Regulation of 17β-hydroxysteroid dehydrogenases in cancer: regulating steroid receptor at pre-receptor stage

Increased intracelullar hormone concentration levels have been shown to be the cause of several endocrine-related cancers including breast, prostate, endometrial, ovarian, cervix, testicular, thyroid, and osteosarcoma. Deregulated expression of steroidogenic enzymes in these tumors seems to be the source of a positive balance in active steroids that bind to the corresponding nuclear receptor, thus ultimately stimulating cell proliferation. Among these enzymes, 17β-hydroxysteroid dehydrogenases catalyze the interconversion between 17-ketosteroids and 17-hydroxysteroids on the last steps of sex hormones biosynthesis and metabolism. To date, 14 isoforms have been identified in vertebrates although only 13 are present in humans. Development and clinical evaluation of specific inhibitors to block their activity is currently under progress especially against the best characterized members 1 to 5. Selectivity and potency of these drugs constitute the main challenge in this new approach to cancer and steroid-dependent diseases treatment at the "pre-receptor level". Here we review the current state of knowledge regarding the deregulation of the expression of some of these enzymes in endocrine-related tumors.     

Effect of reducing agents and uncouplers on the electrical potential generated by mitochondrial ATPase activity

Beef heart submitochondrial particles bound to phospholipids impregnated filters generated an electrical potential upon the addition of ATP. The magnitude of the electrical potential reached depended on the phospholipid mixture composition used for filter impregnation, phosphatidylethanolamine being the active component for the electrical potential generation. Uncoupler FCCP (p-trifluoromethoxy carbonyl cyanide phenylhydrazone) inhibited the transmembrane electrical potential generation by diminishing the electrical resistance of the system as a result of its protonophoric action. However, uncouplers 2, 4-dinitrophenol and dicoumarol did not provoke large modifications of the electrical resistance under the conditions of pH and concentration used, and their action varied with the time elapsed after the submitochondrial particles purification, favouring the idea of the uncoupler interaction with a specific site on the membrane. Addition of sodium dithionite resulted in a higher plateau value for the electrical potential consistent with the promoted increase in ATPase activity. The effect of this agent was reversed by the 2,6-dichlorophenol-indophenol added at equivalent concentrations.     

Interaction of F1-ATPase and its inhibitor peptide. Effect of pH

1. The inhibition of F1-ATPase by its natural peptide inhibitor is mixed non-competitive with two pH optimum values (5.5 and 8.2). 2. A two-step model for the interaction is suggested in which two enzyme conformations would exhibit different affinities for the peptide. 3. At low pH, interaction would be favoured. At high pH, a conformation (not susceptible to inhibition) changes into another (susceptible to inhibition) through the hydrolytic reaction stimulation, due to high pH.     

A diphenyldiselenide derivative induces autophagy via JNK in HTB‐54 lung cancer cells

Symmetric aromatic diselenides are potential anticancer agents with strong cytotoxic activity. In this study, the in vitro anticancer activities of a novel series of diarylseleno derivatives from the diphenyldiselenide (DPDS) scaffold were evaluated. Most of the compounds exhibited high efficacy for inducing cytotoxicity against different human cancer cell lines. DPDS 2 , the compound with the lowest mean GI₅₀ value, induced both caspase‐dependent apoptosis and arrest at the G₀/G₁ phase in acute lymphoblastic leucemia CCRF‐CEM cells. Consistent with this, PARP cleavage; enhanced caspase‐2, ‐3, ‐8 and ‐9 activity; reduced CDK4 expression and increased levels of p53 were detected in these cells upon DPDS 2 treatment. Mutated p53 expressed in CCRF‐CEM cells retains its transactivating activity. Therefore, increased levels of p21^CIP1 and BAX proteins were also detected. On the other hand, DPDS 6 , the compound with the highest selectivity index for cancer cells, resulted in G₂/M cell cycle arrest and caspase‐independent cell death in p53 deficient HTB‐54 lung cancer cells. Autophagy inhibitors 3‐methyladenine, wortmannin and chloroquine inhibited DPDS 6 ‐induced cell death. Consistent with autophagy, increased LC3‐II and decreased SQSTM1/p62 levels were detected in HTB‐54 cells in response to DPDS 6 . Induction of JNK phosphorylation and a reduction in phospho‐p38 MAPK were also detected. Moreover, the JNK inhibitor SP600125‐protected HTB‐54 cells from DPDS 6 ‐induced cell death indicating that JNK activation is involved in DPDS 6 ‐induced autophagy. These results highlight the anticancer effects of these derivatives and warrant future studies examining their clinical potential.     

Interaction of F1-ATPase and its inhibitor peptide. Effect of dinitrophenol, nucleotides and anions

1. ATPase natural inhibitor interacted in a mixed non-competitive manner with compounds affecting hydrolytic activity. 2. Ka's for DNP, HCO3- and free ATP, and Ki's for SCN- and ADP became smaller as inhibitor peptide concentration increased, reflecting an increase in affinity of F1-ATPase for these compounds induced by the peptide. 3. Activators increased the peptide inhibitory effect, whereas inhibitors decreased it. 4. A two-step model for the peptide-enzyme interaction is suggested in which ATP hydrolysis is a key factor.     

Benzo[b]thiophene-6-carboxamide 1,1-dioxides: Inhibitors of human cancer cell growth at nanomolar concentrations

Benzo[b]thiophenesulfonamide 1,1-dioxide derivatives (BTS) were described as candidate antineoplastic drugs. In the hope of finding new compounds with improved antitumour activity and reduced toxicity, we have designed and synthesized a small series of benzo[b]thiophene-6-carboxamide 1,1-dioxide derivatives (BTC) structurally related with the best reported BTS. Growth inhibition of HTB-54, CCRF-CEM and HeLa tumour cells lines at nanomolar concentrations was exhibited by some of the BTC. Hydrophobic substituents on the carboxamide group increased cytotoxicity but substitution by a hydroxy group diminished it, thus pointing to the electronic density on benzo[b]thiophene nucleus as a determinant factor. The process of cell death induced by BTC derivatives was further analyzed in CCRF-CEM cells, where these compounds induced apoptosis in a time and dose-dependent manner and cell cycle arrest at S phase. BTC derivatives also induced a significant increase in intracellular ROS levels in this cell line. Previous treatment of the cells with the antioxidant N-acetyl-cysteine abrogated the induction of apoptosis by BTC indicating that ROS generation is a previous event required to trigger the BTC induced apoptotic process.