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Biomedical subjects

B F Sloane

Publications and source records attributed to B F Sloane.

At least 91 records · Page 5Linked to original sources
PubMed1987

Inhibition of tumor cell induced platelet aggregation by prostacyclin and carbacyclin: an ultrastructural study.

Prostacyclin and its synthetic analog carbacyclin were compared as to their abilities to inhibit tumor cell-platelet interactions. Aggregation of rat platelets was induced in vitro by homologous rat Walker 256 carcinosarcoma cells. The extent of cellular interactions was examined ultrastructurally. The ultrastructural data presented here indicate that the tumor cell-platelet interactions began with individual platelets which initiated platelet chain formation in focal association with tumor cell surfaces. By mid-phase aggregation large homotypic platelet aggregates had formed with tumor cells positioned on the external surfaces of the emboli. Tumor cell-platelet interactions became progressively more extensive as tumor cells became enmeshed with growing platelet aggregates. Prostacyclin and carbacyclin inhibited tumor cell platelet interactions in a dose-dependent manner. Carbacyclin inhibition of tumor cell induced platelet aggregation was longer in duration but carbacyclin was 10-fold less effective than was prostacyclin. We report here that prostacyclin and carbacyclin inhibit both aggregation and the ultrastructural changes associated with tumor cell-platelet interactions.

Animals↗
PubMed1987

Platelet enhancement of tumor cell adhesion to subendothelial matrix: role of platelet cytoskeleton and platelet membrane.

Platelet involvement during tumor cell adhesion to subendothelial matrix was examined in vitro. Platelets were subjected to thrombin stimulation and mechanical lysis and examined for their effects on tumor cell adhesion. These treatments altered the platelet ultrastructure and cytoskeletal integrity. Untreated washed rat platelets (WRP) exhibited extensive adhesion to and spreading on substrates and substantially enhanced tumor cell adhesion to the same substrates (i.e., 250% greater than tumor cells without platelets). Thrombin prestimulation of platelets limited platelet adhesion and spreading and platelet facilitation of tumor cell adhesion. Complete mechanical lysis disrupted both the platelet membrane and the cytoskeleton and eliminated the ability of platelets to adhere or to enhance tumor cell adhesion. Partially lysed platelets resembled membrane ghosts and facilitated tumor cell adhesion by a mechanism independent of spreading and cytoskeletal rearrangement. Fractionation studies indicated that platelet cytoskeletal components played a role in the adhesion process. Pretreatment of WRP with cytochalasin A or B dose dependently inhibited microfilament-mediated platelet spreading and platelet-enhanced tumor cell adhesion. Colchicine and vinblastine induced microtubule depolymerization, but they had no observable effect on platelet spreading or platelet-enhanced tumor cell adhesion. It was concluded that platelet-enhanced tumor cell adhesion to subendothelial matrix depends on an intact platelet cytoskeleton and on a platelet membrane component(s) and is mediated by surface contact between platelets and tumor cells. Furthermore, platelet-mediated tumor cell adhesion to subendothelial matrix may involve two mechanisms: one dependent on, and one independent of, platelet spreading and cytoskeletal rearrangement.

Animals↗
PubMed1987

Inhibition by prostacyclin of the tumor cell-induced platelet release reaction and platelet aggregation.

Prostacyclin was examined for its inhibitory effects on the tumor cell-induced platelet release reaction. Prostacyclin inhibited in a dose-dependent manner tumor cell-induced release of platelet dense granules and alpha-granules concomitant with an inhibition of platelet aggregation. Release was determined by assay of biochemical markers (serotonin for dense granules and beta-thromboglobulin for alpha-granules). A tenfold higher concentration of prostacyclin was required to inhibit completely serotonin release as compared to the concentration required for beta-thromboglobulin release. Correlative ultrastructural studies demonstrated that prostacyclin at doses of over 10 ng/ml inhibited the ultrastructural changes associated with tumor cell-induced platelet shape change and platelet granule release. Platelet aggregates exhibited the retention of granule reservoirs that could potentially be involved in long-term release of biologically active substances.

Animals↗
PubMed1986

Cisplatin and nifedipine: synergistic cytotoxicity against murine solid tumors and their metastases.

