Fen Jiang

Optimization and biological evaluation of celastrol derivatives as Hsp90-Cdc37 interaction disruptors with improved druglike properties.

Heat shock protein 90 (Hsp90) as a molecular target for oncology therapeutics has attracted much attention in the last decade. The Hsp90 multichaperone complex has important roles in the growth and/or survival of cancer cells. Cdc37, as a cochaperone, associates kinase clients to Hsp90 and promotes the development of malignant tumors. Disrupting the Hsp90-Cdc37 interaction provides an alternative strategy to inhibit the function of Hsp90 for cancer therapy. Celastrol, as a natural product, can disrupt the Hsp90-Cdc37 interaction and induce degradation of kinase clients. The study conducted here attempted to elucidate the structure-activity relationship of celastrol derivatives as Hsp90-Cdc37 disruptors and to improve the druglike properties. 23 celastrol derivatives were designed, synthesized, and the biological activities and physicochemical properties were determined. The derivative CEL20 showed improved Hsp90-Cdc37 disruption activity, anti-proliferative activities as well as druglike properties. Additionally, CEL20 induced clients degradation, cell cycle arrest and apoptosis in Panc-1 cells. This study can provide reference for the discovery of novel Hsp90-Cdc37 disruptors.

Novel natural-product-like caged xanthones with improved druglike properties and in vivo antitumor potency.

DDO-6101, a natural-product-like caged xanthone discovered previously in our laboratory based on the pharmacophoric scaffold of Garcinia natural product gambogic acid (GA), shows potent cytotoxicity in vitro but poor efficacy in vivo due to its poor druglike properties. In order to improve the druglike properties and in vivo cytotoxic potency, a novel series of 19 prenyl group-modified derivatives of DDO-6101 was synthesized and evaluated for their in vitro antitumor activity and druglike properties. The SAR and SPR information of these compounds was also obtained. In the light of the in vitro antitumor activity and druglike properties such as aqueous solubility and permeability, compound 6f (named as DDO-6306) was advanced into in vivo efficacy experiment. The results showed that DDO-6306 is more potent than DDO-6101 in vivo and is a promising antitumor candidate for further evaluation.

Synthesis and evaluation of a novel class Hsp90 inhibitors containing 1-phenylpiperazine scaffold

Previously, we identified 1-(2-(4-bromophenoxy)ethoxy)-3-(4-(2-methoxyphenyl)piperazin-1-yl)propan-2-ol (1) as a novel Hsp90 inhibitor with moderate activity through virtual screening. In this study, we report the optimization process of 1. A series of analogues containing the 1-phenylpiperazine core scaffold were synthesized and evaluated. The structure-activity relationships (SAR) for these compounds was also discussed for further molecular design. This effort afforded the most active inhibitor 13f with improved activity in not only target-based level, but also cell-based level compared with the original hit 1.

Discovery and identification of Cdc37-derived peptides targeting the Hsp90–Cdc37 protein–protein interaction

As an attractive anticancer target, the Hsp90 chaperone machine regulates a wide range of oncoproteins. Most of the Hsp90 inhibitors in clinical trials employ the same ATP blockage mechanism while little progress has been achieved with Hsp90–cochaperone complexes. Numerous protein kinases associate with the Hsp90–Cdc37 PPI, a potential target for the treatment of cancers, to implement folding and maturation. In order to explore the key residues of the Hsp90–Cdc37 binding interface for further design of peptide inhibitors, a combined strategy of molecular dynamics simulation and MM-PBSA analysis was performed. Subsequent design and identification of an eleven-residue peptide (Pep-1) directly derived from the Cdc37 binding interface was achieved to exhibit a 6.9 μM binding capacity and 3.0 μM ATPase inhibitory rate. This is the first evidence that a peptide inhibitor not only interferes with Hsp90 ATPase ability but also disrupts the Cdc37–Hsp90 PPI.

Synthesis and evaluation of 4-(2-hydroxypropyl)piperazin-1-yl) derivatives as Hsp90 inhibitors.

We previously reported 4-(3-((6-bromonaphthalen-2-yl)oxy)-2-hydroxypropyl)-N,N-dimethylpiperazine-1-sulfonamide (1) as a novel heat shock protein 90 inhibitor with moderate activity. In our ongoing efforts for the discovery of Hsp90 modulators we undertake structural investigations on 1. Series of the titled compound were designed, synthesized and evaluated. We have found that compounds with a hydroxyl group at C-4 of the aryl ring on the piperazine moiety possess Hsp90 inhibition properties. Compound 6f with improved activity could be further developed and optimized as Hsp90 inhibitor.

Betulinic acid acetate, an antiproliferative natural product, suppresses client proteins of heat shock protein pathways through a CDC37-binding mechanism

CDC37 has emerged as a promising target in antitumor chemotherapy because of its significant role in oncogenic signaling networks. In an effort to discover novel CDC37 inhibitors, a shape-based model derived from celastrol was built. A high-throughput virtual screening of ChemDiv based on the ROCS model has led to the identification of several pentacyclic triterpenes with high shape similarity with celastrol, among which betulinic acid acetate was the most attractive. Bio-layer interferometry assay demonstrated that betulinic acid acetate binds to CDC37 with a KD value (25.7 μM) on the same order of magnitude as that of celastrol. This compound not only shows comparable antiproliferative activity against a series of cancer cell lines, but also causes the degradation of HSP90 client proteins in PC-3 cell lines without inducing the expression of HSP70. In addition, betulinic acid acetate inhibits the function of HSP90 in a manner different from celastrol. The HTRF assay indicated that it cannot inhibit the association between HSP90 and CDC37. Given that it is not an α,β-unsaturated carbonyl compound, betulinic acid acetate can be recognized as the first inhibitor that binds to CDC37 through non-covalent binding.

Hybrids of the Benzofuran Core from Natural Products and the 2,4-Dihydroxy-5-isopropylbenzene Fragment as Potent Hsp90 Inhibitors: Design, Synthesis and Bioevaluation

Several chemical fragments have been confirmed as highly efficient cores for the design of Hsp90 inhibitors. Molecular hybridization of potent fragments has been widely used as a rational drug discovery strategy. In this study, a novel class of hybrids of benzofuran, a privileged core from natural products, and 2,4‐dihydroxy‐5‐isopropyl phenyl, an efficient fragment in Hsp90 inhibitors, were designed and synthesized. Subsequent evaluation confirmed they inhibited cell proliferation and regulated the level of client proteins through Hsp90 inhibition. Some of the hybrids can serve as leads to obtain novel chemotypes of Hsp90 inhibitors. The methods reported here may expand the range of known structural types accommodated by the ATP binding site of Hsp90.