Purine nucleoside phosphorylase deficiency leads to a dGTP-mediated T- lymphopenia, suggesting that an analogue of deoxyguanosine would be selectively effective in T-cell disease. 9-β-D-Arabinofuranosylguanine (ara- G) is relatively resistant to hydrolysis by purine nucleoside phosphorylase and selectively toxic to T cells, but its low solubility has prevented its use in the clinic. 2-Amino-6-methoxy-arabinofuranosylpurine (GW506U) serves as the water-soluble prodrug for ara-G. A Phase I trial in patients with refractory hematological malignancies demonstrated that the clinical responses to this agent were directly related to the peak levels of ara-G 5'- triphosphate (ara-GTP) in target cells. The aim of the present study was to develop and test strategies to increase intracellular accumulation of ara- GTP in primary human leukemia cells of myeloid and B-lymphoid origin. Three strategies were tested. First, incubations with 100 μM ara-G for 4 h produced a linear median accumulation rate of 19 μM/h (range, 2-45 μM/h; n = 15) in lymphoid leukemia cells and 16 μM/h (range, 0.5-41 μM/h; n = 11) in myeloid leukemia cells. Saturation of ara-GTP accumulation was achieved only after 6-8 h exposure in both lymphoid and myeloid leukemia cells, suggesting a rationale for prolonged infusion. Second, a dose-dependent increase in ara-GTP accumulation was observed with incubations of 10-300 μM ara-G for 3 h. Hence, dosing regimens that achieve high plasma levels of ara- G during therapy may increase cellular levels of ara-GTP. Finally, a biochemical modulation approach using in vitro incubation of leukemia cells with 10 μM 9-β-D-arabinofuranosyl-2-fluoroadenine for 3 h, followed by either 50 or 100 μM ara-G for 4 h, resulted in a statistically significant median 1.3-fold (range, 1.1-9.0-fold; P = 0.034) and 1.8-fold (range, 0.9- 10.6 fold; P = 0.018) increase in ara-GTP compared to cells incubated with ara-G alone. Extension of these studies to ex vivo incubations confirmed our in vitro findings. These strategies will be used in the design of clinical protocols to increase ara-GTP accumulation in leukemia cells during therapy.
|Original language||English (US)|
|Number of pages||7|
|Journal||Clinical Cancer Research|
|State||Published - Nov 1997|
ASJC Scopus subject areas
- Cancer Research