Immunosuppressive properties of a series of novel inhibitors of the monocarboxylate transporter MCT-1.

We have recently described the immunosuppressive properties of AR-C117977 and AR-C122982, representatives of a group of compounds identified as inhibitors of lactate transporters (monocarboxylate transporters; MCTs). These compounds demonstrate the potential therapeutic usefulness of inhibiting MCT-1, but their physical and metabolic properties made them unsuitable for further development. We have therefore tried to find analogues with similar immunosuppressive efficacy and a more suitable profile for oral administration. Five analogues of AR-C117977 were synthesised and screened for binding to the transporter, for inhibition of proliferation of both human and rat lymphocytes, for in vivo activity in a model of graft-versus-host (GvH) response in the rat, and in high- and low-responder cardiac transplant models in the rat. There was a good correlation between levels of binding of the five analogues to MCT and their inhibition of lymphocyte proliferation in human and rat cells. Furthermore, activity in both the GvH response and the cardiac transplant models correlated well with the determined concentrations of test compound in plasma. These findings on new analogues of MCT-1 inhibitors have taken us further towards defining the pharmacokinetic properties that may help to identify future drug candidates among inhibitors of MCT-1.

The specific monocarboxylate transporter-1 (MCT-1) inhibitor, AR-C117977, induces donor-specific suppression, reducing acute and chronic allograft rejection in the rat.

BACKGROUND: In a search for immunosuppressive drugs having novel mechanisms, monocarboxylate transporter (MCT-1) inhibitors were identified that markedly inhibited immune responses. Here, we report the effects of AR-C117977, a potent MCT-1 inhibitor, on alloimmune responses in the rat. METHODS: In vitro activity was determined in a rat mixed lymphocyte response (MLR). In vivo activity was tested in a graft versus host response (GVHR) and in both high (DA to PVG) and low (PVG to DA) responder cardiac allograft models. To assess induction of donor-specific suppression recipients of allogeneic hearts surviving longer than 100 days received a second transplant either of the same donor strain or a third-party donor strain. Effects on chronic graft rejection were assessed histologically by evaluating vasculopathy in long-term surviving grafts and in an obliterative bronchiolitis (OB) model. RESULTS: AR-C117977 inhibited the rat MLR and was more potent than cyclosporin A (CsA). In the rat GVHR model, AR-C117977 gave a dose-related inhibition. In the high responder cardiac allograft model, graft survival in excess of 100 days was achieved with AR-C117977 compared with 20 days with CsA and all the long-term survivors exhibited donor-specific suppression on retransplantation. In the low responder model, both AR-C117977 and CsA induced survival in excess of 100 days. Histology of the long-term surviving grafts suggested reduced vasculopathy associated with chronic rejection. Furthermore, AR-C117977 inhibited the occlusion of transplanted trachea in a OB model. CONCLUSION: This report describes a MCT-1 specific inhibitor having immunosuppressive activity on alloimmune responses and inducing donor-specific suppression.

Immunology: turning basic research into a therapy.

One of the driving forces in the field of immunology is the ambition to translate experimental research into novel useful therapies. Therefore, the aim of this mini-review is to exemplify emerging therapies as well as highlight hurdles that need to be overcome before they can be introduced into the clinic.

TNF-blocking therapies: an alternative mode of action?

Despite expanding use of drugs blocking tumour necrosis factor (TNF), their precise mechanisms of action remain unclear. Early assumptions that they act by direct neutralization of the toxic inflammatory effects of TNF might be too simplistic because they explain neither the range of effects observed nor the varying properties of different TNF-blocking agents. Recent studies have demonstrated a key role for mast cell-derived TNF in the increase in lymph node size and the organizational complexity that accompanies a developing immune response. Regulation of this phenomenon might comprise a novel mode of action for TNF-directed therapy: by preventing this lymph node hyperplasia, TNF blockade could modulate immune responses, ameliorating pathology in autoimmune diseases, such as rheumatoid arthritis.

Monocarboxylate transporter MCT1 is a target for immunosuppression.

Current immunosuppressive therapies act on T lymphocytes by modulation of cytokine production, modulation of signaling pathways or by inhibition of the enzymes of nucleotide biosynthesis. We have identified a previously unknown series of immunomodulatory compounds that potently inhibit human and rat T lymphocyte proliferation in vitro and in vivo in immune-mediated animal models of disease, acting by a novel mechanism. Here we identify the target of these compounds, the monocarboxylate transporter MCT1 (SLC16A1), using a strategy of photoaffinity labeling and proteomic characterization. We show that inhibition of MCT1 during T lymphocyte activation results in selective and profound inhibition of the extremely rapid phase of T cell division essential for an effective immune response. MCT1 activity, however, is not required for many stages of lymphocyte activation, such as cytokine production, or for most normal physiological functions. By pursuing a chemistry-led target identification strategy, we have discovered that MCT1 is a previously unknown target for immunosuppressive therapy and have uncovered an unsuspected role for MCT1 in immune biology.