing clonal evolution in rare cells relevant to different types of acute and chronic leukemias. We demonstrate the utility of LC-FACSeq for broad multigene gene panels and its application for monitoring sequential acquisition of mutations conferring therapy resistance and clonal evolution in long-term ibrutinib treatment of patients with chronic lymphocytic leukemia. This technique is generalizable for monitoring of other blood and marrow infiltrating cancers.

HSP90 overexpression potentiates the B-cell receptor and fibroblast growth factor receptor survival signals in chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (CLL) is still an incurable disease despite aggressive chemotherapies including the B-cell receptor (BCR) targeted-inhibitors. Therefore, we assessed the expression status of key signal mediators of the BCR pathway in CLL cells. Indeed, we detected aberrantly elevated levels of CD79a, B-cell adaptor for PI3K (BCAP) and phospholipase C (PLC)γ2, key mediators of BCR signal, in CLL cells. As HSP90 is also overexpressed in CLL cells, we hypothesized that HSP90 could potentiate the BCR signal via stabilization of multiple key components of the BCR-signalosome. We found that HSP90 formed a multi-molecular complex with CD79a, BCAP, PLCγ2, LYN, SYK, Bruton tyrosine kinase (BTK) and AKT and that, pharmacologic inhibition or partial depletion of HSP90 reduced the expression of these signal mediators in CLL cells. In addition, our findings also demonstrated that HSP90 could stabilize the tyrosine phosphatase, PTPN22 which positively regulates AKT phosphorylation, and the constitutively active fibroblast growth factor receptor 3 (FGFR3) in CLL cells. Finally, HSP90 inhibition induced apoptosis in CLL cells in a dose-dependent manner likely via downregulation of anti-apoptotic proteins MCL-1 and XIAP, but not BCL2, reported to be overexpressed in CLL cells. In total, our findings suggest that HSP90-inhibition may sensitize the leukemic B-cells to BCR-targeted agents, particularly those become resistant to these therapies.

Ibrutinib in Chronic Lymphocytic Leukemia: Clinical Applications, Drug Resistance, and Prospects

Bruton’s tyrosine kinase (BTK), a pivotal component of B-cell receptor (BCR) signaling, has been recognized as an important driver of the pathogenesis of chronic lymphocytic leukemia. Ibrutinib is a highly active and selectively irreversible inhibitor of BTK, which has been approved to be effective in both frontline and recurrent therapy of CLL. Acquired resistance has become a greater problem than initially anticipated with the widespread use of ibrutinib. An ongoing exploration of the mechanisms of ibrutinib resistance (IR) in CLL has revealed potentially useful therapeutic targets. New drugs expected to overcome IR in CLL are in the early stages of clinical development. This study aimed to summarize the possible mechanisms of IR and retrospectively analyze promising therapies that might have superior efficacy in overcoming IR.

Mechanisms of B Cell Receptor Activation and Responses to B Cell Receptor Inhibitors in B Cell Malignancies

The B cell receptor (BCR) pathway has been identified as a potential therapeutic target in a number of common B cell malignancies, including chronic lymphocytic leukemia, diffuse large B cell lymphoma, Burkitt lymphoma, follicular lymphoma, mantle cell lymphoma, marginal zone B cell lymphoma, and Waldenstrom's macroglobulinemia. This finding has resulted in the development of numerous drugs that target this pathway, including various inhibitors of the kinases BTK, PI3K, and SYK. Several of these drugs have been approved in recent years for clinical use, resulting in a profound change in the way these diseases are currently being treated. However, the response rates and durability of responses vary largely across the different disease entities, suggesting a different proportion of patients with an activated BCR pathway and different mechanisms of BCR pathway activation. Indeed, several antigen-dependent and antigen-independent mechanisms have recently been described and shown to result in the activation of distinct downstream signaling pathways. The purpose of this review is to provide an overview of the mechanisms responsible for the activation of the BCR pathway in different B cell malignancies and to correlate these mechanisms with clinical responses to treatment with BCR inhibitors.