Calcium channel blockers of 3 chemical classes and calmodulin antagonists have recently been shown to enhance the cytotoxicity of conventional cancer chemotherapeutic agents. We tested the ability of nifedipine, a dihydropyridine class calcium channel blocker, to enhance the cytotoxicity of cisplatin, the current chemotherapeutic of choice against human head and neck tumors and testicular carcinoma. Both in vitro and in vivo, combination therapy with nifedipine and cisplatin resulted in synergistic inhibition of tumor cell proliferation, primary tumor growth and appearance of spontaneous pulmonary metastases. This combination also significantly increased the survival of mice bearing cisplatin-resistant tumors. This is the first indication that calcium channel blockers can enhance the cytotoxicity of cisplatin as well as the first demonstration that calcium channel blockers can enhance cytotoxicity of chemo-therapeutic agent against a solid tumor and its metastases.

Animals↗
PubMed1986

Cathepsin B: association with plasma membrane in metastatic tumors.

The subcellular localization of cathepsin B activity (EC 3.4.22.1) in three murine melanomas of increasing metastatic potential (Cloudman less than B16-F1 less than B16 amelanotic) was determined. Cathepsin B activity was localized in the heavy mitochondrial fraction of normal murine liver but in the light mitochondrial fraction of the metastatic melanomas; the localization of three other lysosomal hydrolases did not shift. Further purification of the light mitochondrial fraction into L-1 (density = 1.045 g/ml) and L-2 (density = 1.07 g/ml) fractions was achieved on a 30% iso-osmotic Percoll gradient. The L-1 fraction of liver and melanomas contained Na+, K+-ATPase activity; the L-2 fraction of liver contained four lysosomal hydrolase (cathepsins B and H, N-acetyl-beta-glucosaminidase, and beta-glucuronidase) and glucose-6-phosphatase activities. Ultrastructural examination revealed that the L-1 fraction consisted of membrane vesicles and the L-2 fraction of secondary lysosomes. In the B16 melanomas cathepsin B and N-acetyl-beta-glucosaminidase activities were found in both L-1 and L-2 fractions. Specific activities of the two enzymes in the plasma membrane (L-1) fractions increased in correspondence with metastatic potential. Cathepsin H and beta-glucuronidase activities were not localized in the plasma membrane fractions of the B16 melanomas. Localization of hydrolytic enzymes in the plasma membrane of metastatic tumor cells could result in focal dissolution of the extracellular matrix and thereby invasion and metastasis.

Acetylglucosaminidase↗
PubMed1985

Inhibition by dihydropyridine class calcium channel blockers of tumor cell-platelet-endothelial cell interactions in vitro and metastasis in vivo.

Three calcium channel blockers of the dihydropyridine class were tested in vitro for their effects on tumor cell-platelet-endothelial cell interactions and in vivo for antimetastatic properties. Felodipine, nimodipine and nifedipine inhibited tumor cell-induced platelet aggregation in vitro in a dose-dependent manner. These compounds also inhibited platelet-enhanced tumor cell adhesion to endothelial cells in vitro. Lung colony formation ("experimental" metastasis) and spontaneous pulmonary metastasis were inhibited by felodipine, nimodipine and nifedipine. From the present studies on three calcium channel blockers of the dihydropyridine class we hypothesize that calcium channel blockers may represent a new generic class of antimetastatic agents.

Animals↗
PubMed1985

Purification and characterization of platelet aggregating activity from tumor cells: copurification with procoagulant activity.

The platelet aggregating component from murine 15091A mammary adenocarcinoma cells was purified by solubilization of activity with CHAPS (3-[(3-cholidamidopropyl)-dimethylammonio]-1-propane sulfonate), fractionation with ammonium sulfate, ion exchange chromatography on DEAE cellulose, and hydrophobic interaction chromatography on dodecyl agarose. A purification of 90-100 fold over the initial cell homogenate was achieved. SDS-PAGE of the purified material resulted in a single major band with a molecular weight of 51,000 +/- 2,000. Procoagulant activity was found to copurify with platelet aggregating activity. Reconstitution with phospholipids was necessary to obtain platelet aggregating activity and procoagulant activity. Trypsin abolished both platelet aggregating and procoagulant activities. The irreversible proteinase inhibitors phenylmethylsulfonyl fluoride, N alpha-p-tosyl-L-lysine chloromethyl ketone, iodoacetamide or phenanthroline had no effect on platelet aggregating or procoagulant activities. Platelet aggregation induced by this material was inhibited by low concentrations of the specific irreversible thrombin inhibitors, dansylarginine N-(3-ethyl-1, 5-pentanediyl) amide and D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone. This is the first report of copurification of tumor cell platelet aggregating and coagulating activities.

