Janus kinase inhibition by ruxolitinib extends dasatinib- and dexamethasone-induced remissions in a mouse model of Ph+ ALL

DEX-Induced SREBF1 Promotes BMSCs Differentiation into Adipocytes to Attract and Protect Residual T-Cell Acute Lymphoblastic Leukemia Cells After Chemotherapy

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignant blood disorder with a high rate of relapse. Patients relapse as a result of minimal residual disease (MRD), which originates from residual T-ALL cells in the bone marrow microenvironment (BMM). In the present study, it is observed that adipocytes increase dramatically in the BMM of T-ALL patients after exposure to chemotherapeutic drugs. Then, it is proved that adipocytes attract T-ALL cells by releasing CXCL13 and support leukemia cell survival by activating the Notch1 signaling pathway via DLL1 and Notch1 binding. Furthermore, it is verified that dexamethasone (DEX) induces adipogenic differentiation by enhancing the expression of SREBF1 in bone marrow mesenchymal stromal cells (BMSCs), and an SREBF1 inhibitor significantly decreases the adipogenic potential of BMSCs and the subsequent ability of adipocytes to support T-ALL cells in vitro and in vivo. These findings confirm that the differentiation of BMSCs to adipocytes induced by DEX contributes to MRD in T-ALL and provides an auxiliary clinical treatment to reduce the recurrence rate.

Puppet masters of B-cell progenitor acute lymphoblastic leukemia: The preB cell receptor and the interleukin 7 receptor α

B-cell progenitor acute lymphoblastic leukemia (BCP-ALL) is enriched for a preB cell phenotype, hinting at a specific vulnerability of this cell stage. Two signaling pathways via the preB cell receptor (preBCR) and the interleukin 7 receptor α (IL-7Rα) chain govern the balance between differentiation and proliferation at this stage and both receptor pathways are routinely altered in human BCP-ALL. Here, we review the immunobiology of both the preBCR as well as the IL-7Rα and analyze the human BCP-ALL spectrum in the light of these signaling complexes. Finally, we present a terminology for preBCR signaling modules that distinguishes a pro-proliferative "phase-I" module from a pro-differentiative "phase-II" module. This terminology might serve as a framework to better address shared oncogenic mechanics of preB cell stage BCP-ALL.

Combined inhibition of BCR-ABL1 and the proteasome as a potential novel therapeutic approach in BCR-ABL positive acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a disease of lymphoid progenitor cells with an often aggressive course and is commonly caused by the BCR-ABL fusion gene t(9;22) in adults. This fusion gene encodes a constitutively active tyrosine kinase that can be effectively inhibited by tyrosine kinase inhibitors (TKIs), with imatinib being the paradigmatic agent of this class. However, BCR-ABL+ ALL cells rapidly develop mutations against many of the available TKIs, and consecutive disease relapse still results in an overall unfavorable prognosis for patients with this disease. To date, allogeneic stem cell transplantation is the only known curative therapeutic option for the mostly elderly patients with BCR-ABL+ ALL. The discrepancy between the limited therapeutic armamentarium and the growing therapeutic need in an aging population is therefore a reason to test drug combinations against BCR-ABL+ ALL. In this study, we demonstrate that the combination of TKIs with proteasome inhibitors efficiently and under certain conditions synergistically exerts cytotoxic effects in BCR-ABL+ ALL cells in vitro with respect to the induction of apoptosis. Both sole and combined treatment of BCR-ABL+ ALL with the proteasome inhibitors bortezomib and ixazomib, respectively, and TKI causes a significantly greater reduction in cell viability than TKI treatment alone in both BCR-ABL+ cell lines TOM-1 and BV-173. In BV-173 cells, we observed a significant reduction in cell viability to only 1.26%±0.46% with bortezomib treatment and 1.57±0.7% with combination treatment, whereas cells treated with dasatinib alone still had a viable percentage of 40.58±2.6%. Similar results were obtained when ixazomib was applied to both cell lines, and apoptosis was induced in both cases (93.36%±2.7% apoptotic BV-173 cells when treated with ixazomib and TKI). The combination of TKI and proteasome inhibitor is efficient in vitro, potentially expanding the spectrum of therapeutic options for patients with BCR-ABL+ ALL.

Combined treatment of graft versus host disease using donor regulatory T cells and ruxolitinib

Donor derived regulatory T lymphocytes and the JAK1/2 kinase inhibitor ruxolitinib are currently being evaluated as therapeutic options in the treatment of chronic graft versus host disease (cGvHD). In this work, we aimed to determine if the combined use of both agents can exert a synergistic effect in the treatment of GvHD. For this purpose, we studied the effect of this combination both in vitro and in a GvHD mouse model. Our results show that ruxolitinib favors the ratio of thymic regulatory T cells to conventional T cells in culture, without affecting the suppressive capacity of these Treg. The combination of ruxolitinib with Treg showed a higher efficacy as compared to each single treatment alone in our GvHD mouse model in terms of GvHD incidence, severity and survival without hampering graft versus leukemia effect. This beneficial effect correlated with the detection in the bone marrow of recipient mice of the infused donor allogeneic Treg after the adoptive transfer.

Novel Treatments for Pediatric Relapsed or Refractory Acute B-Cell Lineage Lymphoblastic Leukemia: Precision Medicine Era

With the markedly increased cure rate for children with newly diagnosed pediatric B-cell acute lymphoblastic leukemia (B-ALL), relapse and refractory B-ALL (R/R B-ALL) remain the primary cause of death worldwide due to the limitations of multidrug chemotherapy. As we now have a more profound understanding of R/R ALL, including the mechanism of recurrence and drug resistance, prognostic indicators, genotypic changes and so on, we can use newly emerging technologies to identify operational molecular targets and find sensitive drugs for individualized treatment. In addition, more promising and innovative immunotherapies and molecular targeted drugs that are expected to kill leukemic cells more effectively while maintaining low toxicity to achieve minimal residual disease (MRD) negativity and better bridge hematopoietic stem cell transplantation (HSCT) have also been widely developed. To date, the prognosis of pediatric patients with R/R B-ALL has been enhanced markedly thanks to the development of novel drugs. This article reviews the new advancements of several promising strategies for pediatric R/R B-ALL.

Activated interleukin-7 receptor signaling drives B-cell acute lymphoblastic leukemia in mice

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a high-risk subtype of B-ALL often associated with genetic variants that alter cytokine receptor signaling, including mutations in the interleukin-7 receptor (IL7R). To investigate whether IL7R variants are leukemia-initiating, we built mouse models expressing activated Il7r (aIL7R). B-cell intrinsic aIL7R mice developed spontaneous B-ALL, demonstrating sufficiency of Il7r activating mutations in leukemogenesis. Concomitant introduction of a knock-out allele in the associated adapter protein Lnk (encoded by Sh2b3) or a dominant-negative variant of the transcription factor Ikaros (Ikzf1) increased disease penetrance. The resulting murine leukemias displayed monoclonality and recurrent somatic Kras mutations and efficiently engrafted into immunocompetent mice. Phosphoproteomic analyses of aIL7R leukemic cells revealed constitutive Stat5 signaling and B cell receptor (BCR)-like signaling despite the absence of surface pre-BCR. Finally, in vitro treatment of aIL7R leukemic B-cells with Jak, mTOR, or Syk inhibitors blocked growth, confirming that each pathway is active in this mouse model of IL7R-driven B-ALL.

Inflammation-driven activation of JAK/STAT signaling reversibly accelerates acute myeloid leukemia in vitro

Acute myeloid leukemia (AML) is characterized by a high relapse rate and dismal long-term overall survival which is related to persistence of leukemia-initiating cells in their niche. Different animal models of myeloid malignancies reveal how neoplastic cells alter the structural and functional characteristics of the hematopoietic stem cell niche to reinforce malignancy. Understanding and disruption of the microenvironmental interactions with AML cells are a vital need. Malignant niches frequently go along with inflammatory responses, but their impact on cancerogenesis often remains unexplored. Here, we uncovered an aberrant production of inflammatory cytokines in untreated AML bone marrow that was proved to promote the proliferation of leukemia cells. This inflammatory response induced an activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in AML blasts as well as bone marrow stromal cells that also fostered leukemia proliferation. Inhibition of JAK/STAT signaling using the selective JAK1/2 inhibitor ruxolitinib resulted in significant antileukemic activity in AML in vitro which is mediated through both cell-autonomous and microenvironment-mediated mechanisms. However, in a xenograft transplantation model, monotherapy with ruxolitinib did not achieve substantial antileukemic activity, possibly suggesting a complementary function of JAK1/2 inhibition in AML.

Synergism between IL7R and CXCR4 drives BCR-ABL induced transformation in Philadelphia chromosome-positive acute lymphoblastic leukemia

Ph⁺ acute lymphoblastic leukemia (ALL) is characterized by the expression of an oncogenic fusion kinase termed BCR-ABL1. Here, we show that interleukin 7 receptor (IL7R) interacts with the chemokine receptor CXCR4 to recruit BCR-ABL1 and JAK kinases in close proximity. Treatment with BCR-ABL1 kinase inhibitors results in elevated expression of IL7R which enables the survival of transformed cells when IL7 was added together with the kinase inhibitors. Importantly, treatment with anti-IL7R antibodies prevents leukemia development in xenotransplantation models using patient-derived Ph⁺ ALL cells. Our results suggest that the association between IL7R and CXCR4 serves as molecular platform for BCR-ABL1-induced transformation and development of Ph⁺ ALL. Targeting this platform with anti-IL7R antibody eliminates Ph⁺ ALL cells including those with resistance to commonly used ABL1 kinase inhibitors. Thus, anti-IL7R antibodies may provide alternative treatment options for ALL in general and may suppress incurable drug-resistant leukemia forms.

