PI3K Signaling in Normal B Cells and Chronic Lymphocytic Leukemia (CLL)

B cells provide immunity to extracellular pathogens by secreting a diverse repertoire of antibodies with high affinity and specificity for exposed antigens. The B cell receptor (BCR) is a transmembrane antibody, which facilitates the clonal selection of B cells producing secreted antibodies of the same specificity. The diverse antibody repertoire is generated by V(D)J recombination of heavy and light chain genes, whereas affinity maturation is mediated by activation-induced cytidine deaminase (AID)-mediated mutagenesis. These processes, which are essential for the generation of adaptive humoral immunity, also render B cells susceptible to chromosomal rearrangements and point mutations that in some cases lead to cancer. In this chapter, we will review the central role of PI3K s in mediating signals from the B cell receptor that not only facilitate the development of functional B cell repertoire, but also support the growth and survival of neoplastic B cells, focusing on chronic lymphocytic leukemia (CLL) B cells. Perhaps because of the central role played by PI3K in BCR signaling, B cell leukemia and lymphomas are the first diseases for which a PI3K inhibitor has been approved for clinical use.

Ibrutinib as Initial Therapy for Patients with Chronic Lymphocytic Leukemia

BACKGROUND

Chronic lymphocytic leukemia (CLL) primarily affects older persons who often have coexisting conditions in addition to disease-related immunosuppression and myelosuppression. We conducted an international, open-label, randomized phase 3 trial to compare two oral agents, ibrutinib and chlorambucil, in previously untreated older patients with CLL or small lymphocytic lymphoma.

METHODS

We randomly assigned 269 previously untreated patients who were 65 years of age or older and had CLL or small lymphocytic lymphoma to receive ibrutinib or chlorambucil. The primary end point was progression-free survival as assessed by an independent review committee.

RESULTS

The median age of the patients was 73 years. During a median follow-up period of 18.4 months, ibrutinib resulted in significantly longer progression-free survival than did chlorambucil (median, not reached vs. 18.9 months), with a risk of progression or death that was 84% lower with ibrutinib than that with chlorambucil (hazard ratio, 0.16; P<0.001). Ibrutinib significantly prolonged overall survival; the estimated survival rate at 24 months was 98% with ibrutinib versus 85% with chlorambucil, with a relative risk of death that was 84% lower in the ibrutinib group than in the chlorambucil group (hazard ratio, 0.16; P=0.001). The overall response rate was higher with ibrutinib than with chlorambucil (86% vs. 35%, P<0.001). The rates of sustained increases from baseline values in the hemoglobin and platelet levels were higher with ibrutinib. Adverse events of any grade that occurred in at least 20% of the patients receiving ibrutinib included diarrhea, fatigue, cough, and nausea; adverse events occurring in at least 20% of those receiving chlorambucil included nausea, fatigue, neutropenia, anemia, and vomiting. In the ibrutinib group, four patients had a grade 3 hemorrhage and one had a grade 4 hemorrhage. A total of 87% of the patients in the ibrutinib group are continuing to take ibrutinib.

CONCLUSIONS

Ibrutinib was superior to chlorambucil in previously untreated patients with CLL or small lymphocytic lymphoma, as assessed by progression-free survival, overall survival, response rate, and improvement in hematologic variables. (Funded by Pharmacyclics and others; RESONATE-2 ClinicalTrials.gov number, NCT01722487.).

β2 -microglobulin normalization within 6 months of ibrutinib-based treatment is associated with superior progression-free survival in patients with chronic lymphocytic leukemia

BACKGROUND

A high pretreatment β2 -microglobulin (B2M) level is associated with inferior survival outcomes in patients with chronic lymphocytic leukemia. However, to the authors' knowledge, the prognostic and predictive significance of changes in B2M during treatment have not been reported to date.

METHODS

The authors analyzed 83 patients treated with ibrutinib-based regimens (66 with recurrent/refractory disease) and 198 treatment-naive patients who were treated with combined fludarabine, cyclophosphamide, and rituximab (FCR) to characterize changes in B2M and their relationship with clinical outcomes.

RESULTS

B2M rapidly decreased during treatment with ibrutinib; on multivariable analysis, patients who received FCR (odds ratio, 0.40; 95% confidence interval [95% CI], 0.18-0.90 [P = .027]) were less likely to have normalized B2M at 6 months than patients treated with ibrutinib. On univariable analysis, normalization of B2M was associated with superior progression-free survival (PFS) from the 6-month landmark in patients treated with ibrutinib-based regimens and FCR. On multivariable analysis, failure to achieve normalized B2M at 6 months of treatment was associated with inferior PFS (hazard ratio, 16.9; 95% CI, 1.3-220.0 [P = .031]) for patients treated with ibrutinib, after adjusting for the effects of baseline B2M, stage of disease, fludarabine-refractory disease, and del(17p). In contrast, in patients treated with FCR, negative minimal residual disease status in the bone marrow was the only variable found to be significantly associated with superior PFS (hazard ratio, 0.28; 95% CI, 0.12-0.67 [P = .004]).

