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R J Bernacki

Publications and source records attributed to R J Bernacki.

86 records · Page 5Linked to original sources
PubMed1977

Concomitant elevations in serum sialytransferase activity and sialic acid content in rats with metastasizing mammary tumors.

Rats with transplantable spontaneously metastasizing mammary tumors have elevated levels of both serum sialoglycoconjugate and serum sialytransferase activity compared with normal female rats or rats with various nonmetastasizing mammary tumors. A direct relationship was observed between the amount of serum protein-bound sialic acid and serum sialyltransferase activity in all rats studied. Serum sialyltransferase activity in rats with a representative metastasizing mammary tumor, SMT-2A, was also correlated with tumor age. Microsomes prepared from the SMT-2A tumor have a sixfold higher sialyltransferase activity than do microsomes prepared from the nonmetastasizing mammary tumor MT-W9B. Normal rat liver microsomes have the same level of activity as microsomes prepared from livers of animals with either SMT-2A or MT-W9B tumors. The data indicate that spontaneously metastasizing mammary tumor cells have an increased production and release, perhaps through cell surface shedding, of a sialyltransferase. It is suggested that this sialyltransferase may increase the serum half-life of certain tumor-specific circulating glycoconjugates by increasing the content of protein-bound sialic acid and may thereby play a role in the immune escape mechanism of metastasizing tumor cells.

Animals↗
PubMed1977

Biochemical characteristics, metabolism, and antitumor activity of several acetylated hexosamines.

We have synthesized several potential inhibitors and/or modifiers of the carbohydrate portion of plasma membrane glycoconjugates. These include fluorinated and actylated analogs of D-glucosamine, D-galactosamine, and D-mannosamine. These compounds have been tested to determine their effects on both[14C] glucosamine and [3H] leucine incorporation into glycoconjugate and on cell growth and viability using P-288 murine lymphoma cells maintained in tissue culture. The most cytotoxic agent tested was 2-acetamido-2-deoxy-1,3,4,6-tetra-O-acetyl-beta-D-glucopyranose or simply beta-pentaacetylglucosamine which prevented cell growth at 10(-4)-10(-3) M. beta-Pentaacetylglucosamine cytotoxicity was correlated with its high lipid solubility, having an octanol/water partition coefficient of 0.424 as compared with 0.278 for the alpha-anomer and 0.017 for N-acetylglucosamine. In vitro metabolism studies with [4C]- and/or [3H]-labeled pentaacetylglucosamine have indicated intracellular de-O-acetylation leading to the biosynthesis of UDP-N-acetylglucosamine, followed by the incorporation of this sugar into cellular glycoprotein. Concomitant with the formation of increased amounts of this nucleotide sugar, intracellular UTP and CTP pools fell to one third normal within 3 h after the administration of 1 mM pentaacetylglucosamine. At present it is unclear whether the cytotoxicity of beta-pentaacetylglucosamine or other similar agents is due to alterations in nucleotide and nucleotide-sugar pools causing a decrease in energy charge and polynucleotide biosynthesis or is due to a direct effect on membrane glycoconjugate biosynthesis.

Cell Division↗
PubMed1975

Regulation of rat-liver glycoprotein: N-acetylneuraminic acid transferase activity by pyrimidine nucleotides.

CMP-N-acetylneuraminic acid: glycoprotein sialyltransferase activities were assayed in rat liver microsomal fractions using desialylated fetuin as the substrate acceptors for N-acetylneuraminic acid. It was found that cytidine nucleotides specifically depressed enzyme activities. CMP was shown to act as a competitive inhibitor with an apparent Ki of 0.62 mM. N-Acetylneuraminic acid at 1.15 mM had no effect on enzyme activities. Uridine nucleotides at 1.15 mM, especially UDP, increased enzyme activities. UDP may act as an allosteric activating agent increasing the apparent V. Other nucleotides, sugars and nucleotide-sugars at similar concentrations affected sialyltransferase activities only slightly. A general mechanism is proposed for the regulation of glycosyltransferase activities by free nucleotides.

Animals↗
PubMed1975

Differential inhibition of rat liver sialyltransferase(s) by various aflatoxins and their metabolites.

