Cytotoxicity of pivoxil esters of antiviral acyclic nucleoside phosphonates: adefovir dipivoxil versus adefovir

Octadecyloxyethyl Adefovir Exhibits Potent in vitro and in vivo Cytotoxic Activity and Has Synergistic Effects with Ara-C in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) continues to be a deadly disease, with only 50-70% of patients achieving complete remission and less than 30% of adults having sustained long-term remissions. In order to address these unmet medical needs, we carried out a high-throughput screen of an in-house library of on- and off-patent drugs with the OCI/AML-2 cell line. Through this screen, we discovered adefovir dipi-voxil (adefovir-DP) as being active against human AML. In addition to adefovir-DP, there are second-generation formulations of adefovir, including octadecyloxyethyl adefovir (ODE-adefovir) and hexadecyloxypropyl adefovir (HDP-adefovir), which were designed to overcome the pharmacokinetic problems of the parent compound adefovir. Given the known clinical benefit of nucleoside analogs for the treatment of AML, we undertook studies to evaluate the potential benefit of adefovir-based molecules. In AML cell lines and patient samples, adefovir-DP and ODE-adefovir were highly potent, whereas HDP-adefovir was significantly less active. Interestingly, ODE-adefovir was remarkably less toxic than adefovir-DP towards normal hematopoietic cells. In addition, ODE-adefovir at a dose of 15 mg/kg/day showed potent activity against human AML in a NOD/SCID mouse model, with a reduction of human leukemia in mouse bone marrow of > 40% in all mice tested within 20 days of treatment. Based on its chemical structure, we hypothesized that the cytotoxicity of ODE-adefovir toward AML was through cell cycle arrest and DNA damage. Indeed, ODE-adefovir treatment induced cell cycle arrest in the S phase and increased levels of pH2Ax, indicating the induction of DNA damage. Furthermore, there was an increase in phospho-p53, transactivation of proapoptotic genes and activation of the intrinsic apoptotic pathway. Subsequent investigation unveiled strong synergism between ODE-adefovir and ara-C, making their coadministration of potential clinical benefit. Expression of MRP4, a nucleoside transporter, appeared to influence the response of AML cells to ODE-adefovir, as its inhibition potentiated ODE-adefovir killing. Taken together, our findings indicate that clinical development of ODE-adefovir or related compounds for the treatment of AML is warranted.

Stable Human Hepatoma Cell Lines for Efficient Regulated Expression of Nucleoside/Nucleotide Analog Resistant and Vaccine Escape Hepatitis B Virus Variants and Woolly Monkey Hepatitis B Virus

Hepatitis B virus (HBV) causes acute and chronic hepatitis B (CHB). Due to its error-prone replication via reverse transcription, HBV can rapidly evolve variants that escape vaccination and/or become resistant to CHB treatment with nucleoside/nucleotide analogs (NAs). This is particularly problematic for the first generation NAs lamivudine and adefovir. Though now superseded by more potent NAs, both are still widely used. Furthermore, resistance against the older NAs can contribute to cross-resistance against more advanced NAs. For lack of feasible HBV infection systems, the biology of such variants is not well understood. From the recent discovery of Na⁺-taurocholate cotransporting polypeptide (NTCP) as an HBV receptor new in vitro infection systems are emerging, yet access to the required large amounts of virions, in particular variants, remains a limiting factor. Stably HBV producing cell lines address both issues by allowing to study intracellular viral replication and as a permanent source of defined virions. Accordingly, we generated a panel of new tetracycline regulated TetOFF HepG2 hepatoma cell lines which produce six lamivudine and adefovir resistance-associated and two vaccine escape variants of HBV as well as the model virus woolly monkey HBV (WMHBV). The cell line-borne viruses reproduced the expected NA resistance profiles and all were equally sensitive against a non-NA drug. The new cell lines should be valuable to investigate under standardized conditions HBV resistance and cross-resistance. With titers of secreted virions reaching >3x10⁷ viral genome equivalents per ml they should also facilitate exploitation of the new in vitro infection systems.

Quercetin-POM (pivaloxymethyl) conjugates: Modulatory activity for P-glycoprotein-based multidrug resistance

BACKGROUND

We previously demonstrated that the bioactivity of quercetin could be improved through conjugation with a hydrolysable pivaloxymethyl (POM) group.

