Pharmacological targeting of PI3K isoforms as a therapeutic strategy in chronic lymphocytic leukaemia

B cell receptor signaling drives APOBEC3 expression via direct enhancer regulation in chronic lymphocytic leukemia B cells

Constitutively activated B cell receptor (BCR) signaling is a primary biological feature of chronic lymphocytic leukemia (CLL). The biological events controlled by BCR signaling in CLL are not fully understood and need investigation. Here, by analysis of the chromatin states and gene expression profiles of CLL B cells from patients before and after Bruton's tyrosine kinase inhibitor (BTKi) ibrutinib treatment, we show that BTKi treatment leads to a decreased expression of APOBEC3 family genes by regulating the activity of their enhancers. BTKi treatment reduces enrichment of enhancer marks (H3K4me1 and H3K27ac) and chromatin accessibility at putative APOBEC3 enhancers. CRISPR-Cas9 directed deletion or inhibition of the putative APOBEC3 enhancers leads to reduced APOBEC3 expression. We further find that transcription factor NFATc1 couples BCR signaling with the APOBEC3 enhancer activity to control APOBEC3 expression. We also find that enhancer-regulated APOBEC3 expression contributes to replication stress in malignant B cells. In total we demonstrate a novel mechanism for BTKi suppression of APOBEC3 expression via direct enhancer regulation in an NFATc1-dependent manner, implicating BCR signaling as a potential regulator of leukemic genomic instability.

Idelalisib and caffeine reduce suppression of T cell responses mediated by activated chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (CLL) is associated with T cell dysfunction. Activated CLL cells are found within the lymphoid tumor micro-environment and overcoming immuno-suppression induced by these cells may improve anti-CLL immune responses. However, the mechanisms by which activated CLL cells inhibit T cell responses, and reagents targeting such mechanisms have not been identified. Here we demonstrate that the ability of in vitro activated CLL cells to suppress T cell proliferation is not reversed by the presence of ecto-nuclease inhibitors or blockade of IL-10, PD-1 and CTLA-4 pathways. Caffeine is both an adenosine receptor antagonist and a phosphatidylinositol-3-kinase, p110δ (PI3Kδ) inhibitor and, at physiologically relevant levels, significantly reversed suppression. Significant reversal of suppression was also observed with the PI3Kδ specific inhibitor Idelalisib but not with adenosine receptor specific antagonists. Furthermore, addition of caffeine or Idelalisib to activated CLL cells significantly inhibited phosphorylation of AKT, a downstream kinase of PI3K, but did not affect CLL viability. These results suggest that caffeine, in common with Idelalisib, reduces the immuno-suppressive activity of activated CLL cells by inhibiting PI3Kδ. These findings raise the possibility that these compounds may provide a useful therapeutic adjunct by reducing immuno-suppression within the tumor micro-environment of CLL.

Idelalisib or placebo in combination with bendamustine and rituximab in patients with relapsed or refractory chronic lymphocytic leukaemia: interim results from a phase 3, randomised, double-blind, placebo-controlled trial

Background

Bendamustine and rituximab (BR) has been a standard of care for the management of patients with relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL). We evaluated the efficacy and safety of adding idelalisib, a first-in-class targeted PI3Kδ inhibitor, to BR in patients with R/R CLL

Methods

This trial was a global, multicenter, double-blind, placebo -controlled trial in adult patients (≥18 years) with R/R CLL requiring treatment for their disease. Patients had to have measurable lymphadenopathy (≥1 nodal lesion ≥2.0 cm in the longest diameter and ≥1.0 cm in the longest perpendicular diameter) by computer tomography or magnetic resonance imaging, disease progression within <36 months since last prior therapy, a Karnofsky Performance Status score ≥60 and adequate bone marrow, liver and kidney function. Key exclusion criteria included histological transformation to an aggressive lymphoma (eg, Richter transformation) or disease refractory to bendamustine. Patients were randomised 1:1 using a central interactive web response system that assigned a unique treatment code for each patient, to receive intravenous BR infusions for a maximum of 6 cycles in addition to blinded study drug matching the assigned treatment of either twice-daily oral idelalisib 150 mg or placebo administered continuously until disease progression or intolerable study drug-related toxicity. Randomisation was stratified based on high-risk features (IGHV, del(17p)/TP53 mutation) and refractory vs relapsed disease. The primary endpoint was progression-free survival (PFS) assessed by an independent review committee in the intent-to-treat population. Overall survival was a key secondary endpoint. Crossover was not permitted to the idelalisib arm at progression. The trial is ongoing (ClinicalTrials.gov # NCT01569295).

