Synthesis and hypoxia selective radiosensitization potential of beta-2-FAZA and beta-3-FAZL: fluorinated azomycin beta-nucleosides.

(18)F-Labelled fluoroazomycin arabinoside ([(18)F]FAZA) is a 2-nitroimidazole (azomycin) based PET tracer used extensively in cancer clinics to diagnose tumour hypoxia. The hypoxia-specific uptake and rapid blood clearance kinetics of FAZA contribute to good tumor-to-background ratios (T/B ratios) and high image contrast. However, FAZA, an alpha-configuration nucleoside, is not transported by cellular nucleoside transporters. It enters cells only via diffusion, therefore not achieving the high uptake and T/B ratios characteristic of actively transported radiopharmaceuticals. The present work describes the synthesis, physicochemical properties and preliminary assessment of the radiosensitization properties of two novel azomycin nucleosides, 1-beta-D-(2-deoxy-2-fluoroarabinofuranosyl)-2-nitroimidazole (beta-2-FAZA) and 1-beta-D-(3-deoxy-3-fluorolyxofuranosyl)-2-nitroimidazole (beta-3-FAZL) (fluorination yields 60% and 55%, respectively). The tosylated precursors required to synthesize the corresponding F-18 labeled radiopharmaceuticals are also reported. The partition coefficients (P) for beta-2-FAZA (1.0) and beta-3-FAZL (0.95) were marginally lower than reported for FAZA (1.1). The radiosensitization properties of both these compounds are similar to that of FAZA, with sensitizer enhancement ratios (SER) of approximately 1.8 for HCT-116 cells.

In vivo evaluation of the uptake of [(123)I]FIAU, [(123)I]IVFRU and [(123)I]IVFAU by normal mouse brain: potential for noninvasive assessment of HSV-1 thymidine kinase gene expression in gliomas.

Radioiodinated 5-iodo-1-(2-fluoro-2-deoxy-beta-D-arabinofuranosyl)uracil (F *IAU) is most commonly used for noninvasive assessment of herpes simplex virus type 1 thymidine kinase (HSV-1-tk) gene expression. However, it does not permeate the intact blood-brain barrier (BBB) because of its moderate lipophilicity. In this work, three iodo-nucleosides, FIAU, IVFRU, and IVFAU, were radiolabeled with iodine-123 and tested for permeation of the BBB in mice and for potential measurement of HSV-1-tk gene expression in gliomas. The results demonstrate that brain uptake and retention of these nucleosides is not directly related to their lipophilicity. The low brain uptake of IVFAU, in conjunction with its higher and constant brain/blood ratio, may reflect greater stability against hydrolysis of the N-glycosidic bond. In vivo PET evaluations of [(124)I]IVFRU and [(124)I]IVFAU in tumor-bearing mice are warranted.

Preparation of the hypoxia imaging PET tracer [18F]FAZA: reaction parameters and automation.

18F-labeling of the nitroimidazole nucleoside analogue 1-(5-fluoro-5-deoxy-alpha-D-arabinofuranosyl)-2-nitroimidazole (FAZA) was developed to use this tracer in PET for detection of hypoxia. Parameters for labeling and hydrolysis were optimized with regard to amount of precursor, temperature and time. Labeling yields reached a maximum of 62+/-4% at 100 degrees C within 5 min using 5 mg of precursor. Hydrolysis was best performed with 1 mL of 0.1 N NaOH at 20 degrees C for 2 min. Transfer of these conditions to an automated synthesizer resulted in an overall radiochemical yield of 20.7+/-3.5%. Absolute yields at EOS were 9.8+/-2.3 GBq of [18F]FAZA ready for injection (n=21; 50 min after EOB; irradiation parameters: 35 microA, 60 min). Thus, a convenient approach suitable for large-scale production of [18F]FAZA was developed by an automated process.

Microwave-assisted (radio)halogenation of nitroimidazole-based hypoxia markers.

Microwave-assisted radiohalogenation for the production of short-lived radiopharmaceuticals has now been applied to the synthesis and radiolabelling of azomycin nucleosides. (Radio)halogens were incorporated either by nucleophilic substitution of a leaving group or by halogen-halogen exchange, in the synthesis of IAZA, IAZP and FAZA. A comparison of conventional labelling and microwave-assisted labelling procedures reflects a clear advantage of the microwave technique.

Dosimetry estimations for 123I-IAZA in healthy volunteers.

UNLABELLED: 123I-Labeled iodoazomycin arabinoside (IAZA) is a marker of hypoxia in vivo. It has been used clinically to image hypoxic tissue in solid tumors, peripheral vascular disease of diabetic origin, blunt brain trauma, and rheumatoid joints and in an animal model of cerebrovascular disease. The radiation dose biodistribution for 123I-IAZA was studied to assess and characterize its suitability as a clinical radiopharmaceutical. METHODS: Six healthy volunteers each received a nominal 185-MBq (5 mCi) dose of 123I-IAZA administered as a slow (1-3 min) intravenous injection in the arm. Anterior and posterior whole-body planar images were acquired for each volunteer beginning immediately after injection and at 1-2, 3-4, 6-8, and 20-24 h after injection. Venous blood samples (0 h predose through 28 h after dosing) and 28-h cumulative urine samples were taken from each volunteer for pharmacokinetic analysis. Radiation dose estimates were performed for all volunteers, with "reference adult" (for men) and "adult female" (for women) phantoms, and both the International Commission on Radiological Protection 30 gastrointestinal tract model and the dynamic bladder model, using the MIRDOSE3 program. Two sets of estimates, 1 using a pharmacokinetic analysis of total serum radioactivity and 1 based on scintigraphic image data, were obtained for each volunteer after 123I-IAZA administration. RESULTS: Two compartments were discernible by pharmacokinetic analysis, and 4 compartments were discernible by image analysis. The urinary bladder wall received the greatest radiation dose (6.3E-02 +/- 8.7E-03 mGy/MBq), followed by the upper large intestinal wall (5.6E-02 +/- 1.2E-02 mGy/MBq), the lower large intestinal wall (5.0E-02 +/- 1.2E-02 mGy/MBq), and the thyroid (4.4E-02 +/- 1.4E-02 mGy/MBq). Approximately 90% of physiologically eliminated radioactivity was excreted through the kidneys. Radioactivity entering the intestinal tract from the gallbladder constituted <10% of biologically eliminated activity. CONCLUSION: The dosimetric analysis of 123I-IAZA in 6 healthy volunteers indicated that both disposition kinetics and radiation dosimetry support its clinical use for imaging tissue hypoxia.

Synthesis of unnatural 7-substituted-1-(2-deoxy-beta-D-ribofuranosyl)isocarbostyrils: "thymine replacement" analogs of deoxythymidine for evaluation as antiviral and anticancer agents.

A group of unnatural 1-(2-deoxy-beta-D-ribofuranosyl)isocarbostyrils having a variety of C-7 substituents [H, 4,7-(NO2)2, I, CF3, CN, (E)-CH=CH-I, -C triple bond CH, -C triple bond C-I, -C triple bond C-Br, -C=C-Me], designed as nucleoside mimics, were synthesized for evaluation as anticancer and antiviral agents. This class of compounds exhibited weak cytotoxicity in a MTT assay (CC50 = 10(-3) to 10(-5) M range) with the 4,7-dinitro derivative being the most cytotoxic, relative to thymidine (CC50 = 10(-3) to 10(-5) M range), against a variety of cancer cell lines. The 4,7-dinitro, 7-I and 7-C triple bond CH compounds exhibited similar cytotoxicity against non-transfected (KBALB, 143B), and HSV-1 TK+ gene transfected (KBALB-STK, 143B-LTK) cancer cell lines possessing the herpes simplex virus type 1 (HSV-1) thymidine kinase gene (TK+). This observation indicates that these compounds are not substrates for HSV type-1 TK, and are therefore unlikely to be useful in gene therapy based on the HSV gene therapy paradigm.

(E)-1-(2'-deoxy-beta-D-ribofuranosyl)-2,4-difluoro-5-(2-iodovinyl)benzene.

This analysis of the title compound, C13H13F2IO3, establishes the orientation of (E)-5-(CH=CH-I) as antiperiplanar (ap) to the C-C bond (5-6 position) of the 2,4-difluorophenyl ring system, with the (E)-5-(CH=CH-I) H atom located in close proximity (2.17 A) to the F4 atom of the 2,4-difluorophenyl moiety.

Synthesis of 1-(2-deoxy-beta-D-ribofuranosyl)-2,4-difluoro-5-substituted-benzene thymidine mimics, some related alpha-anomers, and their evaluation as antiviral and anticancer agents.

A group of unnatural 1-(2-deoxy-beta-D-ribofuranosyl)-2,4-difluorobenzenes having a variety of C-5 substituents (H, Me, F, Cl, Br, I, CF3, CN, NO2, NH2), designed as thymidine mimics, were synthesized for evaluation as anticancer and antiviral agents. The coupling reaction of 3,5-bis-O-(p-chlorobenzoyl)-2-deoxy-alpha-D-ribofuranosyl chloride with an organocadmium reagent [(2,4-difluorophenyl)2Cd] afforded a mixture of the alpha- and beta-anomeric products (alpha:beta = 3:1 to 10:1 ratio). Treatment of the alpha-anomer with BF3.Et2O in nitroethane at 110-120 degrees C for 30 min was developed as an efficient method for epimerization of the major alpha-anomer to the desired beta-anomer. The 5-substituted (H, Me, Cl, I, NH2) beta-anomers exhibited negligible cytotoxicity in a MTT assay (CC50 = 10(-3)-10(-4) M range), relative to thymidine (CC50 = 10(-3)-10(-5) M range), against a variety of cancer cell lines. In contrast, the 5-NO2 derivative was more cytotoxic (CC50 = 10(-5)-10(-6) M range). A number of 5-substituted beta-anomers, and some related alpha-anomers, that were evaluated using a wide variety of antiviral assay systems [HSV-1, HSV-2, varicella-zoster virus (VZV), vaccinia virus, vesicular stomatitis, cytomegalovirus (CMV) and human immunodeficiency (HIV-1, HIV-2) viruses], showed that this class of unnatural C-aryl nucleoside mimics are inactive antiviral agents.

Synthesis of 1-(2-deoxy-beta-D-ribofuranosyl)-2,4-difluoro-5-substituted-benzenes: "thymine replacement" analogs of thymidine for evaluation as anticancer and antiviral agents.

A group of unnatural 1-(2-deoxy-beta-D-ribofuranosyl)-2,4-difluorobenzenes having a variety of C-5 two-carbon substituents [-C...C-X, X = I, Br; -C...CH; (E)-CH=CH-X, X = I, Br; -CH=CH2; -CH2CH3; -CH(N3) CH2Br], designed as nucleoside mimics, were synthesized for evaluation as anticancer and antiviral agents. The 5-substituted (E)-CH=CH-I and -CH2CH3 compounds exhibited negligible cytotoxicity in a MTT assay (CC50 = 10(-3) to 10(-4)M range), relative to thymidine (CC50 = 10(-3) to 10(-5)M range), against a variety of cancer cell lines. In contrast, the C-5 substituted -C...C-I and -CH(N3)CH2Br compounds were more cytotoxic (CC50 = 10(-5) to 10(-6)M range). The -C...C-I and -CH2CH3 compounds exhibited similar cytotoxicity against non-transfected (KBALB, 143B) and HSV-1 TK+ gene transfected (KBALB-STK, 143B-LTK) cancer cell lines expressing the herpes simplex virus type 1 (HSV-1) thymidine kinase gene (TK+). This observation indicates that expression of the viral TK enzyme did not provide a gene therapeutic effect. The parent group of 5-substituted compounds, that were evaluated using a wide variety of antiviral assay systems [HSV-1, HSV-2, varicella-zoster virus (VZV), vaccinia virus, vesicular stomatitis, cytomegalovirus (CMV), and human immunodeficiency (HIV-1, HIV-2) viruses], showed that this class of unnatural C-aryl nucleoside mimics are inactive and/or weakly active antiviral agents.

Synthesis and biological investigations of 5-substituted pyrimidine nucleosides coupled to a dihydropyridine/pyridinium salt redox chemical delivery system.

The syntheses, antiviral activities, and partition coefficients (P) of 3'-O-(1-methyl-1,4-dihydropyridyl-3-carbonyl)-coupled nucleosides are described. These novel compounds were designed in an effort to enhance the lipophilicity, and thereby the delivery to the CNS, without compromising the anti-HSV-1 activity of the parental nucleosides. We have previously reported the synthesis of 3'-O-(1-methyl-1,4-dihydropyridyl-3- carbonyl) analogs of 5-iodo-(5), 5-vinyl-(6), and (E)-5-(2-iodovinyl)-2'-deoxyuridines (7). We now report the synthesis of 5-iodo-3'-O-(1-methyl-1,4-dihydropyridyl-3- carbonyl)-5'-O-acetyl-2'-deoxyuridine (15) and 3'-O-(1-methyl-1,4-dihydropyridyl-3-carbonyl)-2'-deoxyuridine (17). Quarternization of the 3'-O-(3-pyridylcarbonyl) compounds (10,12) using iodomethane afforded the corresponding 1-methyl pyridinium salts (13,14) which were reduced with sodium dithionite to yield the corresponding 3'-O-1-methyl-1,4-dihydropyridyl-3-carbonyl compounds (15,16). The deprotection of 3'-O-(1-methyl-1,4-dihydropyridyl- 3-carbonyl)-5'-O-t-butyldimethylsilyl-2'-deoxyuridine (16) with Bu4N+F- afforded 3'-O-(1-methyl-1,4-dihydropyridyl-3-carbonyl)-2'-deoxyuridine (17). Compounds 5-7 and 15 were evaluated for their antiviral activity in vitro against HSV-1, HSV-2, HCMV, and VZV, and were found to retain anti-HSV-1, HSV-2 and VZV activity as compared to their parental nucleosides (1-3). In addition, the cellular toxicity of 3'-O-(1-methyl-1,4-dihydropyridyl-3-carbonyl)-coupled compounds (5-7 and 15) was found to be lower than the parent nucleosides. The lipophilicity of compounds (5-7,15,17) are enhanced substantially, compared to the parent nucleosides, as indicated by an increase in corresponding P values (1-octanol-water) upon replacement of the C-3' hydroxyl by 1-methyl-1,4-dihydropyridyl-3-carbonyl moiety.

Enzyme-targeted, nucleoside-based radiopharmaceuticals for scintigraphic monitoring of gene transfer and expression.

Enzymes, the expression products of transferred or native genes, offer unique windows of opportunity for clinical diagnosis and therapy. Although some expression products can be monitored in plasma, nuclear medicine imaging (SPECT and PET) offers the unique ability to selectively measure the intensity and regional/spatial distribution of gene expression both in vivo, in situ. Importantly, the superior sensitivity and moderate spatial resolution of the nuclear techniques also enable in vivo kinetic characterization of enzyme-substrate interaction. Indeed, the non-invasive, whole-body assessment of gene expression can only be achieved through imaging techniques. Given today's technology, nuclear imaging techniques uniquely provide the necessary sensitivity required to evaluate the success of the gene delivery and expression (transcription and translation), and to detect unwanted expression by non-target tissues. Enzymes are a special class of proteinacious gene expression products that selectively bind specific substrates for the purpose of molecular biotransformation rather than for signal transduction. In general, enzymes have received much less attention for imaging than receptors and antibodies, despite the enzymes' high substrate specificity and the potential for kinetic evaluation. Enzymes are attractive targets for diagnostic imaging and radioisotope radiotherapy because they convert multiple molecular copies of the substrate (radiotracer) per molecule of enzyme, thereby greatly increasing the ultimate sensitivity relative to the sensitivity offered by receptors that bind with 1:1 stoichiometry. Not surprisingly, enzymes have been the preferred molecular targets to date for scintigraphic imaging of gene therapy. This overview describes opportunities and advances in the utilization of radiolabelled nucleosides and nucleoside bases for imaging in gene therapy, with emphasis on the exploitation of enzyme systems for scintigraphic imaging of gene expression in gene therapy of cancer. Herpes simplex virus type-1 thymidine kinase and bacterial/fungal cytosine deaminase are discussed within the context of gene therapy issues such as gene vectors for targeting and delivery, the bystander effect, and radionucleoside delivery. The utilization of nucleosides as markers of tissue proliferation is discussed with respect to selected enzyme targets.

