Abstract
1049
Objectives: The C-X-C chemokine receptor 4 (CXCR4) is overexpressed in various tumors and plays a key role in tumor pathogenesis. Therefore, CXCR4-targeted molecular imaging can quickly and accurately detect and quantify CXCR4 abnormalities in real time. In this study, we radiolabeled a LY-2510924 derivative with 68Ga and used for differentiation of CXCR4 expression in different breast tumor cell lines to provide a potential noninvasive method for monitoring CXCR4 for the future clinical application.
Methods: The peptides were conjugated with a macrocyclic chelator DOTA to prepare two different precursors(DOTA-LY9969 and DOTA-LY9970) and were radiolabeled with 68Ga (t1/2 = 68min) on a 10 μg scale in pH 5.0-5.5 sodium acetate buffer at 90℃ in 15 min and purified by HLB SPE column(10mg). LogP values and stability in PBS and FBS were determined. The CXCR4 expression of all cell lines was confirmed by western blotting. Tumor cell uptake was examined at 37℃ using MCF-7, MDA-MB-231 and MDA-MB-468 cell lines. PET imaging was performed in Breast cancer xenograft nude mice to evaluate the capacity and specificity of 68Ga-DOTA-peptides to target CXCR4 in vivo.
Results: Western blotting showed higher CXCR4 expression levels in MCF-7 cells than that in MDA-MB-231 and MDA-MB-468 cells. Radio-HPLC showed retention time for 68Ga-DOTA-peptides at 12 ± 0.5 min as compared to free 68GaCl3 at 3.3 ± 0.4 min. The radiochemical purity was 98.0 ± 0.5 % for 68Ga-DOTA-peptides (n=5). Both radio-complexes were stable (> 94%) in in-vitro at 37℃ over a time period of 2 h and determined by Radio-HPLC. Both tracers were highly hydrophilic (LogP = −3.10 and −3.14). Cell uptake for 68Ga-DOTA-LY9970 were 8.62±0.42 %,3.46±0.06 % and 3.24±0.38 % in MCF-7, MDA-MB-231 and MDA-MB-468 cells and 5.25±0.30 %,2.01±0.11 % and 1.99±0.15 % for 68Ga-DOTA-LY9969. Micro PET/CT imaging showed that tracer accumulates specifically in MCF-7 xenograft model and a high tumor-to-background contrast. The images showed T/NT ratio for 68Ga-DOTA-LY9970 was higher than that for 68Ga-DOTA-LY9969. Blocking studies displayed significantly decrease in T/NT and the tissue distribution showed a similar data as PET images. Conclusion: Precursors of DOTA-LY9969 and DOTA-LY9970 were successfully synthesized and characterized. DOTA-LY9970 displayed high CXCR4 specific cell binding in vitro. Micro PET/CT imaging and biodistribution in vivo data showed 68Ga-DOTA-LY9970 could be used to visualize CXCR4 overpression tumors. Further experiments on the efficacy monitoring of LY2510924 and Radiotherapy are ongoing. Research Support: National Natural Science Foundation (Fund No: 81701740)