Ⅰ. Development of glucal-conjugated sterols as novel vascular leakage blocker Ⅱ. Design, synthesis and biological evaluation of STAT3 signaling pathway inhibitor

Abstract

part 1. Vascular endothelial cells form the vascular endothelium as a monolayer that covers the vascular lumen and serves as an interface between circulating blood in the lumen and the rest of the vessel wall. The diverse function of the endothelium is crucial for the maintenance of vascular integrity. The loss of integrity and vascular permeability lead to a macular edema, which is normally accompanied by diabetic retinopathy. Diabetic retinopathy is a serious disease with no approved direct therapeutic agents. Nevertheless, there has been little progress in the treatment of vascular leakage and laser surgery remains the primary treatment. Consequently, medications for the treatment of retinal vascular leakage are urgently needed. We previously designed structurally simplified analogs by introducing the carbohydrate equivalents to cholesterol scaffold on the structural basis of ginsenoside Rk1. These analogs exhibited not only potent anti-apoptotic activity but also a protective effect against the disruption of tight junctions which leads to retinal vascular leakage. In an effort to develop novel therapeutic agents for the treatment of retinal vascular endothelium disorder, a series of glucal-conjugated sterols were identified through design, synthesis and biological evaluation. The structure-activity relationship (SAR) of the glucal-conjugated sterols focusing on the C17-side chain was also established, and a mechanism study with analog 20 indicated that it blocks vascular leakage by enhancing endothelial integrity via the cAMP/Rac/cortactin pathway. In particular, analog 29l, which possesses a cyclopentyl oxime moiety, was shown to have excellent pharmacological effects on retinal vascular leakage in a diabetic mouse model. Currently, further studies on the molecular mechanism and disease model of the sterol analogs are in progress.

part 2. The constitutive activation of signal transducer and activator of transcription 3 (STAT3) is highly implicated in tumorigenesis through its overexpression and constitutive activation in a variety of solid and hematological malignancies. STAT3 modulates critical cellular responses, including cell differentiation, proliferation, apoptosis, angiogenesis, metastasis, and immune responses. Thus, inhibition of the STAT3 signaling pathway has been considered an effective strategy for cancer therapy. We have studied the syntheses of 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) and its analogs and their biological consequences on STAT3. By studying the mechanism of action of 15d-PGJ2 related to STAT3 inhibition, we attempted to discover a hit for a STAT3 inhibitor from the in-house library based on diverse natural products. Specifically, a focused-library of compounds with electrophilic moiety was prepared based on the structural features of known STAT3 inhibitors. By using the focused-library, we expected to improve the efficiency of discovery hit compounds. Analog 21, a deguelin derivative containing exo-olefin, uniquely inhibited STAT3 transcription at a low micromolar level in HeLa cell line. It also inhibited STAT3 phosphorylation without affecting STAT1 phosphorylation and was selectively cytotoxic in human breast epithelial cells transfected with Ras (MCF10A-ras) compared with normal MCF10A cells, suggesting cancer cell-specific inhibitory properties. We selected three parts of analog 21 for the investigation of the substituent effect, confirmation of mechanism of action and assessment of benzopyran moiety as a privileged structure. Based on the results of an in vitro assay of the three-part modified analogs, further studies are in progress to establish the structure-activity relationship of analog 21.