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Biomedical subjects

P F Torrence

Publications and source records attributed to P F Torrence.

At least 127 records · Page 7Linked to original sources
PubMed1977

Polyadenylic-polyxanthylic-polyuridylic acid triple helix.

Poly(xanthylic acid) [X)n] abolished the ability of (A)n-(U)n to induce interferon in "superinduced" (actinomycin D and cycloheximide) primary rabbit kidney cells. Under the same conditions, (X)n had a relatively minor effect on the interferon inducing capacity of (I)n-(C)n. Evidence based on mixing curves, melting profiles, pancreatic ribonuclease resistance and sucrose gradient ultracentrifugation pointed to the conclusion that the following three reactions occur depending on stoichiometry: (1) 2(A)n-(U)n + (X)n leads to (A)n-2(U)n + (A)n-(X)n; (2) (A)n-(U)n + (X)n leads to (A)n-(U)n-(X)n; (3) (A)n-(U)n + 2(X)n + (X)n-(U)n. The second reaction represents the formation of a new triple helix which can also be formed according to the following reactions: (X)n-(U)n + (A)n leads to (A)n-(X)n-(U)n; (A)n-(X)n + (U)n leads to (A)n-(X)n-(U)n.

Binding Sites↗
PubMed1977

The interaction of polyxanthylic acid with polyadenylic acid.

The stoichiometry of interaction between polyxanthylic acid (poly(X)) and polyadenylic acid (poly(A)) was investigated by construction of mixing curves as a function of wavelength. Wavelengths were found which exhibited a break at 48-50 mol % poly(A) or two breaks, one at 48-50 mol % poly(A) and the other at 33-30 mol % poly(A). The melting profile (in 0.1 M salt) of the 50 mol % poly(A) mixture was monophasic (Tm=83 degrees C) at all wavelengths but that of the 33 mol % poly(A) mixture was biphasic showing a transition at Tm=40 degrees C and another at Tm=83 degrees C. Construction of a mixing curve between poly(A) and poly(X) at a temperature of 52 degrees C gave rise to plots which showed only one break (at 49--50 mol % poly(A)) at all wavelengths. Thus, while (at 20 degrees C in 0.1 M salt, pH 7) both poly(A)-poly(X) and poly(A)-2 poly(X) form at their respective stoichiometric end-points, the triplex poly(A)-2 poly(X), upon melting undergoes a disproportionation reaction resulting in the loss of one poly(X) strand and the formation of the poly(A)-poly(X) duplex.

Binding Sites↗
PubMed1977

Improved synthesis and in vitro antiviral activities of 5-cyanouridine and 5-cyano-2'-deoxyuridine.

In order to evaluate the influence of the cyano group on the antiviral activity of pyrimidine deoxyribonucleosides, a moderate yield, unified approach to the synthesis of both 5-cyanouridine and 5-cyano-2'-deoxyuridine was developed. Thus, treatment of the appropriate acetylated 5-bromouracil nucleoside with NaCN or KCN in Me2SO at 90-110 degrees C gave, after deblocking, 35-45% yields of the corresponding 5-cyanouracil nucleosides. 5-Cyanouridine was devoid of significant activity against vaccinia virus, herpes simplex-1, and vesicular stomatitis virus, but 5-cyano-2'-deoxyuridine, while lacking activity against herpes simplex, showed significant inhibition of vaccina virus; for instance, 5-cyano-2'-deoxyuridine inhibited vaccinia virus replication at concentrations 10-20 times that required for inhibition by the known antivirals, 5-iodo-2'-deoxyuridine and 1-(beta-D-arabinofuranosyl)adenine. Replacement of the 5-halogeno substituents of pyrimidine deoxyribonucleosides thus decreases, but does not abolish, antiviral activity.

Animals↗
PubMed1977

Biologic activities of poly (2-azaadenylic acid) and poly (2-azainosinic acid).

Poly (2-azaadenylic acid) [(aza2A)n] and poly(2-azainosinic acid [(aza2I)n], two newly synthesized analogues of (A)n and (I)n, in which CH-2 of the purine ring is replaced by a nitrogen atom, have been evaluated in various biological assay systems. (Aza2A) n formed a complex with (U)n and (br5U)n, and (aza2I)n formed a complex with (C)n and (br5C)n, but these complexes were markedly destabilized relative to the corresponding (A)n or (I)n complexes. The (aza2A)n-and (aza2I)n-derived complexes failed to stimulate the production of interferon in primary rabbit kidney cells and human diploid fibroblasts, under conditions (A)n. (U)n, (I)n. (C)n and (I)n. (br5C)n induced high amounts of interferon. both (aza2A)n and (aza2I)n exerted a marked inhibitory effect on the endogenous RNA directed DNA polymerase (reverse transcriptase) activity associated with murine leukemia virus. They caused a relatively mild inhibition of complement activity in an hemolytic assay system.

Aza Compounds↗
PubMed1976

Polynucleotide displacement reactions: detection by interferon induction.

