Project Summary Multiple myeloma (MM) is an incurable bone marrow (BM) cancer characterized by the production of monoclonal protein (MP). Development of drug resistance and off-target effects limits the efficacy of currently available agents. Therefore, novel therapeutic strategies, including drug delivery strategies, are urgently needed. We have focused on the novel strategy of targeting the trafficking of MP in MM cells by inhibiting the enzyme geranylgeranyl diphosphate synthase (GGDPS). GGDPS inhibitors (GGSIs) disrupt Rab geranylgeranylation, which results in intracellular MP accumulation, ER stress, induction of all three arms of the unfolded protein response pathway and ultimately MM cell death. Our GGSI development efforts have focused on isoprenoid triazole bisphosphonates and our structure-function studies have determined that isoprenoid chain length and stereochemistry impact inhibitor potency as well as in vivo biodistribution. Preclinical studies with our lead GGSIs have demonstrated key drug-like properties, including metabolic stability, prolonged plasma half-life, systemic distribution, in vivo disruption of protein geranylgeranylation and anti-tumor efficacy in a mouse MM xenograft model. Dose-finding and toxicology studies revealed hepatic toxicity as dose-limiting with no effects on hematologic, renal, cardiac or neurologic function. Our preliminary studies revealed that altering the molecular weight of a hyaluronic acid (HA) polymer can limit hepatic uptake and enhance BM uptake and that MM cells readily take up HA. We therefore hypothesize that the therapeutic potential of GGSIs can be optimized via linkage of our GGSIs to HA polymers, thus enhancing delivery of GGSI to the BM and minimizing hepatic uptake and our preliminary studies support this hypothesis. To this end, we will synthesize novel GGSIs that are are based upon our lead compound but either modified at the α- position to allow conjugation to HA or linked to HA through phosphonate prodrug forms (Aim 1) We will perform detailed structural studies, including protein crystallography studies with bound inhibitors, to clarify the mechanisms by which these GGSIs interact with the target enzyme (Aim 1) which will aid in the design of future generations of GGSIs. We will determine the pharmacokinetic/pharmacodynamic profiles and biodistribution patterns of the novel linkable GGSIs and the corresponding HA polymer conjugates (Aim 2). We will investigate the mechanisms regulating GGSI hepatic uptake and toxicity. The efficacy of the lead GGSI-HA conjugates will be assessed in xenograft studies which model extramedullary and medullary disease involvement (Aim 3). In vitro and in vivo studies evaluating the combination of GGSI therapy with clinically used anti-MM agents will be performed. While our current focus is to develop GGSI therapy for treatment of MM, these studies have added significance because this novel approach of drug conjugation to HA to alter biodistribution c...