Antinociception and side effects of L- and D-dipalmitoylphosphatidyl choline liposome-encapsulated alfentanil after spinal delivery in rats

We have observed that spinal liposome administration in the rat resulted in in an allodynia evoked by light touch. We later determined that liposomes composed of D-isomer phospholipids were essentially non-toxic. This study examines the effects of alfentanil encapsulated in liposomes made from the natural L-isomer and synthetic D-isomer of dipalmitoyl phosphatidyl choline on antinoceiception, side effects, and algogenic behaviour. Both unilamellar and multilamellar liposomes were studied. Rats prepared with chronic intrathecal catheters received intrathecal injections of alfentanil (5 or 50 micrograms) in saline or encapsulated in liposomes composed of either L- or D-isomers of dipalmitoyl phosphatidyl choline (DPPC) in unilamellar or multilamellar liposome formulations. Antinociception was measured using the hot plate test (52.5 degrees). Side effects were measured by catalepsy, corneal responses, pinna response, righting reflex, and paw step. Allodynia was measured by lightly stroking the animal's back. Intrathecal alfentanil in saline or in the liposomes produced a dose-dependent increased latency in the hot plate response. Encapsulation of alfentanil in the liposomes produced a significant decrease in the loss of corneal, paw step and righting reflex and a slight decrease in catalepsy and loss of the pinna response. There was no significant difference between liposome preparations in preventing side effects. L-multilamellar-DPPC produced allodynia in 100% of the animals whereas significantly less allodynia was observed with the other preparations. This study indicates that liposomal preparations can significantly enhance the therapeutic ratio of a lipid soluble opioid after spinal delivery. However, the choice of lipids for the formulation of liposomes intended for spinal drug delivery must be considered since the L-isomer and larger lipid load of multilamellar liposomes have a direct spinal effect leading to alledynia. Previous studies have in fact shown that spinal lysolecithin can yield focal demyelination.

Simian immunodeficiency virus infection of macaque primary placental cells

We have characterized the ability of a simian immunodeficiency virus, SIVmne strain E11S, to infect macaque placental trophoblast and Hofbauer cells. These primary placental cells were permissive to SIVmne infection, regardless of gestational age. Virus production by the infected cells was determined as time-dependent viral core antigen p27 production, followed by verification of the proviral gag/LTR DNA sequences in the infected cells using a polymerase chain reaction assay. Of more than six placentas tested, SIVmne infection of placental cells at an early gestational age (i.e., days 55 or 78) produced more than 10-fold the amount of virus core antigen p27 than did placental cells infected at a late gestational age (i.e., days 135 or 165). In addition, SIVmne infection of trophoblast cells was inhibited by SIVmac neutralizing macaque serum but not by normal serum, indicating the specificity of virus infection. Furthermore, the amount of SIV core antigen p27 produced by the virus-infected trophoblast and Hofbauer cells was shown to be dependent on the multiplicity of virus infection. Collectively, our results indicate that macaque trophoblast and Hofbauer cells can be infected by SIV and that both gestational age and viral dose may play a role in the extent of viral infection.

Interaction of manganese-mesoporphyrin with oleic acid vesicles

We investigated the interaction between manganese(III)mesoporphyrin (MnMeso), a metalloporphyrin, and liposome membranes containing oleic acid (OA; cis-9-octadecenoic acid). MnMeso associates preferentially with OA but minimally with egg phosphatidylcholine (EPC). Using small unilamellar vesicles, we characterized the MnMeso-OA binding at neutral pH. Our data suggest that MnMeso binds to the OA bilayer with Kd = 6.8 x 10(-4) M; the binding stoichiometry of MnMeso-OA was 1:3.4. This OA-MnMeso interaction was analyzed further for changes in the T1 relaxation property of MnMeso. OA increased the T1 of MnMeso significantly more than did EPC, suggesting that the OA-MnMeso interaction was stronger than that of PC-MnMeso. The side-chain specificity of the OA interaction with this porphyrin derivative was further supported in an experiment with manganese mesotetra(4-sulfonatophenyl)porphine, which lacks hydrophobic side chains for OA interaction. The association of MnMeso with the OA membrane was proposed according to the structure of MnMeso and OA and further verified using electron microscopy. A strong association of MnMeso with OA, an absorption enhancer of the gastrointestinal tract, may be useful for delivery of MnMeso as an oral contrast agent for magnetic resonance imaging.

