Action of Rifamycin Derivatives on RNA Polymerase of Human Leukemic Lymphocytes

Abstract

The mechanism of inhibition of human RNA polymerase by four rifamycin derivatives was investigated. Derivative AF/013 (3-formyl rifamycin SV: 0-noctyloxime) with strong hydrophobic side chains prevents the polymerase from binding to DNA and also affects the size of RNA synthesized. Derivative benzyl-2'-methylpyrrolo[3,2-cJ-4-desoxy-rifamycin SV) only affects RNA synthesis when RNA polymerase has been previously incubated with the drug or when the reaction was performed at high salt concentration [0.14 M (NH4)2-S041-Our results suggest that these drugs exert their inhibitory actions by binding to the enzyme instead of DNA.The antibiotic rifampicin inhibits DNA-dependent RNA polymerase obtained from prokaryotic cells, but it has no effect on RNA polymerase isolated from higher organisms (1). One rifamycin derivative, AF/013 (3-formyl rifamycin SV:O-n-octyloxime) synthesized by Lepetit S.p.A., Milan, Italy, can inhibit DNA-dependent RNA polymerases isolated from rat liver (2) and calf thymus (3). This drug inhibits initiation of RNA chains (2, 3). We report studies of the action of rifampicin and four rifamycin derivatives: AF/05 (3-formyl rifamycin SV :O-[diphenylmethyl] oxime), AF/013, PR/19 (3'-acetyl-1'-benzyl-2'-methylpyrrolo[2,3-c] 4-desoxyrifamycin SV), and PR/14 (3'-acetyl-1', 2'-dimethylpyrrolo [3,2-c ]-4-desoxy-rifamycin SV) on DNA-dependent RNA polymerase II (or B) isolated from lymphocytes of patients with chronic lymphocytic leukemia.In vitro RNA synthesis by DNA-dependent RNA polymerase proceeds in a stepwise manner (3, 4). The first step involves binding of the enzyme to the DNA template; the subsequent steps are chain initiation, chain elongation, and chain termination. Rifampicin inhibits Escherichia coli RNA polymerase after binding of polymerase to the DNA and before formation of the first internucleotide bonds (1,5,6

Different modes of inhibition of purified ribonucleic acid directed deoxyribonucleic acid polymerase of avian myeloblastosis virus by rifamycin SV derivatives

“…We reported that the inhibition appeared to be the result of a strong cooperative interaction among drug molecules which bind to a hydrophobic region of the reverse transcriptase (Gurgo et al, 1974). As previously found in the inhibition of bacterial (Riva and Silvestri, 1972, for a review), T7 bacteriophage-induced (Chamberlin and Ring, 1972), and mammalian RNA polymerases (Meilhac et al, 1972, andTsai andSaunders, 1973) by rifamycin derivatives, these compounds are more effective when they interact with the reverse transcriptase before initiation of polymerization (Wu and Gallo, 1974). In this article, we present evidence that the differences in the structure of the side chain confer on several rifamycin derivatives the ability to inhibit the viral DNA polymerase with different modes of action.…”

Biochemical Mechanisms of New Molecular Entities (NMEs) Approved by United States FDA During 2001-2004: Mechanisms Leading to Optimal Efficacy and Safety

“…Early studies with rifamycin suggest that these molecules bind tightly to the polymerase, with dissociation half-lives approaching 2 hrs, [52] and prevent the polymerase from binding to DNA [53]. Rifaximin safety profile is attributed to its poor absorption due to a pyridoimidazole ring [54].…”

Mechanism of inhibition of RNA polymerase II and poly(adenylic acid) polymerase by the O-n-octyloxime of 3-formylrifamycin SV

“…The complexity of the RNA polymerase reaction makes studies on post-initiation events relatively difficult. Several factors, such as reinitiation of the enzyme on the template, altered initiation sites on different templates, effects of divalent ions and salt concentrations (Meilhac and Chambón, 1973;Lili and Hartmann, 1973;Tsai and Saunders, 1973 tein (bovine serum albumin, BSA) on the inhibition of RNA polymerase II was also investigated. BSA reduced the extent of inhibition by AF/013, but did not alter the competitive nature of inhibition.…”