Synthesis and in vitro activities of a new antiviral duplex drug linking Zidovudine (AZT) and Foscarnet (PFA) via an octadecylglycerol residue

To prepare a new antiviral duplex drug linking Zidovudine (AZT) and Foscarnet (PFA) via a lipophilic octadecylglycerol residue we condensed 1-O-4-monomethoxytrityl-3-O-octadecyl-sn-glycerol-2-hydrogenphosphonate obtained from 3-O-octadecyl-sn-glycerol with AZT by the phosphonate method. The purified condensation product was de-tritylated resulting in 3'-azido-3'-deoxythymidylyl-(5'-->2-O)-3-O-octadecyl-sn-glycerol, followed by treatment with (ethoxycarbonyl)phosphoric dichloride. The resulting 3'-azido-3'-deoxy-thymidylyl-(5'-->2)-3-O-octadecyl-sn-glycerol-1-O-(ethoxycarbonyl)phosphonate was purified by preparative RP-18 column chromatography. The antiviral duplex drug 3'-azido-3'-deoxythymidylyl-(5'-->2-O)-3-O-octadecyl-sn-glycerol-1-O-phosphonoformate trisodium salt (AZT-lipid-PFA) was obtained after alkaline cleavage of the phosphonoformate ethylester residue. The overall yield of the five step synthesis performed at gram scale was about 30%. According to a supposed pathway AZT-lipid-PFA could be cleaved to yield a mixture of different antiviral compounds such as AZT, AZT-5'-monophosphate, octadecylglycerol-AZT, PFA and octadecylglycerol-PFA, possibly producing additive and/or synergistic antiviral effects. In vitro studies showed that the duplex drug exhibits antiviral activities against HIV and especially against drug-resistant strains and clinical isolates of HSV and HCMV. The E(50) values of AZT-lipid-PFA against HIV ranged between 170 and 200 nM. The half-maximal inhibitory doses (IC(50)) against highly acyclovir (ACV)-resistant HSV isolates determined by a plaque reduction assay ranged between 1.87 and 4.59 microM. Using ganciclovir (GCV)-sensitive, GCV resistant and drug cross-resistant HCMV strains the IC(50)-values of AZT-lipid-PFA were between 2.78 and 1.18 microM. With regard to PFA, the IC(50)-value of AZT-lipid-PFA determined on a multi-drug-resistant HCMV strain was about 90-fold lower than that of PFA, demonstrating the superior antiviral effect of the duplex-drug.

Solid phase ELISA for determination of the virus dose dependent sensitivity of human cytomegalovirus to antiviral drugs in vitro

The main problems in determining the true in vivo susceptibility of human cytomegalovirus (CMV) to antiviral compounds are the influence of the size of the viral inoculum, the variation in the replication capacity of different CMV strains and the subjective evaluation of the inhibition of viral growth in the plaque assay. In this study, a specific assay was developed which reproducibly determines the sensitivity of primary isolates of CMV. The assay includes simultaneous virus titration and determination of the antiviral sensitivity. When individual virus doses were evaluated, the IC50 was generally dependent on the virus dose, except for resistant isolates, where the IC50 did not change irrespective of the dose of virus. The novel method of IC50 calculation takes into account all values derived from the linear part of the inhibition curve. This may better reflect the in vivo conditions, where the antiviral drug encounters different amounts of virus in different organs. Two human fibroblast-derived cell lines showed similar results.

Synthesis and antiviral evaluation of SATE-foscarnet prodrugs and new foscarnet-AZT conjugates

The synthesis of a range of di- and triester derivatives of phosphonoformate (PFA; foscarnet) as potential lipophilic, membrane-soluble prodrugs is described. In addition to normal alkyl esters in the carboxylate and phosphonate residues of PFA, the bioreversible S-(pivaloyl)thioethyl (t-butyl-SATE) group was introduced in an attempt to deliver PFA after bioactivation inside the cells. Furthermore, PFA-AZT conjugates were prepared in order to develop combinational drugs. The key synthetic step was in all cases the formation of the P-C bond to build up the different PFA esters. In contrast to the diester derivatives, the triesters of PFA showed high hydrolytic instability during chromatographic purification. The compounds were evaluated in vitro for their ability to inhibit viruses in several tissue culture systems. All PFA alkyl di- and triesters proved poorly active or inactive against human immunodeficiency virus (HIV) and inactive against hepatitis B virus. In contrast, the PFA-AZT conjugates exhibited significant anti-HIV activity. However, this activity was nearly completely lost in thymidine kinase-deficient cells, suggesting a fast unselective chemical hydrolysis of the conjugates to yield the nucleoside analogue AZT in the cell culture medium. Furthermore, no synergistic effect of PFA and AZT was observed.