title: Metronomic vinorelbine: Anti-angiogenic activity in vitro in normoxic and severe hypoxic conditions, and severe hypoxia-induced resistance to its anti-proliferative effect with reversal by Akt inhibition.
abstract: Metronomic chemotherapy is the protracted, dense administration of low sub-toxic doses of chemotherapy, to inhibit tumor angiogenesis. Vinorelbine is an orally bioavailable vinca alkaloid shown to be useable for metronomic administration. In clinical trials, metronomic vinorelbine has been demonstrated to generate sustainable antitumor efficacy at low nanomolar (nM) concentrations with negligible toxicity. We sought to determine whether the clinically relevant metronomic concentration of vinorelbine is anti-angiogenic in vitro and whether hypoxia, often induced by anti-angiogenic therapy, modifies its effectiveness. We found that the metronomic concentration of 10 nM vinorelbine inhibited human umbilical vein endothelial cell (HUVEC) proliferation, migration, tube formation and sprouting. Severe hypoxia, did not affect the inhibitory effect of metronomic vinorelbine on migration, tube formation and sprouting. However, severe hypoxia reduced its anti-proliferative effect by decreasing its ability to induce G2/M block as it shifted the cell population to the G1 phase and decreased the fraction of the cells in the DNA synthesis S phase. Furthermore, the pro-apoptotic effects of 10 nM vinorelbine were also decreased. Metronomic vinorelbine decreased the Bcl-2/Bax ratio in normoxia whereas the ratio was reduced in severe hypoxia but unaltered by vinorelbine treatment. Akt signals to an anti-apoptotic pathway and we demonstrated that the Akt inhibitor V reversed the protective effect of severe hypoxia. Thus, we provide evidence for the anti-angiogenic basis of metronomic vinorelbine and we show that severe hypoxia mediates resistance to its anti-proliferative effect on endothelial cells. Akt warrants further investigation as a potential target to circumvent this hypoxic resistance.
authors.affiliation: Molecular Oncology Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK.
authors.forename: L
authors.initials: L
authors.lastname: Mavroeidis
authors.affiliation: Molecular Oncology Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK.
authors.forename: H
authors.initials: H
authors.lastname: Sheldon
authors.affiliation: Department of Hematology, School of Medicine, University of Ioannina, University Campus, 45110 Ioannina, Greece.
authors.forename: E
authors.initials: E
authors.lastname: Briasoulis
authors.affiliation: Department of Pharmacology, School of Medicine, University of Ioannina, University Campus, 45110 Ioannina, Greece.
authors.forename: M
authors.initials: M
authors.lastname: Marselos
authors.affiliation: Department of Pharmacology, School of Medicine, University of Ioannina, University Campus, 45110 Ioannina, Greece.
authors.forename: P
authors.initials: P
authors.lastname: Pappas
authors.affiliation: Molecular Oncology Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK.
authors.forename: A L
authors.initials: AL
authors.lastname: Harris
mesh_terms: D059250:Administration, Metronomic; D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D015687:Cell Hypoxia / Q000187:drug effects; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D066298:In Vitro Techniques; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors; D014747:Vinblastine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000077235:Vinorelbine
chemical_list: D020533:Angiogenesis Inhibitors; D000972:Antineoplastic Agents, Phytogenic; D014747:Vinblastine; D051057:Proto-Oncogene Proteins c-akt; D000077235:Vinorelbine