Abstract Inhibition of mutant H-Ras farnesylation with farnesyltransferase inhibitors (FTIs) blocks its binding to membranes and its ability to activate oncogenic signaling. In contrast, inhibition of K-Ras farnesylation with FTIs leads to its prenylation by geranylgeranyltransferase I (GGT-1), and therefore, inhibition of K-Ras prenylation and oncogenic function requires blocking both FT and GGT-1. Furthermore, several proteins downstream of K-Ras that mediate its malignant transforming activity also require farnesylation (e.g.Rheb) or gernaylgeranylation (e.g. Ral). In addition, the ability of mutant K-Ras to induce lung cancer in mouse models is severely hampered when both FT and GGT-1 are conditionally deficient. These observations prompted us to design small molecule dual FT and GGT-1 inhibitors. In this presentation, the development of FGTI-2734 as a novel therapeutic for K-Ras dependent cancers will be described. The presentation will focus on the effect of this dual inhibitor as compared to the selective FTI-2148 and GGTI-2418 on K-ras prenylation, oncogenic signaling and malignant transformation in cancer cells that depend on K-Ras. Citation Format: Kazi Aslamuzzaman, Xiaolei Zhang, Yunting Luo, Ronil Patel, Steven Fletcher, Christopher Cummings, Harshani Lawrence, Andrew Hamilton, Said M. Sebti. Dual inhibitors of FT and GGT-1 as novel therapeutic agents for K-Ras-dependent tumors. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B35. doi: 10.1158/1557-3125.RASONC14-B35