Syntheses of 1-[(2-hydroxyethoxy)methyl]- and 1-[(1,3-dihydroxy-2-propoxy)methyl]- derivatives of 5-substituted-2,4-difluorobenzene: unnatural acyclo thymidine mimics for evaluation as anticancer and antiviral agents.

A group of 1-[(2-hydroxyethoxy)methyl]- (12) and 1-[(1,3-dihydroxy-2-propoxy)methyl]- (13) derivatives of 2,4-difluorobenzene possessing a variety of C-5 substituents (R = Me, H, I, NO2) were designed with the expectation that they may serve as acyclic 5-substituted-2'-deoxyuridine (thymidine) mimics. Compounds 12 and 13 (R = Me, H, I) were inactive as anticancer agents (CC50 = 10(-3) to 10(-4) M range), whereas the 5-nitro compounds (12d, 13d) exhibited weak-to-moderate cytotoxicity (CC50 = 10(-5) to 10(-6) M range) against a variety of cancer cell lines. All compounds prepared (12a-d, 13a-d) were inactive as antiviral agents in a broad-spectrum antiviral screen that also included the human immunodeficiency virus (HIV-1 and HIV-2) and herpes simplex virus (HSV-1 and HSV-2).

Flutamide-hydroxypropy-beta-chiyclodextrin complex: formulation, physical characterization, and absorption studies using the Caco-2 in vitro model.

PURPOSE: The objective of this research was to formulate flutamide (FLT) in hydroxypropyl-beta-cyclodextrin (HPbetaCyD), and to investigate FLT transcellular permeation from the complex using the Caco-2 monolayer in vitro model. METHODS: Classical solubility data were used to derive thermodynamic parameters which, together with Differential Scanning Calorimetry (DSC), (1)H-NMR and (19)F-NMR, were used to characterize and derive stability constants for the FLT-HPbetaCyD complex. The Caco-2 cell line was used to examine the role of HPbetaCyD on the passage of FLT across cell monolayers in vitro. RESULTS: The solubility of FLT in water (1.46 mmol/L) increased almost 170 times (to 243.45 mmol/L) in the presence of 50% (w/v) HPbetaCyD. Solubility data for FLT in aqueous HPbetaCyD were used to derive thermodynamic parameters (DeltaG degrees at 298 K = -3.48, DeltaH degrees = 2.85, DeltaS degrees at 298 K = 21.24). The solubility of FLT in HPbetaCyD increased proportionally with an increase in temperature. The FLT-HPbetaCyD complex had an A(L)-type (DSC) isotherm, consistent with a linear increase in FLT solubility and unchanged stoichiometry. The DSC of free FLT and HPbetaCyD showed endothermic peaks at 110 degrees C and 300 degrees C, respectively. FLT-HPbetaCyD did not display a free-FLT endothermic response, but exhibited broadening of the endothermic peak in the HPbetaCyD region. (19)F- and (1)H-NMR chemical shifts of FLT moved upfield as a function of its increased solubility in the presence of HPbetaCyD. The FLT-HPbetaCyD stability constant, K(s) (1:1) was estimated to be 356 M(-1 )and 357 M(-1), from thermodynamic and (19)F NMR data, respectively. The apical-to-basal permeability coefficient (P(eff) = 4.75 x 10(-5) cm.s(-1)) for FLT across Caco-2 cell monolayers at 37; C increased as HPbetaCyD concentrations were reduced, indicative of transepithelial passage via passive diffusion of available free FLT in solution. Studies in the presence and absence of Ca(2+ )ruled out a significant paracellular transport component. CONCLUSIONS: FLT-HPbetaCyD is a relatively stable, 1:1 inclusion complex. Formation of this complex substantially increases the water solubility of FLT, but HPbetaCyD, except in high dilution, reduces transcellular passage of FLT in the Caco-2 cell in vitro model.

