Study of ascorbate status in murine and human leukaemias

Since mice can synthesize ascorbic acid but man cannot, the ascorbate status in murine and human leukaemia was compared. The decline in plasma ascorbate concentration in both cases indicates that vitamin C deficiency occurs in malignancy. Analysis of tissue ascorbate values in mice also indicated that an enhanced rate of utilization of this vitamin occurs during malignancy, as does an increased rate of excretion, and both events may be responsible for vitamin C deficiency. The hepatic ascorbate values suggest an endeavour by the animals to compensate for the loss through increased synthesis and storage of the vitamin, at least in the early stages of the disease.

Selective staining reactions of involved blood cells prior to symptoms of lymphatic leukemia in mice

After inoculation with lymphatic leukemia virus, blood smears were obtained daily from young Balb/c mice. When the smears were stained with silver nitrate, a cytoplasmic granular deposition was first observed in the circulating polymorphs with a subsequent abrupt disappearance of any staining reaction in the cytoplasm. No further cytoplasmic reaction was noted in these cells. The mononuclear cells demonstrated a gradually increasing intracytoplasmic concentration of granules. Prior to the appearance of leukemic symptoms, the lymphoid cells showed extensive vacuolization. It is suggested that this staining procedure affords a means for identifying cells undergoing malignant transformation before symptoms are discernible in the host.

Role of cyclic AMP in antiserum-induced growth inhibition of murine leukemia L5178Y cells

Heat-inactivated rabbit antiserum, in the absence of complement, induced a 1.5-2-fold increase in cyclic AMP levels in target cells L5178Y leukemia lymphoblasts within 10-20 min after the experiment. This change preceded the previously reported delayed inhibitory effects of antiserum on cell growth such as inhibition of RNA, DNA, and protein synthesis and cell proliferation, suggesting that cyclic AMP may be one of the mediators of the antigen-antibody reactions which occur at the cell surface. Furthermore, the addition of cyclic GMP or excess calcium to either antiserum or cyclic AMP-treated cultures alleviated the growth inhibitory effects of either antiserum or cyclic AMP, substantiating further the hypothesis proposed.

Molecular and cellular mechanisms of leukemic hemopoietic cell differentiation: an analysis of the Friend system

Murine erythroleukemia (MEL or Friend) cells grown in culture and induced to differentiate into cells resembling orthochromatic normoblasts provide a suitable system for uncovering molecular and cellular mechanisms of hemopoiesis and for understanding globin gene regulation. Inducer-treated cells undergo an irreversible commitment to maturation and accumulate large amounts of hemoglobin. Clonal analysis of commitment of individual cells combined with biochemical measurements has revealed that MEL cell differentiation is a highly coordinated set of events (program) leading to the differentiated erythroid state. The developmental program of MEL cells consists of early and late processes. The early events appear to be membrane-mediated processes which operate independently of each other and lead to commitment to terminal maturation and hemoglobin synthesis. Inducer-treated cells express an ability to remember ("memory response") previous exposure to inducer and to continue their differentiation after discontinuous exposure to inducer; expression of "memory response" occurs early in differentiation and affects both the initiation of commitment and accumulation of globin mRNA in a similar manner in inducer-treated cells. Commitment to maturation appears to be the central process responsible for determining the pattern of gene expression, limitation of proliferative activity and nuclear condensation. Commitment, however, can occur independently of hemoglobin synthesis. Although initiation of commitment is associated with early membrane-mediated events (e.g., ion-transport), maintenance and completion of maturation erythroid state is a result of a number of cellular processes. These processes are discussed in relation to the molecular and cellular mechanisms of initiation and completion of MEL cell differentiation. The role of the MEL system as a model for studying mouse and human globin gene regulation is presented.

