title: Development of an etoposide prodrug for dual prodrug-enzyme antitumor therapy.
abstract: Enzyme-prodrug approaches to cancer therapy, theoretically, have the potential to mediate tumor-selective cytotoxicity. However, even if tumor-specific prodrug activation is achieved, enzyme-prodrug systems investigated thus far comprised a single enzyme and a specific prodrug. Although targeted, such systems constitute single-agent therapy, which may be ineffective and/or may promote development of drug resistance. Therefore, a goal of our laboratories was to design and characterize a novel dipiperidinyl derivative of etoposide [1,4'-dipiperidine-1'-carboxylate-etoposide (dp-VP16)] that would act as a prodrug. We envisioned that dp-VP16 would be converted to the active chemotherapeutic agent VP-16 by the same rabbit carboxylesterase (rCE) that we have previously shown to efficiently activate the prodrug irinotecan (CPT-11). This dp-VP16 prodrug might then be used in combination with CPT-11, with both drugs activated by a single enzyme. We evaluated the ability of pure rCE and two human carboxylesterases, hCE1 and hiCE (hCE2), to activate dp-VP16 in vitro, and in neuroblastoma cell lines designed to express/overexpress each enzyme. In SK-N-AS neuroblastoma cell transfectants, expression of rCE or hiCE decreased the IC50 of dp-VP16 as a single agent by 8.3- and 3.4-fold, respectively, in growth inhibition assays. Purified hCE1 did not metabolize dp-VP16 in vitro and did not affect its IC50 in intact cells. The combination indices of sequential exposure to CPT-11 followed by dp-VP16 ranged from approximately 0.4 to 0.6, suggesting that this combination produced greater-than-additive cytotoxicity in neuroblastoma cells expressing rCE. These data provide proof-of-principle that enzyme-prodrug therapy approaches comprised of prodrugs with complementary mechanisms of cytotoxicity that are activated by a single enzyme can be developed.
authors.affiliation: Department of Molecular Pharmacology, St. Jude Children's Research Hospital, 332 North Lauderdale, Memphis, TN 38105, USA.
authors.forename: K Jin
authors.initials: KJ
authors.lastname: Yoon
authors.forename: Jianjun
authors.initials: J
authors.lastname: Qi
authors.forename: Joanna S
authors.initials: JS
authors.lastname: Remack
authors.forename: Kristopher G
authors.initials: KG
authors.lastname: Virga
authors.forename: M Jason
authors.initials: MJ
authors.lastname: Hatfield
authors.forename: Philip M
authors.initials: PM
authors.lastname: Potter
authors.forename: Richard E
authors.initials: RE
authors.lastname: Lee
authors.forename: Mary K
authors.initials: MK
authors.lastname: Danks
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000031:analogs & derivatives / Q000627:therapeutic use; D043182:Carboxylesterase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002384:Catalysis; D002455:Cell Division / Q000187:drug effects; D005047:Etoposide / Q000627:therapeutic use*; D006801:Humans; D020128:Inhibitory Concentration 50; D000077146:Irinotecan; D015394:Molecular Structure; D009447:Neuroblastoma / Q000188:drug therapy* / Q000201:enzymology; D011355:Prodrugs / Q000627:therapeutic use*; D011817:Rabbits; D014407:Tumor Cells, Cultured
chemical_list: D011355:Prodrugs; D005047:Etoposide; D000077146:Irinotecan; D043182:Carboxylesterase; D002166:Camptothecin