title: Pharmacological and biochemical strategies to increase the accumulation of arabinofuranosylguanine triphosphatein primary human leukemia cells.
abstract: 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-beta-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 microM ara-G for 4 h produced a linear median accumulation rate of 19 microM/h (range, 2-45 microM/h; n = 15) in lymphoid leukemia cells and 16 microM/h (range, 0.5-41 microM/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 microM 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 microM 9-beta-D-arabinofuranosyl-2-fluoroadenine for 3 h, followed by either 50 or 100 microM 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.
authors.affiliation: Departments of Clinical Investigation and Hematology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: C O
authors.initials: CO
authors.lastname: Rodriguez
authors.forename: J K
authors.initials: JK
authors.lastname: Legha
authors.forename: E
authors.initials: E
authors.lastname: Estey
authors.forename: M J
authors.initials: MJ
authors.lastname: Keating
authors.forename: V
authors.initials: V
authors.lastname: Gandhi
mesh_terms: D000970:Antineoplastic Agents / Q000097:blood / Q000493:pharmacokinetics; D001087:Arabinonucleosides / Q000097:blood / Q000493:pharmacokinetics; D001088:Arabinonucleotides / Q000097:blood* / Q000493:pharmacokinetics; D001711:Biotransformation; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D007938:Leukemia / Q000097:blood*; D015448:Leukemia, B-Cell / Q000097:blood; D007951:Leukemia, Myeloid / Q000097:blood
chemical_list: D000970:Antineoplastic Agents; D001087:Arabinonucleosides; D001088:Arabinonucleotides; C028771:9-arabinofuranosylguanine; C022206:9-beta-D-arabinofuranosylguanosine 5'-triphosphate; D006160:Guanosine Triphosphate