Phase I study of a novel oral Janus kinase 2 inhibitor, SB1518, in patients with relapsed lymphoma: evidence of clinical and biologic activity in multiple lymphoma subtypes

Genetic methylation and lymphoid malignancies: biomarkers of tumor progression and targeted therapy

Lymphoid malignancies, mainly including lymphocytic leukemia and lymphoma, are a group of heterogeneous diseases. Although the clinical outcome of patients has been significantly improved with current immuno-chemotherapy, definitive biomarkers remain to be investigated, particularly those reflecting the malignant behavior of tumor cells and those helpful for developing optimal targeted therapy. Recently, genome-wide analysis reveals that altered genetic methylations play an important role in tumor progression through regulation of multiple cellular transduction pathways. This review describes the pathogenetic effect of the aberrant genetic methylation in lymphoid malignancies, with special emphasis on potential therapeutic strategies targeting key signaling networks.

New strategies in Hodgkin lymphoma: better risk profiling and novel treatments

Recent advances in Hodgkin lymphoma research are expected to prelude a promising new treatment era for patients and their treating physicians. Scientific investigations over the last few years have provided new insights into risk stratification, and, simultaneously, a plethora of novel targeted therapies are emerging for patients with relapsed and refractory disease. These novel therapies will be tested primarily in high-risk patients because 75% of the patients are cured with conventional therapies. The challenges, as Hodgkin lymphoma therapy moves forward, will be using these biologic insights to identify the patients who may benefit earlier in treatment from these novel agents, and tailoring the therapy to the tumor biology of the patient. These dual aims are intertwined; as our therapeutic arsenal increases, these biologic determinants of risk may themselves inform the design of therapies and the choice of treatments for high-risk patients.

Targeting oncogenic and epigenetic survival pathways in lymphoma

In recent years, several genetic and epigenetic alterations have been identified and linked with deregulated signaling pathways that promote growth and survival of lymphoma cells. These discoveries have raised hopes that a new era of targeted therapy will eventually improve treatment outcome of lymphoma. In this focused review, we summarize emerging preclinical and clinical data supporting the development of novel agents targeting B cell receptor signaling, phosphoinositol-3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) and Janus kinase/signal transducer and activator of transcription (JAK/STAT) oncogenic pathways. Furthermore, we discuss new data on targeting chromatin modulating mechanisms.

Leveraging cancer genome information in hematologic malignancies

The use of candidate gene and genome-wide discovery studies in the last several years has led to an expansion of our knowledge of the spectrum of recurrent, somatic disease alleles, which contribute to the pathogenesis of hematologic malignancies. Notably, these studies have also begun to fundamentally change our ability to develop informative prognostic schema that inform outcome and therapeutic response, yielding substantive insights into mechanisms of hematopoietic transformation in different tissue compartments. Although these studies have already had important biologic and translational impact, significant challenges remain in systematically applying these findings to clinical decision making and in implementing new technologies for genetic analysis into clinical practice to inform real-time decision making. Here, we review recent major genetic advances in myeloid and lymphoid malignancies, the impact of these findings on prognostic models, our understanding of disease initiation and evolution, and the implication of genomic discoveries on clinical decision making. Finally, we discuss general concepts in genetic modeling and the current state-of-the-art technology used in genetic investigation.

Molecular pathways: Jak/STAT pathway: mutations, inhibitors, and resistance

Aberrant activation of the JAK/STAT pathway has been reported in a variety of disease states, including inflammatory conditions, hematologic malignancies, and solid tumors. For instance, a large proportion of patients with myeloproliferative neoplasms (MPN) carry the acquired gain-of-function JAK2 V617F somatic mutation. This knowledge has dramatically improved our understanding of the pathogenesis of MPNs and has facilitated the development of therapeutics capable of suppressing the constitutive activation of the JAK/STAT pathway, now recognized as a common underlying biologic abnormality in MPNs. Ruxolitinib is an oral JAK1 and JAK2 inhibitor that has recently been approved for the treatment of myelofibrosis and has been tested against other hematologic malignancies. A series of agents with different specificities against different members of the JAK family of proteins is currently undergoing evaluation in clinical trials for patients with MPNs, lymphoma, and solid tumors such as breast or pancreatic cancer. Despite the significant clinical activity exhibited by these agents in myelofibrosis, some patients fail to respond or progress during JAK kinase inhibitor therapy. Recent reports have shed light into the mechanisms of resistance to JAK inhibitor therapy. Several approaches hold promise to overcome such resistance.