Findings

Between 26 June 2012 and 21 August 2014, 416 patients with R/R CLL were enrolled; 207 patients were randomised to the idelalisib and 209 to the placebo arm. After the prespecified interim analysis, the Independent Data Monitoring Committee (IDMC) recommended discontinuation and unblinding of the trial due to efficacy. Updated data are presented in this manuscript with a cutoff date of 07 October 2015. Median (95% CI) PFS was 20·8 (16·6, 26·4) and 11·1 (8·9, 11·1) months in the idelalisib and placebo arms, respectively (hazard ratio [HR], 0·33; 95% CI, 0·25, 0·44; P<0·0001) at a median (Q1, Q3) follow-up of 14 (7, 18) months. The most frequent grade 3 or greater AEs were neutropenia (124/207 [60%]) and febrile neutropenia (48/207 [23%]) in the idelalisib arm and neutropenia (99/209 [47%]) and thrombocytopenia (27/209 [13%]) in the placebo arm. Serious AEs included febrile neutropenia, pneumonia and pyrexia and were common in both treatment arms. An increased risk of infection was observed in the idelalisib vs placebo arm.

Interpretation

Idelalisib plus BR is superior to BR alone, improving PFS and OS. This regimen represents an important new treatment option for patients with R/R CLL.

Chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is a malignancy of CD5+ B cells that is characterized by the accumulation of small, mature-appearing lymphocytes in the blood, marrow and lymphoid tissues. Signalling via surface immunoglobulin, which constitutes the major part of the B cell receptor, and several genetic alterations play a part in CLL pathogenesis, in addition to interactions between CLL cells and other cell types, such as stromal cells, T cells and nurse-like cells in the lymph nodes. The clinical progression of CLL is heterogeneous and ranges from patients who require treatment soon after diagnosis to others who do not require therapy for many years, if at all. Several factors, including the immunoglobulin heavy-chain variable region gene (IGHV) mutational status, genomic changes, patient age and the presence of comorbidities, should be considered when defining the optimal management strategies, which include chemotherapy, chemoimmunotherapy and/or drugs targeting B cell receptor signalling or inhibitors of apoptosis, such as BCL-2. Research on the biology of CLL has profoundly enhanced our ability to identify patients who are at higher risk for disease progression and our capacity to treat patients with drugs that selectively target distinctive phenotypic or physiological features of CLL. How these and other advances have shaped our current understanding and treatment of patients with CLL is the subject of this Primer.

Idelalisib therapy of indolent B-cell malignancies: chronic lymphocytic leukemia and small lymphocytic or follicular lymphomas

Chronic lymphocytic leukemia, small lymphocytic lymphoma, and follicular lymphoma are indolent B-cell lymphoproliferative disorders that mainly affect an older population. Although the majority of patients in need of treatment derive significant benefit from conventional chemotherapeutic agents as well as monoclonal antibodies, less toxic and more effective treatments are needed. Novel agents that inhibit the B-cell receptor signaling pathway have shown promising outcomes in these disorders. Idelalisib is a potent selective oral inhibitor of phosphatidylinositol 3-kinase delta and has shown significant clinical activity in B-cell malignancies. In this review, we summarize the clinical trial data using idelalisib as monotherapy or in combination with rituximab for the treatment of relapsed/refractory disease. The adverse effect profile includes autoimmune disorders such as transaminitis, colitis, and pneumonitis. Given the efficacy and manageable toxicity profile of idelalisib, it is being increasingly incorporated into the management of indolent B-cell malignancies.