Mekk3 is essential for early embryonic cardiovascular development.

The early development of blood vessels consists of two phases, vasculogenesis and angiogenesis, which involve distinct and also overlapping molecular regulators, but the intracellular signal transduction pathways involved in these processes have not been well defined. We disrupted Map3k3 (also known as Mekk3), which encodes Mekk3, a member of the Mekk/Ste11 family, in mice. Map3k3-/- embryos died at approximately embryonic day (E) 11, displaying disruption of blood vessel development and the structural integrity of the yolk sac. Angiogenesis was blocked at approximately E9.5 in mutant embryos. Map3k3 disruption did not alter the expression of the genes encoding Vegf-1, angiopoietin or their receptors. The development of embryonic, but not maternal, blood vessels in the placentas of Map3k3-/- embryos was impaired, revealing an intrinsic defect in Map3k3-/- endothelial cells. Moreover, Mekk3 activated myocyte-specific enhancer factor 2C (Mef2c), a transcription factor crucial for early embryonic cardiovascular development through the p38 mitogen-activated protein kinase (Mapk) cascade. We conclude that Mekk3 is necessary for blood vessel development and may be a possible target for drugs that control angiogenesis.

Tyrosine phosphorylation of mitogen-activated protein kinases is necessary for activation of murine macrophages by natural and synthetic bacterial products.

The purpose of these studies was to determine the intracellular signal transduction pathways of bacterial products in murine macrophages from lipopolysaccharide (LPS)-responder C3H/HeN and LPS-nonresponder C3H/HeJ mice. Both LPS and synthetic lipopeptide CGP 31362 (LPP) induced production of tumor necrosis factor alpha (TNF-alpha) in C3H/HeN macrophages. In C3H/HeJ macrophages, however, TNF-alpha was induced only by incubation with LPP. Both LPS and LPP induced tyrosine phosphorylation on proteins with apparent molecular masses of 39, 41, and 45 kD (p35, p41, and p45) in C3H/HeN macrophages, whereas in C3H/HeJ macrophages, tyrosine phosphorylation was induced only by LPP. 20-h incubation with LPS or LPP downregulated TNF-alpha production/secretion and tyrosine phosphorylation in C3H/HeN macrophages induced by additional LPS or LPP. In C3H/HeJ macrophages, however, the downregulation of TNF-alpha production and tyrosine phosphorylation were observed only with LPP. Protein kinase assays, Western blotting analyses, phenyl-Sepharose chromatography, and immunocomplex kinase assay suggested that p45 and p39 were similar or identical to mitogen-activated protein (MAP) kinase 1 and 2, respectively. Pretreatment of macrophages with LPS or LPP did not change the amount of kinase proteins but inhibited the stimulation of kinase activity by the agents. These data suggest that MAP kinases are among target proteins involved in the transduction of LPS and LPP signals that lead to activation of murine macrophages to produce/secrete TNF.

Angiostatin-mediated suppression of cancer metastases by primary neoplasms engineered to produce granulocyte/macrophage colony-stimulating factor.

We determined whether tumor cells consistently generating granulocyte/macrophage colony- stimulating factor (GM-CSF) can recruit and activate macrophages to generate angiostatin and, hence, inhibit the growth of distant metastasis. Two murine melanoma lines, B16-F10 (syngeneic to C57BL/6 mice) and K-1735 (syngeneic to C3H/HeN mice), were engineered to produce GM-CSF. High GM-CSF (>1 ng/10(6) cells)- and low GM-CSF (<10 pg/10(6) cells)-producing clones were identified. Parental, low, and high GM-CSF-producing cells were injected subcutaneously into syngeneic and into nude mice. Parental and low-producing cells produced rapidly growing tumors, whereas the high-producing cells produced slow-growing tumors. Macrophage density inversely correlated with tumorigenicity and directly correlated with steady state levels of macrophage metalloelastase (MME) mRNA. B16 and K-1735 subcutaneous (s.c.) tumors producing high levels of GM-CSF significantly suppressed lung metastasis of 3LL, UV-2237 fibrosarcoma, K-1735 M2, and B16-F10 cells, but parental or low-producing tumors did not. The level of angiostatin in the serum directly correlated with the production of GM-CSF by the s.c. tumors. Macrophages incubated with medium conditioned by GM-CSF- producing B16 or K-1735 cells had higher MME activity and generated fourfold more angiostatin than control counterparts. These data provide direct evidence that GM-CSF released from a primary tumor can upregulate angiostatin production and suppress growth of metastases.