A large variety of displacement reactions between homopolynucleotides and complexes thereof has been demonstrated by interferon induction data obtained in primary rabbit kidney cell cultures superinduced with metabolic inhibitors. The polymers involved in these helix-coil displacement studies were: poly(adenylic acid), poly(inosinic acid), poly(cytidylic acid), poly(uridylic acid), poly(ribothymidylic acid), polylaurusin, poly(7-deazaadenylic acid), poly(7-deazainosinic acid), poly(5-bromocytidylic acid), and poly(5-bromouridylic acid). As monitored by ultraviolet absorbance-temperature profiles, all displacement reactions were directed toward the formation of the helix with the higher thermal stability. Concomitantly, the resulting helix was invariably more active as interferon inducer than the reactant helix, except for some reactions in which poly(7-deazaadenylic acid) was involved. For the latter reactions both the reactant and resultant helices were inactive as interferon inducer. The interferon induction data revealed that all displacement reactions proceeded to completion within 1 h even at temperatures well below the Tm of the reactant helix. The helix-coil displacement reaction could also be monitored by sucrose velocity gradient analysis, and, as evidenced for poly(A)-2poly(I) + 2poly(C) leads to 2poly(I)-poly(C) + poly(A), readily occurred at the cellular level, presumably at the cell surface.

Animals↗
PubMed1976

Triple-helical polynucleotides. Mixed triplexes of the poly(uridylic acid)-poly(adenylic acid)-poly(uridylic acid) class.

By the techniques of interferon induction in primary rabbit kidney cells "superinduced" with metabolic inhibitors, ultraviolet absorbance-temperature profiles, sensitivity to pancreatic ribonuclease A, and sucrose velocity gradient ultracentrifugation, a number of reactions between double-helical RNA and single-stranded RNA or DNA homopolymers were investigated. The polymers involved in these studies were poly(adenylic acid), poly(uridylic acid), poly(ribothymidylic acid), poly(5-bromouridylic acid), poly(deoxythymidylic acid), poly(deoxyuridylic acid), poly(3-methyluridylic acid), poly(2'-O-methyluridylic acid), and poly(2'-azido-2'-deoxyuridylic acid). Two different reaction courses, both leading to the formation of triple helices, were noted: (1) poly(Ux)-poly(A) + poly(Uy) leads to poly(Ux)-poly(A)-poly(Uy) if the Tm of poly(Ux)-poly(A) was higher than the Tm of poly(Uy)-poly(A); (2) poly(Ux)-poly(A) + poly(Uy) leads to poly(Uy)-poly(A)-poly(Ux) if the Tm of poly(Ux)-poly(A) was lower than the Tm of poly(Uy)-poly(A). In these equations, the homopolymer written to the left of poly(A) implies Watson-Crick hydrogen bonding whereas the polymer to the right of poly(A) is involved in Hoogsteen hydrogen bonding.

Animals↗
PubMed1976

Dependence of interferon induction on nucleic acid conformation.

UV and circular dichroism characteristics of duplex analogs belonging to the (A)n-(U)n and (I)n-(C)n series were determined to assign qualitatively the nature of conformational differences caused by 5-pyrimidine and c7 purine substitutions in such duplexes. Evidence is presented which shows that 5-pyrimidine substitution by bromine or methyl changes the duplex conformation of both series in a similar way, if at all. A c7 substitution in the purine ring affects the duplex conformation of the members in the same series similarly, but the conformational change appears to be different for the two series. To wit, it is proposed that in the duplexes the effect of the change (A)n leads to (c7A)n is an increase of the positive base tilt, whereas the change (I)n leads to (c7I)n causes a decrease where (c7A)n is poly (7-deazaadenylic acid) and (c7I)n is poly(7-deazainosinic acid), respectively. Poly(5-bromocytidylic acid) (br5C)n proved to be useful as a sensor strand for the intepretation of the spectroscopic data. The circular dichroism findings correlate well with observations made earlier on the interferon inducing ability for such duplexes, namely, duplexes based on the (c7A)n are inactive as interferon inducers, whereas duplexes based on (c7I)n are potent inducers. Furthermore, a 5-pyrimidine substitution does not substantially affect the interferon inducing ability, unless the thermal stability of the analog becomes critical, as in the case of (A)n-(br5U)n. Thus, this study provides the first evidence to link the interferon-inducing ability of a nucleic acid to a defined physical parameter of double helix, and reinforces the concept that interferon induction is dependent on the recognition of a particular spatial and steric organization of a double-stranded RNA.

Circular Dichroism↗
PubMed1976

Role of purine N-3 in the biologic activities of poly(A) and poly(I).