Dasatinib regulates LPS-induced microglial and astrocytic neuroinflammatory responses by inhibiting AKT/STAT3 signaling

Background

The FDA-approved small-molecule drug dasatinib is currently used as a treatment for chronic myeloid leukemia (CML). However, the effects of dasatinib on microglial and/or astrocytic neuroinflammatory responses and its mechanism of action have not been studied in detail.

Methods

BV2 microglial cells, primary astrocytes, or primary microglial cells were treated with dasatinib (100 or 250 nM) or vehicle (1% DMSO) for 30 min or 2 h followed by lipopolysaccharide (LPS; 200 ng/ml or 1 μg/ml) or PBS for 5.5 h. RT-PCR, real-time PCR; immunocytochemistry; subcellular fractionation; and immunohistochemistry were subsequently conducted to determine the effects of dasatinib on LPS-induced neuroinflammation. In addition, wild-type mice were injected with dasatinib (20 mg/kg, intraperitoneally (i.p.) daily for 4 days or 20 mg/kg, orally administered (p.o.) daily for 4 days or 2 weeks) or vehicle (4% DMSO + 30% polyethylene glycol (PEG) + 5% Tween 80), followed by injection with LPS (10 mg/kg, i.p.) or PBS. Then, immunohistochemistry was performed, and plasma IL-6, IL-1β, and TNF-α levels were analyzed by ELISA.

Results

Dasatinib regulates LPS-induced proinflammatory cytokine and anti-inflammatory cytokine levels in BV2 microglial cells, primary microglial cells, and primary astrocytes. In BV2 microglial cells, dasatinib regulates LPS-induced proinflammatory cytokine levels by regulating TLR4/AKT and/or TLR4/ERK signaling. In addition, intraperitoneal injection and oral administration of dasatinib suppress LPS-induced microglial/astrocyte activation, proinflammatory cytokine levels (including brain and plasma levels), and neutrophil rolling in the brains of wild-type mice.

Conclusions

Our results suggest that dasatinib modulates LPS-induced microglial and astrocytic activation, proinflammatory cytokine levels, and neutrophil rolling in the brain.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1561-x) contains supplementary material, which is available to authorized users.

Repurposing dasatinib for diffuse large B cell lymphoma

To repurpose compounds for diffuse large B cell lymphoma (DLBCL), we screened a library of drugs and other targeted compounds approved by the US Food and Drug Administration on 9 cell lines and validated the results on a panel of 32 genetically characterized DLBCL cell lines. Dasatinib, a multikinase inhibitor, was effective against 50% of DLBCL cell lines, as well as against in vivo xenografts. Dasatinib was more broadly active than the Bruton kinase inhibitor ibrutinib and overcame ibrutinib resistance. Tumors exhibiting dasatinib resistance were commonly characterized by activation of the PI3K pathway and loss of PTEN expression as a specific biomarker. PI3K suppression by mTORC2 inhibition synergized with dasatinib and abolished resistance in vitro and in vivo. These results provide a proof of concept for the repurposing approach in DLBCL, and point to dasatinib as an attractive strategy for further clinical development in lymphomas.

JAK1/2 pathway inhibition suppresses M2 polarization and overcomes resistance of myeloma to lenalidomide by reducing TRIB1, MUC1, CD44, CXCL12, and CXCR4 expression

Monocytes polarize into pro-inflammatory macrophage-1 (M1) or alternative macrophage-2 (M2) states with distinct phenotypes and physiological functions. M2 cells promote tumour growth and metastasis whereas M1 macrophages show anti-tumour effects. We found that M2 cells were increased whereas M1 cells were decreased in bone marrow (BM) from multiple myeloma (MM) patients with progressive disease (PD) compared to those in complete remission (CR). Gene expression of Tribbles homolog 1 (TRIB1) protein kinase, an inducer of M2 polarization, was increased in BM from MM patients with PD compared to those in CR. Ruxolitinib (RUX) is an inhibitor of the Janus kinase family of protein tyrosine kinases (JAKs) and is effective for treating patients with myeloproliferative disorders. RUX markedly reduces both M2 polarization and TRIB1 gene expression in MM both in vitro and in vivo in human MM xenografts in severe combined immunodeficient mice. RUX also downregulates the expression of CXCL12, CXCR4, MUC1, and CD44 in MM cells and monocytes co-cultured with MM tumour cells; overexpression of these genes is associated with resistance of MM cells to the immunomodulatory agent lenalidomide. These results provide the rationale for evaluation of JAK inhibitors, including MM BM in combination with lenalidomide, for the treatment of MM patients.

