Wnt5a causes ROR1 to complex and activate cortactin to enhance migration of chronic lymphocytic leukemia cells

Wnt5a induces ROR1 dependent NF-κB activation to enhance MMP-9 expression and invasiveness in chronic lymphocytic leukemia

Matrix metalloproteinase-9 (MMP-9) facilitates the extravasation and lymphoid-tissue infiltration of chronic lymphocytic leukemia (CLL) cells. Prior studies found that high level expression of MMP-9 in CLL associates more aggressive disease. We find that circulating CLL cells that express high levels the onco-embryonic protein ROR1 express significantly higher levels of MMP-9. Stimulation of CLL cells with Wnt5a could enhance expression and the release of MMP-9 into the culture media and increase the capacity of CLL cells to invade Matrigel in a Boyden-Chamber Assay. Such effects of Wnt5a could not be inhibited by BTK inhibitors such as ibrutinib or zanubrutinib, but could be blocked by zilovertamab, a humanized mAb specific for ROR1. We found that siRNA silencing of NF-κB-p65 or use of an NF-κB inhibitor (CAS 545380-34-5) blocked the capacity of Wnt5a to induce MMP-9 or enhance the invasive capacity of treated CLL cells. Moreover, siRNA directed silencing of MMP9 or treatment with an MMP-9 inhibitor (CAS 1177749-58-4) also blocked the invasive capability of CLL cells induced by Wnt5a. We conclude that Wnt5a-induced ROR1-signaling can induce expression of MMP-9 on CLL cells through activation of NF-κB, thereby enhancing the extravasation and lymphoid-tissue infiltration required for CLL cell trafficking.

The survival grip-how cell adhesion promotes tumor maintenance within the microenvironment

Cell adhesion is warranted by proteins that are crucial for the maintenance of tissue integrity and homeostasis. Most of these proteins behave as receptors to link adhesion to the control of cell survival and their expression or regulation are often altered in cancers. B-cell malignancies do not evade this principle as they are sustained in relapsed niches by interacting with the microenvironment that includes cells and their secreted factors. Focusing on chronic lymphocytic leukemia and mantle cell lymphoma, this Review delves with the molecules involved in the dialog between the adhesion platforms and signaling pathways known to regulate both cell adhesion and survival. Current therapeutic strategies disrupt adhesive structures and compromise the microenvironment support to tumor cells, rendering them sensitive to immune recognition. The development of organ-on-chip and 3D culture systems, such as spheroids, have revealed the importance of mechanical cues in regulating signaling pathways to organize cell adhesion and survival. All these elements contribute to the elaboration of the crosstalk of lymphoma cells with the microenvironment and the education processes that allow the establishment of the supportive niche.

Therapeutic advances in the targeting of ROR1 in hematological cancers

Receptor tyrosine kinases (RTKs) are key cell surface receptors involved in cell communication and signal transduction, with great importance in cell growth, differentiation, survival, and metabolism. Dysregulation of RTKs, such as EGFR, VEGFR, HER2 or ROR, could lead to various diseases, particularly cancers. ROR1 has emerged as a promising target in hematological malignancies. The development of ROR1 targeted therapies is continuously growing leading to remarkable novel therapeutical approaches using mAbs, antibody-drug conjugates, several small molecules or CAR T cells which have shown encouraging preclinical results. In the hematological field, mAbs, small molecules, BiTEs or CAR T cell therapies displayed promising outcomes with the clinical trials data encouraging the use of anti-ROR1 therapies. This paper aims to offer a comprehensive analysis of the current landscape of ROR1-targeted therapies in hematological malignancies marking the innovative approaches with promising preclinical and clinical. Offering a better understanding of structural and functional aspects of ROR1 could lead to new perspectives in targeting a wide spectrum of malignancies.

Siglec-6 as a therapeutic target for cell migration and adhesion in chronic lymphocytic leukemia

Siglec-6 is a lectin receptor with restricted expression in the placenta, mast cells and memory B-cells. Although Siglec-6 is expressed in patients with chronic lymphocytic leukemia (CLL), its pathophysiological role has not been elucidated. We describe here a role for Siglec-6 in migration and adhesion of CLL B cells to CLL- bone marrow stromal cells (BMSCs) in vitro and compromised migration to bone marrow and spleen in vivo. Mass spectrometry analysis revealed interaction of Siglec-6 with DOCK8, a guanine nucleotide exchange factor. Stimulation of MEC1-002 CLL cells with a Siglec-6 ligand, sTn, results in Cdc42 activation, WASP protein recruitment and F-actin polymerization, which are all associated with cell migration. Therapeutically, a Siglec-6/CD3-bispecific T-cell-recruiting antibody (T-biAb) improves overall survival in an immunocompetent mouse model and eliminates CLL cells in a patient derived xenograft model. Our findings thus reveal a migratory role for Siglec-6 in CLL, which can be therapeutically targeted using a Siglec-6 specific T-biAb.

