Purpose: The sigma-2 (σ(2)) receptor is a potential biomarker of proliferative status of solid tumors. Specific synthetic probes using N-substituted-9-azabicyclo [3.3.1]nonan-3α-yl carbamate analogs have been designed and implemented for experimental cancer diagnosis and therapy.
Procedures: We employed the fluorescently labeled σ(2) receptor probe, SW120, to evaluate σ(2) receptor expression in human stem cells (SC), including: bone marrow stromal, neural progenitor, amniotic fluid, hematopoetic, and embryonic stem cells. We concurrently evaluated the intensity of SW120 and 5-ethynyl-2'-deoxyuridine (EdU) relative to passage number and multi-potency.
Results: We substantiated significantly higher σ(2) receptor density among proliferating SC relative to lineage-restricted cell types. Additionally, cellular internalization of the σ(2) receptor in SC was consistent with receptor-mediated endocytosis and confocal microscopy indicated SW120 specific co-localization with a fluorescent marker of lysosomes in all SC imaged.
Conclusion: These results suggest that σ(2) receptors may serve to monitor stem cell differentiation in future experimental studies.