Lipid conjugates of antiretroviral agents. I. Azidothymidine-monophosphate-diglyceride: anti-HIV activity, physical properties, and interaction with plasma proteins

Synthesis, and Some Properties of, Amphiphilic Dinucleoside Phosphate Derivatives of 3′-azido-2′,3′-dideoxythymidine (AZT)

N4-hexadecyl-5′-0-(4-monomethoxytrityl)-2′-deoxycytidine-3′-hydrogenphosphate was reacted with 3′-azido-2′,3′-dideoxythymidine (AZT) according to the hydrogenphosphate method to yield N4-hexadecyl-2′-deoxycytidylyl-(3′-5)-3′-azido-2′,3′-dideoxythymidine. N4-palmitoyl-5′-O-(4-monomethoxytrityl)-2′-deoxycytidine-3′-(2-chlorophenyl)-phosphate was condensed to AZT using the triester method to give N4-palmitoyl-2′-deoxycytidylyl-(3′-5′)-3,-azido-2′,3′-dideoxythymidine. Both dinucleosidephosphates have amphiphilic properties and represent a new class of AZT derivatives in which the polar AZT-5′-monophosphate is masked with lipophilic deoxycytidine residues of variable stability. The AZT derivatives are water soluble, by forming micelles, and as a result of their amphiphilic nature, they can be incorporated into the lipid membranes of liposomes. In contrast to the micellar drug preparations, the liposomal formulations were shown to exert no lytic activity on human erythrocytes. Both AZT derivatives have anti HIV-1 activity in vitro.

Synthesis and in vitro Antiviral Properties of Amphiphilic Dinucleoside Phosphate Derivatives of 2′,3-dideoxycytidine (ddC)

N4-hexadecyl-5′-0-(4-monomethoxytrityl)-2′-deoxycytidine-3′-hydrogenphosphonate and 5′-0-(4-monomethoxytrityl)-2′-deoxythymidine-3′-0-hydrogenphosphonate were condensed with 2′,3′-dideoxycytidine (ddC) according to the hydrogenphosphonate method to yield N4-hexadecyl-2′-deoxycytidylyl-(3′-5′)-2′,3′-dideoxycytidine (N4-hexadecyldC-ddC) and 2′-deoxythymidylyl-(3′-5′)-N4-palmitoyl-2′,3′-dideoxycytidine (dT-N4-palmddC). N4-palmitoyl-2′,3′-dideoxycytidine (N4-palmddC) was synthesized by reacting palmitic anhydride with ddC. Both dinucleoside phosphates have amphiphilic properties and represent a new class of ddC derivatives in which in the case of the dinucleosides, the ddC-5′-monophosphate is masked with lipophilic residues of variable stability. The ddC derivatives can be solubilized in water by micelle formation and, because they have lipophilic residues, they can be incorporated into the lipid membranes of liposomes. The ddC derivatives were shown to have antiviral activities comparable to those of AZT and ddC when tested in vitro against HIV-1-infected HeLa and H9 cells as well as infected human monocytes/macrophages.

Crystallization and phase behavior of fatty acid esters of 1,3-propanediol

Six pure fatty acid esters of 1,3-propanediol (PADE) molecules were investigated. A careful analysis of XRD, DSC as well as SFC results has allowed the determination of their structure and phase behavior. Two beta polymorphs were observed for C10-C18 and three beta polymorphs for C8. The same first polymorph (beta1) was observed for all the samples. The second polymorph (beta2) observed for C12-C18 was different from the second beta-form observed for C8 and C10. For all properties, the short chain length C8 and C10 samples were distinguished from the C12 to C18 samples and this explained much of the observed trends in behavior. Their lamellar packing was similar and has been explained by a simple addition of multiples of the length of a carbon bond to a primitive structure. The estimated long-range order highlighted a geometric effect that enabled the small chain molecules to better order than the longest molecules. The XRD results have been confirmed by DSC. The difference in property between the short and long chain molecules has also been clearly verified by the evolution of the energy of activation for nucleation as well as the enthalpy of melting and confirmed by microscopy measurements. For all the samples, the hardness which increased with increasing chain length is correlated with final %SFC. Avrami analysis of SFC versus time indicated heterogeneous nucleation and spherulitic crystal development from sporadic nuclei, and suggested that the rate of nucleation was higher for longer chain molecules.

Synthesis and biological evaluation of two glycerolipidic prodrugs of didanosine for direct lymphatic delivery against HIV

Novel glycerolipidic prodrugs of didanosine and didanosine monophosphate designed to by-pass the hepatic first pass metabolism were synthesized and tested for their cytotoxicity and anti-HIV-1 activity. Formulation as liposomes of dipalmitoylphosphatidylcholine was elaborated. A simple quantitative HPLC-UV method was developed and validated, and ESI-MS was used for qualitative purpose. These two prodrugs exhibited promising biological activities against HIV-1 in in vitro infected cell culture.

