FUNDAMENTAL STUDY ON THE MICROBIOLOGICAL ASSAY FOR THE DIFFERENTIAL QUANTITATION OF 5-FLUOROCYTOSINE (5-FC) AND 5-FLUOROURACIL (5-FU) AND ITS APPLICATION

Abstract

We have already reported the newly developed local chemotherapy of cancer, in which intratumoral conversion of 5-FC to 5-FU by extrinsic cytosine deaminase (CDase) implanted to the tumor is expected to induce antineoplastic activity at a local site with minimal systemic toxicities. Determination of the tissue concentration of both 5-FC and converted 5-FU is, therefore, very important for evaluating the antineoplastic effects of this local chemotherapy. In this report, we discussed the usefulness o the microbiological assay (Thin layer cup method) using 2 test organisms for the differential quantitation of the drugs in the same material and investigated the tissue concentrations of the drugs in the tumor and the serum.
In vitro studies; The standard curves for 5-FC and 5-FU were obtained by measurement of the zones of inhibition using standard solutions of the drugs. In the used bacteria and the fungi, Micrococcus luteus ATCC 10240 was found to be the most sensitive organism to 5-FU (MIC=0.025 μg/ml). On the other hand, Saccharomyces cerevisiae AKU 4100 was sensitive to 5-FC (MIC=0.4 μg/ml), but had the same sensitivity to 5-FU. The standard curve of M. luteus was affected only by the concentration of 5-FU under the various combinations with 5-FC and 5-FU. On the contrary, the standard curve of S. cerevisiae was affected by the concentration of the sum of both drugs. The concentration of 5-FC (C) in the sample mixed with 5-FC and 5-FU, therefore, could be determined by the difference between the value (A) obtained by S. cerevisiae and that (B) obtained by M. luteus (C=A-B), although the concentration of 5-FU was calculated as (B).
In vivo studies; based on these results, we have made the differential quantitation of the drugs in the practical experiments. 5-FC were administered intraperitoneally to the rats bearing subcutaneous tumors which were previously implanted with the CDase containing capsule at the tumor bed. The pattern of 5-FC concentration curves of the serum and the tumor tissue showed a close similarity. At 1 hour after the administration, 5-FC attained to maximum and were estimated to be 96μg/ml in the serum and 85 μg/g in the tumor. The converted 5-FU attained to maximum at 2 hours and were estimated to be 8μg/ml. 5-FU passed into the blood stream was only 2.5% of that in the tumor.