Animals↗
PubMed1985

Cathepsin B-like activity in viable tumor cells isolated from rodent tumors.

The cathepsin B-like cysteine proteinase activity which has been implicated in tumor malignancy has been attributed to several cellular sources, including viable tumor cells, necrotic tumor cells, and host-inflammatory cells. We have isolated subpopulations of cells from eight rodent tumors of five histological types, using centrifugal elutriation, and verified the cellular composition of the subpopulations cytologically. Ninety-two % or greater of the cathepsin B-like activity was associated with the isolated fractions containing greater than or equal to 95% tumor cells of 86 +/- 2% (SE) viability (beta fractions). The isolated fractions consisting of necrotic tumor cells and inflammatory cells (alpha fraction) apparently contain a cysteine proteinase inhibitor, since both cathepsin B-like and cathepsin H activities in the beta fraction of B16 amelanotic melanomas could be inhibited by addition of the alpha fraction.

Animals↗
PubMed1985

Arrest and extravasation of B16 amelanotic melanoma in murine lungs. A light and electron microscopic study.

The arrest and extravasation of tail vein-injected B16 amelanotic melanoma (B16a) cells, disaggregated from subcutaneous tumors, were studied at intervals from 10 minutes to 5 days in lungs of C57BL6J mice. Tumor cells were found in the pulmonary vasculature at 10 minutes postinjection and were commonly associated with platelets and fibrin. Tumor cells with associated thrombi increased, reaching a peak at 4 hours. Arrest of the B16a melanoma tumor cells appears to involve contact with endothelial plasma membrane, often with adjacent but not interposed platelet and fibrin thrombus formation. The tumor cell-associated thrombi subsequently decreased in frequency and were rarely found after 48 hours. The arrested tumor cells were initially in contact with the endothelial cells, which were gradually displaced by tumor cells achieving contact with the vascular basal lamina (BL). Initial contact with the vascular BL was observed at 4 hours, with a progressive increase in contact over the subsequent 2 days. Blood flow was commonly reestablished past the BL-attached tumor cells after dissolution of the thrombi. Mitotic figures in the tumor cells attached to the BL were frequent after 24 hours and the tumor appeared to proliferate intravascularly along the basal lamina. Penetration of the BL by tumor cell cytoplasmic processes was first observed at 3 days with continued dissolution of the vascular BL developing through day 5. Extravasation occurred through a combination of intravascular tumor cell proliferation and destruction of vascular BL by the B16a cells. Migration or diapedesis of the tumor cells was not observed in any of the time periods studied.

Animals↗
PubMed1984

Cooxidation of 13-cis-retinoic acid by prostaglandin H synthase.

Cooxidative metabolism of 13-cis-retinoic acid (13-CIS) via prostaglandin H synthase was investigated employing ram seminal vesicle microsomes. Oxidation of 13-CIS utilizing H2O2, 13-hydroperoxy-9-cis-11-trans-octadecadienoic acid (13-OOH-18:2), or 1-hydroperoxy-5-phenyl-4-pentene was detected by measurement of O2 incorporation. UV spectroscopy and HPLC of extracted incubation mixtures demonstrated that 13-CIS was metabolized to oxidized derivatives. Similar spectral changes and HPLC profiles were obtained with H2O2, 13-OOH-18:2, or arachidonic acid as substrates. 4-Hydroxy-13-cis-retinoic acid and all trans-retinoic acid were products of cooxidation as well as other polar metabolites. Oxidation was inhibited by the antioxidant butylated hydroxyanisole and the spin trap, nitrosobenzene. These results indicate that 13-cis-retinoic acid is cooxidized by prostaglandin H synthase and suggest a free radical mechanism resembling that of lipid peroxidation.

Animals↗
PubMed1984

Antithrombogenic effects of calcium channel blockers: synergism with prostacyclin and thromboxane synthase inhibitors.

