Simplifying the Chemical Structure of Cationic Lipids for siRNA-Lipid Nanoparticles

We report a potent cationic lipid, SST-02 ((3-hydroxylpropyl)dilinoleylamine), which possesses a simple chemical structure and is synthesized just in one step. Cationic lipids are key components of siRNA-lipid nanoparticles (LNP), which may serve as potential therapeutic agents for various diseases. For a decade, chemists have given enhanced potency and new functions to cationic lipids along with structural complexity. In this study, we conducted a medicinal chemistry campaign pursuing chemical simplicity and found that even dilinoleylmethylamine (SST-01) and methylpalmitoleylamine could be used for the in vitro and in vivo siRNA delivery. Further optimization revealed that a hydroxyl group boosted potency, and SST-02 showed an ID₅₀ of 0.02 mg/kg in the factor VII (FVII) model. Rats administered with 3 mg/kg of SST-02 LNP did not show changes in body weight, blood chemistry, or hematological parameters, while the AST level decreased at a dose of 5 mg/kg. The use of SST-02 avoids a lengthy synthetic route and may thus decrease the future cost of nucleic acid therapeutics.

Regulated expression of P210 Bcr-Abl during embryonic stem cell differentiation stimulates multipotential progenitor expansion and myeloid cell fate

P210 Bcr-Abl is an activated tyrosine kinase oncogene encoded by the Philadelphia chromosome associated with human chronic myelogenous leukemia (CML). The disease represents a clonal disorder arising in the pluripotent hematopoietic stem cell. During the chronic phase, patients present with a dramatic expansion of myeloid cells and a mild anemia. Retroviral gene transfer and transgenic expression in rodents have demonstrated the ability of Bcr-Abl to induce various types of leukemia. However, study of human CML or rodent models has not determined the direct and immediate effects of Bcr-Abl on hematopoietic cells from those requiring secondary genetic or epigenetic changes selected during the pathogenic process. We utilized tetracycline-regulated expression of Bcr-Abl from a promoter engineered for robust expression in primitive stem cells through multilineage blood cell development in combination with the in vitro differentiation of embryonal stem cells into hematopoietic elements. Our results demonstrate that Bcr-Abl expression alone is sufficient to increase the number of multipotent and myeloid lineage committed progenitors in a dose-dependent manner while suppressing the development of committed erythroid progenitors. These effects are reversible upon extinguishing Bcr-Abl expression. These findings are consistent with Bcr-Abl being the sole genetic change needed for the establishment of the chronic phase of CML and provide a powerful system for the analysis of any genetic change that alters cell growth and lineage choices of the hematopoietic stem cell.

Characterization of hematopoietic lineage-specific gene expression by ES cell in vitro differentiation induction system

The continuous generation of mature blood cells from hematopoietic progenitor cells requires a highly complex series of molecular events. To examine lineage-specific gene expression during the differentiation process, we developed a novel method combining LacZ reporter gene analysis with in vitro hematopoietic differentiation induction from mouse embryonic stem cells. For a model system using this method, we chose the erythroid and megakaryocytic differentiation pathways. Although erythroid and megakaryocytic cells possess distinct functional and morphologic features, these 2 lineages originate from bipotential erythro-megakaryocytic progenitors and share common lineage-restricted transcription factors. A portion of the 5' flanking region of the human glycoprotein IIb (alphaIIb) integrin gene extending from base -598 to base +33 was examined in detail. As reported previously, this region is sufficient for megakaryocyte-specific gene expression. However, previous reports that used human erythro-megakaryocytic cell lines suggested that one or more negative regulatory regions were necessary for megakaryocyte-specific gene expression. Our data clearly showed that an approximately 200-base enhancer region extending from -598 to -400 was sufficient for megakaryocyte-specific gene expression. This experimental system has advantages over those using erythro-megakaryocytic cell lines because it recapitulates normal hematopoietic cell development and differentiation. Furthermore, this system is more efficient than transgenic analysis and can easily examine gene expression with null mutations of specific genes.

Acute myelomonoblastic leukemia carrying the PEBP2beta/MYH11 fusion gene

As recurrent chromosome abnormalities in leukemia are highly associated with particular subtypes, the genetic events of specific chromosome alteration must be associated with leukemogenesis and characteristics of the disease. The chromosomal breakpoints involved in inv(16) and t(16;16) have been shown to generate the fusion gene PEBP2beta(CBFbeta)/MYH11. The PEBP2beta/MYH11 fusion transcripts in all 8 patients with M4Eo, 2 of 18 with M4, and one CML in the blastic phase were detected by using RT-PCR and Southern blotting. We demonstrated the marked expression of CD34 and c-KIT (CD117) antigens in myelomonoblastic leukemia cells from all patients carrying this fusion gene, which was in contrast to the patients with M4 but without the fusion gene. These results indicate that immunophenotypic analysis is useful for detection of leukemia with the fusion gene, and that the PEBP2beta/MYH11 fusion gene is involved in immature cells expressing CD34 and c-KIT antigens.

