In vivo toxicity, pharmacokinetics, and anti-human immunodeficiency virus activity of stavudine-5'-(p-bromophenyl methoxyalaninyl phosphate) (stampidine) in mice

Radiolabeled Antibodies for Therapy of Infectious Diseases

Novel approaches to the treatment of infectious diseases are urgently needed. This need has resulted in renewing the interest in antibodies for therapy of infectious diseases. Radioimmunotherapy (RIT) is a cancer treatment modality that utilizes radiolabeled monoclonal antibodies. During the last decade we have translated RIT into the field of experimental fungal, bacterial, and HIV infections. In addition, successful proof of principle experiments with radiolabeled pan-antibodies that bind to antigens shared by major pathogenic fungi have been performed in vitro. The armamentarium of pan-antibodies would result in reducing our dependence on microorganism-specific antibodies and thus would speed up the development of RIT for infections. We believe that the time is ripe for deploying RIT in the clinic to combat infectious diseases.

Vaginal microbicides and their delivery platforms

INTRODUCTION

HIV type 1 infection, despite having fallen by one-third over the past decade, remains a global health concern affecting millions of individuals worldwide. A focal point in contemporary research aimed at global HIV prevention has been the development of safe and efficacious coitally dependent and coitally independent anti-HIV microbicides to curb heterosexual HIV transmission. Despite extensive research efforts to develop novel vaginal antiretroviral (ARV) formulations and intravaginal ring delivery systems, the clinical advancement of microbicides with improved safety, efficacy and tolerability has significantly lagged behind.

AREAS COVERED

This review focuses on the current status of both coitally dependent and coitally independent delivery platforms designed to increase user acceptability and clinical effectiveness of anti-HIV microbicides. The clinical failure of several vaginal microbicide candidates has propelled the field to mechanism-based ARV candidates that act more specifically on viral receptors, viral enzymes and host proteins. Consequently, improved vaginal microbicide delivery strategies that achieve uniform drug distribution with enhanced solubility, sustained drug release, improved product adherence with reduced dosing frequency and lack of effect on the vaginal mucosa and microbiota are being sought.

EXPERT OPINION

Clinical success with vaginal microbicides may best be achieved through the combined effects of ARV compounds that exhibit different mechanisms of action with potent activity against multidrug-resistant HIV and efficacious delivery systems.

Novel immunomodulatory function of 1,3,4-thiadiazole derivatives with leishmanicidal activity

OBJECTIVES

Previously, some nitroheteroaryl-1,3,4-thiadiazole derivatives were identified to have potent activity against Leishmania sp. The present aim was to complete the in vitro analysis, thereby investigating the in vivo efficiency of the analogues 15a, 21a and 21b against infected BALB/c mice.

METHODS

Following parasite inoculation and intraperitoneal drug administration (5 and 20 mg/kg/day) for 5 days, the course and size of cutaneous lesions, histopathology of the liver, parasite loads in the spleen through limiting dilution assay as well as spleen cell activation assays through cytokine secretion profiles were studied in BALB/c mice, over a period of 23 and 30 days post-drug injections.

RESULTS

The analogues significantly decreased lesion size and progression of infection in the liver and spleen, and were associated with granuloma formation, which correlates with disease regression in the liver of murine hosts. Moreover, the analogues had immunomodulatory effects, stimulating interferon-γ expression and suppressing interleukin-10 and interleukin-5 production, favouring type-1 immune responses and resolution of the parasitic infection.

CONCLUSIONS

Our results highlight marked differences between the responses of key anatomical organs to the thiadiazole derivatives in comparison with the current antileishmanial drug, meglumine antimoniate. The in vivo observations provide further evidence on the efficiency of the compounds for Leishmania treatment. The immunomodulatory function plays an essential role in enhancing cell-mediated immunity for complete clearance of the pathogen.

