Development and optimization of a cascade of screening assays for inhibitors of TRF2

The first attempt in synthesis, identification, and evaluation of SEPT9 inhibitors on human oral squamous carcinomas

Septin 9 (SEPT9), a GTPase, known as the fourth cytoskeleton, is widely expressed in various cells and tissues. The functions of SEPT9 are partly similar to other cytoskeletons as a structure protein. Further, SEPT9 can interact with other cytoskeletons, participating in actin dynamics and microtubule regulation. SEPT9 is associated with various diseases, such as cancers. Thus, it could be a potential drug target. However, there are no small molecule SEPT9 inhibitors and the only reported septin inhibitor, forchlorfenuron, has no effects on SEPT9 inhibition from our study results. Therefore, the derivatives of forchlorfenuron were synthesized, and their activities were evaluated by a direct SEPT9 inhibition screening platform, followed by localized surface plasmon resonance (LSPR) and cell-based assays. The screening results conveyed that 6b, 8a, and 8b are SEPT9 inhibitors with IC50 values of 91, 99, and 95 μM, respectively. Also, their binding affinities were 4, 18, and 22 μM, respectively, validated through LSPR. Eventually, the SAR concludes that at the para position, small substituents are tolerated, while at the ortho position, a bulky benzene ring substituent can be the best candidate. In cell-based assays, the IC50 of 6a, 8a, and 8b of human oral squamous carcinomas cytotoxicity were 122, 20, and 21 µM, respectively. Additionally, significant suppression of the cell migration and invasion ability was observed with the 8b treatment. The co-localization study revealed that 8b effectively disrupted the structural organization of SEPT9, microtubules, and actins. This is the first article to systematically study SEPT9 inhibitors and their biological properties, hoping to shed some light on septin research.

Discovery of a selective TRF2 inhibitor FKB04 induced telomere shortening and senescence in liver cancer cells

Telomere repeat binding factor 2 (TRF2), a critical element of the shelterin complex, plays a vital role in the maintenance of genome integrity. TRF2 overexpression is found in a wide range of malignant cancers, whereas its down-regulation could cause cell death. Despite its potential role, the selectively small-molecule inhibitors of TRF2 and its therapeutic effects on liver cancer remain largely unknown. Our clinical data combined with bioinformatic analysis demonstrated that TRF2 is overexpressed in liver cancer and that high expression is associated with poor prognosis. Flavokavain B derivative FKB04 potently inhibited TRF2 expression in liver cancer cells while having limited effects on the other five shelterin subunits. Moreover, FKB04 treatment induced telomere shortening and increased the amounts of telomere-free ends, leading to the destruction of T-loop structure. Consequently, FKB04 promoted liver cancer cell senescence without modulating apoptosis levels. In corroboration with these findings, FKB04 inhibited tumor cell growth by promoting telomeric TRF2 deficiency-induced telomere shortening in a mouse xenograft tumor model, with no obvious side effects. These results demonstrate that TRF2 is a potential therapeutic target for liver cancer and suggest that FKB04 may be a selective small-molecule inhibitor of TRF2, showing promise in the treatment of liver cancer.

Design of Tracers in Fluorescence Polarization Assay for Extensive Application in Small Molecule Drug Discovery

Development of fluorescence polarization (FP) assays, especially in a competitive manner, is a potent and mature tool for measuring the binding affinities of small molecules. This approach is suitable for high-throughput screening (HTS) for initial ligands and is also applicable for further study of the structure-activity relationships (SARs) of candidate compounds for drug discovery. Buffer and tracer, especially rational design of the tracer, play a vital role in an FP assay system. In this perspective, we provided different kinds of approaches for tracer design based on successful cases in recent years. We classified these tracers by different types of ligands in tracers, including peptide, nucleic acid, natural product, and small molecule. To make this technology accessible for more targets, we briefly described the basic theory and workflow, followed by highlighting the design and application of typical FP tracers from a perspective of medicinal chemistry.

N-terminal modified cyclopeptidic mimetics of ApolloTBM as inhibitors of TRF2

Telomeric repeat binding factor 2 (TRF2) plays an important role in protecting telomeres from being recognized as DNA breaks. TRF2 performs its telomere protecting functions partially by recruiting a number of accessory proteins to telomeres through its TRF homology (TFRH) domain. Identification of small molecular compounds which can bind to the TRFH domain of TRF2 and block the interactions between TRF2 and its associated proteins is crucial for elucidating the molecular mechanisms of these protein-protein interactions. Using a previously identified peptidic mimetic of Apollo_TBM as a lead compound, we designed and synthesized a series of novel TRF2 inhibitors by non-peptidic modifications of the N-terminal residues. These compounds can maintain the binding affinities to TRF2 but have much reduced peptidic characteristics compared to the lead compound.