CONCLUSIONS

Normalization of B2M at 6 months in patients treated with ibrutinib was found to be a useful predictor of subsequent PFS and may assist in clinical decision-making.

Minimal residual disease assessed by multi-parameter flow cytometry is highly prognostic in adult patients with acute lymphoblastic leukaemia

The prognostic value of minimal residual disease (MRD) assessed by multi-parameter flow cytometry (MFC) was investigated among 340 adult patients with B-cell acute lymphoblastic leukaemia (B-ALL) treated between 2004 and 2014 using regimens including the hyperCVAD (hyperfractionated cyclophosphamide, vincristine, doxorubicin, dexamethasone, methotrexate, cytarabine) backbone. Among them, 323 (95%) achieved complete remission (CR) and were included in this study. Median age was 52 years (range, 15-84). Median white blood cell count (WBC) was 9·35 × 10(9) /l (range, 0·4-658·1 ×1 0(9) /l). MRD by MFC was initially assessed with a sensitivity of 0·01%, using a 15-marker, 4-colour panel and subsequently a 6-colour panel on bone marrow specimens obtained at CR achievement and at approximately 3 month intervals thereafter. MRD negative status at CR was associated with improved disease-free survival (DFS) and overall survival (OS) (P = 0·004 and P = 0·03, respectively). Similarly, achieving MRD negative status at approximately 3 and 6 months was associated with improved DFS (P = 0·004 and P < 0·0001, respectively) and OS (P = 0·004 and P < 0·0001, respectively). Multivariate analysis including age, WBC at presentation, cytogenetics (standard versus high risk) and MRD status at CR, 3 and 6 months, indicated that MRD negative status at CR was an independent predictor of DFS (P < 0·05). Achievement of an MRD negative state assessed by MFC is an important predictor of DFS and OS in adult patients with ALL.

Complex karyotype is a stronger predictor than del(17p) for an inferior outcome in relapsed or refractory chronic lymphocytic leukemia patients treated with ibrutinib-based regimens

BACKGROUND

Ibrutinib is active in patients with relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL). In patients treated with ibrutinib for R/R CLL, del(17p), identified by interphase fluorescence in situ hybridization (FISH), is associated with inferior progression-free survival despite equivalent initial response rates. Del(17p) is frequently associated with a complex metaphase karyotype (CKT); the prognostic significance of CKT in ibrutinib-treated patients has not been reported.

METHODS

This study reviewed 88 patients treated for R/R CLL at The University of Texas MD Anderson Cancer Center with investigational ibrutinib-based regimens from 2010 to 2013. Pretreatment FISH and lipopolysaccharide-stimulated metaphase cytogenetic analysis were performed on bone marrow.

RESULTS

An adequate pretreatment metaphase karyotype was available for 56 of the 88 patients. The karyotype was complex in 21 of the 56 cases; 17 of the 21 had del(17p) according to FISH. The overall response rate, including partial remission with persistent lymphocytosis, was 94%; 18% had complete responses. In a multivariate analysis (MVA), only CKT was significantly associated with event-free survival (EFS; hazard ratio [HR], 6.6 [95% CI 1.7-25.6]; P = .006). Fludarabine-refractory CLL (HR, 6.9 [95% CI 1.8-27.1], P = .005) and CKT (HR 5.9 [95% CI 1.6-22.2], P = .008) were independently associated with inferior overall survival (OS) in MVA. Del(17p) by FISH was not significantly associated with EFS or OS in MVA.

CONCLUSIONS

CKT is a powerful predictor of outcomes for ibrutinib-treated patients with R/R CLL and may be a stronger predictor of biological behavior than del(17p) by FISH. Because of their relatively poor outcomes, patients with CKT are ideal candidates for studies of consolidative treatment strategies or novel treatment combinations.

CCL3 chemokine expression by chronic lymphocytic leukemia cells orchestrates the composition of the microenvironment in lymph node infiltrates

Previous experiments demonstrated that survival and proliferation of chronic lymphocytic leukemia (CLL) cells depends upon complex cross-talk between CLL cells and accessory cells in the tissue microenvironment. To further dissect these interactions in situ, we analyzed lymph nodes from 43 different patients infiltrated by CLL cells for expression of the chemokine CCL3, Ki-67, macrophages, and T cell subsets by immunohistochemistry. CCL3 expression was detected in 24 of 43 cases (56%), particularly in prolymphocytes and paraimmunoblasts within the proliferation centers. Significantly higher numbers of CD3+ T cells and CD57+ cells were noticed in CCL3 positive cases. Furthermore, denser infiltration of CLL lymph node tissues by CD57+ cells correlated with higher proliferation rates of the CLL cells. In conclusion, we demonstrate an association of CCL3 expression by CLL cells with increased numbers of CD3+ T cells and CD57+ cells in the lymph node microenvironment, which may promote CLL cell survival and proliferation.

CCL3 and CCL4 are biomarkers for B cell receptor pathway activation and prognostic serum markers in diffuse large B cell lymphoma

B cell receptor (BCR) signalling is an important pathway in diffuse large B cell lymphoma (DLBCL). In response to BCR triggering, normal and malignant B cells secrete the chemokines CCL3 and CCL4 to attract accessory cells to the tissue microenvironment. We measured CCL3 and CCL4 serum concentrations in 102 patients with newly diagnosed DLBCL by enzyme-linked immunosorbent assay, investigated their prognostic impact and validated our findings in an independent cohort of 51 patient samples. We also tested CCL3 and CCL4 secretion by DLBCL cells, and the influence of BTK inhibitors on the secretion of these chemokines. High CCL3 (≥40 pg/ml) serum concentrations correlated with higher international prognostic index, lactate dehydrogenase and β2 microglobulin, as did CCL4 (≥180 pg/ml) with advanced Ann Arbor stages. High CCL3 levels correlated with significantly shorter progression-free and overall survival. The in vitro studies demonstrated that activated B cell-like, but not germinal centre B cell-like DLBCL cells, secrete high levels of CCL3 and CCL4 after BCR triggering, which was exquisitely sensitive to BCR pathway inhibition. These findings support CCL3 and CCL4 protein concentrations as biomarkers for BCR pathway activation and prognosis in DLBCL.

Abstract IA08: The microenvironment in CLL: Cellular and molecular players and emerging therapeutic targets

The tissue microenvironment plays an important role of in the pathogenesis of chronic lymphocytic leukemia (CLL), delivering signals that promote the clonal expansion of the malignant B cells, as well as drug resistance. The complex cross talk between neoplastic B cells and the microenvironment, for example in secondary lymphoid organs, has been increasingly well characterized, and several cellular and molecular key players have emerged. Important cells in the CLL microenvironment are monocyte-derived nurselike cells (NLC), mesenchymal stromal cells (MSC), and T cells, which engage in a dialogue with the neoplastic CLL cells, often via specific receptor-ligand pairs. Engagement of CLL surface receptors by ligands in the tissue microenvironment, for example activation of B cell receptor (BCR) signaling, triggering of TNF family members (i.e. BAFF, APRIL), and activation of chemokine receptors and adhesion molecules result in the activation of signaling cascades that support the maintenance and expansion of the CLL clone. BCR signaling plays a particularly important pathogenic role in CLL, based on structural restrictions of the BCR, and signs of BCR-dependent survival and growth of the malignant B cells. Ligand-independent (“autonomous”) and ligand-dependent BCR signaling have been characterized, the latter triggered by (auto-) antigens present in the tissue microenvironment. Based on high response rates and durable remissions in early-stage clinical trials, there is rapid clinical development of inhibitors targeting BCR-associated kinases (BTK, PI3Kδ), which currently are changing treatment paradigms in CLL. Clinical and translational aspects of these new targeted therapeutics will be discussed, along with an outlook into future therapeutic strategies.

Citation Format: Jan A. Burger. The microenvironment in CLL: Cellular and molecular players and emerging therapeutic targets. [abstract]. In: Proceedings of the AACR Special Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(17 Suppl):Abstract nr IA08.

Long-term follow-up of a phase 2 study of chemotherapy plus dasatinib for the initial treatment of patients with Philadelphia chromosome-positive acute lymphoblastic leukemia

BACKGROUND

The long-term efficacy of a combination of chemotherapy and dasatinib in patients with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) is not well established.

METHODS

Patients received dasatinib with 8 cycles of alternating hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone and high-dose cytarabine and methotrexate. Patients in complete remission (CR) continued maintenance dasatinib, vincristine, and prednisone for 2 years, which was followed by dasatinib indefinitely. Patients eligible for allogeneic stem cell transplantation (SCT) received it during their first CR.

RESULTS

Seventy-two patients with a median age of 55 years (range, 21-80 years) were treated; 69 (96%) achieved CR. Among them, 57 (83%) achieved cytogenetic CR after 1 cycle, and 64 (93%) achieved a major molecular response at a median of 4 weeks (range, 2-38 weeks). Sixty-five patients (94%) were negative for minimal residual disease assessed by flow cytometry at a median of 3 weeks (range, 2-37 weeks). Dasatinib-related grade 3 and 4 adverse events included bleeding, pleural/pericardial effusions, and elevated transaminases. With a median follow-up of 67 months (range, 33-97 months), 33 patients (46%) were alive, and 30 (43%) were in CR; 12 underwent allogeneic SCT. Thirty-nine patients died (3 at induction, 19 after relapse, 7 after SCT performed during first CR, and 10 during CR). The median disease-free survival and overall survival were 31 (range, 0.3-97 months) and 47 months (range, 0.2-97 months), respectively. Seven relapsed patients had BCR-ABL kinase domain mutations, including 4 with T315I.

CONCLUSIONS

A combination of chemotherapy with dasatinib is effective in achieving long-term remission for patients with newly diagnosed Ph + ALL.

