concanavalin-a and discodermolide

The in vitro immunosuppressive properties of a novel, marine-derived compound, discodermolide, are reported here. Discodermolide suppressed the proliferative responses of splenocytes in the murine two-way mixed lymphocyte reaction (MLR) and concanavalin A stimulated cultures, with IC50 values of 0.24 microM and 0.19 microM, respectively. There was no evidence of cytotoxicity for murine splenocytes at concentrations of discodermolide as high as 1.26 microM. Similarly, discodermolide suppressed the proliferative responses of human peripheral blood leukocytes (PBL) in the two-way MLR, and Con A and phytohemagglutinin mitogenesis. The IC50 values were 5.65 microM, 28.02 microM, and 30.12 microM for the MLR, Con A, and PHA mitogenic responses, respectively. There was no evidence of cytotoxicity toward human PBL at discodermolide concentrations as high as 80.64 microM. Discodermolide was equally effective, compared with cyclosporine, in suppressing the PMA-ionomycin induced proliferation of purified, murine T cells, with IC50 values of 9.0 nM and 14.0 nM for discodermolide and CsA, respectively. The production of IL-2 by PMA-ionomycin stimulated T cells was not inhibited by discodermolide; however, the percentage of IL-2 receptor-bearing cells as measured by immunofluorescence with 7D4 antibody, specific for the 55-kDa chain (p55) comprising the murine IL-2 receptor, was reduced. The expression of a similar chain comprising the human IL-2 receptor (Tac antigen, p55) by PHA or Con-A-stimulated PBL was similarly suppressed by discodermolide. The precise mechanism of action of discodermolide remains to be elucidated.

Topics: Alkanes; Animals; Carbamates; Cells, Cultured; Concanavalin A; Female; Humans; Immunosuppressive Agents; Interleukin-2; Ionomycin; Lactones; Leukocytes; Lymphocyte Activation; Lymphocyte Culture Test, Mixed; Lymphocytes; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Pyrones; Receptors, Interleukin-2; Spleen; T-Lymphocytes; Tetradecanoylphorbol Acetate

The in vivo immunosuppressive properties of a novel, marine-derived compound, discodermolide, are reported here. Discodermolide was effective in suppressing the graft-versus-host splenomegaly response of BALB/c----CB6F1 (BALB/c X C57BL/6J)F1 grafted mice at 5.0, 2.5, and 1.25 mg/kg, when administered as daily, i.p. injections, for 7 days. Mice treated with 5.0 and 2.5 mg/kg demonstrated a high degree of suppression (219 and 150%, respectively); however, these dosages were associated with some degree of morbidity (2/5 and 4/5 survivors for 5.0 and 2.5 mg/kg, respectively). Mice that were treated with 1.25, 0.625, and 0.313 mg/kg remained healthy after a 7-day regimen, and continued to demonstrate suppression of splenomegaly (106%, 72%, and 76% suppression, respectively). Splenocytes obtained from discodermolide-treated, allogeneic grafted mice were suppressed in their ability to respond in vitro to optimal mitogenic concentrations of concanavalin A, and natural-killer-cell activity directed against YAC-1 tumor cells, compared with vehicle-treated, allogeneic grafted control mice. Lower dosages (2.5 and 1.25 mg/kg) of discodermolide, however, did not affect the subsequent ability of splenocytes obtained from these mice to produce IL-2 following in vitro stimulation with Con A. This was observed to be in contrast to the immunosuppressive activity observed with cyclosporine treatment of mice (150 mg/kg) for the ex vivo suppression of splenocyte production of IL-2. Treatment of normal, nongrafted mice with similar high dosages of discodermolide (5.0 mg/kg) for 4 days did not affect the primary antibody response of mice immunized with sheep red blood cells as measured by hemagglutination activity of their serum. These results suggest that discodermolide's in vivo immunosuppressive action appears not to be that of a generalized immunosuppressive agent and that its specific in vivo mechanism of action warrants further preclinical evaluation.

Topics: Alkanes; Animals; Antibody Formation; Carbamates; Concanavalin A; Cyclosporine; Graft vs Host Reaction; Immunosuppressive Agents; Interleukin-2; Killer Cells, Natural; Lactones; Mice; Mice, Inbred BALB C; Mice, Inbred Strains; Pyrones; Spleen; T-Lymphocytes