Ligand-receptor Interaction between Triterpenoids and the 11β-Hydroxysteroid dehydrogenase type 2 (11βHSD2) Enzyme Predicts Their Toxic Effects against Tumorigenic r/m HM-SFME-1 Cells

Abstract

The present study deals with in silico prediction and in vitro evaluation of the selective cytotoxic effects of triterpenoids on tumorigenic human c-Ha-ras and mouse c-myc cotransfected highly metastatic serum-free mouse embryo-1 (r/m HM-SFME-1) cells. Ligand fitting of five different triterpenoids to 11␤-hydroxysteroid dehydrogenase type 2 (11␤HSD2) was analyzed with a molecular modeling method, and glycyrrhetinic acid (GA) was the best-fitted triterpenoid to the ligand binding site in 11␤HSD2. Analysis of antiproliferative effects revealed that GA, oleanolic acid, and ursolic acid had selective toxicity against the tumor cells and that GA was the most potent triterpenoid in its selectivity. The toxic activity of the tested triterpenoids against the tumor cells showed good correlations with the partition coefficient (logP) and polar surface area values. Time-lapse microscopy, fluorescence staining, and confocal laser scanning microscopic observation revealed that GA induced morphologic changes typical of apoptosis such as cell shrinkage and blebbing and also disrupted the cytoskeletal proteins. Furthermore, GA exhibited a strong inhibitory effect on 11␤HSD2 activity in the tumor cells. Our current results suggest that analysis of the ligand-receptor interaction between triterpenoids and 11␤HSD2 can be utilized to predict their antitumor effects and that GA can be used as a possible chemopreventive and therapeutic antitumor agent. To the best of our knowledge, this is the first report on in silico prediction of the toxic effects of triterpenoids on tumor cells by 11␤HSD2 inhibition.Triterpenoids, which are biosynthesized in plants by cyclization of squalene, are widely distributed throughout the vegetable kingdom, utilized in many food products and the major components of medicinal plants used in Asian countries (1). There is a growing interest in elucidating the biological and pharmacological roles of triterpenoids in analgesic, anti-inflammatory, anti-tumor, hepatoprotective, and immunomodulatory effects (1), and we have been focusing our attention on certain triterpenoids as multifunctional agents for the prevention and treatment of cancer. Recently, we found that ursolic acid (UA) 2 from apples was selectively toxic to tumorigenic human c-Ha-ras and mouse c-myc cotransfected highly metastatic serum-free mouse embryo-1 (r/m HM-SFME-1) cells (2). We further found that glycyrrhetinic acid (GA), a licorice component, was not only selectively toxic to the tumor cells but also more potent than some clinically available antitumor agents in its selectivity (3). SFME cells, which were established by Loo et al. (4), were originally derived from a 16-day-old whole Balb/c mouse embryo and are maintained in a serum-free culture medium. These cells do not undergo growth crisis, maintain their diploid karyotype for extended passages, and are non-tumorigenic in vivo. Consequently, they are non-transformed, behave as primary cultures, have a finite lifespan, and display the characteristics of the CNS progenitor cells (5, 6)....

Structural insight into the ligand-receptor interaction between glycyrrhetinic acid (GA) and the high-mobility group protein B1 (HMGB1)-DNA complex

“…We recently found that GA demonstrated significant growth inhibitory activity toward a CNS tumor cell line [13], suggesting that GA can be utilized for the antitumor drug development. However, whether or not GA can bind to the HMGB1-DNA complex is not known.…”

“…Modeling of the 3D structure of the HMGB1-DNA complex was executed as previously reported [13]. In brief, the HMGB1 (NCBI reference sequence: NP_002119.1) and the duplex sequences and their crystal structure coordinates were loaded into the MOE.…”

“…The binding site selection and exploration for the HMGB1-DNA complex was executed as previously reported [13]. In brief, the Site Finder module of the MOE was used to identify possible ligand-binding pockets within the newly generated 3D structures of HMGB1-DNA.…”

“…We have been focusing our attention on GA as a multifunctional agent for the prevention and treatment of cancer, including downregulation of inflammatory responses associated with cancer. Recently, we found that GA demonstrated a significant selective toxicity towards a central nervous system (CNS) tumor cell line [13]. These reports suggest that targeting HMGB1 with GA treatment could be utilized for controlling the development and progression of cancer.…”

Homology modeling and structural analysis of human <i>γ</i>-glutamylcysteine ligase catalytic subunit for antitumor drug development

“…Our previous study revealed that GSH could be an important factor for the selective toxicity toward central nervous system-derived tumor cells [20], which suggests that targeting the key enzyme for GSH homeostasis, namely GCL, with highly selective inhibitors could be utilized for controlling the development and progression of cancer. GCL is a heterodimeric enzyme with a 73-kDa catalytic subunit and a 31-kDa modifier subunit, and GCLC contains the glutamate, cysteine and ATP binding sites and has catalytic activity even as a monomer [1,21].…”