Role of the tumor microenvironment in CLL pathogenesis

Chronic lymphocytic leukemia (CLL) cells extensively interact with and depend on their surrounding tumor microenvironment (TME). The TME encompasses a heterogeneous array of cell types, soluble signals, and extracellular vesicles, which contribute significantly to CLL pathogenesis. CLL cells and the TME cooperatively generate a chronic inflammatory milieu, which reciprocally reprograms the TME and activates a signaling network within CLL cells, promoting their survival and proliferation. Additionally, the inflammatory milieu exerts chemotactic effects, attracting CLL cells and other immune cells to the lymphoid tissues. The intricate CLL-TME interactions also facilitate immune evasion and compromise leukemic cell surveillance. We also review recent advances that have shed light on additional aspects that are substantially influenced by the CLL-TME interplay.

Receptor tyrosine kinase-like orphan receptor 1: A novel antitumor target in gastrointestinal cancers

Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is a member of the type I receptor tyrosine kinase family. ROR1 is pivotal in embryonic development and cancer, and serves as a biomarker and therapeutic target. It has soluble and membrane-bound subtypes, with the latter highly expressed in tumors. ROR1 is conserved throughout evolution and may play a role in the development of gastrointestinal cancer through multiple signaling pathways and molecular mechanisms. Studies suggest that overexpression of ROR1 may increase tumor invasiveness and metastasis. Additionally, ROR1 may regulate the cell cycle, stem cell characteristics, and interact with other signaling pathways to affect cancer progression. This review explores the structure, expression and role of ROR1 in the development of gastrointestinal cancers. It discusses current antitumor strategies, outlining challenges and prospects for treatment.

Role of the Ror family receptors in Wnt5a signaling

Ror-family receptors, Ror1 and Ror2, are type I transmembrane proteins that possess an extracellular cysteine-rich domain, which is conserved throughout the Frizzled-family receptors and is a binding site for Wnt ligands. Both Ror1 and Ror2 function primarily as receptors or co-receptors for Wnt5a to activate the β-catenin-independent, non-canonical Wnt signaling, thereby regulating cell polarity, migration, proliferation, and differentiation depending on the context. Ror1 and Ror2 are expressed highly in many tissues during embryogenesis but minimally or scarcely in adult tissues, with some exceptions. In contrast, Ror1 and Ror2 are expressed in many types of cancers, and their high expression often contributes to the progression of the disease. Therefore, Ror1 and Ror2 have been proposed as potential targets for the treatment of the malignancies. In this review, we provide an overview of the regulatory mechanisms of Ror1/Ror2 expression and discuss how Wnt5a-Ror1/Ror2 signaling is mediated and regulated by their interacting proteins.

ROR1 expression in mature B lymphoid neoplasms by flow cytometry

Immunophenotyping by flow cytometry is an integral part of the diagnosis and classification of leukemias/lymphomas. The expression of ROR1 associated with chronic B lymphocytic leukemia (CLL) is well described in the literature, both in its diagnosis and in the follow-up of minimal residual disease (MRD) research, however, there are few studies regarding the expression pattern of ROR1 in other subtypes of mature B lymphoid neoplasms. With the aim of evaluating the expression of ROR1 and associating it with the expression of other important markers for the differentiation of mature B lymphoid neoplasms (MBLN), 767 samples of cases that entered our laboratory for immunophenotyping with clinical suspicion of MBLN were studied. ROR1 expression is predominant in CD5+/CD10- neoplasms. Overall, positive ROR1 expression was observed in 461 (60.1%) cases. The CD5+/CD10- group had a significantly higher proportion of ROR1 positive samples (89.9%) and more brightly expressed ROR1 than the other groups. Our results highlight the importance of evaluating ROR1 expression in the diagnosis of MBLN to contribute to the differential diagnosis, and possibly therapy of mainly CLL, and indicate that this marker could be considered as a useful addition to immunophenotypic panels, particularly for more challenging cases.