Development of osteoclasts from embryonic stem cells through a pathway that is c-fms but not c-kit dependent

Osteoclasts are hematopoietic cells essential for bone resorption. To study the derivation of these interesting cells, we developed a stepwise culture system where stromal cells promote embryonic stem (ES) cells to differentiate into mature osteoclasts. Three phases to this differentiation process include (1) induction of hematopoiesis, along with the generation of osteoclast precursors, (2) expansion of these precursors, and (3) terminal differentiation into mature osteoclasts in the presence of 1alpha,25-dihydroxyvitamine D3 . Although the transition of ES cells to the hematopoietic lineage was not blocked by an antibody to c-fms, later phases were dependent on a signaling through this transmembrane receptor as indicated by the finding that anti-c-fms treatment of cells in the second and third phases reduced the number of osteoclasts produced by 75% and more than 99%, respectively. Blockade of signaling through another tyrosine kinase-type receptor, c-kit, did not affect any stages of osteoclastogenesis, although generation of other hemopoietic lineages was reduced to less than 10% of untreated. When small numbers of ES cells were directly cultured under conditions that promote osteoclast differentiation, tartrate-resistant acid phosphatase-positive multinucleated cells were observed at the edge but not inside of colonies. This suggests that some types of cell-cell interactions may inhibit development of mature osteoclasts. The culture system developed here provides an important tool for osteoclast biology.

Myelomonoblastic leukaemia cells carrying the PEBP2beta/MYH11 fusion gene are CD34, c-KIT+ immature cells

To clarify the aspects affected by the PEBP2beta/MYH11 fusion gene involved in the inv(16), we analysed immunophenotypes in myelomonoblastic leukaemias. We found high expressions of CD34 and c-KIT antigens in myelomonoblastic cells from all patients carrying this fusion gene, including two with M4 and one CML blastic phase, in contrast to those with M4 without the fusion gene. These findings indicate that immunophenotyping is useful for detecting a leukaemia with the fusion gene in myelomonoblastic leukaemias and that the PEBP2beta/MYH11 gene is involved in immature cells expressing CD34 and c-KIT antigens.

Development of erythroid cells from mouse embryonic stem cells in culture: potential use for erythroid transcription factor study

We developed an efficient differentiation induction system from mouse embryonic stem (ES) cells into blood cells by coculture on a novel stromal cell line named OP9, in order to analyze molecular mechanisms of hematopoietic cell development and differentiation. ES cells could give rise to adult type definitive erythrocytes, myeloid and B lineage cells via multipotential hematopoietic precursor cells, when the cells were simply cocultured with the OP9 stromal cells. The temporal pattern of the appearance of erythroid lineage cells during the differentiation induction was very similar to that detected in mouse ontogeny. This differentiation induction method should facilitate to dissect the function of erythroid transcription factors during erythroid lineage cell development.

Thrombopoietin enhances proliferation and differentiation of murine yolk sac erythroid progenitors

Thrombopoietin (TPO), the ligand for the receptor proto-oncogene c-Mpl, has been cloned and shown to be the critical regulator of proliferation and differentiation of megakaryocytic lineage. Initially, TPO was not considered to have the activity on hematopoietic lineages other than megakaryocytes. Recently, however, TPO was reported to enhance the in vitro erythroid colony formation from human bone marrow (BM) CD34+ progenitors or from mouse BM cells in combination with other cytokines. We examined the effects of TPO on the colony formation of hematopoietic progenitors in mouse yolk sac. TPO remarkably enhanced proliferation and differentiation of erythroid-lineage cells in the presence of erythropoietin (Epo). This effect was observed even in the absence of Epo. Compared with adult BM, yolk sac turned out to have relatively abundant erythroid and erythro-megakaryocytic progenitors, which responded to TPO and Epo stimulation. TPO similarly stimulated erythroid colony formation from in vitro differentiation-induced mouse embryonic stem (ES) cells whose hematopoietic differentiation status was similar to that of yolk sac. These findings help to understand the biology of hematopoietic progenitors of the early phase of hematopoiesis. Yolk sac cells or in vitro differentiation-induced ES cells would be good sources to analyze the TPO function on erythropoiesis.

Expression of AML1 and ETO Transcripts in hematopoietic cells

Recently, two genes, AML1 and ETO have been isolated from the chromosomal breakpoint of t(8;21). In this study, we isolated and identified fusion transcripts from a leukemic cell line carrying t(8;21). We demonstrated by PCR analysis that these transcripts are consistently expressed in fresh leukemic cells with t(8;21). On the other hand, the wild type of ETO is expressed in several hematopoietic cells from different lineage, while the expression of AML1 was present in all hematopoietic cells investigated. These widespread expression suggests these molecules play an essential role in hematopoiesis.

