Abstract
The novel antifolate lometrexol (5,10-dideazatetrahydrofolate) inhibits de novo purine biosynthesis, and co-incubation with hypoxanthine abolishes its cytotoxicity. The prevention of hypoxanthine rescue from an antipurine antifolate by the nucleoside transport inhibitor dipyridamole was investigated for the first time in nine human and rodent cell lines from seven different tissues of origin. In A549, HeLa and CHO cells, dipyridamole prevented hypoxanthine rescue and so growth was inhibited by the combination of lometrexol, dipyridamole and hypoxanthine, but in HT29, HCT116, KK47, MDA231, CCRF CEM and L1210 cells dipyridamole had no effect and the combination did not inhibit growth. Dipyridamole inhibited hypoxanthine uptake in A549 but not in CCRF CEM cells. Dipyridamole prevented the hypoxanthine-induced repletion of dGTP pools, depleted by lometrexol, in A549 but not in CCRF CEM cells. Thus, the selective growth-inhibitory effect of the combination of lometrexol, dipyridamole and hypoxanthine is apparently due to the dipyridamole sensitivity (ds) or insensitivity (di) of hypoxanthine transport. Both the human and murine leukaemic cells are of the di phenotype. If this reflects the transport phenotype of normal bone marrow it would suggest that the combination of lometrexol, dipyridamole and hypoxanthine might be selectively toxic to certain tumour types and have reduced toxicity to the bone marrow.
Highlights
Growth inhibition curves are shown for A549 and CCRF CEM
The curves obtained for lometrexol + 10,M dipyridamole were almost identical to those obtained for lometrexol alone, indicating that dipyridamole does not affect lometrexol cytotoxicity per se
In A549 (Figure IA), CHO and HeLa cells dipyridamole completely blocked the rescue by hypoxanthine and the curves were the same as for lometrexol ± dipyridamole
Summary
A549 (human lung carcinoma), CCRF CEM (human lymphoblastic leukaemia), CHO Ki (Chinese hamster ovary), HeLa (human cervical adenocarcinoma), HCT116 and HT29, (human colonic carcinoma), KK47 (human transitional cell bladder carcinoma, a gift from Dr S Naito, Kyushu University, Japan), L1210 (mouse lymphocytic leukaemia) and MDA 231 (human breast carcinoma) were all adapted for growth in RPMI1640 medium (Life Technologies, Paisley, UK) supplemented with 10% dialysed fetal calf serum (Globepharm, Esher, UK). Growing suspension cultures L1210 and CCRF CEM cells were seeded at a final density of 104 cells ml-', 0.5 ml per well into 24-well plates (Nunc, Life Technologies) in medium containing hypoxanthine, dipyridamole and lometrexol as indicated in the Results section. All cell counts were made on a model ZI Coulter Counter (Coulter Electronics, UK)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
