Malignant hematopoietic cell lines: in vitro models for the study of anaplastic large-cell lymphoma

Establishment and characterization of TK-ALCL1: a novel NPM-ALK-positive anaplastic large-cell lymphoma cell line

TK-ALCL1, a novel anaplastic lymphoma kinase (ALK)-positive anaplastic large-cell lymphoma (ALK+ ALCL) cell line, was established from the primary tumor site of a 59-year-old Japanese male patient. The immune profile of TK-ALCL1 corresponds to that seen typically in primary ALCL cells, i.e., positive for ALK, CD30, EMA, and CD4, but negative for CD2, CD3, CD5, CD8a, and EBV-related antigens. The rearrangement of the T cell receptor-gamma locus shows that TK-ALCL1 is clonally derived from T-lineage lymphoid cells. FISH and RT-PCR analysis revealed that TK-ALCL1 has the nucleophosmin (NPM)-ALK fusion transcript, which is typical for ALK+ ALCL cell lines. When TK-ALCL1 was subcutaneously inoculated into 6-week-old BALB/c Rag2-/-/Jak3-/- (BRJ) mice, it formed tumor masses within 4-6 weeks. Morphological, immunohistochemical, and molecular genetic investigations confirmed that the xenograft and the original ALCL tumor were identical. The ALK inhibitors Alectinib and Lorlatinib suppressed proliferation in a dose-dependent manner. Thus, TK-ALCL1 provides a useful in vitro and in vivo model for investigation of the biology of ALK+ ALCL and of novel therapeutic approaches targeting ALK.

The Role of NKL Homeobox Genes in T-Cell Malignancies

Homeobox genes encode transcription factors controlling basic developmental processes. The homeodomain is encoded by the homeobox and mediates sequence-specific DNA binding and interaction with cofactors, thus operating as a basic regulatory platform. Similarities in their homeobox sequences serve to arrange these genes in classes and subclasses, including NKL homeobox genes. In accordance with their normal functions, deregulated homeobox genes contribute to carcinogenesis along with hematopoietic malignancies. We have recently described the physiological expression of eleven NKL homeobox genes in the course of hematopoiesis and termed this gene expression pattern NKL-code. Due to the developmental impact of NKL homeobox genes these data suggest a key role for their activity in the normal regulation of hematopoietic cell differentiation including T-cells. On the other hand, aberrant overexpression of NKL-code members or ectopical activation of non-code members has been frequently reported in lymphoid and myeloid leukemia/lymphoma, demonstrating their oncogenic impact in the hematopoietic compartment. Here, we provide an overview of the NKL-code in normal hematopoiesis and discuss the oncogenic role of deregulated NKL homeobox genes in T-cell malignancies.

NKL-Code in Normal and Aberrant Hematopoiesis

Simple Summary

Gene codes represent expression patterns of closely related genes in particular tissues, organs or body parts. The NKL-code describes the activity of NKL homeobox genes in the hematopoietic system. NKL homeobox genes encode transcription factors controlling basic developmental processes. Therefore, aberrations of this code may contribute to deregulated hematopoiesis including leukemia and lymphoma. Normal and abnormal activities of NKL homeobox genes are described and mechanisms of (de)regulation, function, and diseases exemplified.

Abstract

We have recently described physiological expression patterns of NKL homeobox genes in early hematopoiesis and in subsequent lymphopoiesis and myelopoiesis, including terminally differentiated blood cells. We thereby systematized differential expression patterns of eleven such genes which form the so-called NKL-code. Due to the developmental impact of NKL homeobox genes, these data suggest a key role for their activity in normal hematopoietic differentiation processes. On the other hand, the aberrant overexpression of NKL-code-members or the ectopical activation of non-code members have been frequently reported in lymphoid and myeloid leukemia/lymphoma, revealing the oncogenic potential of these genes in the hematopoietic compartment. Here, I provide an overview of the NKL-code in normal hematopoiesis and instance mechanisms of deregulation and oncogenic functions of selected NKL genes in hematologic cancers. As well as published clinical studies, our conclusions are based on experimental work using hematopoietic cell lines which represent useful models to characterize the role of NKL homeobox genes in specific tumor types.

Inhibitor repurposing reveals ALK, LTK, FGFR, RET and TRK kinases as the targets of AZD1480

Many tyrosine kinase inhibitors (TKIs) have failed to reach human use due to insufficient activity in clinical trials. However, the failed TKIs may still benefit patients if their other kinase targets are identified by providing treatment focused on syndromes driven by these kinases. Here, we searched for novel targets of AZD1480, an inhibitor of JAK2 kinase that recently failed phase two cancer clinical trials due to a lack of activity. Twenty seven human receptor tyrosine kinases (RTKs) and 153 of their disease-associated mutants were in-cell profiled for activity in the presence of AZD1480 using a newly developed RTK plasmid library. We demonstrate that AZD1480 inhibits ALK, LTK, FGFR1-3, RET and TRKA-C kinases and uncover a physical basis of this specificity. The RTK activity profiling described here facilitates inhibitor repurposing by enabling rapid and efficient identification of novel TKI targets in cells.

Intrahepatic Xenograft of Cutaneous T-Cell Lymphoma Cell Lines: A Useful Model for Rapid Biological and Therapeutic Evaluation

Cutaneous T-cell lymphomas (CTCLs) are a heterogeneous group of diseases primarily involving the skin that could have an aggressive course with circulating blood cells, especially in Sézary syndrome and transformed mycosis fungoides. So far, few CTCL cell lines have been adapted for in vivo experiments and their tumorigenicity has not been adequately assessed, hampering the use of a reproducible model for CTCL biological evaluation. In fact, both patient-derived xenografts and cell line xenografts at subcutaneous sites failed to provide a robust tool, because engraftment was dependent on mice strain and cell line subtype. Herein, we describe an original method of intrahepatic injection into adult NOD.Cg-Prkdc(scid)Il2rg(tm1Wjl)/SzJ mice liver of both aggressive (My-La, HUT78, HH, MAC2A, and MAC2B) and indolent (FE-PD and MAC1) CTCL cell lines. Six of the seven CTCL cell lines were grafted with a high rate of success (80%). Moreover, this model provided a quick (15 days) and robust assay for in vivo evaluation of CTCL cell lines tumorigenicity and therapeutic response in preclinical studies. Such a reproducible model can be therefore used for further functional studies and in vivo drug testing.

Next-generation sequencing identifies deregulation of microRNAs involved in both innate and adaptive immune response in ALK+ ALCL

Anaplastic large cell lymphoma (ALCL) is divided into two systemic diseases according to the expression of the anaplastic lymphoma kinase (ALK). We investigated the differential expression of miRNAs between ALK+ ALCL, ALK- ALCL cells and normal T-cells using next generation sequencing (NGS). In addition, a C/EBPβ-dependent miRNA profile was generated. The data were validated in primary ALCL cases. NGS identified 106 miRNAs significantly differentially expressed between ALK+ and ALK- ALCL and 228 between ALK+ ALCL and normal T-cells. We identified a signature of 56 miRNAs distinguishing ALK+ ALCL, ALK- ALCL and T-cells. The top candidates significant differentially expressed between ALK+ and ALK- ALCL included 5 upregulated miRNAs: miR-340, miR-203, miR-135b, miR-182, miR-183; and 7 downregulated: miR-196b, miR-155, miR-146a, miR-424, miR-503, miR-424*, miR-542-3p. The miR-17-92 cluster was also upregulated in ALK+ cells. Additionally, we identified a signature of 3 miRNAs significantly regulated by the transcription factor C/EBPβ, which is specifically overexpressed in ALK+ ALCL, including the miR-181 family. Of interest, miR-181a, which regulates T-cell differentiation and modulates TCR signalling strength, was significantly downregulated in ALK+ ALCL cases. In summary, our data reveal a miRNA signature linking ALK+ ALCL to a deregulated immune response and may reflect the abnormal TCR antigen expression known in ALK+ ALCL.

Identification of C/EBPβ target genes in ALK+ anaplastic large cell lymphoma (ALCL) by gene expression profiling and chromatin immunoprecipitation

C/EBPβ (CCAAT enhancer binding protein) is a transcription factor that plays a crucial role in survival and transformation of ALK+ anaplastic large cell lymphoma (ALCL). The aim of this study was to identify the downstream targets of C/EBPβ responsible for ALK-mediated oncogenesis. C/EBPβ was knocked down in ALK+ ALCL cell lines with a C/EBPβ-shRNA, followed by gene expression profiling (GEP). GEP analysis revealed a reproducible signature of genes that were significantly regulated by C/EBPβ. Classification into biological categories revealed overrepresentation of genes involved in the immune response, apoptosis and cell proliferation. Transcriptional regulation by C/EBPβ was found in 6 of 11 (BCL2A1, G0S2, TRIB1, S100A9, DDX21 and DDIT4) genes investigated by chromatin immunoprecipitation. We demonstrated that BCL2A1, G0S2 and DDX21 play a crucial role in survival and proliferation of ALK+ ALCL cells. DDX21, a gene involved in rRNA biogenesis, was found differentially overexpressed in primary ALK+ ALCL cases. All three candidate genes were validated in primary ALCL cases by either immunohistochemistry or RT-qPCR. In conclusion, we identified and validated several key C/EBPβ-regulated genes with major impact on survival and cell growth in ALK+ ALCL, supporting the central role of C/EBPβ in ALK-mediated oncogenesis.

Anaplastic lymphoma kinase activity is essential for the proliferation and survival of anaplastic large-cell lymphoma cells

The roles of aberrant expression of constitutively active ALK chimeric proteins in the pathogenesis of anaplastic large-cell lymphoma (ALCL) have been well defined; nevertheless, the notion that ALK is a molecular target for the therapeutic modulation of ALK+ ALCL has not been validated thus far. Select fused pyrrolocarbazole (FP)-derived small molecules with ALK inhibitory activity were used as pharmacologic tools to evaluate whether functional ALK is essential for the proliferation and survival of ALK+ ALCL cells in culture. These compounds inhibited interleukin 3 (IL-3)-independent proliferation of BaF3/NPM-ALK cells in an ALK inhibition-dependent manner and significantly blocked colony formation in agar of mouse embryonic fibroblast (MEF) cells harboring NPM-ALK. Inhibition of NPM-ALK phosphorylation in the ALK+ ALCL-derived cell lines resulted in significant inhibition of cell proliferation and induction of apoptotic-cell death, while having marginal effects on the proliferation and survival of K562, an ALK- leukemia cell line. ALK inhibition resulted in cell-cycle G1 arrest and inactivation of ERK1/2, STAT3, and AKT signaling pathways. Potent and selective ALK inhibitors may have therapeutic application for ALK+ ALCL and possibly other solid and hematologic tumors in which ALK activation is implicated in their pathogenesis.