Imaging the natural beta-cell mass can not be achieved with drug imaging since no pancreatic beta-cell specific drug exists. However, one pancreatic beta-cell surface specific antibody IC2 exists. see www.immunosigns.com, and has promising features and unique beta-cell specificity in vitro and in vivo. There has already been two proof-of-concepts for the use of IC2 in noninvasive medical imaging by SPECT and BLI, and a third modality is on its way?
Despite immunohistochemistry studies (e.g. from Jean-Claude Reubi) suggesting that somatostatin receptor (SSTR) expression is present in only around 50% of insulinomas, our experience at the Peter MacCallum Cancer Centre in evaluating advanced malignant insulinomas using Gallium-68 DOTA-octreotate PET/CT is that almost all have high SSTR. We have treated a number of patients with Lu-177 DOTA-octreotate peptide receptor radionuclide therapy over the past decade with excellent results. Although I always thought that FDG PET/CT wouldn't be much use with high insulin levels driving FDG into skeletal and cardiac muscle, as occurs when FDG is given to non-fasting patients, we have had a few recent patients with G2-G3 tumours that we did it in for interest and the scan were surprisingly good. I presume that the muscles are either replete with glucose stores or downregulate GLUT-4 transporters. Researchers in the PET Department at your own hospital (Binderup et al) have done some lovely work characterising the prognostic significance of high FDG uptake in neuroendocrine tumours and I'd encourage you to talk with them. F-18 FDOPA has been used by some groups and appears particularly useful in nesidioblastosis in children but we don't have experience of this tracer since it is an awful synthesis and GaTate serves us so well.
For pancreatic adenocarcinomas, FDG PET works very well as a staging test unless the patients have uncontrolled diabetes with hyperglycaemia. We have a protocol to administered short-acting insulin to bring the BGL back into the normal range and then wait until the levels start to rise again, indicating insulin effects have worn off. With this protocol we get very good scans with little skeletal muscle activity and good uptake in almost all pancreatic adenocarcinomas.
Yes I knew about the octreotate based imaging but is the insulinom specificity good enough?
The reason why I ask is due to the fact that I am the disvover a monoclonal autoangtibody IC2 highly specific to the pancreatic beta-cell surface, and exolicit to the beta-cells. Several review have mentioned the potential of IC2 to perform noninnvasive imaging of beta-ceæll function and mass, but in stead of finding a needle in a stack, we would like to investigate IC2 ability to image insulinoma first. The binding of IC2 to beta-cells is somehow couple to insulin secretion, without being a an anti-insulin antibody.
Read more on www.immunosigns.com or www.immunosigns.com/laboratory.
Carl-Henrik Brogren
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