Treatment Selection for Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia in the Era of Tyrosine Kinase Inhibitors

With the advent of tyrosine kinase inhibitors (TKIs), the treatment of Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) has entered a new era. The efficacy of TKIs compared with other ALL treatment options is emphasized by a rapid increase in the number of TKI clinical trials. Subsequently, the use of traditional approaches, such as combined chemotherapy and even allogeneic hematopoietic stem cell transplantation (allo-HSCT), for the treatment of ALL is being challenged in the clinic. In light of the increased use of TKIs in the clinic, several questions have been raised. First, is it necessary to use intensive chemotherapy during the induction course of therapy to achieve a minimal residual disease (MRD)-negative status? Must a patient reach a complete molecular response/major molecular response before receiving allo-HSCT? Does MRD status affect long-term survival after allo-HSCT? Is auto-HSCT an appropriate alternative for allo-HSCT in those Ph+ ALL patients who lack suitable donors? Here, we review the recent literature in an attempt to summarize the current status of TKI usage in the clinic, including several new therapeutic approaches, provide answers for the above questions, and speculate on the future direction of TKI utilization for the treatment of Ph+ ALL patients.

Dasatinib as an investigational drug for the treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia in adults

INTRODUCTION

Acute lymphoblastic leukemia (ALL) with BCR-ABL1 translocation is an aggressive malignancy that is usually treated with intensive chemotherapy with the possibility of allogeneic stem cell transplantation. The encoded fusion protein may be important for leukemogenesis; clinical studies show that dasatinib has an antileukemic effect in combination with steroids alone or intensive chemotherapy. Areas covered: Relevant publications were identified through literature searches (the used terms being acute lymphoblastic leukemia plus dasatinib) in the PubMed database. We searched for original articles and reviews describing the pharmacology and clinical use of dasatinib in ALL with BCR-ABL1. The mechanism of action, pharmacology and clinical study findings are examined. Expert opinion: Dasatinib is associated with a high complete remission rate in ALL when used alone and in combination with steroids or intensive chemotherapy. However, mutations at T315 and F317 are associated with dasatinib resistance. Overall toxicity has been acceptable in these studies and no unexpected toxicity was observed. It is not known whether the antileukemic effect of dasatinib differs between subsets of BCR-ABL1⁺ patients or is attributed to inhibition of the fusion protein alone, or a combined effect on several kinases, and whether dasatinib-containing combination treatment should be preferred in these patients instead of other emerging strategies, e.g. monoclonal antibodies.

Thrombotic microangiopathy as a cause of cardiovascular toxicity from the BCR-ABL1 tyrosine kinase inhibitor ponatinib

The third-generation tyrosine kinase inhibitor (TKI) ponatinib has been associated with high rates of acute ischemic events. The pathophysiology responsible for these events is unknown. We hypothesized that ponatinib produces an endothelial angiopathy involving excessive endothelial-associated von Willebrand factor (VWF) and secondary platelet adhesion. In wild-type mice and ApoE-/- mice on a Western diet, ultrasound molecular imaging of the thoracic aorta for VWF A1-domain and glycoprotein-Ibα was performed to quantify endothelial-associated VWF and platelet adhesion. After treatment of wild-type mice for 7 days, aortic molecular signal for endothelial-associated VWF and platelet adhesion were five- to sixfold higher in ponatinib vs sham therapy (P < .001), whereas dasatinib had no effect. In ApoE-/- mice, aortic VWF and platelet signals were two- to fourfold higher for ponatinib-treated compared with sham-treated mice (P < .05) and were significantly higher than in treated wild-type mice (P < .05). Platelet and VWF signals in ponatinib-treated mice were significantly reduced by N-acetylcysteine and completely eliminated by recombinant ADAMTS13. Ponatinib produced segmental left ventricular wall motion abnormalities in 33% of wild-type and 45% of ApoE-/- mice and corresponding patchy perfusion defects, yet coronary arteries were normal on angiography. Instead, a global microvascular angiopathy was detected by immunohistochemistry and by intravital microscopy observation of platelet aggregates and nets associated with endothelial cells and leukocytes. Our findings reveal a new form of vascular toxicity for the TKI ponatinib that involves VWF-mediated platelet adhesion and a secondary microvascular angiopathy that produces ischemic wall motion abnormalities. These processes can be mitigated by interventions known to reduce VWF multimer size.

In vivo RNAi screening identifies Pafah1b3 as a target for combination therapy with TKIs in BCR-ABL1+ BCP-ALL