Four calcium channel blockers (nimodipine, nifedipine, verapamil and diltiazem) of three chemical classes were tested in vitro for inhibition of platelet aggregation using heparinized human platelet rich plasma. Both ADP- and thrombin-induced aggregation were inhibited as was the biosynthesis of thromboxane A2 in response to ADP or thrombin. However, the IC50's for the calcium channel blockers were greater than or equal to 110 microM. Nimodipine was also tested in combination with prostacyclin, the potent platelet antiaggregatory agent, or with a thromboxane synthase inhibitor, U63557A. At concentrations at which neither nimodipine or prostacyclin inhibited platelet aggregation greater than or equal to 10%, the two compounds is combination synergistically inhibited both ADP- and thrombin-induced platelet aggregation. U63557A inhibited biosynthesis of thromboxane A2 by platelets in response to ADP or thrombin, but did not inhibit either ADP- or thrombin-induced platelet aggregation. However, U63557A in combination with a threshold inhibitory concentration of nimodipine resulted in a synergistic inhibition of platelet aggregation induced by ADP or thrombin. These results suggest that calcium channel blockers may be of therapeutic value as a new class of antithrombogenic agents when used in combination with agents that inhibit either platelet aggregation or synthesis of platelet thromboxane A2.

Adenosine Diphosphate↗
PubMed1984

Cysteine proteinases and metastasis.

Cysteine proteinases are a subclass of endopeptidases which require activation by thiol reagents. A tumor cysteine proteinase which appears to be related to lysosomal cathepsin B has been implicated in the ability of tumor cells to invade the extracellular matrix and to metastasize to secondary sites. Lysosomal cathepsin B can degrade such components of the extracellular matrix as collagen, fibronectin and proteoglycans. Activity of this cathepsin B-like cysteine proteinase (CB) has been correlated with tumor malignancy in a number of tumor lines yet not in all tumor lines studied. CB activity in tumors seems to be associated with the viable tumor cells, probably with the plasma membrane of these tumor cells. CB activity has been measured in the sera, urine, ascites fluid and pancreatic fluid of tumor-bearing patients. CB is released from tumor explants and tumor cells in vitro as well as from normal subcutaneous tissue exposed to tumor-conditioned medium. Cathepsin B from normal tissues is rapidly inactivated above pH 7.0. Therefore, CB in tumor cell membranes or released from tumor cells (or from host cells in response to tumor cells) may not possess proteolytic activity at neutral pH and thus may not facilitate tumor cell invasion. However, CB exhibits enhanced stability at neutral or slightly alkaline pH's. There is not yet definitive proof that CB plays a role in tumor invasion and metastasis. There is, however, an increasing body of correlative evidence relating CB activity and tumor malignancy. This correlative evidence plus preliminary evidence that tumor CB can degrade components of the extracellular matrix in vitro suggests that CB may be one proteinase active in a proteolytic cascade resulting in tumor invasion and metastasis.

Animals↗
PubMed1984

Effect of estrogen on lysosomal enzyme activities in rat heart.

The activities per microgram DNA of five lysosomal enzymes [cathepsin D, cathepsin B, beta-N-acetylglucosaminidase (beta-NAG), beta-glucuronidase, and acid phosphatase] were measured in homogenates of female and male rat (Sprague-Dawley) hearts. Female rats were studied during stages of the estrous cycle and at 3 weeks after ovariectomy. Three-week-postovariectomized female rats and intact male rats were injected subcutaneously with 17 beta-estradiol-3-benzoate. Lysosomal enzyme activities in the male rat heart were more responsive to exogenous estradiol than were activities in the female rat heart. Cathepsin B, beta-NAG, and beta-glucuronidase were increased dramatically in the male rat heart upon short-term administration of estrogen (4 days). In both female and male rat hearts, activities of two lysosomal proteinases, cathepsins B and D, were reduced significantly (approximately 50%) by extended administration of estrogen for 10 days.

Acetylglucosaminidase↗
PubMed1983

Calcium channel blockers: potential antimetastatic agents.

The calcium channel blocker nifedipine (Bay A 1040) was examined for its effects on tumor cell-platelet interactions. In vitro, nifedipine inhibited tumor cell-induced platelet aggregation and platelet enhanced tumor cell adhesion to confluent endothelial cell monolayers and in vivo nifedipine inhibited pulmonary tumor colony formation ("experimental metastasis") by intravenously injected tumor cells. This evidence suggests that calcium channel blockers may be a new class of antimetastatic agents.

Animals↗