Structure-activity relationship of isoprenoid triazole bisphosphonate-based geranylgeranyl diphosphate synthase inhibitors: Effects on pharmacokinetics, biodistribution, and hepatic transporters

Geranylgeranyl diphosphate synthase produces the isoprenoid geranylgeranyl diphosphate, which is used in protein geranylgeranylation. Our previous work illustrates that geranylgeranyl diphosphate synthase inhibitors (GGSIs) disrupt Rab-mediated protein trafficking in cells, inducing the unfolded protein response pathway and apoptosis. Structure-function studies of our GGSIs, which are isoprenoid triazole bisphosphonates, have revealed a complex relationship between GGSI structure and enzymatic, cellular, and in vivo activities. The dose-limiting toxicity of this family of GGSIs is hepatic, and the mechanisms underlying their hepatic uptake are unexplored. Here, we evaluate the pharmacokinetics (PK) and biodistribution of a pair of potent GGSIs that are olefin isomers (homogeranyl [HG] and homoneryl [HN]). We investigate whether these isomers, as well as their a-methylated analogs (HG-me and HN-me), are substrates for key hepatic transporters and explore the effects of these GGSIs on the expression of a panel of hepatic transporters and cytochrome P450s. The PK/biodistribution studies revealed that both systemic exposure and liver levels of HG were significantly higher than that of HN across multiple time points. Conversely, HN was present at 4-fold higher concentrations in the bile at 2 hours postinjection relative to HG. HG-me and HN-me, but not HG or HN, were determined to be substrates of hepatic transport proteins OATP1B1 and OATP1B3. While the hepatic expression of several transporters and cytochrome P450 were altered by GGSI treatment, no significant differences in expression patterns between pairs of olefin isomers were observed. Collectively, these studies reveal that GGSI structure, including olefin stereochemistry, impacts PK profile, biodistribution, and hepatic transporter affinity. Significance Statement: Our understanding of the in vivo structure-activity relationship of our novel geranylgeranyl diphosphate synthase inhibitors has expanded, demonstrating that isoprenoid olefin stereochemistry impacts pharmacokinetic and biodistribution patterns and that other modifications impact transporter affinity. These studies reveal the underlying complexity of the mechanisms regulating hepatic exposure to these agents. Future studies will focus on optimizing tumor-directed geranylgeranyl diphosphate synthase inhibitor delivery while minimizing hepatic uptake.