Activities of Alkoxyalkyl Esters of Cidofovir (CDV), Cyclic CDV, and ( S )-9-(3-Hydroxy-2-Phosphonylmethoxypropyl)Adenine against Orthopoxviruses in Cell Monolayers and in Organotypic Cultures

Abstract

The potencies of several alkoxyalkyl esters of acyclic nucleoside phosphonates against vaccinia virus and cowpox virus were evaluated in cell monolayers and three-dimensional epithelial raft cultures. Prodrugs were at least 20-fold more active than their parent compounds. Octadecycloxyethyl-(S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine emerged as the most potent derivative.Smallpox has been declared eradicated since 1980 (5). However, due to the potential threat of variola virus as a weapon for bioterrorism (4) and the increasing number of infections with monkeypox virus (11), it is essential that adequate antiviral drugs be developed. Cidofovir (CDV) has already proven to be active against orthopoxviruses (9,10,14,16,18). However, this drug needs to be administered intravenously and is potentially nephrotoxic. Recently, it was shown that alkoxyalkyl and alkyl esters of CDV and cyclic cidofovir (cCDV) were more active against vaccinia virus (VV) and cowpox virus (CPV) in human foreskin fibroblasts than their parent compounds due in part to an increased penetration through the cell membrane (13,15). In vivo studies indicate that the prodrugs are highly orally bioavailable and are as effective as parenterally administered CDV for the treatment of VV-or CPV-infected mice (6,7,17).The activities of various alkoxyalkyl esters of the acyclic nucleoside phosphonate (ANP) analogues CDV [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine; HPMPC; Vistide], e Selectivity index (ratio of CC 50 to EC 50 ).

Activities of Several Classes of Acyclic Nucleoside Phosphonates against Camelpox Virus Replication in Different Cell Culture Models

“…However, 3-D cultures of human epithelial cells can be considered more predictive of the in vivo situation, and in this model, there were no cytotoxic alterations of the differentiated PHKs. The EC 50 s of compounds in the first class of ANPs against CMLV were similar to those observed in the HEL and PHK cell lines against two other, related orthopoxviruses, vaccinia virus (strains Lister, Lederle, and Copenhagen) and cowpox virus (strain Brighton) (29,40). Similarly, the selective and potent activity of HPMPO-DAPy against CMLV is consistent with previous reports on vaccinia virus, cowpox virus, and orf virus in both human and ovine cell monolayers (12,16).…”

“…Organotypic epithelial raft cultures are tissue culture systems that allow full differentiation of keratinocyte monolayers via culturing of the cells on collagen gels at the air-liquid interface (1). Poxviruses are epitheliotropic, and both vaccinia and cowpox viruses have already been shown to be able to infect raft cultures of human keratinocytes (29). Surprisingly, we were able to easily infect human keratinocytes with CMLV, even though this virus is responsible for a disease restricted to camels.…”

Cidofovir and (S)-9-[3-Hydroxy-(2-Phosphonomethoxy)Propyl]Adenine Are Highly Effective Inhibitors of Vaccinia Virus DNA Polymerase When Incorporated into the Template Strand

“…(S)-HPMPA and CDV differ only in the structure of the base moiety, so we hypothesized that the two compounds would have a similar mechanism of inhibition. (S)-HPMPA has been shown to be more toxic in mice than CDV (8), but subsequent work has yielded conflicting results on the relative cytotoxicity and therefore selectivity indices between the two drugs (3,5,19,22,36). The latter results are most likely due to differences in the sensitivity of the various cells lines used to (S)-HPMPA and CDV.…”

“…The latter results are most likely due to differences in the sensitivity of the various cells lines used to (S)-HPMPA and CDV. (S)-HPMPA shows greater efficacy against orthopoxviruses in culture (12,19,22,36) and the hexadecyloxypropyl (HDP) ester of (S)-HPMPA is 80-fold more active than the HDP-ester of CDV (5,20). Therefore, we predicted that (S)-HPMPA would have a more profound effect on these aspects of enzyme activity than does CDV.…”

Serine Peptide Phosphoester Prodrugs of Cyclic Cidofovir: Synthesis, Transport, and Antiviral Activity

“…A number of alternative prodrug strategies for enhancing the oral delivery of 1 by incorporating various phosphonate anion masking groups have been documented. [14][15][16][17][18][19][20][21][22] Cyclic cidofovir (cHPMPC, 2, Chart 1) is known to undergo biotransformation to 1when exposed to endogenous cCMP phosphodiesterase. 23, 24 Although cidofovir has been associated with severe kidney toxicity, 25 2 has been reported to be less nephrotoxic, while also exhibiting potent antiviral activity.…”