Abstract
Abstract At present, cancer remains the major cause of human death in the world, accounting for nearly 1 of every 4 deaths. The current focus of modern cancer researches is on cancer early detection and advanced treatments. Diagnostic nuclear imaging using radiopharmaceuticals is playing an increasingly important role in the tumor detection as well as therapeutic applications. In this dissertation, the 99mTc-tricarbonyl-based radiolabeling method was attempted for direct labeling of 99mTc to three different biomacromolecules, including: Herceptin (trastuzumab), histidine-tagged octreotide derivatives and protein-based HSA nanoparticles. The radiochemical properties of the resultant 99mTc-labeled biomacromolecules were characterized and investigated for their potentials on SPECT imaging. Thus, three research projects are included in this dissertation: (I) Direct 99mTc labeling of Herceptin (trastuzumab) by 99mTc(I)-tricarbonyl ion, (II) 99mTc(I) Radiolabeling of histidine-conjugated octreotide derivatives and preliminary in vivo evaluation in AR42J tumor-bearing mice, (III) The novel preparation of 99mTc(I)-labeled human serum albumin (HSA) nanoparticles as a SPECT imaging agent. The first study shows that 99mTc(I)-trastuzumab was prepared by simple incubating Herceptin (trastuzumab) with [99mTc(OH2)3(CO)3]+ in normal saline under mild radiolabeling condition. The tumor-targeting capability of the 99mTc(I)-labeled trastuzumab was validated with high binding affinity to HER-2-overexpressing cancer cells. Well in vitro stability of 99mTc(I)-trastuzumab in serum suggests its potential as a SPECT imaging agent in vivo. The second study shows that octreotide together with its three histidine-tagged octreotide derivatives (his-octreotide, his3-octreotide and his5-octreotide) were successfully synthesized using a facile solid phase peptide synthesis method. This study also shows that all the histidine-tagged octreotide derivatives demonstrated similar high binding affinities as octreotide to the human somatostatin sst2a receptor. [99mTc(OH2)3(CO)3]+ was also applied as an efficient reagent for direct labeling histidine-conjugated octreotide derivatives by a simple mixing procedure under mild condition. Biodistribution and imaging studies of the 99mTc(I)-his3-octreotide and 99mTc(I)-his5-octreotide demonstrated the highest tumor uptake at 4 h and 8 h postinjection, respectively, and both displayed a clear tumor delineation. It is anticipated that the 99mTc(I)-labeled histidine-conjugated octreotide derivatives will be useful for imaging SSTRs-positive tumors. The third study established a new and efficient protocol to prepare 99mTc(I)-HSA-NPs conjugates with high purity and stability. Labeling of 99mTc(I) to HSA-NPs was also performed in the similar mild way as aforementioned, and achieved high radiochemical yield and specific activity. In the future, the HSA-NPs could be further loaded with anticancer drugs for potential therapeutic uses. The versatility and attractive properties suggest that 99mTc(I)-HSA-NPs have great potentials for future theranostic applications.