Transfection with the inducible nitric oxide synthase gene suppresses tumorigenicity and abrogates metastasis by K-1735 murine melanoma cells.

Previous studies from our laboratory demonstrated an inverse relationship between the expression level of inducible nitric oxide synthase (iNOS) and the metastatic potential of murine K-1735 melanoma cells. The purpose of this study was to provide direct evidence that the expression of iNOS suppresses metastatic potential of melanoma cells. Highly metastatic K-1735 clone 4 cells (C4.P), which express low levels of iNOS, were transfected with a functional iNOS (C4.L8), inactive-mutated iNOS (C4.S2), or neomycin-resistance (C4.Neo) genes in medium containing 3 mM NG-methyl-L-arginine (NMA). Positive transfectants were identified by Southern and Northern blot analyses and homogeneous staining with a specific anti-iNOS monoclonal antibody. Semiconfluent cultures of C4.P (parental), C4.Neo.3 (control transfection), C4.S2.3 (inactive iNOS), and C4.L8.5 (functional iNOS) were harvested, and viable cells were injected intravenously into syngeneic C3H/HeN mice and allogeneic BALB/c nude mice. C4.P, C4.Neo.3, and C4.S2.3 cells were highly metastatic whereas C4.L8.5 cells were not metastatic. Experiments with [125I]dUrd-labeled tumor cells demonstrated that the initial arrest in the lung microvasculature did not differ among the lines, but that C4.L8.5 cells died by 48-72 h after injection. Enhanced survival of all K-1735 C4 cells (including C4.L8.5) was found in mice given twice daily injections of 20 mg NMA. The C4.L8.5 cells produced slow growing subcutaneous tumors in nude mice, whereas the other three lines produced fast growing tumors. In vitro studies confirmed that in the absence of NMA the expression of iNOS in C4.L8.5 cells induced apoptosis. Collectively, these data demonstrate that the expression of recombinant iNOS in melanoma cells is associated with apoptosis, suppression of tumorigenicity, and abrogation of metastasis.

Therapy of spontaneous metastases by intravenous injection of liposomes containing lymphokines.

Mice of two different strains were injected subcutaneously with spontaneously metastasizing syngeneic melanomas. After 4 to 6 weeks, the local tumors were removed and, 3 days after surgery, treatment of the metastases was initiated. The treatment consisted of intravenous injections of liposomes containing lymphokines or control supernatant fluids. Liposomes were injected twice weekly for 3 weeks, and the mice were killed 2 weeks later. Seventy-three percent of the mice injected with liposomes containing lymphokines were free of metastases, whereas only 10 percent of the mice treated with control liposomes were tumor-free. These experiments suggest that this form of therapy may provide a valuable addition to the more conventional approaches to the eradication of cancer metastases.

Metastasis results from preexisting variant cells within a malignant tumor.

Clones derived in vitro from a parent culture of murine malignant melanoma cells varied greatly in their ability to produce metastatic colonies in the lungs upon intravenous inoculation into syngeneic mice. This suggests that the parent tumor is heterogeneous and that highly metastatic tumor cell variants preexist in the parental population.

Biological diversity in metastatic neoplasms: origins and implications.

Whether neoplasms are unicellular or multicellular in their origin, the process of tumor evolution and progression can rapidly generate biological diversity. Metastases result from the survival and proliferation of specialized subpopulations of cells within the parent tumor. Metastases may have a clonal origin and different metastases may develop from different progenitor cells. However, as with the primary tumor, the origin of metastases is unimportant since the process of tumor evolution and progression can generate biological diversity within and among different metastatic foci.

Evidence for the clonal origin of spontaneous metastases.

A cultured cell line of the K-1735 melanoma was x-irradiated to induce chromosome breakage and rearrangements and then was implanted into the footpads of syngenic C3H mice. Spontaneous lung metastases were isolated from different animals, established in culture as individual lines, and then karyotyped. Within certain metastases, the same chromosomal abnormality (or abnormalities) (recombinant chromosomes) was found in all the cells examined. Most metastases differed from one another in that they exhibited characteristic combinations of chromosomal markers. These findings indicated that the metastases were clonal and that they probably originated from different progenitor cells.

Protection of mice against fatal herpes simplex type 2 infection by liposomes containing muramyl tripeptide.

