Tumor regression and curability of preclinical neuroblastoma models by PEGylated SN38 (EZN-2208), a novel topoisomerase I inhibitor.
OBJECTIVE
Treatment of neuroblastoma is successful in less than half of patients with high-risk disease. The antitumor activity of a water soluble pegylated SN38 drug conjugate, EZN-2208, was compared with CPT-11 (a prodrug for SN38) in preclinical models of human neuroblastoma.


METHODS
The in vitro cytotoxicity of EZN-2208 was tested by counting trypan blue dye- and Annexin V-positive cells, whereas its therapeutic efficacy was evaluated, in terms of survival, and antitumor and antiangiogenic activities, in s.c. luciferase-transfected, pseudometastatic, and orthotopic neuroblastoma animal models.


RESULTS
EZN-2208 was about 100-fold more potent than CPT-11 in vitro, by inducing apoptosis/necrosis and p53 expression and by reducing hypoxia-inducible factor (HIF)-1α/HIF-2α expression. EZN-2208 gave superior antitumor effects compared with CPT-11 in neuroblastoma xenografts. EZN-2208 treatment always resulted in lack of tumor detection at the end of trials whereas only small therapeutic effects were observed with CPT-11, as assessed by luciferase assay or tumor size, or even by staining histologic sections of tumors with antibodies recognizing neuroblastoma cells and cell proliferation. In a neuroblastoma model resistant to doxorubicin, cisplatin, vincristine, fenretinide, and topotecan, EZN-2208 induced 100% curability. It also blocked tumor relapse after topotecan-vincristine-doxorubicin combined treatment. Mechanistic experiments showed statistically significantly enhanced terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and Histone H2ax staining as well as decreased vascular endothelial growth factor, CD31, matrix metalloproteinase (MMP)-2, and MMP-9 expression in tumors removed from EZN-2208-treated mice and radiating vessels invading the tumor implanted onto the chorioallantoic membranes.


CONCLUSIONS
EZN-2208 should be considered a most promising novel antineuroblastoma agent. An ongoing phase I study in pediatric patients should identify the optimal dose for a phase II study.
Pastorino
Fabio
F
G. Gaslini Children's Hospital, National Cancer Institute, Genoa, Italy. fabiopastorino@ospedale-gaslini.ge.it
Loi
Monica
M
Sapra
Puja
P
Becherini
Pamela
P
Cilli
Michele
M
Emionite
Laura
L
Ribatti
Domenico
D
Greenberger
Lee M
LM
Horak
Ivan D
ID
Ponzoni
Mirco
M
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004195:Disease Models, Animal; D004354:Drug Screening Assays, Antitumor; D005260:Female; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000188:drug therapy* / Q000473:pathology; D009389:Neovascularization, Pathologic / Q000188:drug therapy; D009447:Neuroblastoma / Q000188:drug therapy* / Q000473:pathology; D011092:Polyethylene Glycols / Q000494:pharmacology* / Q000627:therapeutic use*; D015996:Survival Rate; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use
D000970:Antineoplastic Agents; C528970:EZN-2208; D059004:Topoisomerase I Inhibitors; D011092:Polyethylene Glycols; D000077146:Irinotecan; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin