Synthesis and in vitro evaluation of bile acid prodrugs of floxuridine to target the liver

Development of novel liver-targeting glucocorticoid prodrugs

Background

Glucocorticoids (GCs) are widely used in the treatment of inflammatory liver diseases and sepsis, but GC's various side effects on extrahepatic tissues limit their clinical benefits. Liver-targeting GC therapy may have multiple advantages over systemic GC therapy. The purpose of this study was to develop novel liver-targeting GC prodrugs as improved treatment for inflammatory liver diseases and sepsis.

Methods

A hydrophilic linker or an ultra-hydrophilic zwitterionic linker carboxylic betaine (CB) was used to bridge cholic acid (CA) and dexamethasone (DEX) to generate transporter-dependent liver-targeting GC prodrugs CA-DEX and the highly hydrophilic CA-CB-DEX. The efficacy of liver-targeting DEX prodrugs and DEX were determined in primary human hepatocytes (PHH), macrophages, human whole blood, and/or mice with sepsis induced by cecal ligation and puncture.

Results

CA-DEX was moderately water soluble, whereas CA-CB-DEX was highly water soluble. CA-CB-DEX and CA-DEX displayed highly transporter-dependent activities in reporter assays. Data mining found marked dysregulation of many GR-target genes important for lipid catabolism, cytoprotection, and inflammation in patients with severe alcoholic hepatitis. These key GR-target genes were similarly and rapidly (within 6 h) induced or down-regulated by CA-CB-DEX and DEX in PHH. CA-CB-DEX had much weaker inhibitory effects than DEX on endotoxin-induced cytokines in mouse macrophages and human whole blood. In contrast, CA-CB-DEX exerted more potent anti-inflammatory effects than DEX in livers of septic mice.

Conclusions

CA-CB-DEX demonstrated good hepatocyte-selectivity in vitro and better anti-inflammatory effects in vivo. Further test of CA-CB-DEX as a novel liver-targeting GC prodrug for inflammatory liver diseases and sepsis is warranted.

Synthesis of modified bile acids via palladium-catalyzed C(sp3)-H (hetero)arylation

A Pd(II)-catalyzed strategy for the diastereo- and regioselective (hetero)arylation of unactivated C(sp3)-H bonds in bile acids is accomplished with aryl and heteroaryl iodides under solvent-free conditions using the 8-aminoquinoline auxiliary as a directing group. This methodology demonstrated excellent functional group tolerance with respect to aryl/heteroaryl iodides on O-protected N-(quinolin-8-yl)cholyl/deoxycholyl amides to afford β-C(sp3)-H (hetero)arylated products in good-to-excellent yields. Moreover, the 8-aminoquinoline (AQ) auxiliary can easily be removed to obtain modified bile acids.

Transporter-Mediated Drug Delivery

Transmembrane transport of small organic and inorganic molecules is one of the cornerstones of cellular metabolism. Among transmembrane transporters, solute carrier (SLC) proteins form the largest, albeit very diverse, superfamily with over 400 members. It was recognized early on that xenobiotics can directly interact with SLCs and that this interaction can fundamentally determine their efficacy, including bioavailability and intertissue distribution. Apart from the well-established prodrug strategy, the chemical ligation of transporter substrates to nanoparticles of various chemical compositions has recently been used as a means to enhance their targeting and absorption. In this review, we summarize efforts in drug design exploiting interactions with specific SLC transporters to optimize their therapeutic effects. Furthermore, we describe current and future challenges as well as new directions for the advanced development of therapeutics that target SLC transporters.

Advanced prodrug strategies in nucleoside analogues targeting the treatment of gastrointestinal malignancies

Gastrointestinal malignancies are common digestive system tumor worldwide. Nucleoside analogues have been widely used as anticancer drugs for the treatment of a variety of conditions, including gastrointestinal malignancies. However, low permeability, enzymatic deamination, inefficiently phosphorylation, the emergence of chemoresistance and some other issues have limited its efficacy. The prodrug strategies have been widely applied in drug design to improve pharmacokinetic properties and address safety and drug-resistance issues. This review will provide an overview of the recent developments of prodrug strategies in nucleoside analogues for the treatment of gastrointestinal malignancies.

Oligonucleotides Carrying Nucleoside Antimetabolites as Potential Prodrugs

BACKGROUND

Nucleoside and nucleobase antimetabolites are an important class of chemotherapeutic agents for the treatment of cancer as well as other diseases.

INTRODUCTION

In order to avoid undesirable side effects, several prodrug strategies have been developed. In the present review, we describe a relatively unknown strategy that consists of using oligonucleotides modified with nucleoside antimetabolites as prodrugs.

METHODS

The active nucleotides are generated by enzymatic degradation once incorporated into cells. This strategy has attracted large interest and is widely utilized at present due to the continuous developments made in therapeutic oligonucleotides and the recent advances in nanomaterials and nanomedicine.

RESULTS

A large research effort was made mainly in the improvement of the antiproliferative properties of nucleoside homopolymers, but recently, chemically modified aptamers, antisense oligonucleotides and/or siRNA carrying antiproliferative nucleotides have demonstrated a great potential due to the synergetic effect of both therapeutic entities. In addition, DNA nanostructures with interesting properties have been built to combine antimetabolites and enhancers of cellular uptake in the same scaffold. Finally, protein nanoparticles functionalized with receptor-binders and antiproliferative oligomers represent a new avenue for a more effective treatment in cancer therapy.

CONCLUSION

It is expected that oligonucleotides carrying nucleoside antimetabolites will be considered as potential drugs in the near future for biomedical applications.

Roles and action mechanisms of bile acid-induced gastric intestinal metaplasia: a review

Gastric intestinal metaplasia (IM) is a precancerous lesion that increases the risk of subsequent gastric cancer (GC) development. Therefore, the mechanism of IM has been the focus of basic and clinical research. Helicobacter pylori (H. pylori) infection has been recognized as the main pathogenesis of gastric IM. However, more and more studies have shown that chronic inflammation of gastric mucosa caused by bile reflux is the key pathogenic factor of gastric IM. Bile reflux activates the expression of IM biomarkers via the bile acid receptor. In addition, microRNAs, exosomes, and epigenetics are also involved in the occurrence and development of bile acid-induced gastric IM. Currently, the relevant research is still very few. The molecular mechanism of the phenotypic transformation of gastrointestinal epithelial cells induced by bile acids has not been fully understood. This article mainly reviews the physiology and pathology of bile acid, mechanism of gastric IM induced by bile acid, bile acid receptors, and so on, in order to provide reference for further research.

Research progress in the application of bile acid-drug conjugates: A "trojan horse" strategy

Bile acid transporters are highly expressed in intestinal cells and hepatocytes, and they determine the uptake of drugs in cells by modulating cellular entry and exit. In order to improve the oral bioavailability of drugs and investigate the potential application prospects of drugs used to target cancer, numerous studies have adopted these transporters to identify prodrug strategies. Through the connection of covalent bonds between drugs and bile acids, the resulting bile acid-drug conjugates continue to be recognized as similar to natural unmodified bile acid and is translocated by the transporter. The present mini-review provides a brief summary of recent progress of the application of bile acid-drug conjugates based primarily on ASBT, NTCP, and OATP, with the hope of contributing to subsequent research.

Evaluation of Floxuridine Oligonucleotide Conjugates Carrying Potential Enhancers of Cellular Uptake

Conjugation of small molecules such as lipids or receptor ligands to anti-cancer drugs has been used to improve their pharmacological properties. In this work, we studied the biological effects of several small-molecule enhancers into a short oligonucleotide made of five floxuridine units. Specifically, we studied adding cholesterol, palmitic acid, polyethyleneglycol (PEG 1000), folic acid and triantennary N-acetylgalactosamine (GalNAc) as potential enhancers of cellular uptake. As expected, all these molecules increased the internalization efficiency with different degrees depending on the cell line. The conjugates showed antiproliferative activity due to their metabolic activation by nuclease degradation generating floxuridine monophosphate. The cytotoxicity and apoptosis assays showed an increase in the anti-cancer activity of the conjugates related to the floxuridine oligomer, but this effect did not correlate with the internalization results. Palmitic and folic acid conjugates provide the highest antiproliferative activity without having the highest internalization results. On the contrary, cholesterol oligomers that were the best-internalized oligomers had poor antiproliferative activity, even worse than the unmodified floxuridine oligomer. Especially relevant is the effect induced by palmitic and folic acid derivatives generating the most active drugs. These results are of special interest for delivering other therapeutic oligonucleotides.

