Structure-immunosuppressive activity relationships of new analogues of 15-deoxyspergualin. 2. Structural modifications of the spermidine moiety.

A series of new analogues of 15-deoxyspergualin (DSG), an immunosuppressive agent commercialized in Japan, was synthesized and tested in a graft-versus-host disease (GVHD) model in mice. Various substitutions of the spermidine "D" region were made in order to determine its optimum structure in terms of in vivo immunosuppressive activity. Various positions of methylation were first investigated leading to the discovery of the monomethylated malonic derivative 56h in which the pro-R hydrogen of the methylene alpha to the primary amine of the spermidine moiety has been replaced by a methyl group. Synthesis of the similarly methylated analogue of the previously reported glycolic derivative LF 08-0299 afforded 60e which demonstrated a powerful activity at a dose as low as 0.3 mg/kg in the GVHD model and was much more potent than DSG in the demanding heart allotransplantation model in rats. The improvement of in vivo activity was supposed to be related to an increase of the metabolic stability of the methylated analogues compared to the parent molecules. Due to its very low active dose, compatible with a subcutaneous administration in humans, and its favorable pharmacological and toxicological profile, 60e was selected as a candidate for clinical evaluation.

Structure-immunosuppressive activity relationships of new analogues of 15-deoxyspergualin. 1. Structural modifications of the hydroxyglycine moiety.

A series of new analogues of 15-deoxyspergualin (DSG), an immunosuppressive agent currently commercialized in Japan, was synthesized and tested in a graft-versus-host disease (GVHD) model in mice. Using the general concept of bioisosteric replacement, variations of the hydroxyglycine central "C" region were made in order to determine its optimum structure in terms of in vivo immunosuppressive activity. By this way, the malonic derivative 13a was discovered as the first example of a new series of potent immunosuppressive agents encompassing a retro-amide bond linked to the hexyl-guanidino moiety. Structure-activity relationships of this series were studied by synthesizing compounds 13g-i and 13k-s. Variation of the "right-amide" of 13a led to the urea 19a and the carbamates 23 and 27a which proved to be equally active as DSG in our GVHD model. Finally 27a was found to be the most potent derivative, being slightly more active than DSG in a heart allotransplantation model in rats. Due to the absence of chiral center in its structure and to its improved chemical stability compared to DSG, 27a was selected as a candidate for clinical evaluation.

T cell repertoire expression in murine recipients of bone marrow transplant after LF 08-0299 (Tresperimus) administration.

LF 08-0299 (Tresperimus), a novel immunosuppressive compound, has been previously shown to prevent graft-versus-host disease in murine models. In this study, we investigated the influence of LF 08-0299 on the TCR Vbeta repertoire of irradiated F1 recipient mice reconstituted with either syngeneic or parental bone marrow cells. We showed that a partial blockade of thymic differentiation occurred in normal mice under treatment at the transition CD4-/CD8- to CD4+/CD8+, and that this blockade was fully reversible. Despite the effect on the thymus, normal T cell repertoire negative selection was preserved following syngeneic bone marrow transplantation. We further assessed whether LF 08-0299 administration could modify Vbeta T cell expression in irradiated recipients reconstituted with parental bone marrow cells. In our murine parental to F1 transplant model, abnormal TCR Vbeta3, Vbeta5, Vbeta6 and Vbeta11 expression was demonstrated in peripheral lymph nodes of irradiated recipients. Moreover, Vbeta6 and Vbeta3 T cell populations were overexpressed. Administration of LF 08-0299 modified the pattern of Vbeta T cell expression. The expansion of Vbeta6 T cells was selectively inhibited under LF 08-0299 therapy and, in contrast, Vbeta5 T cells were overexpressed. Lymph node histological analysis showed that LF 08-0299 administration fully prevented the graft-versus-host reaction occurring in untreated recipient mice.

Tolerance in a rat cardiac allograft model after short-term treatment with LF 08-0299. Absence of clonal deletion and evidence of CD4+ suppressor cells.

