Augmentation of cytotoxic responses by prostaglandin E2

Preclinical studies of antitumor prostaglandins by using human ovarian cancer cells

Pleiotropic actions of antitumor prostaglandins (PGs) on tumor cells are reviewed including our preclinical results focused on human ovarian cancer. Regarding inhibition of cell proliferation, antitumor PGs exerts its action as a G1 blocking agent. The cyclopentenone PGs inhibit myc oncogene expression while inhibiting the cell cycle progression and results in apoptotic cell death and growth inhibition. Cyclopentenone PGs inhibit growth of various tumors transplanted to mice or nude mice and show adjuvant effects to cis-diamminedichloroplatinum(II) (CDDP). In order to elucidate a role of antitumor PGs in immune systems, relevance of effects on tumor growth with those on the immune systems are also discussed with our results.

The effect of prostaglandin E2 and indomethacin on the cytotoxic response to mycobacterial antigens

The effect of prostaglandin E2 and indomethacin on the generation of cytotoxic T-lymphocytes in response to Mycobacterium tuberculosis (MTB) antigens was compared between healthy controls and rheumatoid arthritis patients. Peripheral blood mononuclear cells (PBMC) from 16 healthy individuals and 15 RA patients were stimulated for 7 days with an irradiated, sonicated preparation of MTB in the presence or absence of PGE2 or indomethacin and assayed for cytotoxic activity on autologous target cells prepulsed with MTB. The mean cytotoxic activity generated was lower in patients than in controls. Exogenous PGE2 suppressed the cytotoxicity directed against MTB pulsed targets in 12 of 16 controls, but in only 1 of 11 patients. Indomethacin enhanced this cytotoxicity in only 2 of 16 controls but in 6 of 10 RA patients. When effector cells were derived from the synovial fluid, PGE2 again had no effect and indomethacin enhanced the cytotoxicity. Our data suggest that the depressed cytotoxic response of RA patients to MTB may be due to the production of endogenous PGE2. Cyclooxygenase inhibitors commonly used in the treatment of RA may influence MTB induced cytotoxicity in patients. In addition to their anti-inflammatory effects within the joint, non-steroidal anti-inflammatory drugs may potentially enhance cytotoxic reactions which are induced by antigens, such as MTB cross-reactive heat shock proteins.

Modulation of human lymphocyte response to phytohemagglutinin by antineoplastic prostaglandins

The effects of antineoplstic prostaglandins (PGs) (PGE1, PGE2, PGA1, PGA2, delta 7-PGA1, PGD2, PGJ2 and delta 12-PGJ2) on human peripheral blood lymphocyte (PBL) responses to phytohemagglutinin (PHA) were studied in vitro. All PGs used in this study alone had no mitogenic effect on the PBL. The PBL response to PHA was significantly stimulated at low concentrations (10(-7) and 10(-8) M) of the PGE series while the high concentration (10(-5) M) markedly inhibited the PHA response. PGA1 and PGA2, metabolites of the PGE series, and also delta 7-PGA1 stimulated the PHA response in a dose-dependent manner between 10(-6) and 10(-8) M, and showed a significant stimulatory effect at 10(-6) M while significantly inhibiting the PHA response at 10(-5) M. Similarly, 10(-6) and 10(-7) M (but not 10(-8) M) of PGD2 stimulated significantly the PHA response. PGJ2 and delta 12-PGJ2, which are metabolites of PGD2, also stimulated the PHA response in a dose-dependent manner between 10(-6) and 10(-8) M, and had a significant stimulatory effect at 10(-6) and 10(-7) M. The degree of the stimulatory effect was most marked with the PGD2 series among the antineoplastic PGs examined in this study. On the other hand, PGs (PGF1 alpha and PGF2 alpha) having no antineoplastic effect did not show such effects on the PHA response. These results suggest that antineoplastic PGs may have immunoregulatory effects through negative and positive feedback.