Despite the addition of tyrosine kinase inhibitors (TKIs) to the treatment of patients with BCR-ABL1⁺ B-cell precursor acute lymphoblastic leukemia (BCR-ABL1⁺ BCP-ALL), relapse both with and without BCR-ABL1 mutations is a persistent clinical problem. To identify BCR-ABL1-independent genetic mediators of response to the TKI dasatinib, we performed in vivo and in vitro RNA interference (RNAi) screens in a transplantable syngeneic mouse model of BCR-ABL1⁺ BCP-ALL. By using a novel combination of a longitudinal screen design and independent component analysis of screening data, we identified hairpins that have distinct behavior in different therapeutic contexts as well as in the in vivo vs in vitro settings. In the set of genes whose loss sensitized BCR-ABL1⁺ BCP-ALL cells to dasatinib, we identified Pafah1b3, which regulates intracellular levels of platelet-activating factor (PAF), as an in vivo-specific mediator of therapeutic response. Pafah1b3 loss significantly sensitized leukemia cells to the multiple TKIs, indicating that inhibition of PAFAH1B3 in combination with TKI treatment may be an effective therapeutic strategy for BCR-ABL1⁺ BCP-ALL patients. PAF-induced cell death as well as surface levels of PAF receptor (PAFR) in our model are altered upon dasatinib treatment and depend on the local leukemia microenvironment; the response of Pafah1b3 KO vs overexpressing cells to dasatinib is also dependent on microenvironmental context. Antagonism of the PAFR partially reverses the observed sensitization to TKI treatment upon Pafah1b3 loss in vivo, suggesting that signaling via the PAF/PAFR pathway is at least partially responsible for this effect.

Aiding and Abetting: How the Tumor Microenvironment Protects Cancer from Chemotherapy

Disease recurrence following cancer therapy remains an intractable clinical problem and represents a major impediment to reducing the mortality attributable to malignant tumors. While research has traditionally focused on the cell-intrinsic mechanisms and mutations that render tumors refractory to both classical chemotherapeutics and targeted therapies, recent studies have begun to uncover myriad roles for the tumor microenvironment (TME) in modulating therapeutic efficacy. This work suggests that drug resistance is as much ecological as it is evolutionary. Specifically, cancers resident in organs throughout the body do not develop in isolation. Instead, tumor cells arise in the context of nonmalignant cellular components of a tissue. While the roles of these cell-extrinsic factors in cancer initiation and progression are well established, our understanding of the TME's influence on therapeutic outcome is in its infancy. Here, we focus on mechanisms by which neoplastic cells co-opt preexisting or treatment-induced signaling networks to survive chemotherapy.

New Approaches to the Management of Adult Acute Lymphoblastic Leukemia

Traditional treatment regimens for adult acute lymphoblastic leukemia, including allogeneic hematopoietic cell transplantation, result in an overall survival of approximately 40%, a figure hardly comparable with the extraordinary 80% to 90% cure rate currently reported in children. When translated to the adult setting, modern pediatric-type regimens improve the survival to approximately 60% in young adults. The addition of tyrosine kinase inhibitors for patients with Philadelphia chromosome-positive disease and the measurement of minimal residual disease to guide risk stratification and postremission approaches has led to additional improvements in outcomes. Relapsed disease and treatment toxicity-sparing no patient but representing a major concern especially in the elderly-are the most critical current issues awaiting further therapeutic advancement. Recently, there has been considerable progress in understanding the disease biology, specifically the Philadelphia-like signature, as well as other high-risk subgroups. In addition, there are several new agents that will undoubtedly contribute to additional improvement in the current outcomes. The most promising agents are monoclonal antibodies, immunomodulators, and chimeric antigen receptor T cells, and, to a lesser extent, several new drugs targeting key molecular pathways involved in leukemic cell growth and proliferation. This review examines the evidence supporting the increasing role of the new therapeutic tools and treatment options in different disease subgroups, including frontline and relapsed or refractory disease. It is now possible to define the best individual approach on the basis of the emerging concepts of precision medicine.

Germline Genetic IKZF1 Variation and Predisposition to Childhood Acute Lymphoblastic Leukemia

Somatic genetic alterations of IKZF1, which encodes the lymphoid transcription factor IKAROS, are common in high-risk B-progenitor acute lymphoblastic leukemia (ALL) and are associated with poor prognosis. Such alterations result in the acquisition of stem cell-like features, overexpression of adhesion molecules causing aberrant cell-cell and cell-stroma interaction, and decreased sensitivity to tyrosine kinase inhibitors. Here we report coding germline IKZF1 variation in familial childhood ALL and 0.9% of presumed sporadic B-ALL, identifying 28 unique variants in 45 children. The majority of variants adversely affected IKZF1 function and drug responsiveness of leukemic cells. These results identify IKZF1 as a leukemia predisposition gene, and emphasize the importance of germline genetic variation in the development of both familial and sporadic ALL.

