In vivo imaging of long term stem cell trafficking/engraftment is enabled by a human somatostatin receptor type-2 (hSSTR2) mutant that has the desirable features of being muted in altering stem cell signaling and function

Objectives Following long term stem cell trafficking and engraftment is important for understanding their fate and therapeutic potential. Reporters (enzymes, transporters, receptors) can alter cellular milieu/function. We tested whether a hSSTR2 mutant is signaling deficient in stem cells and can serve to image these cells in vivo.

Methods HS5 human mesenchymal stem cells were stably transfected with hemagglutinin A (HA) tagged-hSSTR2, mutant receptor or vector. cGMP and cAMP production as well as growth inhibition in response to ligand were tested. Differentiation was tested. In vivo, 6 mice were injected subQ with HS5 cells transfected with HA-SSTR2, mutant or vector and HeyA8 ovarian cancer cells. 3 weeks later, imaging was performed with FDA approved 111In-octreotide. To assess trafficking and engraftment, transfected HS5 cells were instead given intracardiac 1 day after subQ HeyA8 injection.

Results Mutant receptor did not elicit cGMP production, inhibit forskolin-induced cAMP production or inhibit growth in response to ligand; whereas, wild-type receptor did. HS5 cells expressing either receptor differentiated into bone and fat-like cells. In vivo, after co-injection or HS5 systemic injection, HeyA8 tumors incorporating HS5 cells expressing mutant or wild-type receptor showed increased uptake. Ex vivo biodistribution analysis confirmed results (P<.05 mutant or wild-type vs vector).

Conclusions A hSSTR2 mutant, that has the desirable features of being muted in altering stem cell signaling and function, can serve as a reporter of long term stem cell trafficking/engraftment.