Structure-Based Design of a Potent and Selective YTHDC1 Ligand.

N6-Adenosine methylation (m6A) is a prevalent post-transcriptional modification of mRNA, with YTHDC1 being the reader protein responsible for recognizing this modification in the cell nucleus. Here, we present a protein structure-based medicinal chemistry campaign that resulted in the YTHDC1 inhibitor 40, which shows an equilibrium dissociation constant (Kd) of 49 nM. The crystal structure of the complex (1.6 Å resolution) validated the design. Compound 40 is selective against the cytoplasmic m6A-RNA readers YTHDF1-3 and YTHDC2 and shows antiproliferative activity against the acute myeloid leukemia (AML) cell lines THP-1, MOLM-13, and NOMO-1. For the series of compounds that culminated into ligand 40, the good correlation between the affinity in the biochemical assay and antiproliferative activity in the THP-1 cell line provides evidence of YTHDC1 target engagement in the cell. The binding to YTHDC1 in the cell is further supported by the cellular thermal shift assay. Thus, ligand 40 is a tool compound for studying the role of YTHDC1 in AML.

1,4,9-Triazaspiro[5.5]undecan-2-one Derivatives as Potent and Selective METTL3 Inhibitors.

N6-methyladenosine (m6A) is the most frequent of the 160 RNA modifications reported so far. Accumulating evidence suggests that the METTL3/METTL14 protein complex, part of the m6A regulation machinery, is a key player in a variety of diseases including several types of cancer, type 2 diabetes, and viral infections. Here we report on a protein crystallography-based medicinal chemistry optimization of a METTL3 hit compound that has resulted in a 1400-fold potency improvement (IC50 of 5 nM for the lead compound 22 (UZH2) in a time-resolved Förster resonance energy transfer (TR-FRET) assay). The series has favorable ADME properties as physicochemical characteristics were taken into account during hit optimization. UZH2 shows target engagement in cells and is able to reduce the m6A/A level of polyadenylated RNA in MOLM-13 (acute myeloid leukemia) and PC-3 (prostate cancer) cell lines.

Structural and Dynamic Insights into Redundant Function of YTHDF Proteins.

Three YTH-domain family proteins (YTHDF1, YTHDF2, and YTHDF3) recognize the N6-methyladenosine (m6A) modification of mRNA in cells. However, the redundancy of their cellular functions has been disputed. We investigate their interactions with m6A-containing RNA using X-ray crystallography and molecular dynamics (MD). The new X-ray structures and MD simulations show that the three proteins share identical interactions with the m6A-containing RNA and have similar intrinsic plasticity, thus evidencing the redundant roles of the three proteins in cellular functions.

Small-Molecule Inhibitors of METTL3, the Major Human Epitranscriptomic Writer.

The RNA methylase METTL3 catalyzes the transfer of a methyl group from the cofactor S-adenosyl-L-methionine (SAM) to the N6 atom of adenine. We have screened a library of 4000 analogues and derivatives of the adenosine moiety of SAM by high-throughput docking into METTL3. Two series of adenine derivatives were identified in silico, and the binding mode of six of the predicted inhibitors was validated by protein crystallography. Two compounds, one for each series, show good ligand efficiency. We propose a route for their further development into potent and selective inhibitors of METTL3.

Understanding the structural basis of substrate recognition by Plasmodium falciparum plasmepsin V to aid in the design of potent inhibitors.

Plasmodium falciparum plasmepsin V (PfPMV) is an essential aspartic protease required for parasite survival, thus, considered as a potential drug target. This study reports the first detailed structural analysis and molecular dynamics simulation of PfPMV as an apoenzyme and its complexes with the substrate PEXEL as well as with the inhibitor saquinavir. The presence of pro-peptide in PfPMV may not structurally hinder the formation of a functionally competent catalytic active site. The structure of PfPMV-PEXEL complex shows that the unique positions of Glu179 and Gln222 are responsible for providing the specificity of PEXEL substrate with arginine at P3 position. The structural analysis also reveals that the S4 binding pocket in PfPMV is occupied by Ile94, Ala98, Phe370 and Tyr472, and therefore, does not allow binding of pepstatin, a potent inhibitor of most pepsin-like aspartic proteases. Among the screened inhibitors, the HIV-1 protease inhibitors and KNI compounds have higher binding affinities for PfPMV with saquinavir having the highest value. The presence of a flexible group at P2 and a bulky hydrophobic group at P3 position of the inhibitor is preferred in the PfPMV substrate binding pocket. Results from the present study will aid in the design of potent inhibitors of PMV.