Promises and pitfalls of targeted agents in chronic lymphocytic leukemia

Targeted agents have significantly improved outcomes for patients with chronic lymphocytic leukemia, particularly high-risk subgroups for whom chemoimmunotherapy previously offered limited efficacy. Two classes of agent in particular, the Bruton tyrosine kinase inhibitors (e.g., ibrutinib) and the B-cell lymphoma 2 inhibitor, venetoclax, induce high response rates and durable remissions in the relapsed/refractory and frontline settings. However, maturing clinical data have revealed promises and pitfalls for both agents. These drugs induce remissions and disease control in the majority of patients, often in situations where modest efficacy would be expected with traditional chemoimmunotherapy approaches. Unfortunately, in the relapsed and refractory setting, both agents appear to be associated with an inevitable risk of disease relapse and progression. Emerging patterns of resistance are being described for both agents but a common theme appears to be multiple sub-clonal drivers of disease progression. Understanding these mechanisms and developing effective and safe methods to circumvent the emergence of resistance will determine the longer-term utility of these agents to improve patients' quality and length of life. Rational drug combinations, optimised scheduling and sequencing of therapy will likely hold the key to achieving these important goals.

Survey of ex vivo drug combination effects in chronic lymphocytic leukemia reveals synergistic drug effects and genetic dependencies

Drug combinations that target critical pathways are a mainstay of cancer care. To improve current approaches to combination treatment of chronic lymphocytic leukemia (CLL) and gain insights into the underlying biology, we studied the effect of 352 drug combination pairs in multiple concentrations by analysing ex vivo drug response of 52 primary CLL samples, which were characterized by "omics" profiling. Known synergistic interactions were confirmed for B-cell receptor (BCR) inhibitors with Bcl-2 inhibitors and with chemotherapeutic drugs, suggesting that this approach can identify clinically useful combinations. Moreover, we uncovered synergistic interactions between BCR inhibitors and afatinib, which we attribute to BCR activation by afatinib through BLK upstream of BTK and PI3K. Combinations of multiple inhibitors of BCR components (e.g., BTK, PI3K, SYK) had effects similar to the single agents. While PI3K and BTK inhibitors produced overall similar effects in combinations with other drugs, we uncovered a larger response heterogeneity of combinations including PI3K inhibitors, predominantly in CLL with mutated IGHV, which we attribute to the target's position within the BCR-signaling pathway. Taken together, our study shows that drug combination effects can be effectively queried in primary cancer cells, which could aid discovery, triage and clinical development of drug combinations.

Bruton's Tyrosine Kinase (BTK) Inhibitor (Ibrutinib)-Suppressed Migration and Invasion of Prostate Cancer

INTRODUCTION

Bruton's tyrosine kinase (BTK) inhibitors have long been known in the treatment of B-cell malignancies. Recently, BTK inhibitors have also become promising novel treatment reagents for prostate cancer. The current study was designed to investigate expression of BTK in prostate cancer tissues in comparison with benign hyperplasia and effect of BTK inhibitor on prostate cancer cell proliferation, migration and invasion.

METHODS

BTK expression was assessed by immunohistochemistry; migration and invasion prostate cancer cell lines (DU145 and PC3) were assessed by Transwell migration and wound-healing assay; cancer cell proliferation was assessed using MTT assay kit; expression of matrix metalloproteinases-2 and -9 (MMP-2 and MMP-9) was assessed by immunoblotting.

RESULTS

Strong expression of BTK was detected in the prostate cancer tissues, especially in the tumors from prostate cancer patients with bone metastasis. BTK inhibitor (Ibrutinib) significantly inhibited cell proliferation, migration and invasion of prostate cancer cells as well as protein synthesis of MMP-2 and MMP-9 by the tumor cells. Overexpressing BTK could partially but significantly block the inhibitory effect of Ibrutinib on cell proliferation, migration and invasion, and protein synthesis of MMP-2 and MMP-9 of the cancer cells.

CONCLUSION

These findings suggested that BTK could serve as not only a biomarker but also a therapeutic target for the prostate cancer and that Ibrutinib may be applied as a therapeutic drug for the prostate cancer.

