Potent farnesyltransferase inhibitor ABT-100 abrogates acute allograft rejection

Farnesyltransferase inhibitors (FTIs) inhibit the function of Ras, a GTPase involved in carcinogenesis and T cell activation. We evaluated the in vitro and in vivo immunomodulatory properties of a rationally designed FTI, ABT-100.

The effects of ABT-100 on human peripheral blood mononuclear cell (PBMC) proliferation and the expression of the T cell activation markers CD25 and CD69 were studied. In a Wistar to Lewis rat heterotopic cardiac transplant model, ABT-100 was orally dosed alone or with a subtherapeutic course of cyclosporine (CsA). The degree of graft immune cell infiltrate was determined.

ABT-100 potently inhibited PBMC proliferation, but did not decrease expression of CD25 and CD69 during activation. Treatment with 25, 50 and 100 mg/kg ABT-100 BID increased allograft mean survival time (MST) to 12.8+/-3 days, 13.5+/-5 days and 13.8+/-3 days, respectively (vs 6.5+/-3 days for controls, p<0.001 by log rank). A subtherapeutic course of CsA increased MST to 12.7+/-3 days (p<0.001 vs control). Combination with ABT-100 at 25 and 100 mg/kg BID improved MST to 18.7+/-5 days and 19.5+/-4 days (both p<0.001 vs control and respective monotherapy groups). ABT-100 treatment at 100 mg/kg BID significant decreased the amount of graft infiltrate (2.5+/-4 mononuclear cells/high power field (hpf) vs 29+/-11 cells/hpf, p<0.001).

This is the first report that a specific FTI delays the development of acute rejection and supports the strategy of inhibiting Ras to impart immunomodulation. The antirejection and anticarcinogenic effects make FTIs a potentially useful adjunct in the antirejection regimens of malignancy-prone organ transplant recipients.