INFLUENCE OF BOTH SALVAGE AND DNA-DAMAGE RESPONSE PATHWAYS ON RESISTANCE TO CHEMOTHERAPEUTIC ANTIMETABOLITES

The resistance of 3 human embryo fibroblast cell lines to the antimeta bolites methotrexate (MTX), N-phosphonacetyl-L-aspartate (PALA) and 5- fluorouracil (5-FU) has been studied. The cell lines were of common ge netic origin, all originating from the normal KMS parental cell line, which was irradiated with Co-60 to produce the immortalised derivative KMST which, in turn, was transfected with an activated N-ras oncogene to produce the tumourigenic KN-NM cell line. Previous work from this group, using dialysed versus nondialysed serum, has provided evidence for the involvement of salvage pathways of purine and pyrimidine biosy nthesis in the increased resistance to antimetabolites of those cell l ines (KMST and KN-NM) tending towards increased tumourigenicity. The p resent study has extended this work by using the nucleoside and nucleo base transport inhibitor dipyridamole, to further assess the contribut ion of the salvage pathways to the increased cellular resistance to th e three antimetabolites. The salvage pathways were found to contribute to the resistance of cell lines to PALA and MTX, but had no effect on the resistance to 5-FU. The addition of excess uridine in the case of PALA, and hypoxanthine plus thymidine in the case of MRX, could be us ed to ''rescue'' cells from the effects of dipyridamole-induced salvag e pathway inhibition. The data will be discussed in relation to 1. the effect of limited substrate availability, 2. the induction of DNA dam age and DNA damage-response pathways, and 3. DNA-damage protection by the salvage pathways of purine and pyrimidine biosynthesis.