The Development of a Novel Tumor -Specific MRI Contrast Agent Targeting the High Affinity Folate Receptor: In Vitro and in Vivo Specificity, Toxicity, and Biodistribution
Konda, Sheela Devi
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https://hdl.handle.net/2142/87220
Description
Title
The Development of a Novel Tumor -Specific MRI Contrast Agent Targeting the High Affinity Folate Receptor: In Vitro and in Vivo Specificity, Toxicity, and Biodistribution
Author(s)
Konda, Sheela Devi
Issue Date
2002
Doctoral Committee Chair(s)
Erik C. Wiener
Department of Study
Molecular and Integrative Physiology
Discipline
Molecular and Integrative Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Health Sciences, Speech Pathology
Language
eng
Abstract
The need to develop target-specific MRI contrast agents to aid in disease characterization remains highly essential. Here, we present a generation four polyamidoamine (PAMAM) dendrimer conjugated to folic acid that specifically targets the high affinity folate receptor (hFR) overexpressed on more than 80% of ovarian tumors. We tested the hypothesis that folate-dendrimers can specifically image tumors expressing the hFR with MRI. Conjugating folate to dendrimers results in specific binding of these macromolecules to cells expressing the hFR and enables specific imaging of hFR expression by tumors in vivo. Tumor cells expressing the hFR showed a 650% increase in mean fluorescence characterized by a rapid rise to 325%, followed by a slow increase to 650%, and a 2709% increase in uptake of 153Gd(III). This required both the expression of the hFR and the attachment of folic acid to the dendrimer. Excess free folic acid inhibited both the increases in fluorescence and radioactivity uptake of hFR-positive cells. The folate-dendrimer increased the in vitro longitudinal relaxation rate of hFR-positive cells by 110% at 1.2T, and was inhibited by free folic acid. In vivo treatment of hFR-positive ovarian tumor xenografts with the folate-dendrimer chelate resulted in a 33% contrast enhancement after 24 hours and was significantly different compared to results with a nonspecific agent. This contrast enhancement was absent in hFR-negative tumors and was inhibited by free folic acid. The internalization of the linear diethylenetriamine pentaacetic acid (DTPA) chelate kills some tumor cells expressing the hFR in vitro. Toxicity results show that the ovarian tumor cells exhibited a lower percent viability, 68.3%, compared to control cells, 83.4%. Treatment with free folic acid resulted in a statistically similar percent viability as the control cells. Tumor cell toxicity is consistent with internalization of the folate-dendrimer, which could result in either the release of gadolinium within endosomes or anti-folate activity of the folate-dendrimer. The biodistribution of the radiolabeled 153Gd-folate-dendrimer is favorable. The agent accumulates significantly more within hFR-positive tumors (3.64% injected dose/g) than hFR-negative tumors (at or below background) following 24 hours. Folate-conjugated dendrimer-based MRI contrast agents are a promising approach to target-specific diagnosis.
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