Pre-clinical evaluation of a 213Bi-labeled 2556 antibody to HIV-1 gp41 glycoprotein in HIV-1 mouse models as a reagent for HIV eradication

Background

Any strategy for curing HIV infection must include a method to eliminate viral-infected cells. Based on our earlier proof-of-principle results targeting HIV-1 infected cells with radiolabeled antibody (mAb) to gp41 viral antigen, we embarked on identifying a suitable candidate mAb for preclinical development.

Methodology/Principal Findings

Among the several human mAbs to gp41 tested, mAb 2556 was found to have high affinity, reactivity with multimeric forms of gp41 present on both the surface of virus particles and cells expressing HIV-1 Env, and recognition of a highly conserved epitope of gp41 shared by all HIV-1 subtypes. Also, mAb 2556 was the best in competition with HIV-1+ serum antibodies, which is an extremely important consideration for efficacy in the treatment of HIV patients. When radiolabeled with alpha-emitting radionuclide 213-Bismuth (²¹³Bi) - ²¹³Bi-2556 efficiently and specifically killed ACH-2 human lymphocytes chronically infected with HIV-1, and HIV-1 infected human peripheral blood mononuclear cells (hPBMCs). The number of binding sites for ²¹³Bi-2556 on the surface of the infected cells was >10⁶. The in vivo experiments were performed in two HIV-1 mouse models – splenic and intraperitoneal. In both models, the decrease in HIV-1 infected hPBMCs from the spleens and peritoneum, respectively, was dose-dependent with the most pronounced killing of hPBMCs observed in the 100 µCi ²¹³Bi-2556 group (P = 0.01). Measurement of the blood platelet counts and gross pathology of the treated mice demonstrated the lack of toxicity for ²¹³Bi-2556.

Conclusions/Significance

We describe the preclinical development of a novel radiolabeled mAb reagent that could potentially be part of an HIV eradication strategy that is ready for translation into the clinic as the next step in its development. As viral antigens are very different from “self” human antigens - this approach promises high selectivity, increased efficacy and low toxicity, especially in comparison to immunotoxins.

Stampidine as a promising antiretroviral drug candidate for pre-exposure prophylaxis against sexually transmitted HIV/AIDS

INTRODUCTION

Pre-exposure prophylaxis (PrEP) is an evolving new approach to prevention of sexually transmitted HIV-1 that employs antiretroviral (ARV) agents prior to potential HIV-1 exposure in an attempt to reduce the likelihood of HIV-1 infection postexposure. The identification of new ARV agents with potent activity against multidrug-resistant HIV remains an unmet and urgent challenge in the field of PrEP.

AREAS COVERED

This article reviews the preclinical and early clinical activity and safety profile of stampidine, a novel antiretroviral (ARV) drug candidate that exhibits remarkable subnanomolar to low nanomolar in vitro antiretroviral potency against genotypically and phenotypically nucleoside reverse transcriptase inhibitor (NRTI)-resistant primary clinical HIV isolates, non-nucleoside RT-resistant HIV-1 isolates. Stampidine has a favorable pharmacokinetic profile in mice, rats, dogs and cats with 25 or 50 mg/kg tolerable dose levels yielding micromolar plasma concentrations that are 1000-fold higher than its in vitro IC(50) value against HIV. Stampidine has a favorable, safety profile in mice, rats, dogs and cats and it showed significant in vivo ARV activity in HIV-infected Hu-PBL-SCID mice as well as FIV-infected domestic cats. Furthermore, it did not cause any maternal toxicity, developmental toxicity or teratogenicity in rabbits treated at 10 - 40 mg/kg/day dose levels. In a recently completed first-in-human Phase I clinical trial, stampidine did not cause dose-limiting toxicity at single dose levels ranging from 5 to 25 mg/kg.

EXPERT OPINION

The favorable safety and activity profile of stampidine warrants its further development as a promising next-generation PrEP candidate to prevent the sexual transmission of HIV-1. The discovery of stampidine as a potent antiretroviral agent represents a significant step forward in the development of effective therapeutic as well as preventive strategies against HIV/AIDS.

