Real time, non-invasive, in vivo imaging of targeted drugs to solid tumors via a high affinity ligand: Implications to improving targeted -drug delivery
Abstract
The use of high affinity ligands to target drugs specifically to tumor cells is receiving increased attention as methods to reduce the toxicity of chemotherapeutic agents are pursued. The therapeutic potencies of such targeted drugs, however, depend on different parameters than those controlling normal drug delivery, including: (1) the efficiency and rate of targeted drug delivery to the site of the disease, (2) the rate of drug uptake by the tumor cell, and (3) the rate and efficiency of drug release from its targeting ligand during transit to the tumor cell and following subsequent uptake by the malignant mass. To quantitate these various contributions to tumor delivery, we have designed a series of fluorescent folate conjugates as surrogates of folate-linked drugs. Using intravital two-photon microscopy, we show (and quantify) the accumulation of these folate-targeted molecules into FR+ tumors as a function of time in live tumor-bearing mice. Quantitative analyses of these images reveal both the kinetics of targeted drug penetration into solid tumors as well as the spatial distribution of the captured drug within the tumor tissue. We find that saturation of all folate receptors in a malignant mass occurs within 5 min of intravenous injection (or 100 min of intraperitoneal injection). In order to determine the effect of the size of folate-conjugates in their penetration and accumulation in FR-positive solid tumor tissue, a series of folate-PEG-rhodamineconjugates of different sizes was synthesized, characterized, and their dynamic accumulation in solid tumors in vivo was analyzed. It was found that the macromolecular folate-conjugates circulate longer in the blood, and extravasate slowly into the tumor tissue. However, similar to the low molecular weight folate-drug conjugates, no “binding site barrier effect” was observed in the spatial distribution of the folate-targeted macromolecules. Therefore, it was concluded that it is possible to efficiently target macromolecular therapeutics via the folate receptor by conjugating them to folic acid and allowing longer times for their significant accumulation into solid tumor tissue.
Degree
Ph.D.
Advisors
Low, Purdue University.
Subject Area
Biochemistry
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