P6981, An Arylstibonic Acid, Is a Novel Low Nanomolar Inhibitor of cAMP Response Element-Binding Protein Binding to DNA

Abstract

Several basic leucine zipper (B-ZIP) transcription factors have been implicated in cancer, substance abuse, and other pathological conditions. We previously identified arylstibonic acids that bind to B-ZIP proteins and inhibit their interaction with DNA. In this study, we used electrophoretic mobility shift assay to analyze 46 arylstibonic acids for their activity to disrupt the DNA binding of three B-ZIP [CCAAT/enhancer-binding protein ␣, cyclic AMP-response element-binding protein (CREB), and vitellogenin gene-binding protein (VBP)] and two basic helixloop-helix leucine zipper (B-HLH-ZIP) [USF (upstream stimulating factor) and Mitf] proteins. Twenty-five arylstibonic acids showed activity at micromolar concentrations. The most active compound, P6981 [2-(3-stibonophenyl)malonic acid], had halfmaximal inhibition at ϳ5 nM for CREB. Circular dichroism thermal denaturation studies indicated that P6981 binds both the B-ZIP domain and the leucine zipper. The crystal structure of an arylstibonic acid, NSC13778, bound to the VBP leucine zipper identified electrostatic interactions between both the stibonic and carboxylic acid groups of NSC13778 [(E)-3-(3-stibonophenyl)acrylic acid] and arginine side chains of VBP, which is also involved in interhelical salt bridges in the leucine zipper. P6981 induced GFP-B-ZIP chimeric proteins to partially localize to the cytoplasm, demonstrating that it is active in cells. P6981 inhibited the growth of a patient-derived clear cell sarcoma cell line whose oncogenic potential is driven by a chimeric protein EWS-ATF1 (Ewing's sarcoma protein-activating transcription factor 1), which contains the DNA binding domain of ATF1, a B-ZIP protein. NSC13778 inhibited the growth of xenografted clear cell sarcoma, and no toxicity was observed. These experiments suggest that antimony containing arylstibonic acids are promising leads for suppression of DNA binding activities of B-ZIP and B-HLH-ZIP transcription factors.

What turns CREB on? And off? And why does it matter?

“…It is, therefore, a specific inhibitor for CREB but also for fos/junD (EC50 13.9 vs. 2.5) [113] and binds to CD4 + T cells [114]. Furthermore, NSC 13778 blocks the binding of TFE3 type 1/2 to the specific promoter element [115], while its derivative P6981 had a stronger effect on CREB inhibition [116]. However, neither substance is commercially available.…”

Targeting CREB in Cancer Therapy: A Key Candidate or One of Many? An Update

“…Notably, binding to CD4+ T cells, stibavirin has been described as HIV-1 entry inhibitors [134]. Finally, P6981 compound is an NSC 13,778 derivative which better suppresses DNA binding of CREB in respect with stibavirin [135].…”

Pathological Unfoldomics of Uncontrolled Chaos: Intrinsically Disordered Proteins and Human Diseases

“…Further screening of stibonic acids identified additional very active but promiscuous inhibitors of bZip (CREB) and bHLHZip (USF and Mitf) proteins. 297,298 Rudenko and co-workers 299 screened 54 498 molecules for inhibitors of ΔFosB DNA binding. They identified two, C2 and C6, that were active in follow-up assays.…”