Targeting the JAK-STAT pathway in lymphoma: a focus on pacritinib

INTRODUCTION

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway mediates signaling by cytokine, chemokine and growth factor receptors on cell surface to the nucleus. JAK/STAT pathway is aberrantly activated in a variety of lymphomas, with a dual role of promoting cell survival/proliferation and immune evasion.

AREAS COVERED

This review describes the preclinical rationale behind the development of JAK inhibitors in lymphoma, some of which are being evaluated in Phase I/II studies, and summarizes the characteristics and clinical results of different JAK inhibitors in clinical development. Available preclinical and clinical data about JAK inhibition in lymphoid malignancies were reviewed using a PubMed access. To date, pacritinib (SB1518), a selective JAK2/FLT3 inhibitor is the first and only JAK inhibitor that has been evaluated in patients with relapsed lymphoma.

EXPERT OPINION

The preclinical rationale behind the development of pacritinib in lymphoproliferative neoplasms is strong, as the deregulation of the JAK/STAT pathway is involved in the pathogenesis of multiple lymphoma subtypes, although with different mechanisms. Pacritinib demonstrated safety and early clinical efficacy in a variety of lymphoma histologic types, providing the first proof of principle of the potential clinical value of targeting JAK/STAT pathway in lymphoma.

Dysregulation of JAK-STAT pathway in hematological malignancies and JAK inhibitors for clinical application

JAK-STAT (Janus associated kinase-signal transducer and activator of transcription) pathway plays a critical role in transduction of extracellular signals from cytokines and growth factors involved in hematopoiesis, immune regulation, fertility, lactation, growth and embryogenesis. JAK family contains four cytoplasmic tyrosine kinases, JAK1-3 and Tyk2. Seven STAT proteins have been identified in human cells, STAT1-6, including STAT5a and STAT5b. Negative regulators of JAK-STAT pathways include tyrosine phosphatases (SHP1 and 2, CD45), protein inhibitors of activated STATs (PIAS), suppressors of cytokine signaling (SOCS) proteins, and cytokine-inducible SH2-containing protein (CIS). Dysregulation of JAK-STAT pathway have been found to be key events in a variety of hematological malignancies. JAK inhibitors are among the first successful agents reaching clinical application. Ruxolitinib (Jakafi), a non-selective inhibitor of JAK1 & 2, has been approved by FDA for patients with intermediate to high risk primary or secondary myelofibrosis. This review will also summarize early data on selective JAK inhibitors, including SAR302503 (TG101348), lestaurtinib (CEP701), CYT387, SB1518 (pacritinib), LY2784544, XL019, BMS-911543, NS-018, and AZD1480.

Phospho-specific flow cytometry identifies aberrant signaling in indolent B-cell lymphoma

Background

Knowledge about signaling pathways in malignant cells may provide prognostic and diagnostic information in addition to identify potential molecular targets for therapy. B-cell receptor (BCR) and co-receptor CD40 signaling is essential for normal B cells, and there is increasing evidence that signaling via BCR and CD40 plays an important role in the pathogenesis of B-cell lymphoma. The aim of this study was to investigate basal and induced signaling in lymphoma B cells and infiltrating T cells in single-cell suspensions of biopsies from small cell lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL) and marginal zone lymphoma (MZL) patients.

Methods

Samples from untreated SLL/CLL and MZL patients were examined for basal and activation induced signaling by phospho-specific flow cytometry. A panel of 9 stimulation conditions targeting B and T cells, including crosslinking of the B cell receptor (BCR), CD40 ligand and interleukins in combination with 12 matching phospho-protein readouts was used to study signaling.

Results

Malignant B cells from SLL/CLL patients had higher basal levels of phosphorylated (p)-SFKs, p-PLCγ, p-ERK, p-p38, p-p65 (NF-κB), p-STAT5 and p-STAT6, compared to healthy donor B cells. In contrast, anti-BCR induced signaling was highly impaired in SLL/CLL and MZL B cells as determined by low p-SFK, p-SYK and p-PLCγ levels. Impaired anti-BCR-induced p-PLCγ was associated with reduced surface expression of IgM and CD79b. Similarly, CD40L-induced p-ERK and p-p38 were also significantly reduced in lymphoma B cells, whereas p-p65 (NF-κB) was equal to that of normal B cells. In contrast, IL-2, IL-7 and IL-15 induced p-STAT5 in tumor-infiltrating T cells were not different from normal T cells.

Conclusions

BCR signaling and CD40L-induced p-p38 was suppressed in malignant B cells from SLL/CLL and MZL patients. Single-cell phospho-specific flow cytometry for detection of basal as well as activation-induced phosphorylation of signaling proteins in distinct cell populations can be used to identify aberrant signaling pathways.