Regulation of Mcl-1 expression in context to bone marrow stromal microenvironment in chronic lymphocytic leukemia

A growing body of evidence suggests that the resistance of CLL cells to apoptosis is partly mediated through the interactions between leukemia cells and adjacent stromal cells residing in the lymphatic tissue or bone marrow microenvironment. Mcl-1, an anti-apoptotic protein that is associated with failure to treatment is up-regulated in CLL lymphocytes after interaction with microenvironment. However, the regulation of its expression in context to microenvironment is unclear. We evaluated and compared changes in Mcl-1 in CLL B-cells in suspension culture and when co-cultured on stromal cells. The blockade of apoptosis in co-cultured CLL cells is associated with diminution in caspase-3 and PARP cleavage and is not dependent on cytogenetic profile or prognostic factors of the disease. Stroma-derived resistance to apoptosis is associated with a cascade of transcriptional events such as increase in levels of total RNA Pol II and its phosphorylation at Ser2 and Ser5, increase in the rate of global RNA synthesis, and amplification of Mcl-1 transcript levels. The latter is associated with increase in Mcl-1 protein level without an impact on the levels of Bcl-2 and Bcl-xL. Post-translational modifications of protein kinases show increased phosphorylation of Akt at Ser473, Erk at Thr202/Tyr204 and Gsk-3β at Ser9 and augmentation of total Mcl-1 accumulation along with phosphorylation at Ser159/Thr163 sites. Collectively, stroma-induced apoptosis resistance is mediated through signaling proteins that regulate transcriptional and translational expression and post-translational modification of Mcl-1 in CLL cells in context to bone marrow stromal microenvironment.

Abstract 1023: Duration of signaling through IgM and IgD receptors differentially influences cell survival and BCL6-regulated CCL3/4 chemokine production in Chronic Lymphocytic Leukemia (CLL)

B-cell receptor (BCR) signaling is a central pathogenetic mechanism in CLL. Most CLL cells express both IgM and IgD receptors, and increased responsiveness to IgM stimulation correlates with poor disease outcome and with expression of IGHV-unmutated immunoglobulin receptors (U-CLL). In contrast, the relevance of IgD signaling remains poorly understood.

The aim of the present study is to characterize functional differences between IgM and IgD signaling in CLL in terms of protection from in vitro apoptosis, BCR signaling activation and CCL3/4 chemokine secretion and to explore the mechanism through which CCL3/4 are regulated, with a focus on their transcriptional repressor BCL6.

CLL cells were stimulated with anti-IgM and anti-IgD; 48-hour cell viability and BCR expression were analyzed by flow cytometry; phosphorylation of the BCR-signaling related molecules HS1 and ERK after 2, 5, 15, 30, 60 minutes of stimulation were analyzed by Western Blot and flow cytometry; BCL6 protein expression by Western Blot and CCL3/4 secretion by ELISA were tested after 3, 6, 9, 12, 24 hours of stimulation.

Anti-IgM stimulation protected CLL cells from in vitro apoptosis to a greater extent than anti-IgD and U-CLL were more responsive to anti-IgM as compared to cells carrying IGHV-mutated receptors (M-CLL) (p = 0.0022; n = 13 M-CLL vs. n = 11 U-CLL). In line with this finding, U-CLL expressed higher levels of surface IgM, as compared to M-CLL (p&lt;0.0001; n = 40 M-CLL vs. n = 33 U-CLL). IgM stimulation induced protracted HS1 and ERK phosphorylation up to 30 minutes following receptor engagement, as analyzed in 10 M-CLL and 10 U-CLL cases. In contrast, IgD stimulation induced short-lived phosphorylation of both proteins, which rapidly returned to baseline. U-CLL cells were more responsive than M-CLL to both anti-IgM and anti-IgD stimulation. High CCL3/4 secretion was detected after anti-IgM, in particular in U-CLL. Surprisingly low, if any, induction of both chemokines was detected after stimulation of IgD receptors. Interestingly, increased CCL3/4 production and concomitant BCL6 protein downregulation were observed after 6 and up to 12 hours following anti-IgM but not anti-IgD stimulation.

In conclusion, IgM stimulation induces a long-lived signaling response, increased CLL-cell survival and CCL3/4 secretion, in particular in U-CLL; in contrast, IgD signaling is short-lived and has minimal effects on protection from apoptosis and chemokine secretion. BCL6 protein downregulation induced by anti-IgM parallels CCL3/4 production, suggesting a functional link between BCL6 expression and CCL3/4. Taken together, these evidences suggest that the differential functional outcomes of IgM and IgD signaling might be related to the duration of the signaling response and support the relevance of IgM signaling in CLL pathogenesis.

