Impact of α-modifications on the activity of triazole bisphosphonates as geranylgeranyl diphosphate synthase inhibitors

Impact of fixed phosphorus position on activity of triazole bisphosphonates as geranylgeranyl diphosphate synthase inhibitors

Geranylgeranyl diphosphate synthase (GGDPS) produces the 20-carbon isoprenoid species used in protein geranylgeranylation reactions. Inhibition of GGDPS has emerged as a novel means of disrupting the activity of geranylgeranylated proteins in cancers such as myeloma and osteosarcoma. We have focused on developing a series of isoprenoid triazole bisphosphonate-based GGDPS inhibitors, demonstrating a complex structure-activity relationship (SAR), not only at the enzymatic level, but also at the cellular and whole organism levels. To further investigate this SAR, we have prepared a family of novel derivatives that have a fixed phosphorus position by virtue of vinyl, epoxy or cyclopropyl groups that incorporate the α-carbon position. Additional modifications include compounds with homocitronellyl chains instead of homogeranyl or homoneryl chains. All new compounds were evaluated in GGDPS enzyme assays and in cellular assays involving a panel of human myeloma and osteosarcoma cell lines. The homocitronellyl derivatives displayed markedly reduced activity in both enzymatic and cellular assays. While all of the homogeranyl/homoneryl vinyl/epoxy/cyclopropyl compounds had relatively similar activity in the enzyme assay (IC50's 0.37-2.87 μM), the cellular potencies varied more dramatically (ranging from 10 nM to no activity at 100 μM), depending on the olefin stereochemistry, the specific α-carbon modification and the tumor cell type. These findings, coupled with POM-prodrug and membrane permeability studies, support the hypothesis that there are specific membrane transporters mediating cellular uptake of these GGDPS inhibitors. Future studies focused on the identification of the membrane transporters responsible for the cellular uptake will enable further understanding of this complex SAR.

A review of click chemistry in the synthesis of organophosphorus triazoles and their biological activities

Organophosphorus compounds, characterized by the incorporation of phosphorus into organic molecules, play a critical role in various fields such as medicine, agriculture, and industry. Their unique electronic properties and versatility make them essential in developing therapeutic agents, pesticides, and materials. One prominent class of organophosphorus compounds is organophosphorus heterocycles, which combine the benefits of both phosphorus and cyclic structures. Triazoles, a class of nitrogen-containing heterocyclic compounds, are particularly notable for their broad biological activities, including anticancer, antiviral, antibacterial, and antioxidant effects. Traditional methods for synthesizing triazoles often encounter challenges such as low yields and non-selective products, whereas click chemistry provides a more efficient and reliable alternative. The copper-catalyzed azide-alkyne [3 + 2] cycloaddition, a cornerstone of click chemistry, allows for the rapid and selective formation of triazoles under mild conditions. When functionalized with organophosphorus groups, triazoles not only retain but often enhance their biological activities, improving their potency, selectivity, and stability. This review covers the synthesis of organophosphorus-functionalized triazoles via click chemistry and explores their molecular structure, including the coordination chemistry of these compounds. The behavior and interactions of these organophosphorus derivatives with various metal ions are also addressed, as these interactions significantly influence their chemical reactivity, stability, and bioactivity.

The current landscape of 1,2,3-triazole hybrids with anticancer therapeutic potential: Part I

Cancer, with its steadily increasing morbidity and mortality, will continue to pose a threat to humanity over an extended period. Chemotherapeutics play an indispensable role in cancer treatment, and hundreds of drugs have been approved for this purpose. Nevertheless, the fight against cancer remains a formidable challenge. This is mainly due to the emergence of multidrug resistance and the severe side effects associated with currently available anticancer drugs. Consequently, there is an urgent imperative to explore novel chemotherapeutic agents. 1,2,3-Triazoles belong to one of the most privileged classes of nitrogen-containing five-membered heterocycles and are regarded as prominent sources for the development of innovative anticancer chemotherapeutics. 1,2,3-Triazole hybrids, which possess multitargeted mechanisms of action within the cancer progression pathway, hold the potential to overcome multidrug resistance and mitigate side effects. Furthermore, several 1,2,3-triazole hybrids have already been approved for cancer therapy or are currently under clinical evaluation. This clearly demonstrates that 1,2,3-triazole hybrids are valuable scaffolds in the treatment and eradication of cancer. This review aims to provide insights into the anticancer therapeutic potential of 1,2,3-triazole hybrids, along with their mechanisms of action, crucial aspects of design, and structure-activity relationships (SARs). It encompasses articles published from 2021 onward.

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.

α-Amino bisphosphonate triazoles serve as GGDPS inhibitors

Depletion of cellular levels of geranylgeranyl diphosphate by inhibition of the enzyme geranylgeranyl diphosphate synthase (GGDPS) is a potential strategy for disruption of protein transport by limiting the geranylgeranylation of the Rab proteins that regulate intracellular trafficking. As such, there is interest in the development of GGDPS inhibitors for the treatment of malignancies characterized by abnormal protein production, including multiple myeloma. Our previous work has explored the structure-function relationship of a series of isoprenoid triazole bisphosphonate-based GGDPS inhibitors, with modifications having impact on enzymatic, cellular and in vivo activities. We have synthesized a new series of α-amino bisphosphonates to understand the impact of modifying the alpha position with a moiety that is potentially linkable to other agents. Bioassays evaluating the enzymatic and cellular activities of these compounds demonstrate that incorporation of the α-amino group affords compounds with GGDPS inhibitory activity which is modulated by isoprenoid tail chain length and olefin stereochemistry. These studies provide further insight into the complexity of the structure-function relationship and will enable future efforts focused on tumor-specific drug delivery.