Effects of prostaglandin E2 (PGE2) and drugs affecting PGE2 degradation on acute rejection of rat cardiac allografts

Systemic administration of prostaglandin E2 (PgE2) has been reported to prolong graft survival of heart transplants. We investigated the influence of systemic injection of two compounds which inhibit the endogenous degradation of PgE2 (CL42A and CL68A) and of local infusion of PgE2 into the transplant on the survival time of rat cardiac allografts. Both CL42A and CL68A gave increased graft survival time in two rat strain combinations, though this was not predictable in individual rats. Locally infused PgE2 gave slight, but not significant prolongation of graft survival in some recipients. Combined PgE2 and cyclosporin A, however, gave significant prolongation of graft survival time compared with cyclosporin A treatment alone. When local PgE2 treatment was begun 5 days after transplantation, graft survival time was prolonged in almost all the rats. Manipulation of the local PgE2 concentration thus seemed to have a positive effect on graft survival, possibly due to down-regulation of certain cells of the immune system by PgE2.

Purification of natural killer-like Kurloff cells and arachidonic acid metabolism

Pulmonary and splenic Kurloff cells have been purified from estrogen-treated guinea pig. Enzymatic digestion of lung tissue and mechanical dispersion of cells yielded about 650 x 10(6) viable cells. After centrifugal elutriation and centrifugation on continuous Percoll gradient, a population of high-density (1,100 g/ml) pulmonary Kurloff cells were obtained with high viability (approximately 99%) and purity (approximately 99%). Splenic Kurloff cells have been isolated by disruption of spleen tissue and centrifugation on continuous Percoll gradient. High-density splenic Kurloff cells (150 x 10(6) cells per spleen) were also obtained with high purity (approximately 99%) and viability (approximately 99%). Pulmonary and splenic Kurloff cells were incubated with various concentrations of arachidonic acid (10, 30 and 100 microM) in the absence or presence of 2 microM ionophore A23187. With 10 microM arachidonic acid the relative production of cyclooxygenase products was the following: TxB2 greater than PGE2 approximately PGI2. For an arachidonic acid concentration superior to 10 microM, the profile of release was PGE2 much greater than TxB2 greater than PGI2. Arachidonic acid metabolism through the 5-lipoxygenase pathway was also studied by incubating pulmonary or splenic Kurloff cells with 10 microM arachidonic acid in the absence or presence of 2 microM ionophore A23187, or in some experiments, with 2.5 microM leukotriene A4. Reverse phase HPLC profiles clearly indicated that high-density Kurloff cells did not express 5-lipoxygenase activity. However, these cells showed the ability to convert exogenous leukotriene A4 into leukotriene B4 suggesting the presence of LTA4 hydrolase activity. These data have been confirmed by a sensitive RIA method. This study constitutes the first report on the purification of pulmonary Kurloff cells and on arachidonic acid metabolism by these cells. The possible implications of Kurloff cells in various biological events are discussed.

The effect of prostaglandins and indomethacin on cytotoxic T-lymphocytes and their precursors

The effect of prostaglandins of the E and F series on the generation of cytotoxic T-lymphocytes (CTL) was investigated. High concentrations (10(-6)-10(-7) M) of prostaglandin E2(PGE2) inhibited the generation of both antigen-specific CTL and "activated" killers from precursor cells. Virtually no effect on the growth and cytotoxic activity of antigen-specific CTL clones was detectable. As with prostaglandins of the F series, lower concentrations of the E series (10(-8)-10(-9) M) enhanced the generation of antigen-specific CTL but inhibited the generation of lymphokine and spontaneously-activated CTL. When endogenous PG production was blocked with indomethacin, the generation of antigen-specific CTL was enhanced in bulk culture. Indomethacin also increased the frequency of allo-reactive CTL precursors and in anti-fluorescein responses it created conditions in which suppression was overridden. These results indicate that prostaglandins can exert both negative and positive regulatory effects on an antigen-specific cytotoxic response and can influence the apparent specificity of the cytotoxic cells that are generated.