Novel approaches for designing 5'-O-ester prodrugs of 3'-azido-2', 3'-dideoxythymidine (AZT).

3'-Azido-2',3'-dideoxythymidine (AZT, 1, zidovudine, RetrovirTM) is used to treat patients with human immunodeficiency virus (HIV) infection. AZT, after conversion to AZT-5'-triphosphate (AZT-TP) by cellular enzymes, inhibits HIV-reverse transcriptase (HIV-RT). The major clinical limitations of AZT are due to clinical toxicities that include bone marrow suppression, hepatic abnormalities and myopathy, absolute dependence on host cell kinase-mediated activation which leads to low activity, limited brain uptake, a short half-life of about one hour in plasma that dictates frequent administration to maintain therapeutic drug levels, low potential for metabolic activation and/or high susceptibility to catabolism, and the rapid development of resistance by HIV-1. These limitations have prompted the development of strategies for designing prodrugs of AZT. A variety of 5'-O-substituted prodrugs of AZT constitute the subject of this review. The drug-design rationale on which these approaches are based is that the ester conjugate will be converted by hydrolysis and/or enzymatic cleavage to AZT or its 5′-monophosphate (AZT-MP). Most prodrug derivatives of AZT have been prepared by derivatization of AZT at its 5'-O position to provide two prominent classes of compounds that encompass: A) 5'-O-carboxylic esters derived from 1) cyclic 5'-O-carboxylic acids such as steroidal 17b-carboxylic acids, 1-adamantanecarboxylic acid, bicyclam carboxylic acid derivatives, O-acetylsalicylic acid, and carbohydrate derivatives, 2) amino acids, 3) 1, 4-dihydro-1-methyl-3-pyridinylcarboxylic acid, 4) aliphatic fatty acid analogs such as myristic acid containing a heteroatom, or without a heteroatom such as stearic acid, and 5) long chain polyunsaturated fatty acid analogs such as retinoic acid, and B) masked phosphates such as 1) phosphodiesters that include monoalkyl or monoaryl phosphate, carbohydrate, ether lipid, ester lipid, and foscarnet derivatives, 2) a variety of phosphotriesters that include dialkylphosphotriesters, diarylphosphotriesters, glycolate and lactate phosphotriesters, phosphotriester approaches using simultaneous enzymatic and chemical hydrolysis of bis(4-acyloxybenzyl) esters, bis(S-acyl-2-thioethyl) (SATE) esters, cyclosaligenyl prodrugs, glycosyl phosphotriesters, and steroidal phosphotriesters, 3) phosphoramidate derivatives, 4) dinucleoside phosphate derivatives that possess a second anti-HIV moiety such as AZT-P-ddA, AZT-P-ddI, AZTP2AZT, AZTP2ACV), and 5) 5'-hydrogen phosphonate and 5'-methylene phosphonate derivatives of AZT. In these prodrugs, the conjugating moiety is linked to AZT via a 5'-O-ester or 5'-O-phosphate group. 5'-O-Substituted AZT prodrugs have been designed with the objectives of improving anti-HIV activity, enhancing blood-brain barrier penetration, modifying pharmacokinetic properties to increase plasma half-life and improving drug delivery with respect to site-specific targeting or drug localization. Bypassing the first phosphorylation step, regulating transport and conferring sustained release of AZT prolong its duration of action, decrease toxicity and improve patient acceptability. The properties of these prodrugs and their anti-HIV activities are now reviewed.