LF 08-0299 is a new immunosuppressive compound. In a fully mismatched rat cardiac allograft model (Dark Agouti [DA]-->Lewis [LEW]), long-term unresponsiveness was observed after LF 08-0299 short-term treatment (20 days). Survival of additional cardiac and skin DA allografts, and rejection of third-party (Brown Norway [BN]) skin allografts demonstrated induction of a donor-specific tolerance state. The aim of this study was to investigate mechanisms of cardiac acceptance in this model. LEW rats with long-term surviving heart grafts (LTS LEW) were examined for their immune proliferative and cytotoxic responses toward donors (DA) and third-party (BN) antigens. Normal proliferative responses were observed and limiting dilution analysis did not reveal a reduction of T cytotoxic cell precursors. In our model, tolerance exists despite the presence of cells reactive with donor alloantigens. In vivo adoptive transfer of serum from LTS LEW failed to transfer unresponsiveness, indicating that serum factors do not seem to be involved in tolerance maintenance. Transfer of spleen cells, obtained from LTS LEW, showed specific prolongation of DA cardiac allografts in syngeneic hosts. Moreover, these cells were able to induce the rejection of third-party BN grafts. These results suggest that although LTS LEW possessed suppressor cells, they remained immunocompetent in recognizing and responding to third-party alloantigens. Purified CD4+ cells transferred unresponsiveness to secondary hosts, but CD8+ cells did not. Taken together, these results suggest that tolerance to donor alloantigens after treatment with LF 08-0299 in the rat cardiac allograft model is most likely due to induction of specific CD4+ suppressor cell activity, rather than induction of suppressive serum factor and selective elimination of antidonor helper or cytotoxic cell precursors (clonal deletion).

Prevention of lethal graft-versus-host disease following allogeneic bone marrow transplantation in mice by short course administration of LF 08-0299.

We investigated the ability of LF 08--0299, a new immunosuppressive compound, to prevent murine graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT). A short term LF 08--0299 treatment at optimal dosage protected more than 75% of recipient mice from lethal GVHD induced either across minor antigens alone or the full H2 barrier. Furthermore, LF 08--0299 still prevented lethal GVHD when treatment was delayed to 10 days post-BMT. Long-term LF 08--0299-treated survivors were free of clinical signs of GVHD, and histopathologic examination of liver, skin, and intestines was normal, demonstrating that recipient mice did not develop chronic GVHD. We assessed the immunocompetence of long-term surviving recipient mice. Results from MLR and CTL assays were weak whereas responses against unrelated H2 antigens were reduced but still preserved. Moreover, in vivo transfer experiments demonstrated that spleen cells from long-term survivors were unable to induce lethal GVHD in irradiated recipients of host origin, while spleen cells injected in irradiated recipients of a host-unrelated H2 were fully competent to induce a lethal GVHD. Together these results indicate that stable chimeric recipient mice were specifically tolerant to host antigens. We further showed that while LF 08--0299 can protect recipient mice from lethal GVHD, it also preserved a graft-versus-leukemia effect when mice were inoculated with P815 tumor cells. These data suggest that LF 08--0299 may be a novel pharmaceutical agent that would prevent GVHD in human unrelated bone marrow transplantation.

IMOCUR stimulates production of immunoglobulins; preliminary results concerning a correlation between in vitro and in vivo experiments.

The bacterial extract IMOCUR is described as an in vivo stimulant of antibody production during animal testing and human clinical trials. Using a slightly modified procedure (13) dealing with in vitro immunoglobulin production by C57B1/6 mouse spleen cells, we have shown that IMOCUR potentiates spontaneous IgM production. In order to explore the putative relation between this in vitro activity and the current in vivo control test (stimulation of plaque-forming cell production after sheep red blood cell injection to Balb/c mouse), we have assayed 10 lyophilisates in vitro and in vivo before and after heat inactivation (80 degrees C, 7 days in a saturated water atmosphere). Results have shown that this treatment inhibits, respectively, totally and partially in vivo and in vitro activities. Thus the in vitro technique seems to be appropriate for the control of activity of the various batches of IMOCUR. Experiments are under way to clarify the mathematical correlation which may exist between the in vitro and in vivo experiments.

Implications of prostaglandin E2 synthesis and phospholipase C activation in potentiation of T-cell proliferation by LF 1695.

Murine spleen cells, T-enriched by nylon wool filtration, proliferate in the presence of a protein kinase C stimulator and a calcium ionophore. Using this cell proliferation system, we show that LF 1695 can potentiate phorbol myristate acetate (PMA) action in the presence of A 23187. This potentiation can be due to PGE2 inhibition since it is found that lipopolysaccharide (LPS) or A 23187 induced PGE2 release from spleen cells is inhibited by LF 1695. Indomethacin and LF 1695 gave similar stimulation of spleen cell proliferation, and exogeneously added PGE2 inhibits this phenomenon. Considering two of the main early components of intracellular signal transduction, LF 1695 induces IP3 release and calcium mobilization. However, the compound is not mitogenic per se. These results show that LF 1695 behaves only as a costimulant for T-cell proliferation.