The effects of E series prostaglandins on blastogenic responses in vitro and graft vs. host responses in vivo

In this study the ability of prostaglandin E1 (PGE1), Misoprostol (a stable analog of PGE1), and 16,16-dimethyl PGE2 (a stable analog of PGE2) to suppress immune responses in vitro and in vivo was determined. All of the compounds caused a titratable (10(-6) to 10(-9) M) suppression of Con A blastogenesis and the mixed lymphocyte response whereas there was only slight inhibition of the LPS response. When either 16,16-dimethyl PGE2 (30 ug/mouse) or Misoprostol (60 ug/mouse) was administered daily in vivo, there was a significant suppression of splenomegaly in F1 mice (C57Bl/6 x CBA) which had been injected with parental (C57Bl/6) spleen cells. We conclude that prostaglandins of the E series can function as immunosuppressive reagents both in vitro and in vivo. In the future they may serve to augment existing forms of immunosuppressive therapy.

Effects of polyunsaturated fatty acids and of their oxidation products on cell survival

The stimulatory, cytostatic and cytotoxic effects of polyunsaturated fatty acids, prostaglandins, thromboxanes, hydroperoxy fatty acids, hydroxy fatty acids and leukotrienes on normal and tumor cells are described. Their effects are related to the ability of the cells to undergo lipid peroxidation. The significance of controlled peroxidation of selected polyunsaturated fatty acids in the control of tumor development is examined. It is suggested that selected polyunsaturated fatty acids if used at appropriate concentrations may have a protective role against cancer development by inducing and/or mediating cytotoxic reactions in malignant cells directly or indirectly through the intermediacy of immune cells.

Effect of in vivo administration of prostaglandins and interferon on natural killer activity and on B-16 melanoma growth in mice

We investigated the effect on in vivo administration of 16,16-dimethyl-prostaglandin E2 (di-M-PGE2) alone and in combined treatment with alpha-beta interferon (IFN) on NK activity in normal, cyclophosphamide (CY)-treated, tumor bearing or irradiated and bone marrow reconstituted mice and on B-16 melanoma growth. Normal mice inoculated with IFN (30,000 U/mouse, 24 hr before testing) showed a significant increase in NK activity, while those treated with di-M-PGE2 (10 micrograms/mouse daily X 4 days) showed a suppressed NK response. No difference was observed between mice treated with di-M-PGE2 alone and those treated with di-M-PGE2 associated with IFN. In immunosuppressed animals single treatments were slightly (di-M-PGE2) or not (IFN) effective, while the combined administration of di-M-PGE2 and IFN caused a marked increase in NK activity. Moreover, di-M-PGE2 was able to accelerate the recovery rate of NK activity in bone marrow-reconstituted murine chimeras, suggesting that the synergistic effect of prostaglandins and IFN could derive from the action of di-M-PGE2 on progenitor pre-NK cells and of IFN on effector cells. Finally, we observed a good correlation between the enhancement of the NK activity and the tumor growth inhibition.

Antagonistic regulation of cytotoxic T lymphocyte activation by prostaglandin E2 and L-ornithine

Two macrophage-mediated immunoregulatory substances, prostaglandin E2 and L-ornithine, were found to mediate antagonistic effects. Both substances were previously shown to inhibit the activation of cytotoxic T lymphocytes under certain conditions. Our experiments now show that high doses of L-ornithine counteract the inhibitory effect of PGE2, and that PGE2 counteracts the inhibitory effect of high doses of L-ornithine; i.e. both substances can also augment cytotoxic responses in the presence of high concentrations of the other component. The direction of the immune regulatory effects of these substances is, therefore, expected to depend on the endogenous levels of PGE2 and L-ornithine in the individual animal at the site of immunization.