A. Stevens, P. Morris, R. Iles
Jul 1, 1984
Citations
4
Influential Citations
173
Citations
Quality indicators
Journal
British Journal of Cancer
Abstract
The nuclear magnetic resonance (NMR) method makes it possible to analyse the chemical constituents of living animals or humans repeatedly and non-invasively. It has mainly been applied to the study of endogenous phosphorylated or carbon containing compounds (Gadian, 1982; Iles et al., 1982) but could equally be used to trace the metabolic fate of exogenously administered substances such as drugs. At present it is necessary to kill many animals in order to determine the fate of a drug at its target site (or at the sites where it is detoxified) and it is almost impossible to obtain such information in humans. By using new in vivo NMR techniques it should be possible to follow the metabolic fate of a drug either in an animal or patient. The most favourable atomic nucleus for studies of this kind is 19F: there is no background from endogenous compounds, 19F gives intense NMR signals with a wide chemical shift range, and many fluorinated drugs are in clinical use. In this paper we describe the use of '9F NMR to monitor the metabolism of 5-fluorouracil in tumours and in the liver. The fluorinated pyrimidines, 5-fluorouracil (5FU), 5-fluorouridine (FUrd) and 5-fluoro-2-deoxyuridine (FdU) are widely used in the treatment of disseminated human cancers, especially of the gastrointestinal tract, breast and ovary (Martindale, 1982). The metabolism of these drugs has been extensively studied and it is clear that with a few important exceptions they participate in the same pathways as uracil and its metabolites (Figure 1). Treatment with fluorinated pyrimidines produces two major effects in cells: (i) inhibition of DNA synthesis by inhibition of dTMP synthetase (EC 2.1.1.41) by fluorodeoxyuridine monophosphate (FdUMP) (Heidelberger, 1974); and (ii) alteration in the processing and function of some types of RNA because of extensive incorporation of 5FU in place of uracil (Heidelberger, 1974; Carrico & Glazer, 1979). Which of these effects accounts for the major antitumour property of these drugs is a matter of contention. Recent studies have been directed at developing combined chemotherapeutic regimens which incorporate the fluorinated pyrimidines with drugs such as methotrexate, thymidine or PALA (Goulian et al., 1980; Bedikian et al., 1981; Au et al., 1982) or. developing new analogues (Sakurai, 1981). In both cases the aim is to alter the rate and fate of metabolism of the drug and hence increase its therapeutic efficacy. Major problems in this area are the provision of precise methods with the ability to quantify all aspects of metabolism of the drug: its metabolites are unstable and difficult to detect. Pogolotti et al. (1981) and Sommadossi et al. (1982) have overcome many of these problems, but conventional analysis of uptake into solid tumour models has a number of difficulties, not least in satisfactory removal of the tissue. Studies on 5FU metabolism in cell culture cannot give information about the uptake or fate of the drug in an intact tumour (Pogolotti et al., 1981), while plasma pharmacodynamics give at best only a very indirect assessment of a drug's efficacy (Cano et al., 1981). We were able to follow the metabolism of i.v. injected 5FU in situ both in implanted tumours and livers of C57 mice by `9F-NMR using surface coils. Livers were examined in either female C57 or C57BI/Cbi mice. Lewis lung carcinomas were implanted in female C57BI/Cbi mice by s.c. injection of 2.5 x 104 viable tumour cells (obtained by trypsin/DNase digestion) over the sacral region and studied at a mean diameter of 6-7 mm. Animals were anaesthetised using sodium pentobarbitone 60mgkg-1 by i.p. injection. A 25mgml-1 solution of 5FU (Roche Products) was then injected into the jugular vein. For NMR spectroscopy mice were secured vertically within a purpose built probe. By means of an abdominal incision a flat one turn 7mm diameter radiofrequency (R.f.) coil was placed on the surface of the liver. To prevent evaporation and to electrically insulate the coil, the liver surface was covered with a thin plastic film. In the case of tumour-bearing mice the coil was laid over the