Immunosuppressive effects of DTCM-G, a novel inhibitor of the mTOR downstream signaling pathway

Background: A newly developed compound, 3-[(dodecylthiocarbonyl)methyl]- glutarimide (DTCM-G), has been shown to inhibit nuclear translocation of c-Fos/c-Jun in a murine macrophage cell line. Herein, we studied the immunosuppressive properties and potency of DTCM-G. METHODS: Using purified mouse T cells, the in vitro effects of DTCM-G on activation, cytokine production, proliferation, and cell cycle progression were assessed, and a possible molecular target of DTCM-G was investigated. In a BALB/c (H-2) to C57BL/6 (H-2) mouse heart transplantation model, transplant recipients were administered DTCM-G, a calcineurin inhibitor (tacrolimus), and a nuclear factor-κB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ). Treatment drugs were administered daily for 14 days after transplantation. Alloimmune responses were assessed in addition to graft survival time. RESULTS: After anti-CD3+anti-CD28 monoclonal antibody stimulation, DTCM-G significantly suppressed proliferation, interferon-γ production, and cell cycle progression of activated T cells but not CD25 expression or interleukin-2 production. These effects were accompanied by inhibition of 70-kDa S6 protein kinase phosphorylation, a downstream kinase of the mammalian target of rapamycin. The addition of tacrolimus and DHMEQ to DTCM-G resulted in a robust inhibition of T-cell proliferation. In vivo combination therapy of DTCM-G plus either tacrolimus or DHMEQ significantly suppressed alloreactive interferon-γ-producing precursors and markedly prolonged cardiac allograft survival. Furthermore, combination of all three agents markedly inhibited alloimmune responses and permitted long-term cardiac allograft survival. Conclusions: DTCM-G inhibits T cells by suppressing the downstream signal of mammalian target of rapamycin. DTCM-G in combination with tacrolimus and DHMEQ induces a strong immunosuppressive effect in vivo.