Sialyltransferase(s) activity [CMP-N-acetylneuraminic acid:glycoprotein sialyltransferase(s) E.C. 2.4.99.1] was assayed using asialofetuin as a substrate in a total microsomal fraction obtained from rat liver. Rats pretreated with phenobarbital or methylcholanthrene demonstrated a decrease in membrane bound sialyltransferase(s) activity of 27% and 18%,respectively. Microsomes prepared from phenobarbital treated rats were incubated in vitro with aflatoxins B1, B2, B2a, G1, or G2 in the presence or absence of an NADPH generating system. Following this treatment the microsomes were reisolated, washed and assayed for sialyltransferase(s) activity. Aflatoxin B1 and B2a inhibited sialyltransferase(s) by 46% and 55%, respectively, while aflatoxin G1 inhibited sialyltransferase(s) by 54%. Aflatoxins B2 and G2 were only slightly inhibitory. It is proposed that the enzyme inhibition caused by these various aflatoxins is due to binding of these agents to the membranes resulting in a local disruption of the membrane and a change in enzyme conformation.

Aflatoxins↗
PubMedDate not supplied

In vitro degradation of extracellular matrix by human ovarian carcinoma cells.

Better in vitro models are needed to elucidate the mechanisms underlying tissue destruction by human tumor cells. To address this matter recently isolated and characterized human ovarian carcinoma cell lines derived from either primary tumors, ascitic effusions or metastatic growths were plated in direct contact with extracellular matrix (ECM) previously deposited on culture dishes by bovine corneal endothelial cells. Light and electron microscopy of four of the five ovarian tumor cell lines demonstrated morphologic digestion with penetration of ECM by tumor cell microvilli, along with associated rarefaction. The ability of these same ovarian tumor cell lines to solubilize specific carbohydrate and protein moieties present in intact ECM was assessed with the use of metabolically prelabeled ECM employing tritiated fucose, galactose, glucosamine and proline. Results from these studies corroborated morphologic observations in which four of the five tumor cell lines tested extensively solubilized radiolabeled ECM. The kinetics of radiolabel release from ECM illustrated that three of the four invasive tumors released [3H]fucose, [3H]glucosamine and [3H]proline at high rates. Normal human ovarian fibroblasts and mesothelial cells were observed to be unable to digest ECM and this was consistent with their inability to release radiolabeled material from prelabeled ECM. The results from these studies suggest that some ovarian carcinomas have the ability to degrade basement membrane components. Knowledge regarding the mechanisms responsible for tissue degradation may eventually lead to the development of new chemotherapeutic modalities designed to restrict tumor cell invasion, growth and metastasis.

Cells, Cultured↗
PubMedDate not supplied

Inhibition of human ovarian carcinoma cell- and hexosaminidase- mediated degradation of extracellular matrix by sugar analogs.

Human ovarian carcinoma (HOC) cell beta-N-acetylglucosaminidase (beta-NAG, EC 3.2.1.30) was found to be present in three isoenzymatic forms. All three forms were capable of degrading ECM. Therefore, inhibitors of beta-NAG were sought as potential anti-invasive agents. Two sugar analogs, 2-acetamido-2-deoxy-1,5-gluconolactone (CD80110) and 2-acetamido-1,5-imino-1,2,5-trideoxy-D-glucitol (CD 86022), were evaluated for their ability to inhibit 1) human ovarian carcinoma beta-NAG isoenzyme activities, 2) degradation of radiolabeled ECM mediated by HOC cells and beta-NAG, and 3) cell growth. Both compounds were found to be competitive inhibitors of beta-NAG isoenzyme activities, with Ki values similar for all isoenzymes (2-8 microM). CD 80110 and CD 86022 inhibited HOC cell-mediated degradation of [3H]glucosamine labeled ECM without notable effect on cell growth. Enzyme-mediated degradation of ECM was also inhibited by both sugar analogs. Analysis of degradation products after cell- or enzyme-mediated digestion of ECM revealed a decrease in the amount of both free aminosugars and high molecular material caused by inhibitors. These results support a role for beta-NAG in degradation of extracellular matrix components and suggest the usefulness of hexosaminidase inhibitors as potential antiinvasive agents.

1-Deoxynojirimycin↗
PubMedDate not supplied

Antimetastatic activity of adriamycin in combinations with proteinase inhibitors in mice.

The antimetastatic activity of adriamycin in combination with proteinase inhibitors was investigated in mice bearing the metastatic tumors L1210 leukemia, Lewis lung carcinoma or M5076 sarcoma. Leupeptin, a cathepsin B inhibitor, when administered as a single agent was devoid of antimetastatic activity but some therapeutic activity was noted in mice with Lewis lung carcinoma when the agent was administered in combination with adriamycin. Pepstatin A, a cathepsin D inhibitor, had no effect as a single agent in mice with L1210 leukemia but displayed some antimetastatic activity in mice with Lewis lung carcinoma. In mice with M5076 sarcoma the combination of pepstatin A and adriamycin resulted in antimetastatic activity significantly greater than that observed with each agent alone. These results suggest that combinations of proteinase inhibitors with antitumor drugs such as adriamycin, might result in more effective antimetastatic treatment.

Animals↗