title: Preclinical and clinical development of the cyclin-dependent kinase inhibitor flavopiridol.
abstract: Flavopiridol is the first potent inhibitor of cyclin-dependent kinases (cdks) to reach clinical trial. In the majority of solid tumor cell lines and xenografts, flavopiridol induces cell cycle arrest and tumor growth inhibition. This is reflected in clinical outcomes: across multiple Phase II trials there are subsets of patients with prolonged stable disease, although few responses have been observed. Flavopiridol displays sequence-dependent cytotoxic synergy with chemotherapy agents. These effects are most marked when chemotherapy precedes flavopiridol. In the case of DNA-damaging agents that impose S-phase delay, flavopiridol-mediated cdk inhibition disrupts the phosphorylation of E2F-1, leading to inappropriate persistence of its activity, inducing apoptotic pathways. This mechanism has been exploited in a Phase I trial of sequential gemcitabine and flavopiridol that has produced promising results. Flavopiridol is also synergistic with taxanes. Inhibition of cyclin B-cdk1 by flavopiridol accelerates exit from an abnormal mitosis associated with taxane-induced cell death and reduces the phosphorylation of survivin, preventing its stabilization and the cellular protection it affords after taxane exposure. The sequential combination of docetaxel and flavopiridol has been investigated in a Phase I trial in patients with advanced non-small cell lung cancer, and a randomized Phase II study is under way. Initial schedules of flavopiridol used prolonged continuous infusions that produced nanomolar levels of drug thought to be capable of achieving cdk inhibition based on results in tumor cell lines. Recently, it has been discovered that micromolar concentrations are likely to be more effective, and shorter infusions that achieve a higher C(max) have now been adopted. Loading followed by maintenance infusions are also under development, designed to achieve sustained micromolar drug levels. Clinical trials remain complicated by the absence of pharmacodynamic end points to confirm target inhibition.
authors.affiliation: Department of Medical Oncology and Lowe Center for Thoracic Oncology, Dana-Farber Cancer Institute, Brigham and Women's Hospital, Boston, Massachusetts, USA. geoffrey_shapiro@dfci.harvard.edu
authors.forename: Geoffrey I
authors.initials: GI
authors.lastname: Shapiro
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle; D002986:Clinical Trials as Topic; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D004334:Drug Administration Schedule; D005419:Flavonoids / Q000493:pharmacokinetics* / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D009369:Neoplasms / Q000188:drug therapy; D010880:Piperidines / Q000493:pharmacokinetics* / Q000494:pharmacology* / Q000627:therapeutic use; D014407:Tumor Cells, Cultured
chemical_list: D005419:Flavonoids; D010880:Piperidines; C077990:alvocidib; D018844:Cyclin-Dependent Kinases