Gliotoxin analogues as inhibitors of reverse transcriptase. 1. Effect of lipophilicity

Cytotoxic metabolites from the antarctic psychrophilic fungus Oidiodendron truncatum

Two new epipolythiodioxopiperazines, named chetracins B and C (1 and 2), and five new diketopiperazines, named chetracin D (4) and oidioperazines A-D (5, 10, 12, and 13), were isolated from the fungus Oidiodendron truncatum GW3-13, along with six known compounds (3, 6, 7, 8, 9, and 11). Their structures were elucidated by extensive NMR, MS, and CD analyses, as well as chemical transformation. An in vitro MTT cytotoxicity assay revealed potent biological activity for 1 in the nanomolar range against a panel of five human cancer lines.

Reactivity of reverse transcriptase toward (s4U,U)n copolymers and spin-labeled nucleic acid lattices

Spin-labeled copolymers of 4-thiouridine and uridine (ls4U,U)n] that contain various amounts of spin label (l) were synthesized by either (i) chemical alkylation of the 4-thiouridine-uridine copolymers (s4U,U)n prepared by copolymerizing 4-thiouridine 5'-diphosphate (s4UDP) and UDP or (ii) copolymerization of spin-labeled s4UDP with UDP using polynucleotide phosphorylase. The effect of (s4U,U)n and (ls4U,U)n on avian myeloblastosis virus (AMV) RNA-dependent DNA polymerase (RNA-dependent DNA nucleotidyltransferase, EC 2.7.7.7; reverse transcriptase) was studied to determine whether the presence of potentially reactive thiol groups or spin labels enhances the inhibitory properties of the copolymers as compared to (U)n. Inhibition by (s4U,U)n gradually increases as the percentage of thiolation increases. Enhanced inhibition by (s4U,U)n appears to be due to the interaction of the thiol groups of (s4U,U)n with the thiol group(s) of the polymerase, because inhibition by (s4U,U)n (8% thiolated) in the presence of dithiotreitol resembles that by (U)n. In contrast, inhibition by (ls4U,U)n containing 3% spin label resembles that by (U)n; however, increasing the spin label to 6% or 12% results in enhanced inhibition by (ls4U,U)n as compared to that by (U)n, and dithiothreitol has no effect on enhanced inhibition by (ls4U,U)n. These results suggest that the mechanism of inhibition observed with (ls4U,U)n with a ls4U:U ratio > 1:33 differs from the mechanism for (s4U,U)n and involves complex formation between the spin label and the essential Zn2+ of RNA-dependent DNA polymerase.