Substance P – A Possible PET Diagnostic Agent

Substance P (SP) has been known to trigger biological responses by linking to NK 1 receptors. The presence of functional NK1 receptors has already been documented in malignant brain tumors of glial origin, medullary thyroid cancer, non-small cell lung cancer and pancreatic carcinoma 99mTc and 188Re radiolabeled SP was tested for cell surface binding after incubation with NK1 receptor expressing U-87 MG cells, and negative control cell line L-929 and preliminary whole-body biodistribution studies were carried out with 99mTc labeled SP using a hybrid SPECT/CT YAP(S)PET small-animal tomography scanner. Our results using 99mTc and 188Re radiolabeled SP, demonstrated the affinity of these radioconjugates for NK1 receptor expressing cells, showing pronounced cell surface binding after incubation with U-87 MG cells, compared to the negative control cell line L-929. Further preliminary whole-body biodistribution studies with 99mTc labeled SP using a hybrid SPECT/CT YAP(S)PET small animal tomography scanner, confirmed previous findings about the localization of specific SP binding sites. Following the success of 68Ga-DOTATOC, and knowing that receptor targeted imaging may provide better diagnostic outcomes in comparison with registering a high glucose uptake in the affected area using 18F-FDG, we believe that it would be interesting to consider new radiochemistry approaches of radiolabeling SP with 68Ga. 68Ga (or other PET radionuclides) may provide better screening and possible detection of malignant brain tumors of glial origin, but also other diseases known to express NK1 receptors