The Experts below are selected from a list of 93 Experts worldwide ranked by ideXlab platform
Barbara L. Pope - One of the best experts on this subject based on the ideXlab platform.
-
the immunostimulatory compound 7 allyl 8 oxoguanosine Loxoribine induces a distinct subset of murine cytokines
Cellular Immunology, 1995Co-Authors: Barbara L. Pope, J P Macintyre, E Kimball, Spencer H S Lee, Lubing Zhou, G R Taylor, Michael G. GoodmanAbstract:C8- and N7, C8-substituted guanine ribonucleosides comprise a class of molecules with potent immunostimulatory activity for a variety of humoral and cellular immune responses. Although it has been suggested that the immunostimulatory activity may be partially mediated by cytokine production, to date there has been no systematic evaluation of the spectrum of cytokines elicited by these nucleosides. In this study, we examine the cytokines produced by murine spleen cells in response to the di-substituted guanosine analog Loxoribine (7-allyl-8-oxoguanosine). First, the levels of cytokine mRNA in spleens from vehicle- or Loxoribine-treated mice were compared using PCR analysis with a panel of cytokine-specific primers. Enhancement of IL-1 alpha, TNF-alpha, TNF-beta, IL-6, IFN-alpha, and IFN-gamma mRNA was seen in the spleens of Loxoribine-treated mice. IL-12 mRNA responses were more complex, with an increase in the p40 chain and a decrease in the p35 chain. In contrast, no increase was seen for mRNA levels of IL-2, IL-3, IL-4, IL-5, IL-7, or GM-CSF. ELISA assays on the supernatants of Loxoribine-treated spleen cells demonstrated that IL-1 alpha, IL-6, TNF-alpha, and IFN-gamma were all produced in a dose-dependent fashion with TNF-alpha produced first, followed by IL-6 and IFN-gamma, and last by IL-1 alpha. IFN-alpha beta activity rose as quickly as TNF-alpha, leveling off at 8 to 12 hr, and was supplanted by a later-occurring surge of IFN-gamma production. IL-1 alpha, IL-6, TNF-alpha, and IFN-gamma were also detected in the sera of mice injected with Loxoribine. When antibodies against the relevant cytokines were tested, only anti-IFN-alpha beta inhibited NK activity or lymphocyte proliferation and, in both cases, activity was partially restored by the addition of exogenous IFN-alpha beta. Taken together, these data indicate that Loxoribine induces the production of a selective cohort of cytokines all of which have been shown to have immunostimulatory activity. However, only IFN-alpha beta appears to play a role in the enhancement of NK activity and lymphocyte proliferation.
-
7-Allyl-8-oxoguanosine (Loxoribine) inhibits the metastasis of B16 melanoma cells and has adjuvant activity in mice immunized with a B16 tumor vaccine
Cancer Immunology Immunotherapy, 1994Co-Authors: Barbara L. Pope, Joann Sigindere, Erika Chourmouzis, Philip Macintyre, Michael G. GoodmanAbstract:We have shown previously that Loxoribine exhibits adjuvant activity for B cells, activates natural killer (NK) cells, and enhances the activation of lymphokine-activated killer cells by interleukin-2 (IL-2). In this study, we examined Loxoribine for protective effects in a B16 melanoma lung tumor metastasis model. Significant inhibition of B16 metastasis was seen in mice given a single injection of 2 mg Loxoribine as late as day 3 of tumor growth but the greatest inhibition (96%) was seen in mice given four injections of Loxoribine on alternate days starting the day before tumor injection. In experiments in which both IL-2 and Loxoribine were administered, both agents were active when tested alone, but the combination of IL-2 and Loxoribine gave significantly greater inhibition of metastasis. Loxoribine partially inhibited the development of tumors in mice that had been depleted of NK cells by the administration of anti-asialo-GM1 or anti-NK1. 1 antibodies and in NK-deficient beige mice. In all cases, protection was seen only when smaller tumor inocula were injected. Taken together, these data suggest that both NK and non-NK cell populations or effector mechanisms with antitumor activity were activated by Loxoribine. Since substituted guanosine analogs have been shown to have adjuvant activity in B cell systems, we evaluated whether Loxoribine was active as an adjuvant in a tumor protection model. Mice immunized with both irradiated tumor cells and Loxoribine developed a significantly lower number of lung tumors when challenged by live B16 tumor cells, whereas mice injected with either vaccine or Loxoribine alone were not protected. There was a clear dose response seen with both Loxoribine and the vaccine preparations. These data suggest that Loxoribine may be useful in tumor therapy as an immunomodulator or as an adjuvant for use with tumor vaccines.
