A GSH-resistant FK228 analogue containing a stable disulfide bond.

FK228 is a potent natural pan HDAC inhibitor approved by the FDA for the treatment of cutaneous T-cell lymphoma as well as peripheral T-cell lymphoma. It is generally believed that the mechanism of FK228 acting on HDACs is by reducing its disulfide bond after entering the cell, and the dithiol group may chelate with Zn2+ and form a weak reversible covalent bond with cysteine in the catalytic pocket of HDACs, therefore inhibiting the activity of HDACs. However, due to the weak stability of the disulfide bond in FK228, it has been difficult to obtain direct evidence for the above conjecture. Thus, improving the stability of the FK228 disulfide bond will help to explore the exact mechanism of FK228. In this study, based on the stability and target-induced covalent properties of the Cysteine-Penicillamine (Cys-Pen) disulfide bond reported previously, the Pen was introduced into the modification of FK228. Specifically, the d-Cys in FK228 was replaced by d-Pen, the total synthetic pathway was optimized, and the novel synthetic FK228 analogue (FK-P) stability was verified. FK-P can also be used as a new drug molecule in the future to participate in the research of related biological mechanisms or the treatment of diseases.

Development of Lysine Crotonyl-Mimic Probe to Covalently Identify H3K27Cr Interacting Proteins.

Histone lysine crotonylation (Kcr) is one newly discovered acylation modification and regulates numerous pathophysiological processes. The binding affinity between Kcr and its interacting proteins is generally weak, which makes it difficult to effectively identify Kcr-interacting partners. Changing the amide of crotonyl to an ester increased reactivity with proximal cysteines and retained specificity for Kcr antibody. The probe "H3g27Cr" was designed by incorporating the ester functionality into a H3K27 peptide. Using this probe, multiple Kcr-interacting partners including STAT3 were successfully identified, and this has not been reported previously. Further experiments suggested that STAT3 possibly could form complexes with Histone deacetylase HDACs to downregulate the acetylation and crotonylation of Histone H3K27. Our unique design provided intriguing tools to further explore Kcr-interacting proteins and elucidate their working mechanisms.

Chemo-Selective Cys-Pen Disulfide for Proximity-Induced Cysteine Cross-Linking.

Disulfide-rich architectures are valuable pharmacological tools or therapeutics. Besides, a ligand-induced conjugate strategy offers potential advantages in potency, selectivity, and duration of action for novel covalent drugs. Combining the plentiful disulfide-rich architecture library and ligand-induced conjugate via thiol-disulfide interchange would supply great benefits for developing site specific covalent inhibitors. Cysteine-cysteine (Cys-Cys) disulfide bonds are intrinsically unstable in endogenous reductive environment, while cysteine-penicillamine (Cys-Pen) disulfide bonds show satisfactory stability. We envisioned the Cys-Pen disulfide as a potential ligand-induced covalent bonding warhead, and this disulfide could reconstruct with the protein cysteine in the vicinity of the peptide binding site to form a new disulfide. To evaluate our design, protein PLCγ1-c src homology 2 domain and RGS3-PDZ domain were tested as models. Both proteins were successfully modified by Cys-Pen disulfide and formed new disulfides between proteins and peptides. The new disulfide was then analyzed to confirm it was a newly formed disulfide bond between Pen of the ligand and a protein Cys near the ligand binding site. HDAC4 was then chosen as a model by utilizing its "CXXC" domain near its catalytic pocket. The designed Cys-Pen cyclic peptide inhibitor of HDAC4 showed satisfactory selectivity and inhibitory effect.

Structure-based design and SAR development of novel selective polo-like kinase 1 inhibitors having the tetrahydropteridin scaffold.