Feasibility and efficacy of CD19-targeted CAR T cells with concurrent ibrutinib for CLL after ibrutinib failure

We previously reported durable responses in relapsed or refractory (R/R) chronic lymphocytic leukemia (CLL) patients treated with CD19-targeted chimeric antigen receptor-engineered (CD19 CAR) T-cell immunotherapy after ibrutinib failure. Because preclinical studies showed that ibrutinib could improve CAR T cell-antitumor efficacy and reduce cytokine release syndrome (CRS), we conducted a pilot study to evaluate the safety and feasibility of administering ibrutinib concurrently with CD19 CAR T-cell immunotherapy. Nineteen CLL patients were included. The median number of prior therapies was 5, and 17 patients (89%) had high-risk cytogenetics (17p deletion and/or complex karyotype). Ibrutinib was scheduled to begin ≥2 weeks before leukapheresis and continue for ≥3 months after CAR T-cell infusion. CD19 CAR T-cell therapy with concurrent ibrutinib was well tolerated; 13 patients (68%) received ibrutinib as planned without dose reduction. The 4-week overall response rate using 2018 International Workshop on CLL (iwCLL) criteria was 83%, and 61% achieved a minimal residual disease (MRD)-negative marrow response by IGH sequencing. In this subset, the 1-year overall survival and progression-free survival (PFS) probabilities were 86% and 59%, respectively. Compared with CLL patients treated with CAR T cells without ibrutinib, CAR T cells with concurrent ibrutinib were associated with lower CRS severity and lower serum concentrations of CRS-associated cytokines, despite equivalent in vivo CAR T-cell expansion. The 1-year PFS probabilities in all evaluable patients were 38% and 50% after CD19 CAR T-cell therapy, with and without concurrent ibrutinib, respectively (P = .91). CD19 CAR T cells with concurrent ibrutinib for R/R CLL were well tolerated, with low CRS severity, and led to high rates of MRD-negative response by IGH sequencing.

Drug Review: Ibrutinib

Ibrutinib is an irreversible BTK inhibitor, characterized by high selectivity and potency. It has revolutionized the therapy of B-cell lymphomas, especially chronic lymphocytic leukemia (CLL) and mantle cell lymphoma. Importantly, it has expanded the armamentarium for those patients who are refractory to conventional chemoimmunotherapy. This small-molecule inhibitor has shown efficacy in this difficult-to-treat subset – those with del(17p)/TP53-mutated CLL. Its immunomodulatory properties make it an excellent choice for combining with other immunotherapeutic agents such as venetoclax. The drug is not without drawbacks. The need for indefinite therapy and the presence of adverse effects such as infection, bleeding, hypertension, and arrhythmia temper our enthusiasm for this versatile drug. But overall, ibrutinib's favorable risk profile and lack of myelosuppression make it an ideal therapy for the elderly and those with multiple comorbidities.

Integrative Analysis of Long Noncoding RNAs in Patients with Graft-versus-Host Disease

BACKGROUND

Chronic graft-versus-host disease (cGVHD) remains a major cause of late non-recurrence mortality despite remarkable improvements in the field of allogeneic hematopoietic stem cell transplantation. Although recent studies have found that B-cell receptor (BCR)-activated B cells contribute to pathogenesis in cGVHD, the specific molecular mechanisms of B cells in this process remain unclear.

METHODS

In our study, human long noncoding RNA (lncRNA) microarrays and bioinformatic analysis were performed to identify different expressions of lncRNAs in peripheral blood B cells from cGVHD patients compared with healthy ones. The differential expression of lncRNA was confirmed in additional samples by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

The microarray analysis revealed that 106 of 198 differentially expressed lncRNAs were upregulated and 92 were downregulated in cGVHD patients compared with healthy controls. Intergenic lncRNAs accounted for the majority of differentially expressed lncRNAs. A KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis showed that the differentially expressed mRNAs, which were coexpressed with lncRNA, between the cGVHD group and the healthy group were significantly enriched in the BCR signaling pathway. Further analysis of the BCR signaling pathway and its coexpression network identified three lncRNAs with the strongest correlation with BCR signaling and cGVHD, as well as a series of protein-coding genes and transcription factors associated with them. The three candidate lncRNAs were further validated in another group of cGVHD patients by qRT-PCR.

CONCLUSIONS

This is the first study on the correlation between lncRNA and cGVHD using lncRNA microarray analysis. Our study provides novel enlightenment in exploring the molecular pathogenesis of cGVHD.

Preclinical Evaluation of a Novel SHIP1 Phosphatase Activator for Inhibition of PI3K Signaling in Malignant B Cells

PURPOSE

PI3K signaling is a common feature of B-cell neoplasms, including chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL), and PI3K inhibitors have been introduced into the clinic. However, there remains a clear need to develop new strategies to target PI3K signaling. PI3K activity is countered by Src homology domain 2-containing inositol-5'-phosphatase 1 (SHIP1) and, here, we have characterized the activity of a novel SHIP1 activator, AQX-435, in preclinical models of B-cell malignancies.

