Targeting dendrimer-chelates to tumors and tumor cells expressing the high-affinity folate receptor.
OBJECTIVE
The authors developed a new method for delivering contrast agents to tumors and tumor cells. Gadolinium complexes of folate-conjugated dendrimer-chelates increased the longitudinal relaxation rate of tumor cells expressing the high-affinity folate receptor, hFR. The coupling of folate to polymeric chelates, composed of a dendrimer backbone, targets these chelates to endogenous folate binding proteins. These proteins exist in both the serum of patients with cancer and on the cell surface of many human cancers of epithelial origin.


METHODS
The authors attached folic acid to a generation four ammonia core polyamidoamine dendrimer. The folate-dendrimer was reacted with 2-(4-isothiocyanatobenzyl)-6-methyl-diethylenetriaminepentaacetic acid to form the polymeric chelate f-PAMAM-TU-DTPA. For fluorescent studies, the generation four dendrimer was reacted with fluorescein-5-isothiocyanate and carboxytetramethylrhodamine succinimidyl ester, followed by capping the remaining amines with succinic anhydride.


RESULTS
The study results show that cells accumulate the folate-conjugated dendrimer in a receptor specific manner. Tumor cells expressing the high-affinity folate receptor showed a 650% increase in the mean fluorescence. This increase occurred with a rapid rise to 325%, followed by a slow increase to 650%. It required both the expression of the hFR and the coupling of folic acid to the dendrimer. Excess free folic acid inhibited the binding of the folate conjugated polymer. Fluorescent microscopic study showed that the folate-conjugated dendrimer binds to the cell surface and is accumulated within the cells. Treatment of tumor cells that express the hFR with gadolinium complexes of the folate-conjugated polymeric chelate increases the longitudinal relaxation rate by 110%. This increase was inhibited by an excess of free folic acid.


CONCLUSIONS
These data demonstrate that folate-conjugated magnetic resonance imaging contrast agents represent a promising new approach to tumor targeting.
Wiener
E C
EC
Biomedical Magnetic Resonance Laboratory, College of Medicine, University of Illinois, Urbana-Champaign, USA.
Konda
S
S
Shadron
A
A
Brechbiel
M
M
Gansow
O
O
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002614:Chelating Agents; D003287:Contrast Media / Q000378:metabolism*; D050091:Dendrimers; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D016650:Fluorescein-5-isothiocyanate / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism; D019786:Gadolinium DTPA / Q000378:metabolism; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008856:Microscopy, Fluorescence; D011073:Polyamines / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012235:Rhodamines / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000378:metabolism
D002352:Carrier Proteins; D002614:Chelating Agents; D003287:Contrast Media; D050091:Dendrimers; D005456:Fluorescent Dyes; D058973:Folate Receptors, GPI-Anchored; C104700:PAMAM Starburst; D011073:Polyamines; D011956:Receptors, Cell Surface; D012235:Rhodamines; D005492:Folic Acid; D016650:Fluorescein-5-isothiocyanate; D019786:Gadolinium DTPA