-
Guanosine Derivatives as Immunostimulants. Discovery of Loxoribine
Nucleosides and Nucleotides, 1994Co-Authors: Robert Chen, Michael G. Goodman, Dennis C. Argentieri, Stanley C Bell, Levelle E. Burr, Jon H. Come, Jacquelyn H. Goodman, Dieter H. Klaubert, Maryanoff Bruce E, Barbara L. PopeAbstract:Abstract 7-Allyl-8-oxoguanosine (Loxoribine, 5) was selected from a series of guanosine derivatives for further evaluation as an immunostimulant. Numerous related analogs were also synthesized and evaluated: 2′,3′-ketals of 5 are particularly interesting because they are active, apparently without being cleaved to the free nucleoside.
-
Loxoribine 7 allyl 8 oxoguanosine activates natural killer cells and primes cytolytic precursor cells for activation by il 2
Journal of Immunology, 1993Co-Authors: Barbara L. Pope, Erika Chourmouzis, L Victorino, J P Macintyre, R J Capetola, Catherine Y LauAbstract:Guanine ribonucleosides that have been substituted at the C8 position with bromine or thiol groups have been shown previously to activate NK cells and to act as sparing agents for IL-2 in the generation of LAK cells. Herein, we examined a disubstituted guanosine, 7-allyl-8-oxoguanosine (Loxoribine), for the ability to activate NK cells and to interact with IL-2 in the generation of LAK cells. Loxoribine enhanced the NK activity of murine spleen cells with optimal activity occurring after 10 h of culture at concentrations ranging from 50 to 150 microM. The response was, however, short lived, approaching baseline levels by 24 h of culture. In contrast, if spleen cells were cultured with a suboptimal concentration of IL-2 (10 U/ml) in combination with Loxoribine, a prolonged and enhanced cytolytic activity was seen. The enhancement was greatest if the Loxoribine and IL-2 were both added to the cultures at the beginning of the incubation period. Analysis of the expression of the alpha-chain of the IL-2 receptor after Loxoribine stimulation indicated that gene transcription was enhanced within 4 h, and cell surface expression was observed on NK1.1+ Thy1+ and NK1.1+ Thy1- cell populations within 24 h of Loxoribine treatment. The priming of LAK cell precursors by Loxoribine did not appear to be mediated by IFN-alpha/beta, because anti-IFN antibodies did not block either the activation of cytolytic cells by IL-2 or the expression of IL-2 receptors after culture with Loxoribine. These data suggest that one mechanism by which cytolytic precursor cells are primed by Loxoribine to respond to IL-2 faster and with enhanced cytolytic activity may be through the expression of high affinity IL-2 receptors due to the up-regulation of the alpha-chain.