Citation Format: Elisa ten Hacken, Cristina Scielzo, Susan O'Brien, William G. Wierda, Michael J. Keating, Paolo Ghia, Federico Caligaris-Cappio, Jan A. Burger. Duration of signaling through IgM and IgD receptors differentially influences cell survival and BCL6-regulated CCL3/4 chemokine production in Chronic Lymphocytic Leukemia (CLL). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1023. doi:10.1158/1538-7445.AM2015-1023

Ibrutinib: a paradigm shift in management of CLL

B-cell receptor (BCR) signaling plays a vital role in B-cell malignancies; Bruton tyrosine kinase is a critical mediator of this signaling. BCR signaling, either constitutively or following antigen binding, leads to activation of several downstream pathways involved in cell survival, proliferation and migration. The efficacy observed in studies of the Bruton tyrosine kinase inhibitor, ibrutinib, confirms that BCR signaling is critical for the growth of B-cell malignancies. Ibrutinib characteristically induces redistribution of malignant B cells from tissues into the peripheral blood and rapid resolution of adenopathy. Furthermore, ibrutinib therapy results in normalization of lymphocyte counts and improvement in cytopenias. Ibrutinib has been shown to have an excellent safety profile and does not cause myelosuppression. Early data from combination studies of ibrutinib with anti-CD20 monoclonal antibodies have shown more rapid responses compared to those seen with ibrutinib monotherapy. Current data strongly support continued clinical evaluation of ibrutinib in B-cell malignancies.

The phosphoinositide-3-kinase (PI3K)-delta and gamma inhibitor, IPI-145 (Duvelisib), overcomes signals from the PI3K/AKT/S6 pathway and promotes apoptosis in CLL

The functional relevance of the B-cell receptor (BCR) and the evolution of protein kinases as therapeutic targets have recently shifted the paradigm for treatment of B-cell malignancies. Inhibition of p110δ with idelalisib has shown clinical activity in chronic lymphocytic leukemia (CLL). The dynamic interplay of isoforms p110δ and p110γ in leukocytes support the hypothesis that dual blockade may provide a therapeutic benefit. IPI-145, an oral inhibitor of p110δ and p110γ isoforms, sensitizes BCR-stimulated and/or stromal co-cultured primary CLL cells to apoptosis (median 20%, n=57; P<0.0001) including samples with poor prognostic markers, unmutated IgVH (n=28) and prior treatment (n=15; P<0.0001). IPI-145 potently inhibits the CD40L/IL-2/IL-10 induced proliferation of CLL cells with an IC50 in sub-nanomolar range. A corresponding dose-responsive inhibition of pAKT(Ser473) is observed with an IC50 of 0.36 nM. IPI-145 diminishes the BCR-induced chemokines CCL3 and CCL4 secretion to 17% and 37%, respectively. Pre-treatment with 1 μM IPI-145 inhibits the chemotaxis toward CXCL12; reduces pseudoemperipolesis to median 50%, inferring its ability to interfere with homing capabilities of CLL cells. BCR-activated signaling proteins AKT(Ser473), BAD(Ser112), ERK(Thr202/Tyr204) and S6(Ser235/236) are mitigated by IPI-145. Importantly, for clinical development in hematological malignancies, IPI-145 is selective to CLL B cells, sparing normal B- and T-lymphocytes.

Outcomes of Patients With Chronic Lymphocytic Leukemia and Richter's Transformation After Transplantation Failure

PURPOSE

Allogeneic stem-cell transplantation (SCT) induces long-term remission in a fraction of patients with high-risk chronic lymphocytic leukemia (CLL) or Richter's transformation (RT). Our purpose was to determine the outcomes of patients whose disease progressed after allogeneic SCT.

PATIENTS AND METHODS

We retrospectively analyzed the outcomes of 72 patients (52 with CLL and 20 with RT) who underwent allogeneic SCT between 1998 and 2011 and had documented progression after transplantation. Twenty-two (31%) never had a response, and 50 (69%) had a response but experienced relapse after a median of 7 months (range, 2 to 85 months). Forty-eight patients who were receiving or were candidates to receive post-SCT cell-based therapies were not included in this analysis.

RESULTS

The median age at time of transplantation was 58 years (range, 30 to 72 years). Sixty-two patients (86%) received more than two treatment regimens and 37 (51%) received more than three treatment regimens before SCT. Sixty-six patients (92%) had active disease at the time of transplantation. The 2- and 5-year survival rates were 67% and 38% (patients with CLL) and 36% and 0% (patients with RT). The patients who developed acute or chronic graft-versus-host disease had a longer overall survival (OS; P = .05). In a multivariable analysis, RT or low hemoglobin at the time of SCT predicted shorter OS. Chronic graft-versus-host disease and an initial response to SCT predicted longer OS.

CONCLUSION

Patients with CLL in whom allogeneic SCT fails may have a response to and benefit from salvage therapies, and their prognosis is relatively good.

Self-enforcing feedback activation between BCL6 and pre-B cell receptor signaling defines a distinct subtype of acute lymphoblastic leukemia

Studying 830 pre-B ALL cases from four clinical trials, we found that human ALL can be divided into two fundamentally distinct subtypes based on pre-BCR function. While absent in the majority of ALL cases, tonic pre-BCR signaling was found in 112 cases (13.5%). In these cases, tonic pre-BCR signaling induced activation of BCL6, which in turn increased pre-BCR signaling output at the transcriptional level. Interestingly, inhibition of pre-BCR-related tyrosine kinases reduced constitutive BCL6 expression and selectively killed patient-derived pre-BCR(+) ALL cells. These findings identify a genetically and phenotypically distinct subset of human ALL that critically depends on tonic pre-BCR signaling. In vivo treatment studies suggested that pre-BCR tyrosine kinase inhibitors are useful for the treatment of patients with pre-BCR(+) ALL.