Targeting SYK kinase-dependent anti-apoptotic resistance pathway in B-lineage acute lymphoblastic leukaemia (ALL) cells with a potent SYK inhibitory pentapeptide mimic

The present study found that the pentapeptide mimic C-61, targeting the substrate binding P-site of SYK tyrosine kinase acted as a potent inducer of apoptosis in chemotherapy-resistant SYK-expressing primary leukemic B-cell precursors taken directly from relapsed B-precursor leukaemia (BPL) patients (but not SYK-deficient infant pro-B leukaemia cells), exhibited favourable pharmacokinetics in mice and non-human primates, and eradicated in vivo clonogenic leukaemia cells in severe combined immunodeficient mouse xenograft models of chemotherapy-resistant human BPL at dose levels non-toxic to mice and non-human primates. These in vitro and in vivo findings provide proof of principle for effective treatment of chemotherapy-resistant BPL by targeting SYK-dependent anti-apoptotic blast cell survival machinery with a SYK P-Site inhibitor. Further development of C-61 may provide the foundation for therapeutic innovation against chemotherapy-resistant BPL.

Aryloxy phosphoramidate triesters: a technology for delivering monophosphorylated nucleosides and sugars into cells

Prodrug technologies aimed at delivering nucleoside monophosphates into cells (protides) have proved to be effective in improving the therapeutic potential of antiviral and anticancer nucleosides. In these cases, the nucleoside monophosphates are delivered into the cell, where they may then be further converted (phosphorylated) to their active species. Herein, we describe one of these technologies developed in our laboratories, known as the phosphoramidate protide method. In this approach, the charges of the phosphate group are fully masked to provide efficient passive cell-membrane penetration. Upon entering the cell, the masking groups are enzymatically cleaved to release the phosphorylated biomolecule. The application of this technology to various therapeutic nucleosides has resulted in improved antiviral and anticancer activities, and in some cases it has transformed inactive nucleosides to active ones. Additionally, the phosphoramidate technology has also been applied to numerous antiviral nucleoside phosphonates, and has resulted in at least three phosphoramidate-based nucleotides progressing to clinical investigations. Furthermore, the phosphoramidate technology has been recently applied to sugars (mainly glucosamine) in order to improve their therapeutic potential. The development of the phosphoramidate technology, mechanism of action and the application of the technology to various monophosphorylated nucleosides and sugars will be reviewed.

In vivo toxicity studies of europium hydroxide nanorods in mice

Lanthanide nanoparticles and nanorods have been widely used for diagnostic and therapeutic applications in biomedical nanotechnology due to their fluorescence and pro-angiogenic properties to endothelial cells, respectively. Recently, we have demonstrated that europium (III) hydroxide [Eu(III)(OH)(3)] nanorods, synthesized by the microwave technique and characterized by several physico-chemical techniques, can be used as pro-angiogenic agents which introduce future therapeutic treatment strategies for severe ischemic heart/limb disease, and peripheral ischemic disease. The toxicity of these inorganic nanorods to endothelial cells was supported by several in vitro assays. To determine the in vivo toxicity, these nanorods were administered to mice through intraperitoneal injection (IP) everyday over a period of seven days in a dose dependent (1.25 to 125 mg kg(-1) day(-1)) and time dependent manner (8-60 days). Bio-distribution of europium elements in different organs was analyzed by inductively coupled plasma mass spectrometry (ICPMS). Short-term (S-T) and long-term (L-T) toxicity studies (mice euthanized on days 8 and 60 for S-T and L-T, respectively) show normal blood hematology and serum clinical chemistry with the exception of a slight elevation of liver enzymes. Histological examination of nanorod-treated vital organs (liver, kidney, spleen and lungs) showed no or only mild histological changes that indicate mild toxicity at the higher dose of nanorods.

Mucosal safety of PHI-443 and stampidine as a combination microbicide to prevent genital transmission of HIV-1

OBJECTIVE

To investigate the in vitro and in vivo mucosal safety of a nonnucleoside reverse transcriptase (RT) inhibitor (PHI-443) and a nucleoside analogue RT inhibitor (stampidine)-based anti-HIV microbicide either alone or in combination.

DESIGN

In vitro and in vivo studies using three-dimensional vaginal epithelia integrating Langerhans cells and 16 New Zealand White rabbits, respectively.

SETTING

Research laboratory.

INTERVENTION(S)

Rabbits in groups of four were exposed intravaginally to a gel with and without 1% PHI-443, 1% stampidine, or 1% PHI-443 plus 1% stampidine for 14 days. Cytokine/chemokine release by three-dimensional co-cultures in the presence and absence of PHI-443 or stampidine.

MAIN OUTCOME MEASURES(S)

Histologic scoring of vaginal tissue for mucosal toxicity at 24 hours after dosing. Simultaneous evaluation of levels of 10 cytokines (granulocyte-macrophage colony-stimulating factor, interleukin-1 alpha, interleukin-13, macrophage inflammatory protein-1 beta, granulocyte colony-stimulating factor, interleukin-18, tumor necrosis factor-alpha, interleukin-6, interleukin-1 beta, and interferon-gamma) and 6 chemokines (epithelial neutrophil-activating peptide-78, interleukin-8, monocyte/macrophage chemoattractant protein-1, macrophage inflammatory protein-3 alpha, interferon-inducible protein-10, and regulated upon activation of normal T-cell expressed and secreted) in culture media by a multiplexed chemiluminescence-based immunoassay.

RESULT(S)

In the rabbit model, repeated intravaginal administration of PHI-443 plus stampidine via a gel formulation at concentrations nearly 2,000 and 10,000 times higher than their respective in vitro anti-HIV IC(50) values did not result in vaginal irritation. The levels of proinflammatory cytokines/chemokines secreted by multilayered human genital epithelia integrating Langerhans cells were unaffected by prolonged exposure to PHI-443 or stampidine.

CONCLUSION(S)

The combination of PHI-443 and stampidine was noncytotoxic to vaginal epithelial cells, nonirritating to vaginal mucosa, and did not induce the secretion of proinflammatory cytokines and chemokines by co-cultures of human genital epithelia and Langerhans cells. These attributes are particularly useful for the clinical development of PHI-443 and stampidine as a combination microbicide and as a prophylactic anti-HIV agent to curb genital transmission of HIV-1 by semen.

Limitations of the Human-PBL-SCID Mouse Model for Vaginal Transmission of HIV-1

PROBLEM

SCID mice reconstituted with human peripheral blood lymphocytes (PBL) are amenable to vaginal transmission of HIV-1. We investigated the effectiveness of this model to establish systemic HIV-1 infection.

METHOD OF STUDY

Eighty progesterone-primed C.B-17 SCID mice were reconstituted with human-PBLs and intravaginally inoculated with CCR5 HIV-1 (BaL or 92BR09) infected human-PBLs in the presence of human semen. After two weeks, viral RNA load in spleen, peritoneal lavage (PL), and serum was quantitated by the nucleic acid sequence-based amplification method.

RESULTS

In five independent experiments, spleen from 8/60 (13.3%), PL from 7/60 (11.6%), and serum from 16/56 (28.5%) mice were positive for BaL HIV-1 infection. Similarly, spleen from 4/20 (20%), PL from 1/20 (5%) and serum from 5/20 (25%) mice vaginally inoculated with 92BR09-infected human-PBLs were positive for HIV-1. A one-sided power analysis using normal approximation revealed that at 5% significance level, the overall response rate need to increase form 0.29 to 0.9 and 80% of the control groups needs to achieve a response rate between 6/10 and 9/10 to make the assay feasible.

CONCLUSION

The incidence of vaginal transmission of CCR5 HIV-1 in the human-PBL-SCID mouse was low and variable, which constitutes a major disadvantage for preclinical evaluation of vaginal microbicides.

Effect of change in nucleoside structure on the activation and antiviral activity of phosphoramidate derivatives

Changing the nucleoside group of a series of phosphoramidate derivatives affects the enzyme mediated hydrolysis rate of the compounds. d4T and AZT-substituted analogs were activated by enzymes such as lipases, esterases, and proteases. On the other hand, 3dT-substituted derivatives were comparatively less prone to hydrolysis under similar experimental conditions. From the experimental results, we propose that the most preferable nucleoside group for enzyme activation is d4T rather than AZT or 3dT. Additionally, we also observed that depending on the enzymes used the chiral selectivity of the enzymes for the phosphorus center of these phosphoramidate derivatives differed, demonstrating the importance of the nucleoside structure for this class of compounds.

Enzymatic hydrolysis of stampidine and other stavudine phosphoramidates in the presence of mammalian proteases

Mammalian proteases have not been implicated in the metabolism of any nucleoside phosphoramidate prodrug. The results presented herein provide unprecedented and conclusive experimental evidence that mammalian proteases are capable of hydrolyzing stavudine phosphoramidates. Specifically, cathepsin B and Proteinase K are able to metabolize stampidine and other phosphoramidate derivatives of stavudine. Additionally, cathepsin B exhibits chiral selectivity at the phosphorus center. The elucidation of the metabolic pathways leading to activation of stampidine may provide the basis for pharmacologic interventions aimed at modulating the metabolism and thereby improving the therapeutic window of stampidine as an anti-HIV agent.

Stampidine: a selective oculo-genital microbicide

Adenoviruses (ADVs) are causative agents of severe and extremely contagious ocular and genital infections associated with conjunctivitis, genital ulcers and urethritis. Yet, no functional antiviral compounds are currently available against adenoviral infections. We discovered halogen-substituted phenyl phosphoramidate derivatives of stavudine (STV/d4T) as a new class of dual-function anti-human immunodeficiency virus (HIV) agents with potent and selective anti-ADV activity. The lead compound, stampidine [5'-(4-bromophenyl methoxyalaninylphosphate)-2',3'-didehydro-3'-deoxythymidine], was the most potent non-toxic dual-function antiviral agent. Stampidine displayed remarkable in vitro and in vivo anti-HIV activity against drug-sensitive and drug-resistant HIV strains. Stampidine was non-cytotoxic and nonirritating to mucosal epithelial cells. Several preclinical studies conducted thus far, suggest that stampidine has clinical potential as a dual-function topical agent for the prevention and/or effective treatment of oculo-genital ADV/HIV infections.

Protease-mediated enzymatic hydrolysis and activation of aryl phosphoramidate derivatives of stavudine

Several proteases are capable of hydrolyzing the aryl substituted phosphoramidate derivatives of stavudine resulting in the formation of the active metabolite, alaninyl d4T monophosphate. Subtilisin Protease A, Subtilisin Griseus, Subtilisin Carlsberg, Papaya, Bacillus were amongst the most effective proteases in hydrolyzing stavudine derivatives and specificity of their activity was confirmed using several protease inhibitors to block the hydrolysis of these phosphoramidate derivatives. We found that these proteases exhibit chiral selectivity at the phosphorus center of stavudine derivatives. Our results indicate that cellular proteases may be responsible for the activation of these phosphoramidate derivatives. In addition, we show that the enzymatic hydrolysis takes place at the carboxymethyl ester side chain of these pro-drugs and the direct attack on the phosphorus center by these enzymes does not occur. Finally, we describe a novel activation pathway hitherto unknown for the activation and viral inhibitory characteristic shown by these phosphoramidate derivatives of stavudine.

Lipase-mediated stereoselective hydrolysis of stampidine and other phosphoramidate derivatives of stavudine

Enzymatic hydrolysis of stampidine and other aryl phosphate derivatives of stavudine were investigated using the Candida Antarctica Type B lipase. Modeling studies and comparison of the hydrolysis rate constants revealed a chiral preference of the lipase active site for the putative S-stereoisomer. The in vitro anti-HIV activity of these compounds correlated with their susceptibility to lipase- (but not esterase-) mediated hydrolysis. We propose that stampidine undergoes rapid enzymatic hydrolysis in the presence of lipase according to the following biochemical pathway: During the first step, hydrolysis of the ester group results in the formation of carboxylic acid. Subsequent step involves an intramolecular cyclization at the phosphorous center with simultaneous elimination of the phenoxy group to form a cyclic intermediate. In the presence of water, this intermediate is converted into the active metabolite Ala-d4T-MP. We postulate that the lipase hydrolyzes the methyl ester group of the l-alanine side chain to form the cyclic intermediate in a stereoselective fashion. This hypothesis was supported by experimental data showing that chloroethyl substituted derivatives of stampidine, which possess a chloroethyl linker unit instead of a methyl ester side chain, were resistant to lipase-mediated hydrolysis, which excludes the possibility of a direct hydrolysis of stampidine at the phosphorous center. Thus, our model implies that the lipase-mediated formation of the cyclic intermediate is a key step in metabolism of stampidine and relies on the initial configuration of the stereoisomers.

Stampidine is a potential nonspermicidal broad-spectrum anti-human immunodeficiency virus microbicide

OBJECTIVE

Stampidine (2,'3'-didehydro-3'-deoxythymidine-5'-(p-bromophenyl methoxy alaninyl phosphate) is a novel aryl phosphate derivative of stavudine/d4T with broad-spectrum anti-HIV activity in vitro and in vivo. This study investigated the potential utility of stampidine as a nonspermicidal microbicide.

DESIGN

Prospective, controlled study.

SETTING

Center for Advanced Preclinical Sciences and Reproductive Biology Department.

PATIENT(S)

Seven sperm donors.

ANIMAL(S)

Fifty-two sexually mature, female and twenty-four male New Zealand white rabbits.

INTERVENTION(S)

Human semen and genital tract epithelial cells were exposed to stampidine (up to 1 mM). Ovulated does in subgroups of 12 were artificially inseminated with rabbit semen pretreated with stampidine (1 mM) or vehicle. Does in subgroups of four and three, respectively, were exposed intravaginally to a gel or a thermoreversible ovule formulation with and without 0.5%, 1.0%, or 2.0% stampidine (9 to 36 mM) for 14 days.

MAIN OUTCOME MEASURE(S)

Effect of stampidine on human sperm motility, kinematics, penetration through cervical mucus, and epithelial cell viability. Reproductive parameters on gestation day 8. Vaginal tissues were histologically scored 24 hours after dosing.

RESULT(S)

Exposure of human sperm to stampidine even at a concentration 10(6)-times higher than its in vitro anti-HIV-1 activity (50% inhibitory concentration = 1 nM) had no adverse effect on sperm motility, kinematics, cervical mucus penetrability, or the viability of vaginal and endocervical epithelial cells. Reproductive indices of pregnancy rate, embryo implantation, and preimplantation losses were not affected by pretreatment of rabbit semen with stampidine. Gel formulations of 0.5% to 2.0% stampidine (9 to 36 mM) lacked mucosal toxicity.

CONCLUSION(S)

The broad-spectrum anti-HIV agent stampidine had no adverse effect on sperm functions, was not cytotoxic, and did not induce mucosal toxicity. Stampidine has clinical potential as a prophylactic microbicide without contraceptive activity.

Phenyl phosphoramidate derivatives of stavudine as anti-HIV agents with potent and selective in-vitro antiviral activity against Adenovirus

Adenoviruses are responsible for a broad range of clinical diseases that may be associated with high mortality, including pneumonia, hepatitis, encephalitis, hemorrhagic cystitis, nephritis, and gastroenteritis in immunocompromised patients, including HIV-infected individuals. Here we report the identification of halo-substituted stavudine phenyl phosphoramidate derivatives as a new class of dual-function anti-HIV agents with potent and selective anti-adenovirus (ADV) activity. We examined the investigational stavudine phenyl phosphoramidate derivative stampidine and 12 structurally similar stavudine derivatives for anti-ADV activity. All 13 derivatives of stavudine, including stampidine, were substantially more potent than stavudine and inhibited ADV-induced plaque formation at nanomolar IC(50) values. Compounds with halo substitutions in the phenyl ring as well as the unsubstituted compound 607 were more potent than compounds with methoxy, methyl, or cyano substitutions. Compound 113 (stampidine) with a 4-Br substitution and compound 609 with a 4-Cl substitution were identified as the most potent lead anti-ADV agents. Compound 113/Stampidine inhibited ADV-induced plaque formation in skin fibroblasts in a concentration-dependent fashion with a mean (+/-S.E.M.) IC(50) value of 17 +/- 2 nM without any evidence of cytotoxicity even at 100 microM. Similarly, compound 609 inhibited ADV-induced plaque formation with an IC(50) value of 27 +/- 3 nM. We next sought to determine if the lead compounds 113 and 609 can also inhibit other viruses. Both compounds exhibited potent anti-HIV activity at nanomolar concentrations. However, neither compound exhibited any antiviral activity against non-HIV viruses, including Cytomegalovirus (CMV), Type I or Type II herpes simplex viruses (HSV-1, HSV-2), enterovirus ECHO 30, or respiratory syncytial virus (RSV) (IC(50) > 100 microM). The remarkable anti-ADV potency of the lead compounds stampidine and compound 609 warrants the further development of these promising new antiviral agents for possible clinical use in ADV infected patients.

Development and evaluation of a thermoreversible ovule formulation of stampidine, a novel nonspermicidal broad-spectrum anti-human immunodeficiency virus microbicide

Stampidine [2',3'-didehydro-2',3'-dideoxythymidine 5'-[p-bromophenyl methoxyalaninyl phosphate], a prodrug of stavudine (STV/d4T) with improved anti-HIV activity, is undergoing development as a novel nonspermicidal microbicide. Here, we report the stability of stampidine as a function of pH, preparation of a novel thermoreversible ovule formulation for mucosal delivery, its dissolution profile in synthetic vaginal fluid, and its mucosal toxicity potential as well as systemic absorption in the rabbit model. Stampidine was most stable under acidic conditions. Stampidine was solubilized in a thermoreversible ovule formulation composed of polyethylene glycol 400, polyethylene glycol fatty acid esters, and polysorbate 80. Does were exposed intravaginally for 14 days to an ovule formulation with and without 0.5%, 1%, or 2% stampidine corresponding to 1 x 107- to 4 x 107-fold higher than its in vitro anti-HIV IC50 value. Vaginal tissues harvested on Day 15 were evaluated for mucosal toxicity and cellular inflammation. Additionally, does were exposed intravaginally to stampidine, and plasma collected at various time points was assayed by analytical HPLC for the prodrug and its bioactive metabolites. Stampidine did not cause mucosal inflammation. The vaginal irritation scores for 0.5-2% stampidine were within the acceptable range for clinical trials. The prodrug and its major metabolites were undetectable in the blood plasma. The marked stability of stampidine at acidic pH, its rapid spreadability, together with its lack of mucosal toxicity or systemic absorption of stampidine via a thermoreversible ovule may provide the foundation for its clinical development as an easy-to-use, safe, and effective broad-spectrum anti-HIV microbicide without contraceptive activity.

In vivo antiretroviral activity of stampidine in chronically feline immunodeficiency virus-infected cats

Here we report the antiretroviral activity of the experimental nucleoside reverse transcriptase inhibitor (NRTI) compound stampidine in cats chronically infected with feline immunodeficiency virus (FIV). Notably, a single oral bolus dose of 50 or 100 mg of stampidine per kg resulted in a transient >/=1-log decrease in the FIV load of circulating peripheral blood mononuclear cells in five of six FIV-infected cats and no side effects. A 4-week stampidine treatment course with twice-daily administration of hard gelatin capsules containing 25 to 100 mg of stampidine per kg was also very well tolerated by cats at cumulative dose levels as high as 8.4 g/kg and exhibited a dose-dependent antiretroviral effect. One of three cats treated at the 25-mg/kg dose level, three of three cats treated at the 50-mg/kg dose level, and three of three cats treated at the 100-mg/kg dose level (but none of three control cats treated with placebo pills) showed a therapeutic response, as evidenced by a >/=1-log reduction in the FIV load in peripheral blood mononuclear cells within 2 weeks. The previously documented in vitro and in vivo antiretroviral activity of stampidine against primary clinical human immunodeficiency virus type 1 isolates with genotypic and/or phenotypic NRTI resistance, together with its favorable animal toxicity profile, pharmacokinetics, and in vivo antiretroviral activity in FIV-infected cats, warrants further development of this promising new NRTI compound.

Structure-based design and engineering of a nontoxic recombinant pokeweed antiviral protein with potent anti-human immunodeficiency virus activity

A molecular model of pokeweed antiviral protein (PAP)-RNA interactions was used to rationally engineer FLP-102((151)AA(152)) and FLP-105((191)AA(192)) as nontoxic PAPs with potent anti-human immunodeficiency virus (anti-HIV) activities. FLP-102 and FLP-105 have been produced in Escherichia coli and tested both in vitro and in vivo. These proteins depurinate HIV type 1 (HIV-1) RNA much better than rRNA and are more potent anti-HIV agents than native PAP or recombinant wild-type PAP. They are substantially less toxic than native PAP in BALB/c mice and exhibit potent in vivo activities against genotypically and phenotypically nucleoside reverse transcriptase inhibitor-resistant HIV-1 in a surrogate human peripheral blood lymphocyte (Hu-PBL) SCID mouse model of human AIDS. Rationally engineered nontoxic recombinant PAPs such as FLP-102 and FLP-105 may provide the basis for effective salvage therapies for patients harboring highly drug-resistant strains of HIV-1. The documented in vitro potencies of FLP-102 and FLP-105, their in vivo antiretroviral activities in the HIV-infected Hu-PBL SCID mouse model, and their favorable toxicity profiles in BALB/c mice warrant the further development of these promising new biotherapeutic agents.

Metabolism of stavudine-5'-[p-bromophenyl methoxyalaninyl phosphate], stampidine, in mice, dogs, and cats

We examined the pharmacokinetics and metabolism of the experimental nucleoside reverse transcriptase inhibitor compound stampidine in mice, dogs, and cats. Also reported is the identification of p-bromophenyl sulfate (p-Br-Ph-S) as a major in vivo phase II metabolite of stampidine. Liver cytosol was shown to take part in the hydrolysis of stampidine to form alaninyl-STV-monophosphate (Ala-STV-MP), 2',3'-didehydro-3'-deoxythymidine (STV), and p-bromophenol; p-bromophenol was further sulfonated by sulfotransferase to form p-Br-Ph-S. Notably, plasma concentrations of stampidine >4 logs higher than its IC(50) value can be achieved in both dogs and cats after its p.o administration at a 100-mg/kg dose level. In dogs as well as cats, stampidine was metabolized to yield micromolar concentrations of the active metabolites ala-STV-MP and STV, which is similar to the metabolism of stampidine in mice. These findings encourage the further development of this new antiviral agent for possible clinical use in human immunodeficiency virus-infected patients.

Stampidine is a potent inhibitor of Zidovudine- and nucleoside analog reverse transcriptase inhibitor-resistant primary clinical human immunodeficiency virus type 1 isolates with thymidine analog mutations

We report the antiretroviral activity of stavudine-5'-(p-bromophenyl methoxyalaninyl phosphate) (stampidine [STAMP]), a novel aryl phosphate derivative of stavudine, against primary clinical human immunodeficiency virus type 1 (HIV-1) isolates. STAMP inhibited each one of nine clinical HIV-1 isolates of non-B envelope subtype and 20 genotypically and phenotypically nucleoside analog reverse transcriptase inhibitor-resistant HIV-1 isolates at subnanomolar to low-nanomolar concentrations.