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Biomedical subjects

G Poste

Publications and source records attributed to G Poste.

At least 109 records · Page 6Linked to original sources
PubMed1982

Analysis of the fate of systemically administered liposomes and implications for their use in drug delivery.

Functional and ultrastructural studies of liposomes injected i.v. into inbred C57BL/6N mice were performed to determine whether free liposomes can traverse capillaries. In the liver and spleen, organs with discontinuous (sinusoidal) capillaries, ultrastructural and cell fractionation studies revealed that small (300- to 800-A diameter), sonicated, unilamellar liposomes were more efficient in penetrating liver sinusoids to interact with hepatocytes than were large (0.5- to 10-micrometers) multilamellar liposomes. Ultrastructural studies of the behavior of liposomes in the continuous capillaries of the lungs revealed that circulating phagocytic cells engulf the liposomes in the capillaries. Transcapillary migration of free liposomes was not observed. We conclude that free liposomes are unable to extravasate to reach the alveoli for subsequent engulfment by alveolar macrophages. Instead, liposomes in the lung capillaries are engulfed by circulating blood phagocytes which subsequently migrate to the alveoli to become alveolar macrophages. Experiments on the recruitment of blood monocytes into the lungs subjected to whole- or partial-body X-radiation confirmed that transfer of i.v.-injected liposomes to the alveolar compartment was mediated by blood monocytes. The inability of liposomes to escape from continuous capillaries and their rapid uptake by circulating and fixed phagocytic cells calls into question the feasibility of using liposomes to "target" drugs to cells in extravascular tissues.

Animals↗
PubMed1982

Comparison of the metastatic properties of B16 melanoma clones isolated from cultured cell lines, subcutaneous tumors, and individual lung metastases.

Tumors produced by s.c. injection of uncloned B16 melanoma cell lines contain clonal tumor cell subpopulations with widely differing metastatic properties, including clones that are nonmetastatic. Similar metastatic heterogeneity exists in clones isolated from the same cell lines cultured in vitro. In B16 melanoma sublines (B16-BL6, B16-BV8, and B16-BP8) selected for enhanced invasive and metastatic behavior, the proportion of clones with high metastatic capacity is increased relative to the parent cell line. The cellular composition of metastases produced by s.c. or i.v. injection of the uncloned parent cell line has also been examined. Some metastases are populated by clones with indistinguishable metastatic properties (intralesional clonal homogeneity) while others yield clones with different metastatic properties (intralesional clonal heterogeneity). The range of clonal diversity in heterogeneous metastases is, however, substantially less than in the parent line. The number of metastases yielding clones with heterogeneous metastatic phenotypes is higher for "spontaneous" metastases arising from s.c. tumors than in "experimental" metastases produced by i.v. injection of single-cell suspensions. Studies using B16 cells bearing specific biochemical markers indicate that clonally homogeneous metastases are of monoclonal origin and that metastases populated by clones with heterogeneous metastatic phenotypes are of polyclonal origin.

Animals↗
PubMed1981

Interactions among clonal subpopulations affect stability of the metastatic phenotype in polyclonal populations of B16 melanoma cells.

Analysis of the metastatic properties of clones isolated from mouse B16 melanoma cell lines (B16-F1 and F10) shows extensive cellular heterogeneity and the presence of subpopulations that have widely differing metastatic abilities. This pattern of metastatic heterogeneity is maintained during serial passage in vitro and in vivo. In contrast, even a short serial passage of individual clones isolated from these heterogeneous parent lines results in rapid emergence of variant subclones that have different metastatic properties. If several clones are mixed and cocultivated, this instability is not expressed. These data suggest that, in polyclonal populations, the various clonal subpopulations somehow interact with one another to "stabilize" their relative proportions within the population. Restriction of clonal diversity by selective killing of the majority of clones in a polyclonal population eliminates the stabilizing restraints and stimulates rapid emergence of new subpopulations to create heterogeneous populations containing a new panel of phenotypically diverse subpopulations that then reach stable proportions until the next selection pressure(s) is encountered.

Animals↗
PubMed1981

The role of plasma membrane receptors and the kinetics of macrophage activation by lymphokines encapsulated in liposomes.

The kinetics of activation of tumoricidal functions in mouse macrophages incubated with macrophage-activating factors (MAF) released by mitogen-stimulated lymphocytes (free MAF) and MAF encapsulated with liposomes (liposome-MAF) have been compared. Development of tumoricidal activity requires incubation of macrophages with free or liposome-encapsulated MAF for a minimum of 4 hr. Macrophages incubated with MAF for 4 hr were not cytotoxic when tumor target cells were added immediately after removal of MAF, but they were highly cytotoxic when allowed to complete a "lag" phase before being exposed to tumor cells. The duration of the lag phase varied with different activation protocols. The levels of cytotoxic activity induced by liposome-encapsulated MAF was consistently higher than that obtained with free MAF. Studies using inhibitors of endocytosis demonstrated that internalization of the liposome carrier is required for activation by liposome-MAF and that activation does not result from MAF leaking from liposomes and binding to MAF receptors on either the plasma membrane or the membrane of endocytic vesicles. Comparison of the efficiency of macrophage activation by MAF encapsulated in liposomes of differing internal volume revealed that large multilamellar and large unioligolamellar liposomes were more efficient in activating peritoneal exudate macrophages than were small unilamellar liposomes. Measurement of the volume of liposome contents internalized by macrophages from these three types of liposomes revealed that maximum cytotoxicity required internalization of a given volume of MAF-containing lymphocyte supernatants, after which no further increase in cytotoxicity occurred.

Animals↗
PubMed1981

Biochemical, morphological, and ultrastructural studies on the uptake of liposomes by murine macrophages.

The interaction of multilamellar liposomes with mouse peritoneal macrophages cultured in vitro has been examined. The principal mechanism of liposome uptake by these cells is by phagocytic engulfment. Studies with radiolabeled liposomes demonstrated that they are incorporated into macrophages as intact structures and that treatment of macrophages with inhibitors of phagocytosis prevents liposome uptake. Incubation of macrophages with liposomes containing encapsulated fluorescein-labeled bovine serum albumin resulted in localization of fluorescence within discrete cytoplasmic vacuoles. Ultrastructural observations confirmed that liposomes were internalized and were enclosed within phagosomes. Electron microscopy also revealed that, by 24 hr following phagocytosis, adjacent phagosomes containing liposomes prepared from bovine brain phosphatidylserine, egg phosphatidylcholine, and lysolecithin (mol ratio, 4.95/4.95/0.1) fused within the cytoplasm. In contrast, phagosomes containing neutral liposomes consisting solely of egg phosphatidylcholine did not fuse and remained as discrete single structures. Negatively charged bovine brain phosphatidylserine/egg phosphatidylcholine/lysolecithin liposomes were phagocytosed at a much faster rate (12 times faster) than were neutral egg phosphatidylcholine liposomes.

Animals↗
PubMed1980

The pathogenesis of cancer metastasis.

Metastases do not result from random survival of cells released from the primary tumour but from the selective growth of specialised subpopulations of highly metastatic cells endowed with specific properties that befit them to complete each step of the metastatic process.

Animals↗
PubMed1980

Pulmonary localization of intravenously injected liposomes.

Clearance from the circulation and tissue distribution of liposomes of differing size, surface charge, and composition injected IV into BALB/c mice have been examined. Large (500-3,400 nm diameter) liposomes are cleared from the circulation more rapidly than small sonicated liposomes (less than 100 nm diameter). Negatively charged liposomes are cleared more rapidly than neutral or positively charged liposomes of the same size. The major site at which liposomes injected IV accumulate, irrespective of their composition, is the liver. Accumulation of liposomes at extrahepatic sites, such as the lung, is influenced by liposome size, charge, and composition. Optimal localization and retention of liposomes in the lung were achieved with large negatively charged multilamellar and reversed evaporation phase liposomes containing phosphatidylserine (PS/PC, 3:7 mol ratio; PS/PC/LL 4.95:4.95:0.1 mol ratio).

Injections, Intravenous↗
PubMed1980

Arrest and metastasis of blood-borne tumor cells are modified by fusion of plasma membrane vesicles from highly metastatic cells.