High degree of myeloid differentiation and granulocytosis is associated with t(8;21) smoldering leukemia

The t(8;21) is a frequent chromosome abnormality in acute myeloid leukemia (AML), particularly associated with M2 of the French-American-British (FAB) classification, but also found in a few patients with myelodysplastic syndrome (MDS). The two genes involved in the t(8;21) have been recently isolated and the cDNA of the AML1/ETO fusion gene identified. We have investigated a series of AML and MDS patients by a reverse transcriptase-polymerase chain reaction (RT-PCR) and analyzed the clinical and laboratory features of leukemia with t(8;21). The t(8;21) was only found in a subset of M2, which had the clinical and hematological features distinct from those M2 without t(8;21). M2 with t(8;21) was associated with a significantly higher myeloid differentiation and with a good response to chemotherapy. Moreover, among the patients with refractory anemia with excess of blasts in transformation (RAEB-T) the t(8;21) was also significantly associated with a higher myeloid differentiation and a good response to chemotherapy. M2 patients with t(8;21) could be distinguished on a number of hematological parameters, eg white blood cell count and percentage of bone marrow myeloblasts and promyelocytes, from RAEB-T carrying the t(8;21). Based on these findings we suggest that leukemia patients carrying t(8;21) can be grouped into two types; overt acute myeloid leukemia (M2) and smoldering or slowly evolving myeloid leukemia.

Identification of two transcripts of AML1/ETO-fused gene in t(8;21) leukemic cells and expression of wild-type ETO gene in hematopoietic cells

The t(8;21) is a common chromosomal abnormality, preferentially associated with acute leukemia showing features of myeloid differentiation. Recently, two genes--AML1, which has a unique runt domain, and ETO (MTG8)--have been isolated from the chromosomal breakpoint. In this study, we isolated and identified two fused transcripts from a leukemic cell line carrying t(8;21). AML1 and ETO were fused at the same position in these transcripts. One of the transcripts codes a unique domain, including two zinc finger domains and three proline- and one leucine-rich region. The other transcript codes only for one proline- and leucine-rich region but lacks zinc finger domains. We demonstrated by polymerase chain reaction (PCR) analysis that 1) these two transcripts are consistently expressed in leukemic cells with t(8;21) obtained from patients and 2) expression of AML1 was not restricted to the particular stage of hematopoietic differentiation but was present in all hematopoietic cells investigated. We also provide evidence that two wild types of ETO transcripts containing the region of the ETO gene in fused transcripts are expressed in hematopoietic cells from different lineages. The widespread expression of AML1 and ETO in hematopoietic cells suggests a fundamental role of these proteins in hematopoiesis. Furthermore, the differences in the carboxy termini of ETO may modulate the activity of fused proteins resulting from the chromosomal translocation t(8;21).

In utero manipulation of coat color formation by a monoclonal anti-c-kit antibody: two distinct waves of c-kit-dependency during melanocyte development

Previous studies on mice bearing various mutations within the c-kit gene, dominant white spotting (W), indicate the functional role of this tyrosine kinase receptor in the development of melanocytes, germ cells and hematopoietic cells. Despite the availability of mice defective in the c-kit gene and a respectable understanding of the molecular nature of c-kit, however, it is not clear at what stage of gestation c-kit is functionally required for the development of each of these cell lineages. To address this question, we have used a monoclonal anti-c-kit antibody, ACK2, as an antagonistic blocker of c-kit function to interfere with the development of melanocytes during embryonic and postnatal life. ACK2 injected intradermally into pregnant mice entered the embryos where it blocked the proper development of melanocytes. This inhibitory effect was manifested as coat color alteration in the offspring. Furthermore, ACK2 injection also altered the coat color of neonatal and adult mice. Based on the coat color patterns produced by ACK2 administration at various stages before or after birth, the following conclusions are drawn: (i) during mid-gestation, c-kit is functionally required during a restricted period around day 14.5 post-coitum when a sequence of events leading to melanocyte entry into the epidermal layer occurs; (ii) during postnatal life, c-kit is required for melanocyte activation which occurs concomitantly with the hair cycle which continues throughout life after neonatal development of the first hair.

Differentiation of growth signal requirement of B lymphocyte precursor is directed by expression of immunoglobulin

During B cell differentiation, at least three stages can be defined in terms of their growth signal requirement by using two different growth signals, which are recombinant interleukin 7 (IL-7) and a stromal cell clone PA6 which does not produce IL-7; first a PA6 dependent stage, second a PA6 + IL-7 dependent stage and third an IL-7 dependent stage. In order to test the possibility that this differentiation of growth signal requirement is controlled by the expression of functional immunoglobulin molecules, we have investigated the frequencies of PA6 + IL-7 dependent and IL-7 dependent cells which are present in the bone marrow of either mu-chain or kappa-chain gene transgenic mice. In a mu-chain gene transgenic mouse, the frequency of PA6 + IL-7 dependent cells is selectively reduced, while that of IL-7 dependent cells is selectively reduced in a kappa-chain gene transgenic mouse. This result suggests that expression of a functional mu-chain gene drives PA6 + IL-7 dependent cells to differentiate into the subsequent IL-7 dependent stage. Likewise, when mu-chain positive IL-7 dependent cells express a functional light-chain gene, their growth signal requirement changes into an IL-7 unreactive stage.