Different BCR/Abl protein suppression patterns as a converging trait of chronic myeloid leukemia cell adaptation to energy restriction

BCR/Abl protein drives the onset and progression of Chronic Myeloid Leukemia (CML). We previously showed that BCR/Abl protein is suppressed in low oxygen, where viable cells retain stem cell potential. This study addressed the regulation of BCR/Abl protein expression under oxygen or glucose shortage, characteristic of the in vivo environment where cells resistant to tyrosine kinase inhibitors (TKi) persist. We investigated, at transcriptional, translational and post-translational level, the mechanisms involved in BCR/Abl suppression in K562 and KCL22 CML cells. BCR/abl mRNA steady-state analysis and ChIP-qPCR on BCR promoter revealed that BCR/abl transcriptional activity is reduced in K562 cells under oxygen shortage. The SUnSET assay showed an overall reduction of protein synthesis under oxygen/glucose shortage in both cell lines. However, only low oxygen decreased polysome-associated BCR/abl mRNA significantly in KCL22 cells, suggesting a decreased BCR/Abl translation. The proteasome inhibitor MG132 or the pan-caspase inhibitor z-VAD-fmk extended BCR/Abl expression under oxygen/glucose shortage in K562 cells. Glucose shortage induced autophagy-dependent BCR/Abl protein degradation in KCL22 cells. Overall, our results showed that energy restriction induces different cell-specific BCR/Abl protein suppression patterns, which represent a converging route to TKi-resistance of CML cells. Thus, the interference with BCR/Abl expression in environment-adapted CML cells may become a useful implement to current therapy.

Oncogenic kinase fusions: an evolving arena with innovative clinical opportunities

Cancer biology relies on intrinsic and extrinsic deregulated pathways, involving a plethora of intra-cellular and extra-cellular components. Tyrosine kinases are frequently deregulated genes, whose aberrant expression is often caused by major cytogenetic events (e.g. chromosomal translocations). The resulting tyrosine kinase fusions (TKFs) prompt the activation of oncogenic pathways, determining the biological and clinical features of the associated tumors. First reported half a century ago, oncogenic TKFs are now found in a large series of hematologic and solid tumors. The molecular basis of TKFs has been thoroughly investigated and tailored therapies against recurrent TKFs have recently been developed. This review illustrates the biology of oncogenic TKFs and their role in solid as well as hematological malignancies. We also address the therapeutic implications of TKFs and the many open issues concerning their clinical impact.

The role of STAT3 in leading the crosstalk between human cancers and the immune system

The development and progression of human cancers are continuously and dynamically regulated by intrinsic and extrinsic factors. As a converging point of multiple oncogenic pathways, signal transducer and activator of transcription 3 (STAT3) is constitutively activated both in tumor cells and tumor-infiltrated immune cells. Activated STAT3 persistently triggers tumor progression through direct regulation of oncogenic gene expression. Apart from its oncogenic role in regulating gene expression in tumor cells, STAT3 also paves the way for human cancer growth through immunosuppression. Activated STAT3 in immune cells results in inhibition of immune mediators and promotion of immunosuppressive factors. Therefore, STAT3 modulates the interaction between tumor cells and host immunity. Accumulating evidence suggests that targeting STAT3 may enhance anti-cancer immune responses and rescue the suppressed immunologic microenvironment in tumors. Taken together, STAT3 has emerged as a promising target in cancer immunotherapy.

Ruxolitinib/nilotinib cotreatment inhibits leukemia-propagating cells in Philadelphia chromosome-positive ALL

Background

As one of the major treatment obstacles in Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ALL), relapse of Ph⁺ALL may result from the persistence of leukemia-propagating cells (LPCs). Research using a xenograft mouse assay recently determined that LPCs were enriched in the CD34⁺CD38⁻CD58⁻ fraction in human Ph⁺ALL. Additionally, a cohort study demonstrated that Ph⁺ALL patients with a LPCs phenotype at diagnosis exhibited a significantly higher cumulative incidence of relapse than those with the other cell phenotypes even with uniform front-line imatinib-based therapy pre- and post-allotransplant, thus highlighting the need for novel LPCs-based therapeutic strategies.

Methods

RNA sequencing (RNA-Seq) and real-time quantitative polymerase chain reaction (qRT-PCR) were performed to analyze the gene expression profiles of the sorted LPCs and other cell fractions from patients with de novo Ph⁺ALL. In order to assess the effects of the selective BCR–ABL and/or Janus kinase (JAK)2 inhibition therapy by the treatment with single agents or a combination of ruxolitinib and imatinib or nilotinib on Ph⁺ALL LPCs, drug-induced apoptosis of LPCs was investigated in vitro, as well as in vivo using sublethally irradiated and anti-CD122-conditioned NOD/SCID xenograft mouse assay. Moreover, western blot analyses were performed on the bone marrow cells harvested from the different groups of recipient mice.

Results

RNA-Seq and qRT-PCR demonstrated that JAK2 was more highly expressed in the sorted LPCs than in the other cell fractions in de novo Ph⁺ALL patients. Combination treatment with a selective JAK1/JAK2 inhibitor (ruxolitinib) and nilotinib more effectively eliminated LPCs than either therapy alone or both in vitro and in humanized Ph⁺ALL mice by reducing phospho-CrKL and phospho-JAK2 activities at the molecular level.

Conclusions

In summary, this pre-clinical study provides a scientific rationale for simultaneously targeting BCR–ABL and JAK2 activities as a promising anti-LPCs therapeutic approach for patients with de novo Ph⁺ALL.

