RAP1A and plasma cell myeloma: We previously reported the discovery of C2-substituted thienopyrimidine-based bisphosphonate (C2-ThP-BP) inhibitors of the human geranylgeranyl pyrophosphate synthase (GGPPS).16,17 These compounds can effectively block geranylgeranylation of relevant GTPases (e.g. RAP1A), induce apoptosis in blood cancer cells, such as of multiple myeloma (MM) by selective intracellular binding and inhibition of GGPPS.