title: Variolin B and its derivate deoxy-variolin B: new marine natural compounds with cyclin-dependent kinase inhibitor activity.
abstract: Variolin B (VAR-B) is a natural product isolated from the sponge Kirkpatrickia variolosa, found in Antarctica. VAR-B has been shown previously to possess potent pro-apoptotic activity. This study was undertaken to investigate the mechanism of action of chemically synthesised VAR-B and its analogue deoxy-variolin B (dVAR-B). In different human cancer cell lines both compounds inhibited colony formation, caused cell cycle perturbations and induced apoptosis at concentrations ranging from 0.1 to 2 microM. LoVo/Dx cells over-expressing Pgp were equally sensitive as the parental cell line to VAR-B and dVAR-B, indicating that variolins are not substrates of Pgp. Although variolins induced an increase in the levels of p53 with an increase in p21, their cytotoxicities did not appear to be dependent on p53 status as their potency was comparable in cells with wild-type p53, or in sub-lines with inactivated p53. Both VAR-B and dVAR-B prevent the cells from entering S phase, blocking cells in G1 and cause an accumulation of cells in G2. The apoptosis induced by VAR-B and dVAR-B occurs very rapidly in some cell lines (e.g., Jurkat leukaemia cells) and is already evident 4h after the beginning of treatment. Although intercalation of dVAR-B in DNA has been demonstrated, neither VAR-B nor dVAR-B produce detectable breaks in DNA. These results are consistent with the in vitro biochemical assays that also demonstrated that dVAR-B is not topoisomerase I or II poison. Instead, each of these variolins appears to inhibit cyclin-dependent kinases (CDKs) in the muM range. CDK1-cyclin B, CDK2-cyclin A and CDK2/cylin E complexes were inhibited in a range of concentrations lower than those required to inhibit the activity of CDK4/cyclin D or CDK7/cyclin H complexes. In conclusion, these variolins are a new class of CDK inhibitors that activate apoptosis in a p53-independent fashion and thus they may be effective against tumours with p53 mutations or deletions.
authors.affiliation: Department of Oncology, Mario Negri Institute for Pharmacological Research, Via Eritrea 62, Milan, and Division of Pediatric Oncology, Catholic University A. Gemelli, Rome, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Simone
authors.forename: Eugenio
authors.initials: E
authors.lastname: Erba
authors.forename: Giovanna
authors.initials: G
authors.lastname: Damia
authors.forename: Faina
authors.initials: F
authors.lastname: Vikhanskaya
authors.forename: Angela M
authors.initials: AM
authors.lastname: Di Francesco
authors.forename: Riccardo
authors.initials: R
authors.lastname: Riccardi
authors.forename: Christian
authors.initials: C
authors.lastname: Bailly
authors.forename: Carmen
authors.initials: C
authors.lastname: Cuevas
authors.forename: José Maria
authors.initials: JM
authors.lastname: Fernandez Sousa-Faro
authors.forename: Maurizio
authors.initials: M
authors.lastname: D'Incalci
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy* / Q000473:pathology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001372:Aza Compounds / Q000494:pharmacology*; D053148:Caspase 3; D020169:Caspases / Q000032:analysis; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000473:pathology; D018844:Cyclin-Dependent Kinases / Q000032:analysis* / Q000037:antagonists & inhibitors*; D004273:DNA, Neoplasm / Q000032:analysis; D006801:Humans; D011743:Pyrimidines / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D001372:Aza Compounds; D004273:DNA, Neoplasm; D011743:Pyrimidines; C474921:variolin B; D018844:Cyclin-Dependent Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases