Cytotoxicity, cell-cycle perturbations and apoptosis in human tumor cells by lipophilic N4-alkyl-1-beta-D-arabinofuranosylcytosine derivatives and the new heteronucleoside phosphate dimer arabinocytidylyl-(5'-->5')-N4-octadecyl-1-beta-D-arabinofuranosylcytosi ne.

The arabinofuranosylcytosine (AraC) derivative N4-octadecyl-1-beta-D-arabinofuranosylcytosine (NOAC) and its (5'-->5')-heterodinucleoside phosphate analog NOAC-AraC were compared with AraC for cytotoxicity, cell-cycle dependence, phosphorylation by deoxycytidine (dC) kinase and apoptosis induction in native, AraC- or NOAC-resistant HL-60 cells. NOAC was cytotoxic in all cells with three to seven-fold lower IC50 concentrations than those of NOAC-AraC or AraC. In contrast to NOAC-AraC, the lipophilic monomer NOAC overcame AraC resistance, inducing apoptosis in more than 80% of native and AraC-resistant HL-60 cells. This suggests that NOAC-AraC may be cleaved intracellularly only at very slow rates to AraC and NOAC or to the 5'-monophosphates, whereas NOAC exerts different mechanisms of action from AraC. In vitro the dimer was cleaved by phosphodiesterase or human serum to NOAC, AraC and AraC monophosphate. In contrast to AraC, N4-alkylated AraC derivatives with alkyl chains ranging from 6-18 C atoms were not substrates for dC kinase. Furthermore, treatment of the multidrug-resistant cell lines KB-ChR-8-5 and KB-V1 with the N4-hexadecyl-AraC derivative NHAC did not induce P-170 glycoprotein expression, suggesting that the N4-alkyl-AraC derivatives are able to circumvent MDR1 multidrug resistance. The in vivo activity of liposomal NOAC in a human acute lymphatic leukemia xenograft model confirmed the antitumor activity of this representative of the N4-alkyl-arabinofuranosylcytosines.

Comparative pharmacokinetic and cytotoxic analysis of three different formulations of mitoxantrone in mice.

Two liposomal formulations of mitoxantrone (MTO) were compared with the aqueous solution (free MTO) in terms of their pharmacokinetic behaviour in ICR mice and cytotoxic activity in a nude mouse xenograft model. The three different formulations of MTO [free MTO, phosphatidic acid (PA)-MTO liposomes, pH-MTO liposomes] were administered intravenously (three mice per formulation and time point) at a dose of 4.7 micromol kg(-1) for free MTO, 6.1 micromol kg(-1) for PA-MTO and 4.5 micromol kg(-1) for pH-MTO. The concentrations of MTO were determined using high-performance liquid chromatography (HPLC) in blood, liver, heart, spleen and kidneys of the mice. Additionally, the toxicity and anti-tumour activity of MTO was evaluated in a xenograft model using a human LXFL 529/6 large-cell lung carcinoma. The dose administered was 90% of the maximum tolerated dose (MTD) of the corresponding formulation (8.1 micromol kg(-1) for free MTO, 12.1 micromol kg(-1) for PA-MTO and pH-MTO). The pharmacokinetic behaviour of PA-MTO in blood was faster than that of free MTO, but the cytotoxic effect was improved. In contrast, pH-MTO showed a tenfold increased area under the curve (AUC) in blood compared with free MTO, without improvement of the cytotoxic effect. This discrepancy between the pharmacokinetic and cytotoxic results could be explained by the fact that MTO in pH-MTO liposomes remains mainly in the vascular space, whereas MTO in PA-MTO liposomes is rapidly distributed into deep compartments, even more so than free MTO.

Oral antitumour activity in murine L1210 leukaemia and pharmacological properties of liposome formulations of N4-alkyl derivatives of 1-beta-D-arabinofuranosylcytosine.

