Purpose: The specificity of a novel EGF-Cy5.5 fluorescent optical probe was assessed in vivo using CW fluorescence imaging accomplished via an ICCD camera.
Methods and Materials: Imaging was performed on mice with MDA-MB-468 cancer, known to overexpress EGFr, and contrasted against an analogous cell line, MDA-MB-435, that does not express EGFr. Fluorescence images on mice bearing s.c. inoculated tumors were obtained every 6 seconds for a period of 20 minutes following i.v. injection of 17 nmol of ICG, Cy5.5, or EGF-Cy5.5 and every 24 hrs thereafter for up to 192 hrs. In addition, mice with MDA-MB-468 tumors were injected i.v. with anti-EGFr antibody C225 24 hrs prior to injection of EGF-Cy5.5.
Results: Monitoring the time-sensitive fluorescence intensity confirms that ICG and Cy5.5 show no favorable binding to tumor, regardless of EGFr expression level. In contrast, EGF-Cy5.5 exhibits selective accumulation only in the MDA-MB-468 tumor. Moreover, tumor uptake of EGF-Cy5.5 tumors was blocked by pre-injection of C225 antibody, demonstrating specificity of the targeted contrast agent. Data further demonstrate that ICG and Cy5.5 fluorescence are completely absent from the tumor site, regardless of EGFr expression level, 24-hrs post injection. Similarly, little EGF-Cy5.5 fluorescence was detected in the EGFr-negative tumor after 24 hrs, however, for the MDA-MB-468 tumor, EGF-Cy5.5 fluorescence did not reach undetectable levels until 192 hrs. Pharmacokinetics further demonstrate specific uptake of targeting agent in vivo.
Conclusion: We show the ability to use CW imaging to track the pharmacokinetics of low-dose of non-specific and targeting fluorophore in vivo.
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