The ability to achieve tumor selective expression of therapeutic genes is an area that needs improvement for cancer gene therapy to be successful. One approach to address this is through the use of promoters that can be controlled by external means, such as hyperthermia. In this regard, we constructed a replication-deficient adenovirus that consists of a mutated herpes simplex virus 1 thymidine kinase (mTK) fused to enhanced green fluorescent protein (EGFP) under the control of the full-length human heat shock (HS) 70b promoter. The virus (AdHSmTK-EGFP) was evaluated both in vitro and in vivo in oral squamous cell carcinoma SCC-9 cells for expression of both mTK and EGFP. The in vitro expression of mTK-EGFP was validated using both 3H-penciclovir and fluorescence-activated cell sorting assays. These studies show that specific expression could be achieved by heating the cells at 41°C for 1 h, whereas little expression was observed using high doses of virus without hyperthermia. The vector was also evaluated in vivo by direct intratumoral injection into mice bearing SCC-9 xenografts. These studies demonstrated tumor expression of mTKEGFP after ultrasound heating of the tumors by radioactive biodistribution assays, histology and microPET imaging. These in vivo results, which demonstrate HS-inducible transgene expression using PET imaging, provide a means for noninvasive monitoring of heat-induced gene therapy in local tumors, such as oral squamous cell carcinomas.
Representative coronal (a) and transaxial (b) microPET images of mice bearing two SCC-9 xenografts in the axillary thorax 4 h after administration of 18F-FHBG. The mice were injected intratumorally with 1x109 pfu of AdHSmTK-EGFP 48 h before the imaging session, and the tumors on the left were heated at 41°C for 1 h 1 day before imaging. Standard uptake values (SUVs) were determined from the microPET data for the heated and nonheated tumors at 1, 2, and 4 h after injection of 18F-FHBG (c). The SUV data is presented as the mean±s.e.m. for each tumor (n = 3).
Parry JJ, Sharma V, Andrews R, Moros EG, Piwnica-Worms D, Rogers BE. PET imaging of heat-inducible suicide gene expression in mice bearing head and neck squamous cell carcinoma xenografts. Cancer Gene Ther 2009; 16(2): 161-70.