Apical sodium-dependent bile acid transporter, drug target for bile acid related diseases and delivery target for prodrugs: Current and future challenges

Apical Sodium-dependent Bile Acid Transporter (ASBT) actively reabsorbs bile acids (BAs) from the gut lumen. This process is a critical step in the enterohepatic circulation (EHC) of BAs and plays important roles in the homeostasis of BAs in the body. Therefore, ASBT is considered a favorite target for intervention to regulate the levels of BAs, cholesterol, lipid and glucose etc. In addition, ASBT is also a popular delivery target for developing prodrugs, due to its intestinal localization, high expression and high uptake capacity. In the past ten years, ASBT has been the focus by both academia and pharmaceutical industry as research targets not only for BA-related diseases but also for prodrug delivery. Numerous studies have been published and many candidate ASBT inhibitors are being developed. Here we review and summarize the current states of ASBT research with a focus on the therapeutic applications of ASBT as a target for therapy as well as a delivery target for prodrugs. The current and future challenges in ASBT research and outlook of drug developments are discussed.

Mechanism of a Novel Camptothecin-Deoxycholic Acid Derivate Induced Apoptosis against Human Liver Cancer HepG2 Cells and Human Colon Cancer HCT116 Cells

BACKGROUND

Camptothecin (CPT) is known as an anticancer drug in traditional Chinese medicine. However, due to the lack of targeting, low solubility, and instability of CPT, its therapeutic applications are hampered. Therefore, we synthesized a series of CPT-bile acid analogues that obtained a national patent to improve their tumour-targeting chemotherapeutic effects on liver or colon cancers. Among these analogues, the compound G2 shows high antitumor activity with enhanced liver targeting and improved oral absorption. It is significant to further investigate the possible anticancer mechanism of G2 for its further clinical research and application.

OBJECTIVE

We aimed to unearth the anticancer mechanism of G2 in HepG2 and HCT116 cells.

METHODS

Cell viability was measured using MTT assay; cell cycle, Mitochondrial Membrane Potential (MMP), and cell apoptosis were detected by flow cytometer; ROS was measured by Fluorescent Microplate Reader; the mRNA and protein levels of cell cycle-related and apoptosis-associated proteins were examined by RT-PCR and western blot, respectively.

RESULTS

We found that G2 inhibited cells proliferation of HepG2 and HCT116 remarkably in a dosedependent manner. Moreover, G2-treatment led to S and G2/M phase arrest in both cells, which could be elucidated by the change of mRNA levels of p21, p27 and Cyclin E and the increased protein level of p21. G2 also induced dramatically ROS accumulated and MMP decreased, which contributed to the apoptosis through activation of both the extrinsic and intrinsic pathways via changing the genes and proteins expression involved in apoptosis pathway in both of HepG2 and HCT116 cells.

CONCLUSION

These findings suggested that the apoptosis in both cell lines induced by G2 was related to the extrinsic and intrinsic pathways.

Synthesis, pharmacological evaluation, and mechanistic study of adefovir mixed phosphonate derivatives bearing cholic acid and l-amino acid moieties for the treatment of HBV

