BTS-71-412 - IN-VITRO PROFILE OF A NOVEL PYRAZOLINONE IMMUNOSUPPRESSANT

The effect of BTS 71 412, 4-acetyl-1-(4-chlorophenyl)-3-(2-methylthiophenyl)-3-pyrazolin-5-one, has been determined on a variety of immune reactions in vitro in order to gain a further insight into the mechanisms whereby this novel immunosuppressive drug suppresses cell and antibody mediated immune responses in vivo. BTS 71 412 markedly inhibited [H-3]thymidine incorporation by mouse splenocytes activated with concanavalin-A (IC50 = 20.1 mu M), phytohaemagglutinin (IC50 = 4.6 mu M), lipopolysaccharide (LPS) (IC50 = 3.2 mu M), anti-IgM (mu-chain specific) (IC50 = 2.6 mu M), or mixed lymphocyte culture (IC50 = 8.4 mu M). Activity of BTS 71 412 was not associated with a reduction in cell viability. BTS 71 412 also prevented [H-3]thymidine incorporation by the murine HT-2 helper T-cell clone when cultured with IL-2 (IC50 = 7.6 mu M) or IL-4 (IC50 = 7.3 mu M), enriched Thy-1(+) T-lymphocytes stimulated with phorbol 12-myristate 13-acetate plus ionomycin (IC50 = 3.6 mu M), and enriched B220(+) B-lymphocytes stimulated with LPS (IC50 = 3.0 mu M). Splenocytes cultured with BTS 71 412 produced lower levels of interleukin (IL)-2, IL-10 and interferon-gamma when stimulated with concanavalin-A (IC50 values 42 mu M, 22 mu M and 60 mu M, respectively). The compound suppressed in vitro antibody responses to keyhole limpet haemocyanin (IC50 = 2.3 mu M), but did not reproducibly inhibit IL-6 or tumour necrosis factor alpha production by adherent peritoneal macrophages stimulated with LPS in vitro. These data indicate that BTS 71 412 specifically inhibits both B- and T-lymphocyte activation and proliferation but does not affect macrophage activation in vitro.