Folate receptor specific anti-tumor activity of folate-mitomycin conjugates.
OBJECTIVE
Folate receptor (FR) targeted drug conjugates were prepared by covalently attaching the vitamin folate, to the potent anticancer drug, mitomycin C (MMC). One such conjugate, called EC72, was synthesized with an intramolecular disulfide bond, and it was found to exhibit efficacious anti-tumor activity against FR-expressing M109 tumors in a manner that yielded no gross or microscopic toxicity, even to FR-positive kidneys.


METHODS
EC72's specificity was demonstrated by two methods: (1) blocking EC72's activity with an excess of co-administered folic acid (FA) in M109 tumor bearing mice and (2) the absence of therapeutic activity in mice bearing FR-negative tumors. The importance of having a cleavable bond in the conjugate was also exemplified, since EC110 (a folate-MMC conjugate constructed with a more resilient amide bond) failed to produce anti-M109 tumor activity. EC72's therapeutic potential was found to decrease with respect to the increasing size of subcutaneous tumor. However, a combination therapy with paclitaxel reproducibly improved the anti-tumor efficacy relative to either agent alone at well tolerated dose levels and with no apparent increase in toxicity. A more advanced folate-MMC conjugate was also synthesized in an effort to improve activity. Thus, EC118, a molecule constructed with both a reducible disulfide bond and an acid-labile hydrazone bond in the linker region, was tested and found to produce a significantly greater number of tumor regressions of more established M109 tumors than that achieved with EC72.


CONCLUSIONS
Overall, these data indicate that folate-targeted drug therapy alone, or in combination with paclitaxel, may be a novel and effective clinical approach towards treating FR-positive cancers.
Reddy
Joseph A
JA
Endocyte, Inc., 3000 Kent Ave., West Lafayette, IN 47906, USA,
Westrick
Elaine
E
Vlahov
Iontcho
I
Howard
Stephen J
SJ
Santhapuram
Hari Krishna
HK
Leamon
Christopher P
CP
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D002352:Carrier Proteins / Q000502:physiology*; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D051379:Mice; D016685:Mitomycin / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D011956:Receptors, Cell Surface / Q000502:physiology*
D000972:Antineoplastic Agents, Phytogenic; D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D016685:Mitomycin; D005492:Folic Acid