EXPERIMENTAL DESIGN

In vitro activity of AQX-435 was evaluated using primary CLL cells and DLBCL-derived cell lines. In vivo activity of AQX-435, alone or in combination with the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, was assessed using DLBCL cell line and patient-derived xenograft models.

RESULTS

Pharmacologic activation of SHIP1 using AQX-435 was sufficient to inhibit anti-IgM-induced PI3K-mediated signaling, including induction of AKT phosphorylation and MYC expression, without effects on upstream SYK phosphorylation. AQX-435 also cooperated with the BTK inhibitor ibrutinib to enhance inhibition of anti-IgM-induced AKT phosphorylation. AQX-435 induced caspase-dependent apoptosis of CLL cells preferentially as compared with normal B cells, and overcame in vitro survival-promoting effects of microenvironmental stimuli. Finally, AQX-435 reduced AKT phosphorylation and growth of DLBCL in vivo and cooperated with ibrutinib for tumor growth inhibition.

CONCLUSIONS

Our results using AQX-435 demonstrate that SHIP1 activation may be an effective novel therapeutic strategy for treatment of B-cell neoplasms, alone or in combination with ibrutinib.

Ibrutinib Treatment for First-Line and Relapsed/Refractory Chronic Lymphocytic Leukemia: Final Analysis of the Pivotal Phase Ib/II PCYC-1102 Study

PURPOSE

The safety and efficacy of ibrutinib, a once-daily Bruton's tyrosine kinase (BTK) inhibitor, in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) was demonstrated in this phase Ib/II study. Extended follow-up up to 8 years is described, representing the longest follow-up for single-agent ibrutinib, or any BTK inhibitor, to date.

PATIENTS AND METHODS

Phase Ib/II PCYC-1102 (NCT01105247) and extension study PCYC-1103 (NCT01109069) included patients receiving single-agent ibrutinib in first-line or relapsed/refractory CLL/SLL.

RESULTS

Overall response rate was 89%, with similar rates in first-line (87%; complete response, 35%) and relapsed/refractory settings (89%; 10%). Estimated 7-year progression-free survival (PFS) rates were 83% in first-line and 34% in relapsed/refractory settings. Forty-one patients had CLL progression (n = 11 with Richter's transformation). Median PFS was not reached with first-line ibrutinib. In relapsed/refractory CLL/SLL, median PFS was 52 months overall, 26 months in patients with chromosome 17p deletion, 51 months with 11q deletion, not reached with trisomy 12 or 13q deletion, and 88 months in patients without these cytogenetic abnormalities. Estimated 7-year overall survival rates were 84% in first-line and 55% in relapsed/refractory settings. Grade ≥3 adverse events (AE) in >15% of patients were hypertension (28%), pneumonia (24%), and neutropenia (18%). These grade ≥3 AEs generally declined over time, except hypertension. AEs leading to discontinuation in ≥2 patients were observed only in the relapsed/refractory setting (sepsis, diarrhea, subdural hematoma, and Richter's transformation).

CONCLUSIONS

With up to 8 years of follow-up, sustained responses and long-term tolerability of single-agent ibrutinib were observed with treatment of first-line or relapsed/refractory CLL/SLL, including high-risk CLL/SLL.

Selective targeting of NAMPT by KPT-9274 in acute myeloid leukemia

Treatment options for acute myeloid leukemia (AML) remain extremely limited and associated with significant toxicity. Nicotinamide phosphoribosyltransferase (NAMPT) is involved in the generation of NAD⁺ and a potential therapeutic target in AML. We evaluated the effect of KPT-9274, a p21-activated kinase 4/NAMPT inhibitor that possesses a unique NAMPT-binding profile based on in silico modeling compared with earlier compounds pursued against this target. KPT-9274 elicited loss of mitochondrial respiration and glycolysis and induced apoptosis in AML subtypes independent of mutations and genomic abnormalities. These actions occurred mainly through the depletion of NAD⁺, whereas genetic knockdown of p21-activated kinase 4 did not induce cytotoxicity in AML cell lines or influence the cytotoxic effect of KPT-9274. KPT-9274 exposure reduced colony formation, increased blast differentiation, and diminished the frequency of leukemia-initiating cells from primary AML samples; KPT-9274 was minimally cytotoxic toward normal hematopoietic or immune cells. In addition, KPT-9274 improved overall survival in vivo in 2 different mouse models of AML and reduced tumor development in a patient-derived xenograft model of AML. Overall, KPT-9274 exhibited broad preclinical activity across a variety of AML subtypes and warrants further investigation as a potential therapeutic agent for AML.

PDGFD induces ibrutinib resistance of diffuse large B‑cell lymphoma through activation of EGFR

Ibrutinib, an FDA approved, orally administered BTK inhibitor, has demonstrated high response rates to diffuse large B-cell lymphoma (DLBCL), however, complete responses are infrequent and acquired resistance to BTK inhibition can emerge. The present study investigated the role of the platelet-derived growth factor D (PDGFD) gene and the ibrutinib resistance of DLBCL in relation to epidermal growth factor receptor (EGFR). Bioinformatics was used to screen and analyze differentially expressed genes (DEGs) in complete response (CR), partial response (PR) and stable disease (SD) in DLBCL treatment with ibrutinib, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to analyze enriched the signaling pathways increasing DEGs. The Search Tool for Interactions of Chemicals database was used to analyze the target genes of ibrutinib. An interaction network of DEGs, disease-related genes and ibrutinib was constructed. The expression of PDGFD in tissues that were resistant or susceptible to DLBCL/ibrutinib was detected via immunohistochemistry (IHC), and the expression of PDGFD in DLBCL/ibrutinib-resistant strains and their parental counterparts were examined via reverse transcription-quantitative PCR and western blot analyses. Subsequently, a drug-resistant cell model of DLBCL/ibrutinib in which PDGFD was silenced was constructed. The apoptosis of the DLBCL/ibrutinib-resistant strains was examined using MTT and flow cytometry assays. EGFR gene expression was then assessed. At the same time, a PDGFD-interfering plasmid and an EGFR overexpression plasmid were transfected into the DLBCL drug-resistant cells (TMD8-ibrutinib, HBL1-ibrutinib) separately or together. MTT was used to measure cell proliferation and changes in the IC₅₀ of ibrutinib. A total of 86 DEGs that increased in the CR, PR and SD tissues were screened, and then evaluated with GO and KEGG. The interaction network diagram showed that there was a regulatory relationship between PDGFD and disease-related genes, and that PDGFD could indirectly target the ibrutinib target gene EGFR, indicating that PDGFD could regulate DLBCL via EGFR. IHC results showed high expression of PDGFD in diffuse large B-cell lymphoma tissues with ibrutinib tolerance. PDGFD expression in ibrutinib-resistant DLBCL cells was higher compared with in parental cells. Following interference with PDGFD expression in ibrutinib-resistant DLBCL cells, the IC₅₀ value of ibrutinib decreased, the rate of apoptosis increased and EGFR expression decreased. In brief, EGFR overexpression can reverse the resistance of DLBCL to ibrutinib via PDGFD interference, and PDGFD induces the resistance of DLBCL to ibrutinib via EGFR.

Adenosine-producing regulatory B cells in head and neck cancer

Background

Multiple mechanisms of immunosuppression have been identified in the tumor microenvironment including regulatory B cells (B_reg). Recently, we have shown that B_reg suppress T cell function by production of adenosine (ADO). However, the autocrine effect of ADO on B cells and the role of B_reg in head and neck cancer remains unclear.

Methods

Blood (n = 42) and tumor tissue (n = 39) of head and neck cancer patients and healthy donors (n = 60) were analyzed by FACS. The effect of ADO on phenotype, intracellular signaling pathways, Ca²⁺ influx and ADO production was analyzed in B_reg and effector B cells (B_eff) by FACS, luminescence and mass spectrometry. The blockage of the ADO receptor A_2A was analyzed in a murine head and neck cancer model.

Results

ADO-producing B_reg were found in tumor tissue and peripheral blood. ADO inhibited the intracellular Bruton’s tyrosine kinase (BTK) and Ca²⁺ influx only in B_eff. The inhibition of BTK by ibrutinib mimicked the effect of ADO, and ibrutinib reduced the production of ADO by downregulation of CD39 in vitro. The inhibition of ADO receptor A_2A significantly reduced tumor mass and increased B cell infiltration, in vivo.