Small mitochondrial Arf (smArf) protein corrects p53-independent developmental defects of Arf tumor suppressor-deficient mice

The mouse p19^Arf (human p14^ARF) tumor suppressor protein, encoded in part from an alternative reading frame of the Ink4a (Cdkn2a) gene, inhibits the Mdm2 E3 ubiquitin ligase to activate p53. Arf is not expressed in most normal tissues of young mice but is induced by high thresholds of aberrant hyperproliferative signals, thereby activating p53 in incipient tumor cells that have experienced oncogene activation. The single Arf mRNA encodes two distinct polypeptides, including full-length p19^Arf and N-terminally truncated and unstable p15^smArf ("small mitochondrial Arf") initiated from an internal in-frame AUG codon specifying methionine-45. Interactions of p19^Arf with Mdm2, or separately with nucleophosmin (NPM, B23) that localizes and stabilizes p19^Arf within the nucleolus, require p19^Arf N-terminal amino acids that are not present within p15^smArf We have generated mice that produce either smARF alone or M45A-mutated (smArf-deficient) full-length p19^Arf proteins. BCR-ABL-expressing pro/pre-B cells producing smArf alone are as oncogenic as their Arf-null counterparts in generating acute lymphoblastic leukemia when infused into unconditioned syngeneic mice. In contrast, smArf-deficient cells from mice of the Arf^M45A strain are as resistant as wild-type Arf^+/+ cells to comparable oncogenic challenge and do not produce tumors. Apart from being prone to tumor development, Arf-null mice are blind, and their male germ cells exhibit defects in meiotic maturation and sperm production. Although Arf^M45A mice manifest the latter defects, smArf alone remarkably rescues both of these p53-independent developmental phenotypes.

Polymeric immunoglobulin receptor promotes tumor growth in hepatocellular carcinoma

Deregulation of the immune system is believed to contribute to cancer malignancy, which has led to recent therapeutic breakthroughs facilitating antitumor immunity. In a malignant setting, immunoglobulin receptors, which are fundamental components of the human immune system, fulfill paradoxical roles in cancer pathogenesis. This study describes a previously unrecognized pro-oncogenic function of polymeric immunoglobulin receptor (pIgR) in the promotion of cell transformation and proliferation. Mechanistically, pIgR overexpression is associated with YES proto-oncogene 1, Src family tyrosine kinase (Yes) activation, which is required for pIgR-induced oncogenic growth. Specifically, pIgR activates the Yes-DNAX-activating protein of 12 kDa-spleen tyrosine kinase-Rac1/CDC42-MEK (extracellular signal-regulated kinase kinase)/ERK (extracellular signal-regulated kinase) cascade in an immunoreceptor tyrosine-based activating motif (ITAM)-dependent manner to promote cell transformation and tumor growth, although pIgR itself does not contain an ITAM sequence. Additionally, the combination of pIgR and phosphorylated Yes (p-Yes) levels serves as a prognostic biomarker for hepatitis B surface antigen-positive and early-stage hepatocellular carcinoma (HCC) patients. Moreover, pharmacological targeting of MEK/ERK or Yes represents a therapeutic option for the subgroup of patients with pIgR/p-Yes-positive HCC based on our results with both cancer cell-line-based xenografts and primary patient-derived xenografts.

CONCLUSION

Our findings reveal the molecular mechanism by which pIgR promotes cancer malignancy, suggest the clinical potential of targeting this pathway in HCC, and provide new insight into the oncogenic role of immunoglobulin receptors. (Hepatology 2017;65:1948-1962).

Dynamic pre-BCR homodimers fine-tune autonomous survival signals in B cell precursor acute lymphoblastic leukemia

The pre-B cell receptor (pre-BCR) is an immature form of the BCR critical for early B lymphocyte development. It is composed of the membrane-bound immunoglobulin (Ig) heavy chain, surrogate light chain components, and the signaling subunits Igα and Igβ. We developed monovalent quantum dot (QD)-labeled probes specific for Igβ to study the behavior of pre-BCRs engaged in autonomous, ligand-independent signaling in live B cells. Single-particle tracking revealed that QD-labeled pre-BCRs engaged in transient, but frequent, homotypic interactions. Receptor motion was correlated at short separation distances, consistent with the formation of dimers and higher-order oligomers. Repeated encounters between diffusing pre-BCRs appeared to reflect transient co-confinement in plasma membrane domains. In human B cell precursor acute lymphoblastic leukemia (BCP-ALL) cells, we showed that frequent, short-lived, homotypic pre-BCR interactions stimulated survival signals, including expression of BCL6, which encodes a transcriptional repressor. These survival signals were blocked by inhibitory monovalent antigen-binding antibody fragments (Fabs) specific for the surrogate light chain components of the pre-BCR or by inhibitors of the tyrosine kinases Lyn and Syk. For comparison, we evaluated pre-BCR aggregation mediated by dimeric galectin-1, which has binding sites for carbohydrate and for the surrogate light chain λ5 component. Galectin-1 binding resulted in the formation of large, highly immobile pre-BCR aggregates, which was partially relieved by the addition of lactose to prevent the cross-linking of galectin-BCR complexes to other glycosylated membrane components. Analysis of the pre-BCR and its signaling partners suggested that they could be potential targets for combination therapy in BCP-ALL.

Synergism of FAK and tyrosine kinase inhibition in Ph+ B-ALL

BCR-ABL1⁺ B progenitor acute lymphoblastic leukemia (Ph⁺ B-ALL) is an aggressive disease that frequently responds poorly to currently available therapies. Alterations in IKZF1, which encodes the lymphoid transcription factor Ikaros, are present in over 80% of Ph⁺ ALL and are associated with a stem cell-like phenotype, aberrant adhesion molecule expression and signaling, leukemic cell adhesion to the bone marrow stem cell niche, and poor outcome. Here, we show that FAK1 is upregulated in Ph⁺ B-ALL with further overexpression in IKZF1-altered cells and that the FAK inhibitor VS-4718 potently inhibits aberrant FAK signaling and leukemic cell adhesion, potentiating responsiveness to tyrosine kinase inhibitors, inducing cure in vivo. Thus, targeting FAK with VS-4718 is an attractive approach to overcome the deleterious effects of FAK overexpression in Ph⁺ B-ALL, particularly in abrogating the adhesive phenotype induced by Ikaros alterations, and warrants evaluation in clinical trials for Ph⁺ B-ALL, regardless of IKZF1 status.

Management of adult Ph-positive acute lymphoblastic leukemia

Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL) has been regarded for decades as the ALL subgroup with the worse outcome. It represents the most frequent genetic subtype of adult ALL, and increases progressively with age. The introduction of tyrosine kinase inhibitors (TKIs) has enabled to obtain complete hematologic remissions (CHRs) in virtually all patients, including the elderly, to improve disease-free survival and overall survival, as well as to increase the percentage of patients who can undergo an allogeneic stem cell transplant (allo-SCT).

The current management of adult Ph+ ALL patients relies on the use of a TKI with or without chemotherapy followed by an allo-SCT, which still remains the only curative option. Minimal residual disease screening is permitting not only a better stratification of patients, but has also allowed to reconsider the role of autologous stem cell transplant for a set of patients who do not have a donor or are not eligible for an allo-SCT. At present, clinical challenges are represented by the emergence of resistant mutations, particularly the gatekeeper T315I, for which alternative approaches, comprising novel TKIs or therapies based on the combination of TKI with immunotherapeutic strategies, are being considered in order to overcome resistance.

Treatment of Experimental Candida Sepsis with a Janus Kinase Inhibitor Controls Inflammation and Prolongs Survival

Janus kinases (JAK) are intracellular tyrosine kinases that transduce cytokine-mediated signals to the nucleus, promoting gene expression. Cytokines play a major role in microbial sepsis, which is often associated with uncontrolled inflammation leading to death. JAK inhibitors have been used for the treatment of several autoimmune diseases by modulating immune response, but they have never been tested against microbial sepsis. Ruxolitinib is a small-molecule inhibitor of JAK1/2 proteins, which are involved in the downstream signaling pathway of the vast majority of proinflammatory and anti-inflammatory cytokines. We therefore studied the effect of ruxolitinib in a mouse model of sepsis due to Candida albicans. When ruxolitinib therapy (50 mg/kg [of body weight]/day) was started 1 day before infection, the median survival time was reduced by 3 days, the fungal loads in all organs were higher, the inflammation was significantly less, and serum tumor necrosis factor alpha (TNF-α) and interleukin 10 (IL-10) levels and IL-10/TNF-α ratios were higher than in controls. When ruxolitinib therapy (50 to 1.5 mg/kg/day) was started 1 day after infection, an inverted-U relationship was found, with 6.25 mg/kg/day prolonging median survival time by 6 days, resulting in similar fungal loads, less inflammation, and similar cytokine levels but higher IL-10/TNF-α ratios than the controls. The optimal dose of ruxolitinib controlled infection and prolonged survival with less inflammation than in control animals. Administration of JAK inhibitors may be a promising therapeutic adjunct that needs further investigation.

Targeting BCR-ABL and JAK2 in Ph+ ALL

In this issue of Blood, Appelmann et al provide evidence for prolonged survival and prevention of resistance in a mouse model of Philadelphia chromosome–positive (Ph+) acute lymphoblastic leukemia (ALL) by combined targeting of the BCR-ABL kinase and Janus kinase 2 (JAK2) with dasatinib and ruxolitinib, respectively.

Ph+ ALL: drawing strength from a benign past

In this issue of Blood, Mallampati et al report on the discovery of a new mechanism of tyrosine kinase inhibitor (TKI) resistance, which is mediated through TKI-mediated priming of mesenchymal stem cells (MSCs) in the bone marrow (BM).