Protease induction of hemoglobin synthesis but not terminal cell division in K562 cells

Several protease preparations of varied specificity increased hemoglobin levels in K562 cells. These are the first enzymes shown to stimulate this process in these cells. Hemin, at a concentration at which it did not act as a potent inducer of hemoglobin production, was found to synergistically stimulate induction by proteases. As seen in some other cell types, six different protease preparations also stimulated K562 cell yield. Hemin did not enhance the protease stimulation of cell yield, but was, instead, slightly inhibitory. Trypsin was one of the most potent inducers of the proteases tested. A combination of trypsin with a "synergistic" concentration of hemin did not decrease the size of K562 cells during induction of hemoglobin production, suggesting that these cells were not irreversibly differentiated nor induced to terminal cell division by this treatment. This was supported, although not proven, by an assay that demonstrated no progressive decrease in the rate of cell multiplication associated with the induction of hemoglobin synthesis.

Synergistic growth inhibiting effect of nitrous oxide and cycloleucine in experimental rat leukaemia

Nitrous oxide (N2O) inactivates the vitamin B12-dependent enzyme methionine synthetase with subsequent impairment of folate metabolism and a reduction of cellular proliferation. Indications exist that this effect is antagonized by S-adenosylmethionine (SAM), and it was investigated whether combination with an inhibitor of SAM synthesis, cycloleucine, would result in increased inhibition of growth in rat leukaemia model (BNML). Leukaemic growth was compared in untreated rats, in rats treated with either nitrous oxide/oxygen (1:1) or cycloleucine (50 mg kg-1 i.p.), and in rats receiving both agents. Combined treatment resulted in the strongest reduction of leukaemic infiltration in spleen and liver, and this reduction often was more than the added effects of single treatments. Peripheral leukocyte counts were also lowest after combined treatment. The deoxyuridine suppression test, measuring folate-dependent de novo synthesis of thymidine, was more severely disturbed with combined treatment. Levels of vitamin B12 in plasma were reduced in rats receiving N2O, but an increase in plasma folate occurred in all treated rats. These results indicate that a reduction of SAM synthesis by cycloleucine can increase the disturbance of folate metabolism that is caused by nitrous oxide, with a potentiation of the effects on leukaemic growth.

Interaction between feline leukaemia virus subgroups in the pathogenesis of erythroid hypoplasia

The interaction of feline leukaemia virus (FeLV) of subgroups A and C in the pathogenesis of erythroid hypoplasia in cats was studied. Weanling kittens infected with FeLV-A became permanently viraemic but remained haematologically normal over a period of 36 weeks. Similar kittens inoculated with FeLV-C, which produces erythroid hypoplasia when administered to newborn kittens, neither became viraemic nor developed the disease. However, weanling kittens inoculated with a mixture of FeLV-A and C became viraemic, first with FeLV-A and then additionally with FeLV-C, and the emergence of FeLV-C into the blood coincided with the advent of erythroid hypoplasia. When FeLV-C was inoculated into five older cats which had been viraemic with FeLV-A for several months previously, it appeared in the plasma of three of the cats and erythroid hypoplasia was diagnosed in two of these, 16-20 weeks after infection with FeLV-C. These results show that FeLV-A enhances the growth of FeLV-C in cats and overcomes their age-related resistance to FeLV-C. Also, the appearance of FeLV-C in the plasma of cats viraemic with FeLV-A indicates that erythroid hypoplasia will subsequently occur rapidly. These findings are relevant to the origin of FeLV-C isolates and their occurrence in nature.

Plasma membrane lipid order of leukemic and normal immature avian erythroid cells

Mammalian erythroblasts and their leukemic counterparts contain characteristic disordered regions of plasma membrane identified as putative membrane protein collection sites. In order to determine whether erythroid cells which do not enucleate contain homologous membrane domains, immature avian erythroid precursor cells and avian erythroleukemic cells were examined using merocyanine 540 (MC540), a fluorescent dye whose binding is sensitive to the packing of membrane lipids. Results were found to contrast with previous studies of the murine equivalents of these cells. In birds, normal erythroid precursors, including basophilic erythroblasts from the bone marrow and spleen of anemic animals, contained no detectable (less than 0.1%) cells which were stained by the dye. But cells from chicks infected with avian erythroblastosis virus (AEV) did stain. Considering the pattern of staining observed on AEV-erythroblasts relative to other leukemic and normal phenotypes, however, we conclude that neither normal nor leukemic avian erythroid cells contain a functional equivalent to the membrane protein collection sites found on their mammalian counterparts.

Alterations in plasma lipoproteins and heparin-releasable lipase activities in mice bearing the GRSL ascites tumor

The lipoproteins in GR mice bearing the transplanted GRSL ascites tumor were characterized by density gradient ultracentrifugation and SDS-polyacrylamide gel electrophoresis. In control mice the major proportion of the lipoproteins was found in the HDL density range, but on days 4 and 5 following tumor transplantation a gradual shift into the LDL density range was observed. At the same time the apolipoprotein E content increased at the expense of apolipoprotein A-I. VLDL became moderately elevated. On days 6 and 7 all lipoproteins except VLDL reached extremely low values. The C-apolipoproteins showed a remarkable shift in their relative proportions. Plasma lecithin:cholesterol acyltransferase activity showed no significant alteration in the course of tumor growth, but the triacylglycerol lipases in postheparin plasma were strongly decreased. Lipoprotein lipase had already started to decline on day 2 following tumor transplantation. However, when assayed in the presence of heat-inactivated control plasma, a decrease was not observed before day 5. This is suggestive of a depletion of a plasma cofactor preceding the final disappearance of the enzyme itself, and is compatible with the changing apolipoprotein C pattern. Hepatic lipase showed a 50% reduction between days 3 and 4. The lipoprotein alterations in tumor-bearing mice are explained as a direct consequence of the decreased lipase activities.

Transcriptional control of the bovine leukemia virus genome: role and characterization of a non-immunoglobulin plasma protein from bovine leukemia virus-infected cattle

Using cloned bovine leukemia virus (BLV) DNA as a probe in the dot blot hybridization technique, we demonstrated that the expression of the BLV genome in infected lymphocytes is blocked in vivo at the transcriptional level. This blocking effect is due to a non-immunoglobulin protein present in the plasma but not in the serum of BLV-infected cattle. The plasma BLV-blocking protein also blocks the expression of the BLV genome in fibroblast cells of bovine and nonbovine origin infected with BLV in vitro. The plasma BLV-blocking factor has no inhibitory effect on the expression of Rauscher murine leukemia virus and feline leukemia virus in monolayer culture. The plasma BLV-blocking factor is not an interferon molecule. As determined by gel filtration chromatography, the plasma BLV-blocking factor has an apparent molecular weight of ca. 150,000.

Interaction between erythroblasts and macrophages in vitro: effect of neuraminidase-treatment of erythroblasts and the role of serum factors

Some factors influencing the interaction in vitro between dimethylsulphoxide-induced Friend leukaemia erythroblasts (IFLE) and syngeneic mouse peritoneal macrophages (M phi) have been investigated. Desialation of erythroblasts by treatment with neuraminidase resulted in a significant increase in their association with and ingestion by M phi. In addition, the interaction with M phi of both neuraminidase-treated and untreated IFLE was found to be influenced by a heat-stable serum factor. gamma-globulin markedly enhanced the weak IFLE-M phi interaction which occurred at low serum concentration suggesting that the heat-stable factor may be an immunoglobulin. Desialation of the IFLE-rendered them agglutinable by peanut lectin which was used as a probe for neuraminidase-induced membrane changes. By contrast, cycloheximide treatment of IFLE which also enhances their interaction with M phi, did not result in the exposure of receptors for this lectin. It is proposed that both desialation and cycloheximide treatment of IFLE lead to secondary alterations in their membrane structure which renders them recognizable by M phi.

