Abstract
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Objectives In our previous study, we generated a panel of aptamers able to distinguish liver cancer cells from normal liver cells using the technique of cell-based systematic evolution of ligands by exponential enrichment (SELEX) 1, a technique with which aptamers are selected with living cells without prior knowledge of the targets. All aptamers, named as JHIT1, JHIT2, JHIT3, JHI4, JHIT5, JHIT6, JHIT7, have different Kd value in the range of 64-349 nM and different binding ability toward human hepatoma cells HepG2 in vitro 2. Aptamer JHIT1 has the higher Kd value but more binding percentage than aptamer JHIT2. The aim is to observe the possibility of radioiodine labeled aptamerJHIT1 and JHIT2 and their ability to be probes for targeted radio-imaging or radiotherapy in liver cancer in vivo.
Methods Aptamers (JHIT1, JHIT2) and random library were radiolabeled with radioiodine 131 (131I) with method of Iodogen 3. Radiochemical purity of radioiodine labeled aptamer JHIT1, JHIT2 and random library was measured repeatedly in different time points in three solutions: phosphate buffer solution (PBS), saline solution and rat plasma. Radioiodine labeled aptamers and library were injected into heterotopic xenograft model of hepatocellular liver cancer in nude mice. Series of SPECT imaging were performed. Visual inspection and quantitative analysis of tumor to background ratio were studied about the SPECT images.
Results The labeling rate of three single stranded DNA was (88.46%±2.10%). Radiochemical purity of radioiodine labeled single stranded DNA was(89.67%±0.67%) and (90.06%±1.67%) in PBS and saline solution respectively at the time point of 4 hours and (72.99%±7.53%) in rat plasma at the time point of 1 hour. Twenty four hours later, radiochemical purity of labeled single stranded DNA in PBS, saline solution and rat plasma was (74.43%±2.60%), (81.16%±2.74%) and (65.49%±11.25%) respectively. SPECT imaging showed fast clearance from blood through the kidneys and hepatobiliary system and unsatisfying radioisotope accumulation in the tumor. Quantitatively analysis showed the highest ratio of tumor to background was 1.69 in 2 hours of aptamerJHIT1, 2.64 in 4 hours of aptamer JHIT2 and 1.63 in 4 hours of random library.
Conclusions Our data suggested that the aptamers can be labeled with radioiodine efficiently and are stable in PBS and saline solution within 4 hours, with relatively poor stability in plasma. Further modification of aptamers is needed to be probes as targeted imaging or radiotherapy of liver cancer in vivo. AptamerJHIT2 might be slightly better than aptamerJHIT1 in vivo. Acknowledgment:The Project-sponsored by SRF for ROCS, SEM and supported by National Natural Science Funds of China (81101866), Sci-tech Development Program of Guangdong Province(2014A020212581)