UNCOUPLING OF 2-FLUORO-2-DEOXYGLUCOSE TRANSPORT AND PHOSPHORYLATION IN RAT HEPATOMA DURING GENE-THERAPY WITH HSV THYMIDINE KINASE

This animal study investigates the application of positron emission to mography (PET) with tracers of tumour metabolism for monitoring suicid e gene therapy with herpes simplex virus thymidine kinase (HSVtk). Aft er transplantation of HSVtk-expressing Morris hepatoma cells into ACI rats, dynamic PET measurements of F-18-labeled 2-fluoro-2- deoxyglucos e (FDG) uptake were performed in animals 2 days (n = 7) and 4 days (n = 5) after the onset of therapy with 100 mg ganciclovir (GCV)/kg body weight as well as; after administration of sodium chloride (n = 8). Th e arterial FDG plasma concentration was measured dynamically in an ext racorporeal loop and the rate constants for FDG transport (K-1, k(2)) and FDG phosphorylation (k(3)) were calculated using a three-compartme nt model modified for heterogeneous tissues. Also, quantification usin g the metabolic rate of FDG turnover and the standardized uptake value (SUV) was done. Furthermore, the thymidine incorporation into the tum our DNA was determined after i.v. administration of H-3-thymidine. An uncoupling of FDG transport and phosphorylation was found with enhance d K-1 and k(2) values and a normal k(3) after 2 days of GCV treatment. The increase in FDG transport normalized after 4 days whereas the pho sphorylation rate k(3) increased. Quantification using the metabolic r ate or the SUV showed congruent but less sensitive results compared wi th the modeling approach. The thymidine incorporation into the DNA of the tumours declined to 10.5% of the controls after 4 days of GCV trea tment. The data indicate that PET with (18)FDG and C-11-thymidine may be applied for monitoring of gene therapy with the HSVtk/GCV suicide s ystem. Increased transport rates are evidence of stress reactions earl y after therapy. The measurement of thymidine incorporation into the t umour DNA can be used as an indicator of therapy efficacy.