Structural Insight into Geranylgeranyl Diphosphate Synthase (GGDPS) for Cancer Therapy

Geranylgeranyl diphosphate synthase (GGDPS), the source of the isoprenoid donor in protein geranylgeranylation reactions, has become an attractive target for anticancer therapy due to the reliance of cancers on geranylgeranylated proteins. Current GGDPS inhibitor development focuses on optimizing the drug-target enzyme interactions of nitrogen-containing bisphosphonate-based drugs. To advance GGDPS inhibitor development, understanding the enzyme structure, active site, and ligand/product interactions is essential. Here we provide a comprehensive structure-focused review of GGDPS. We reviewed available yeast and human GGDPS structures and then used AlphaFold modeling to complete unsolved structural aspects of these models. We delineate the elements of higher-order structure formation, product-substrate binding, the electrostatic surface, and small-molecule inhibitor binding. With the rise of structure-based drug design, the information provided here will serve as a valuable tool for rationally optimizing inhibitor selectivity and effectiveness.

Geranylgeranyl diphosphate synthase: Role in human health, disease and potential therapeutic target

Geranylgeranyl diphosphate synthase (GGDPS), an enzyme in the isoprenoid biosynthesis pathway, is responsible for the production of geranylgeranyl pyrophosphate (GGPP). GGPP serves as a substrate for the post-translational modification (geranylgeranylation) of proteins, including those belonging to the Ras superfamily of small GTPases. These proteins play key roles in signalling pathways, cytoskeletal regulation and intracellular transport, and in the absence of the prenylation modification, cannot properly localise and function. Aberrant expression of GGDPS has been implicated in various human pathologies, including liver disease, type 2 diabetes, pulmonary disease and malignancy. Thus, this enzyme is of particular interest from a therapeutic perspective. Here, we review the physiological function of GGDPS as well as its role in pathophysiological processes. We discuss the current GGDPS inhibitors under development and the therapeutic implications of targeting this enzyme.

Conjugate reduction of vinyl bisphosphonates

Vinyl bisphosphonates can be readily prepared by condensation of an aromatic aldehyde with the tetraester of a methylenebisphosphonate, and reduction of the resulting olefin is an attractive strategy for the preparation of monoalkyl geminal bisphosphonates. Conjugate reduction through use of variations on the Stryker approach has proven to be an efficient method for that reduction, even in the presence of aromatic substituents that also could be reduced. Furthermore, remote olefins in an isoprenoid chain survive this conjugate reduction unaffected, allowing access to isoprenoid-substituted triazole bisphosphonates of interest as potential inhibitors of terpenoid biosynthesis.

Geranylgeranyl diphosphate synthase inhibitor and proteasome inhibitor combination therapy in multiple myeloma

Background

Multiple myeloma (MM) remains an incurable malignancy, despite the advent of therapies such as proteosome inhibitors (PIs) that disrupt protein homeostasis and induce ER stress. We have pursued inhibition of geranylgeranyl diphosphate synthase (GGDPS) as a novel mechanism by which to target protein homeostasis in MM cells. GGDPS inhibitors (GGSI) disrupt Rab geranylgeranylation, which in turn results in perturbation of Rab-mediated protein trafficking, leading to accumulation of intracellular monoclonal protein, induction of ER stress and apoptosis. Our lead GGSI, RAM2061, has demonstrated favorable pharmacokinetic properties and in vivo efficacy. Here we sought to evaluate if combination therapy with GGSI and PI would result in enhanced disruption of the unfolded protein response (UPR) and increase anti-MM efficacy.

Methods

MTT assays were conducted to evaluate the cytotoxic effects of combining RAM2061 with bortezomib in human MM cells. The effects of RAM2061 and/or PI (bortezomib or carfilzomib) on markers of UPR and apoptosis were evaluated by a combination of immunoblot (ATF4, IRE1, p-eIF2a, cleaved caspases and PARP), RT-PCR (ATF4, ATF6, CHOP, PERK, IRE1) and flow cytometry (Annexin-V). Induction of immunogenic cell death (ICD) was assessed by immunoblot (HMGB1 release) and flow cytometry (calreticulin translocation). Cell assays were performed using both concurrent and sequential incubation with PIs. To evaluate the in vivo activity of GGSI/PI, a flank xenograft using MM.1S cells was performed.

Results

Isobologram analysis of cytotoxicity data revealed that sequential treatment of bortezomib with RAM2061 has a synergistic effect in MM cells, while concurrent treatment was primarily additive or mildly antagonistic. The effect of PIs on augmenting RAM2061-induced upregulation of UPR and apoptotic markers was dependent on timing of the PI exposure. Combination treatment with RAM2061 and bortezomib enhanced activation of ICD pathway markers. Lastly, combination treatment slowed MM tumor growth and lengthened survival in a MM xenograft model without evidence of off-target toxicity.

Conclusion

We demonstrate that GGSI/PI treatment can potentiate activation of the UPR and apoptotic pathway, as well as induce upregulation of markers associated with the ICD pathway. Collectively, these findings lay the groundwork for future clinical studies evaluating combination GGSI and PI therapy in patients with MM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40164-022-00261-6.