Microenvironment dependency in Chronic Lymphocytic Leukemia: The basis for new targeted therapies

Chronic Lymphocytic Leukemia (CLL) is a prototype microenvironment-dependent B-cell malignancy, in which the neoplastic B cells co-evolve together with a supportive tissue microenvironment, which promotes leukemia cell survival, growth, and drug-resistance. Chemo-immunotherapy is an established treatment modality for CLL patients, resulting in high rates of responses and improved survival, especially in low-risk CLL. New, alternative treatments target B-cell receptor (BCR) signaling and the Chemokine (C-X-C motif) Receptor 4 (CXCR4)-Chemokine (C-X-C motif) Ligand 12 (CXCL12) axis, which are key pathways of CLL-microenvironment cross talk. The remarkable clinical efficacy of inhibitors targeting the BCR-associated kinases Bruton's tyrosine kinase (BTK) and phosphoinositide 3-kinase delta (PI3Kδ) challenges established therapeutic paradigms and corroborates the central role of BCR signaling in CLL pathogenesis. In this review, we discuss the cellular and molecular components of the CLL microenvironment. We also describe the emerging therapeutic options for CLL patients, with a focus on inhibitors of CXCR4-CXCL12 and BCR signaling.

Abstract 4881: Targeting the CXCR4 chemokine receptor thwarts stromal cell mediated drug resistance in B-cell acute lymphoblastic leukemia (B-ALL)

CXCR4 inhibitors Plerixafor (small molecule) and BKT140 (peptide) interfere with CXCR4 activation, signaling and bone marrow homing of leukemia cells. Adhesion of B-ALL cells to bone marrow stromal cells (BMSC) through CXCR4/CXCL12 protects leukemia cells from cytotoxic drugs, and causes cell adhesion-mediated drug resistance (CAM-DR). Due to the critical role of the CXCR4/CXCL12 axis in B-ALL cell adhesion to bone marrow stromal cells (BMSC), we hypothesize that targeting CXCR4 will attenuate CAM-DR in B-ALL.

All tested B-ALL cell lines and xenografts were found to be positive for surface expression of CXCR4, using 12G5 mAbs. Pre-treatment with Plerixafor (10μg/ml) or BKT140 (10μg/ml) significantly inhibited the spontaneous migration of B-ALL cells beneath BMSCs in vitro (Pseudoemperipolesis/PEP) to levels that were 61.4 ± 3.3% or 53.2 ± 5.6%, of respective controls (mean ± SEM, p&lt;0.05). B-ALL cell line and xenograft B-ALL cell chemotaxis towards CXCL12 (100ng/ml) was also abrogated by pre-incubation with 10μg/ml Plerixafor (mean ± SEM, 26.7 ± 4.9% of control, p&lt;0.05) and 10μg/ml BKT140 (mean ± SEM, 18.3 ± 4.7% of control, p&lt;0.05). In order to better dissect CXCR4 function in B-ALL, we established two CXCR4 knock out cell lines, TANOUE-CXCR4-KO and NALM6-CXCR4-KO, using Zinc Finger Nuclease and CRISPR Cas9 technologies respectively. Chemotaxis to 100ng/ml CXCL12 and PEP beneath BMSCs for TANOUE-CXCR4-KO was 10.3 ± 0.48%, n=3 (p&lt;0.05) and 50.06 ± 2.5%, n=4 (p&lt;0.05) respectively, in comparison to TANOUE wild type control without any drug treatment. For NALM6-CXCR4-KO chemotaxis and PEP was 43.1%, n=1 and 41.8 ± 1.9%, n=4 (p&lt;0.05) respectively in comparison to NALM6 wild type control without any drug treatment.

CAM-DR experiments with ICN12 xenograft-BMSC co-culture showed significantly enhanced cytotoxicity when cells were treated with a combination of 100nM Dexamethasone (DEX) and 10μg/ml Plerixafor (66.1 ± 5.6% viability, n=3, p&lt;0.05) or 10μg/ml BKT140 (59.7 ± 6.07% viability, n=3, p&lt;0.05) as compared to DEX alone (87.3 ± 2.6% viability) at 48 hours. Similarly, pre-incubation of NALM6 cells with 10μg/ml Plerixafor/BKT140 showed significantly enhanced cytotoxicity (57.93±3.26%, n=3, p&lt;0.05 and 54.2±3.26%, n=3, p&lt;0.05 respectively) in comparison to DEX alone (72.38±0.25%, n=3). BMSCs rescued NALM6 cells from DEX induced cytotoxicity but failed to rescue NALM6-CXCR4-KO cells indicating that CXCR4 is the central mechanism used by stromal cells to provide drug resistance to ALL cells. Collectively, these findings provide a rationale for clinical targeting of CXCR4 in patients with B-ALL.

