Escherichia coli mediated biosynthesis and in vitro anti-HIV activity of lipophilic 6-halo-2',3'-dideoxypurine nucleosides

Abstract

A series of 6-substituted 2',3'-dideoxypurine ribofuranosides (ddP) was enzymatically synthesized with live E. coli in an effort to enhance the lipophilicity of this class of anti-human immunodeficiency virus (HIV) compounds and thereby facilitate drug delivery into the central nervous system. All 6-halo-substituted ddPs were substantially more lipophilic, as defined by their octanol-water partition coefficient (P), than their nonhalogenated congeners 2',3'-dideoxyinosine (ddI) or 2',3'-dideoxyguanosine (ddG). For this class of compounds, log P's ranged from +0.5 to -1.2 in the following order: 6-iodo, 2-amino-6-iodo greater than 6-bromo, 2-amino-6-bromo greater than 6-chloro, 2-amino-6-chloro greater than 6-fluoro, 2-amino-6-fluoro much greater than ddG greater than ddI. These compounds were evaluated in vitro for ability to suppress the infectivity, replication, and cytopathic effect of HIV. 2-Amino-6-fluoro-, 2-amino-6-chloro-, and 6-fluoro-ddP exhibited a potent activity against HIV comparable to that of ddI or ddG and completely blocked the infectivity of HIV without affecting the growth of target cells. The comparative order of in vitro anti-HIV activity was 2-amino-6-fluoro, 2-amino-6-chloro, 6-fluoro greater than 2-amino-6-bromo greater than 2-amino-6-iodo, 6-chloro greater than 6-bromo greater than 6-iodo. These compounds also exhibited potent in vitro activity against HIV-2 and 3'-azido-3'-deoxythymidine-resistant HIV-1 variants. All 2-amino-6-halo-ddPs and 6-halo-ddPs were substrates for adenosine deaminase (ADA) and were converted to ddG or ddI, respectively. In the presence of the potent ADA inhibitor 2'-deoxycoformycin, 6-halo-substituted ddPs failed to exert an in vitro antiretroviral effect. These dideoxypurine nucleoside analogues represent a new class of lipophilic prodrugs of ddG and ddI that possess the potential for more effective therapy of HIV-induced neurologic disorders.

Central nervous system targeting of 2',3'-dideoxyinosine via adenosine deaminase-activated 6-halo-dideoxypurine prodrugs

“…(mm) tIn- (mm) k., (min-') khyd (mm-) (g-min/ml) (>g. min/ml) (ml/mi/kg) system initially developed by Bodor et al (5), but the degrees of enhancement of delivery of AZT to CNS that have been reported are highly variable from laboratory to laboratory (7,10,20,21). Recent findings that a series of lipophilic 6-halo-ddPs exhibit activity against HIV in vitro (11,18,35,36) and that their activities were completely abrogated in the presence of an ADA inhibitor (23,35,36) coupled with preliminary indications of enhanced CNS delivery via this approach in rats (2), suggest a promising new enzyme-based strategy for improving the delivery of dideoxynucleosides to the CNS. The activity of ADA in human brain tissue is relatively high (37), further supporting the potential of this approach for the treatment of patients with AIDS dementia complex.…”

“…ddl was provided by the National Institute of Allergy and Infectious Diseases and was used as received. The preparation of the four 6-halo-ddPs tested in the present study-6-fluoro-ddP (6-F-ddP), 6-Cl-ddP, 6-bromo-ddP (6-Br-ddP), and 6-iodo-ddP (6-I-ddP)-has been described previously (23). All other compounds were commercially available and were used as received.…”

Effects of 6-Chloro-2',3'-Dideoxyguanosine (6-Cl-ddG) in Surface Lymph Nodes of Rhesus Monkeys (Macaca mulatta) Chronically Infected with Simian Immunodeficiency Virus (SIVmac239).

“…The 6-chloro-2', 3'-dideoxyguanosine (6-Cl-ddG) is a highly lipophilic antiretroviral drug [9,15,22], whose antiretroviral activity is as high as that of ddG or that of AZT in vitro [22]. Manouilov et al demonstrated that lipophilicity is a key element in the targeting of antiretroviral drug to lymph nodes [14].…”

Pharmacokinetics of dideoxypurine nucleoside analogs in plasma and cerebrospinal fluid of rhesus monkeys

“…We previously studied the penetration of a series of dideoxypyrimidine nucleoside analogs into cerebrospinal fluid (CSF) and demonstrated that it ranged from over 20% for zidovudine to less than 5% for zalcitabine and that the degree of penetration into CSF was determined by the nucleobase rather than the alterations to the ribose sugar (5). In addition, in subsequent clinical trials the degree of drug penetration into CSF appeared to correlate with efficacy in treating AIDS dementia (19,20).A number of dideoxypurine (ddP) nucleoside analogs have also demonstrated antiretroviral activity in in vitro screening assays (14,15,17,21), and ddI was recently approved for clinical use. 2Ј,3Ј-Dideoxyadenosine (ddA) has a degree of activity similar to that of ddI, but it is almost instantaneously deaminated to ddI in vivo (9).…”

“…A series of 6-halogenated 2Ј,3Ј-dideoxyguanosine (ddG) and ddI analogs which act as prodrugs of ddG and ddI are currently in the preclinical phase of drug development. The 6-halo-ddP analogs are more lipophilic than the parent drugs, as measured by n-octanol partitioning (22), and were synthesized in an attempt to improve the penetration of ddG and ddI into the CNS (17,21,22). Studies in rodents have demonstrated enhanced penetration of the 6-halo-ddP prodrugs into the CNS as well as enhanced penetration of ddG and ddI, presumably as a result of dehalogenation of the 6-halo-ddPs by adenosine deaminase in the CNS (ADA) (16,22).…”