title: Folate receptor-specific antitumor activity of EC131, a folate-maytansinoid conjugate.
abstract: EC131, a new folate receptor (FR)-targeted drug conjugate, was prepared by covalently attaching the vitamin folic acid (FA) to a potent microtubule-inhibiting agent, maytansinoid DM1, via an intramolecular disulfide bond. When tested on cells in culture, EC131 was found to retain high affinity for FR-positive cells and to provide FR-specific cytotoxicity with an IC(50) in the low nanomolar range. The activity of EC131 was completely blocked in the presence of an excess of free FA, and no activity was detected against FR-negative cells. When evaluated against s.c. FR-positive M109 tumors in BALB/c mice, EC131 showed marked antitumor efficacy. Furthermore, this therapeutic effect occurred in the apparent absence of weight loss or noticeable organ tissue degeneration. In contrast, no significant antitumor activity was observed in EC131-treated animals that were codosed with an excess of FA, thus demonstrating the targeted specificity of the in vivo activity. EC131 also showed marked antitumor activity against FR-positive human KB tumors, but not against FR-negative A549 tumors, in nude mice with no evidence of systemic toxicity during or after the therapy. In contrast, therapy with the free maytansinoid drug (in the form of DM1-S-Me) proved not to be effective against the KB model when administered at its maximum tolerated dose (MTD). Taken together, these results indicate that EC131 is a highly potent agent capable of producing therapeutic benefit in murine tumor models at sub-MTD levels.
authors.affiliation: Endocyte, Inc., West Lafayette, Indiana 47906, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Reddy
authors.forename: Elaine
authors.initials: E
authors.lastname: Westrick
authors.forename: Hari K R
authors.initials: HK
authors.lastname: Santhapuram
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Howard
authors.forename: Michael L
authors.initials: ML
authors.lastname: Miller
authors.forename: Marilynn
authors.initials: M
authors.lastname: Vetzel
authors.forename: Iontcho
authors.initials: I
authors.lastname: Vlahov
authors.forename: Ravi V J
authors.initials: RV
authors.lastname: Chari
authors.forename: Victor S
authors.initials: VS
authors.lastname: Goldmacher
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Leamon
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D004354:Drug Screening Assays, Antitumor; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007624:KB Cells; D020714:Maximum Tolerated Dose; D008453:Maytansine / Q000737:chemistry / Q000494:pharmacology*; D029755:Maytenus / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010936:Plant Extracts / Q000494:pharmacology*; D011956:Receptors, Cell Surface / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D002352:Carrier Proteins; C521363:EC131 conjugate; D058973:Folate Receptors, GPI-Anchored; D010936:Plant Extracts; D011956:Receptors, Cell Surface; D008453:Maytansine; D005492:Folic Acid