GGTI 2133, a peptidomimetic inhibitor of geranylgeranyl transferase type I (GGTase I; IC50= 38 nM), exhibits 140-fold selectivity towards GGTase I compared to farnesyltransferase (IC50= 5,400 nM). The compound effectively inhibits the geranylgeranylation of RAP1A (IC50= 10 µM) without affecting the farnesylation of H-Ras (IC50= >30 µM). Moreover, GGTI 2133 reduces the growth, migration, and invasion of oral squamous cell carcinoma (OSSC) cells to 75, 45, and 27% of control levels, respectively. When administered intraperitoneally at 5 mg/kg per day, it prevents eosinophil infiltration into the airways in a mouse model of allergic bronchial asthma, although it does not reduce chemokine levels. Additionally, GGTI 2133 thwarts naloxone-induced contraction of ileum in rats experiencing morphine withdrawal syndrome and mitigates the severity of withdrawal symptoms in vivo (ED50= 0.076 mg/kg).