Natural-product inhibitors of human DNA ligase I

Abstract

Enzymatic activity mediated by recombinant human DNA ligase I (hLI), in conjunction with tannin removal procedures, has been applied to a natural-product screen involving approximately 1000 plant extracts and various pure compounds. The primary hLI activity assay involved the measurement of the amount of radiolabelled phosphate in a synthetic nucleic acid hybrid that becomes resistant to alkaline phosphatase as a result of ligation. A bioactivity-guided fractionation scheme resulted in the isolation of ursolic [IC50=100 micrograms/ml (216 microM)] and oleanolic [IC50=100 micrograms/ml (216 microM)] acids from Tricalysia niamniamensis Hiern (Rubiaceae), which demonstrated similar DNA ligase inhibition profiles to other triterpenes such as aleuritolic acid. Protolichesterinic acid [IC50=6 micrograms/ml (20 microM)], swertifrancheside [IC50 = 8 micrograms/ml(11)microM)] and fulvoplumierin [IC50=87 micrograms/ml (357 microM)] represent three additional natural-product structural classes that inhibit hLI. Fagaronine chloride [IC50=10 micrograms/ml (27 micronM] and certain flavonoids are also among the pure natural products that were found to disrupt the activity of the enzyme, consistent with their nucleic acid intercalative properties. Further analyses revealed that some of the hLI-inhibitory compounds interfered with the initial adenylation step of the ligation reaction, indicating a direct interaction with the enzyme protein. However, in all cases, this enzyme-inhibitor interaction did not disrupt the DNA relaxation activity mediated by hLI. These results indicate that, although the same enzyme active site may be involved in both enzyme adenylation and DNA relaxation, inhibitors may exert allosteric effects by inducing conformational changes that disrupt only one of these activities. Studies with inhibitors are important for the assignment of specific cellular functions to these enzymes, as well as for their development into clinically useful antitumour agents.

Protolichesterinic acid enhances doxorubicin-induced apoptosis in HeLa cells in vitro

“…Protolichesterinic acid was able to induce apoptosis through a caspase-dependent pathway in androgen-sensitive (LNCaP) and androgen-insensitive (DU-145) human prostate cancer cells [9] and in HeLa cells [10]. In in vitro assays, protolichesterinic acid showed inhibitory action against 5-lipoxygenase from porcine leucocytes [11], platelet-type 12-lipoxygenase [12], human DNA ligase I [13] and DNA polymerase of HIV-1 reverse transcriptase [14]. In the last years, many studies demonstrated that some natural products exhibited a synergic antitumour effect with conventional chemotherapeutic agents [15][16][17][18].…”

SCR7 is neither a selective nor a potent inhibitor of human DNA ligase IV

“…There have been several attempts to identify DNA ligase inhibitors by screening of synthetic chemical and natural product libraries that have met with limited success. These have mainly involved radioactive-based assays and the screening of a relatively small number of compounds [7–9]. A series of small molecule inhibitors with differing specificities for the three human DNA ligases were identified by a structure-based approach using the atomic resolution structure of the DNA binding domain of human DNA ligase I complexed with nicked DNA [2,10].…”

Oleanolic acid and related derivatives as medicinally important compounds

“…These results indicate that, although the same enzyme active site may be involved in both enzyme adenylation and DNA relaxation, inhibitors may exert allosteric effects by inducing conformational changes that disrupt only one of these activities. Studies with inhibitors are important for the assignment of specific cellular functions to these enzymes, as well as for their development into clinically useful antitumour agents [54].…”