Molecular pathogenesis of mantle cell lymphoma

Mantle cell lymphoma is a B cell malignancy in which constitutive dysregulation of cyclin D1 and the cell cycle, disruption of DNA damage response pathways, and activation of cell survival mechanisms contribute to oncogenesis. A small number of tumors lack cyclin D1 overexpression, suggesting that its dysregulation is always not required for tumor initiation. Some cases have hypermutated IGHV and stable karyotypes, a predominant nonnodal disease, and an indolent clinical evolution, which suggests that they may correspond to distinct subtypes of the disease. In this review, we discuss the molecular pathways that contribute to pathogenesis, and how improved understanding of these molecular mechanisms offers new perspectives for the treatment of patients.

Novel therapies for aggressive B-cell lymphoma

Aggressive B-cell lymphoma (BCL) comprises a heterogeneous group of malignancies, including diffuse large B-cell lymphoma (DLBCL), Burkitt lymphoma, and mantle cell lymphoma (MCL). DLBCL, with its 3 subtypes, is the most common type of lymphoma. Advances in chemoimmunotherapy have substantially improved disease control. However, depending on the subtype, patients with DLBCL still exhibit substantially different survival rates. In MCL, a mature B-cell lymphoma, the addition of rituximab to conventional chemotherapy regimens has increased response rates, but not survival. Burkitt lymphoma, the most aggressive BCL, is characterized by a high proliferative index and requires more intensive chemotherapy regimens than DLBCL. Hence, there is a need for more effective therapies for all three diseases. Increased understanding of the molecular features of aggressive BCL has led to the development of a range of novel therapies, many of which target the tumor in a tailored manner and are summarized in this paper.

Molecular targeted approaches in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a malignancy of mature B cells characterized by the translocation t(11;14) that leads to aberrant expression of cyclin D1. Response to first-line chemotherapy is good, but most patients relapse, resulting in a median survival of 5 to 7 years. The important PI3K/AKT/mTOR pathway can be targeted with small molecules. mTOR inhibitors have clinical activity and temsirolimus has been approved in Europe. Second-generation mTOR inhibitors and the PI3K inhibitor CAL-101 offer additional means to target the pathway. Promising results with the BTK inhibitor PCI-32765 suggest that B-cell receptor signaling could play a role. For unknown reasons, MCL appears to be particularly sensitive to disruption of protein homeostasis. The proteasome inhibitor bortezomib achieves responses in up to 50% of relapsed patients. Much work has been done in elucidating the mechanism of its cytotoxicity, its incorporation into combination therapies, and the development of second-generation proteasome inhibitors. Deacetylase and HSP90 inhibitors are also promising classes of drugs that can synergize with proteasome inhibitors. Finally, BH3 mimetics are emerging as tools to sensitize tumor cells to chemotherapy. Participation in clinical trials offers patients an immediate chance to benefit from these advances and is essential to maintain the momentum of progress.

Pacritinib (SB1518), a JAK2/FLT3 inhibitor for the treatment of acute myeloid leukemia

FMS-like tyrosine kinase 3 (FLT3) is the most commonly mutated gene found in acute myeloid leukemia (AML) patients and its activating mutations have been proven to be a negative prognostic marker for clinical outcome. Pacritinib (SB1518) is a tyrosine kinase inhibitor (TKI) with equipotent activity against FLT3 (IC₅₀=22 n) and Janus kinase 2 (JAK2, IC₅₀=23 n). Pacritinib inhibits FLT3 phosphorylation and downstream STAT, MAPK and PI3 K signaling in FLT3-internal-tandem duplication (ITD), FLT3-wt cells and primary AML blast cells. Oral administration of pacritinib in murine models of FLT3-ITD-driven AML led to significant inhibition of primary tumor growth and lung metastasis. Upregulation of JAK2 in FLT3-TKI-resistant AML cells was identified as a potential mechanism of resistance to selective FLT3 inhibition. This resistance could be overcome by the combined FLT3 and JAK2 activities of pacritinib in this cellular model. Our findings provide a rationale for the clinical evaluation of pacritinib in AML including patients resistant to FLT3-TKI therapy.