Conclusion

Our data demonstrate the presence of a novel ADO-producing B_reg population within the tumor microenvironment in mice and humans. A new model is proposed on how ADO-producing B_reg can influence the function of B_eff cells in healthy donors and cancer patients. Thus, the modulation of the ADO pathway in B cells may serve as a therapeutic approach for cancer patients.

Electronic supplementary material

The online version of this article (10.1007/s00262-020-02535-6) contains supplementary material, which is available to authorized users.

Role of Non-Coding RNAs in the Development of Targeted Therapy and Immunotherapy Approaches for Chronic Lymphocytic Leukemia

In the past decade, novel targeted therapy approaches, such as BTK inhibitors and Bcl2 blockers, and innovative treatments that regulate the immune response against cancer cells, such as monoclonal antibodies, CAR-T cell therapy, and immunomodulatory molecules, have been established to provide support for the treatment of patients. However, drug resistance development and relapse are still major challenges in CLL treatment. Several studies revealed that non-coding RNAs have a main role in the development and progression of CLL. Specifically, microRNAs (miRs) and tRNA-derived small-RNAs (tsRNAs) were shown to be outstanding biomarkers that can be used to diagnose and monitor the disease and to possibly anticipate drug resistance and relapse, thus supporting physicians in the selection of treatment regimens tailored to the patient needs. In this review, we will summarize the most recent discoveries in the field of targeted therapy and immunotherapy for CLL and discuss the role of ncRNAs in the development of novel drugs and combination regimens for CLL patients.

Pharmacodynamic Analysis of BTK Inhibition in Patients with Chronic Lymphocytic Leukemia Treated with Acalabrutinib

PURPOSE

To determine the pharmacodynamic relationship between target occupancy of Bruton tyrosine kinase (BTK) and inhibition of downstream signaling.

PATIENTS AND METHODS

Patients with chronic lymphocytic leukemia (CLL) enrolled in a phase II clinical trial (NCT02337829) with the covalent, selective BTK inhibitor acalabrutinib donated blood samples for pharmacodynamic analyses. Study design included randomization to acalabrutinib 100 mg twice daily or 200 mg once daily and dose interruptions on day 4 and 5 of the first week. BTK occupancy and readouts of intracellular signaling were assessed sequentially between 4 and 48 hours from last dose.

RESULTS

Four hours from last dose, BTK occupancy exceeded 96% and at trough, was higher with twice daily, median 95.3%, than with once daily dosing, median 87.6% (P < 0.0001). By 48 hours from last dose, median free BTK increased to 25.6%. Due to covalent binding of acalabrutinib, free BTK is generated by de novo synthesis. The estimated rate of BTK synthesis varied widely between patients ranging from 3.6% to 31.4% per day. Acalabrutinib reduced phosphorylation of BTK and inhibited downstream B-cell receptor (BCR) and NFκB signaling. During dosing interruptions up to 48 hours, expression of BCR target genes rebounded, while phosphorylation of signaling molecules remained repressed. In vitro cross-linking of IgM on CLL cells obtained 36 to 48 hours from last dose upregulated CD69, with high correlation between cellular free BTK and response (R = 0.7, P ≤ 0.0001).

CONCLUSIONS

Higher BTK occupancy was achieved with twice daily over once daily dosing, resulting in deeper and more sustained inhibition of BCR signaling.

Anti-BAFF-R antibody VAY-736 demonstrates promising preclinical activity in CLL and enhances effectiveness of ibrutinib

The Bruton tyrosine kinase inhibitor (BTKi) ibrutinib has transformed chronic lymphocytic leukemia (CLL) therapy but requires continuous administration. These factors have spurred interest in combination treatments. Unlike with chemotherapy, CD20-directed antibody therapy has not improved the outcome of BTKi treatment. Whereas CD20 antigen density on CLL cells decreases during ibrutinib treatment, the B-cell activating factor (BAFF) and its receptor (BAFF-R) remain elevated. Furthermore, BAFF signaling via noncanonical NF-κB remains elevated with BTKi treatment. Blocking BAFF interaction with BAFF-R by using VAY-736, a humanized defucosylated engineered antibody directed against BAFF-R, antagonized BAFF-mediated apoptosis protection and signaling at the population and single-cell levels in CLL cells. Furthermore, VAY-736 showed superior antibody-dependent cellular cytotoxicity compared with CD20- and CD52-directed antibodies used in CLL. VAY-736 exhibited in vivo activity as a monotherapy and, when combined with ibrutinib, produced prolonged survival compared with either therapy alone. The in vivo activity of VAY-736 is dependent upon immunoreceptor tyrosine-based activation motif (ITAM)-mediated activation of effector cells as shown by using an ITAM-deficient mouse model. Collectively, our findings support targeting the BAFF signaling pathway with VAY-736 to more effectively treat CLL as a single agent and in combination with ibrutinib.