B16 mouse melanoma sublines in culture spontaneously shed intact plasma membrane vesicles. These vesicles can be fused with the plasma membrane of cells from homologous and heterologous B16 sublines by using polyethylene glycol and phytohemagglutinin-P. Fusion of vesicles from a highly metastatic subline (F10) that localizes exclusively in the lung with cells from a poorly metastatic subline (F1) significantly increased the ability of F1 cells to become arrested in the lung and form metastases in this organ. In contrast, fusion of F1 vesicles with F10 cells did not alter the ability of vesicle-modified cells to localize in the lung or form lung metastases. F10 vesicle-modified F1 cells reverted to their original arrest behavior and metastatic capacity after removal of F10 vesicle components from the plasma membrane. The changes in the arrest and metastatic behavior of F10 vesicle-modified F1 cells were highly highly specific. Vesicles from other B16 sublines that are poorly metastatic and show limited localization in the lung (F1, FLLr, and F10Lr) did not modify the arrest behavior and metastatic capacity of FU cells. These results suggest that the differences in the abilities of the F1 and F10 sublines to localize in the lung are determined by differences in cell surface properties.

Animals↗
PubMed1980

Design of liposomes to improve delivery of macrophage-augmenting agents to alveolar macrophages.

Factors affecting the localization of liposomes injected i.v. in the lung have been studied to identify the optimal type of liposome for delivery of macrophage-activating agents to the lung to augment the tumoricidal activity of alveolar macrophages (AM). Comparison of pulmonary retention of liposomes of differing size, surface charge, and composition following i.v. injection into inbred mice revealed that large multilamellar (MLV) and reversed-phase-evaporation (REV) liposomes are arrested in the lung more efficiently than are small unilamellar liposomes of identical lipid composition. MLV and REV containing negatively charged amphiphiles arrest in the lung more efficiently than do neutral MLV's or REV's or MULV's and REV's containing positively charged amphiphiles. Comparison of the ability of liposomes containing a variety of negatively charged amphiphiles to localize in the lung established that optimal localization was achieved using MLV and REV prepared from phosphatidylserine (PS) and phosphatidylcholine (PC) (3:7 mol ratio) or PS:PC:lysolecithin (4.95:4.95:0.1 mol ratio). The proportion of these liposomes retained in the lung after i.v. injection was constant over a wide dose range (0.02 to 20 mumol phospholipid per mouse), but hemodilution due to i.v. inoculation of liposomes in volumes exceeding 0.2 ml reduced retention in the lung. Uptake of liposomes by AM was demonstrated by showing that i.v. injection of PS:PC MLV liposomes containing fluorescein-labeled bovine serum albumin resulted in localization of fluorescence within AM recovered by pulmonary lavage. Similarly, AM recovered after i.v. injection of PS:PC MLV liposomes containing lymphokine preparations rich in macrophage-activating factor (MAF) activity exhibited tumoricidal activity. In contrast, macrophages recovered from control animals given injections of unencapsulated MAF or liposomes containing lymphocyte supernatants without MAF activity were devoid of cytotoxic activity. Neutral (PC) MLV liposomes containing MAF, which show only very limited retention in the lung, were ineffective in activating AM in situ. We conclude that negatively charged MLV liposomes (PS:PC, 3:7 mol ratio) localize efficiently in the lung and that macrophage-activating agents encapsulated within such liposomes can successfully activate lung macrophages in situ.

Animals↗
PubMed1980

The influence of cell surface properties on the arrest of circulating melanoma cells.

B16 mouse melanoma sublines cultured in vitro spontaneously shed intact vesicles of plasma membrane. These vesicles can be fused with the plasma membrane of cells from homologous and heterologous B16 sublines using polyethylene glycol (PEG) and phytohemagglutinin (PHA). The ability of FI cells to arrest in the lung and form metastases in this organ is significantly increased by fusion of vesicles from a highly metastatic subline (F10) that localizes exclusively in the lung with cells from another subline (F1) which is poorly metastatic and produce few lung metastases. In contrast, fusion of F1 vesicles with F10 cells does not reduce their ability to localize in the lung of form lung metastases. Vesicle-treated F1 cells revert to their original arrest behavior and metastatic capacity following removal of F10 vesicle components from the plasma membrane. The changes in the arrest and metastatic behavior of F1 cells induced by F10 vesicles are highly specific. Vesicles from other B16 sublines which show limited abilities to localize in the lung (F1, F1(1r) and F10(1r) fail to modify the arrest behavior of F1 cells. These results suggest that the differences in the ability of the F1 and F10 sublines to localize in the lung are determined by differences in surface properties.