Intravenous administration of liposomes containing muramyl tripeptide phosphatidylethanolamine, a lipophilic derivative of muramyl dipeptide that activates macrophages to a cytolytic state in situ, significantly protected mice against lethal challenge with herpes simplex virus type 2. These findings suggest that the systemic activation of macrophages by liposomes containing an immunomodulator can lead to prophylaxis of severe infections caused by herpesviruses.

Human monocytes activated by immunomodulators in liposomes lyse herpesvirus-infected but not normal cells.

Highly purified peripheral blood monocytes from normal human donors were activated in vitro by incubation with liposomes containing immunomodulators such as recombinant human gamma interferon, human lymphokines, or muramyl dipeptide. The ability of liposomes containing immunomodulators to activate monocytes to a cytotoxic state capable of discriminating between virus-infected and uninfected cells was shown by activated monocytes recognizing and destroying herpes simplex virus type 2-infected cells while leaving uninfected cells unharmed .

Dynamic change in phosphorylated platelet-derived growth factor receptor in peripheral blood leukocytes following docetaxel therapy predicts progression-free and overall survival in prostate cancer.

In a placebo-controlled randomised study of the platelet-derived growth factor receptor (PDGFR) inhibitor imatinib mesylate and docetaxel in metastatic prostate cancer with bone metastases (n=116), no significant differences in progression-free and overall survival were observed. To evaluate pharmacodynamic correlates of outcomes, we assessed the association of plasma platelet-derived growth factor (PDGF) isoform kinetics and PDGFR inhibition with progression-free and overall survival by individual treatment arm. We found that in the docetaxel-placebo arm alone, the probability of decrease in PDGFR phosphorylation (Pr-Decr-pPDGFR) above 0.5 (vs 30 months (HR 3.1; P=0.04 in log-rank test). By contrast, in the docetaxel plus imatinib arm, the association of Pr-Decr-pPDGFR >0.5 with a rise in plasma PDGF isoform concentrations and inferior survival was not observed. The data suggest that dynamic changes in PDGFR phosphorylation in peripheral blood leukocytes predict docetaxel efficacy. Rising plasma PDGF concentrations may explain and/or mark docetaxel resistance. Validation and mechanistic studies addressing these unexpected findings should anticipate a confounding influence of concurrent PDGFR inhibitor therapy.

Tumoricidal activity of human monocytes activated in vitro by free and liposome-encapsulated human lymphokines.

Human peripheral blood mononuclear cells from normal donors obtained by separation on a Percoll gradient were incubated with free or liposome-entrapped lymphokines produced from concanavalin A-stimulated lymphocytes and then were tested for cytotoxic activity against tumor cells. The treated monocytes lysed tumorigenic melanoma and glioblastoma target cells, but had no effect on three types of nontumorigenic target cells. The activation of monocytes to become tumoricidal was caused by macrophage-activating factor (MAF) and not by contamination with endotoxins, concanavalin A, or interferon. The endocytosis of liposomes containing MAF, but not of those containing control supernatants, led to the activation of cytotoxic properties in the monocytes. Activation by liposome-encapsulated MAF was very efficient and required less than 1/800th of the amount of free MAF necessary to achieve the same levels of cytotoxicity. Thus, the encapsulation of mitogen-induced MAF in liposomes could provide an effective approach for the activation of blood monocytes in situ.

Increased adherence of sickled and phosphatidylserine-enriched human erythrocytes to cultured human peripheral blood monocytes.