Identification of the Axis β-Catenin-BTK in the Dynamic Adhesion of Chronic Lymphocytic Leukemia Cells to Their Microenvironment

In the microenvironment, cell interactions are established between different cell types to regulate their migration, survival and activation. β-Catenin is a multifunctional protein that stabilizes cell-cell interactions and regulates cell survival through its transcriptional activity. We used chronic lymphocytic leukemia (CLL) cells as a cellular model to study the role of β-catenin in regulating the adhesion of tumor cells to their microenvironment, which is necessary for tumor cell survival and accumulation. When co-cultured with a stromal cell line (HS-5), a fraction of the CLL cells adhere to stromal cells in a dynamic fashion regulated by the different levels of β-catenin expression. In non-adherent cells, β-catenin is stabilized in the cytosol and translocates into the nucleus, increasing the expression of cyclin D1. In adherent cells, the level of cytosolic β-catenin is low but membrane β-catenin helps to stabilize the adhesion of CLL to stromal cells. Indeed, the overexpression of β-catenin enhances the interaction of CLL with HS-5 cells, suggesting that this protein behaves as a regulator of cell adhesion to the stromal component and of the transcriptional regulation of cell survival. Inhibitors that block the stabilization of β-catenin alter this equilibrium and effectively disrupt the support that CLL cells receive from the cross-talk with the stroma.

The signaling pathways activated by ROR1 in cancer

The receptor tyrosine kinase orphan receptor 1 (ROR1) is a receptor for WNT5A and related Wnt proteins, that play an important role during embryonic development by regulating cell migration, cell polarity, neural patterning, and organogenesis. ROR1 exerts these functions by transducing signals from the Wnt secreted glycoproteins to the intracellular Wnt/PCP and Wnt/Ca⁺⁺ pathways. Investigations in adult human cells, particularly cancer cells, have demonstrated that besides these two pathways, the WNT5A/ROR1 axis can activate a number of signaling pathways, including the PI3K/AKT, MAPK, NF-κB, STAT3, and Hippo pathways. Moreover, ROR1 is aberrantly expressed in cancer and was associated with tumor progression and poor survival by promoting cell proliferation, survival, invasion, epithelial to mesenchymal transition, and metastasis. Consequently, numerous therapeutic tools to target ROR1 are currently being evaluated in cancer patients. In this review, we will provide a detailed description of the signaling pathways regulated by ROR1 in cancer and their impact in tumor progression.

To β or Not to β: How Important Is β-Catenin Dependent and Independent WNT Signaling in CLL?

WNT pathways play an important role in cancer development and progression, but WNT pathways can also inhibit growth in melanoma, prostate, and ovarian cancers. Chronic lymphocytic leukemia (CLL) is known for its overexpression of several WNT ligands and receptors. Canonical WNT signaling is β-catenin-dependent, whereas non-canonical WNT signaling is β-catenin-independent. Research on WNT in CLL focuses mainly on non-canonical signaling due to the high expression of the WNT-5a receptor ROR1. However, it was also shown that mutations in canonical WNT pathway genes can lead to WNT activation in CLL. The focus of this review is β-catenin-independent signaling and β-catenin-dependent signaling within CLL cells and the role of WNT in the leukemic microenvironment. The major role of WNT pathways in CLL pathogenesis also makes WNT a possible therapeutic target, directly or in combination with other drugs.

Role of casein kinase 1 in the amoeboid migration of B-cell leukemic and lymphoma cells: A quantitative live imaging in the confined environment

The migratory properties of leukemic cells are commonly associated with their pathological potential and can significantly affect the disease progression. While the research in immunopathology mostly employed powerful indirect methods such as flow cytometry, these cells were rarely observed directly using live imaging microscopy. This is especially true for the malignant cells of the B-cell lineage, such as those originating from chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). In this study, we employed open-source image analysis tools to automatically and quantitatively describe the amoeboid migration of four B-cell leukemic and lymphoma cell lines and primary CLL cells. To avoid the effect of the shear stress of the medium on these usually non-adherent cells, we have confined the cells using a modified under-agarose assay. Surprisingly, the behavior of tested cell lines differed substantially in terms of basal motility or response to chemokines and VCAM1 stimulation. Since casein kinase 1 (CK1) was reported as a regulator of B-cell migration and a promoter of CLL, we looked at the effects of CK1 inhibition in more detail. Migration analysis revealed that CK1 inhibition induced rapid negative effects on the migratory polarity of these cells, which was quantitatively and morphologically distinct from the effect of ROCK inhibition. We have set up an assay that visualizes endocytic vesicles in the uropod and facilitates morphological analysis. This assay hints that the effect of CK1 inhibition might be connected to defects in polarized intracellular transport. In summary, 1) we introduce and validate a pipeline for the imaging and quantitative assessment of the amoeboid migration of CLL/MCL cells, 2) we provide evidence that the assay is sensitive enough to mechanistically study migration defects identified by the transwell assay, and 3) we describe the polarity defects induced by inhibition or deletion of CK1ε.

