Noninvasive Detection of Human-Induced Pluripotent Stem Cell (hiPSC)-Derived Teratoma with an Integrin-Targeting Agent 99mTc-3PRGD2

Purpose

Since their discovery in 2006, induced pluripotent stem cells (iPSCs) have gained increasing interest for tissue regeneration and transplantation therapies. However, teratoma formation after iPSC transplantation is one of the most serious drawbacks that may limit their further clinical application. We investigated here whether human iPSC-derived teratomas could be detected by an integrin-targeting agent ^99mTc-PEG₄-EPEG₄-c(RGDfK)]₂ (^99mTc-3PRGD2).

Methods

Human-induced pluripotent stem cells (hiPSCs) were generated and characterized. In vitro integrin α_vβ₃ expression levels of hiPSC- and hiPSC-derived teratoma cells were determined by flow cytometry. ^99mTc-3PRGD2 was prepared, and planar gamma imaging and biodistribution studies were carried out in teratoma-bearing severe combined immunodeficient (SCID) mice. Positron emission tomography (PET) imaging of teratomas with 2-deoxy-2-¹⁸F]fluoro-d-glucose (¹⁸F-FDG) was also performed for comparison. Integrin α_vβ₃ expression in teratoma tissues was determined by immunofluorescence staining.

Results

^99mTc-3PRGD2 showed high (2.82?±?0.21 and 2.69?±?0.73%ID/g at 0.5 and 1 h pi, respectively) and specific (teratoma uptake decreased from 2.69?±?0.73 to 0.53?±?0.26%ID/g after blocking with cold 3PRGD2) uptake in teratoma tissues, and planar gamma imaging demonstrated the feasibility of noninvasively detecting the teratoma formation with ^99mTc-3PRGD2. ¹⁸F-FDG showed low teratoma uptake and thus failed to detect the teratomas. Ex vivo immunofluorescence staining validated the integrin α_vβ₃ expression in the vasculature during teratoma formation.

Conclusion

Gamma imaging with ^99mTc-3PRGD2 is a promising approach for the noninvasive monitoring of tumorigenicity after hiPSCs transplantation.