Regression of LNCaP human prostate tumor xenografts in athymic nude mice by 13-cis-retinoic acid and androgen ablation

The present study was designed to investigate the effects of 13-cis-retinoic acid (13-cis-RA) (100 micrograms/mouse/day) and androgen ablation (castration) alone and in combination on growth of a human prostatic carcinoma line (LNCaP) transplanted to athymic nude mice as an experimental model. The results of these studies suggest that; (1) androgen ablation (castration) significantly decreased the size of LNCaP xenograft as compared to untreated animals; (2) when 13-cis-RA was administered to nude mice carrying established tumors (0.51 +/- 0.04 cm3), the tumor size was significantly reduced as compared to untreated controls (0.65 +/- 0.06 cm3 versus 1.63 +/- 0.12 cm3). About 50% of the animals in this group showed xenografts necrosis followed by complete regression of tumors by five months; (3) the combination of androgen ablation and 13-cis-RA treatment to nude mice carrying tumors showed synergistic effect in decreasing the tumor size. These results indicate that combination therapies based on androgen ablation and retinoid administration may be a useful approach for the treatment of prostate cancer.

Antinociception and side effects of liposome-encapsulated alfentanil after spinal delivery in rats

We investigated the spinal antinociceptive and supraspinally mediated side effects of intrathecal (IT) alfentanil after delivery in saline or when encapsulated in liposomes of different lipid constituencies in rats. Rats prepared with chronic IT catheters received IT injections of alfentanil (1, 3, 10, 30, or 50 micrograms) prepared in either saline or in one of three liposome formulations (dipalmitoyl phosphatidyl choline [DPPC], DPPC containing 20% by weight of dipalmitoyl phosphatidyl glycerol [DPPC-DPPG], or DPPC containing 20 weight percent of cholesterol [DPPC-CHOL]). Antinociception was measured by hot-plate (HP) test (52.5 degrees C). In separate groups of halothane-anesthetized rats, plasma alfentanil concentrations were measured (2-120 min) after 50 micrograms IT alfentanil given in either saline or liposomes. Antinociception was measured by tail withdrawal upon its immersion in water 52.5 degrees C. Supraspinal side effects of the drug were tested by measuring catalepsy and the eye blink evoked by touching the cornea. IT alfentanil in saline produced a dose-dependent increase in the HP response latency and this effect was accompanied by a similar dose-dependent increase in the incidence of catalepsy and blockade of corneal responses, indicating a rapid supraspinal redistribution. The HP dose-response curve for IT alfentanil delivered in liposomes was shifted slightly to the right, as compared to saline vehicle, but liposome encapsulation totally abolished the side effects that were otherwise observed at the highest IT alfentanil dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of rates of intracellular metabolism of zidovudine in human and primate peripheral blood mononuclear cells

3'-Azido-3'-deoxythymidine (AZT) is a drug of choice for the treatment of AIDS. On the basis of pharmacokinetic data, the nonhuman primate Macaca nemestrina has been shown to be a suitable animal model for use in the study of the disposition of AZT. However, since AZT is activated to its metabolite, the AZT triphosphate (AZTTP), intracellularly, we investigated the intracellular activation of AZT in peripheral blood mononuclear cells (PBMCs) of healthy and simian immunodeficiency virus-infected macaques and compared it with that in PBMCs obtained from human volunteers. At 5 microM extracellular AZT, both human and macaque PBMCs rapidly convert AZT to AZT monophosphate (AZTMP) (84% of total phosphorylated products) in 4 h. Increases in AZTMP levels of 7.7- and 12-fold were observed in human and macaque PBMCs, respectively, when the extracellular AZT concentration increased from 0.45 to 14.4 microM. Similar ratios of AZT metabolites, AZT diphosphate (AZTDP)/AZTTP (0.7 to 1.4), AZTMP/AZTDP (3 to 14), and AZTMP/AZTTP (3 to 19), over the same AZT concentration range were observed in both human and macaque PBMCs, suggesting that these cells have similar capacities to phosphorylate AZT. Simian immunodeficiency virus-infected macaque PBMCs showed a fivefold increase in intracellular AZT and AZTMP levels and a twofold increase in AZTDP and AZTTP levels (picomoles per 10(7) cells) when compared with those in the uninfected cells (at 4 h with 0.9 microM extracellular concentration). This increase in AZT metabolite levels has also been reported for human immunodeficiency virus-infected PBMCs. Collectively, given the similarities in phosphorylation profiles between healthy and infected human and macaque PBMCs, we conclude that the macaque is a suitable animal model for use in the study of factors that can effect the in vivo phosphorylation of AZT.

Effect of MTP-PE liposomes and interleukin-7 on induction of antibody and cell-mediated immune responses to a recombinant HIV-envelope protein

We investigated the ability of human recombinant interleukin-7 (IL-7) to enhance the immune responses of mice vaccinated with either the alum-associated or liposome-formulated recombinant human immunodeficiency virus (HIV)-envelope protein, env-2-3SF2 (a nonglycosylated denatured gp 120 of HIV-1SF2 produced in genetically engineered yeast). Pathogen-free (C3H) mice were vaccinated on days 0, 14, and 28 with 10 micrograms of either the alum-associated env-2-3SF2 or liposome-formulated env-2-3SF2, both containing a lipophylic muramyl tripeptide, MTP-PE. Liposome-formulated IL-7 (5 micrograms/mouse) or empty liposomes were given on days 7, 14, 21, and 28. Antibody response against the immunized antigen, evaluated on day 21 and day 35 or 42, showed that liposome-formulated antigen induced higher antibody titer than did alum-associated antigen, and these antibody responses can be enhanced by concurrent administration of IL-7 liposomes. Spleen cells were harvested on day 21 and day 35 or 42 to evaluate cytotoxic T lymphocyte responses directed against autologous cells infected with vaccinia virus-expressing HIV-envelope protein. Mice treated with liposome-formulated antigen expressed the highest cytotoxic t-lymphocyte (CTL) activity, regardless of whether IL-7 liposome was given as an immune potentiator. In contrast, spleen cells from mice vaccinated with alum-associated antigen exhibited minimal CTL response, which was enhanced by concurrent IL-7 liposome treatment. Collectively, IL-7 liposome treatment enhanced the antibody production of the alum-associated or liposome-formulated env-2-3SF2, whereas its enhancement of CTL activity was detected only in mice vaccinated with alum-associated antigen.

Metabolism of 3'-azido-3'-deoxythymidine (AZT) in human placental trophoblasts and Hofbauer cells

3'-Azido-3'-deoxythymidine (AZT) is currently under clinical investigation to assess its potential to inhibit maternal-fetal HIV transmission. To determine the activation of AZT to its phosphorylated metabolites by placental cells, we characterized the intracellular phosphorylation of AZT in two major cell types of the placenta, namely trophoblasts and Hofbauer cells. Although phosphorylation of AZT in trophoblast and Hofbauer cells is 50- to 100-fold lower than that in human lymphocytic cell lines or activated lymphocytes, both cell types are capable of activating AZT to AZT triphosphate (AZTTP) at a level comparable to that of resting lymphocytes. We found that AZT monophosphate (AZTMP) was the major phosphorylated AZT metabolite, while AZT diphosphate (AZTDP) and AZTTP constituted less than 4% of the intracellular phosphorylated AZT pool. This result was independent of AZT concentration and exposure time in both types of placental cells. The rate-limiting step in the conversion of AZT to AZTTP was determined to be thymidylate kinase-catalyzed conversion of AZTMP to AZTDP. Trophoblasts and Hofbauer cells exhibited different time-course and concentration-dependent profiles of intracellular AZT phosphorylation, suggesting that these two placental cells may have anabolic or catabolic enzymes of different composition or efficiency. AZTTP decayed in both trophoblasts and Hofbauer cells with a half-life of 4-6 hr. These results should be useful in rationally designing AZT dosage regimens to treat HIV-infected women for prevention of maternal-fetal HIV transmission.

Differential disposition of soluble and liposome-formulated human recombinant interleukin-7: effects on blood lymphocyte population in guinea pigs

The effects of liposome formulation on interleukin-7 (IL-7)-dependent lymphopoietic activity was investigated based on the pharmacokinetics and tissue distribution profile of soluble and liposome-formulated recombinant human IL-7. Using 125I-IL-7, we determined the role of liposome formulation on in vivo IL-7 disposition by analyzing injection site, blood, tissue, and urinary kinetics. Following a 30- to 40-microgram subcutaneous dose of soluble IL-7, most of the IL-7 was eliminated through urinary excretion within 24 hr. An equivalent subcutaneous dose of liposome-encapsulated IL-7 resulted in a peak level less than one-tenth that seen with soluble drug but produced sustained blood and urinary levels for 5 days. The bioavailability of liposome-encapsulated IL-7 was comparable to that of soluble IL-7, as determined by both blood and urinary data. Kinetic analysis of IL-7 at the subcutaneous injection site indicated that liposome encapsulation significantly reduced the rate of disappearance at the injection site. Studies with a mixture of 40% liposome-encapsulated and 60% soluble IL-7 gave an intermediate response between that of soluble IL-7 and that of liposome-encapsulated IL-7. Characterization of blood cells from IL-7-treated animals indicated that treatment with two weekly doses of mixed IL-7 liposomes (40% liposome encapsulated IL-7) significantly increased the total numbers of lymphocytes by day 14.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological response of recombinant interleukin-7 on herpes simplex virus infection in guinea-pigs

We investigated the biological activity of human recombinant interleukin-7 (rhIL-7) on guinea-pig cells in vitro and in vivo. RhIL-7 can stimulate plastic non-adherent cells of guinea-pigs to proliferate in vitro at a degree comparable to that of human cells. Administration of rhIL-7 to guinea-pigs significantly increased their white blood cell concentration, specifically the lymphocyte population. The effect of rhIL-7 on circulating blood cells was dose dependent, in that 14 doses of twice daily subcutaneous injections at 8 x 10(5) U kg-1 and 2.4 x 10(6) U kg-1 rhIL-7 increased peripheral blood lymphocyte concentrations by 38% (p = 0.047) and 139% (p = 0.0005), respectively, compared with the placebo group. Two weekly doses of rhIL-7 liposome (5.6 x 10(6) U kg-1 dose, equivalent to 11.2 x 10(6) U kg-1 total dose) elicited a similar effect on the lymphocyte population, comparable to that of the twice daily administrations of 8 x 10(5) U kg-1 soluble rhIL-7 for 7 days (7 days x two doses/day x 8 x 10(5) U kg-1 = 11.2 x 10(6) U kg-1 total dose). However, the increased lymphocyte count induced by rhIL-7 administration did not protect guinea-pigs from the primary herpes simplex virus (HSV)-2 infection. Only when rhIL-7 was given in association with HSV-antigen gD in an antigen-specific mode did it exhibit an enhanced protective effect against the sublethal dose of genital HSV-2 challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition of antigen-presenting liposomes in vivo: effect on presentation of herpes simplex virus antigen rgD

Antigen-presenting liposomes (APLs) containing a lipophilic derivative of muramyl tripeptide (MTP-PE) have previously been shown to enhance the immunotherapeutic effects mediated by HSV recombinant protein gD (rgD) after HSV type 2 infection is established. In this study, both the in vivo disposition of rgD and the immunological activity of in vivo-delivered rgD were determined. Following intravenous administration, most of the liposome-encapsulated rgD accumulated rapidly, mainly in the spleen, while most of the soluble rgD was quickly eliminated through the kidney. We have compared the T-cell stimulatory effects of macrophages, B cells and dendritic cells from the spleens of animals treated with rgD in vivo. Of these antigen-presenting cells, only adherent macrophages, isolated from the spleens of animals treated with rgD encapsulated in APLs for 90 minutes, were capable of stimulating HSV-sensitized autologous T and B cells. Additional in vitro exposure of macrophages to rgD was not required. In contrast, spleen macrophages from HSV-sensitized animals exposed to either empty liposomes or free rgD did not exhibit such immune responses, indicating that the immunobiological effect of the rgD delivered in APLs is antigen- and carrier-specific. The enhanced delivery of antigen to spleen cells, coupled with MTP-PE immunostimulatory activity, may be the key factors for the enhanced therapeutic effects observed in treating HSV-2 disease in guinea pigs. This approach will be useful to enhance the induction of secondary immune responses in postinfection vaccination schemes.

Effect of zidovudine on human placental trophoblast and Hofbauer cell functions

We have optimized a procedure to isolate placental trophoblasts and Hofbauer cells simultaneously in a quantity sufficient for short-term cultures and then used these placental cells to investigate the effects of zidovudine (ZDV) on trophoblast and Hofbauer cell functions. Of more than 10 term placentas tested, ZDV inhibits DNA synthesis of trophoblasts in a concentration-dependent manner with half the maximal inhibitory concentration (IC50) of 9.88 +/- 1.35 microM. Of the hormones evaluated, production of progesterone by trophoblasts is most sensitive to ZDV (IC50 = 3.65 +/- 0.29 microM). The inhibitory effect of ZDV on the secretion of placental lactogen and choriogonadotropin by the trophoblasts was detected only at a much higher concentration (> or = 60 microM). ZDV does not affect trophoblast or Hofbauer cell protein synthesis. Collectively, our results indicate that at clinically relevant concentrations (< or = 10 microM), ZDV significantly inhibits both the DNA synthesis of placental trophoblasts and their production of progesterone, while having a minimal effect on protein synthesis of both types of placental cells.

Liposome-formulated interleukin-2 as an adjuvant of recombinant HSV glycoprotein gD for the treatment of recurrent genital HSV-2 in guinea-pigs

The use of interleukin-2 (IL-2) as an adjuvant to enhance an antigen-induced immunotherapeutic effect was investigated using guinea-pigs with established HSV-2 infection. Animals treated with four weekly doses of liposome-formulated IL-2 (2.7 x 10(5) U kg-1 dose) overlapping two biweekly doses of an HSV-recombinant glycoprotein D (rgD) treatment demonstrated approximately 70% reduction in HSV-2 recurrent disease compared with placebo (p less than 0.005). Combination therapy rgD plus liposome-formulated IL-2 exhibited approximately 30% greater therapeutic effect than either agent alone (p less than 0.05). Liposome formulation of IL-2 was essential to elicit the adjuvant effect. Identical biweekly dosing or more frequent daily dosing of soluble IL-2 did not produce additional therapeutic effects, suggesting the role of liposome targeting to lymph nodes. Although rgD plus liposome-formulated IL-2 induced a marginal early antibody response to rgD, there was no significant increase in overall antibody response. Combination therapy increased the frequency of minimally positive HSV lymphoproliferative response.

Antiviral activity and dose optimum of recombinant macrophage colony-stimulating factor on herpes simplex genitalis in guinea pigs

The antiviral activity of recombinant human macrophage CSF (M-CSF) against genital herpes simplex virus type-2 (HSV-2) infection in guinea pigs was investigated. M-CSF stimulates proliferation of human and guinea pig peripheral blood monocytes, specifically the plastic adherent esterase-positive mononuclear cells. When anti-HSV-2 activity of M-CSF was evaluated in guinea pigs by 6 daily injection (s.c.) of M-CSF at various doses (5 x 10(5) to 7 x 10(7) U/kg), we found 2 x 10(6) U/kg to be the optimum dose for protective efficacy against primary HSV-2 infection. Either at a lethal, 5 x 10(5) pfu, or sublethal 5 x 10(4) pfu of virus challenge, animals treated with the optimum regimen of M-CSF exhibited lower herpetic lesion scores (p less than 0.005), and lower mortality (p less than 0.025) than animals in placebo group. M-CSF treatment increased the HSV-infected cell killing activities of plastic-adherent mononuclear cells, indicating that in vivo administration of M-CSF may activate the antiviral effects of guinea pig macrophages that may play a role in protection against severity and mortality of herpetic disease.

Antiviral activity and dose optimum of recombinant macrophage colony-stimulating factor on herpes simplex genitalis in guinea pigs

The antiviral activity of recombinant human macrophage CSF (M-CSF) against genital herpes simplex virus type-2 (HSV-2) infection in guinea pigs was investigated. M-CSF stimulates proliferation of human and guinea pig peripheral blood monocytes, specifically the plastic adherent esterase-positive mononuclear cells. When anti-HSV-2 activity of M-CSF was evaluated in guinea pigs by 6 daily injection (s.c.) of M-CSF at various doses (5 x 10(5) to 7 x 10(7) U/kg), we found 2 x 10(6) U/kg to be the optimum dose for protective efficacy against primary HSV-2 infection. Either at a lethal, 5 x 10(5) pfu, or sublethal 5 x 10(4) pfu of virus challenge, animals treated with the optimum regimen of M-CSF exhibited lower herpetic lesion scores (p less than 0.005), and lower mortality (p less than 0.025) than animals in placebo group. M-CSF treatment increased the HSV-infected cell killing activities of plastic-adherent mononuclear cells, indicating that in vivo administration of M-CSF may activate the antiviral effects of guinea pig macrophages that may play a role in protection against severity and mortality of herpetic disease.

Physical and biological characterization of antigen presenting liposome formulations: relative efficacy for the treatment of recurrent genital HSV-2 in guinea pigs

Antigen presenting liposomes (APLs) containing both liposome encapsulated (44%) and free (56%) recombinant glycoprotein D of herpes simplex virus type-2 (rgD-2) were characterized with respect to the interaction of the antigen with the lipid bilayer and the biological activities provided by each form of rgD-2. We found that free rgD-2 added externally to empty liposomes exhibited some biological activities both in vitro and in vivo, although we could not detect any significant adsorption and/or insertion of this form of rgD-2 into the lipid bilayer. Compared to APLs containing both forms of rgD-2, purified liposomes containing only encapsulated rgD-2 gave only 50% of the relative activity in vitro as measured by their ability to stimulate rgD-2 specific lymphocyte proliferation, and 67% of the relative activity in vivo as measured by their immunotherapeutic effect on recurrent genital HSV-2 disease in guinea pigs (P less than 0.05). These data indicate that while liposome encapsulated rgD-2 is essential for the elicitation of immunogenic responses, the free soluble rgD-2 in the APL formulation also acts in concert to generate an optimum immunotherapeutic efficacy.

Antigen-presenting liposomes are effective in treatment of recurrent herpes simplex virus genitalis in guinea pigs

The therapeutic and immunologic effects of a liposome preparation containing both a macrophage activator, muramyl-tripeptide-phosphatidylethanolamine, and a recombinant antigen, glycoprotein D of herpes simplex virus type 1, have been investigated. This preparation was tested in vitro for the ability to stimulate peripheral blood lymphocytes and in vivo for the control of recurrent herpes genitalis in guinea pigs. Our results show that the liposome-antigen-adjuvant preparation is capable of enhancing antigen-specific lymphocyte stimulation, which may be related to the observed 75% suppression of the frequency and severity of reactivation of recurrent herpes simplex virus type 2 genitalis compared with that of placebo controls.

Kinetic and ultrastructural studies of interactions of target-sensitive immunoliposomes with herpes simplex virus

The bilayer phase of dioleoylphosphatidylethanolamine (PE) can be stabilized with palmitoyl-IgG monoclonal antibody to the glycoprotein gD of the herpes simplex virus (HSV). Interactions of PE immunoliposomes with the target virions were characterized by analyzing the kinetics of lipid mixing, by liposomal content release, and by ultrastructural studies. As revealed by a resonance energy transfer assay, lipid mixing between PE immunoliposomes and virions was very rapid, with a second-order rate constant (kapp) of 0.173 (min)-1 (microgram/mL virus)-1. In comparison, content release from PE immunoliposomes was much slower and exhibited multiple-phase, mixed-order kinetics, indicating that liposome destabilization involved fusion of liposomes with HSV. The extent and the apparent rate of liposome destabilization were strongly dependent on liposome concentration. This was evident by the fact that only one to two liposomes were destabilized by each virus particle at low liposome concentration (0.1 microM). For higher liposome concentrations (1-10 microM), this value was 35-104. This finding implies that collision among the virus-bound liposomes is essential for the eventual collapse of PE immunoliposomes to form the hexagonal (HII) equilibrium phase which was observed using freeze-fracture electron microscopy. Studies employing soluble gD, immobilized on latex beads, indicated that a multivalent antigen source is essential for PE immunoliposome destabilization. Immediately after liposome-virus binding, fusion of liposome with the viral membrane then follows. Upon growth of the fusion complexes, which increase to 35-104 liposomes for each virus, an eventual collapse of the structure results, driving PE to its equilibrium structure of HII phase.

Interactions of target-sensitive immunoliposomes with herpes simplex virus. The foundation of a sensitive immunoliposome assay for the virus

Interactions between target-sensitive (TS) immunoliposomes and herpes simplex virus (HSV) were investigated. Target sensitivity of phosphatidylethanolamine (PE) immunoliposomes is a result of the ability of acylated monoclonal anti-HSV glycoprotein D (gD) to stabilize the bilayer phase of PE, whereas by itself, PE does not form stable liposomes (Ho, R. J. Y., Rouse, B. T., and Huang, L. (1986) Biochemistry 25, 5500-5506). Upon binding of these immunoliposomes to HSV antigen-containing gD, destabilization of PE immunoliposomes was observed. By encapsulating either a self-quenching fluorescent dye, calcein, or alkaline phosphatase inside the liposomal compartment, the HSV-induced destabilization of TS immunoliposomes was shown to be target-specific. Neither Sendai, Semliki Forest, nor Sindbis virus could significantly destabilize the TS immunoliposomes. Moreover, HSV-induced liposome destabilization could be inhibited by free anti-gD (the same antibody used in TS immunoliposomes) but not by monoclonal anti-HSV glycoprotein B, indicating that the interaction was antigen-specific. Destabilization could also be induced by binding to truncated gD (tgD), but only when in a multivalent form immobilized on latex beads. Truncated gD is a cloned, 312-amino acid fragment of HSV-gD that lacks the transmembrane segment. Preincubation of soluble tgD with the TS immunoliposomes failed to induce destabilization and, in addition, abolished the tgD-bead-induced destabilization. This finding strongly indicated that multivalent binding is essential for TS immunoliposome destabilization. Using alkaline phosphatase encapsulated in the liposomes, TS immunoliposomes could be used to detect HSV in fluid phase with 50% signal recorded at 5 microliters of 3.2 x 10(3) pfu/ml; at least 10-fold more sensitive than the standard double-antibody sandwich enzyme-linked immunosorbent assay. The interactions described here may be useful in designing a homogeneous and sensitive immunoliposome assay.

Target-sensitive immunoliposomes as an efficient drug carrier for antiviral activity

We have shown previously that target-sensitive immunoliposomes composed of palmitoyl antibody stabilized phosphatidylethanolamine bilayers could be destabilized by binding to the target cells (Ho, R. J. Y., Rouse, B. T., and Huang, L., Biochemistry (1986) 25, 5500-5506). Target-sensitive immunoliposome-encapsulated and free cytotoxic drugs of nucleoside analogs cytosine-beta-D-arabinoside (AraC) or acycloguanosine (acyclovir, ACV) were compared for their antiviral efficacy and cell cytotoxicity. Target-insensitive immunoliposomes and nontargeted liposomes were also investigated. When the mouse fibroblast L929 cells were infected at low multiplicity with herpes simplex virus, AraC encapsulated in target-sensitive immunoliposomes composed of transphosphatidylated egg phosphatidylethanolamine effectively inhibited virus replication and had far less cell cytotoxicity than free drug. As a measure of cytotoxicity, the drug concentration required to inhibit 50% of [3H]thymidine incorporation from 6 to 42 h (CD50) was determined. For free AraC, this value was 0.3 ng/ml, whereas for target-sensitive immunoliposome-encapsulated AraC, the CD50 exceeded 1 microgram/ml. However, target-sensitive immunoliposome-encapsulated AraC was virus inhibitory (50% effective dose = ED50) at 1.8 ng/ml. A free drug concentration of at least 1000-fold greater was required for comparable antiviral activity. A similar phenomenon was observed when ACV was administered via target-sensitive immunoliposomes. The CD50 values of the free and target-sensitive immunoliposome-encapsulated ACV were 12.5 ng/ml and 1.4 micrograms/ml, respectively, whereas the ED50 values of the free and target-sensitive immunoliposome-encapsulated ACV were 1.1 and 125 ng/ml, respectively. Consequently, our results indicated the superiority of target-sensitive immunoliposomes at drug delivery, especially when drugs were cytotoxic to cells. The use of liposomes of the target-insensitive variety provided some enhancement of activity, but this was several-fold less than that observed with target-sensitive immunoliposomes. In addition, the nucleoside transport inhibitors, p-nitrothiobenzylinosine and dipyridamole, were shown to inhibit the liposome-mediated antiviral activity of AraC. This finding indicated that site-specific cytosolic delivery of nucleoside analogs by target-sensitive immunoliposomes involved a cellular nucleoside transport system. A mechanism of action is proposed.

Trypsin induced destabilization of liposomes composed of dioleoylphosphatidylethanolamine and glycophorin

Destabilization of liposomes composed of phosphatidylethanolamine (PE) and purified glycophorin of human erythrocytes was studied with the release of an entrapped fluorescent dye, calcein. Proteolytic cleavage of liposomes by trypsin induced a rapid increase of turbidity and the leakage of calcein from the liposomes. Kinetic experiments indicated that the destabilization was a second order reaction, i.e. it required liposome collision. Using N-(7-nitro-2,1,3-benzoxadiazol-4-yl) PE as a fluorescent probe for the formation of hexagonal phase of PE, tryptic digestion of the liposomes resulted in a higher tendency of the PE bilayer to transform into the hexagonal phase. We propose that hexagonal (or inverted micellar) structures are involved in the trypsin induced liposome destabilization.

Forms of adenylate cyclase, activation and/or potentiation by forskolin

Activation of different forms of adenylate cyclases (AC) by forskolin and displacement of [14,15-3H]dihydroforskolin binding from membranes by forskolin in the absence or presence of specific stimulatory hormone and beta, gamma-imidoguanosine 5'-triphosphate (Gpp(NH)p) have been studied. These conditions have been used to generate forskolin dose-response curves of AC activation. A plot of enzyme activation versus apparent forskolin-binding showed a linear and a nonlinear relationship, respectively, in the absence or presence of the other two stimulators. The latter relationship can be fitted by two linear regression lines with a defined intercept, the slopes of which represent two distinct binding-activation (B-A) effects. The B-A effects of forskolin for rat adipocyte and liver membranes in the absence of stimulatory hormone and Gpp(NH)p were 10 and 8 (pmol X min-1) X (pmol)-1, respectively. The B-A effects for the same membranes in the presence of the other two stimulators were 69 (high) and 13 (low) (pmol X min-1) X (pmol)-1 for adipocyte membrane, and 83 (high) and 9 (low) (pmol X min-1) X (pmol)-1 for liver membrane. The ratio of potentiation of forskolin-activated enzyme activity to the unmodified forskolin-stimulated activity (P-A ratio) was determined without the binding data. At 3 microM forskolin, with and without 230 epinephrine and 10 microM Gpp(NH)p, the P-A ratio was 3.7, decreasing to 1.1 with the addition 100 microM forskolin. The line representing a high B-A effect and a resulting high P-A ratio appears to describe the interactions between forskolin and the AC stimulated by epinephrine and Gpp(NH)p. The line of low B-A effect may represent the interaction between forskolin and the basal AC. Two peaks of AC activity were eluted from forskolin-Sepharose column. They have apparent differences in sensitivity to Gpp(NH)p and affinity for forskolin. Based on the results available thus far, with consideration for known limitations of the methodology, a working model has been proposed for forskolin activation of AC.

A dose-response study of forskolin, stimulatory hormone, and guanosine triphosphate analog on adenylate cyclase from several sources

We have described relationships involving forskolin stimulation of adenylate cyclase (AC) from a variety of sources and the potentiation of forskolin effects by stimulatory hormones (glucagon, ACTH, and epinephrine) and beta, gamma-imidoguanosine 5'-triphosphate (Gpp(NH)p). The effects on AC were examined using membrane preparations of rabbit adipocytes, rat adipocytes, rat erythrocytes, and rat liver. Also examined was the AC of liver membranes of rat pretreated with pertussis toxin as well as that solubilized from rat liver membranes. Maximal forskolin stimulation of AC in all preparations studied revealed a consistent 10-fold increase in AC activity. The EC50 for forskolin was 10 microM for rat liver, 15 microM for rabbit and rat adipocytes and 17 microM for rat erythrocyte AC stimulation. In all cases the AC activity attained by forskolin stimulation was further enhanced by stimulatory hormones in a dose-dependent manner. Furthermore, a combination of all three activators (forskolin, stimulatory hormone, and Gpp(NH)p) resulted in an even greater overall stimulation to levels ranging from 25- to 30-fold over unstimulated activity levels. In the presence of saturating levels of each stimulatory hormone and Gpp(NH)p, the EC50 for forskolin diminished markedly to the range of 0.5 to 4.0 microM. In the absence of any apparent tissue specificity for forskolin stimulation, the general pattern of these results further implicates the catalytic site of the AC complex as the site of forskolin activation. Furthermore, activation of additional components of the complex by Gpp(NH)p and tissue specific hormones may further influence the AC activity and thereby potentiate the stimulation by forskolin.