ROR1: an orphan becomes apparent

Since its initial identification in 1992 as a possible class 1 cell-surface receptor without a known parent ligand, receptor tyrosine kinase-like orphan receptor 1 (ROR1) has stimulated research, which has made apparent its significance in embryonic development and cancer. Chronic lymphocytic leukemia (CLL) was the first malignancy found to have distinctive expression of ROR1, which can help distinguish leukemia cells from most noncancer cells. Aside from its potential utility as a diagnostic marker or target for therapy, ROR1 also factors in the pathophysiology of CLL. This review is a report of the studies that have elucidated the expression, biology, and evolving strategies for targeting ROR1 that hold promise for improving the therapy of patients with CLL or other ROR1-expressing malignancies.

The Ror-Family Receptors in Development, Tissue Regeneration and Age-Related Disease

The Ror-family proteins, Ror1 and Ror2, act as receptors or co-receptors for Wnt5a and its related Wnt proteins to activate non-canonical Wnt signaling. Ror1 and/or Ror2-mediated signaling plays essential roles in regulating cell polarity, migration, proliferation and differentiation during developmental morphogenesis, tissue-/organo-genesis and regeneration of adult tissues following injury. Ror1 and Ror2 are expressed abundantly in developing tissues in an overlapping, yet distinct manner, and their expression in adult tissues is restricted to specific cell types such as tissue stem/progenitor cells. Expression levels of Ror1 and/or Ror2 in the adult tissues are increased following injury, thereby promoting regeneration or repair of these injured tissues. On the other hand, disruption of Wnt5a-Ror2 signaling is implicated in senescence of tissue stem/progenitor cells that is related to the impaired regeneration capacity of aged tissues. In fact, Ror1 and Ror2 are implicated in age-related diseases, including tissue fibrosis, atherosclerosis (or arteriosclerosis), neurodegenerative diseases, and cancers. In these diseases, enhanced and/or sustained (chronic) expression of Ror1 and/or Ror2 is observed, and they might contribute to the progression of these diseases through Wnt5a-dependent and -independent manners. In this article, we overview recent advances in our understanding of the roles of Ror1 and Ror2-mediated signaling in the development, tissue regeneration and age-related diseases, and discuss their potential to be therapeutic targets for chronic inflammatory diseases and cancers.

Lyn Phosphorylates and Controls ROR1 Surface Dynamics During Chemotaxis of CLL Cells

Chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) are malignancies characterized by the dependence on B-cell receptor (BCR) signaling and by the high expression of ROR1, the cell surface receptor for Wnt-5a. Both, BCR and ROR1 are therapeutic targets in these diseases and the understanding of their mutual cross talk is thus of direct therapeutic relevance. In this study we analyzed the role of Lyn, a kinase from the Src family participating in BCR signaling, as a mediator of the BCR-ROR1 crosstalk. We confirm the functional interaction between Lyn and ROR1 and demonstrate that Lyn kinase efficiently phosphorylates ROR1 in its kinase domain and aids the recruitment of the E3 ligase c-CBL. We show that ROR1 surface dynamics in migrating primary CLL cells as well as chemotactic properties of CLL cells were inhibited by Lyn inhibitor dasatinib. Our data establish Lyn-mediated phosphorylation of ROR1 as a point of crosstalk between BCR and ROR1 signaling pathways.

