Comparing the use of radiolabeled SSTR agonists and an SSTR antagonist in breast cancer: does the model choice influence the outcome?

* Correspondence: [email protected] Department of Radiology & Nuclear Medicine, Erasmus MC, Rotterdam, South Holland, Netherlands To the Editor With interest we read the recent publication of Dude et al. (2017) on the evaluation of somatostatin receptor (SSTR) agonists and an antagonist for SSTRmediated imaging of breast cancer using positron emission tomography. In this study the authors compared 2 SSTR agonists (DOTA-Tyr-octreotide and DOTATyr-octreotate) and the SSTR antagonist (NODAGA-JR11) in in vitro binding and saturation studies and in in vivo imaging and biodistribution studies. To our surprise their results demonstrated both agonists to have a more favorable receptor binding affinity and a better tumor uptake in vivo, whereas the saturation assay resulted in more binding sites for Ga-DOTA-Tyr-octreotide on the used breast cancer cell line (ZR75–1) than Ga-NODAGA-JR11 and Ga-DOTA-Tyroctreotate. The reported results are in contrast with previously published studies comparing radiolabeled DOTA-Tyr-octreotate and DOTA-JR11 in various tumor models (Dalm et al., 2016; Nicolas et al., 2017; Reubi et al., 2017; Wild et al., 2014), including our recent publication on the use of SSTR agonists and antagonists for targeting of breast cancer (Dalm et al., 2017). The main explanation given by the authors for the contradicting results is the use of an endogenously SSTR expressing breast cancer cell line, ZR75–1, in contrast to transfected cell lines, cell lines of other cancer types and non-cancerous cell lines used in earlier studies evaluating SSTR-targeting radiotracers. Concerning the above mentioned explanation of the authors, we have the following remarks: