title: Collaboration between hepatic and intratumoral prodrug activation in a P450 prodrug-activation gene therapy model for cancer treatment.
abstract: Presently, we investigate the mechanisms whereby intratumoral expression of a cyclophosphamide-activating hepatic cytochrome P450 gene enhances therapeutic activity when cyclophosphamide is given on an every 6-day (metronomic) schedule. In P450-deficient 9L gliosarcomas grown in severe combined immunodeficient mice, metronomic cyclophosphamide substantially decreased tumor microvessel density and induced a approximately 70% loss of endothelial cells that began after the second cyclophosphamide treatment. These responses were accompanied by increased expression of the endogenous angiogenesis inhibitor thrombospondin-1 in tumor-associated host cells but by decreased expression in 9L tumor cells. These antiangiogenic responses preceded tumor regression and are likely key to the therapeutic activity of metronomic cyclophosphamide. Unexpectedly, 9L/2B11 tumors, grown from 9L cells infected with retrovirus encoding the cyclophosphamide-activating P450 2B11, exhibited antiangiogenic responses very similar to 9L tumors. This indicates that the tumor endothelial cell population is well exposed to liver-activated cyclophosphamide metabolites and that intratumoral P450 confers limited additional anti-endothelial cell bystander activity. In contrast, an increase in apoptosis, which preceded the antiangiogenic response, was substantially enhanced by intratumoral P450 2B11 expression. 9L/2B11 tumor regression was accompanied by an overall loss of tumor cellularity and by substantial enlargement of remaining P450-immunoreactive tumor cells as the number of P450-positive tumor cell decreased and the P450 protein content declined with cyclophosphamide treatment. We conclude that metronomic cyclophosphamide regresses P450-expressing tumors by two independent but complementary mechanisms: increased tumor cell killing via intratumoral P450-catalyzed prodrug activation, coupled with strong antiangiogenic activity, which is primarily associated with hepatic prodrug activation.
authors.affiliation: Division of Cell and Molecular Biology, Department of Biology, Boston University, Boston, MA 02215, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Ma
authors.forename: David J
authors.initials: DJ
authors.lastname: Waxman
mesh_terms: D020533:Angiogenesis Inhibitors / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism; D002452:Cell Count; D049109:Cell Proliferation / Q000187:drug effects; D003520:Cyclophosphamide / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2; D042783:Endothelial Cells / Q000187:drug effects / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D015316:Genetic Therapy; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051379:Mice; D016513:Mice, SCID; D008954:Models, Biological; D009369:Neoplasms / Q000201:enzymology* / Q000473:pathology / Q000628:therapy*; D009389:Neovascularization, Pathologic; D011355:Prodrugs / Q000378:metabolism*; D051381:Rats; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism; D019700:Thrombospondin 1 / Q000235:genetics / Q000378:metabolism
chemical_list: D020533:Angiogenesis Inhibitors; D011355:Prodrugs; D019700:Thrombospondin 1; D003520:Cyclophosphamide; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D000072467:Cytochrome P450 Family 2; C090278:cytochrome P-450 CYP2B11 (dog)