Growing evidences have shown that the IL-6/IL-6R signal pathway promotes the tumor growth, angiogenesis, invasion and migration in various cancers, especially for epithelial ovarian cancer. Hence, including anti-IL-6 antibody (Siltuximab) and anti-IL-6R antibody (Tocilizumab), more and more therapeutic drugs targeting IL-6/IL-6R pathway were developed to block their activity. The molecular imaging of IL-6R is a significant factor for predicting tumor response to IL-6/IL-6R targeted drugs. However, few probes targeting IL-6R were designed and used for the specific detection. The purpose of this study was to develop and evaluate a novel radiotracer, (99m)Tc-HYNIC-Aca-LSLITRL, for SPECT imaging of interleukin-6 receptor. The expression of IL-6R was determined by western blot, immunofluorescence and immunohistochemistry. HYNIC-Aca-LSLITRL and HYNIC-Aca-TLQASIL were synthesized, and then were labeled with 99mTc. The stability and the cell-binding assay were performed. Ovarian tumor xenografts were established and subjected to SPECT imaging after injection of these two radiopharmaceuticals with or without excess primary peptides. The biodistribution of these two radiotracers was performed in nude mice bearing C13K tumors. (99m)Tc-HYNIC-Aca-LSLITRL and (99m)Tc-HYNIC-Aca-TLQASIL were obtained in >95 % labeling yield with favorably stability. In vitro studies demonstrated that the interleukin-6 receptor was overexpressed in ovarian cancer C13K cells. The SPECT imaging of interleukin-6 receptor and biodistribution studies showed that (99m)Tc-HYNIC-Aca-LSLITRL had higher tumor uptake and significantly lower kidney accumulation compared to (99m)Tc-HYNIC-Aca-TLQASIL. (99m)Tc-HYNIC-Aca-LSLITRL could be a promising agent for SPECT imaging of interleukin-6 receptor of ovarian cancer especially for those anti-IL-6R drugs under clinical trials, such as tocilizumab.
Keywords: 99mTc-HYNIC-Aca-LSLITRL; 99mTc-HYNIC-Aca-TLQASIL; Interleukin-6 receptor; Molecular imaging; Ovarian cancer.