Synthesis, radiolabeling, and biodistribution of putative metabolites of iodoazomycin arabinoside.

Scintigraphic evaluation of patients with advanced oncological disease showed uptake of radioactivity in the brain following administration of the hypoxic imaging agent 123I-iodoazomycin arabinoside (123I-IAZA). Three proposed metabolites of IAZA--methyl 5-deoxy-5-iodo-D-arabinofuranoside, methyl 2,3-di-O-acetyl-5-deoxy-5-iodo-alpha-D-arabinofuranoside, and 1-(5-deoxy-5-iodo-alpha-D-arabinofuranosyl)-2-aminoimidazole (IAIA)--were synthesized, radiolabeled with 125I, and investigated in normal and tumor-bearing murine models for their contribution to this unusual phenomenon. The three compounds were readily radiolabeled by melt or solvent exchange procedures. Biodistribution data indicated rapid blood clearance, rapid excretion, and little tissue accumulation in the brain. IAIA showed significant tumor to blood ratios at 4 h (4.3:1) and liver to blood ratios at 24 h (30:1).

Reporter gene imaging: effects of ganciclovir treatment on nucleoside uptake, hypoxia and perfusion in a murine gene therapy tumour model that expresses herpes simplex type-1 thymidine kinase.

Perfusion, hypoxia and nucleoside uptake during ganciclovir therapy were determined in a murine HSV-1 TK-expressing tumour model (KBALB-STK). HSV-1 TK mRNA transcription in this cell line was confirmed by RT-PCR. BALB/c mice bearing KBALB-STK tumours accumulated (E)-5-(2-[125I]iodovinyl)-2'-fluoro-2'-deoxyuridine ([125I]IVFRU) (2.54% injected dose.g-1) and could be readily detected with planar imaging following administration of [131I]IVFRU. However, a single dose of ganciclovir (100 mg.kg-1 intraperitoneally) decreased tumour uptake of [125I]IVFRU to 0.33% injected dose.g-1. Subsequent single daily doses of ganciclovir over 3 consecutive days had a negligible effect on [125I]IVFRU uptake, which remained low. Tumour perfusion during 3 days of ganciclovir treatment was monitored with intravenous [99Tcm]HMPAO. Tumour perfusion increased from day 0 (no ganciclovir treatment) with 1.83% injected dose.g-1 tumour, to a maximum at day 2 (3.77% injected dose.g-1). In the same animals, accumulation of [3H]misonidazole decreased from 0.70% injected dose.g-1 at day 0 to a minimum at day 3 (0.24% injected dose.g-1), indicating that tumour tissue had become less hypoxic over the ganciclovir regimen. The uptake of [125I]IVFRU into the acid insoluble fraction of KBALB-STK cells in vitro in the presence of ganciclovir (2.0 microM) was completely inhibited, leading to a 57% decrease in total cellular accumulation of radioactivity. However, cytosolic entrapment of [125I]IVFRU was not affected by the presence of ganciclovir. These results indicate that the mechanisms leading to IVFRU exclusion during ganciclovir treatment of HSV-1 TK-expressing tumours can be attributed, at least partially, to inhibition of [125I]IVFRU-nucleotide incorporation into DNA.

Drug Delivery Systems--Fifth US-Japan Symposium. 12-17 December 1999, Lahaina, Hawaii.

The field of drug delivery is moving rapidly from the more efficacious delivery of 'old' drugs, to the delivery of therapeutic peptides, proteins, oligonucleotides and genes. Liposomes, polymers, microbubbles, nanoparticles, wafers and chips are the jargon, and entrepreneurialism is the prevailing force. Indeed, the scientific spirit is overwhelmed by the push to market, as fledgling companies compete or collaborate with the established pharma industry in converting concepts into profits. The 'Holy Grail' is a slice of the multi-billion dollar global market for these specialized, high-tech products.