Celebrating 20 Years of IGHV Mutation Analysis in CLL

The division of CLL into 2 broad subsets with highly significant differences in clinical behavior was reported in 2 landmark papers in Blood in 1999.^1,2 The simple analysis of the mutational status of the IGV regions provided both a prognostic indicator and an insight into the cellular origins. Derivation from B cells with very low or no IGV mutations generally leads to a more aggressive disease course than derivation from B cells with higher levels. This finding focused attention on surface Ig (sIg), the major B-cell receptor, and revealed dynamic antigen engagement in vivo as a tumor driver. It has also led to new drugs aimed at components of the intracellular activation cascades. After 20 years, the 2 senior authors of those papers have looked at the history of the observations and at the increasing understanding of the role of sIg in CLL that have emanated from them. As in the past, studies of CLL have provided a link between biology and the clinic, enabling more precise targeting which attacks critical pathways but minimizes side effects.

Acalabrutinib plus Obinutuzumab in Treatment-Naïve and Relapsed/Refractory Chronic Lymphocytic Leukemia

Acalabrutinib is a selective irreversible Bruton tyrosine kinase (BTK) inhibitor that does not affect IL2-associated tyrosine kinase or antibody-dependent cellular cytotoxicity, making it an attractive candidate for combination therapy with anti-CD20 antibodies. We investigated acalabrutinib plus obinutuzumab in a phase Ib/II study (NCT02296918) of patients with treatment-naïve or relapsed/refractory chronic lymphocytic leukemia (CLL). Nineteen treatment-naïve and 26 relapsed/refractory patients were treated with acalabrutinib (100 mg twice daily) until progression and obinutuzumab (cycle 1: 100 mg day 1, 900 mg day 2, 1000 mg days 8 and 15; cycles 2-6: 1,000 mg day 1). Grade 3/4 adverse events occurred in 71% of patients. Overall response rates were 95% (treatment-naïve) and 92% (relapsed/refractory). Thirty-two percent of treatment-naïve and 8% of relapsed/refractory patients achieved complete remission. At 36 months, 94% (treatment-naïve) and 88% (relapsed/refractory) were progression free. Acalabrutinib plus obinutuzumab was well tolerated, producing high and durable responses in treatment-naïve and relapsed/refractory CLL. SIGNIFICANCE: Rituximab plus the less selective BTK inhibitor ibrutinib has not shown benefit in CLL; however, the selective BTK inhibitor acalabrutinib plus the antibody-dependent cellular cytotoxicity-enhanced antibody obinutuzumab yielded durable responses that deepened over time in treatment-naïve and relapsed/refractory CLL, supporting the evaluation of this approach in larger, comparative studies in CLL.This article is highlighted in the In This Issue feature, p. 327.

Advances in covalent kinase inhibitors

This comprehensive review details recent advances, challenges and innovations in covalent kinase inhibition within a 10 year period (2007–2018).

Amelioration of age-related brain function decline by Bruton's tyrosine kinase inhibition

One of the hallmarks of aging is the progressive accumulation of senescent cells in organisms, which has been proposed to be a contributing factor to age-dependent organ dysfunction. We recently reported that Bruton's tyrosine kinase (BTK) is an upstream component of the p53 responses to DNA damage. BTK binds to and phosphorylates p53 and MDM2, which results in increased p53 activity. Consistent with this, blocking BTK impairs p53-induced senescence. This suggests that sustained BTK inhibition could have an effect on organismal aging by reducing the presence of senescent cells in tissues. Here, we show that ibrutinib, a clinically approved covalent inhibitor of BTK, prolonged the maximum lifespan of a Zmpste24^-/- progeroid mice, which also showed a reduction in general age-related fitness loss. Importantly, we found that certain brain functions were preserved, as seen by reduced anxiety-like behaviour and better long-term spatial memory. This was concomitant to a decrease in the expression of specific markers of senescence in the brain, which confirms a lower accumulation of senescent cells after BTK inhibition. Our data show that blocking BTK has a modest increase in lifespan in Zmpste24^-/- mice and protects them from a decline in brain performance. This suggests that specific inhibitors could be used in humans to treat progeroid syndromes and prevent the age-related degeneration of organs such as the brain.

Harnessing the Effects of BTKi on T Cells for Effective Immunotherapy against CLL

B-cell receptor (BCR) signaling and tumor–microenvironment crosstalk both drive chronic lymphocytic leukemia (CLL) pathogenesis. Within the microenvironment, tumor cells shape the T-cell compartment, which in turn supports tumor growth and survival. Targeting BCR signaling using Bruton tyrosine kinase inhibitors (BTKi) has become a highly successful treatment modality for CLL. Ibrutinib, the first-in-class BTKi, also inhibits Tec family kinases such as interleukin-2–inducible kinase (ITK), a proximal member of the T-cell receptor signaling cascade. It is increasingly recognized that ibrutinib modulates the T-cell compartment of patients with CLL. Understanding these T-cell changes is important for immunotherapy-based approaches aiming to increase the depth of response and to prevent or treat the emergence of resistant disease. Ibrutinib has been shown to improve T-cell function in CLL, resulting in the expansion of memory T cells, Th1 polarization, reduced expression of inhibitory receptors and improved immune synapse formation between T cells and CLL cells. Investigating the modulation of BTKi on the T-cell antitumoral function, and having a more complete understanding of changes in T cell behavior and function during treatment with BTKi therapy will inform the design of immunotherapy-based combination approaches and increase the efficacy of CLL therapy.

In vitro metabolism of ibrutinib in rat, dog and human hepatocytes using liquid chromatography combined with diode-array detection and Q-Exactive Orbitrap tandem mass spectrometry

RATIONALE

Ibrutinib is a potent Bruton's tyrosine kinase inhibitor which has shown promising efficacy against various B-cell malignancies. Its metabolic profiles have not been disclosed. The aim of this study was to investigate the metabolism of ibrutinib in the hepatocytes of rat, dog and human.

METHODS

Ibrutinib was incubated with hepatocytes at 37°C for 2 h, after which the samples were analyzed using ultrahigh-performance liquid chromatography with diode-array detection and Q-Exactive Orbitrap tandem mass spectrometry (UHPLC/DAD-Q-Exactive-Orbitrap-MS). The acquired data were processed using MetWorks™ software.

RESULTS

A total of 20 metabolites were structurally identified by their MS and MS² data. M1 and M5 were unambiguously identified using authentic standards. The biotransformation of ibrutinib involved hydroxylation, hydration, oxygenation, epoxide hydrolysis, dehydrogenation, dealkylation and GSH conjugation.

CONCLUSIONS

Humans have a relatively low capability for metabolizing ibrutinib. Compared with rat, dog had closer metabolic profiles to humans and would be more suitable for toxicity studies. This study provides more valuable information with respect to the in vitro disposition of ibrutinib.

BTK inhibitors synergise with 5-FU to treat drug-resistant TP53-null colon cancers

Colorectal cancer (CRC) is the fourth cause of death from cancer worldwide mainly due to the high incidence of drug-resistance. During a screen for new actionable targets in drug-resistant tumours we recently identified p65BTK - a novel oncogenic isoform of Bruton's tyrosine kinase. Studying three different cohorts of patients here we show that p65BTK expression correlates with histotype and cancer progression. Using drug-resistant TP53-null colon cancer cells as a model we demonstrated that p65BTK silencing or chemical inhibition overcame the 5-fluorouracil resistance of CRC cell lines and patient-derived organoids and significantly reduced the growth of xenografted tumours. Mechanistically, we show that blocking p65BTK in drug-resistant cells abolished a 5-FU-elicited TGFB1 protective response and triggered E2F-dependent apoptosis. Taken together, our data demonstrated that targeting p65BTK restores the apoptotic response to chemotherapy of drug-resistant CRCs and gives a proof-of-concept for suggesting the use of BTK inhibitors in combination with 5-FU as a novel therapeutic approach in CRC patients. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.