Polo-like kinase 1 (Plk1) is a validated target for the treatment of cancer. In this report, by analyzing amino acid residue differences among the ATP-binding pockets of Plk1, Plk2 and Plk3, novel selective Plk1 inhibitors were designed based on BI 2536 and BI 6727, two Plk1 inhibitors in clinical studies for cancer treatments. The Plk1 inhibitors reported herein have more potent inhibition against Plk1 and better isoform selectivity in the Plk family than these two lead compounds. In addition, by introducing a hydroxyl group, our compounds have significantly improved solubility and may target specific polar residues Arg57, Glu69 and Arg134 of Plk1. Moreover, most of our compounds exhibited antitumor activities in the nanomolar range against several cancer cell lines in the MTT assay. Through this structure-based design strategy and SAR study, a few promising selective Plk1 inhibitors having the tetrahydropteridin scaffold, for example, L34, were identified and could be for further anticancer research.

Design, synthesis and bioevalucation of novel 2,3-dihydro-1H-inden-1-amine derivatives as potent and selective human monoamine oxidase B inhibitors based on rasagiline.

Parkinson's disease (PD) is associated with elevated levels of hMAO-B in the brain, and MAO-B has been recognized a successful target for developing anti-PD drugs. Herein we report rasagiline derivatives as novel potent and selective hMAO-B inhibitors. They were designed by employing fragment-based drug design strategy to link rasagiline and hydrophobic fragments, which may target a hydrophobic pocket in the entrance cavity of hMAO-B. Different linkers such as -OCH2-, -SCH2-, -OCH2CH2-, -OCH2CH2O-, -OCH2CH2CH2O- were tried. A promising selective hMAO-B inhibitor D14 with similar inhibitory activity as rasagiline and improved isoform selectivity was yielded. The selectivity profile of compounds reported herein suggests that we can further develop more potent hMAO-B inhibitors with high isoform selectivity through this strategy.

Design, synthesis, and biological evaluation of novel highly selective polo-like kinase 2 inhibitors based on the tetrahydropteridin chemical scaffold.

Polo-like kinase 2 (Plk2) is a potential target for the treatment of cancer, which displays an important role in tumor cell proliferation and survival. In this report, according to the analysis of critical amino acid residue differences among Plk1, Plk2 and Plk3, and structure-based drug design strategies, two novel series of selective Plk2 inhibitors based on tetrahydropteridin chemical scaffold were designed and synthesized to target two specific residues, Lys86 and Tyr161 of Plk2. All compounds were evaluated for their inhibitory activity against Plk1-Plk3 and the cellular inhibition activity on six different human cancer cell lines. All efforts led to the identification of the most potent compounds C2 (3.40 nM against Plk2) and C21 (4.88 nM against Plk2) from the first and second series of selective Plk2 inhibitors respectively. Additionally, the selectivity of C21 over Plk1/3 was significantly increased with the selectivity indexes of 12.57 and 910.06. Moreover, most of our compounds exhibited antitumor activity in the nanomolar range in the MTT assay, indicating that our compounds, especially C2 and C21 could be promising Plk2 inhibitors for further anticancer research.

From monoclonal antibodies to small molecules: the development of inhibitors targeting the PD-1/PD-L1 pathway.

Cancer immunotherapy has made an extraordinary journey from bench to bedside. Blocking the interactions between programmed cell death protein 1 (PD-1) and its ligand, PD-L1, has emerged as a promising immunotherapy for treating cancer. Here, we review the development of drugs targeting the PD-1/PD-L1 pathway. We discuss the monoclonal antibodies (mAbs) approved or in clinical trials, peptides and patented small molecules developed against this pathway. Such compounds have the potential to treat cancer as well as chronic virological diseases. We also detail PD-1/PD-L1 interactions, an understanding of which will be useful for the rational design of small-molecule therapeutics that disrupt the PD-1/PD-L1 pathway. It is likely that more mAbs targeting the PD-1/PD-L1 pathway will be approved for the treatment of a range of cancers. By contrast, it is likely to be more difficult to successfully develop small molecules or peptides and for them to reach the clinic.