Poly(c3A) (poly 3-deazaadenylic acid) and poly(c3I) (poly 3-deazainosinic acid) differ in biological reactivity from their parent compounds poly(A) and poly(I) and from their 7-deaza counterparts poly(c7A) and poly(c7I). Three parameters of biological reactivity were evaluated : (1 degree) interferon induction, (2 degrees) anti-complement activity, (3 degrees) reverse transcriptase inhibition. Unlike poly(A)-poly(U), poly(I)-poly(C) and poly(I)-poly(br5C), the mixtures of poly(c3A) + POLY(U), poly(c3I) + poly(C), and poly(c3I) + poly(br5C) failed to elicit an interferon response in "super-induced" primary rabbit kidney cells; Poly(I) and its analogs poly(c3I) and poly(c7I) inhibited hemolytic complement activity, whereas poly(A) and its analogs poly(c3A) and poly(c7A) failed to do so. Both poly(I) and poly(c7I), but not poly(c3I), lost their anti-complement potency when annealed to either poly(C) or poly(A)-poly(U). Similarly, poly(I) and poly(c7I), but not poly(c3I), suppressed the interferon inducing ability of poly(A)-poly(U), suggesting that both poly(I) and poly(c7I), but not poly(c3I), added to poly(A)-poly(U) to form a triple-helical structure. Poly(I), poly(C7I) and poly(c7A)exerted a distinct inhibitory effect on turine leukemia virus, while under the same conditions poly(c3I) and poly(c3A) showed little, if any, inhibitory effect.

Animals↗
PubMed1976

Effect of cytosine, arabinoside, iododeoxyuridine, ethyldeoxyuridine, thiocyanatodeoxyuridine, and ribavirin on tail lesion formation in mice infected with vaccinia virus.

Mice infected intravenously with vaccinia virus develop characteristic lesions over the entire tail surface. This experimental virus infection presents a highly sensitive and reliable model for evaluating the antivaccinia activity of antiviral compounds. Ara-C (1-beta-D-arabinofuranosylcytosine), ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), IUdR (5-iodo-2'-deoxyuridine) as well as two novel analogs of IUdR, EtUdR (5-ethyl-2'-deoxyuridine), and NCSUdR (5-thiocyanato-2'-deoxyuridine), were found to inhibit the formation of vaccinia tail lesions, when administered intraperitoneally once daily for 7 days starting immediately after virus infection. The order of (decreasing) activity was: ara-C greater than IUdR greater than NCSUdR greater than ribavirin greater than EtUdR. Various drug combinations, involving IUdR + ara-C, NCSUdR + ara-C, NCSUdR + IUdR, NSCUdR + ribavirin, etc., were evaluated but none proved more efficacious than either compound administered alone.

Animals↗
PubMed1975

Polynucleotide duplexes based on poly(7-deazaadenylic acid).

In order to find a poly(A)-poly(U) analog which could not form a triple-stranded complex and which would have a sufficiently high thermal stability to survive under physiological conditions, the interaction of poly(7-deazaadenylic acid) (poly(c-7A)) with modified polyuridylic acids was examined. Mixing curves constructed by the method of continuous variation, isosbestic points and thermal melting profiles proved that poly(c-7A) formed only 1:1 complex with polyribothymidylic acid and poly(5-bromouridylic acid) (Tm values of 50 and 72 degrees C respectively, in 0.15 M NaCl, 0.01 M KH2 PO4, 0.001 M MgCl2, pH7). In addition poly(c-7A) formed a 1:1 complex with poly(I) (Tm equals 22 degrees C in 0.46 M salt, pH 7), and presumed duplexes were observed in the interaction of poly(c-7A) with poly(dT), poly(2'-azido-2'-deoxyuridylic acid) and poly(2'-O-methyluridylic acid) (Tm values of 35, 32 and 41 degrees C respectively, in 0.10 M NaCl, pH7).

Adenine Nucleotides↗
PubMed1975

Biological, biochemical, and physicochemical evidence for the existence of the polyadenylic-polyuridylic-polyinosinic acid triplex.

When primary rabbit kidney cell cultures are treated with either polyadenylic acid-polyuridylic acid or polyadenylic acid-polyribothymidylic acid (poly(rT)) and then judiciously exposed to actinomycin D and cycloheximide, high titers of interferon are found in the extracellular medium ("superinduction") (Vilcek, J. (1970) Ann. N. Y. Acad. Sci. 173, 390-403; Tan, Y. H., Armstrong, J. A., Ke, Y. H., and Ho, M. (1970) Proc. Natl. Acad. Sci. U. S. A. 67, 464-471). If polyinosinic acid is added 1 hour prior to, simultaneously with, or 1 hour after the active interferon inducers, dramatic reductions in interferon production from the "superinduced" cells result. Based on experiments involving sucrose gradient ultracentrifugation, pancreatic ribonuclease A resistance, ultraviolet mixing curves, and ultraviolet absorbance-temperature profiles, the explanation for this phenomenon was determined to be the formation of polynucleotide triplexes in the following way: poly(A)-poly(U) + poly(I) yields poly(A)-poly(U)-poly(I)poly(A)-poly(rT) + poly(I) yields poly(A)-poly(rT)-poly(I). In addition, based on similar methodology, the following reactions involving these triplexes were demonstrated: poly(A)-2 poly(I) + poly(U) yields poly(A)-poly(U)-poly(I) + poly(I)poly(A)-2 poly(I) + poly(rT) yields poly(A)-poly(rT)-poly(I) + poly(I)POLY(A)-2 poly(I) + 2 poly(U) yields poly(A)-2 poly(U) + 2 poly(I) and POLY(A)-poly(U)-poly(I) + poly (U) yields poly(A)-2 poly(U) + poly(I).

Adenine Nucleotides↗