Aberrantly expressed Wnt5a in nurse-like cells drives resistance to Venetoclax in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of neoplastic B lymphocytes with high levels of Wnt5a in the plasma. Currently, the cell source of Wnt5a remains controversial. The receptor of Wnt5a is ROR1, whose expression is associated with disease progression and resistance to venetoclax, a BCL-2 inhibitor approved for the treatment of CLL. In this study, we found that the levels of Wnt5a in the plasma of CLL patients were positively correlated with absolute monocyte counts, but not lymphocyte counts. We cultured monocyte-derived nurse-like cells (NLCs) from patients with CLL, and detected Wnt5a expressed in NLCs. Flow cytometry and transwell assays showed that the antibody neutralizing Wnt5a inhibited the enhanced survival and migration in CLL cells co-cultured with NLCs. Furthermore, we performed a drug screening with CLL cells cultured with or without NLCs with a library containing 133 FDA-approved oncology drugs by using high-throughput flow cytometry. We observed a significant resistance to venetoclax in CLL cells co-cultured with NLCs. Immunoblot revealed the activation of NF-κB with enhanced expression of MCL-1 and BCL-XL in CLL cells co-cultured with NLCs. Neutralizing Wnt5a or blocking NF-κB pathway significantly decreased the expression of MCL-1 and BCL-XL, which leads to enhanced sensitivity to venetoclax in CLL cells co-cultured with NLCs. In conclusion, our data showed that NLCs could be one of the sources of Wnt5a detected in patients with CLL, and Wnt5a-induced NF-κB activation in the CLL microenvironment results in resistance to venetoclax in CLL cells.

Longitudinal analyses of CLL in mice identify leukemia-related clonal changes including a Myc gain predicting poor outcome in patients

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy mainly occurring at an advanced age with no single major genetic driver. Transgenic expression of TCL1 in B cells leads after a long latency to a CLL-like disease in aged Eµ-TCL1 mice suggesting that TCL1 overexpression is not sufficient for full leukemic transformation. In search for secondary genetic events and to elucidate the clonal evolution of CLL, we performed whole exome and B-cell receptor sequencing of longitudinal leukemia samples of Eµ-TCL1 mice. We observed a B-cell receptor stereotypy, as described in patients, confirming that CLL is an antigen-driven disease. Deep sequencing showed that leukemia in Eµ-TCL1 mice is mostly monoclonal. Rare oligoclonality was associated with inability of tumors to develop disease upon adoptive transfer in mice. In addition, we identified clonal changes and a sequential acquisition of mutations with known relevance in CLL, which highlights the genetic similarities and therefore, suitability of the Eµ-TCL1 mouse model for progressive CLL. Among them, a recurrent gain of chromosome 15, where Myc is located, was identified in almost all tumors in Eµ-TCL1 mice. Interestingly, amplification of 8q24, the chromosomal region containing MYC in humans, was associated with worse outcome of patients with CLL.

CD4+ T cells sustain aggressive chronic lymphocytic leukemia in Eμ-TCL1 mice through a CD40L-independent mechanism

Chronic lymphocytic leukemia (CLL) is caused by the progressive accumulation of mature CD5+ B cells in secondary lymphoid organs. In vitro data suggest that CD4+ T lymphocytes also sustain survival and proliferation of CLL clones through CD40L/CD40 interactions. In vivo data in animal models are conflicting. To clarify this clinically relevant biological issue, we generated genetically modified Eμ-TCL1 mice lacking CD4+ T cells (TCL1+/+AB0), CD40 (TCL1+/+CD40-/-), or CD8+ T cells (TCL1+/+TAP-/-), and we monitored the appearance and progression of a disease that mimics aggressive human CLL by flow cytometry and immunohistochemical analyses. Findings were confirmed by adoptive transfer of leukemic cells into mice lacking CD4+ T cells or CD40L or mice treated with antibodies depleting CD4 T cells or blocking CD40L/CD40 interactions. CLL clones did not proliferate in mice lacking or depleted of CD4+ T cells, thus confirming that CD4+ T cells are essential for CLL development. By contrast, CD8+ T cells exerted an antitumor activity, as indicated by the accelerated disease progression in TCL1+/+TAP-/- mice. Antigen specificity of CD4+ T cells was marginal for CLL development, because CLL clones efficiently proliferated in transgenic mice whose CD4 T cells had a T-cell receptor with CLL-unrelated specificities. Leukemic clones also proliferated when transferred into wild-type mice treated with monoclonal antibodies blocking CD40 or into CD40L-/- mice, and TCL1+/+CD40-/- mice developed frank CLL. Our data demonstrate that CD8+ T cells restrain CLL progression, whereas CD4+ T cells support the growth of leukemic clones in TCL1 mice through CD40-independent and apparently noncognate mechanisms.