Relation between Friend leukemia virus-induced leukemia and genetic control of the host

Hematological assays of inbred specific pathogen-free (SPF) mice of ten different strains inoculated with Friend leukemia virus (FLV) were performed chronologically to assess whether the genetic control of the host may play an important role in viral oncogenicity. Mice strains C57BL/6J, B10 (H-2b) and B10D2 (H-2d) were FLV-resistant, BALB/c, DBA/2N (H-2d), RFM (H-2f), AKR and 80% of CBA/JN (H-2k) were FLV-sensitive (polycythemia) and C3H/He, B10Br and 20% of CBA/JN (H-2k) were FLV-sensitive (anemia). Only the AKR strain mice showed a spontaneous regression of splenomegaly. These results indicate that there is not a strong but a weak correlation between the H-2 haplotype and the reaction to FLV. The main phenomenon in the anemic mice was the monotonous proliferation of the naked blastic cell, whereas that in the polycythemic mice was the enormous increase of the mature erythroblast and the decrease of the naked blastic cell in the later phase. These facts suggest that the naked blastic cell in the mice with polycythemia are reactive and that in the mice anemia truly neoplastic.

Expression of multiple isozymes of granulocyte, monocyte, and macrophage esterases in polycythemic Friend erythroleukemia cells

We examined the expression of cytochemical markers of myeloid and monocyte-macrophage differentiation in conjunction with ultrastructural studies of different malignant erythroleukemic cells isolated from mice infected with the Friend polycythemic virus complex (FLV-P). The amounts of fluoride-sensitive and resistant nonspecific esterase activity increased with the progression of malignancy. Isoelectric focusing resolved this enzyme activity into 13 isozymes in the most malignant Friend cell type tested. These same isozymes were found in the adherent cell population of normal spleens. Two of these isozymes were shown to have chloroacetate esterase activity characteristic of granulocytes. Despite these myeloid and monocyte characteristics, light and electron microscopy showed no morphological evidence of differentiation in either of these lineages. This study demonstrates that the Friend erythroleukemic cell contains markers of three different hemopoietic cell types. The expression of myeloid, monocytic, and erythroid traits in these erythroleukemic cells can be used to monitor their malignant progression.

Expression of a transformation-related protein (p53) in the malignant stage of Friend virus-induced diseases

Stage 1 (pre-malignant) and stage 2 (malignant) cells derived from mice infected with Friend murine leukemia virus or polycythemia-inducing Friend virus complex were examined and compared for the expression of a transformation-related cellular protein, p53. Stage 2 cells were found to express high levels of p53, whereas stage 1 cells did not express detectable levels of this protein. These results indicate that p53 may be a marker for transformed cells present in the second stage of diseases induced by Friend murine leukemia virus or polycythemia-inducing Friend virus complex.

[Alterations in composition of sterols and in properties of erythrocyte membranes in rats with Shvetz experimental leukemia and after UV irradiation]

Amount of cholesterol was distinctly decreased but content of scvalene, lanosterol, 7-dehydrocholesterol and 7-beta-hydroxycholesterol--increased in erythrocyte membranes of rats with Shvetz experimental leukosis. At the same time, osmotic stability of erythrocytes and a pattern of acidic erythrogramms were altered. After UV irradiation of rats amount of cholesterol was increased as well as other unidentified substances appeared in erythrocyte membranes. These alterations appear to be one of factors responsible for development of body resistance to leukosis.

Occurrence of disseminated intravascular coagulation in rat BNML leukaemia despite lack of leucocyte procoagulant activity

Signs of disseminated intravascular clotting were observed during the development of BNML myelomonocytic leukaemia in rats, when the peripheral leucocyte count exceeded 20,000/microliters and more than 50% blasts were present in the circulation. BNML cells, harvested from blood and tested in appropriate systems, were found devoid of any procoagulant activity (PCA) even following prolonged in vitro incubation with endotoxin. Thus, it appears that these rat leukaemic cells share the same inability to express PCA which had been previously described in peripheral blood mononuclear cells from normal rats. Conceivably, in this rat model, leucocyte PCA does not represent a major trigger of intravascular coagulation and blood clotting is initiated by other, mainly plasmatic, pathways.