New molecular targets in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a malignancy of mature B cells characterized by aberrant expression of cyclin D1 due to the translocation t(11;14). Epigenomic and genomic lesions in pathways regulating B-cell activation, cell cycle progression, protein homeostasis, DNA damage response, cell proliferation and apoptosis contribute to its pathogenesis. While patients typically respond to first-line chemotherapy, relapse is the rule resulting in a median survival of 5-7 years. The PI3K/AKT/mTOR appears as a key pathway in the pathogenesis and can be targeted with small molecules. Most experience is with mTOR inhibitors of the rapamycin class. Second-generation mTOR inhibitors and the PI3K inhibitor CAL-101 are novel options to more effectively target this pathway. Bruton's tyrosine kinase inhibition by PCI-32765 has promising activity and indicates immunoreceptor signaling as a novel therapeutic target. Up to 50% of relapsed patients respond to the proteasome inhibitor bortezomib suggesting that MCL may be particularly sensitive to disruption of protein homeostasis and/or induction of oxidative stress. Recent work has focused on elucidating the mechanism of bortezomib-induced cytotoxicity and the development of second-generation proteasome inhibitors. DNA hypomethylating agents and histone deacetylase inhibitors effect epigenetic de-repression of aberrantly silenced genes. These epigenetic pharmaceuticals and HSP90 inhibitors can synergize with proteasome inhibitors. Finally, BH3 mimetics are emerging as tools to sensitize tumor cells to chemotherapy. Participation in clinical trials offers patients a chance to benefit from these advances and is essential to maintain the momentum of progress. Innovative trial designs may be needed to expedite the clinical development of these targeted agents.

Predicting treatment outcome in classical Hodgkin lymphoma: genomic advances

Classical Hodgkin lymphoma is considered a highly curable disease; however, 20% of patients cannot be cured with standard first-line chemotherapy and have a dismal outcome. Current clinical parameters do not allow accurate risk stratification, and personalized therapies are lacking. In fact, Hodgkin lymphoma (HL) is often over- or undertreated because of this lack of accurate risk stratification. In recent years, the early detection of chemoresistance by fluorodeoxyglucose positron emission tomography has become the most important prognostic tool in the management of HL. However, to date, no prognostic scores or molecular markers are available for the early identification of patients at very high risk of failure of induction therapy. In the last decade, many important advances have been made in understanding the biology of HL. In particular, the development of new molecular profiling technologies, such as SNP arrays, comparative genomic hybridization, and gene-expression profiling, have allowed the identification of new prognostic factors that may be useful for risk stratification and predicting response to chemotherapy. In this review, we focus on the prognostic tools and biomarkers that are available for newly diagnosed HL, and we highlight recent advances in the genomic characterization of classical HL and potential targets for therapy.

Lestaurtinib inhibition of the Jak/STAT signaling pathway in hodgkin lymphoma inhibits proliferation and induces apoptosis

Standard cytotoxic chemotherapy for Hodgkin Lymphoma (HL) has changed little in 30 years; the treatment for patients with relapsed or refractory disease remains challenging and novel agents are under development. JAK/STAT constitutive activation plays an important role in the pathogenesis of HL. Lestaurtinib is an orally bioavailable multikinase inhibitor that has recently been shown to inhibit JAK2 in myeloproliferative disorders. The potential role of Lestaurtinib in HL therapy is unknown. We have analyzed the effect of Lestaurtinib treatment in five HL cell lines from refractory patients, L-428, L-1236, L-540, HDML-2 and HD-MY-Z. At 48 h, a dose-dependent cell growth inhibition (23%–66% at 300 nM) and apoptotic increment (10%–64% at 300 nM) were observed. Moreover, Lestaurtinib inhibited JAK2, STAT5 and STAT3 phosphorylation and reduced the mRNA expression of its downstream antiapoptotic target Bcl-xL. In addition, we have analyzed the effect of Lestaurtinib treatment in lymph nodes from four classic HL patients. We observed a decrease in cell viability at 24 hours of treatment in three patients (mean decrease of 27% at 300 nM). Our findings provide, for the first time, a molecular rationale for testing JAK2 inhibitors, specifically Lestaurtinib, in HL patients.

Beyond chemotherapy: new agents for targeted treatment of lymphoma

An improved understanding of the molecular biology of cancer cell growth and survival and the role of the microenvironment in supporting the survival of cancer cells, including lymphoma cells, has led to the identification of a number of potential therapeutic targets. Despite these advances, drug development for lymphoma remains slow, inefficient, and frequently unfocused. Future work should focus on identifying 'driver' molecular defects of oncogenic pathways that can be targeted therapeutically, discovering predictive biomarkers for treatment response, and prioritizing promising drugs to accelerate their approval. This Review summarizes the current development status of novel agents for lymphoma and discusses strategies to move the field forward.