UCSF

Currently, the conventional synthesis of a radiolabeled VRC01 tracer to target the HIV reservoir in the human body is a two-step process. This process involves quality control tests of both the intermediate DFO-VRC01 conjugate and the 89Zr-DFO-VRC01 product. A streamlined process could be made if characterization of the intermediate was eliminated by having the DFO chelate to the 89Zr, followed by the immediate conjugation of the VRC01 by the 89Zr-DFO. This method was explored by synthesizing 89Zr-DFO-PEG¬3¬-Azepin-mAb/protein using a light-induced one pot synthesis that could perform the radiolabeling and photoconjugation sequentially, bypassing the need to characterize an intermediate. Methods: A DFO-PEG3-ArN3 chelate was mixed with 89Zr-oxalate to form 89Zr-DFO-PEG3-ArN3, immediately followed by the addition of mAb/protein and irradiation by an LED light. The crude reaction was purified using both PD-10 and G-100 size exclusion chromatography. The eluate obtained by the purification columns were analyzed by size exclusion HPLC. Results: The photoconjugation was successful for the synthesis of 89Zr-DFO-PEG3-Azepin-HSA, 89Zr-DFO-PEG3-Azepin-Cimzia, and 89Zr-DFO-PEG3-Azepin-VRC01. However, the photoconjugation conversion did not go to completion, resulting in 89Zr-DFO-PEG3-Azepin present in the crude reaction. Size exclusion PD-10 column purification gave inadequate separation of the 89Zr-DFO-PEG3-Azepin-mAb/proteins from 89Zr-DFO-PEG3-Azepin. G-100 column purifications significantly improved the separation of 89Zr-DFO-PEG3-Azepin-mAb/protein from 89Zr-DFO-PEG3-Azepin. However, the labeled Azepin was still present in smaller percentages. The binding assay conducted to determine immunoreactivity of 89Zr-DFO-PEG3-Azepin-VRC01 and 89Zr-DFO-VRC01 gave dissociation constants in the 0.4-20 nM range, comparable to previous findings. Conclusion: The photoconjugation method was successful in synthesizing 89Zr-labeled HSA, Cimzia, and VRC01. The G-100 size exclusion column gave sufficient separation of 89Zr-DFO-PEG3-Azepin-mAbs/protein from 89Zr-DFO-PEG3-Azepin. The photoconjugation method did not affect the binding properties of 89Zr-DFO-PEG3-Azepin-VRC01 to the gp120 protein. Further work for more efficient photoconjugation and purification will be needed to foster future applications.