PURPOSE

Present study aimed to evaluate MDR (multidrug resistance)-modulatory activity of the quercetin-POM conjugates.

STUDY DESIGN/METHODS

MDR-modulatory activity was determined by measuring cytotoxicity of various anticancer agents to MDR MES-SA/Dx5 cell lines upon combination with the quercetin-POM conjugates.

RESULTS

The quercetin-7-O-POM conjugate (7-O-POM-Q) was significantly more potent than quercetin in reversing MDR, which recovered the cytotoxicity of various anticancer agents with EC50 values of 1.1-1.3 µM. A series of mechanistic studies revealed that 7-O-POM-Q competes with verapamil in binding to the same drug-binding site of the major MDR target, Pgp (P-glycoprotein), and inhibits Pgp-mediated drug efflux with a similar potency as verapamil. The physicochemical properties of 7-O-POM-Q were then evaluated, which confirmed that 7-O-POM-Q has remarkably enhanced cellular uptake and intracellular localization compared with quercetin. Additionally, it is noteworthy that 7-O-POM-Q undergoes slow hydrolysis to quercetin over a prolonged period of time.

CONCLUSION

The quercetin-POM conjugate showed significantly improved MDR-reversing activity compared with quercetin, which could be attributed to its capacity to maintain high intracellular concentrations.

Loco-regional cancer drug therapy: present approaches and rapidly reversible hydrophobization (RRH) of therapeutic agents as the future direction

Insufficient drug uptake by solid tumors remains the major problem for systemic chemotherapy. Many studies have demonstrated anticancer drug effects to be dose-dependent, although dose-escalation studies have resulted in limited survival benefit with increased systemic toxicities. One solution to this has been the idea of loco-regional drug treatments, which offer dramatically higher drug concentrations in tumor tissues while minimizing systemic toxicity. Although loco-regional delivery has been most prominent in cancers of the liver, soft tissues and serosal peritoneal malignancies, survival benefits are very far from desirable. This review discusses the evolution of loco-regional treatments, the present approaches and offers rapidly reversible hydrophobization of drugs as the new future direction.

Amidate prodrugs of 9-[2-(phosphonomethoxy)ethyl]adenine as inhibitors of adenylate cyclase toxin from Bordetella pertussis

Adenylate cyclase toxin (ACT) is the key virulence factor of Bordetella pertussis that facilitates its invasion into the mammalian body. 9-[2-(Phosphonomethoxy)ethyl]adenine diphosphate (PMEApp), the active metabolite of the antiviral drug bis(POM)PMEA (adefovir dipivoxil), has been shown to inhibit ACT. The objective of this study was to evaluate six novel amidate prodrugs of PMEA, both phenyloxy phosphonamidates and phosphonodiamidates, for their ability to inhibit ACT activity in the J774A.1 macrophage cell line. The two phenyloxy phosphonamidate prodrugs exhibited greater inhibitory activity (50% inhibitory concentration [IC50] = 22 and 46 nM) than the phosphonodiamidates (IC50 = 84 to 3,960 nM). The inhibitory activity of the prodrugs correlated with their lipophilicity and the degree of their hydrolysis into free PMEA in J774A.1 cells. Although the prodrugs did not inhibit ACT as effectively as bis(POM)PMEA (IC50 = 6 nM), they were significantly less cytotoxic. Moreover, they all reduced apoptotic effects of ACT and prevented an ACT-induced elevation of intracellular [Ca(2+)]i. The amidate prodrugs were less susceptible to degradation in Caco-2 cells compared to bis(POM)PMEA, while they exerted good transepithelial permeability in this assay. As a consequence, a large amount of intact amidate prodrug is expected to be available to target macrophages in vivo. This feature makes nontoxic amidate prodrugs attractive candidates for further investigation as novel antimicrobial agents.