The oral cytostatic activity in L1210 mouse leukaemia of the two new N4-alkyl derivatives of 1-beta-D-arabinofuranosylcytosine (AraC), N4-hexadecyl- and N4-octadecyl-1-beta-D-arabinofuranosylcytosine (NH-AraC, NO-AraC) was investigated. In contrast to AraC, both derivatives were highly cytostatic after oral application as liposome formulations. With treatment schedules of five consecutive dosages or with two applications on days 1 and 4 after intravenous tumour cell inoculation with a total dose of 470-1000 mg/kg NH-AraC or NO-AraC, 70%-100% of the treated animals were cured. The lethal dose in healthy ICR mice after a single intraperitoneal application, corresponding to the LD50, was 524 mg/kg for NO-AraC, whereas NH-AraC proved to be less toxic. The haematological toxicity remained moderate for both drugs with a mild leucopenia and a drop in platelet counts, which recovered 4-6 days after treatment. The erythrocytes were not affected and haemolytic toxicities were absent. As non-haematological toxicities, at high drug concentrations, a pronounced atrophy of the rapidly dividing epithelia of the small intestines and of the white pulp of the spleen were observed. The blood levels of NH-AraC given orally reached values comparable to those after parenteral application of a four-times lower dose of NH-AraC, suggesting a moderate bioavailability. Thus, these two lipophilic derivatives of AraC are compounds with a potential for the oral treatment of malignant diseases.

Cell cycle-dependent cytotoxicity and induction of apoptosis by liposomal N4-hexadecyl-1-beta-D-arabinofuranosylcytosine.

The clonogenic growth inhibition, the cell cycle dependence of N4-hexadecyl-1-beta-D-arabinofuranosylcytosine (NHAC) cytotoxicity and the capability to induce apoptosis in ara-C-sensitive and -resistant HL-60 cells were investigated and compared with arabinofuranosylcytosine (ara-C). In the clonogenic assay with sensitive HL-60 cells, ara-C was slightly more effective than a liposomal preparation of NHAC, whereas in the resistant cells, NHAC revealed its potency to overcome ara-C resistance, resulting in a 23-fold lower 50% inhibitory concentration compared with ara-C. Cell cycle dependent cytotoxicity and induction of apoptosis were studied by flow cytometry, using the bromodeoxyuridine-propidium iodide and terminal transferase method respectively. In contrast to ara-C, NHAC exerted no phase-specific toxicity at low concentrations (< 40 microM). At higher concentrations the S-phase-specific toxicity increased, probably resulting from ara-C formed from NHAC. NHAC induced apoptosis at higher drug concentrations than ara-C, however apoptosis appeared not to be limited to the S-phase cells. Apoptosis occurred in both cell lines within 2-4 h after drug exposure. These results give further evidence that NHAC exerts its cytotoxicity by different mechanisms of action than ara-C and might therefore be active in ara-C-resistant tumours.

Cellular pharmacology of a liposomal preparation of N4-hexadecyl-1-beta-D-arabinofuranosylcytosine, a lipophilic derivative of 1-beta-D-arabinofuranosylcytosine.

The in vitro deamination, cytotoxicity, cellular drug uptake, distribution and cellular pharmacology in HL-60 cells of N4-hexadecyl-1-beta-D-arabinofuranosylcytosine (NHAC), a lipophilic derivative of arabinofuranosylcytosine (ara-C), were studied. Compared with ara-C, NHAC in liposomal formulations was highly resistant to deamination, resulting in levels of formation of arabinofuranosyluracil 42 and ten times lower in plasma and liver microsomes respectively. The cytotoxicity of NHAC was independent of both the nucleoside transporter mechanism and the deoxycytidine (dCyd) kinase activity as demonstrated by co-incubating NHAC with dipyridamole and/or dCyd. In ara C-resistant HL-60 cells NHAC was still cytotoxic, requiring drug concentration only 1.6 times higher than sensitive cells. Uptake of NHAC was six times higher and was not inhibited by dipyridamole. The pharmacokinetics of NHAC revealed that its intracellular half-life is 4.8 times longer than that of ara-C. Ara-CTP formation and incorporation into DNA was up to 25-50 times lower than that of ara-C and contributed only marginally to the cytotoxic effects of NHAC. These results indicate that, because of the significantly increased stability, the transporter-independent uptake and the dCyd-kinase-independent cytotoxicity, NHAC might be active in ara-C-resistant cells.