Citation Format: Shubhchintan Randhawa, Dipanjan Ghosh, Amnon Peled, Richard E. Davis, Jan A. Burger. Targeting the CXCR4 chemokine receptor thwarts stromal cell mediated drug resistance in B-cell acute lymphoblastic leukemia (B-ALL). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4881. doi:10.1158/1538-7445.AM2014-4881

Safety and activity of ibrutinib plus rituximab for patients with high-risk chronic lymphocytic leukaemia: a single-arm, phase 2 study

BACKGROUND

Ibrutinib, an orally administered covalent inhibitor of Bruton's tyrosine kinase (BTK), is an effective treatment for relapsed chronic lymphocytic leukaemia (CLL). We investigated the activity and safety of the combination of ibrutinib with the monoclonal antibody rituximab in patients with high-risk CLL.

METHODS

In this single-arm phase 2 study, we enrolled adult patients with high-risk CLL at the MD Anderson Cancer Center (Houston, TX, USA). All enrolled participants had high-risk cytogenetic abnormalities (deletion 17p, TP53 mutation, or deletion 11q) or a short progression-free survival (PFS <36 months) after previous first-line chemoimmunotherapy. Patients with symptomatic disease requiring therapy received 28-day cycles of once-daily ibrutinib 420 mg together with rituximab (375 mg/m(2), intravenously, every week during cycle 1, then once per cycle until cycle 6), followed by continuous daily single-agent ibrutinib 420 mg until disease progression or until toxicities or complications precluded further treatment. The primary endpoint was progression-free survival in the intention-to-treat population. This study is registered with ClinicalTrials.gov number NCT01520519, and is no longer accruing patients.

FINDINGS

Between Feb 28, 2012, and Sept 11, 2012, we enrolled 40 patients with CLL with high-risk disease features, 20 of whom had deletion 17p (del[17p]) or TP53 mutations (16 previously treated, four untreated), 13 had relapsed CLL with deletion 11q (del[11q]), and seven a PFS less than 36 months after first-line chemoimmunotherapy. 18-month PFS in all patients was 78·0% (95% CI 60·6-88·5), whereas in those with a del(17p) or TP53 mutation it was 72·4% (45·6-87·6) Toxicity was mainly mild to moderate in severity (grade 1-2). Diarrhoea occurred in ten (25%) patients (grade 1 in nine patients and grade 2 in one), bleeding events in 14 (33%) patients (eight grade 1 and five grade 2), nausea or vomiting in 15 patients (38%) (ten grade 1 and five grade 2), and fatigue in seven (18%) patients (four grade 1 and three grade 2). Five patients (13%) had grade 3 infections (two lung infections, one upper respiratory tract infection, one sepsis, and one mucositis), and no grade 4 or 5 infections occurred. One patient had grade 4 neutropenia.

INTERPRETATION

The encouraging safety and activity of ibrutinib and rituximab in this population of patients with high-risk CLL merits further investigation of this combination.

FUNDING

Pharmacyclics Inc, Cancer Prevention and Research Institute of Texas, Leukemia and Lymphoma Society, National Cancer Institute, MD Anderson Cancer Center.

The bruton tyrosine kinase inhibitor ibrutinib (PCI-32765) blocks hairy cell leukaemia survival, proliferation and B cell receptor signalling: a new therapeutic approach

B cell receptor (BCR) signalling plays a critical role in the progression of several B-cell malignancies, but its role in hairy cell leukaemia (HCL) is ambiguous. Bruton tyrosine kinase (BTK), a key player in BCR signalling, as well as B cell migration and adhesion, can be targeted with ibrutinib, a selective, irreversible BTK inhibitor. We analysed BTK expression and function in HCL and analysed the effects of ibrutinib on HCL cells. We demonstrated uniform BTK protein expression in HCL cells. Ibrutinib significantly inhibited HCL proliferation and cell cycle progression. Accordingly, ibrutinib also reduced HCL cell survival after BCR triggering with anti-immunoglobulins and abrogated the activation of kinases downstream of the BCR (PI3K and MAPK). Ibrutinib also inhibited BCR-dependent secretion of the chemokines CCL3 and CCL4 by HCL cells. Interestingly, ibrutinib inhibited also CXCL12-induced signalling, a key pathway for bone marrow homing. Collectively, our data support the clinical development of ibrutinib in patients with HCL.

Bruton's tyrosine kinase: from X-linked agammaglobulinemia toward targeted therapy for B-cell malignancies

Discovery of Bruton's tyrosine kinase (BTK) mutations as the cause for X-linked agammaglobulinemia was a milestone in understanding the genetic basis of primary immunodeficiencies. Since then, studies have highlighted the critical role of this enzyme in B-cell development and function, and particularly in B-cell receptor signaling. Because its deletion affects mostly B cells, BTK has become an attractive therapeutic target in autoimmune disorders and B-cell malignancies. Ibrutinib (PCI-32765) is the most advanced BTK inhibitor in clinical testing, with ongoing phase III clinical trials in patients with chronic lymphocytic leukemia and mantle-cell lymphoma. In this article, we discuss key discoveries related to BTK and clinically relevant aspects of BTK inhibitors, and we provide an outlook into clinical development and open questions regarding BTK inhibitor therapy.

