The roots of Rhododendron mucronulatum Turzaninov have been used in Oriental traditional medicine for the treatment of dysuria, fever, increase of digestive activity and tonics in China and Korea. Activity guided isolation of the roots of Rhododendron mucronulatum Turzaninov has led to the isolation of three flavonoids, one flavan 3-ol and one proanthocyanidin. Chemical investigation of the 80% Me2 CO extract from the roots of Rhododendron mucronulatum led to the isolation and identification of five compounds: taxifolin (1), taxifolin 3-O-β-D-glucopyranoside (2), quercetin 3-O-α-L-arabinofuranoside (3), (-)-epicatechin (4), procyanidin B-3 (5). To investigate the antioxidative and antiinflammatory effects of these compounds, their 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities and the protein levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in LPS-stimulated HaCaT cells were also quantified by western blotting and their end products, nitric oxide (NO) and prostaglandin E2 (PGE2 ), respectively. Compounds (1-5) showed potent DPPH radical scavenging compared with positive controls (L-ascorbic acid). Also, compounds 1 and 2 dose-dependently inhibited the expressions of inflammatory mediators, NO and PGE2 , suggesting they are promising candidates as antiinflammatory agents.

Histone deacetylases (HDAC) inhibition is now well established as a new approach for solid and hematological tumor therapy. Studies with different HDAC inhibitors showed broad activity toward cancer cells, i.e. activation of proapoptotic pathway and inhibition of antiapoptotic pathway, induction of cell differentiation, antiangiogenic activity and synergism with other cancer therapeutics. Several HDAC inhibitors have demonstrated therapeutic benefits and are under clinical investigations as mono- or combi-therapy in various cancer cell lines such as cutaneous T-cell lymphoma (CTCL) with SAHA launched in 2006. Highly water-soluble CKD-581 is a potent and novel pan HDAC inhibitor developed in our institute. In this study, we analyzed first the in vitro growth inhibitory effect of CKD-581 on various cancer cells by MTT assay and inhibition of HDAC enzymes as well as its antitumor efficacy in human colon, prostate, and lung xenograft models. In addition, western blotting analysis for acH3, acH4 and p21 (WAF-1/CIP-1) and fluorescence-activated cell sorting analysis were performed to verify the associated molecular mechanisms involved in CKD-581 mediated cell death and cell cycle progression. CKD-581 showed strong cytotoxicity against several cancer cell lines including HCT-116, PC-3, A549 and H460 with IC50 values ranging from 10 nM to 100 nM. Its cytotoxicity was closely related with potent inhibitory activity against human HDAC1 and HDAC6 enzymes at single nMs. In various cancer cell lines, CKD-581 induced acetylation of histone and expression of tumor suppressor proteins involved in apoptosis pathway. CKD-581 significantly inhibited the in vivo growth of human tumor xenografts (HCT-116, PC-3, A549 and H460) in nude mice in a dose-dependent manner. Treatment of CKD-581 (60, 80, 100 mg/kg, b.i.wk, i.p.) caused 50-70% reduction in the mean tumor volume compared with controls. It is of note to observe that CKD-581 was highly efficacious when orally administered to nude mice bearing HCT 116. To correlate the pharmacodynamics with pharmacokinetics of CKD-581 in nude mice (HCT-116), we analyzed the kinetics of histone acetylation in tumors and plasma drug exposure at the end of 3 weeks of treatment (80 mg/kg, b.i.wk, i.p.), where Tmax of CKD-581 in tumor and in plasma were 4 h and 0.25 h after dosing, respectively and AUClast in tumor was 2.6 times higher than that of in plasma. CKD-581 is a potent HDAC inhibitor and showed a strong cytotoxicity against many cancer cell lines, demonstrated through the various in vitro and in vivo studies. Moreover, significant antitumor efficacy was shown in nude mice bearing several human tumors. Its potency together with excellent pharmacokinetic properties warrants further clinical investigations of CKD-581. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5435.