Pharmacokinetic properties and interactions with blood components of N4-hexadecyl-1-beta-D-arabinofuranosylcytosine (NHAC) incorporated into liposomes.

N4-Hexadecyl-1-beta-D-arabinofuranosylcytosine (NHAC) is a new lipophilic derivative of 1-beta-D-arabinofuranosylcytosine (ara-C) with strong antitumour activity. The interactions of NHAC incorporated into small unilamellar liposomes of different compositions with blood components were evaluated. In comparison with ara-C, NHAC is highly protected against deamination to inactive arabinofuranosyluracil (ara-U) in human plasma, resulting in only 2% conversion into ara-U after 4 h incubation at 37 degrees C, whereas from ara-C more than 80% was deaminated. In in-vitro incubations with human blood, it was found that NHAC was transferred from the liposomes at about 47% efficiency to plasma proteins, particularly to albumin and to the high and low density lipoproteins. The remaining part of NHAC was bound to erythrocytes (50%) and to leucocytes (3%). The addition of poly(ethylene) glycol-modified phospholipids to the liposomes (PEG liposomes), which were composed of soy phosphatidylcholine and cholesterol (plain liposomes), did not significantly prevent the fast transfer of NHAC from the liposomes to the blood components. Pharmacokinetic studies in mice revealed that NHAC had biphasic kinetics in blood with a t1/2 alpha of 16 min and a t1/2 beta of 3.8 h when the drug was formulated in plain liposomes and a t1/2 alpha of 15 min and a t1/2 beta of 9.67 h in PEG liposomes, respectively. NHAC was predominantly distributed in the liver with 29% of the injected dose found after 30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular pharmacology of N4-hexadecyl-1-beta-D-arabinofuranosylcytosine in the human leukemic cell lines K-562 and U-937.

The mechanisms of cytotoxicity, cellular drug uptake, intracellular drug distribution, cellular pharmacokinetics, formation of arabinofuranosylcytosine triphosphate (ara-CTP), and DNA incorporation of N4-hexadecyl-1-beta-D-arabinofuranosylcytosine (NHAC), a new lipophilic derivative of arabinofuranosylcytosine (ara-C) formulated in small unilamellar liposomes, were determined in vitro in the human leukemic cell lines K-562 and U-937. Furthermore, the induction of erythroid differentiation by NHAC was tested in K-562 cells. The cytotoxicity of NHAC in both cell lines was not influenced by the deoxycytidine (dCyd) concentration or the presence of the nucleoside-transport-blocking agent dipyridamole as demonstrated in coincubations with dCyd and/or dipyridamole, whereas in contrast, the cytotoxicity of ara-C was decreased additively by both drugs. As compared with ara-C, the uptake of NHAC displayed up to 16- and 5-fold increases in K-562 and U-937 cells, respectively, depending on the drug concentration. Studies of the drug distribution and pharmacokinetics of NHAC revealed a depot effect for NHAC in the cell membranes, resulting in half-lives 2.6 and 1.4 times longer than those of ara-C in the two cell lines. The ara-CTP concentrations derived from NHAC were 150- and 75-fold lower at a drug concentration of 1 microM in K-562 and U-937 cells, respectively. The DNA incorporation of the drugs observed after incubation with 2 microM NHAC was 60- and 30-fold lower as compared with that seen at 2 microM ara-C in the two cell lines. Furthermore, NHAC was capable of inducing irreversible erythroid differentiation to a maximum of only 22% of K-562 cells, whereas ara-C induced differentiation at a drug concentration 100-fold lower in 50% of the cells. These results indicate a mechanism of cytotoxicity for NHAC that is independent of the nucleoside transport mechanism and the phosphorylation pathway and suggest that the mechanisms of action of NHAC are significantly different from those of ara-C. Therefore, NHAC might be used for the treatment of ara-C-resistant malignancies.

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.