Mining the Microenvironment for Therapeutic Targets in Chronic Lymphocytic Leukemia

ABSTRACT

The leukemia cells of patients with chronic lymphocytic leukemia (CLL) are highly fastidious, requiring stimulation by soluble factors and interactions with accessory cells within the supportive niches of lymphoid tissue that comprise the leukemia microenvironment. The advent of therapies that can disrupt some of the stimulatory signaling afforded by the microenvironment has ushered in a new era of targeted therapy, which has dramatically improved clinical outcome and patient survival. Future advances are required for patients who develop intolerance or resistance to current targeted therapies. These may be found by investigating novel drugs that can inhibit identified targets, such as the pathways involved in B-cell receptor signaling, or by developing agents that inhibit additional targets of the leukemia microenvironment. This review describes some of the molecules involved in promoting the growth and/or survival of CLL cells and discusses targeting strategies that may become tomorrow's therapy for patients with CLL.

Tyrosine Kinase ROR1 as a Target for Anti-Cancer Therapies

Receptor tyrosine kinase ROR1 plays an essential role in embryogenesis and is overexpressed in many types of malignant tumors. Studies have demonstrated that it plays an important role in oncogenesis by activating cell survival signaling events, particularly the non-canonical WNT signaling pathway. Antibody-based immunotherapies targeting ROR1 have been developed and evaluated in preclinical and clinical studies with promising outcomes. However, small molecule inhibitors targeting ROR1 are underappreciated because of the initial characterization of ROR1 as a peusdokinase. The function of ROR1 as a tyrosine kinase remains poorly understood, although accumulating evidence have demonstrated its intrinsic tyrosine kinase activity. In this review, we analyzed the structural and functional features of ROR1 and discussed therapeutic strategies targeting this kinase.

Tumor microenvironment acidity modulates ROR1 to promote epithelial-mesenchymal transition and hepatocarcinoma metastasis

The tendency of hepatocarcinoma to metastasize results in a high rate of mortality, making it a hot research topic in cancer studies. Although an acidic tumor microenvironment has been proven to promote cancer metastasis, the underlying regulatory mechanisms remain poorly defined. Here, we found that acidic conditions significantly enhanced cell migration and invasion ability in hepatocellular carcinoma, and the expression of receptor tyrosine kinase-like orphan receptor 1 (ROR1) was distinctly upregulated in acid-treated cells. In addition, siRNA-mediated knockdown of ROR1 could effectively inhibit acid-induced cell migration, invasion and epithelial-mesenchymal transition (EMT). Importantly, neutralization of acidic environments with NaHCO3 could downregulate acid-stimulated ROR1 expression, thereby retarding cell metastatic potential. Notably, the formation of metastatic nodules was significantly increased after intrapulmonary injection of acid-stimulated cancer cells, and this was inhibited by pretreating with NaHCO3. In summary, we reveal that an acidic tumor microenvironment modulates ROR1 expression to promote tumor metastasis, providing not only a better understanding of molecular mechanisms related to metastasis, but also a promising target for tumor management.

Chronic Lymphocytic Leukemia

Patients with chronic lymphocytic leukemia can be divided into three categories: those who are minimally affected by the problem, often never requiring therapy; those that initially follow an indolent course but subsequently progress and require therapy; and those that from the point of diagnosis exhibit an aggressive disease necessitating treatment. Likewise, such patients pass through three phases: development of the disease, diagnosis, and need for therapy. Finally, the leukemic clones of all patients appear to require continuous input from the exterior, most often through membrane receptors, to allow them to survive and grow. This review is presented according to the temporal course that the disease follows, focusing on those external influences from the tissue microenvironment (TME) that support the time lines as well as those internal influences that are inherited or develop as genetic and epigenetic changes occurring over the time line. Regarding the former, special emphasis is placed on the input provided via the B-cell receptor for antigen and the C-X-C-motif chemokine receptor-4 and the therapeutic agents that block these inputs. Regarding the latter, prominence is laid upon inherited susceptibility genes and the genetic and epigenetic abnormalities that lead to the developmental and progression of the disease.

