Reporter gene imaging: Effects of ganciclovir treatment on nucleoside uptake, hypoxia and perfusion in a murine gene therapy tumour model that expresses herpes simplex type-1 thymidine kinase

Perfusion, hypoxia and nucleoside uptake during ganciclovir therapy were de termined in a murine HSV-1 TK-expressing tumour model (KBALB-STK). HSV-1 TK mRNA transcription in this cell Line was confirmed by RT-PCR. BALB/c mice bearing KBALB-STK tumours accumulated (E)-5-(2-[I-125]iodovinyl)-2'-fluoro- 2'-deoxyuridine ([I-125]IVFRU) (2.54% injected dose.g(-1)) and could be rea dily detected with planar imaging following administration of [I-131]IVFRU. However, a single dose of ganciclovir (100 mg.kg(-1) intraperitoneally) de creased tumour uptake of [I-125]IVFRU to 0.33% injected dose.g(-1). Subsequ ent single daily doses of ganciclovir over 3 consecutive days had a negligi ble effect on [I-125]IVFRU uptake, which remained low. Tumour perfusion dur ing 3 days of ganciclovir treatment was monitored with intravenous [Tc-99(m )]HMPAO. Tumour perfusion increased from day 0 (no ganciclovir treatment) w ith 1.83% injected dose.g(-1) tumour, to a maximum at day 2 (3.77% injected dose.g(-1)). In the same animals, accumulation of [H-3]misonidazole decrea sed from 0.70% injected dose.g(-1) at day 0 to a minimum at day 3 (0.24% in jected dose.g(-1)), indicating that tumour tissue had become less hypoxic o ver the ganciclovir regimen. The uptake of [I-125]IVFRU into the acid insol uble fraction of KBALB-STK cells in vitro in the presence of ganciclovir (2 .0 mu M) was completely inhibited, leading to a 57% decrease in total cellu lar accumulation of radioactivity. However, cytosolic entrapment of [I-125] IVFRU was not affected by the presence of ganciclovir. These results indica te that the mechanisms leading to IVFRU exclusion during ganciclovir treatm ent of HSV-1 TK-expressing tumours can be attributed, at least partially, t o inhibition of [I-125]IVFRU-nucleotide incorporation into DNA. (C) 2000 Li ppincott Williams & Wilkins).