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 [3H]thymidine incorporation by mouse splenocytes activated with concanavalin-A (IC50 = 20.1 microM), phytohaemagglutinin (IC50 = 4.6 microM), lipopolysaccharide (LPS) (IC50 = 3.2 microM), anti-IgM (mu-chain specific) (IC50 = 2.6 microM), or mixed lymphocyte culture (IC50 = 8.4 microM). Activity of BTS 71 412 was not associated with a reduction in cell viability. BTS 71 412 also prevented [3H]thymidine incorporation by the murine HT-2 helper T-cell clone when cultured with IL-2 (IC50 = 7.6 microM) or IL-4 (IC50 = 7.3 microM), enriched Thy-1+ T-lymphocytes stimulated with phorbol 12-myristate 13-acetate plus ionomycin (IC50 = 3.6 microM), and enriched B220- B-lymphocytes stimulated with LPS (IC50 = 3.0 microM). 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 microM, 22 microM and 60 microM, respectively). The compound suppressed in vitro antibody responses to keyhole limpet haemocyanin (IC50 = 2.3 microM), 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.