Janos Szebeni

Fc-receptor-mediated targeting of antibody-bearing liposomes containing dideoxycytidine triphosphate to human monocyte/macrophages

Abstract— Liposomes bearing surface‐attached antibody (L‐Ab) molecules can be used for various purposes including the immunospecific delivery of drugs or other materials to antigenic target cells. In this study, L‐Ab were prepared to deliver an anti‐human immunodeficiency virus (HIV) drug, dideoxycytidine triphosphate (ddCTP) to human monocyte/macrophages. Cells of the monocyte/macrophage lineage are an important reservoir of HIV‐1. A mouse monoclonal antibody IgG2a was labelled with 125I and modified using N succinimidyl‐3‐(2‐pyridyldithio)propionate (SPDP) as a heterobifunctional reagent in order to conjugate with liposomes to produce a covalent bond (thioether). SPDP‐modified antibody was incubated with liposomes containing 5 mol% of maleimido phenyl butyrate phosphatidylethanolamine (MPB‐PE) at room temperature (21°C) for 24 h. L‐Ab were separated from free and aggregated antibodies by centrifugation. L‐Ab were characterized by measuring particle size and binding to anti‐mouse IgG‐sepharose. Ninety five per cent of the liposomal (L‐Ab) lipid label was bound to anti‐mouse IgG‐sepharose, whereas only 7% of plain liposomes were bound, indicating non‐specific binding. Uptake of L‐Ab was measured in human monocyte/macrophages as a function of time and compared with that of plain liposomes. The uptake increased with time and it was 4–6 times greater than that of plain liposomes although part of that effect may have been due to unreacted MPB groups.

Effects of thymidine and uridine on the phosphorylation of 3'-azido-3'-deoxythymidine (zidovudine) in human mononuclear cells.

The effects of thymidine and uridine on the phosphorylation of 3-azido-3-deoxythymidine (AZT) were studied in various human mononuclear cell preparations. Thymidine suppressed [3H]AZT phosphorylation in the same concentration range (20 to 100 microM) in which it antagonizes the anti-human immunodeficiency virus activity of AZT. Uridine, in turn, had no influence on AZT phosphorylation, just as it has no effect on the anti-human immunodeficiency virus activity of AZT. These findings are consistent with a close relationship between the inhibition of AZT phosphorylation and the influence of physiological nucleosides on the antiviral activity of AZT.

Effect of dipyridamole on transport and phosphorylation of thymidine and 3′-azido-3′-deoxythymidine in human monocyte/macrophages

Dipyridamole (DPM), a commonly used coronary vasodilator and antithrombotic drug, was shown recently to potentiate the antiviral effect of 3-azido-3-deoxythymidine (AZT) in HIV-1 infected human monocyte-derived macrophages (M/M) in vitro. We report in the present study that in uninfected M/M, DPM markedly inhibited cellular uptake of [3H]thymidine (dThd) and its incorporation into the nucleotide pools, particularly the dThd-triphosphate pool. In contrast, DPM did not affect cellular uptake and phosphorylation of [3H]AZT. Since dThd counteracts the phosphorylation and antiviral action of AZT, these findings support the hypothesis that the potentiation of the anti-HIV effect of AZT is due, at least in part, to differential inhibition of nucleoside salvage.

Differential inhibition of 2'-deoxycytidine salvage as a possible mechanism for potentiation of the anti-human immunodeficiency virus activity of 2',3'-dideoxycytidine by dipyridamole

Dipyridamole, a commonly used coronary vasodilator and antithrombotic drug, was recently shown to potentiate the activity of 3-azido-3-deoxythymidine and 2,3-dideoxycytidine against the human immunodeficiency virus type 1 (HIV-1) in human monocyte-macrophages in vitro. We report in the present paper that in uninfected monocyte-macrophages dipyridamole significantly inhibits cellular salvage of [3H]deoxycytidine, whereas it does not affect the salvage of [3H]dideoxycytidine. Similar differential inhibition by dipyridamole of the salvage of thymidine, as opposed to 3-azido-3-deoxythymidine, was reported previously (G. V. Betageri, J. Szebeni, K. Hung, S. S. Patel, L. M. Wahl, M. Corcoran, and J. N. Weinstein, Biochem. Pharmacol. 40:867-870, 1990). Taken together, these observations suggest that inhibition of the salvage of competing physiological nucleosides may explain or contribute to the potentiating effect of dipyridamole on these antiviral dideoxynucleoside drugs.

Dipyridamole potentiates the activity of zidovudine and other dideoxynucleosides against HIV-1 in cultured cells

Dipyridamole (DPM, Persantine), a potent inhibitor of nucleoside transport, is commonly used as a coronary vasodilator and inhibitor of platelet aggregation in the treatment of cardiovascular diseases. For the past few years, there has also been increasing interest in its use in cancer chemotherapy, as a potentiator of the cytotoxic effects of antitumor agents. We have found that DPM also potentiates the antiviral effects of 3-azido-3-deoxythymidine (AZT) against HIV1 in primary cultures of human monocyte/macrophages, in phytohemagglutinin (PHA)-stimulated human T lymphocytes, and in human T-lymphoblastoid (CEM-SS) cells. In the CEM-SS cells, furthermore, DPM decreases the cytotoxicity of AZT.