Design, Synthesis And Development Of Transporter Targeting Agents For Image-Guided Therapy And Drug Delivery

Author

Ning Tsao, The University of Texas Graduate School of Biomedical Sciences at HoustonFollow

Date of Graduation

5-2013

Document Type

Dissertation (PhD)

Program Affiliation

Experimental Therapeutics

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

David J. Yang, Ph.D.

Committee Member

Franklin C. Wong, M.D., Ph.D., J.D.

Committee Member

Edward Jackson, Ph.D.

Committee Member

Osama Mawlawi, Ph.D.

Committee Member

Wei Hu, M.D., Ph.D.

Abstract

The purpose of this study was to design, synthesize and develop novel transporter targeting agents for image-guided therapy and drug delivery. Two novel agents, N4-guanine (N4amG) and glycopeptide (GP) were synthesized for tumor cell proliferation assessment and cancer theranostic platform, respectively. N4amG and GP were synthesized and radiolabeled with ^99mTc and ⁶⁸Ga. The chemical and radiochemical purities as well as radiochemical stabilities of radiolabeled N4amG and GP were tested. In vitro stability assessment showed both ^99mTc-N4amG and ^99mTc-GP were stable up to 6 hours, whereas ⁶⁸Ga-GP was stable up to 2 hours. Cell culture studies confirmed radiolabeled N4amG and GP could penetrate the cell membrane through nucleoside transporters and amino acid transporters, respectively. Up to 40% of intracellular ^99mTc-N4amG and ^99mTc-GP was found within cell nucleus following 2 hours of incubation. Flow cytometry analysis revealed ^99mTc-N4amG was a cell cycle S phase-specific agent. There was a significant difference of the uptake of ^99mTc-GP between pre- and post- paclitaxel-treated cells, which suggests that ^99mTc-GP may be useful in chemotherapy treatment monitoring. Moreover, radiolabeled N4amG and GP were tested in vivo using tumor-bearing animal models. ^99mTc-N4amG showed an increase in tumor-to-muscle count density ratios up to 5 at 4 hour imaging. Both ^99mTc-labeled agents showed decreased tumor uptake after paclitaxel treatment. Immunohistochemistry analysis demonstrated that the uptake of ^99mTc-N4amG was correlated with Ki-67 expression. Both ^99mTc-N4amG and ^99mTc-GP could differentiate between tumor and inflammation in animal studies. Furthermore, ⁶⁸Ga-GP was compared to ¹⁸F-FDG in rabbit PET imaging studies. ⁶⁸Ga-GP had lower tumor standardized uptake values (SUV), but similar uptake dynamics, and different biodistribution compared with ¹⁸F-FDG. Finally, to demonstrate that GP can be a potential drug carrier for cancer theranostics, several drugs, including doxorubicin, were selected to be conjugated to GP. Imaging studies demonstrated that tumor uptake of GP-drug conjugates was increased as a function of time. GP-doxorubicin (GP-DOX) showed a slow-release pattern in in vitro cytotoxicity assay and exhibited anti-cancer efficacy with reduced toxicity in in vivo tumor growth delay study. In conclusion, both N4amG and GP are transporter-based targeting agents. Radiolabeled N4amG can be used for tumor cell proliferation assessment. GP is a potential agent for image-guided therapy and drug delivery.

Keywords

glycopeptide, Imaging probe, PET imaging, SPECT imaging, guanine, theranostics, drug delivery system