Targeting Casein Kinase 1 (CK1) in Hematological Cancers

The casein kinase 1 enzymes (CK1) form a family of serine/threonine kinases with seven CK1 isoforms identified in humans. The most important substrates of CK1 kinases are proteins that act in the regulatory nodes essential for tumorigenesis of hematological malignancies. Among those, the most important are the functions of CK1s in the regulation of Wnt pathways, cell proliferation, apoptosis and autophagy. In this review we summarize the recent developments in the understanding of biology and therapeutic potential of the inhibition of CK1 isoforms in the pathogenesis of chronic lymphocytic leukemia (CLL), other non-Hodgkin lymphomas (NHL), myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and multiple myeloma (MM). CK1δ/ε inhibitors block CLL development in preclinical models via inhibition of WNT-5A/ROR1-driven non-canonical Wnt pathway. While no selective CK1 inhibitors have reached clinical stage to date, one dual PI3Kδ and CK1ε inhibitor, umbralisib, is currently in clinical trials for CLL and NHL patients. In MDS, AML and MM, inhibition of CK1α, acting via activation of p53 pathway, showed promising preclinical activities and the first CK1α inhibitor has now entered the clinical trials.

Wnt5a enhances proliferation of chronic lymphocytic leukemia and ERK1/2 phosphorylation via a ROR1/DOCK2-dependent mechanism

Patients with chronic lymphocytic leukemia (CLL) have high plasma-levels of Wnt5a, which can induce phosphorylation of ERK1/2 and enhance CLL-cell proliferation. Such effects could be inhibited by treatment with an ERK1/2 inhibitor, ERK1/2-specific siRNA, or cirmtuzumab, an anti-ROR1 mAb. The CLL-derived line, MEC1, expresses Wnt5a, but not ROR1. MEC1 cells transfected to express ROR1 (MEC1-ROR1) had higher levels of phosphorylated ERK1/2 than parental MEC1, or MEC1 transfected with ROR1ΔPRD, a truncated ROR1 lacking the cytoplasmic proline-rich domain (PRD), or ROR1^P808A a mutant ROR1 with a P→A substitution at 808, which is required for complexing with the Rac-specific-guanine-nucleotide-exchange factor DOCK2 upon stimulation with Wnt5a. We silenced DOCK2 with siRNA and found this repressed the capacity of Wnt5a to induce ERK1/2 phosphorylation in MEC1-ROR1 or CLL cells. CLL cells that expressed ROR1 had higher levels of phosphorylated ERK1/2 or DOCK2 than CLL cells lacking ROR1. Although we found ibrutinib could inhibit the phosphorylation of ERK1/2 and DOCK2 induced by B-cell-receptor ligation, we found that this drug was unable to inhibit Wnt5a-induced, ROR1-dependent phosphorylation of ERK1/2 or DOCK2. This study demonstrates that Wnt5a can induce activation of ERK1/2 and enhance CLL-cell proliferation via a ROR1/DOCK2-dependent pathway independent of BTK.

Actin regulators in cancer progression and metastases: From structure and function to cytoskeletal dynamics

The cytoskeleton is a central factor contributing to various hallmarks of cancer. In recent years, there has been increasing evidence demonstrating the involvement of actin regulatory proteins in malignancy, and their dysregulation was shown to predict poor clinical prognosis. Although enhanced cytoskeletal activity is often associated with cancer progression, the expression of several inducers of actin polymerization is remarkably reduced in certain malignancies, and it is not completely clear how these changes promote tumorigenesis and metastases. The complexities involved in cytoskeletal induction of cancer progression therefore pose considerable difficulties for therapeutic intervention; it is not always clear which cytoskeletal regulator should be targeted in order to impede cancer progression, and whether this targeting may inadvertently enhance alternative invasive pathways which can aggravate tumor growth. The entire constellation of cytoskeletal machineries in eukaryotic cells are numerous and complex; the system is comprised of and regulated by hundreds of proteins, which could not be covered in a single review. Therefore, we will focus here on the actin cytoskeleton, which encompasses the biological machinery behind most of the key cellular functions altered in cancer, with specific emphasis on actin nucleating factors and nucleation-promoting factors. Finally, we discuss current therapeutic strategies for cancer which aim to target the cytoskeleton.

MicroRNA dysregulation and multi-targeted therapy for cancer treatment

We established that loss of miR-15a/16-1 genes on chromosome 13q14 is the most common alteration in Chronic Lymphocytic Leukemia (CLL) and that miR-15/16 are crucial negative regulator of BCL-2, an antiapoptotic gene overexpressed in most CLLs and in many other malignancies. We have also shown that miR-15/16 target ROR1, a cell surface receptor for Wnt5a which can enhance growth/survival of CLL cells. Interestingly, ROR1 is expressed by many cancers, but not by normal adult tissues. Moreover, Venetoclax, the anti-Bcl-2 drug, and Cirmtuzumab, the monoclonal antibody against ROR1, are synergistic in killing CLL cells. Since an additional miR-15/16 locus exists on chromosome 3q25 (miR-15b/16-2), we generated a knocked out mouse model to study its the role in cancer. We observed that the KO mice developed predominantly CLL. Thus, we generated a double knock out mouse model where both miR-15/16 loci were deleted. Surprisingly we observed that 77% of double KO mice developed Acute Myeloid Leukemia (AML). Based on these evidences, we anticipate that also AMLs with low miR-15/16 expression, overexpression of BCL2 and expression of ROR1, would show an excellent response to a combination therapy with Venetoclax and Cirmtuzumab, since both drugs target the same malignant cells that have lost miR-15/16.

Wnt5a induces ROR1 to recruit cortactin to promote breast-cancer migration and metastasis

ROR1 is a conserved oncoembryonic surface protein expressed in breast cancer. Here we report that ROR1 associates with cortactin in primary breast-cancer cells or in MCF7 transfected to express ROR1. Wnt5a also induced ROR1-dependent tyrosine phosphorylation of cortactin (Y421), which recruited ARHGEF1 to activate RhoA and promote breast-cancer-cell migration; such effects could be inhibited by cirmtuzumab, a humanized mAb specific for ROR1. Furthermore, treatment of mice bearing breast-cancer xenograft with cirmtuzumab inhibited cortactin phosphorylation in vivo and impaired metastatic development. We established that the proline at 841 of ROR1 was required for it to recruit cortactin and ARHGEF1, activate RhoA, and enhance breast-cancer-cell migration in vitro or development of metastases in vivo. Collectively, these studies demonstrate that the interaction of ROR1 with cortactin plays an important role in breast-cancer-cell migration and metastasis.

Cutting Edge: ROR1/CD19 Receptor Complex Promotes Growth of Mantle Cell Lymphoma Cells Independently of the B Cell Receptor-BTK Signaling Pathway

Inhibitors of Bruton tyrosine kinase (BTK), a kinase downstream of BCR, display remarkable activity in a subset of mantle cell lymphoma (MCL) patients, but the drug resistance remains a considerable challenge. In this study, we demonstrate that aberrant expression of ROR1 (receptor tyrosine kinase-like orphan receptor 1), seen in a large subset of MCL, results in BCR/BTK-independent signaling and growth of MCL cells. ROR1 forms a functional complex with CD19 to persistently activate the key cell signaling pathways PI3K-AKT and MEK-ERK in the BCR/BTK-independent manner. This study demonstrates that ROR1/CD19 complex effectively substitutes for BCR-BTK signaling to promote activation and growth of MCL cells. Therefore, ROR1 expression and activation may represent a novel mechanism of resistance to inhibition of BCR/BTK signaling in MCL. Our results provide a rationale to screen MCL patients for ROR1 expression and to consider new therapies targeting ROR1 and/or CD19 or their downstream signaling pathways for MCL-expressing ROR1.

Cirmtuzumab blocks Wnt5a/ROR1 stimulation of NF-κB to repress autocrine STAT3 activation in chronic lymphocytic leukemia

Coculture of nurse-like cells (NLCs) with chronic lymphocytic leukemia (CLL) cells induced leukemia cell phosphorylation of STAT3 (pSTAT3), which could be blocked by anti-Wnt5a antibodies or the anti-ROR1 monoclonal antibody, cirmtuzumab. Time-course studies revealed Wnt5a could induce activation of NF-κB within 30 minutes, but required more than 3 hours to induce pSTAT3. Culture of isolated CLL cells for 24 hours revealed Wnt5a-induced expression of interleukin 6 (IL-6), IL-8, CCL2, CCL3, CCL4, and CXCL1, which in turn could induce pSTAT3 in unstimulated CLL cells within 30 minutes. We found that Wnt5a could induce CLL cell expression of NF-κB target genes, including IL-6, and that this effect could be blocked by cirmtuzumab or drugs that inhibit NF-κB. Examination of CLL cells and plasma collected from patients treated with cirmtuzumab revealed reduced levels of phosphorylated p65 and diminished expression of NF-κB and STAT3 target genes in CLL cells, as well as lower plasma levels of IL-6, in the samples after therapy. Collectively, these studies indicate that Wnt5a/ROR1-dependent signaling contributes to CLL cell activation of NF-κB, which in turn causes autocrine IL-6-induced activation of pSTAT3. As such, this study demonstrates that cirmtuzumab can inhibit leukemia cell activation of both NF-κB and STAT3 in patients with CLL.