Preclinical and early clinical evaluation of the oral AKT inhibitor, MK-2206, for the treatment of acute myelogenous leukemia

PURPOSE

Recent studies suggested that AKT activation might confer poor prognosis in acute myelogenous leukemia (AML), providing the rationale for therapeutic targeting of this signaling pathway. We, therefore, explored the preclinical and clinical anti-AML activity of an oral AKT inhibitor, MK-2206. Experimental Methods: We first studied the effects of MK-2206 in human AML cell lines and primary AML specimens in vitro. Subsequently, we conducted a phase II trial of MK-2206 (200 mg weekly) in adults requiring second salvage therapy for relapsed/refractory AML, and assessed target inhibition via reverse phase protein array (RPPA).

RESULTS

In preclinical studies, MK-2206 dose-dependently inhibited growth and induced apoptosis in AML cell lines and primary AML blasts. We then treated 19 patients with MK-2206 but, among 18 evaluable participants, observed only 1 (95% confidence interval, 0%-17%) response (complete remission with incomplete platelet count recovery), leading to early study termination. The most common grade 3/4 drug-related toxicity was a pruritic rash in 6 of 18 patients. Nevertheless, despite the use of MK-2206 at maximum tolerated doses, RPPA analyses indicated only modest decreases in Ser473 AKT (median 28%; range, 12%-45%) and limited inhibition of downstream targets.

CONCLUSIONS

Although preclinical activity of MK-2206 can be demonstrated, this inhibitor has insufficient clinical antileukemia activity when given alone at tolerated doses, and alternative approaches to block AKT signaling should be explored.

CD49d is the strongest flow cytometry-based predictor of overall survival in chronic lymphocytic leukemia

PURPOSE

Although CD49d is an unfavorable prognostic marker in chronic lymphocytic leukemia (CLL), definitive validation evidence is lacking. A worldwide multicenter analysis was performed using published and unpublished CLL series to evaluate the impact of CD49d as an overall (OS) and treatment-free survival (TFS) predictor.

PATIENTS AND METHODS

A training/validation strategy was chosen to find the optimal CD49d cutoff. The hazard ratio (HR) for death and treatment imposed by CD49d was estimated by pooled analysis of 2,972 CLLs; Cox analysis stratified by center and stage was used to adjust for confounding variables. The importance of CD49d over other flow cytometry-based prognosticators (eg, CD38, ZAP-70) was ranked by recursive partitioning.

RESULTS

Patients with ≥ 30% of neoplastic cells expressing CD49d were considered CD49d+. Decrease in OS at 5 and 10 years among CD49d+ patients was 7% and 23% (decrease in TFS, 26% and 25%, respectively). Pooled HR of CD49d for OS was 2.5 (2.3 for TFS) in univariate analysis. This HR remained significant and of similar magnitude (HR, 2.0) in a Cox model adjusted for clinical and biologic prognosticators. Hierarchic trees including all patients or restricted to those with early-stage disease or those age ≤ 65 years always selected CD49d as the most important flow cytometry-based biomarker, with negligible additional prognostic information added by CD38 or ZAP-70. Consistently, by bivariate analysis, CD49d reliably identified patient subsets with poorer outcome independent of CD38 and ZAP-70.

CONCLUSION

In this analysis of approximately 3,000 patients, CD49d emerged as the strongest flow cytometry-based predictor of OS and TFS in CLL.

The microenvironment in chronic lymphocytic leukemia (CLL) and other B cell malignancies: insight into disease biology and new targeted therapies

Over the last decade, the active role of the microenvironment in the pathogenesis of B cell lymphomas has been recognized, delivering signals that favor clonal expansion and drug resistance. We are only beginning to understand the complex cross talk between neoplastic B cells and the tissue microenvironment, for example in secondary lymphoid organs, but some key cellular and molecular players have emerged. Mesenchymal stromal cells, nurselike cells (NLC) and lymphoma-associated macrophages (LAM), in concert with T cells, natural killer cells and extracellular matrix components participate in the dialog with the neoplastic B cells. B cell receptor signaling, activation via TNF family members (i.e. BAFF, APRIL), and tissue homing chemokine receptors and adhesion molecules are important in the interaction between malignant B cells and their microenvironment. Disrupting this cross talk is an attractive novel strategy for treating patients with B cell malignancies. Here, we summarize the cellular and molecular interactions between B cell lymphoma/leukemia cells and their microenvironment, and the therapeutic targets that are emerging, focusing on small molecule inhibitors that are targeting B cell receptor-associated kinases SYK, BTK, and PI3Ks, as well as on immunomodulatory agents and T cell mediated therapies. Clinically relevant aspects of new targeted therapeutics will be discussed, along with an outlook into future therapeutic strategies.