The deficiency of nucleos(t)ide analogues (NAs) as anti-hepatitis B virus (HBV) drugs in clinical use is attributable to their insufficient enrichment in liver and non-target organ toxicity. We aimed to develop potent anti-HBV adefovir derivatives with hepatotrophic properties and reduced nephrotoxicity. A series of adefovir mono l-amino acids, mono cholic acid-drug conjugates were designed and synthesized, and their antiviral activity and uptake in rat primary hepatocytes and Na⁺-dependent taurocholate co-transporting polypeptide (NTCP)-HEK293 cells were evaluated. We isolated compound 6c as the optimal molecular candidate, with the highest antiviral activity (EC₅₀ 0.42 μmol/L, SI 1063.07) and highest cellular uptake in primary hepatocytes and NTCP-HEK293 cells. In-depth mechanistic studies demonstrated that 6c exhibited a lower toxicity in HK-2 cells when compared to adefovir dipivoxil (ADV). This is because 6c cannot be transported by the human renal organic anion transporter 1 (hOAT1). Furthermore, pharmacokinetic characterization and tissue distribution of 6c indicates it has favorable druggability and pharmacokinetic properties. Further docking studies suggested compounds with ursodeoxycholic acid and l-amino acid groups are better at binding to NTCP due to their hydrophilic properties, indicating that 6c is a potential candidate as an anti-HBV therapy and therefore merits further investigation.

Enhanced Liver Targeting of Camptothecin via Conjugation with Deoxycholic Acid

Camptothecin (CPT) shows potent anticancer activity through inhibition of topoisomerase I. However, its water insolubility and severe toxicity limit its clinical application. Coupling with bile acid moieties is a promising method for liver-targeted drug delivery, which takes advantage of the bile acid receptors on hepatocytes. In this study, we evaluated the potential liver targeting and stability of a deoxycholic acid-CPT conjugate (G2). The competitive inhibition of antitumor activity experiment based on bile acid transporters was performed using the MTT method. The effects of deoxycholic acid on uptake of G2 and CPT were assessed in 2D and 3D HepG2 cell models. The stability of G2 and CPT was evaluated in vitro (in simulated gastric fluid, simulated intestinal fluid, and fresh rat plasma). Finally, biodistribution of G2 and CPT was investigated in Kunming mice following oral administration. The results showed that deoxycholic acid pretreatment could significantly reduce the antitumor activity and cellular uptake of G2 in HepG2 cells, but had no distinct effects on CPT. Meanwhile, G2 exhibited better stability compared with CPT. More importantly, biodistribution study in mice demonstrated that the liver targeting index of G2 increased 1.67-fold than that of CPT. Overall, the study suggests that conjugation with deoxycholic acid is a feasible method to achieve liver targeting delivery of CPT.

Mechanism of hepatic targeting via oral administration of DSPE-PEG-cholic acid-modified nanoliposomes

In oral administration, gastrointestinal physiological environment, gastrointestinal epithelial cell membranes, and blood circulation are typical biological barriers to hepatic delivery of ligand-modified nanoparticle drug delivery systems. To elucidate the mechanism of oral hepatic targeting of cholic acid receptor-mediated nanoliposomes (LPs) (distearoyl phosphatidylethanolamine–polyethylene glycol–cholic acid-modified LPs, CA-LPs), evaluations were performed on colon cancer Caco-2 cell monolayers, liver cancer HepG2 cells, and a rat intestinal perfusion model. CA-LPs, ~100 nm in diameter, exhibited sustained-release behavior and had the greatest stability in rat gastrointestinal fluid and serum for both size and entrapment efficiency. CA-LPs demonstrated highest transport across Caco-2 cells and highest cellular uptake by HepG2 cells. The enhanced endocytosis of CA-LPs was found to be mediated by Na⁺/taurocholate cotransporting polypeptide and involved the caveolin-mediated endocytosis pathway. Further, we used fluorescence resonance energy transfer (FRET) technology to show that the CA-LPs maintained their structural integrity in part during the transport across the Caco-2 cell monolayer and uptake by HepG2 cells.

