Abstract
1721
Objectives Induction of herpes simplex virus-1 thymidine kinase (HSV-TK) expression using adenoviral vectors (Ad) is monitored with specific PET probes during targeted cancer gene therapy. Manny commonly used gene delivery vectors lack tissue specificity and can be detrimental to non-target tissues. Recently, a modified mammoglobin promoter- (MPE2-) controlled Ad was developed to induce HSV-TK expression specifically in breast cancer. Herein, we have analyzed [18F]FLT and [18F]FHBG uptake in a mouse breast cancer model after injection with the mammary-specific AdMPE2-TK or the non-specific AdCMV-TK.
Methods Cell uptake studies were performed using murine MTHJ cells(mammary tumor cell line developed in transgenic mice carrying the oncogenic polyoma middle T antigen gene). Cells were incubated with AdMPE2-TK or AdCMV-TK. Dynamic small animal PET studies were done in FVB mice bearing two 4-6 weeks old MTHJ tumors. One tumor was injected with AdMPE2-TK or AdCMV-TK prior to the PET studies with [18F]FLT and [18F]FHBG.
Results [18F]FLT showed uptake (300 %ID/mg protein at 2 h) in uninfected MTHJ cells, [18F]FHBG did not. [18F]FLT uptake using AdMPE2-TK remained unaffected, whereas uptake increased with AdCMV-TK (800 %ID/mg protein at 2 h with 50 pfu/cell). In contrast, [18F]FHBG showed uptake in the presence of both promoters (300-400 %ID/mg protein at 2 h). To produce similar effects, higher concentrations of the mammary-specific promoter were necessary (250 pfu/cell vs. 50 pfu/cell). In vivo uptake of [18F]FLT and [18F]FHBG in the tumor was enhanced by 12% and 83%, respectively, in the presence of AdCMV-TK, while this was less visible with AdMPE2-TK. Biodistribution revealed increased [18F]FHBG tumor uptake of 20% in the presence of AdMPE2-TK and 83% using AdCMV-TK.
Conclusions Ad vectors bearing both promoters AdMPE2-TK and AdCMV-TK induce functional expression of HSV-TK in murine breast cancer in vitro and in vivo. Effects of the mammary-specific promoter were less pronounced compared to the non-specific promoter