Self-assembled nucleo-tripeptide hydrogels provide local and sustained doxorubicin release.

Self-assembled nucleo-peptide hydrogels have a nanofibril structure composed of noncovalent molecular interactions between peptide groups as well as π-π stacking and Watson-Crick interactions via complementary nucleobases. These hydrogels have specific benefits for biomedical applications due to their DNA-like interactions in addition to the well-known advantages of peptide biomaterials: biocompatibility, extracellular matrix (ECM)-like structure, and bottom-up design. Inspired by the nucleobase stacking structure, we hypothesized that nucleo-peptides would be able to deliver the DNA-intercalating chemotherapeutic, doxorubicin (Dox) in a sustained manner when delivered locally to a solid tumor. Ade-FFF nucleo-peptide hydrogels were able to load a high concentration of Dox (1 mM) and demonstrated continuous release under in vitro degradation conditions. We adopted an in vivo tumor-bearing mouse model to evaluate the delivery of Dox by Ade-FFF hydrogels. We found that Dox-containing hydrogels reduced tumor growth and resulted in greater apoptosis-mediated cell death in the tumor as evidenced by caspase-3 expression. Pharmacokinetics and biodistribution studies also supported the observation that Dox delivery by an Ade-FFF hydrogel improves sustained delivery in the local tumor site. This study demonstrates the potential of self-assembled nucleo-peptides in biomedical applications by using their distinctive DNA-like structure.

Hypo-osmolar Formulation of Tenofovir (TFV) Enema Promotes Uptake and Metabolism of TFV in Tissues, Leading to Prevention of SHIV/SIV Infection.

Oral preexposure prophylaxis (PrEP) has been approved for prophylaxis of HIV-1 transmission but is associated with high costs and issues of adherence. Protection from anal transmission of HIV using topical microbicides and methods congruent with sexual behavior offers the promise of improved adherence. We compared the pharmacokinetics (PK) and ex vivo efficacy of iso-osmolar (IOsm) and hypo-osmolar (HOsm) rectal enema formulations of tenofovir (TFV) in rhesus macaques. Single-dose PK of IOsm or HOsm high-dose (5.28 mg/ml) and low-dose (1.76 mg/ml) formulations of TFV enemas were evaluated for systemic uptake in blood, colorectal biopsy specimens, and rectal CD4+ T cells. Markedly higher TFV concentrations were observed in plasma and tissues after administration of the HOsm high-dose formulation than with all other formulations tested. TFV and TFV diphosphate (TFV-DP) concentrations in tissue correlated for the HOsm high-dose formulation, demonstrating rapid uptake and transformation of TFV to TFV-DP in tissues. TFV-DP amounts in tissues collected at 1 and 24 h were 7 times and 5 times higher, respectively (P < 0.01), than the ones collected in tissues with the IOsm formulation. The HOsm high-dose formulation prevented infection in ex vivo challenges of rectal tissues collected at 1, 24, and 72 h after the intrarectal dosing, whereas the same TFV dose formulated as an IOsm enema was less effective.

Effects of a Nutritional Protein-Rich Drink on the Pharmacokinetics of Elvitegravir, Cobicistat, Emtricitabine, Tenofovir Alafenamide, and Tenofovir Compared With a Standard Meal in Healthy Japanese Male Subjects.

This study investigated the effects of ingested meal types on the pharmacokinetics of elvitegravir (EVG), cobicistat (COBI), emtricitabine (FTC), tenofovir alafenamide (TAF), and tenofovir (TFV) following a single administration of the single-tablet regimen (STR) of EVG/COBI/FTC/TAF (150/150/200/10 mg) in Japanese HIV-negative healthy subjects (n = 12). In this open-label, randomized, 3-way crossover study, the bioequivalence of the EVG/COBI/FTC/TAF STR following ingestion of a nutritional protein-rich drink with a reference treatment of taking a standard breakfast was evaluated. Administration under fasted conditions, no food intake, resulted in decreases in the mean AUCinf and Cmax of EVG by 50% and 57%, respectively, relative to the administration with a standard breakfast, whereas the systemic exposure of EVG with a nutritional protein-rich drink was comparable to that with a standard breakfast. The mean AUCinf and Cmax of COBI, FTC, TAF, and TFV were comparable regardless of meal intake or meal types. Although the package insert of the EVG/COBI/FTC/TAF STR states that the medication is recommended to be taken with food, this study provides an additional insight into HIV-1-infected patients that a light meal like a nutritional protein-rich drink can be an alternative to a standard meal.

Apigenin, a novel candidate involving herb-drug interaction (HDI), interacts with organic anion transporter 1 (OAT1).

BACKGROUND: Apigenin is a flavonoid compound, widely distributed in natural plants. Various studies have suggested that apigenin has inhibitory effects towards several drug transporters, such as the organic anion transporting (OAT) polypeptides, 1B1 and 1B3 (OATP1B1 and OATP1B3). However, the mechanism by which apigenin interacts with OAT1 has not been well studied. METHODS: MDCK cells stably-expressing OAT1 were used to examine the inhibitory effects of apigenin on OAT1. UPLC-MS/MS was used to evaluate the in vitro and in vivo effects of apigenin on the uptake of acyclovir by OAT1. Cytotoxicity was determined by the cell viability, MTT assays. RESULTS: Apigenin effectively inhibited the activity of OAT1 in a dose-dependent manner with an IC50 value of 0.737µM. Pre-incubation of cells with apigenin caused a time-dependent inhibition (TDI) of OAT1. Additionally, we examined the interactions between apigenin and acyclovir or adefovir. Data showed that apigenin (1µM) significantly blocked the uptake of acyclovir by OAT1 in vitro with an inhibition rate of 55%. In vivo, apigenin could increase the concentration of acyclovir in plasma when co-administered with acyclovir. Importantly, the MTT assays showed that, at a dose of 50µM, apigenin significantly reduced the cytotoxicity of adefovir and substantially increased cell viability from 50.6% to 112.62%. CONCLUSION: Our results demonstrate that apigenin regulates OAT1, and can cause TDI or herb-drug interaction (HDI) when used in combination with acyclovir or adefovir. Therefore, apigenin could be used as a nephroprotective agent when used in combination with the substrates of OAT1.

Compartmental approach to assess bioequivalence compared to the noncompartmental approach.

OBJECTIVE: The objective of this study is to evaluate the relative performance of individual or population compartmental analysis (ICA or PCA) vs. noncompartmental analysis (NCA) in estimating the systemic exposures of drugs to assess bioequivalence (BE) between original and generic formulations in the case of limited datasets. METHODS: BE study data of adefovir, finasteride, and tiropramide were chosen. The analyses were performed for the 1) original dataset, 2) limited dataset with small size for which the number of subjects was decreased to half, and 3) limited dataset with minimal-sampling timepoint of 9 samples. As for NCA and ICA, the Cmax and AUCinf were estimated using WinNonlin®. The PCA was implemented in NONMEM® and then Monte Carlo simulation was utilized to generate 10,000 sets of Cmax and AUCinf. RESULTS: The 90% confidence intervals (CIs) of the original datasets of the 3 drugs were all within BE acceptance criteria regardless of the analysis method. For small-sample-size datasets of adefovir and finasteride, BE results were maintained. In tiropramide, the lower boundary of CI computed from ICA or PCA results was less than 0.800 for the 3 small sample sizes (n = 22, 16, 10), but that of NCA results was less than 0.800 for only the smallest sample size (n = 10). As for the minimal-sampling timepoint, results were within the BE acceptance criteria for all of the 3 analyses. CONCLUSIONS: Compartmental approaches can provide a complementary method for BE assessment, as well as being used for restricted-design studies.

Liquid oral suspension adefovir dipivoxil (GS-02-526): an update on treatments for hepatitis B infection.

Though the global epidemiology of hepatitis B virus infection has declined due to effective immunization, chronic hepatitis B (CHB) remains a serious public health problem and there is still a need for more treatment options that are efficient, safe and simple for different kinds of CHB patients. Adefovir dipivoxil (ADV) liquid suspension (GS-02-526), as a new form of oral ADV, not only has competent antiviral efficacy, but is also more convenient for patients with swallowing difficulties or patients with impaired renal function requiring dosage adjustment. The clinical data evaluating the safety, tolerability and antiviral activity of liquid suspension of ADV as well as its tablet are summarized in this article. The availability of liquid oral suspension of ADV would allow more patients to receive timely and reasonable antiviral treatments.

Pharmacokinetics of a multipurpose pod-intravaginal ring simultaneously delivering five drugs in an ovine model.

Multipurpose technologies that simultaneously protect from sexually transmitted infections and unintended pregnancy are urgently needed. Pod-intravaginal rings (IVRs) formulated with the antiretroviral agents (ARVs) tenofovir, nevirapine, and saquinavir and the contraceptives etonogestrel and estradiol were evaluated in sheep. Steady-state concentrations were maintained for 28 days with controlled, sustained delivery. This proof-of-principle study demonstrates that pod IVRs can deliver three ARVs from different mechanistic classes and a progestin-estrogen combination over the wide range needed for putative preventative efficacy.

Mechanism for effective lymphoid cell and tissue loading following oral administration of nucleotide prodrug GS-7340.

GS-7340 is a prodrug of tenofovir (TFV) that more efficiently delivers TFV into lymphoid cells and tissues than the clinically used prodrug TFV disoproxil fumarate, resulting in higher antiviral potency at greatly reduced doses and lower systemic TFV exposure. First-pass extraction by the intestine and liver represents substantial barriers to the oral delivery of prodrugs designed for rapid intracellular hydrolysis. In order to understand how GS-7340 reduces first-pass clearance to be an effective oral prodrug, its permeability and stability were characterized in vitro and detailed pharmacokinetic studies were completed in dogs. GS-7340 showed concentration-dependent permeability through monolayers of caco-2 cells and dose-dependent oral bioavailability in dogs, increasing from 1.7% at 2 mg/kg to 24.7% at 20 mg/kg, suggesting saturable intestinal efflux transport. Taking into account a 65% hepatic extraction measured in portal vein cannulated dogs, high dose GS-7340 is nearly completely absorbed. Consistent with the proposed role of intestinal efflux transport, coadministration of low dose GS-7340 with a transport inhibitor substantially increased GS-7340 exposure. The result of effective oral absorption and efficient lymphoid cell loading was reflected in the high and persistent levels of the pharmacologically active metabolite, TFV diphosphate, in peripheral blood mononuclear cells following oral administration to dogs. In conclusion, GS-7340 reaches the systemic circulation to effectively load target cells by saturating intestinal efflux transporters, facilitated by its high solubility, and by maintaining sufficient stability in intestinal and hepatic tissue.

Tenofovir disoproxil fumarate in pregnancy and prevention of mother-to-child transmission of HIV-1: is it time to move on from zidovudine?

OBJECTIVES: Zidovudine (ZDV) has been the cornerstone of antiretroviral (ARV) therapy for pregnant women infected with HIV-1 in the prevention of mother-to-child transmission (MTCT) and remains the only licensed ARV for use in pregnancy. We explored the current and future roles of tenofovir disoproxil fumarate (TDF) in the prevention of MTCT of HIV-1. METHODS: We reviewed the published literature by conducting database searches of in vitro, animal and clinical studies, reported in journals and at conferences, using the search terms Tenofovir/gs4331/viread, pregnant/pregnancy, lactate, lactation, natal, reproduce/reproduction, placenta/placental, malformation, and teratogenicity/teratogenic. RESULTS: In a macaque model, perinatal exposure to very high dose tenofovir resulted in bone toxicity in some offspring. However, perinatal use of TDF, both single dose and as part of highly active antiretroviral therapy in women, has been well tolerated in the short term by mothers and their infants. Further, the addition of single-dose TDF to single-dose nevirapine (SD-NVP) during delivery following maternal ZDV use during pregnancy significantly reduces the frequency of nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance. CONCLUSIONS: The addition of TDF to SD-NVP reduces NNRTI resistance. The role of TDF in this setting and during pregnancy for reducing rates of MTCT requires investigation. While short-term toxicity data are encouraging, long-term follow-up of exposed mothers and infants is required.

An oral TLR7 agonist is a potent adjuvant of DNA vaccination in transgenic mouse tumor models.

In vivo electroporation of plasmid DNA (DNA-EP) is an efficient and safe method for vaccines resulting in increased DNA uptake, enhanced protein expression and increased immune responses to the target antigen in a variety of species. To further enhance the efficacy of DNA-EP, we have evaluated the toll-like receptor7 (TLR7) agonist-2, 9, substituted 8-hydroxyadenosine derivative or SM360320--as an adjuvant to vaccines against HER2/neu and CEA in BALB-neuT and CEA transgenic mice (CEA.Tg), respectively. SM360320 induced in vivo secretion of interferon alpha (IFNalpha) and exerted a significant antitumor effect in CEA.Tg mice challenged with a syngenic tumor cell line expressing CEA and an additive effect with a CEA vaccine. Additionally, combination of SM360320 with plasmid encoding the extracellular and transmembrane domain of ratHER2/neu affected the spontaneous tumor progression in BALB-neuT mice treated in an advanced disease setting. The antitumor effect in mice treated with DNA-EP and SM360320 was associated with an anti-CEA and anti-p185(neu) antibody isotype switch from IgG1 to IgG2a. These data demonstrate that SM360320 exerts significant antitumor effects and can act in association with DNA-EP for CEA-positive colon cancer and HER2-positive mammary carcinoma. These observations therefore emphasize the potential of SM360320 as immunological adjuvant for therapeutic DNA vaccines.

Metabolic activation of pradefovir by CYP3A4 and its potential as an inhibitor or inducer.

Metabolic activation of pradefovir to 9-(2-phosphonylmethoxyethyl)adenine (PMEA) was evaluated by using cDNA-expressed CYP isozymes in portal vein-cannulated rats following oral administration and in human liver microsomes. The enzyme induction potential of pradefovir was evaluated in rats following multiple oral dosing and in primary cultures of human hepatocytes. The results indicated that CYP3A4 is the only cDNA-expressed CYP isozyme catalyzing the conversion of pradefovir to PMEA. Pradefovir was converted to PMEA in human liver microsomes with a K(m) of 60 microM, a maximum rate of metabolism of 228 pmol/min/mg protein, and an intrinsic clearance of about 359 ml/min. Addition of ketoconazole and monoclonal antibody 3A4 significantly inhibits the conversion of pradefovir to PMEA in human liver microsomes, suggesting the predominant role of CYP3A4 in the metabolic activation of pradefovir. Pradefovir at 0.2, 2, and 20 microM was neither a direct inhibitor nor a mechanism-based inhibitor of CYP3A4, CYP2D6, CYP2C9, CYP2C19, CYP2E1, and CYP1A2 in human liver microsomes. In rats, the liver was the site of metabolic activation of pradefovir, whereas the small intestine did not play a significant role in the metabolic conversion of pradefovir to PMEA. Daily oral dosing (300 mg/kg of body weight) to rats for 8 days showed that pradefovir was not an inducer of P450 enzymes in rats. Furthermore, pradefovir at 10 microg/ml was not an inducer of either CYP1A2 or CYP3A4/5 in primary cultures of human hepatocytes.

Biological effects of short-term or prolonged administration of 9-[2-(phosphonomethoxy)propyl]adenine (tenofovir) to newborn and infant rhesus macaques.

The reverse transcriptase inhibitor 9-[2-(phosphonomethoxy)propyl]adenine (PMPA; tenofovir) was previously found to offer strong prophylactic and therapeutic benefits in an infant macaque model of pediatric human immunodeficiency virus (HIV) infection. We now summarize the toxicity and safety of PMPA in these studies. When a range of PMPA doses (4 to 30 mg/kg of body weight administered subcutaneously once daily) was administered to 39 infant macaques for a short period of time (range, 1 day to 12 weeks), no adverse effects on their health or growth were observed; this included a subset of 12 animals which were monitored for more than 2 years. In contrast, daily administration of a high dose of PMPA (30 mg/kg subcutaneously) for prolonged periods of time (>8 to 21 months) to 13 animals resulted in a Fanconi-like syndrome (proximal renal tubular disorder) with glucosuria, aminoaciduria, hypophosphatemia, growth restriction, bone pathology (osteomalacia), and reduced clearance of PMPA. The adverse effects were reversible or were alleviated following either complete withdrawal of PMPA treatment or reduction of the daily regimen from 30 mg/kg to 2.5 to 10 mg/kg subcutaneously. Finally, to evaluate the safety of a prolonged low-dose treatment regimen, two newborn macaques were started on a 10-mg/kg/day subcutaneous regimen; these animals are healthy and have normal bone density and growth after 5 years of daily treatment. In conclusion, our findings suggest that chronic daily administration of a high dose of PMPA results in adverse effects on kidney and bone, while short-term administration of relatively high doses and prolonged low-dose administration are safe.

Adefovir dipivoxil: a new antiviral agent for the treatment of hepatitis B virus infection.

BACKGROUND: Hepatitis B virus (HBV) infection is a major problem worldwide and an important cause of chronic liver disease and cirrhosis. Currently available treatments include interferon alfa-2b, lamivudine, and adefovir dipivoxil. Adefovir dipivoxil is an acyclic nucleotide analogue that was developed in part to improve on the limitations of earlier therapies. OBJECTIVE: This article is a review of available data on the clinical pharmacology, virology, efficacy, tolerability, and clinical use of adefovir dipivoxil. METHODS: A search of the English-language literature indexed on MEDLINE from 1966 to July 2003 was performed using the terms adefovir, PMEA, and Bis-POM PMEA. Pertinent abstracts from scientific meetings on infectious diseases and hepatology were also included. The manufacturer of adefovir dipivoxil provided additional information. These materials were supplemented by US Food and Drug Administration briefing documents and other unpublished materials. In vitro and preclinical studies were included in the review, as were Phase II and III clinical trials. RESULTS: In vitro, adefovir dipivoxil concentrations exceed those necessary to inhibit both wild-type and lamivudine-resistant isolates of HBV. In clinical trials, adefovir dipivoxil was clinically and virologically effective in patients in whom lamivudine therapy had failed due to the presence of lamivudine-resistant HBV. The drug was generally well tolerated. The risk of nephrotoxicity, the most notable adverse effect of adefovir dipivoxil at previously used higher doses, has been substantially reduced at the currently recommended dosage of 10 mg/d. CONCLUSION: Based on the data reviewed adefovir dipivoxil is an effective and well-tolerated alternative for the treatment of HBV infection, including disease that is lamivudine resistant.

Enhanced inhibition of HIV-1 replication in macrophages by antisense oligonucleotides, ribozymes and acyclic nucleoside phosphonate analogs delivered in pH-sensitive liposomes.

An antisense oligodeoxynucleotide against the human immunodeficiency virus type 1 (HIV-1) Rev response element, a ribozyme complementary to the HIV-1 5'-LTR, and the reverse transcriptase inhibitors 9-(2-phosphonylmethoxyethyl) adenine (PMEA) and (R)-9-(2-phosphonylmethoxypropyl)-adenine (PMPA) inhibited virus replication in monocyte-derived macrophages more effectively when delivered in pH-sensitive liposomes compared to the free drugs.

Human renal organic anion transporter 1 (hOAT1) and its role in the nephrotoxicity of antiviral nucleotide analogs.

hOAT1 is a renal membrane protein able to efficiently transport acyclic nucleoside phosphonates (ANPs). When expressed in CHO cells, hOAT1 mediates the uptake and cytotoxicity of ANPs suggesting that it plays an active role in the nephrotoxicity associated with cidofovir CMV therapy and high-dose adefovir HIV therapy. Although efficiently transported by hOAT1, tenofovir did not show any significant cytotoxicity in isolated human proximal tubular cells, which correlates with the lack of nephrotoxicity observed in HIV-infected patients on prolonged tenofovir therapy.

Antiviral efficacy and pharmacokinetics of oral adefovir dipivoxil in chronically woodchuck hepatitis virus-infected woodchucks.

The antiviral efficacy of orally administered adefovir dipivoxil was evaluated in an 18-week study (12 weeks of treatment and 6 weeks of recovery) conducted with woodchucks chronically infected with woodchuck hepatitis virus (WHV). Adefovir dipivoxil is a prodrug of adefovir designed to enhance its oral bioavailability. Following administration of 15 mg of adefovir dipivoxil per kg of body weight in four WHV-infected animals, the mean maximum concentration of adefovir in serum was 0.462 microg/ml, with an elimination half-life of 10.2 h, and the oral bioavailability of adefovir was estimated to be 22.9% (+/-11.2%). To study antiviral efficacy, the animals were divided into three groups. There were six animals each in a high-dose group (15 mg/kg/day) and a low-dose group (5 mg/kg/day). A vehicle control group consisted of five animals because WHV DNA was detectable only by PCR at the time of the study in one of the original six animals. Efficacy was evaluated by determining the levels of WHV DNA in serum. The geometric mean WHV DNA level for the high-dose group diminished by >40-fold (>1.6 log(10)) after 2 weeks of treatment and >300-fold (>2.5 log(10)) at 12 weeks. There was a >10-fold reduction in five of six low-dose animals by 2 weeks, but levels were unchanged in one animal. By 12 weeks of treatment there was a >45-fold (>1.6 log(10)) reduction of WHV DNA levels, and serum WHV DNA levels were below the limit of quantification in three of six animals. Viral DNA levels returned to pretreatment levels during the 6-week recovery period. There were no clinically significant changes in body weight, hematology, or serum chemistry values, including bicarbonate or lactate, in any of the treated animals. No histologic evidence of liver injury was apparent in the biopsies. Under the conditions of this study, adefovir dipivoxil was an effective antihepadnaviral agent.

Inhibition of intestinal metabolism of the antiviral ester prodrug bis(POC)-PMPA by nature-identical fruit extracts as a strategy to enhance its oral absorption: an in vitro study.

PURPOSE: To explore the usefulness of fruit extracts as enhancers of the oral absorption of esterase-sensitive prodrugs. METHODS: Inhibition of esterase-mediated degradation by nature-identical fruit extracts was evaluated using 1) p-nitrophenylacetate (model substrate for esterase-activity) in rat intestinal homogenates and 2) bis(isopropyloxycarbonyloxymethyl)-(R)-9-[(2-phosphonomethoxy++ +)propyl]adenine [bis(POC)-PMPA] (esterase-sensitive prodrug of the antiviral agent PMPA) in Caco-2 cell homogenates and in intestinal homogenates from rat, pig and man. Subsequently, transport of the ester prodrug was studied across Caco-2 monolayers in the presence or absence of fruit extracts. RESULTS: In homogenates from rat ileum, the esterase activity could be reduced significantly by the inclusion of fruit extracts (1%): the initial enzymatic degradation of p-nitrophenylacetate was inhibited by 77% (strawberry), 16% (passion fruit) and 57% (banana). A similar inhibition of bis(POC)-PMPA metabolism by fruit extracts was observed in intestinal homogenates from several species and in homogenates from Caco-2 cells. Transport of total PMPA across Caco-2 monolayers was enhanced 3-fold by co-incubation with strawberry extract (1%). The fraction of intact prodrug appearing in the acceptor compartment increased from virtually zero to 67%. CONCLUSIONS: The results suggest that co-incubation with nature-identical fruit extracts might be useful as a strategy to enhance the transepithelial transport of esterase-sensitive prodrugs through inhibition of intracellular metabolism of the prodrug.

Administration of 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA) to gravid and infant rhesus macaques (Macaca mulatta): safety and efficacy studies.

9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA) significantly inhibits viral reverse transcription and has been reported to sustain low virus load in SIV-infected rhesus monkeys. Based on these findings, studies were conducted to assess the safety, efficacy, and placental transfer of PMPA when administered once daily subcutaneously to gravid rhesus monkeys during the second and third trimesters and their offspring (30 mg/kg/day). Fetuses (SIV-infected, N = 6; noninfected, N = 6) were monitored sonographically, and maternal/fetal blood samples were collected at select time points for hematologic, clinical chemical, virologic, immunologic, and pharmacologic assessments. Newborns were delivered by cesarean section at term and nursery reared for postnatal studies. Infants were administered PMPA once daily beginning on day 2 of life until 9 months postnatal age. Results of these studies have shown significant placental transport of PMPA, with peak fetal levels at 1 to 3 hours post-maternal administration; a significant and sustained reduction in viral load in SIV-infected fetuses and infants; and marked improvements in outcome (e.g., survival, growth, health) in SIV-infected offspring. However, decreased infant body weights and alterations of select serum biochemical parameters (e.g., decreased phosphorus levels, elevated alkaline phosphatase) have been shown to occur in approximately 67% of PMPA-treated infants, with severe growth restriction and bone-related toxicity in approximately 25% of animals studied. These data suggest that although PMPA holds great promise for HIV-infected patients, there is the potential for bone-related toxicity at chronic, high dosages, particularly in infants.

Toxicity associated with high dosage 9-[(2R,5R-2,5-dihydro-5-phosphonomethoxy)-2-furanyl]adenine therapy off attempts to abort early FIV infection.

9-[(2R,5R-2,5-dihydro-5-phosphonomethoxy)-2-furanyl]adenine, or D4API, was tested in the feline immunodeficiency virus (FIV) infection model and found to be significantly more inhibitory in vitro than its parent compound 9-phosphonylmethoxethyl adenine (PMEA). Cytotoxicity was less than for PMEA or azidothymidine (AZT) for culture periods of 7 days, but more toxic after 10 days. D4API was rapidly absorbed by cats following subcutaneous inoculation, with a plasma half-life of less than 1 h after intravenous inoculation and between 2 and 3 h after subcutaneous injection. Peripheral blood mononuclear cells collected from cats given a single dose of D4API were refractory, however, to FIV infection in vitro for up to 24 h. Given its prolonged intracellular phase and high selectivity index, high dose D4API therapy was tested for its ability to abort an acute (i.e. 2 week) FIV infection. A divided daily dose of D4API, which was one-fourth the toxic dose and 125 times the concentration that would totally inhibit virus replication in vitro, completely abrogated the anticipated viremia and antibody responses. Unfortunately, a majority of treated/uninfected and treated/infected test cats died acutely of drug toxicity after 47 days of treatment. Toxicity in vivo mirrored what was observed in vitro, being precipitous and cumulative in nature. Toxic signs included widespread hepatic and lymphoid necrosis. A surviving treated/FIV infected cat remained healthy to day 175 when the study was terminated; antibodies appeared 2 months later than in untreated/infected cats and virus was only detectable at low levels on day 175. In contrast, untreated/infected cats were viremic and antibody positive from 3 to 4 weeks post-infection onwards. Therefore, it was possible to alter, but not abort, an early FIV infection with prolonged, high-dose D4API treatment.

Inhibitory effect of 9-(2-phosphonylmethoxyethyl)adenine on visna virus infection in lambs: a model for in vivo testing of candidate anti-human immunodeficiency virus drugs.

The acyclic nucleoside phosphonate analog 9-(2-phosphonylmethoxyethyl)adenine (PMEA) was recently found to be effective as an inhibitor of visna virus replication and cytopathic effect in sheep choroid plexus cultures. To study whether PMEA also affects visna virus infection in sheep, two groups of four lambs each were inoculated intracerebrally with 10(6.3) TCID50 of visna virus strain KV1772 and treated subcutaneously three times a week with PMEA at 10 and 25 mg/kg, respectively. The treatment was begun on the day of virus inoculation and continued for 6 weeks. A group of four lambs were infected in the same way but were not treated. The lambs were bled weekly or biweekly and the leukocytes were tested for virus. At 7 weeks after infection, the animals were sacrificed, and cerebrospinal fluid (CSF) and samples of tissue from various areas of the brain and from lungs, spleen, and lymph nodes were collected for isolation of virus and for histopathologic examination. The PMEA treatment had a striking effect on visna virus infection, which was similar for both doses of the drug. Thus, the frequency of virus isolations was much lower in PMEA-treated than in untreated lambs. The difference was particularly pronounced in the blood, CSF, and brain tissue. Furthermore, CSF cell counts were much lower and inflammatory lesions in the brain were much less severe in the treated lambs than in the untreated controls. The results indicate that PMEA inhibits the propagation and spread of visna virus in infected lambs and prevents brain lesions, at least during early infection. The drug caused no noticeable side effects during the 6 weeks of treatment.