The precise mechanism by which sickle erythrocytes (RBC) are removed from the circulation is controversial, although it is possible that enhanced recognition of these cells by circulating mononuclear phagocytes could contribute to this process. We investigated this possibility by interacting sickle cells with cultured human peripheral blood monocytes. Our results show that both irreversibly sickled cells (ISC) and deoxygenated reversibly sickled cells (RSC) had a higher avidity for adherence to monocytes than did oxygenated sickle and normal RBC. ISC were the most adherent cell type. Adherence of RSC to monocytes was found to be reversible; reoxygenation of deoxygenated RSC resulted in a significant decrease in RSC--monocyte adherence. Concomitant with alterations in sickle RBC adherence were alterations in the organization and bilayer distribution of membrane phospholipids in these cells. Specifically, enhanced adherence was associated with increased exposure of RBC membrane outer leaflet phosphatidylserine (PS) and phosphatidylethanolamine, whereas lack of adherence was associated with normal patterns of membrane phospholipid distribution. To investigate the possibility of whether the exposure of PS in the outer membrane leaflet of these cells might be responsible for their recognition by monocytes, the membranes of normal RBC were enriched with the fluorescent PS analogue 1-acyl-2[(N-4-nitro-benzo-2-oxa-1,3-diazole)aminocaproyl]-phosphatidy lse rine (NBD-PS) via transfer of the exogenous lipid from a population of donor phospholipid vesicles (liposomes). RBC enriched with NBD-PS exhibited enhanced adherence to monocytes, whereas adherence of RBC enriched with similar amounts of NBD-phosphatidylcholine (NBD-PC) was not increased. Furthermore, preincubation of monocytes with PS liposomes resulted in a approximately 60% inhibition of ISC adherence to monocytes, whereas no inhibition occurred when monocytes were preincubated with PC liposomes. These findings strongly suggest that erythrocyte surface PS may be a ligand recognized by receptors on human peripheral blood monocytes and that abnormal exposure of PS in the outer leaflet of the RBC membrane, as found in sickle RBC, might serve to trigger their recognition by circulating monocytes. Our results further suggest that abnormalities in the organization of erythrocyte membrane phospholipids may have significant pathophysiologic implications, possibly including shortened cell survival.

Activation in vitro of mouse macrophages by syngeneic, allogeneic, or xenogeneic lymphocyte supernatants.

Macrophages from normal C57BL/6 mice, those with a subcutaneous B16 melanoma, and mice immunized against the tumor were examined for in vitro cytotoxicity to B16 tumor cells. Macrophages were treated by incubation with supernatants from B16 cells grown either in unmixed cultures or in cultures containing syngeneic, normal, or sensitized allogeneic (A mouse), or xenogeneic (rat) lymphocytes. The various treated and untreated macrophages were then cultured for 5 days with viable B16 cells prelabeled with 125I-5-iodo-2'-deoxyuridine; the cultures were terminated, and the extent of destruction of the B16 target cells was determined from the amounts of radioactivity remaining in adherent tumor cells. Of the untreated macrophages, only those from immunized mice were cytotoxic to the tumor cells; macrophages from normal and tumor-bearing mice became cytotoxic by incubation with supernatants from cultures containing lymphocytes from immunized syngeneic mice, sensitized allogeneic mice, or sensitized rats; and macrophages incubated with supernatants from cultures containing normal nonsensitized allogeneic or xenogeneic lymphocytes showed no cytotoxicity. Thes results suggested that macrophages from tumor-bearing animals are potentially cytotoxic to their syngeneic tumors and can be activated by mediators released from sensitized syngeneic, allogeneic, and/or xenogeneic lymphocytes in vitro.

Enhanced metastatic potential of tumor cells harvested from spontaneous metastases of heterogeneous murine tumors.

These studies demonstrated that cells populating spontaneous metastases are, in general, more metastatic than the cells populating the parent neoplasm, thereby providing direct evidence that the process of metastasis is selective and not random. The tumors used in these studies were the UV-2237 fibrosarcoma, an in vitro cloned line (C-40) from the UV-2237 tumor, and the K-1735 melanoma, all of which are syngeneic to the C3H/HeN (mammary tumor virus-negative) mouse strain; the M5076 reticulum cell sarcoma and the Lewis lung carcinoma 3LL, which are syngeneic to the C57BL/6 mouse strain, were also used. All tumors were implanted sc into the footpads of syngeneic mice, and several resulting spontaneous metastases were isolated and established in culture as individual cell lines. For each tumor system, comparison was made of the ability of parent tumor cells and cells isolated from several spontaneous metastases to produce either experimental or spontaneous metastases. Cells populating spontaneous metastases produced by heterogeneous and poorly metastatic tumors were significantly more metastatic than the cells of their respective parent tumors. In contrast, cells populating metastases produced by previously selected tumors did not differ significantly in metastatic potential from cells populating their parent tumors. In such systems, metastasis appeared to be random.

Role of natural killer cells in the destruction of circulating tumor emboli.

A close correlation was demonstrated between levels of host natural cytotoxic (NC) and/or natural killer (NK) cell activity and capacity to eliminate blood-borne tumor cells. The outcome of experimental metastasis of several tumors with defined biologic behavior was studied in syngeneic mice exhibiting low NK cell activity [3-wk-old normal mice and cyclophosphamide (Cy)-treated adult mice] and high NK cell activity (normal adult mice). An iv injection of metastatic tumor cells into 3-week-old or Cy-treated mice markedly enhanced experimental pulmonary metastasis. The increased incidence of metastasis in mice exhibiting low activity of NK cells was not due to enhanced tumor cell arrest in the lung but rather to increased tumor cell survival. Boosting the NK activity of 3-week-old, but not Cy-treated, mice with interferon inducers inhibited metastasis formation. The adoptive transfer of spleen cells from syngeneic mice or allogeneic nude mice that have high NK activity shortly before (but not after) iv tumor challenge abrogated the Cy-induced enhancement of metastasis. The reactive lymphoid cells were non-T, nonadherent to nylon wool, sensitive to Cy treatment, and endowed with a natural ability to kill tumor cells during a short (12-24 hr) period. The conclusions were that NC-NK cells are important in host defense against circulating tumor cells and therefore can prevent the development of tumor cells into metastases.

Organ selectivity for implantation survival and growth of B16 melanoma variant tumor lines.

The fate of bloodborne malignant melanoma cells selected for their enhanced ability to form lung colonies was examined to determine how specific tumor cells are arrested in certain organs during the experimental metastasis process. After murine B16 melanoma variant tumor cell lines with low (B16-F1) or high (B16-F10) survival and growth potential in vivo were admisistered by iv or intracardiac injections into syngeneic C57BL/6 mice, the quantitative distribution of [125l]5-iodo-2'-deoxyuridine (125IUDR)-labeled cells in the organs and subsequent formation of metastatic lung colonies were assessed. The initial distribution of viable tumor cells was dependent on the route of injection: Soon after iv injection, more 125IUDR-labeled B16 cells were localized in the lungs and fewer in the blood and other organs than after intracardiac injection. However, 1 day after the injection, the number of viable tumor cells in the lungs was independent of the route of injection, and at 14 days the quantity of resulting lung tumor colonies was similar. Variant line B16-F10 cells were better arrested and formed more tumors per input cell than B16-F1, regardless of the injection route. B16-F10 yielded only lung tumor colonies, whereas B16-F1 formed some extrapulmonary tumor growths. The results suggested that the ultimate fate of circulating tumor cells was not determined solely by nonspecific arrest in the capillary bed of the first organ encountered, and that in vivo selection could produce tumor line variants with organs preferences.

Effects of levamisole on in vivo and in vitro murine host response to syngeneic transplantable tumor.

The effects of levamisole were studied in vivo and in vitro on two murine tumors, B16 melanoma and adenocarcinoma 15091, syngeneic to the mouse strains used. Administration of levamisole before tumor transplantation enhanced the early appearance of neoplasms but did not affect the overall incidence or course of tumor growth as compared with that observed in controls given saline injections or animals given levamisole with lethally X-irradiated tumor cells. Administration of the drug 1 day before iv injection of tumor cells significantly reduced the incidence of pulmonary nodules, but if the drug was given 3 or 5 days before tumor challenge, the incidence of nodules was increased. Lymphocytes or macrophages from normal mice given levamisole had no effect on tumor cells in vitro, whereas lymphocytes incubated with levamisole in vitro enhanced tumor cell growth. When lymphocytes and tumor cells were mixed in vitro, lymphocytes from animals treated with the drug formed larger multicell clumps with tumor cells than did those from normal controls. We concluded that levamisole did not protect the mice against the tested tumors.

Use of young nude mice for selection of subpopulations of cells with increased metastatic potential from nonsyngeneic neoplasms.

The purpose of these studies was to investigate whether young (3-wk-old) nude mice, which lack functional T-lymphocytes and demonstrate low natural killer cell activity, could serve as in vivo models for the selection of metastatic subpopulations of cells from heterogeneous allogeneic melanomas. Three-week-old BALB/cAnN or N:NIH(S) nude mice received iv injections of single cells harvested from either the B16 or K-1735 melanoma. Individual pulmonary metastases were harvested 4 weeks later and implanted sc into nude mice to expand the population. Cells from each of these metastases colonized in the lungs of 3-week-old nude mice and 6-week-old normal syngeneic mice with significantly higher efficiency than did cells from the parent tumors. It was concluded that, in addition to being a useful in vivo model for ascertaining the metastatic potential of neoplasms, the healthy young nude mouse could be used for selecting and maintaining tumor cell variants of high metastatic potential room heterogeneous allogeneic tumors.