Everolimus Induces Rapid Plasma Glucose Normalization in Insulinoma Patients by Effects on Tumor As Well As Normal Tissues

Background. Mammalian target of rapamycin inhibitor everolimus administered to four insulinoma patients rapidly controlled hypoglycemia (Kulke et al., N Engl JMed 2009; 360: 195-197). We wanted to identify the kinetics of everolimus effects on controlling hypoglycemia and understand underlying mechanisms.Methods. Three consecutive patients with a metastasized symptomatic insulinoma were started on 100 mu g of octreotide subcutaneously three times daily. Because of persisting hypoglycemias, treatment with daily 10 mg of oral everolimus was initiated. Serial plasma glucose levels and serum insulin levels were measured. Computer tomography (CT) scans were performed beforeandafter 2and 5 months of treatment. [18F] fluoro-2-deoxy-d-glucose positron emissiontomography (F-18-FDG-PET) scans, to visualize glucose metabolism, were made before and after 2 weeks, 5 weeks, and 5 months of treatment. The F-18-FDG uptake quantified as the maximum standardized uptake value.Results. All patients achieved control of hypoglycemia on everolimus within 14 days. Insulin levels were 2.5- to 6.3-fold elevated before start of treatment and declined 14%-64% after 4 weeks of treatment. CT scans showed stable disease at 2 months in all patients, with progressive disease after 5 months in one. Before treatment, both the tumor lesions and the muscles and myocardium showed high F-18-FDG uptake. Everolimus reduced tumor and muscle F-18-FDG uptake after 2 weeks by 26% +/- 14% and 19% +/- 41%, and after 5 months by 31% +/- 13% and 27% +/- 41%.Conclusions. Everolimus normalizes plasma glucose levels in metastatic insulinoma within 14 days, coinciding with a lower glucose uptake in tumor and muscles and declining (pro)insulin levels. This effect on tumor as well as normal tissues explains the rapid controlling of hypoglycemia. The Oncologist 2011;16:783-787