Animals↗
PubMed1980

Rat alveolar macrophages are susceptible to activation by free and liposome-encapsulated lymphokines.

Alveolar macrophages (AM) obtained from F344 rats were rendered tumoricidal by incubation in vitro with cellfree culture supernatant fluids rich in macrophage-activating factor (MAF) activity harvested from mitogen-stimulated F344 rat lymphocytes. AM activated by this procedure destroyed syngeneic, allogeneic, and xenogeneic tumor cells but were not cytotoxic for nonneoplastic cells. MAF was encapsulated in multilamellar lipid vesicles (liposomes) and its ability to render AM tumoricidal was compared with that of free (unencapsulated) MAF. Liposome-encapsulated MAF rendered AM cytotoxic at concentrations up to 16,000 times lower than free MAF. These data demonstrate that AM can respond in vitro to lymphokines and that MAF encapsulated within liposomes is far more efficient in rendering AM tumoridical than free MAF.

Adenocarcinoma↗
PubMed1980

In vitro selection of murine B16 melanoma variants with enhanced tissue-invasive properties.

New assay methods have been devised to quantitate tumor cell invasion of tissues of differing histological complexity maintained as organ cultures in vitro (chorioallantoic membrane of chicken, mouse urinary bladder, and canine blood vessel. In addition to quantitating tumor cell invasion, these methods also allow recovery of invasive cells for comparison with noninvasive cells. These methods have been used to select variant sublines from murine B16-F1 and B16-F10 melanoma lines that display significantly greater tissue-invasive abilities than the parent lines. B16 variant sublines selected in vitro for increased invasiveness through the bladder wall or vein also show a significant increase in their ability to form spontaneous and experimental metastases in vivo. In contrast, cells from the same parent cell line selected for increased invasiveness through the chorioallantoic membrane do not show significant alterations in metastatic behavior. We conclude that invasive variants can be isolated from the parent B16 tumor by several in vitro methods and that the level of expression of the invasive phenotype in vivo may be determined by the severity of the selection procedure in vitro.

Amnion↗
PubMed1979

Lectin-mediated agglutination of murine lymphoma cells. Cell surface deformability and reversibility of agglutination by saccharides.

Agglutination of S49 mouse lymphoma cells by Ricinus communis I agglutinin can be reversed by the competing haptenic saccharide, lactose, soon after agglutination, but after further incubation in the absence of lectin the agglutination reaction could not be reversed by lactose and the cells remained as multicell aggregates. The irreversibility of S49 cell agglutination was time, temperature and lectin concentration dependent and its onset correlated with ultrastructurally observed deformation of adjacent cell surfaces and an increase in the proportion of adjacent cell surface areas in close apposition within multicell aggregates. Pretreatment of S49 cells with cytochalasin B or cytochalasin B plus vinblastine enhanced R. communis I agglutinin-mediated agglutination, while vinblastine alone and fluoride plus azide had essentially no effect. When drug-treated cells were agglutinated and then incubated in lectin-free drug-containing media for various times prior to lactose addition, the drug effects were more pronounced. Cytochalasin B alone or with vinblastine inhibited lactose reversal of S49 cell agglutination compared to the drug-free controls, while fluoride plus azide enhanced hapten reversibility. Electron microscopic analysis revealed that the onset of agglutination irreversibility correlated with cell surface deformation in the drug-treated cells. Cell aggregates that were more readily reversible by lactose (fluoride plus azide) were unchanged or less deformed, while S49 aggregates treated with cytochalasin B plus vinblastine were more deformed compared to controls without drugs. These experiments suggest a role for cell surface deformability as an important secondary effect during lectin-mediated cell agglutination of S49 lymphoma cells.

Agglutination↗