Pronucleotides: toward the in vivo delivery of antiviral and anticancer nucleotides

To overcome the many hurdles preventing the use of antiviral and anticancer nucleosides as therapeutics, the development of a prodrug methodology (i.e., pronucleotide) for the in vivo delivery of nucleotides has been proposed as a solution. The ideal pronucleotide should be non-toxic, stable in plasma and blood, capable of being i. v. and/or orally dosed, and intracellularly convertible to the corresponding nucleotide. Although this goal has yet to be achieved, many clever and imaginative pronucleotide approaches have been developed, which are likely to be important pharmacological tools. This review will discuss the major advances and future directions of the emerging field of antiviral and anticancer pronucleotide design and development.

Tris lipidation: a chemically flexible technology for modifying the delivery of drugs and genes

1. One of the major challenges in the development of pharmaceuticals is their formulation with other materials to give them the desired bioavailability profile when administered into the body. 2. We have developed a flexible platform technology (Tris lipidation) to simply and effectively alter the lipophilicity of drugs. As implied by the name, the technology uses the common buffer Tris as a linker between the drugs of interest and a domain of variable hydrophobicity. 3. We demonstrate, using a mouse melanoma model, that Tris-lipidated conjugates of the widely used cytotoxic and anti-inflammatory drug methotrexate (MTX) display enhanced potency in the local treatment of tumours and reduced systemic toxicity when compared with the unconjugated drug. 4. With genes now being predicted to be the pharmaceuticals of the future, we show that Tris-lipidated cationic peptides can efficiently deliver DNA into (transfect) cells in culture. Furthermore, by comparing the abilities of variants of these Tris-based cationic lipids to transfect cultured cells, we demonstrate that modifications made to variable regions of Tris-lipidated compounds can dramatically alter their delivery profiles.

Liposomes as drug delivery system: a strategic approach for the treatment of HIV infection

As the number of individuals infected with human immunodeficiency virus (HIV) is growing dramatically throughout the world, it is important to develop strategies to improve the treatment of this deadly disease. It is now well established that macrophages play a central role in HIV pathogenesis, acting as reservoirs for dissemination of virus throughout the immune system. As liposomes are naturally taken up by cells of the mononuclear phagocytic system, liposome-based therapy represents a convenient approach to improve the delivery of anti-HIV agents into infected cells improving thereby the efficacy of drugs and reducing their adverse side-effects. A more specific targeting of HIV-infected cells could also be obtained by using liposomes bearing surface attached-antibodies. This review details the applications of liposomes as drug carriers for the treatment of AIDS. It also gives an overlook of the different strategies that could be explored to control the progression of the disease in infected individuals.

Nucleoside conjugates. 15. Synthesis and biological activity of anti-HIV nucleoside conjugates of ether and thioether phospholipids

A series of the anti-HIV nucleoside conjugates of either (1-O-alkyl) and thioether (1-S-alkyl) lipids linked by a pyrophosphate diester bond has been synthesized as micelle-forming prodrugs of the nucleosides to improve their therapeutic efficiency. These include AZT 5'-diphosphate-rac-1-S-octadecyl-2-O-palmitoyl-1-thioglycerol (1), 3'-azido-2',3'-dideoxyuridine 5'-diphosphate-rac-1-S-octadecyl-2-O-palmitoyl-1-thioglycerol (2) 2',3'-dideoxycytidine 5'-diphosphate-rac-1-S-octadecyl-2-O-palmitoyl-1-thioglycerol (3), and AZT 5'-diphosphate-rac-1-O-tetradecyl-2-O-palmitoylglycerol (4). The conjugates form micelles by sonication (mean diameters ranging 6.8-55.5 nm). Conjugate 1 protected 80% of HIV-infected CEM cells as low as 0.58 microM and lost the protection at 180 microM due to prevailing cytotoxicity, while the conjugate started to show the cytotoxicity at 100 microM. Pharmacokinetics studies showed a significant increase of half-life values (t1/2) of AZT and AZddU2 (respective t1/2 = 5.69 and 6.5 h) after administration of conjugates 1 and 2, while those after administration of AZT and AZddU were 0.28 and 0.89 h, respectively. The fractions of the prodrugs 1 and 2 converted to the parent compounds AZT and AZddU were 36% and 55%, respectively. The results indicate that AZT and AZddU thioether lipid conjugates 1 and 2 warrant further investigation.

Fatty acid conjugates of xenobiotics

In this review, we discuss the formation and toxicity of fatty acid conjugates of xenobiotics. Conjugates formed in vivo and in vitro and those detected as contaminants are reviewed. Due to the lipophilic nature of these conjugates, they may accumulate in various body organs and cause toxic manifestations. In vivo formation of these fatty acid conjugates appears to be catalyzed by enzyme(s). Fatty acid ethyl esters are the most widely studied esters and have been implicated in the onset or pathogenesis of myocardial and pancreatic diseases in alcoholics. In experimental animals, studies on 2-chloroethyl linoleate, palmitoylpentachlorophenol and oleoyl and linoleoyl anilides clearly indicate that lipid conjugates of xenobiotics are involved in target organ toxicity. These findings warrant further detailed studies to isolate and identify other fatty acid conjugates and to evaluate their toxicity. Thorough toxicokinetic and metabolic studies are also needed to identify putative toxic agents. Identifying these agents could help in understanding the mechanism of pathogenesis associated with lipid conjugation. Finally fatty acid conjugates of drugs (prodrugs), have been shown to have increased half-lives and long-lasting dose-response. Thus these conjugates may be useful for enhancing the therapeutic potential of drugs and should be explored further.

