Lonafarnib is a well-characterized, late-stage, orally active inhibitor of farnesyl transferase, an enzyme involved in modification of proteins through a process called prenylation. It is Investigated for use/treatment in Progeria, Cancer, Hepatitis D. Lonafarnib completely inhibits Rheb prenylation and phosphorylation of S6 ribosomal protein in cell culture, indicating a lack of alternative Rheb prenylation. Other groups have demonstrated that inhibition of protein synthesis via inactivation of eukaryotic elongation factor (eEF2) could be an alternate mechanism of lonafarnib induced growth inhibition that is independent of RAS/p70S6K eEF. Adverse effects included fatigue, diarrhea, dyspnea and neutropenia and respiratory insufficiency.