Medicinal Chemistry of Nucleoside Phosphonate Prodrugs for Antiviral Therapy

Considerable attention has been focused on the development of phosphonate-containing drugs for application in many therapeutic areas. However, phosphonate diacids are deprotonated at physiological pH and thus phosphonate-containing drugs are not ideal for oral administration, an extremely desirable requisite for the treatment of chronic diseases. To overcome this limitation several prodrug structures of biologically active phosphonate analogues have been developed. The rationale behind the design of such agents is to achieve temporary blockade of the free phosphonic functional group until their systemic absorption and delivery, allowing the release of the active drug only once at the target. In this paper, an overview of acyclic and cyclic nucleoside phosphonate prodrugs, designed as antiviral agents, is presented.

New prodrugs of Adefovir and Cidofovir

New Adefovir (PMEA) prodrugs with a pro-moiety consisting of decyl or decyloxyethyl chain bearing hydroxyl function(s), hexaethyleneglycol or a (5-methyl-2-oxo-1,3-dioxolen-4-yl)methyl unit were prepared starting from the tetrabutylammonium salt of the phosphonate drug and an appropriate alkyl bromide or tosylate. Analogously, two esters of Cidofovir [(S)-HPMPC] bearing a hexaethyleneglycol moiety were prepared. The activity of the prodrugs was evaluated in vitro against different virus families. A loss in the antiviral activities of the hydroxylated decyl or decyloxyethyl esters and hexaethyleneglycol esters of PMEA against human immunodeficiency virus (HIV) and herpesviruses [including herpes simplex virus (HSV), varicella-zoster virus (VZV), and human cytomegalovirus (CMV)] occurred in comparison with the parent compound. On the other hand, the (5-methyl-2-oxo-1,3-dioxolen-4-yl)methyl ester of PMEA showed significant activities against HIV and herpesviruses. (S)-HPMPC prodrugs exhibited anti-cytomegalovirus activities in the same range as the parent drug, whereas the anti-HSV and anti-VZV activities were one- to seven-fold lower than that of Cidofovir.

Synthesis and antiviral bioactivities of 2-cyano-3-substituted-amino(phenyl) methylphosphonylacrylates (acrylamides) containing alkoxyethyl moieties

An efficient reaction under microwave irradiation has been developed for the synthesis of a series of novel 2-cyano-3-substituted-amino(phenyl) methylphosphonylacrylates (acrylamides) II. The products obtained in shorter reaction time with moderate yields are fully characterized by elemental analysis, IR, (1)H, (13)C, and (31)P NMR spectral data. The role of introducing various substituents and the effect of incorporating alpha-aminophosphonates with an alkoxyethyl moiety into the parent cyanoacrylate (acrylamide) structure are investigated. Among the studied compounds, both II-17 and II-24 displayed good in vivo curative, protection, and inactivation effects, which were comparable to those of the commercial reference ningnanmycin (inhibitory rates of 58.8, 60.2, 78.9% and 60.0, 58.9, 85.5%, respectively, at 500 mg/L against TMV). To the best of the authors' knowledge, this is the first report on the synthesis and antiviral activity of the title compounds II.

Rapidly Reversible Hydrophobization: An Approach to High First-Pass Drug Extraction

We have investigated a rapidly reversible hydrophobization of therapeutic agents for improving first-pass uptake in locoregional drug therapy. This approach involves the attachment of a hydrophobic moiety to the drug by highly labile chemical linkages that rapidly hydrolyze upon injection. Hydrophobization drastically enhances cell-membrane association of the prodrug and, consequently, drug uptake, while the rapid lability protects nontargeted tissues from exposure to the highly active agent. Using the membrane-impermeable DNA intercalator propidium iodide, and melphalan, we report results from in vitro cellular internalization and toxicity studies. Additionally, we report in vivo results after a single liver arterial bolus injection, demonstrating both tumor targeting and increased survival in a mouse tumor model.

Synthesis and antiviral bioactivities of alpha-aminophosphonates containing alkoxyethyl moieties

A simple, efficient, and general method has been developed for the synthesis of various alpha-aminophosphonate derivatives 4a-4l by treatment of substituted benzaldehydes and aniline with bis(2-methoxyethyl)- or bis(2-ethoxyethyl) phosphite under microwave irradiation without solvents and catalysts. The products were characterized by elemental analysis, IR, 1H-NMR, 13C- and 31P-NMR spectra. The X-ray crystallographic data of the representative compound 4l was determined. The new alpha-aminophosphonate derivatives were found to possess moderate to good antiviral activity.