Tumor uptake and elimination of 2 ',2 '-difluoro-2 '-deoxycytidine (gemcitabine) after deoxycytidine kinase gene transfer: Correlation with in vivo tumor response

Purpose: We hypothesized that tumor uptake and elimination of 2',2'-difluor o-2'-deoxycytidine/2',2'-difluoro-2'-deoxycytidine 5'-triphosphate (dFdCyd/ dFdCTP) would be altered after dCK gene transfer and that this change would result in an enhanced cytotoxic effect. To test this hypothesis, we examin ed dFdCyd/dFdCTP uptake and clearance in HT-29 human colon carcinoma xenogr afts in nude mice by high-performance liquid chromatography (HPLC) and fluo rine-19 magnetic resonance spectroscopy (F-19 MRS). Experimental Design: HT-29 tumors were grown from cells infected with eithe r the retroviral vector alone (LNPO-LacZ) or vector containing the dCK gene (LNPO-dCK). HPLC and F-19 MRS analyses were performed after a single 160 m g/kg i.p. Injection of dFdCyd. Tumor response was determined in animals rec eiving a similar dosing schedule of dFdCyd. Results: HPLC experiments revealed an increased tumor accumulation of dFdCT P in xenografts overexpressing dCK compared with wild-type controls (P less than or equal to 0.05). dFdCTP in the dCK-infected tumors was easily ident ified at 24 h postinjection. Conversely, no dFdCTP could be detected in the control xenografts 14 h postinjection. Subsequent F-19 MRS experiments con firmed an altered uptake, revealing a 2.5-fold greater accumulation of dFdC yd/dFdCTP in the dCK xenografts. Whereas a modest tumor growth delay was ob served in the wild-type tumors receiving dFdCyd, dCK xenografts demonstrate d a marked tumor growth delay following treatment (P less than or equal to 0.05). Conclusions: These data support the hypothesis that increased expression of dCK cDNA in HT-29 xenografts results in an enhanced dFdCTP accumulation an d prolonged elimination kinetics, and ultimately a potentiated in vivo tumo r response to dFdCyd. Related to these effects, changes in the overall tumo r metabolism of dFdCyd/dFdCTP was detectable by noninvasive F-19 MRS. These data are relevant to future preclinical and clinical studies evaluating dC K gene transfer and dFdCyd therapy.