-
in vivo activation of natural killer cells and priming of il 2 responsive cytolytic cells by Loxoribine 7 allyl 8 oxoguanosine
Cellular Immunology, 1993Co-Authors: Barbara L. Pope, Joann Sigindere, Erika Chourmouzis, R J Capetola, Philip J Macintyre, Catherine Y LauAbstract:Abstract Guanine ribonucleosides which have been substituted at the N7 and/or C8 positions have been shown previously to activate natural killer (NK) cells and to act as sparing agents for interleukin-2 (IL-2) in the in vitro generation of lymphokine activated killer (LAK) cells. In this paper we examined a disubstituted guanosine, 7-allyl-8-oxoguanosine (Loxoribine), for the ability to activate NK cells and to interact with IL-2 in the generation of LAK cells in vivo . Following iv administration, Loxoribine enhanced murine splenic NK activity in a dose-related fashion, with optimal responses occurring at 3 mg/mouse. Enhanced lysis of YAC-1 cells was seen within 6 hr of injection and NK activity remained elevated for over 96 hr. Mature B and T cells were not required for NK activation since SCID mice responded to Loxoribine within the same dose range as did the normal, immunocompetent mice. Both effector and precursor cells were eliminated by the administration of anti-asialo GMI antibodies and NK activation was totally blocked in mice injected with anti-NK 1.1 antibodies. To test whether Loxoribine would act as a sparing agent for IL-2 stimulated LAK activation, mice were injected with 2 mg Loxoribine followed by twice daily administration of 10,000 units IL-2. In assays performed 48, 72, and 96 hr after injection of Loxoribine, the cytolytic activity with the combination therapy exceeded the activity expected from the algebraic sum of the responses to the individual agents. Single injections of 2 mg Loxoribine and 25,000 units IL-2 also stimulated NK/LAK activity, but the greatest enhancement was seen when Loxoribine was administered 24 hr before the IL-2. Analysis of mRNA transcripts for the α chain of the IL-2 receptor indicated that gene transcription was enhanced within hours of Loxoribine administration.
Catherine Y Lau - One of the best experts on this subject based on the ideXlab platform.
-
Loxoribine 7 allyl 8 oxoguanosine activates natural killer cells and primes cytolytic precursor cells for activation by il 2
Journal of Immunology, 1993Co-Authors: Barbara L. Pope, Erika Chourmouzis, L Victorino, J P Macintyre, R J Capetola, Catherine Y LauAbstract:Guanine ribonucleosides that have been substituted at the C8 position with bromine or thiol groups have been shown previously to activate NK cells and to act as sparing agents for IL-2 in the generation of LAK cells. Herein, we examined a disubstituted guanosine, 7-allyl-8-oxoguanosine (Loxoribine), for the ability to activate NK cells and to interact with IL-2 in the generation of LAK cells. Loxoribine enhanced the NK activity of murine spleen cells with optimal activity occurring after 10 h of culture at concentrations ranging from 50 to 150 microM. The response was, however, short lived, approaching baseline levels by 24 h of culture. In contrast, if spleen cells were cultured with a suboptimal concentration of IL-2 (10 U/ml) in combination with Loxoribine, a prolonged and enhanced cytolytic activity was seen. The enhancement was greatest if the Loxoribine and IL-2 were both added to the cultures at the beginning of the incubation period. Analysis of the expression of the alpha-chain of the IL-2 receptor after Loxoribine stimulation indicated that gene transcription was enhanced within 4 h, and cell surface expression was observed on NK1.1+ Thy1+ and NK1.1+ Thy1- cell populations within 24 h of Loxoribine treatment. The priming of LAK cell precursors by Loxoribine did not appear to be mediated by IFN-alpha/beta, because anti-IFN antibodies did not block either the activation of cytolytic cells by IL-2 or the expression of IL-2 receptors after culture with Loxoribine. These data suggest that one mechanism by which cytolytic precursor cells are primed by Loxoribine to respond to IL-2 faster and with enhanced cytolytic activity may be through the expression of high affinity IL-2 receptors due to the up-regulation of the alpha-chain.
-
in vivo activation of natural killer cells and priming of il 2 responsive cytolytic cells by Loxoribine 7 allyl 8 oxoguanosine
Cellular Immunology, 1993Co-Authors: Barbara L. Pope, Joann Sigindere, Erika Chourmouzis, R J Capetola, Philip J Macintyre, Catherine Y LauAbstract:Abstract Guanine ribonucleosides which have been substituted at the N7 and/or C8 positions have been shown previously to activate natural killer (NK) cells and to act as sparing agents for interleukin-2 (IL-2) in the in vitro generation of lymphokine activated killer (LAK) cells. In this paper we examined a disubstituted guanosine, 7-allyl-8-oxoguanosine (Loxoribine), for the ability to activate NK cells and to interact with IL-2 in the generation of LAK cells in vivo . Following iv administration, Loxoribine enhanced murine splenic NK activity in a dose-related fashion, with optimal responses occurring at 3 mg/mouse. Enhanced lysis of YAC-1 cells was seen within 6 hr of injection and NK activity remained elevated for over 96 hr. Mature B and T cells were not required for NK activation since SCID mice responded to Loxoribine within the same dose range as did the normal, immunocompetent mice. Both effector and precursor cells were eliminated by the administration of anti-asialo GMI antibodies and NK activation was totally blocked in mice injected with anti-NK 1.1 antibodies. To test whether Loxoribine would act as a sparing agent for IL-2 stimulated LAK activation, mice were injected with 2 mg Loxoribine followed by twice daily administration of 10,000 units IL-2. In assays performed 48, 72, and 96 hr after injection of Loxoribine, the cytolytic activity with the combination therapy exceeded the activity expected from the algebraic sum of the responses to the individual agents. Single injections of 2 mg Loxoribine and 25,000 units IL-2 also stimulated NK/LAK activity, but the greatest enhancement was seen when Loxoribine was administered 24 hr before the IL-2. Analysis of mRNA transcripts for the α chain of the IL-2 receptor indicated that gene transcription was enhanced within hours of Loxoribine administration.
-
In vivo enhancement of murine natural killer cell activity by 7-allyl-8-oxoguanosine (Loxoribine).
International journal of immunopharmacology, 1992Co-Authors: Barbara L. Pope, Joann Sigindere, Erika Chourmouzis, R J Capetola, Catherine Y LauAbstract:Abstract 7-Allyl-8-oxoguanosine (Loxoribine) is a novel immunostimulatory compound which has been shown previously to enhance the antibody synthesis of antigen-stimulated B-lymphocytes. In this report, Loxoribine was tested for the ability to activate murine natural killer (NK) cells. In studies in which mice were given a single subcutaneous (s.c.) or intravenous (i.v.) injection of Loxoribine, splenic NK cell activity was increased in a dose-related manner with clear enhancement seen within 2 h of drug administration. The enhancement was optimal at 48 h but persisted for a minimum of 4 days. Slow and continuous administration of Loxoribine via subcutaneously implanted infusion pumps successfully enhanced the NK activity for several days after all of the pump contents had been delivered. Peak NK responses were seen following s.c. or i.v. administration of 2–3 mg Loxoribine per mouse in sesame oil, intralipid, or saline vehicles. Significant oral activity was seen after the administration of 8–10 mg/mouse in sesame oil or intralipid. The in vivo enhancement of NK activity was observed in spleen, blood, and bone marrow but was negligible in lymph nodes and thymus. Multiple injections of optimal concentrations of Loxoribine did not tend to enhance the NK activity above that seen with a single injection, suggesting that the timing of injections was critical for optimal responsiveness.
Sante Tura - One of the best experts on this subject based on the ideXlab platform.
-
cytotoxic combination of Loxoribine with fludarabine and mafosfamide on freshly isolated b chronic lymphocytic leukemia cells
Leukemia & Lymphoma, 1999Co-Authors: Annalisa Pellacani, Patrizia Tosi, Pier Luigi Zinzani, Emanuela Ottaviani, Massimo Magagnoli, Patrizia Albertini, Sante TuraAbstract:Fludarabine has shown a definite clinical activity in B-cell chronic lymphocytic leukemia (B-CLL). Recently it has been demonstrated that Loxoribine, a guanine ribonucleotide derivative, is able to increase the cytotoxicity of fludarabine in B-CLL cells, in vitro. We have here extended these findings by testing the activity of Loxoribine in combination with fludarabine and mafosfamide. As we have previously demonstrated, Loxoribine enhances the activity of fludarabine at all concentrations, while only lower doses of mafosfamide seem to be positively affected by Loxoribine. The combination of fludarabine and mafosfamide is synergistic on CLL cells, and the cytotoxic activity is increased by the addition of Loxoribine. We have also evaluated the pro-apoptotic activity of each drug, both alone and in combination; these results are concordant with the cytotoxicity data, thus demonstrating that, even though Loxoribine is more active in combination with fludarabine than with mafosfamide, the efficacy of the triple combination is higher than that obtained with any other agent alone or in double combination.
-
Loxoribine affects fludarabine activity on freshly isolated b chronic lymphocytic leukemia cells
Leukemia & Lymphoma, 1997Co-Authors: Patrizia Tosi, Pier Luigi Zinzani, Annalisa Pellacani, Emanuela Ottaviani, Massimo Magagnoli, Sante TuraAbstract:Purine analogues like fludarabine have been shown to be superior to conventional therapy for B-cell chronic lymphocytic leukemia (B-CLL). In order to improve the activity of fludarabine, we tested its combination with Loxoribine, a guanine ribonucleotide derivative, known to enhance the sensitivity of B-CLL cells to cytotoxic drugs. B-CLL cells from 6 patients were studied; co-incubation with Loxoribine 100μ M increased the activity of fludarabine by 12% to 48%, as demonstrated by XTT colorimetric assay; while 1000μM Loxoribine exerted a protective effect. Accordingly, fludarabine-induced apoptosis was enhanced by the addition of Loxoribine 100μM (39% increase). These results indicate that the combination of Loxoribine and fludarabine could be of interest in B-CLL
Erika Chourmouzis - One of the best experts on this subject based on the ideXlab platform.
-
7-Allyl-8-oxoguanosine (Loxoribine) inhibits the metastasis of B16 melanoma cells and has adjuvant activity in mice immunized with a B16 tumor vaccine
Cancer Immunology Immunotherapy, 1994Co-Authors: Barbara L. Pope, Joann Sigindere, Erika Chourmouzis, Philip Macintyre, Michael G. GoodmanAbstract:We have shown previously that Loxoribine exhibits adjuvant activity for B cells, activates natural killer (NK) cells, and enhances the activation of lymphokine-activated killer cells by interleukin-2 (IL-2). In this study, we examined Loxoribine for protective effects in a B16 melanoma lung tumor metastasis model. Significant inhibition of B16 metastasis was seen in mice given a single injection of 2 mg Loxoribine as late as day 3 of tumor growth but the greatest inhibition (96%) was seen in mice given four injections of Loxoribine on alternate days starting the day before tumor injection. In experiments in which both IL-2 and Loxoribine were administered, both agents were active when tested alone, but the combination of IL-2 and Loxoribine gave significantly greater inhibition of metastasis. Loxoribine partially inhibited the development of tumors in mice that had been depleted of NK cells by the administration of anti-asialo-GM1 or anti-NK1. 1 antibodies and in NK-deficient beige mice. In all cases, protection was seen only when smaller tumor inocula were injected. Taken together, these data suggest that both NK and non-NK cell populations or effector mechanisms with antitumor activity were activated by Loxoribine. Since substituted guanosine analogs have been shown to have adjuvant activity in B cell systems, we evaluated whether Loxoribine was active as an adjuvant in a tumor protection model. Mice immunized with both irradiated tumor cells and Loxoribine developed a significantly lower number of lung tumors when challenged by live B16 tumor cells, whereas mice injected with either vaccine or Loxoribine alone were not protected. There was a clear dose response seen with both Loxoribine and the vaccine preparations. These data suggest that Loxoribine may be useful in tumor therapy as an immunomodulator or as an adjuvant for use with tumor vaccines.
-
Loxoribine 7 allyl 8 oxoguanosine activates natural killer cells and primes cytolytic precursor cells for activation by il 2
Journal of Immunology, 1993Co-Authors: Barbara L. Pope, Erika Chourmouzis, L Victorino, J P Macintyre, R J Capetola, Catherine Y LauAbstract:Guanine ribonucleosides that have been substituted at the C8 position with bromine or thiol groups have been shown previously to activate NK cells and to act as sparing agents for IL-2 in the generation of LAK cells. Herein, we examined a disubstituted guanosine, 7-allyl-8-oxoguanosine (Loxoribine), for the ability to activate NK cells and to interact with IL-2 in the generation of LAK cells. Loxoribine enhanced the NK activity of murine spleen cells with optimal activity occurring after 10 h of culture at concentrations ranging from 50 to 150 microM. The response was, however, short lived, approaching baseline levels by 24 h of culture. In contrast, if spleen cells were cultured with a suboptimal concentration of IL-2 (10 U/ml) in combination with Loxoribine, a prolonged and enhanced cytolytic activity was seen. The enhancement was greatest if the Loxoribine and IL-2 were both added to the cultures at the beginning of the incubation period. Analysis of the expression of the alpha-chain of the IL-2 receptor after Loxoribine stimulation indicated that gene transcription was enhanced within 4 h, and cell surface expression was observed on NK1.1+ Thy1+ and NK1.1+ Thy1- cell populations within 24 h of Loxoribine treatment. The priming of LAK cell precursors by Loxoribine did not appear to be mediated by IFN-alpha/beta, because anti-IFN antibodies did not block either the activation of cytolytic cells by IL-2 or the expression of IL-2 receptors after culture with Loxoribine. These data suggest that one mechanism by which cytolytic precursor cells are primed by Loxoribine to respond to IL-2 faster and with enhanced cytolytic activity may be through the expression of high affinity IL-2 receptors due to the up-regulation of the alpha-chain.
-
in vivo activation of natural killer cells and priming of il 2 responsive cytolytic cells by Loxoribine 7 allyl 8 oxoguanosine
Cellular Immunology, 1993Co-Authors: Barbara L. Pope, Joann Sigindere, Erika Chourmouzis, R J Capetola, Philip J Macintyre, Catherine Y LauAbstract:Abstract Guanine ribonucleosides which have been substituted at the N7 and/or C8 positions have been shown previously to activate natural killer (NK) cells and to act as sparing agents for interleukin-2 (IL-2) in the in vitro generation of lymphokine activated killer (LAK) cells. In this paper we examined a disubstituted guanosine, 7-allyl-8-oxoguanosine (Loxoribine), for the ability to activate NK cells and to interact with IL-2 in the generation of LAK cells in vivo . Following iv administration, Loxoribine enhanced murine splenic NK activity in a dose-related fashion, with optimal responses occurring at 3 mg/mouse. Enhanced lysis of YAC-1 cells was seen within 6 hr of injection and NK activity remained elevated for over 96 hr. Mature B and T cells were not required for NK activation since SCID mice responded to Loxoribine within the same dose range as did the normal, immunocompetent mice. Both effector and precursor cells were eliminated by the administration of anti-asialo GMI antibodies and NK activation was totally blocked in mice injected with anti-NK 1.1 antibodies. To test whether Loxoribine would act as a sparing agent for IL-2 stimulated LAK activation, mice were injected with 2 mg Loxoribine followed by twice daily administration of 10,000 units IL-2. In assays performed 48, 72, and 96 hr after injection of Loxoribine, the cytolytic activity with the combination therapy exceeded the activity expected from the algebraic sum of the responses to the individual agents. Single injections of 2 mg Loxoribine and 25,000 units IL-2 also stimulated NK/LAK activity, but the greatest enhancement was seen when Loxoribine was administered 24 hr before the IL-2. Analysis of mRNA transcripts for the α chain of the IL-2 receptor indicated that gene transcription was enhanced within hours of Loxoribine administration.
-
In vivo enhancement of murine natural killer cell activity by 7-allyl-8-oxoguanosine (Loxoribine).
International journal of immunopharmacology, 1992Co-Authors: Barbara L. Pope, Joann Sigindere, Erika Chourmouzis, R J Capetola, Catherine Y LauAbstract:Abstract 7-Allyl-8-oxoguanosine (Loxoribine) is a novel immunostimulatory compound which has been shown previously to enhance the antibody synthesis of antigen-stimulated B-lymphocytes. In this report, Loxoribine was tested for the ability to activate murine natural killer (NK) cells. In studies in which mice were given a single subcutaneous (s.c.) or intravenous (i.v.) injection of Loxoribine, splenic NK cell activity was increased in a dose-related manner with clear enhancement seen within 2 h of drug administration. The enhancement was optimal at 48 h but persisted for a minimum of 4 days. Slow and continuous administration of Loxoribine via subcutaneously implanted infusion pumps successfully enhanced the NK activity for several days after all of the pump contents had been delivered. Peak NK responses were seen following s.c. or i.v. administration of 2–3 mg Loxoribine per mouse in sesame oil, intralipid, or saline vehicles. Significant oral activity was seen after the administration of 8–10 mg/mouse in sesame oil or intralipid. The in vivo enhancement of NK activity was observed in spleen, blood, and bone marrow but was negligible in lymph nodes and thymus. Multiple injections of optimal concentrations of Loxoribine did not tend to enhance the NK activity above that seen with a single injection, suggesting that the timing of injections was critical for optimal responsiveness.
Michael G. Goodman - One of the best experts on this subject based on the ideXlab platform.
-
the immunostimulatory compound 7 allyl 8 oxoguanosine Loxoribine induces a distinct subset of murine cytokines
Cellular Immunology, 1995Co-Authors: Barbara L. Pope, J P Macintyre, E Kimball, Spencer H S Lee, Lubing Zhou, G R Taylor, Michael G. GoodmanAbstract:C8- and N7, C8-substituted guanine ribonucleosides comprise a class of molecules with potent immunostimulatory activity for a variety of humoral and cellular immune responses. Although it has been suggested that the immunostimulatory activity may be partially mediated by cytokine production, to date there has been no systematic evaluation of the spectrum of cytokines elicited by these nucleosides. In this study, we examine the cytokines produced by murine spleen cells in response to the di-substituted guanosine analog Loxoribine (7-allyl-8-oxoguanosine). First, the levels of cytokine mRNA in spleens from vehicle- or Loxoribine-treated mice were compared using PCR analysis with a panel of cytokine-specific primers. Enhancement of IL-1 alpha, TNF-alpha, TNF-beta, IL-6, IFN-alpha, and IFN-gamma mRNA was seen in the spleens of Loxoribine-treated mice. IL-12 mRNA responses were more complex, with an increase in the p40 chain and a decrease in the p35 chain. In contrast, no increase was seen for mRNA levels of IL-2, IL-3, IL-4, IL-5, IL-7, or GM-CSF. ELISA assays on the supernatants of Loxoribine-treated spleen cells demonstrated that IL-1 alpha, IL-6, TNF-alpha, and IFN-gamma were all produced in a dose-dependent fashion with TNF-alpha produced first, followed by IL-6 and IFN-gamma, and last by IL-1 alpha. IFN-alpha beta activity rose as quickly as TNF-alpha, leveling off at 8 to 12 hr, and was supplanted by a later-occurring surge of IFN-gamma production. IL-1 alpha, IL-6, TNF-alpha, and IFN-gamma were also detected in the sera of mice injected with Loxoribine. When antibodies against the relevant cytokines were tested, only anti-IFN-alpha beta inhibited NK activity or lymphocyte proliferation and, in both cases, activity was partially restored by the addition of exogenous IFN-alpha beta. Taken together, these data indicate that Loxoribine induces the production of a selective cohort of cytokines all of which have been shown to have immunostimulatory activity. However, only IFN-alpha beta appears to play a role in the enhancement of NK activity and lymphocyte proliferation.
-
Loxoribine induces chronic lymphocytic leukemia b cells to traverse the cell cycle
Blood, 1994Co-Authors: Michael G. Goodman, Susan B Wormsley, John C Spinosa, Lawrence D PiroAbstract:Leukemic B cells from a majority of patients with chronic lymphocytic leukemia (CLL) enter the cell cycle upon stimulation in vitro with Loxoribine, a potent 7,8-disubstituted guanine ribonucleoside immunostimulant. In the absence of added costimulants, a proportion of these cells become activated and undergo DNA synthesis and mitosis accompanied by a marked increase in expression of an array of cell surface activation antigens. The resultant activated B-CLL cells exhibit greatly enhanced sensitivity to cycle-active cytotoxic drugs. This approach may be of potential value in the therapy of CLL.
-
7-Allyl-8-oxoguanosine (Loxoribine) inhibits the metastasis of B16 melanoma cells and has adjuvant activity in mice immunized with a B16 tumor vaccine
Cancer Immunology Immunotherapy, 1994Co-Authors: Barbara L. Pope, Joann Sigindere, Erika Chourmouzis, Philip Macintyre, Michael G. GoodmanAbstract:We have shown previously that Loxoribine exhibits adjuvant activity for B cells, activates natural killer (NK) cells, and enhances the activation of lymphokine-activated killer cells by interleukin-2 (IL-2). In this study, we examined Loxoribine for protective effects in a B16 melanoma lung tumor metastasis model. Significant inhibition of B16 metastasis was seen in mice given a single injection of 2 mg Loxoribine as late as day 3 of tumor growth but the greatest inhibition (96%) was seen in mice given four injections of Loxoribine on alternate days starting the day before tumor injection. In experiments in which both IL-2 and Loxoribine were administered, both agents were active when tested alone, but the combination of IL-2 and Loxoribine gave significantly greater inhibition of metastasis. Loxoribine partially inhibited the development of tumors in mice that had been depleted of NK cells by the administration of anti-asialo-GM1 or anti-NK1. 1 antibodies and in NK-deficient beige mice. In all cases, protection was seen only when smaller tumor inocula were injected. Taken together, these data suggest that both NK and non-NK cell populations or effector mechanisms with antitumor activity were activated by Loxoribine. Since substituted guanosine analogs have been shown to have adjuvant activity in B cell systems, we evaluated whether Loxoribine was active as an adjuvant in a tumor protection model. Mice immunized with both irradiated tumor cells and Loxoribine developed a significantly lower number of lung tumors when challenged by live B16 tumor cells, whereas mice injected with either vaccine or Loxoribine alone were not protected. There was a clear dose response seen with both Loxoribine and the vaccine preparations. These data suggest that Loxoribine may be useful in tumor therapy as an immunomodulator or as an adjuvant for use with tumor vaccines.
-
Guanosine Derivatives as Immunostimulants. Discovery of Loxoribine
Nucleosides and Nucleotides, 1994Co-Authors: Robert Chen, Michael G. Goodman, Dennis C. Argentieri, Stanley C Bell, Levelle E. Burr, Jon H. Come, Jacquelyn H. Goodman, Dieter H. Klaubert, Maryanoff Bruce E, Barbara L. PopeAbstract:Abstract 7-Allyl-8-oxoguanosine (Loxoribine, 5) was selected from a series of guanosine derivatives for further evaluation as an immunostimulant. Numerous related analogs were also synthesized and evaluated: 2′,3′-ketals of 5 are particularly interesting because they are active, apparently without being cleaved to the free nucleoside.
