title: XR5944: A potent inhibitor of estrogen receptors.
abstract: The anticancer drug XR5944 was originally developed as a topoisomerase inhibitor and was subsequently shown to be a transcription inhibitor. It has shown exceptional anticancer activity both in vitro and in vivo and was significantly more potent than traditional topoisomerase inhibitors. The solution structure of the XR5944/DNA complex recently obtained in our laboratory indicates that XR5944 bis-intercalates at the 5'-(TpG):(CpA) site of duplex DNA, which is found in the consensus DNA-binding site of estrogen receptor (ER). Thus, we tested the ability of XR5944 to inhibit ER activity both in vitro and in cultured cells. In electrophoretic mobility shift assays, it is seen that the DNA binding of recombinant ERalpha protein, as well as ER from nuclear extracts, is inhibited by XR5944 in a dose-dependent manner. In luciferase reporter assays, XR5944 inhibited the reporter gene expression from an estrogen response element-containing promoter but not from a basal promoter sequence that lacks any cis-acting elements. In contrast, the RNA polymerase inhibitor actinomycin D inhibits the transcription from both the above-mentioned promoters. The specificity of XR5944 activity is displayed by a separate reporter assay in which the transactivation of reporter gene expression by Sp1 proteins was not inhibited by XR5944. Collectively, these data suggest that XR5944 is capable of specifically inhibiting the binding of ER to its consensus DNA sequence and its subsequent activity. This represents a novel mechanism of ER inhibition, which may allow the development of agents capable of overcoming resistance to current antiestrogens.
authors.affiliation: College of Pharmacy, University of Arizona, 1703 East Mabel Street, Tucson, AZ 85721, USA.
authors.forename: Chandanamali
authors.initials: C
authors.lastname: Punchihewa
authors.forename: Adrian
authors.initials: A
authors.lastname: De Alba
authors.forename: Neil
authors.initials: N
authors.lastname: Sidell
authors.forename: Danzhou
authors.initials: D
authors.lastname: Yang
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D004273:DNA, Neoplasm / Q000737:chemistry; D003609:Dactinomycin / Q000494:pharmacology; D024202:Electrophoretic Mobility Shift Assay; D004967:Estrogens / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D008156:Luciferases / Q000235:genetics; D010619:Phenazines / Q000737:chemistry / Q000494:pharmacology*; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors* / Q000235:genetics; D020218:Response Elements / Q000187:drug effects; D016329:Sp1 Transcription Factor / Q000378:metabolism; D013379:Substrate Specificity / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D004967:Estrogens; D010619:Phenazines; D011960:Receptors, Estrogen; D016329:Sp1 Transcription Factor; C434883:XR5944; D003609:Dactinomycin; D008156:Luciferases