Transporter-targeted cholic acid-cytarabine conjugates for improved oral absorption

Cytarabine has a poor oral absorption due to its rapid deamination and poor membrane permeability. Bile acid transporters are highly expressed both in enterocytes and hepatocytes and to increase the oral bioavailability and investigate the potential application of cytarabine for liver cancers, a transporter- recognizing prodrug strategy was applied to design and synthesize four conjugates of cytarabine with cholic acid (CA), chenodeoxycholic acid (CDCA), hyodeoxycholic acid (HDCA) and ursodeoxycholic acid (UDCA). The anticancer activities against HepG2 cells were evaluated by MTT assay and the role of bile acid transporters during cellular transport was investigated in a competitive inhibition experiment. The in vitro and in vivo metabolic stabilities of these conjugates were studied in rat plasma and liver homogenates. Finally, an oral bioavailability study was conducted in rats. All the cholic acid-cytarabine conjugates (40μM) showed potent antiproliferative activities (up to 70%) against HepG2 cells after incubation for 48h. The addition of bile acids could markedly reduce the antitumor activities of these conjugates. The N(4)-ursodeoxycholic acid conjugate of cytarabine (compound 5) exhibited optimal stability (t1/2=90min) in vitro and a 3.9-fold prolonged half-life of cytarabine in vivo. More importantly, compound 5 increased the oral bioavailability 2-fold compared with cytarabine. The results of the present study suggest that the prodrug strategy based on the bile acid transporters is suitable for improving the oral absorption and the clinical application of cytarabine.

Synthesis of cholic-acid-carrying polymer and in-vitro evaluation of hepatoma-targeting nanoparticles decorated with the polymer

The specific interaction between bile acids and the bile acids transporters provides a promising way for hepatoma-targeted drug delivery. We synthesized an amphipathic polymer containing cholic acid (CA), the main bile acids in body, and prepared CA-functionalized nanoparticles to target hepatoma cells. Poly-[3-(4-vinylbenzonate)-7, 12-dihydroxy-5-cholan-24-oic acid] (PVBCA) was synthesized by introducing methyl cholate onto polyvinyl benzoate polymer backbone, and was characterized by (1)H-NMR, FT-IR, and GFC. PVBCA can be incorporated onto PLGA nanoparticles surface via the emulsion-solvent evaporation procedure, resulting in the nanoparticles carrying CA moieties on their surface. The binding of CA moieties to the bile acids' transporters on the cell membrane enhances the cellular uptake of the nanoparticles significantly. The SMMC-7721 cell uptake of PVBCA-decorated nanoparticles increases with amount of incorporated PVBCA and is 2- to 2.8-fold higher than that of the normal PLGA nanoparticles. By exclusion of specific endocytosis pathways using chemical inhibitors, we found that the uptake mechanism of PVBCA-decorated nanoparticles was mainly attributed to clathrin-and-caveolae-independent endocytosis, which was distinct from that of PLGA nanoparticles. The present study provides a simple and versatile method for hepatoma-targeted delivery of nanoparticles.

New 3'-O-aromatic acyl-5-fluoro-2'-deoxyuridine derivatives as potential anticancer agents

New aromatic and aliphatic 3'-O-acyl-5-fluoro-2'-deoxyuridine derivatives were synthesized and evaluated as candidates for prodrugs against various cancer cell lines. As the most promising candidate for antimalignant therapeutics was found a dual-acting acyl derivative 7h, which apparently released not only the known anticancer nucleoside, 5-fluoro-2'-deoxyuridine (FdU), but also an additional active metabolite, acetylsalicylic acid, reinforcing thus therapeutic effect of FdU. Promising therapeutic indices showed also some aromatic dicarboxylic acids derivatives decorated with FdU esters (11 and 12).

Repurposing FDA-approved drugs as therapeutics to treat Rift Valley fever virus infection

There are currently no FDA-approved therapeutics available to treat Rift Valley fever virus (RVFV) infection. In an effort to repurpose drugs for RVFV treatment, a library of FDA-approved drugs was screened to determine their ability to inhibit RVFV. Several drugs from varying compound classes, including inhibitors of growth factor receptors, microtubule assembly/disassembly, and DNA synthesis, were found to reduce RVFV replication. The hepatocellular and renal cell carcinoma drug, sorafenib, was the most effective inhibitor, being non-toxic and demonstrating inhibition of RVFV in a cell-type and virus strain independent manner. Mechanism of action studies indicated that sorafenib targets at least two stages in the virus infectious cycle, RNA synthesis and viral egress. Computational modeling studies also support this conclusion. siRNA knockdown of Raf proteins indicated that non-classical targets of sorafenib are likely important for the replication of RVFV.