Interfering with HuR–RNA Interaction: Design, Synthesis and Biological Characterization of Tanshinone Mimics as Novel, Effective HuR Inhibitors

Abstract

The human antigen R (HuR) is an RNA-binding protein known to modulate the expression of target mRNA coding for proteins involved in inflammation, tumorigenesis, and stress responses and is a valuable drug target. We previously found that dihydrotanshinone-I (DHTS, 1) prevents the association of HuR with its RNA substrate, thus imparing its function. Herein, inspired by DHTS structure, we designed and synthesized an array of ortho-quinones (tanshinone mimics) using a function-oriented synthetic approach. Among others, compound 6a and 6n turned out to be more effective than 1, showing a nanomolar K and disrupting HuR binding to RNA in cells. A combined approach of NMR titration and molecular dynamics (MD) simulations suggests that 6a stabilizes HuR in a peculiar closed conformation, which is incompatible with RNA binding. Alpha screen and RNA-electrophoretic mobility shift assays (REMSA) data on newly synthesized compounds allowed, for the first time, the generation of structure activity relationships (SARs), thus providing a solid background for the generation of highly effective HuR disruptors.

Targeting the interaction between RNA-binding protein HuR and FOXQ1 suppresses breast cancer invasion and metastasis

“…During the last decade, we and others reported the identification of small molecules that interfere HuR-RNA interactions through high-throughput screening 23 and one group published the structure-based design and optimization of an initial top hit 22 .…”

“…We 17,18 and others [19][20][21][22] have sought to identify small molecule inhibitors that interfere with HuR-mRNA complex. These small molecules show moderate to high binding affinity to HuR in different biochemical assays and have been validated as HuR inhibitors 23 .…”

Exploration of ligand binding modes towards the identification of compounds targeting HuR: a combined STD-NMR and Molecular Modelling approach

“…Among them, dihydrotanshinone (DHTS), which is a nanomolar disruptor of HuR–RNA binding 23 , has potent HuR-dependent antitumor activity in vivo and is able to inhibit HuR multimerization 24 , 25 . Starting from the DHTS scaffold, medicinal-chemistry efforts led to the discovery of a series of small molecules called Tanshinone Mimics (TMs) with improved affinity and potency compared to DHTS 26 . Summing up, and going beyond the state of the art of HuR modulators available so far, the identification of the key druggable pockets on the surface of HuR is the essential milestone for discovering new molecular scaffolds.…”

RNA-Targeted Therapies and High-Throughput Screening Methods

“…Based on the structure of DHTS, a series of tanshinone mimics were synthesised. Among these, tanshinone mimic 6a and 6n were more potent HuR/ARE-RNA disruptors when compared to DHTS [141]. 6a and DHTS bind at the same region of HuR, illustrating potential structure-activity relationships (SARs) for HuR inhibitors [141].…”

“…The tanshinone mimics affected cell viability in breast and pancreatic cancer cells. However, each of these mimics was less efficient when compared to DHTS [141].…”