New lipophilic alkyl/acyl dinucleoside phosphates as derivatives of 3'-azido-3'-deoxythymidine: inhibition of HIV-1 replication in vitro and antiviral activity against Rauscher leukemia virus infected mice with delayed treatment regimens

The antiretroviral activity of two new lipophilic derivatives of azidothymidine (AZT), N4-hexadecyl-2'-deoxyribocytidylyl-(3',5')-3'-azido-2',3'-deoxythy midine (N4-hexadecyldC-AZT) and N4-palmitoyl-2'-deoxyribocytidylyl-(3',5')-3'-azido-2',3'-deoxythy midine (N4-palmitoyldC-AZT) was evaluated in comparison to AZT. In vitro the drugs were tested in human immunodeficiency virus 1 (HIV-1) infected CD4+ HeLa and H9 cells. The in vivo antiviral effect of these derivatives was analysed in Rauscher leukemia virus (RLV) infected mice. The derivatives were incorporated into small liposomes. In vitro both derivatives inhibited virus proliferation in both HIV-1 infected cell lines in a similar dose-responsive manner as AZT. In a plaque reduction assay, using HeLa cells, the IC50 values were 0.035 microM for AZT, 0.5 microM for N4-hexadecyldC-AZT and 4.5 microM for N4-palmitoyldC-AZT, whereas p24 antigen analysis on H9 cells gave IC50 values of 0.005 microM, 0.05 microM and 0.05 microM, respectively. RLV infected mice were treated with intermittent schedules i.p. or i.v. on days 1, 6, 11, and days 16 or 0, 3, 7, and 11 after infection. Regimens with further delayed drug application were on days 3, 7, and 11 and 7 and 11 only. While i.p. treatment with total doses of 380-1140 mg/kg free AZT resulted in 10-30% inhibition of RLV induced splenomegaly, the derivatives gave inhibitions of 37-94%. Late onset of treatment with the derivatives was significantly more effective as compared to free AZT. Intravenous treatment with N4-hexadecyldC-AZT was effective, but with AZT was inactive. The discrepancy in antiviral activity of the AZT derivatives found between the in vitro and in vivo test systems emphasizes the importance of investigating the activity of drug derivatives in vivo.

Isolation of experimental anti-AIDS glycerophospholipids by micro-preparative reversed-phase high-performance liquid chromatography

The experimental anti-AIDS glycerophosphatidic acid: nucleoside (sn-1/sn-2 diacylglycerol:dideoxynucleotide) drugs 3'-azido-3'-deoxythymidine monophosphate diglyceride (AZT-MP-DG) and 2',3'-dideoxycytidine monophosphate diglyceride (ddC-MP-DG) were isolated and purified by reversed-phase high-performance liquid chromatography (HPLC). The chromatographic separation was based on the glycerophospholipid moiety of the drugs and detection of the nucleoside component. The separations were optimized on method development columns packed with the stationary phase to be used in the micro-preparative column and monitored by a UV detector. Fractions were collected and analyzed for purity by analytical-scale HPLC and by thin-layer chromatography (TLC). The purity of the recovered drugs based on UV and light-scattering detection and on TLC was greater than 99%. The purified compounds were isolated for studies on structure confirmation, physical, biophysical and formulation properties and anti-HIV efficacy in culture.

Lipid conjugates of antiretroviral agents: release of antiretroviral nucleoside monophosphates by a nucleoside diphosphate diglyceride hydrolase activity from rat liver mitochondria

The release of the 5'-monophosphates of the antiretroviral nucleoside analogs 3'-azido-3'-deoxythymidine, 3'-deoxythymidine and 2',3'-dideoxycytidine from the corresponding nucleoside diphosphate diglycerides as a result of rat liver mitochondrial enzymatic activity is shown. The three analogs appeared to be about equally active as substrate for this pyrophosphatase activity which showed maximum conversion rates of 3-6 nmol min-1 mg protein-1 at substrate concentrations between 500 to 800 microM. These results may contribute to the biochemical explanation for the observed anti-HIV activity of this type of phospholipid conjugates in vitro.

High-performance liquid chromatographic analysis of 3'-azido-3'-deoxythymidine monophosphate diglyceride, an anti-HIV glycerophospholipid

A reversed-phase chromatographic method is described for the analysis of an experimental anti-AIDS drug 3'-azido-3'-deoxythymidine monophosphate diglyceride (AZT-MP-DG) [J.M. Steim et al., Biochem. Biophys. Res. Commun. 171, 458-464 (1990)] [1], a phosphatidic acid derivative of AZT. Analytical conditions were based upon conventional separations of glycerophospholipid species. Where AZT-MP-DG was monitored by UV absorption, there were two wavelength maxima. The response was linear in the concentration range used in this study. The peak was characterized by absorbance ratios with a rapid scanning UV detector.