Ferrokinetic and erythrocyte survival studies in healthy and anemic cats

Erythrocyte survival and ferrokinetic studies were adapted to the cat. For 5 clinically healthy 4- to 9-month-old cats, mean 51Cr-labeled erythrocyte survival was 144 hours, and mean plasma 59Fe-labeled transferrin disappearance halftime was 51 minutes. Erythrocyte use of radioiron was rapid and efficient, with 50% to 80% of labeled iron incorporated into the erythron by 100 hours after injection into the cat. Six cats with feline leukemia virus infection were studied. For 2 cats with erythroid aplasia associated with C subgroup of feline leukemia virus, erythrocyte survival times were similar to those determined for the healthy cats, but plasma radioiron disappearance half time and erythrocyte use of radioiron were markedly diminished.

Erythrocyte survival studies in a rat myelogenous leukemia

To determine the extent intrinsic erythrocyte defects and/or extrinsic factors were involved in anemia of rats bearing Shay chloroleukemia (SCL), survival of 3H-DFP labeled erythrocytes was studied in leukemic and nonleukemic hosts. Red blood cells labeled before induction of leukemia, were rapidly lost from the peripheral circulation of SCL rats in terminal stages of disease. However, labeled erythrocytes from terminal SCL animals displayed normal lifespans when transfused into nonleukemic controls. Thus the anemia of this leukemia probably resulted from extrinsic factors associated with the leukemic process. Hemorrhage appeared to be primarily responsible for the anemia of this disease.

Inhibition of normal erythropoiesis in mice with Friend virus induced erythroleukemia

Mice in which erythroleukemia was induced by the Friend murine leukemia virus produced inhibitors of normal erythropoiesis. The inhibitors were released into media conditioned by bone marrow cells from leukemic, but not normal mice. The inhibitors were active at high dilution against normal erythroid progenitors (CFUE) in S-phase. Colony formation by CFUE from leukemic mice was stimulated by the same preparations of inhibitor. Fractionation of inhibitory media by gel filtration chromatography revealed 2 protease-sensitive, macromolecular components and a small molecular weight species. The cells responsible for production of the CFUE inhibitors were adherent, possessed macrophage but not T or B cell markers, and did not express viral antigens. The CFUE inhibitors were distinguishable from the previously described inhibitor of granulocyte-macrophage precursors, CFUC LIA, by antigenic specificity and cellular origin.

Effects of aclacinomycin-A on murine leukemia

Effects of aclacinomycin-A (ACM) on leukemic cells and normal hematopoietic stem cells were studied for the purpose of evaluating the usefulness of this agent as an antileukemic agent. ACM suppressed not only leukemic colony-forming unit (LCFU) in the radiation-induced murine erythroleukemia, but also normal hematopoietic stem cells (CFU-S, CFU-C) in mice. However, LCFU was the most sensitive to ACM. After the administration of ACM at a dose of 5 mg/kg. LCFU was suppressed to 0.02 of the control on day 3 and recovered within 5 days. Splenic CFU-S and CFU-C were suppressed to the nadirs on day 2 and day 1, respectively, and they recovered within 5 days. On the basis of the differences in the sensitivities to ACM and recovery patterns between LCFU and normal hematopoietic stem cells. ACM at a single dose of 5 mg/kg was administered every 3 days (total dose of 25 mg/kg) into leukemic mice, and the increase in mean lifespan obtained 113.9%. Effectiveness of ACM in the treatment of acute leukemia was discussed.

Deoxycytidine and deoxythymidine kinase activities in plasma of mice and patients with neoplastic disease

In C57BL x DBA/2 F1 (hereafter called BD2F1) mice inoculated with P815 neoplasms and in AKR mice with spontaneously developing leukemia, significant amounts of plasma deoxycytidine and thymidine kinase activities were detected in advanced disease. Undetectable or low levels of such kinase activities were observed in normal BD2F1 and in control AKR mice. Initial studies with leukemia patients revealed increased amounts of plasma deoxycytidine and thymidine kinase activities correlating favorably with the peripheral white blood cell counts. Initial studies with small numbers of patients with solid tumors revealed significant activities of both kinases in plasma of patients with four different cancers. Healthy volunteers revealed enzyme activities only insignificantly above background.